DOCUMENT RESUME

ED 223 814 CE 034 294

TITLE Television Equipment Repairman, 7-3. MilitaryCurriculum Materials for Vocational and TechnicalEducation.

INSTITUTION Air Force Training Command, Keesler AFB, Miss.; OhioState Univ., Columbus. National Center for Researchin Vocational Education.

SPONS AGENCY Office of Education (DHEW), Washington, D.C.PUB DATE 78NOTE 519p.PUB TYPE Guides Classroom Use Materials (For Learner)

(051)

EDRS PRICE MF02/PC21 Plus Postage.DESCRIPTORS Color; Electronic Equipment; *Equipment Maintenance;

Military Personnel; Military Training; PostsecondaryEducation; Safety; Secondary Education; *ServiceOccupations; Supervisory Methods; *TechnicalEducation; *Television Radio Repairers; *VideoEquipment

IDENTIFIERS Military Curriculum Project

ABSTRACTThese military-developed curriculum materials consist

of four volumes of individualized, self-paced text and workbooks foruse by those studying to become television equipment repairmen.Covered in the individual volumes are the following topics:supervision, training, and maintenance techniques (supervision andtraining, safety, maintenance principles, and testing equipment);equipment maintenance (power supplies, monitoring facilities, audiosystems, and color television); auxiliary equipment; and systemsmaintenance (troubleshooting, repair, and diagnosing systemtroubles). Each chapter contains objectives, coded text, exercises,and answers keyed to the text for self-evaluation. (MN)

***********************************************************************Reproductions supplied by EDRS are the best that can be made

from the original document.***********************************************************************

DOCUMENT RESUME

ED 223 814 CE 034 294

TITLE Television Equipment Repairman, 7-3. MilitaryCurriculum Materials for Vocational and TechnicalEducation.

INSTITUTION Air Force Training Command, Keesler AFB, Miss.; OhioState Univ., Columbus. National Center for Researchin Vocational Education.

SPONS AGENCY Office of Education (DREW), Washington, D.C.PUB DATE 78NOTE 519p.PUB TYPE Guides - Classroom Use - Materials (For Learner)

(051)

EDRS PRICE MF02/PC21 Plus Postage.DESCRIPTORS Color; Electronic Equipment; *Equipment Maintenance;

Military Personnel; Military Training; PostsecondaryEducation; Safety; Secondary Education; *ServiceOccupations; Supervisory Methods; *TechnicalEducation; *Television Radio Repairers; *VideoEquipment

IDENTIFIERS Military Curriculum Project

ABSTRACTThese military-developed curriculum materials consist

of four volumes of individualized, self-paced text and workbooks foruse by those studying to become television equipment repairmen.Covered in the individual volumes are the following topics:supervision, training, and maintenance techniques (supervision andtraining, safety, maintenance principles, and testing equipment);equipment maintenance (power supplies, monitoring facilities, audiosystems, and color television); auxiliary equipment; and systemsmaintenance (troubleshooting, repair, and diagnosing systemtroubles). Each chapter contains objectives, coded text, exercises,and answers keyed to the text for self-evaluation. (MN)

************************************************************************ Reproductions supplied by EDRS are the best that can be made *

* from the original document. *

***********************************************************************

MILITAW CURRICULUM MERIAIS

The military-developed curriculum materials in this course

package were selected by the National Center for Research in

Vbcational Education Military Curriculum Prcject for dissemr

ination to the six regional Curriculum Coordination Centers and

other instructional materials agencies. The purpose of

disseminating these courses was to make curriculum materials

developed by the military more accessible to vocational

educators in the civilian setting.

The course materials were acquired, evaluated by project

staff and practitioners in the field, and prepared for

dissemination. Materials which were specific to the military

were deleted, copyrighted materials were either omitted or appro-

val for their use was obtained. These course packages containcurriculum resource materials which can be adapted to support

vocational instruction and curriculum development.

The National CenterMission Statement

" " -"The National Center for Research inVocational Educatbn's mission is to increasethe ability of diverse agencies, institutions,and organizations 10.1solve educational prob-lems relating to individual career planning,preparation, and progression. The NationalCenter fulfills its mission by:

Generating knowledge through research

Developing educational programs andproducts

Evaluating individual program needsand outcomes

Installing educational programs andproducts

Operating information systems andservices

Conducting leadership development andtraining programs

FOR FURTHER INFORMATION ABOUTMilitary Curriculum Materials

WRITE OR CALLProgram Information OfficeThe National Center for Research in Vocational

EducationThe Ohio State University

_ 1960 Kenny Road, Columbus, Ohio 43210Telephone: 614/486-3655 or Toll Free 800/

848-4815 within the continental U.S.(except Ohio)

Military CurriculumMaterials for

Vocational andTechnical Education

Information and FieldSmices Divir,ion

The Vatierml Center for Researchin Vocritional Education

,meffrer'"^:""""'".",...",...

MilitaryCurriculum MaterialsDissemination Is .

kkr.; Lai.11.:46115111;agaa.L......

an activity to increase the accessibility ofmilitary-developed curriculum materials tovocational and technical educators.

This project, funded by the U.S. Office ofEducation, includes the identification andacquisition of curriculum materials in printform from the Coast Guard, Air Force,Army, Marine Corps and Navy.

Access to military curriculum materials isprovided through a "Joint Memorandum ofUnderstanding" between the US. Office ofEducation and the Department of Defense.

The acquired materials are reviewed by staffand subject matter specialists, and coursesdeemed applicable to vocational and tech-nical education are selected for dissemination.

The National Center for Research inVocational Education is the U.S. Office ofEducation's designated representative tocquire the materials and conduct the project

activities.

Project Staff:

Wesley E. Budke, Ph.D., DirectorNational Center Clearinghouse

Shirley A. Chase, Ph.D.Project Director

6

What MaterialsAre Available?

How Can TheseMaterials Be Obtained?

I . ...

. .

One hundred twenty courses on microfiche(thirteen in paper form) and descriptions ofeach have been provided to the vocationalCurriculum Coordination Centers and otherinstructional materials agencies for dissemi-nation.

Course materials include programmedinstruction, curriculum outlines, instructorguides, student workbooks apd technicalmanuals.

The 120 courses represent the followingsixteen vocational subject areas:

AgricultureAviationBuilding &ConstructionTrades

ClericalOccupations

CommunicationsDrat lingElectronicsEngine Mechanics

Food ServiceHealthHeating & AirConditioning

Machine ShopManagement &

SupervisionMeteorology &

NavigationPhotographyPublic Service

The number of courses and the subject areasrepresented will expand as additional mate-rials with application to vocational andtechnical education are identified and selectedfor dissemination.

Contact the Curriculum Coordination Centerin your region for information on obtainingmaterials (e.g., availability and cost). Theywill respond to your request directly or referyou to an instructional materials agencycloser to you.

CURRICULUM COORDINATION CENTERS

EAST CENTRALRebecca S. Douglass

Director100 North First StreetSpringfield, IL 62777217/782-0759

MIDWESTRobert PattonDirector1515 West Sixth Ave.Stillwater, OK 74704405/377 -2000

NORTHEASTJoseph F. Kelly, Ph.D.Director225 West State StreetTrenton, NJ 08625609/292.6562

NORTHWESTWilliam DanielsDirectorBuilding 17Airdustrial ParkOlympia, WA 98504206/753-0879

SOUTHEASTJames F. Shill, Ph.D.DirectorMississippi State UniversityDrawer DX

Mississippi State, MS 39762

601/325-2510

WESTERNLawrence F. H. Zane, Ph.D.

Director1776 University Av-Honolulu, HI 96822808/948-7834

'

TELEVISION EQUIPMENT REPAIRMAN

Table of Contents

Course Description

Volume 1 A

Supervision, Training, and MaintenanceTechniques - Student Text

Supervision, Training, and MaintenanceTechniques - Workbook

Volume 1

Equipment Maintenance - Student Text

Equipment

Volume 2

Auxiliary Equipments

Auxiliary Equipments

Volume 3

Systems Maintenance

Systems Maintenance

Maintenance - Workbook

- Student Text

- Workbook,

- Student Text

- Workbook

uorresponaence uourse

Page 1

Page 3

Page 123

Page 165

Page 276

Page 313

Page 425

Page 468

Page 491

Course Description

This course is designed to upgrade the Apprentice (semi-skilled) worker to the Specialist (skilled) and/or the Technician (advanced) level. It containsbasic review information as well as supervisory training. A television equipment repair person (specialist) is expected to install, maintain, repair, monitor,and analyze the performance of television systems and equipment producing radiated or cable transmitted signals. Operation and maintenance ofassociated test equipment is also required.

The technician level person is expected to install, troubleshoot, repair, inspect, overhaul, and modify television systems producing radiated or cable trans-mitted signals; maintain associated peculiar test equipment; monitor, govern, and analyze.the performance of television systems; and direct performancechecks and measurement of operational and spare television equipment using precision test and measuring instruments to insure contir"mus acceptablesystems and equipment during operating periods. He/she must also coordinate activities with production agencies to insure availability of an operatingsystem to support production requirements; and supervise television maintenance activities.

The following outlines the scope of each volume:

Volume 1A

Volume 1

Supervision, Training, and Maintenance Techniques covers not only supervision and training, but also safety, maintenanceprinciples, oscilloscopes and test accessories, power and frequency test equipment, and electrcn tube and semiconductortesting.

Equipment Maintenance discusses power supplies, sync generators, the camera chain, monitoring facilities, audio systems,and color television. The first chapter on requirements and applications was deleted because of its reference to militaryspecific organization and forms.

Volume 2 Auxiliary Equipments discusses the maintenance requirements and operation of additional equipment required to supportvarious functions of television systems including studio lightina systems, intercom facilities, special effects, prompting facilities,audio and video recording systems as well as specialized equipment required for maintaining television equipment. A discussionof relay equipment, television VHF and UHF transmitters, receivers, antennas, and associated circuitry is presentet in thisvolume.

Volume 3 Systems Maintenance covers troubleshooting, repair, and diagnosing system troubles. The chapters on operational responsibilitiesand installation and modification were deleted because of references to military specific organization, procedures, and forms.

Each of the chapters has objectives, coded text, exercises, and answers keyed to the text for self-evaluation. A volume review exercise is provided, but noanswers are available. This material presents basic review material as well as supervisory concerns in the television equipment repair trade for student self-study. The course would be best used in conjunction with a laboratory or on-the-job learning situation.

101111111111 VOCAMIAl QZJATUIF

TELEVISION EQUIPMENT REPAIR MAN Correspondence Course /

Developed by: Occupational Arse:

United States Air Force Electronics

Development and Cost:Review Dates

Unknown

810.25

Print Pages:

505

Availability:Military Curriculum Project, The Centerfor Vocational Education. 1960 KennyRd., Columbus, Ohl 43210

Suggested Badiground:

Basic electronics

Target Audiences:

Grades 10-adult

Organization of Materials:

Student workbooks with objectives, assignments, chapter review exercises and answers, and volume review exercises; text

Type of Instruction:

Individualized, self-paced

Type of Materials:

Volume 1A Supervision, Training, and Maintenance

No. of Pages: AverageCompletion Time:

Techniques 118 Flexible

Workbook 41

Volume 1 Equipment Maintenance 105 Flexible

Workbook 39

Volume 2 Auxiliary Equipment 110 Flexible

Workbook 41

Volume 3 Systems Maintenance 21 Flexible

Workbook 20

Supplementary Materials Required:

None

FOPmeow 0:11011101owe, 5 crf Expires July 1, 1978

30455 01A 7207 7511

CDC 30455

TELEVISION EQUIPMENT

REPAIRMAN

(AFSC 30455)

Volume lASupervision, Training, and Maintenance Techniques

Extension Course InstituteAir University

ii

PREPARED BYCOMMUNICATIONS SYSTEMS DEPARTMENT

3380TH TECHNICAL SCHOOL (ATC)KEESLER APB, MISSISSIPPI

EXTENSION COURSE INSTITUTE;GUNTER AIR FORCE BASE, ALABAMA

THIS PUBLICATION HAS BEEN REVIEWED AND APPROVED BY COMPETENT PERSONNEL OFTHE PREPARING COMMAND IN ACCORDANCE WITH CURRENT DIRECTIVES ON

DOCTRINE, POLICY, ESSENTIALITY, PROPRIETY, AND QUALITY.

Preface

IN THIS COURSE we discuss and analyze principles and maintenance of theinstrument landing system (ILS), terminal very-high-frequency omnirange(TVOR). and tactical air navigation system (TACAN)the aids to navigationclassed as flight facilities equipment. The purpose of this and succeedingvolumes is to assist you through self-study in obtaining knowledge necessary toperform maintenance tasks assigned to you. Emphasis is placed on principles oftlight facilities equipment rather than particular models of equipment. Oc-cassionally. specific equipment is discussed because we consider it to berepresentative of the type, or because it includes features also found in otherequipment. An understanding of these principles is essential to all phases ofNAVAIDS maintenance.

This volume deals with supervision, training, maintenance techniques, safety,and test equipment. Chapter I covers the supervision expected of a trainedNAVAIDS repairman and your responsibilities toward the Air Force con-tinuous training program. The second chapter is on safety, with emphasis onsafe maintenance practices and emergency action. References to this subjectwill reccur throughout this course.

Succeeding chapters describe maintenance principles, both preventive andcorrective, and include management. technical orders, test equipment, andspecific procedures for printed circuits. The information in these chaptersshould enable you to employ test equipment confidently, ,....mose substituteswhen necessary, and evaluate measurements correctly.

If you have questions on the accuracy or currency of the subject matter of thistext, or recommendations for its improvement, send them to Tech Tng Cen(TTOC). Keesler AFB. NiS 39534.

If ycu have questions on course enrollment or administration, or on any ofECI's nstructional aids (Your Key to Career Development. Study ReferenceGuides. Chapter Review Exercises. Volume Review Exercis, and CourseExamination), consult your education officer, training officer. or NCO, as ap-propriate. If he can't answer your questions, send them to ECI, Gunter AFB.Alabama 36118. preferably on ECI Form 17, Student Request for Assistance.

This volume is rated at 36 hours (12 points).Material in this volume is technically accurate, adequate, and current as of

January 1972.

ill

Li 1 3

Contents

Chapter

Preface

Page

Iii

1 Supervision and Training 1

2 Safety 10

3 Maintenance Principles 22

4 Oscilloscopes and Test Accessories 51

5 Power and Frequency Test Equipment 99

6 Electron Tube and Semiconductor Testing 116

iv

Supervision and Training

THE QUALITY of communications-electronic's systems depends on allmaintenance personnel performing theirassigned tasks at the right time, in the rightplace, with proper equipment, and in a

professional manner. To accomplish this, wemust employ the basic element of allorganizationssupervision.What is a

supervisor? How do we become supervisors?Why are some supervisors more successful thanothers? These questions are simple to answer ifwe memorize short statements. but statementsdo not make a successful supervisor.

2. You are probably asking yourself, "Whydo I have to worry about supervision?" Thismay be trueotoday. but as you gain experienceand knowledge. you may be placed in a

position requiring managerial knowledge, suchas a shift supervisor or trainer. To be asuccessful supervisor in this C-E career field,you must:

Use proper management techniques.Train others.Understand maintenance managementpractices.Maintain the equipment assigned to yourshop in peak operating condition by usingproper maintenance techniques andapplicable technical publications.

3. In this chapter we will examine only thefirst two items Jisted above. As we discuss theseitems indiVidually in this and succeedingchapters, keep in mind that, in actual practice,you may be involved with some or all of theseitems simultaneously.I. Supervision

1-1. The odds are highly in favor of yourbeing a supervisor sometime during your firsthitch. The Air Force works on the principlethat each member of an organization must beable to lead as well as to follow.

1-2. Just what is a supervisor? A supervisoris a person who directs the efforts of one ormore people in getting a job done. He is aleader and a manager as well. Not only does helay out the details of a job. assign and adviseworkers, but in many cases he has to assembleequipment and materials. Further. he must ratehis workers and account for their time and the

CHAPTER 1

materials they use. The quality of hissupervision is measured by the degree ofsuccess he achieves. There are four areas wewould like to eXplore briefly on thissubjectresponsibilities, employee relations,production, and performance reports.

1-3. Responsibilities. Responsibility isdirectly proportional to the importance of theassigned position. The desire to assumeresponsibility does not qualify a man for asupervisory job; he must be able to accept theresponsibility without reservation.

1-4. As a supervisor, your responsibilitieswill never cease. You will have a responsibilityto your mission, ta higher headquarters, to yourunit and other units, and to personnel underyour supervision. Often, it will seem that yourresponsibilities conflict with each other. Underthese conditions you must choose one course ofaction and proceed. You should have theauthority to assume your responsibilities, andyou must always remember never to assignresponsibilities without also delegatingsufficient authority to assure that the courseyou have chosen can be followed.

1-5. You, must have the courage to "stickyour neck out" when the occasion arises, to actcontrary to all advice when your judgmentdemands it, and to be willing to take full blamewhen things go wrong. As a supervisor,regardless of how you person_ally may feel, youmust be decisive and act promptly.

1-6. Responsibility to the mission.Responsibility to the mission is your primaryobjective. Your responsibilities to your unitand your personnel are secondary. There willbe times when you will have to disregard theneeds and feelings of your subordinates inorder to accomplish the mission. At such times,the esteem your men hold fcr you will sufferunless they have been thoroughly indoctrinatedwith responsibilities to the mission. You shouldimpress this fact upon them through talks,discussions, training, and personal example. Inspite of such orientations, not all of yourpersonnel will support you in this. There arealways some who place personal desires beforeduty; however, they will eventually fall in lineand follow the majority.

14. Resounsibility to your superiors. This is

another objective you must realize. Wheh y

fail to support your superiors, you jeopardize

your own efforts. When you criticize your

supervisors and their methods, you, in turn.invite criticism by your subordinates. They are

simply following your example. To avoki this,

carry out the directives of your superiors as if

they were your own. Should you disagree with

the directives, take up your disagreement with

your superior and not with your subordinates.

If the directive still stands after you havepresented your disagreement, carry it out to the

best of your ability without excuse, alibi, or anyattempt to pass" the buck.

1-8. At times you may be directed to dosomething contrary to directives from higherheadquarters. When this happens, do nothesitate to bring it to the attention of yoursuperior. If you are still directed to carry out

his original instructions, do so withoutreluctance. In such a situation your superiorassumes full responsibility for his action. You

must realize that he is nearer to the top and

knows more than you do about the overallmission. Responsibility to the mission is yourprime interest, regardless of how unpleasant the

order may seem.1-9. Responsibility to yourself Although

you know that your commander and yourworkers have their own opinions of yourability; you rpm constantly analyze yourself.

The following checklist can serve you as a

guide.a. Understand my organization.

(1) Know the functions of my unit andhow they contribute to the total

.nission.(2) Show each worker how his job fits into

the overall picture.(3) Determine lines of authority and

responsibility.(4) Determine number and type of

workers required in my unit.

(5) Make logical duty assignments basedon clear lines of responsibility andauthority.

b. Get the work out.(1) Give directions that are simple,

understandable, and specific.(2) Review work for progress in meeting

schedules.(3) Coordinate the work of my unit and

take action as necessary.(4) See that my workers do what is

rightfully expected of them.

(5) Emphasize the control of cost.(6) Minimize overtime in my unit.(7) Resolve my production problems

immediately.

c. Plan and schedule work.(1) Know the work capability of my unit.(2) Know the workload of my unit.(3) Plan priorities of work and schedule

accordingly.(4) Plan for best use of manpower, space,

and equipment.(5) Establish rcaiistic goals for the group.(6) Have my group participate in setting

its own goals.(7) Plan to meet deadlines and

emergencies.(8) Plan and schedule overtime when

necessary.d. Improve work methods.

) Anoallyez. e operations of my unit as a

(2) Evaluate present methods ofperforming jobi.

(3) Develop and apply improved

methods.(4) Encourage and assist workers in

submitting their ideas.e. Determine performance requirements.

(1) Determine what is expected of eachworker.

(2) Discuss tentative requirements witheach worker concerned.

(3) Make final determination ofrequirements based on needs ofmanagement, supervisory experience,

and workers' suggestions.(4) Evaluate objectively each worker's

performance based on requirements.

f Develop workers.I ) Select right person for the job.

(2) Help worker make adjustments on new

job.(3) Determine training needs of workers

and provide training.(4) Measure results of training in terms of

production cost and improved skills,attitudes, and other factors.

(5) Let workers know how they are doing.

(6) Discuss career opportunities with

workers..(7) Develop an understudy.

g. Maintain a cooperative workforce.(I) See that workers are rewaroed for jobs

well done.(2) Commend entire group on

performance when deserved.

(3) Transfer and reassign workers for the

best use of their abilities.(4) Earn worker's confidence and loyalty.

(5) Encourage workers to discuss theirproblems with me.

(6) Adjust differences fairly and

objectively.(7) Keep workers informed.

(8) Develop and maintain effectivediscipline within the work group.

(9) Initiate corrective and punitiveactions as needed.

(10) Insure safety Ind welfare of workers.h. Improve myself.

( I ) Recognize my "shortcomings."(2) Improve my technical knowledge and

skills.(3) Improve my ability to get along with

people.(4) Develop a cooperative relationship

with my workers, my superiors, andother personnel.

(5) Develop a good attitude toward myjob and the base.

1-10. Employee Relations. Much has beenwritten in psychology books about how you canget along better with other people.Considerable emphasis has been placed in base-level management training programs on thewhy and how of working with people in a teamspirit to reach a common goal.

I -1 I. Factors in good relations. In place of along discussion here on the factors concerningemployee reiations, we will list the normalfoundations necessary for good employeerelations and then -present an outline of aneffective procedure for handling humanproblems. The following items will aid you withmany employee relation problems. They are notall-inclusive, but are enough to give you a startin the right direction. As you observesupervisors at work and gain experience, youcan add to the list.

a. Let each worker know how he is gettingalong.

(1) Figure out what you expect of him.(2) Point out ways he can improve his

work.(3) Praise in public, criticize in private.

b. Give him credit where credit is due.(1) Look for extra or "beyond the call of

duty" type of performance..(2) Tell him while its "hot."

c. Tell people in advance about changes thatwill affect them.

(1) Tell them why, if you know.(2) Sell them on the idea of accepting the

change.d. Make the best use of each person's ability.

(I ) Look for that extra ability that maynot be in use.

(2) Never stand in a man's way.1-12. Handling problems. You may have

trouble at times handling problems. You maybe confronted with difficult situations whichappear to have no solution. There are,fortunately, tried and true procedures whichyou can (*se to help solve these problems. A

3

procedure you can apply in a difficult situationis as follows:

a. Get the facts.(1) Review the record.(2) Find out what rules and regulations

apply.(3) Talk with the individual concerned.(4) Get opinions and feelings.(5) Be sure you have the complete story.

b. Weigh and decide.(1) Fit all the facts together.(2) Consider their bearing on each other.(3) Decide what possible courses of

action are available.(4) Check practices and policies of your

organization at your level.(5) Consider the solutions and their

effects on the individual or group, andon work.

(6) Don't jump to conclusions.c. Take action.

(1) Will you handle this yourself?(2) Will you require help?(3) Should you refer this problem to your

supervisor?(4) Make your decision and time your

actions to fit your decision.(5) Don't pass the buck.

d. Check results.(1 )(2)(3)

(4)

How soon will you follow up?How often will you need to check?Observe changes in output,relationships, and attitudes.Has your action increased ordecreased the work output of theindividual or group?

1-13. Production. Whether your unit is on alarge base or at a remote site and whether yourunit is responsible for organizational-, field-, ordepot-level maintenance, the end results arewhat count. There are four natural divisionsfalling under production: (I ) assignment ofwork, (2) review of work quality, (3)production controls, and (4) performancestandards. First, let's look at assignment 'Ofwork.

1-14. Assignment of work. Giving orders ormaking job assignments is an important anddifficult part of a trainer's duties. Individualsreceiving instructions are all different in theirpersonality makeup. Some people just naturallyresent being "told" what to do. Still others maynot resent orders but. because of their own lackof initiative, tend to blame their supervisor fortheir own mistakes because of his inability toproperly assign work. On the other hand, thereare people who seem to have a "knack" forreceiving instructions and carrying them outsuccessfully.

1 7

1-15. Regardless of the kinds of peopk inyour work group, you should remember that themanner in which work is assigned may be thekey to the successful completion of any job.The following 10 rules are good ones to followwhen making assignments

(I) Be well informed about the work youassign.

(2) Give each man a job you know he can do.(3) Give clear, brief instructionsspeak

clearly.(4) Do not take head-nodding as

understanding. Invite questions fromtrainees.

(5) Repeat your instructions if they are notunderstood. This may save much timeand unnecessary work in the long run.

(6) Give orders through proper channels.(7) Demonstrate steps or job tasks wherever

necessary.(8) Put complex instructions in writing,

choosing each word with care.(9) Do not give too many orders at one time.(10) Know your mentheir abilities,

qualifications, and limitations.1-16. In connection with item (10), you must

learn what each man can do best. Perhaps oneis especially good at inspection. Another mayhave the knack of untying knotty maintenanceproblems. It's only good common sense toplace a man where he can do his best work. But.remember this, just because a man does one jobexceptionally well, it is not always advisable tokeep him in. that job indefinitely. He should bewell rounded in his training, and be able toperform all of the required duties of his jobdescription, his AFSC, and the Specialty.Training Standard. Your job is easier whenevery man can perform well on all the duties inhis specialty.

1-17. Review of work quality. When youinspect a completed task, give it a thoroughexaminationnot just a quick once-over. Thereare at least two good reasons for a thoroughcheck .

1-18. First, the equipment that has beenworked on must operate properly for thesuccess of the mission, and it must be in safeoperating condition. Second, inspection ofcompleted work may be turned into anexcellent learning device for the man intraining. Your method or technique ofreviewing completed work determines theinspection's usefulness as a teaching device.Where is a better place for the trainee to learnthan on the equipment?

1-19. Properly reviewing job assignmentsrequires a considerable amount of skill andtact, as well as a thorough understanding of the

mechanics of the job. As you talk to thf worker,stress both the strong and weak points of hiswork, Praise work that has been performedskillfully but do not tolerate sloppy work..Avoid criticism, sarcasm, or personalreferences since thesc comments may cut deeperthan you realize and leave the worker with astrong feeling of dislike for you. in brief, don'tjust use words. Demonstrate correct proceduresand give the man the opportunity to correct hisfaults.

1-20. There is one other thing you shoulddo. Don't check completed work only., but alsocheck job progression. In short, don't wait untilthe job is finished, because a job sometimes hasto be redone if an error enters the picturebefore the job is completed.. Failure to checkjob progression may cause loss of time andwork output and, in the end, may lead to harshfeelings and loss of ambition on the part of theman who finds his efforts wasted because hewas forced to do the same job over.

1-21. Production controls. Productioncontrols include mechanical and graphicalstandrrds, time budgeting, and workscheduling. Mechanical standards are largelydetermined by your Specialty TrainingStandard and the type of test equipment andtools required on the job. Graphical standardscan be accomplished at the shop or higher levelwith specially designed forms and graphs. Achart can show you at a glance what man isworking on what job, how the job isprogressing, what aircraft and system isinvolved, and so on.

1-22. Performance standards. One of thebiggest problems you face is the determinationof performance standards. In some cases, thesestandards are prepared and handed to you fromhigher authority. In other cases, you are facedwith devising standards of your own which willfit the job to be done.

1-23. You are usually faced with measuringperformance from two standpointstheindividual worker and groups of workers.Usually, the task is eased somewhat by the factthat the worker in the group is doing the sametype of work as his fellow workers. However,evaluation of performance must beaccomplished, and it must be valid from thelevel of the worker as well as the supervisor.

1-24. Performance standards are day-by-dayqualities which you, as a supervisor, shouldobserve. You should make mental notes, orperhaps even written ones which may bereferred to in the future. Be mentally alert andkeenly observant of the jobs performed by thoseyou supervise.

4

18

1°

11

1-25. Noncommissioned Officer andAirman Performance Reports. Another areathat you will find of major importance, as asupervisor, is the NCO and airman performancereport. The preparation of this report requiresmany of the qualities outlined in the precedingparagraphs. The performance report requirescareful attention as it is the primary tool inmaking nominations for training, specialassignments, and other special actions. Inaddition, this document is an important part ofthe Air Force promotion system.

1-26. The importance of proper evaluationof all personnel cannot be overemphasized. As

a supervisor, you have the continuingresponsibility for the preparation of accurate,honest, and objective performance reports.When it becomes necessary for you to submit areport. it is imperative that you be thoroughlyfamiliar with the instructions in AFM 39-62,Noncommissioned Officer and AirmanPerformance Reports. This manual will giveyou the correct form number and complete andup-to-date instructions on the preparation andsubmission of the performance report.2. Training

2-1. Because of constant changes incommunications and electronics equipment in

the Air Force, training is a continuousrequirement. When you enter the Air Force,you are trained on equipment that is currentlybeing used. Later, as newer models aredeveloped, you require additional training toqualify you to maintain them efficiently.

2-2. Besides the equipment. there are manyother facets of your job you must learn toadvance in your career field. How fast youadvance depends largely upon how hard youwork and how well you take 4frIvantage of themany opportunities for training to improveyourself technically, culturally, and militarily.

2-3. General Plan for Air Force Training.Since training is always an important part ofyour Air Force career, you should know thetraining systems and methods employed. Insome instances, you are required to advise andtrain other airmen to acquire the knowledgesand skills you already possess. But before youstart training others, let us look at the systemsthrough which you may be trained.

2-4. Although there are definite trainingprograms preparing airmen for the many jobs inthe C-E career field, each person, to a

considerable extent, must look after his owninterests. You already know that skill levelsand promotions are related; so how do youmove from the 3 skill level to the 9 skill level?For a start, look at figure I.

2-5. This figure shows the route that your arefollowing in your Air Force career. You

attended a technical training course to reachyour present 3-level AFSC. You are nowentering on-the-job training (OJT), to qualifyyou for the 5-level AFSC. This will he followedby another period of OJT to qualify you for the7-level AFSC. You become qualified for the 9-level AFSC by experience in the unit to whichyou are assigned. There is formal schooltraining that you may take to help qualify youfor the 9 level. The only mandatoryprerequisite for the 9 level is a passing grade onthe USAF Supervisory Test.

2-6. Another possibility is.to qualify for onespecialty at the 5 level, and then qualify in yetanother specialty at the 5 level beforeadvancing to the 7 level in either one of the twospecialties. Such qualifications are throughformal school and on-the-job training; this isknown as lateral training. This means trainingfrom one ladder to another in the 30 CareerField in those AFSCs designated by Air ForceHeadquarters.

2-7. At various times in your career, you maybe enrolled in a formal school course. You willfind that these cpurses are identified .by acombination of 1etters and numbers. Theprincipal identification is the AFSC number. Inaddition to this, courses usually have a numberplus a three-letter prefix and a title.

2-8. For example, take Course 3ABR30430,Radio Relay Equipment Repairman. The 3 tellsyou that it is an ATC resident technical trainingtype course. The A tells you that it is an airmancourse (officer courses begin with the letter 0);the B tells you that it is a basic technical course;and the R tells you that it is a resident (formalschool) course conducted by the Air TrainingCommand. The title is shown by the words"Radio Relay Equipment Repairman."

2-9. You will find a large number of coursesdescribed in Air Force Manual 50-5, FormalSchools Catalog. Each has a title andalphabetical-numerical identification similar tothe one just described.

2-10. The Dual-Channel Concept of On-the-Job Training. Note by referring again tofigure 1 that there are three general ways ofincreasing your usefulness to the Air Force andadvancing your caregr- at the sametimetraining in a formal technical school, on-the-job training, or a combination of these two.

OJT is divided into two elementscareerdevelopment and job proficiAlcy development.

2-11. Career development. Careerdevelopment is the acquiring of generalbackground knowledge required forunderstanding military and career areafunctions. In this element you study the general

Air Force subjects, principles of yourequipment, and the specific information

5

Li

® S L r...EvELAFSC

r USAF SUPERVISORYTEST

ADVANCEDTECHNICAL COURSES

AWARD OF 7 SKILL LEVEL AFSC

REQUEST FOR UPGRADING.AF FORM 1098

SUPERVISOR'S R ECOMME NOAT ION

CAREER DEvELOPmENTCOURSE A

SUPERVISOR'S CERTIFI-CATION OF PROFICIENCY

JOB PROFICIENCY GUIDES

. AWARD OF 5 SKILL LEVEL AFSC

REQUEST FOR UPGRADINGAF FORM 1098

SUPERVISOR'S RECOMMENDATION

CAREER DEVELOPMENTLOURSE

SUPERVISOR'S CERTIFI-CATION OF PROFICIENCY

JOB PROFICIENCY GUIDES

AWARD OF 3 SKILL LEVEL AFSC

TECHNICAL SCHOOLEND-OF-COURSE TEST

FORMAL BASIC1 ECHNICAL COURSE

BASIC MILITARY TRAINING

-4RECRU.INENT

Ftgure I Norma iiI progressiun. duaI-channel concept.

6 2

necessary to perform the duties of your AFS. Inbrief, the first step you take to qualify for ahigher skill level and higher rank in the AirForce is to study the applicable CareerDevelopment Course (CDC), of which this isthe first volume. This volume contains thegeneral knowledge you need to pursue yourcareer in whatever job you may be assigned inthe 304 career field.

2-12. Job proficiency development. Jobproficiency development is primarily theacquisition of skill by actually performing theduties and tasks of an AFSC; secondarily, it isthe application of the knowledge you learnedfrom studying the CDC. Your supervisorduring your on-the-job training uses as hisguide the applicable Job Proficiency Guide(JPG).

2-13. OJT involves practical application.You are placed in an operational situationrequiring you to perform certain specific tasks.As you acquire skill in the simpler tasks of yourspecialty, you are given other tasks which aremore and more difficult. Thus, you constantlybroaden your knowledge and skill until youmaster all the elements of your job. In themeantime, the Air Force benefits from yourproductiveness while you are learning.

2-14. Learning in an OJT sifuation is theresult of the close association of the trainee andthe skilled technician who serves as the trainer.Note, however, that this coach-pupil methoddoes not preclude short periods of groupinstruction. Group instruction is sometimes themost practical way for elaborating on matterspresented in the CDCfurther explanations ofsuch things as essential theory, backgroundmaterial, safety precautions, and so onthat alltrainees must know.

2-15. Look again at figure I , and note thatthe path you have followed to qualify for the 3-level AFSC is the completion of a formal basictechnical course. You proceed to the 5 level byon-the-job training. This entails satisfactorycompletion of the applicable CDC andreceiving the supervisor's certification ofproficiency based upon the standards in theJPG. You must also serve a minimum of 6months in OJT status.

2-16. The-re are many supplemental specialcourses that offer formal school instruction inspecialized areas, such as a particular model ortype ofsradio equipment. Since these courses donot award the 5-level AFSC, you still must

7

study the CDC, serve the minimum of 6 monthsin your duty assignment at the 5 level, and berecommended by your supervisor for award ofthe 5-level AFSC. Some of the special andsupplemental courses are "shredouts" and areidentified by a suffix.

2-17. As already noted, to advance stillfurther in your career, you take a moreadvanced CDC, plus a minimum of 12 monthsin OJT, to qualify you for the 7 level.

2-18. There is one other special requirementfor advancing to the 7 level. All trainees musttake either ECI Course 6, Management for AirForce Supervisors, or a comparable on-basecourse usually called Management-1 (MGT-l).Either management course provides you withthe vital knowledge managing men andmaterials so that your unit can make itsmaximum contribution to the mission of thebase. Usually, most airmen training for the 7

level take the MGT-I course on the base. If notpracticable, in isolated outposts or wherever

, the MGT-I course is not given, then ECICourse 6 is acceptable.

2-19. After completing a minimum of I

year's experience in the 7-level AFSC,completing the corresponding CDC, and beingrecommended by your supervisor, you will beawarded the 7 level (subject to the approval of

the Consolidated Base Personnel Office,CBP0). Qualification to the 9 level is based onexperience and supervisory ratings. Althoughthere are a few 9-level formal courses, they donot qualify you for the 9-level AFSC; finalaward depends on recommendation of thesupervisor and approval of the commander.

2-20. OJT Record Documents. You havebeen in the Air Force long enough to know thatthere are many records on file which concernyou. This recordkeeping was started by yourrecruiter and continues throughout yourtraining and total service. Although you don'testablish records nor post them, you do havethe responsibility of checking them foraccuracy at least once a year. So far as trainingrecords go, the most important to you is AFForm 623, Consolidated Training Record, as itis your only complete record of your training.

2-21. AF Form 623, Consolidated TrainingRecord. Much of the success or failure of anOJT program is determined by how well theindividual training records are maintained.Completeness, currency, and accuracy ofentries on the Consolidated Training Recordare often determining factors in deciding awardor withdrawal of AFSCs, entry into orwithdrawal from OJT status, assignment orwithdrawal of proficiency pay status, orselectivity for preferred assignments. The

Consolidated Training Record is an official AirForce document and requires as muchconsideration and care in its maintenance a:,any other official record. The knowledge,attention, and skill applied to the propermaintenance of training records are asimportant as the actual training conducted

2-22. AF Form 623 has four pages which aresubdivided into 11 parts on which to record theairman's progress and proficiency in OJT. Eachsection is individually identified according toits designated purpose. This permits therecording of all upgrade, lateral, and retrainingconducted on the job, in career development,and in formal courses. The form may also beused to record training which occurs afterupgrading has taken place. A copy of thedocuments supporting entries to AF Form 623may be filed with the form.

2-23. The AF Form 623 is not completeuntil the Air Force specialty training standardand/or the job proficiency guide for theappropriate Air Force specialty are made a partof the training records.

2-24. Since the AF Form 6.23 must beavailable immediately to the supervisor, it isordinarily maintained in your immediateworking area; however, it may be maintained inthe squadron. When you are transferred, the AFForm 623 must accompany your fieldpersonnel records to the new organization. It isnormally expected that training will becontinued unless you are specificallywithdrawn from training by the gainingorganization. If the gaining organizationdiscontinues the training, then the authority fordiscontinuance (appropriate personnel actionor orders) must be recorded on the AF Form'623.

2-25. Specialty Training Standard (Srs).The Specialty Training Standard for each AFSCis developed from AFM 39-1. An Air Forcespecialty description states the tasks whichairmen must be able to perform and theknowledge they must have. By the use of theself-contained code key, the standard indicates:

a. The extent to which personnel should betrained on each knowledge and task in order toqualify for upgrading to a specified skill level.

b. The extent to which airman coursesprovide training on each of the listed tasks andknowledges.

2-26. Your acquaintance with this documentis necessary since your initials as well as yourtrainer's are required to indicate that variousphases of your training are completed.

2-27. In addition, it might be of interest toyou to know that the Specialty TrainingStandard is the source of authority establishing

8

the content of the technical training courses,one of which some of you may have completedat Kees ler AFB. MS.

2-28. Unit Document Lis:ing (UDL.). Baremention of this document is all that is necessaryat present. The 'UDL gives a picture of howmany airmen, by AFSC, wade, and specific jobtitle, are available and how many jobs there are.For the AFSs which are short of personnel,additional men are trained; for tho,:.eovermanned, none can be trained,

2-29. Other Types of Airman TechnicalTraining. In addition to the two main types.oftrainingOJT and resident schoolsthere areseveral other kinds. These are briefly discussedbelow.

2-30. The field training program. Thistraining is conducted by Air TrainingCommand field and mobile trainingdetachments and traveling teams from ATCtechnical training centers. These units operateat the bases where there is a training need andthey conduct formal classroom instruction forairmen. The scope of this program isworldwide.

2-31. A field training detachment is. adetachment or school, controlled by AirTraining Command, permanently assigned toan Air Force base or other activity. The mobiletraining detachment, also controlled by ATC,travels to various bases as needed. It issupported by a mobile training unit whichcarries along with it the necessary training aidsand equipment. A traveling team consists ofone or more qualified instructors sent tosupport a one-time training requirement at thesite of the requesting activity.

2-32. The field training programencompasses a large variety of training activity.Generally, it offers the technical instructionnecessary to qualify personnel in thcknowledges, skills, and techniques required tosuccessfully operate. maintain, and controlassigned C-E equipment, aerospace and missilesystems, and their associated direct supportequipment.

2-33. Although training programs havenumerous and various names, don't let thatmake you forget that all training programs haveone major purposeto qualify the right manfor the right job and to assure the highest levelof proficiency in operational and maintenancepersonnel. So, in order to qualify personnelwith these capabilities, the Air Force must useas many types ot training programs aspracticable.

2-34. Airman on-the-job retraining. Asprovided by AFM 39-4, retraining isdesigned to qualify an airman in an Air Force

22

L

specialty not in the progression ladder of acurrently awarded AFSC. The principalobjectives of on-the-job retraining are:

a. To reduce the number of surplus airmenin grade and skill by retraining them intorequired grades and skills.

b. To prevent indiscriminate retraining ofairmen from required grades and skills.

2-35. In other words, the Air Forceendeavors to maintain a supply of airmen in thegrades and skills that are needed by initialtraining or by retraining them from grades andskills that become surplus.

2-36. If you should be retrained, you wouldmove from the career field in which youpresently hold an AFSC into another careerfield, or you might train to qualify for adifferent suffix to your AFSC.

9

2-37. Special training. Special training is

formal training that qualifies you inmaintaining new or special equipment.Normally, all special training courses are shortand are designed to meet emergencyrequirements. No AFSC is awarded uponcompletioni. of a special training course unlessspecifically approved by Headquarters USAF.

2-38. For futher information concerning theadministration of on-the-job retraining and on-the-job training under the dual-channelconcept. you can refer to the Air Force manualswhich prescribe the administration of these

programs. These manuals are AFM 50-234.On-the-Job Training and AFM 39-4, Airman'Retraining/Lateral Training Programs.

2-39. At this time, work the chapter reviewexercise for Chapter I in your workbook.

16

CHAPTER 2

Safety

TWO PRINCIPAL factors to consider whenyou learn how to maintain any piece of AirForce equipment are: how to maintain theequipment properly, and how to maintain itsafely,

2. Though you may think of these two factorsas being one in the same. there is a differencefor the purpose of our discussion in thischapter. Of course, if you don't maintainequipment properly, you may, at the same time.be maintaining it unsafely, for impropermaintenance is often the cause .of accidents.Furthermore, you may maintain a power sawproperly and, at the same time, get careless andfind your hand or fingers in the path of thewhirling blade. So, let us think of maintainingequipment Ain the two ways statedproperly(getting the job done quickly and accurately)and safely (preventing any injury to yourself orothers).

3. In this chapter you will learn about goodhousekeeping. accidem causes. fire prevention,first aid. radioactivity, off-duty safety. andaccident reporting.

4. You migrteask yourself. "Why is safety soimportant?" Offband, you might say. "Becauseis saves hves, prevents injuries, and protectsproperty." Well, that's true enough. but thereare some other important reasons. You want toearn promotions and progress in your career.don't you? Of course. You'll find that yoursupervisors will note not only how efficient youare on the job but also how safely you work.They aren't interested in productivity at thecost of preventable accidents. If you're a safeworker as well as an efficient one. you willstand a better chance of earning that promotionand also win the approval of your fellowairmen. If you know the principles andpractices of safe operation of shop equipment.you'll be able to give a timely warning to afellow airmana warning that might even savehis life!

3. On-Duly Safety3-1. The safety-conscious airman knows that

accidents are preventable and that good

10

housekeeping and good fire prevention practicewill eliminate most of them. The sate andsuccessful completion of a job demandsneatness and cleanliness in the work area.

3-2. Good Housekeeping. The first rule ofgood housekeeping is personal cleanliness. Ifyou are an orderly person and present a goodappearance, it will probably be reflected inyour work. A person who keeps himself cleanhas developed a habit which is carried over intoall his actions. You have made a great stride inthe right direction if you have learned to keepyourself and your clothing neat and clean. .

3-3. Next. there is your work area. Manyaccidents can be prevented, and much loss oftime and pain may he avoided if you keep yourwork area clean and orderly. For example, oilspilled on thc floor can cause you or another toslip and be injured seriously. If oil or fuel isspilled. cover it with an approved compound:pr better still. clean it up immediately. Keep thefloor or ramp free of obstructions. You can tripover an extension cord or a dropped tool andinjure yourself.

3-4. Some units that you will disassemblehave small parts which can be easily lost,broken. or mixed with other parts. To avoid theloss of time while you hunt or acquire anotherpart. keep your bench top in a neat and orderlycondition. A cluttered bench makes effectivework almost impossible and is the starting placefor an accident. Worn out or reparable partsshould be disposed of promptly in the correct.placesnot on the floor.

3-5. Other items that always find their wayinto your work area are soft drink bottles. Theyshould be kept in the break area and in theproper container. A broken bottle is a verydangerous object. Candy and gum wrappersbelong around candy and gurnor in a wastebasket. Never drop gum on the floor. It soilsthe floor when you step into it. and can cause a

3-6, Every shop has a designated place kirtoolboxes when they are not in use. Keep theniin place and keep the lids closed. It does notrequire much time or effort to open the box

when you reed a tool, and you may preventsomeone from cutting or bruising his shin.Most shops have a tool board to keep specialtools available to all who may need them. Keepunused tools in their proper place.

3-7. If your shop maintains a stockroom.keep cases and other goods stacked neatly inthe prescnbed location and to the designatedheight. This prevents damage to the storeditems and also makes them easily availablewhen they are needed.

3-8. Good ventilation is conductive to goodwork. Ventilation is actually necessary for thegood health and safety of personnel. Your workoutput drops off considerably if you . areuncomfortably hot or cold, or if there is a lackof fresh air. If the air is dusty in your shop. or iffumes are present. consult your supervisor ortrainer so that he can be made aware of thecot ditions under which you are working andcan take the necessary corrective action.

3-9. Proper lighting is another requisite fordoing good work. Definite standards have been'set up by the Air Force to provide the correctillumination I r all installations. These shouldbe followed, since good lighting works hand inhand with good housekeeping to eliminatemany accident hazards.

3-10. Accident Causes, Effects, andControls. It is trueaccidems are preventable.The law of cause and effect is the basicingredient in all accidents. Accidents do nothappen without a reason. and the identification.isolation. and control of causes are the basicprocedures of all accident preventiontechniques. Even natural elements can becontrolled to some extent, and it is only in therealm of such phenomena as lightning, storms.or floods that accidents are extremely difficultto prevent. However, even the effects of thesecan be minimized, as in the case of securingaircraft when strong winds are expected.

3-11. Indirect causes. Theoretically.preventable accidents may be traced to causesoriginating in the heredity and environmentof individuals. These beginnings may furthermanifest themselves in unsafe personalcharacteristics which allow an individual toperform an unsafe act or overlook or toleratean unsafe condition which may result in anaccident. The injuries, property damage. andloss of combat capability which followcomplete the costly sequence. The detectionand elimination of unsafe personalcharacteristics. such as inattentiveness.excitahihty. impatience. and stubborness. arenormally extremely difficult. On the otherhand, the elimination of unsafe acts and

11

conditions is a relatively simple and effectivemeans of accident prevention.

3-12. Direct. causes. As the last and mostobvious element f the cause sequencepreceding an accident, unsafe acts andconditions may be considered the immediate ordirect cause of any accident. When this directcause is removed, the sequence is interruptedand the accident cannot happen. Usually.unsafe acts and conditions can be anticipated,readily identified. and eliminated almostimmediately upon discovery. Because of this,practical accident prevention measures aredesigned to prevent or eliminate direct causes.and suitable controls have been developed forthis purpose.

3-13. Approximately one-fifth of all USAFground accidents result from Governmentmotor vehicle operations. However. less than 5percent of all injuries to military and civilianpersonnel are attributed to this source, sincenot all motor vehicle accidents result inpersonal injury. Of the total number of theseaccidents. some three-quarters are caused byunobserved backing. excessive speeds for roadconditions. exceeding speed limits. followingtoo closely, and failure to yield right of way.All of these unsafe acts can be eliminated.

3-14. Approximately two-thirds of the totalAir Force accident experience remaining is

sustained in activities such as aircraft andmotor vehicle maintenance, sports andrecreation. and domestic activities.

3-15. Direct costs. Each year accidents causehundreds of deaths and thousands of injuries toAir Force personnel. These fatalities andinjuries, most of which could have beenprevented, impose a tremendous direct cost onthe Government for medical care. insurancepayments. claims, compensation for civilianemployees, and related services. Accident costs,carefully computed over a representative periodof time. permit accurate estimates of theaverage direct cost of each fatality, injury. andfirst aid case. When these costs are addedtogether. the total is staggering, and shouldemphasize to everyone the necessity forpreventing accidents. Equally as important asmoney costs is the toll in humansufferingsomething that cannot be evaluatedin dollars and cents.

3-16. An additional drain on Governmentfunds happens when equipment, property. andsupplies are destroyed or damaged bypreventable accidents. Not only is the cost ofrepair or replacement significant. butoperations may also be seriously handicapped ifparts or replacements are not immediatelyavailable. When aircraft or motor vehicles are

ot,.. of operation for any length of Ime.assigned missions may be delayed, n ha

tazzical situation the results could bL critit:al.3-17. Indirc cr costs. In additic 1 tu c..!

costs, every accident involves indir,:ct costsestimated to be several times those that can h.:readily counted. Indirect costs include the lossof time and production of the injured and thosewho aid them, timc lost by curious orsympathetic people at the scene of the accident,time lost in investigation, cost of trainingreplacements. interference with operations, anddamaged equipment. Though less tangible thandirect costs. indirect losses can be computedand totaied in the overall cost of any accident.Any installation can establish a valid indirectcost ratio by calculating these losses over arepresentative period of time and comparingthe total with equivalent direct costs. Studiesindicate that the ratio of indirect to direct costsis at least 4 to I. For every one dollar of directaccident costs, there are at least four dollars ofindirect costs. Again, these losses can beprevented !

3-18. Accident control. Usually accidentscan be prevented through adequate safetyengineering and education. But there are somepeople who are a hazard to themselves andothers because they fail to comply withaccepted safety standards. It is these persons forwhom the strict enforcement of safety practicesis necessary, backed by prompt correctiveaction. No organized accident prevention effortcan be successful without effective enforcement.because accidents are frequently the directresult of the violation of safety principles. Thisis particularly true of vehicle accidents, manyof which are caused by unsafe acts constitutingtraffic law violations.

3-19. To be completely effective, accidentprevention controls cannot be applied -hit ormiss." All engineering, education, training.supervision, and enforcement measureS must bebased on factual evidence and directed towardthe solution of specific problems. Only in thisway can controls be adequately applied.

3-20. Fire Prevention. Closely allied withgood housekeeping and absolutely necessaryfor any organization is a smooth working fireprevention system, since the best cure for anyfire is to prevent its occurrence. To do thisrequires that you carry out ali safet%precautions with regard to the prevention Offires. It also means that you must know what todo and how to do it when a fire does occur.

3-21. Precautions. Many fires are caused bycarelessness and poor housekeeping. Oily ragsthrown in a corner are excelient material for ahealthy fire. Poor storage practice. especiallyof inflammable materials, has caused many

1

avoida:ile fires. Overloaded electrical outletscoupled with defective circuit breakers mayako cause a fire. No smoking signs were madeto he observed; lighted cigarettes and matchesthrown in wastepaper baskets full of, paper arenot usually put out by the fall. Here are a fewprecautions ;hat you shoule observe withregard to fire prevention; yoti can probably addto the list from your own experiences andwarnings that you have read or heard.

a. Do not allow oily rags to accumulate.b. Observe the signs in the :AO SMOKING

areas.c. Never allow your clothing to become

saturated with fuel or oil. If it should becomethat way accidentally. change your clothing assoon as it is possible.

d. Do not permit gasoline, kerosene, jet fuel,or any other inflammable fuels to be stored inopen containers.

e. Always make sure that the static lines arein place and that the aircraft is groundedproperly before you work on it.

1. Never deposit cigarettes or matches in awastebasket even if they appear to be out.

g. Do not open any oxygen valve near aflame or a lighted cigarette.

3-22. When fires do occur, you must beready to fight them quickly and effectively. Thismeans that you should knoW the telephonenumber of the base fire department, thelocation of the fire extinguisher, and which typeof extinguisher to use for the type of fire youare fighting.

3-23. The telephone number for the base firedepartment is usually posted in large ,letters.These posters are spaced at intervals in theshop, in the barracks, and on the flight line. Asa rule, the base telephone directory has thisnumber printed in large letters on the coverpage or on one of the first pages of the book. Ifalarm boxes are installed on your base, learnwhere they are and how to use them.

3-24. Fire extinguishers. Fire extinguishersfor the most part look alike, but a fire canincrease if you use the wrong type ofextinguisher on it. Figure 2 shows you whattypes of fires each extinguisher can be used onand its effective range. Above all, find thelocation of the fire extinguisher in your workarea. determine what type it iS, and plan howyou are going to use it if the occasion shouldpresent itself.

3-25. Radiation Prevention. You may. inthe future, be required to work aroundradioactive material or materials that have beencontaminated by radiation. You must be awareof the safety precautions to observe and. aboveall, you must instantly recognize the radiation

26

Type ofEstinguisher

,

Pump- Tank Soda Acid Foam Types.CarbonDioxide

Chloro-broriomethane

Use on-

I

Type A Fires:Wood. trash.paper. waste,

'

Type A Fires:Wood, t rash.paper. waste.

Type B Fires!Casoftne. oiland oil basematerial var-nigh... etc.

Type C Fires:Electrical fires.conlined fires onoil, ordinarycombustibles.

Type Fires: IElectrical fires.

May alsobe used on

Wood. trash.paper. wame.

Type A and Bfires.

Small fires.

Methodof using,

.Direct streamat base of:lames.

I

Work close forpenetration. Dt-race stream atbase of flames.

,

Apply completeblanket of foamover surface,Avoid a directstream on oilsurfaces.

Apply so that gasfloods material ina wave-working withdraft. Extinguisherlasts only fewseconds.

Direct streamon base of lireor hot surface.

Effectiverange

,

JO to 40 feet 30 to 40 feet 3 to 6 feet,

15 to 30 feet

Principle ofextinguish-Tent

,

Cools burningsurfaces belowignition point,Any streamgenerated tendsto smotherflames. Practi.catty no gasl eeeee nasals.

blankets burningmaterial withfroth or foam.which excludesoxygen. Coolsand insulatessurface from heatBlanket preventsflaehbacks,

Flame issmothered byheavy blanketof nentlammable gas.

Upon contactwith flame orhet surface, theliquid teinte a heavysmotheringvapor.

Wa rning Never use oncharged electri-cal equipment,varnish. oils orother fuels. Pro-tect from fresaing.

Never use oncharged *loser,-cal equipment.varnish. oils orother fuels. Pre-tact from freezing.

Never use oncharged electrical equipment.Protect f rom(teasing.

,

COZ will not sup-port life. Avoidextended exposurein area where ithas been used. es-pecially in pits.

De not use inclosed Uliquid comes intecontact with skinor eyes, washimmediately withwater followed bymedical treatment.

Figure 2. The use of common fire extinguishers.

warnings. We have prepared a general list ofprecautions that must he observed. Remember,.you cannot: see radioactivity and it may beseveral hours before you feel the effects ofradiation.

3-26. Precautions. Observe the followingrules when you work arounu radioactivematerial:

a. You must have a physical examination ifyou are exposed to radiation. If you areworking around radiation.. you will bescheduled tor an examination periodically.

h. Re sure that the base monitor briefs you(m the measures and hazards involved.

e. You must wear protective clothing whileworking around radioactive materials.

Always wear a film badge and or a pocketdosimeter when you are around radioactivity.

e Practice good hygiene. Wash your handsand face thoroughly hetore eating or smoking.

t Do not eat. drink. smoke. or chew eum inthe area.

g Report any scratch or cut made hy a

radioactive object. Such scratches may causeseveresores and hg very slow in healing.

13

h. Do not wear personally owned items suchas watches and rings. They may becomecontaminated.

i. Do not handle telephones. reports, orother similar objects while you wear protectivegloves. Your gloves may contaminate them.

j. Do not breathe dust or metallic particleswhich come from radioactive materials.

3-27. AFTO 9 series. The AFTO 9 seriesforms help you identify radioactive material.These forms are yellow with a red symbol. The00-110A series technical orders contain acomplete description of the forms andinstructions for handling cclitaminated items.Figure 3 shows a radiation warning placard.AFTO Form 9C. Be alert for radiation warningplacards. tags. or tables: any time you see one.take the necessary precautions.

3-28. The AFTO 9 series forms and theirsizes are listed as follows:

a AFTO Form 9. Radiation WarningPlacard. is. 18 'x 24 inches

h. AFTO Form 9A. Radiation Warning Tag,is 3 1/2 X. 6 1/4 inches.

YELLOW BACKGROUND MAGENTA INSIGNIA BLACK TYPE

AFTO

ApPROVA L. OF BUDGET BLJFIEu NOT REQUIRED

CAUTION

RADIOACTIVE

MATERIAL

AUTHORIZED ENTRANCE ONLYCONTACT

RADIOLOGICAL MONITOR OR SUPERVISOR IN CHARGE

Form.JUL III CPREVIOUS EDITIONS OF TmIS FORM ARE OBSOLETE AF C16 11211411 IBM

Figure 3 Radiation viarning placard .

c. AFTO Form 9B, Radiation WarningTable, is 6 1/2 x 6 inches.

d. AFTO Form 9C. Radiation Area.Restriction Placard, is 18 x 6 inches.

e. AFTO Form 9D, Radiation IngestionHazard Placard, is 8 1/2 x 11 inches.

1 4

f. AFTO 1-orm 9E. Area Restriction. NoRadiation Material Placard. is '14 x 5 inches.This placard warns personnel about takingradioactive material into the posted area.

3-29. Accident Reporting. If you areinvolved in an accident, yoursupervisor and

28

the ground safety office will he required to fillout forms reporting the circumstances and theextent of damage and injuries sustained.Although there are several forms, the USAFForm 711 and 711a. GroundAccident/Incident Report. is the one that willconcern you most. Your supervisor willcomplete this form from your, information.Your cooperation will be necessary. Accidentsare reported on forms prescribed by AFR127-4 and involve.

Injuries to Air Force military and civilianpersonnel or those stationed, assigned. oremployed at Air Force installations.

Injuries to non-Air Force personnelresulting from Air Force ground operations.

Accidents and incidents resulting indisabling injuries and/or property damage of525 or more. Such accidents are referred to as-reportable ground accidents." When anaccident is reported for any of the foregoingreasons, all injuries without regard to theirextent or amount will be included.

4. First Aid4-1. Air Force Pamphlet 50-55. GMT First

Ail!. is an excellent publication for studyingfirst aid. But first aid is so important to you. toyour friends, and even to total strangers that thefundamentals should be repeated in thispublication.

4-2. There arc two types of emergencies thatfew people escape meeting some time in theirhves. These emergencies require first aid orlives can be lost. They are: (1) emergencytreatment of wounds or serious cuts and (2)artificial respiration for victims of electricalshock or drowning.

4-3. You don't have tw be a doctor ormedical technician to help an injured person.For that matter, accidents seem to happen more

often than not beyond the convenience ofprofessional help. The life of an injured yrson,therefore, often is held in the hands of manypeople. Let's be sure we are ready.

4-4. Emergency Treatment. To treat awounded person. you should be able to carryout the three life-saver steps which follow:

STOP the bleeding.PREVENT or TREAT shock.PROTECT the wound.

Memorize these three steps and learn thesimple methods of carrying them out.

4-5. Control of bleeding. Uncontrolledbleeding may cause or increase shock and resultin death. Stop any severe bleeding immediately.To stop bleeding. first apply pressure to thewound with a dressing or. if necessary, somesubstitute material such t.ls a clean shirt,handerchief. etc. Be sure to use clean materials.Place the dressing or cloth against the woundand apply firm pressure. See figurn4. Continuethe pressure as long as needed. Use anadditional dressing to cover the wound ifnecessary, Wrap the tails of the dressing aroundthe wounded part and tie the ends to hold thedressing firmly against the wound.

4-6. If the wound is on an arm or leg and ifthe bleeding continues, place the patient on hisback with the wounded arm or leg raised. Thebleeding is only slowed, not stopped. by raisingthe arm or leg. so you still have to use thedressing and pressure. DO NOT raise the limbif you think the bone is broken. Moving abroken arm or leg is dangerous, since it mayresult in further injury to the victim and mayincrease shock.

4-7. Often you can reduce or stop bleedingby applying hand or finger pressure at variouspoints on a patient's body. The locations ofthese points are shown in figure 5. The pressure

rigure 4 Moo the hleetlingpad r Jrcssink,

15

IN FROW1 C.7 THE EAR

THC JAM10 THE NECK

CIEHIND THE COLLAR DONE

ON THE INNER SIDEOF THE ARM

IN THE GROIN'

0 TOURNIQUET

Figure 5. Stop the bleedingpressure points.

points in the groin and neck are particularlyimportant. If the wound is too high on the legfor a tourniquet to be applied, the pressurepoints in the groin can be used. A neck pressurepoint should be used when the casualty has aprofusely bleeding scalp wound. Use the neckpressure point only as a last resort when othermethods of stopping bleeding have failed.Figure 4 shows a means of applying pressurewith the hand. This method may also be usedon the head and neck pressure points, using theindex and middle fingers. The heel of the hand,is used to apply pressure to the groin.CAUTION: Do not apply pressure to bothneck points at the same time. You would cut oftthe blood supply to the brain, which wouldcause unconsciousness and death.

4-8. A tourniquet shourd be Used only forsevere, life-threatening hemorrhaging thatcannot be controlled by other means. It shouldbe used only when severe bleeding involves anextremity in which the large arteries aresevered, or in case of partial or completeseverance of a body part. These are the onlyinstances where the application of a tourniquetis justified. If necessary to use a tourniquet,follow the procedure illustramd in figure 6.

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4-9.. A tourniquet should be tightened onlyenough to stop arterial bleeding (gushing ofblood from the wound). The veins will continueto bleed slightly until the limb is drained of allblood; thus, bleeding will not be reduced byfurther tightening of the tourniquet.

4-10. Always place the tourniquet betweenthe wound and the heart, and, in most cases, aslow as possible above the wound. However, inthe case of bleeding below the knee or elbow, atourniquet should be placed just above therespective joints. When possible, protect theskin by putting a tourniquet over the smoothsleeve or trouser leg. CAUTION: The victimshould be seen by a medical officer as soon aspossible once the tourniquet is applied. Thetourniquet should not be loosened by anyoneexcept a medical officer prepared to stop thebleeding by other means and to restore theblood volume by transfusion. Repeatedloosening of the tourniquet by inexperiencedpersonnel -is extremely dangerous, because thelife of the individual is endangered by furtherloss of blood.

4-11. Prevention and treatment of shock.Shock is a condition of great weakness of thebody. It can, and often does, result in death

1. MAKE A LOOP AROUND THE LIMB. 2. PAZ A STICK UNDER ThE LCOP.

3. TIGHTEN JUST ENOUGH TO STOP BLEEDING. 4. SECIME TOURNIQUET IN PUCE

Figure 6. Stop the Dieedingteurnlyuet.

Shock may tie caused oy any kind of injury; andthe more severe the injury, the more likely theoccurrence of shock. Shock may not appear forsome time after injury. Always treat an accidentvictim for shock whether or not he hassymptoms of shock.

4-12. Symptoms of shock are not difficult torecognize. A person in shock may show one ormore of the following conditions:

a. He may tremble and appear nervous.b. His pulse becomes rapid and weak.c. He may be excessively thirsty.d. He may become quite pale and wet with

sweat.e. He may gasp for air and may even faint.f He may vomit or complain of nausea.

Again, remember to treat for shock. Don't waitfor one of the above symptoms to appear.

4-13. The same procedures are used toprevent and to treat shock. The first step is tomake the victim comfortable. He should bekept lying down in order for greater amount ofblood to flow to the head and chest where it isneeded most. Loosen his belt and any othertight-fitting clothing. Make sure there are nobroken bones before you move him. Cover himto keep him warm and prevent chilling. If he isunconscious. place him face down with his headturned to one side to prevent choking should hevomit. If he is conscious, give him some liquid(nonalcoholic) to drink to replace body fluid.

4-14. Protect the wound. The third and finalstep is to protect the wound from infection andfurther injury. Tear or cut the clothing around

17

the wound and be careful not to touch it withyour hand. Cover the wound with a steriledressing and bandage if available. Do not touchthe side of the dressing that goes next to thewound. Tie something around the body or limbto hold the dressing securely in place. Once thedressing is applied, do not remove it.

4-15. Artificial Respiration. Artificialrespiration is a means of causing air to flowinto and out of the lungs of an individual whenhis normal breathing system ceases to function.

4-16. Uses. Artificial respiration is notrestricted to the treatment of victims ofelectrical shock. Even though we are primarilyconcerned with electrical shock in thisdiscussion, we should Also mention a fewadditional uses for artificial respiration. It mayalso be used to stimulate breathing inindividuals whose breathing has stopped as aresult of drowning, carbon monoxide or othergas poisoning, smoke, overexposure to heat, orsuffocation. When breathing is inadequate, thevictim is always pale or blue in color. In carbonmonoxide poisoning, the symptoms may begiddiness, weakness, headache, vomitingthenunconsciousness.

4-17. Obstructions to breathing. Animportant consideration in any method ofartificial respiration is that the air passagewaybe open. If there is an obstruction, air cannotenter the lungs regardless of the method used.There are three main causes for obstruction.The first is liquid, false teeth, or other foreignmatter in the mouth or throat. The second is

Figure 7. Pulling the lower jaw outward.

relaxation of the jaw. The tongue, attached tothe relaxed jaw, falls backward and blocks thethroat (called "swallowing the tongue"). Thethird is the position of the neck. When the neckis bent forward so that the chin is down close tothe chest, there is a tendency for the throat tobecome "kinked" and block the passage of air.The air passageway can be kept open by placingthe head in a position with the chin juttingoutward.

4-18. Methods. There are four basicmethods of artificial respiration recognized bythe Air Force. They are as follows:

Mouth-to-mouth (exhaled-air).Back-pressure-arm-lift (B-P-A-L).Back -pressure-hip-lift (B-P-H-L).Chest-pressure-arm-lift (C-P-A-L).

Of the four methods, the mouth-to-mouthmethod has proven to be the most effectivibecause it can be used even though the victimhas suffered severe burns or injuries. It is thesurest method for getting oxygen into the lungsand should always be used when conditionspermit.

Figure 11. Pulling the lower jaw outward on children.

4-19. Using the mouth-to-mo.lth ',exhaled-Dir.) method you force air into the victim's lungswith your own mouth. Since you retain only aportion cif the oxygen from the air which youinhale, the air you breathe into the victim'slungs contains a sufficient amount of oxygen torevive him

4-20. The step-by-step procedure foradministering mouth-to-mouth artificialrespiration is as follows:

Step I. Turn the victim on his back.Step 2. Clean the mouth, nose, and throat. If

foreign matter such as vomit or mucus is visiblein the mouth, nose, and throat, wipe it awayquickly with a cloth or by passing the index andmiddle fingers through the throat in a sweepingmotion. When these areas appear to be clear.proceed as quickly as possible.

Step 3. Place the victim's head in the "sword-swallowing" position. The head must be placedas far back as possible so that the front of theneck is stretched.

Step 4. Hold the lower jaw up. Approach thevictim's head, preferably from his left side.Insert the thumb of your left hand between thevictim's teeth at the midline as shown in figure7. Pull the lower jaw forcefully outward so thatthe lower teeth are further forward than theupper teeth. Hold the jaw in this position aslong as the victim is unconscious.. A piece otcloth may be wrapped around the thumb toprevent injury by the victim's teeth. In the caseof young children (under age 3), where yourthumb would obstruct too much of the mouth,or in a victim whose mouth cannot be opened,proceed as follows. Grasp the angles of thelower jaw just below the ear lobes with both ofyour hands, one on each side of the victim'shead as shown in figure 8. Lift the lower jawforcefully outward so that the lower teeth arefurtner forward than the upper teeth. At thesame time, pull the lower lip down with thethumbs to open the mouth. Hold the jaw in thisposition as long as the victim is unconscious.

Step 5. Close the victim's nose bycompressing it between the thumb andtorefinger of the right hand as shown in figure9. In the case of young children or in a victimwho has tight jaws, block the victim's nose toprevent air leakage by pressing your right cheekagainst the nasal opening as shown in figure 10.(The hands will be occupied elsewhere.)

Step 6. Blow air into the victim's lungs. Takea deep breath, and cover the victim's openmouth with your open mouth making anairtight contact. In the case of a baby, therescuer's mouth can cover both the mouth andnose with an airtight contact. Blow rapidlyuntil the chest rises. If the chest does not risewhen you blow in, improve the position of the

At7.).

Figure 9. Closing the victim's nose.

victim's air passageway, and blow moreforcefully. Always blow forcefully into adultsand gently into children.

Step 7. Let air out of the victim's. lungs.After the chest rises, quickly break lip contactwith the victim, and allow the victim to exhaleby himself. Repeat steps 6 and 7 vigorously atan approximate rate of 12 times per minute foran adult. Use shallow puffs of air at the rate of20 times per minute for a child. A smoothrhythm is desirable, but split-second timing isnot essential. Continue rhythmically withoutinterruption until the victim starts breathing oris pronounced dead.

4-21. An alternate method of the exhaled-airmethod can be accomplished with the use of aplastic device called an airway, which is shownin figure 11. This device tends to increaseefficiency because it prevents the tongue fromfalling back into the throat. It also is moresanitary. But never refrain from administeringthe oral mouth-to-mouth method because this

Figure 10. Closing the victim's nose in thecase of small children.

19

device is not available. CAUTION: DO NOTuse this plastic device on children under 3 yearsof age.

4-22 The procedures are the same as for theoral method with the exception of your positionand placing the airway in the victim's mouth.Extreme caution should be exercised wheninserting the airway so as not to damage thethroat.

4-23. Assume a position at the top of thevictim's head. Insert the long end (short end forchildren 3 years of age and over) into the throatwhile holding the head back as shown in figure12. If necessary, hold the tongue down toprevent it from getting in the way whileinserting the airway. Insert the airway until'theflange rests lightly against the lips. Once thetube is inserted, retain the same position andplace the hands as shown in figure 13. Pinch thenose with your thumbs and press the flange withyour index fingers to prevent any air leakage.

Figure t t. riutic device.

Be sure to hold the chin upward and. towardyourself at all times.

4-24. Blow into the tube, watching for thechest to rise, as indicated by figure 14. Whenthe chest moves, remove your mouth and allowthe victim to exhale. Repeat this process in thesame manner as in steps 6 and 7 of the oralmethod. The first obvious indications that thevictim is responding to your efforts will be agurgling or gasping for air sound and possiblecoughing and gagging.

4-25. If the victim appears to be breathing tosome degree, keep his air passageway open untilhe aWakens by maintaining the support of hislower jaw. If his tongue or fingernails are bluerather than pink, he is not breathing adequatelyand still requires assistance.. You shouldbreathe air into the victim's lungs each time thevictim himself breathes in. Synchronize yourtiming to assist him.

4-26. After either method of -.exhaled-airartificial respiration has been performed for aperiod of time, the victim's abdomen may bulgefrom the air blown in the victim's stomach. Airinflation of the stomach is not dangerous;

Figure 12. With devicefirst step.

however, inflation of the lungs is much easierwhen the stomach is empty. If the rescuer seesthe abdomen bulging, he should interruptblowing for a few seconds and press with hishand on the upper abdomen between naval andbreastbone, causing the air to be "burped."Since this maneuver may cause the victim tovomit, the rescuer must be ready to roll thevictim's head to the side and clean the throat atonce.

4-27. The drowning victim usually swallowslarge amounts of water. When the rescuerperforms the first few breaths of exhaled-airartificial respiration. the water may be forcedfrom the stomach into the victim's throatbecause of pressure transmitted through thediaphragm by the extending lungs. The rescuermust be Mart to this possibility and roll thevictim's head to the side immediately so that thewater and other, materials may drain out.Exhaled-air artificial respiration should beresumed as quickly as possible.

4-28. The drowning victim may or may nothave water in the lungs. This water cannot beremoved from the lungs satisfactorily by anymeans; however, exhaled-air artificialrespiration will still be effective.

Figure 13. With devicesecond step.

20

Figure 14. With devicezthird step.

5. Off-Duty Safety5-1. A man assigned to a hazardous

operation as part of his daily duty is consciousof that danger and prepares himselfaccordingly. He is also under almost constantsuperdsion during duty hours and is told whathe should and should not do to remain aliveand healthy. He knows that if he violatesregulations and directives he will bereprimanded or disciplined for his wrongdoing. Thus, he is kept in line.

5-2. Now follow this same airman afterhours. He showers, relaxes, and looks aroundfor some recreation. His carefulness usuallyrelaxes right along with his body. Perhaps hedecides to go to the hobby shop, play somesport, or go for a drive. For these activities,there is no safety officer to caution him; manytimes,.there are no posters to warn him and nosupervisor to admonish him. He is strictly onhis own, and, as the facts and figures prove,often without the ability to handle theassignment. Let's take a look at some Of thehazards that might confront ths airman andwhat he should do to meet them. This sectionwill deal with such items as safe driving duringoff-duty hours, safety in sports, safe conduct inthe barracks, and safety in hobby shopactivities.

5-3. Safety in Driving. As a source of off-duty pleasure, the automobile rates top billingwith Air Force personnel. Unfortunately, it isalso their, greatest threat to life and limb. Forexample, in 1966 private motor vehicles drivenby Air Force personnel were responsible formore than 443 deaths and 3,150 disablinginjuries, and those statistics haven't improvedin 1971.

5-4. About one-fifth of all Air Force groundaccidents can be.directly attributed to unsafeoperation of private vehicles. These accidents

34

are many times more severe than accidents inGovernment vehicles. with injuries reachingapproymately one-third of all groundaccidents. The major contributing factors toprivate vehicle accidents include exceeding ordropping far below speed limits. improperspeeds for road conditions. fatigue and fallingasleep. disregarding traffic controls. driving onthe wrong side of the road. .following tooclosely. and unsafe or improper passing. Thesecauses account for approximately 90 percent ofthe unsafe acts of drivers.

5.5. What can you do to reduce the off-base.off-duty accident rate? First of all. learn thetraffic laws that are in effect in your particularlocation. Second. observe these laws strictly.Consider several factors ragarding the exactobservance of traffic laws.

Never try to travel too far in too short aperiod of time. This can be assured by youradhering to the local travel policies.

Don't continue driving when you aresleepy or overtired. Remember that when youhave an accident you endanger not onlyyourself but the driver and passengers of othervehicles as well.

Make sure your car is in good mechanicalcondition before starting on a trip.Malfunctioning brakes. lights. and windshieldwipers. as well as badly worn tires. are veryconducive w auto accidents.

Keep in mind that alcohol and driving donot mix.

Observe speed limits: highways are notintended to be race tracks.

5-6. You can undoubtedly add many 'moreprecautions to the ones listed. So. it' you wantto go on living with a whole and sound bodyand have a desire to help others do the same,drive carefully.

5-7. Safety in Sports. Sports should occupya very important place in your Air Force life.Military planners are becoming more and moreconscious of this fact as a means for helpingpeople do their jobs better and developthemselves physically. Among the morecommon athletic activities sponsored by the AirForce. both during duty hours and off duty. arcswimming, football, boxing. wrestling.basketball, baseball, track. and golf. Whenproperly organized and supervised, theseactivities do much to train the airmanphysically and mentally. However, whenengaged in improperly, they become a source ofdanger and often a cause of injury.

21

5-8. You will do well to read the Air ForceSports Manual, AFM 215-2. This Air Forcepublication, intended primarily for athleticdirectors, will prove itself very helpful to you indeveloping an attitude of sports safety.

5-9. Safety in Barracks. At first glance,barracks life seems to be perfectly harmless.However, by the very fact that so many differenttypes of men are living in one building, thebarracks can be a source of a great manyaccidents which are not always accidental.

5-10. Horseplay should never be tolerated inthe barracks. During morning cleanups andG.I. parties, serious injury can be and often iscaused by happy-go-lucky broom and mopwielders who exhibit their prowess as fencingexperts rather than cleaners.

5-11. Smoking in bed is a practice that leadsto many unpleasant results. Dispose of cigarettebutts in butt cans and not in the center aisle ofthe bay. In case of a fire in the barracks, use thesame procedure for extinguishing and reportingfires as we have already outlined.

5-12. Safety In the Hobby Shop. The basehobby shop. and most modern bases have one,is a good place to relax after a day's work anddo something useful and practical with yourspare time. Even though most hobby shops arebuilt and equipped with a realization that theusing personnel are not fully skilled in whatthey are doing, you must still exercise care inusing the equipment provided.

5-13. Carpentry equipment is especiallydangerous. Such tools as motor-driven saws,power drills, and other wood-shapingequipment should be used with caution andaccording to directives. Failure to do so couldresult in irreparable bodily injuries. Here are afew desirable items which every hobby shopuser should note.

Make sure you are well oriented on theuse of equipment.

Use safety guards at all times.Make sure the floor around machines is

free from stumbling and tripping hazards.Keep the floor clear of sawdust and

scraps.

5-14. Bear in mind that hobby shop SOPswere written fo,r your protection and to insurethat the equipment will fulfill its rated time ofserviceability. It is to your advantage to becomecompletely familiar with all operatingprocedures before you attempt to use any pieceof hobby shop equipment

5-15. At this time work the Chapter ReviewExercise for Chapter 2 in your workbook.

2;1

CHAPTER 3

Maintenance Principles

IN THE MODERN confmunications-electronics field, operational requirements haveplaced unbelievable demands on C-E systems.Now our equipment must be faster and moreaccurate. with pc (. rmance capabilitiesunheard of even a decade ago.Communications-electronics systems must becapable of providing communications aroundthe world under all environmental conditions.

2. Basically, reliability must bemanufactured into the equipment,- but anotheraspectmaintenancewill affect thisreliability. Poor reliability results in failure,which jeopardizes the success of the mission;therefore. equipment has to be designed forease of maintenance. But even with all themethods we now have to reduce themaintenance effort, complex electronicequipment must still be maintained by a well-trained repairman. This is you. You are a vitalcontributor to the reliability of the equipment.You are depended upon to report failures andto feed back data from which the causes offailures may be determined. Maintenance of the,equipment is. of course, your responsibility.

3. Retaining equipment in, or restoriii it to,a serviceable condition requires the applica-tion of established maintenance pro .cedurestroubleshooting and repair. To doyour work, you must thoroughly understandelectronic principles and must become familiarwith the operation of the equipment systems.You must know proper troubleshooting andrepair principles, and how to use applicabletechnical publications such as technical orders,schematics, and wiring diagrams. (Note: Wediscuss technical orders in the last section ofthis chapter.) Repair principles include repairof printed circuits, replacement of transistors,and cable fabrication. Finally, you must knowhow to test the finished job in a minimum oftime.

6. Preventive Maintenance6-1. The best maintenance is preventive in

22

nature, with potential failures being detectedand corrected before they have a chance todevelop. Preventive maintenance consists of themeasures taken periodically or when needed toachieve maximum efficiency in performance. toinsure continuity of service, to reduce majorbreakdowns, and to lengthen the useful lice ofthe equinment or system.

6-2. This form of maintenance consistsprincipally of inspecting, cleaning, andlubricating equipment during periodicinspections. It is aimed at discoveringconditions which, if not corrected, may lead tomalfunctions that will require major repair. Atypical example of this type of maintenance is arequirement for the bearings of a motor to belubricated at given intervals. If this is not done,the bearings may become dry and burn up andpossibly destroy the whole motor and otherassociated equipment. Today some motors havesealed bearings that are permanentlylubricated, but the thought behind thescheduied maintenance procedures applies toall electronic equipment.

6-3. Inspection, Cleaning, andLubrication. Inspecting, cleaning, andlubricating electronic equipment is one of themost important jobs that you have as anelectronic equipment repairman. Most of thiswork is done as you perform preventivemaintenance routines. While you areperforming these routines, you should becontinuously alert for potential defects in theequipment. such as worn parts or overheatedcomponents. Find the cause of these defects,and correct the trouble. If you perform routinesproperly, you greatly lessen the possibility offuture failures and malfunctions.

6-4. Technical manuals of preventivemaintenance instructions outline the step-by-step procedures to killow when you inspect,clean, and lubricate equipment. The purpose ofthis section is to give you the general principlesupon which these procedutes are based.

6-5. Inspection. One of the most importantsteps in performing preventive or correctivemaintenance is a complete visual inspection.Many defects in electronic equipment are foundthis wal.. You must visually inspect theequipment tor discolored. hurnt. or crackedresistors and capacitors, loose connections;loose mountings; faulty tuhes; sluggish or dirtyrelays. overheated transformers and motorhousings. and defective insulators. Theimportance of the visual inspection cannot beoveremphasized. Make this inspection verycarefidly. Many simple troubles have beenoverlooked and their correction has becometime-consuming because someone neglected toperform the visual inspection properly.

6-6. 'At times potential troubles can be foundby touch As an example, feel the couplingtransformerS. They should be cool even afterthe equipment has been operating a relativelylong time, If they are hot. something is wrong.The transformers in the power supplies shouldhe rather hot, but not hot enough to burn yourhand.

6-7. During the inspection, carefully notethe areas that will require special attentionwhen you start cleaning the equipment. Mostdust can be easily removed by a vacuumcleaner, hut more stubborn dirt. grime, grease.and corrosion require other methods ofcleaning.

6-8. Cleaning. The first step in cleaningelectronic equipment is to remove all dust, dirt,and foreign particles with a vacuum cleaner orcompressed air, When cleaning withcompressed air, be careful that it does notdamage fragile parts and be sure that thealignment is not disturbed by your carelesshandling of the air nozzle. Damage can beprevented by not using excessive air pressureand by careful handling of the air hose. A softdust brush can, be used to some advantage,provided you exercise the proper care. After theloose dirt has been removed from theequipment. use a clean tintless rag moistenedwith appmved cleaning solvent to removeremaining dirt and grease spots.

6-9. Proper precautions must he observed inthc storage and,.. use of cleaning solvents.Trichloroethylene is one recommended solventfor cleaning electronic equipment. Note,however, that trichloroethylene is toxic andshould be used only in a well-ventilated room.Where reference is made in technicalpublications to the use of carhon tetrachloridefor cleaning purposes. trichloroethylene is to besuhstituted. Carbon tetrachloride is eight tintes.15 toxic as trichloroethylene and no moreeffective as a cleaner. Trichloroethylene should

23

nut be used for cleaning thermoplastics,"doped" coils, or natural rubber.

6-10. Remove any corrosion found duringthe visual inspection. Clean dirty, corrodedtube pins and relay prongs with crocus cloth orfine ( # 0000) sandpaper and then wipe themclean with a dry cloth. Clean fuse ends andcable connector pins in the same manner.

6-11. Lubrication. For lubricationinstructions, use the applicable equipmenttechnical manuals in your organization.Equipment technical manuals give you specificinstructions on the type of lubricants to use.how to apply them, and the intervals at whichthey will be applied. The following, however, isapplicable to the lubrication of any electronicequipment:

Before lubrication, clean all the surfaces tobe lubricated with a lint-free clothdampened with a solvent.Do not overlubricate. Accumulation ot' oilor grease and dirt may cause seriousdamage to movable parts.Wipe off excess lubricant to prevent itsdripping on electrical parts.

6-12. Climatic Deterioration Prevention.The purpose of climatic deteriorationprevention is to help prevent arcing. frequencydrift, short circui.ts, and the generaldeterioration caused by excessive humidity.condensation, and the resultant growth tit'fungus. These are constant threats to electronicequipment operation. The treatment tominimize these deteriorating forces is listed inthe USAF publication. AFTO 12-1-3,Climatic Deterioration Prevention Treatment,Electronic Test and CommunicationsEquipment.

6-13. You should be particularly concernedwith the necd for climatic deteriorationprevention in hot, humid areas. Normally, youwill not be required to do this type of workunless you are performing depot-levelmaintenance. But even if you are not allowed toperform this job in Your unit, you shouldrecognize adequate treatment and the need foradditional treatment. Some adverse climaticconditions and their effects are listed in thefollowing paragraphs.

6-14. Relative humidity. This is a termdescribing the relative amount of water vaporin the air. It is usually expressed as a percentageof the total amount of water the air can hold ata given ,temperature. Thus. 50 percent meansthe air contains one-half the total wafer it canhold. and 100 percent means it contains all it iscapable of holding. Air can hold more water asits temperature increases. In tropical areas the

3

relative humidity varies between 60 and 100percent. This high humidity accounts foi thecondensation of moisture, or sweating, onvarious parts of radio and radar equipmentswhen they undergo temperature changes.Condensed moisture on insulating materialsreduces their insulating qualities and results inarc-over and shorts between terminals. Thewater vapor may also be absorbed by theinsulation. The treatment described later slowsdown the absorption of moisture and keepscondensation away from the terminals. Highhumidity also causes corrosian of metals. Othersources of moisture include fog, salt spray, andrain, which cause similar deterioration ofinsulation.

6-15. Teinporwure. In general. equipmentmay encounter extreme temperatures. rangingfrom 65° F. to a maximum of 135° F., undervarious conditions of high humidity, fog, rain,salt spray. salt air, cold, insects, fungi, dust, etc,

6-16. Variations of temperature causemoisture to be breathed through any smallcracks, pinholes, or vents in the eguipment. Asthe temperature rises, the aif inside a piece ofequipment expands and is expelled, in part.through the openings and vents. When thetemperature falls, the air inside the equipmentcontracts, and outside air is admitted throughal4 openings and vents. The moisture which isbreathed into the equipment destroys theinsulating qualities of dielectrics and corrodesthe metal. Keeping the filaments turned onhelps keep equipment dry. This method,however, depends on local policy andconditions.

6-I.". Fungus. This is a form of plant life thatfeeds on materials of vegatable and animal'origin, including paper, cotton, and such thingsas dead insects and other fungi. It may bespread by wind, dust. dirt. and insects such asants. flies, and mites. Growth may take place onmaterials other than those of organic origin if aspot of dust or other nutrient substance ispresent. Fungi thrive in high humidities andtemperatures. Fungus growth causes decay.accelerates the deterioration of insulatingmaterials, and short-circuits items such asrelays. jacks. and keys. A fungicidal compoundin the coating material used in climaticdeterioration treatment retards the growth ofthis fungus.

6-18. Some of the effects of moisture andfungi are contained in the following list. Befamiliar with the effects of moisture and fungion materials and parts. Read and study this iisteprefully.

Moisture causes swelling that may movethe supports out of alignment. resulting inbinding of parts.

24

Moisture provides elect mai. leakagepaths. caUsing flashover and crosstalk.Fungus growth reduces resistance betweenparts mounted on plastic to an extentwhere th e. item is useless._

o Rotting caused by moisture destroys-.tanning and protective materials..High temperature and moisture vaporcause rapid corrosion.Different metals having differentpotentials cause electrolysis whenmoisture is present.

6-19. Chmatic Deterioration Treatment.There is a preventive treatment which, ifproperly applied to electronic equipment,provides a reasonable degree of protection. Itguards against fungus growth, moisture,corrosion, salt spray, insects, cold, desert heat,etc. The treatment consists of using anapproved lacquer or varnish coating appliedwith a spray gun and/or brush. A briefdescription of the procedure in the propersequence is as follows:

Make all repairs and adjustmentsnecessary for the proper Operation of theequipment.Disassemble the equipment and strip It asfar as necessary: to reach inaccessiblepoints.Clean all parts thoroughly of dirt, dust,rust, and fungi. Cover parts such as aircapacitors, relay contacts, and openswitches with masking tape.

Dry equipment thoroughly to dispelmoisture that the circuit elements haveabsorbed.Spray all circuit elements with two orthree coats of protective compound.Allow equipment to dry; it must notremain tacky.Remove masking tape and touch up with abrush all points misSed by the spray.Reassemble the equipment.Retest, readjust. and realign theequipment; mark all sets with MFP(moisture fungi-proofed) to show thatthey have been treated.

7. Corrective Niaintenance

7-1. Corrective maintenance is defined as"returning equipment io operational status orserviceability." Obviously. this .return tooperational status first requires locating andrepairing the trouble in the equipment. Sin,:elocation of troubles is commonly referred to as-troubleshooting." corrective maintenance canbe more completely defined d s-troubleshooting kind repairing electronicequipment.- Corrective maintenance

38

procedures are outlined in the appropriateequipment manuals. A more detailed discussionof testing principles appears in the TO31 I 141 series. Basic ElectronicsTechnology and Testing Practices.

7-2. Because your career field includes alarge number and variety of equipments, weshall not discuss how to apply correctivemaintenance to specific equipment. Instead, weshall discuss generally the principles ofcorrective maintenance. You must knowsomething about basic measurements, theavailability of troubleshooting data,troubleshooting, repair. alignment, andperformance testing.

7-3. Basic Measurements. In order toperform checks (performance tests) andtroubleshooting, the repairman must bethoroughly familiar with the principles and useof test equipment. You must apply all the basicmeasurement principles required in doingcorrective maintenance. You must be able tomeasure voltage, current, resistance,waveshapes. frequency. power. modulation.standing-wave ratio, and field intensity, and totest electron tubes. Checklists for minimumperformance standards, contained in technicalmanuals, prescribe the required standard to befollowed. These tests are an inherent part oftroubleshooting and should be used wheneverpossible.

7-4. In corrective maintenance, youtroubleshoot in order to locate the defectivesystem, component chassis, circuit, and, finally,the defective part. After replacement or repair,you must test the unit (or the system), and applythe performance-testing criteria. Therefore, it isimperative for you. the repairman, to learn howto make all the different measurements. Theorder in which the basic measurements aregiven is not a specific order of preference. Anymeasurement can be a first step, dependingupon your ability to azalyze the existingprobJems and then to correct them.

7-5. Voltage and current measurements. In aproperly operating electronic circuit. the valuesof voltage and current in the circuit fill withincertain specific limits. Hence, a voltage orcurrent measurement can given us an excellentclue as to the cause of a malfunction.

7-6. Point-to-point voltage measurements.compared with available voltage charts. help usto locate troubles quickly and easily. Therepairman should keep in mind that. in certaincases, a voltmeter (particularly one of lowsensitivity used on a low range) may distrubsome circuits to such a degree as to render theminoperative. As a rule, current measurementsare not often taken in the course of testing.

25

unless the ammeter is an integral part of theequipment under test.

7-7. Resistance measurements. Becauseresistance measurements are valuable when youare locating trouble, many maintenancemanuals contain point-to-point resistancecharts that are referenced to points in theequipment. Without these charts our resistancemeasurements in a complicated circuit are slowprocess. Sometimes we must unsolder one sideof a particular resistor in order to preventerroneous readings. Two precautions to betaken when an ohmmeter is used are: (1) thecircuit under test must have all power removed,and (2) any meters, tubes, or tansistors that maybe damaged by the ohmmeter must be removedbefore any measurement is undertaken.

7-8. Waveform measurements. Waveformmeasurements are very important, and areapplicable to all electronic devices. It isnecessary that you know the waveformsassociated with a circuit. After observing theseon an oscilloscope, you can determine whetherthe circuits are operating normally. You mustremember, however, that all oscilloscopes havecertain limitations. You must know theselimitations before you can properly evaluatethe waveshapes.

7-9. Frequency measurements. It is veryimportant that receivers and transmitters beaccurately set to their assigned frequencies.Setting a transmitter or receiver to a specificfrequency is generally done with a frequency-measuring device. There are several types offrequency meters, some more accurate thanothers. Quick frequency checks are generallymake with a simple resonant-circuit wavemeter.We will discuss frequency meters in more detailin Chapter 5 of this volume. Since thewavemeter is very sensitive, it is very useful indetermining the fundmental frequency in acircuit having multiple harmonics.

7-10. In the UHF band, the extremely smallvalues of capacitance and inductance requiredfor resonance make it necessary to use either aresonant-cavity or a resonant coaxial-line typeof wavemeter. Since both the resonant-cavityand the resonant coaxial-line type wavemeterabsorb less energy from the circuit under test,these wavemeters are more accurate than eitherthe reaction or theathe absorption types. Ifeither is calibrated against a primary frequencystandard, you may use it as a secondaryfrequency standard.

7-1 I. Another method of measuring ultra-high frequencies makes use of a Lecher line. Ameter indicates the peaks (or nulls) of astanding wave that appears on a folded wire orbar (Lecher line) that is resonated to that

particular frequency. The distance betweeo thepeaks (or nulls) is measured, and thewavektIth is calculated.

7-1 2. Po w e r measurements. Themeasurement of DC power and low-frequencyAC power presents little or no problem to theelectronic repairman. Rut, as frequencyincreases, you need- a variety of power-measuring instruments and a knowledge oftheir operation and application.

7-13. In the course of routine rnaintenanCe,power-level and power-output measurements inthe audio-frequency range have to be made.These measurements are generally expressed indecibels (power ratios). The decibel indicatesthe power in a circuit with respectto zero or toa standard reference level. The power output ofa transmitter is generally measured with athermocouple ammeter in conjunction with adummy load. Absolute power is not measuredoften, since routine operating indicationsprovide enough information about transmitterperformance. In the UHF portions of thespectrum, power is measured with a meteremploying a temperture-sensitive- element orbolometer.

7- I 4. Modulation measurements. Whenintelligence is superimposed on an RF carrier,a phenomenon known as modulation takesplace. RF may be modulated in amplitude.frequency, or phase. Each method ofmodulation has certain advantages over theothers. However, at this point we are concernedwith measuring the degree of modulation.

7-15. The transmitter carrier is adjusted sothat efficient modulation takes place. ,When thepercent of modulation is low, the transmitterefficiency is not fully utilized; when it is high(in excess of 100 percent), serious distortionresults. Precise amplitude-modulationmeasurements are made with an oscilloscope.They may show the actual modulation envelopeor a trapezoidal pattern, depending on themethod of connecting the oscilloscope to thetransmitter under test.

7-16. Standing-wave ratio measurements. Asyou recall, these measurements are useful forthe purpose of repair, preventive maintenance,checking, and making adjustments totransmitters. A transmission line that is notterminated in its characteristic impedance hasstanding waves of voltage and current along itslength. These are caused by reflectionsoccurring at the end of the line. The reflectedwave varies continuously in phase in much thesame way that the incident wave varies. Atpoints a half-wavelength apart, the voltage .ismaximum. At points one-quarter of awavelength from each voltage maximum, there

26

is a voltage minimum. The ratio of themaximum to minimum voltage is known as thevoltage standing-wave ratio (VSWR), orfrequently. the standing-wave ratio (SWR). A:.;gh SWR indicates a poor impedance matchwhich results in a loss of power in the line, anda low SWR indicates a good match with lowloss in the line. An SWR of I:1 is perfect and isseldom obtained.

7-17. Field intensity measurements. Themagnitude of a radio wave at a given point isknown as the field intensity or field strength ofthat wave; it is usualiy measured in millivolts ormicrovolts per meter. The field strength of aradio wave is determined by measuring the RFvoltage induced into a receiVing antenna.

7-18. Several types of test equipment formeasuring field strength (known as ratio testsets and field strength meters) are available foreach frequency range. They make it possible tomeasure either the relative or the absolutemagnitude of field intensity produced by anexcited transmitter antenna. They also enableus to determine the efficiency and thedirectivity characteristics of the.antenna. Thesemeasurements are useful when we are (1)selecting transmitter antenna sites. (2) makingsurveys of field intensities, and (3) locatingsources of radio-frequency interference.

7-19. The measurement of relative fieldstrength can be made with rather simple testequipment; sometimes a grid-dip meter willsuffice. Other test equipment circuits use apickup antenna. a diode (or crystal). and amicroammeter. With this type of equipment. themeter reading indicates the relative strength ofthe field acting on the pickup antenna; it is notdirectly proportional to the field intensity(because of the nonlinearity of the crystal).

7-20. Troubleshooting Data. Whentroubleshooting. you must use all availableresourcessuch as specific data on yourequipment (this data is found in TMs).measurement techniques, and personalexperience of fellow workers. The technicalmanual for a particular unit or set contains adetailed explanation of the theory of operationof each circuit in the unit, block diagrams.practical wiring diagrams, and schematicdrawings of each circuit. It shows the locationsof test points and the readings (voltage andresistance) or waveshapes that should hepresent. The TM also contains troubleshootinganalysis charts, alignment, and minimumperformance checks.

7-21. Diagrams, The block diagrams showthe mechanical and the electricalinterrelationships between the stages in thesystems. You must become thoroughly familiar

ce\N

Figure 15 Vacuum tube, plug. and connector numbering system.

with block diagram analysis in order toproperly apply troubleshooting principles.

7-22. Schematic diagrams include allcomponents and show all the connections(power. input, and output) to other units. Theyare shown in boldface type in the list ofillustrations of TMs so that they can be locatedrapidly. These diagrams will greatly aid you inlocating faulty components,

7-23. Socket and connector data. Viewedfrom the bottom, pin connections on tubes andtube sockets are numbered in a clockwisedirection, as viewed in figure 15. If viewedfrom the top. they are numbered in thecounterclockwise direction. For example, onoctal sockets the first pin clockwise from thekeyway is pin I. Pin numbers appear both onthe schematic and the wiring diagrams so thatany tube element can be readily located. Figure15 also shows an example of a tube and itssocket, which are counted from right to left ofthe red dot.

7-24. Figure 15 is an example of a typicalplug connector. Generally, plug connectors arenumbered on the side to which the associatedconnector is attached. To avoid confusion,some individual pins are identified by letterswhich appear directly on the connector.

7-25. The voltage and resistance chartscontained in the equipment technical orders

show the normal voltage and resistance valuesat the pins of the connectors and tube sockets.Figure 16 is a typical chart showing themeasurement values at each connection. Whentaking meter readings, you must comply withall information contained under "NOTES."

7-26. Component illustrations. In theprocess of troubleshooting, it is sometimesdifficult to locate components. Front, top, andbottom views aid us in locating and identifyingparts. The illustrated parts breakdowncontained in technical orders presents apictorial view of all components in the unit. Anexample of a pictorial illustration is shown infigure 17. The information contained therein isrequired when ordering parts. Pin connectionsat tube sockets, plugs, and receptacles arenumbered or lettered on the various diagrams.

7-27. Troubleshooting. A communications-electronics equipment repairman is like adetective. He must find out whether or not apiece of equipment is working properly. And ifnot, why not. When you run through aperformance test, you are looking for clues totell you how the equipment is operating. If youdiscover that the operation of the equipment isnot up to the standards, or if trouble has beenreported. you must continue your detectivework. Troubleshooting is a process ofel: -nination. There are indications that givedefinite clues as to where the trouble may be.

27

41

too.

1 -1301

0

04 K40

Wv 1307

5

-it6 3

150Go

11.6U7/3011 13AU7/31114

7-1301

6AL 5 /3726 RAL5/5724

A1.4.1725 6R.W5713 3607

3607

6 3 AC

Eno,'xv -13TO

ISO -12 51 hiISO

CO

co3

0

SOK

NOTES

I-ALL VOLTAGES AND RESISTAXCE READINGS MEASUREDTO GROuND UNLESS SPECIFIED OTHERWISE

3-SUBASSEMBLY IS REmOVED FRC66 MAIN CHASSIS WHENMAKING RESISTANCE MEASUREMENT

3-RESIST AKE IS Wins IN OHmS UNLESS mARK ED "K"FOR Mamba OR "m" FOR mEGON66

4-ALL VOLTAGES ARE D C POSITIVE MEASURED WITH ASINIPSON mODEL 2IMJLTIMETER UHL EIS INDICA TEDOTHEMSE,

3-*INDICATES.A VACUUM TUBE VOLTMETERUSED.

4-4.INLESS OTHERWISE STATED, ALL wEASuRENENTS ARETAKEN WITH ALL CONTROLS IN mAXIMUIA CLOCKWISEPOSITION

- TUBE CONDUCTING- TUBE HOT CONDuCTING.

!I-RESISTANCE VALUES ARE MTN WELD, TME LINE,vOL TAGES ABOVE THE Lime

Figure 16. Voltage and resistance measurements.

Begin by eliminating as many components orcircuits as your observations have shown to beoperating properly. Some parts can beeliminated by the symptoms alone, whileelimination of others may call for the use of testequipment. Regardless of the methods used,every part eliminated brings you closer to thesource of the trouble.

18

7-28. You will find troubleshooting analysischarts in your equipment technical manuals.These cover the malfunctions that have beerfound to occur over and over again in thatequipment. In addition to these commontroubles that have been covered in thetroubleshooting charts, you will find manytroubles peculiar to the specific set (or system)

42

on which you are working. The unusualproblems force you to use your informationresources and your experience to solve them.Every malfunction requires a thorough analysisas a part of the troubleshooting procedure. Thisis a challenge you must be prepared to accept;only on your own initiative can you succeed.We have described some of the resources youcan use in your analysis. In addition to usingthese resources, you must know how to use thetest equipment.

10

L

7-29. You must be able to recognize anysymptoms of troubles (detected through routinechecks or as reported). Failure to do so mayresult in the loss of many man-hours. Withoutintensive observation of equipment, the first in-dications of trouble may be overlooked. Manytroubles can be spotted through indicatorpresentations, equipment meter readings, and-performance reports. Some troubles such as lowreceiver sensitivity, however, are not readily ap-parent and must be detected by periodic per-

CP05A3KC104K CAPACITOR, FIXED, PAPER DIELECTRIC (mIL-C-25A)2 REI3C4-17 RESISTOR, FIXED, FILM, 56.000 OHMS 1, 1 w 23 RC20OF101J RESISTOR, FIXED, COMPOSITION (MIL-R-11C) 2

RC2OGF203.1 RESISTOR, FIXED, COMPOSITION (mIL-R-11C) 1

5 Cm15C750J CAPACITOR, FIXED, mICA DIELECTRIC (mIL-C-5A) 1

6 Cm1513150K CAPACITOR, FIXED, MICA DIELECTRIC (mIL-C-5A1 2RC2OGF633J RESISTOR, FIXED, COMPOSITION imiL-R-11C) 1

8 RC2OGF2231 RESISTOR, FIXED, COMPOSITION ImIL-R-11C) 29 4C2OGF362.1 RESISTOR, FIXED, COMPOSITION imIL-R-11C) 1

10 RC42GF6831 RESISTOR, FIXED, COMPOSITION (mIL-R-11C) 2TI RE13C4-10 RESISTOR FIXED, FILM, 270,000 OHMS in, 1 2 'or 1

12 Cm1S8100( CAPACITOR, FIXED, MICA DIELECTRIC 1

11 RE i3C4-21 RESISTOR, FIXED, FILM, 620,000 OHMS I:, 1 2 w 1

0.415C121J CAPACITOR, FIXED, MICA DIELECTRIf: (mIL-C-SA) 1

Figure 1 7 Component illustration,

29

LITERATURE PERFORMANCE EQUI PM ENT

BLOCK 1, TROUBLE DETECTION ANC ISOLATION TO A SUBSYSTEM

EPL (wHEREAVAILABLE)

FACTORYTEST DATA

GENERALSYSTEM

T.,S CHARTS

OBSERVATIONAND PERFORMANCE

CHECKS

4-1SYSTEM

METERS

SYSTEMINDICATORS

<-1

BLOCK 2, SUBS'YSTEM TROUBLESHOOTING

INDIVIDUALSUBSYSTEM TiS

CHARTS

SUBSYSTEMBLOCK

DIAGRAM

SIGNALROUTING

DIAGRAMS

WAVESHAPESECTION OF

TO

TESTEQUIPMENT

WAVESHAPEOR

VOLTAGEANALYSIS

INDICATORS

SYNCHROSCOPE

SIGNALGENERATOR

mULTImETER

BLOCK 3, CIRCUIT AND COMPONENT TROUBLESHOOTING.1COMPONENT

BLOCKDIAGRAMS

SCHEMATICDIAGRAMS

VOLTAGEAND RESISTANCE

CHARTS

COmPONEN TIDEN TI F ICA TION

CHARTS

00'

111. IIMIN 011 NM OMMIND IM MINIM IM 4. 01M 0111 01M NNW.

wAvESHAPEANALYSIS

TUBE TESTINGVISUAL INSPECTION

VOLTAGE ANDRESISTANCE

MEASUREMENTCIRCUIT

ANALYSIS

SYNCHROSCOPE

TUBE TESTER

Figure 18. Troubleshooting chart.

SIGNALGENERATOR

mULTImETER

1

1

1

1

1

1

1

formance checks. To minimize downtime(inoperative period), you must develop a systemof troubleshooting. This should includeexamination of all available equipment records,evaluation of operator's comments, andperformance of operational checks whenpossible.

7-30. Locating the trouble is usually themost difficult step in corrective maintenanceand is therefore the one to which we give themost emphasis. A mechanic's troubleshootingtechnique is based on his knowledge of theoperational standards and diagrams of theequipment. So, as part of the technique, youmust be able to read and understand technicalliterature, such as cabling charts, schematics,block diagrams, and voltage and resistancecharts.

7-31. The troubleshooting chart, shown infigure 18. illustrates the proper troubleshootingprinciples. This chart will help you develop asystematic method of troubleshooting. First, byobservation and by making performancechecks, you eliminate all the subsystems whichare functioning properly. Next, by furtheranalysis. isolate the trouble to a subsystem.Then trace or isolate the trouble to a circuit,and from there to a specific part or parts. Thisis done through further analysis, visual in-spections. tube testing, waveshape and voltagemeasurements, and finally, resistancemeasurements. Some of the necessary literatureand test equipment required are shown in thechart.

7-32. Figure 18 shows that the first step oftroubleshooting is trouble detection andisolation to a subsystem. To do this, you mustunderstand the performance standards, knowhow the equipment is operating, and be able torecognize symptoms.

7-33. Having located the trouble in a par-ticular subsystem. you are now ready to isolatethc trouble within that portion of the equip-ment. The subsystem may consist of many unitsor components. In the next step (block 2 of fig.18). you localize the trouble to a majorsubgroup or unit.

SIGNL.INPUT

*-6N-6101ST AGE

2a sTce

3STGE

7-34. Isolation of the specific circuit beginsafter you have localized the trouble to a unit. Acommon technique of isolating the trouble isthe half-split method. You can apply thisteihnique to almost any situation. The object isto isolate the defective stage as rapidly aspossible. We will use the block diagram of anelectronic system in figure 19 to illustrate thispractice.

7-35. Stage I is the signal source, and theoutput is taken from stage 8. If the indicatedtrouble is no signal output, the first point to:check would be point D. This checkpoint islocated at the center of the chain. If the signalis present in the output when the appropriatesignal is injected at poin, D, stages 5 through 8are therefore eliminated. The second check-point is B. This usually divides the remainingsection. If no signal is in the output when thesignal is injected at this point, the trouble isisolated to stage 3 or 4. When the trouble hasbeen isolated to one stage, check the com-ponents there, using the schematic diagrams.Had there been no output when the propersignal was injected at point D, the troublewould have been somewhere between stage 5and the output.

7-36. An oscilloscope, multimeter, or signalsubstitution is generally used to isolate thetrouble to one stage. If a tube is involved, it isusually checked first, or a tube known to begood is substituted in its place. If the tubeproves to be good, additional checks are made,using an oscilloscope or voltohmmeter.

7-37. To aid in these final checks, technicalmanual references should be used. In somecases a schematic is all that is necessary; inothers, voltage charts, resistance chart, orwaveforms may be needed. However, there isno substitute for good, logical thinking. Theimportant things to remember are:

Use your block diagram.Narrow the trouble down as far aspossible with indications from the equip-ment itself.Look for the most common troubles (badtubes) first.

ST AGE5 16.-41110

Figure 19. Typical half-split method

31

Li

STGE6

of troubleshooting.

LL)

STAGE7

SIGNALOUTPUT

A

STG6

In most cases, check voltages orwaveshapes before measuring resistinice.Most important, think it out and andlyzethe symptoms carefully before remr:vingcomponents. A little effort in this direc-tion can save a lot of time and labor.Check your records. Do not overlook theimportance of your fellow workcr'sprevious experience. This same troublecould have happened to him.

7-38. General Repair. Since each repair isan individual problem and differs from theprevious one in some respect, it is almost im-possible to set up a routine or a production-linetechnique and adhere to it. There are certainprinciples, however, that should be followed inall cases if you are to complete the repair withthe least arriount of time and expenditure ofparts. Let's discuss two of the principles thatapply to general repair.

7-39. Look phase. When a piece of equip-ment needs repair, clean it first. Remove allforeign matter and dry the equipmentthoroughly. By reviewing the. section onpreventive maintenance in this chapter, youwill become more familiar with the methods ofcleaning electronic equipment.

7-40. Since operating symptoms usually in-dicate the source of trouble, understandingthem shortens your work in repairing the equip-ment. Such symptoms should be described onthe AFTO Form 349 or 350, which is placed onthe equipment by the repairman. These formswill be discussed in the next section of thismanual.

7-41. Before you start the actual repair, givethe equipment a thorough visual check andreplace all of the damaged parts. This will sim-plify your work. If this is a piece. of equipmentthat you know well, you may easily spot defectsduring the visual check.

7-42. Replacement of parts. A replacementpart should occupy the same position as did theoriginal, and should be an exact duplicate ofthe old part. When a part is to be replaced, it isnecessary to check the reference symbol in theschemati.; and the illustrated parts breakdowntechnical manual. The illustrated parts break-down technical manual contains informationyou need to order the parts.

7-43. When an exact replacement is notavailable, however, use a part which is in ac-cordance with the description of the original inthe maintenance parts list or the appropriatestock catalog. Even though a part may have thesame electrical value as the original, if it differsin physical size, it may cause trouble in high-frequency circuits.

7-44. In replacing parts, use the same groundpoint as did the original wiring. before un-soldering a part, note the position of the leads.if the part (such as a transformer) is to beremoved, tag each of the ieads. In addition, youshould draw a simple circuit diagram beforeyou remove any parts. Be careful not to damageother leads or components by pulling, pushing,or burning them.

7-45. Circuit Alignment. It should be clearthat it is impossible (or very impractical) tomanufacture electronic components with novariations at all in the values. And, of course,you also understand that aging of parts,climatic conditions, vibrations, etc., may causethe values of components to change. Because ofthis, variable components are provided in sometuned circuits that require circuit alignment.Thus, by a slight retuning or adjustment fromtime to time, the optimum performancespecified in the maintenance manuals or by themanufacturer may be attained.

7-46. Reduced sensitivity or reduced outputmay indicate a need for alignment; however,alignment should not be undertaken until theequipment has otherwise been checked out.Every piece of equipment that is operatingpoorly requires maintenance, but it does notfollow that every piece of equipment that needsmaintenance also needs alignment. However,repairs that require the replacement of com-ponents or the redressing of wiring may makesubsequent alignment necessary. Therefore, youshould not attempt alignment until all troubleshave been cleared and all defective partsreplaced. It cannot be stressed too highly thatbefore alignment is attempted, all available in-structional or maintenance literature should becarefully consulted.

7-47. Performance Testing. A performancetest is a check made to determine the conditionor the operating efficiency of the equipment.The first checks are performed when the equip-ment is initially installed. Such checks will con-tinue to be performed periodically (at thebeginning of each shift, for example), at theconclusion of either preventive or correctivemaintenance, and at any other time there isreason to believe the equipment is operatingbelow accepted standards. At these times it isnecessary that you check the equipment againstthe indicated performance standards in thetechnical manual, using the proper test equip-ment. While these checks do reveal improper ordefective operating circuitry, in many cases asimple adjustment will correct the malfunction.

32 4 6

8. Repair of Printed Circuits andTransistor Replacement8-1. The printed circuit assembly is a com-

paratively recent development in the electronicfield. Printed circuits have replaced con-ventionally wired circuits in practically all ap-plications.

8-2. Print circuits are easy totroubleshoot. since all leads can easily be seenand the circuit components are readily ac-cessible. Generally, the measurements of com-ponents can be made from the component sideof the board.

8-3. This section deals with the generalrepair of printed circuits and not with specificequipment. Before you begin repair of printedcircuity in specific equipment, read the ap-plicable technical manuals. The quality controldirectives pertinent to a particular system willalso govern methods of repair as you will see inthe next section.

8-4. Types of Printed Circuits. A true prin-ted circuit is a pattern comprising printedwiring and printed component parts, all formedin a predetermined pattern. There are severaltypes of printed circuits, some of which arelisted below.

Chemically deposited. Formed by thereaction of chemicals in an applied electricalfield.

Embossed foil. Formed by indenting ametal foil into an insulating base and removingthe unwanted raised portion.

Etched. Formed by chemical or chemicaland electrolytic action. and removal of the un-wanted conductive material.

These printed circuits mentioned are only a fewof many. We shall not try to explain all of them.

8-5. PrecautiOns. Printed-circuit bases.made from fiberglass laminates or some otherplastic materials, are delicate in comparison tometal chassis and must be handled accordingly.Some precautions are:

Be careful in removing and installingprinted-circuit assemblies.Carefully remove separable componentparts. Undue flexing may break the con-ductive pattern.Avoid excessive deposits of solder whichmay cause short circuits.Use the least amount of heat possible forconductor repair.Always use a heat sink for removal andreplacement of components.Use small tools and handle themproperly:

8-6. Circuit Tracing. Circuit tracing of theprinted-circuit assembly is generally simpler

than that of conventional wiring, because of theuniform layout of the conductors in a printed-circuit assembly. Printed-circuit assemblieshave the path of the conductive pattern paintedopposite the component side. Here, on this op-posite side. the component is marked with theschematic symbol to aid in troubleshooting.The latest assemblies have test points with theappropriate voltage readings indicatee Somebases are translucent. and a 60-watt lampplaced opposite the side being traced will helpyou to locate connections.

8-7. Tube socket test adapters may be usedto measure the voltage while the equipment isin operation. The adapters let you get to eachpin socket without damaging the printed circuitcircuitry.

8-8. Resistance or continuity measurementsof coils, resistors. and capacitors can be madefrom the component side of the assembly. Thevoltage measurements can be made on eitherside of the panel, but on the conductor side, aneedlepoint probe should be used.

. 8-9. Removal and Replacement of Com-ponents. The removal and replacement ofdefective components on a printed-circuitboard is not difficult. but it does require a cer-tain amount of care because of the fragile con-struction of the board. Misuse of a solderingiron or the use of improper handtools canresult in the need for complete replacement of aprinted-circuit component repairs involve theremoval and replacement of resistors andcapacitors.

8-10. How components are mounted. Com-ponents may be mounted on printed-circuitboards in the following ways. Each type ofmounting 'may require slightly differenttechniques in the removal.

The component lead is cold formed into atapered pin that is pressed into a platedhole and soldered.A tapered wrap is swaged to thecomponent lead and then inserted.The bare component lead is passedthrough an eyelet and soldered.Cold wire wrap secures component to theterminal pins.

8-11. Recommended tools. The tools used torepair metal chassis are not practical in therepair of printed circuits. Printed circuits aresmall and should be repaired only with smalltools. Although many diversified tools might beused for the various special jobs, here is a list ofthose tools most frequently used.

Printed circuit board repair vise.Heat sink.Long-nose pliers.Soldering aid with forked end.

33

4-/

37-watt soldering iron with iron-clad tip.Stiff wire brush.Diagonal cutters.Cleaning solvent.60/40 solder.Wiping cloth.Solder sucker (coaxial-type braid soakedin liquid resin).

8-12. Troubleshooting and repair aids.There are many things that may aid you in thetroubleshooting and repair of printed circuits.The most important "aid" is to practice goodcommon sense. The following items will helpyou in the repair of printed circuits.

Magnifying glass. Aids in locating verysmall breaks in the conductors.Needlepoint probe. An aid inmeasurements, since the varnish coatingon the circuit must be broken through ifyou are to make proper contact.Light. Facilitates circuit tracing if theboard is translucent.Silicone resin varnish. Repaired areasshould be cleaned and then recoated withsilicone resin varnish for protectionagainst shorts.

8-1 3. Service terminal componentreplacement. Replacement of resistors andcapacitors may be done in either of two ways.The faulty component can be cut away from theboard and the leads remaining on the board canbe reshaped for use as soldering terminals forthe new component. In the second method thedefective component and its leads are com-pletely removed from the board and the newcomponent, soldered into its place on theboard. The first method is more commonlyused because it is easier to do under normalmaintenance conditions and offers less chanceof heat damage.

8-14. The steps in repairing printed circuitsin this manner are listed below and shown infigure 20.

CLiPPED'LEA:

SERVICE .7 ERmINALL`2-'-"---:-----r NE* CCMPONENT

SERVICEERAINI.i. r"-

BENG NEN COmPONENTRADiuS

SERv:CE. ERMINAL

NEW COMPONENT ATTACHEDTO SERVICE TERMINAL

SERViCE TERMINAL CRIMPEDTO CLIPPED LEAD

A

Figure 20 Service terminal method.

Remove the defective component by clip-ping :he lead 3/16 of an inch from Pile top ofthe terminal wrap.

Straighten the pnds of the clipped leads.Clean each lead.Slide the service terminal ltig (as shown in

fig. 20, detail A) over the clipped lead. Tne tipof the clipped lead must be flush with the top ofthe service terminal. Clip off any excess leadmaterial and crimp (squeeze) the serviceterminal lug to the clipped lead.

Cut the new component leads to length sothat the tip of the lead is at least flush with theservice terminal lug to be crimped, as indicatedin figure 20, detail B.

If the component is a solid-state device orprecision resistor, a heat sink, similar to theone shown in figure 21, must be used.

Solder the service terminal lug with asuitable well-tinned iron and a minimumamount of solder.

8-15. CAUTION. Care must be used toavoid applying heat to the printed-circuit boardor the component.

8-16. In reattaching a comPonent that hasbeen clipped on one end only, the serviceterminal lug should be rotated 180°.

8-17. Complete component replacement.This second method of removal andreplacement of defective components is moredifficult than the first; it requires more precisework, but it is a neater and more effectivemethod. Thc complete removal andreplacement of a defective component is usuallydone by depot level maintenance. personnel.Listed below are the more important steps forcomplete replacement of a detectivecomponent.

(1) Secure the printed circuit board in a testjig or vise type of gripping holder.

(2) Grasp the lead on one end of thedefective component with the forked end of thesoldering aid. This should be done as close tothe component's body as possible. If you haveany doubts as to whether or not the componentis defective, place a heat sink on the lead asclose to the component as possible.

(3) Apply the soldering iron to thecomponent lead (on the side of the heat sinkaway from the component), being especiallycareful not to acutually touch the eyeletthrough whieh the lead is soldered.

(4) When the solder within the eyelet beginsto flow, use a gentle lifting motion with thesoldering aid or heat sink to remove thecomponent lead front thc eyelet.

(5) Repeat the preceding steps on the otherlead of the component. Clean both eyelets; besure to remove all traces of resin.

34

48

Figure 21 keat sink.

(6) Stiape the leads of the new component tomatch those of the faulty component justremoved. Insert the component leads into theeyeiet.

(7) Hold the new component with a pair oflong-nose pliers (or use a heat sink) to protectthe component. Apply the soldering iron to thecomponent lead and allow solder to run intothe eyelet.

(8) Turn the board over and make sure thesoldered connection is secure. There should bea small solder bead formed. Be sure to do allsoldering operations in as little time aspossible. since excessive heating causes theprinted wiring to tear loose from the phenolic.

(9) Repeat the two previous steps to securethe other lead.

8-18. NOTE: When using the long-nosepliers as a heat sink, wrapping a rubber bandaround the handles to hold them closed aroundthe component lead makes it possible for you touse both hands in soldering.

8-19. Wire Wrap Connections. There aremany different types of wire connections thatyou will be required to make. It is beyond thescope of this course to show all the types, butwe will show you some of the more commonlyused wire wraps.

8-20. Eyelet terminal wire wraps. To replacea wire lead into an eyelet, use the followingprocedure:

(1) Strip and tin leads to be connected.(2) Insert lead into eyelet (see fig. 22).(3) Wrap the lead around the terminal and

crimp it to provide a good electricalconnection. Several satisfactory wraps areshown in figure 22, detail A.

35

8-21. Terminal wire wraps. These are muchthe same as eyelet connections, except that thewire is wrapped around a turret. To use thistype of wrap, follow this procedure:

Strip and tin the leads to be connected.Wrap the lead around the terminal turrent

as shown in figure 22, detail B. Make at leastone and not more than two complete turnsaround the terminal. NOTE: Jumper leads areconnected to the lower portion of the terminalwhile the components are connected to theupper portion.

Solder the lead to the terminal.

8-22. Old lead wrap. When replacing adefective component and using the remains ofthe old leads as connections, clean the old leadwire wrap to provide a good electricalconnection. The following procedure is thebest.

Remove the defective component byclipping the lead approximately 1/8 inch fromthe component body.

Straighten the leads remaining on theboard.

Clean., the leads to assure a goodconnection.,

With needle-nose pliers, bend into loopsthe leads remaining on the board.

Insert the leads of the new component asshown in figure 22, detail C, and solder theconnection,

8-23. New component wrap. The newcomponent wrap method is much the same asthat shown in figure 22, detail C. Thefollowing steps result in a good electricalconnection when you are installing the newcomponent:

J

OuTENnuko

ILL L/StTIONOF

PE INEIIINGCONTOuo OT*115 vISINLE

CONIONE NTLINO

INNERPING

IL,Lu$ TEA itOu OFF IL LE TING

CONTOvE OF115 vISIILS

,ONTOL' rcIRE VISIBL

IL I. T 4 $ONOT TILL I iikO

LUSTIAIONOF FIFTrIERING

(A) COmPONERT REMOVAL & REPLACEMENT

NEAT CONTONENT

JUNIPERLINO

III) TURRET WIRE WRAP

IC) OLD LEAD WRAP

OLDLIAO

INE tLP,T00Tinv- IF. t

NE COIAPONENT

ID) NEW LEAD WRAP

Figure 22. Wire wrap connections.

(1) Remove the defective component byclipping the leads 1/8 inch from the oldcomponent body.

(2) Straighten the leads remaining on theboard.

(3) Clean the leads to assure a goodconnection.

(4) Center the new component between theclipped leads and wrap the component leadsaround the clipped leads as shown in figure 22,detail D.

(5) Crimp the component lead to the clippedlead to provide a good connection. Removeexcess wire.

(6) Solder the new connection.

36

8-24. Repair of Printed-Circuit Boards.Cracks and crazes (surface separations that donot extend completely through the body of theboard) are considered for repair only if all thefollowing conditions are met: (1) The crackmust not run under, or appear to run under, aconductor on either side of the board. (2) Nosingle crack can be more than 5/8 inch inlength. (3) there will be no more than tworeparable cracks on a board. (4) no cracks mayoriginate at either of the mounting edges orfrom the other edges of the board to within 1

inch of either mounting edge. (5) No cracksmay extend in a line parallel to the mountingedge of the board. If the printed-circuit boards

So

are not damaged to a point beyond repair. theyshould be fixed. A crack in the base can allowmoisture to collect and form unwantedconductive paths between the conductors. Toprevent this, the cracks must be sealed. This canbe done by using an epoxy-resin compoundapplied as follows:

Secure board so that it will be held steady.Use proper size equipment.

Drill a small hole at each end of thecrack. This prevents the crack from extending.

Open the crack on both sides of the basematerial, using a saw, .a gouging tool, or a knifeto a depth sufficient to receive the epoxy-resin.

Clean the open crack and the surroundingarea with an approved solvent or by scrapingwith a knife.

Apply the ready-mixed epoxy-resincompound and allow the air to cure it forapproximately 24 hours.

Reclean the surface and varnish therepaired area.

8-25. In addition to the repair of crackedprinted-circuit boards, you should have someidea of how to repair raised foil when it isdamaged beyond serviceable condition.Remember to handle printed-circuit assembliescarefully and to use a low-wattage solderingiron and low-temperature solder.

8-26. There are two methods that can beused in the repair, depending upon the size ofthe damaged area. If the break is small, asshown in figure 23, details A and 13, in bothsides of the break, then flow solder across theopen area.

Figure 23, Open conductors.

8-27. Figure 23, detail C, shows a largerbreak in the foil. Tin both sides of the break;lay a piece of solid hook-up wire across theopening and solder it to each side of the break.Bare wire may be used if the break is not toolarge.

8-28. In WM instances where the break islarge, it may be more feasible to **jump" thedamaged area. This may be done by installing awire from one component eyelet to the next inseries.

8-29. If the printed circuit foil becomesraised from the board as shown in figure 24,clip off the raised section. The repair of theclipped-off foil then would be the same asrepairing an open conductor, as shown infigure23, details B and C, depending on how largethe raised area is.

Figure 24. Raised foil repair.

8-30. Transistor .Replacement. Specialemphasis should be placed on our discussion'regarding replacement of transistors. In manyinstances, these components are mounted veryclose to the printed-circuit board. Thiscloseness in itself makes a difficult situation,which is compounded by the fact that thetransistor can be damaged by the application ofexcessive heat. In view of this, specialprecautions must be taken when a transistormust be replaced. Some transistors have socketconnections much like a regular vacuum tubewhich, of course, makes the replacement verysimple. However, the type that is mostcommonly used must be soldered in place. Thefollowing procedures outline the methods forreplacing transistors:

Secure the assembly holding the transistorin a test jig or a vise.

Cut away the transistor body as shown infigure 25.

CUT ALL LEADS

37

volarw.

r-

Figure 25. Transistor replacement.

Heat the remaining leads and when theyare loose, pull them out.

Clean the excess solder from tfie eyelets.Shape the leads of the replacement to

conform with the faulty component. Insert thenew transistor.

Grasp the lead as close to the transistorbody as possible with a pair of long-nose phers.The pliers will function as a heat sink as well ashold the transistor in place.

Flow solder into the eyelet. Repeat thisstep until all leads are securely fastened. Whenreplacing a transistor, it must-be.rememberedthat excessive heat will daniage the transistor.

9. Cable Maintenance9-1. Occasionally, you will fabricate cables

for electronic equipment. It will be yourresponsibility to insure that they are correctlymade and checked. An improperly constructedcable may cause a piece of equipment to beinoperative, prevent it from taking part in astrategic mission, and even cost the lives of AirForce personnel. It is well, therefore, that wediscuss here the proper procedures forconstructing, checking and repairing cables.

9-2. The material used in cable constructionshould meet all the specifications in theequipment technical manual or theauthorization for the particular installation.

9-3. Cable lengths, of course, depend on theplacement of the units. The various cablesrequired, their use, and their length limitationsare usually described in the equipmenttechnical manual or in the installationdirectives. In most cases, high-voltage cablesare fabricated at the factory. The materialsnecessary for other cables, supplied in bulk,consist of the wire to be used and the cablecovering. Normally the fittings for terminatingthese cables are supplied with the bulkmaterial. Vinyl plastic cable covering is themost common covering in use at the present,time.

9-4. Cables should be made long enough sothere is sufficient slack for connecting anddisconnecting the plugs from their receptacles.If the cable lengths are nos specified, you mayhave to tailor them to fit the installation afterthe units have been installed.

95. Mulliconduclor Cables. Multi-conductor cables vary from those havingtwo leads to those having many leads. In thistype of cable several different wire sizes may berequired, depending on the amount of currenteach must carry. The amount of insulationrequired on any lead is determined by thepotential that exists along the lead. Forextremely high voltages, a special high-voltagecable is used. The exact specifications for allmuluconductor cables may be found in theappropriate technical manual on theequipment.

9-6. Coaxial Cable. Most electronic systemsuse coaxial cable and connectors. Figure 26

38

shows an example of a coaxial cable and theassembly of the connectors. When hat:ling orworking near coaxial cables, observe thefollowing precautions:

Never bend a coaxial cable sharplybecause of its special construction.

Check to insure that the bend radius is atleast six times the diameter of the cable.

Do not use spot ties unless specified.Use only cushion-type clamps. The

clamps must not fit around the cable tighsly.Always allow some slack between

mounted equipment and the first clamp.Carefully inspect a coaxial cable for cuts,

flat spots, and other evidence of abuse beforeinstalling.

9-7. Cable Identification. Generally,electronic equipment (to facilitate theinstallation and troubleshooting of wiring) willhave the wiring and coaxial cables identified bya letter/number combination. Theletter/number identification is stamped directlyon the wire or on sleeving attached to it. Onstandard wiring the idcntification number isstamped on the wire at 15-inch intervals andwithin 3 inches of each break and terminatingpoint. Wires from 3 to 7 inches in length arestamped near the center only; wires less than 3inches in length are not identified. Wiringidentifications are stamped in blackexceptAC wires which are stamped in red. Coaxialcables, multiconductor cables, multiconductorcables, unjacketed shielded cables, wires whichdo not retain a machine-imprintedidentification, and wires with a rough surfacewhich do not take a clear imprint are ideptifiedby sleeving at the ends only. In any case, allequipment wiring will have some form ofidentification. For specific information onwiring identification, refer to the equipmenttechnical order.

9-8. Safely Wiring. Electrical connectors,emergent.y devices, and some electronicequipment are secured with safety wire, wherespecified in appropriate directives, to preventinjury to people and equipment. For securingcoupling parts of AN connectors, usecorrosion-resisting steel lock wire. (Use .032-inch lock wire whenever possible.) For securingemergency devices where it may be necessary tobreak the wire quickly, use aluminum or copperwire. Zinc-coated carbon steel wire is used inlocations where the wire may come into contactwith magnesium. Only new wire should be usedwhen securing equipment. Do not attempt toreuse old safely wire on any item that requiresreplacement.

9-9. Two principles of safety wiring areillustrated in figure 27. The double twiss

NUT GLAND WASHER

(A)

CLAMPING SLEEVE

(C)

43,

INTERNALSHOULDER

(D)

(E)

(F)

Figure 26. Coaxial cable and connector.

method, shown in figure 27, detail A, should beused whenever possible. The single wiremethod, shown in figure 27, detail B, should beused in only the following cases:

For emergency devices.For safety wiring in areas difficult to

reachFor small screws in a closely spaced

pattern, as illustrated in figure 27. detail B.9-10. Bonding and Grounding. The

principles to be followed in the preparationand installation of bonding and groundconnections arc as follows: Bonding andgrounding connections (1) protect theetwipment and personnel from lightningdischarge and electrical shock. (2) preventdevelopment of RF potentials, and (3) providecurrent-return paths. When making bonding or

39

grounding connections, observe the followingprecautions and principles.

Bond or ground parts to the primarystructure (main frame) where practicable.

Make bonding or ground connections insuch a way as not to weaken any part of theequipment structure.

Bond parts individually wheneverpossible.

Make bonding or grounding connectionsagainst smooth, clean surfaces.

Install bonding or grounding connectionsso that vibration, expansion. contraction, ormovement incident to normal use will notbreak or loosen the connection.

Whenever possible. locate bonding andgrounding connections in protected areas nearholes, inspection doors, or other accessible

53

MODIrICATIONS

63 O of this publication has (have) been deleted in

adapting this material for inclusion in the "Trial Implementation of a

Model System to Provide Military Curriculum Materials for Use in Vocational

and Technical Education." Deleted material involves extensive use of

military forms, procedures, systems, etc. and was not considered appropriate

for use in voCational and technical education.

Oscilloscopes and Test Accessories

FROM YOUR training and experience, youknow how useful the oscilloscope andsynchroscope are for observing waveforms. Thepictorial presentation of waveforms makes itpossible to analyze the operation of manyelectronic (and some mechanical) systems.Malfunctions can usually be pinpointed bywavcform inspections. You know also thatthese instruments can be used to makemeasurements of current. voltage, andfrequency. On the basis of such facts, it isapparent that oscilloscopes and synchroscopesare test equipments of utmost importance toyou and are, therefore. worthy of study.

2. In this chapter we describe the makeup ofoscilloscopes and synchroscopes. Much of thediscussion about their operation is, no doubt, areview for you. Our coverage is sufficientlycomplete to insure your understanding thefunctions and capabilities of these testequipments so that you can be sure that they are

TESTSIGNAL

LOw VOLTAGEPOwERSUPPLY

110V60 we LINE

)___01VERTICALINPUT

CHAPTER 4

properly used. Circuit analysis is unnecessary,since most of the circuits within oscilloscopesand synchroscopes are conventional ones thatyou should know. Specialized circuits maydiffer considerably in design because ofdifferences between manufacturers,butfunctionallythey are similar. Therefore,we will stress functions rather than circuits.

12. Functional Analysis of Oscilloscopes

12-1. The basic oscilloscope (fig. 30)includes a cathode-ray tube, a sweep generator,horizontal and vertical deflection amplifiers,and power supplies. The synchroscope (see fig.31) is a sophisticated oscilloscope which iswidely used in maintenance procedures. Itcontains special circuits which provideadditional capabilities. The signal channel ofthe synchroscope contains frequency-compensating circuits which permit a muchwider frequency range than is provided by the

VERTICALDEFLECTIONAMPL WIER

.0 HIG04 VOLTAGEPOWER

SUPPLYCATHODE- Rm TUBE

Ex TSYNC

SWEEPGENERATOR

sORIZONTALDEFLECTIONAMPLIFIER

Figure 30. Basic oscilloscope.

5 I

HO RtZONTALINPUT

TEST SIGNAL

VOLTAGE

CALIRRATUR

SwEEP

CALISRATO3

T.LOW>... VOLTAGE

POWERSuPRLY

110 VOLT N,GO Hs LINE 1

SYNC

ArAPLIFISR

EXTSYNC

VERTICALINPUT

VERTICALOECLECTIONAMPLIFIER

VOLTAGENIGH

istyPOWERSuP c531

SWEEP NARK°,GENERATOR GENERATCR

IRETRACE

AMPLIFIERSLANKING

EXPANDED

SwEEP

HORIZONTALOEFLECTION

AMPLIFIER

Figure 31. Synchroscope.

general-purpose oscilloscope. Thepotentiometer used as a synchronizingamplifier with its own controls to providetriggered sweeps. Retrace blanking, markergenerators, and voltage calibrators, which arenot ordinarily found in the general-purposeoscilloscope, are also included in the circuitryof the synchroscope; these features will becovered under special circuits.

12-2. Cathode-Ray Tu.be. As you know, theheart of an oscilloscope is the cathode=ray tube.This is a special type of electron tube (see fig.32) in which electrons emitted by a cathode arefocused and accelerated to form a narrow beamhaving high velocity. The beam is controlledand directed so that it strikes a flourescent

ANODECATHODE 1

CONT ROLFILAMENT GRID

/HORIZONTAL

INPUT

CAT MOCK -RAY TUBE

INTENSIT

MOOUL AT ION

Z-AXISINPUT

screen, whereupon light is emitted at the pointof impact to produce a visual indication of thebeam position. The electronic process offorming, focusing, accelerating, controlling,and deflecting the electron beam isaccomplished by the electron gun inconjunction with the vertical and horizontaldeflecting plates. A flourescent screen visuallyindicates the movement imparted to theelectron beam. An aquadag (graphite) coating,which partially covers the inside of the glassenvelope, provides a return path for electronsand at the same time serves to shield theelectron beam electrostatically from externalelectrical disturbances.

12-3. Electron gun. A simplified form of theelectron gun is shown in figure 32. The cathode

ANODE2

A01.1 AD AGCOATING

FLUORESCENTSCREEN

Figure 32. Electrostatic cathode-ray tube.

525 6

4400V

14112

+100V

Figure 33. Electron beam deflection

is an oxide-coated metal cylinder which, whenproperly heated, emits electrons. Theseelectrons are attracted toward the acceleratingand focusing anodes, which are highly positivewith respect to the cathode. To reach theseanodes, the electrons are forced to pass througha tiny circular opening in a cylindrical controlgrid. The control grid effectively concentratesthe electrons and starts the formation of abeam. Electrons leaving the grid aperturecontinue to travel toward the focusing anode(anode No. 1) and accelerating anode (anodeNo. 2). Note that the anodes are alsocylindrical in shape and have openings topermit beam passage. Between these two anodesis an electrostatic field, shown by the dashedlines in figure 32. which causes the electrons toconverge into a more concentrated beam. Thus.this electrostatic field serves as an electron lenswhich focuses the electrons in somewhat thesame manner that a convex lens focuses a beamof light. The focal length of the electron lens ischanged by varying the potential on anode No.I by means of a potentiometer located on thefront panel of the oscilloscope. The potentialon the second, or accelerating, anode remainsconstant. The intensity of the beam (number ofelectrons in the beam) is varied by varying thegrid potential with respect to the cathode, thuspermitting more or fewer electrons to flow.Because the potentials applied to the grid andboth anodes are taken from a common voltagedivider network, any change made in the settingof the intensity control requires an adjustmentin the setting of the focus control, and viceversa.

12-4. Electrostatic deflection. Electrostaticbeam deflection is accomplished through theuse of two pairs of parallel plates located oneach side above and below the beam. Twoplates are horiiontally oriented so that they areperpendicular to the two vertical plates; thus.the electrons must pass between the plates ofeach set t deflection anodes (see fig. 33). If no

electric field exists.between the plates of eitherpair, the beam follows its normal straight-lin,path, and the resulting spot is at or near thecenter of the screen. A voltage potentialapplied to one set of plates causes the beam tobend toward the plate that has the positivepotential. and away from the plate that has thenegative potential. Deflection of the beamoccurs virtually instantaneously since itpossesses an infinitesimal mass, and thebending is in direct proportion to theamplitude of the voltage applied to the plates.The second pair of plates influences the beamin the same manner except that the bendingoccurs in a plane perpendicular to the first. Theplates located nearest the gun structure aregenerally designated as th ,. y-axis deflectionplates, and those nearest the screen as the x-axis plates. A voltage that is variable andrecurrent with time, when applied to either setof plates. causes the spot to move back andforth across the screen along a straight line.The movement of the spot across the screen'appears as a solid line when its cyclic rateexceeds the persistence of human vision or thepersistence of the phosphor material formingthe screen.

12-5. Nearly all applications of electrostatic-type cathode-ray tube require that each pair ofdeflection plates act on the beam independentlyand simultaneously. This produces a motion ofthe spot along a line which is the resultant ofthe forces exerted by the deflection plates. Inthis case, the electron beam is continually actedupon by two forces which are at right angles toeach other. Figure 33 illustrates the resultantspot motion produced by independentdeflection voltages applied simultaneously tothe x and y axes. When the sliders ofpotentiometers R I and R2 are at groundpotential, all four deflection plates are atground potential and the spot appears at 0 onthe screen. If the slider of R2 is moved in anegative direction, horizontal deflection plateHP2 becomes negative with respect to HP1, andthe electron beam is repelled by this negativevoltage. Under the action of this repulsion. thespot moves to point x on the screen. If theslider of R 1 is moved in the positive direction,vertical deflection plate VP I becomes positivewith respect to VP2, causing the beam to beattracted from point x to point m. Now, if theabove adjustments of R I and R2 are madesimultaneously and at the same rate, theresultant of the electrostatic forces exertedalong the x and y axes causes the spot to moveto point in along the line om. If the samecontrol setup is turned in the other direction,the spot moves alone the line on. Thus, it isdemonstrated that when two -voltages. whether

53

51

lay

DEFLECTIONPLATES

-20V

ELECTRONKAU

."

Figure 34. Deflection sensitivity.

;hey be steady voltages Cir variable in nature,are applied simultaneously, one to each pair ofdeflection plates, the position of the spot at anyinstant is proportional to the resultant of thesimullaneous forces exerted upon the beam atthat instant.

12-6. Deflection sensitivity. The distancethat the spot may be moved upon the viewingscreen in either the horizontal or. the verticaldirection by a potential of 1 volt applied to thedeflection plates is the deflection sensitivity forthe axis under consideration. This is usuallygiven in millimeters per DC volt by themanufacturer, as one of the cathode-ray tube'scharacteristics. The most accurate way ofmeasuring deflection sensitivity is to apply aknown DC potential directly to the deflectionplates and then to measure the distance the spotmoves. This distance, in millimeters, divided bythe voltage applied, is the deflection sensitivityfor that pair of deflection plates (expressed inmm/volt). Most cathode-ray tubes havesensitivities of less than 1 mm/volt.

1 2-7. Another way of expressing the abilityof an applied voltage to cause beam deflectionis called the deflection Actor. Deflection factoris the voltage required on a pair of deflectionplates to produce unit deflection of the spot,and is usually expressed at DC (or RMS) voltsper inch. If a tube has a deflection factor of 60VDC per inch, the spot moves a total distanceon the screen of 1 inch for every 60 voltsapplied to the deflection plates; hence, 120VDC would displace the spot 2 inches.

12-8. If an AC voltage is applied to one pairof the deflection plates, the spot is neverstationary on Lae screen of the scope becausethe deflection of the beam is at all timesproportional to the instantaneous voltage onthe deflection plates. As a result, the electronbeam scans the screen in such a manner as toproduce a straight, luminous line, the length ofwhich is determined by the peak-to-peak valueof the voltage. It can be seen from figure 34

54

that, when an AC voltage is applied to thevertical deflection plates, the electroa beam isdeflected upward and downward from its restpusition by equal amounts. Assume that thevertical deflection system shown in figure 34has a deflection factor of 40 VDC per inch andthat the sine-wave voltage applied to the plateshas a peak-to-peak value of 40 volts. Underthese conditions, the upward and downwarddeflections from the center are each 1/2 inch,producing a vertical line I inch long. The spotretraces this path at the frequency of theapplied signal.

12-9. The x and y deflection sensitivities forcathode-ray tubes employing electrostaticsystems are'not equalthe vertical, or y,platesgenerally have the greater sensitivity. Theinequality results from the differences in theirpositions with repsect to the viewing screen,because it is not a practical design to mountboth sets of plates at a common distance fromthe screen. The most desirable characteristicsfor a particular application should be chosen.For example, if the ultimate in deflectionsensitivity is essential, then (1) the tube must belong. (2) the second anode potential must bekept low, and (3) the effective spacing of thedeflection plates must be small. If the tube mustbe short or if the anode voltage must be kepthigh for purposes of best spot size and highbrilliance, the sensitivity is reduced. A methodoften used for increasing deflection sensitivityis to increase the time during which thedeflection potentials may act upon the beamand to decrease the spacing between plates.This can be done effectively by installing long,closely spaced plates that bend away from thedeflection path to permit a wide angle ofdeflection without interception of the beam bythe plates.

12-10. Fluorescent screen. In order toconvert the energy of the electron beam intovisible light, that area where the beam strikes(labeled screen in fig. 34) is coated with aphosphor chemical which, when bombarded byelectrons, has the property of emitting light.This property is known as fluorescence.Theintensity of the spot on the screen dependsupon two factorsthe speed of the electrons inthe beam and the number of electrons thatstrike the screen at a given point per unit oftime. The amount of light per unit area whichthe phosphor is capable of emitting is limitedand, once the maximum has been reached, any

.further increase in the electron bombardmenthas no further effect on the intensity of thelight. In practical cases, the intensity iscontrolled by varying the number of electronsthat are allowed to reach the screen. Allfluorescent materials have some afterglow,

5 6-

01)

which varies with the screen material and withthe amount of energy expended to cause theemission of light.

12-11. The length of time required for thelight output to diminish by a given amount afterexcitation has ceased is the persistence of thescreen coating. The general classification ofscreen materials is in.terms of long, medium, orshort persistence. Various phosphors are usedin oscilloscope work. each for specificapplications. For example, white and blue-white phosphors of short and very shortpersistence are used where photographicrecords are taken of screen patterns. Again, forgeneral service work, where visual observationis most important. a green phosphor havingmedium persistence is used. In viewing a line orpattern that is traced by a moving spot of light,the persistence of humah vision, as well as thatof the screen material, plays an important part.When the pattern is retraced at a rate of 16times or more a second, the persistence of theeye retains the image from each previous sweep;therefore. the spot in its movement is no longerdistinguishable as a spot, and the path traveledappears as a continuous illuminated line. In thecase of long-persistence phosphor materials, thepersistence of the screen rather than the eye isthe governing factor, and the scanning raterequired to produce a solid line is substantiallylower.

12-12. Aquadag coating. As we havepreviously described, the fluorescent screen ofa cathode-ray tube is bombarded by a beam ofelectrons. If these electrons were allowed toaccumulate upon the screen, the screen wouldsoon acquire a negative charge that wouldeffectively repel and disperse the electronbeam, thus blocking the tube in its primaryfunction. However, this does not occur becausethe beam. upon striking the screen, dislodgeselectrons from its surface (a process known assecondary emission). These dislodged electronsare attracted to positively charged tubeelements, whereupon they are returned to thepower supply. When the number of secondaryelectrons conducted away from the screenequals the number of electrons that return tothe screen plus those that are delivered to thescreen, there is no accumulation of charge.Present-day cathode-ray tubes have a coating ofgraphite painted upon the inner surfaces butnot connected with the screen. The functions ofthis coating are ( ) to collect and returnsecondary electrons to the power supply. (2) toserve as an electrostatic shield against externalelectrical fields. and (3) in some tube types, toact as au accelerating anode.

55

12-13. Basic Circuits, Oscilloscopes andsynchroscopes require power supplies,amplifiers, and sweep generator circuits.

12-14. Power supplies. High-voltage andlow-voltage power supplies are required for theoperation of scopes. The high-voltage powersupply provides operating potentials to thecathode-ray tubes. The low-voltage powersupply provides operating potentials to the'associated amplifiers and oscillators.

12-15. The output of the high-voltage powersupply is usually over 1000 VDC, dependingupon the size of the cathode-ray tube. Itspolarity is negative to permit the second anodeand the deflection plates to be operated atground potential; this also provides anadditional safety factor. Half-wave rectificationand a simple resistance-capacitance filternetwork aye used for these high-voltageapplications because the current required tooperate the cathode-ray tube is very small. Avoltage divider, which includes the focus andintensity controls, provides the necessaryoperating potentials for the various cathode-raytube electrodes.

12-16. The output of the low-voltage powersupply is usually in the 250- to 400-volt range.Full-wave rectification and a pi-type filternetwork are used in this power supply becauseof the moderate current, good regulation, andlow ripple voltage requirements.

12-17. Both the low-voltage and high-voltage power supplies use a commonsecondary on the power transformer. Thisdesign, in conjunction with the use of half-waverectification for the high-voltage supply,permits a saving in copper as well as space,because the low-voltage secondary provides aportion of the high-voltage output.

12-18. Vertical and horizontal ampltfiers.The deflection system of the cathode-ray tube isrelatively insensitive, requiring voltages on theorder of several hundred volts for full-scaledeflection. Therefore, it is necessary to useamplifiers to increase the amplitudes of thevoltages for, both the vertical and horizontaldeflection plates so that test signals of lowamplitudes may be 'effectively presented.

12-19. Most oscilloscopes use a cathodefollower input stage followed by push-pullamplifiers to obtain better linearity at theoutput of the horizontal and vertical deflectionchannels. One of the most important advantagesof using push-pull amplifiers, instead of single-ended amplifiers, is that the deflection platesproduce a uniformly balanced field with respectto the second anode of the cathode-ray tube.This eliminates the tendeficy for the spot to

5J

RETRACE

I..-- TRACEFORWARD "j TtmE

TIME

IONIZATIONPOTENTIAL

DEIONIZATIONPOTENTIAL.

Figure 35. Thyratron sweep waveform.

defocus as the electron beam approaches thelimits of tne viewing area. From a given powersupply, a push-pull amplifier candeliver twicethe output signal that a single-ended stage candeliver. Moreover, push-pull operation tends toreduce the generation of internal noise. The useof a cathode follower as an output circuitprovides the advantages of a higher inputimpedance and less frequency discriMination.

12-20. In synchroscopes and some general-purpose oscilloscopes, the design of theamplifiers provides complex frequency-compensating networks and direct coupling inplate, grid, and/or cathode circuits, to extendthe high- and low-frequency response. Widefrequency response, however, is obtained at theexpense of signal gain. Thus, to broaden theresponse, the number of amplification stagesmust be increased if the same deflectionsensitivity is desired.

12-21. When an amplifier is used betweenthe signal source and the deflection plates ofthe cathode-ray tube, the signal is faithfullyreproduced only when the amplifier over-loading point and frequency range are not ex-ceeded. The overloading point is reachedwhen the amplitude of the signal unaerobservation exceeds the dynamic operatingcapabilities of the input amplifier.(Ncilloscopes using a simple potentiometer asan input gain control are especially susceptibleto overloading conditions. High input signallevels can produce deflection voltages so largethat the display dimensions exceed the viewingarea dimensions; signal extremities are notvisible. Such a display is not usable in thiscondition; therefore, the-gain control must be

56

decreased until the point is reached where thecontrol is so near the end of its rotation thatadequate control of the display dimensions isdifficult to obtain. Two other difficultiesencountered with the use of a single gaincontrol are frequency discrimination and phasedistortion. As the higher input frequencies arevaried, they are adversely affected by the gaincontrol because of the shunting effects of thedistributed capacitance of the high-resistancepotentiometer rotor to ground. The problem iscomplicated by the fact that the shunting effectis increased or decreased for the samefrequency with a change in the resistancesetting. Phase distortion is also a function ofthis control for the sam-e reason.

12-22. Many oscilloscopes include a step-type, frequency-compensated attenuator switchpreceding the first vertical amplifier and gaincontrol to reduce the effects of overloading,frequency discrimination, and phase distortion.This switch often provides a direct-currentposition, connecting the grid of the first verticalamplifier so that circuits producing a direct-current restoration may be observed andmeasured. Attenuators of this type are seldomencountered in the horizontal amplifier.because routine maintenance proceduresgenerally require the use of the internal time-base generator and also because the sensitivityof the horizontal amplifier is lower due to thelocation of the horizontal deflection plateswithin the cathode-ray tube.

I 2-23. Sweep generators. The sweepgenerator circuits in many general-purposeoscilloscopes employ a thyratrun to generate asawtooth sweep. The sweep generator provides

60

TI ME

Figure 36. Multivibrator sweep.

a wide range of fundmental sawtoothfrequencies with a reasonably linear forwardtrace and a rapid retrace time for general-purpose time-base applications (see fig. 35).The advantage of a thyratron sweep circuit overthe simpler gaseous discharge circuits is moreliable synchronization of the sawtooth sweepwith other waveforms in various harmonic.subharmonic. and phase relationships toproduce a stationary display.

12-24. The operation of the thyratron sweepgenerator is based upon the fundamentalprinciple of charging a capacitor througn aresistance from a constant potential source (seefig. 35). The frequency of the sweep generatoris primarily determined by the time constant ofthe charge time capacitor and resistor, but theexact frequency is also affected by theionization and deionization levels of thethyratron. In general, increasing the resistance-capacitance (RC) time constant decreases thesawtooth frequency, while decreasing this timeconstant increases the frequency. At the lowerfrequency sweeps. the desired control over thegenerator frequency is more positive acting andmore easily obtained by the use of a high-resistance potentiometer to increase the RCtime constant.

12-25. The forward trace time of the sweepoccurs when the amount of charge accumulatedwithin the timing capacitor increases with equalincrements of time. The forward trace, then, isproduced by the charge time of the resistor-capacitor combination. Near the end of theforward trace time. the amplitude of thecharging wave becomes equal to the ionizationlevel of the thyratron sweep tube. At this timein the cycle. the gas-filled tube conducts to

57

discharge the time charging capacitor. Whenthe RC combination has been discharged to thepoint where the deionization potential of thethyratron is reached, the thyratron ceases toconduct. This portion of the sawtooth wave iscalled the flyback. or retrace, time. Thesawtooth waveform is completed at this point,and the circuit continuously repeats the entirecycle of events. There are three generally usedterms to describe the sweep with this mode ofsweep generator operation: continuous, free-running, and recurrent.

12-26. Vacuum tubes and transistors are alsocommonly used to produce sawtooth sweepsignals for, driving the horizontal deflectionamplifiers. Multivibrators of various types, aswell as blocking oscillators, are used togenerate these signals. Multivibrators used forthe generation of sawtooth signals areasymmetrical; that is, two pulses are producedper operating cycle, but they are of unequaltime duration. The longest pulse is used toderive the forward trace time, while the shortestpulse is used to derive the retrace time, asshown by the dotted lines in figure 36 Acomparatively large capacitor is placed acrossthe output terminals of the multivibrator toconvert the rectangular pulses into .a sawtoothsweep signal. Blocking oscillators are usable assweep generators, but general-purposeoscilloscopes used by the Air Force seldomhave blocking oscillator sweep circuits.

12-27. Sawtooth sweep signals derived fromconstant voltage sources, such as those justdescribed: do not produce a sweep of sufficientlinearity for some applications. The reason isthat the charging voltage follows anexponential curve instead of the desired

61

3

11+

Ia

0

SYNC$RONIZItdGVOLTAGE N..

GRIDVOLTAGE .;

+ I

IONIZATIONPOTENTIAL

DEIONIZATIONPOTENTIAL

TIME

Figure 37. Synchronizing the sweep.

straight line. By replacing the resistor in an RCtime-determining network with a pentodevacuum tube, a more linear sWeep can beobtained. The high plate resistance of thepentode, together with its constant currentproperties. makes it well suited for thispurpose.

12-28. In addition to linearity,synchronization is important. While it is truethat a stationary display can be obtained byadjusting the sweep generator to someharmonic or subharmonic relationship with theunknown signal in the vertical amplifier, it doesnot mean that the dispiay remains stationaryindefinitely. Fluctuations in either the sweep ortest signal, or both, cause the two signals to losethis synchronism. If the sweep is not preciselyin step with the voltage under test, the resultingdisplay is a moving display, and unless themovement is very slow, the display isunintelligible to the observer. Many times, it isextremely difficult to obtain a stationarydisplay despite the harmonic relationship of thetest and sweep signals.

12-29. Although more stable synchronousoperations, can be obtained with vacuum-tubeand solid-state sweep circuits than with athyratron sweep circuit, many oscilloscopesemploy the thyratron because it permits simplerdesign and is satisfactory for ordinaryapplications. A method of locking the sweepgenerator to the frequency of the test signal isto inject a portion of the test signal beingprocessed in the vertical amplifier into the gridof the thyratron. For example. if nosynchronizing voltage is applied to the gridof.the thyratron, the sweep generator becomesuncontrolled and operates in a free-running

58

condition; i.e., its frequency is governed solelyby the RC time constant of the circuit, shownby the solid line sawtooth signal in figure 35.Reference to figure 37 shows that even thoughthe solid line synchronizing sine wave does notmaterially affect the free-running sweepfrequency, synchronism is obtained. If thesweep signal tended to change along the timeaxis, the sine wave would trigger the thyratronto terminate the forward trace time. Figure 37also shows how the horizontal sweep is broughtinto synchronism if the same sine-wavefrequency is advanced in phase by 0°. Note thedotted line sine-wave and sawtooth sweepportions.

12-30. Special Circuits. As we havementioned earlier, scopes may have specialcircuits to make them more accurate andversatile.

12-31. Triggered sweep. The sawtooth sweepgenerator in the general-purpose oscilloscopesis usually of the free-running type. Although asynchronizing signal injected into the sweepgenerator can control and initiate the sweep,the free-running frequency of the sawtoothsweep must .closely match or be some multipleof the synchronizing signal to provide lock-inoperation. Consequently, when thesynchronizing signal consists of random pulses.or pulses having low repetition rate.satisfactory displays cannot be obtained,Consider the case where a pulse of 1/2 Asec inwidth is to be observed at a repetition rate of1000 pulses per second (PPS). The sawtooth

sweep would have to be about I Asset: long todisplay the pulse; however, for each pulseobserved there are 999 idle sweep periods ofthe time .base generator. Loss of

62

aoass°/".4.141 i4v1 /13 15/131

A a

Figure 38. Triggered .sweep and displays.

synchronization during the 999 idle periodscould produce an erratic display, because thepulse could be located in a different positionfor each successive sweep. Furthermore, inmost cases. the observed pulse is small and faintas compared with the long, bright baselinerepresenting the idle periods.

12-32. To overcome this difficulty, the

synchroseope was developed.-It has a triggered

or driven sweep which is time controlled.During quiescent signal conditions, thecapacitor in thc time-determininrnetwork is

held in a discharged state. The spot remains atthe left-hand side of the scope viewing areaduring this time. When a synchronizing pulse ofthe proper amplitude and polarity is derivedfrom the signal under investigation, the sweep-

forming capacitor is permitted to charge,commencing a single sweep. Following theattenuator of the vertical amplifier is an

artificial delay line or a low-pass filter circuitwith a cutoff frequency higher than the highestfrequency to be passed. One purpose of thisdelay circuitry is to retard the signal to beobserved until the sweep has been initiated by aportion of the input signal. which is notdelayed. If the delay were not used, the initialportion of the waveform would not appear onthe trace, because a certain amount of time istequired for the input signal voltage to rise tothe level needed to trigger the sweep circuit.

12-33. The delay period may be fixed orvariable, lf the delay is variable, the triggeredsweep may be initiated to lead or lag the signal

59

source by some predetermined amount topermit investigations of any portion of aparticular waveform. Figure 38,A, shows theundistorted waveform displayed by a singlesweep from the internal time-base generator. Infigure 38,B. the sweep frequency and delaywere changed so that the sweep would beinitiated 20 issec after the start of the waveformto be displayed. The undesired detail of the linesegment represented by line ab is eliminated bythe delay circuit, and the entire step pulse isexpanded .along the horizontal direction.Changing the sweep frequency and delaying thesweep for 45 Asec, as shown in figure 38,C,permits an even greater expansion of the steppulse for the examination of any detail alongthe peak of the pulse.

12-34. A secondary purpose of the delay lineis to provide a means of reflection, a series ofaccurately spaced pulses suitable for calibrationof short time intervals. To accomplish this, aswitch is provided to cause a mismatch in thetermination of the delay line so that when asharp pulse is fed into the line, a series ofreflections will occur similar to those shown infigure 39. Since the time required for a pulse totravel down the line and back is 1 Msec, a seriesof pulses occurring I Asec apart is produced.Of course, each successive pulse is smallerbecause of losses in the delay line, but asignificant number is available for most high-speed calibration purposes.

12-35. Sweep calibrator. The .length of the

sweep signal used for general waveform

hgure 39. Marker pulses tram a mismatched &la!, hnc.

Inspection need not be cahbrated. Thi- sweepcontrols are manipulated until a certainreference waveform specified by themaintenance routine is obtained. In manymaintenance applications, however, calibrationof the time axis is necessary. Such calibration ismade with a sweep calibrator which supplies ahighly stable output tit* known frequency.Consider the case where the output from thesweep calibrator provides a sine-wave signal of

1 megahertz per second (MHz) which isinjected into the vertical deflection amplifier.The horizontal amplifier and sweep controkare then adjusted to produce a single sine-wavecycle display 1 inch wide. Since 1 MHzcorresponds to a cyclic period of I ihsec. thehorizontal sweep is not calibrated for 1

hcsec/inch. If the sweep calibrator supplies afrequency of 10 kHz, a cyclic period of 100hcsee is obtained. A trace made to be I inchlong, therefore, has a horizontal sweepcalibrated at 100 hcsec/inch. Expanding thedisplay to 4 inches results in a calibration of 25p..sec/i n c h.

12-36. Retrace time is atso ,.t,ncluded in thistype of time axis calibration. and thus producesa small error. The retrace time generallyoccupies only a small percent of the total sweeptime; therefore, this calibration error canusually be neglected. In those applicationswhere such an error cannot be tolerated, amarker generator must be used.

12-37. Marker generator. Sweep-timecalibration is made with the aid of markerpulses produced by accurately adjusted tunedcircuits. Ma-ker pulses are often produced bythe "ringing- of a succession of tuned circuitsby the sweep oscillator itself, or hy a separateoscillator of the multivibrator type, whichproduces a continuous series of harmonicsspaced at convenient intervals.

12-38. Some types of internal markergenerators are connected by suitable amphfiersto the grid of the cathode-ray tube and are alsocontrolled by the sweep generator so that both

'the sweep and the markers are initiated at zero

60

:itne. In this way the sv cep is dividedinfo :qual increments. The displayatrace isiniensified during that period of the markersignal which makes the grid-to-cathodepot..ntiat less negative. The displayed signal:rum the vertical araphfier is then :choppedup- into a i,eries of bright segments of knownlength in terms of time: Typical markerintervals are switch seleieu to give 0.2-, I-, 10-

100-. and 500-ihsec markers.12-39. Another method, using the vertical

deflection amplifier, mixes a succession of fixedmarkers with the signal under hwestigation.Figure 40.A, shows a signal undergoinginspection that does not have markers; thus,there is no way of gauging whether the pulsesare of the correct width or whether the spacingbetween the pulses is accurate. By injectingmarker pulses into the vertical amplifier,spaced at accurately known intervals (see fig.40,11), we can now determine whether or notthe pulses are arriving at the precise timedesired and whether or not they are of thecorrect width.

12-40. Other types of markers, such as signalor absorption markers, are also used. Thesetypes of markers are generally obtained fromauxiliary equipment and are injected or mixedwith the signal under observation at the verticalinput terminak of the oscilloscope orsynchroscope.

12-4 I. Voltage calibrator. In many test anualignment procedures, a signal of knownamplitude and waveform is required at theinput of an amplifier, so that the resultantoutput of the amplifier may be observed,measured, and analyzed.

12-42. The amplitude of the waveformdisplayed may be measured by using a deviceknown as a voltage, calibrator. Voltagecalibrators may be manufactured as auxiliaryequipment. or they may be featured as part ofthe internal circuitry.

12-43. The fixed reference type tit voltagecalibrator clips the peaks ot the 60-hertz ACfilament source to closely approxinute theshape of a square wave. The chpping diodes actalso as clamps to produce a fixed peak-to-peaksignal of 3 volts at an wtput terminal. Injectionof this 3-volt peak-to-peak signal into thevertical amplifier permits you to manipulate thecontrols to obtain a display deflected to someconvenient number of divisions on the scopecalibration gnd. 1 he calibrating signal is thenreinoed and. without changing any controlsettings. the unknown signal is hubst II wed togive a new display The number of diisionsthe calibration end are counted and the peak-to-peak signal is calculated: the calculation is

11

A

CW

Figure 40. Marker injection.

hosed upon proportionate deflection withrespect to the original display.

12-44 Other voltage calibrators provide avariable calibrated control. permitting you tomeasure the amplitude of displayed signals bycomparing the unknown voltage with a variableamplitude pulse of known value. The displayedamplitude of the calibrating signal is adjustedto equal the amplitude of the displayed signalunder investigation. The reading of thecalibrated control may then be used directly orit may he calculated, as required.

12-45 Retrace blanking. The sawtoothwaveform generated by the sweep generator hasbeen discussed in detail with respect to thetrace time, hut little has been said about theretrace. or flyhack, time.

12-4t) Retrace time is the time required toswitch the electron beam from the right-handside of the viewing area to the left-hand sideprior to initiating a new sweep. The timerequired to switch the beam varies with circuitconstants. ranging from a few percent of thetotal sawtooth sweep time in special-purposeoscilloscopes to as much as 15 percent ingeneral-purpose oscilloscopes. The intensity ofthe retrace depends upon the fundamentalsawtooth repetition rate. If the fundamentalrepetition rate is low, the retrace is still clearlyvisible, even though the retrace, as comparedwith the forward trace, is extremely rapid.

12-47. Displays of low-frequency waveformsare least affected by retrace time, since thepercentage of the waveform lost during thetrace is small. The effect of this portion of thesawtooth sweep becomes progressively moreno(iceable until at some higher frequency a fullcycle is displayed during retrace.

12-48. Rectangular waveform displays athigh .repttition rates can become confusing1.(ecare of the retrace portion 9f the display(sec fig. 41). A segment of a recurring cycle isdispioed. consisting of a series of rectangularpulses that are periodically blanked inaccordance with sonic circuit operating cycle.The disola is confusing because it does notshow the waveform expected.

b I

err

12-49. To overcome this difficulty, a pulseof the proper amplitude and polarity is used todrive the grid of the 'cathode-ray tube to cutoffduring retrace time. Thus, retrace blanking isactually an interruption of the electron beamduring the time when the beam is beingswitched from the right-hand side to the left-hand side of the viewing area prior to the nextsweep. When the sawtooth sweep is initiatedonce again, the grid of the cathode-ray tube isunblanked, permitting the electron beam toexcite the screen phosphor.. 12-50. Figure 42 shows the same signal aspreviously shown in figure 41, but with retraceblanking taking place. Notice that the retracetime used throughout the discussion shows thatretrace time can prevent the display of aconsiderable portion of the total signal underobservation. This is true whenever therepetition frequency is high enough. As we havepreviously explained, the loss of the pulse isdue to a relatively long retrace time and cannotbe altered by retrace blanking.

12-51. Expanded sweep. Circuitry to permitthe expansion of selected segments of theedisplay in the horizontal direction are featuredin many types of oscilloscopes andsynchroscopes. By the use of such equipment,the leading and trailing edges of expandedpulsesespecially in radar maintenanceroutinescan be explained in much greaterdetail. A positioning potentiometer is used tocontrol a delay trigger circuit so that theexpanded sweep commences at any selectedpoint with respect to the normal forward traceof the sawtooth sweep. Additionalamplification of the sweep from the triggerpoint produces a sawtooth waveform that isdeliberately distorted by a known factor. Thisadded amplification is fixed to some value suchas 3X, 5X, or 10X, or a switch may beprovided to select the expansion factor desired.The switch is calibrated as a multiplier so thatthe sweep rate through the expanded portion ofthe display may be calculated. Provision ismade in some of these instruments for adjustingthe expansion notch to a width that is 15 to 25percent of the total sweep length anywherealong the length of tne normal sawtooth length.

r2

11111,

VERTICAL AXIS SIGNAL.TIME flp RESULTANT OSCILLOSCOPE

DISPLAY

Figure 41 Effect of retrace.

13. Oscilloscope Controls and OperatingConsiderations

I 3-1. You are well aware of the fact that themeasurement and comparison of waveforms is avery important part of the circuit analysis usedin troubleshooting. In some circuits (forexample, pulse circuits), waveform analysis isindispensable. Waveforms may be observed attest points s,hown in waveforrh charts orschematic diagrams that are a part of Air Forcetechnical manuals supplied for each equipment.You should realize, however, that thewaveforms given in instruction hooks are oftenidealized and do not show some of the detailsthat are normally present when the acualwaveform is displayed on an oscilloscope. orsynchroscope. Nevertheless, by comparing theobserved waveform with the referencewraveform, faults can be localized rapidly'.

62

13-2. If there is no trouble present in theequipment, a waveform observed at a point inthe equipment should closely resemble thereference waveform given for that test point.The reference waveforms supplied in thetechnical manuals are the criteria of propercircuit performance. However, test equipmentitself or the use of test equipment can causedistortion of the observed waveforms, eventhough the equipment is operating normally.We discuss several of the most common causesof these conditions in this sectionand alsoremind you of some practical considerationsand precautions ot importance.

I 3-3. Controls. Most Air Force technicalmanuals clearly state when and wnere toconnect an oscilloscope int,) a circuit toperform preventive or corrective maintenanceprocedures. These manuals also have

66

51

HORIZONTAL AXIS SIGNAL(DOTTED LINES SNOW TIME WHENBLANKING PULSES ARE ACTIVE)

TIME

Figure 42. Effect of retrace blanking.

illustrations to show you the appearance of thedesired waveform at selected points. The choiceand manipulation of oscilloscope controls,except for special routines, is left to yourdiscretion. NOTE: Unfortunately, displaysoften show waveforms at points not discussedby these manuals; in addition, the displaysshown may be modified by adjustment ofcontrols which are not mentioned in the text ofthe routine, because you are expected tomanipulate the controls without beinginstructed to do so.

13-4. Focus and intensity. The two basiccontrols affecting the readability of the scopedisplay are the beam intensity and focusingcontrols. These two controls are consideredtogether because they interact to such an extentthat the adjustment of one usually requires theadjustment of the other.

13-5. The intensity control is used tu adjustthe spot to the brightness desired. When thespot has no motion, ir becomes brighter; larger,and out of focus as the intensity control is

63

rotated toward maximum intensity. Furtherrotation of this control produces secondaryemission effects, causing a halo around thespot. When the halo appears, the intensitycontrol must be decreased to eliminate the halobefore the fluorescent screen is permanentlydamaged. The halo from an excessively brightspot disappears to some extent when theelectron beam is subjected to the deflectionfields, because the energy in the electron beamis distributed over a much greater area. The useof the spot in this condition produces a widetrace and tends to obliterate or mask anyavailable fine detail.

13-6. The focus control is used to produce around spot with a clearly defined edge. Astationary spot becomes smaller and charperwhen the focus control is rotated toward themaximum value. Further rotation of thiscontrol beyond the focal point again, producesan out-of-focus spot.

13-7. A poorly focused spot can result in anelliptical instead of a round spot. When the

6 7

Figure 43. Poor focusing.

elliptical spot is set into motion under theinfluence of deflecting fields, it is noticeable asa line of variable thickness. For example. if theellipse is lying horizontally, it produces a thinline only at the peaks of a sine wave, while thepositive- and negative-going portions of thesine wave are considerably thickened, as shownin figure 43.

13-8. Depending upon the velocity of thespot, an increase in spot intensity may berequired, because the rapidly moving spot doesnot remain in one position long enough to fullyexcite the phosphor screen of the cathode-raytube. This effect may often be observed whenyou are viewing sqaure waves where the riseand decay times are extremely rapid (see fig.44).

13-9. Gain. The basic controls thatdetermine the size of the oscilloscope displayare potentiometers used as the horizontal andvertical gain controls. The horizontal gaincontrol permits the width of the display to beincreased or decreased; similarly, the verticalgain control permits the height of the display tobe increased or decreased.

13-10. An attenuator preceding the gaincontrol is sometimes encountered and is usuallyassociated with the vertical amplifier. The stepattenuator, often referred to as a multiplier, isusually calibrated in steps of IX, 3X, 10X,30X, and 100X; the attenuation at each step is

Figure 44. Effect of trace speed on beam intensity.

64

expressed with respect to the attenuation rangeat step 1 X. Operation of this control, results inabrupt changes in the oscilloscope displaybecause ot sharp changes in the input signallevel. The attenuator is called a multiplierbecause the oscilloscope can be-used as a directreading, peak-to-peak voltmeter, once thevertical amplifier is calibrated. Calibration isaccomplished by setting the attenuator to I X,injecting a signal of known amplitude, follwedby a display adjustment to vertical dimensionsof convenient known height. Advancing thegain control too far for a given signal orapplying a signal that exceeds the amplificationcapabilities of the horizontal or verticalamplifiers results in overloading and,consequently, distortion.

13-1 I , Interpretation of an observedwaveform depends greatly upon properproportioning of the horizontal and verticaldimensions of the oscilloscope display.Uncertainty or lack of knowledge concerningthe signal that an amplifier is processing,together with improper display proportioning,can lead to an erroneous conclusionconcerning the test circuit. Figure 45 shows thedisplay of a trapezoidal waveform where thehorizontal and vertical dimensions areacceptable. By contrast. if both the horizontaland vertical gain controls are changed in arandom manner so that the change in thevertical direction predominates to produce theoscilloscope display shown in figure 45,A, thecharacteristics of the trapezoidal waveformshown in figure 45,B, become masked. If youhad no previous knowledge that the waveformwas supposed to be a trapezoid, you couldreach the erroneous conclusion that the displaywas a sawtooth waveform. On the other hand, ifyou know that the circuit processes atrapezoidal wave and wish to closely inspect thewaveform for any irregularities, such aproportioning of the display is entirelyacceptable and advisable. Changing thehorizontal and vertical gain controls once moreto the opposite extreme so that the display isexaggerated predominantly in the horizontaldirection produces a waveform like that shownin figure 45,C. Under these conditions, thetrapezoidal waveform viewed on theoscilloscope screen could be interpreted as asawtooth waveform with excessive retrace time.

13-1 2. A height-to-width ratio ofapproximately 2:3 or 4:5 provides optimumdisplay proportions for general-purposewaveform examinations. Once you are certainof the waveform you are inspecting, expansion(maintaining the same ratio) or exaggeration ofthe waveform in the vertical or horizontal

66

ATRAPEZOIDAL WAVEFORM INCORRECTLY PROPORTIONED;

VERTICAL GAIN HIGH, HORIZONTAL GAIN LOW

TRAPEZOIDAL WAVEFORM CORRECTLY PROPORTIONED

TRAPEZOIDAL WAVEFORM INCORRECTLY PROPORTIONED:VERTICAL GAIN LOW, HORIZONTAL GAIN NIGH

Figure 45 Vertical-co-horizontal proportioning.

direction to observe waveform irregularitiesmay be very advantageous.

13-13. Sometimes the signal at the pointunder examination is so small that a display ofmore than 1/2 inch in the vertical dimensioncannot be obtained. The horizontal dimensionof the display must also be reduced so that thedisplay is correctly proportioned. A reductionin beam intensity, followed by a refocusing ofthe spot, generally produces a display that iseasier to view.

13-14. Positioning. The vertical andhorizontal positioning controls permit you toshift the position of the entire desplay to anyportion of the viewing area desired. Theyertical positioning control is a continuouslyvariable potentiometer that permits the displayto be moved up or down by any amount,including those positions away from theviewing area. Similarly, the horizontalpositioning control permits the side-to-sidemovement of the entire display.

65

13-15. Occasionally, during an examinationof a waveform, irregularities may be noticed ator near some extremity of the display. Thedisplay may be enlarged by means of otherscope controls and then positioned by thehorizontal and vertical positioning controls sothat the irregularity under inspection appearswithin the center of the viewing area. Theremainder of the signal, of which theirregularity is only a small part, is thendeflected off the screen toward the neck of thecathode-ray tube where these portions of thesignal cannot be viewed. At the edges of thetube, the display being deflected off the screenwidens and becomes considerably blurred atthe rim of the tube. This distortion is due to thecurvature and reinforcing thickness of the glassat this point of the tube envelope.

13-10. When expanding a display for thepurpose of close signal inspection, you mayalso expect some distortion at or near themaximum control positions. Such distortionshould not be attributed to the cathode-raytube, because it is due to nonlinearitycharacteristics of the horizontal and verticalamplifiers.

13-17. The horizontal and verticalpositioning controls also serve a secondarypurpose. Since the structural imperfections inthe manufacture of cathode-ray tubes may causethe beam to strike at some point other than thecenter of the screen when no deflecting signalsare applied, it is necessary to provide somemeans of positioning the beam. This is usuallydone by applying small DC potentials to thedeflection plates by means of potentiometerssimilar to those described earlier andillustrated in figure 33.

13-18. Polarity reversal. Comparisonbetween the reference waveform and the displayobtained from operating equipment can best bemade if it is known which direction the spotmoves when a positive voltage is applied.Normally, oscilloscopes provide an upwardspot deflection with a positive input signal.However, some oscilloscopes provide a

switching arrangement in the vertical amplifier.whereby the beam can be switched to provideeither an upward or a downward deflectionwith a positive input signal. This switch may belocated in the grid section of the vertical inputamplifier or at the grid pr grids of the verticaloutput amplifier.

13-19. Frequency. The coarse and finefrequency controls of an oscilloscope permityou to chanue the trequency of the sawtoothsweep generator. The course frequency controlis a multiposition rotary su.itch that permits youto select the desired range of sawtooth

frequencies by selecting the forward swecr timecharging capacitor. The fine frequer,is a potentiometer that allows the adiesuies ,:!the sweep circuit time constant to ,biain th-exact frequency needed to prcAide (.1

display;13-20. The selection of different types of

horizontal amplifier signals is.also determinedby the setting of the coarse frequency control.Five or six positions of the coarse frequencycontrol are used to cover the full frequencyrange of the internal shwtooth sweep generator.Sine-wave signals are widely used for time-basesweep applications. Such signals are easilyobtained from the 60-hertz power sourcewithin the oscilloscope. This 60-hertz, or linesweep. signal is usually available at the coprsefrequency control, but some oscillosopesprovide this signal from a separate terminal. Insome applications, the 60-hertz signal is notsuitable for the best display. A "direct" positionis provided on the coarse frequency control topermit the use of sine waves at frequenciesother than 60 Hz and to display waveformsresulting from time bases other than thoseavailable within the scope. The sawtooth sweepgenerator is disabled by the coarse frequencycontrol when either the line sweep function orthe direct function is selected.

13-21. The fine frequency control, inconjunction with the coarse frequency control,permits you to select the time base required todisplay as many cycles or pulses as desired toview the waveform under investigation. Thiscontrol is uncalibrated, except for markingswhich permit you to estimate some previousposition. Calibration of this control is notrequired because you are not actually interestedin the time-base frequency. except as a means ofobtaining a convenient display. The frequencyof the time-base sweep generator can be easilydetermined by injecting a known frequency intothe vertical amplifier and then manipulating thecoarse and fine frequency controis for astationary pattern of one complete cycle. Underthese conditions, if the injected signal is a sinewave of 1000 Hz, then one sine wave lasting1/1000th of a second is displayed by onesawtooth wave, also lasting for 1/100th of a

second. Therefore, the frequency of the time-base sweep generator is also 1000 Hz and isthus a 1:1 frequency ratio. If the pattern is notstationary, then the method described is notvalid and cannot be used with accuracy. It iseasy to stop an oscilloscope waveformdisplayed by use of these controls if thefrequency of the waveform under investigationis within the frequency limits of theoscilloscope.

13-22. Thus far, our discussion of the coarse66

and tin:: frequency conirri: nas been limited totnose cases where the swecp trequeetcy is equalto the frequency of tne waveform underinvestigation. Let us briefly recall two caseswhere the time-base swe,T frequency is loweror higher than the frequency of the waveformapplied to the vertical input terminals.

13-23. Whenever two or more completecycles of an input waveform are displayed,whether stationary or not, the frequency of thetime-base sweep generator is lower than that ofthe input waveform. When the display isadjusted for a stationary pattern. the frequencyof the time-base generator may be calculated, ifthe input frequency is known, by dividing theinput frequency by the number of completecycles displayed.

13-24. Many apparently odd and unusablepatterns arc displayed on the oscilloscope whenthe frequency of the time-base sweep generatoris higher than the frequency of the waveformunder investigation. Such patterns are notentirely unusable since they may convey usefulinformation to the observer.

13-25. Assume you have a sine-wave inputsignal of 60 Hz to the vertical amplifier. At thesame time, the time-base generator is furnishinga sweep signai to the horizontal amplifier at20 Hz to give a stationary display. Refer to

figure 46,A. One complete sweep of the time-base generator displays only one-half of thesine wave before returning to the left-hand sideof the scope viewing area. If the sine wave startsfrom zero toward its maximum value at thcsame instant that the time-base generator startssweeping from its zero value, then the entirepositive portion of the sine wave (points a, h.and c.) is displayed during this sweep. As thegenerator once more initiates its sweep, the sinewave is at its zero point, going toward itsmaximum negative value. The display at the endof this second sweep shows one complete sinewave, with the positive half positioned over thetop of the lower half.

13-26. Now assume that the sawtooth sweepis initiated at point b, the maximum positivevalue of the sine wave, at the same instant that asweep is initiated. A second stationary pattern.as shown in figure 46,B. can be obtained undersimilar conditions by changing the phase of the60-hertz sine-wave input with respect to thesweep of the time-base generator.

13-27. The entire positive-to-negativealternation of the input waveform is displayedduring the first sweep of the time-basegenerator. After being returned to the left-handside of the viewing area during the retraceperiod, the sweep is initiated tor the secondtime to display negative-to-positive alternationof the sine wave. Once again, the time-base

TIME

SECONO 41GO

/

I itit

120SEC

A

Figure 46. Patterns when sweep-to-signal ratio is 2:1.

generator has used two sweeps to display onecomplete cycle of the input waveform.

13-28. In either case cited, the inputwaveform has been "chopped up" into twosegments for the display. Figure 47 shows thestationary displays presented by an oscilloscopefor a vertical-to-horizontal frequency ratio of1:3. The 1:3 ratio is shown for two differentphase relationships. These traces may also beinverted, depending again upon the phaserelationships between the two signals.

13-29. Synchronizing. The synchronizingcontrol found on all oscilloscopes permits aportion of the signal beigg amplified in thevertical section to be injected into the time-basegenerator for the purpose of pro'ducing a

stationary waveform display.I 3-30. Throughout our dicussion about

time.base sweep controls, we have emphasizedthe stationary display. A signal supplied to thevertical amplifier which. bears some integralfrequency, and phase relationship to the signalproduced by the horizontal amplifier producesa stationary display. A consideration of thefrequency tolerances and stabilitycharacteristics of electronic equipment, ingeneral.. shows that it is improbably to

67

e

consistently maintain these frequency andphase requirements. Therefore, thesynchronizing control is included as a par Ofthe oscilloscope circuitry to obtain a stationarydisplay for a detailed waveform investigation.

13-31. A potentiometer is used as !hesynchronizing control, to permit you to injec*.as much of the synchronizing signal as

necessary to produce a stationary displaypattern. The adjustment of this control is no-.critical, but the use of too much synchronizingsignal can cause severe distortion of Owobserved signal. This is due to erraticfunctioning of the time-base generator.

13-32. If the synchronizing control Is

advanced too far, the amplitude of eite

synchronizing signal produces a distortedsweep signal. Inspection of figure 48 revealsthat the excursion of the injected signal hasinitiated two sweeps per cycle of the appliedsignal. Under these conditions, the resultanttime base was plotted against the applied signalproduced by the vertical amplifier to obtain agraphical representation of the scope display. asshown in figure 49. The display is undesiraolein this form because it is difficult to visuali-tethe type of signal applied at the vertical inputterminal. Despite the undesirable double

Me I /GO SECOND

I ,i

I II

0

TIME ---11

Figure 47. Patterns when sweep-to-signal ratio is 3:1.

SYNCHRONIZINGSIGNAL

IONIZ ATIONPOTENTIAL

DISTORTED SWEEPSIGNAL

DE IONIZ ATIONPOTENTIAL

TIME -PrFigure 48. An effect of excess synchronizing

signal upon the sweep.

68

TIME IP,VERTICAL INPUT

RESULTANT DISPLAY

Figure 49 Display resulting from a distorted stable sweep.

sweep, inspection of the resultant time basewith respect to the synchronizing signal shownin figure 48 shows that the repetition rate of thetime-base signal remains constant. The patternremains stationary, being continuouslydisplayed as a signal trace, until correctiveaction is taken.

13-33. Another example of excessivesynchronizing signal amplitude is shown infigure 50 and 51. Investigation of figure 50shows how the frequency of the time-basegenerator has become unstable because of

CHARGE

incorrect sychronizing control adjustment.Note that the amplitude and length of the linearsweep are different for each sawtooth. This timebase is plotted against the signal output fromthe vertical amplifiers to obtain the resultingdisplay shown in figure 51.

13-34. The synchronizing signal may beinjected directly into the time-base generatorfrom a source external to the scope. The needfor external sync depends chiefly upon the typeof signals undergoing observation.

13-35. Intensity modulation. Many scopesprovide an external terminal for the injection ofa signal directly into the cathode-ray tube,through its grid or cathode circuit, to modulatethe moving electron beam. This terminal iscalled by one of two common namesZ-axisinput or intensity modulation input.

13-36. Variation of the grid-to-cathodepotential changes the density of the electronbeam within the cathode-ray tube and in thismanner determines the intensity of the lightemitted from the fluorescent screen.

13-37. Although any type of waveformproduces intensity modulation, the preferredtype of signal is in the form of sharp pulses topermit precise measurement of the time intervalbetween pulses. These pulses, termed markers,should be of short duration with a highrepetition rate with respect to the signal beingexamined. The resultant display on thecathode-ray tube will have a number ofalternate bright or dark spots corresponding to

.14SCIHONANL

'ZINCSY RO

IONIZATIONPOTENTIAL

DISTORTEDSwEEPSIGNAL

DEIONIZATIONPOTENTIAL

TIME

Figure 50. Distorted sweep caused by improperly adjusted sync.

69

TIMEVERTICAL INPUT RESULTANT DISPLAY

Figure 51. Display resulting from a distorted unstable sweep.

the occurrence of the markers, depending uponwhether they increase or decrease the beamintensity.

13-38. If the marker signal is introduced atthe grid of the cathode-ray tube, negative pulsescut off the electron beam so that no trace isproduced; during the next interval, the beam ispermitted to stroke the fluorescent screen toproduce a normal intensity. spot. If, on theother hand, the marker pulses are positive, thebeam intensity is increased so that a trace ofincreased brilliance can be observed; during thenext interval, the beam is returned to normalintensity. The amplitude of the marker signal isrelatively unimportant, except that theamplitude of the negative marker signals mustbe sufficient to drive the grid of the cathode-raytube to cutoff. When the marker signal isproduced at the cathode of the display tube, thepolarity of the marker signals must beinterchanged to maintain the conditionspresented in the preceding paragraph.

13-39. In most scopes that provide thisfeature, the intensity modulation circuit is. asimple RC network. The frequency of themarker signal must lie within the passband ofthe Z-axis circuit, or frequency discrimination

70

in the form of signal differentiation will takeplace.

13-40. The input terminal for the Z-axis isnot always located on the front panel of theoscilloscope. It is often found on the rearchassis apron.

13-41. Operating Considerations. Theoscilloscope and synchroscope are subject tolimitations and malfunctions, just as any otherelectronic device. Although some precautionsfor scopes have been previously stated orimplied, we also include them here for addedemphasis and convenience.

13-42. Precautions. When you useoscilloscopes, it is advisable never to operatean oscilloscope with the case removed, sincehigh voltages are exposed that can cause fatalshock. Removal of the case also reducesshielding of the instrument from stray externalfields.

13-43. Extreme caution should be exercisedby personnel handiing cathode-ray tubes. Thegiass envelope incloses a high vacuum; unduestresses and rough handling can cause seriousinjury, due to tube impiosion. The fluorescentcoating of the cathode-ray tube is extremelytoxic. When handling broken cathode-raytubes, avoid contact with this material.

13-44. Remember that a bright spot must notbe permitted to, remain in a stationary positionon the fluoreseent screen; the energy of theelectron beam concentrated in a small area willburn the screen coating. Remember also toprovide a good bonding between theoscilloscope, operating equipment, and ground.Grounding is a good general practice toeliminate electrical shock hazards and toproduce clear displays that are free of stray

, noise signals. Ground connections can begreatly improved by placing the equipmentbeing tested, the oscilloscope, and otheraccessory equipment on a large sheet ofconductive material insulated from theworkbench top. A single connection betweenthe metal sheet and ground can then be made.There is usually an exception to any rule, andthose circuits that operate above ground are theexception. When dealing with this type ofcircuit, (1) insulate the oscilloscope fromground, (2) use caution during measurement,and (3). break the connection as soon as themeasurement is completed.

13-45. Know the operating condition ofyour scope and other test equipment.Maintenance routines using a signal generatorand a scope are misleading and inconclusive ifeither or both test equipments are causing, orcontributing to, a faulty display.

13-46. Input impedances of oscilloscopesare generally high enough to produce negligibleloading of the circuit under observation; soimpedance matching is seldom required.,However, the input impedance of the scopemust be higher than or equal to the impedanceof the circuit under investigation if detuningand loading effects are to be avoided. Technicalmanuals supplied for scope maintenanceusually state this impedance in terms of aresistance shunted by a capacitor. Low-impedance coaxial cables are often used inpulse maintenance engineering teehniques. It isimperative in these cases to consider the types,lengths, and input impedances of theconnecting leads. High-impedance frequency-compensated probes are often provided asaccessories for the oscilloscope to prevent anyloading and detuning effects of resonant high-frequency circuits. These probes are discussedlater in this chapter.

1 3-47. Oscilloscope test leads should beadequately shielded to prevent undesiredcoupling effects. The lengths of open wire leadsand their attendant stray capacitance to ground,coupled with a high input impedance. can cause

the oscilloscope amplifiers to develop an

appreciable display from random or Amysignals.`The shielding of the test leads should

71

be connected to the ground terminals adjacentto their input terminals to prevent interactionof common impedance ground loops betweendifferent terminal points on the scope panel.This is especially important when observingpulses, while using external synchronizing andtriggering cables; otherwise you risk erratictriggering of the sweep generator.

13-48. Voltages which overload the inputcircuits of the oscilloscope should not beapplied to the input terminals. This precautionapplies to the external synchronizing and Z-axis input terminals as well as the vertical andhorizontal input terminals. Vertical andhorizontal amplifiers often contain anattenuator to. provide control over largeamplitude signals, but many of these sameoscilloscopes do not provide similar controlsfor the synchronizing or Z-axis input channels.When working with large amplitude signals atoscilloscope inputs lacking attenuators, wrapthe insulated test lead around the inputerminal concerned to provide sufficientcoupling.

13-49. Some oscilloscopes provide a secondvertical input terminal connected by a strap tothe oscilloscope ground terminal. The purposeof the two vertical input terminals is to providefor the observation of balanced signal sources;the strap is used to ground the unused terminalduring inspection of single-ended amplifiers.

13-50. Malfunctions. Malfunctioningcircuitry within the oscilloscope can causeerratic and faulty displays, or it can causedifficulties in the manipulation of variousoperating controls. Potentiometers used as thevariable amplitude control of vertical andhorizontal amplifiers develop small scratches inthe resistive element oi on the rotor contactfrom small abrasive particles contained in dust.As the rotor moves over the marred resistiveelement, noise signals are generated, creating adisplay which is extremely ragged inappearance and which may or may not bearsome resemblance to the original input signal.The characteristic "grass" display resultingfrom noise signals may disappear as soon as thecontrol is released, ccintinuing the display ofthe original input signal. On the other hand, the"grass" display may persist, indicating poorcontact between the rotor and the resistiveelement at that point. Other causes of noisedisplays are poor input connections andmicrophonic amplifier tubes.

13-51. The input impedance of the firstamplifier is quite high, making the dicilloscopesusceptible to stray external signals. Externalfields, especially at powerline frequencies, canbe picked up by unterminated oscilloscope

7,)

-

Til

Cc

observation. Figure 53 is an example of theeffect these devices can have upon the displayof sine waves.

Figure 3. Distortion caused hy tuw-frequency hum.

14. A Typical Oscilloscope14-1. Now that you have learned the basic

principles of an oscilloscope, let's study thewaveform interpretation and controls of atypical multitrace oscilloscope. The functionalcircuits and front panel controls of mostoscilloscopes are very similar. Therefore, weexplain only the functions and controls of amodel commonly used in communications andelectronics maintenance.

14-2. Figure 54 is a front panel view of theTektronix 585A with type 82 plug-in unitinstalled. Like most test equipment, it is

composed of numerous sections andsubsections which have specific functions toperform. As each section is discussed, all frontpanel controls associated with that section arealso discussed..Throughout this discussion youwill be referred to figure 54 to locate thecontrols.

1 4-3. Sweep Generation a n dSynchronization. The versatility' of anyoscilloscope depends largely upon its sweepand sweep synchronization circuits. To obtain astable presentation. the sweep circuits must beable to produce a sweep voltage that is in syncwith the displayed signal. The sweep generatormust also he able to produce a sweep voltagebeginning at selected times with respect to thevertical signal. If the sweep generator can dothese things. then it is possible to present anydesired part of the vertical signal on the CRTindicator. Some oscilloscopes accomplish thesefunctions by using dual-sweep generators thatcall operate either separately or in conjunction\sith each other. To show these-principles. let's

73

use the oscilloscope shown in figure 54. TheHORIZONTAL DISPLAY switch on the upperright front of this oscilloscope is used to selectthe desired sweep function. These functions,reading counterclockwise around the controlfrom 2 o'clock, are as follows:

"A" SINGLE SWEEP."A" SWEEP."A" SWEEP DELAYED BY "B"SWEEP."B" SWEEP INTENSIFIED BY "A"SWEEP."B" SWEEP.EXTERNAL SWEEP(UNATTENUATED -X1).EXTERNAL SWEEP (ATTENUATED -X10).

Let's discuss these in the order of most frequentuse, starting with the A SWEEP.

14-4. A sweep. When this sweep function isselected, the A sweep generator and its.associated circuits function independently ofthe B sweep. the A sweep circuit is made up ofthese units:

A synchronized sweep trigger generator.A sweep generator.A horizontal sweep amplifier.

14-5. The trigger generator generates thetrigger for the sweep generator. This trigger issynchronized by the signal being displayed by a6.3-volt AC line signal, or by an external syncsignal. When using this type of oscilloscope, itis up to you to decide how thesweep can bemost effectively synced and then set theassociated front panel control to the desiredtrigger source position. Now let's discuss thefactors that must be considered when makingthis decision.

14-6. To analyze a waveshape, we must beable to see it clearly. Without sweepsynchronization, you can see the signal but inmost cases it is nothing but a blur. Anindiscriminately triggered sweep starts withoutregard to time displacement of the signal beingdisplayed. Each succeeding sweep starts at adifferent relative time with respect to the signalon the vertical deflection plates. This causes thesignal to appear to run across the face of the

indicator. Figure 55 is an example of anunsynchronized display of a uniform sine wave.The running effect can be eliminated byadjusting the sweep frequency until it is thesame as or an exact multiple of the verticalsignal; however, this method is impracticalsince even the slightest signal variatiOns requirereadjustment of the sweep frequency. If thesweep is started at exactly the same point withrespect to the vertical signal, each trace

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presents the exact same portion of the verticalsignal. This action is shown in figure 56. Notethat each time the sweep occurs, the sameportion of the vertical signal is traced on theindicator. To obtain this type of sweep, the

74

oscilloscope sweep generator is triggered by (1)an external signal of a frequency that is equal toor a multiple of the vertical signal or (2) by thevertical signal itself. Now let's see how this isaccomplished.

76

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Figure 55 Unsynchronized sine-wave display.

14-7. The oscilloscope shown in figure 54can be synchronized by a line, internal, orexternal signals. depending on the setting of theTRIGGERING SOURCE switch (upper right).In the INTERNAL SYNC positions, a sampleof the input signal is taken from the verticalamplifier: in the EXTERNAL SYNC positions,a sample is taken from an external sync signal

vENTICAL SIGNAL

NON,ZONTAL WEI. SIGNAL

2

that is connected to the TRIGGER INPUT jack(fig. 54, upper right); and in the LINE position,the oscilloscope 6.3-volt, 60-hertz filamentsignal is used.

14-8. At this point it is important toremember that the sync signal selected by theTRIGGERING SOURCE switch does nottrigger the sweep generator but triggers thetrigger generator, which in turn produces atrigger for the sweep generator.

14-9. Now let's look a little deeper and seewhat happens under the various triggeringconditions. When the TRIGGERINGSOURCE switch is in one of its INTERNALpositions, a sample of the input signal is talc_from the vertical amplifier and fed as an inputto the trigger generator circuits. The first thingthat the trigger generator does to the inputsignal is set its reference level. This level isdetermined by the setting of theTRIGGERING LEVEL control (see fig. 54,top center). Figure 57 shows the input signal atfour different reference levels ranging frommaximum negative (Level A) to maximumpositive (Level D). The triggering level lineshown in figure 57 is the reference level that theinput signal must cross for the trigger generatorto produce a sweep trigger. Now let's see whathappens when the TRIGGERING LEVELcontrol is set to each of the four referencelevels shown in figure 57.

Figure 56. Synchronized display.

75

TRIGGERGENERATOROUTPUTS

1110

TRIG LEVEL "a"Pas SLOPEr TRIG LEYEL "5"

.,NEG SLOPE

TRIG LETEL "C"NEG SLOPE

Figure 57. Effects of triggering level and slope control.

Level A. This reference level is obtainedby setting the level control to its makimumnegative position. Note that as the signalalternates above and below this reference level,it never crosses the triggering level and thus nosweep trigger is generated.

Level B. As the level control is turned inthe positive direction, reference level B isobtained. With this reference level setting, youcan see that the triggering level is crossed attime TI and at time T2. Now, to obtain a stablesweep for any given signal, iv do not want todevelop sweep triggers at more than one pointon the signal. Look again at figure 54 and notethe TRIGGER SLOPE switch. It is the toggleswitch located between the TRIGGERINGLEVEL and TRIGGERING SOURCEcontrols. With this switch in the positiveposition, the trigger generator produces atrigger only on the positive slope of the inputsignal as it passes the triggering level (T1). Forthis same signal and with the switch in th6negative position, a sweep trigger is producedat T2. The trigger and the conditions under

76

TRIG LEVEL "C"POS SLOPE

which the trigger is generated are shown beloweach trigger point, T1, 12, T3, and 14, infigure 57.

Level C. Now assume that you change theTRIGGERING LEVEL control to obtainsignal reference level C. As the signal alternatesabove and -below reference level C, it crossesthe triggering level at times 13 and 14. If theSLOPE control is set to its positive position,the sweep trigger is produced at 14. With theSLOPE control in its negative position, thesweep trigger is produced at T3.

Level D. Setting the TRIGGERINGLEVEL control to its maximum positiveposition results in the signals' riding referencelevel D. Once again the signal never crosses thetriggering level and no trigger is produced.

14-10. Now you should be able to come toan important conclusion; that is, to insure thata sweep trigger is generated, the initial settingof the TRIGGER LEVEL control should he ator near midrange.

14-11, Now let's assume that you do not

7247.)

wish to trigger the sweep with the verticalsignal In this case you must use either theEXTERNAL or LINE positions of theTRIGGERING SOURCE switch. In each ofthese positions. the trigger generator functionsthe same as it did in the INTERNAL position.When using these positions, you mustremember that to obtain a stable presentationthe sweep triggers must be produced at thefrequency of or at a frequency that is a multipleof the signal being displayed. Because of its 60-hertz frequency, the LINE SYNC position haslittle practical value except in cases such aschecking for ripple in power supplies or hum insignal lines. 'External sync, however, is

frequently used when troubleshooting or signaltracing. In many equipments a master limingsignal is used to produce all other signals. It istherefore convenient to connect this signal tothe TRIGGER INPUT jack (fig. 54, upper rightcorner) for use as an external sync signal. Whenyou are testing signals from different points inthe equipment where signal amplitudes andshapes vary, the use of a standard sync signaleliminates the necessity for continualreadjustment of the triggering controls.

14-12. Another factor to be considered whensynchronizing the trigger generator is thefrequency of the sync signal. Wide variations in

sync signal frequencies require adjustments inthe input circuits of the trigger generator. Lookagain at the TRIGGERING SOURCE switch infigure 54. Note that there are three internal and.three external positions. These differentpositions adjust the trigger generator inputcircuits for various frequencies of input signals.In either of the high-frequency sync positions(FIF SYNC), the trigger generator circuitscouple the sync signal directly to the sweepgenerator for use as a sweep trigger. In all otherpositions the trigger generator functions asdiscussed in the previous paragraphs.

14-13 Before going on to the sweep

generator. let's summarize. The triggergenerator produces a trigger for the sweepgenerator. The TRIGGER LEVEL and SLOPEcontrols are set to produce this trigger when thesync signal is at the desired level and swingingin the desired. direction. The sync signal musthave a definite frequency relationship to thevertical signal in order to produce a stabletrace.

14-14, A typical sweep generator may

consist uf a sweep multivibrator, a MillerIntegrator. a holdoff cathode follower, and atrigger gate interconnected, similar to thegenerator shown in figure 58. Normally, youwill find tha«he mukivihrator is a bistable typeand ctvinges state only when triggered. With

77

this type of sweep multivibrator, it is possible tostart and stop the sweep at specific times.

14-15. When a trigger is received from thetrigger generator, the state of the sweepMultivibrator changes, and a negative levelpulse is coupled to an RC network in the gridcircuit of the Miller integrator. The charge rateof the capacitor in the RC network is heldconstant by a feedback between the plate and

grid circuits of the integrator; thus theintegrator produces a very linear sawtoothwhich is coupled to the horizontal amplifiers.The sawtooth output of the integrator 'is alsocoupled to the holdoff circuit. This circuitadjusted so that when the integrator outputreaches a required level (this level is a functionof the indicator deflection factor and thephysical length of the sweep desired), theoutput of the holdoff circuit retriggers thesweep multivibrator back to its normal restingstate. The sweep is thus terminated and will notstart again until the next trigger is receivedfrom the trigger generator.

14-16. Before going on, there are twoimportant points you should remember:

(1) The generator is set to produce a

sawtooth of a specific amplitude. The TIMEPER CENTIMETER control (fig. 54, just tothe right of the indicator) varies with the rate ofch-trge, not the amplitude.

(2) When using the scope, if you notice thatthe sweep is not of the proper physical length,first check to see if the sweep generator outputis the correct amplitude. If it is not, yourproblem may be only an improper feedbackadjustment. This adjustment is usually made byan internal sweep length control such as theone shown in figure 58.

14-17. Now look at the triiger gate blockshown in figure 58. This block controls the biason the sweep multivibrator when it is at rest.When operating the scope in the A SWEEPfunction, the trigger gate is controlled by theSTABILITY control (fig. 54, top center, smallknob). The STABILITY control sets the biason the trigger gate, which in turn controls thebias on the sweep multivibrator. To set theSTABILITY control, you perform thefollowing steps:

(I) Set the control fully counterclockwise.(2) Turn control clockwise until a sweep

fi rst appears.(3) Turn control counterclockwise again

until the sweep just disappears.

Now the sweep multivibrator can be triggeredas soon as a signal is connected. .-

14-18. To see more clearly how the sweepgenerator works, you should be able tovisualize what is happening at each of the major

(

signal points. Let's assume that a sine-wavesignal is applied to the vertical input of theoscilloscope. You set the TRIGGERINGSOURCE switch to the proper internalposition, the TRIGGER SLOPE switch tonegative, and the TRIGGERING LEVEL to 0volt. Under these conditions, the sweep startswhen the negative alternation is applied to thevertical plates.

14-19. Look now at figure 59 and see howthe sweep circuits accomplish this. WaveshapeA is the vertical input signal, and waveshape Bis the same signal applied to the input of thetrigger generator. With the controls set as statedin the previous paragraph, the trigger generatorproduces sweep triggers (signal C) each time itsinput (signal B) passes through zero in anegative-going direction (points 1, 2, 3. and 4).The first trigger is applied to the sweepmultivibrator and causes its output to gonegative (signal D). During the time the sweepmultiyibrator output is negative, the sweepgenerator output rises at a linear rate (signal E).Part of the sweep signal is fed to the holdoffcircuit, where it causes the output of:the holdoffcircuit to rise (signal F). The output of theholdoff circuit is the bias on the sweepmultivibrator. When signal F reaches point X.'the sweep multivibrator is retriggered back toits resting state and the sweep is terminated.The sweep circuits remain at rest until the next

F ROMTRIG GEN

UNBLANKING 4411

TRIGGERGATE

STABILITY

It--1110 SWEEPMV

-trigger is received from the trigger generator(signal C, pulse # 3) and the same actions arerepeated. The darkened areas of tfie inputsignal (signal A) are thus traced on theindicator as the presentation shown at H in

, figura 59.14-20. You may wonder how the indicator is

blanked during retrace time. In the scope infigure 54, for example, the indicator isnormally biased to cutoff and is allowed toconduct only when sweeping. This is done bytaking the positive output of the sweepmultivibrator and coupling it to the CRT as anunblanking signal (signal G, fig. 59). Since thesweep multivibrator determines sweep lengthand the unblanking signal is of the exact sameduration as the sweep,.only thc sweep is visible.

14-21. Let's go back now and discuss theTIME PER CENTIMETER control in a littlemore detail as it applies to period andfrequency measurements. As a maintenanceman you will measure pulse widths, periods,frequencies, and any other events that may be afunction of time. The TIME PERCENTIMETER control indicates exactly whatits name implies; that is, it indicates the timerequired for the electron beam to deflect 1

centimeter horizontally. It is relatively simplefor you to determine the number of centimetersthat the beam is deflected horizontally andthen, with a little mathematics (number of

TIME/CM

HOLDOFFCF

110MILLER

INTEGRATOR

Figure 58. Sweep generator

78

82

HORAMP

INTERNALSWEEPLENGTHCONTROL

Avelficak.siGNAL

TouGGEll GENINPUT

TOIGGE I GENOu T PUT

Sire EP NT

EPEE'', OUT

PE EOSACItVIA VIOLOOVV CF

TO CIITING

Figure 59. A sweep generation and display.

centimeters times the setting of the TIME PERCENTIMETER control), determine the timefor any event associated with the display signal.As for frequency measurements, frequenciescan be readily determined by use of thefollowing formula:

Frequency wtime per cycle

.... ISM,

control as shown in A, B, and C of figure 60.The sweep length is always 10 centimeters.Frequency determination under theseconditions is as follows:

a. The A setting of the TIME PERCENTIMETER control is 1 I.Esec. Note that1/2 cycle occupies the full sweep. The time percycle is 20 Asec. You can calculate thefrequency by using the following formula:

Frequency..time per cycle

(F

14-22. For an example of frequencymeasurements, look at figure 60. Here a 50-kHz sine wave is an input to the oscilloscopeshown in figure 54. The TRIGGER LEVELand TRIGGER SLOPE controls al'e set todevelop sweep triggers at the 0-volt level of thenegative slope. Now consider three differentsettings of the TIME PER CENTIMETER One

79

F w 50.000 Hz20 ;n-6

trouble encountered with this m: hod of

immosami10111111111111111111Pii11111011.11111101.`alla

INDICATOP PRESENTATIONS

0111111111111110NRIMMIINMiNira 11110M111

2 USEC

Figure 60. Frequency caIcuIatIon.

frequency determination is that it is verydifficult to determine when the scope displaysexactly 1/2 cycle. If you err in determining thetime for a half cycle, this error is compoundedby doubling the value to determine the time percycle. When possible, you should not usesettings of the TIME PER CENTIMETERcontrol that present less than one cycle.

b. The B control setting of 2 Asec results in aone-cycle presentation. Here again it-is difficultto determine when exactly one cycle ispresented; however, this time the error is notcompounded by multiplying.

c. The C control setting of 5 Asec results in adisplay of 2 1/2 cycles. Here the point at whichthe signal crosses the zero reference line ismuch more definite because of the steepness ofits slope, and a more accurate calculation canbe made.

14-23. There are several ways you cancalculate the frequency in this case; thefollowing method is recommended. Onecentimeter represents 5 p.sec; therefore, the full10-cm sweep represents 50 Asec (5 X 1050). The time for 2 1/2 cycles is then 50 p.sec,and the time per cycle is 20-p.sec

80

50(2-.5 = 20).

111141111.111111111MILIMILIWOHNIME0010111001111100

5 USEC

F = 50.000 Hit x IO"

In practice you will find that the most accuratefrequency determinations are obtained bysetting the time controls for presentations of 2to 10 cycles.

14-24. B sweep. The B SWEEP position ofthe HORIZONTAL DISPLAY switch shown infigure 54 selects another set of circuitscontaining a trigger generator and sweepgenerator that operate similarly to the A sweepand triggering circuits. Look at the B sweeptime-base controls in figure 54, and note thesimilarity to the A sweep time-base controls.Since their functions and operations aresimilar, it is not necessary to cov..m- them again.

14-25. "B" buensified by "A." Until now wehave discussed a single sweep function with itsassociated triggering circuits. Used alone, theaddition of another sweep generator and itsassociated circuits adds nothing to thecapability of the oscilloscope. However, whenone sweep is used to modify the other sweep,much is added to the scope's capabiliiies.

8

14-26. The two sweep generators in theoscilloscope in figure 54 can be triggered by thesame synchronizing signal or by separatesignals. Regardless of the trigger source. thereare two sweep voltages and two unblankingvoltages that can be applied to the indicator.This particular scope uses the unblankingvoltage of the A sweep to intensity-modulate aportion of the B sweep. The intensified portionmay be expanded to give you an enlargedpresentation.

14-27. In the "B" INTENSIFIED BY "A"position of the HORIZONTAL DISPLAYswitch, the B sweep generator functionsnormally. When triggered, it develops a

sawtooth horizontal sweep voitage and a

positive unblanking signal. These signals arecoupled to the indicator, and a normal sweeppattern begins. The sawtooth sweep voltage isalso sent to a trigger pickoff circuit. The triggerpickoff circuit is set to produce a trigger pulsewhen the B sweep sawtooth voltage rises tosome predetermined (pickoffl point. The biason the pickoff circuit can be varied so that thepickoff point can occur at any desiredamplitude of the sawtooth voltage. In theoscilloscope shown in figure 54, the pickoffpoint is controlled by the DELAY-T1MEMULTIPLIER control. This is thc secondcontrol from the bottom on the right-hand side.Regardless of the slope of the sweep voltage. italways takes the same voltage to deflect thebeam 1 centimeter; therefore, the delay controlwhich sets the voltage of the pickoff point iscalibrated in centimeters. The delay time (thetime between the beginning of the sweep andthe start of the intensified portion) is thencalculated by multiplying the setting of the "B"TIME PER CENTIMETER control by thenumber of centimeters on the DELAY-T1MEMULTIPLIER control.

14-28. Now let's see how this sweepintensification works, using a practicalexample. Look at figure 61. Signal A is a 40-kHz input that is applied as a vertical input andas an input to trigger generator B. Time-base 13controk are set as follows: (1) TRIGGERINGSOURCE to INT. (2) TRIGGERING LEVELto 0. and (3) TRIGGER SLOPE to positive.Signal B in figure 61 shows the output of triggergenerator B. Note that a trigger is producedwhen the input signal (signal A in fig. 61)reaches point X. This trigger is fed to the Bsweep generator. It initiates a sawtooth sweepvoltage (signal C) and a positive unblankingpuke (signal D). The sawtooth sweep voltageand the unblinking pulse are coupled throughappropnate circuits to the indicator to unblankand sweep the electron beam horizontallyacross the scope.

8 I

14-29. Before going on. let's assume that theA sweep generator is set for a 5-u.sec-per-centimeter.sweep, the STABILITY control isfully clockwise, and the B sweep generator isset for a 20-msec-per-centimeter sweep. Also,assume that the indicator beam is deflected 1

centimeter for every 15 volts of sweep signal(signal C). You have set the DELAY-TIMEMULTIPLIER control to 3 1/3 centimeters,which means that the delay pickoff circuitproduces a 'trigger (signal E, fig. 61) when thesweep has moved 3 1/3 centimeters. Now let'slook a little closer at how the pickoff trigger isproduced. The sweep voltage (signal C) is fed tothe pickoff circuit. Remember that the delaytime was to be 3 1/3 centimeters. If horizontaldeflection takes 15 volts per centimeter, then 31/3 centimeters require 50 volts. What thedelay control actually does is set the pickoffcircuit bias so that the sawtooth (signal C) mustrise to 50 volts before the pickoff. circuit istriggered. Now the xrigger from the pickoffcircuit (signal E) is fed to the A sweepgenerator. The A sweep generator is triggeredand p:oduces a sawtooth sweep voltage (notshown ,n fig. 61) and an unblanking pulse(signal F. fig. 61). The indicator circuitscombine the A and B sweep unblanking pulses(signal G. fig. 61). This combining of theunblanking pulses results in an increase in CRTcurrent, thus intensifying the trace for a periodequal to the unblanking pulse time of sweep A(pattern H of fig. 61).

14-30. Look again at the A sweepunblanking pulse in figure 61 (signal F). Notethat it lasts for 50 ihsec. If the TIME PERCENTIMETER control is set to 5 ihsec percentimeter as previously stated, then the Asweep generator produces a sawtooth of thesame amplitude as the B sweep sawtooth but ina shorter time.

A sweep time = 5 ihsec/cm x 10 cm =50 Asec.B sweep time = 20 ixsec/cm x 10 cm =200 Msec.

In this application the A sweep sawtooth is notused, but its unblanking pulse is used. Thispuke is equal in duration to the A sweepsawtooth, so its duration must also equal 50Asec. The indicator sweep is the result of themuch slower B sweep signal. so the.50-ihsec Asweep unblanking pulse intensifies the B sweepfor only 2 1 2 centimeters (50 Asec, 20 4sec percentimeter = 2 1 2 cm),

14-31. Now let's summarize what we knowabout the ''B INTENSIFIED BY A'function.

The B sweep is triggered and functwnsjust like the A sweep.

Ar

4 AnAPVERTICAL . NPLiT TO VERT DEF PLATES AND TRIGGER GEN

TRIGGER GENERATOR CluTPuT

5Ev

8 SWEEP OUTPUT TO MORIZONTAL AMPLIFIERSAND DEt.ov PICKOFF

1

8 SWEEP LINISLANKIND PULSE = 200 uSEC

PICICCFP IG TO "A" SWEEP GENEf/ATOP

A SWEEP UNBLANKING IPULSE

50 USEC

I50v

5 fa- A B

I COMBINED UNBLANICINGI PULSES

I I II i

Ime--- 3-1, 3 Cm --Wye 2- 1.2 C" --limits, 4- II

I I

t

CIA ----owl

1

1

1 I

11,

fill 11I i AIII

A : II AV IF I v T

I

I

I

I4,

Kr--- 60-2/3 uSECINTENSIFIEDAREA 3-1,3 USEC

Lem 30 ;AEC --al

,NOIClog OISPL A

Figure 61. Intensified sweep

8 2

-741

The B sweep sawtooth voltage is fed to a HORIZONTAL DISPLAY control (fig. 54) topickot'f circuit that produces a trigger for the "A" DELAYED BY "B" position.the A sweep generator at a timedetermined by the DELAY-T1MEMULTIPLIER control.The A sweep unblanking pulse intensifiesa portion of the B sweep.You can select the portion of the B sweepthat you wish to intensify by varying thesetting of the DELAY-TIMEMULTIPLIER control:

14-32. There are times when you may wishto use this intensification principle todetermine the frequency of the signal beingdisplayed, the period or pulse width of thesignal, or the signal rise time. To do this,rttluce the setting of the A sweep TIME PERCENTIMETER control until the A sweepunblanking pulse is so short that the intensifiedportion of the trace appears as a smallintensified dot.

14-33. Now look at figure 62. This figureshows three examples of how ihe intensified dotcan be used. In figure 62,A, you can determinethe frequency of the displayed signal in thefollowing manner:

First, place the dot at point X by settingthe DELAY-TIME MULTIPLIER control tozero centimeters.

Now turn the MULTIPLIER control untilthe dot moves to point Y, a distance thatrepresents one cycle, and record the controlsetting.

Subtract setting X from setting Y (theresult in this case should equal setting Y. sincesetting X is zero). Now multiply this differenceby the setting of the "131- TIME PERCENTIMETER control to obtain the time percycle. Convert the time per cycle to frequencyby the formula F = . This same procedurecan be used to determine the pulse width infigure 62.B, or the time between pulses in figure.62.C. You may wonder why it is necessary todo this when you can simply count-the numberof centimeters directly off the face of theindicator. This can be done, but not with theaccuracy obtained by using the micrometer typeDELAY-T1ME MULTIPLIER control. Theseare only a few examples of how the intensifiedsweep can he used; however, in your day-to-dayperformance of maintenance. I am sure you willfind maw, other useful applications.

14-34. You will . find it convenient at timesto he able to obtain an expanded view of oneparticular part of a display. This is probably themost important application of the intensifiedsweep. %his can be done hy intensifying thearea you wish to expand and switching the

83

A

Figure

8

62. Measuring time with the intensity dot.

7

14-35. "A" delayed by "B." This sweep:unction is relatively simple. The onlydifference between it and the 13"INTENSIFIED. BY "A" is that the indicatorreceives only the A sweep unblanking pulse andthe A sweep sawtooth. The B sweep circuits aretriggered just as they were in the "B"INTENSIFIED BY "A"; however, the B sweepoutputs are not used by the indicator. The Bsweep sawtooth triggers the pickoff circuit,which in turn triggers the A sweep. Thishappens at a time when the part of the inputsignal to be intensified is present at the verticalplates. The A sweep sawtooth and A sweepunblanking pulses are coupled to the indicatorcircuits and allow the intensified area to bedisplayed over the entire 10 cm.

14-36. Figure 63 shows more clearly whathappens. The intensified sweep shown in figure63,F, is obtained while the HORIZ^NTALDISPLAY switch is in the "B" INTENSIFIEDBY "A" position. The HORIZONTALDISPLAY switch is then switched to the "A"

A VERTINPUT

g B SWEEP SAWTOOTH

...1

c B SWEEP UNBLANKING

DELAYED BY "IV position. The ver nexttrigger received results in the generation of a Bsweep sawtooth (fig. 63,B) and a* 1,3 sweepunblanking p,.!lse (fig. 63.C). The 13 unhlankingpulse is not used. However, the B sweepsawtooth is fed to the pickoff circuit and whenit rises to the pickoff point (fig. 63. 13). the Asweep is triggered:The A sweep sawtooth (fig.63,D) and the A sweep unblanking pulse (fig.63,E) arc coupled to the indicator. Illus. theintensified area between X and Y of figure63,F. is displayed aerbss the entire face ot theindicator, as shown in figure 63,G.

14-37. The intensity-modulation principlecan also be used to compare parts of a serialpulse train. Look at the display in figure 64.A.If you want to compare pulse A and pulse B.the best way is to superimpose one upon thelther. Let's see what steps are necessary to dothis with the oscilloscope shown in figure 54.

Set the HORIZONTAL DISPLAY switchto the "13- INTENSIFIED BY "A" position andadjust the "A" TIME/CM and the DELAY-

111111

PICKOFF POINT

D A SWEEP SAWTOOTH

E A SwEEP UNBLANKING

B INTENSIFIED BY A

Figure 63. Displa% expansion

84

A DELAYED BY B

to

Zolpulse (fig. 54, +GATE B jack) and the pickofftrigger output jack (fig. 54, DLY'D TRIGjack).

14-38. When the B sweep unblanking pulsestarts, it is coupled via the DLY'D TRIG jackto the A sweep generator. The A sweepgenerator is triggered and its unblanking pulse

A intensifies the pulse A area on the indicator.The pickoff circuit was already set to trigger theA sweep, so the pulse B area is intensifed. Nowthink about what is happening. Each 5 sweeptriggers the A sweep twice, once at thebeginning of the sweep_and once at the pickoff:point. Now switch the HORIZONTALDISPLAY switch to the "A" DLY'D BY "B"position. The first time the A sweep is triggeredit displays pulse A, and the second time it istriggered, it displays pulse B. This display isshown in figure 64,B, with the two pulses notquite matched, A slight adjustment of theDELAY-T1ME MULTIPLIER control willmove pulse B from where it is shown in figure64,B, and position it directly over pulse A asihown in figure 64.C.

14-39. The oscilloscope shown in figure 54is capable of two other sweep applications thatare not a function of the dual-sweep generatorprinciple, so sees take a look at them.

14-40. -A" single sweep. Look again atfigure 54 and note the HORIZONTALDISPLAY switch position that is labeled "A"SINGLE SWEEP; also observe the RESETbutton above and to the right of the display..witch. With the-switch in this position, a single'sweep (one time across the scope) is obtainedeach time the RESET button is depressed. Youreyes and mind can obtain very little knowledge;rom seeing a signal for so short a time;however, with a camera and high-speed film apicture can be taken of this single trace. Thispicture then becomes a permanent record of thefunction displayed and the function can beanalyzed at your leisure.

14-41. External sweep. Most oscilloscopeshave provisions for the direct application of anexternal signal to the horizontal amplifiers. TheEXTERNAL SWEEP function is especiallyapplicable if you are to compare the phases oftwo sine waves. One signal is applied to thcvertical input and the other signal is applied tothe horizontal circuits via the HORIZONTALINPUT jack (fig:54, just to the right of theHORIZONTAL DISPLAY switch). With theHORIZONTAL DISPLAY switch in the X1losition, the horizontal input signal is fed

TIME Mt:Li IPLIER controls until Pulse B is Jirectly to the horizontal amplifiers. In themtensitied XIO position, the horizontal input signal is

Cunnect a small capacitor (approximately attenuated by a factor of 10 before application100 mmt) between the B sweep unblanking to the horizontal amplifiers. Figure 65,A,

"IS" INTENSIFIED SY "A"

A"A" DELAYED BY "A"

Figure 64 Pulse comparison

85

FREQUENCIES EQUAL90° OUT OF PHASE

FREQUENCIES EQUALPBASE RELATION0° TO 900 OR 900 TO 150°

FREQUENCIES EQOALIN PHASE OR 1110° OUT OF PHASE

Figure 65. Lissajous patterns.

shows the display obtained when applying twosine waves of equal frequency. but 90° out ofphase. This pattern and the other patterns offigure 65 are based on equal horizontal andvertical deflections (the venical inputattenuator must be adjusted to make the verticaldeflection equal to the horizontal deflection).An oval pattern such as shown in figure 65,8, isobtained when the phase difference is between0° and 90° or between 90° and 180°. A singleline presentation as shown in figure 65,C, isobtained when the signals are in phase or 180°out of phase. Figure 65,D, is the displayobtained when the horizontal and vertical inputsignals are not of the same frequency. These arethe basic Lissajous patterns which you learned

86

FREQUENCIESNOT EQUAL

in basic electronics, and they may be used tomeasure unknown frequencies when you have aknown standard, or to calculate phasedifferences in known signals

14-42. The Plug-In Unit. The oscilloscope,like many other pieces of test equipment, u.,esvarious plug-in units to increase its versatility.The oscilloscope shown in figure 54 has a type82, dual-trace plug-in unit installed. This plug-in unit is just one of many that can be installedin the oscilloscope. All of these plug-in unitsprovide preamplification and/or attenuation ofthe vertical input signal. Other functionsperformed by the various plug-in units follow:

Vertical positioning of the display.Acceptance of two vertical input signals.

Display of either of two verticri inputsignals separately.

Alternate display of two vertical inputsignals on separate baselines.

Chopped display of two input signalsalternately selected and displayed on separatebaselines while the sweep is in progress.

Display of the algebraic sum of twovertical input signals.

14-43. Your choice of the plug-in unit youwish to use depends on the frequency responsenecessary, pulse characteristics, and the type ofdisplay that provides the most convenientanalysis of the signal. You will learn of manyneeds through practical experience. To aid youin making the proper choice, let's discuss theuse of plug-in unit controls to obtain thefunctions listed above.

14-44. Vertical positioning. All plug-in unitshave ftont panel vertical positioning controls.This control references the input signal so thatit can be moved vertically on the indicator. Theinput signal is applied to a paraphase amplifier,which produces two outputs that are 1800 outof phase. These two signals are amplified, andeach is applied to a vertical plate. One signal isapplied to the upper deflection plate, and theother to the lower deflection plate to produce apush-pull vertical deflection. The VERTICALPOSITION control varies the DC referencelevel that these two signals ride and thuspositions the signal in the vertical plane.

14-45. The input selector. The input signal isapplied to the INPUT jack either directly or viaan attenuator probe. In the AC position of theINPUT selector switch (see fig. 54), a capacitoris placed in series with the input signal. Thiscapacitor eliminates any DC component of theinput signal. If you wish to check DC levels orDC reference levels of AC signais, place theINPUT selector switch in the DC position. Inthis position the signal is directly coupled tothe vertical preamplifier.

14-46. The input attenuator. All verticalinput signals are applied to an input attenuatornetwork. The amount of attenuation is afunction of the VOLTS/CM control (see fig.54). The positions of this control indicate theamplitude of the input voltage necessary todeflect the beam I centimeter vertically; thus, ifthe switch is in the 5-volt position, an inputsignal will deflect the beam 1 centimeter forevery 5 volts amplitude. Look at theVOLTS/CM control and the display shown infigure 66. The signal displayed occupies 3.5 cmvertically,.and the VOLTS/CM control is set at

87

the 0.5-volt position. You can calculate itspeak-to-peak voltage amplitude as' follows:

Volts/cm X cm of deflection amplitude (peak to peak)0.5 x 3.5 as 1.75 volts

I CO

111111111111r1M11e=or

VA ?I CO CONTIOL

Figure 66. Measuring aMplitude.

14-47. To measure the amplitude of a DCsignal, you first set the sweep baseline to somelogical reference level before applying thesignal. You use the VERTICAL control to dothis. Now when you apply the signal, you needonly to determine the distance in centimetersthat the baseline has moved and multiply thisfigure by the setting of the VOLTS/CM control.An example of a DC voltage measurement isshown in figure 67. Note where the baselinewas set prior to the application of the inputsignal. If you count the number of centimeters,you can see that the input signal moved thebaseline 2 1/4 centimeters. The VOLTS/CMcontrol in the figure is set to the 5-voltposition; therefore, the amplitude of the DCinput equals 11.25 volts (5 X 2 1/4 i 11.25).

14-48. You may at times be required todetermine the DC reference level of an ACsignal. To do this, place the INPUT selectorswitch in the AC posiiion. With theVERTICAL POSITION control,.set the signalto some reference level. Place the INPUTselector to the DC position and deteritine thenumber of centimeters that the reference levelshifted. In figure 68,A, the signal is shown setto a zero reference level with the INPUT

SASELIETE , TERSICIvL PPLICRT!ON

1111111111111111111111111IIIIIIIII

11111111111111111111111111111111111111111111111111121111111111111111111111101111111111111111111:111111111111111

IMONESETImo 1E1001

VOLTS/Cu

2-1/4CM

C1*

/T

vOL TSiCu Chs 0E0 z VOLTS$ S 3-1,4. 111$v

Figure 67. Measuring DC voltages.

selector in the AC position. Figure 68,B, showsthat the reference level shifted 1 centimeterwhen the INPUT selector was set to the DCposition. The DC reference voltage of thissignal can be determined by multiplying thesetting of the VOLTS/CM control by 1

centimeter. If the VOLTS/CM control was setto its 20-volt position in the example of figure68, the DC reference level would be: 1 cm X20 volts/cm = 20 volts.

14-49. Dual trace. The principles discussedthus far apply to all types of preamplifiers. Indual-trace preamplifiers (the one shown infigure 54) these functions are duplicated, and inaddition there is an input attenuator and.,avertical control for both the A and B seaionsof the preamplifier. In addition to dualcontrols, the dual-trace plug-in unit has twovertical input jacks and a switchingmultivibrator. The switching multivibrator andits associated cificuits arc used to alternatelyselect one of the two vertical inputs on ar time-sharing basis for application to the verticalamplifiers.

14-50. If you wish to compare two signalsfor phase, amplitude. shape, or any otherreason, connect one input to the B section andthe other input to the A section (see fig. 54).

For ka two-sweep comparison you perform thefollowing setup procedure:

Place the MODE switch (see lig. 54) inthe "A" ONLY position and adjust the Avertical positioning and the A attenuatorcontrols until the presentation occupies theupper half of the display area (see fig. 69,A).

Pl-ace the MODE switch in the "B" ONLYposition and adjust the B vertical positioningand B attenuator controls until the B inputoccupies the lower half of the display area (seefig. 69,B).

Place the MODE switch in the ALTER(alternate) position and the dual-sweep displayis as shown in figure 69,C.

14-51. With this setup, the A vertical inputsignal triggers the sweep circuits, is coupled tothe vertical plates, and is displayed. When thefirst sweep is completed, the switchingmultivibrator is then used to select the Bvertical input. The next sweep displays the Bvertical input signal. This switching action isrepeated at the end of each sweep. If you wishto use this type of display to check the phaserelationship of two signals, use an externaltrigger source of known relationship to thesignals under test. Internal triggering shouldnot be used because each signal would triggerits own sweep and the phase relationship couldnot be checked.

1111111111111111111111111riLIIIIIMICILIMN

, 1011131MIIINIIMINIM11111=111111111

NeP Level.

imLiT SELECTOR

R-C 0-C

EMINIMONIMIMA MAW111111111.1111111111110

IftLi1 SELECTOR

Figure 68. Measuring DC' reference levels .

889

-eb

A ONLY

5 ONLY

r211111C311111010

111211=21111102

Figure 69 Signal comparison using alternate mode.

14-52. In the CHWPED mode of operationthe multivibrator in the plug-in unit switchesthe vertical inputs continuously as the indicatoris swept. If two sine waves that are equal infrequency but opposite in phase (fig. 70,A) areapplied as A and B inputs, a display similar tothe oneshown in figure 70,C. is obtained. Theoutput of the switching multivibmtor is shownin figure 70,B. The A input is displayed eacntime the output of the multivibrator is at itshigh level, and the B input signal is d',,playedeach time the output of the multivibrator is atus lower level. The resultant display is shownin figure 70,C.

14-53 We have stated previously that therhoice of plug-in units for a particular

89

ALTERNATE

applicAtion depends on many factors, factorsthat you will learn through continued use of theoscilloscope in the performance of day-to-daymaintenance. Sometime, after you have attainedyour 5 level, you may be called upon to help setup a maintenance shop, and you will have todecide what plug-in units your shop will needto best accomplish the assigned tasks. Whenthis happens, you will have to apply principleslearned in this CDC plus knowledge acquiredon the job in making the selection. Beforeleaving the oscilloscope and going on to othertest sets. let's discuss built-in calibration andindicator control circuits.

14-54. Calibration. In the performance ofyour job there are many times when you must

measure signal levels and signal excursions Indisplayin r. signals to see if they meet pri rerspecifications. it is necessary to know that yourscope is properly calibrated. There are twocalibration check procedures that you mustperform.frequently. These are:

Volts per centimeter.Attenuator probe.

14-55. To perform these checks, you need astandard that provides a square wave of knownamplitude. In the ase of the oscilloscopeshown in figure 54, such a source is provided asa built-in feature. This circuit is called theamplitude calibrator. Its control and outputjack are located in the lower right corner of thefront panel (see fig. 54). The various positionson the amplitude calibrator control provide, at

A

vERT INPUT

8vERT INPUT

2millammimmmWWI '14,,

A VERT IOPUTSELECTED

vERT INPUTSELECTED

the CAL OUT jack, a square-wave signalranging from 0.2 millivoit peak to petk to 100V.,Its peak to peak. This output is applied as averocal input to determine whether theVOLTS/CM control is accurately calibrated.After you 'Awe checked the VOLTS/CMcontrol and found it to be accurate, theattenuator probes are placed between the CALOUT jack and the VERT IIPUT jack todetermine their accuracy.

14-56. When checking the attenuator probes,it is also necessary to check them to see if theycause any differentiation or integration of theinput signal. lf, when the CAL OUT isconnected directly to the vertical input, aperfect square wave is presented on theoscilloscope indicator, but distortion is noted

111111MEMEMMEMHIMMUUMBHUUMUUHUMMEMEMMEMEM

SWITCNING AV

SIG A

SIG B

Figure 70. Chopped mode

90

WINNIUMMINU1IHH111,211HHUHHIMICLOHNUGOMMEMEN

C.IOPDED DISPLAY

11111111111111111111111111111111111111111111

111111111111111111111111111

APROBE INTEGRATION

II1111111111V111111111111111111111111111.111111111111111111111111111111111

PROBE DIFFERENTIATION

CORRECTED DISPLAY

Figure 71. Adjusting the attenuator prr be.

with the probe in the line, then an adjustmentof the probe is necessary. Two common types ofprobe distortion arc shown in figure 71, A andB. The distortion shown in figure 71,A, is dueto integration, and that shown in figure 71.13, isdue to differentiation. Probe distortion canusually he eliminated by adjusting the capacitorwithin the probe until the display appears asshown in figure 71,C. There is no set schedulefor performing these calibrations, but you willfind it good practice to check your scope in thismanner before each use of the probes.

14-57. Indicator Controls. There are fourfront panel controls associated with theindicator of the oscilloscope shown in figure54. The SCALE ILLUM controls the intensityof a light that illuminates the centimetermarkings on the etched scale in front of theindicator face. The FOCUS andASTIGMATISM controls are uses together toobtain a clearly defined horizontal trace acrossthe face of -the indicator. The INTENSITYcontrol sets trace brightness by varying theemission of the indicator cathode. Once set, theSCALE,. 1LLUM. the FOCUS, and the

91

`1=t-

111111111111p11111111111M111111110111111111111111111111111111111111111

ASTIGMATISM controls will usually need noreadjustment; however, the INTENSITYcontrol may need resetting for each new signalmeasured. This is due to the fact that theillumination of the trace is a function of boththe strength of the electron beam and thefrequency of the sweep. It may also benecessary to adjust the intensity when you wishto look at the leading and trailing edges ofpulses that have very short rise and fall times. Itis good practice to turn the intensity downwhen you leave your oscilloscope for extendedperiods, because a high-intensity beam willburn the coating on the indicator face.

15. Probes15-1. In this section we discuss probes which

are commonly used to extend the capabilities ofmeters and oscilloscopes. Two important typesof probes are high-voltage and isolation probes.Their construction, purpose, and use'shouldclearly understood since they are necessaryaccessories for many kinds of measurement.

15-2. High-Voltage Probes. Test

instruments usually have a voltage measuringrange that extends up to a maximum of 2.(100volts. Relatively few have ranges that extend upto 6000 volts. When it is necessary to measurevoltages.that exceed the maximum rated voltageof your test instrument, you must extend thevoltage range to a higher value. There are twoways to do this: (1 ) Connect an externalmultiplier resistor of suitable value in serieswith the input circuit of the test instrument or(2) use a capacitive divider circuit. We showhow each of these ways is used in probesdesigned for high-voltage measurements.

15-3. The multiplier resistors normally usedwith 20,000 ohms/volt VOMs and VTVMs aregenerally of the high-voltage cartridge type,using a spiral film-type resistive elementprinted on a ceramic core, as illustrated infigure 72. The probe body housing for theremovable multiplier resistor is composed of aninsulating material having a high dielectricstrength and a low leakage factor. Safety flangesare normally placed on the probe body tominimize surface leakage and corona and toprotect the operator's hand froM high-voltageshock or RF burns. The probe tip may bepointed for making proue contact, or it may beof the clip-on type for a more permanentconnection. An insulated handle is providedfor protection from electrical shock. A shieldedcable is normally used from the probe to themeter to eliminate stray field pickup. Anintern shield, grounded to the external cableshield, is used to ground accumulatedelectrostatic charges and thus minimize theck.,,,sibility of RF flashover voltages.

15-4. Figure 73 shows a resistor probeconnected to a volt-ohm-milliammeter (VOM).

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You must bear in mind that the input resistanceof the VOM is changed for each setting of theDC voltage range switch. Therefore, thecalculated value of the multiplier resistorrequired to obtain a given multiplying factor isvalid only for the particular range switchsetting that was used in the original calculation.By contrast, the value of the multiplier resistorneed be calculated only once for all meterrange settings if a VTVM is used. As shown infigure 74, the range switch of a VTVM select,: adefinite proportion of the input voltage forapplication to the voltmeter bridge circuit. Butsince the VTVM tube draws no current fromthe input circuit, the resistance of the voltagedivider located in the input circuit is constantfor all ranges. Thus, the probe multiplies eachrange of the VTVM by the same factor.Therefore, the same resistor may be used withall range scales This is not true, however, forVTVM models having different values ofinternal voltage divider resistance.

15-5. The internal resistor contained in theprobe body also provides circuit isolation. Thisresistor, usually having a value of I megohm,performs a double function: (1) it reduces thecapacitance which the probe introduces to thecircuit under test, and (2) it acts as the resistheelement of an RC filter network to aid in theremoval of high-frequency AC componentsfrom the output of the measured equipment.

15-6. For example, the combined total inputcapacitance of the VTVM, inciuding the inputcable of the probe and the test probe itself, isapproximately 100 picofarads. Th;scapacitance, if applied across the circuit undertest as shown in figure 75, loads down andunbalances the RF circuits while you are

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measuring the associated DC voltages with theVTVM Your DC measurements under thesecircumstances are both erroneous andmisleading. Therefore. the isolation resistorcontained in the probe used with a VTVM isnecessary to remove or reduce these capacitiveeffects from the circuit being tested. A case inpoint be the measurement of the DC gridbias of a high-frequency oscillator, Eliminationof the cable shielding does not eliminate thecapacitive effects because stray fields are theninduced into the tested equipment through theunshielded cable. Therefore, you must insert ahigh-ohmage resistor between the circuit testpoint and the shielded cable from the VTVMinput voltage divider circuit (see fig. 76).Although there still is some capacitance from'he probe tip to ground. it is comparatively;mall. If the original reactance of the probe isin the neighborhood of 100.000 ohms for aparticular test circuit frequency and you injecta series I-megohm resistor into the circuit, thetotal impedance is greater than a megohm. Thismakes the reactive component only 10 percent

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rather than the original 100 percent of the totalinput impedance.

15-7. The resistor probe is also employedwith an oscilloscope to measure peak-to-peakwaveform values or simply to observe thegeneral form of the measured waveform.Furthermore. the input terminals of mostscopes are rated at 600 volts maximum;therefore, the probe is used to prevent theapplication of excessive voltage that may, at thevery least. distort the reproduced waveform or,more seriously, puncture the input capacitor,damage or burn out the internal scopeattenuator resistors, carbonize terminals stripsby an arc-over process, or cause additionalattendant damage by completely overloadingthe input scope amplifier. The isolating resistorin the probe add the internal resistance of theoscilloscope may be used as a form of voltagedivider network for either DC or low-frequencymeasurements and, in some cases, provides avoltage reduction ratio as high as 1000:1. A10,000-volt signal, in this instance, wouldcause an actual value of 10 volts to be applied

DC

Figure 7 4 . Probe connected to VTVNI.

93

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Figure 75. Effective input capacitance.

to the vertical input terminals cif the scope.Unfortunately, some oscilloscopes do notprovide an internal resistance network acrossthe vertical terminals; therefore, you may haveto construct a voltage divider network toprotect the scope input circuits.

15-8. By simply connecting a large ohmageresistor, such as 1 megohm, across thc verticalinput terminals of the scope, the requiredvoltage division can be obtained. However, thistype of resistive voltage divider has limitationswhich may preclude its use. The AC voltagedivision is not accurate at the higherfrequencies because the amount of capacitancepresent between the probe body and groundchanges with each new probe position. Inaddition, stray fields in the vicinity of the

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unshielded parts of your probe produceundesirable currents which distort the observedwaveforms. Therefore, if this be the case, youcannot use this method to measure the exactamplitude and waveshape of a signal.

15-9. In the capacitive divider probe, thehigh voltage under test is applied across twocapacitors connectcd in series. Figure 77,A,shows a diagram of the actual capacitive probe,and figure 77,B, illustrates tne voltage dividingarrangement which protects the scope. Theinput voltage is divided across CI and C2 offigure 77.8, in inverse proportion to theircapacitive value. Normally, CLiv-made muchsmaller than C2 so that most of the voltage willbe dropped, or lost, across the capacitor. Thcremaining voltage, dropped across C2, is small

SHIELDEDCABLE

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Figure 76. DC probe with isolating resistor.

94

vTV)4

enough for safe application to the vertical scopeterminals. The formulas required for thecalculation of the capacitor values to providethe desired division of the applied high voltageare as follows:

NOTE:

E2C2El E3 E2

CI

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E3 stepdown ratio (R)-E2

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where: El is the voltage drop across Cl, E2 isthe voltage drop across C2, and E3 is thevoltage applied to the divider network.

15-10. The high-voltage capacitance dividerprobe must contain an extremely high inputimpedance to prevent loading of the circuitunder test. This high impedance is provided byusing a high-voltage rectifier tube as aninexpensive capacitor with a breakdown voltageof up to 15,000 or 20,000 volts. The probemust have a body which provides high-voltageinsulation features in its makeup, and the probemust be shielded to prevent stray field pickupwhich would distort the desired scopewaveform. In figure 77,A, trimmer capacitorC2 and tube capacitance Cl form a voltagedivider network. This trimmer capacitor, whichis normally incorporated within the probebody. may be varied to provide the propervoltage ratio for application to theoscilloscope. The normal ratio is 100:1.Therefore, with an applied signal of 20,000volts to the probe tip, only 200 volts appearacross C2 and are delivered to the verticalterminals of the scope. In this case, the voltagebreakdown rating of C2 need be only slightlyhigher than approximately 200 volts. Since the

input and shielded cable capacitances,represented by C3 in figure 77,A, are inparallel with the trimmer capacitor located inthe probe, C2 must be readjusted to the propervoltage stepdown ratio each time a differentcable or scope is used with the probe.

15-11. If the stepdown voltage ratio is lb0:1and you measure 1000 volts, only 10 volts isapplied to the scope. In this instance, you maycalibrate the scope screen so that 1 volt is equalto 1 square; therefore, 10 volts approximate 10vertical squares of height and represent 1000volts of measured signal. The calibrationprocedure required to obtain a 10:1 or 100:1voltage ratio is relatively simple. Many scopesdo not contain a compensated input circuit,and therefore the oscilloscope trace varies indirect proportion to the input capacitancevariation. This effect causes the probecalibration to change. Additional waveformdistortion is apparent on such a scope becauseof frequency discrimination and phase-shiftdistortion. If the scope contains a compensatedinput, the following sequence of calibrationapplies:

a. Connect the vertical terminals of yourscope directly across some low-impedance,low-voltage source, and set the scope stepattenuator to its "times one" (x I ) position.

b. Vary the vernier attenuator for anyconvenient number of squares of screendeflection.

c. Connect the probe between the voltagesource Oecified in step a above and the verticalscope terminals, and advance the scope stepattertuator to its "times 100" scale (x 100).The waveform should now occupy the exactsame number of scale divisions as it didpreviously.

d. If the number of squares occupied by thewaveform are different from the numberobtained in step b above, adjust the probetrimmer capacitor with an insulated

A

Figure 77. Capacitive voltage divider.

95

screwdriver until the waveform is the same.Now the scope is calibrated to receive ofany voltage applied to the probe tip, providedthat you always use the same connecting cableand scope.

15-12. Isolation Probes. We have aireadyspoken of the isolation feature of high-voltageprobes, but more needs to be said about prohesdesigned especially to provide isolation.

15-13. Across the vertical terminals of anoscilloscope there is normally a resistiveelement of from 0.1 to 2.0 megohms, in parallelwith a small amount of capacitance. Thecapacitance is a combination of the capacitancenormally present across the vertical terminalsand the capacitance of the probe and itsshielded cable. When such a scope is used inconjunction with a shielded cable and probe, itcontributes from 0.1 to 2.0 megohms ofresistance and from 40 to 90 picofarads ofcapacitance in shunt with the output of thecircuit under test. If the circuit under test has ahigh output impedance or contains high-frequency components, this test equipmentshunting effect detunes resonant circuits, loadsother circuits, or simply distorts the desiredwaveforms. This undesirable condition isprevented or its effect decreased if you increasethe impedance shunting the tested circuit. Youcan do this by using a low-capacitance high-impedance probe of proper design. Figure 78

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Figure 78 Compensated low-capacitance isolation probe

illustrates the method of connecting a smallvariable capacitor in parallel with a largeresistor within the probe head. This parallelcombination is in series with the shielded cableand, consequently, is in series with the scopeinput. The scope-blocking capacitor isrelatively large, so its rcactance at highfrequencies can be considered negligible. Thesmall variable capacitor, Cl, in series with the

96

scope, c.;,;,ie, :,nd robe capacitance, CLdeLreases the total eftective capacit,inee andthereby increase:, the capacitive reactance. Thelarge value resistor. R I, acts as-an isolatingresistor. as discussed previously, and alsoeffectively decreases the total inputcapacitance These two parallel circuits, whichare effectively connected in series, act as avoltage divider and, of course, decrease theamplitude of the AC signal being measured.Although this decrease in amplitude is wantedin a high-voltage probe. it is one of theunfortunate side effects of compensation and istermed probe attenuation..15-14. The amount of probe attenuation

must remain fairly constant duringmcasurement at both low and high frequencies.Therefore, not only must the RIC1 provide avoltage ratio of 100:1, 10-1, or some otherfraction, but RIC! must be equal to R2C2 ofthe scope, probe. and cable. With these twotime constants equal, the arrangement dividesAC voltages at all frequencies by the sameratio, except when either resonance orantiresonance effects change the voltagedelivered to thc scope. (Thc latter effects occurso rarely that they may be neglected in mostcases.)

15-15. Another way to provide isolation isto use a probe that is constructed by connectingan additional resistor. R, across the verticalscope terminals, as shown in figurc 79. Thus,the isolating resistor and R comprise a resistiveattenuation path for DC. This protects thescope blocking capacitor from DC voltagesurges and, in addition, stabilizes the scopeimpedance as the vertical vernier control isvaried. A probe of this design has one primarydisadvantage; it may cause too much resistanceloading on critical high-impedance DC circbits.Therefore. this type of probe is normally notused in such circuits unless a capacitor isinserted in series with the probe tip to blockDC.

15 - ! 6. Yet another way to provide isolationis to use a cathode-follower probe. It has acathode-follower circuit within the probe bodyto obtain a very high input and low outputimpedance characteristic. This type of probehas excellent high-frequency response and,since its input impcdance is higher than itsoutput impedance. it acts as ati impedancetransformer. Figure 8t; illustrates the schematicdiagram of thc probe. The light circuit loadingof this probe results from the use of a 6-megohm resistor shunted by approximatel 10picofarads of stray circuit capacitance. Asshown. the 6-megohrn resistor, the 0.05-microfarad coupling capacitor, and the 300-ohm cathode resister are all in series and

10

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Figure 79. Isolation probe with shunting resistor.

shunted across the output of the circuit undertest. The output from the cathode follower isobtained across ,the 300-ohm cathode resistorwhich is in parallel with the high impedance ofthe scope (or other test instrument). Therefore,the scope input circuit does not load down thecathode-follower output.

15-17. Shielding and Loading Effects ofProbes. As you may have surmised from ,theforegoing discussion, the test leads or cable thatyou use as the electrical link between a VOM,VTVM, or sctpe and the equipment under testbecomes an integral part of the test instrument.You can use many different types ofinterconnections, such as two independentseparated wires, two parallel wires in a cordarrangement, or a probe and shielded cable.The effect of the shunting input capacitancemay be negligible in one circuit under test andmay completely upset the normal operation ofother circuits under te' t. In some cases, the useof unshielded test leads results in spuriouspulse- or hum-voltage pickup. which distortsthe signal applied to the VTVM or scope. ThiS

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condition can exist because a magnetic field isproduced around each wire having currentflowing through it, and a potential betweenwires establishes an electrostatic field at rightangles to the magnetic field. The magnetic fieldo produced represents a lumped value ofinductance along the wires. The electrostaticfield represents a lumped value of capacitancebetween the wires. Unfortunately, each time theleads are moved or shifted, the distancebetween them changes, and this changes thedistributed capacitance between the wires orbetween the wires and nearby objects. At higherfrequencies, the inductance and capacitancevalues may cause the tested circuit to actuallyoscillate and produce ri,isleading meter.indications. Also, the use of unshielded open-wire test leads and probes may have otheradverse eftects; for example. the test leads mayact as an antenna and radiate a signal from anisolated or shielded circuit section to othercircuit sections to cause circuit crosscoupling,regeneration, or oscillation. In addition, thisstray field and adjacent circuit pickup or

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97

101

crosscoupling may be fed directly to your scopeand be integrated with the desired scope triceto provide confusing or ambiguous results.

15-18. A shielded input cable does no:always correct the difficulties encountered withtwin-wire unshielded test leads. Both theshielded cable capacitance to ground and theVTVM or scope input capacitance may cause aloading effect on the circuit under test. In fact,errors in peak-to-peak signal measurement, aswell as waveform distortion, may be evident. Aswe have explained previously, the use of anisolating resistor within your probe decreasesthe loading effect of your shielded cable andavoids the possibility of detuning high-frequency reuonant circuits under test. In someareas of low-frequency measurement, however,the unshielded cable has less loading effect thanthe shielded test lead.

15-19. The use of a high-voltage 100:1capacitance probe is a distinct advantage exceptwhen the output of the tested circuit is belowabout 5 or 10 volts. Theselow voltages willproduce probe output signals less than 0.05 or0.1 volt, which may not provide sufficientdeflection for a good display.

15-20. The input impedance of a capacitordivider high-voltage probe is relatively high,but it becomes less as the frequency increases.At extremely high frequencies, the probeimpedance becomes so low that this type probecannot be used because of its loading effects.

15-21. When connecting test equipment to acircuit, you should always have some idea ofthe internal impedance of the circuit. Thisknowledge is necessary because the loadingeffect on the circuit is not determined solely bythe shunt capacitance or inductance of the testequipment and leads. Since this shuntcapacitance or inductance is in parallel with theinternal impedance of the circuit under test (asshown in fig. 81), it is the relative values of thereactance and the internal impedance whichdetermine whether or not the loading isappreciable. If Z is small compared to Xc,there is little or no effective loading. However.if Z is large in '.:omparison, the loading is heavy

98

PROBE TIP

IN rETINALIMPEDANCE Z

CAPACITOR VERTICAL ilonoiTSPIUNTINOIMPEDANCE

OSCILLOSCOPE onVTem

Figure 81. Probe and cable loading.

enough to alter the operation of the testedcircuit and distort the peak-to-peak signal orobserved waveform. It is on the basis of thisreasoning that we can say a given shuntimpedance loads down a high-impedancecircuit more heavily than it does a low-impedance circuit.

15-22. Safety Precautions. As a safetyprecaution, the meter or scope ground terminalshould be physically connected to the probecable shield and to either the chassis or the B-line of the equipment being tested. If you donot ground the test instrument in this manner.it may be electrically hot and present a severeshock danger. When you test circuits containingno power transformer, you should remember toconnect an isolation transformer between theequipment being tested and the line. Thisprevents you from shorting out the powerline ifthe meter case or chassis should becomeinadvertently or accidentally grounded. Formaximum safety, the wearing of insulated shoesis advisable; if shoes which have exposed nailhu.ids are worn, you should stand on a rubbermat or other insulated material. Keep one handin your pocket at all times, and hold the probeby its handle with your other hand. Connect theprobe tip to the equipment to be tested prior tothe application of power. We have reviewedthese precautions because you should bear themin mind whenever high voltages are measured.

15-23. At this time work the Chapter ReviewExercises for Chapter 4 in your workbook.

L

Power and Frequency Test Equipment

IN ADDITION TO the test instruments alreadycovered, there are many test instrumentsdesigned to test television, flight facilities, andradio equipments and many others designed formicrowave measurements. In this chapter wewill discuss the most important and commonlyused in electronic test instruments that C-Erepairmen need to perform their job. Theinstruments included are those that measurepower and frequency. Signal generators willalso be considered, since they are requi.'ed fortesting and troubleshooting.

16. Power Measuring Instruments

16-1. Electrodynamic wattmeters are widelyused for thc measurement of power. Otherpower-measuring instruments of importanceare: output power meters, bolometer bridges,and calorimeters.

16-2. Electrodynamic Wattmeters., Theelectrodynamic wattmeter measures powertaken from alternating-current or direct-current power sources. When measuring ACpower, this instrument indicates the in-phase orreal power. It can be modified, however, toindicate reactive power instead of real power.This instrument uses the reaction between themagnetic fields of two current-carrying coils

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Figure 82 Circuit of an electrodynam4 wattmeter.

99

CHAPTER

(or sets of coils), one fixed and the other.movable (see fig. 82). When the currentthrough the fixed-position field winding(s) isthe same as the current through the load, and

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Figure 83. A compensated wattrneter.

the current through the moving coil isproportional to the load voltage, theinstantaneous pointer rotation is proportionalto the instantaneous power. Since the movingsystem cannot follow rapid variations in torquebecause of its longer natural period ofvibration, its deflected position is where theaverage driving torque is equal to the restoringtorque of the springs. Meter deflection is thusproportional to the average power.

16-3. The dynamometer-type wattmeterautomatically compensates for the power factorerror of the circuit under test, since it indicates,only the power resulting from in-phasecomponents of current and voltage. With out-of-phase relationships, a current peak throughthe moving coil never occurs at the same instantas the voltage peak across.the load. The result

103

q601.11

is less pointer deflection than when the currentand voltage are in phase.

16-4. The simple meter shown in figure 82indicates that power is being consumed afterthe load is disconnected. This difficulty can beeliminated by incorporating two compensatingwindings, mounted with the primary fixed-coilcurrent windings, as shown in figure 83. Thesestationary windings produce a magnetic fluxproportional to the current through the movingcoil. As shown by the arrows in figure 83, thecurrents through the current windings and thecompensating coils flow in opposite directions.Since these opposing fields cancel with the loadremoved from the circuit, the meter willindicate zero power.

16-5. Electrodynamic wattmeters are subjectto errors arising from various factors, such astemperature and frequency characteristics ofthe moving system. Aside from heat dissipationin the various coils, heat through the controlmechanism will cause the springs to lengthenand lose tension, producing deflection errors.Figure 84 illustrates cne mechanical equivalentof the electrodynamic wattmeter. Largecurrents within the circuit will also produceappreciable error. Therefore, the maximumcurrent range of electrodynamic wattmeters isnormally restricted to about 20 amperes. Whenlarger AC load currents are involved, a currenttransformer of suitable range is used inconjunction with the wattmeter. However, whenmeasuring total power, a current transformercannot be used if the AC circuit under testcontains a DC component.

16-6. The voltage range of wattmeters isgenerally limited to several hundred voltsbecause pf heat dissipation within the voltagecircuit. However, the voltage range can beextended by using external voltage multipliers.

16-7. Wattmeters used as laboratory

Figure 84. Mechanism of a wattmeter.

100

standards have an accurac; of O. percent,high-grade portable wattmeters have anaccuracy of 0.2 to 0.23 percent, and nigh-gradeswitchboard-wattmeters have an accuracy of 1percent. Because electrodynamic wattmetererrors increase with frequency, the accuracydecreases appreciably for frequencies above1000 hertz.

16-8. When using, an unshieldedelectrodynamic wattmeter, you should notplace it in the vicinity of stray magnetic fields.Also take care not to exceed the current.voltage, and power ratings of the wattmeter.Damage may result when any of these ratings isexceeded, although excessive meter deflectionmay occur only when the power rating isexceeded.

16-9. The electrodynamic wattmeter may beconverted into an instrument for measuringreactive power by replacing the resistance,which is normIlly in series with the voltagecoil, by a large inductance. A 90° current lagwithin the voltage coil provides a direct readingproportional to the reactive power in thecircuit. Compensating networks must be used tocause the phase chift to be exactly 90°.

16-10. Output Power Meters. Unlike theelectrodynamic wattmeter. the output powermeter is restricted to the measurement of the

Figure 85. Basic output power meter circuit.

dissipated power in a selective resistive loadprovided by the instrument inself. A diagram ofa simple output power meter is shown in figure

E:85. The power is where E is the voltmeter

reading. Since R is a fixed resistance of knownvalue, the voltmeter can be calibrated to readdirectly in watts. By using different values of Ror by providing various multiplier resistors inthe voltmeter, it is possible for you to extendthe range of the instrument. For themeasurement of AC power. a tappedtransformer can be used for extending the range(see tig. VI). The voltmeter Is usually calibratedto read watts or decibels.

16-11. Dh meters. A db meter is a rectifiertype of AC voltmeter or an AC electronicvoltmeter calibrated in db. The db meter can beincorporated as part of a volt-ohm-milltammeter, and the same jacks and switch

104

ACVTVII

Figure R6. Tapped transformer for output power meter.

positions used for AC voltage measurementsare used for db measurements. When the dbmeter is calibrated, a reference point, based ona specific power or value of voltage across aspecified resistance, is selected to represent 0db. Many electronic voltmeters use a db scalebased on I milliwatt into a 600-ohm load torepresent 0 db. Based on this reference point,various voltage readings could be made on thelow AC voltage scale. To provide a singlecalibrated db scale for use on all db ranges, -I-db numbers corresponding to the voltage ratiosexisting between successive ranges and the lowAC range are computed for each range. Thesenumbers, shown on the front panel of theinstrument, are added algebraically to eachsuccessive range reading to produce the correctvalue for that range.

16-12. It should be cleariy understood thatthe term "decibel" does not, in itself, indicatepower. It does indicate a ratio or comparisonbetween two power levels that permits you tocalculate the power. Often, it is more desirableto express performance measurements in termsof decibels by using a fixed power level as areference. The original standard reference levelw as 6 milliwatts, but to simplify calculations, astandard level of I milliwatt has been adopted.Thus, when the expression dbm is seen, itshould be understood that the reference level is

milliwatt.16-13. Vu meters. The volume unit (vu)

meter, used in audio equipment to indicateaudio level, is a special kind of power meter. Itsmeter movement has a rapid rise and a slowfall, so that it follows the audio peaks andmodulation envelopes. The unit ofmeasurement is the volume unit, which isnumerically equal to 1 db above or below thereference level of 1 milliwatt into a 600-ohmload. A change of I vu is, therefore, the same asa change of 1 dbm. It should be emphasizedthat a vu meter can always be used as a dbmeter; however, a db meter can be used as a vumeter only when the audio output is a steadytone. Some vu- meters arc calibrated to readpercentage of modulation, as well as volumeunits, when calibrated to the equipment withwhich they are used.

101

16-14. Boiometer Bridges. Themeasurement of power an also be made with abolometer bridge instrument. A bolometer is aspecially constructed element of temperature-sensitive material._ The active material can be ashort, ultra-thin wire (called a barretter), asemiconductor bead supported between twopigtail leads (called a thermistor), or a thinconducting film of small dimensions. The mostcommon types of bolometers used to measurelow power at high frequencies are barrettersand thermistors.

16-15. When RF power is applIW to abolometer element, the power absorption bythe element heats the element and causes achange in its electrical resistance. Thus, abolometer can be used in a bridge circuit sothat small resistance changes can be easilydetected and power measurement accomplishedby the substitution method (that is, su itutionof DC or low-frequency power to proluce anequivalent heating effect). A D'Arsonval metermovement is usually employed as the nullindicator. According to one principle ofmeasurement (the principle used in thebalanced bridge), the bridge is initiallybalanced with low-frequency bias power; thenRF power is applied to the bolometer, and thebias power is gradually removed until .:hebridge is again balanced. The actual RF poweris equal to the bias power removed. Accordingto another principle of measurement (theprinciple used in the unbalanced bridge), thebridge is not rebalanced after the RF power isapplied. Rather, the indicator reading isconverted directly into pow0 by use of acalibration previously performed. Figure 87illustrates the basic bolometer bridge circuit.The bolometer element must be: (1) physicallysmall to be highly sensitive, (2) equallyresponsive to low-frequency and RF power,and (3) matched to the RF input powerline.

16-16. Calorimeters. Calorimeters (heatmeasuring devices) are the most accurate of allinstruments for the measurement of high power.

Figure 87. Basic bolometer bridge circuit.

10 J

97

They depend on the complete conversion of theinput electromagnetic energy into heat. Directheating requires the measurement of the heatne,effect on the medium, or load, terminating theline. Indirect heating requires thc measurementof the heating effect on a medium or body otherthan the original powcr absorbing material.Power measurement with true caiorimetermethods is based solely on temperature, mass,and time. Substitution methods use a knownlow-frequency power to produce the samephysical effect as an unknown RF power beingmeasured. Calorimeters are classified as static(or nonflow) types and circulating (or flow)types.

16-17. The static calorimeter uses athermally shielded body and, since an isolatedbody loses little heat to a surrounding medium,the temperature increase of the body is in directproportion to the time of applied power. Theproduct of the rate of temperature rise in thecalorimetric body and its heat capacity equalsapplied power. Figure 88 illustrates a static-type calorimeter.

16-18. Flow calorimeters are . classified by(1) the type of circulating method used (open orclosed), (2) the type of heating used (direct orindirect). and (3) the type of measurementperformed (true calorimetric or substitution).Water or other calorimetric fluid is used onlyonce in an open system. An overflow system isused to maintain a constant rate of flow. Closedsystems recirculate the fluid continuously bymeans of a pump, and a cooling system restoresthe fluid to ambient temperatures prior to itsreturn to the calorimeter. Closed systems aremore elaborate, but this self-contained methodpermits the use of fluids other than water.

16-1 9. Flow calorimeters provide theprimary standards for the measurement of high-power levels and, in conjunction withcalibrated directional couplers, attenuatch's.power dividers, or other similar devices, serveto standardize medium- and low-power

ISOLATEDCALORIMETRIC

BODY

RFPOWER

LOW- FREQUENCYPOWER

TEMPERATURE

Figure 88. Static calorimeter.

102

measuring instruments. The meawrernent timedepends upon the required time for te enteringfluid to reach the outlet where the risetemperature is measured.

16-20. The circulating fluid may serve in adual capacity as the dissipative medium andcoolant, using the direct heating method, orsolely as a coolant, using thc indirect heatingmethod. Because of its excellent thermalproperties and high dielectric loss at 1000 MHzor higher, water is normally used in bothheating methods. Water is rarely used as thefluid at frequencies lower than 1000 MHzbecause of insufficient dielectric losses. Theindirect heating method offers a widerfrequency and power range coverage and can beused in substitution type measurements.

16-21. Substitution methods do not involvedirect heat-dissipation measurement of movingfluid. Greater accuracy is obtained becauseknown low-frequency power is substituted forunknown RF power, with all othermeasurement parameters remaining constant.

FLOW REGULATOR

R F POWER

?

r-1Flow MITE/AWAY SEOPEN OR CLOSED/

THERMOPILE OR OMERTEMPERATURE OFFERENCE

MEASURING ounceCALI GRATED

LOW- ricsOUCPCYPOWER

Figure 89. Flow calorimeter.

The accuracy depends on the exactness of thelow-frequency power determination and on thedegree that all factors remain fixed during thesubstitution of one type of power for another.Figure 89 illustrates a flow calorimeter usinglow-frequency power substitution. Twodifferent measurement techniques are possiblewith this type of meter: (1) the calibrationtechnique and (2) the balance technique.

16-22. The calibration technique uses anadjustable known power to reproduce exactlythe same temperature indication originallyobtained by the unknown RF powermeasurement.

16-23. The balance technique uses an initiallow-frequency power (P1) to provide a steady-state temperature rise in the calorimetric fluid.

1 06

qt

or Nowt*CALIMATED

LOW- FNIGUINCYPOwEN

INLET OUTLETTENINENTuRE TEIIMPERATUNE

Figure 90. Balanced flow calorimeter.

When unknown RF power is applied, theoriginal power (P1) is reduml to a new power(P2) to maintain the same temperatureindication. Therefore, the actual pcwer equalsPI P2. Figure 90 illustrates a widely usedmethod of power measurement, using abalanced-flow calorimeter. Temperature-sensitive resistors are bridge connected as thethermometric elements and are balanced atambient temperature prior to the application ofpower. Low-frequency balancing power and theunknown RF power are applied to maintain thebridge at null. This occurs when thetemperature rise due to the unknown RF powerequals the temperature rise which is due to theknow low-frequency power.

16-24. Airflow calorimeters use thesubsitution power principle and are used in theUHF region to measure power on the order of20 watts. This instrument consists primarily ofa coaxial line section containing a tungstenfilament center conductor within an evacuatedenvelope, to act as both the low-frequency andRF load. A thermopile indicates thetemperature difference between the forced airthat enters and leaves the coaxial inclosure thathouses the termination.

17. Frequency Test Instruments

17-1 There are several types of frequencytest instruments which are useful to theelectronics repairman. These are wavemeters.grid-dip meters. heterodyne (beat) frequencymeters. and frequency counters.

17-2. Wavemeters. Wavemeters are of twobasic types: (I) reaction 3n d (2) absorption.

103

Both types are passive; that is, both absorb partof the output power of the equipment whosefrequency is undergoing measuremen: Thereaction wavemeter abs `-'s very little powerand is, therefore, preft..7.eo for use whenfrequencies in low-power equipment are to bemeasured. An indication of resonance issupplied by the equipment undergoingmeasurement, usually in the form of anammeter of suitable range. The absorptionwavemeter is more accurate than the reactionwavemeter, but it absorbs slightly more powerfrom the device under test. Since it tends toload the equipment undergoing examination, itsuse is generally restricted to high-poweredequipment. The indicator of resonance, usuallya meter or a lamp, is connected into the tankcircuit of the wavemeter. When the ultra-highradio frequencies (300 to 3000 MHz) arereached, it is physically impossible to use theordinary type of absorption wavemeter. Thereason for this is that such small values ofcapacitance and inductance are required forresonance at these high frequencies, that it ishot feasible to manufacture them. If thewavemeter type of frequency meter is to be usedin this region of the radio-frequency spectrum,it is necessary to use either a resonant-cavity orresonant-line type of frequency meter.

17-3. For conducting preliminaryadjustments on transmitters and for generalexperimental work, the simple resonant-circuitwave-meter is a valuable tool. However,wavemeters cannot be used where accuratemeasurements are required, because they tendto detune self-excited oscillator circuits towhich they are coupled. The brightest lampindication or highest meter indication normallyregisters the fundamental frequency. Therefore.this type of meter is very useful (1) for checkinga transmitter to determine whether or not themaster oscillator is operating close to thecorrect fundamental frequency. (2) forchecking the neutralization of an amplifier, (3)for detecting the presence of radio-frequencyparasitic oscillations. and (4) for determining

DEVICE UNEENTEST

1 0

LMOM 411MWM .NM M./wAVENETEPI

Figure 91 React ion -type wavemeter

EXTERNAL rCOIL

INDICATOR

DEVICE UNDERTEST 1Mi 11111= 1111111. MEMO

WAVEMETER

Figure 92. Absorption-type wavemeter.

radiated field strength in relative measurementterms.

17-4. Reaction wavemeters. The circuit of araction-type wavemeter, containing a coil anda variable capacitor, is shown in figure 91. Therange of frequency measurement of thewavemeter is changed by the use of plug-incoils. The coil, which is external to thewavemeter, is loosely coupled to the circuitwhose frequency is to be measured. Theresonant frequency of the waverneter is madeequal to the frequency of the circuit undermeasurement by varying tne capacitor. At somepoint within the frequency range of thecapacitor-coil combination, the indicatingdevice will indicate maximum or minimumdeflection, depending upon the circuit locationof the indicator. When the wavemeter isadjusted to the resonant point (maximumloading effect), it is important that the coupling

CIRCUITUNDER TEST

be reduced to the point which produces abarely usable indication. If the coupling is not 04.reduced, a sharp indication of resonance wil1not be obtained and a consequent error will beintroduced.

1 7-5. Absorption wavemeters. Theabsorption wavemeter, shown in figure 92, isbasically the same as the reaction wavemeterpreviously discussed. An inspection of figure92 shows that the indicator has been includedas part of the internal circuitry of theabsorption wavemeter. The fixed capacitor,connected across the terminals of the indicatinglamp, has a much greater capacitance than thevariable capacitor. This large capacitancepermits a voltage to be developed at resonanceto light the lamp, and at the same time it hasnegligible effect on the resonant circuit becauseof its low reactance.

17-6. When this type of wavemeter iscoupled into the circuit under test, care must beused as resonance is approached so that thelamp will not burn out. The dial should berotated slowly and, as the lamp begins to glow,the wavemeter coupling should be reduced. Forgreater accuracy, the wavemeter should becoupled so that maximum brilliance is only afaint glow. A well-constructed instrument willprovide an accuracy of 0.25 to 2 percent.Because of changes in capacitance or inductionfrom vibration or from temperature andhumidity changes, it is often necessary torecheck the calibration.

17-7. Grid-Dip Meters. It is often desirable

Figure 93. Grid-dip meter.

104

106

UNKNOWNINPUT

FREQUENCYDETECTOR

VARIABLEFREQUENCYOSCILLATOR

AFAMPLIFIER

Figure 94. Block diagram of a basicheterodyne frequency meter.

to determine the approximate frequency of atuned circuit before power is applied to it. Sucha determination can be made with aninstrument called a grid-dip meter. Thisinstrument is essentially an oscillator, as shownin figure 93. The variable capacitor iscalibrated in kilohertz or megahertz. To make ameasurement, the coil is coupled inductively tothe tuned circuit under test. The variablecapacitor is adjusted until the meter iddicates aminimum grid current. At this point, the tunedcircuit under test is absorbing the maximumamount of energy from the grid-dip oscillator.Therefore, the grid-dip meter is tuned to thefrequency of the circuit under test. Thisfrequency is read directly on the calibrated dialof the instrument.

17-8. Since the grid-dip meter generates asignal. it is an active instrument. A widefrequency range is obtained by using plug-intype coils. It is designed so that the coil can beinductively coupled to the circuit under test.For maximum accuracy, the grid-dip, metershould be loosely coupled so that the dip ingrid current is distinct.

17-9. Heterodyne-Frequency Meters.Frequency can be measured more accuratelywith a specially designed instrument called aheterodyne-frequency meter. It is a precisioninstrument that measures an unknownfrequency by heterodyning it with a knownfrequency which is obtained from a calibrated,high-precision, variable-frequency oscillator(VFO). When zero beat is obtained, theunknown frequency is that of the VFO. Thezero-beat indicator in test equipment of thistype is generally a pair of headphones;however, some heterodyne-frequency metersemploy an oscilloscope for this purpose.

17-10. Operation. The basic heterodynemeter (shown in the block diagram of figure 94)is a calibrated variable oscillator with

105

associated circuits, which heterodynes againstthe frequency to be measured. Coupling isarranged between the frequency meter and theoutput of the device under test. The calibratedoscillator is then tuned so that the differencebetween the oscillator frequency and theunknown frequency is in the audio-frequencyrange. This difference in frequency is known asthe beat frequency; when- detected andamplified, it is audible in a headset. This regionof beat frequencies is shown diagrammaticallyin figure 95. Starting at point A on the figure, avery high-pitched rtzle can be heard in theheadset. As the two frequencies are broughtcloser to the same value (decreasing difference),the tone decreases in pitch down to point B.Here the tone is replaced by a-series of rapidclicks.

17-11. As.the process continues still further,the clicks decrease in rapidity until they stopaltogether at point C. This is the point of zero

AIMNOMERANI

MYCN OrKAT NOTE

NINON COCLOS ONNO MONO

POINTOF EXACT

ZENOSEAT

FotECWINCY OinrontNet

INCREASING

NEP MD

INONVIONNI

Figure 95. Beat frequency diagram.

10J

beat, where the frequency generated in thecalibrated oscillator is equal to the frequency ofthe unknown signal being measured. Fo: allpractical purposes, zero beat is obtained. whenclicks are heard at rather infrequent intervals.since it is extremely difficult to maintain acondition of absolute silence in the headsetover a prolonged interval of time. When theincoming signal is fairly strong, the clicks aresharp and distinct. When the signal is weak, thezero-beat condition is evidenced by a slowlychanging swishing or rushing sound in theheadset.

17-12. If one of the tWo original frequenciesis varied still further, the rtpidity of clicksincreases to point D. At ths point, a low-pitched tone is heard. Further variation in thesame direction causes a gradual increase inpitch until point E is reached, where the beatnote becomes inaudible again. This region ofincreasing pitch on both sides of the zero beatis characteristic of this procedure.

17-13. After the zero beat is obtaint:!, thedial reading, when properly interpolated,corresponds to the frequebcy undermeasurement. Aura/ beats, heard by the use ofheadphones, may be acceptable to obtain anapproximate indication of zero beat. It shouldbe apparent that this method leaves a smalldoubtful region in the shaded area, BCD onfigure 95. The generally accepted audible rangeof the normal human ear has a lower limit of 15to 20 hertz. Under these circumstances, thearea BCD could represent an error of 30 to 40hertz, 'or more in some cases.

17-14. To overcome this type of difficulty,simple oscilloscope circuitry is included as apart of wme heterodyne-frequency meters toprovide exceptional sensitivity. The sensitivityof the device increases with the amount ofamplification preceding the cathode-ray tube.No vertical deflection occurs at the zero-beatcondition. An effective indicator suitable forincorporation within a frequency meter uses anelectron-ray indicator tube. The sensitivity ofthis simple deyice is excellent. Other types ofvisual indicators are vacuum-tube voltmeters,rectifier-type audio-frequency voltmeters, andneon lamps.

17-15. The variable-frequency oscillator(VFO) is the source of the signals used inmaking frequency checks on receivers andtransmitters. One of the prime requisites of thevariable-frequency oscillator is stability ofoscillations. As you know, there are variousmeans of obtaining this stability.

17-16. The use of plug-in coils or switches isgenerally unsatisfactory since they aremechanically unstable. Many VFOs are tuned

106

by having their tuning capacitor rotated by aprecision-type split bronze worm wheel and ahardened stainless steel worm gear. Thisportion of the tuning unit is not readilyreplaced without materially affecting thecalibration of the frequency meter. Whenconstruction throughout the meter is sturdy andhigh-grade ceramics are used as insulators inthe oscillator circuit, a precise frequencycalibration will hold over a long period of time.

17-17. The circuit usually employed as thevariable-frequency oscillator is the electron-coupled oscillator. One of the reasons for thischoice of oscillator circuit is that the outputfrequency can be made very stable with respectto loading conditions in the output circuits.Another reason is that with the use of screen-grid tubes, the generated frequency can bemade relatively independent of tube supplypotentials, as long as the ratio of the plate-to-screen potentials is maintained near the desiredvalue. Sometimes frequency-determiningelements of the VFO are inclosed within atemperature-compensating oven to prevent theeffects of ambient temperature.

17-18. Crystal checkpoints. Accumulatederrors from changes in temperature, humidity.and power-supply potentials, as well as roughhandling, can be corrected at a number ofplaces throughout the tuning range of theinstrument. This can be done by means of thebeat notes between the fundamental frequencyof the VFO (or its harmonics) and thefundamental frequency of crystal oscillator (orits harmonics).

17-19. The harmonics of both oscillators arepresent in an unbroken series, with decreasingamplitude as the order of the harmonicincreases. Since any harmonic of one oscillatorbeating with any harmonic of the other canproduce a beat note, there is considerablevariation in the strength of the beat notes as thedial is tuned across its tuning range. Forconvenience and accuracy, the relatively strongbeat notes are chosen as crystal checkpoints.

I 7-20. By calibrating and correcting at acrystal checkpoint, the heterodyne-frcquencymeter is adjusted so that the frequencygenerated by the variable-frequency oscillatorat a given dial setting is actually the same as thefrequency listed opposite the dial setting in thecalibration book.

17-21. Calibration hook. The calibrationbook is a very important part of the frequencymeter; in fact, the book is so important that itbears the same serial number as the instrumentitself. The information contained within thisbook is a list of the dial settings and thecorresponding frequencies produced by themeter at those dial settings. Concise operating

1 i

le2

CULb....EIDIENTH ORAMATKIN Os THE

YERNIER HEAOING

HAIN TuNINGDIAL

311100.0 01A1. HUNDREDS16.0 Kim TubuND mat

.1 VERNIER

3171.1 COMPLETE READING

Figure 96. Heterodyne frequency meter dial.

instructions for the frequency meter are alsoincluded. Crystal checkpoints are usuallyentered in this book in red-ink numerals at thetop and bottom of each page, and apply only tothe settings on that page, while the black-inkedentries are the settings for the actual measuredfrequency.

17-22. Main tuning dial. The main tuningdial is an assembly to two mechanical driveunits connected to the variable-frequencyoscillator tuning capacitor. A drum dial,located behind a small window (see figure 96),indicates the setting of the main tuning dial inunits of 100 per division. The main tuning dialitself is the large drive dial on the front panel ofthe meter. It is calibrated in units of 1 perdivision. For one complete revolution of themain tuning dial, representing 100 units, thedrum dial will move one division. A vernier ismounted in a fixed position above and on theoutside edge of the main tuning dial. Thevernier indicates tenths of a division of themain tuning dial.

13. Frequency Counters

18-1. The frequency counter is an electronic

INPUTC>I AMPL .

measuring instrument designed to register anddisplay, by digits, the number of cycles thatoccur during a specific time interval. Thisinstrument permits the rapid, directmeasurement of the frequency of period of asignal.

1 8-2. Frequency counters havepredominantly used electron tubes, but there isa definite trend toward the increased use oftransistors and magnetic devices. Althoughcounters differ in many details, they are allessentially the same. The differences areprimarily those of capabilities and range. This,of course, means that their circuitry differs. incomplexity. Since the details of difference aretoo numerous to discuss in this course, let usgive our attention to the principles of operationand the essential sections contained withinthese instruments.

18-3. Functional Sections. Figure 97 shows

INPUTSECTION

GATESECTION

TIME BASESECTION

DISPLAYSECTION

RESETSECTION

Figure 97. Block diagram of a frequency counter.

a block diagram of a basic frequency counter.The signal to be measured is fed into the inputsection, where it is amplified, and shaped beforereaching the gate section. The purpose of thetime-base section is tu generate a stable squarewave of known frequency. The output from thetime-base section is modified by the gatesection to provide a pulse for the reset section,and to develop a precise time interval fortransfer of the unknown signal to the displaysection. The display section counts the numberof pulses and gives a digital readout. This, in

AMPL.

NEGATIVE FEEDBACK

SQUARER

Figure 98. Input section.

107

11.

TO GATE SECTION

/e 3

INPUT

Figure 99. Schmitt trigger circuit.

brief, is what takes place; but you need to knowmore about each of the sections to understandhow a counter operates.

18-4. Input section. The input sectionconsists oC one or more amplifiers and asquarer stage. Figure 98 shows two stages ofamplification preceding the squarer. TheseamPlifiers are conventional types; therefore, weneed not analyze them. The indicated negativefeedback may be obtained in a number of waysto increase the input imped4nce and stabilizethe system. The squarer shapes the signal into anear perfect rectangular waveform. Because theSchmitt trigger circuit is particularly well suitedfor this, it is commonly used. A review of theoperation of this type of squarer will reveal whyit is an excellent waveshaping circuit for

counters.18-5. The basic Schmitt trigger circuit is

actually a bistable multivibrator (see figure 99).We have chosen to use electron tubes forexplanation purposes, but bear in mind thattransistors (NPN or PNP types) are also used.Although component values and bias voltagesare quite different, the operating principles andcircuit configuration are fundamentally alike

for electron tubes and transistors. Biasadjustments are critical for proper operation.Switching from full conduction to cutoff of theamplifying device is virtually instantaneous.This rapid switching is a very desirable feature.

108

1,1 t3

11:1TO GATE SECTtON

of course, since it produces an output signalwith steep leading and trailing edges. Let usnow briefly discuss why biasing is critical andhow rapid switching occurs.

18-6. Refer again to figure 99. Note that in abasic Schmitt trigger circuit, the plate of VI iscoupled via a voltage divider to the grid of V2.The capacitor connected across the upperportion of this voltage divider is to increase theinitial response of V2 to a voltage change onthe plate of VI . Note also that the cathoderesistor is common to VI and V2; it thereforeprovides feedback coupling in addition to biasfor both tubes. The bias is established by Rkand Rg so that VI is cut off and V2 isconducting its maximum. Consequently, theplate of VI is at a high voltage (practically B-I-)and the plate of V2 is at a low voltage. This isthe normal stable state when there is no signalinput to the circuit shown.

18-7. We have intentionally distorted theinput signal in figure 99 to point out that theshape of the input signal is not critical, which isanother advantageous feature of this circuit.Tube VI is biased below cutoff to a degree thatprevents noise signals from actuating thecircuit. This adjustment is important, since onlythe signal under test should trigger the circuit.Once the bias is adjusted, VI will be driven intoconduction at a prescribed signal voltage. Wesee, in figure 99, that this voltage is reached at

114)

leek

time T1. and V I conducts. Instantaneously, theplate voltage of V 1 decreases, therebydecreasing the grid voltage of V2; thus, thecathode voltage of V2 decreases. Because thecathodes of V I and V2 are direct coupled, thisdecrease in cathode voltage effectivelydecreases the bias on V I and causes it toconduct harder. In other words, we haveregenerative feedback, which accounts for therapid switching action from one stable state tothe other state. Between the times T1 and T2.V I is conducting and V2 is cut off. At time T2the process works to reverse the stable states ofthe tubes, VI is driven to cutoff, and V2 goes tofull conduction. Study the waveforms in figure99 and note that at times T3 and T4 switchingoccurs exactly as described at times T1 and T2,respectively. The recurring rectangular outputis seen to have a frequency which is identical tothat of the input signal; the period is the timeinterval between TI and T3.

18-8. Schmitt trigger circuits vary a greatdeal in design, depending upon therequirements that must be met, such asswitching times and driving voltage. Like othermultivibrators, the output can be taken fromthe plate of either tube. Modifications irSchmitt trigger circuits, however, do not changethe operating principles that we have covered.

18-9. The output from the Schmitt triggercircuit or another type squarer is fed out of theinput section into the gate section. Beforediscussing the gate section, however, we need tolearn what is contained within the time-basesection, since the output of this section is alsofed into the gate section. The precision of thecounter is greatly dependent upon theoperation of the units within the time-basesection.

SQUARER100 1114s

18-10. Time-base section. The units thatcomprise the time-base section are shown infigure 100. You know there are many kinds ofsinusoidal crystal oscillators. Whichever kind isused, its crystal is contained within atemperature-controlled oven to insure a highdegree of frequency stability. A constant outputfrequency is of utmost importance. Loadingeffects upon the oscillator are reduced byfeeding its output into a buffer amplifier. Wehave shown only one stage of amplification, butyou should realize that more amplifiers may beemployed. The squarer shapes the sine wavegenerated by the oscillator. Often, the squareris simply a limiter stage that clips the positiveand negative alternations to produce a squarewave. The square-wave output is applied to aseries of decade frequency dividers.

18-11. Each frequency divider steps downthe frequency by a fixed ratioin this case10:1. One popular way is to differentiate theoutput of the squarer and to use every tenthpositive- or negative-going pulse to trigger amonstable multivibrator. Since you shouldalready know how frequency divisions can beaccomplished, we will not discuss circuitry.

18-12. Our block diagram shows sixfrequency dividers (see figure 100), each ofwhich gives an output square wave that is one-tenth the frequency of its input. By .a selectorswitch, the desired time period is chosen andsent to the gate section. The time markings onthe selector switch correspond to the period ofthe respective frequencies. Less dividers may beused if a wide range is not necessary. Countersdesigned for high-frequency measurements usehigher frequency crystals and may also have aheterodyne unit to extend its low frequencyrange.

10 USEC

0

10 Lola

0.1 AsSEC

1 AMC 0.1 SEC0 10 1SEC 00

TO GATE SECTION

t***1.14.14114,_

4411160---'

10 SEC

0

0.1 kHz }-11m10Hs

DECADEFREQUENCY DIVIDERS

Figure WO, Time-base section.

109

ill

1 Ng111M

0.1 Rs

111111111113 11Y1111111

PROM INPUT SECTION 0---1 - POSITIVEA AND

GATE

CISTASLENULTIVIENATOR

ISISTASLEMULTIVIERATON

MI

0-416/V-a.s1

12

c FNOU TINE EASE SECTION

t1

11 111

TO DISPLAY SECTION

0 JLto

Figure 101 Gate section.

18-13. Gate section. Here, again, we areconfronted with numerous ways ofaccomplishing the desired results. The systemthat we will explain demonstrates the necessaryfunctions that must be performed by the gatesection. Refer again to figure 97 and note thatthe gate section has two inputs (one from theinput section and one from the time-basesection) and two outputs (one to the resetsection and one to the display section).Recalling what we previously said, you knowthat both inputs are rectangular waveforms. Letus now find out how these inputs are used andwhat outputs are produced.

18-14. At point A in figure 101, we see theinput rectangular waveform that has thefrequency of the signal under test. After beingdifferentiated, it appears at point B as a seriesof alternately positive and negative pulses.These pulses are applied to a circuit that gates

110

TO RESET SECTION

when two positive inputs are receivedsimultaneously (this circuit is called a positiveAND gate). This gate is normally disabledbecause the input from point Y is normally low.Both multivibrators, MI and.M2, are normallyset to have a low output at points S and Y,respectively.

18-15. Looking now at point C in figure101, we see the input waveform from the time-base section. This waveform is differentiated asshown at point D. Because of the diode in serieswith the input to M I ,only the negative-goingpulses (calied clock pulses) appear at point E.These pulses will not actuate MI when it is inits normal stable state. The same is true for M2,which is receiving negative-going clock pulsesalso.

18-16. Thus far, we have established thenormal state of affairs. The AND gate isdisabled, so no output pulses appear at point 0

l 1 44

to he fed into the display section. Moreover,until a change ot stgte is effected in MI, there isno pulse at point S to 1-e fed out into the resetsection.

18-17. Let us now apply an input (called aread pulse) to point R. This pulse actuates MIat time TO. Immediately the voltage at S goeshigh and stays high until time T I. At TI, theclock pulse to M 1 (point E) is effective andrestores M 1 to its normal state. Note that thisaction has produced a positive pulse at point Swhich goes out to the reset section. This samepulse is differentiated and appears at point X asa positive and a negative trigger pulse. Thepositive trigger pulse does not affect M2, butthe negative ones do. Thus, at time T1, point Ygoes high and stays high until time T2, whenthe clock pulse to point restores M2 to itsnormal state. During the time interval TI to T2(which is the period of the time-base signal), theAND gate is enabled. This means that pulsesappear at point 0. These pulses, which have thefrequency of the signal under test, are fed out tothe display section, where they are counted.Therefore, a count is made for the precise timeinterval, T1 to T2. When Y returns to a lowvoltage at time T2, the entire section is back toits normal state. No further action occurs untilanother read pulse is injected at point R. Readpulses may be applied by manual operation 'orby automatic recycling controls.

18-18. The time relationships of the signalscan be readily seen in figure 102. Study thisfigure in conjunction with figure 101. Noteparticularly that the output to the reset section(point S) precedes the output to the display

POINTS I p110 PICSOCI PIANO

POWS(*PAO PULS!)

POINT S

POINT

POINT

POINT 0

FIguee 102. Frequency counter waveshapes.

section (point 0). Although we show only fiveoutput pulses at point 0; you should realize thatseveral thousand or more pulses may occurduring the time interval TI and T2.

18-19. As you know, there are other gatingarrangements that could produce similaroutputs. Multivibrators may be tube ortransistor types. Sometimes magnetic bistabledevices are used in place of multivibrators.Nevertheless, the system we have just discussedshould give you a general idea of the purposeand function of the gate section.

18-20. Reset section. The function of thissection is to reset (or preset) the counting unitswithin the display section. Remember that anoutput pulse from the gate section is fed intothe reset section before the display sectionreceives its input signal. This is necessary, ofcourse, because the counters must be cleared(reset to zero) prior to the initiation of thecounting period.

18-21. The reset section consists of amechanical or electronic relay, e.g., a thyratrontube and associated circuitry to feed resetpulses to all o the counting units. By shapingand amplifying the input pulse from the gatesection, this relay develops triggers of sufficientpower to drive all the counting units back totheir zero setting. Each time a read pulse isinjected into the gate section, the reset sectionis actuated. Therefore, if the read is automatic,so also is the reset.

18-22. Display section. This sectiongenerally contains five or more counting unitsconnected in cascade. These units total anddisplay the number of pulses fed from the gatesection during the counting period.

18-23. A counting unit recycles on everytenth pulse. More specifically, the unit registersnine pulses and resets itself to zero on the tenthpulse. When it resets, it sends a pulse (called acarry) to the next counting unit. Since all theunits operate in an indentical manner, eachsubsequent unit registers a count which isgreater by a factor of 10. Thus, the first unitregisters ones; the second, tens; the third,hundreds; the fourth, thousands; the fifth, tenthousands; and so on. Five counting units willregister a maximum of 99,999.

18-24. The display is generally an in-linereadout of the frequency count (see fig. 103).This type readout can be obtained in severalways. The Nixie indicator, patented by theBurroughs Corporation, is a popular deviceused to provide in-line readout. It is a gas-filledtube that has one anode and 10 stacked coldcathodes that are shaped like numerals from 0to 9. Each cathode has a separate inputterminal. When a voltage is applied between theanode and any one of the cathodes, an

t. 110

/o

® 00.0 ®Figure 103. In-line readout.

ionization glow appears around the energizedcathode. Thus, the cathode's numeral shape isilluminated to provide a visud readout.

18-25. The display illustrated in figure 103consists of six Nixie indicators. The countdisplayed shows the frequency of the signalunder test to be 79,502 Hz, if the counting timeis 1 second. If, however, the counting time is 10seconds, the signal frequency is 7,950.2 Hz.

18-26. Measurements. As you haveobserVed, most frequency counters are designedto measure a wide grange of frequencies.Therefore, let's see how greater accuracy can beattained by using the counter wisely.

18-27. Let us assume, for example, that acounter has a display of five digits, asillustrated in figure 104. We will also assumethat when the time interval selectOr switch is setat 0.1 sec, a reading of 08573 is obtainable(see fig. 104,A). If we know the frequency isbelow 100 kHz, then this reading means thatthe signal frequency is 85,730 ± 10 Hz, sincethe least significant digit (3) may be nearly afull count off either way. By moving theselector switch to 1 sec, a more accuratereading of 85,737 ± 1 Hz is obtained (see fig.104,B). If the counter has a 10-sec selectorswitch position, a still more accurate readingcan be obtained, but you must realize that themost significant digit (8 in this case) will not bedisplayed. The readout (see fig. 104,C) of57374 will, therefore, mean the frequency is85,737.4 ± 0.1 Hz; the digit 8 is known from

0.1SEC GATE

1SEC GATE

10SEC GATE

Figure 104. Reading sequence.

112

the previous reading. By taking successivereadings in this manner, you can ifhprove theaccuracy of measurement appreciably.

18-28. Ordinarily, 10 sec is the longest timeinterval (gate) available. This limits theaccuracy obtainable for low-frequencymeasurements since relatively few pulses arecounted during the time interval. Suppose theunknown signal frequency is between 10 Hzand 100 Hz. If the longest time interval used is10 sec, the reading will be off from 0.1 to 1

percent. If the signal frequency is between 1 Hzand 10 Hz, tne accuracy is from 1 percent to 10percent off. So you see the lower the frequency,the lower the accuracy.

18-29. To attain an accurate measurement ofa low-frequency signal, provision can be madefor the counter to measure the period of theunknown signal. This method is quite simpleand easily accompiished. The inputs to the gatesection from the input section and time-basesection are interchanged by a switch (see fig.105). This makes the unknown signal establishthe gate time for counting the frequency of thetime-base signal. By using a high-frequencytime-base signal. the counting units will registera large number of pulses during one period ofthe unknown signal. The period of theunknown signal. The period of the unknownsignal can be determined, since each pulsecounted represents a known amount of time.For example, let us assume a readout of100,000 when the time-base selector is set on10Asee (100-kHz time base signal). From thisreading, we know that 100,000 pulses werecounted. Since each pulse represents 10 gsec,the time interval is 100,000 x 10 gsec1,000,000 ± 10 Asee. This time is the periodof the unknown signal; thus, 1 ± 0.00001 Hz isthe unknown signal frequency. The accuracy ofthis measurement is 1 part in 100,000. or 0.001percent. By comparison, if the unknown signalfrequency is counted during the longer time-base period of 10 millisec, a readout of 00100is obtained and the accuracy is 1 part in 100, or1 percent. So we note a marked difference.Even greater accuracy can be achieved with theperiod measurement method in the low-frequency range if a 1-megahertz output isavilable from the time-base section. A I -MHzsignal will provide I -Asec counts and, for thecase cited, an accuracy of 0.00001 percent.

18-30. The ratio of two frequencies can bedetermined with a counter by letting the lowerfrequency establish the time interval (gate) andfeeding the higher frequency into the inputsection. The higher frequency is counted duringt.ne peroid of the lower frequency. This countis actually the ratio of the higher to the lower

ll 6

UNKNOWNINPUT

SIGNAL SECTION

COUNTINGINPUT

0-411610 GATESECTION

go TO DISPLAY

MEI AIM . ....;

LSTINE BASE

ECTION

GATE TIMECONTROL

Figure 103. Period counter arrangement.

frequency. For example, if a 40-Hz signal isused to establish the time gate and a 20-kHzsignal is counted, 500 hertz of the 20 kHz willbe counted and displayed. This readout, 500, isthe ratio 20 kHz/40 Hz.

18-31. Some counters are designed so thatthe time gate can be started by one signal andstopped by another. This capability is valuablefor certain types ,of measurements. Suchcounters are called time-interval meters..

18-32. As mentioned earlier, counters aremade to be very versatile. The usefulness of thisinstrument depends on your knowledge of thecounter's capabilities and an understanding ofthe matters which we have just discussed.

19. Signal Generators

19-1. Since signal generators comprise alarge and diverse group of tell equipment, wewill highlight their important features anddescribe them in a general manner. A signalgenerator usually consists of three majorsections: ( 1 ) a variable-frequency oscillatorwith a meter which indicates its output level.(2) a modulating circuit. and (3) an outputattenuator. The circuits are usually shielded toprevent the oscillator from radiating its signalto the equipment under test. When the switch isin the CW position. the output of the oscillatoris a continuous modulated wave.

19-2. The Oscillator.. In most signalgenerators. the oscillator is variable over aspecific frequency range. When the equipmentis designed for a special purpose, however, theoscillator may generate one or more specificfrequencies.

19-3. The oscillator is made as stable aspossible. As you know, stability is difficult to

' achieve when a VFO' is employed. For thisreason, some signal generators have a crystaloscillatoi which provides a standard reference

I 13

1110 TO RESET

frequency for the VFO. The VFO can becompared with the standard prior to using thetest equipment, and any deviations in frequencycan be corrected.. 19-4. An LC-type oscillator is generally usedto generate frequencies below 300 MHz. AHartley or modified Hartley oscillator circuit isvery popular. Above 300 MHz, a klystrom-typeoscillator is commonly, used because itprovides a highly stable UHF output. Bandswitches are used to place different componentsof various values into the oscillator circuit sothat the oscillator can operate over a widerange of frequencies.

19-5. The Modulator. Most signalgenerators have circuits to modulate theiroutput. AM or FM may be used, dependingupon the purpose for which the test equipment.is designed. Three types of AM are employed:sinusoidal, square wave, and pulse. Thesinusoidal type of modulation is most oftenused with the LC oscillators. Reflex klystronoscillators are modulated with a square wave tominimize incidental frequency modulation.Pulse modulation is frequently found in signalgenerators that produce simulated signals forvarious types of electronic equipment. WhenFM is used, the modulator varies the outputfrequency with a sine wave or with a linearsweep signal.

19-6. Output Attenuator. The outputattenuator is an important and useful part of asignal generator. When a signal generator doesnot have a calibrated attenuator, the strength ofthe output signal is *not known and theusefulness of the test equipment is limited.

19-7. The two types of attenuators commonlyused are the resistor and the waveguide. Bothare suitable for frequencies below 200 MHz,but the waveguide type is used almostexclusively above 200 MHz. The attenuator

/0 f

may be calibrated in one continuous range, butit is not uncommon for it to be calibratedseveral steps. To prevent stray raCiiation fromaffecting the calibrated output, the attenuatorshould be well shielded. The accuracy of theattenuator depends upon the requirements. Ahigh degree of accuracy is obtainable with awaveguide because its attenuation is determinedby its physical dimensions.

20. Calibration and Repair ofTest Equipment

20-1. The accuracy and performance of test

equipment in your shop can mean thedifference between a system that is functioningproperly and one that is just getting by and not

fulfilling its mission responsibility. As a

repairman, you will be responsible for theequipment assigned to your shop. Operatinginstructions are sometimes found on the frontcover of the test equipment; however, explicitinstructions are contained in the 1 series ofapplicable technical orders (T0s). To insurethat the system is operating at iis maximumcapability, it is mandatory that you be

thoroughly familiar with the operation of thetest equipment necessary to maintain the system

at its peak performance.20-2. There is a 1 technical order for each

piece of test equipment you have in the shop.To obtain the necessary TOs, check TO

0 1-33 (test equipment index) for a listing ofpublications applicable to the test equipment inyour inventory. The missing TOs should beordered through the channels established by

your organization.20-3. Categories of Test Equipment. For

maintenance purposes, test equipment is

divided into four categories. These are:

(1) Category I. Operational equipmentinstalled in systems. subsystems, or equipmentwhose performance parameters are to be

measured, verified, or tested.(2) Category II. Peculiar precision

measurement equipment used to check out.maintain, and calibrate Category I equipment.("Peculiar- is applied to precision measurementequipment designed for and used with only onesystem, subsystem, or equipment. as contrastedwith "common" items, which have general-purpose cross-system application).

(3) Category III. Common commerical andmilitary precision measurement equipment used

for maintenance, troubleshooting, testing,verification, and calibration of Category I andII, equipment.

(4) Category IV. Standards and accessories

used to calibrate Category II and IIIequipment. This equipment normaliy is located

I 14

in and used by the base Precision MeasurementEouipmeht Laboratory.

20-4. Responsibilities for Test Equipment.There are two organizations that have theprimary responsibilities for maintaining allequipment in Categories I and 11. These are (I)

the using organization of which you are a part

and (2) the bas.;s' Precision MeasurementEquipment Laboratory (PMEL). A:, part of theusing organization, you have the responsibilityfor the calibration of all Category I and IIequipment, with the following exceptions:

Base PMEL calibrates all general-purpose

and commercial Category 11 test equipment that

can be moved to the PMEL. This does notinclude test equipment that must be calibratedwhile it is in your bench equipment.

Maintenance of test equipment thatrequires special skills or special equipment(whether it be Category I or 11) that is availableonly at the PMEL is the responsiblity of the

base PMEL.

20-5. If you are in doubt as to whose area of

responsibility a particular piece of testequipment falls into, go to your technical order

file and look it up in TO 33K-1-100.R espo nsi bi lities and Calibration MeasurementAreas. This TO lists all test equipment in the

Air Force inventory, tells who is responsiblefor its calibration, lists any applicable TOcontaining the procedures for calibration, andlists the maximum number of days betweenrequired calibrations.

20-6. Calibration of Test Equipment. ThePMEL should automatically reschedule your

test equipment and call for it when calibrationis required. If you should determine that

calibration is required sooner than the

scheduled date, then you must contact PMELand have them reschedule that particular testset. When possible, regular calibrationrequirements must be reported by you to thePMEL to insure prompt compliance.

20-7. Test equipment that is an integral partof your equipment and cannot he removed, but

which requires special skills and equipment forcalibration. may be calibrated by the usingorganization with the assistancc of PMELpersonr.el.

20-8. You are a part of the lowest echelon in

the test equipment calibration ladder. Eachhigher step in the ladder has standards

available to be used in the calibration of testequipment. The standards of each next higherechelon can then be used to check the standards

of the lower echelons. At the top of this ladderis the National Bureau of Standards for

Electrical and Electronics Equipment. Boulder,

116

4s)

Colorado, And the National Bureau of Standardsfor Electromechanical and Dimensional Equiment,Washington, DC.

20-9. You may have standards in your shop;if so. these standards are called shop standards.A shop standard is defined as a precisionmeasurement equipment known to have beenofficially calibrated and certified fOr use as acomparison in checking other items in themaintenance shop. These standards are notused for routine maintenance functions unless

an emergency exists or all like items areinoperative.

20-10. It is extremely important that you bethoroughly familiar with your test equipment.Knowing how to use it effectively and care forit properly cannot be overemphasized. Properly.used, it will provide you with years ofdependable service. Know its capabilities, andit will aid you immeasurably in theperformance of your equipment maintenance.

20-11. At this time work the chapter reviewexercise for Chapter 5 in your workbook.

///

CHAPTER 6

Electron Tube end Semiconductor Testing

TO BE OF practical use in the field, a testermust provide a simple mcans to appraise thecondition of an electron tube orsemiconductor. A field-type tester is designedto simply indicate how the tube or device undertest compares with the manufacturer'sstandards. These standards are predeterminedparameters and ratings that have been obtainedby exacting laboratory methods. Although thefield-type tester does not tell you that a tube ordevice necessarily functions as it should in aparticular circuit, it does provide 'a quick wayof finding a substandard tube orsemiconductor. In this chapter, we discuss thecircuits used in testers and the indications ofvarious tests. So that you can better evaluate thereadings obtained from field-type testers, wealso point out some limitations of theseinstruments.

21. Electron Tube Testing21-1. There are two different types of tube

testers commonly used in the field. Thesetesters, which are distinguished by the maintube characteristic they check, are known as the,emission tester and the transconductance tester.Field-type tube testers may also be capable ofperforming short circuit, noise, gas, 6athodeleakage, and filament activity tests.

21-2. Emmission Testers. The emission-type tube tester indicates the condition of thecathode emitting surface. Usually, the end ofthe useful life of a tube is preceded by areduction in emissivity; that is, the cathodebecomes unable to supply the number ofelectrons necessary for proper tube operation.Also, if the tube has an open element, the defectprevents proper emission, and the testerindicates it as a weak or bad tube.

21-3. The emission-type tester has severaldisadvantages. Since the manufacturer of a tubedoes not state a definite 100-percent emissionpoint which could be used for reference, theemission test is not conclusive. High emissiondoes not necessarily indicate a good tube,because this condition might be present in a

tube with a faulty grid structure or in one whichhas a highly emissive spot on its cathode; veryhigh emission has also been observed justbefore a tube fails completely. Furthermore.low emission does not necessarily indicate inall cases that a tube is near its end-of-life point.Another disadvantage of the emission test isthat gas may be liberated within the tube whenAC test voltages are applied, unless the test ismade quickly. Also, because the tube is notoperated with its recommended DC electrodevoltages in this test, it is not tested under actualoperating conditions. Sometimes a tube willshow normal emission and yet not operateproperly. The reason for this is that theefficiency of a grid-controlled tube depends onthe ability of the grid voltage to control theplate currect. The emission-type tester checksonly the plate current developed and not theability of the grid to control the plate current.

21-4. To %.heck the emission of a grid-controlled tube (triode or multigrid types). thetube is 'connected as a half-wave rectifier, asshown in figure 106. The rated filan.ent poweris furnished by the tester. The plate and grids ofthe tube are connected. DC milliammeter MIand variable resistor RI are connected in serieswith the tube, and the entire circuit isconnected in series with the tube. and the entirecircuit is connected across a secondary of

Figure lOh. Emission test circuit.

Itov110 CPS

ara-)

traiwormer TI. Since the plate and grids areconnected, the tube functions as a dioderectifier. conducting current only on thealternate half cycles when the plate and gridsare positive with respect to the cathode. Theanmunt of current that flows is an indication otthe condition St. the cathode emitting surface.On emission-type tube testers. the milliammeterscale is usually divided into three 'areas whichare labeled good, weak and bad, or othersimilar designations. Thus. when using anemission-type tube tester. you will notdetermine the actual current flow through thetube. hut only the general condition of the tube.

21-5. The emission test for diode detectorand rectifier tubes and the diode portion ofmultisection tubes is similar to the emission testfor grid-controlled tubes. The rated filamentpower is furnished by the tester, and an AC testsig.tal is applied to the diode when switch SI isclosed. The amplitude of the test signal may bevaried by the tapped secondary of transformerT1. and current through the tube can also beregulated by variable resistor RI. The amountof current flowing through the test circuit ismeasured by meter MI. The value of thiscurrent depends on the electron emissionwithin the tube, and therefore. is an indicationof the condition of the tube.

21-6. *Transconductance Testers. Thetransconductance type of tester provides a moreaccurate evaluation of the condition of a grid-controlled tube than the emission-type testersbecause it measures the amplification ability ofthe tube under simulated circuit conditions.The transconductance is measured and thencompared with the ratings of the tubemanufacturer. The meter scale of this type oftube tester may be cafibrated to read thetransconductance (Gm) in micromhos. Oftenthe scale is divided into sections that '..,licatewhether the tube is good, weak, or cad. Avoltage or power- amplifier tube is considereddefective when its transconductance decreasesto 70 percent of the value stated in standardtube tables; the oscillator section of a convertertub.; is considered defective when itstransconductance decreases to 60 percent oftable values.

21-7. As you know. the term"transconductance (also called mutualconductance) indicates the effect of the controlgrid voltage upon the plate circuit of a tube.This characteristic is expressed mathematicallyas the ratio of a change in plate current to asmall change in control grid voltage, with allothei electrode voltages held constant. Theequ,ition for transconductance is:

Gm IPEg

I 17

where Om is the transconductance inmicromhos. i lp is the change in plate currentin microamperes. and Eg is the change incontrol grid voltage. When the control gridvoltage changes I volt, the current change inmicroamperes is equll to the transconductancein microhms. Thus,,if a I-volt change in controlgrid voltage produces a 200-microamperechange in plate 'current, the tube has atransconductance of 200 micromhos. Thetransconductance of a tube may be measured bytwo methods: one is the static (DC) method andthe other is the dynamic (AC) method.

21-8. Static method. In the static (alsocalled the grid shift) method of measurinztransconductance, the DC bias voltage on thecontrol grid of the tube under test is changed.and the resultant change in the steady platecurrent is measured with a DC milliammeter.The simplified circuit for this test is shown infigure 107. Filament voltage is furnished to thetube under test by the tube tester. When switchSI is set at position I , a negative bias voltage isapplied to the control grid of the tube and theresultant plate current is measured by meterMI. Switch SI is then set at position 2; thecontrol grid bias becomes less negative and theplate current increases in value. r' esistor R3 isadjusted so that current through the test circui,produces a known voltage drop across resistorR2. The transconductance can then bedetermined by the change of plate currentdivided by the voltage drop across resistor R2.To simplify testing. the meter scale can bedivided into good, weak, and bad sections inthe same manner as on many emission-type.testers. When this type of circuit is used to testvarious types of tubes, .he voltages applied tothe electrodes must be made adjustable so thatthe correct operating conditions for aparticular tube may by obtained.

21-9. Dynamic method. The dynamicmethod of determining transconductancemakes use of a circuit which applies an AC test

TUSEUNDO TEST

Figure 107. Transconductance static test circuit.

12i

//A

TYPEUNDERTEST

r".

VI I

UI

.=11 I I

TI

120v40 Me

Figure 108. Transconductance dynamic test circuit.

signal and a DC bias voltage to the control gridof the tube under test. A simplified circuit forthis test is shown in figure 108. The tube undertest serves as the load for rectifier VI. With afixed value of bias voltage (Eg) applied to thecontrol grid of the tube under test, the circuitoperates as a simple full-wave rectifier. On thehalf cycle of the AC voltage, when plate 1 ofrectifier V1 is positive, there is current flowthrough resistor RI, and the force exerted onthe pointer of meter MI attempts to deflect thepointer in one direction. When plate 2 ofrectifier VI becomes positive, current flowsthrough resistor R2, and the force exerted onthe pointer of meter M 1 is equal and oppositeto thc previous force. Since these alternationscccur at a relatively rapid rate (60 times asecond), the resultant force exerted on themeter pointer is zero; consequently, the meterpointer remains stationary in the ZEROposition if there is a fixed DC bias.

21-10. In addition to the fixed DC biasvoltage, an AC voltage from the secondary oftransformer T1 is applied to the control grid ofthe tube under test. When this AC voltambecomes negative at the same time that plate 1of VI is positive, the plate current of the tubeunder test decreases for this half cycle. Thiscurrent flows through resistor R 1 , decreasingthe deflecting force on the meter pointer in onedirection. When the AC voltage applied to thecontrol grid becomes positive, this voltageincreases the plate current of the tube undertest. During this half cycle, plate 1 of VI ispositive and the current through R2 increases.As a result, the deflecting force on the meterpointer during this half cycle exceeds the forceexerted during the previous half cycle. Hulce,the meter deflection is undirectional and isproportional to the difference of the currents inRI and R2 resulting from the application of the

118

AC voltage to the grid of the tube under test.Therfore, the meter indicates the: change inplate current produced by a change in gridvoltage under dynamic conditions. The metercan be calibrated in micromhos, or the meterscale can be divided into sections to indicategood, weak, or bad. Any pronounced deviationfrom the rated, or normal, transconductancefor a specific tube indicates a defertivP tube.

21-11. Additional Test Circuits. Besidestesting emission or transconductance, there areseveral other useful tests that can be made.

21-12. Short-circuit and noise test. It is veryimportant that you apply the test for short-circuited elements to a tube of doubtful qualitybefore any other tests are made. This procedureprotects the meter (or any other indicator) fromdamage. Also, it follows logically that if a tubeunder test has elements which are short-circuited, there is no further need to applyadditional tests to that tube. 3hort-circuit testsusually indicate leakage resistance less thanabout 1/4 megohm. The proper heater voltageis applied so that any tube elements whichmight short as a result of the heating processwill be detected. The short-circuit test is similarto the test used to detect noisy (microphonic)or loose elements. Since the only differencebetween the two tests is in the sensitivity of thedevice used as an indicator, the noise test willbe discussed as part of the short-circuit test.

21-13. Figure 109 shows a basic circuit usedfor detecting shorted elements within a tube.With the plate circuit switch set at position 2, asshown, the plate of the tube under test isconnected to the leg of the transformersecondary containing the neon lamp. All otherelements are connected through switches to theother leg of the secondary. If the plate elementis shorted to any other element of the tube, thetransformer secondary circuit is completed; as aresult, both plates of the neon lamp glow sinceAC is applied to the lamp. If no short exists, noindication will be present (or only one plate ofthe neon lamp will glow because of rectification

TulEUNOE0TEST

321:==MIM

MSSTEST

Figure 109 Short circuit and noise test circuit.

122

hy the tube), Each ot the other elements istested hy means 01 the switching arrangementshow n. Resistor R2 limits the curren«hroughthe neon lamp to a sate value. Resistor R Ihypasses any small alternating currents in thecircuit which might he caused by straycapacitance and thus prevents the neon lampfrom indicating erroneously. Tapping the tubelightly is recommended to detect looseelements which might touch when the tube isvibrated.

21-14. The noise test is.. in effect. nothingmore than a very sensitive short-circuit test. Infigure 109, two leads are taken from the neonlamp (one lead from each side) and brought toexternal receptacles which are labeled noisetest. An external amplifier and a speaker (notincluded with the equipment) are connected tothese receptacles. Perhaps the handiestamplifier for this test is an ordinary radioreceiser. The antenna and ground terminals ofthe receiver are connected to the noise-testjacks. and a normal short-circuit test is madewhile you are tapping the tube. If tube elementsarc loose (hut perhaps not loose enough toindicate on the neon lamp), loud crashes ofnoise (or static) will be heard from the receiverover and above the amount of noise that isnormally present. The noise test may also bemade without-the use of the high-gain amplifier,merely by inserting the leads from a pair ofheadphones into the noise-test receptacles. Thelatter check. of course, is not as sensitive as thetest made with the amplifier but is generallymore sensitive than the short-circuit test madewith thc neon lamp as an indicator.

21-15. Gas test. In all vacuum-type electrontubes, the presence of gas is undesirable. Whengas is present. the electrons emitted by thecathode collide with the molecules of gas.These collisions cause electrons to be dislodgedfrom the gas molecules. and positive gas ionsare formed. These ions are attracted by (andcluster around) the negatively biased tontrol

Figure 110. Gas test circuit.

119

grid of the tube. If the amount of gas in the tubeis appreciable, the resulting flow of grid currentis noticeably high. The basic circuit used for thegas test is shown in figure 110. With switch S

set to position I. a certain value of platecurrent is measured by the DC milliammeter. Ifthere is no gas (or a negligible amount) presentin the tube, throwing switch S to position. 2does not change (he plate current reading. Ifgas is present, current flows through the gridresistor (large value), causing a voltage dropwith the polarity as shown. The net effect is toreduce the negative bias voltage on the grid ofthe tube. resulting in an increase- of platecurrent. Small plate current increases arenormal; large increases indicate excessive gas.

21-16. Cathode leakage test. When a tubewhich uses an indirectly heated cathodedevelops noise, it is likely that a leakage path ispresent between the cathode sleeve and theheater wire. This is true because in the design ofa tube the heater must be placed as close as

,possible to the cathode so that maximum tubeefficiency is attained. Continual heating andcooling of the tube structure may cause smallamounts of the insulation between the cathodeand heater to become brittle or to deteriorate,leaving a high-resistance leakage path betweenthese elements. Under extreme conditions, theinsulation may shift enough to allow actualcontact of the elements. Since the heater andcathode are seldom at the same potential, anyform of leakage causes noise to develop in thetube. The cathode is normally maintained at ahigher positive potential, because cathode biasis the most common type of bias used. Theheater circuit is usually grounded to the chassis,either on one side of the filament supply or by acentertap arrangement. Therefore, if a

resistance path is present, a leakage currentmay flow from the heater to the cathode. Thus,the cathode receives electrons. Assuming theexistence of high-resistance leakage, the currentflow from the heater to the cathode will varywith any vibration of the tube, becausevibration will vary the amount of resistance. Ifthe cathode and heater are completely shorted(zero ohms), it is impossible for the tube todevelop any cathode bias.

21-17. Figure 111 shows a basic circuitwhich is used to detect leakage between theheater and cathode elements of a rabe. Withswitch S set to position 2, a certain value ofplate current flows. When switch S is thrown toposition 1, the cathode becomes a floatingelement; if no leakage path is present, the platecurrent should fall to zero. If the elements arecompletely shorted, the plate c irrent readingremains the same as the initial reading (switch S

123

l/5"-

10

Figure 111. Cathode leakage test circuit.

in position 2): if they are only partially shorted,a plate current less than normal but greaterthan zero is indicated.

21-18. Filament activity test. The filamentactivity test is used to determine theapproximate remaining life of an electron tubeinsofar as the longevity of the cathode emitter isconcerned. The test is based on the principlethat the cathode in almost all electron tubes isso constructed that a decrease of 10 percent ofthe rated filament or heater voltage causes noappreciable decrease in emission.

21-19. On tube testing equipmentincorporating this test, there is a two-positionswitch (filament activity test), which has oneposition marked NORMAL and the othermarked TEST. The switch remains in theNORMAL position for all the tests other thanthe filament activity test. When the switch is setto the TEST position, the filament (or heater)voltage applied to the tube under test is reducedby 10 percent.

21-20. The filament activity test isperformed as follows: After the quality test ismade, the TUBE TEST button is helddepressed, and the FILAMENT ACTIVITYTEST switch is set to the TEST position. If theindicator shows a decreased reading after areasonable time is allowed for the cathode tocool, the useful life of the tube is nearing itsend.

21-21. A PRECAUTION: Before the tube tobe tested is inserted in the correct test socket,be certain all front panel controls are set to thepositions listed for that type of tube in the datachart furnished with the tester. This precautionis necessary to prevent excessive voltages frombeing applied to the tube elements (especiallythe filament).

22. Semiconductor Testing22-1. Since semiconductor devices are

extensively used in electronic equipments, it is

120

important to know how these devices can betested. We will cover the checks that indicatethe condition and quality of crystal diodes andtransistors in this section. Circuits with whichthese checks can be made are also presented tofurther your understanding of semiconductortesting.

22-2. Diode Testers. General-purposegermanium and silicon diodes can be checkedwith a static-type tester or a dynamic-typetester. Zener diodes are tested to determinehow well and at what voltage they regulate.

22-3. Static diode tester. A common type ofcrystal diode tester is a combination ohmmeter-ammeter. Measurements of forward resistance,reverse resistance, and reverse current may bemade with this instrument. The condition of thecrystal rectifier under test can then bedetermined by comparison with typical valuesobtained from test information furnished withthe tester or from the manufacturer's datasheets. The simplified circuit of a crystal diodetester is shown in figure 112. A check whichprovides a rough indication of the rectifyingproperty of a diode is the ratio of the diode'sreverse and forward resistance at a specifiedvoltage.

22-4. Dynamic diode tester. To effectivelytest crystal diodes used for some specialapplications, it is necessary to obtain reverseresistance measurements for a large number ofdifferent voltage levels. This can be doneefficiently by using a dynamic diode tester inconjunction with a cathode-ray oscilloscope todisplay the diode reverse-current-versus-voltage curve.

22-5. A simplified circuit of a diode dynamictester is shown in figure 113. The test voltagefrom the input transformer is applied acrossresistor R4 and the parallel combination ofresistor R5 and rectifier CR1. Crystal diodeCR1 rectifies the voltage developed acrossresistor R5, and the resultant half-wave

DIODEUNDERTEST

Rt R2

Figure 112. Semiconductor diode reverse-to-forwardresistance test circuit.

1 24

20v60 4%

R7EF

RESISTOR

I 0100EUNDERTESTLL--J

Figure 113. Semiconductor diode dynamic test circuit.

rectified voltage is applied to the horizontalinput of an external oscilloscope. The amountof horizontal sweep of the associatedoscilloscope is. therefore, proportional to theinput voltage which is applied to the diodeunder test and the reference resistor.

22-6. The input test voltage is appliedthrough resistor R3 to the moving arm ofselector switch S3. With switch S3 in the REFposition, a test current flows through internalreference resistor R7 and current measuringresistor R6. The internal reference resistor canbe adjusted to equal the value of the minimumacceptable reverse resistance of the diode undertest. A value of 500K may be typical for a newdiode, and a value of 250K may be acceptablefof the same type diode which has been in use.The signal developed across resistor R6 isapplied to the vertical input of the externaloscilloscope. Thus, the voltage drop acrossresistor R6 produces a vertical deflection of theoscilloscope trace which is proportional to thecurrent through the test circuit. The action ofcrystal rectifier CR 3 causes thi> signal to beapplied to the oscilloscope only during thesame hal4 cycle that the horizontal sweepvoltage is applied. As a result, during eachactive half cycle, a diagonal straight line isdisplayed on the oscilloscope, as shown infigure I I 4.A. This pattern is the reference traceto which the characteristic curve of the diodeunder test can be compared.

22.7. When selector switch S3 is turned toihe DIODE position, current flows throughresistor R6. In this case, the voltage applied tothe oscilloscope horizontal input remains the

121

OSCILLOSCOPE0 NORIZONTAL

INPUT

_OSCILLOSCOPEvERTICAL

INPUT

same, but the vertical input indicatesinstantaneous values of the reverse current inthe test diode. This 'results in a curved line traceon the oscillok-Ope, as shown in fugure 114,B.This is the dynamic characteristic curve ofreverse current versus voltage for the diodeunder test. When selector switch S3 is in theDIODE position and AUTO switch S2 isclosed, the test current is applied alternately tothe diode under test and to the referenceresistor. This gives a display of both tracessimultaneously on the oscilloscope. Theswitching operation is accomplished by relayK1. Voltage applied to this relay throughswitch S2 is rectified by CR2. Current flowingthrough the relay is controlled by resistor R2,which is adjusted so that the relay armature willvibrate and produce a minimum amount ofjoining of the, diode and reference resistortraces. The vibration of the relay is rapidenough to create the illusion of a simultaneousdisplay of the diode and reference resistor testcurrent patterns on the associated oscilloscope(see fig. I14,C).

22-8. Trace 'calibration is done by closingSI. The input signal is rectified and the

A 8

Figure 111. Semiconductor diode linearity test.

12-,3

//7--

Figure I IS. Zener diode I versus E test circuits.

pulsating direct current indiates the signal levelon the DC microammeter. Adjustment ofresistor RI permits calibration of the meter toread the voltage developed across thesecondary winding of transformer T2.

22-9. Regulator diode tests. Zener(avalanche) diodes, which are used for voltage-regulating applications, may be checked by theuse of a dynamic tester in conjunction with anoscilloscope. This tester develops signals todisplay the diode reverse-current-versus-voltage curve on the associated oscilloscope,for determination of the diode's Zener voltage,dynamic impedance, and noise characteristic.

22-10. In figure 115, we show a simplecircuit that can be used to obtain a dynamiccharacteristic curve of a Zener diode. TheAC input is adjusted until the display shows thebreakdown operation as illustrated on thescope screen of figure 115. The crystal diodeblocks the negative alternation Of the input,thereby preventing forward conduction of theZener diode; thus, the trace shows only reversecurrent versus voltage. Note that the reverse-current signal is developed across the 1-ohmresistor and is applied to the vertical inputterminals of the scope; the voltage across theZener is applied to the horizontal inputterminals of the scope. This makes the verticalaxis of the scope represent current, and thehorizontal axis represent voltage. If the axes are

122

calibrated, the Zener breakdown voltage, Vz,and dynamic impedance, Zz, can bedetermined.

22-11. When you wish just to check theoperating voltage of the Zener diode, thecircuit shown in figure 116 can be used. Adjustthe variable resistor to obtain the value of

4 DC

Figure 116. Zener voltage test circuit

trto

operating current specified for the Zener diodeunder test. If the Zener diode is good, thereading on the DC voltmeter will e0oftsrmclosely to the rated operating voltage. Forexample. a 15-volt Zener diode under testshould cause the voltmeter to indicate near 15volts. The acceptable tolerance, of course,depends upon the application and is somethingyou must know.

22-12. Transistor Testers. We will discusstransistor tests that are of practical value to amaintenance repairman. The basic circuits areillustrated so that you can understand the testfor ( I ) collector leakage current, (2) punch-through voltage, (3) direct-current gain, and (4)hybrid parameters.

22-13. Collector leakage current test. As youknow, the amount of collector leakage currentis normally a very small value (about 10microanips or less). The collector leakagecurrent will be appreciable, however, when thetransistor is contaminated, internally shorted,or damaged by overheating. A measurement ofcollector leakage current can, therefore,indicalP the condition of a transistor.

22-14. Figure 117 shows the method ofdetermining collector leakage current. Whenthc transistor is connected as illustrated, theamount of collector-to-base leakage current.leo. can be read directly on the DCtnicroammeter. The reading should checkclosely with the manufacturer's value of leo atthe specified collector-to-base voltage, Vcb.This current is also referred to as collectorcutoff current or reverse current.

22-15. Punch-through voltage test. Thepunch-through voltage (Vpt) is that Vcb atwhich the collector-base barrier region haswidened sufficiently to contact the base-emitterbarrier region. This effectively eliminates thebase region; therefore, transistor action isstopped and collector-to-emitter resistance isgreatly reduced. The punch-through voltagecan be applied without damaging the transistorif the collector current is limited to prevent

ADJUSTABLEDC VOLTS

1.tgurc.117. Collector leakage current teSt circuit.

123

ADJUSTABLEREGULATEDDC VOLTS

Figure 118. Punch-through test circuit.

over-heating. When the collector-to-basevoltage is lowered below the punch-throughvalue, normal transistor action will resume.

22-16. The value of punch-through voltageis generally specified only for switching-typetransistors. A circuit that can be used to checkthe Vpt of a transistor is shown in figure 118.The transistor is biased to its typical operatingvalues; then the collector voltage is increaseduntil voltmeter V2 shows a sudden increase.Thisincrease is caused by the increased currentflow through RE when punch-through occurs.The reading of VI is the punch-through voltageof the transistor under test.

22-17. Direct-current gain test. The ratio ofthe output direct curent to the input directcurrent indicates the direct-current gain of atransistor. This parameter is useful ?when atraniistor is used in a low-frequency poweramplifier, switching control, and logic circuits.If the direct-current gain decreases with age,the reduced amplification can producedistortion and changes in impedance whichcause mismatching.

22-18. Direct-current gain is commonl)specified for the CE configuration and isdesignated p or hie. This parameter, p, is equalto the direct-currant ratio [Sib. A method ofdetermining this. ratio for PNP transistors isshown in figure 119. After adjusting for properbiases, the milliammeters are read to obtain thevalues of lc and lb. NPN transistors can betested simply by reversing the polarity of the

127

//9

Figure 119. Direct-current gMn test circuit.

bias supplies and reversing the meterconnections.

22-19. Another test circuit uses a nulldetector as shown in figure 120. This circuit isbiased for an NPN transistor. Biases must beadjusted to the specified values for thetransistor under test. The differences of thevoltages V1 and V2 are indicated on the nulldetector. By adjusting the potentiometer,voltage VI is made equal to V2, and the nullindicator reads zero. Hence,

le V2/R2 RIlb VI/RI R2

when VI V2

22-20. Note that there is linear relationbetween current gain and RI since R2 is fixedvaiue. It is, theretore, possible to calculate adial on the potentiometer to read p directly:The maximum p that can be measured will, ofcourse, be the maximum ration R I/R2obtainable with the tester

ADJUSTABL EDC VOL TS

Figure 120. Null detector direct-current gain test circuit.

124

22-21. When testing for direct-current gain.you should disconnect the transistor, from itscircuit. Any associated circuit that shunts thetransistor will introduce error.

22-22. Hybrid parameter tests. When atransistor is considered to be four-terminalnetwork (see fig. 121), various relationsbetween input and output voltages and currentscan be defined in terms of AC parameters.These are known as small-signal parametersthat indicate the performance capabilities andcharacteristics of a transistor.

22-23. Most manufacturers' transistor datasheets specify hybrid (h) parameters; hi is theinput impedance in ohms with the outputshorted (fig I 22,A); hr is the reverse voltagegain, or ratio of VI to V2, with the input open

Ii $2

INPUT OUTPUTTERMINALS 611 I I 2 T MURAL S

Figure 121. Four-terminal network.

circuited (fig. 122,B); hr is the forward currentgain, or ratio of i2 to i 1 , with, the outputshorted (fig. 122,C); and ho is the outputadmittance in mhos with the input opencircuited (fig. 122,D). To indicate whether theparameter is for the common base, commonemitter, or common collector transistor circuit,an additional subscript (b, e, or c) is added tothe h parameter. For example, the commonbase forward current gain, which is the same asa , is designated hfb; and the common emitterforward current gain, which is the same as /3. isdesignated hk.

22-24. Since we know that a and is arerelated by the following equations,

ce P--- and /3I I

it follows that

hf b hfe htband hfe1 + hie hfb

/2.0

Lif';3)-

1*ri lemem .*

I'llatell100111

0". lVWNI.S

1.2

Figure 122. Hybrid parameter equivalent circuits.

Thus, regardless of how current gain of atransistor is specified, you can determine itsgain capability. Values of hfb usually rangefrom 0.95 to 0.99; values of hfe range fromabout 20 to 100. Hybrid parameters aregenerally specified as shown in figure 123.

22-25. A basic transistor test set formeasuring h parameters is shown in figure 124.A single AC meter, M, calibrated to read

voltage and current values, is used inconjunction with calibrated voltage source. 02.and current signal source. 01, to determine thefour hybrid parameters of a common basetransistor configuration. The magnitude of theoutput from the voltage and current signalsources is controlled by range switches, whichare not shown in this basic circuit diagram. Theparameter to be measured is chosen by a singleselector (four ganged switches), which alsoconnects the proper bias. Since the emitter biassupply has an internal dynamic resistance ofapproximately 10 megohms, it may beconsidered an open circuit for AC.

22-26. Let us consider each position of theselector td see how each parameter isdetermined.

o. Position I. The calibrated voltagegenerator, 02, applies e2 to the collector, andthe meter reads the 'circuit current 12 (theresistor RI develops the signal that is measuredby the meter M). Since the emitter is open-circuited for AC, the value of hub is the ratioe2/12.

b. Position 2. Note that meter M is nowconnected between the emitter and ground and,therefore, reads the voltage el . The calibratedgenerator 02 applies e2 to the collector. Theratio el/e2 is the value of hrb.

c. Position 3. The calibrated currentgenerator, GI, is connected to the emitter. Thismeans the value of il is known. The meter Mnow reads the input voltage el. Because theoutput circuit is virtually short-circuited (R2 isa small resistor), the value of h, is the ratio ofil/e I.

d. Position 4. The cnlibrated currentgenerator is connected to the emitter; thus il isknown. The metm- NA in conjunction with shunt

PARAMETER MINIMUMVALUEDESIGN

CENTER

.

MAXIMUM DIMENSION

hob 0.1 0.11 1.3 A4, mhos

ht. (1) 30 42 66 non

htb 25 29 33 ohms

0.1 X 10-3 0.3 X 10-3 1.3 X 10-3 non

Figure 123. Example of hybrid parameter values.

125

12J

/2/

St LecToePOUTIOM P411414E224

kb2 I%

3 hils

- 4 1

,

hob

Figure 124. Hybrid parameter test circuit.

R2 reads the collector current, which is i2. Theratio 12/0 gives us the value of hfb.

22-27. The tester we have just discussed is,of' course, a very simple one. Transistor testersfor general use in the field are more complexsince they are designed for both in-circuit andout-of-circuit testing. Moreover, they provide

US. GOVERNMENT PRINTING OFFICE: MS-441420/ 67

AUGAFS, ALA (760240) MOO

for short-circuit tests, bias selection, betameasurement, and collector reverse-currenttests. In other words, a practical transisiortester generally incorporates all circuits that wehave discussed separately, plus other testingfeatures.

22-28. At this time, work the Chapter reviewexercises 'for Chapter 6 in yc Jr workbook.

126 1 3

/ 2Z

30455 01A 22WORKBOOK

SUPERVISION,. [RAINING, AND MAINTENANCE TECIINIQUES

C:.41_ 641tVACAINGCRE

SRG

This workbook places the materials you need where you need thcm while youarc stud)ing. In it. ou will find the Study Reference ,Guide, the Chapter Reviewlivereiscs and their answers. and the Volume Review Exercise. You can easilycompare textual references with chapter exercise it6ms without flipping panshack and forth in your text. You will not misplace any one of these essentialstudy materials. You, will have a single reference pamphlet in the proper sequencefor learning.

These devices in your workbook arc autoinstructional aids. They take theplaee of the teacher who would be directing your progress if you were in aclassroom. The workbook puts these self-teacheri into one booklet. If you willfollow thc study plan given in -Your Key to Carcer Development," which is-in your course packet.- you will be leading yourself by easily learned steps tomdstery of your text.

If you have any questions which you cannot answer by referring to "YourKey to Career Development" or your course material, use ECI Form 17, "StudentRequest for Assistance." identify yourself and your inquiry fully and send it toEC I.

Keep the rest of this workbook in. your files. Do not return anY other partof it to EC.

EXTENSION COURSE INSTITUTE

Air University

131

TABLE OF CONTENTS

Study Reference Guide

Chapter Review Exercises

Answers for Chapter Review Exercises

Volume Review Exercise

ECI Form No. 17

132,

STUDY REFERENCE GUIDE

1 11,e tlav Guide as a Study Aid. It emphasizes all important study areas of this volume. Usethe Guide for review before you take the closed-hook Course Examination.

2. the Guide for Foihnv-up after you complete the Course Examination. The CE resultsw It he sent to on on a postcard. w hich will indicate -Satisfactory" or "Unsatisfactory- comple-tion, '1 he card w ill li.st Numbers relating to the items missed. Locate these numbers in theGuide and draw a line under the Guide Number. topic. and reference. Review these areas toinsure onr mastery of the course.

GuideVuuther

Guide .Vunthen thhuigh 024001 Supervision and Training; Supervision: pages

1.5

002 'Ft:lining: pages 5.9

ou t Safely; On-Duty Safety: pages 10.15

004 I :rst Aid: pages 15-20

005 Otf-Duty Safety: pages 20-21

Maintenance Principles; PreventiveMaintenance; pages 22-24

Otr Corrective Maintenance: paies 24-32

(10s Repair of Printed Circuits and TransistorReplacement; pages 33.38

o09 Cable Maintenance: pages 3840

010 Maintenance Management; pages 4046

011 Technical Order System: pages 46-50

012 Oscilloscopes and Test Accessories:Functitinal Analysis of Oscilloscopes:Cathode-Ray Tuhe --Vertical and HorizontalAmplifiers: pages 51-56

GuideNumber

013 Functional Analysis of Oscilloscopes: SweepGeneratorsExpanded Sweep; pages 56-62

014 Oscilloscope Controls and OperatingConsiderations: ControlsFrequency; pages62-67

015 Oscilloscope Controls and OperatingConsiderations: SynchronizingMalfunctions; pages 67-73

016 A Typical Oscilloscope: Sweep Generationand SynchronizationA Sweep; pages 73-80

017 A Typical Oscilloscope: B SweepIndicatorControls: pages 80-91

018 Probes; pages 91.98

019 Power and Frequency Test Equipment;Power Measuring Instruments; pages 99-103

020 Frequency Test Instruments; pages 103-107

021 Frequency Counters: pages 107.113

0" Signal Generators; pages 113.115

023 Electron Tube and Semiconductor Testing;Electron Tube Testing: pages 116-120

024 Semiconductor Testing; pages 120-126

1.33

12C

CHAPTER REVIEW EXERCISES

The following exercises are study aids. Write your answers in petwil in the space provided after caeh

exercise. Immediately after completing each set of exercises, check your responses against the answers for

that set. Do not submit your answers to ECI for grading.

CHAPTER I

Objective; To demonstrate a knowledge of supervision principles and the types of training programs

available to the airman, whether formal, informal. correspondence, on base, or off base.

1. What is a supervisor? (1-2)

2. With the assignment of responsibility, what else is due to the supervisor? (1 -4)

3. Where does a supervisor's primary responsibility lie? (1-(,)

4. How demanding are the responsibilities of a supervisor to himself? ( 1 -9)

S. In solving an employee relations problem, what steps should you use? 41-12)

6. Must all workers be told how, when, and what to do in work assignment? ( I-14-16)

7. Give two reasons for a thorough examination of a completed repair job on a piece of equipment. ( 1- I 8)

8. How can you measure a worker or group of workers as to performance? (1-22.23)

9. Why is the performance report so important? (1-25)

10. You have successfully arrived at the 7 level in your chosen career field. How can you quality foi the

9 level (superintendent)? (2-5)

1 3

I I . What is lateral training? (2.6)

I 2. Formal airman courses are identified by the AFSC, by title, and by letter prefixes and suffixes, asneeded. What does the first letter in the prefix tell you? (2-8)

1 ;. What are the two divisions of on-the-job training? (2-10)

14. What is the nieannig of the term "career development"? (2-11)

15. In which phase uf the Dual-Channel Concept would you make the greatest progress in perfecting theskilk in your chosen field? (2-12,13)

I o. What must you do in order to receive the award uf the 5 or 7 skill level of yuur AFSC? (2-15)

17. Why is the AF Form 623. Consolidated Training Record, so important to the airman? (2-21)

Is. What trainine publication lists the knowledge required of a person on a certain job task? (2-25)

19. In what three ways is the Field Training Program conducted? (2-10)

20. Suppose that the Air Force has a surplus of airmen qualified in a certain AFSC. What is its must likelyontrse of action? (2-34)

CHAPTER 2

_

i(hiItve to demonstrate a knowledge of the principles and objeCtives uf ground safety applicable to thecommunications-electronics repairulinfs jub.

I. What is the objective of safety education? (Intro.-1-4)

3

135

can a start be made MI good house:xt:;!::ty! 3.21

3. How does a clutteied workbench affect yout work? (3.4)

4. What is the bask ingredient of all accidents? (3-10)

S. While accidents involving Air Force people and Property can be described iwterms of money costs. what

is the most dangerons effect they can have? 13-16).

6. What must you have before an organized accident prevention effort can be successful? (3.18)

7. What is the best method for the prevention of tires? (3-20,21)

8.. Which type of fire extinguisher would you use to extinguish a gasoline fire? 1324: Fig 2)

9. How can you know thSt you are in an area contaminated by radioactivity? (3-27)

10. What kind of accidents should be reported? (3-29)

11. You don't live many years before you meet two types of common emergencies. What are they? (4.2)

12. What are the three life-saver steps in the treatment of a serious cut or wound? (4-4)

13. Name three ways to stop bleeding. (4-5-8)

14. What should you always treat an accident victim lot , whether or not he has the symptoms? (4-I

1364

7 21

5:715)

/1I 5. What are the sytnptoms of shock? (4-12)

16. What is arttficial respiration? (4-15)

.17. Although there are four methods of artificial respiration, why is the mouth-to-mouth method the mosteffective? (4-18)

18. What are the seven steps for administering mouth-to-mouth artificial respiration? (4-20)

19. What are the indications that the victim is responding to artificial respiration? (4-24)

.20. What can you do to reduce the off-base, off-duty, privately owned vehicle accident rate? (5-5)

21. What good authority is available on sports safety? (5-8)

22. Why is life in the barracks subject to accidental injuries and deaths? (5-9-11)

23. List the safety items that every hobby shop user should be familiar with. (5-13)

CHAPTER 3

Objective: To demonstrate a knowledge of maintenance principles, printed card repair, man-hour reporting,matittenance data collection system, organizational structure, Chief of Maintenance functions, productimprovement program, and the scope and application of technical order systems.

I. During what type of maintenance procedures are you likely to detect circuits which are in marginalcondition? (6-2)

2. What would you look for when making a visual inspection of resistors and capacitors? (6-5)

5 13"

3. NVhat is the piimary consideration when using solv:nti'' 16 9 )

4. What is the purpose of climatic deterioration prevention? (6-12)

5. In what TM can you find resistance measurements? (7-7)

6. What is the first precaution you must observe before making a resistance check?17-7)

7. Name some uses of SWR measurements? (7-16)

8. In what direction are the bottoms of tube sockets counted? (7-23)

9. Where would you find the normal voltage and resistance values at the pins of connectors and tube

sockets? (7-25)

10. List some things that you should include in your method of troubleshooting? (7-28.29)

11. Refer to figure 19 in the text. Using the half-split method. where would you check if there is no output

from stage ,8 and a check shows no output at point D?(7-34)

12. Why is it necessary to try to replace a defective component with one of identical characteristics .ind

physical size? (742)

13. At what point in the corrective maintenance procedures would you normally align a circuit? (7-46)

14. What is determined by a performance test? (7-47)

15. Why is it necessary to handle printed circuits with care?18-5

138

lo. What type uf solder do yuu use tu repair printed circuits? (8-11)

17. Name four types of wire wraps that you may be required to make? (8-19-23)

18. What is the smallest radius that you can bend a coaxia) cable? (9-6)

li). What dues a red printed identification code on a line signify? (9-7)

20, At what point on a ground wire 6 inches long would the wire identification code be printed? (9-7)

21 , When should you use the sinele-wire safety method? (9-9)

22. Why is it necessary that bonding and grounding connections be properly made? (9-10)

13J

MODIFICATIONS

Rey of this publication has (have) been deleted in

adapting this material for inclusion in the "Trial Implementation of a

Model System to Provide Military Curriculum Materials for Use in Vocational

and Technical Education." Deleted material involves extensive use of

military forms, procedures, systems, etc. and was not considered appropriate

for use in vocational and technical education.

CHAPTER 4

Objectives: To demonstrate a knowledge of the components of an oscilloscope and how they operate, and to

show ability to operate a sample synchroscope by analyzing presentations under given operating conditions.

I . List the basic circuits that make up an oscilloscope. (12-1)

2. Name four of the five special features usually found on a synchroscope. (12-1)

3. Mat are the functions of the anodes in a cathode-ray tube? (12-3)

4. How is the deflection sensitivity of an oscilloscope usually expressed? (12-6)

S. If I SO VDC causes a 3-inch displacement of the spot on the face of an oscilloscope, what is the

deflection factor? (12-7)

-- 141 i

b. What is generally used as the screen coati4., genciai purpos:. CRT? (12-10)

7. What happens to the electron beam if the lead con:tee:in the aquadag to the powe 7. supply is open?(12-12)

8. What type of rectifier is normally used in the high-voltage power supply of an oscilloscope? (12-15)

9. What type of rectifier is normally used in the low-voltage power supply of an oscilloscope? (12-1(,)

10. What type of gas tube is used for sweep generators? (12-23)

11. Why must an oscilloscope sweep be linear? (12-27)

12. How is a stationary display obtained? (12-28,29)

13. What is the distinguishing feature of a synchroscope? (12-31,32)

14. If the sweep calibrator is set for 10 4sec/inch and the signal under test makes a complete cycle in 4 inches.

what is the signal frequency? (12-35)

15. What is the purpose of a voltage calibrator on an oscilloscope? (1242,43)

16. What is the purpose of retrace blanking? (1246,50)

17. After you have adjusted the intensity control, what other control may you have to adjust? (13-4)

18. When a halo appears around the spot on an oscilloscope screen, what control should you adjust? ( 1 3-5 )

to. When the spot is elliptical on the screen, what control should you adjust? (13-7)

20. What happens if you increase the gain control too much? (13-10)

21. What height-to-width ratio.provides optimum display proportions for general purpose waveformexatiiinations? (13-12)

22. What controls do you use to center the spot on the screen? (13-14)

23. II J stable display of 2 cycles ('or a I-kHz signal appears on a scope, what is the sweep frequency?t 13-23)

24. What happens if you advance the synchronizing control too far? (13-32,33)

25. What is the purpose of the Z-axis in an oscilloscope? (13-35,36)

26. List precautions that you should take when using an oscilloscope to protect yourself and theequipment. (1342,44)

27. What indication do you get when there is poor contact between the rotor and the resistive element inthe vertical gain potentiometer? (13-50)

18. When operatine the Tektronix 585A (fig. 65) in the "B" INTENSIFIED BY "A" sweep function,unhlanking is a function of which sweep unblanking pulse and intensification is a function of whichsweep unblanking pulse? (14-26-31)

11

143

VP

29. Name the oscilloscope control that performs each lunction listed below.

a. Determines input voltage required to deflect beam 1 cm vertically.b. Sets voltage level required to trigger the trigger generator.c. Positions intensified area of display.d. Selects desired sweep and unblanking signals.e. Adjusts trigger generator input circuits.j: Adjusts slope of sweep sawtooth.g. Selects sync signal slope that is to trigger the trigaer generator

Selects dual or single vertical input functions.(Sec. 14, all paras.)

30. For best results, which triggering should you always use when checking phase relationships with thedual-trace oscilloscope plug-in adapter? (14-51)

31. What type of meter has a valid multiplying factor for all ranges when a highvoltage probe is used? (15-4)

32. List two purposes of a high-voltage resistive probe. (15-4.5)

33. lithe small capacitor of a high-voltage capacitive probe is 5 ppf and the step-down ratio is 50. what is

the value of the other capacitor? (15-8,9)

CHAPTER 5

Objective: To demonstrate a knowledge of the circuits used to check power and frequency.

1. What power does an ordinary AC wattmeter measure? (16-2)

2. What is the purpose of the compensating coils used in wattmeters? (16-4)

3. Wattmeters are usually limited to approximately how much current? (16-5)

4. What would you use to extend the range of a wattmeter to measure high AC power? (16-5)

5. Why does the accuracy of a wattmeter decrease when it is used to measure power above 1 kHz? (16-7)

ty. What is the standard reference level for dbm? (16-12)

7. What type of meter would you use to clteck the input power to a transmitter? (16-13)

S. What measurement is the equivalent to I vu? (16-13)

9 In what power-measuring instrument is a thermistor commonly used? (16-14)

10. What power-measuring instrument uses an ultra-thin wire to measure power at microwave frequencies?

(1(-14)

11. What instrument would you use to get the most accurate measurement of high power? (16-16)

12. What fluid is normally used in flow ca1oriumeters that measure power at 1000 MHz and higher?

(1(-18-20)

13. List four types of frequency test instruments. (17-1)

14. What type of wavemeter is more suitable for measuring the frequency of low-power equipment? (17-2)

15. You want to check the approximate frequency of a tuned circuit before applying power. What type

of meter would you use? (17-7)

16. What type of frequency meter uses a VFO for its internally generated frequency? (17-9)

rwarilor.

/ 3 7

17. What indication do you get when the frequency of the set under test and the frequency ot the V1.0 of

the heterodyne frequency meter are equal? (17-9)

18. What must you use with a heterodyne frequency meter when measuring frequencies at crystal

checkpoints? (17-20)

19. What circuit is used in the input section of a frequency count to shape the output pulse? (18-4,5)

20. What section of the frequency counter contains the decade frequency dividers? (18-10)

21. What is the purpose of the read pulse in the frequency counter? (18-17)

22. What section provides the input td the input section of the frequency counter? (18-20)

23. If the gate-time selector switch of a frequency counter is set on 0.1 second and its readout is 47302,

what is the frequency of the signal under test and the accuracy of the reading? (18-27)

24. How can you increase the accuracy of a frequency counter when measuring a high frequency? (18-27)

25. What happens to the accuracy of a frequency meter at lower frequencies? (18-28)

26. List three major sections usually found in a signal generator. (19-1)

27. What type of oscillator is commonly used in a signal generator above 300 MHz? (19-4)

28. You have a bench mockup with an oscilloscope installed as part of the test harness. Who has the

responsibility for repair of this oscilloscope? (204)

14

1 4 t;

l3i

34. What technical order du you refer to if you are in doubt as to the responsibility of calibrating a certainpieLe of test equipment? (20-5)

CHAPTER 6

Objective: To demonstrate a knowledge of the circuits used to test vacuum tubes and transistors.

1. State three disadvantages of an emission-type tube tester. (21-3)

2. The transconductance of an amplifier tube should be at least what percent of its rated value to beconsidered acceptable'? (21-6)

3. Concerning transconductance, (a) what is it and (h) what does it indicate? (21-7)

4. What method of measuring transconductance is being used when DC bias is held constant and an ACtest signal is applied to the grid of the tube under test? (21-9)

5. To protect the tester meter from damage. what test should you perform first on a tube? 121-12)

6. What tube check is a very sensitive short-circuit test? (21-14)

7. What are the symptoms of a tube with cathode leakage? (21-16)

t3. A tube is considered substandard if a noticeable decrease in emission occurs during a filament activitytest. What percent of the rated value must the emission decrease to indicate substandard operation?(21-18)

c). What indicates the rectifying ability of a crystal.diode? (22-3)

15

147

10. When using the dynamic diode tester m figure 113, what curve is diTlayed on a scope to analy/i thebehavior of a crystal diode? (2:4)

11. A Zener diode regulates at approximately what voltage? (22-10)

12. How is collector leakage or cutoff current designated? (22.14)

13. What hybrid values correspond to alpha and beta for a kransistor? (22-23)

14. If htb is 0.96, what is the value of hfe? (22-241

15. If hfe is 50, what is the value of htb? (22-24)

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148

ANSWERS FOR CHAPTER REVIEW EXERCISES

CHAPTER 1

I .A supervisor is a person who directs the efforts of one or more people in getting a job done.

Adequate authority must go hand in hand with the assignment of a responsibility. Under mostcircumstances, workers would doubt the wisdom of a supervisor who has been given inadequate or no

authority on the job.

A supervisor's primary responsibility is always to the mission. Other considerations may be important,

but are secondary.

4. Using a checklist as a guide. the supervisor must understand his organization, plan and get the work out,determine performance requirements, train workers, and work at self-improvement.

5. The following steps are the best in solving a problem: (I) get the facts; (2) weigh and decide; (3) take

action, and (4) cheek results,

6. While some workers know what to do without being told, others will resent the supervisor who does not

specifically lay out each detail. Then there are some who want instructions and cheerfully carry them

out. No matter the type of workers. the supervisor must be sure that all know their duties.

7. A thorough examination of a job will ( 1) reveal whether the equipment will operate successfully and

safely and (2) afford an opportunity to review with the worker the steps he has taken. This review can

be used as a teaching device.

8. The Specialty Training Standard is your guideline so far as-the skills and knowledges of a job are

concerned. In many cases, you have to devise your own standards of measurement for workers against

workers.

The performance report is the primary source for information on training, assignments, special actions,

and promotion.

W. By experience on the job, a passing score on the USAF Supervisory Test, and a recommendation from

your supervisor.

1 I .Lateral training is qualifying as a 5 level in a specialty other than your own before qualifying for the 7

level.

12. The first letter in the prefix tells you whether it is for airmen or officersA for airmen and 0 for

officer courses.

13. Career development and job proficiency development.

14. Career development is the acquiring of the background knowledge and specific information needed to be

able to perform the duties of the AFSC in question.

15. Your greatest progress in perfecting your skills would be on-the-job training under the applicable Job

Proficiency Guide.

17

1 4

16. Be certified by your supervisor, and serve a stipulated period in OJT status.

17. The AF Form 623 is the only complete recOrd of training.

18. The specific Specialty Standard defines the task knowledge levels.

19. By field training detachments permanently assigned to a unit, by mobile training detachments, or by

traveling teams.

20. The airmen will be given ou-the-job training into a related AFSC in which there is a shortage.

CHAPTER 2

I. The more you know about the potential hazards of your job and off-duty activities, the better yourchances for an accident-free life. You must periodically expose yourself to instruction in safe

procedures for your own sake as well as for others.

2. By acquiring the habit of personal cleanliness and neatness, you will automatically extend the same

habits to your work area.

3. A cluttered workbench makes effective work almost impossible and is the starting place for an accident.

4. The basic ingredient of all accidents is the law of cause and effect.

5. The missions of the Air Force may fail through accidents to people and equipment. This is the most

dangerous effect.

6. You must have effective enforcement because accidents are frequently the direct result of violation of

safety principles.

7 . Good housekeeping prevents fires. Overloaded electric circuits, accumulation of oily-wastes and rags,careless handling and storage of flammable or explosive materialall add up to poor housekeeping and

become fertile causes of tires.

8. A foam-type extinguisher would be used on gasoline fires.

9. Where AFTO 9 series forms are displayed.

10. Report all accidents resulting injury or property damage.

I 1. Wounds or cuts and drownings are emergencies most of us face.

12. In treating a serious cut or wound (I ) stop the bleeding, (2) prevent or treat shock, (3) protect the

wound.

13. When trying to stop bleeding (1) apply a bandage and pressure directly to the cut, (2) apply hand or

finger pressure at various points on a patient's body, and (3) apply a tourniquet (a tourniquet should be

uscd only for source, life-threatening hemmorrhaging that cannot be controlled by other means).

18

///g14. You should always treat an accident victim for shock.

15. The symptoms of shock are: (a) trembling and apparent nervousness; (b) rapid and weak pulse; (c)excessive thirst: (d)becurning quite pale and perspiring; (e) gasping for air and even fainting; and(1) vomiting or complaining of nausea.

16. Artificial respiration is a means of causing air to flow in and out of the lungs of a person when his normalbreathing system ceases to function.

17. Mouth-tomouth artificial respiration can bc used even though the victim has suffered serious fractures .

burns, or uther injuries. It is also the surest method of getting oxygen into the lungs.

18. (1) Turn the victim on his back: (2) clean the mouth, nose, and throat; (3) place victim's head in the"sword swallowing position"; (4) hold the lower jaw up; (5) close the victim's nose; (6) blow air into.the victim's lungs; and (7) let air out of victim's lungs.

19. The first indications of the victim responding to artificial respiration will be a gurgling or gasping forair and possibly coughing and gagging.

20. Learn the traffic laws that are in effect in your location and observe these laws strictly.

21. The Air Force Sports Manual, AFM 215-2, is an authority on sports safety.

Barracks life, like home life, can produce many accidents. Carelessness and horseplay are common causes.

23. (a) Make sure you are well oriented on the use of the equipment; (b) use safety guards at all times;(c) make sure that the floor around machines is free from stumbling and tripping hazards, andId) keep the floor clear of sawdust and scraps.

CHAPTER 3

I. Preventive maintenance procedures are designed to detect conditions that may lead to malfunctions. Thisincludes marginal operations.

2. Resistors and capacitors that are discolored, burnt, or cracked.

3. Adequate ventilation.

4. To prevent arcing. frequency shift, short circuits, and general deterioration due to excessive humidity,condensation. and the resultant growth of fungi.

5. The maintenance manual for the particular piece of equipment on which you are working.

6. Remove power from the circuit under test.

7. To indicate a poor or good impedance match. in making repairs, for preventive maintenance, and inchecking and making adjustments to transmitters.

S. Clockwise.

19

151

9. In the voltage and resistance charts in yOur equipment tedmical otde,s.

10. Examination of all available equipment records. evaluation of operator's comments, and performanceof operational checks when possible.

11- Point B.

12. Because in high-frequency circuits. the dit ferent characteristics may cause the circuit frequenc tochange.

13. After all repairs haVe been corrected, and only then if it is absolutely necessary.

14. The operating efficiency of the equipment.

15. Because the materials used are very fragile.

16. 60/40 solder.

17. Eyelet terminal wire, terminal wire, old lead, and new component wraps.

18. Six times the diameter of the coaxial cable.

19. That it is an AC line.

10. Near the center.

11.

For emergency devices, for areas difficult to reach, and on small screws in a closely spaced pattern.

Bonding and grounding connections must be made properly to protect equipment and personnel 11-oinlichtning discharges and electrical shock, to prevent development uf RF potentials. and to providecurrent return paths.

20

1 54)

CHAPTER 4

1. Cathode-ray tube, sweep generator, horizontal and vertical deflection amplifiers, and power supplies.

2. Triggered sweep, retrace blanking, marker generator, and voltage calibrator.

3. The anodes accelerate the electrons and focus the beam.

4. In millimeters per DC volt.

5.5(1 VI`C

= 50 VDC per inch.3 in.

6. Green phosphor.

7. lt disperses and illuminates the screen.

8. Because the current required to opetme a CRT is very small, a half-wave rectifier is normally used.

9. Full-wave. The current required is moderate.

10. Thyratron.

11. To prevent distortion of the displayed signal.

12. By synchronizing the sweep generator with the incoming signal.

13. The sweep of a synchroscope is triggered.

1 10614. = 25 kHz.4 X 10 psec 40

15. To enable you to use the oscilloscope as a voltmeter.

16. To keep the electron beam from being seen during fly-back time.

17. The focus control.

18. The intensity control.

19. The focus control.

20. The vertical amplifier is overdriven and the display is distorted.

21_ A height-to-width ratio of 2:3 or 4:5 is optimum. These ratios usually assure that a true representationof the wave is displayed.

22. The vertical and horizontal positioning controls.

100023. 400 Hz.1.5

24. The sweep generator operates erratically and the display is distorted.

15. For intensity modulation of the electron beam by the input signal.

26. Do not operate an oscilloscope when its case is removed and be sure the oscilloscope is properlygrounded. Handle a CRT ,:arefully, do not allow a bright spot to remain stationary on a CRT screen.

27. Grass on the display.

11

1 54

2N. B. A.

. a. Volts/on.b. Triggering level.c. Delay.time multiplier.tl. Horizontal display.e. Triggering source.I. Time!cm.g. Trigger slope.h. Mode.

30 Me external signal. This keeps each signal from triggering its own sweep.

31. VTVM.

$2. It decreases the effect of boltmeter loading and provides isolation.

.13. C2 = 5 (50 . 1) puf = 245 upf.

CHAPTER 5

1. Real or in.phase.

2. To insure a zero reading with no load.

3. 2') ainperes.

A eurrent transformer.

5. The accuracy decreases because at high frequencies magnetic fields affect the meter.

(). I milliwatt,

7. A vu meter.

8. I dbin.

9. Bolometer.

10. Bolometer.

11 . Calorimeter.

1.2. Water is used at frequencies above 1000 MHz because of its excellent thermal qualities.

1$. Wavemeter. grid-dip meter. heterodyne frequency meter, and frequency counter.

14. Reaction type.

23

15 j

15. Grid.dip meter.

I. Ileterodyne frequency meter.

17. The best frequency is zero.

18. Calibration book.

19. Schmitt trigger circuit.

20. Time-base section.

21. To activate the gate section.

22. The gate section.

Arr*:

I 013. 473,020 ± 10 Hz is the frequency. Accuracy is X 100 percent = 0.002 percent.

4.73 X 105

24. By taking readings for progressively longer time-gate intervals.

25. The accuracy decreases.

26. A VFO, a modulating circuit, and an output attenuator.

27. A klystron-type oscillator.

28. The using organization.

29. TO 33K-1-01, Calibration Procedures and Responsibilities. This TO lists all test equipment and tellswho is responsible for its calibration.

CHAPTER 6

I . a. A definite 100-percent point is not known.b. High emission does not necessarily indicate a good tube.c. The tube is not tested during simulated operating conditions.

2. 70 percent.

(6) It indicates the amplifying ability of a tube.

4. When an AC test signal is applied to the grid, the dynamic method of measuring transconductance isbeing used,

5. The short-circuit test. If the tube is shorted and other tests are made, the high current could damage thetube tester.

15624

6. Noise.

7. Noise when the tithe vibrates.

8. If the emission decreases more than 10 percent during the filament activity test, the tube is consideredsubstandard.

9: The ratio of the reverse-to-forward resistance.

D. The reverse current-versus-voltage curve.

11. Breakdown or Zener.

12. By the symbol lc°.

13. 1-1tb and hfe.

14. hte 0.96 24.1 0.96 0.04

5015. ht-b = 3T)-74.-7 = 0.98.

25

15

STOP-1.MATCH ANSWER

SHEET TO THISEXERCISE Nvn.BER.

30455 01A 22

2.USE NUMBER 1PENCIL.

VOLUME REVIEW EXERCISE

Carefully read the following:

DO'S:

1. Check the "course." "volume," and "form" numbers from the answer sheetaddress tab against the "VRE answer sheet identification 'number" in therighthand column of the shipping list. If numbers do not match, take actionto return the answer sheet and the shipping list to ECI immediately with anote of explanation.

2. Note that numerical sequence on answer sheet alternates across from columnto column.

3. Use only medium sharp #1 black lead pencil for marking answer sheet.4. Circle the correct answer in this test booklet. After you are sure of your

answers, transfer them to the answer sheet. If you have to change an answeron the answer sheet. be sure that the erasure is complete. Use a clean eraser.But try to avoid any erasure on the answer sheet if at all possible.

5. Take action to return entire answer sheet to ECI.

6. Keep Volume Review Exercise booklet for review and reference.

7. If niandatorily enrolled student, process questions or comments through yourunit trainer or OJT supervisor.If voluntarily enrolled student, send questions or comments to ECI on ECIForm 17.

DON'TS:

I. Don't use answer sheets other than one furnished specifically for each reviewexercise.

2. Don't mark on the answer sheet except- to fill in marking blocks. 'Doublemarks or excessive markings which overflow marking blocks will register aserrors.

3. Don't fold, spindle, staple, tape, or mutilate the answer sheet.

4. Don't use ink or any marking other than with a #1 black lead pencil.

NOTE: TEXT PAGE REFERENCES ARE USED ON THE VOLUMEREVIEW EXERCISE. In parenthesis after each item number on the VREis the Text Page Number where the answer to that item can be located.When answering the items on the VRE, refer to the Text Pages indicatedby these Numbers. The VRE results will be sent to you on a postcardwhich will list the actual VRE items you missed. Go to the VRE bookletand locate the Text Page Numbers for the items missed. Go to the text andcarefully review, the areas covered by these references. Review the entireVRE again before you take the closed-book Course Examination.

27

.1.56

Multiple Choice

' 1. (001) As a supervisor, your primary objective is responsibility to

a. your unit.b. the mission.

c. your superiors.d. your subordinates.

(003) "Praise in public, criticize in private" is a part of what principle of supervision?

a. Telling people in advance about changes that will affect them.b. Letting each worker know how he is getting along.c. Making the best use of each person's ability.d. Giving credit where credit is due.

3. (003) When you review a man's record in solving a personnel problem, you are

a. weighing and deciding.b . checking results.c. getting the facts.d. taking action.

4. (004) Production controls include all of the following except

a. time budgeting. c. management analysis.b. scheduling of work. d. mechanical standards.

5. (005) Course 3ABR30334 is

a. an Air National Guard course.b. a basic technical course.

6. (007) On-the-job training is conducted

c. a Reserve officer course.d. an instructor course.

a. within the unit where the airman is assigned.b. at resident technical schools as graduate training.c. in special schools established by Hq USAF.d. solely through correspondence courses and group study classes.

7. (008) Which of the following is the source of authority establishing the content of technical trainingcourses?

a. Specialty Training Standard. c. Job Proficiency Guide.b. Airman Classification Manual. d. Unit Document Listing.

8. (011) Approximately what percent of all USAF ground accidents result from Government motorvehicle operations?

a. 10 percent.b. 20 percent.

c. 30 percent.d. 40 percent.

28

1 5 j

/ 17

g. (012) Which of the following is not a type of tire?

3. Type A.b. Type B.

c. Type C.d. Type D.

W. (012) Soda-acid fire extinguishers have an effective range of

a. 40 to 50 feet.b. 30 to 40 feet.

c. 15 to 30 feet.d. 3 to 6 feet.

11. (013) If you work around radioactive material or materials, which of the following is not true?

a. Wear protective clothing.b. Do not eat while in the area.c. Good hygiene is unnecesary.d. Wear a film badge.

12. (015) Which Air Force publication prescribes the forms to be used for accident reporting?

a. AFR 27-4.b. AFR 100-27.

c. AFR 124-7.d. AFR 1274.

13. (016) A tourniquet, once applied, should be loosened only if

a. a doctor does it.b. the blood has stopped gushing.c. the wound is close to the foot.d. the patient is turning blue in his face.

14. (017) Artificial respiration must be applied if the patient

a. is not 'preathing. c. is weak from loss of blood.b. has been poisoned. d. is suffering from a back injury.

15. (018) Which method of artificial respiration is the most effective?

3. Chest-pressure-arm4ift. c. Back-pressure-hip-lift.b. Back-pressure-arm-lift. d. Mouth-to-mouth.

16. (019) Concerning the mouth-to-mouth method of artificial respiration, you should force air into thevictim's lungs approximately how many times per minute for an adult and for a child, respectively?

a. 8 and 12.b. l6 and 1.2.

c. 12 and 20.d. 20 and 16.

/

17. (020) An airman driving an Air Force vehicle is safer than when driving his personally ownedautomobilebecause

a. his Air Force job has built-in safety reminders.b. Air Force vehicles are in perfect mechanical condition.c. the Air Force has special punishments for careless drivers.d. driving Air Force vehicles requires more skill than driving private ones.

29

/57g

18. (022) Mita of the following is included in preventive maintenance?

a. Inspection and installation.b. Inspecting, cleaning, and lubricating the equipment.c. Bench check of equipment. siting. and lubrication.d. Climatic deterioration prevention and periodic overhaul.

19. (023) Whkh of the following abrasives should you use tu clean reby contats?

a. Coarse sandpaper.b. Emery cloth.

c. Crocus cloth.d. Steel wool.

20. (024) Which of the following is not a true statement about fungi?

a. Fungus is a form of animal life that feeds on paper and cotton.b. Fungi thrive in high humidity.c. Fungus growth causes deterioration of insulation.d. Fungi cause decay.

11. (025) Which of the following is a precaution to observe when using an ohmmeter?

a. Remove any transistors that may be damaged by the ohmmeter.b. Apply low voltage only to the circ-uit.c. Turn on the high voltage first.d. Observe polarity across resistances.

12. (026) Which of the following is usually measured with a meter containing a bolometer?

a. DC power. c. Percent of modulation.b. AC power in the audio range. d. UHF transmitter output power.

13. (031) Refer to figure 19 of the text. The primary of the output transformer uf stage 2 is open. \Midiof the following statements is true?

a. There is no output with a signal injected at point A.b. The output is weak with 3 signal injected at point D.c. There is no output with a signal injected at point F.d. The output is normal from ell points of signal injection.

24, (032) What is the final step in corrective maintenance?

a. Giving the equipment a performance check.b. Isolating the trouble to a subsystem.c. Replacing the defective component.d. Eliminating all properly functioning subsystems.

25. (033) What type of printed circuit is formed by indenting a metal foil into an insulating base and

removina the unwanted raised portion?

a. Etched. c. Chemically deposited.b. Embossed foil: d. Electrolytic indentation.

2b. (033-034) What wattage rating soldering iron is most appropriate for work with printed circuits?

:I. 5-watt.1). 35-watt.

c. 100-watt.d. 250-watt.,

27. (034) An advantage of the complete component replacement method of replacing components on aprinted-circuit board, as compared to the service terminal component replacement method, is thatthe former

a. can be easily done by squadron maintenance personnel.b. does not require the use of a vise or heat sink.c. requires standard size tools only.d. is neater and more effective.

(036) You can consider repairing a crack in a printed-circuit board when

a. the crack runs under a conductor.the crack is parallel to the mounting edge of the board.

c. the crack does not start at either of the mounting edges.d. there are no more than three repairable cracks on the board.

24. (037) When replacing a transistor. what is the most important thing to remember?

a. Not to apply an excessive amount of heat.b. Not to use any type of pliers to hold or shape the transistor leads.c. To leave all excess solder remaining on the eyelet to solder the new component.d. Always use a very hot soldering iron to prevent holding the iron in place for long intervals.

30. 1038) When working with coaxial cables used in electronic equipment, you should check to be sure that

a. spot ties are always used.h. they are loosely bent to prevent damage.c. the clamps fit around the cable tightly.d. they do not have a bend radius of more than six times the cable diameter.

31. (040) Which level of maintenance performs cleaning where such cleaning does not require disassemblyof the equipment?

a. Depot.b. Field.

c. Limited.d. Organizational.

32. (041) Which of the following units collects, maintains, and analyzes data relating to the maintenancecomplex?

a. Programs analysis. c. Data control.b. Control analysis. d. Data surveillance.

33. (042) Which element of maintenance control manages and controls those maintenance actionsscheduled in the maintenance plan which change equipment or facility status?

a. Materiel control c. Quality control.b. Plans and scheduling. d. Job control.

31

162

34. (042) All of the following are included in Quality Control except

a. Technical order library. c. Deficiency control.b. Deficiency analysis. d. Standardization and evaluation.

35. (044) You have discovered that Airman Jones was loaned to another work center yesterday for 4 hours,but you thought at the time that he was at the orderly room and turned in an exception card to reflectthis situation. To correct this erroneous entry that is charged to your work center, you should turn inonly

a. a transferee card.b. a correction 'clrd.c. a correction card and a backdated card.d. another exception card with the corrected information.

36. (045) Which of the following is not a responsibility of Maintenance Control?

a. Act as the critical item monitor for the maintenance complex.b. Provide the maintenance input to the programming function.c. Maintain liaison with the maintenance property custodians.d. Identify and verify not-operationally-ready-supply (NORS) conditions.

37. (046) Equipment deficiencies of a routine nature are normally reported through the

a. maintenance data collection system.b. USAF product improvement program.c. maintainability program.d. reliability program.

38. (046) What type of technical order will direct the corrective action when a condition exists that maycause the loss of an aircraft?

a. Urgent action. c. Routine action.b. Record action. d. Immediate action.

39. (048) TO 0-1-01 is the index to

a. Air Force NI&RTs. c. airborne electronics TOs.b. general aircraft TOs. d. ground electronics TOs.

40. (048) TO 0-2-1 provides

a. dates of all current TOs.b. an alphabetical list of equipment TOs.c. a list of technical orders in numerical order.d. an alphabetical list of commercial publications.

41, (048-049) The procedures for distribution and storage of TOs is explained in

a. TO 00-5-1,b. TO 00-5-2.

c. TO 0-1-01.d. TO 0-4-1.

32 1 6 3

42. 4049) Concerning a TO number composed of three parts separated by dashes, what is true e- the partfollowing the first dash?

a. ft is the subgroup designator.b. It is the major group designator.c. It is the series number.J. It is the base number.

4,t. ;050) fo-deficiencies are reported if

a. the information in the TO is incorrect, to whatever degree.b. they adversely affect performance of the mission.c. a drawing is affected.d. a change is impending.

44. (053) Which statement describes electrostatic deflection in a CRT?

a. Instantaneous beam deflection toward the positive plate.h. Instantaneous beam deflection toward the negative plate.c. Circular sweep deflection caused by a rotating potential around the deflection coil.d. Beam deflection proportional in length to the deflection voltage frequency.

45. (054) What is the vertical deflection sensitivity of an oscilloscope if a 150 VDC applied to its verticaldeflection plates deflects the spot 3 centimeters?

a. 0.2-mm/volt.b. 0.5-inm/volt.

c. 4.5-mm/volt.'d. 5-mm/volt.

46. (054) What is the amplitude of the voltage applied if the spot is deflected 2.5 inches on anoscilloscope that has a deflection factor of 50 VDC/inch?

a. 0.05 volt.b. 12.5 volts.

c. 20 volts.d. 125 volts.

47. (055) What is usually the output of the low-voltage power supply of an oscilloscope?

a. Over 1000 volts. c. Between 250 volts and 400 volts.b. Between 500 volts and 750 volts. d. Less than 200 volts.

48. 055) To obtain full-scale deflection on a cathode-ray tube, how much internal voltage is applied by thevertical and horizontal amplifiers to the deflection plates?

a. Several millivolts. c. Several hundred volts.b. Several volts. d. Several thousand volts.

4'). 1056-057) A portion of a test signal is applied to the grid of the thyratron within an oscilloscope toobtain

a. focus. c. synchronization.h. intensity control. d. positioning.

33

164

50. (057) A thyratron sweep generator operates in what mide of operation?

a. One-shot.b. Blocked.

c. Triggered.d. Free-running.

51. (059) What is the distinguishing feature of a synchroscope?

a. Its triggered sweep.b. Its voltage calibrator.c. Its marker generator.d. Its sweep calibrator.

51. (061) Which of the following are least affected by the retrace time of an oscilloscope?

a. Sine waves.b. Square waves.

c. High-frequency waveforms.d. Low-frequency waveforms.

53. 1061) What is the purpose of the blanking pulse and to what CRT element is it applied?

a. It is applied to the cathode and drives it to cutoff during retrace time.b. It is applied to the control grid and drives it to Cutoff.during retrace time.c. It is applied to the cathode and holds it at cutoff during equipment warmup.d. It is applied to the control grid and holds it at cutoff during equipment warmup..

54. (063) What two oscilloscope controls interact to the extent that an adjustment of one usually requiresan adjustment of the other?

a. Focus and intensity.b.-focus and positioning.

c. Gain and positioning.d. Frequency and gain.

55. (064) The optimum height-to-width ratio for general-purpose waveform displays is approximately

a. 1:2 or 2:1.b. 2:1 or 2:3.

c. 2:3 or 4:5.d. 4:5 or 5:4.

5 . (065) The controls that are used to shift the entir CRT display to any desired portion of the viewingarea are the

a. centering controls. c. positionine controls.b. deflection controls. d. displacement controls.

57. (066) What is the frequency of the time-base generator if five complete cycles of a 25kHz test signalare displayed on the scope?

a. 2.5 kHz.b. 5 kliz.

c. 30 kHz.d. 125 kHz.

58. 1067) The purpose of the synchronizing control is to

a. apply a portimulthe vertical signal to the sweep circuit.b. apply a portion of the horizontal signal to the sweep circuit.c. adjust the amplitude of the sweep signal.d. adjust the frequency of the sweep signal.

34

59. (069) To produce markers by intensity modulation, the marker signal is fed to the

a. vertical input.b. horizontal input.

c.. sync input.d. Z-axis input.

O. (0694)70) A series of posit iveloing marker pukes applied to the cathode of a CRT will appear in the

t ace as

a. bright spots.I. dark spots.

c. positive-going pulses.d. negative-going pulses.

61. (071) Which of the following does not cause a "grass" display?

a. A bad input potentiometer. c. Poor input connections.b. Microphonic amplifier tubes. d. A faulty intensity control.

62. (075) Which of the following best describes how the sweep generator of the 585A oscilloscope istrieeered when operating in its internal triggering mode?

a. A sample of the vertical signal is fed to the sweep generator as a trigger signal.b. A 6.3-volt filament signal is fed to a trigger generator circuit which, in turn, produces a sweep

generator trigger.c. A sample of the vertical signal is fed to the trigger generator which, in turn, develops a sweep

generator trigger.d. A 6.3-volt filament signal is used to trigger the sweep generator via a differentiating network.

63. (077) An important point to remember about the TIME PER CENTIMETER control of anoscilloscope is that it

a. varies the rate of charge of the sawtooth sweep generator, not the amplitude of the output voltage.

b. varies the amplitude of the sawtooth sweep generator output voltage, not the rate of charge.

c. causes the holdoff circuit to trigger a horizontal sweep voltage.

d. triggers the sweep multivibrator to the rest position after each horizontal sweep.

Special Situation. Questions 64 through 67. The controls on a Tektronix 585A (see figure 54 of the test) are

set as follows:

"A" TRIGGERING SOURCE - INTERNAL

"A" TRIGGERING SLOPE POSITIVE"A" TRIGGERING LEVEL - 0

"A" TIME/CM - 50 psecHORIZONTAL DISPLAY "A""A" STABILITY - clockwise until the sweep appears and then

counterclockwise until it just disappears.

64. (075-077) The triggering source switch is switched to the EXTERNAL position and two related signals

are appliedone to the VERTICAL INPUT jack and one to the TRIGGER INPUT jack. This results in

a. an unsynchronized display.b. no display.c. a sweep starting when the vertical input passes through 0 in the positive direction.d. a sweep starting when the trigger input passes through 0 in the positive direction.

35

65. W78) When a signal is applied to the VERTU_ AL INPUT jack with "A' TRIGGERING SOL ::(.1onINTERNAL, a display is obtained. Where does this dispI4 start?

a. At 0 and goes negative.b. At 0 and goes positive.c. At maximum positive and goes negative.d. At maximum negative and goes positive.

66. (079) A signal of unknown frequency is apphed and 21/2 cycles are displayed. What is the siendl frequency"

a. 5 kHz.b. 10 kHz.

c. 50kHz.d. 100 kHz.

67. 1079) A 40-kHz signal is applied as a vertical input. How many cycles are displayed?

a. 1/2.

b. 2.c. 20.d. 40.

Special Situation. Questions 68 through 71. The Tektronix 585A (refer to figure 54 of the text) is set Lip asfollows:

HORIZONTAL DISPLAY switch"B" TRIGGERING SOURCE"B" TRIGGERING SLOPE"B" TRIGGERING LEVEL"B" STABILITY"B" TIME/CM"A" STABILITY"A" TIME/CMA 5-kHz square wave is applied toDELAY-TIME MULTIPLIER

- "B"- INTERNAL

(- ) NEGATIVE- (0) ZERO- set for triggered operation0.2 msfully CW (free-running position)

- 0.1 msthe VERTICAL INPUT jack.

- 5.0

68. (078-080) With the stated conditions, which of the following best describes the display obtained?

a. A 10cycle display of uniform intensity.b. A 1-cycle display of uniform intensity.c. A 10-cycle display with the last 5 cycles intensified.d. A 1-cycle display with the positive alternation intensified.

69. (080-083) Which of the following best describes the display obtained when the HORIZONTAL DISPLAYswitch is placed in the "B" INTENSIFIED BY "A" position?

a. A 5-cycle intensified trace.b. A 5-cycle trace of normal intensity.c. A 10-cycle trace of normal intensity.d. A I 0-cycle trace with the last 5 cycles intensified.

36

aos70. (080-083) How must the controls be set to present a 10-cycle display with the second cycle intensified?

a. HORIZONTAL DISPLAY to "IV INTENSIFIED BY "A." "B" TIME/CM to 0.5 millisecond. andDELAY.TIME MULTIPLIER to 1.0.

b. "B" TIME/CM to 0.5 ms. "A" TIME/CM -to 20 psec. and the DELAY-TIME MULTIPLIER to 1.0.HORIZONTAL DISPLAY to "A" DELAYED BY "B," "A" TIME/CM to 20 psec, andDELAY-TIME MULTIPLIER to 2.0.

d. HORIZONTAL DISPLAY to "B" INTENSIFIED BY "A." "A" TIME/CM to 20 psec. andDELAY-TIME MULTIPLIER TO 1.0.

71. (084) Which of the following best describes the display obtained when the HORIZONTAL DISPLAYswitch is placed in the "A" DELAYED BY "B" position?

a. A 10-cycle trace with the last 5 cycles intensified.h. A 10-cycle normal intensity trace.c. A 5-cycle normal intensity trace.d. A 5-cycle intensified trace.

72. (081) When operating the Tektronix 585A in the "B" INTENSIFIED BY "A" sweep function, how isunblanking accomplished?

a. By the A sweep unblanking pulse only.b. By the B sweep unblanking pulse only.c. By both the A and B sweep unblanking pulses.d. By the A sawtooth sweep voltage.

73. (083) When operating the 585A oscilloscope, how is the sweep trigger initiated when the HORIZONTALDISPLAY SWITCH is in the "A" SINGLE SWEEP position?

a. The B sweep sawtooth is fed to a pickoff circuit which, in turn, develops an A sweep trigger.b. An external trigger input is fed directly to the A sweep generator.c. The sweep trigger is produced by depressing the RESET button.d. The sweep trigger is produced by the A trigger generator.

74. (085.086) When checking the phase relationship of two signals by using Lissajous patterns, you shouldalways

a. set the amplitude of both input signals so that each signal gives the sanie amount of vertical deflection.b. set the vertical horizontal input attenuation for equal horizontal and vertical deflection.c. use one signal to trigger the A sweep and the other signal to trigger the B sweep.d. use an external trigger of known relationship to the signals under test.

75. (087) Refer to figure 54 of the text. Concerning the dual-trace plug-in unit, when the INPUT selectorswitch is in the AC position, which choice is correct?

a. The DC reference level of AC sienals may be checked.b. A capacitor is placed in series with the INPUT jack.c. The input signal.is amplified and fed to the horizontal plates.d. The INPUT jack is connected to the primary of an isolating transformer.

37

1 6

76. (W,)-0901 Two calibratimi checks frequently performed on an oscilloscope are

a. sweep amplitude and astiematism.b. vertical input and attenuator probe.c. volts per centimeter and astigmatism.d. volts per centimeter and attenuator probe.

77. (090) A 10:1 attenuator probe is connected between the CAL OUT jack and the "A" VERTICAL INPUTjack (refer to figure 65 of the text). The amplitude calibrator control is set to its 2-volt position and the"A" VOLTS/CM control is set to 0.5 volt. The "A" INPUT control is in the AC position and the MODEcontrol is set to "A" only. How many centimeters should the signal occupy vertically?

a. 4.0. c. 0.4.b. 2.5. d. 0.25.

78, (0)2) When using a high-voltage probe with a VOM,

a. a multiplier resistor is unnecessary.b. the multipher resistor is of low value.c. the input resistance is constant.d. the multiplying factor changes with the range used.

79. (093) What is the maximum voltage rating of most scope input terminals?

a. 400 volts.b. 600 volts.

c. 800 volts.d. 1000 vclis.

80. (094-095) Refer to figure 77,B, of the text. A capacitive voltage divider consisting of a 240- ppf and a60-.ppf capacitor has 100 volts as its input. If the output is taken across the 240- ppf capacitor, whatis the step-down ration of the voltage divider?

a. 5:1. c. 4:1.b. 5:2. d. 3:1.

81. (095) In order that the high-voltage capacitance divider probe not loud the circuit under test, the mputof the probe must contain

a. an extremely high impedance.b. a very large capacitance.c. an extremely low impedance.d. a high-resistance shunt.

82. (096) When using a scope to perform high-frequency circuitry tests, capacitive loading of the circuitunder test is virtually eliminated by

a. elimination of cable shielding.b. using a high-resistance isolation probe.c. adding series inductance to cancel the capacitive reactance.d. detuning the circuit under test until after the DC measurements have been made.

38

j

s3. 109$1 fo have sufficient deflection for a good display, a high-voltage probe should not reduce the test'signal below approximately

a. 5 vOlts.h. I volt.

c. 0.5 volts.-d. 0.1 volt.

x4. I OW The accuracy of tte electrodynamic wattmeter is seriously affected by current exceeding

a. :1 amperes.b. 10 amperes.

c. 20 amperes.d. 50 amperes.

( IOW Above what frequency does the accuracy of an electrodynamic wattmeter decrease considerably?

a. 60 Hz.b. 200 Hz.

c. SOO Hz.d. 1000 Hz.

86. (101) In what type meters are thermistors commonly used for the measurement of low power at highfrequencies?

a. Wattmeters.b. Bolometers.

c. Calorimeters.d. Wavemeters.

87 1103) The reaction wavemeter is preferred for measuring

a. frequencies at low-power levels.b. frequencies at high-power levels.c. power at hiah frequencies.d. power at low frequencies.

8S, (104-105) What instrument can be used to determine frequency of a tuned circuit before power is appliedto the circuit?

a. Absorption wavemeter. c. Grid-dip meter.b. Reaction wavemeter, d. Q-meter.

50. 1105) Which of the following is a precision instrument which uses a calibrated variable-frequencyoscillator?

a. Electronic voltmeter.b. Heterodyne-frequency meter.c. Absorption wavemeter.d. Fluxineter.

90. (106) What circuit is usually employed at the variable-frequency oscillator of a heterodyne-frequencymeter?

a. Crystal oscillator. c. Hartley oscillator.b. Colpitts oscillator. d. Electron-coupled oscillator.

9 t. 1108) What is the function of a Schmitt trigge; ciicuit in a frequency counter?

a. Divider.b. Multiplier.

c. Reset.d. Squarer.

92. .(111) In which section of a frequency counter are you likely to find a thyratron tube?

a. Gate.b. Reset.

c. Input.d. Display.

93. (112) If the counting time of a frequency counter is 0.01 second and the five-digit readout is 05783.what is the frequency under teit?

a. 57.83 Hz.b. 578.3 Hz.

c. 57,830 Hz.d. 578,300 Hz.

94. (112-113) How can the ratio of two frequencies be determined using a frequency counter?

a. Use the higher frequency as the gating signal and the lower frequency as the input signal.b. Use the lower frequency as the gating signal and the higher frequency as the input signal.c. Start the timing gate with the lower frequency signal and stop it with the higher frequency signal.d. Take two readout readings and divide the higher by the lower.

95. (113) What type of AM is most often used with LC oscillators of signal generators?

a. Pulse.b. Gated.

c. Sinusoidal.d. Square wave.

96. (114) What technical order lists all test equipment in the Air Force inventory and tells who isresponsible for its calibration?

a. TO 0-1-33.b. TO 33-1-14.

c. TO 31-1-141.d. TO 33K-1-100.

97. (116) Which choice is correct concerning the emission-type tube tester?

a. It checks only the plate current developed.b. It test the 100-percent emission point.c. It shows the ability of the grid to control current.d. It indicates conclusively the condition of a tube.

98. (117) A voltage or power-aniplifier tube is considered defective when its transconductance decreases towhat percent of specified value?

a. 50 percent.b. 60 percent.

c. 70 percent.d. 80 percent.

99. (118-119) By increasing the sensitivity of the indicating device, 3 tube tester designed to test for shortcircuits may be used to test for

a. transconductance. c. gassy conditions.b. low emission. d. microphonics.

40 171

/6"/I Oft (110) (athode leakage caused by particle breakage will

a not materially affect the tubes operation .caum: nuctophomc IIOISC

c. completely short the eathode.d. hurn out the filament.

101, I 2t1 The lament activity test.is based on the principle that no appreciable decrease in emission of aneleetron tube will be caused by decreasing its rated heater voltage by what percent?

a. i. c. 15.b. 10. d. 20.

102 1121) Refer to figures 113 and 114 of the text. The action of which listed component shown in figure113 is primarily responsible for the combination of the individual traces shown in figure 114 into theseemingly composite trace shown in figure 114.C?

a. SI. c. S3.b. S2. d. K1.

103. (123) What is the leakage current flow between collector and base sometimes referred to as?

a, Collector cutoff current. c. Zener current.b. Punch-through current. d. Input base current.

104. (124) /row many hybrid parameters are there for a transistor in any one configuration?

a. 3. c. 12.b. 4. d. 15..

105. (124) If a transistor has its hfe = 49. what is its common base forward current gain?

a. 50. c. 1.02.h. 49. d. 0.98.

106. 11251 Refer to figure 124 of the text. Which choice is correct concerning meter M when the selectoris iti position 2?

a. Reads the current through RI.b. Reads the voltage supplied by G2.c. Reads the voltage drop across RI.d. Connected between the emitter and ground.

30455 01 1166

. CDC 30455

TELEVISION EQUIPMENT REPAIRMAN(AFSC 30455)

Volume 1

Equipment Maintenance

MIIVINMUNNWIIIIIIIMMUNMWMAMVNIOMIWYMNIMINAMWOVIW11/14.14NAMININVIII nvanwwwtwommitinvoinvAnmmtvwKinituvivomsinNvAssulwma%%14%%1MWINIANAW

Extension Course Institute

Air University

173

Preface

THIS COURSE consists of three volumes. It is designed to further your train-ing toward the achievement of 5- and 7-level proficiency. If you are trainingto attain a 5 skill level, ycu should complete CDC 30000 in addition to this

course. If you are training to attain a 7 skill level, you should complete cpc30001 in addition to this course. We bring this to your attention because CDC30455 is a TV specialty course. It does not cover JTS items that are commonto other 30 career field specialties. Such items are contained in CDC 30000 andCDC 30001 for 5- and 7-skill-level training, respectively. Although all the otherJTS items are covered in this course, you must realize that some JTS knowledgerequirements will be met fully when you have acquired the related proficiency onspecific equipments. Our treatment endeavors to give you knowledge so that youcan more readily understand the principles that underlie the operation of TVequipments. This knowledge will facilitate further training on TV equipmentsand better enable you to cope with TV maintenance problems.

Chapter 1 deals principally with the 'prime equipments that make up a TVsystem. However, we discuss first your specialty in a general manner by identify-ing 5- and 7-skill-level responsibilities, classifying systems, and describing AirForce applications of television. Chapter 2 covers all types of TV power suppliesto preclude unnecessary npetition in the chapters that follow. In chapter 3 weprogress from the simple noninterlace sync generator to the more complex interlacetypes. The units of a camera chain are functionally analyzed in chapter 4. Chapter5 covers the various types of monitors employed in a TV system. Microphones,audio amplifiers, and audio consoles are discussed in chapter 6. Our final chapteris devoted to color TV. We point out the special requirements of the standardcolor TV system and describe the equipments peculiar to this system.

If you have questions on the accuracy or currency of the subject matter ofthis text, or recommendations for its improvement, send them to Tech Tng Cen

(TSOC), Kees ler AFB, MS 39534.

If you have questions on course enrollment or administration, or on any ofECI's instructional aids (Your Key to Career Development, Study ReferenceGuides, Chapter Review Exercises, Volume Review Exercise, and Course Exami-nation), consult your education officer, training officer, or NCO, as appropriate.If he can't answer your questions, send them to ECI, Gunter AFB, Alabama36114, preferably on ECI Form 17, Student Request for Assistance.

This volume is valued at 39 hours (13 points).

.174

lii

/6,7

Contents

chapter

PrefacePage

ill

1 REQUIREMENTS AND APPLICATIONS 1

2 Pi:mu SUPPLIES 173 SYNC GENERATORS 344 THE CAMERA CHAIN 495 MONITORING FACILITIES 666 THE AUDIO SYSTEM 787 COLOR TELEVISION 96

175

iv

Change a

Page in, par, 2. line 3. Delete -cla,sifying sys,tem."

Page M. par. 3. Octet.: nd replace with tile10110%k ing two par:it:x.11)h%

"It you have question% on Inccurrency of the subject matter of

accuracy orthis text. or

recommendations tor impriweinent. theml'ech Cen ( Soo. Keesler F13. NIS

3(4514.

"It you lia%c questnms on course enrollmentor administration, or on an!, of EC1's instruc-tional aids ( Your Ke.., to Career Devclopment.Study Reference C hapter Review Exer-cises. Volume Review Ivercise. and Course Ex-amination t. consult our education officer. train-ing officer, or l( 0. a:, appropriate. If he can'tan%IA el" your questions. send them to ECI.Ciunter AFII, AL 36114. preferably on EC1Form 17. Student Request for Assistance.-

Page 1, intro., line II. Change "educaion" to"education."'

Page I. par. 1-3, lines 5 and 6. Change "pro-during" to "producing.-

Page 2. par. 1-7, line I. Change "Job Train-ing Standard .ITS f" to "Specialty Training Stand-ard (S Fs).-

Page 3. par. 1-7. line 4. Change 'ITS" to-STS.- I.ine 1 I. Change "ITS" to "STS.- Par.1-9. line Z. Change *Ts- to "STS." Linc 4.Change ".ITS" to "STS.- Lines 5 through 9.Delete sentence beginning: "Also note that

Page 4. Delete figure 2.Page% 4 and 5. Delete paragraph% 1-16

through 1-20.Page 5, 2-1. Delete the second sentence.Pages 5 and 6. Delete paragraphs 2-2 through

2-6.Page 6. par. 2-7. line 5. Insert "Department

of Defense- before "DOD" and enclose DOD inparentheses.

Page 7. Delete paragraph 2-10.Page 7. Delete figure 5.Page 1 I. col. I. line II. Change "pkmned"

to "panned.-In Section 1 renumber paragraphs.Page 5-2, line 7. Change "frequence- to

"frequency .

Page 21. par. 5-14. line 7. Insert "regulated"between "the" and "voltage.**

Par, 5-15. line 9. .After "accordingly.- insert"the change in base current.-

Page 11 par. 5-16, line I. Insert "unregulatedtillage- between "if" and -Vu."Page 24. par. 5-3(1. Delete "Re- on line 14

and delete lines 15 through 31. Replace with thefollow Mg7 "Transistor 03 and the base circuit of04 are.the collector load of 02. 03 is a highimpedance to a-c. but a low impedance to d-c.

thus allowing the desired d-c current through02. l'he capacitor prevents spurious high-fre-quency oscillations. Zeller Z2 establishes the ref-erence for 03. and amplifier operation is ad-justed to the optimum condition with the variableemitter resistor. Ally change in 02 collector cur-rent will be felt on the base of 04."

Page 25. par. 5-33. line 7. Delete the sentencebeginning: "The circuit containing 03 . . .

Page 25. par. 5-33. lines II and 12. Insert"emitter follower" between "of- and "04."

Page 28. Paragraph now numbered "5-41"should be "5-44.- Change the first sentence toread: "The symptoms just mentioned for theopen-circuited rectifier are thc same for a short-circuited rectifier.-

Page 29. par. 6-8. last line. Change "and" to"to."

Page 33, ... par. 6-30. Delete last sentence andreplace with: "However, HV rectifier filamentswill not normally be visible."

Page 70. par. 12-14. Change this paragraph toread:

12-14. Sync. section. Thc signal at TP3 shouldhave the same waveform as shown at TPI. Thissignal is capacitively coupled into the sync sepa-rator stage 03. 03 has no fixed forward biasand is cutoff. Only the most negative or syncportion of thc input composite signal providesforward bias and drives 03 into conduction.Illus. only thc snyc signals are amplified and ap-pear as positive pulses at TP4.

Page 82, par. 14-18, line 9. Change "velocity"to "dynamic."

Page 93, par. 16-6. line 3. Delete thc sentencebeginning 'in the amplifier circuits...."

Page 95. par. 16-19, line 4. After "attenuator,"delete "is, as you already know, nothing morethan a gain control; therefore, it."

Page 105. par. 18-26, last sentence, Delete"TO 31S4-1-1 A and."

Page 115. col. I. line I. Add "hundred" be-twccn "several- and "thousand."

Workbook

Chapter Review Exercises

Page 2, item 2. Change ".ITS" to "STS."Page 2. Delete items 7. 8, 9, and 10.Page 3. Delete items IL 12. 13. 14 -and 19.Page 3. Delete item 16. Change "CDA" to

"DCA."

' 176

o'

MODIFICATIONS

of this publication has (have) been deleted in

adapting this material for inclusion in the "Trial Implementation of a

Model System to Provide Military Curriculum Materials for Use in Vocational

and Technical Education." Deleted material involves extensive use of

military forms, procedures, systems, etc. and was not considered appropriate

for use in vocational and technical education.

17 7

Power Supplies

C UPPLYING THE proper amount and kindLlof power to electronic equipment is of the ut-most importance. A faulty power supply willcause malfunctions that may seriously impair theperformance of a TV system. It is therefore im-perative for you to thoroughly understand theprinciples that -underlie the operation of powersupplies used for TV. In this chapter we willdiscuss various types of low-voltage and high-voltage power supplies found in both transmittingand receiving equipments. Significant differencesin rectifier outputs will be brought to your atten-tion. Regulator circuits incorporating solid-statedevices will be analyzed to further your under-standing of these devices and also to review prin-ciples applicable to electron tube regulators. Forpractice in diagnosing troubles, we will presentsymptoms and then proceed to determine theprobable trouble.

4. Power Requirements

4-1. Most television equipments you will en-counter are designed to operate on 115-volt and60-cycle power. Line voltage variations of -..t.10percent are generally tolerable. Such power is

available from local electric companies. In lo-calities where only higher voltages are provided,stepdown transformers can be installed. Whereno commercial source of primary power can behad, it is necessary to resort to an engine-drivengenerator. Generator units ranging from 3 to 15kw are employed for television service. Sincethese units do not accurately maintain 60 cps,you need bear in mind that synchronization prob-lems may occur unless the sync generator is crys-tal controlled. Crystal control is also needed ifthe power is 50 cps instead of 60 cps. This willbe discussed further in later chapters.

4-2. These and other sources of primarypower (such as atomic-driven generators) area-c, but we know that the bulk of the powerrequired is d-c. Although d-c can be generateddirectly in many ways, rectification of a-c is the

17

CHAPTER 2

most practical means of obtaining the amountsneeded to operate TV equipments. A-c to d-cpower supplies also filter and regulate (if re-quired) to provide the various d-c voltages andcurrents needed. From here on when we speakof a power supply, we will mean a unit thatconverts a-c to d-c power. It may or may nothave a transformer input designed for a single-phase or polyphase line. It must have rectifiersand components for filtering the ripple to anacceptable level. In addition, for highly stableouputs, it will have a regulator. By presentingthe various type..., of power supplies used in TVequipments at the outset of this course, we willavoid unnecessary repetition in later chapters.

4-3. From your experience and training youare aware that power supplies differ considerablyin design and capacity. The power suppliesneeded in a TV system depend upon the typesof equipment (camera, sync generator, monitor,etc.), the .complexity of the equipment, and thecomponents contained within a particular equip-ment. There are noteworthy differencrs due tothe requirements peculiar to tubes, transistors,or other active components.

4-4. Tubes and transistors are used exten-sively in the many types of equipments that youwill maintain. Generally speaking, tubes andtransistors must be supplied well-regulated d-cvoltages. As you know, receiver-type electrontubes commonly operate with voltages, fromabout 100 to 300 volts, and transmitting typesmay be designed for plate voltages of 1,000 voltsor more. By contrast, transistors ordinarily re-quire only 5 to 20 volts; in fact, some operateat a fraction of a volt. Although transistors oftendraw as much current as electron tubes, theyrequire far less power because of their low op-erating voltage. Furthermore, transistors andother solid-state devices do not consume powerfor emission as do thermionic tubes. You wouldtherefore expect to find marked differences be-tween d-c power supplies designed for tubes and

76

7/

PIALF-WAVE

A

11

CENTER-TAP FULL-WAVE

Figure 9. Basic rectifier circuits.

those designed for solid-state devices. These dif-ferences, however, are principally those of powerand voltages rather than circuit configuration.Excepting the filament circuit for tubes. the samebasic half-wave and full-wave rectifier arrange-ments are used to convert a-c to d-c power.Moreover, associated regulator circuits are es-sentially alike.

4-5. Camera tubes have special d-c require-ments for highly stable voltages and currents.Several hundred volts for positive and nertivepotentials are needed. A typical power supplyfor an image orthicon must provide an adjustablecurrent-regulated output of hundreds of milliam-peres in addition to voltage-regulated outputs.We will study a transistorized version of such asupply shortly.

4-6. Picture tubes, particularly large ones, callfor d-c voltages as high as 20,000 volts or more.High-voltage power supplies for picture tubes areordinarily unregulated. This is because there isvery little current drain and the load is virtuallyconstant. The circuits to be analyied in the finalsection of this chapter will point up the importantfeatures of high-voltage power supplies commonlyused for these tubes.

4-7. Besides tubes and solid-state devices, TVequipments contain control mechanisms, relays,.and instruments that require d-c power. Conse-quently, provision must be made to supply thesecomponents, thus contributing to the differencesyou will find between power supplies.

S. Low-Voltage Power Supplies5-1. You have previously studied basic rec-

tifier circuits. filters, and regulators; therefore, itshould suffice to briefly review the importantinformation. Instead of reviewing electron-tubecircuits, however, solid-state versions of familiarconfigurations are shown and discussed. Ouranalysis of selected regulator circuits is intended

1 s

BRIDGE FULL-WAVE

to further your understanding, which will enableyou to troubleshoot more effectively and main-tain low-voltage power supplies. The increasinguse of solid-state devices for rectification and reg-ulation justifies the attention given to them atthis level of your training.

5-2. Rectifier Arrangements and Characteris-tics. The three basic rectifier configurations 'areillustrated in figure 9. These single-phase recti-fier circuits have characteristics which are worthkeeping in mind. As a maintenance man, youshould know what to expect by way of d-c out-put, ripple frequence, and peak-inverse voltage( PIV) for a given a-c input. Figure 10 showsthe approximate normal values for each arrange-ment. Compare the values and note the differ-ences. The half-wave circuit is the simplest, butnote its low ripple frequency. This, of course.means better filtering circuitry is required toobtain a satisfactory output. Also, the peak-in-verse voltage across the diode (tube or solid-state rectifier) is about twice the applied a-cpeak voltage (secondary for transformer input).Both full-wave types have the advantages oflower percent ripple, higher ripple frequency,and lower peak-inverse voltage.

5-3. To be sure you understand the meaningof thc values given in figure 10, let us cite a

TYPVRECTIFillt

MAXIMUM0-C yOLIS

C4"CtIOI/POUT FILTERply

elPPLEPICOUENCT

CPS

UPOILTIOyyEFOlto

HLF-Avg I A E 7 B E I A.flCENTER-1 0 7 E I 1 E 21 ~VS

CR100E 1 i g I 1 E 21

MSTE z AC PLIED EEPECTIYE VOLTS MASI= PeEOUEACT GT C APPLIED

Fic;ure 10. Table id values for basic rectifier circuit.).

1 7

/

Page IS. After paragraph 4-7. add new para-graphs 4-8 through 4-24. including new chapterreview exercises and answers.

4-8. To refresh your memory, the principles ofsolid state devices will he reviewed. Rather thanattempt to present the physics involved in solid

state theory. wc will consider their effect on elec-

tron current flow in thc externat circuit.

160

4-9. The direction of current flow has con-fused many students. One theory has currentflowing from positive to negative. This is calledconventional current flow. Transistors increasethe confusion by adding hole movement frompositive to negative. The theory we will adoptis that of electron current flow. This is in thedirection of electron drift, or from negative topositive. Refer to foldout 1, figure A (at the backof tais supplement). In these solid state symbols,the arrowheads indicate the direction of con-ventional current flow. Because electron currentflow is always toward the most positive potential,it will always be against the arrowhead.

4-10. Semiconductor Material. The ability of amaterial to conduct an electric current is directlyproportional to the number of free electrons avail-able in the material. Good conductors have manyfree electrons, whereas insulators Lave very few.Semiconductors fall between the two. A micro-scopic study reveals that most solids have acrystal structure. The atoms of crystals are ar-ranged in a specific pattern or lattice. When animpurity is added to the semiconductor material,its atoms join the crystal structure pattern. Ex-amples are shown in foldout 1, figure B. If theimpurity atoms have more electrons than thesemiconductor atoms, the lattice has extra or freeelectrons. This is called n-type material. If theimpurity atoms added have less free electronsthan the semiconductor atoms, the resulting crys-tal structure will have vacancies or holes due tothis lack of free electrons. This is called p-typematerial. The n- and p-type impurities appreciablyalter the conductivity of the semiconductor. Theyare diffused into the material to obtain a wantedvalue of conductance. The semiconductor is thensaid to be doped.

4-11. Diodes. A diode consists of a p-typeand an n-type material joined in the manufactur-:ng process. At this junction, a depletion regionor space charge region is formed. This region,called a barrier potential, is an electric field ordifference of potential caused by recombina-tion. While it is not directly measurable, it is rep-resented in foldout 1, figure C, as an imaginarybattery. Note the polarity in relation to the n andp material.

4-12. Bias. An external battery connectedacross the diode, as shown on the left of figureD of foldout 1, is said to forward-bias the diode.The external and imaginary batteries are in seriesand aiding. Electron current will flow in the cir-cuit from negative to positive. Increasing the ex-ternal potential will increase the current. Unlesscurrent flow is limited by external circuitry, ex-cessive forward bias will result in excessive heatand crystal structure breakdown. In a semicon-ductor, this heat causes a decrease in resistance

3

and a further increase in current. This is thermalrunaway and destroys the device.

4-13. Connecting the battery across the diode,as shown on the rieht of figure D of foldout 1,will reverse bias it. Because the external bat-tery and the imaginary battery oppose eachother, little or no current will flow. The imagi-nary battery or barrier potential will always equalthe external voltage applied unless the material'slimit is exceeded. Thus, if an external voltagelarger than the maximum possible barrier po-tential is applied, the crystal structure will alsobreak down and be destroyed.

4-14. Rectification. If we understand whathappens when voltage is applied in either po-larity, it is easy to see how the diode rectifieswhen forward-bias current flow is high. Reversebias results in almost zero current flow. If an a-csignal is applied, electron current flows freely dur-ing one half cycle and little or no current flowsin the other half cycle. Figure E of foldout 1 istiv voltage-current characteristic curve for bothbias conditions.

4-15. Zener diodes. Zener diodes are p-njunctions that change resistance greatly with asmall change in applied voltage. They differ fromnormal p-n junctions in that a reverse bias of suf-ficient potential causes crystal breakdown and acharge emission but does not destroy the diode.Therefore, when a proper load resistor is placedin series with a Zener diode, large changes in ap-plied voltage may occur without causing a changein voltage across the Zener diode. It can be seenthat it has similar characteristics to the conven-tional gas-filled voltage regulator tube (VR).Like the VR tube. it also starts conducting at aparticular voltage and continues to conduct vary-ing amounts of current at a fixed voltage dropacross the device. Because the Zener diode op-erates with reverse bias, it will be inserted in acircuit the opposite of a normal diode. In otherwords, in a circuit the arrowhead will point inthe direction of electron current flow.

4-16. Transistors. In figure F of foldout 1, wehave two p-n junctions in one crystal. The bat-teries have biased one junction in the forwarddirection and the other in reverse. Figure E ofthe foldout shows that for the same amplitudeof applied voltage, the current for the forwardbias is much greater than for the reverse bias.Therefore, a p-n junction biased in the forwarddirection is the equivalent of a low resistanceand the p-n junction biased in the reversedirection is the equivalent of a high resistance.From the liower formula (P = FR), you cansee that for a given current the power developedin a high-resistance element is greater than thatdeveloped in a low-resistance element. Applyinga signal to the low-resistance section (forward

is increased. gate current increases. This galecurrent increase lowers the value of anode volt-age necessary for break over (forward breakovervoltage). Normally, the SCR is operated wellbelow forward breakover voltage and thc gatesignal is large enough to trigger or turn the de-vice on.

4-24. When the device is triggered, it is in-dependent of gate control. It remains in the high-conduction state until the hol4ing current pointis reached. Quick turnoff can be achieved byapplying a reverse bias.

biased p-n junction) and taking it from the high-resistance element (reverse biased p-n junction)produces a power gain. This combination ofp-n junctions has transferred the signal from alow-resistance circuit to a high-resistance circuit.The word "transistor" is a contraction of theterms "transfer" and "resistor."

4-17. The two junctions in figure F of thefoldout are formed with two n-tylie materials andone p-type. This is called an n-p-n transistor. Thejunctions may also be formed with two p-typematerials and one n-type. This is a p-n-p transis-tor. The three regions or sections are called theemitter, base, and collector. Normal operationhas the emitter-to-base junction forward biasedand collector-to-base junction reverse biased. Re-ferring to figure A, foldout 1, the two types oftransistors are shown. The arrowhead is on theemitter lead and indicates the direction oppositethat of d-c electron current flow. The first letterof the transistor type indicates the polarity of theemitter with respect to the base. Therefore, thep-n-p type has the emitter positive with respectto the base. The n-p-n types have the emitternegative with respect to the base. Figure G offoldout 1 is an example of forward bias cur-rent flow in an n-p-n transistor. A p-n-p willhave opposite polarities and direction of currentflow. Consider the transistor in a circuit as a vari-able resistor in a voltage divider network. Withno forward bias, the transistor is a very high re-sistance. As forward bias is applied, its resistancedecreases and current increases. This will assistyou in understanding the circuits described in thischapter.

4-18. Unlike the electron tube, the transistoris classified by circuit connections or configura-tions. Compare the transistor configurations andthe well-known electron tube connections shownin figure H of the foldout. The common emitterconfiguration designated by CE corresponds tothe conventional grounded cathode connectionfor the triode tube (figure HI of the foldout).The common base, CB, and common collector.CC, configurations correspond to the groundedgrid and cathode follower tube connections. re-spectively (see figures H2 and H3 of the fold-out). We will use the letter designations CE,CB, and CC as indicated; the first C stands forcommon and the second capital letter identifiesthe electrode.

4-19. The predominant circuit configurationused with junction transistors is the commonemitter. The CE current amplification factor iscalled the forward current transfer ratio; it is

represented by beta, or hre. It reflects the ef-fect that a change in base current, In, has uponcollector current. with a constant collector-

Pikemitter voltage, The value of g for a particu-lar transistor can be found in a transistor manual.

4-20. Two special-purpose devices are the uni-junction transistor and the silicon controlled rec-tifier (SCR). These devices are designed forrapid switching purposes. Because they have twostable states, they are said to be bistable. Let'ssee how they operate.

4-21. Unijunction Transistor. Like a diode, theunijunction has a single p-n junction. However,it has two leads connected to the n region. As-suming the initial state to be that shown on theleft of figure I of the foldout, the p-n junctionis reverse biased. Consider the n region as avoltage divider (normally, about 5 K to 10K ohms). If the total voltage from base 1 tobase 2 is +10 volts, the voltage halfway be-tween base 1 and base 2 is +5 volts. Since thep region is at 0 volts, the junction is reversebiased. Only a minute amount of emitter cur-rent can flow and conduction is at a low level.This state is maintained until the voltage on theemitter is increased to about +5 volts. Once thep-n junction becomes forward biased, currentrapidly rises to a high-level state (right portionof figure I of foldout 1). Thus, whether the uni-

: junction is in the high-level state or low-level statedepends on the bias conditions. These devices canbe designed to conduct heavily at any desiredfraction of the applied base 2 voltage.

4-22. Silicon Controlled Rectifier (SCR). TheSCR is basically a four-layer n-p-n-p semi-conductor device. In the left-hand portion of fig-ure J of the foldout, we see that the device has

three contacts---a cathode, anode, and gate.Like a rectifier, it conducts mainly in one direc-tion. Under reverse bias conditions, the de-vice operates in a manner similar to a conven-tional rectifier as it has a slight reverse leakagecurrent. However, it does not conduct immedi-ately in the forward direction. As the voltage isincreased at the anode, a value is reached atwhich the current increases rapidly. This is calledthe forward breakover voltage. At this point, thehigh int-...rnal resistance of the device changes to alow value and current increases rapidly. Now thedevIze is considered "on" or triggered. It willremain in this high conduction state until theanode voltage drops to a value which cannotmaintain the breakover current. This current iscalled holding current. Below this value of for-ward current, the SCR returns to its high-resis-tance state and current ceases to flow. Now theswitch is "off." Follow the gate current curve inthe right-hand portion of figure J of foldout 1.

4-23. The breakover point of an SCR can becontrolled by injecting a signal at the gate. Thus,it can be turned on and off at will. With no sig-nal applied, gate current is zero. As the signal

5

.18-)

particular example. Assuming a 60-cps effectivea-c input (E) of 300 volts, figure 10 tells us thatthe maximum d-c output for a center-tap full-wave rectifier is about 0.7E = 0.7 X 300v =210v with a ripple frequency of 2f = 2 x 60cps --a-- 120 cps. The diodes must withstand apeak-inverse voltage of 1.4E = 1.4 x 300v =420v. As you see, these values can be quickly

and readily determined if you know the informa-tion contained in figure 10.

5-4. Having reviewed the: basic single-phaserectifier circuits. let us now c-on$ider some three-phase circuits. Using a three-phase input greatlyincreases the quality of the output. You can seethe reason for this in figure 11,A. The unfilteredoutput waveform clearly shows why the ampli-

AC INPUT1. .1 ..

-!

UNFILTERED DC OUTPUT,:-,'

RIPPLE

% FREQ.

10

r

Ail

V I/f = VT

.

3gIN NM V\nerr

18 31TOUTA

---80 ---01012 ,::11

A. COMPARISON OF SINGLE.PHASE AND B. THREE-PHASE HALF-WAVE RECTIFIERTHREE-PHASE HALF-WAVE RECTIFICATION CIRCUIT

Figure II. Half-wave Rectification.

19

1.8q

/77

A

A. CENTER-TAPPED Y SECONDARIESB. SEPARA1E Y SECONDARIES (PHASES Ak5 IN EFFECT

CENTER-TAPP ED)

Figure 12. Three-phase renter-tap rectifier circuit.

tude of the ripple is greatly reduced when athree-phase unit is employed. Note the markeddecrease in the percent of ripple. Observe alsothat the ripple frequency is tripled, which facili-tates filtering and improves regulation.

5-5. Figure 11,B, shows a simple three-phasehalf-wave rectifier circuit. Trace out any onephase and it becomes apparent that the circuitis that of a single-phase half-wave rectifier. Thus,a three-phase unit is no more than a combinationof three single-phase units. Since each phase isdisplaced by 1200, the filter is charged threetimes rather than once per cycle and the result-ant output is the composite of the output of eath',phase.

5-6. Because this rectifier unit requires Morerectifiers and a three-phase source, it is largerand more costly than a single-phase unit. Likethe single-phase unit, a three-phase unit can betransformerless. When transformers are used, theprimary windings may be connected either delta

4. (A) or wye (Y).

5- 7. We have spoken only of a three-phaseunit. but a polyphase ha!f-wave rectifier mayconsist of any number of phases. It stands torer.son that tne greater the number of phases.the lesser the percent ripple and the better theoutput. Regardless of the number of phases, theoperation of a polyphase unit is fundamentallythat of single-phase units feeding a common loadin time sequence.

5-8. Although polyphase units overcome thedisadvantages of low-frequency ripple, a capaci-tor-input filter still develops a high Ply. Eachrectifying diode must withstand approximatelytwice the peak secondary phase voltage (line-to-neutral voltage).

5-9. As with half-wave rectifiers, the d-c out-put of center-tap rectifiers can be improved byusing a polyphase network. Two 3-phase net-works are shown in figure 12. Notice that anyone phase is identical to the single-phase center-tap rectifier circuit in figure 9,B. So again apolyphase rectifier can be regarded as a com-bination of single-phase rectifiers operating intime sequence to supply a common load.

5-10. A basic three-phase bridge rectifierworkMg from a A secondary is shown in figure13,A. Trace out a single phase and prove to

A

THREE-PHASE

HALF-WAVEFULL-WAVE

CENTER-TAP,

BRIDGE

UNFILTEREDDC VOLTAGEOUTPUT

1,114:tqF ORM

"eNeN ,.................,

% RIPPLE IS 4 I

RIPPLEFREQUENCY 31 i 61 61

Figure 13. Threephuse bridge rectifier circuit.

201 86

i7g

.C)

yourself that the circuit is identical to the oneshown in figure 9.C. The combined output of thethree phases which are operating 1200 apart pro-duces a waveform that has a low-percent ripple(4 percent) and a high ripple frequency (sixtimes the input frequency j). When we comparethc output of the bridge rectifier with the othertypes in figurc 13,8. we sec that the bridge recti-fier affords the advantages of fuil-wave rectifica-tion at a high d-c output voltage.

5-11. Voltage Regulators. Keeping the outputof a d-c power supply constant is of critical im-portance in many TV applications. It may beabsolutely necessary to use voltage regulators orcurrent regulators in conjunction with the recti-fier unit. Some power supplies will have bothvoltage and current regulation.

5-12. Regulator units may be quite simple,using a single thermistor VR tube or Zener diode.On thc other hand. complicated units will usean array of tubes or solid-state devices. Althoughsolid-state regulators are similar to electron-tuberegulators. they can be fashioned in many dif-fercnt ways. The fact.that either n-p-n or p-n-ptransistors can be used permits considerable di-versity in design. We will progress from thesimple to the more involved circuits by explain-ing the operation of representative shunt andseries type regulators.

(Vu

THERMISTOR

- -Vti 2 UNREGULATED DC VOLTAGE INPUTVR = REGULATED DC VOLTAGE OUTPUT

A

1.RANGE OF OPERATION.'

THERMISTOR 1. Rs

rHERmisrom

CURR ENT

Figure 14. Thermtster shunt regulator.

21

Figure 15. Zener diode regulator.

5-13. Shunt types. Two reasons for the useof shunt voltage yegulators are: (1) their lowcost in the simplest form and (2) their inherentoverloak nd short-circuit protection. Essentially,a shunt voltage regulator consists of a limitingresistor in series with the load and a variableresistance component in parallel (shunt) with theload. The circuit shown in figure 14,A, is a simpleshunt regulator unit. R is the series limiting re-sistor. The combination of Rs and the thermistoris the variable resistance that parallels the load.This circuit is capable of stabilizing the d-c out-put voltage against variations of input voltageand load (current drain) over comparativelywide ranges (see fig. 14,B). Although simple,it is very inefficient because of the power con-sumed in the regulator unit itself.

5-14. The Zener diode regulator circuit (seefig. 15) is comparable to the VR (voltage regu-lator) tube- circuit. The voltage across the Zene.:diode is virtually constant and independent ofcurrent. Diode current must be limited by a serieslimiting resistor R of proper size. The operationof the circuit is very simple, since the voltageVR, remains practically constant so long as theinput and load variations stay within the speci-fied limits of the Zener diode. Like VR tzlbes,Zene: diodes can be connected in series to pro-vide different regulated voltage values. Theyhave numerous voltage and power ratings, with5-percent, 10-percent, or 20-percent tolerances.

5-15. If the Zener diode regulator is not sat-isfactory, an arrangement like that shown in (*s-ure 16,A, may be used. Here we see a p-n-ptransistor connected across the output to regu-late the voltage. Note that the collector-to-basedifference in potential is held constant by a Zenerdiode. Therefore, any change in voltage causedby either the input or load affects the base-to-emitter current IR. Accordingly, MR is am-plified by approximately. the p factor, hirE. Thecurrent change Ale through the transistor

18

R I

A

Figure 16. Transistor shunt regulator.

counteracts any voltage change. For example,suppose the load draws more current; the voltageon the load side would tend to decrease. Basecurrent In will decrease and cause an amplifieddecrease in Ie. In effect, the decrease in Iccompensates for the increase M load current soas to maintain the same voltage drop across Rl.We see, then, that any change in Va is counter-acted to regulate the voltage. Assume that theload current decreases, and reason through theregulating action that results.

5-16. Now consider what takes place if Vuwere to rise. Wouldn't Ia increase and causethe transistor to conduct more heavily? Becausethe transistor conducts more heavily, the currentthrough R1 must increase. Practically all of therise in Vu is therefore dropped across R1, andVR remainr practically the same. For a de-crease in Vu, the reverse action occurs.

5-17. Another circuit possibility is that shownin figure ,16,B. The emitter is kept at a constantpotential by the Zener diode. Thus, any voltagevariation appearing across the output terminals

22

is sensed by the transistor's base as an input sig-nal. Again we have amplifier action, and thecurrent through the transistor changes to regu-late the output voltage, V.

5-18. An advantage of this circuit is that Vacan be adjusted to a desired fixed level. Thisfeature makes it possible to set Va at a higheror lower value to compensate for aging or for

V T 41

THERMISTOR

A

IMO

Figure 17. Series-type voltage regulator.

187

IFO

different load requirements. Resistors R2 and R4establish the rangc of voltage for bias that canbe tapped off R3. The bias determines the tran-sistor's quiescent (operating) point and its d-cresistance. In other words, by Changing the biassetting, we change the transistor's resistance sothat a greater or lesser amount of the inputvoltage appears at the output terminals. For in-stance, to increase the d-c output voltage, Vic,the movable contact to R3 must be moved down-ward. This will decrease the forward bias on then-p-n transistor. Since the transistor conducts lesscurrent, less current flows through RI, whichmeans the voltage drop across 111 is decreased.Accordingly, the output voltage, Vn, is in-creased. From the .viewpoint of voltage division,we have simply increased output resistance bydecreasing the transistor's forward bias. Propor-tionately more of the applied input voltage is

therefore "seen" at the output terminals. To ob-tain a lower value of regulated voltage, Vn, ofcourse. the movable contact is moved upward(more positive) to increase the transistor's for-ward bias.

5-19. A Zener diode does not need a "start-ing" voltage surge; therefore. it does not requirethe associated circuitry necessary to ionize a VRtube.

5-20. A drawback of any shunt type regulatoris its low efficiency. We can appreciate this whenwe realize that the output power is divided be-tween the load and the shunting circuit; at no-load the shunting circuit dissipates the full out-put power. Consequently, proportionately largeamounts of output power are wasted, particularlywhen the loads are small. For this reason, thesmall-load efficiencies of shunt regulators arenotably low.

5-21. Series voltage regulator. A series typeregulator can have comparatively high small-loadefficiencies. That is because, as its name implies,the regulating device (a variable resistance) is inseries with the load. In figure 17,A, we see howa thermistor is used to prevent voltage changescaused by variations in load. The thermistor actsas a variable resistor in a voltage divickr circuit.If the load resistance decreases, tending to lowerVn. the resistance of the thermistor decreasesas a result of the additional heating caused bythe increased load current. This action keeps theratio of the thermistor's 'resistance and load re-sistance about the same. Since the voltage d. "-sion of the input is virtually unchanged, Vn isregulated. When a decrease in load occurs, thethermistor's resistance increases to regulate Vn.

5-22. Although a thermistor regulates fairlYwell ynder changing load conditions. it will notregulate input variations. In fact, it makes reg-

23

ulation worse instead of better..-Asrme-that theinput Vt. increases. What happens? Current increases, causing the drop across the-thermistor todecrease. This is just the oppositv of what wewant. The drop across the regulating deviceshould increase to prevent-a rise in V.

5-23. A series-rigplator circuit that regulatesboth load and inpur.variations is shown in figureI7,B. Moreover, the transistor's amplifying cap-ability improves regulation. The n-p-n transistoris a sensitive variable resistance. Because itsbase itheld at a fixed potential by the Zenerdiode, any change in Vu or Vn affects thetransistor's bias. The drop across the transistor,VrE, changes to stabilize Vu. Let us brieflydescribe how the circuit operates.

5-24. Consider first a change in load. We willassume that it increases. This tends to lowerVn /and increase the potential difference be-tween the emitter and base. Since the base-to-emitter forward bias is increased, the transistorconducts more heavily. Therefore, VvE is low-ered and counteracts the decrease in Vn. So

we have regulation. If the load decreases, thebias decreases to regulate Vu. In a similarfashion any variation of the input Vu causesa bias change. The drop across the transistorautomatically increases if Vu increases, or de-creases if V/. decreases. Such action maintainsVn nearly constant. Be sure you understandwhy this is so. Study figure 17.B, and determinethe sequence of events for all the possible condi-tions of change.

5-25. We can get better regulation by using acircuit such as the one shown in figure 17,C.Note the 01 is a p-n-p transistor, whereas 02is a n-p-n transistor. Inasmuch as each transistoramplifies, this arrangement is quite sensitive andcan give excellent output-voltage stability overthe designed range. Observe also that the outputof this circuit can be adjusted by R3, as ex-plained earlier.

5-26. After we go through one condition ofchange you should be able to analyze the per-formance of the circuit for the remaining three.We will describe the behavior of the circuit forthe condition of increased load. This leaves theconditions of decreased load, increased inputV1., and decreased input VI; for you to figureout

5-27. To prevent Vu from dropping with anincrease in load, VrE of 01 must decrease.Let's keep this in mind and see if it will occur.Any decrease in VI; iS felt in full at the emitterof 02, but is felt only in part at the base of 02.Here's why: Since the drop across the Zeilerode is constant, any voltage change appears4n-tirely across RI, from the emitter

180

7%2

ground. However, this is liot so for thc base of02. It "sees" only a fractional amount t.

change which is tapped off of R3 in the voltagedivider circuit (R2, R3, and R4). You recallthat for an n-p-n transistor the base is more posi-tive than the emitter. Then if the emitter dropsmore (becomes less positive) than does the base,the bias increases. Such being the case, 02 con-ducts more heavily. Note that the collector cur-rent of 02 is actually the base current Ili of 01.We know, then, that an increase in IR of 01causes 01 to conduct more heavily and its Veyto drop accordingly. Isn't this what we wish tohappen?

5-28. From the standpoint of bias on 01, itsbase becomes less positive (more ILgative withrespect to its emitter) because 02 conductsmore heavily. Since Q1 is a p-n-p transistor,the bias increases and causes the voltage Veyacross 01 to drop as in our previous analysis.

5-29. However you choose to analyze the cir-cuit, the outcome will be the same: regulation.

5-30. Let us now look at a more complexvoltage regulator which is similar to a type youmay have to maintain. Note in figure 18 that05, 06, and 07 are connected in parallel; they

serve as serics-reeulating transistors in the nega-tive line of the supply. These transistors arecontrolled by the amplifying network which in-cludes Q1, 02, 03, and 04. The transistor Q1senses any voltage change at its base since Zenerdiode Z 1 keeps 01's emitter vthage constant.The amplified change becomes inverted at 01'scollector and appears on the base of 02. An-other amplified inversion occurs at the collectorof 02 which is also the base input to 04. Theamplifier circuit containing 03 is a regenerativefeedback arrangement which increases the inputchange to the base of 04. To understand this,observe that a double inversion is realized ingoing from the base of 04 to the collector of 03;one inversion occurs from base to collector of04 and another from emitter to collector of 03.Because this is a regenerative loop, the capaci-tor is used to prevent high-frequency oscillation.Any spurious high frequency is shunted by thecapacitor across 03; since there is no inversionacross 03, the feedback loop for high frequen-cies is degenerative. Zener Z2 establishes thereference for Q3, and amplifier operation is ad-justed to th e. optimum condition with the vari-aim:: emitter resistor (this is a factory adjust-ment and normally nced not be made again).

V0 A

L 0T J

A U

G S

E T

07

Figure 18. Complex series voltage regulator

24

-Lauri

1 ISV60INPUT

C I

Figure 19. Switching-type voltage regulator.

5-31. The output of 04 is taken from itsemitter, so the output is in phase with the changeapplied to its base. This output controls 05which in turn controls the other two paralleledseries-regulating transistors 06 and 07.

5-32. As in previous circuits, we will assumea particular condition and determine the regula-ting action that results. Let us suppose that theregulated voltage V8 tends to rise (becomemore positive). To counteract this, the voltagedrop across 05, 06, and 07 must increase. Wewill see whether this occurs.

5-33. If V8 increases, the base of Q1 goesmore positive. Since it is an n-p-n transistor itconducts harder and its collector becomes lesspositive. This makes the base of p-n-p transistor02 less positive, which causes it to conductharder also. Consequently, the collector of 02and base of 04 become more positive. The cir-cuit containing 03 regeneratively feeds back thecollector output of 04 to drive the -base of Q4even more positive. (You should be able to fig-ure out why this is true.) Because the base of04 goes more positive, so must its emitter. Thisaction decreases the forward bias on p-n-p tran-sistor 06. thereby causing it to conduct less. The

IDE

25

reduced voltage drop across the emitter resis-tance of 05 decreases the forward bias appliedto the bases of 06 and Q7. We note, therefore,that 06 and 07 conduct less, as does 05. Theresult Is that the voltage drop increases acrossthese three regulating transistors. This is whatwe said should occur to counteract the assumedincrease in Vit. If V8 would try to decrease,the opposite actions would occur. Regulation isexcellent because this circuit is highly sensitiveand reacts instantly to prevent variations in out-put voltage caused by load or input.

5-34. Switching regulators. Besides the vari-ous types of shunt and series voltage regulators,there are switching regulators that have opera-ting efficiencies approaching 100 percent. Theseregulators use semiconductor switching devicessuch as unijunction transistors (UJT) and sili-con control rectifiers (SCR) in a variety of con-trol circuits.

5-35. The switching regulator circuit shownin figure 19 is unique in several respects. Noticethat the SCR's are part of the rectifying bridgecircuit. Regulation is accomplished by control-ling the firing point of the SCR's. An SCR issimilar to a thyratron, but its forward drop and

1.90

turn-off times are about one-teeth those of athyratron. As much as 50 amperes can behandled by high-current SCR's. The SCR's inthis circuit are fired by gate pulses which aredeveloped' when the UJT conducts. The timerelationship of the gate pulses to the start timeof each I15-a-c input alternation determines theconducting time of the SCR's (see fig. 20). Bysensing load voltage variations, the gate pulsesare electrically delayed or advanced to adjustthe conduction time of the SCR's. This effec-tively delivers the proper amount of current toC2 so that it maintains a virtually constantcharge voltage which is V. Because a chokeinput filter is used, the diode D is needed sothat current can continue to flow through thechoke L and load when both SCR's are cut off.

5-36. To understand how the gate pulses are

ACINPUT

GATE PULSES

RECTIFIEROUTPUT

GATE PULSES

RECTIFIEROUTPUT

produce& study the upper circuit shown in fig- 071tire 19. The output from the full-wave center-tap rectifier is clipped by Zener diode Z. Thisclipped waveform appears across the UJT cir-cuit and also across R in series-with C I. TheUJT acts as a switch; it does not conduct untilthe emitter reaches a prescribed potential. Whenthe applied voltage rises to its clipped value, Clcharges to the emitter potential which fires theUJT. After discharging CI, the UJT cuts off.This on-off action of the UJT once per alterna-tion of the input produces the gate pulses thatare applied to the SCR's. Whichever SCR hasthe forward-biased anode at the time a gatepulse occurs will fire; thus, the SCR's fire alter-nately (see fig. 20).

5-37. Since the time at which a g pulse isgenerated depends on the charge time of CI, the

i i iSCRI

,

SCR2 SCR 1

CONDUCTS CONDUCTS CONDUCTS

_A 1

CONDSUCCRT IS

N

illi.o60CONDUCTS

SCR2 SCR I

CONDUCTS

IM411111Figure 20. Waveforms for switching voltage regulator.

26 19i

A

ZR

8

Figure 2,1: Constant-current regulators.

gate can be delayed or advanced by increasingor decreasing the charge time, respectively. Thisis done electrically by the circuit containingn-p-n transistor Q. For example, if the voltageVi; tends to risc, a positive error voltage, sensedat the base of 0, causes Q to conduct harder.Thus. current is diverted from CI and its chargetime is increased. As a result, the gate pulsesare delayed. From figure 20 you see that theSCR's conduction time is decreased. This re-ducer the charge on C2, thereby counteractingany increase in VII. On the other hand, if achange in load or input tends to decrease V1{,the gate pulses are advanced. The SCR's conductlonger. and C2 charges more to regulate V.Determine why this occurs and you will under-stand how this regulator maintains a constantvoltage output under varying load or input con-ditions. '

27

/ Is5-38. Constant-Current Regulators. In con-

trast with a voltage regulator, the current regu-lator stabilizes output current, In, rather thanoutput voltage, V. Its primary function is tosupply a constant current to the load. To do this,the regulating deyice must prevent a change inoutput current.

5-39. Figure 21,A, shows a circuit that canbe used. Instead of sensing the voltage acrossthe output terminals, the transistor senses thecurrent through RI. Any current change deve-lops a voltage change across RI, which altersthe bias of the p-n-p transistor. The transistorresists the current changes. For example, an in-crease in current will increase the voltage acrossRI and make the emitter less positive. This de-creases the base-to-emitter forward bias of thep-n-p transistor and decreases the current flowthrough it. Thus, the transistor action opposesany change in I.

5-40. The circuit shown in figure 21,B, hasthe added feature of adjustment by R2. Note*that it uses an n-p-n transistor, and the sensingresistors RI and R2 are on the load side. Al-though this circuit is somewhat different, it regu-lates In in much the same manner as the onepreviously described. Suppose, again, In triesto increase. The emitter becomes more positiveand the base-to-emitter forward bias of the n-p-ntransistor decreases. This means that the in-crease in current is opposed by the tratisistoraction. On the other hand, if In tries to de-crease, the base-to-emitter bias increases. Sinceany change in current affects the bias, the tran-sistor counteracts the change and thereby regu-lates the output current.

5-41. Improved regulation is achieved byamplifying the error applied to the control tran-sistor. This is illustrated in figure 22. The tran-sistor 02 serves as a d-c amplifier. Output cur-rent can be adjusted to the desired value withR2. Otherwise, this circuit corresponds to thecircuit shown in figure 21,A, and regulates inthe same manner.

5-42. Symptoms and Troubles. Aside fromthe use of solid-state devices in place of electrontubes, circuit configurations for solid-state powersupplies have been shown to be similar or iden-tical to electron-tube power supplies. For thisreason, troubleshooting procedures are practi-cally the same with regard to circuitry. Often themalfunction of a power supply is the fault ofthe rectifying device. Electron-tube diodes fail;so also do metallic and crystal rectifiers. Cer-tain faults can be attributed directly to the recti-fier: (1) open-circuited rectifier, (2) short-cir-cuited rectifier, (3) high forward-voltage drop,(4) high leakage current, and (5) overheated

Figure 22. Constant-current regulator with il-camplifier.

rectificr. The symptoms associated with thesefaults can be readily detected, since they causcobvious and sometimes serious trouble.

5-43. An open-circuited rectifier causes a lowerd-c output or no d-c output. If the rectifierunit is a full-wave or polyphase type, the d-coutput would be reduced when one rectifier isopen-circuited. If it is a single-phase half-waverectifier, there will be no d-c output.

5-41. Improved regulation is achieved byamplifying the error applied to the control tran-circuited rectifier. In addition, there will be ex-cessive heating and a-c will appear at the output.Unless short-circuit protection is built into thepower supply, other circuit components can bepermanently damaged.

5-45. For a solid-state rectifier, either a highforward-voltage drop or a high leakage currentwill cause lowered cl-c output and increasedheating. A high forward-voltage drop is causedby an increased forward resistance, whereas ahigh leakage current is caused by a decreasedreverse resistance. Whichever fault occurs, therectification ratio is reduced accordingly, andlikewise the efficiency of the rectifier.

5-46. An overheated rectifier may be causedby faults (2), (3), or (4) mentioned previously,and also can be caused by excessive loadine orinadequate cooling. Regardless of the cause, arectifier that is heated beyond its safe limits willbe short-lived or completely destroyed. Whcnthe source of the trouble is the rectifier itself,replacement of the rectifier will return the cir-cuit to normal operation. However, when theoverheating is the result of loading or improperheat dissipation, the trouble will persist after therectifier has been replaced, unless correctivemeasures are taken to insure proper loading andcooling.

5-47. When a power supply has a regulatorunit, a defective solid-state device (thermistor,

Zener diode, transistor. etc.) rna be thc sourceof t:ouble. Thc sympioms will ranee sfrom anincreased or reduced d-c output (regulated ornot) to no d-c output. The symptoms and trou-ilk's are dependent upon the complexity of thecircuitty as well as the type of -regulator unitemployed. We cannot, therefore, speak on thissubject in a general manner. For any particu-lar unit, you will have to depend on your basicknowledges and reasoning ability to determinethe cause of a malfunction. To give you somepractice, we will describe symptoms and diag-nose specific troubles in one of the circuits juststudied.

5-48. If the output voltage of the regulator infigure 18 is abnormally high and unregulated,the trouble will likely be in the circuit of 01.Because there is no regulation, we know 01 isnot functioning properly. Moreover, we can rea-son that the collector voltage of 01 must bc highto cause a high output voltage. Three troublesthat can give these symptoms are: (1) an openbetween the Voltage Adjust and + output ter-minal; (2) an open transistor, 01; and (3) anopen Zener diode. Z1. For each of these trou-bles the series-reaulating transistors 05. 06, and07 will have an abnormally high forward bias.Therefore. practically all of the. d-c input VI. is"seen" as unregulated voltage at the output ofthe regulator. Be certain that you understandwhy the troubles specified can give the symp-toms described. This may require your restudy-ing the regulating principles involved.

6. High-Voltage Power Supplies6-1. By means of a step-up single-phase or

polyphase transformer, a-c voltaaes can be in-creased to the necessary levels to obtain desiredrectified high voltages. Thc high d-c voltages re-quired for TV equipments arcin the order ofthousands of volts. For high-p-Ower equipmentssuch as those needed for broadcasting, the high-voltage (HV) supply must deliver considerable

II -4AC INPUT...4

12Fipure 23. Conventional voltage doubler.

2819 7)

current. Such supplies use the same full-wavesingle-phase and polyphase rectifier circuits thatwe discussed in the preceding section. Of course.the input transformers must step up the vol-taues to the required peak values, and compo-nents must be rated to handle high voltages andcurrents. I.ike low-voltage power supplies, tubeand solid-state rectifiers are used. .

1)-2. Since high-power H V supplies do not dif-fer in operating principles from those just stud-ied. we will give our full attention to varioustypes of low-power HV supplies that are foundin TV equipments. Although these HV suppliesdevelop 20.000 volts or more. load current is

relatively small. We will explain how such out-puts can be obtained by voltage multipliers andby rectification of pulses or an oscillating vol-tage.

6-3. Usually the a-e source and d-c load aresufficiently stable so that regulation is not neces-sary. However, a regulated high voltage is re-quired for some applications. Therefore, we willanalyze circuits which keep the voltage outputconstant under varying load conditions. Thefinal portion of this section is given to diagnosingtroubles from given symptoms.

6-4. Voltage Multipliers. If a voltage multi-plier is used, it is not necessary that a transfor-mer step up the a-c voltage to as high a value.In fact. a hiuh d-c voltage can be developed byvoltage multiplication without a transformer atall. Let us review two types of rectifying circuitsthat produce a d-c output voltage which is bouttwice the peak a-c input voltage; then we willexplain how higher multiples of voltage can bedeveloped from a given source.

6-5. Com.enthmal voltage doubler. In figure 23the rectifiers are connected so that they conductforward current on alternate half-cycles. Duringthe positive alternations of the secondary voltage,the upper rectifier conducts 11. and the capacitorCI charges to the peak secondary voltage E.During the negative alternations of the secondaryvoltage. the lower rectifier conducts 12 and thecapacitor C2 charges, also to the peak secondaryvoltage E. Since the polarity of the charge onC2 is scries-aiding the charge on CI, the voltageacross the output terminals is 2E (approximately2.8 times the secondary rms voltage)..Inasmuchis both the charging (via the rectifier) and dis-charging (via the load) of CI and C2 constitutethe ripple, the ripple frequency is twice the fre-quency of the input a-e. This doubler is essen-tially a full-wave rectifier; both the positive andnegative alternations feed power to the load.

6-6. A disadvantage of this circuit is that theinput and output are at different d-c voltagelevek. l the lower output terminal is grounded.

29

IAS

the lower end of the secondary is E volts d-cabove ground. On the other hand. if one sideof the input is grounded (as will necessarily bethe case for a-c taken directly from a powerline), neither of the output terminals can begrounded.

6-7. Caulide voltage multipliers. A circuit thatpermits one side of both input and output to begrounded is shown in figure 24. Moreover, byadding sections (the heavy-lined circuitry in fig-ure 24,B), any desired multiplication of voltagecan be obtained. After we analyze the operationof the cascade doubler, we can readily explainhow higher degrees of multiplication are ac-

quired.6-8. For convenience, let us consider the neg-

ative alternations first (see fig. 24.A). Duringthese alternations. CR1 keeps Cl charged to E(about 1.4 rms), with a polarity as indicated inthe figure. On the positive alternations. C2 iskept charged by the conduction of CR2. WhenCR2 conducts (forward direction), C2 "sees"

.the peak a-c input voltage which is series-aidingthe voltage across CI, Thus, the input peak Eplus the voltage E on CI charges C2 and 2E.

6-9. Although full-wave rectification occurs.the output capacitor C2 is charged only duringthe positive half-cycle. Consequently, the ripple

A

CR4

C4

CR3

CR2

C2

CR I

Figure 24. Cascade voltage doubler and quadrupler.

19 4:

a

Figure 25. Cascade voltage multipliers.

frequency of the cascade doubler is that of ahalf-wave rectifier, equal to the a-c input fre-quency. This means that, like the half-wave rec-tifier, the cascade doubler is not suited for heavyloads. Regulation is poor and filtering is difficult.

6-10. For light loads that require a high d-cvoltage, the cascade circuit is quite popular, sinceit can be built up to provide the desired level ofoutput. Refer to figure 24,B, and note that theheavily lined circuitry is a. replica of the cascade

doubler circuit. It is therefore possible to in-crease t!,e d-c voltage in multiples of two by

adding on doubler circuits.6-11. The lightly lined circuit of figure 24,B,

is identical to that of figure 24,A, and operazesin the same manner. The heavily lined circuitdiffers only in that the. voltage across the inputcapacitor C3 is 2E rather than E. Capacitor C3is kept charged to 2E by the action of CR1 andCR3. These -two rectifiers effectively place C3

in parallel with C2. Whenever the charge on C3

is less than that of C2, CR3 is forward biased.So when CR1 becomes forward biased duringthe negative half-cycle of the source a-c input,C3 is charged by C2. We see, therefore, thatthe output capacitor C2 feeds the input capaci-tor C3.

6-12. Note that the d-c voltage with respectto ground (or common) at point a is E, at point

b is 2E, at point c is 3E, and at point d is 4E.Additional sections will give 5E and 6E, 7E and8E, and so on. Figure 25,A, shows how the cir-

cuit may be represented schematically.

6-13. A similar cascade voltage multiplier cir-

cuit is illustrated in figure 25,B. For the samenumber of sections, however, only half of the

value of d-c voltage is developed. Resistors are

used to replace the diodes that conduct duringthe negative input alternation. Each resistor per-mits the upper-line capacitor to charge throughthe a-c source to the potential of the lower-linecapacitor. Observe in figure 25,B, that the upper-line and lower-line capacitors in the first section(likewise, in subsequent sections) are chargedto the peak input a-c. This multiplier drawssource current only on the positive input altern-ation. As a quadrupier, it requires three resistorsand three more capacitors than the circuit offigure 24,B.

6-14. Either type of cascade voltage multiplieris particularly useful as a high-voltage low-cutrentsupply. Tube, metallic, or crystal rectifiers canbe used. Each rectifier must withstand twice thepeak input a-c in the reverse direction. Regard-less of the amount of multiplication, the maxi-mum PIV on any single rectifier is 2E. Makesure you understand why this is true. Also proveto yourself that the ripple frequency is the same

V I

HORIZONTALOUTPUT

V2BOOST

VOLTAGE

HV

TO NOR.DEFLECTION

COILS

a.

A

HORIZONTALOUTPUT

HV

BOOSTvOLTAGE

Figure 26. Flyback NV system.

TO NOR,DEFL. COILS

as the Input a-c regardless of the amount of mul-tiplication.

6-15. Pulse and Oscillator Types. Althoughhigh-voltage transformer can bc excited by the

-4) 5-volt a-c line, it is more practical to use att.:irmpulte, an oscillating, or a transient voltage for

,,../sAcicatipn when the high-voltage d-c load is

mall. You know, for example, that the high-,'.,voltage supplied to a picture tube is commonly

excited by the horizontal output stage in a TVreceiver. The current drain, which is less thanI ma., does not adversely affect the operation ofthe stage.

646. After briefly discussing flyback pulse-type high-voltage supplies which should be famil-iar to.you, we will analyze the operation of some-what more complex supplies which incorporateregulating circuitry.

6-17. Flyback HV system. Thc.,circuits shownin figure 26 arc representative HV suppliesthat arc pulsed by the horizontal output ampli-

II

sc

NV SILICONCARTRIOGE

C2

C3

Ff,gure 27. Regulated HI/ power supply.

VOLTAGEAOJUST

31

fier. Both systems employ autotransformer ac-tion to produce a high-voltage spike during theflyback time of thc horizontal sweep. This short-duration pulse applied to rectifien VI keeps CIcharged to provide a high d,c voltage output.Because the ripple frequency is that. (JP fhe hori-zontal sweep (usually 15.750 lvps), filtering is

readily accomplished with -,a small capacitor(about 500 =/:-/z4).

6-18.A!lthotigh different flyback transformersare entpleyed7-both systems develop a boost volt-age. The diode V2 (damper for the horizontaldeflection coils) provides rectification of the fly-back overshoot pulse, thereby charging C2 andC3 to a higher than B+ d-c voltage. This boostvoltage is usually applied to the plate of the hori-zontal output tube and may also be applied toother circuits.

6-19. A definite advantage of the flyback HVsystem is its dependency upon the horizontal out-put for excitation. If there is no horizontal out-put, there is no high voltage. Thus, a failure inthe horizontal output removes the high voltagefrom the picture tube. This prevents a stationaryspot from appearing on the screen which mayburn or desensitize it.

6-20. Regulated HV systems. As mentionedearlier, most HV systems do not need to be regu-lated. Nevertheless, it is well that you understandhow regulation is obtained when required. Thetwo systems that we have selected to explainoperate on different principles. Unlike the fly-back pulse type, both are excited with oscilla-tors which are regulated by sensing-error voltagesin the HV output.

6-21. The system shown in figure 27,A, is

made up of a high-frequency oscillator, conven-tional voltage doubler, and voltage divider ar-rangement that amplifies any error voltage de-veloped across RI. We have drawn the circuitof VI so that you can readily recognize it as aHartley type oscillator. The _oscillating signal is

impressed across the primar)fots the transformer,T. Now iiace through the:ctialit containing thetransformer's secondary, R1, C3, andC2. Compare this circuirwitttlhat of figure 23and you will see that `itl'is,-eiientially the same.The resistor RI is naffaa to develop a bias forV4. Moreover, it is resistor that anychange in the HV outpus ettsed and coupledto the grid of V4. The circuiRontaining V4 andV5 operates as a variable voltage divider thatadjusts the screen grid potential of VI. A changein screen grid potential changes the amplificationfactor of VI and therefore the amplitude of theoscillating signal. Since this signal is the excita-tion to the HV rectifiers, any change in its am-plitude affects the high-voltage d-c output.

1.96'

/59

CUTOFFBIAS

INPUTTO 01

COLLECTORCURRENT

01

M1GMVOLTAGEEXCITATION

IPMOO NMI/ OEM

A

I ICUTOFF

BIAS lo OOP OONIM IIMMO OlOta

I I

I

0 -A---V1-I I I

Figure 28: Wavefortns associated with figure 27, B.

6-22. Now let's look at specific cases. Assumea load variation that would tend to change theHV output. Suppose load current increases. TheHV would tend to drop because C2 and C3 de-liver more current. This means that V2 and V3pass more current and the average currentthrough RI increases; capacitor Cl acquires amore negative charge. With increased bias ap-plied, V4 conducts less, thereby decreasing thebias on VS. Thus, the voltage at the plate ofV4 rises, applying a more positive potential tothe screen grid of Vl. Since this increases theamplitude of the oscillating signal generated, ex-citation is increased to counteract the drop inHV caused by loading. Opposite actions wouldoccur if the HV tended to rise.

6-23. Excellent regulation is achieved becausethe error voltage is amplified by both V4 andVS in the voltage divider circuit. Thinking ofthis circuit in terms of resistance, note that whenthe error. makes the resistance of V4 increase,theta is an immediate resistance decrease of VS.Conversely, a resistance decrease of V4 causesa resistance increase of VS.

6-24. Because excitation is obtained from afree-running oscillator, provision should be madeto remove high voltage from a picture tube orcamera tube when there is sweep failure. Suchprotection is not needed, however, if a drivenoscillator is employed. The system shown in fig-ure 27,B, contains such an oscillator. Transistor01 is driven "on" and "off" by the input signal

32

applied to its base (see fig. 28,A). Each tune01 cuts off, the auto transformer is shock-ex-cited and oscillates as iliustrated at its naturalresonant frequency. As soon AS QI is driven intoconduction. however, the oscillations cease. Youneed bear in mind that there is no HV excitationwhen 01 is "on."

6-25. The operation of this system is normallydependent upon positive trigger pulses which gatethe SCR. It is so designed that the SCR will notfire unless gated. Since the positive triggers whichgate the SCR are obtained from thc horizontaloutput (flyback pulses), the system becomes in-operative- when there is no horizontal output. Toclarify this, we will assume that no input triggersare present and will determine the condition ofthe system. With the SCR off, CI charges and Q Iis forward biased. As pointed out, when 01 isconducting there are no oscillations; therefore.thcre is no HV output. The system will stay thisway indefinitely.

6-26. Now let us apply a positive inputtrigger. Once the SCR is gated. CI rapidly dis-charges; this reverse biases Ql. Because 01 cutsoff, the transformer is shock excited and C2 ischarged via the rectifying diode to develop anHV output. After CI has discharged. the SCRcuts off and CI again charges to the bias whichcauses 01 to conduct. Transistor 01 remainsconducting until another trigger fires the SCRand the cycle is repeated.

6-27. If you understand what has been said

9 /

so far, you will easily follow our explanation ofhow this system regulates its HV output. We willassume the HV output tries to increase. Observein figure -27.B, that thc increase is sensed onthe cmittcr of 01. Since the emitter is mademorc positive, the base must have a higher po-tential before 01 will conduct Such being thecase. Cl will charge to a higher potential. Notein figure 28,B. that this effectively reduces theconduction time of Ql. Because the amount ofprimary current is likewise reduced, the ampli-tude of excitation is decreased as illustrated. Thedecrease in excitation counteracts the HV in-crease and therefore regulates the system. Theopposite actions occur when the HV tends todecrease. It will benefit you to figure this out.You should also determine how the voltage ad-just potentiometer affects the system.

6-28. We need to mention that the Zenerdiodes are connected in series from the collectorof 01 to ground as a protective measure. Uponcutoff, the _collector voltage rises and falls sharplyto values that may exceed the transistor's maxi-mum ratcd inverse-peak or punch-through volt-age. These Zener diodes have breakdown volt-ages below the transistor's maximum ratedvalues; therefore. they shunt damaging positiveor negative pulses to ground.

6-29. Symptoms and Troubles. Many of thesymptoms and troubles found in HV power sup-plies are similar to those discussed for low-volt-age supplies. However, troubles related to high-frequency excitation have symptoms peculiar toan HV system. To bring this to your attention.let us cite specific symptoms and determine, aspreviously done. the possible trouble or troubles.

6-30. Suppose the kinescope suddenly goesblank. the picture and raster disappear. Sincethc kinescope needs high voltage to have a raster,we can reasonably suspect that the trouble maybe in the HV supply. Quick visual checks shouldbe made. however, before investigating the HVcircuits. The filaments of the kinescope, the tubesin the low-voltage power supply, and those inthe horizontal circuits should be checked to de-termine that they are lit. Unless the tubes in thehorizontal circuits are lit, the HV circuit will nothave excitation. Assuming that all is well up to

this point, let us look into the HV system. If thedamper diode and HV rectifier are tubes, bothshould be lit. Ordinarily, since the HV rectifiertube obtains its filament voltage from the flybacktransformer (see fig. 26), a lit rectifier tube in-dicates that excitation is present.

6-31. Having completed the visual checks,turn the equipment "off" and discharge the high-voltage .supply. Ohmmeter readings can now betaken to check the high-voltage fuse and the re-sistor in the HV lead and to make continuitychecks. An open in the HV circuit, of course,will give the symptoms previously described.

6-32. If ohmmeter checks reveal that nothingis wrong, voltmeter readings may indicate thetrouble. Do not attempt to measure the highvoltage unless special high-voltage probes areused. Even lit tubes cat be defective. As youknow, . you must substitute or check the tubeswhen voltage readings are abnormal.

6-33. Certainly, there may be variations in thesequence of checks, but sound thinking based onthe symptoms observed is important. This can-not be done unless you have a thorough know-ledge of the operating principles of HV powersupplies. It is evident that a symptom or set ofsymptoms can be caused by many types oftroubles.

6-34. In a regulated HV system, symptoms canpoint to a specific type of trouble. For example,suppose the HV of the circuit in figure 27,A, isunstable and lower than normal. The fact thatit is unstable immediately points to the sensingcircuit because changes in the HV load are notbeing regulated. Furthermore, since the HV islower than normal, we can reason that the outputof oscillator V1 is below normal. Let us considera irouble in the sensing circuit that will causethese symptoms.

6-35. Suppose Cl is shorted. There will beneither a bias nor an error voltage developed onthe grid of V4. Because the grid of V4 is atground potential, the plate voltage of V4 will below. Consequently, there is a lower voltage ap-plied to the screen grid of Vl. This causes anabnormally low oscillator output amplitude andaccounts for a decreased Hy. So we see thatwhen Cl is shorted, the symptoms described willoccur.

33

1 9

/g/

CHAPTER 3 S

Sync Generators

TBE SYNC GENERATOR establishes theTV pulse rates; therefore, it is often called

the heart of a TV system. It can also be con-sidered the nerve center since its signal-gener-ating and waveshaping circuits control the timingsequence that governs the operation of the entiresystem. Such vital functions should be well un-derstood by maintenance personnel. To furtheryour knowledge of the operating principles in-volved, we have selected various types of syncgenerators for study in this chapter. We progressfrom a simple noninterlace type to the more com-plex interlace types.

2. Many of the circuits are basic ones thatwere analyzed in your previous training; there-fore, our analysis will, for the most part, bebased on block diagrams. Only special circuitswill be discussed in detail. Our objective is toenable you to analyze the operation of a varietyof sync generators so that you can perform main-tenance on the many types found in AF appli-cations.

7. Nonintorlace Syne Gnerators7-1. The sync generator is a simple noninter-

lace (also called a sequential or progressive)system produces a minimum of signal outputs.We will identify these signals and explain howthey may be produced. A more elaborate systemwill then be studied. The basic sections, perti-nent waveforms, and possible adjustments areconsidered for both types of sync generators cov-ered in this section.

7-2. Simplest Type. The essential outputs forany TV system are sync and blanking signalS.As you know, two sync signals are necessary,one to control horizontal scanning and the otherto control vertical scanning. Two blanking sig-nals are also required to prevent the horizontaland verticartetaices from appearing during theflyback times. The simple sync generator illus-trated in figure 29 contains a blanking mixer thatproduces a composite 'blanking waveform. This

34

mixer, in addition to the horizontal and verticaloscillator, constitute the three basic sections ofthis sync generator.

7-3. In a noninterlace system there is no needfor any tie-in between the horizontal and verti-cal oscillators. A variation in frequency of oneor the other changes the frames per second orlines per frame. For many practical purposesthis is of no consequence and is not noticeable.The vertical oscillator can be a blocking oscil-lator (tube or transistor type) that is locked-inwith the 60-cycle line. A vertical sweep signalcan be obtained from this oscillator since a saw-tooth waveform appears across the blocking ca-pacitor during the cutoff time. This waveformcan be amplified and fed to the vertical deflec-tion coils, as indicated in figure 29. Recall thata blccking oscillator generates sharp pulses whenthe tube (or transistor) conducts. Note in theblock diagram that these pulses are fed to thevertical sync buffer and the blanking mixer. Thebuffer, of course, minimizes loading effects onthe oscillator and also provides amplification.

7-4. Either by means of a waveshaping net-work or by special circuit design, the horizontaloscillator generates the signal for horizontalscanning. In addition, like the vertical oscillator.it produces sync pulses which are applied to abuffer amplifier. Its frequency is usually in thevicinity of 20 kc. Observe in figure 29 that thisoscillator's output is also fed to the high voltagerectifier that is readily eicited via a step-uptransformer. This atnounts to having a flybackHV system, the operation of which was discussedin the previous chapter.

7-5. Adjustments that affect vertical linearityand height are generally made in the verticaloscillator section. Tuning provisions are ordi-narily not provided since the frequency is 60cps and locked to the line. The horizontal oscil-lator section has adjustments that make it pos-sible to change the amplitude of the outputs;tuning may or may not be variable, depending

upon the particular system. If this very simpletype of sync generatur is adjusted to produce aI5.75-kc horizontal frequency, its output pulsescan be used for lockina a standard broadcastTV receiver.

7-6. Multiple-Pulse Type. Figure 30 shows async generator that produces several pulse wave-forms: mixed sync, mixed blanking, vertical

drive, and horizontal drive signals'. Such avariety of outputs may be required for a moreelaborate noninterlace system. The mixed synccan be inserted with the camera's output to ob-tain a composite video signal for single-cabletransmission or for modulation. The mixedblanking signal is fed to the camera as are theseparate vertical and horizontal drive pulses. Un-like the simple sync generator previously dis-cussed, this sync generator produces sync andblanking pulses that differ in pulse width. Thevertical and horizontal blanking pulses are usu-ally greater than twice the width of their cor-responding sync pulses. Waveshaping and pulse-forming circuits are therefore necessary to bringabout this difference.

7-7. Functional analysis. The 60-cps line sig-nal is shown in figure 30 to be the input to awaveshaping network, called a squarer andpeaker, which is nothing more than an over-driven amplifier and differentiating circuit. Be-cause the 60-cps input signal causes positive andnegative clipping, a square-wave output is ob-

60CPS f\LINE

TO VERTICAL DEFLECTION

V ERTICALOSC

tained from the amplifier. This output is appliedto a short-time constant RC series circuit so thatpositive- and negative-going spikes appear acrossthe 'resistor. The positive-going spikes preciselysynchronize the vertical oscillator frequency withthe 60-cps line frequency. The shaping of thevertical oscillator output pulses to a prescribedheight and width is done by the vertical ampli-fier-clipper. The amplifier-clipper output pulses lare applied to a blanking shaper and also to adrive shaper. In addition to squaring-up thevertical pulse, the drive shaper narrows it toabout half the width of the vertical blankingpulse. These narrowed pulses are fed into thesync mixer and out to the camera(s) for trig-gering the vertical sweep.

7-8. The horizontal oscillator is a free-run-ning type designed to operate with some block-ing action. Pulses from it are shaped for hori-zontal blanking and drive. Like the verticaldrive shaper, the horizontal drive shaper de-creases the pulse width so that it is about halfthat of the horizontal blanking pulse. The outputof the horizontal drive shaper is used to triggerthe camera's horizontal sweep; this output is alsosent to the sync mixer.

7-9. Both the blanking mixer and sync mixerare designed so that the horizontal pulses do notappear in the output during the vertical pulsetime. Figure 31,A, illustrates how this is easilyaccomplished by clipping the horizontal pulses

HORIZONTALOSC

V

BLANKINGMIXER

VERTICAL$ YNC

BUFFER

MIXBLANKING

BUFFER

HVERTICALSYNC

MIXEDBLANK

IIHORIZONTAL]SYNC HORIZONTAL

BUFFER SYNC

TO HORIZONTAL DEFLECTION HVRECTIFIER

Figure 29. Simple noninterlace sync generator.

35

U LI

110P HV

/q3

60-CPS-110LINE

SQUARER&

PEAKER TP1

HORIZONT&LOSC

VERTICALOSC

TPS

TP2

HORIZONTALBLANKINGSHAPER

VERTICALAmPL &

CLIPPER TP3

VERTICALDRIVE

SHAPER

VERTICALBLANK

SHAPER

V

BLANKINGMIXER

TO CA64EqAy 12 4 v DRIVE

SYNCMIXER

MIXED-19.BLANKING

silMORIZONTALDRIVE

SHAPER

Figure 30. Mullipulse nonirueriace sync generafor.

that ride the vertical pulse. Figure 31,B, furtherillustrates that because of the difference in pulsewidths, horizontal sync (same for drive) is re-sumed before the vertical blank pulse terminates.Therefore, the horizontal -oscillator will belocked-in before picture information appears onthe screen. For example, if the vertical syncpulse is half that of a 1620-psec blanking pulse,we can determine the number of 15.75-kc hori-zontal syncs (63.5-psec pulse period) that willbe present during vertical blanking by dividing810 psec by 63.5 /Awe. This gives us 12 hori,zontal sync pulses before picture information ap-pears on the screen.

7-10. Adjustments add troubles. Adjustmentsand alignment of the pulses are made in thepulse-forming circuits of the clipper cr shapers.Since the vertical oscillator does not generatethe sweep waveform, as was the case for thesimple sync generator described, linearity andheigln adjustments are not needed. Provision ismade, however, to adjust the output puke widthof the vertical oscillator if this is critical. Ordi-narily. the vertical oscillator will not be tunable.But a transformer feedback-type horizontal os-cillator will likely be slug tuned; for versatility,this oscillator may be so designed that it can betuned to operate at the 15.75-kc standard scanrate.

7-11. Let us give some thought to troublesthat can be indicated by waveform presentations.Suppose. for example. that the vertical pulse ofthe mixed sync output is abnormally wide; a

36

Ta6

TTT

MIXEDSYNC

0 CAMERAH DRIVE

check of the mixed blanking output is norma!,as illustrated in figure 31,B. It it. logical to sus-pect that the trouble is in the pulse-shaping cir-cuit of the vertical drive shaper. This can beconfirmed by testing the signals at TP4 and TP3,figure 30. A different trouble would be indi-cated if the vertical blanking pulse was also toowide. The signals illustrated at TPI and TP2should point up the trouble. Depending uponthe shapes of the waveforms at these test points,you can isolate the trouble to a section: squarerand peaker, vertical oscillator, or vertical am-plifier/clipper. Similarly, troubles that evidencethemselves as waveform abnormalities can betracked down and identified with a particularsection.

8. Interlace Sync Generators

8-1. When many of us think of interlacescanning, a complicated composite signal comesto mind. This is natural since the Electronic In-dustries Association (EIA. formerly RETMA)composite signal standards are widely used. Inthe latter portion of this section we will analyzethe sync generator required to produce standardoutput waveforms. But before becoming in-volved with such a complex sync generator, it is

well for you to realize that interlace scanningcan be accomplished with a relatively simplesync generator. A simple type may be quitesatisfactory for certain closed circuit applica-tions: this being the case. a more costly, elabo-rate type would not be warranted. Since you may

20i

mAl

AT)

NI stOSYNC _11 1 1 1

c

Nut°10. AMINO

MONIZONTI. SYNCImo

1J1JL

Figure 31. Noninterlace multiplepuIse wavefornls.

have to maintain a simple interlace sync gener-ator, you should know what it consists of and un-derstand how it functions. Furthermore, by study-ing its basic sections and the requirementspeculiar to any interlace system. you can furtheryour understanding of the more complex so-phisticated types.

8-2. Requirements for Interlace. Unlike thenoninterlace system. an interlace system musthave a rigid control established between the hor-izontal and vertical scanning. Such control canbe achieved in either of two ways: (1) each

oscillator, vertical and horizontal, can be pre-cisely timed. or (2) a fiked timing relationshipbetween the horizontal and vertical scans canbe maintained. Since the first way demands ex-treme stability, the second way is more prac-tical. By using a master oscillator and counters( frequency dividers), a fixed timing relation-ship is maintained such that the ratio of scan-ning frequencies is constant. You know that thestandard ratio in this country is 262 -I- 1/2, whichis the quotient obtained when 15.750 pps is divi-ded by .60 pps. It is absolutely essential thatthis quotient be an integral number plus a half.This insures that the vertical scan will alternatelyterminate on a half line and whole line, therebypositioning successive sets of lines (fields) be-tween each other.

8-3. Basic sections. In figure 32 are thefour basic sections of an interlace sync genera-

tor. Admittedly. four sections are inadequate toprovide the degree of reliability needed for prac-tical applications. Nonetheless. let us discussthese sections because they are essential to allour standard-frequency interlace sync genera-tors.

8-4. Since the master oscillator (mo) gener-ates the timing pulses that govern the entire sys-tcm. it must be highly stable. There are varioustypes that can be designed to meet this require-ment. In your previous training you have studiedmultivibrators and blocking oscillators that arecommonly used; therefore, you should have littledifficulty recognizing and understanding the op-eration of modified versions that may be used.The mo generally has an adjustment to alter itsfrequency. Other adjustments may also be pro-vided to vary its pulse width and to set the

midpoint of its range. In a standard system, itwill generate pulses at twice the horizontal scanfrequency (31.5 kc). These pulses are divided bythe 2:1 counter to provide timing the horizontal'sync and blank to the standard line scan rate(15.75 kc). The vertical scan rate is establishedby the 525: I counter section which divides themo pulses to produce 60 pps for timing the verti-cal sync and blank.

8-5. In case you do not fully appreciate the

fixed ratio relationship that is maintained by thisscheme of counters, let us note the results whenthe mo frequency shifts. Suppose the mo outputincreases to 32,550 pps. Dividing by two wefind the horizontal scan rate is 16,275 cps.

Dividing by 525, the vertical scan rate is 62cps. This tells us that there are more lines persecond and move fields per second than normal,but our primary interest is in the number of lines

per field. This ratio is determined by dividing16,275 cps by 62 cps. Doing so, we learn thatthere are still 2621/2 lines per field. Whatevermo frequency change you may assume will givethe same ratio; therefore, you must conclude that

this ratio 2621/2 is fixed for the system if thecounters divide properly.

8-6. Counters. Three commonly used circuits

60 PPSI°525:1

COUNTERVERTICAL SYNC/BLANK

31.5-KCMO

H-VMIXER MIXED SYNC/BLANK

6.2:1COUNTER

HORIZONTAL SYNC/BLANK

15,750 PPS

sections of interlace sync generator.Figure 32. Basic

37

2 0

A.

5:1OUT

SYNC IN

5 2 3 4 I 2 3 4 3

I I1 II I I I II II 1

e i1

)II

a

i

1

TP1 I

TP2

:AULT IVIBRA TOR 5:1 COUNTER

SYNC IN

B.

+VCC

TP1

TP2

5

5

BLOCKING OSCILLATOR 51 COUNTER

0.1IOM

TP25:IOUT

SYNC IN

TP1

P2

C. 5:1 STEPCOUNTER

1 2 3 4 5

Figure 33. Common types of counters.

38'2 0 3

r"

for dividing pulse frequencies in sync generatorsare the m iltivibrator counter, the blocking-oscil-lator counter. and the step-counter. These cir-cuits are shown for your review in figure 33.Recognize the similarity of the transistor con-figuration with the tube circuits whicl, are per-haps more familiar to you. The operating prin-ciples are identical whether tube or transistor.Since you should know how these circuits func-tion, we will not analyze them in this course.However, we will point out a few significantfacts for you to remember. In figure 33,A, notethat the time constant of the base circuit 01 isshorter than that of Q2. This is evident from thewaveforms at TP1 and TP2 which show 02 con-ducting (Q, cut off) for two pulse periods andcut off (01 conducting) for three pulse periods.The resistors R1 and R2 are necessary to properlybias the transistors. These resistors would not beneeded in a similar tube multivibrator. Figure33.B. shows the transistor version to be very muchlike a conventional tube blocking oscillator:munter. Bias, of course, is different; it can be ad-justed with R. The step-counter, figure 33,C, cor-responds to the tube step-counter you have stud-icd. Recall that the step-charging circuit worksinto a blocked oscillator. By means of R, bias canbe adjusted to unblock the oscillator and dis-charge C at the prescribed level. Unlike theother two types of counters, this circuit is notfree-running. Incoming pulses directly controlthe count; therefore, it is less susceptible to mis-count caused by trigger frequency variations. Itis more precise, but it is limited to a maximumcount of about 10, because the steps do not in-crease in equal increments (see fig. 33,C). Sta-bility of the count incomes more subject to cir-

vCC

INPUT

RESONANTSTABILIZER

cuit variations as the voltage step decreases at thehigher levels.

8-7. The stability of the trigger's amplitude isimportant for all three counters mentioned. Fur-thermore, the higher the count, the more strin-gent becomes the stability requirement. Al-though special circuits have been designed forhigh vaunts, a simple resonant circuit can im-prove' stability to a marked degree. Figure 34shows how such a circuit modifies the normalgrid waveform of the blocking oscillator counter.The resonant stabilizer is tuned to approxi-mately 1.5 the free-running oscillator frequencyso as to produce a trough just prior to the de-sired fifteenth trigger pulse. Consequently, thepreceding pulses that are likely to trigger theoscillator prematurely appear well below theconduction level.

8-8. Not as commonplace as other circuits,the phainastron circuit can be designed for reli-able counting. Ordinarily, this circuit is em-ployed for pulse delay, but let us consider howits operation lends itself to counting. Figurt35 shows the phantastron counter circuit andwaveforms which we will refer to in our expla-nation. Specific potentials have been chosen togive you an idea of the magnitude of voltagesinvolved. These values should be regarded asapproximate and, of course, will depend on theparticular tube employed.

8-9. To begin, note that there is one outputpulse (waveform e.) for every five input pulses(waveform e1). Every fifth input pulse triggersthe phantastron to cause a complete cycle of itsoperation. This circuit is not free-running; itmust be activated by a negative-going pulse. In

INPUT 1111111117111171

TP

15CONDUCTION..... LEVEL

OUTPUT I

10

SINE WAVETHROUGH

Figure 34. Stabilized blocking oscillator.

39

20g

/97-

5 3 5OV

.SV

41 IC1V

I0v

-- -5V

s+z 300V

733v

130V

100y

ISV

110v

53 70v

30V

14, .111111 50V

- ISV

3%,

Figure 35. Phantastron counter and associatedwaveforms.

its prctriggered condition there is no plate ;:ur-rent; thus the plate i at B + potential. However,cathode current flows since grid 2 draws cur-:cut. Because grid 3 is biased at a less positivepotential (ek3) than the cathode,-this grid doesnot draw current and prevents current flow tothe plate. Study the waveform values immedi-ately prior to t5. These potentials will persistuntil the circuit is triggered.

3-10. You can best understand the action ofthe phantastron when it is triggered by dividincit into three successive phases. The first phaseis an extremely rapid change which occurs whenthe negative trigger, coupled through Cl to thecontrol grid, causes ek to decrease. This de-creases the bias between grid 3 and the cathode.thereby permitting plate current to flow. Con-sequently, plate voltage ei, drops to give regen-erative feedback and drives the control grid in-stantaneously to a negative value ( 5v). Youcan see the effects of this action by studying thet5 waveforms in figure 35. The second phase isa slow linear change. After the- trigger, C1gradually goes positive because of counteractionof the decreasing plate voltage e1,. The time con-stant of this change is effectively extended bythe amplifying action of the tube. It is worth-while to point out that during this second phasethe input pulses at times tl, t2, t3, and t4 arcIneffective. In fact, they arc blocked by the ac-tion of the disconnect diode DI. From thewaveforms illustrated. you can see the changesthat take place during this phase. The thirdphase is initiated when eK rises to such a valuethat the bias between the cathode and grid 3cuts off plate current. When this happens thecircuit reverts back to its pretriggered condition.The next trigger, t5, causes the cycle to recur.

8-11. Observe that the output is taken off thecathode and applied across C2 and R2 in se-ries. The time constant R2C2 is short for thewaveform eK so that positive-and negative-goingspikes appear across R. The diode D2 passesonly the negative spikes as illustrated in figure35.

8-12. The phantastron is quite stable underpower supply variations. Changes of supply volt-age vary the d-c potentials proportionally on thetube 'elements and arc therefore minimized; over-all circuit performance is virtually unaffected.Because the pulse width can be varied by a d-cvoltage, the circuit can be remotely controlledthrough unshielded cables. Note also in figure35 that control-grid bias is variable. A changein this bias alters the pulse width so that thephantastron can be adjusted for its designedcount. Although we chose to illustrate a five

402a "6

945

31.5-KCMASTER

OK

1\11,KTAL CONTROL

REACTANCECONTROL

31.3.4C OSC 111"52 TP1

31,500 PPS

D-CAMPLIFIER

2 ICOUNTER

1311

OPP

WI.43".ON

SI

PHASEDET ECTOR

1113.CPS POWER LINE

L =1112100 PPS 300 PPS

"'""'<>"'"4/0 It 1 3 ITP2 TP3

HORIZONTAL13,750..PPS

OUTPUT

COUNTERS

HON I, VERTMIXER

porn I. VERTSYNC/SLAM

OUTPUT

Figure 36. Random interlace sync generator.

count, much higher counts can be readily ob-tained.

8-13. Random Interlace Type. In addition tothe basic sections, a practical interlace sync gen-erator will contain an afc network and a crystalcontrol oscillator. Figure 36 shows their inclu-sion and arrangement. However, since we havediscussed counters, let us first consider howpulses of a desired width and shape can be ob-tained as outputs from the counters. By studyingthe output waveforms, you will see why this syncgenerator is called a random interlace type. Thenwe will discuss afc and the use of the crystalcontrol oscillator for calibration.

8-14. Outputs. With the switch 52 in the po-sition shown (fig. 36), the 31.5-kc signal is sup-

A. HORIZONTAL

S. VERTICAL

C. HON II VERTSYNC/BLANK

Figure 37. Output waveforms random interlace sync generator.

41

! Imollpil MIK.

TPII

VERTICAL1100PPSOUTPUT

plied by the mo to the 2:1 counter to develophorizontal output pulses and to the 15:1 andsubsequent counters to develop vertical outputpulses. We see that both horizontal and verticalpulses are fed into a mixer, the output of whichis a composite signal. The three outputs from thissync generator are the minimum required. Thehorizontal and vertical outputs synchronize anddrive the scanning circuits to produce the properraster. The output pulses of the mixer are sentto the camera for blanking and become the sync/blank pulses in the camera's composite video oufrput signal. Indeed this is a simple system, butit is important to recognize that the require-ments for interlace are met. This is brought toyour attention in figure 37, which shows the time

I I

I

I

206

relationships of horizontal and vertical pulses persecond (pps). Note that a full horizontal period(H) precedes the vertical pulse (left side),whereas a half period (0.5H) precedes the nextvertical pulse. Thus, them is thc half-line timedifference between successive fields which is

needed for interlace.8-15. Since the outputs illustrated are ideal-

ized, you may well ask how they are shaped.Clipper and shaper circuits were mentioned ear-lier, but none are identified in the block diagramof figure 36. This is because counters can be de-signed to produce properly shaped pulses. Re-member that a rectangular pulse is obtainedfrom a multivibrator counter. The pulse width ofthis counter is easily altered by adjusting the rel-ative time constants of the feedback circuits.Moreover, by regulating these time constants,frequency can be kept at a specified value. Ifanother type of counter is Amployed, the pulsemay be too narrow. A small shunting capacitor,connected across the counter's output, will effec-tively widen the pulse. A clipping diode can beincorporated to square the pulse at a prescribedlevel.

8-16. Referring to figure 37,C, you find thatno horizontal pulses are present during the timeof the vertical pulse. For the length of the verti-cal pulse, there is no sync signal for the monitor'shorizontal oscillator. Such being the case, thefrequency of this oscillator can shift and, as aresult, the scan may not interlace. In other words,interlace is not insured since horizontal sync isnot continuous. Because the relationship of al-ternate fields is a matter of probability, this scan-ning is appropriately called random interlace. Asyou would expect, random interlace is noticeable,but for some apptications it is satisfactory. On asmall screen kinescope, picture quality is ade-quate for good viewing.

8-17. Afc and calibration. The purpose of afcin an interlace sync generator is to lock-in the60-cycle field rate with the 60-cycle power line.Unless this is done, a 60- or 120-cycle humpickup will create raster distortion and/or shad-ing changes that move vertically across thescreen. The afc does not eliminate the pattern ofdisturbance(s) caused by such pickup, but itdoes make the pattern stationary. A stationarypattern is far less annoying to the viewer thana continuously moving one. In fact, with 60-cycle lock-in a small amount of hum pickup willgo unnoticed. Afc is therefore a feature foundin virtually all interlace sync generators, not justrandom types.

8-18. The afc network illustrated in figure 36consists of a phase detector (discriminator), ad-c amplifier, and a reactance control circuit.

The phase detector may be one of several typesyou should know. Whichever type is 'used, itwill have two inputs: the vertical 60-pps syncgenerator output and the 60-cps line signal. TheOast: detector develops a d-c error voltage when-ever there is a phase difference between thesetwo inputs. Note in the block` diagfarn that theoutput of the phase detector (error voltage) isamplified by a d-c amplifier before it is appliedfor control purposes. This amplification is usuallyneeded. Depending upon the type counters. theerror voltage may not be coupled to the counterchain as shown in our diagram. We can be cer-tain, however, that the error voltage will be sentto a reactance control circuit which acts to changethe mo frequency. The reactance control sectioncan employ a reactance tube amplifier or a solidstate device such as a varicap (other names aresemicap, varactor diode, etc.). A varicap is aspecially designed crystal diode that has a greaterthan ordinary variation of capacitance withchanges in reverse bias. By applying the errervoltage to a reverse-biased varicap, capacitanccchange can be used to control the frequency ofthe 31.5-kc mo. If properly designed, the mowill automatically adjust to minimize any fre-quency difference between the inputs to thephase detector. This means that the vertical out-put signal is locked-in to the 60-cycle line.

8-19. Although afc functions to hold the syncoutputs to their proper frequencies, it is nec-essary that the mo and counters be within aprescribed range for lock-in. Moreover, interlacedepends upon the sync generator's frequency re-lationships. To insure proper operation, it istherefore necessary to calibrate the mo and count-ers.

8-20. You should first calibrate the mo so thatits free-running frequency is 31.5 kc. Switch SI(see fig. 36) must be put in the OFF position.This removes any error voltage which affects themo. Using an oscillocope, tune the mo until itsfrequency is exactly that of the 31.5-kc crystaloscillator. There will probably be amplitudechecks and adjustments specified for any particu-lar mo. When you are sure that the mo has theprescribed output, the counters can then be cal-ibrated.

8-21. Counters are checked successively start-ing with the one nearest the mo. Thus, in thevertical counter chain the 15:1 counter is cali-brated first. Leave SI in the OFF position. Youshould follow the calibrating procedures and usethe test equipment prescribed by the manufac-turer. After calibrating all counters, switch SIto the ON position, and the generator shouldlock in rigidly with the 60-cycle power-line fre-quency. However. in the event that the power-

422 U

2d'°

line frequency is not 60 cps. leave SI in theOFF position. Either the mo or crystal oscillatorcan he selected with switch S2. The mo offersno advantage when thc afc is disabled.

8-22. Standard Interlace Type. There are non-standard systems, designed for special purposes,that can reliably interlace using a very simplesync waveform. Such systems, however, havemarginal performance capabilities.for general ap-plications and have insufficient reliability forbroadcasting. Consequently. most American TVsystems use EIA (RETMA) sync waveformstandards. Although these systems must employa relatively complex sync generator, a standard-ized system offers many advantages over systemsthat have less rigorous requirements. Beforeundertaking an analysis of the sync generatorneeded, we will review the EIA signal wave-forms. A thorough knowledge of the details ofthis waveform is essential to ah understandingof the workability of the system as a whole.

8-23. Signal standards. Although you are fa-miliar with the EIA standard waveforms illus-trated in figure 38, it is well to call to mind thefunctions of the various pulses involved. In ad-dition to the sync and blanking pulses that havebeen discussed previously, this signal containsequalizing pulses. Moreover, it has a serratedvertical sync pulse. These equalizing pulses andserrations are distinctive features that providecontinuous horizontal sync and insure proper in-terlace.

8-24. A group of six narrow equalizing pulsesimmediately precedes the vertical sync pulse, anda similar group of six follows it. These pulsesoccur at twite the line frequency (31.5 kc). Thisdoubling of frequency is necessary if alternatefields are to be properly synchronized for inter-lacing. Note that the first. third. and fifth equal-izing pulses are used as horizontal sync for thefields that end in a complete line (period H);whereas, the second, fourth. and sixth equalizingpulses arc used for the fields that end in a halfline (0.5H). Besides maintaining horizontalsync, the equalizing pulses serve to time pre-cisely the vertical sync pulses.

8-25. If vertical sync is not precise. interlaceis jeopardized. A slight discrepancy in the verti-cal scan will cause the lines of alternate fieldsto come together. This effect. called pairing, re-duces vertical resolution and the line structurebecomes visible at normal viewing distance. Be-cause the time between the last horizontal pulseand the vertical sync differs by 0.5H for alternatefields, the residual charge from the integratingcircuit ( in the receiver or monitor) differs also.Figure 39..A. shows how this residual charge willintrodwc a discrepancy in the vertical sync. Fig-

urc 39,8, shows how the equalizing pulses pre-vent this inherent discrepancy which would cause"pairing." This should remind you how vitalequalizing pulses are, to the system.

8-26. Unless the vertical sync pulse is serratedas shown, horizontal sync will be disrupted. Ex-amine this serrated pulse and observe that thetrailing edge of the serration is used for horizon-tal synchronization. A differentiating circuit inthe receiver or monitor develops pulses of thecorrect polarity when the trailing edge of theserration occurs. Like equalizing pulses, the ser-rations muit have twice the horizontal scan fre-quency to accomodate alternate fields.

8-27. The times and tolerances for the var-ious pulses are specified in figure 38. A tableof values is given in figure 40 for your con-venience. Both of these figures contain much in-formation that is pertinent to the maintenanceof a standard sync generator. Checks of pulsewidths and adjustments will necessitate referenceto these standards. It will benefit you, therefore,to read the explanatory notes and relate thewaveforms and values. The close tolerances in-dicate the stability required of the sync genera-tor. The variety of waveforms points up the factthat the sync generator must be a relatively com-plex piece of equipment.

8-28. Functional analysis. The block diagramin figure 41,A, shows the essential sections thatfunction to produce the standard sync wave-forms. Bear in mind that these sections may bemade up of several stages and associated cir-cuitry. Furthermore, remember that the circuitswithin these sections are basic ones or modifiedversions of circuits covered in your fundamen-tals training. Our purpose is to analyze the func-tional relationships of the various sections. Onceyou grasp how the standard waveforms can besynthesized, you will better understand the op-eration of this type sync generator.

8-29. Refer to figure 41,A. You should recog-nize the sections to the far left in the diagram.The mo section contains a crystal-controlledoscillator (not shown) for calibration and islocked in by the afc section. To obtain the verti-cal 60 pps, a 525:1 counter chain is used.Generally this chain consists of counters thatdivide the frequency in steps of 7:1, 5:1, 5:1,and 3:1. The 60-pps signal is used for ale andis also fed to the vertical sections indicated. Ex-cept for the vertical drive output which is sent tothe camera, the outputs from these sections arecoupled into other sections for further process-ing. A signal from the 31.5-kc mo is divided by2: I counter to obtain the standard horizontal linerate of 15.75 kc. We see that this signal is ap-plied to a delay section from which four outputs

43

20

2°'

BLACK NEGATIVE DIRECTION THAI----10° A

N141----3HEQUALIZING PULSEINTERVAL

O SYNC SIGNAL

It ANNING SIGNAL

VERTICAL DRIVING SIGNAL

HORIZONTAL DRIVING SIGNALEQUALIZINGPULSE--SEENOTE II

111wwummTTT irrinnVINT STNCP1-711-11111.111n=110 PULSEINTERVAL INT TTTTT alt 1 ID 12 NPULSES.........0111

'111 .1'1111'1+v

MOT Is

11.44V imam

NOTE

I- N-TINE P101 STAN I' OP ONE LINE TO STANT OP MIXT LINE.2- Y-TINE TTTTT OF 0101 FIELD TO STANT OP MIXT PIELD.11. LIADENJ ANO TRAILING 1001110f VERTICAL DRONNO AND VERTICAL

BLANKING SIGNALS SHOULD DE CONPLITS IN LISS THAN S.W.a- all TOL MUNCH. APO UNITS 1110111 IN THIS DRAWING All PERMISSIBLE

DELT PON 1.0110 TIME VARIATIONS.TIMAIG ADAISTIIENT. IP ANT. MUST INCLIMNI THIS CONDITION.

6- THE VERTICAL DRIVING PULSE OURATmg MALL SI taw *SAW. THEHoNIZONTAL OIIIYWO PULSE OVIATX111 SHALL NE t IN t 11.6113N.

P. THE TINE RELATIONSHIP AND VATIP01113 Of THE BLANKING AND SYNC111:MALS SHALL SI 15501 THAT THEM ADDITION DILL RESULT IN ASTANDARD IIIITMA SISHAL. TNE Till RELATIONINIP *UST SE ADJU TTTTT 1IN ORDER TO SATIIIPT THIS BILATIONNIIP PON THE CONDITION 114111Till BLANEING SiGNAL IS DILATED 1111T11 NISPECT TO TNE SYNC SIGNALoven TN! RANGE FRON SIN TO SAN.

- TNE STANDARD REINA yALUES OF PREQUSNCY AND NATI DP CHANGE OPPRIGUINCY POI HIE HORIZONTAL COMPONENTS OF THE SYNC SIGNAL ATINE OuTPUT OP THE PICTURE LINE AMPLIFIER SHALL ALSO IDTHE lecommemoto syNc olorlAvon.

- ALL RISE AND DICAT TINES TO SI mIASUNID II Twil 11.1 AND S.tAIPLITUDI REPININCE LINES.

Figure 38.

DETAIL Aa11.114

11.5411

VER.: SYNCPULS!

6.11111

.2.mil Ind 11.119111 MAX. V

DECAY Till SIMI MAX. LipRI NOTE,

111.176113/11111t

T .4-PDETAIL -

DECAY TIME SAW ItAX.Tip111111141 OM SAIL

DETAIL s CC SEE NOTE II

11.17161 OAR.SEE NOTE II

NOTE S

NOTE

11.111±11.11111.1-431

SAM PGI. 5.5 0/-1.104

RISE Thal 11.6611I MAX.DECAY T161111.6rts MAX.

III NOTE

4-01IIPHOTE

RISE Ale !MCAT TIMES TO SI EQUAL0111 LISS NAN RISE AND DECAY TimerOP NOIIIIONTM. SLANKIN11.-.1111NOTE L

11.11

NI- TIN TIME OP oceumnsat OP THE LEADING INS OP ANT NORIZUNTALPULSE 'V" OP ANT Stour or go 1101111CINTAL PULSES APPEARING UN ANYOP Thy IXITPUT SIGNALS PROM A STANDARD MC ottaiATom SHALL NOTDIPPER Pate *say* ST GORE THAN 11.1K41111 8111111 H 13 WI AVERAGEINTERVAL EETWEIN THE LEADING /DOES OP THE PULSES AS DITERINNIDST AN AVERAGING PROCESS CAR11110 OUT OVER A PERIGD OF HOT Leos111611$6 HON MORE THAN US LINES.

11 - EQUALIZISSO PULSE AREA SHALL SI SETVIEN SAS AMPS.' Of 11111 AREAOP A HORIZONTAL STMC PULSE.

It THE OVERSHOOT ON ANT OP Mt r111.515 MIT NOT EXCEED ES.13 - Till OUTPUT LIYIL OP TIII KANSAS tifNAL ANO TN! SYNC NONAL

NOT VARY MK THAN IS WIDER TNE POLLOIFING CONDITIONS@

A. THE AC VOLTAGE SUPPLYINS Till SYNC GENERATOR MST BE RI MINANO! PETWEEN 11111 ARO INV AND MUST HOT VARY MORI THAN STDUBMOS TEST.

S. A PEtoOD DP SWUM CONTIMAUS OPERATION MALI SI CON-SIDERED AGIQUATI PON THIS MEASUREMENT. APTIN WITAPLEyoulsesP.

C. TFA eau AusieUT MUST SI IN T111 RANGE 61111181 ANDAl 01011111 C. AND NUST NOT CHANGE 160111 THAN IS D1GREFS C.DUPING INS TEST.

II - absuITYCHT ant II POSSIBLE WINCH Looms AM SIAINININLINTS SO THAT WICT NATIO CAA SI $ET TO T111 *MAL VALUE.

EIA (RETMA) standards.

2ioI .3

are taken. These outputs are delayed by differ-ent amounts to properly time the sections theyactivate. Delays can be achieved by a multivi-brator or phantastron. but a network of passivecomponents (inductors and capacitors) is oftenused to form a delay line. The delay line consistsof many pi sections of series inductance andshunt capacitance. Different delays are tappedoff at the junctions as desired up to the maxi-

11111011

=1,

al

mum obtainable from the line. Outputs of therequired time delay can thereby be obtained tocontrol the circuits that form the horizontal sync,notch pulses, horizontal blanking, and horizontaldrive. Note in the diagram that the horizontaldrive section develops an output from the gen-erator; the outputs from other sections are pro-cessed further. Observe also that the 31.5-kcsignal is sent to a delay section so that the timing

SERRATED VERTSYNC

.1111111111

A. WITHOUT EQUALIZING PULSES

yr,

411

SERRATED VERTSYNC

1. Aft

8. wITH EQUALIZING PULSES

Figure 39. Equalizing pulses.

45

TABLE OF F,IJN;AMcNTAL PUI.SEZ

PULSE PULSE RATE DUrAIION IN i DURATION IN RE PETIITIONIDENTITY (Freq in pps) = 63.5 microsec) M:CROSECONDS RATE

Min Nom Mcv: tcps)

H SYNC. 15,750 - 0.075H - 0.0E9ii 4.46 5.08 5.68 15,750

H BLANKING 15,7543 0.165H - 0.1dH 10.5 11.0 11.43 15,753EQUALIZING 31,500 0.035H - 0.045H 2.2 2.5 2.9 60

V SYNC 31,500 0.42H - 0.4411 24.? 27.5 20.1 60

V SERRATION 3%500 0.061H - 0.079H 3.85 4.45 5.05 60

V BLANKING 60 13.111 - 21.0H 833.4 1000.1 1333.3 60

H DRIVE 15,750 0.08H - 0.1811 5.25 7.6 11.43 1.5,750

V DRIVE 60 6.55H - 21.0H 416.5 575.0 1333.3 60

Figure 40. Table q' pulse vtandards.

of the equalizing pulse section and vertical pulsesection can be controlled.

8-30. The processing or synthesis of wave-forms is accomplished by mixing and clipping theoutput signals of the various sections just men-tioned. It is easily seen in fipre 41,A. that thecomposite blanking signal is formed by combin-ing the output pulses of the vertical blank sectionwith those of the horizontal blank section. Theblanking signal from the mixer/clip section is

shown to be an output from the sync generator.To determine how the sync composite is formed,you will have to study the waveforms illustratedin figure 41.B. These waveforms are identified

EON LINE

ARCg PPS

OFF COUNTERS525,I

MO31.5KC

VERTDRIVE

by letter or number to correspond with the signalsindicated in the block diagram. By combiningthe output 1 from the equalizing pulse sectionwith outputs 2. 3, and 4 from the mixer./clip sec-tions, waveform 5 is produced. The final stand-ard sync signal is obtained by clipping waveform5 along the dotted iines. This, of course, is doneby the sync/clip section.

8-31. Note that signal a is used to eliminatethe horizontal pulses of signal b for the timedaration 9H; likewise, signal a eliminates thenoich pulses for 9H of time. This is evident fromwaveforms 2 and 3. respectively, Of paricularinterest is the manner in which waveform 4 is

.51VERTBLAME

514

RHPULSE

01vERT.PULSE

DELAY

COUNTER2:1

15.1317VIIPIDELAy

01 EQUALIZINGPULSE

a

MIXERCLIP

MIXER.CLIP

V

SERRATINGPULSE

NORPULSE

NOTCHPULSE

o.OR&LANK

NORDRIVE

MIXER

3-NPULSE

MIXERCU

1--4--

MIXERCLIP

SYNCCLIP

Figur,, 41, .4. Interlace sync generator-, block diapram.

46 21,

:ER t Ct.DRirr

51ANORDS

ANg

.OPICONT AL"- DRIVE

a S

a.

47

re)

developed. Signal d from the vertical delay sec-tion is mixed with signal e so the 3H pulse willbe triggered by the leading edge of a serratingpulse. Since signal h is e inverted, the trailingedee of the..first serration will always occur 0.5Htime after the start of the 3H vertical sync pulse.This insures the correct time placement of theserrations to maintain continuous horizontal sync'during the vertical sync interval.

8-32. Examine closely the time relationshipsof the various pulses shown. Be sure you see theneed for notch pulses. Determine what pulsesestablish the width of the horizontal sync.

8-33. Trouble diagnosis. If you know thestandard sienals and how they are formed, youcan often diagnose troubles by waveform analy-sis. Let us cite a particular case in support ofthis fact.

8-34. Viewing the sync output sienal on anoscilloscope, you can sec pulses regularly appear-ing midway between the horizontal sync pulses.

48

Upon closer observation, the unwanted pulsesarc found to have the same width as the'equaliz-ing pulses. This indicates that signal 3 in figure41.B. is not being supplied to remove the equaliz-ine pulse between horizontal sync_ pulses Thetrouble therefore is in the notch pulse sectionTo confirm this diagnosis. you should check theoutput from the notch pulse section.

R-35. Adjustments are critical in a sync eerat or of this type. Since much of the timine isdcpendent upon multivibrator action, a variationin capacitance can set the outputs off in fre-quency and/or pulse width. Such trouble ean bedetected by checking waveforms; and adjustmentmay be all that is needed. Adjustment instruc-tions will be given by the manufacturer of aparticular piece of equipment along with illus-trated signals at test points. With this informa-tion, coupled with an understanding of the prin-ciples that have been discussed. many syncgenerator troubles can be readily diagnosed.

The Camera Chain

As. ALREADY STATED in Chapter 1, allTV systems contain three basic elements

a pickup device, control equipment, and repro-duction or display equipment. We have dis-cussed and studied representative types of powersupplies and sync generators which are a part ofany system. These items are necessary for the.proper operation of the camera chain; however.it is important that we know that a camera mayhave a self-contained power supply, sync gener-ator, and other components. As we make a de-parture from the simple system, we find addi-tional components such as the switcher anddistribution amplifiers. In this chapter we willdiscuss Or construction, function, care, trouble-shooting, and repair of the camera chain ele-ments.

9. Cameras9-1. A camera is an instrument that records

a scene in one form or another. The simple boxcamera changes a scene to a recorded image ona piece of film. The TV camera converts a sceneto an electrical signal. The basic items thatmake up a TV camera are a pickup device, acontrol and timing system, an output circuit, andof course a source of power. The exact arrange-ment of these items will vary with a particulararrangement for a specific need. The wide useof TV in broadcast, industry, and education hasled to a great variety of camera models, andmore are being added each day. In this sectionwe will classify cameras as to the type of pickuptube used. There are a number of pickup tubesin use today and new ones are being experi-mented with; however, we will limit our discus-sion to the vidicon and image orthicon types.

9-2. Vidicon Cameras. The vidicon camerais a very popular choice of military and indus-try because it can be constructed in a small pack-age and still deliver a good signal. The size ofthe vidicon camera has led to its use in certaintypes Of broadcast applications. Some of the ad-

CHAPTER 4

vantages of the vidicon camera are low operatingcost, simple circuitry (which accounts for its

- small size), high signal-to-noise ratio (whensufficient light is available), and ease in settingup.

9-3. Tube construction. One reason that thevidicon camera can be constructed in a smallpackage is that the vidicon tube is small in size.A standard vidicon tube, as shown in figure 42,is 1 inch in diameter and approximately 6 in-ches long. There are some smaller tubes only

inch in diameter and 3 inches long which aregiving satisfactory results. Although the tube is

small, it contains an electron gun which pro-duces a scanning beam and a photoconductivefaceplate. The fdceplate is a transparent con-ducting material coated with a photosensitivesubstance a few microns thick. The electron gunwhich produces the scanning beam has the usualheater, cathode, control grids and acceleratingand shaping grids. Focus, deflection, and align-ment of the electron beam are accomplished bythe use of external coils. In some cameras thealignment coil is replaced with permanent mag-nets and in others no alignment method is used.

9-4. The transparent conducting material is

connected to a fixed positive potential. Whenlight strikes the photosensitive layer it becomesconductive in relation to the amount of light.A dark spot will act as an insulator, whereas alight spot becomes conductive. The photosensi-tive layer then takes on a pattern of positivecharges, the amount of charge being directly pro-portional to the amount of light striking the spot.

'The electron beam coming from the electron gunscans each spot and neutralizes -it. The current,which is a product of this neutralization, flowsthrough a load resistor, thus developing a videosignal. This signal voltage may be coupled to avideo amplifier stage.

9-5. Care and handling. There are some pre-cautions you should keep in mind when using avidicon camera. Remember that as light strikes

49

216

GRID NO. 4

FACEPLATE

%1Mt NIM461,ACCEL ERATING

GRIO

rpm() NO. 3

CONTROL OLD

CATHODE

"NEATER

-11..

W//0/ IRMASIGNAL OUTPUT

PROM PHOTOCONDUCTIVEEL EMINT S

POCUSINGCOIL

LIGHRIENT COIL

HORIZONTAL ANDVERTICAL DEFLECTION

COILS

Figure 42. Cutaway view of vidicon tube.

the photoConductive material, current flows inproportion to the intensity of the light. If a cam-era is focused on a fixed spot of high intensitylight, the current in the photosensitive materialcan cause or inuge burn. Any time one partic-ular area of the photosensitive material is usedmore than the other areas, it leaves a burn orimage when the pattern is changed; therefore, toavoid a burn pattern, you should adjust the cam-era scanning to utilize the maximum useful areaof the photosensitive material at all times. Thephotosensitive material should never be exposedto an image of the sun; therefore, it is advisableto always cap the lens when a camera is beingmoved in or through an area where sunlight orany high intensity light is present. Another pointto remember when using, handling, or storing avidicon tube is to avoid tube positions that couldcause loose particles in the neck of the tube tofall on the photosensitive area. Like most tubesthe vidicon may be damaged by rough handlingand abuse; always be careful when moving cam-eras or tubes. Operational adjustments, such asapplying excessive electrode voltage, can alsocause damage to vidicon tubes. Furthermore, ifthe beam is turned on when vertical and hori-zontal scans are not functioning, a spot burn canquickly damage the tube. Now that we have re-viewed the major precautions to be observedwhen using a vidicon camera, let us discuss theoperation of this type of camera.

9-6. Adjustments and alignments. There area number of adjustments and alignments that arenecessary before a vidicon camera can be oper-ated. At this point we will assume that all thenecessary wiring is completed from camera tomonitor, that proper power is connected, and.that the sync generator is connected and opera-ting properly. If for any reason, there is doubt

50

*CLAMFROM Gt. ASSENVELOPE

as to the presence of either the horizontal orvertical sweep, it can be checked with a scope.After power has been applied, sufficient time forwarmup (generally from 10 to 20 minutes forvacuum-tube circuits) should be allowed beforethe actual adjustments and alignments are made

9-7. The initial picture on the monitor will bea circle or part of a circle that shows the photo-sensitive (mosaic) mounting section. If this isnot visible, the beam control will have to be ad-justed until a pattern does appear. This patternshould be visible even though there is not a lensor tumination present. When you have a visiblepattern, proceed to make initial centering andsize adjustments so that the circle is no longervisible at the corner of the picture. The camerascanning should now be adjusted for the maxi-mum useful area of the mosaic. If the beamcontrol is critically adjusted, you will be able tosee small specks or flecks, which are small im-perfections in the photosensitive surface (mo-

vocoscmena,

IGOE

v1010 I VIMOUTPUT

HORIZONTALIL ANAINGFIPTVOINT

TP3

WON OUTPUT TOCANIRA CONTROL UNIT

Pe Am CONTE:IL AND VERTICALal TAKING PROsi CAVIRA CONTROlUNIT

VIOICON PROTICTION VONA'.Enos CANER* CONTROL UNIT

VERTICAL OM ECM/. S GNALROA CANER* CONTROL UNIT

otoLECTIONTORE

HORIZONTAL DEFLECTIONMONO. FIN*

CONTROL UvIT

Ficure 43. Block diagram of vidicon TV canirra.

21 7

saic). If you adjust beyond this critical point,the picture will go to an all-white condition andyou will lose sync stability.

9-8. Now the camera is ready to be set upfor viewing an actual scene so that final adjust-ments can be made. It is best, of course, to usea fixed pattern such as a resolution chart. Makecertain that the lens is in position and that thereis proper illumination. Now center the cameralens in front of the chart and adjust the beamcontrcl to obtain a picture of the chart. Thevertical and horizontal controls may require re-adjustment to obtain picture lock-in. Now youcan adjust the lens for optical focus, and theelectrical focus may also be adjusted at this time.Since there is interaction between controls, it is

usually necessary to readjust each of them forthe best definition.

9-9. Block diagram analysis. Although thereare numerous variations and arrangements, fig-ure 43 shows a block diagram of a basic vidiconcamera. The inputs are from a camera-controlunit which may or may not be a separate unit;this unit will be discussed later. Since the vidi-con tube is the heart of the camera, we mustunderstand its signal output. If a scope is con-nected to Testpoint 1 (Tp 1), a pattern similar tofigure 44 should bc seen. Of course, the por-tion representing the picture information de-pends upon the scene being viewed. The hori-zontal and vertical blanking pulses are similar tothose illustrated. If the scope is moved to Tp 2,the same pattern is seen larger in amplitude. Thevideo amplifier stage will further amplify the sig-nal to drive a caftode follower which is used asoutput stage. A scope check of Tp 3 will showthe pattern indicated at the other testpoints butsmaller in amplitude than at Tp 2. The cathodefollower circuit minimized loading effects andprovides impedance matching.

9-10. Image Orthicon Cameras. An imageorthicon camera is generally thought of as a stu-dio camera because it is relatively large. In ad-dition, the image orthicon camera usually willhave an attached viewfinder that enables theoperator to see exactly what the camera is pick-ing up or viewing. The overall size of the cam-era plus viewfinder makes for a comparativelylarge unit which weighs approximately 100pounds. Weight and size are being reduced byusing solid-state components and printed circuitsin newer models of the image orthicon (I0)camera. The 10 camera has been adapted forfield use where there is a need for high sensitiv-ity or studio quality production.

9-11. Tube construction. It is important thatyou understand the 10 tube construction andhow it operates because the overall functioningof the camera centers around the operation ofthe 10 tube. Figure 45 is a cutaway drawing ofan IO tube. For study purposes, we have divi-ded the 10 tube into three sectionsthe image,scanning, and multiplier sections. The imagesection receives the light from a subject as it is

focused on the photocathode. The photocathodeemits electrons in proportion to the amount oflight received from the subject. The electrons areaccelerated toward the target, which is compar-able to the photoconductive faceplate of the vidi-con. Electrons strike the target, a glass mem-brane approximately .0001 inch thick, and causesecondary emission. This leaves the target with apositive charge. Since the glass target is verythin, the same charge pattern appears on thebeam side, where it will be scanned. To keepthe target from being burned by a stationarypattern, an orbiter coil is used to move the pat-tern at a rate of 1 rpm. This is not a rotationof the image, but a shifting about of the entirepattern. This precaution against image burn issomething not found in a vidicon.

HORIZONTAL BLANKING

VERTICAL BLANKING

PICTURE INFORMATION

Figure 44. Video and blanking signals trom TV camera tube (not to scale).

51

21 "6

ORBITER COIL

IMAGEACCEL ERA TOR

GRID NO 6

PHOTOCATHODE

SCENE BEINGTELEVISED

CAMERALENS

HORIZONTAL ANDSEAM VERTICALDECELERATOR FOCUSINGDEI LECTION COILSGRID NO. S REAM COIL MULTIPLIER ALIGNMENTACCEL ERATOR FOCUS COIL

GRID NO. 4 GRID NO. 3FIVE-STAGEMULTIPLIER

MULTIPLIEDBEAM

ETURN SEAM

ff:MZ40=W2AM-e'.!IMAGE TRANSFER

VIA PHOTOEL ECTRONS

IMAGE SECTION SCANNING SECTION MULTIPLIER SECTIONTARGETSCREEN CATHODE

TARGET REAMFORBING

GRID NO 2

Figure 45. Cutaway view ol image nrthicon tube.

21J

REAMCONTROL.GRID 60 I

'ILAN( NTS

22o

9-12. The scanning unit of the 10 uses anelectron gun similar to tho-e used in vidicon orother types of cathode-ray tubes. The beamfrom the gun strikes the target and gives up elec-trons in proportion to the amount of positivecharge on the target. The remaining electronsarc rcturned to the electron multiplier unit. Thebeam position and overall intensity are con-trolied by the beam accelerator. the horizontaland vertical deflection coils, and the focus coils.The multiplier focus element provides additionalcontrol of the return beam. which is directed intothe multiplier unit. You will recall that the vidi-con does not have a return beam; its signal out-put is taken directly from the photoconductiveelement.

9-13. After the IO's return beam passes themultiplier focus and the end of the electron gun.the beam strikes the first multiplier dynode of thefive-stage multiplier section. Electrons strike theplate of a dynode with enough force to causesecondary emission. The amount of multiplica-tion depends on the number of dynodes andvoltages applied. The output from the electronmultiplier section will be determined primarilyby the number of electrons in the returned beam.The brighter image returns fewer electrons to themultiplier stage, because it causes a greater posi-tive charge on the target.

9-14. The 10 tube has what is considered ahigh gain because of the multiplier unit. Sinceit has a high gain, it does not require a high-gain video amplifier. By comparison, since thevidicon does not have a high gain, it requiresa cascode video amplifier followed by additionalamplifier circuits. Since the 10 tube amplifies,it is a source of noise. By contrast. the vidicontube generates little noise but its associated videoamplifiers constitute a source of noise.

9-15. Care and handling. The care and han-dling of an 10 tube is important, from the stand-point of both economy and performance. Takethe simple procedure of installing an 10 tube.If you try to force shoulder pins into their sockets,you may damage the tube beyond repair. Thismeans a loss of more than a thousand dollars.You should allow sufficient time for an 10 tubeto warm- -up before operating it. If the targetheater is controlled manually, be careful to pre-vent overheating, which will cause loss of resolu-tion and may permanently damage the tube.Also remember that new tubes should be placedin operation for several hours before they arestored to keep as spares. Moreover, all 10's thatare kept as spares should be used in a camerafor sevesal hours each month to keep them free

53

from any trace of gas. Gas may appear in a tubewhich is stored for a prolonged period. A wordof caution about handling or moving an 10 tubeneed be mentioned here. You should alwaysavoid placing the tube in a position that alloWsloose particles in the tube to fall upon the targetor photocathode. It is easy to accidentally put atube in a near-vertical position when installingor removing it. Do not yield to the temptationof setting a tube down on its face; this maycause internal and external damage. When acamera is in operation, observe position pre-cautions; do not point the camera straight downfor a bird's-eye view.

9-16. A knowledge of a large number of de-tails concerning 10 tube applications is neces-sary to insure proper operation and optimumperformance at all times. The physical orienta-tion limitations have been discussed; however,there are other considerations which will affectthe operational life of an 10 tube. Operating

.temperatures must be maintained within limits.Target-scanning adjustment limitations must becarefully set to avoid a raster burn which wouldruin the tube. A dynode spot must be eliminatedby slight defocusing. An ion spot should bedetected and action taken to return the tube forreprocessing. Watch for and eliminate target-screen pattern pickup. These are trouble areaswhich must be carefully watched.

9-17. Performance. The overall performanceof a pickup tube is what determines the choice ofa camera for a particular application. The vidiconand the image orthicon pickup tubes are the mostcommon clioices. The vidicon has found wideapplication in fields other than studio work; how-ever, the 10 is used almost exclusively in studioapplications. The following comparison of thevidicon and 10 will give you an idea of theadvantages and disadvantages of each tube.

Vidicon

I. Operating cost is ap-proximately $0.10 perhour.

2. Average output signallevel is approximately15 millivolts.

3. Output signal level issubject to change withvarying light levels.

4. Low tube-noise char-acteristics result in anexcellent signal-to-noise ratio at a lightlevel of approximately200 foot-candles.(Ratio-300 to 1).

Image Orthicon

1. Operating cost is approxi-mately $2.00 per hour.

2. Average output signallevel is approximately 50millivolts.

3. Output signal level isstable over a wide rangeof light levels.

4. Inherent tube noiselimits the signal-to-noiseratio at all light levels.(Average ratio-40 to 1).

Vidicon

S. Picture smear resultswhen uncontrollable.fast-moving objects arebeing televised.

6. Simple external cir-cuitry results in small:inexpensive cameras.

Image Ormicon

5. Picture smear is not a

problem when faA-mov-ing objects are being tele-vised.

6. Detailed, complex cir-cuitry results in large. ex-pensive cameras.

9-18. The vidicon and 10 tubes are bothwidely used; picture quality is the scale of com-parison. The 10 tube pickup ability is compara-ble to photographic film with an American Stand-ard Association (ASA) Speed or Exposure Indexof approximately 8000, with some rated as highas 10,000. This speed, plus the spectral responseapproaching that 'of the human eye, makes thisan ideal tube for camera use where light levelsrange from deep shadow to bright sunlight. Al-though the present vidicon tubes produce high-quality pictures only if there is sufficient light,they are being improved so that they can attainstudioluality performance at relatively low lightlevels. Furthermore, experimental wdrk is beingdone to develop the vidicon for wider use withcolor cameras. Research is being conducted toexplore the possibility of developing an 10 orsimilar tube that can pick up all three colors.If such a tube is developed, a single tube wouldreplace the three 10 tubes used in present-daycolor cameras.

9-19. Adjustments and aliymnents. This sec-tion will not give you any specific adjustmentsor ai;gnments for a camera because the Air Forcepun:ha:es off-the-shelf items from various com-panies. However, there arc .ome eeneral guide-lines to be followed when making adjustmentson cameras. Just as in the section on care andhandling. we will present information pertinentto pickup tubes. For all of the items discussed inthis section, you must refer to the instructionsmanual of the particular camera .for specific de-tails. Thc simple process of mounting a cameraon a pedestal requires an adjustment in themounting position for the best balance. If youchange lenses or add more lens units to a turret.you will have to rebalance the camera.

9-20. Since you have already studied the careand handling of the :10 tube, let us assume thclens turret has been removed, and thc 10 hasbeen removed and replaced. When you replacethe lens turret or other lens assembly, do notovertighten, yet be sure to tighten the turret re-tainer(s) enough to prevent any lens rocking. Ifit becomes necessary to remove any of the coilassemblies in a camera, you rifay- have to par-tially remove an assembly to gain access to re-taining springs and clips which hold plug-in jacks.The bellows of the blower must be carefullyremoved. In some camcras. you will have toturn the assemblies to a certain position to get to

ORITHICAFOCUS

+300VFROM

CAMERACONTROLCHASSIS

MULTIPLIER

FOCUS

TARGET

IMAGE

FOCUS

GI0

BASE PIN 2

G30

BASE PIN 3

TARGET

SMOULDER PIN 6

BIAS SUPPLYCAMERA CONTROL

CHASSIS

BEAMGI CONTROL

BASE PIN 12

G6

SHOULDER PIN I

500VFROM H.V. IN CAMERA

Figure 46. Coools on camera control unit.

54

222

the plugs. If at any time you are required toremove or unsolder any leads, you should labeleach one before removal to prevent any mixup.

9-21. Since operating temperatures must bemaintained within limits, heaters and blowers areused. A motor must be oiled on schedule, asrecommended by the manufacturer, for satisfac-tory performance and maximum life. Wheninstalling a new motor, you should check manu-facturers instructions as to oiling it before oper-ating. Of course, be certain that the bellows areproperly installed; cooling will be impaired if theairflow is misdirected.

9-22. Once the mechanical adjustments aremade on the camera, the electrical adjustmentscan be made. Before you make any electricaladjustments, the camera (with a standard 10tubc ) should be turned on and allowed to warmup for one-quarter to one-half hour with thelens capped. Read the instructions carefully andfollow them closely when you uncap the lens andadjust grid No. 1 (beam adjust on camera con-trol). An improper procedure can cause per-manent damage to the IO tube, since a coldphotocathode target will retain a permanentimage.

9-23. During the warmup time, you mustcheck to determine that the deflection circuits arefunctioning properly and that the beam is "over-scanning" the target. Overscanning the targetprevents burning the target with a smaller thannormal raster. After warmup time, set the targetvoltage at approximately 2 volts negative andadjust grid No. 1 voltage (beam control on thecamera control unit) until a rough-textured pic-ture of No. 1 dynode appears on the monitor.A very slight adjustment of the target voltagemay be necessary; if so, this adjustment also ismade at the camera control. Now you are readyto check the alignment coil current by moving theorthicon focus control (voltage on grid No. 4)back and forth. If the alignment coil current isnot set correctly, the dynode spot will move upand down or back and forth. However, if thecurrent is correct, the spot will just go in and outof focus. Always keep the beam current as lowas possible during test and operational service toobtain the best picture quality and to minimizetube noise.

9-24. At this point, uncap the lens, open theiris, focus on a test pattern, and proceed to makevoltage and current adjustments by means of thecamera controls (target and beam) located on thecamera control unit. The target voltage is slowlyincreased until you just see the test pattern. Thetarget voltage should be increased along with thebeam urrent to obtain the best and most uni-form shading and low noise. The actual amount

of voltage increase will depend on the brightnessand contrast of the scene being televised. Anadjustment of grid No. 5 (beam decelerator)should now be made to obtain the most uniformshading from the center to the edge of the pic-ture. Next, adjust grid No. 3 (multiplier focus)for maximum signal output. Grid No. 6 (imageaccelerator) may now be adjusted to produce asharply focused straight line on the monitor; ifit is out of adjustment, the pattern will be slightlyS-shaped.

9-25. The adjustments just described are roughsettings that will require refinements which varysomewhat depending on the camera or cameratube used. Figure 46 is a diagram of a voltagedivider circuit and the controls necessary to pro-vide the voltages for an 10 tube. You will noticea voltage spread from +300v to 500v whichprovides voltages to four controls..Notice that the500v is derived from the HV power Supplyin the camera. The No. 1 (beam control) picksup bias voltage from the bias rectifier in thecamera control unit.

9-26. Other electrical adjustments to be madeare the alignment coil current and focus current.The coil current provides magnitude and directionof the magnetic field around the coil. Alignmentcontrols are normally found on the camera, butthe current is derived from a separate powersupply. The focus coil is a single coil whichreceives current from a current regulated powersupply. (This power supply is located on a sep-arate chassis and is usually rack-mounted.) Theorbiter coil is not adjustable, but can be switchedon or off. The coil is a protective feature andshould be used at all times. If the target heateris used for quick warmup, be sure and turn it offwhen operating temperature is reached; other-wise, the target may be damaged. This is trueif the heater is not thermostatically controlled asin some cameras.

9-27. Diagram analysis and troubleshooting.Assume that we are checking a camera that isfunctioning properly and that we are doing this tobecome familiar with all of the correct wave-shapes. You know that the scanning beam isaccelerated to the target by the tube elements;however, before die return beam will give usany information or intelligence, it must scan thetarget. You recall that the target scan must bein an orderly manner or sequence; therefore, wemust control the position of the beam at all times.This control is provided by the horizontal andvertical deflection coils. The deflection voltageswhich are fed to these coils are usually generatedwithin the camera but they are triggered bypulses from the camera control (which will bediscussed in the next section). These pulses

55

223

VERTICALSAWTOOTH

GENERATOR

VERTICALFEEDBACK

MIXER

4

\1\1\VERTICALAMPLIFIER

VERTICALOUTPUT

ELANKINGMIXER

MAUI

ji-n-HON HUIZONTALWTOOTHRENATO*

DRIVE

13.7SOCPS

BLANKINGOUTPUT

UNNAU

VERTICALOEFLECTION

COILS

NNIt..

PHASESPLITTER

TA(

TO TARGET

1.0TUBE

HORIZONTALOAMPER

irn

CAMERAPREAMPLIFIER

HORIZONTALDRIVER

HORIZONTALOUTPUT

TRANSFORMER

Figure 47. Simplified block diagram of image orthicon camera.

originate in the sync generator. Figure 47 is ablock diagram showing basic sections and wave-forms necessary to produce a video output fromthe camera to the camera control.

9-28. For a typical camera, vertical deflectionis accomplished in the following manner. Thevertical drive pulse from the camera control iscoming in at a 60-cps rate and triggers the ver,tical sawtooth generator. This signal is amplifiedby a number of stages to drive the vertical de-flection coils. As indicated by the diagram, asignal is fed back to the vertical feedback mixer;thus, the signal is reinforced and linearity isimproved. A signal is also sent to drive theblanking mixer w)ich combines the blankingpulse of both the ,ertical and horizontal sweepsignals. A point which is sometimes missed in thestudy of the vertical deflection system is thedirection of scan. We study the scanning of thepicture tube in a monitor and find it is from topto bottom; however, the camera tube normallyscans from bottom to top. By using a bottom-to-top scan, we can use an off-the-shelf camera lenswith the TV camera. There are times when Wewant to scan from top to bottom such as when weproject a film image directly on the camera tube,

56

HORIZONTALDEFLECTION

COIL

in which case the image is right side up..- There-fore, if a camera is to be used for both purposes,it is necessary to reverse the direction of scan.On some cameras, there will be a switch toreverse the direction of scan. It may be markedas scan reversal, normal/film, or in some othermanner to indicate the direction of scan. Areversal of scan requires only that the polarity ofthe vertical deflection coils be reversed. Verticalcentering is accomplished by applying a voltageacross the deflection coils; however, this is a volt-age which can be varied. If the camera is de-signed for reverse scan, it will probably have twocentering adjust controls which can be preset forboth directions of scan.

9-29. Using a scope to signal trace throughthe various stages of a camera, you will see wave-forms similar to those shown in figure 47. How-ever, for a particular camera adjustment, youshould refer to the specifications for that camera.The number of waveforms and their configura-tions will be determined by the number of stagesnecessary to achieve signal amplification. Witha bit of thought, you should be able to reason outthe sicnal shape at the various places in thediagram2

2

9-30. You remember that the horizontal drivepulses are coming in at a frequency of 15,750cps. This gives the standard ratio of 262 1/2horizontal sweeps to 1 vertical sweep. Since thehorizontal pulses are at a higher frequency. theyrequire more shaping; therefore, the drive pulsestrigger a sawtooth generator which drives a saw-tooth phase splitter. Notice that thc phase splitterhas two output signals that are 1800 out of phasewith.each other. These two signals drive two sep-arate stagesa driver and a damper. The pri-mary of the output transformer is so connectedthat the output signals of the driver and damperare added and thus reinforced to give a strongsweep signal out. The output from the trans-former goes to the horizontal deflection coils tothc 10 protection circuit and the HV pulse ampli-fier which drives the HV rectifier. Depending onthe type of camera, the pulse distribution maybe sent to additional points, such as a preampli-fier.

9-31. Once thc vertical and horizontal deflec-tion voltages are generated and applied to causethe beam to scan the target image, a video pic-ture signal is generated. This signal is amplifiedby the video preamplifier section which may becomposed of a number of stages. The pream-plifier section may be built into the camera orit may be a plug-in unit; in any case, it serves tostrengthen. shape. and compensate the signal. Itis designed to give an overall high-quality re-sponse. Its output goes o the viewfinder andvia cable to the camera control unit. A blockdiagram of the preamplifier is not included be-cause the signal waveforms are essentially thesame throughout; what variatiOns there are maybe peculiar to the particular camera.

9-12. Troubleshooting a camera with a scopeis relatively easy so far as locating the stage orbasic circuit is concerned. For example, if youhad a straight horizontal line on the viewfinder,you would immediately check the deflection cir-cuits. After you had determined that the deflec-tion circuit is not faulty, you would simply checkthe output of the stages until you located thetrouble. Having located the stage, the scopecould be used to find the point in the stagewhere the signal was absent or improper. As yougain experience, you will recognize linearity dis-tortion and know exactly where to look for thetrouble. If it is vertical linearity, the trouble isprobably in the feedback circuit. Suppose thehorizontal linearity is poor; you would check thewaveforms of the horizontal circuits. If you findfrom the indications that there is no sufficientblanking signal, you should immediately checkthe blanking circuits with a scope to determine ifthe signai is absent or just weak. When a trouble

57

is noticed on a monitor, for example the view-finder monitor on the camera, you must not im-mediately assume that the camera is at fault.The more experienced maintenance man will al-ways know to compare the viewfinder with thecamera control monitor and perhaps with a lineor utility monitor. The camera control has abuilt-in scope that can be used as an aid totroubleshooting. Picture monitors and the built-in scopes . will be discussed in the next chapter,but let us look now at camera control unit andits controls.

10. Camra Control10-1. We have chosen to discuss the 10 cam-

era control because .an understanding of it willenable you to maintain other camera controlconsoles. Earlier, you were made aware of anumber of controls that are located on the cam-era control. In addition to the controls relatedto the camera, the control unit performs thenecessary steps to obtain a composite television.signal.

10-2. Function. Including controls and cir-cuits, we can list six basic functions that can beperformed by the camera control unit.

Remote adjustment of the various voltagepotentials necessary to the operation of the 10camera.

Correction for shading.Correction for black and white compress-

ion.Provision for signal amplification to the

level required for transmission.Adjustment for proper blanking and black

level.Addition of sync pulses in a simple system.

(In a complex system. the sync pulses are addedin the switcher, which will be discussed in thenext numbered section.)

10-3. Operational adjustments. The remoteadjustments of the various voltage potentialsnecessary to operate the 10 camera were dis-cussed in the previous section under the headingAdjustments and alignments and illustrated infigure 46. The adjustments we will considerhere have to do with the picture shading andblack-to-white fidelity. You must realize thatit takes two maintenance men to set up a cameraproperly, one man on the camera and one on thecamera control. They must be able to talkclearly and work together to get a good videosignal.

10-4. The camera control amplifies a videosignal coming from the preamplifier in thecamera; meanwhile, other things are also hap-pening. (see fig. 48). While the video signal is

225

1411.

VI0110

Culla*F ROY hLIPION

viOTO

P.O. AMCGINIRA1011

OIvT RINASHIC GIN

ILANKINIICUPP,.

CLIPPCI CLIPPTIIPPPPP ROI

Jar,. CLALIPIR

Oilr/ iCALTAUPLI /ID

IlLCI MOTEMOTO.

CLANIPOR

71GOAT KALI

GAJITCONTIOL --10. FIST

COROOUTPUT

[ CLANPIIII

411.

HNCAMPLIPIOR

NOMZONTORITI P.O.

LINC GIN

NONIZONTALWAGING

HAPUPIII

HORIZONTALNIAOINOCONTROL

NORIZONTALPULLS ANI

PULAROUTPUT

TOCLAPPERS

COTICALPUlli

AMPLIPISI

MAIROMPER

NMUZONTALNAZI

AMP

Figure 48. Block diagram of camera control unit.

being amplified, it may lose its d-c component;the cbmper circuits restore it. To further in-crease the overall flat response for the wideband of frequencies (approximately 8 mc), it isnecessary to use frequency-compensating circuitsand degenerative feedback.

10-5. Blanking signals from the sync genera-tor are fed into the blanking clipper, which iscoupled to the output of the video amplifier,thus adding blanking to the video signal. An-other output of the blanking clipper is used asan input for the setup amplifier. This is a cath-ode follower stage which is coupled to one ofthe final video amplifier stages. A definite re-z tionship is therefore established between signallack and reference black. Notice that the sync

signal is not inserted until the final output, andthen to only one of the output points.

10-6. Shading and stretch circuits. Shadingsignals are also added at the video amplifier tocompensate for horizontal or vertical shading.Some shading compensation is added in thecamera; however, to improve the picture, moreshading compensation is inserted in the cameracontrol video amplifier. The horizontal shading

58

+OPTICALIIINAVAG

VORTICAL110401110

0 PPPPPP OP

di VORTICALWTI

OUTPUT

IC OUT

PIC OUI

OUT

is inserted at the input of the first video ampli-fier, whereas the vertical shading is inserted atthe cathode of the clipper amplifier. The shad-ing signal can be varied until it is equal in am-plitude but opposite in phase to any spurioushorizontal or vertical shading signals which maybe present; thus, any undesired shading can becanceled.

10-7. As already mentioned, the controls areinitially adjusted when the camera is set up atthe start of the day, with the exception of screw-driver adjustments which are set up and leftalone. On most of the camera control units, theonly time that you need to readjust the screw-driver-type controls is when you change tubesor a tube deteriorates. There are other controls(fig. 49) that are adjusted from the cameracontrol console after the camera is all set upand operating. Before these controls can be ad-justed, the camera must be operating and fo-cused on a scene; if the scene is normal, theswitches will be in the normal position. If thescene is mostly white, SI and the white stretchswitch S2 will be put in the stretch position; if itis a dark scene, SI and the black stretch switcl

226

S3 will be placed in the stretch position. Thestretch circuits adjust the point of operation upand down the characteristic curve of the tube.The white stretch circuits amplify the whitescenes which were compressed due to the char-acteristics of the 10 tube. The black scenes areamplified to correct for the black-scene corn-preision. which will normally take, place in akinescope. Therefore, with this correction made,the scene being viewed will be displayed cor-rectly. The corrections made by the stretch cir-cuits increase the amplitude of the signals abovethe standard levels; therefore, the gray scalegain control circuit is incorporated to afford anadjustment back to the standard video level.

10-8. Trouble diagnosis. With the precedingdictussion still in mind and using figure 48 as areference, what stage(s) would you Check firstif you found that your predominently whitescenes looked more gray than white? Your firstaction should be to use the white stretch control.If this does not correct the problem, then youshould check the gray scale amplifier circuit andthen proceed to check the white stretch circuit(operation of switches and voltage dividers).If the black scenes seemed to be washed out,

...you should check the same amplifier and theblack stretch circuit. If you notice blankingsignals appearing on the control monitor but noton the viewfinder, you should check the blank-ing clipper. Other determinable troubles arecaused by loss of drive to the vertical and hori-zontal deflection circuits. Such troubles produce

TV-INPUT

symptoms that lead you to check the associatedamplifier circuits. When there is a loss of biasvoltage, you need to check the bias rectifiercircuit or the preceding horizontal circuits. It isimportant- to realize that your troubleshootingspeed depends in large measure upon yourability to reason through a problem and alsoupon your understanding of this equipment.

10-9. Not all camera control units are console-mounted. There are also field-type unitsThe field units perform the same basic functionas the console units and the circuits are about thesame. Their function controls are located on theoutside of the unit. However, those controls thatare associated with the adjustment of the picturand waveform monitor are usually located in leconvenient places, such as recessed panels onthe top or sides. These controls will be placedand grouped differently on the field unit becausethey are designed for portability.

11. Switchers and Video Amplifiers11-1. In a complex system, a switcher may be

a sophisticated piece of equipment. We willconsider the functions it can serve and describethe manner in which they are accomplished. Aswitcher contains video amplifiers which, as youknow, are used extensively throughout a TVsystem. Therefore, our discussion of video am-plifiers will be broad in scope and applicable tovirtually all equipments employing them.

11-2. Switchers. Switching equipment is neces-sary in all but the simplest television installation.

NORMAL

STRETCH

SW2 STRETCH

NORMAL

+v

RI WHITE STRETCH

5W3 STRETCH

NORMAL

v

B+

OUTPUT

GRAY'SCALEGAIN

R2 BLACK STRETCH

Figure 49. Schematic al stretch and gray scale circuit.

.59

227

INPUTS

1 2 3 4 5 6 7 a 90 0AMP

MONITORINPUT

SYNCINPUT

AMP

'FADER A

t4

MONITORSWITCH

0

A

RELAY

J

IMION 70.

PREVIEWOUTPUT

0 RELAY

AMP

PREVIEW CHANNEL

FADER CHANNEL

FADERLEVERS

1

FADER B

PROGRAMTRANSF ER

SWITCH

A

1

A

2

PROGRAM OUTPUT

Figure SO. /Block diagram ot a typical video switcher.

60 22

A

A

It functions so that the video output from one ofseveral television signal sources can be selectedand sent to one of several outgoing paths in adistribution system. In a complex closed-circuitapplication, switching equipment is set up to

also provide for program monitoring and pre-viewing; video switching between studio cam-eras. film cameras, and remote pickups; and spe-cial effects such as fading and lap dissolving.

11-3. Video switchcrs, which may operateeither directly or remotely by relay, employpushbutton switching. Zero time interval duringthe transfer woutd be ideal, but since this is im-practical. switchers are designed to effect thetransfer in one of two ways. either gap switchingor overlap. For camera switching, a slight overlapis generally introduced; the second signal isswitched in before the first is removed. Thisdouble termination, or make-before-break, pre-vents undesirable flashes and avoids black areas.For preview monitors. however, and for mastercontrol switching between programs, the transferis made over live lines, and gap, or break-before-make. switching is employed. Both the gap andthe overlap methods permit video transfer witha minimum of picture disturbance.

11-4. Block diagram analysis. Switchingequipment. in addition to making the signaltransfer, also performs several other functions.Synchronization is inserted, and the transfer issmoothly made with fade-ins and fade-outs, lapdissolves, or such special effects as diagonalwipes. Or. instead of switching, two signals maybe superimposed (as when titles are flashed overa picture). or mixed in split-screen montages.Furthermore, thcre are provisions for preview-ing the video and monitoring the output line.

11-5. The switching equipment, to performthese various tasks, includes the following com-ponents: the basic switching unit, or relay chas-sis; thc fadcr assembly; isolation and gainstages; special effects and lap-dissolve amplifiers.which may be fed back to the video input forpreviewing before switching; and mixing or out-put amplifiers, where synchronization is added.

11-6. Figure 50 is the block diagram of aversatile switcher with a number of inputs; somearc for local, noncomposite inputs (studio andfilm cameras), and others are for composite ornoncomposite inputs from remote sources orfrom additional local cameras. In addition, thepreview channel contains an input which is usedfor monitorine the line or off-the-air signal.Note that the program transfer switch permitsthe preview channel to be used for the programoutput while thc two fader channels are beingused for the previewing output to preset lapdissolves. fades. or superpositions. The signal is

61

strengthened and isolated for distribution byvideo amplifiers. These amplifiers will be stud-ied subsequently.

11-7. Suppose that you have a camera signalto input 1 of figure 50. The signal could beselected from fader A or fader B for amplifica-tion in the fade channel. From the programtransfer switch to the preview output or theprogram output. ,it picks up the sync signal.Since this is a camera signal, the sync input isnecessary for inserting the sync pulses prior totransmission. The monitor input is used whena composite video input is obtained from areceiver or picture monitor. Observe that thisinput can be transferred to the preview outputor to the program output.

11-8. There are complicated switchers com-posed of standard relay racks with pushbuttonpanels suitable for a more complex video switch-ing system. They arc designed for use in astudio control room or a master control roomand can be set up to handle from six to twelveinputs and from two to six outputs. Automaticcircuits which insert the local synchronizing sig-nal permit the handling of remote inputs, and theaddition of a panel of jacks and video patchcords provides rapid and efficient output dis-tribution. The pushbutton panels may be housedin any remote location convenient for programmonitoring, and the relays which accomplish theactual switching may also be located where mostconvenient. This permits full flexibiEty in sta-tion layout, and simplifies the addition of studiofacilities to handle expanded operations. Even amodest or simple installation should be plannedand equipped with regard to possible futureexpansion in order that discarded facilities andadditional cost will be kept to a minimum.

11-9. Trouble diagnosis. Normally the switcheris regarded as a trouble-free piece of equip-ment. Perhaps from your own experience youhave drawn this conclusion. Although fewtroubles occur in a switcher, they do occuroccasionally; therefore, it will be much easier toquickly troubleshoot and repair a switcher if youknow some probable troubles. Again referringto figure 50, suppose that you punch up a pre-view of number one input and you get a verygood picture. However, when you punch it upon fader A, you cannot get a program outputmonitor picture. This is assuming, of course,that the fader control is moved in the "in"position. But, when you go to fader B, you geta picture; thus, you draw the conclusion that abad amplifier or a bad switch contact can be thetrouble. The next logical step is to check an-other input to fader A and sec if you get apicture. If you do get a picture. the amplifier

22J

Figure 51. Simplified a-c circuit of RC-coupledamplifiers showing shunting capacitances.

is good; you should then check continuity frominput 1 to the amplifier. Since the switches cancause trouble, you must observe the relationshipsof the various switches. The trouble can possi-bly be the result of one or more faulty switches.If the trouble is in a switch, it will usually beindicated by picture noise or erratic operation.Many times this trouble can be eliminated bycleaning the switch contacts.

11-10. Video Amplifiers. You know fromprevious training that video amplifiers are wide-band amplifiers with a frequency range extend-ing from a low value of cps up into the mega-cycles. These amplifiers are gsed extensivelythroughout a TV system. They are .found where-ever there is a requirement to amplify a complexwaveform.

11-11. Types. Performance characteristics ofvideo amplifiers depend in large measure uponthe type used. Three common types are picturesignal (or vision), isolation (or utility), andpulse. Their names are indicative of their func-tion and application. Picture signal amplifiersmust have a sufficiently wide band to handlethe frequencies necessary for good picturefidelity. Such amplifiers are found wherever itis necessary to strengthen the picture signal. Re-call that such amplification is accomplished inthe camera. Monitors, which are covered in thefollowing chapter, also incorporate many stagesof this type of amplifier. Both isolation and pulseamplifiers are used for distribution purposes. Insuch casesi they are called DA's (distributionamplifiers). Isolation amplifiers are designed forvery broad response (up to 8 mc or more), buthave comparatively low gain. They serve pri-

Figure 52. Effects of load resistance On frequencyresponse of an RC-coupled amplifier.

marily ac buffers to isolate one videu eircuit fromanother and are located at junction points in avideo distribution network. The pulse amplifierii employed for pulse distribution; e.g., kora thesync generator to various camera units. Also,many are used within equipments for pulse am-plification. Their handpass response and charac-teristics depend upon the pulse shape they muststrengthen or reproduce.

1 1 -1 2. Broadening bandwidth. BCCjUse themeans of broadening the frequency response oftransistor amplifiers is identical in principle withthat of electron-tube amplifiers, our treannentwill be for the most part a review. Nevertheless,it should-make you mindful of the distinczivedesign of video amplifiers and aware of the factthat transistor amplifiers can be so designed. Wewill discuss matters pertaining to frequency re-sponse limitations, and broadening bandwith forwideband signals.

11-13. Any type of coupling, except directcoupling, causes the low frequencies to be at-tenuated and shifted in phase. Resistance capaci-tance (RC) coupling causes a certain amount of

+ vcc

Figure 53. Low-frequency compensating circuit.

trouble at the low end of the band mainly be-cause the reactance of the capacitor increases asfrequency decreases. Since it is in series with theinput, to the succeeding stage, this reactancecauses gain losses and time delays for low fre-quencies. Unless very low frequencies are re-quired, however, the coupling capacitance cangenerally be made large enough to minimizethese effects. Thus, RC coupling poses no seriouslimitations to low-frequency response. On theother hand, impedance coupling and transformercoupling do. These latter types are inherentlypoor for low-frequency amplification because theload impedance decreases atid-becomes more andmore inductive as frequency decreases. Thiscauses appreciable frequency and phase distor-tion.

11-14. The transistor itself has a great deal todo with high-frequency response; its alpha cut-

62 230

off frequency and internal capacitances arelimiting factors. It should have very low internalcapacitances and its alpha cutoff frequencyshould be well above the required upper limit ofresponse. Special high-frequency types are mostsuitable for video applications.

11-15. Shunting capacitances are shown infigure 51 as output capacitance C. and inputcapacitance CI. These capacitances are made upof the transistor's internal capacitances plus wir-ing and, stray circuit capacitances. C. and C,arc in parallel with the load; so the higher thefrequency. the lower the load impedance. Conse-quently. frequency distortion and phase distortionbecome worse with increasing frequency.

11-16. Because of .these frequency-responsedefects, it is not possible to achieve the frequencyresponse necessary for video-signal fidelity un-less modifications are made. Let's give our atten-tion, therefore, to the ways in which bandwidthcan be extended.

11-17. Like an RC-coupled electron-tube am-plifier. an RC-coupled transistor amplifier can bedesigned to handle video signals satisfactorily.The curves in figure 52 show that reducing thevalue of load resistance (R',. is less than Rt.)gives a much broader response. This broaden-ing is acquired at the cost of overall gain. Notealso that the low-frequency response is sacrificedsomewhat. Gain can be improved by using addi-tional stages. but there is no improvement inlow-frequency response. In fact, it is depreciated.Moreover, to reduce the load resistance beyonda certain point is impractical and costly. There-fore. in addition to having a comparatively smallvalue of load resistance, an RC-coupled videoamplifier often contains frequency-compensatingcircuits to extend its response over the requiredrange.

11-18. The parallel arrangement of Rgy andCl.r shown in figure 53 constitutes a low-fre-quency 'compensating circuit. Capacitance CLIPis of such a value that it is virtually a short circuitto midfrequencies and high frequencies, but itoffers increasing reactance to low frequencies;the lower the frequency, the greater the react-ance. Therefore. only the low frequencies are af-fected. The proper combination of Rip andCit. raises the gain and causes phase shiftswhich compensate for the attenuation and phasedistortion caused by the coupling capacitor C.As a result. uniform response is extended to in-clude the desired low frequencies.

11-19. Although all shunting capacitances thatattenuate high frequencies cannot be eliminated,their undesirable effects can be. This is done bymeans of sresonant czaking circuits which use the

cashunting pacitances. High-frequency compen-

63

sation can be achieved by shunt, series, or series-shunt peaking.

.11-20. Note in figure 54,A, that the inductorL is in shunt with C. and Cl. Such an arrange-ment is called shunt peaking (or shunt compen-sation). The indnetance of L goes into parallelresonance with the shunting capacitance, therebyincreasing the load impedance at high fre-quencies (see fig. 54,C) and widening band-width, as shown.

11-21. Series peaking (or series compensa-tion) uses an inductance to form a series resonantcircuit with CI (see fig. 54,B). As resonance isapproached, the current through C, increases andcompensates for the loss of gain caused by C..Frequency response is approximately the same asthat for shunt peaking; this is also illustrated byfigure 54,C.

11-22. Figure 55 shows a video amplifierthat employs shunt-series peaking and low-fre-quency compensation. The type(s) of compensa-tion and the amount necessary depend largelyupon the application and the bandwidth of thevideo signal.

11-23. Another way to broaden bandwidth isby means of feedback. Knowing that degenera-tive feedback reduces all types of distortion, it isnot surprising to find this type of feedback widtlyused in transistor video amplifiers to extendbandwidth and improve fidelity. Either part Ofall of an emitter resistor can be unbypassed toprovide degenerative action. This method differsin no way from that used in electron-tube ampli-fiers. In fact, the CC amplifier (also called anemitter folldwer) corresponds to a cathode fol-lower. Both the emitter follower and cathodefollower are, in essence, video amplifiers that usea maximum amount of degenerative feedback(the entire output signal voltage is fed back tothe input). Although no voltage gain can berealized, the follower does give current andpower gain and is most useful for matching ahigh impedance to a low impedance.

11-24. A true emitter follower (CC amplifier)has no impedance between the collector and a-cground. If a resistor of low value is inserted inthe collector circuit, a voltage gain can be ob-tained by taking the output from the collector.Actually, this amounts to having a CE ampli-fier with emitter follower action. By properlyproportioning the collector and emitter resistors,the amplifier can be made to suit many videoapplications. --

11-25. Degenerative action can be obtainedin other ways. Regardless of the means chosento acquire negative feedback, thc effect is thesame; frequency response is extended.

23i

4

A SHUNT PEAKING A-C CIRCUIT B SERIES PEAKING A-C CIRCUIT

RESONANTPEAKING

FREQUENCY

EXTENDEDHIGH-FREQUENCY

ESPONSE

WITHOUTCOMPENSATION

FREQUENCY

C EFFECT OF PEAKING CIRCUITS ON BANDWIDTH

Figure 54. High-frequency compensation.

11-26. We .need mention here that for an r-fcarrier system, r-f and i-f amplifiers must havean overall bandwidth which is broad enough topass all the video information. The bandwidthof tuned amplifiers is broadened by: (1) lower-

cPIANING C

LOVAIRCOUCNCYCOMPIPISATIOIM

Figure 55. Video amplifier with compensation circuits.

64

ing the Q of the tank circuits, (2) close coupling,and (3) stagger tuning. By one or a combina-tion of these ways, the required band of fre-quencies can be developed for detection and sub-sequent video amplification.

11-27. Comparison of transistor and tubevideo amplifiers. Although a high gain (about40 clh) can be obtained from a single transistoraraplifier, input and output impedance require-ments limit the gain to much lower values. Ordi-narily it takes two transistor stages to obtain again comparable to a single pentode tube ampli-fier. Even so, the power supply requirementsand space occupied by transistor amplifiers areconsiderably less than those of tube amplifiers.

11-28. Good quality transistors with high-fre-quency cutoff values (20 mc and better) areplentiful nowadays. Therefore, attaining thehigh-frequency response needed for a video sig-nal poses no serious problem. In fact, with low-gain per stage, the high-frequency response maybe quite adequate for excellent performance.Considering the adaptability f transistors todirect coupling, it is not surprising to find this

Figure 56. Transistor video amplifiers.

coupling used extensively to insure low-fre-quency response and d-c transfer. The use ofdirect coupling and low-gain amplification makescompensating circuits unnecessary in many cases.Although we showed that a transistor video am-plifier circuit may incorporate compensating cir-

6

65

cuits, you should realize that some do not. Figure56 shows two such circuits which are common-place. Note the simplicity of these arrangements.You should recognize these configurations andknow why video amplification is attainable with-out compensating circuitry.

2 L

CHAPTER 5

Monitoring Facilities

ONITORING facilities and the number of"VI video display equipments depend largelyupon the size and complexity of a system. As amaintenance man, you are well aware of theimportance of monitors. Undoubtedly, much ofyour troubleshooting and repair has directly orindirectly involved various types of monitors. Re-gardless of the type os configuration, monitorshave certain essential sectons. in this chapterwe will identify these sections and discuss, in acomparative manner, the viewfinder, utility; andcombination (camera control or master) moni-tors. As before, we have chosen to analyzetransistor circuitry. By so doing, we can furtheryour transistor training while discussing the op-erating principles of monitor equipment. Test-points and waveforms relevant to adjustments,alignment, and tuning are also discussed. Usinga block diagram of a master monitor, we willdiagnose troubles from known symptoms.

12. Monitors

12-1. Technical personnel rely upon monitorsto check the condition of the television pictureand video waveform being transmitted; therefore,both picture monitors and waveform monitors areneeded. Picture monitors use direct-view displaykinescopes and contain many of the essentialsections found in TV receivers. Many of theprinciples covered in this chapter will be fullyapplicable to our study of receivers in the fol-lowing volume. Since monitors reproduce apicture from a video-frequency signal, the signalis generally taken directly from a video line.However, in an extensive closed-circuit system,provision is made for monitors to take the de-modulated output of a receiver. For r-f distribu-tion, the receiver's r-f and i-f sections are neces-sary to obtain the video-frequency signal for themonitor. The picture monitor is used in thismanner because it is designed to have a broaderbandpass and better gray-scale reproductioncharacteristics than the video section of a com-

234 66

.2

parable receiver. In other words, the receiver-monitor combination gives a higher qualitypicture than a receiver designed for ordinaryviewing. We mention this to point up the qualita-tive superiority of picture monitors.

12-2. The combination of waveform monitorand picture monitor is used in conjunction withthe camera control unit studied in the precedingchapter. The waveform monitor displays thevideo signal on a CRT so that the waveformcan be checked against the signal standards ofthe system. A combination monitor, picture andwaveform, is also used as a master monitor todisplay the picture and video signal being trans-mitted. More will be said about master monitorsafter we have considered picture and waveformmonitors separately.

12-3. Essential Sections. Figure 57 shows theblock diagram of a picture monitor. The com-posite video signal is fed into the video section,which consists of video amplifiers and a d-c re-storer. This section contains sufficient amplifyingstages to develop the output signal strength re-quired. Note that there are two outputs takenfrom the video section of this monitor. One out-put signal is obtained from the d-c restorer cir-cuit and sent to the cathode or grid of the kine-scope. This signal, which contains all the pictureinformation, effectively modulates the intensityof the kinescope's electron beam. The othersignal that is coupled into the sync section is usedto obtain timing pulses for the vertical and hori-zontal section. We should mention here that thesync section is not essential to all monitors. Forexample, recall that the viewfinder monitor usesthe camera's output signal, which does not con-tain any sync pulse. This type monitor willmost likely have separate inputs of horizontal andvertical drive for timing the horizontal andvertical sections, respectively. In our block dia-gram we have indicated a switch S. Many pic-ture monitors provide such a switch so that eithersync pulses (from the sync section) or drive

Figure 57. Sections of a picture' monitor.

pulses (from separate inputs) may be selectedfor timing purposes. The vertical section, ofcourse, generates and shapes the signal that issent to the yoke's deflection coil for verticallyscanning the kinescope's screen. Usually, a ver-tical blank signal is also obtained from thissection and applied to the kinescope's grid orcathode to insure beam cutoff during verticalflyback. The horizontal section develops signalsfor horizontal scanning and blanking. In addi-tion, this section provides the excitation signalfor the high-voltage d-c supply. Low voltage isdeveloped from the 60-cps line input as shown.

12-4. Look now at figure 58 and observe thatthe waveform monitor's block diagram differsfrom that of a picture monitor (fig. 42). Youshould recognize the waveform monitor to be acathode-ray oscilloscope (CRO). It employs acathode-ray tube (CRT) and uses electrostaticdeflection. The signal to be observed is appliedto the electrodes of the CRT after being amplifiedby the video section. Switch 51 permits selec-tion of a calibrating signal so that time andamplitude measurements can be read from thescope presentation. A square-wave signal ofknown amplitude and period is supplied by the

iA calibrating section. The displayed calibrating sig-nal is readily adjusted to markings on the scope'sface. Therefore, when the composite video signalis selected by SI, pulse widths and voltage valuescan be determined. Remember, however, thatthe scope's gain controls should not be disturbedonce they have been adjusted to give a calibratedreading. Testing with a waveform monitor isjust like using a high-quality CRO that has cali-brating capabilities. The sweep section is similaralso, but is designed to sweep at a submultiple ofthe picture signal field or line rate. In a standardsystem, it ordinarily sweeps at one-half the fieldor line rate; thus 30 cps or 7875 cps, respectively.

67

This one-half field or line rate permits viewingtwo complete periods of the yerpcAl ar horizontalvideo waveforms. r~ There are otWee featuresunique to this CRO, but we will not investigatethem here. A detailed block diagram of a mastermonitor will reveal these features; therefore, wehave reserved our discussion of them until later.Our purpose here is simply to identify the es-sential sections of the waveform monitor andhave you compare this monitor with a picturemonitor with regard to its basic makeup.

12-5. Types of Monitors. Although you haveused and maintained many types of monitors,perhaps you have given little thought to why sucha variety of circuits is found within them. Someof this variety is a matter of the designer's choice;however, the number of stages and refinementsis mostly dictated by performance requirementsfor a particular type of monitor. By type wemean whether it is a viewfinder, utility (line),or combination (camera control or master) moni-tor. These types contain the essential sectionsdiscussed; however, the circuitry within the sec-tions may differ considerably. This is mainlybecause each type serves a different monitoringpurpose.

12-6. The viewfinder used with the imageorthicon camera is a comparatively uncom-plicated picture monitor. Its video section mayhave just two broadband amplifiers and a d-crestorer circuit: Its vertical section, which is

triggered by input vertical drive pulses, will havea blocking oscillator or multivibrator, one or twodriver stages, and an output amplifier. The sameis triit for the horizontal section, except of coursethat it 'IS trigiared by horizontal drive pulses andis designed for a much higher frequency. Someviewfinders have several stages to develop acomposite blanking signal derived from the videoinput. These stages 'Owe, amplify, and mix toproduce the bkplijImpulses of the width and

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COMPOSITEVIDEO 0.--10.INPUT

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LOWVOLTAGESUPPLY

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HORIZONTAL SECTION

Figure 59. Block diagram of stages within a utility monitor.

amplitude desired. Since a small-screen (4 to 6inches) kinescope is used, the requirements forgood picture resolution are not difficult to meet.The viewfinder's priniary purpose is to orient thecamera for video pickup, so it need not displaythe high-quality picture that must be displayedfor evaluation, control, or detailed viewing.

12-7. Utility monitors are employed mostlyfor viewing the televised scene at various loca-tions throughout a system. They are placed withinthe studio for previewing and line monitoring.In a closed-circuit system, they are commonlyused as the terminal display equipment for gen-eral viewing. The size of the kinescope is de-termined by the particular application. In class-rooms and offices, 24-inch tubes are generallysatisfactory. In a studio, 17-inch or 8-inch tubesare adequate for continuity checks or cueingwork. Depending upon tube size and resolutionnecessary, utility monitors may have few or manystages per section. Moreover, you will find manyrefinements or basic circuits which improve theoverall picture quality.

12-8. Figure 59 shows a block diagram of autility monitor that contains the minimum num,ber of stages practical. We will investigate thecircuitry cf each of these stages shortly. For now,

68

it is sufficient that you recognize what stagesconstitute a utility monitor. Unlike the view-finder, this monitor obtains its sync from thecomposite yideo input. A sync separator is there-fore an integral part of a utility monitor. Notealso that the horizontal oscillator is indirectlycontrolled by the horizontal sync pulses whichare used for afc.

12-9. A combination picture and waveformmonitor is always associated with the cameracontrol unit. When this combination is connectedacross the outgoing circuit, it is called a mastermonitor. The master monitor visually displaysthe results of all mixing, switching, gain adjust-ment, and other signal manipulations. As pointedout earlier, the waveform monitor has built-incalibration facilities for measurement purposes.Because this type of monitor is designed forpicture and signal analysis, it must meet high-quality performance specifications. Consequently,it contains a greater number of stages and moresophisticated circuitry than either the viewfinderor utility monitor.

12-10. Transistor Circuits. Practical transistorcircuits are connected in figure 60 to make up amonitor schematic. To stress their operationalfeatures and pertinent components, only the nec-

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69

23 7

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Figure 61. Wavetorms illustrating the presence ot anerror tor atc.

essary circuits are shown. Special circuits foundin manufacturers' schematics are too numerousand varied to include. Our treatment is neces-sarily limited, but will be valuable to you insofaras you understand the functions of each stage andtheir relationship to each other. The most com-mon transistor configurations have been selected.To acquaint you more with p-n-p transistor bi-asing and interconnections, we chose to use thistype transistor throughout. Bear in mind, how-ever, that n-p-n transistors can be used as well,but the d-c bias voltages must be positive. Re-gardless of the transistor type (p-n-p or n-p-n),waveforms and circuit functions are the same.'As we progress through this schematic, note howsimilar these stages are to comparable tube stageswhich you have studied.

12-11. Video section. Any of the three tran-sistor configurations can be used for the inputvideo amplifier. In figure 60 we show a com-mon-collector (CC) video input stage becausethis configuration is most popular. Recall thatthe CC arran3ement presents a higher inputimpedance and minimizes distortion caused bycollector-base capacitive feedback. Generally ahigh input impedance is desirable, which explainsthe choice of the CC amplifier. At testpoint TP1(fig. 60), you see that the composite video signalis identical to the input in phase and waveform.There is no need for compensating circuits sincethe emitter-follower action of 01 gives the neces-sary broadband response to faithfully reproducethe input video. Direct coupling to transistOr02 insures maximum low-frequency transfer andalso biases the base of 02.

70

12-12. The video output stage shown has twooutputs which are seen at TP2 and TP3. AtTP2 the signal is inverted with respect to the in-put because it is taken off the collector of 02.This signal goes to the cathode of the kinescope.Cathode drive is frequently preferred. since itrequires about 20 percent less signal voltage thangrid drive for the same beam modulation. Toobtain the necessary driving power, transistor02 is supplied a high collector bias from thc boostsupply (damper circuit of horizontal section).The desired broadband response is attained withshunt peaking (coil L) and the unbypassed emit-ter resistor. This resistor also serves to counter-act bias variations caused by temperature.Moreover, it develops the video signal (seen atTP3) which is needed for the sync section.

12-13. D-c restoration is accomplished by theclamping action of diode DI in conjunction withthe coupling capacitor Cl. The waveform illus-trated at TP2 shows that the video signal isclamped to the peaks of the sync pulses.

12-14. Sync section. The signal at TP3 shouldhave the same waveform as shown at TPI. Thissignal is capacitively coupled into the sync sepa-rator stage via the base of 03. The couplingcapacitor is of such a value that thc transistorQ3 is self-biased to amplify only the sync pulses.In other words, the transistor biases itself belowcutoff; only the most negatiye portion oi the inputcomposite signal drives 03 into conduction. Thus,the sync signal appears as positive-going pulsesat TP4.

12-15. The separated sync signal is capaci-tively coupled to the base of 04. Transistor 04and its associated circuitry comprise a phase-splitter amplifier (also called a phase inverter).As illustrated in figure 60, sync signals of equalamplitude but opposite phase are present at thecollector and emitter of 04. This stage uses fixedbias to properly amplify and clip the signal.

12-16. Vertical section. The vertical sectionconsists of a vertical oscillator and an outputamplifier containing transistors 05 and 06, re-spectively. From the block diagram (fig. 59),recall that this section receives its timing pulsesfrom the sync section. We see on the schematicin figure 60 that negative-going sync pulses fromthe collector of 04 are applied across an RCintegrating circuit. The resistor in series with. theinput capacitance to the blocking oscillator is along-time constant circuit for the horizontal syncpulses. Consequently, only the vertical syncpulses are developed to trigger Q5. You shouldrecognize the blocking oscillator arrangementincorporating Q5. The free-running frequencyof this oscillator is adjusted to be slightly lessthan the vertical sync frequency. This is readily

236

done by changing 05's base bias with the V-holdcontrol (see fig. 60). The blocking oscillator isused because it shows less variation with tem-perature than a transistorized multivibrator: Be-sides having better stability, the blocking oscilla-tor has fewer components. Although a blockingoscillator ordinaril generates a pulse, a sawtoothwaveform can bt by connecting a ca-pacitor of the proper value across the output; inthis case, the capacitor is across the emitter re-sistor. The amplitude of the signal coupled to thevertical output amplifier is adjustable. This isaccortiplished with the height control (labeled"Ht" on the schematic).

12-17. Note that the bias on the base of 06can be varied. This adjusts the vertical linearityby changing the operating point of the transistor.The control is labeled "V-Lin" on the schematicand is used in conjunction with the height controlto obtain a properly proportioned vertical displayon the scope screen. As you know from experi-ence, both of these controls must be adjusted toproduce a linear vertical scan of correct ampli-tude. The function of the vertical output am-plifier is to drive the vertical deflection coils.Unlike the tube version of this stage, a trans-former is not necessary for matching. The outputimpedance of the transistor circuit is low enoughto match the impedance of the vertical deflectioncoils. Thus. the output is shown to be capaci-tively coupled directly to the vertical deflectioncoils in the yoke. At the low field frequency(60 cps). the impedance of these coils is mostlyresistive; so a sawtooth waveform is seen at TP5.Thc amplitude of the sawtooth current dependsupon the kinescope usedabout 500 ma peak topeak is typical. This means that a power tran-sistor is needed since better than 1 watt of poweris ordinarily required. Efficiency of this stage isnecessarily low, because it must operate class Afor linear amplification. As in tube applications.class AB or B push-pull operation may be usedwhen higher efficiency at greater power levels isrequired.

12-18. A vertical blanking signal is showndevelokd off the end of the tapped L.F. chokethat serves as a collector load impedance. Notethat negative-going pulses are sent to the grid ofthe kinescope. This insures beam cutoff duringvertical retrace. There are other ways to achieveeffective vertical blanking. For example, posi-tive-going pulses can be developed off the col-lector and applied to the kinescope's cathode.

12-19. Horizontal section. Let us quickly' in-vestigate thc schematic to identify the stages inthc horizontal section. The circuits that includeD2, D3. and 07 constitute the afc for holdingthe hori4mtal oscillator on frequency. Transis-

tor 08 and its associated components are easilyseen to be a blocking oscillator which feeds pulsesto the base of 09. The pulses are amplified bythe. driver stage consisting of Q9 and a pulsetransformer. The next- stage, of course, is thehorizontal output amplifier.. From this finalstage, power must be developed to supply outputsto the HV supplies, boost supply, afc input,horizontal blanking circuit, and horizontal de-flecting coils.

12-20. The inputs to the horizontal section aretaken from the phase-splitter. Off the collectorof Q4, negative-going sync pulses are appliedacross a short-time constant RC (differentiating)circuit. Therefore, negative- and positive-goingspikes appear at the cathode of liode D2, asshown. In like manner, positive-going sync pulses(off the emitter of Q4) are changed into positive-and negative-going spikes at the anode of diodeD3. At the same instant that D3 conducts apositive-going spike, D2 conducts a negative-going spike of equal amplitude. Being of op-posite polarity, they cancel and therefore do notaffect.the base bias of 07. However, if the saw-tooth signal coupled into TP6 is not exactly mid-way between peaks at the instant D2 and D3conduct (see fig. 61), an error voltage changesthe base bias of 07. This change is amplifiedand applied to the base of 08, accordingly, thefrequency of the blocking oscillator is controlled.

12-21. Our brief description of the phase de-tector and d-c amplifier for afc should beadequate for you to note that afc principles arethe same as for tubes. Solid-state versions ofother afc arrangements do not differ appreciablyfrom those . you have previously encountered.

12-22. On the schematic in figure 60, the basebias of 07 is shown to be adjustable with the H-hold control. This adjustment indirectly estab-lishes the free-running frequency of the hori-zontal oscillator by setting the base bias of 08.Transistor 08 should be biased so that the afcoperates over its maximum designed range ofcontrol. Unlike the vertical oscillator, the hori-zontal oscillator is designed to give a pulse output.The circuit illustrated uses a three-winding trans-former. The pulses generated by the blockingoscillator are inductively coupled to the trans-former's tertiary winding. This winding invertsthe pulses from the collector circuit; thus, a strongnegative pulse is fed to the base of 09. The posi-tive overshoot, if there is one, does not affectQ9 since 09 is biased at cutoff (both base andemitter are at d-c ground).

12-23. Transistor 09 is connected as a classB, CE amplifier. It serves to develop sufficientdrive for the horizontal output stage. The posi-tive-going pulses developed at its collector appear

71

2 3 J

as negative pulses at the base of 010 due to theaction of the coupling transformer. Because ofthe inversion that occurs from base to collector,the pulses seen across the load impedance (col-lector to ground) are positive-going as illustrated.AB in a comparable tube horizontal Output stage,the shape of the output waveform must be suchthat it produces a sawtooth current through thedeflection coils. This same waveform is fed backto the phase detector via a long time constantRC circuit. The voltage developed across C2is thejefore a sawtooth signal which is seen atTP6.

12-24. Boost and high-voltage rectifying cir-cuits receive their excitation from the horizontaloutput stage. Note that the negative d-c boostvoltage is developed by the damping diode D4.The Circuits containing D5 and D6 are half-waverectifiers that develop the positive d-c voltagesneeded for the kinescope.

12-25. Although we have shown no provisionto adjust the width of the horizontal scan, thereare several ways to do this. A common way isto insert a variable ferrite-core inductor in serieswith the deflection coils. Another way is to usea horizontal output transformer that has a vari-able air gap. It is also possible to provide avariable bias which alters the gain of the outputamplifier. Such width controls practically alwaysaffect the high-voltage afc feedback and blank-ing circuits. For this reason, monitors may nothave a width control; instead, their hotizontaloutput circuit is designed to overscan slightly.Sometimes a shorted-turns linearity sleeving isused to adjust both horizontal linearity andpicture width (see fig. 62,A). The sleevearound the neck of the kinescope changes thepicture width when it is moved forward or back-ward. It can also be adjusted to improve lin-earity of the horizontal scan. Another method toadjust linearity (see fig. 62,B) employs a per-manent bar magnet and saturable inductor inseries with the deflection coils. Depending uponthe closeness of the magnet, magnetic saturationoccurs and thereby alters the scanning wave-form. When pioperly adjusted, a linear scan isobtained.

12-26. Kinescope. The kinescope in a tran-sistor monitor is essentially the same as that in atube set, but it usually has a smaller screen diam-eter and beam deflection angle. Most transis-tor monitors use 90°, 8-14 inch, aluminizedrectangular picture tubes, because transistormonitors have tended to be battery- or low-power sets. Larger screens and wider deflectionangles are not economically practical for suchsets. Aluminized screens are commonplace.since they produce good brightness at cam-

72

parativeiy low beam currents, average values of75 to 150 /la for transistor monitors.

12-27. Prerent-day kinescopes have from fiveto seven electrodes. These electrocks are used invarious ways to electrostatically control picturebrightness and focus. The cathode-to-gid po-tential is made variable OVL,T a range of severaltens of volts so that the intensity of the beam,and thus picture brightness, can be adjusted.From a potentiometer, 100 to 300 positive d-cvolts is applied to the first anode. Sometimes ina pentode kinescope, the first and second anodeare connected to prcwide a focus control. .Elec-trostatic focus control is being used extensively.Ordinarily, you control the focus by adjustingthe potential on one of the accelerating anodes.

1248. In addition to electrostatic controls,there are magnetic adjustments that are impor-tant. No doubt you have found that these ad-justments differ somewhat because of manu-facturing differences. Electromagnet controlshave been replaced for the most part by perman-ent magnet adjustments. External magnets,mounted about the kinescope, are used in tran-sistor and tube monitors to serve several pur-poses, such as preventing ion burns, focusing,centering, and picture correction. Ion-trapmagnets are not needed for aluminized screensbut are used for other types. A clamp securesthe ion-trap magnet around the neck. By design,

SATURABLEINDUCTORAJJ

Pi DEFLCOILS

A. SHORT.TURNS SLEEVE B. SATURABLE INDUCTOR

Figure 62. Methods of adjusting horizontal linearity.

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Figure 63. Combination monitor block diagram.

the electron gun is aimed into the neck wall.When the ion-trap magnet is properly adjusted,the electrons are redirected along the beam axis,but the heavier ions are not. The ions strike ananode, and the screen is protected from theirbombardment and the burning damage that re-sults. A focusing magnet is sometimes used in-stead of or in conjunction with electrostaticfocusing. A magnet, called a beam-centeringmagnet, is also fitted around the neck of akinescope for steering the beam so that it iscentered within the final anode aperture. Inaddition, a picture-centering magnet, which isusually adjustable with a lever or knob, positionsthe picture properly on the screen. Lastly, amagnet is fitted against the flare of the tube tocorrect for geometric distortions and eliminatecorner shadowing. Beginning at the tube base,you will ordinarily find these magnets mountedin the following order: ion-trap, focusing, beamcenterin* picture centering, and picture correc-tion.

73

cRO

13. Master Monitor13-1. Earlier we briefly discussed the com-

bination monitor, and pointed out that it is usedto maintain a constant check on the picturequality and signal waveform. It can be con-nected to a switching arrangement so that thetransmitted information or any of several cam-eras can be monitored. When used in this man-ner, it is correctly called a master ninnitor. How-ever, this name is also applied to a combinationpicture and waveform monitor assembled in asingle console or field case. In this section wewill consider how such an assembly may bemade. By investigating a block diagram, wewill show how the picture and waveform moni-tors can be interconnected. Because of theinterdependency of some stages, certain symp-toms are readily related to specific troubles.Therefore, we will diagnose troubles after ana-lyzing the block diagram.

13-2. Functional Analysis. The block diagramin figure 63 illustrates the relationships of thevarious stages and circuits that comprise a mu-

24i

ter monitor. Moreover, this diagram shows howswitches provide versatility and comtnonize cer-tain stages so that they serve both -the pictureand waveform sections. Althoughl' this typemonitor is more complex than either the pictureor waveform monitor taken singularly, you willnote, as we progress, that it is quite simple inSOUle respects.

13-3. Picture sections. Beginning at the up-per left of the block diagram, observe that thekinescope signal goes through four stages ofvideo amplification. The video amplifiers aredesigned to have excellent response for a widevideo band (about 8 mc). To achieve suchhigh-quality performance, the gain of each stageis comparatively low. This explains why it isgenerally necessary to use numerous stages todevelop the signal drive for the kinescope. Thed-c restorer is shown as a separate circuit, butmay in some sets be an integral part of the lastvideo stage. Sometimes d-c restoration is as-sociated with sync separation so that it may berepresented differently in the block diagram ofa. particular set. The composite video signal forsync separation is usually obtained from thelast video amplifier. Depending upon the gainof the sync separator, the separated sync is

coupled to an amplifier, 33 indicated in figure63. This amplifier may not be round in somesets.

-13-4. With switch S1 in the position illustra-ted, the separated sync signal goes to both thevertical and horizontal sync amplifiers. The in-put circuit of the vertical amplifier integratesthe signal; therefore, only the vertical syncpulses arc developed. These pulses becomeamplified and trigger the vertical oscillator. Ob-serve that there are two outputs from the verticaloscillator, one goes to switch S3 (which will bediscussed shortly) and the other goes to thevertical deflection amplifier which serves as abuffer and driver stage. Since the vertical out-put amplifier is often a push-pull circuit, it may

HORIZONTALA SWEEP

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be represented by two blocks. Regardless, itsfunction is the same; namely, to produce a linearsawtooth with adequate power for full verticaldeflection of the kinescope's beam.

13-5. Returning to switch S1 and noting thesignal path through the horizontal section, youfind stages corresponding to those just describedin the vertical section. You know, however, thatthe input circuit to the horizontal sync amplifiermust differentiate the sync signal to obtain onlythe horizontal sync information. Then the hori-zontal sync pulses are amplified to trigger thehorizontal oscillator. You may ask, "Why isn'tafc used?" Unlike many picture monitors, whichmay be connected almost anywhere in the sys-tem, a master monitor is connected at the trans-mitting end. Its video input is therefore far lesssubject to noise. Because of the high signal-to-noise ratio, the horizontal sync pulses can beused to reliably irigger the horizontal oscillator.This gives better control and dispenses with theextra circuitry for indirect control by afc. Inthis respect, at least, the master monitor is sim-pler. The other horizontal stages are similar tothose of a picture monitor, but for a mastermonitor their outputs are somewhat different.In addition to driving the output amplifier, thehorizontal deflection amplifier sends an outputvia a delay line (or delay multivibrator) toswitch S3. Therefore, it serves the waveformmonitor also. The horizontal output amplifierhas but one output indicated. It does not pro-vide an output to the high-voltage power supply.The d-c high-voltage for the kinescope of thistype monitor has stringent requirements whichare best met by a separate high-voltage powersupply unit. This type power supply was studiedin Chapter 2, Section 6 (see fig. 27).

13-6. Up to this point, switch S1 has beencoasidered set at the position shown in figure63. It is worthy to note that by means of thisswitch, separated-sync, external-sync, or drivesignals can be selected as inputs to the horizon-tal and vertical sections. Study the diagam tosee how this is done. External sync is generallypreferred when the monitor is used as a switch-ing or line monitor, whereas drive inputs areused for monitoring camera equipments.

13-7. Waveform CRO. The, input to theCRO's video section is selected by switch S2.When S2 is in the position shown, the videosignal waveform is displayed on the CRO'sscreen. This signal may be obtained from acommon video signal source if the CRO inputand ICINE input terminals are connected to-gether. Thus, separate input terminals enablethe operator to observe the same or differentvideo signals on the kinescope and CRO. When

742 4

S2 is switched to the CAL position, a square-..wave signal of known amplitude is displayed on

laoinv the CRO's screen. As explained earlier, such asignal makes it possible to calibrate the CRO

fi':;and thus make direct measurement readings ofucw :calk observed waveform. Note that the calibra-b5e::_.,4.tion circuit (CAL CKT block in fig. 63) obtains

its input as SI. No mattcr what .position SI is

in. horizontal pulses (separated sync, externalsync. or H-drive) are applied to the calibration

...circuit. This circuit is generally nothing morethan a clipper network that clips the pulses at .aprescribed known upper and lower limit.

13-8. Like the video section of the kinescope.and for the same reason, four stages of videoamplification are provided. We also see d-crestoration employed. The processed video signalis applied to the vertical deflecting plates (notshown) of the CRT. Bear in mind that we arenow dealing with electrostatic deflection: Whena sawtooth of proper frequency is applied to tfirehorizontal deflecting plates of the CRT, Thevideo signal waveform is displayed. Let us iPeY.our attention therefore to the means by whikfrthe sawtooth signal is obtained for horizontal de-flection.

13-9. Switch S3 is marked V (vertical) andH (horizontal). In the H position, pulses fromthe horizontal deflection amplifier are sentthrough a variable delay circuit to the input ofthe pulse amplifier. The output of this ampli-fier synchronizes the CRO sweep generator sothat the sawtooth signal produced has one-halr-the frequency of the horizontal oscillator (the:source of the pulses). If the horizontal oscillatorfrequency is 15,750 cps, then the CRO sawtoothfrequency is 7,875 cps. Since the latter is thehorizontal sweep frequency. two cycles of thehorizontal video waveform are displayed on theCRT's screen. The variable delay circuit makes itpossible to delay the start time of the horizontalsweep in order to observe two compleib horizon-tal blank and sync pulses in the videomaveform.To examine vertical pulses, S3 is set in the Vposition. When this is done, the dashed line inthe diagram shows that a switch at the CROsweep generator is closed to ground. This in-creases the time constant and decreases thefree-running .frequency of the sweep generatorto a value slightly less than one-half the verticaloscillator frequency. When synchronized, thesweep frequency is exactly 30 cps for a 60-cpsvertical rate. Consequently, two cycles of thevertical video waveform are displayed on theCRT's screen.

13-10. The sweep-expand stage permits an op-erator to expand a portion of the waveform andthereb)e carefully scrutinize it. Figure 64 shows

the effect.,oft this..stigsgrt swjtch S4 .of.figure63 is usa Nbtecr ffie liaciiiidassweepwaVersk lenta'aitii4ITv4R"Nqis9W1i2 EXP.The otiipurirloill tfiâ .00 *Nplifti is ofthe same amplitudI Riii onVieTrentietiortionproduces a sweep.' that portiOn liriR 'wave-form, in time interval ti to t2, islp?eati'acrossthe full width of the scope screen asIn other words, this portion of the waveform isexpanded since full horizontal deflection occursin a shorter time interval. The modified sweepthat effects the expansion is formed by clippingthe normal sawtooth (see fig. 64,A), then am-plifying the clipped waveform to the same am-plitude as the normal horizontal sweep signal.

13-11. An additional feature provided onmaster monitors is a switch to select pulse-crossdisplay. We have not shown this switch in figure63 since it would complicate the diagram. Ashort explanation should suffice for you to realizewhat this switch does. When it is set toPULSE CROSS position, the video signal is sentto the CRT's cathode or control grid, the expand-horizontal sweep signal is applied to the hori-zontal deflecting plates, and the expand-verticalsweep is applied to the vertical deflecting plates.

. The video signal intensity modulates the beamas it scans horizontally and vertically. You arefamiliar with the pulse-cross display pattern.Since this pattern is used as a convenient meansof checking blank, sync, and drive pulses, it willbe discussed with test patterns in the next vol-

L,-ume. It is adequate here for you to appreciate

how a pulse-cross pattern can be obtained by aswitching arrangement.

13-12. Trouble Diagnosis. To logically de-termine the source of a trouble from a CRO orpicture display, you must call upon your knowl-edge of monitor circuits and their functipns. Toillustrate this fact, and to give you some practice,let's diagnose some different types of troublesfrom symptoms that can be observed on a mas-ter monitor.

13-13. Negative picture display. When a pic-ture appears like that shown in figure 65,A,you should know that the video signal is inverted.This means it has the opposite polarity to whatit should have. Using a CRO, you can check theinput video signal to see if it has the properpolarity. Referring to figure 63, note that thepolarity can readily be checked with the wave-form monitor. The amplitude of the input videoshould be checked also because too strong a sig-nal can cause this symptom. An excessive inputmay overdrive one of the video amplifiers butstill be coupled to the next stage. Such bypassingcan cause the signal to have the wrong polarity

75

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when it reaches the kinescope. However, if youfind the video input signal proper, you should usethe CRO to signal trace the video seetion. Agrid-to-plate (or base-to-collector) short cancause this trouble. The fault may also be agassy tube.

13-14. Half-black and hall-white display. Thedisplay illustrated in figure 65,B. could also ap-pear white for the top half and black for thebottom half. In either case. you should knowthat this trouble is the result of a heater-to-cathode short. With a bit of thought, you willrealize that the 60-cps heater voltage on thecathode cuts the beam off for half the raster andturns it on for the other half.

13-15. Insufficient picture height. If the con-dition illustrated in figure 65.C, cannot be cor-rected by adjusting the vertical height and linear-ity control, you should suspect the trouble to bein the vertical section. The vertical oscillator orvertical output stage should be checked.

13-16. Insufficient picture width. Too narrowa picture (fig. 65,13) which cannot be corrected

77

by horizontal-width adjustment indicates troublein the horizontal section. A weak tube (ortransistor) in the horizontal oscillator, driver, oroutput stage will produce this symptom. A checkof boost voltage and low-voltage d-c supplyshould be made, since inadequate d-c potentialswill reduce- the width of the horizontal scan.

13-17. Insufficient height and width. Whenthe picture is small in size (fig. 65,E), the faultis usually in the low-voltage d-c supply. Ofcourse, it can be the result of a combination ofthe two previous troubles described.

13-18. Other abnormal displays. Entire booksare devoted to depicting abnormal displays andidentifying these displays to specific troubles. Ad-mittedly, we have but touched on the numerouspicure symptoms that indicate trouble in a moni-tor. In your experience you have no doubt en-countered the ones mentioned and many more,such as blooming, tearing, distorted patterns,keystoning, etc. As you apply the principles pre-salted in this chapter, you will better understandthe probable cause(s) of such displays.

CHAPTIR 6

The Audio System

TT IS TRUE THAT some television applica-tions, such as surveillance, require only the

video system. However, in most television sys-tems, audio is necessary to augment the videoinformation, either as part of the program ma-terial or as intercommunications relative to theprogram production. In this chapter we will dis-cuss microphones, audio amplifiers, and audiocontrol consoles. Intercom systems wM be dis-cussed in the next volume.

2. The audio requirements for any given tele-vision system depend upon the function of thesystem. Just as a simple television system con-sists of one pickup camera and one monitor, soa simple audio system consists of one micro-

. phone, an amplifier, and one speaker. A moder-ate system will have several sound inputs; thesewill originate from the floor microphones andthe announcer's or commentator's microphone.The various inputs are ,I.finbined and sent out ona transmission line to one or several speaker set-ups. An additional monitor may be provided forcontrol room use if necessary.

3. A television system which is intended forthe presentation of more varied program mate-rial will demand a more complex audio system.Such a system would be one in which live-camerastudios and a film studio furnish program mate-rial for_ distribution to classrooms. From theseveral microphones in the studios, the voice sig-nals are fed to the audio control console in thecontrol room. Other inputs to the control consolecome from the film studio and tape recorder.These signals are switched or mixed with the

c. signals from the live studios and amplified to acontrolled level. The output from the consolethen goes to the distribution network, with spareoutputs available for patching to any other loca-tion where sound reproducing equipment is setup.

4. In addition to the output for the distribu-tion network, the audio control console feeds themixed program audio directly to the controlroom and also to a program monitor bus. A

36

studio monitor speaker is patched of/ a mutingrelay; the speaker is thereby rendered inopera-tive to prevent acoustical feedback when studiomicrophones are operating.

S. From this discussion you can easily see thethree major divisions of equipment used to pro-duce an audio signal. A microphone, an ampli-fier, and a control console are used to convertan audio signal to electrical impulses, which arethen amplified and fed to the console. Here,levels are set and the switching is accomplished.

14. Microphones14-1. A microphone is a device which con-

verts sound into an electrical signal, and appliesthis signal to an amplifying circuit. Followingsufficient amplification, the electrical signal isused to drive a reproducer or to modulate a car-rier frequency for transmission. The, generalcharacteristics of the most widely used types ofmicrophones, dynamic, carbon, crystal, and ca-pacitor will be discussed in this soction. Each ofthese basic types of microphones employs a spe-cific fundamental principle of operation.

14-2. The basic operation of a microphone isdependent upon pressure of sound waves. Theangles at which the sound waves strike the dia-phragm of a microphone depend upon the posi-tioning of the microphone in relation to thesound source. If the sound wave, strike the dia-phragm at nonuniform angles, different fre-quencies will exert different pressures and causethe microphone to be directional in its frequencyresponse. Most microphones are directional atfrequencies above 2000 cps. Special construc-tion of the microphone housing or case mayproduce additional directivity at frequencies be-low 2000 cps. Examples of specially constructedmicrophones are the "shotgun" and "reflector"types. Nondirectional microphones also requirespecial design considerations. For nondirectivityit is necessary to design the housing so that sig-nals from all directions exert uniform pressure onthe diaphragm. The microphone which is de-

24

NI TUNECAVIT

DIAINNAGIN

GNILL

RETAININGRING

AIR VENT%OE

maw'

AIN CHAMBER

A

MAGNET TUNE

Figure 66. Dynamic microphone (A) mechanicaldetails and (B) circuit diagram.

signed for general-purpose use is polydirectional;this type of microphone is usually mechanicallyadjustable to achieve the desired pattern ofpickup.

14-3. Dynamic. The dynamic, or so-calledmoving-coil type, is the most widely used. Be-cause of its low (and adjustable) impedance, itcan be installed with long cables without seriousadverse effect to the overall audio system; it is

not easily damaged by rough handling and is notparticularly sensitive to blasts (instantaneoussound peaks). A dynamic mike contains a coilmade of a large number of turns of extremelythin metal ribbon attached to the diaphragm.This coil is insulated from the diaphragm by athin coat of insulating varnish. The coil extendsfrom the diaphragm to a point between the polesof a powerful permanent magnet. When soundwaves strike the diaphragm, the coil moves backand forth within the magnetic field between thepoles of the permanent magnet and cuts themagnetic lines of force. An illustration of amicrophone designed to operate on this principleis shown in figure 66,A. This action induces acurrent in the coil in direct proportion to thesound piessure exerted on the disphragm.

79

14-4. The dynamic microphone elements arenormally housed in a fiteial shell iiicr coveredwith a metal grill and silk cloth to prevent dam-age from foreign particles and to minimize dustcollection. The improvement in frequency re-sponse of this type of microphone over othertypes lies in the inclusion of an echo compensa-tion circuit, which consists of an air chamber be-tween the housing elements and an air-vent tube;the length and diameter of the air-vent tube con-trol the echo-compensating action of the airchamber.

14-5. The impedance of the moving coil in thedynamic microphone is approximately 50 ohms;therefore, the coil may be connected to an am-plifier by means of long cables. There aremicrophones available with built-in matchingtransformers to match low-Z of 30, 50, and 250ohms or high-Z up to 50K ohms. A switch isbuilt in to select the various impedances. Thefrequency response of this type of microphone isreasonably flat over the range from 40 cps to

.10,000 cps. Since the output voltage level is onlyabout 0.00004 volt, a preamplifier must be usedfor adequate amplification. The circuit diagramof the dynamic (moving coil) microphone is Il-lustrated in figure 66,B.

14-6. The ribbon microphone, a variation of'the dynamic microphone using the moving coilprinciple, is widely used in studio operations. Ithas no real diaphragm, and its operation de-pends upon the velocity of air. Therefore, it issometimes called a velocity or pressure gradientmicrophone. The microphone, as shown by dia-gram in figure 67,A, consists of a powerful horse-shoe-shaped electromagnet or permanent magnet,M, with special pole pieces between which a thincorrugated metal ribbon, R, is suspended. Theends of this ribbon are connected to the primaryof a special step-up transformer.

14-7. The construction details of the ribbonmicrophone are illustrated in figure 67,B. Themicrophone should be placed so that the incom-ing sound will strike it at right angles, as thosefrom the side have practically no effect. Thesound striking the ribbon causes it to vibrate andthus cut some of the magnetic lines of force be-tween :ae pole pieces. This action generates avoltage in the ribbon that is coupled to the gridof an amplifier via a special step-up transformer.Since the ribbon microphone is sensitive to veloc-ity, it should be covered or otherwise shieldedwhen used outdoors or in drafty areas, where airtends to produce undesirable ribbon vibrations.

14-8. The voltage output of the velocity mi-crophone across 250 ohms is 0.0002 volt. Thecorrugated ribbon has a resistance of only afraction of an ohm; therefore, the matching

247

ERMANENTMAGPIE T

MATOONGTRANSFORMER

4unmota,imwumot fffil1P111301 I

ICARBONMASS

DIAPHRAGM

I

SATILRY \TRANSFORMER

Figure 67. Velocity microphone (A) circuit diagram and DIAPHRAGM

(B) construction details.

transformer is usually built into the microphoneto reduce losses. The frequency response ispractically flat from 30 to 15,000 cps. The lowimpedance of the velocity microphone permits along cable connection to the amplifier, but thecable must be well shielded because of the possi-bility of a-c hum pickup.

14-9. Carbon. The carbon microphone iswidely used in intercommunications and cueingsystems, and will be discussed more fully in Vol-ume 2, Auxiliary Equipments. In the carbonmicrophone, a constant direct current is permittedto flow through a mass of carbon granules. Assound waves vibrate the diaphragm, its resultantmotion alternately compresses and releases pres-sure on the mass of carbon particles. The chang-ing pressure on the carbon causes the resistancevalue of the total mass to change, thus permitting

80

Tun

TRANSFORMER

TUBE

Figure 68. Carbon microphone (A) cross sectional view,(II) single-button circuit diagram. and (C) double-buttan

circuit diagram.

24

either more or less direct current passage. Across section of a typical carbon microphone isshown in figure 68,A; A and B are heavy steelrings. The ridge in one and the groove, D, in theother hold the diaphragm, C, very tightly. Thediaphragm is made of a very tough steel alloyand is generally designed to be from 0.001 to0.002 inch thick. The small ring, G, is screwedinto the large steel ring, B, to adjust the dia-phragm tension so that its natural period of vi-bration will be above the desired audio-fre-quency range. The central portion of the dia-phragm is gold plated on each side to insuregood contact. The back of the microphone isclosed except for a series of holes that permitthe air and sound to reach the back of the dia-phragm. The bridge, E, entends across the open-ing in the front of the microphone and supportsthe front carbon granule cup, or button, F. Asimilar one is supported by the back. These car-bon cups. or buttons, do not touch the diaphragmand are partly filled with fine carbon grains. Thesize of these grains' determines the sensitivity ofthe instrument, and soft felt washers prevent thecarbon from getting out of the cup.

14-10. Figure 68,8, illustrates both the me-chanical structure and the equivalent electricalcircuit of the simple single-button carbon micro-phone. The single-button carbon microphone ischaracterized by high output level and rugged-ness. It is practically unaffected by heat andhumidity. When space and weight are limitedin an installation, its high output is advantageousbecause fewer amplifier circuits will be required.The output ranges from 0.1 to 0.3 volt across anormal transformer impedance of 50 to 100ohms.

14-11. To secure a more uniform responsefrom various frequencies, the double-button typeof carbon microphone, illustrated in figure 68,C,is generally used in place of the single-buttontype. As you can see, the diaphragm is placedbetween two cups which contain carbon grains.Vibration causes the grains of carbon on oneside of the diaphragm to be compressed; at thesame time, it causes the grains of carbon on theopposite side of the diaphragm to be loosened.This action permits more current flow throughthe first carbon button than through the second.The output voltage of the double-button carbonmicrophone ranges from 0.02 to 0.07 volt acrossa normal transformer impedance of 200 ohms.

14-12. The frequency response is uniformfrom 60 to 1000 cps. Above 1000 cps, the re-sponse increases rapidly, becoming more than15 db higher at 2500 cps than it was at 1000cps. The response then remains uniform up toapproximately 6000 cps, where there is a marked

falling off in response. Because of its poor re-sponse to the higher audio frequencies as well asits. high noise level (hiss), the carbon micro-phone is not used extensively for general tele-vision purposes.

14-13. Crystal. The crystal microphone re-quires no energizing potential source such as thebattery used with the carbon microphone. It re-quires no transformer or other coupling device.Its output, although not as high as the carbonmicrophone output, is adequate for direct appli-cation to the grid circuit of an amplifier, Thesefeatures, plus its inherent simplicity and compactsize, make this type of microphone uniqueamong the devices designed to convert soundwaves into electrical impulses.

14-14. Crystal microphones can be dividedinto two typesthe diaphragm type and thesound cell type. The crystal element used ineither type can be permanently damaged by hightemperatures. This limits the number of usefulapplications. However, the crystal microphone isstill widely used as a high-quality microphone forcommunications, both military and commercial.Figure 69,A, is a diagram showing the bimorphcrystal unit; it can be seen that sound wavesstriking the diaphragm will cause the diaphragmto vibrate. These vibrations are transferred tothe surface of the crystal by means of the con-necting pin. The fidelity of this type instrumentis approximately equal to that of most double-button carbon microphones; however, the fre-quency response extends to a much higher range.In the crystal microphone there is no backgroundhiss or noise generated in the microphone itself.However, noise pickup on cables which arelonger than 30 feet does limit the use of crystalmicrophones in television.

14-15. The sound cell is another type ofcrystal microphone. As shown in figure 69,B,the back-to-back crystal elements are inclosedwithin a rectangular bakelite frame sealed bytwo flexible membranes. No diaphragms are re-quired in a sound cell microphone because themembrane imparts the sound pressure directlyto the crystals, which produce the resultant a-cvoltage.

14-16. Capacitor. A capacitor microphonegenerally consists of two electrodes separated bya very thin dielectric, usually air. One electrodeis the diaphragm and the other is a rigid platewhich has the same area as the diaphragm. Thediaphragm motion changes the spacing betweenthe two electrodes, varying the capacitance. Ifa d-c voltage is applied across this combination,the changes in spacing will produce changes inthe capacitor charge which can be obtained as ana-c voltage. This device has a very linear pres-

81

2 4

290DAMPING

SEPARATING !LASS

PRESSURE FROGSOUND FIELD PLATSAnon

SEALINGNENSRANE

PRESSURE FROMSOUND FIELD

PLATECOMINNATION

Figure 69. Crystal microphone (A) cross sectional view of diaphragm and crystal and(B) cross sectional view of sinek sound cell unit.

sure response and a wide frequency response; itcan be easily tuned to highez resonant frequen-cies because the diaphragm is the only movingpart. It has a good high-frequency response andis relatively insensitive to mechanical noise be-cause of its stiffness of construction. The capaci-tor microphone requires an external powersource and is adversely affected by high orchanging humidity.

14-17. The output voltage will be small;therefore, amplification will be required and theleads must be kept very short to avoid pickingup stray field noise. This type of microphone hasnot been used extensively because of the neces-sity for battery operation to avoid hum pickup.However, new developments with solid-state am-plifiers built into the microphone housing havechanged this situation.

14-18. Comparison of Microphones. The char-acteristics of the various microphones are sum-marized in figure 70, which lists the variousmajor types of microphones, together with theiroutput level in db and their frequency range incycles per second. From the table, you can see

that from the standpoint of output level the carpbon type is best and from the standpoint of fre,quency range the velocity type is best

14-19. Adjustments and Maintenance. Itshould be said that most of the difficulties withmicrophones are caused by misuse or carelesshandling. Nevertheless, let us mention a few ad-justments that can be made on a microphone.The polydirectional microphone may be any ofthe basic types which have an adjustable aper-ture. When the aperture is fully open, the micro-phone has a bidirectional pattern; when the

MICROPHONETYPE

FREQUENCY RANGE SIGNAL-TO- EXAMPLES AVERAGE DB VOLTAGE

IN CYCLES NOISE OF OUTPUT OUTPUT OUTPUTIMPEDANCE

DYNAMIC

MOVING COIL 30 YO 20,000

RIBBON 30 TO 20,000

MEDIUM

MEDIUM

CARBON

SINGL E-BUTTON 70 TO 6000

DOUBLE-BUTTON 60 TO 6000

LOW

LOW

CRYSTAL UP TO 14,000 HIGH

CAPACITOR 20 TO 15,000 HIGH

L0-230 50 & 250

Z (50K )

-55 TO -" 0.00004V

250 OHMS -55 TO -40 0.0002V

50 TO 100 OHMS -45 0.3V

200 OHMS -35 TO -45 0.07V

5 MEG OHMS -50 TO -60

30,150 OR 600 OHMS -53

Figure 70. Comparison of microphones.

82

250

aperture is closed, the microphone is nondirec-tional. At shutter settings between the open andclosed positions, the microphone is unidirectional.Some microphones are designed with blast fil-ters which are adjustable and require settingscommensurate with the operating conditions.

14-20. The maintenance of microphones willnot be so much in the microphone itself, butrather in the cords and connectors. If, for in-stance, you were told a carbon microphone didnot have an adequate output, the first thing youshould check is the carbon granules for a"packed" condition. This condition is caused byexcessive current which causes the carbon gran-ules to stick. Carbon granules that are packedcan sometimes be loosened if you turn off theapplied current and shake the microphone whileholding it in various positions. If this does notcorrect the situation, you may have to replacethe carbon granule mass. Do not shake a dyna-mic microphone as this will not accomplish any-

thing desirable and may damage the internalunit.

15. Audio Amplifiers i .P

15-1. We know that l'auditi.frequencies rangefrom about 15 cps to 20 kc. TV equipments thatamplify signals for sound reproduaBiLlimployamplifiers designed for this low-frequency range.It is the task of such amplifiers to strengthen theaudio signal and reproduce it faithfully. Thedominant requirements are, therefore, gain andfidelity. In this section we will discuss how theserequirements are met with transistor amplifier.These amplifiers and the principles involved arevery similar to electron-tube audio amplifiers.Your knowledge of tube amplifiers will enableyou to make comparisons as we progress from thegeneral characteristics to specific types of audioamplifiers. We will distinguish between pream-plifiers, drivers, and power amplifiers. Illus-trated circuits will be described and the effects

TYPE PNP AMPLIFIERS NPN AMPLIFIERSCORRESPONDING

TIME AMPLIFIERS

CE

.. .

: . . .:.a

OUT

galAroOUT ma

421

IL..

(lib

NO ,

elI I

C$40 0e

l II

.....ill.41pi OUT

40

OUT

CC

..

..

1\0

_

OUT

,....

I,.

AIOUT

......

el1\of

,

QIII) OUT

Figure 71. Basic transistor amplifier circuits and the corresponding electron-tube versions.

83

----ITEM CE AMPLIFIER CB AMPLIFIER CC AMPLIFIER

,

INPUT RESISTANCE 300 2000 OHMS 10 300 OHMS 20K 300K OHMS

OUTPUT RESISTANCE 5K 50K 1 OOK 500K 50 OHMS 5K,

VOLTAGE GAIN'

300 r 1500 500 2000 LESS THAN 1,

CURRENT GAIN 25 50 LESS THAN 1 25 50

POWER GAIN 25 40 OB 20 30 DB 10 20 DB

Figure 72. Table of typical value ranges for the CE, CB, and CC amplifiem

of bias adjustments will be explained for push-pull amplifiers.

15-2. General Characteristics. All three tran-sistor configurations are used in audio amplifiercircuits. The basic circuits are shown in figure71. Note that these transistor amplifiers are thecounterparts of well-known electron-tube ampli-fiers. Although transistor amplifiers have lowerinput and output impedances than have electron-tube amplifiers, the CE, CB, and CC amplifiershave impedance characteristics corresponding tothose of the grounded-cathode, grounded-grid,and grounded-plate (cathode follower) ampli-fiers, respectively. Note in figure 72 the rangeof values that can be generally expected for inputand output impedances of transistor amplifiers.Also note in this figure the different ranges ofcurrent, voltage, and power gain that are obtain-able for each type of amplifier. This should giveyou an idea of their sensitivities.

15-3. Coupling. The fidelity of an audioamplifier can be improved or impaired by thecoupling. As with electron-tube amplifiers,.coupling can be put into four main categories:(1) direct, (2) RC (resistance and capac-itance), (3) transformer, and (4) impedancecoupling. However, it must be realized that theimpedance values for transistors are consider-ably lower than for tubes.

15-4. When impedance matching is satisfac-tory, we can use either direct or RC coupling.As shown in figure 73,A, direct coupling givesan excellent low-frequency response, thus indi-cating high fidelity from zero cps (d-c) upwardthrough the audio range. The upper frequencylimit (half-power point, 3 db below midfre-quency gain) is dependent upon the shuntingcapacitances of the amplifier. The same is truefor the RC-coupled amplifier with regard to itsupper frequency limit (see fig. 73,B). Its lowtrfrequency limit (half-power point) is establishedprimarily by the size of the coupling capaci-tance. Since the coupling capacitive reactanceincreases as frequency decreases. low, frequen-cies are attenuated. Thus, gain falls Off toward

84

FREQUENCY -A DIRECT COUPLING

FREQUENCY

B RC COUPLING

FREQUENCY --"41bC UNTIMED CAUMNG

Fiyure 73. Typical rryponve climes for varioustypes of coupiing.

2 5 2

zero cps as indicated by the response curve,figure 73.B. RC coupling is used when d-c mustbe blocked (not coupled).

15-5. Untuned impedance (LC) coupling ortransformer coupling blocks d-c as does RCcoupling. Transformer coupling has the addedcapability of matching impedances. Recall fromyour knowledge of transformers that the primary"sees" the secondary impedance times the turnsratio squared of the transformer:

= (N' ) Z.

Therefore, by means of a transformer, the im-pedance reflected into the amplifier circuit canbe made to have a value that produces thedesired gain. We note in fignre 73,C, however,that the frequency-response curve is not flatfor untuned LC or transformer coupling. Thisis because the impedance is frequency-depend-ent, inductive for low frequencies and capaci-tive for high frequencies.

15-6.. Load. The load impedance of An

amplifier is usually resistive throughout most ofits operating range. As is the case with electron-tube amplifiers, gain is a function of load. Theplots depicted in figure 74 are representative ofthe curves of gain for the three transistor con-figurations. Noteworthy are the following facts:

Highest current gains A, are obtained forlow values of load resistance. (CE and CCamplifiers yield substantial current gains. Forthe CB amplifier it is always less than one.)

Cain= UNTO arms

111

ex

CILLICTIN

um. 8111111/1000

yournpaci

Figuee 74. Gain versus load resistance curves.

10M

100

10 100 1K 10K 100K

LOAD RESISTANCE (OHMS)

Figure 75. Input resistance versus load resistancecurves.

1M

Highest current gains A, are obtained forhigh values of load resistance. (CB and CEamplifiers produce appreciable voltage gains.For the CC amplifier it is elways less than one.)

Highest power gain G occurs when :theproduct of the current and voltage gain is great-est. Since the CE amplifier has both high cur-rent gains and high voltage gains, its powergains are necessarily the highest.

15-7. A study of the curves in figure 74 willgive you an appreciation of the advantagesoffered by each configuration, It is of interestto observe in figure 75 that the input impedanceis also a function of load impedance. Thisshould be expected since we know that the inputis not independent of the output for transistoramplifiers. Note how greatly the input resistanceof the CC amplifier varies with load resistance.

15-8. Preamplifiers. Audio preamplifiers &::designed to increase the gain of low-level signalsfrom transducers such as microphones andrecorder-reproducer heads. They are operatedclass A at power levels in the_ order of micro-microwatts or microwatts. Since the signals areso very small, special attention must be givento the noise factor, input impedance, and cou-pling.

15-9. Noise factor. Generally speaking, tran-sistors are noisier than tubes. However, junctiontransistors can be fabricated to operate withnoise factors comparable to tubes (3 to 5 db).

85

253

'

40

eaa, 30

33

20

.5 S S IICOLLICTO* VOLTAGO. Vc (VOLTS)

A

40

30

a 20

10

30

25

20

a

10

to

imeatieNeY (1C/500

e

too 100 1000 10,00a

SIGNAL 30131110E RUM ANCE 1014141

Figure 76. Typical curves showing how the noise factor of a transistor preamlifier is affectedby (A) collector voltage and emitter current, (B) frequency, and (C) signal source resistance.

The noise factor is affected mainly by the opera-ting point, the signal frequency, and the signalsource resistance.

15-10. The curves in figure 76,A, show thatthe noise factor changes with collector voltageVcE and emitter current IE Notice howrapidly the noise factor increases as VcE israised above 2 volts. Increases in IE have a lessmarked effect, but nevertheless depreciate thequality. Consequently, the operating point of apreamplifier is selected so that both VcE and1E are quite low in value.

15-11. Note in figure 76,B, how the noisefactor is dependfnt upon the signal frequency.The poorest (highest) noise figures occur at

.11.111=ID

A

the lower end of the audio range. They continueto improve as frequency increases well beyondthe upper limit of the audio frequencies, 20 kc.Above 50 kc, however, they gradually becomeworse.

15-12. The variation of noise factor as afunction of signal source resistance is shown infigure 76,C. This curve indicates that the best(lowest) noise factors result when the signalsource has a resistance between 100 and 2000ohms.

15-13. Input resistance. Since, to obtain alow noise factor, it is desirable to use a sienalsource resistance in the range of 100 to 2000ohms, the amplifier's input resistance should also

cc

10OOP

Figure 77. Two ways of increasing the input resistance of a CE amplifier.

86

254

be within this range. Recall that maximumpower transfer occurs when the source resistanceand load resistance are equal. In this case, theamplifier input resistance is the load resistance.

15-14. Both the CB and CE amplifiers haveinput resistances within the desired range (seefig. 72). The CB amplifier is used when a verylow input resistance or a high output impedanceis wanted. When the input resistance of a CEamplifier is satisfactory, this type amplifier isgenerally preferred because of its higher powerand current gain capability.

15-15. If it is necessary to use a signal sourceof high resistance, such as a crystal pickup head,a high input resistance preamplifier is needed.Since the CC amplifier has a hig41 input resist-ance (20K ohms to 800K ohms), it can bereadily matched to the source. There is a dis-advantage. however, inherent in this amplifier.Its input resistance changes greatly with small

+ .05

+ lv

HEADPHONES

11/

A+ 3v

variations of load (as shown in fig. 75). TheCE amplifier does not have this drawback butits input resistance is ordinarily less than 2000ohms. Fortunately, its input resistance can bemade as high as 20,000 ohms in one of twoways: (1) by placing a large resistor Res inseries with the input to the base (see fig. 77,A)or (2) by inserting a small resistor R. inseries with the emitter (see fig. 77,B). Bothways attenuate the signal input, but the CEamplifier has a notably high gain to Overcomethis loss.

15-16. Coupling. Direct coupling will giveexcellent low-frequency response down to zerocps (see fig. 73,A). Some basic circuits areillustrated in figure 78. The bias values shownshould be regarded as. representative. Figure78,A, shows a simple amplifier that has its out-put signal directly coupled to headphones. Infigure 78,B, we see two stages of amplification.

+ tv

+6,

A. SINGLE 3TAGE LOAD B. COMPLEMENTARY ARRANGEMENT OF INTERSTAGE 'COUPLING

C. DIRECT COUPLING OF AMPLIFIERS HAVING LIKE TRANSISTORS (NPN TYPES ILLUSTRATED)

Figure 78. Direct coupling.

87

250

4.

Figure 79. Interstage RC couoling.

The first stage uses a p-n-p transistor, whereasthe second stage uses an n-p-n transistor. Thiscircuitry is said to be complementary. Note thatthe n-p-n obtains its base bias from the p-n-pstage. Another two-stage circuit is shown infigure 78,C. The bias is not obtained by acomplementary arrangement. Both 01 and 02are n-p-n transistors. A resistor in- series withthe emitter of 02 is used to establish the desiredoperating point for the second stage. Since thisresistor is unbypassed, there is signal degenera-tion. Thus, gain is reduced, but stability is en-hanced.

15-17. Stability is generally a problem when-ever direct interstage coupling is employed. Thisis because any d-c change in one stage is coupledinto the next stage and amplified.

15-18. A simple way to prevent the transferof d-c variations from one stage to the next is touse RC coupling. A two-stage RC-coupled .

amplifier is illustrated in figure 79. The capac-itor CI blocks d-c, but couples a-c from the

311

OUTPUT

A

Figure 80.

collector of 01 to the base oi Q2. Since, how-ever, capacitive reactance increases as "frequencydecreases, the lower frequencies of a-c areattenuated. Consequently, gain falls off to zerocps (fig. 73,B). Thc principles pertaining toRC-coupled electron-tube amplifiers apply totransistor amplifiers also. The low-frequencyhalf-power point depends upon many factors:the electrical size of the coupling capacitor, theload impedance of the input impedance of mefollowing stage, and the emitter resistor bypasscapacitor. Capacitors CI and C3 should be aslarge as feasible; C2 and C4 should be largeenough to prevent low-frequency degeneration.

15-19. Untuned transformer coupling alsoprovides d-c isolation of the stage. The troublewith this type of coupling is its poor low-fre-quency response. This can be corrected by theinclusion of a low-frequency compensation cir-cuit. In figure 80, the components Ro andCLF present a higher load impedance to thelow frequencies than to the highs. This effec-tively boosts the power of the low frequencies togive a more uniform gain response (see fig.80.B).

15-20. Driver and Power Amplifiers. Ampli-fier stages designed primarily to raise the powerlevel of the sienal are known as driver andpower amplifiers. Driver stages usually de-velop power in the order of milliwatts. Poweramplifiers develop watts or hundreds of milli-watts of power. This distinction based on powerlevels is approximate at best. The power levelsof driver and power amplifiers depend on theequipment in which they are used. A driveramplifier, as its name implies, is used to drivea succeeding stage. Thus, the driver stage de-livers power to another driver stage or to a poweramplifier. Power amplifiers build the signal

LOW-FREQUENCYCMPENSATION

FREQUENCY

a

Transformer coupling with Iow-frequency compensation.

88A..jtJ

Figure 81. Class B push-pull amplifier.

power to the necessary level to operate a devicesuch as a speaker.

15-21. Single-ended. Circuit arrangementsfor single-ended driver and power amplifiers donot differ to any marked degree from the classA preamplifiers just covered. Drivers and poweramplifiers operate at higher collector voltagesand currents, however, and are carefullymatched for power transfer. Transformer cou-pling is very useful for matching. Such cou-pling also improves efficiency since the d-c lossesare reduced. Impedance coupling (LC) is

sometimes used to obtain a higher efficiency,but it has poor low-frequency response.

15-22. Efficiency is quite important at highpower levels so it is a matter of concern, par-ticularly for power amplifiers. As long as weoperate class A, efficiency will be poor. Ifsingle-ended amplifiers are used, there is nochoice; fidelity demands linear class A opera-tion.

15-23. Push-pull. Fidelity can be realized athigher efficiencies by a push-pull circuit arrange-ment. Improved efficiency and fidelity can beattained with push-pull amplifiers operatingclass A. Just as in the case of electron-tubepush-pull operation, even-harmonic distortion isminimized. If the circuit, is perfectly symmet-rical. such distortion is completely eliminated.Because of this fact, push-pull amplifiers candeliver greater power for an allowable amountof distortion than can two single-ended ampli-fiers. Moreover, push-pull amplifiers can beoperated class B and class AB since even-har-monic (nonsymmetrical) distortion can be can-celed. Provided there is good circuit symmetry,excellent linearity can be achieved with classAB operation and fairly good linearity is possi-ble with class B operation.

15-24. Because of its simplicity, let's beginwith a class B transformer-coupled type. Notethat the ciriuit shown in figure 81 resemblesclosely the corresponding electron-tube class Bpush-pull amplifier. Again we have chosenn-p-n transistors to bring out this similarity.

89

Remember that p-n-p transistors can be usedinstead, proVided the bias polarities are re-versed. This goes without saying for all transistorcircuits.

15-25. Observe in figure 81 that there is noforward base-emitter bias; both the base andemitter of 01 and 02 are at d-c ground po-tential. Therefore, 01 and 02 are cut off; withno-signal input (the static condition) LI =0and Ie2 = 0.

15-26. A signal applied to the primary of theinput transformer will produce signals at oppo-site ends of the center-tapped secondary 1800out of phase as shown. Therefore, when thebase of 01 "sees" a negative alternation, thebase of 02 "sees" a positive alternation, andvice versa. Because both 01 and 02 have zerovolts base-emitter bias, each will conduct duringpositive alternations and remain cut off duringnegative alternations. Since their inputs are180° out of phase, 01 is conducting (Id)while 02 is cut off, and 02 is conducting (Ida).while 01 is cut off. In other words, 01 and 02conduct alternately to supply output current(Li + 1,2) throughout the entire cycle (360° ).

15-27. This circuit arrangement amounts tohaving two symmetrically arranged single-endedamplifiers supplying a common load. Figure82,A, is a dynamic curve of a single-endedamplifier. Figure 82,B, is the dynamic curve ofa push-pull amplifier; note that this curve ismerely the combination of the dynamic curvesof two single-ended amplifiers. Because of the180° phase relationship of the input and thecircuit arrangement, the positive direction ofbase currents Int and 1b2 are opposite; also, thepositive direction of collector currents LI and1,2 are opposite. The input signal wave is pro-tected on the dynamic curve diagram in figure82,C. We see that the output waveshape is thecomposite of the current Id and leb as pre-viously explained. This diagram is useful inas-much as it depicts clearly the accuracy of signalreproduction, thus fidelity. Note the distortionthat occurs as the signal approaches and passesthrough zero..,ais is called crossover distortion.The output wele eontains odd harmonics of thesignal frequen0,

15-28. CroWiv,ei distortion can be eliminatedby biasing 01 aid 02 in the forward direction.A simple biasing- arrangement is illustrated infigure 83. The resistor R is made variable sothat we can adjust the bias for class AB operationor class A operation. If properly adjusted forclass AB operation, the crossover effect is notevident in the output. A comparison of figure84,A, and figure 84,B, shows why this is so.The nonlinearity is effectively canceled and ex-

25'7

SASE CURRENT No)

A

A. DYNAMIC CURVE OP A SINGLE TRANSISTOR

S. DYNAMIC CURVE OP PUOIPULL ARRANOIMINT

C. WAVIFORMS

Figure 82. Class B push-pull curves.

cellent fidelity achieved. If R is adjusted for classA operation, the output waveshape is the result-ant of the individual waveshapes as illustratedm figure 84,C.

15-29. It seems that since class AB operationis more efficient than class A operation, class ABwould always be preferred. The output wave-shape looks as good for class AB as it does forclass A. This is because we have assumed per-fectly matched transistors and symmetrical cir-cuitry. Suppose, however, that the transistors

Figure 83. Push-pull amplifier that can be biasedclass AB or class A.

90

are not perfectly matched or that the circuit isnot perfectly symmetrical; the dynamic curves forQ1 and Q2 would no longer be identical. Forsuch a condition, the outputs from a class AB anda class A push-pull amplifier are shown in fig-ure 85,A, and 85,B, respectively. It is quiteobvious that the output for class AB operation isdistorted. This nonsymmetrical distortion is aresult of the presence of even harmonics. Thus,we need to realize that class AB operation re-

'CLASS AB

CLASS A

OUTPUT

AAR OUTPUT

INPUT

Figure 84. Typical output waveforms.

quires matched transistors and circuit symmetryif high fidelity is desired. Such requirementssomewhat offset the higher efficiency it offers.

15-30. Inverter driver. It is not necessary touse a transformer to obtain input signals of op-posite phase for a push-pull amplifier. The cir-cuit in figure 86 shows how a driver amplifiercan be designed to produce output signals thatare 1800 out of phase. Resistors RI and R2are of such ohmic values as to provide the pro-per base bias for linear class A operation. Resis-

256

AiA

INPUT

Figure 85. Wave/orms resulting when a push-pull circuit is not symmetrical /or (A) class ABoperation, and (8) class A operation.

tors R3 and R4 are equal in value so that thesignal outputs are the same in amplitude. Thenormal phase inversion from base to collectoroccurs across R3, whereas across R4 the signaloutput is in phase with the input.

15-31. Emitter follower action accounts for thephase of the signal across R4. This action alsoaccounts for the fact that input impedance ishigher than ordinary and the output impedanceis lower to match the input impedance of the

push-pull stage. Another advantage offered isthe improved frequency response. Better fre-quency response can be attributed to two things:degenerative (negative feedback) action and ca-pacitive coupling.

15-32. We took care to say capacitive couplingrather than RC coupling since crystal diodesCR1 and CR2 are used in place of resistors.These are discharge diodes that prevent the ca-pacitors CI and C2 from taking on a charge

PHASE INVERTERDRIVER

Figure 86.

PUSHPULL CLASSPOWER AMPLIFIER

Capacitively coupled input to a mah-pull amphlier.

91

2 5 j

;.(4-`1

EUTPUT

Figure 87. Push-pull amplifier using complementarysymmetry.

which would bias the push-pull amplifier wellbelow cutoff. Inasmuch as the transistors drawbase current during half a cycle for class Boperation, rectified base currents flow into Cl andC2. If CR1 and CR2 were not connected in thecircuit as shown, a negative charge would buildup to reverse-bias the push-pull transistors. Thiswould correspond the grid-leak biasing electrontubes. To preclude this unwanted base biasing,CR1 conducts whenever Cl becomes negativewith respect to ground, and CR2 conducts when-ever C2 becomes negative with respect to ground.Thus, these discharge diodes function to main-tain zero volts base bias.

15-33. Complementary symmetry. An ar-rangement made possible by the use of an n-p-nand a p-n-p transistor is shown in figure 87. Thissimple push-pull amplifier circuit affords thebenefits of capacitive coupling, yet does not re-quire a phase inverter and does not require dis-charge diodes.

15-34. Input phase inversion is unnecessarysince at zero base bias the n-p-n transistor (01)and p-n-p transistor (Q2) conduct on alternatehalf-cycles of the input. When the input signal ispositive going, Q1 conducts and 02 is cut off.When the input signal is negative going, Q2 con-ducts and 01 is cut off. Thus, push-pull opera-tion takes place as a result of the complementaryaction of the transistors.

15-35. Note that h1 and Ib2 flow in oppositedirections. If the transistors are properlymatched, these two currents will be equal. Be-cause they are equal and opposite, the resultantcharging current flowing into the coupling ca-pacitor is zero. Since no charge will develop toreverse-bias the bases, discharge diodes are notneeded.

15-36. The basic circuit just discussed illus-trates how simplicity and improvement of apush-pull amplifier circuit can be attained byusing n-p-n and p-n-p transistors together. Manyvaried circuits take advantage of the comple-mentary features of transistors. Such circuitshave no electron-tube counterparts.

92

,25016. Audio Consoles

16-1. The audio console is the nerve centerfor the audio portion of TV production, just as thesync generator is the heart of the video equip-ment. However, the basic functions are vastlydifferent. Whereas the sync generator provided astandard, the audio console does much more. Inthis section we shall see just how much more aswe study the functions, signal paths, mixing ac-tion, and monitoring facilities which are all a partof the audio console. An audio console will bedesigned to handle audio signals from micro-phones, tape recorders, special effects consoles,and other sources as necessary for sound pro-duction.

16-2. Functions. There are many functionswhich could be listed; however, for our purposes,we will consider those functions performed byamplifiers, switches, mixers, and monitors. Ofcourse for the console to carry out its functionsthere must be certain auxiliary equipment at-tached, as indicated by the various input andoutput terminations of figure 88. Most consolescontain their own power supply.

16-3. Amplifiers. In an earlier part of thischapter when microphones were discussed, youwill mall that the dynamic microphone was de-termined to be the best for fidelity. This micro-phone, however, requires a preamplifier (pre-amp) due to its low output voltage. Therefore,the audio console has built-in preamplifiers,which give sufficient signal level to drive theprogram and monitor amplifiers. The preampsused in this unit (see fig. 88) have external gaincontrols, which are located on the front of theconsole along with the other input controls. Thesecontrols are actually labeled "mixer." The pro-gram amplifier is also a multistage amplifierwhich falls in the class of a driver. This ampli-fier also has a gain control, which is the mastercontrol that enables the operator to adjust for thecorrect output level, as indicated on the VUmeter.

16-4. Switches. The control consoles areequipped with a number of multiple contactdouble throw lever switches. These switches areused to perform a number of functions, somesingly and4ome as multiple functions. The tapeinput is an example of a single function. Whenthe switch Is in either the program or monitorposition, the only function is applying the tapesignal to the respective amplifier. The micro-phone selector switches use an additional set ofcontacts to control the muting relay which re-moves the monitor speaker from the circuit. Also,the muting relay controls the on-the-air alertlight.

26u

PREAmP

MIG

TAPE

SP E ALEF F E CT S

AL) X

mON

P ROGR AMAMP

vuMIXES

1 PGIA

CUE SI

Figure 88. Block diagram of an audio console.

16-5. There are other switches, such as SI.which are used to select the various circuits tobe monitored. There is a switch, not shown infigure 88. which enables the operator to selectwhat he wishes to monitor on the phone jack.It should be mentioned that figure 88 is a blockdiagram of a simple console; the more elaboratecontrol consoles have many more switches.

16-6. Mixers. The mixers consist primarily ofthe variable attenuators which are incorporatedwith the various amplifiers. In the amplifier cir-cuits, the mixers are nothing more than gain con-trols. In the tape input, auxiliary input, andspecial effects, they serve as gain controls for thecue circuit. For those who have not actuallyworked on a control console, there might be somequestion as to why they are called mixers. Thiscan best be explained by saying that as one inputsignal is used to replace another, one signal willhe increased as the other is decreased. In thisinstance the operator will increase the gain onone input mixer control while decreasing the

93

El PROGRAMLINE OUT

MONITORAMP

EXT MON

CONTROLR00/4SPEAKER

MUTINGRELAY

gain for the other. If two inputs are to be usedat the same time. then the two mixer controlswill be set to give the proper balance or desiredmixing of the signals coming into the console.They will also be set to give the correct overallamount of output signal.

16-7. Monitors. The console incorporates aVU meter which is used to monitor the signallevel out to the line and the external monitor.When you are using the mixer controls, the VUmeter is very important for adjusting and main-taining the correct level out. The headset moni-tor (not shown on the block diagram) is alsoused for adjusting balance; however, since theoperator's sense of volume is not good enoughto set the level out, the VU meter is needed.

16-8. The various speaker connections alsoserve as monitors in the control room at remotelocations and other miscellaneous installations.Like a headset, the speaker serves to give youan idea of the output level, but is not exactenough when adjusting for the correct level while

261

monitoring tapes or live programs. It should hementioned that some of the control consoles haN eselective scale adjustments for the meters,whereas others require modification of the padcircuit to change the meter scale.

16-9. Signal Paths. Again looking at figure88, we see that there arc a number of possiblesignal paths. In this diagram we have a totalof six inputs and three outputs. Remember thatthis is a simple setup. There are many moreinputs and outputs in. the more elaborate setupsthat have talkback circuits incorporated for class-room work. In the diagram illustrated, start withmicrophone number 1 and trace a signal paththrough the preamp, level selector switch (pro-gram "P" position), program amplifier, VUmeter. line out pad or extension monitor pad tothe output. If switch SI were in the PGM posi-tion, the output from the program amplifier wouldalso be coupled to the monitor amplifier andcontrol room speaker terminal.

16-10. As shown in the diagram, all of theinput signals can be connected to the programamplifier and monitor amplifier at one time.Let us suppose that you have a studio programthat requires the use of all the microphones andalso requires specific sound effects which are re-corded on tape. In this case. you must use thecue circuit to set the tape to a desired spot.With SI in the cue position, a signal is fed to themonitor amplifier. At the right moment, you usethe selector switch to send the signal to the pro-gram line. Thus, the tape input is mixed intoand becomes part of the program.

16-11. Performance Adjustments. Three typesof adjustments of primary concern are elimina-tion of hum in the circuits, prevention of erraticaction from switch contacts, and accurate controlof output.

16-12. Hum balance. It should be mentionedat this point that hum is not usually a problemwith a transistorized control console. However,the tube type consoles with a-c filaments aresubject to hum distortion. To eliminate this prob-lem, you will need to adjust the hum balancecontrol, which is found in the power-supply sec-tion. To make the hum adjustment, set allinput selector switches to the center or off posi-tion. If there is an input that cannot be turnedoff, it should be terminated in a resistance sinceit may. pick up hum in a manner similar to anantenna. After all input circuits are either off orterminated, turn the master gain all the wayclockwise. If the preamp is in the circuit follow-ing the selector switch, turn the preamp gain ormixer to minimum, fully counterclockwise. Nowyou are ready to adjust the hum control forminimum hum in the output of the program line.

94

16-13. SWitch contacts. The switch contactscan be a source of much trouble duLt to theirposition in the line relative to the amplifiers.When a switch spring becomes bent, it will notclose properly; therefore, you must adjust it forgood contact. If a contact becomes burned orotherwise pitted. erratic. action nmy result. Switchcontacts should be carefully checked and ad-justed or aligned for smooth action. This is truefor both rotary and lever action switches.

16-14. Overdriven output. When setting upthe output level. the important thing to remem-ber is that your accuracy can be no better thanthe VU meter reading. In other words, you willnot be able to properly set the Output unless sourVU meter is accurate. Depending on the console.you may find various methods of calibrating theVU meter. If you find the meter is improperlycalibrated, it must be recalibrated against aknown standard. In some cases it will he neces-sary to change the resistors in the pad circuit toget the correct VU meter calthranon. Youshould realize the importance of output levelcontrol .since this signal goes to a recorder. a livebroadcast, or a five CCTV nemork. Therefore.any distortion which results from the merdrivenoutput causes a loss of intelligence.

16-15. Symptoms and Troubles. The troublesdiagnosed here are only a few that may causethe symptoms described. Some of the troublesmay have many other symptoms which will en-able you to determine the most likely cause of amalfunction.

16-16. Hum. As already mentioned, some ofthe hum problems are found in both transistorand tube-type sets. However, we know thattroubles with hum are less frequent with transis-tor units because they do not use heater voititges.Most of the hum picked up in a transistor' unitwill be from the preamps. amps, long microphoneleads, and other types of inputs. The tube-typecontrol ctinSoles are different because of the a-cfilaments. The hum balance adjustment proce-dure has already been discussed in the previoussection; however, this adjustment will suffice onlyif all components are in good condition. Forexample, if you attempt to make the hunt adjust-ment and find that the control does not have anyeffect, there is another reason for thc hum. Insome models of the control console you will findthe hum adjustment to he nothing more than ad-c voltaue that can be varied from one side ofthe filaments to the other. In essence, this appliesa positive potential on the filaments with re-spect to the cathode, causine a current flow fromthe cathode to the filaments rather than frontfilaments to cathode. Thus. any hum whichmi2ht ordinarily be coupled front the filaments

262

47,1

will be blocked. Now if you were not able tomake the hum adjustment with the hum balancecontrol. there is a good possibility that the voltageis missing from the hum balance adjust. De Pend-ing on the console model, you may have as muchas 40 volts at the center tap of the balance con-trol; this viiTtage is usually obtained from ableeder circuit in the B+ supply. Therefore,when there is a hum control failure, you shouldcheck the power supply voltage and the balancevoltage source.

16-17. Feedback. Recall that the muting re-lay is used to mute the speaker. If this fails,sound may be fed back from the speaker to themicrophone. There are two possible places tolook for the cause of this troubleone is therelay which does the muting. and the other isthe switch which controls the relay. Of courseyou can easily determine whether the switch isfaulty by using another selector switch to see ifthe relay is activated. If the relay is activatedand the speaker is muted, you know that thetrouble is in the switch. If the relay is not ac-tivated, then it should be checked. Another thingto remember about sound feedback is that thehigher audio frequencies will usually cause moredifficulties than the lower frequencies. Also, donot overlook the possibility of sound feedbackfrom extension monitors in adjacent rooms. Thesesources of sound can also be troublesome.

16-18. Microphone. Since the microphone isthe signal source in an audio system, it can also

I.

be the source of troubles. The microphone inmost all instances will require a preamp as in-dicated on the block diagram. There are manytroubles that are attributable to the microphoneitself, such as broken cords, loose connections,and corroded terminalsall of which could causeweak or erratic output. This is in addition toany other internal damage to the microphone;and, of course, any of these symptoms could belocalized to the microphone by substitution of aknown good microphone. If the trouble is in thepreamp, then of course it would be a. matter ofchecking tubes and other items or perhaps circuittracing the preamp. However, a weak signalwotild usually be a weak tube in the circuit. Otherpossibilities, although less probable, are low B+,low filaments, component value change, andother minor items.

16-19. Erratic mixers. The mixer control isone part of the control console which is usedextensively and causes some trouble during oper-ation. The mixer or variable attenuator is, asyou already know, nothing more than a gaincontrol; therefore, it has a sliding arm contact.The sliding contact may become dirty and causenoisy operation of the control, This will be veryapparent in the use of the control, as you willhear the static or jumps in gain rather than asmooth change. The trouble can be eliminatedby cleaning the wiper arm contacts with a goodcontact cleaner, or some other cleaner as recom-mended by the manufacturer.

CHAPTER 7

Color Television

BESIDES THE natural appeal of color TVthere are numerous practical advantages

that account for its development and use. Wewill discuss its use in the Air Force. point outsome of its advantages, and indicate its futureutilization. Although a color TV system has muchin common with a monochrome system, youshould understand the special requirements forcolor TV. We will review these requirementsbefore you study the camera chain and colormonitor. Our coverage intends to reinforce yourknowledge of color TV and to further yourunderstanding of the principles involved. Withthe increased use of color systems, it is highlyprobable that you will have to maintain colorTV equipment.

17. Applications and Requirements17-1. Despite the complexity and expense of

color TV, the Air Force employs it it. .aany

areas and is programing it for wider use. Themore important areas of application are broughtto your attention in this section before investigat-ing the requirements of a color system.

17-2, Air Forces Uses of Color TV. The ad-vantage to the Air Force of a color system overa monochrome system depends largely upon thenature of the subject matter being televised.Where color plays an important part in thc de-lineation and recognition of the equipment ormaterial being ust4 a TV system which will

faithfully reproduce those characteristics is ob-viously desirable. The detail response of a colorsystem is superior to that of a monochrome sys-tem. Because of the expense involved, a colorsystem confined to one use only may not be ad-vantageous. Usually a base or installation willhave color facilities for application in a numberof areas. such as weather, missiles. medicine, andothers too numerous to list.

17-3. Weather. The use of color closed-circuittelevision in a base weather station is practicaland greatly facilitates information transmission.Monochrome closed-circuit television has proved

eP511-

valuable in transmitting weather data to otherinterested facilities; color increases the quality of

information which can be transmitted since

weather charts and maps usc several colors todenote highs, lows, fronts. etc. Accurate presen-tation of high-detail maps and charts demandsgood quality cameras. The addition of coloreliminates some of the printed ineormation onthese maps. but conveys the same amount ofinformation. Since the definition auainablc withcolor TV is superior to monochrome TV. color isparticularly suited to this application.

17-4. Missiles. Color television systems, likethe monochrome. systems described earlier in

this volume. arc also used to monitor the opera-tions of guided-missile installations. Dangerousoperations, such as missile launching and testingof machinery under extreme mechanical stress,require remote location of operators and super-visors; the extensive use of color coded controlsand materials makes the color closed-circuit tele-vision monitoring system particularly effective.

Inasmuch as small missiles can often he observedin relative safety from short distances. TV moni-toring is not required; however, as a safety pre-caution. TV monitoring is necessary for largemissile launching activities.

17-5. Medicine. Some major hospit:ils haveinstalled color closed-circuit TV systems foi med-ical training purposes. Recent developments incolor TV equipment include a color camera es-pecially designed for hospital usc. The camera.with associated mirror and lights, can be remotelycontrolled from anywhere in the hospital. Whenproperly located in the surgical room. the colorcamera permits large groups of medical studentsto view from a remote distance an entire opera-tion in realistic detail. Autopsy rooms icid dentalclinics are other locations where direct observa-tion is extremely difficult due to limited' space.The use of color TV in thesL: localities providesthe same training capabilities as in the operatingroom. Such color systems have alread provedto be of tremendous value in training medical

students. and it seems reasonable to predict thatthe number of hospitals using color closed-circuit`TV systems for this purpose will rapidly increase.

17-6. nlwr. General surveillance, hazardousmonitoring, weather service, and training con-stitute thc bulk of color closed-circuit TV ap-plications. An example of tactical capabilities inthe military application. of TV is Air Force re-connaissance. A color closed-circuit TV linkenables a large group of command personnel.located at a remote point, to observe the enemyterrain simultaneously with the pilot and ob-server, thus facilitating a more rapid transmissionof vital information. Color TV. in this applica-tion, has a definite advantage over monochromesince camouflaced areas are more easily dis-covered when the picture is reproduced in color.Many colors that blend perfectly when viewedin monochrome stand out as being artificial in

actual color.17-7. Requirements of Color TV. To appre-

ciate the re'quirements of a color TV system. youneed to know the properties of color. Moreover.you need to know the perceptive characteristicsof the human eye to understand what informa-tion must be contained in a color video signal.A brief review of color principles ,should sufficeto call to mind those factors that have an impor-tant bearine on thc compatibility. bandwidth. andsync requirements. We will show how these re-quirements arc met when we describe the camerachain and monitors of a color system.

17-8. Color and color perception. The exactprocess by which the human eye is able to trans-late light of different wavelengths into color sen-sations is not fully understood. However, experi-ments have shown that almost the full range ofcolor sensations can be obtained by mixing red.blue, and green light iii various proportions.These three colors arc called additive primaries.Additive primaries arc not restricted to blue.green. and red. Any three colors can be usedso long as no two of them produce the third whenmixed. Thc widest range of color is obtained.however, when blue. green. and red are chosen.For this reason. these three additive primaries areused for color TV.

17-9. It is appropriate here to distinguish be-tween additive and subtractive primaries. Addi-tive primaries are so called because they aresources of color light which arc added (mixed)to produce a desired color. By contrast. sub-tractive primaries are absorbers of color lightwhich subtract or remove certain colors fromwhite light to create color. Whereas a knowledgeof subtractive primaries is important to severalfields 4 study (e.g.. photography and color

97

;5'3'printing), a knowledge of the additive primariesis more pertinent to the study of color TV.

17-10. A discussion of color as applied tocolor TV would be relatively simple if all thathad to be considered were the various colors oflight obtainable by mixing various proportions ofblue, green. and red. But the variety of colors,called hue, is only one of the three basic proper-ties of color perception. The other two propertiesthat must be considered are saturation (orpurity) and luminance (or brightness). Satura-tion is the term that describes the amount of whitelight mixed with the hue. For example, pink isa red hue diluted or mixed with a considerableamount of white. A zero saturation of red hue iswhite light, whereas a 100-percent saturation ofred hue is pure redthus no white light. Broadlyspeaking. the pale or pastel shades of hue areless saturated than the vivid shades of hue. Lumi-nance is the term that describes the brightness orintensity of colored light. Although luminance,saturation. and hue are interrelated, they are

. distinct properties which you should understand.17-11. A chart used for the study of color is

the chromaticity diagram which reveals the re-lationships between the different colors and colormixtures. Figure 89 shows a chromaticity dia-gram which is useful to determine the hue andsaturation required to produce a particular color.This tongue-shaped diagram is numbered aroundits perimeter from 400 to 700 millimicrons, whichis the wavelength range of the visible spectrum.If figure 89 were in color, you could see that thecolor changes are gradual from point to, point.The deep shades are present at the outer edge ofthe diagram. Any point on the perimeter repre-sents a pure color (100 percent saturation).Moving inward to the white area. the colorsbecome lighter; pastel shades appear; and then awhitish area is seen. roints within the diagramrepresent different mixtures of color (hue) anddifferent saturations. For example. the midpointon a straight line connecting pure green and purewhite representi a color having a yellowish greenhue and a saturation of 50 percent.

17-12. The area inclosed by the triangle13.G,R, as illustrated in figure 89, contains all thehues and saturations that are specified by FCCfor color TV. The colors outside the triangle arerelatively unimportant since they rarely occur innature. Excellent color fidelity is therefore at-tainable in a color TV system that transmits therange of hues and saturations within the FCCchromaticity triangle.

17-13. Because a chromaticity diagram doesnot include luminance, we need look to figure90. which illustrates the relative response of thehuman eye to the various colors in the spectrum.

260

510

520

530

SAO

GREEN

550COLOR GAMUTINDICATING PRIMARIES

560

500

570 0.9eiN

Ci

580

oltStPSG'

590

600

620490

480

470

460

450 400

BLUE

Figure 89. Chromaticity diagram.

Of the three TV primaries, note that green ap-pears the brightest. In white light the proportionsof the color primaries sensed by the eye are 59percent green, 30 percent red, and 11 percentblue. If you keep these color proportions con-stant while slowly decreasing light intensity, thebrightness changes from white through progres-sively darker shades of gray to black. Therefore,brightness is achromatic even though it containsthe three color components.

17-14. Although color has three properties,the eye's ability to perceive them depends uponthe size of the image (object or area) beingviewed. For relatively large images, the eye seesthe full range of hue, saturation, and brightnesspresent. As size decreases. the eye becomes lessdiscerning and partially colorblind. So much sothat for very small images, it sees colors as shadesof gray from black to white. This is to say, theeye is completely colorblind with regard to fine

98

660700-74

REO

detail; therefore, only luminance is needed sincethe eye is incapable of sensing the hue and satu-ration of very small images. These perceptivecharacteristics are used to alivantage in colorTV, as we will point out shortly.

17-15. Compatibility and bandwidth. Com-patibility is a requirement that must be met forcolor broadcasting. This means that (1) a colorvideo signal must provide a standard black-and-white (monochrome) signal, (2) chrominanceinformation must be contained within the stand:ard TV bandwidth, and (3) the chrominancesignal must not interfere with the monochromesignal. These requirements are met by the Na-tional Television System Committee (NTSC)color system. Since the NTSC system is usedthroughout this country, you need to understandthat it is compatible with the standard mono-chrome system.

266

I 0

0.8

0.6

0.4

0.2

400 500

WAVELENGTH IN MILLIMICRONS

600

Figure 90. Luminance curve showing sensitivity of human eye.

17-16. The first requirement is met by trans-mitting a composite black-and-white video signalhaving practically identical waveform standardsfor amplitude modulation (AM), synchroniza-tion, and blanking as a monochrome system.A spectrum analysis of this signal (see fig. 91)shows that the frequencies constituting it do notoccupy the entire band, but occur in clusters nearharmonics of 15,750 cps, the scanning line fre-quency. Such being the case, frequencies con-stituting the chrominance signal can be dis-tributed between these clusters within the 4.5-mcrange without disturbing the black-and-white sig-

ND 0 C P S

111

CLUSTERS OF MONOCHROMEFREQUENCIES

700

nal. This is how the NTSC color system satisfiesthe second and third requirements for compati-bility. By modulating an odd harmonic of one-half the line scanning frequency, the chrominancefrequencies are placed in the spectrum midwaybetween the ,clusters of the monochrome frequen-cies. This principle is called interleaving. A fre-

quency of 3.58 mc, which is approximately the455th harmonic of 1/2 X 15,750 cps, is used asthe color (chrominance) carrier. In a r-f trans-mission system, it is called a subcarrier since thecomposite video signal modulates the r-f carrier.

CLUSTERS OF CHROMINANCEFREQUENCIES

VI

11

11

111,111 1 III Jilin5 . 75 K C

DIFFERENCE

Figure 91.

141-4/Psi7.875 KC

DIFFERENCE

Interkuving f chrominance frequencies.

99

26 7

I] TO 4.5 MC

COI LIR 4001r54 *AC

L UMINAACE ANC,1',I. 50 ST NuAn moNoc,,ROME 04,

REOU ENC ----IP

cmSiOmm. ANC Eb NWIDirm .AO

I I 0

4--.11-04 s

osrAc osucmc

:`.

Figure 92. Bandwidths lor NTSC color video.

.VHF and UHF carrier systems will be coveredlater in Volume 2.

17-17. In addition to rigid adherence to theFCC monochrome bandwidth requirements, thereare bandwidth requirements peculiar to theNTSC color system. The bandwidths assigned tothe chrominance frequencies are based on theperceptive characteristics of the human eye de-scribed earlier. Video picture information isdivided into two parts: ( I ) luminance which iscalled the Y or M signal (from here on referredto as Y) and (2) chrominance which consists ofcomponents called I and Q signals. The Y sienaloccupies the same bandwidth as the standardmonochrome signal. Large. medium, and verysmall images are adequately televised within thisbandwidth. Because the eye is colorblind forvery small images, the Y (luminance) signal issufficient. Consequently, the chrominance signalis not required and the bandwidth can be reducedconsiderably for the I and Q components. Boththe I and Q signals contain the three primaries,but in differOtt proportions. The hue for the Icomponent ranges from cyan to orange. Thisrange of color was selected for medium sizeimages because it gives adequate color fidelity.Medium size images are televised well within avideo range of 1.5 mc; therefore, the I compo-nent is assigned this range. Only large imagesneed the 0 component, which when comhqiedwith the I gives the full color spectrum. A videorange of 500 ke (0.5 mc) is ample to conveylarge image information.

1748. What has been said thus far concerningbandwidth is illustrated in figure 92. Note thatthe bandwidth for the luminance signal is thesame as that for the standard monochrome signal.Because the chrominance signal is a modulatedsignal having a 3.58-mc reference. the band-width shown extends above and below this fre-quency. For the I component. the full 1.5-mcrange is used to produce the lower sideband. btitonly a 0.5-mc range is used to produce the uppersideband. By having a vestigial upper sideband,

100

1 frequencies are kept within the standard videobandwidth. This is not necessary for the%) com-ponent, however, since its full range is only O.mc. An entire upper and lower sideband is there-:ore used. Observe that both thc I and 0 corn-punents arc present over a 0.5-mc video range.thereby providing maximum color for large-sizeareas; whereas, only the I component is presentfrom 0.5 mc to 1.5 mc. thc range in which thefull color spectrum is not required for middlesize images.

17-19. Sync. The waveforms of horizontaland vertical sync pulses for color TV are no dif-ferent from those for monochrome TV. Thereare slight frequency differences; however, theyare well within the tolerance limits of a mono-chrome system. For color, the horizontal (line)sync is 15,734 cps instead of 15,750 cps. and thevertical (field) sync is 59.94 cps instead of 60cps. Besides the horizontal and vertical sync, a3.58-mc signal sync is used in thc NTSC system.This signal would not be needed if the 3.58-mccolor carrier were transmitted in the chrominancesignal. But it isn't. The color carrier is com-pletely suppressed in the modulation process fortwo reasons: (1) to reduce beat frequency in-terference and (2) to attain higher transmitterefficiency. Being absent. the 3.58-mc carriermust be inscrted by the local oscillator of a colorreceiver or monitor. It is extremely importantthat the local oscillator frequency and the trans-

"mitter's 3.5 epmc reference frequency are syn-chronized, beLitse color distortion will result ifthey are not. Therefore, immediately followingeach horizontal sync pulse. a burst of the 3.58-mcreference signal is transmitted. This sync is calledthe color burst signal. Note in figure 93 that it is

1,7 HORIZONTAL SYNC

BURST OF3.58 MC

MIN. OF 8 CYCLES

HORIZONTAL BL ANK

I.

Figure 93. Color burst sync.

268

placed on the back porch of the horizontal blankpulse.

17-20. Chrominance circuits. Having re-viewed. the compatibility, bandwidth, and syncrequirements for color TV, let's identify the ad-ditional circuitry needed in an NTSC color cam-era chain and monitor.

17-21. The color camera chain consists of acolor camera, camera control unit, sync gen-erator, processing amplifier, and colorplexer. Fordistribution and versatility, a switcher and aDA network are used. In the following sectionwe will discuss each of these units in some detail,but we wish here to point out that chrominanceinformation must be handled as well as lu-

minance information. Generally speaking, thisnecessitates closer tolerances and more complexunits. The color camera contains a special opticalsystem, three camera tubes with their associatedpreamplifiers, and video networks. Consequently,the camera control panel must control three cam-era tube outputs and their relationships. Becausea 3.58-mc sync is required, the color sync gener-ator must provide this frequency and the keying(flag burst) pulse to properly time the 3.58-mcsynchronizing signal. Whereas in a monochromecamera chain the camera control unit processesthe video, in a color camera chain signal proces-sing plus additional functions are done by aprocessing amplifier unit. Another unit not foundin a monochrome camera chain is, of course, thecolorplexer. It performs the functions necessaryto produce the composite color video signal. Thisentails matrixing, filtering, delays, modulation,and mixing to produce the composite color video.Obviously, there are many more functions per-formed in a color camera chain than there areperformed in a monochrome camera chain:

17-22. As in the camera chain, chrominancecircuits add appreciably to the complexity andsophistication of color monitors. You should

1...COLORCAMERA

BLUE

BLANK

realize, however, that there are many functionswhich they have in common with the mono-chrome monitor. The luminance signal is

handled in the same manner by both. A colormonitor must handle the chrominance signal also.This requires eircuits to detect, process, and sep-arate the primary color signals that are neededto drive a color kinescope. Our coverage ofcolor monitors, in the final section of this chapter,will concentrate on these circuits.

18. The Camera Chain18-1. Figure 94 shows a block diagram of a

color camera chain. In this section we will de-scribe the functions performed by each block inthe diagram. Particular attention will be given tofeatures that are unique to an NTSC color sys-tem.

18-2. Cameras. The color camera is muchlarger than the same type monochrome cameradue to the increase of circuitry necessary for thethree pickup tubes and the optical system. Alllive pickup color cameras use three identicalpickup tubes with an associated optical light-splitting system to provide simultaneous blue,

green, and red signals. With the exception of thethree pickup tubes and the associated opticallight-splitting system, color cameras are similar tomonochrome cameras which you studied in

Chapter 4 of this volume. As in monochrometelevision, two types of pickup cameras are avail-ableone using image orthicon pickup tubes andone using vidicon tubes. These cameras use alight-splitting system like the one shown in figure

95.18-3. Optical system. To develop the color

TV signal, the color TV camera must first splitthe televised scene into three separate lightimages, blue, green, and red. Figure 95 showsa sketch of an optical system used in a three-tubecolor TV camera. On the left are the objective

vI0E0& V ORIVE

GREEN

RED

& V ORIVELBCAMERA

CONTROLPANEL

COLOR vIDEO

TO MASTERMONITOR

PROCESSINGAMPLIFIER

ORIVE

8

ORIVE

BLANK

SYNCGENERATOR

SECTION

3.311mC

COLORPLEXER

BURST FLAG

SYNC

2.(043 94. Block diagram ol camera chain.

101

COMPOSITECOLOR

vi0E0OUTPUT

LICNT 111.

TWIRIT

011/ICTIvEErSES

LulICLST;OMATISIACORRECTOR

TRVIOLET..... FODeCHINiCAlt TER

/.

G

ik) \/ 1- SLUE rErLECT1mG 04CrolOIC

lalue TrnmmING cpl.TU- FRONT SURFACE asirrOna

0 PiORIEONTAI. ASTIG/AATMAI CORRECTORet: RELEC11mG OtomloicGnEr TrimmING rL TER

G1 - NEUT./AL OONSIT ILTODPI ao TIVAlemo4C Fe: TER

Figure 95. Color camera lens system.

lenses mounted on a rotating turret, which isvery similar to the turret used in the mono-chrome camera. Three types of lenses, wide-angle, normal, and telephoto, are normallymounted on the turret; and the cameras may beequipped with the zoom-type lens. The threelenses on the turret do not split up the light intothree primary colors, as only one lens is used atone time. Again referring to figure 95, you seethat the light enters one objective lens andfollows a path toward the pickup tubes.

18-4. After passing through the selected lens,light passes through the condenser lens. It thenpasses through die dichroic trimming filter whichremoves the ultraviolet and infrared portions ofthe spectrum. The vertical astigmatism compen-sator then corrects the distortion of optical focuscaused by light passing through the dichroicmirrors at an angle. Light then enters the opticalorbiter (image orbiter), a rim-driven glasswedge which is mounted in a geared ring drivenby a motor through a gear train. The imageorbiter is a device which rotates the cameraimage in a slow, continuous elliptical orbit, un-detectable to the TV viewer. Its purpose is toprevent image "burn-in" or "sticking" of theimage orthicon pickup tube. Sticking occurs af-ter a camera is held stationary on a hieh con-trast scene for 10 to 30 seconds or more. Anegative image remains visible for intervalsranging from a few seconds to several minutes,depending upon the age of the tube and theseverity of the burn. Rotation of the opticalimage falling on the photocathode is a practicalway to prevent the image orthicon from sticking.This is accomplished in the color camera by the

102

orG /trot

iiiIII

1 ELLE1CA'UNE

optical orbiter. The image moves in a circle,and the duration of each orbiting cycle is 1

minute. A DC motor, acting through a geartrain, drives the optical wedge mounted in ageared ring. Since the light at this point iscommon to all three pickup tubes, individualelectrical orbiters are not necessary for eachtube. Upon leaving the optical orbiter, the lightpasses through the relay lenses, where thelength of the optical path is increased to providespace for the dichroic mirrors and associatedelements. Between the relay lenses is the iris,which is used to adjust the amount of light to bepassed to the pickup tubes.

18-5. A dichroic mirror is designed to reflecta specific light and pass all others. In figure 95,mirror A will reflect blue light but pass red andgreen light. The blue light is reflected to theface of a front-surface mirror which reflects thelight to the pickup tube designated for blue sig-nal output. The red and green light passesthrough the blue-reflecting dichroic mirror tored-reflecting dichroic mirror, E. The greenlight continues through mirror E to the greenpickup tube. The red light is reflected by mirrorE to front-surface mirror J, where it is reflectedto the red pickup tube.

'18-6. The three camera tubes are adjusted tohave equal output when the televised scene isthe RETMA chart. Notice that B, F, and H areblue, green, and red trimming filters. Thesefilters are placed in the light paths to adjust thespectral response of the color camera pickuptube. The spectral response of the combincdcamera tubes should be equal to that of themonochrome camera. The spectral response in

2t)

the nionochrome camera is very similar to thespectral response:of thc human eye, as shownin figure 90. Since the dichroic mirrors haverather broad spectral responses. thc trimmingfilters placed in the three light paths are adjustedso that the total or combined rcsponse ap-proaches that of the human eye. The trimmingfilters are adjusted according to light conditions;mdoors they are adjusted to artificial light, out-._doors they arc adjusted to natural light.

18-7. In the red and green light paths aretwo neutral density filters (G. I. fig. 95). Sincethe three camera tubcs are adjusted to haveequal outputs where televising a white or neutralscene. neutral density filters must be placed inthe red and green light paths to compensate forthe unequal response of thc cye to the hues thatmake up white light. Rec4ll from figure 90iliat the eye rciponds differently to the variouscolors in white light. The filters reduce thelight in the red and green paths to equal theamount in the blue path.

18-8. The additional horizontal astigmatismcorrector. D. in the blue light path is used tobalance all three light paths astigmatically.Additional correction is not needed in the greenand red paths, as each of these colors passesthrough additional dichroie mirrors.

18-9. Canwra tubes. Camera pickup tubesused for color production are usually an im-proved typc or design. The most commonly usedimage orthicon is an improved version of thetube originally designed for monochrome use.Since the color signal is a combination of theoutput from three tubes. the output from thetubes must he uniform. This requires a pre-cision tube with an output frce from spurioussignals.

18-10. Many of the changes made to improvethe image orthicon tube for color operation arenot physically perceptible: however, thcy areevident in tubc performance. Reduction ofscreen-to-tareet spacing cxtends the contrastrange and improves the signal-to-noise ratio be-low the "knee." Closer spacing (from threethousandths to one thousandth of an inch) al-lows the screen to collect more of the secondaryelectrons from the target; this eliminates ran-doni secondary redistribution of the targetelectrons and minimizes "ghost" and "halo"effects. The new :. tubes arc much more sensi-tive due to the ise of an improved photocathode,nficroniesh screen:, and dynode coating and con-struction.

18-11. You will recall that with the mono-chrome tubc wc operate thc 'image orthiconabove the "knec.- For color operation, how-ever. the image orthicon must be operated at

103

27i

the "knee" to give a more uniform signal freefrom spurious signals.

18-12. The newer vidicon is also of an im-proved design; the sensitivity of the mosaic orphotosensitive material has been increased. Pres-ently, experiments are being conducted to de-velop a combination tube which will functionmuch the same as a vidicon but have the pickupsensitivity of an image orthicon.

18-13. Camera Controls. Color camcra sys-tem controls for setup and adjustments are lo-cated on both the camera and the camera con-trol panel. Viewfinders mounted on the cameraare used as an aid in camera alignment. Aftersetup and adjustment the only controls that greused for operation are those located on thecamera control panel.

18-14. Viewfinder and camera mounted con-trols. The controls for adjustment of the cameraare arranged at the rear of the camera, whereasfocus. brightness, and contrast adjustments forthe viewfinder kinescope are located on theviewfinder panel. A series of pushbuttons per-mits the camera operator to observe a mono-chrome image of a single channel or any com-bination of the red, blue. and green channels.These pushbuttons are located on the viewfinderpanel.

18-15. Controls to adjust the camera includethe blue and red skew controls and Q controlsfor the, three channels. The skew controls areused to adjust to one rectangular shape the blueand red images. The Q controls are linearityadjustments. Also included are conventionalheight and width controls for individual andoverall adjustment of the three channels. Thecolor camcra image orthicon has a dynode gaincontrol for each tube; this control is not found onthe monochrome camera. These controls arelocated on the pickup tube chassis.

18-16. There are video preamplifiers for eachof thc pickup tubes; these are individual unitsmuch the same as those used for monochromeequipment. These preamplifiers are differentfrom monochrome because they are adjustable;one stage has a cathode peaking control for ad-justing tilt at thc low-frequency end of the re-sponse curve and another stage has a high peak-ing adjustment circuit.

18-17. Control panel. Mounted on the cam-era control panel is a group of symmetricallyarranged operating controls for each of the threeimage orthicons. Colored knobs identify ,thecontrols with their respective channels. The in*dividual channel controls include horizontal andvertical centering alignment, orthicon focus,multiplier focus. image focus, and image accel-erator voltage settings in each color channel.

18-18. The master gain (iris) and masterpedestal controls, both of which are located onthe camera control panel, serve as the, onlyoperating controls once the camera has beenaligned. The master gain control operates aselsyn generator which drives a selsyn motor inthe camera to control the iris in the opticalsystem. The master pedestal controls the levelof pedestal voltage inserted into the signal atthe processing amplifier.

18-19. You can readily see by comparisonthat the controls of a monochrome system andtheir functons are similar to those in the colorsystem. However, due to recent developmentsand improvements in tube, component, and cir-cuit design, there may be slight variations in thenumber and location of controls for color cam-eras.

18-20. Processing Amplifier. Observe in figure94 that the processing amplifier is connected tothe camera control panel, sync generator, andcolorplexer. It performs a number of importantfunctionsthose accomplished by the cameracontrol unit in a monochrome system pius sev-eral others. Its functions can be itemized asfollows: video amplification, cable compensa--don, shading and gamma correction, regenera-tion of drive pulses and blanking pulses, genera-tion of signals for test purposes, and electronicswitching. The networks employed for thesefunctions are essentially video amplifiers, multi-vibrators, and waveshaping circuits which youhave studied. Our coverage will therefore beconfined to describing the inputs and. outputsfrom the processing amplifier so you can betterunderstand its purpose in a color system.

18-21. Figure 94 shows that the processingamplifier receives three inputs from the syncgeneratorvertical (V) drive, horizontal (H)drive, and blanking pulses. Both the H and theV drive input signals separately trigger mul-tivibrators which regenerate the H and V drivepulses. Thus, the pulse widths of the H and Vdrive outputs are made independent of the origi-nal pulse widths supplied by the sync generator.Precision components are used to maintain Hand V drive pulse widths within the close toler-ances required for the color system. The blankinput from the sync generator is amplified andclipped before it is fed out to the camera controlpanel as a standard blanking signal.

18-22. Note that the Blue (B), Green (G),and Red (R) video signals are received by theprocessing amplifier via the camera controlpanel. Just as in a monochrome system, shading,corrections must be made. The horizontal andvertical shading generators are driven by the Hand V drive pulses. Besides shading corrcctions,

104

it is necessary to make gamma correcWns. Re-call that gamma is a factor that indicates therelationship of brightness variations between thcoriginal scene and the reproduced image. Be-cause of the inherent nonlinearity in a systcm(principally the kinescope's characteristics), itis necessary to incorporate gamma correctingamplifiers. These amplifiers are designed to pro-duce nonlinearity which is the inverse of thatcaused by the rest of thc system. When neces-sary, provision is also made to compensate forattenuation and distortion caused by intercon-necting cables. This is generally done withplug-in units. the number used depending uponthe lengths of the cables involved. Althoughwe have not designated the B, G, and R signaloutputs differently, bear in mind that they aredifferent from the B, 0, 4and R inputs. Theoutputs are corrected video signals. These sig-nals are fed to the colorplexer, which in turnprovides another input to the processing ampli-fier unit. This input is sent to an electronicswitcher network, which is used in conjunctionwith the monitoring facilities. We sec in figure94 that there is a video output to the mastermonitor. By a switch arrangement, it is possibleto monitor the B. G, R. or Y signal separately(monitors will be discussed in the next section).It is also possible to select a composite of thccolor signals, such as blue-green, or red-blue-men. Moreover, calibration signals can besupplied by the processing amplifier unit to thevideo output for observation on the mastermonitor. So you see that the processing ampli-fier is designed to provide signals for checkingpertinent waveforms.

18-23. Sync Generator. In Chapter 3, Section8. you studied the standard monochrome syncgenerator. Since the NTSC color system is com-patible, the sync generator for a standard mono-chrome system can be used to supply the H andV blanking. drive, and sync signals necded forcolor. We just pointed out that improvementof thesc signals (closer pulse width tolerances)is accomplished by the processing amplifier.You know, however, that a 3.58-mc sync (colorburst signal) must also be transmitted. There-fore, two additional outputs are shown in figure94--a 3.58-mc carrier (r-f subcarrier) and aburst flag signal,

18-24. The 3.58-mc (actually 3.579545 mc)signal is obtained from a color frequency stand-ard generator. This generator is a crystal-con-trolled oscillator which is kept in a temperature-regulated oven. The oscillator generates a highlystable signal (about ±.3 cps per mc) for thccolorplexer and countdown circuits of a standardmonochrome sync generator. Whcn thc

272

2(05.

NuTs 40046PROCESSINGAmIlLiFIER

8

00 Ey...4r4

0-4 I MCF IL l'ER

0. I 5 MCFIL TER

0.0.5 MCF IL TER

EL

DELAY

DOUBLYBALANCED

MODULATOR

4

DELAY

TODELAY

DOUBLYBALANCED

MODULATOR

ADJUSTPHASE

SHIFTER

Figure 96. Block diagram of colorpleser.

31.4685-kc (instead of 31.5 kc) is counteddown, you get the slightly different line andfield frequencies (15,734 cps and 59.94 cpsrespectively).

18-25. A burst flag generator develops a

series of rectangular pulses at the horizontal linefrequency. These pulses are timed to place the3.58-mc burst on the back porch of the horizon-tal blanking pulse. Because this is done in thecolorplexer by a gating (keying) circuit, theburst flag is sent from the sync generator unit tothe colorplexer. as shown in figure 94. It standsto reason that the burst flag signal must beprecisely timed and locked in by the horizontalline frequency of the color system. Furthermore,the width of the burst flag pulse permit at leasteight complete cycles (see fig. 93) of 3.58 mc.

18-26. Colorplexer. The functions of filtering,phasing, modulating, and mixing, which occur inthe colorplexer unit, are vital to the operation ofan NTSC color system. It is therefore essentialthat you understand these various functions. Toidcntify and relate them. we can use to advantagethe diagram of a colorplexer shown in figure96. Note that inputs are received from the pro-cessing amplifier and the sync generator. Thecolorplexer modifies and combines these inputs tonroduce a composite color video output. ThisJutput signal contains all the frequencies neces--.try to *transmit luminance, color, sync. and

105

2 73

mossyKEYER

3.58 MC BURST SYNCFLAG

INPUTS FROMSYNC GEN

COMPOSITEmopyloE0

OUTPUT

blanking information to a monitor for a color dis-play. Beginning with the B. G, and R signal in-puts, we will investigate the manner in which thecomposite color video output is obtained. Thefacts discussed concerning compatibility andcolor perception underlie the design and opera-tion of this unit. We suggest, therefore, that youreview these facts if you have difficulty follow-ing our explanation. We will not attempt to delve

into the mathematical aspects of color signal for-mation since this is not necessary to convey the

principles and processes involved. A detailedtreatment of this subject can be found in TO31S4-1-1A and numerous commercial publica-

tions.18-27. Matrix and filter sections. The three

inputs from the processing amplifier are the pri-mary color signals that originate at the colorcamera. These signals (B, G, and R) are appliedto the matrix section of the colorplexer (see fig.

96). This section combines the primary colorsignals to produce the luminance (Y) signal andtwo color signals (I and Q). This is done byresistance networks and phase inverters. In fig-ure 97 we have illustrated an arrangementwhereby the proper proportions and polarities ofthe primary color signals are obtainedlo producethe desired Y, I, and Q outputs. For simplicity,let's assume that the color camera is picking uppure white light. In this case, the B, G, and R

S R

O 0 ?

PHASEINVERTER -NMAM

1111=r PHASEINVERTER

I PHASEINVERTER

= .1,13 + .59G 4 .30R

RI

-.320 - .28G + .60R

R2

0 .= .310 - .52G > .2IR

R3

Figure 97. Colorplexer matrix circuits.

signal inputs should all be of equal. amplitude.We know, however, that because of the percep-tive characteristics of the human eye, white is notseen unless the proportions of the primary huesare 11 percent blue, 59 percent green, and 30

percent red. Since Y is the white signal. it musthave these proportions; thus. Y = .11130 + .590

.30g as shown. Note how this i% accom-plished by voltage divider circuits. The resistorsconnected ,to the B. 0. and R lines differ invalue, of course: so the proper amount of eachsignal is developed acros the common outputresistor R I. Similarly, the I and 0 signals aredeveloped across 112 and R3. respectively. Adifference is that the T signal has two negativecomponents and the Q signal has one. Conse-quently. phase inverters arc placed in the B andG divider circuits of the matrix, and in the 6divider circuit of the 0 matrix. As you ean see.the color signals are I = .32B .280 +.60R and 0 = .31B .526 + .21W Boththe I and 0 signals arc zero if the camera ispicking up pure white light as we assumed. Forexample, suppose thc B. G. and R inputs to thematrix are each lv (equal for white light). Sub-stituting lv for B. G. and R in the expression forI ahd Q. we get I = 0 and 0 = 0. However.if any cokred light is being picked up. there willbe an 1 or 0 signal or both.

18-28. The I color signal is obtained fororangish hues. and t!?e 0 color signal is obtainedfor bluish-red (magenta) hues. We should men-tion here that I and 0 can have a negative polar-ity. For bluish-green (cyan ) hues. a -I signal isobtained; for yellowish-green hues, a 4) signalis obtained. Figure 98 shows thc values and po-larities for I and Q signals of fully saturated pri-mary and secondary colors.

GREEN

1

1

1

4

[YELLOW RED MAG-ENTA BLUE

.60

-.28

-.52

r

.21

.28

-.32

.52

011=111/0 0.11111.

CYAN i I

C-

-.60

Figure 98. 1 and Q sienals for primary and secondary colors.

106

27 4

REFERENCECARRIER 4-00

40

.63R

90°

+ 0

Figure 100. Vector diagram of color signals.

lationships of the inpuu. Therefore, the I modu-lator's output contains the I color information assideband frequencies. Likewise, the Q modula-tor's output contains the Q color information assideband frequencies. Bear in mind, however,that modulated I and Q outputs are 900 out ofphase with each other.

18-32. Mixer section. Refer again to figure96 and note the inputs to the mixer. This sectioncombines the luminance, color, and sync infor-mation to form the composite color video outputthat is transmitted.

18-33. Figure 101 illustrates the signal devel-opment for the indicated color elements. Highsaturations of red, blue, green, and yellow areconsidered to be 100-percent saturated colors.Those saturations of green and yellow are con-sidered as 50 percent saturated colors. Theshaded areas of the three camera signal outputwaveforms (B, C, and D) t4present the whitecomponent of the 50 percent saturated green andyellow.

2 708

1800-01.

18-34. By applying the formula Y = .30R+ .11B + .59G to all three camera tube outputsignals for any one color, the Y signal waveformat E will be developed. When applied to a black-and-white receiver, this video waveform willrepresent the brightness charactristic of the colorelements illustrated.

18-35. The I signal is developed by applyingthe formula I = .60R + .32B .280 to thethree camera signal output waveforms for anycolor. Similarly, the Q signal for the illustratedcolor elements can be developed by application ofthe formula, Q = .21R + .31B .520. TheI and Q signals, combined in quadrature, formthe chrominance signal; the signal phases andamplitudes for the illustrated colors are indicatedat H. The high saturation of green. for example,has a chrominance signal amplitude of .59 at acertain phase. The amplitude and phase are de-termined by the amplitudes of 1 and Q pro-duced for the green.

, --18-29. From the matrix section, the Y. I, and

0 signals go to a filter section. Recall that thebandwidth requirement is different for each ofthese signals (refer to fig. 92). We explainedearlier that the bandwidths are based on the eye'scolor-detecting characteristics. As the imagebecomes smaller, the eye fails to detect coloraccurately until color is not perceived at all.

Thus. color signals can have comparatively nar-row video bandwidths; the Q signal having thenarrowest. from 0 to 500 kc. Since the Q signalis delayed most by its filter. it is necessary to in-sert an additional delay following the I filter andeven more delay following the Y filter (see fig.96). It is important that these delays be correct.Otherwise, the signal relationships will not be

proper and color distortion results.18-30. Modulator section. Observe in figure

96 that the I signal is fed into a doub:y balancedmodulator which has a 3.58-mc input. The sameis true for the CI signal. Note, however, that the3.58-nic input to the Q channel is delayed 90°

more than the 3.58-mc input to the I channel.Note also that the 3.58-mc is received, via anadjustable phase shifter and 57° delay, from thesync generator. The adjustable phase shifter cir-cuit makes it possible to align the 3.58-mc inputto the standard reference, which is shown in fig-ure 99 as 0°. This figure illustrates the phaserelationships of the I and Q signals to the colorcarrier and to each other. The outline of thechromaticity diagram and the FCC color triangleare shown so that you can see the range of huesand saturations that are encompassed by the Iand Q signals. A more complete vector diagramis shown in figure 100. This diagram can be cor-related with figure 98 and also with figure 99.

18-31. We mentioned previously that the Iand Q signals are each sent to a doubly balancedmodulator. This type of modulator develops an

amplitude-modulated output that containsneither of the input signals.--The output does

nonetheless contain the sidebandfrequencieswhich depend upon the amplitude and phase re-

COLOR CARRIERREFERENCE

0°

Figure 99. Position ot 1 and Q vectors on chromaticity diagram.

107

2 7

2(40c

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18-36. Note that the pale green chrominancesubcarrier vector has not changed in phase fro:,1the hiehly saturated green, but is merely reducedin amplitude in order to convey the effect Of re-duced saturation. Comparison of the chrorni-nance signal envelopes for the two saturations ofgreen at I show the amplitude difference due tosaturation change. When combined with thebrightness signal at J. however. the two compositesignal waveforms have little total difference inamplitude for the two greens, but the briehtnesscomponent of the low saturation oi green isgreater than that for high saturation of the samecolor. Note that the chrominance signal chancesphase as hue changes, and amplitude varies assaturation varies. Au ...:brominance signal ampli-tude is reduced for the same hue, the correspond-ing brightness signal will increase.

18-37. Figure 102 indicates the video modu-lation for one horizontal scanning line containingfully saturated primary and secondary color bars.The figures at the left of the chart ind:cate per-centages of modulation. The brightness signal foreach bar is the a-c axis of each chrominance sig-nal, forming the stairstep pattern from black to

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white. The video swing frorn black to white isshown at its maximum tolerance. withmwhite at10-percem modulation. This provides a contrastrange from 70-percent modulation to 10-percemmodulation. or 60 perent ot the total m,dulationenvelope. Black. then. represents 0 percent ofthis 60-percent range. The brightness sigmd forthe colors, from left to right, represents the fol-lowing percentaees of this 60-percent range ofcontrast: blue, 11 percent; red. 30 percent: ma-genta, 41 percent; green. 59 percent; cyan. 70percent; yellow, 89 percent; white 10(1 percent.The green. cyan. and yellow chrominance signalsovershoot zero modulation. with yellow repre-senting maximum modulation overshoot. Sincefully saturated colors are rarei) telecast. how-ever this condition is unlikely to occur.

18-38. The inputs from the sync genek.ator areadded in the mixer section. Figure W2 showsthe presence of the horizontal blank. horizontalsync, and color sync burst. Remember that thesync signal input also includes the pulses for ver-cal blank and sync. These pulses have the samewaveforms as those for the standard monochromesignal. The horizontal sync pulses occurring dur-

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ing vertical blankintz time will each be followed

by a color sync burst. This, of course, insurescok)r synchronizadon before the vertical blankterminates and the picture begins.

9. Color Monitors19-1. Color monitoring equipment can be di-

vided into two classes: (a) three-input monitorsfor viewing the color signals as they leave thecamera chain and (b) single-input monitors forviewing the composite color sienal from thecolorplexer or. in the ease of closed-circuit sys-tems. for use as receivers at remote points. Figure103.A. is a simplified block diagram of a three-input monitor. As is apparent from the blockdiagram. these monitors consist of three identicalvideo amplifiers (one for each of the red. green.and blue channels). Of course. deflection andconvergence circuitry. a tricolor kinescope, and apower supply are used. This type is generallyconsitlerral as test equipment. Figure 103,B, is

2 7

TRI-COLOR

KINESCOPE

the simplified block diagram of a typical single-input color monitor of the type generally used asremote receivers in closed-circuit systems. This

type of monitor is designed for continuous oper-ation and uses circuits that are adaptable asclosed-circuit system receivers where severe op-erating conditions are a factor.

19-2. Figure 103 does not show circuits orfeatures common to a monochrome monitor.Such functions as sync separation, scanning, andd-c re3toration are accomplished in the sameways br color monitors as for monochrome types.The three-input color monitor amounts to threevideo channels, one for each primary color sig-nal. The single input monitor, however, incor-porates a number of features that are unique. Wewill therefore give our attention to this lattertype monitor. Moreover, we will describe the de-modulation and matrixing method that is em-ployed to attain maximum color fidelity in acompatible system (see fig. 104).

. 19-3. Luminnnee Section. Although the lum-inance section corresponds to the video section ofa monochrome monitor, there is a differenc.c thatis shown in figure 104. The Y delay unit isplaced in this section so that the luminance sig-nal will have the proper time relationship withthe chrominance signal when it arrives at thematrix section. The Y delay Must be equal tothe delay caused by the chrominance bandpassfilter in the demodulation section. This is impor-tant since, as we mentioned earlier, incorrecttime relationships will cause color distortion.

19-4. Preceding the second video amplifier isa brightness control (not shown), which is iisedto adjust the d-c reference and thus the overallpicture luminance. A contrast control.is locatedin the video output stage just as in a monochromemonitor.

19-5. Burst Control Oscillator Section. Beforethe chrominance signals can be detected, it'snecessary to reinsert the 3.58-mc color referencesignals. A 3.58-mc signal is generated in theburst control oscillator section by an afc crystaloscillator. Since the locally generated 3.58-mc

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1Y-6. The input to the bur.it amplifier comesfrom the first video amplifier. Observe thatthere is another input to this section v.hich goesto a keyer. circuit. The keyer is triggered by apulse from the horizontal output stage. Such anarranuement acti%ates the burst amplifier so thatit pases the color burst sync to the phase dctector. The other input to the phase detector is sup-plied by the local 3.58-me oscillator. As youknow, the phase detector produces a d-c poten-tial (error voltage) if the inputs differ in phase.The error voltage is applied to a reactance con-trol circuit (such as a reactance tube amplifieror varicap semiconductor diode), which regu-lates the oscillator frequency. Thus, the 3.58-mc oscillator output is kept in phaSe with the3.58-me color burst sync signal.

19-7. To establish the proper phase relation-ships for demodulatine the 1 and 0 signals. the3.58-mc signal is dela;.ed 90 before reachingthe 0 demodulator. We will discuss shortly why

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19-8. Another output from this section is de-rived from the phase detector and applied to thecolor killer. Like the error voltage. this outputis a d-c potential. It is used to effectively blockthe video input to the chrominance demodulatorsection.

19-9. Chrominance Demodulator Section. Re-ferring to figure 104. you see that the video inputto the chrominance demodulators goes first tothe bandpass amplifier. Another input to thisamplifier comes from the color killer. The colorkiller is nothing more than an amplifier thatgates the bandpass amplifier when a color videosignal is received. On the other hand, the colorkiller biases the bandpass amplifier to cut offwhen a monochrome signal is received. The op-eration of the color killer is dependent upon thed-c potential developed by the phase detector. Ifa color video is present, there is a color burstsync signal applied to the phase detector, and ad-c output voltage to the color killer is produced.Thus, the color killer only gates the bandpassamplifier when color burst sync is detected. Sincea monochrome video signal does not have thecolor burst sync, the burst is not detected andthe color killer cuts off the bandpass amplifier.Simply stated, the color killer kills color when amonochrome signal is received. It prevents colornoise from appearing in the black-and-white dis-play.

19-10. For a color sipal input, the bandpassamplifier filters and boosts the gain of the chro-minance signal which is sent to the I and Q de-modulators. These are synchronous demodula-tors. This type of demodulator is phase selective.It functions much like an electronic switch, de-tecting the amplitude of one input at'the peak ofthe other input. For example, the I demodulatordetects the amplitude of the input chrominancesignal each time the input 3.58-mc signal reachesits peak. Since the 3.58-mc signal is in phasewith the 3.58-mc reference color carrier, this de-modulator detects the amplitude of only the I(in phase) component. In other words, the 3.58-mc carrier is reinserted so that only the I colorinformation is detected. To obtain the Q colorsignal, it is necessary to reinsert the 3.58-mcsignal in quadrature (90° out of phase) withthe reference signal. In figure 104, note that the3.58-mc input is delayed 90° before reaching theQ demodulator. Consequently, the Q demodula-tor detects the amplitude of the Q (quadrature)component of the chrominance signal. By thistechnique. it is therefore possible to extractseparately the I and 0 color information from thechrominance signal.

113t 281

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19-11. The outputs of both the I and Q de-modulators are sent to phase splitter amplifiers.This is done because +I and I as well as.+Q and Q signals are needed to develop theprimary B, G. and R signals within the matrix.section.

19-12. Matrix. Section. The matrix section'combines the inputs from the chrominance de-modulator section ( +I, I, +Q, and Qnals) with the Y signals from the luminance sec-tion in the proportions required to produce B, Giand R signals. Figure 105 illustrates the resis-tance network that can be employed to combinethe prescribed amount of each input. Note infigure 104 that the I (cyan) signal is appliedto the blue matrix and the green matrix, whereasthe +I (orange) signal is applied to the red matrix. Also, the Q (yellowish-green) signal isapplied to the geen matrix, whereas the +Q(magenta) signal is applied to the blue matrixand the red matrix. The algebraic expressions,given in figure 105 for the B, G, and R signals'specify the polarities and amounts of the Y, I,and Q signals that comprise the output of eachmatrix.

19-13. Obviously, the resistance matrix net-works are similar to those described when wecovered the colorplexer. It should be pointsd.out, however, that the B and G outputs are madeadjustable. This is done so that these outputs

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can be adjusted to compensate for the luminancedifferences of the three phosphors in the tri-color kinescope. Since the red ph9sphor pro-duces the lowest luminance, thered output isordinarily the fixed reference to Which the blueand green outputs are adjusted. This is com-monly referred to as the temperature adjustment.Color temperature describes the color quality oflight. The "hotter" the color temperature, thewhiter the light; the "colder" the color tem-perature, the yellower the light. As you wouldexpect, the adjustments are made to producehot light (white as possible) for a white testsignal. More will be said about these adjust-ments later.

19-14. The output from each matrix is ampli-fied to the level needed to drive the tricolorkinescope. D-c restoration is accomplished se-parately for the B, G, and R signal outputs sincethey differ when color video is rervived. Theamplifiers and d-c restorers are shown in figure104 to be units within the matrix section. Theoutputs from this section are coupled directly tothe grids of the tricolor kinescope.

19-15. Tricolor Kinescope. The principal partsof the tricolor kinescope are illustrated in figure106. In the same figure there is an enlargedview of the phosphor dot viewing screen, theshadow mask, and the three-electron gun as-sembly. This is inclosed by the glass envelope

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1-,nd external shield. When you know the tricolorkinescope construction, you will underftand whyalignment and adjustment of the three beams iscritical.

19-16. Phosphor dot viewing screen. Thephosphor dot viewing screen will be referred tofrom here on as the color screen. Amoung thefundamental distinctions between the color tubeand the monochrome tube is the difference inphosphor materials. In monochrome a uni-form phosphor coating is used; however, thecolor screen (see fig. 106) is composed of anorderly array of small closely spaced phosphordots. These dots ar c. arranged in triangulargroups, or trios, accurately deposited in inter-laced positions on a glass surface. Each trio ofdots re- -esents the three primary colorsblue,green. A red. Although the color dots areseparate, they are close enough to meet resolu-tion requirements by glowing their respectivecolors when bombarded by electrons. Thebrightness of each dot depends on the strengthof the electron beam striking that dot.

19-17. Shadow mask. The shadow mask(see fig. 106) is a thin metal plIte of super-nickel alloy located between the rnosphur dotscreen and the electron gun assembly. It hasapproximately the same curvature as the colorscreen; the monochrome tube dces not have acomparable element. The shadow mask has

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114 282

AOUAOAGCOATING

several thousand holes, one for each trio ofphosphor dots. These holes are spaced and thehole edges are beveled so that an equal hole ispresented to the beam for any angle of beam.deflection. Thus, the shadow .mask providescolor, separation by shadowing two of the threedots from two of the three electron beams whileexposing the proper dot to bombardment bythe correct beam. Therefore, three beams fromthe three guns converge at the hole in themask, the beams pass through the hole, diverge,and strike the respective red, green, and bluephosphor dots.

19-18. Electron guri. The three-gun assem-bly, shown in figure 106, is made as one unitand is mounted in the neck of the picture tube.The three electron guns are approximately par-allel to each other with a very slight tilt towardthe central axis of the tube. The guns are 120°apart and are so small in diameter that theslight tilt causes the three beams to converge atthe shadow mask. Some static convergencecorrection will be necessary for final adjustment.

19-19. Each of the three guns consists of afilament, a cathode, control grid, acceleratorgrid, focusing anode, and ultor anode. The ultoris the electrode in the gun to which is appliedthe highest voltage prior to deflection. Thehighest voltage in the tube is applied to theaquadog coating.

19-20. Glass envelope and external shield.The glass envelope (see fig. 106) of the colorkinescope is the same as for the monochrome,with the possible exception of shape. The shapeof the color tube is changed to accommodate theshadow mask and the three electron gun as-sembly. This means the front is extendedslightly for the shadow mask, and the neck ofthe tube is larger in diameter for the electrongun assembly. The neck of the color tube islonger to accommodate the accessories whichinclude the convergence assembly, blue lateralmagnet, purifying magnet, color equalizer as-sembly, and deflecting yoke.

19-21. The metal shield placed around thebell portion of the tube shields the electron beamfrom stray magnetic fields. In some monitorsthat have metal cabinets, the shield is not nec-essary. In the early versions of this tube, theshield was an internal part of the tube. Thisimprovement over the early models is indicativeof the trend in refinements of color kinescopes;doubtless, there will be many more.

19-22. Maintenance Requirements. The main-tenance requirements for color monitors arenecessarily more involved than those of mono-

28,,

273chrome monitors. Alignment and adjustmentprocedures are provided by the manufacturer Ofa specific color set. Because of the similaritiesin the basic design of monochrome and colorTV monitors, adjustments such as height, width,linearity, etc., are practically the same; Theseadjustments were discussed in Chapter 5; there-fore, we will consider only important adjust-ments peculiar to the color monitor in the follow-ing parawsphs.

19-23. Since equipment design varies, we willcover only those functions common to colorTV monitors in general. For a more extensivecoverage of this area, you can refer to TO31-1-141.

19-24. Convergence. Two types of control,static and dynamic, are developed in the con-vergence circuits of a color TV monitor. Staticconvergance is a steady control. It is accom-plished with a d-c voltage to cause convergencein the center portion of the display. By con-trast, dynamic convergence is a varying conuol.It is accomplished with a parabolic voltagewhich primarily affects the outer edges of thedisplay. The combination 'of these two controlvoltages is used to align each electron beamwith its respective series of phosphor dots. Whenall three electron beams are properly aligned, awhite trace should be produced on the face ofthe kinescope.

19-25. A simple observation can be made todetermine whether static and dynamic conver-gence adjustments are proper. With video in-formation applied to the monitor, mmmine theedges of the objects. If you can distinguish oneor more definite colors, convergence needs ad-justment.

19-26. Purity adjustments. Purity describesthe accuracy with which an individual electronbeam strikes its own series of phosphor dots.When an eiectron beam overlaps . its dots andpartially strikes the dots of another color, huesof colors are noticeable. An evmination of theouter edges of the kinescope will divulge anycolor impurities. Purity adjustments will be nec-essary if color hues are apparent.

19-27. Temperature adjusiments. Tempera;ture denotes the correct combination and in-tensity of colors from the matrix system to pro-duce a white balance, hot light. Deflects intemperature adjustment can be readily detectedun the face of the kinescope. By rotating thebrightness control through its 1full range, deter-mine if the background changes to any color hueor range of hues. Should the backgroundchange, temperature adjustments will be neces-sary

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30455 01 21

WORKBOOKEquipment Maintenance

CRP- Iika-IMANG 41p5 11-41)\11

SRG

This workbook places the materials you need where you need them while youare studying. In it, you will find the Study Reference Guide, the Chapter ReviewLxercises and their answers. and the Volume Review Exercise. You can easilycompare textual references with chapter exercise items without flipping pageshack and forth in your text. You will not misplace any one of these essentialstudy materials. You will have a single reference pamphlet in the proper sequencefor learning.

These devices in your workbook are autoinstructional -aids. They take theplace of the teacher who would be directing your progress if you were in aeiassroom. The workbook puts these self-teachers into one bookkt. If you willfollow the study plan given in "Your Key to Career Development." which isin your course packet. you will be leading yourself by easily learned steps tomaqcry of your text..

If you have any questions which you cannot answer by referring to "YourKey- to Career Development** or your course material. use ECI Form 17. StudentRequest for .Assktance.- identify yourself and your inquiry fully and send it to

Keep the rest of this workbook in your files. Do not return any other partof it to ECL

EXTENSION COL RSE INSTITUTE

Air University

286

-ne

TABLE OF CONTENTS

uidy lIch:Ivace Guide

Ch;Apter R. iew xerckes

Fxerk:kes

\ ohmic Revie\%

EU Form No. 17

287

217

STUDY-REFERENCE GUIDE

1. Use this Guide as a Study Aid. It emphasizes all important study areas of this volume.

2. Use the Guide as you complete the Volume Review Exercise and for Review after Feedbackon the Results. After each item number on your VRE is a three digit number in parenthesis.That number corresponds to the Guide Number in this Study Reference Guide which showsyou where the answer to that VRE item can be found in the text. When answering the items in

your VRE, refer to the areas in the text indicated by these Guide Numbers. The VRE resultswill be sent to you on a postcard which will list the actual VRE items you missed. Go to your VREbooklet and locate the Guide Number for each item missed. List these Guide Numbers. Then goback to your textbook and carefully review the areas covered by these Guide Numbers. Review theentire VRE again before you take the closed-book Course Examination.

3. Use the Guide for Follow-up after you complete the Course Examination. The CE results willbe sent to you on a postcard. which will indicate "Satisfactory" or "Unsatisfactory" completion.The card will list Guide Numbers relating to the questions missed. Locate these numbers in theGuide and draw a line under the Guide Number, topic, and reference. Review these areas toinsure your mastery of the course.

GuideNumber Guide Numbers 100 through 123

100 Your Career Field and Specialty, pages 1-5

101 TV in the Air Force: General; Mission ofDepartment of Defense; Mission of Mainte-nance Unit; Advantages of Television; In-struction, pages 5-9

102 TV in the Air Force: Security; Traffic Con-trol; Surveillance; Weather Service; Haz-ardous Monitoring; Command Assignments,pages 9-13

103 TV Systems, pages 13-16104 Introduction to Power Supplies; Power Re-

quirements; Low-Voltage Power Supplies:General; Rectifier Arrangements andCharacteristics, pages 17-21

105 Low Voltage Power Supplies: Voltage Reg-ulators, pages 21-27

106 Low Voltage Power Supplies: Constant-Current Regulators; Symptoms and Trou-bies; High-Voltage Power Supplies: Gen-eral; Voltage Multipliers. pages 27-31

107 High Voltage Power Supplies: Pulse andOscillator Types; Symptoms and Troubles.pages 31-33

108 Introduction to Sync Generators; Noninter-lace Sync Generators, pages 34-36

109 Interlace Sync Generators: Requirementsfor Interlace; Random Interlace Type.pages 36-43

GuideNumber

110 Interlace Sync Generators: Standard Inter-lace Type. pages 43-48

111 Introduction to the Camera Chain; Cam-eras; Image Orthicon Cameras. pages 49-57

112 Camera Control; Switchers and Video Am-plifiers: General; Switches, pages 57-62

113 Switches and Video Amplifiers: Video Am-plifiers. pages 62-65

114 Introduction to_ Monitoring Facilities; Mon-itors. pages 66=73

115 Master Monitor, pages 73-77116 Introduction to the Audio 'System; Micro-

phones, pages 78-83117 Audio Amplifiers: General; General Char-

acteristics; Preamplifiers. pages 83-88118 Audio Amplifiers: Driver and Power Am-

plifiers, pages 88-92119 Audio Consoles. pages 92-95120 Introduction to Color Television; Applica-

tions and Requirements. pages 96-101121 The Camera Chain: Cameras: Camera

Controls; Processing Amplifier. pages 101-104

122 The Camera Chain: gync Generator: Col-orplexer. pages 104-111

123 Color Monitors. pages 111-115

CHAPTER REVIEW EXERCISES

1. In solid state symbols, what do the arrow-heads indicate? (4-9)

2. What is 'the conductivity of a material de-pendent upon? (4-10)

3. Why are impurities added to semiconductormaterial? (4-10)

4. Why is the depletion region represented by a

6. Explain thermal runaway. (4-12)

7. What happens to the barrier potential whenreverse bias is applied? (4-13)

8. What is the result of applying an a-c signalto a diode? (4-14)

9. What is the main difference between a nor-mal diode and a Zener diode? (4-15)

10. How is a power gain achieved in a transistor?(4-16)

11. In which direction is a base-collector junctionbattery? (4-11 ) normally baised? (4-17)

5. What is the polarity arrangement of the ex-ternal battery and barrier potential for for-ward bias? (4-12)

12. What is the polarity of the emitter and col-lector with respect to the base in a forwardbiased n-p-n transistor? (4-17)

28j

?7

13. What do the letters designate in transistor configuation titles? (4-18)

14. How is the common emitter amplification factor represented? (4-19)

15. What determines whether a unijunction is conducting at a high- or

low-level state? (4-21)

16. What is the value of anode voltage required to trigger an SCR called?(4-22)

17. How can the forward breakover point be controlled? (4-23)

MODIFICATIONS

Page 3 of this publication has been deleted in adapting this material

for inclusion in the "Trial Implementation of a Model System to Provide

Military Curriculum Materials for Use in Vocational and Technical Education."

Deleted material involves extensive use of military forms, procedures,

systems, etc. and was not considered appropriate for use in vocational and

technical education.

6 5'0

28, The better the quality desired in a picture.

CHAPTER 2

Objectives: To demonstrate (1) knowledges inpower supply requirements for TV systems and(2) skill in troubleshooting these systems.

1. Three major factors that will affect thepower supplies needed for a TV system are:(1) the of equipment.. (2) the

of the equipment. and (3) the ..within a particular equipment. (4-3)

2. Match the most appropriate power supplrequirement in Column B to the compo-nents in Column A by writMg the Apha-betical designator in the blank.Column A

Cameratube.

2. Picturetube.Receivertube.

4. Transistor.

PAGES 282 & 283 ARE MISSING DUE TO MISNUMBERING.

4

291

a. Regulated 3()o\h. Regulated 400c. Unregulated I 7.()(H tv

Unregulated 5.Regulated I 5v

II

3. Identify the three basic low-voltage rectifiercircuits. (5-2)

4. If the effective secondary voltage is 200volts a-c at 60 cps, the approximate out-put of a full-wave bridge rectifier will be

d-c volts with a ___-cps ripplefrequency. The diodes must withstand apeak-inverse voltage of about volts.(5-3; Fig. 10)

5. What is .:he ripple frequency of any three-phase full-wave rectifier? (5-4; 10; Fie. 13)

6. If load current decreases for the regulatorcircuit shown in figure 16.A. what will hap-pen to the current through: (1) the tran-sistor and (2) the series resistor? (5-15)

7. If the input unregulated voltage V in fig-ure 17.B. increases, what will happen to theforward bias applied to the transistor andwhy? (5-23. 24)

8. For the circuit shown in figure 17.C, an ad-justment upward on R3 causes Q2 to con-duct (more. less); thus the drop across QIwill (increase, decrease) and VI; will (in-crease. decrease). (5-25-28; F12. 17)

9. If the voltage adjust shown in figure 18 ismoved downward, what will happen to thepositive potentials at the following points?(Answer: increase, decrease, no change)(5-30-33)a. Base of Q2b. Emitter of Q4c. Collector of Q4d. Base of Q3e. Collector of Q3I. Base of Q7

10. As a result of an output load current in-crease in switching regulator circuit (fig.19). transistor Q conducts (more, less),gate pulses are (advanced, delayed), andthe conduction time of the SCR's is (in-creased, decreased). (5-35-37)

11. When the output adjust R2 in figure 22 ismoved upward, transistor Q2 conducts(more, less), thereby causing an (increased,decreased) regulated current to be deliveredto the load. (5-41)

12. Using the circuit of figure 9,C, match thesymptoms with the most probable trouble.(5-42-46)

Symptomsa. Reduced output.

no overheating60-cycle ripple.

b. Reduced output.120-cycle ripple.

c. Reduced output.heat, 60-cycleripple.

d. No output.

5 29-'4

Trouble_ I. Open rectifier._ 2. Shorted rec-tifier._ 3. Open ca-pacitor._ 4. Leaking ca-pacitor._ 5. Open trans-former.

pig"

13. The conventional voltage doubks shown infigure 23 has a sinusoidal volt4e across itssecondary of 400 volts rms at 500 cps.Determine the following: (6-5. 6)

a. Output voltage d-c volts (approxi-mately).

b. PIV on diodesc. Charee per capacitor d-c volts

(approximately).d. Ripple frequency ____ cps.

14. If a peak voltage input of 150 volts is ap-plied to the cascade multiplier circuit in fig-ure 25,A, the d-c voltage at point c is

volts and at point f is volts. (6-12)

15. The cascade multiplier circuit shown in fig-ure 25.B, draws input current only on the

alternation. 6-13)

16. State two advantages of a flyback HV sys-tem. (6-17, 19)

17. Sketch a flyback HV system havine a boostvoltage developed from a secondard wind-ing. (6-17)

,18. Referrine to the HV reeulator circuit shownin figure 27.A. and assuming the load volt-

6

age tends to increase. indicate vhether thevoltage becomes more positive, less positive,more negative, less negative, or remainsthe same at the following points: (6-21-23)

a. Plate of Vb. Plate of V4c. Suppressor grid of V/ .. .

d. Screen grid of V/e. Control grid of V/I. Ungrounded side of C3 _

19. When the voltage adjust in figure 27.13, ismoved toward ground. the conduction tuneof Q1 How does this affect theHV output? Is the firing frequency of theSCR affected? (6-24-27)

20. It is reported to you that the picture andraster on a monitor suddenly disappear. Af-ter making all visual checks and everythingI filaments. fuses. and connections 1. looksnormal what check is made next'? ( 6-30.31 )

21. Suppose the HV of figure 27.A. is unstableand higher than normal. What compo-nent(s) under what condition (5 ) wouldgive these symptoms? ( 6-34. 35

24)5

in:7)

CHAPTER 3

Obiectives: ) Demonstrate knowledges of the 7. he section. shown in

operation, adjustment and repair of sync genera- figure 30. narrows the vertical pulse for

tors and ( 2) exercise skill in the use of sche- vertical sync. (7-7)

matic diagrams.

I. Name three basic sections of a simple non-interlace sync generator. (7-2)

2. State why there is no need for a tie-in be-tween the vertical oscillator and horizontaloscillator in a noninterlace system. (7-3)

3. What sections supply the inputs to theblanking mixer of the simple noninterlacesync generator? (7-2. 3)

4. What outputs does the horizontal oscillator

provide in a simple noninterlace system?

(7-4)

5. In the simple noninterlace sync system offigure 29. adjustments for a distorted verti-cal scan can be made in thesection. (7-5)

6 What is the purpose of a squarer andpeaker section in the multiple-pulse nonin-terlace sync generator? (7-7)

8. For the multiple-pulse sync system de-

scribed. the 833-ysec horizontal sync pulse

is developed by the section from ahorizontal pulse of. about -ysec dura-tion. (7-8, 9)

.9. Indicate whether the sections shown in fig-ure 30 depend upon the vertical oscillator(vo), horizontal oscillator (ho). both, orneither for proper operation. (7-7-10)

a. Blanking mixerb. Vertical drivec. Squarer and peakerd. Sync mixere. Horizontal blank

10. Sketch the waveforms ot blanking mix andsync mix showing their time relationships.(7; Fig. 31)

11. If the vertical blanking pulse is 850 yseclonger than vertical sync, how many 16-7-

kc horizontal syncs will appear during ver-tical blank? (7-9)

12. If the vertical blanking and drive pulses ofthe multiple-pulse noninterlace sync genera-

7

2 9,1

.46(p

tor (fig. 30) are too wide, what section 19. How can the stability of a bloiking oscilla-needs adjusting first? (7-10, 11) tor counter be improved? (8-7)

13. Referring to figure 11, in what section is 20. Why is the phantastron counter a reliablethere probably trouble if the horizontal type? (8-8-12)pulses of the mixed blanking output are toonarrow, but H drive is normal? Why?(7-11)

14. Why must the ratio of horizontal to verticalscan in an interlace system be constant?(8-2)

15. The standard lines per field for interlacein this country arc (8-2)

16. Identify four basic sections of an interlacesync generator. (8-3)

21. Referring to figure 35, what is the cathodepotential when, plate current is cut off? ( 8-8-10)

22. Draw and label the block diagram of arandom interlace sync generator having afcand crystal control. (8-13)

23. What will result if the time difference be-tween the last horizontal pulse and the ver-tical sync/blank is H instead of alternatelyH and 0.5H as illustrated in figure 37? (8-14, 16)

17. The 525:1 counter section divides the mo 24. The absence of during ver-pulses to obtain sync and blank tical blanking can cause random interlace.timing. (8-4)(8-16, 24)

18. List three commonly used counting circuits. 25. For calibration of counters using thc mo,(8-6)the aft; switch is put in the _ position.(8-20. 21)

8

26. In what order should you calibrate thecounters in a counter chain? Why? (8-21)

17. Match the signals identified in Column B 29.to the function stated in Column A. (8-24-27)

Column AI. Maintains proper a.

horizontal syncduring vertical sync b.time._ 2. Insures precise tim- c.ing of the vertical d.scan._ 3. Maintains properhorizontal sync im-mediately beforeand after verticalsync._ 4. Provides verticalsync.

Column BEqualizingpulse.Serratingpulse.3H pulse.Horizontalsync.

28. The time between the start of vertical sync

and the edge of the first serrationis set to equal 0.5H. (8-26)

WhatHowtive?

is the function of the notching section?would you know when it is inopera-(8-29)

30. Why is the 9H section needed to form thestandard sync waveform? (8-31)

31. Refer to the block diagram (fig. 41,A) anddetermine in which section(s) there is prob-ably trouble if five equalizing pulses recordsprecede vertical sync and seven follow;everything else is normal. (8-33; Fig. 41)

CHAPTER 4

Objectives: (1) To demonstrate knowledges ofthe function and operation of the vidicon andimage orthicon cameras and (2) to show skillin the care. troubleshooting. and repair of thecamera chain elements.

1. Give the dimensions for the standard vidi-con tube. _ inch(es ) in diameter and

inch(es) long. (9-3)

1. Skctch a vidicon tube and indicate the face-plate, signal output terminal, and electrongun. (9-3; Fig. 42)

9

3. State the3. 4)

purpose of the electron gun. (9-

4. A bright image focused on the mosaic of avidicon for a long period will cause an im-age (9-5)

5. It (is. is not) necessary to have a lens inplace on a vidicon camera to make initialbeam adjustment. (9-7)

296

6. What equipment and conditions are neces-sary when making final adjustments on avidicon camera to obtain the best picturedefinition? (9-8)

7. Sketch a block diagram of a vidieon camerashowing the pickup and amplifier stages andshow waveform(s) at test points. (9-9;

Figs. 43 and 44)

8. Sketch an image orthicon tube and namemajor elements. (9-11; Fig. 45)

9. State the major construction difference(s)between an image orthicon and a vidiconcamera tube. (9-11. 12)

10. Image electrons are accelerated from the10 photocathode to the where theycause secondary emission. (9-11)

11. To set an 10 tube on its face may causedamage to the due to loose particlesfalling in the tube. (9-15)

12. If you were to choose between a vidiconand an image orthicon camera to use in a

10

24s1low-light level studio, which camerayou choose? (9-17)

13. Write in thc blanks preceding the followingstatements the camera pickup tube pr.:-ferred or is best described by the statement.This will be either a vidicon or image orthi-con. (9-17)

a. Operating cost is approx-imately $0.10 per hour.

b. Average output signal levelis approximat 50 milli-volts.

c. Output signal level is stableover a wide range of lightlevels.Inherent tube nois.: limitsthe signal-to-noise ratio.

e. Fast-moving objects causepicture smear.

f. Requires simpler ernalcircuitry, therefore smallercameras.

14. The proper installation of the bkmer bel-lows will insure proper as air flowwill not be impaired. (9-21)

15. Suppose you are setting up an 10 cameraand you notice that the target voltage needsadjusting. What is the source of target volt-age and where is it adjusted? (9-23. 25 )

16. Sketch a block diagram and sho thewaveforms of the horizontal section of an10 camera. (9-28, Fig. 47)

4-AN

What basic stages comprise each of the 10. What two controls affect the height of thefollowing sections? (12-8; Fig. 59) picture? (12-17)a. Video.b. Sync.c. Vertical.d. Horizontal.

6. Match thc signal described in Column Bto thc circuit in which it is found in ColumnA by placing the alphabetical designator ofColumn B in the blanks provided in Column.A. ( I2-13-24)

Column A Column B1. DC restorer. a. 60-cps sawtooth.2. Horizontal b. 15.750 pps.

oscillator. c. Clamped video3. Damper. composite.4. _ .Afc. d. d-c boost.5. _._ Vertical oscilla*-

tor.c.

f.

Differentiatedsync.60-pps blankiruc.,

7. Briefly explain how the sync sienals areseparated by 03 in fieure 60. (12-14)

11. Blanking at 60 pps is developed from thestage of figure 60. (12-

18)

12. If the horizontal oscillator tended to in-crease in frequency, how would the afcprevent it? (12-20)

13. Besides frequency. what is a noteworthydifference between the horizontal and ver-tical oscillator? (12-22)

14. What control sets the frequency of the hor-izontal oscillator? Where is it located in

figure 60? (12-22)

8. The vertical sync is separated from thehorizontal by means of a/an cir- 15. What circuits in figure 60 could not functioncuit. (12-16) properly if transistor 010 failed? (12-23,

24)

9 In figure 60. the picture height is adjusted 16. If corner shadowing of the picture is evi-at the output of the dent, what adjustrrrent should be made?(12-16) (12-28)

13 2 9 6

eplqo

17. Why are numerous video amplifiers usedin a master monitor? (13-3)

18. How does the horizontal oscillator frequencycontrol in a master monitor differ from thatin a receiver picture monitor? (13-5)

19. Why is a separate high-voltage power sup-ply used in a Master monitor? (13-5)

20. The waveform monitor has a horizontalsweep selection of cps for observingthe vertical pulse waveforms and cpsfor observing the horizontal pulse wave-forms. (13-9)

11.

,;q7

How is sweep expa n accompigished' 1310)

Using the block diagram in figure 63. nia:hthe probable trouble in Column Bthe abnormal display &scribed in ColumnA by writinu the alphatieal desienators otColumn B in the blanks in Column A.(13-14-18)

CHAPTER 6

Objectives: (1) To apply knowledge of the per-formance characteristics of the different typesof microphones; (2) to identify the functionsof an audio control console and audio amplifier;(3) to diagnose troubles from given symptomsby use of schematic diagrams.

1. List the four common types of microphones.(14-1 )

2. Match the type of microphone in ColumnB to the description which describes it.bestin Column A by writing the alphabeticaldesignators of Column B in the blanks pro-vided in Co'iumn A. (14-3. 9. 14 and 16)

14

Column A

Blackraster.

2. White ver-tical line.

3. __ insufficientheieht.

4. _ Top halfwhite.bottomhalf black.

Column

Column B

Horizontal oscillatorfailure.Cathode-to-grid sholin kinescope.Gassy CRT.%%cal: vertical outputamplifier.High-voltage failure.

I. __ Uses carbon grains asa variable resistame.

1 Makes use of fkxingbimorph unit to gen-erate a-c.

3. It has a coil made ofthin metal ribbon at-!ached to thediaphragm.

4. It has two electrode,.one flexing and one

29j

Cr )114 1,,

When ,hoosing a mierophone on the basis

01 one ha\ ing the best frequency range.hieh of the four major types would be

hest.' 1 i4-181

Suppose you have a studio situation in

hiJi a poly directional microphone is pick-

In tip sit.k noise. What adjustment wouldyou mak,: t. eliminate this'? ( 14-19 )

Match the tube configuration listed in Col-umn B to the transistor configuration in

Column A by writing the alphabetical des-ignators of (,'olumn B in the blanks pro-\ ided in Column A. i 15-2)

Ci,lumn A Cohonn B

I . CE. a. Cathode follizmer.

2. CB. b. Grounded cathode.3. . CC. c. Grounded grid.

d. Phase splitter.

6. Briefly compare tubes and 7ansistors withregard to coupling. :Jain. and noise. (15-3. 6. and 9: Fig. %. A )

Using figure 74. determine the voltage. cur-rent. and power gain for a CE amplifier

ing a !OK load resistance. (15-6)

The amplifier gives the highesturrent gains. (15-6)

9. The amplifier gives the highest

voltage gains. (15-6)

10. Hie amplifier gives the highest

power gains. (15-6)

I I. With regard to input impedance in the audiorange. identify the amplifier listed in Col-umn B and match it to the characteristicdescribed in Column A by writing the alpha-betical designators of Column B in theblanks provided in Column A. (15-7)

Column A Cohunn 11

I. Highest impedance. a. CC.2. Lowest impedence. b. CE.3. Most frequency

dependent.c. CB.

12. The noise factor of a transistor varies ( in-

versely. .directly) with frequency in the

audio range. (15-11 )

13. What are the distinctive features of eachof the following: preamplifier. driver, andpower amplifier? (15-8. 20-23)

14. Why can higher efficiency and better fi-

delity be attained with push-pul operation?(15-23)

15 .30'.2

15. For what class of operation should the biason a push-pull amplifier be adjusted foreach of the following: (15-23-29)a. Ma.ximum efficiency ___________.b. Maximum fidelityc. High efficiency and fidelity

16. In figure 83. if class A operation is to beadjusted to class AB. would you increaseor decrease R? Why? (15-28)

17. List the major functional units which are apart of the audio console. (16-2)

18. Mixing action is accomplished by adjustingthe of the various inputs to ac-complish a composite output of the desiredbalance. (16-6)

19. Sketch a signal circuit for microphone nom-her I to program line out (16-9'. Hi!.

20. The program director calls you ;0 sa timeis some background hunt in ins hca..!,.et.What would you check first? I 6-12

21. The output for program audio is set toroiven level on the . _ . (16-1-1)

CHAPTER 7Objectives: (1) To test understanding of theprinciples and requirements of color TV: (21To identify features of a color camera; (3) todemonstrate skill in the adjustment and align-ment of a color camera; and (4) to demonstrateknowledge in the maintenance and troubleshoot-ing of a color monitor.

I. For observing enemy terrain, a good choicewould be TV because it can bet-ter reveal any _ areas. (17-61

16

Use the block diagram in figure SX Anddetermine the most probable source ol trou-ble. Microphone number 3 is in operationon stage and r.icrophone numbers

1 and 2on the floor; the control room operator sasthat he is picking up static wrien he ask.,for a signal boost from the stage micro-phone. The floor microphones are gi% logplenty of sienal and no static. ( 16-18. 191

2. The sensation of colors, other than theprimaries. is achieved in color TV 1-P. moonl2various proportions of . and

7-10 I

3. Identify the properties of color that musthe transmitted to itehk.e color f:Lk'Iit\ I 17'-14

30i

Pq

29 44. The NTSC color broadcasting system re- 9. List some of the major differences between

quires which of the following? (Check those the monochrome and color cameras. (18-2)required.) ( 17-15-19)

a Compatibility of color and mono-chrome.

b _____ Color to use a wider bandwidth.c Color and monochrome both use

AM.d. Chrominance information to be 10. Why is it necessary to divide the light spec-

interleaved with monochrome. trum in the optical system of a color cam-e. _____ Color and monochrome to use the era? ( 18-3 )

same sync waveforms but differentfrequencies.

f The color carrier to be suppressedprior to transmission.

ON,

5. When televising a detailed weather map,what can be done to improve color per-ception? (17-17)

6. What units are found in a color camerachain that are not used in a monochromecamera chain? (17-21)

7. List five requirements of an NTSC colorsystem that are additional to those of astandard monochrome system. (17-21)

8. Draw a block diagram of the NTSC camerachain. (18-1; Fig. 94)

11. What would possibly happen if the opticalorbiter were not operating? (18-4)

12. Which filter(s) are used to balance thelight on the camera pickup tubes. ( 18-7

13. List some of the improvements made inimage orthicons used for color operations.(18-10;

14. Indicate what controls on the camera. theviewfinder, and the camera control panelmake a color system easily distinguishablefrom monochrome systems. ( 18-13-19 )

15. What camera adjustments are made to cor-rect the shape of the red image to make itthe same shape as the ereen image? (18-15)

30217

29516. The image orthicon tube provides signal 21. The burst flag pulses are timed to place the

amplification in addition to its prime func- sync on the back porch of thetion. How can the color camera 10 be ad- horizontal pulse. (18-25)justed? (18-15)

17. State the basic difference (s) in the pream-plifiers used in monochrome and color 10cameras? (18-16)

18. Name the functions performed by the pro-cessing amplifier in a color camera chain.(18-20)

22. Match the frequency listed in Column Bto the signal identified in Column A bywriting the alphabetical designators of Col-umn B in the blanks provided in ColumnA. (18-23-25)

Column A1. Color carrier.2. Burst flag.3. H-drive.

Column Ba. 59.94 cps.b. 31.47 kc.c. 3.58 mc.d. 60 cps.

23. Draw a block diagram of a NTSC color-plexer. (18-26; Fig. 96)

19. From what equipment listed in Column Bdoes the processing amplifier obtain theinputs specified in Column A. Specify bywriting the alphabetical designators of Col-umn B in the blanks provided in ColumnA. (18-21, 22) 24. The color signals that are used for modu-

lation are designated andColumn A Column B each is obtained from a (18-27)

1. _ H-drive. a. Color camera.2. _ Composite b. Contsol panel.

video. c. Sync generator.3. _ B, 0, and R d. Colorplexer.

signals.

20. How do the line and field frequencies es-tablished in the sync generator section of anNTSC color system compare with those ofa standard monochrome system? (18-24)

25. Match the hue listed in Column B to thesignal identified in Column A by writingthe alphabetical designators of Column Bin the blanks provided in Column A. (18-27, 28)

Column A1. __ +I.2. ___ Q.3. + Q.4. + Y.5.

314;

18

Column Ba. White.b. Red.c. Cyan.d. Magenta.e. Orange.f. Yellowish-ireen.

26. Why are the Y and I signals additionally 33. The d-c voltage applied to control the colordelayed? ( 18-29 ) killer is developed by the

(19-8)

27. The I modulated signal is degreesout of phase with the reference carrier andthc Q modulated signal is degrees 34. The color killer cuts off theout of phase with the I modulated signal. when a signal is received. (19-9)

(18-30, 31)

28. What information is contained in the output 35. The I and Q signals are detected bysignal from the mixer of a colorplexer? demodulators. (19-10)(18-32)

29. The chrominance signal changes phase as 36. Why are phase splitters needed in the

changes and varies in amplitude as chrominance demodulator section? (19-11 )varies. (18-36)

30. What sections are essentially different for 37. Color temperature is adjusted by means ofa sinele-input color monitor as compared a potentiometer in the and

to a three-input type? (19-1, 2 Fig. 103) matrix.. (19-13)

31. The luminance section of a NTSC color 38. Match the items in Column A to a func-monitor corresponds to the section tion(s) in Column B by writing the nu-of a standard monochrome monitor. (19-3) merical designators of Column A in the

blanks provided in Column B. (19-15-21)

Column A Column B1. Phosphor a. ._ One of three that

dot. glows a specific2. Trios. color.

32. Draw a block diagram of the burst control 3. Shadow b. _ Triangular grouposcillator section of a NTSC color monitor. mask. that will glow with

( 19-5 ) 4. Hole in three colors.mask. c. _ Shields the screen

5. Three-gun from stray electrons.assembly. d. Permits passage of

t5

30,1

.c.7c=;

Column A Column B 39. How can you determine it con% ergmcc.6. External the converged purity, or temperature adjustment are ne,.-

shield. beams. essary? i 19-22-27.)e. Provides three elec-

tron beams.f. Provides protection

from stray magneticfields..

20

ANSWERS FOR CHAPTER REVIEW EXERCISES

d41/4?ANSWERS FOR CHAPTER REVIEWEXERCISES

I. .1he direction of conventional current flow.(4-9)

2. The number of free electrons available in thematerial. (4-10)

3. To increase the conductivity to a wantedvalue. (4-10)

4, The region is an electric field or differenceof potential. (4-11)

5. The polarities are arranged so that the po-tentials are in series and aiding. (4-12)

6. Heat generated by current flow causes a de-crease in resistance and a further increase incurrent. This will continue until the deviceis destroyed. (4-12)

7. The barrier potential will increase to equalthc reverse bias potential. (4-13)

R. Rectification. (4-14)9. Breakdown in the reverse direction does not

destroy the Zener device. (4-15)10. Signal input to the forward biased or low re-

sistance section is transferred to a reversebiased or high resistance element. (4-16)

II. Normally reverse biased. (4-17)12. The emitter is negative .with respect to the

base. The collector is positive with respect tothc base. (4-17)

13. The C stands for common, the second letterindicates the emitter, base, or collector. (4-18 )

14. Beta, 0, or he,. (4-19)15. Whether the p-n junction is forward or re-

verse biased. (4-21)16. Forwz;rd breakover voltage. (4-22)17. A gate current increase will lower thc anode

voltage value required for breakover. (4-23)

S GOVERNMENT PRINTING OFFICE:1911445-036/115

CHAPTER 2

I. Types, complexity. components. (4-3)1. I. b.

7. c.3. a.4. e.(4-4-6)

3. Half-wave, full-wave center-tap. and full-wave bridge. (5-2)

4. 280v, 120 cps, 280v. (5-3; Fig. 10)5. Six times the input line frequency; thus. 60

cps would produce a 360-cps ripple. (5-4.10; Fig. 13)

6. ( I ) The transistor current increases.(2) The current through the series re-

sistor remains constant. (5-15)7. Forward bias decreases because the emitter

voltage becomes more positive; therefore, it

approaches the base positive voltaile whichis held constant by the Zener diode. (5-23. 24)

71

306

.;9

8. More. decrease. increase. (5-25-28; Fig.17)

9. a. Increase.b. Decrease.c. No change.d. Decrease.e. Decrease.f. Decrease.(5-30-33)

10. Less. advanced, increased. (5-35-37)11. Less, decreased. (5-41)12. a. 1.

b. 4.c. 2.d. 5.(5-42-46)

13. a. 1120. b. 1120. c. 560. d. 1000. (6-5, 6)

14. 450, 900. (642)15. Positive. (6-13)16, Easy filtering and dependency on horizon-

tal output. (6-17, 19)17. Check your sketch with figure 26,A. (6-

17)18. a. Less negative.

b. Less positive.c. Remains .the same.d. Less positive.e. Less negative.f. Remains the same (practically).(6-17)

19. Increases. The HV becomes more positive.No, because gating frequency is unaffected.(6-24-27)

20. Check the resistor in the high-voltage lead.(6-30, 31)

21. If V4 has an open plate. cathode. or fila-ment, the screen grid voltage of VI willincrease, giving high amplitude output. Thishigher output will not be sensed and cor-rected because V4 is open. (6-34. 35)

CHAPTER 3

1. Vertical oscillator, horizontal oscillator, andblanking mixer. (7-2)Frequency shifts between the vertical oscil-lator and horizontal oscillator will not ordi-narily affect the operation of a noninter-lace system to a noticeable degree. (7-3)

3. Vertical oscillator and horizontal oscillator.(7-2, 3)

4. Horizontal sync, blank, and scan: also high-voltage excitation. (7-4)

5. Vertical oscillator. (7-5)6. To provide sharp pulses to precisely syh-

chronize the vertical oscillator to the 60-cps line frequency. (7-7)

I. V.:rtical drive shaper. ( 7-7)8. Horizontal drive shaper. 1666. (1-8. 9 )

v. a. Both.b. Vo.

Neither.d. Both.e. Ho.(7-7-10)

W. Check your sketch with figurc 31. (7:Fie. 31 )

1 I. 14. (7-9)12. The vertical amplifier and clippzr section

should be adjusted first to narrow the ver-tical blanking pulse. This adjustment willalso narrow the vertical drive pulse. hutfurther adjustment of the vertical drive sha-per may be necessary to obtain the propervertical drive pulse duration. (7-10. 1 )

13. It is likely that the horizontal blankingshaper is not fUnctioning properly becausenormal H drive would indicate that thc hen-zontal oscillator is operating normally. Thiscan be checked at TP5. (7-11)

14. Unless the ratio of horizontal to verticalscan is held constant, the lines per fieldwill chanee and the system cannot be de-signed to interlace. (8-2)

15. 262+1/2. (8-2)16. "a. 31.5 kc mo.

b. 2:1 counter.c. 525:1 counter.d. H-V mixer.(8-3)

17. Vertical. (8-4)18. Multivibrator, blocking-oscillator. and step

counter. (8-6)19. Insertion of a resonant circuit as illustrated

in figure 34 can improve stability of a block-ine-oscillator counter. (8-7)

20. The phantastron counter is reliable sinceit is a stable circuit that cannot be easilpretriegered (note ep waveform and func-tion of DI in fig. 35). (8-8-12)

21. When plate current is cut off. e,. rises toB+ ; the ek waveform in figure 35 showsek = 40v at this time. ( 8-8-10 )Check your block diagram with fieure 36.(8-13)

23. If the time difference between the last hori-zontal pulse and the vertical sync 'blank isrepeatedly H, no interlace will occur. Fieldswill fall upon each other and the lines perframe will be half that of an interlacedframe. 8-14. 1 6)

14. Horizontal sync or equalizing pulses. 8-1(24)

25. OFF. (8-20. 21)

1 n

30

26. Counters must be calibrated successivelyfrom the mo end to thc output becausc eachcounter depends upon the proper outputfrom the one that precedes it. (8-21)

27. I. b.2. a.3. a.4. c.(8-24-27)Trailing. (8-26)The notchine pulses eliminate the equal-izing pulses when only horizontal syncpulses should be present. If the notchingsection were inoperative, equalizing pulseswould appear midway between horizontalsync pulses. (8-29)

30. The 9H section is needed to block the hori-zontal and notching pulses (fie. 41.B. sig-nals b and c) durine the time that equal-izing pulses and serrated vertical sync areformed. (8-31)

31. The vertical pulse delay section becausethe 3H pulse is being triggered too soon.

(8-33; Fig. 41)

29.

CHAPTER 4

I 6.17:

18.

19.

20.

1-. 1 inch. 6 inches. (9-3)2. See figure 42. (9-3; Fie. 42)3. To produce and give initial control to thc

electron beam. (9-3, 4)4. Burn. (9-5)5. Is not. (9-7)6. A resolution chart; proper illumination; ver-

tical. horizontal, and beam controls ad- 21.

justed; lens in position and preset; elec-

trical focus ready for adjustment. (9-8)7. See figures 43 and 44. (9-9; Figs. 43 and 22.

44)8. Sec figure 45. (9-11; Fig. 45 )9. The image orthicon has an image accelera-

tor section and a beam multiplier, whereasthe vidicon does not. (9-11. 12) 23.

10. Tareet. (9-11)II. Target. (9-15) 24.

12. Image orthicon. (9-17)13. a. Vidicon.

6. Image orthicon. 25.

c. Image orthicon.d. Image orthicon.e. Vidicon.I. Vidicon. 26.

(9-17)14. Cooling: (9-21)15. The voltage is supplied from a voltage di-

vider network located on the camera control 27.

chassis and is adjusted by a potentiometer.Thc voltage source is a negative I-1V recti- 28.

23

3 u,,

fier in the camera and B+ supply on thecamera control chassis. (9-23. 25)Compare to figure 47. (9-28; Fig. 47)a. Remote adjustments of voltages in cam-

era.b. Correction for shading.c. Correction for black and white compres-

sion.d. Provision for signal amplification.e. Adjustment for proper blanking and

black level.f. Addition of sync pulses.(10-2)Working with the camera man. adjust theremote controls until the voltages appliedto the camera give the best focus and pic-ture resolution (viewed on the picture mon-itor). If necessary, adjust to correct forshading, black or white compression. blank-ing, and black level. (10-3)a. At the output of the first video amplifier.b. In the gray scale amplifier.c. At the input of the first video amplifier.d. At the output of the last video amplifier.

e. In the clipper dmplifier.(10-4-7; Fig. 48)Black stretch is achieved in the circuit il-

lustrated in figure 49 by adjusting the cath-ode bias when SI and S3 are in the Stretchposition and S2 is set at Normal. This is

accomplished with potentiometer R2 whichcauses the operating point of the tube toshift so that the signal's black positions areamplified more than normal. (10-7)Troubles could be a fault in the horizontalpulse amplifier and/or the horizontal shad-ing control (10-8)Since the field camera control unit is de-signed for portability, it is made compact,with the result that some of its controlsare less conveniently located than those ofa studio console type. (10-9)Check your drawing with figure 50. (11-6;Fig. 50)Use program transfer switch to connect pre-view channel to program output and thefader channel to preview output. (11-6)1. C.2. c.3. d.(11-9)1. c.2. b.3. a.( 1141)Isolation amplifiers are used at junctionpoints in a distribution system. (11-11)Waveform or shape. (11-11)

29. Broadens or increases. (11-17)3(J. Check your sketch against figure 55. + I 1-

22; Fia. 55)31. A CC amplifier, which is the counterpart

of a cathode follower, has maximum de-generative feedback and therefore excellentfrequency response. ( 11-23)

31. In ficure 56.A. transistor 01 is connectedas a CC amplifier and'02 as a CE amplifier.In figure 56. B. 01 is connected as a CCamplifier. 02 as a CE in caseode with 03which is connected as a CB amplifier. (11-28; Fig. 56)

33. Frequency compensation is not neededwhen direct coupling, degenerative feed-back. anclor low-gain circuitry is employedto give the desired %broadband response.(11-28)

CHAPTER 5

1. 1. c; 2. b; 3. c; 4, a. (12-1. 2)2. Master. (12-2)3. Check your diaaram against figure 57.

( 12-3 )4. The viewfinder monitor does not contain

a sync separator because its input fromthe camera has no sync information. (12-3)

5. a. Video amplifiers and d-c restorer. (12-8; Fig. 59)

b. Sync separator and pulse amplifiers.c. Vertical oscillator and amplifier.d. Afc. horizontal oscillator, pulse ampli-

fier. and damper.6. 1. c.

2. b.3. d,4. e.

5. a.

(12-13-24)7. The sync pulses are the most negative-going

portion of the input signal to the base 03which is self-biased well below cutoff; there-fore, only these pulses drive the p-n-p tran-sistor to conduction and appear as positive-going pulses on 03's collector. (12-14)

8. Integrating (long-time constant RC). (12-16)

9. Vertical oscillator. (12-16)10. Both the heiaht and vertical linearity con-

trols affect the height of the picture.(12-17)

11. Vertical output. (12-18)12. If the horizontal oscillator frequency in-

creases slightly, the sawtooth fed to thephase detector (at TP3) will produce anerror voltage (see-fig. 61, C) that increases

24

the negative bias on 07's base:. thus. thebias on Q8's base decreases (become% lessnegative) thereby reducing the blocking rateto counteract the frequency increase. t 12-20 )

13. The horizontal oscillator generates a pulseoutput whereas the vertical oscillator de-velops a sawtooth output, (12-22)

14. The horizontal hold control establishes thebias and therefore the frequency of thehorizontal oscillator. In figure 60. this con-trol is seen to be in the afc d-c amplifierstage. ( 12-22)

15. If 010 failed the followin g. circuits wouldnot function properly : horizontal deflection.horizontal blanking. high-voltage rectifiers.damper. video output amplifier oo boostvoltage), and afe (no feedback ). 12-23.24)

16. The picture correction magnet .hould.adjusted to eliminate corner shadowing.( 12-28 )

17. Numerous video amplifiers are needed in a

master oscillator to obtain the broudbandresponse for high fidelity. (13-3

18. .A master monitor's horizontal oscillator fre-quency is controlled directly by the hori-zontal sync. w hereas a recek er picturemonitor uses a d-e output from an arc ar-rangement. ( 13-5)

19. The stringent requirements for hieh voltageare best met with a separate well-regulatedsupply. ( 13-5)

20. 30. 7875. t 13-9)21. An expanded sweep signal is developed by

clipping and amplifying the normal sweepas illustrated in figure 64. (13-10)I. e.

2. a.3. d.4. b.( 13-14-181

CHAPTER 6

I. a. Dynamic.b. Carbon.c. Crystal.d. Capacitor. ( 14-1)

1. I. b.1. c.3. a.

4. d.(14-3, 9. 14. and I

3. Dynamic. (14-18)4, Set the shutter aperture to open. making

it bdirectional. ( 14-19 )

303

1 h.control room operator or program monitor.

2. c,3. a.

15-2The types of coupling used for tubes and

transmors are basically the same: however.

Ilk: impedance values involved are muchlow er for transistors. Depending on the load.

ains equal ,to those of tube audio ampli-fiers can he obtained with transistor audioamplifiers. Transistors are ordinarily noisierthan tubes. but can be operated to obtain

low noise factors. (15-3. 6. and 9: Fig.

Voltage,gain = 250. current gain = 12. andpo%er 2ain = 40 db are the indicated valuesin fimre 74 for a CE amplifier. (15-6)('C. i 15-6)

4) CB, (15-6)W. CE, (15-6)H . I. a.

2. c.

.1 a.15-7

; 2. fir.crsel . 15-11)13. Preamplifiers are characterized by their low

pim,:r levels and comparatively low noisefactors. privers are medium power linear:implifiers. Power amplifiers operate at rel-atively high power levefs: therefore, push-pull arrangements are used to obtain higher

efficiencies. (15-8. 20-23)14 Higher efficiencies can be attained because

push-pull amplifiers will give linear oper-ation when operated class AB or B. Higher

fidelity is attainable because even-harmonicdistortion is minimized for class A operationand reduced for class AB operation. (15-23)

15. a. Class B. (15-23-29)h. Class A.c. Class AB.

16. Increase R. This makes thc bases less posi-tive: thus, it biases the n-p-n transistors

into cutoff for a portion of each cycle.

(15-28)17. a. Amplifiers. c. Mixers,

b. Switches. d. Monitors.(16-2)

18. Gain, (16-()19. See figure 88. (16-9)

.balance. (16-12)21. VI: meter, (16-14)22, Tite mixer or gain control connected to the

amplifier for microphone number 3 prob-ably has a dirty wiper arm. This could

cause a weak signal which would meanmore gain required. It could cause erratic .action and thus a static to be heard by the

25

311i

(16-18. 19)

CtiAPTER 7

I. Color. camouflaged. (17-6)2. Blue. green. and red. (17-10)3. Hue. saturation, and brightness. (17-14)

4. a. v ; ; .

(17-15-19)5. Move in or use a zoom lens for closeups

so the image is larger on the pickup tubeface. The larger the image. the better thecolor perception. (17-17)

6. Processing amplifier and colorplexer. (17-21 )

7. a. Closer tolerancesb. More complex unitsc. Special optical systemd. Three camera tubese. A 3.58-mc sync signal.

(17-21)8. Check your drawing with fieure 94. (18-1)

9. a. Color camera is larger and has morecircuitry.

b. Color camera has three or more pickup

tubes. whereas monochrome uses only

one.c. Color camera has a more complex op-

tical system.( 18-2 )

10. The color television camera must have ablue, green, and red light image. (18-3)

1 1. There would be danger of imaee burn to

all three pickup tubes. (18-4)12. The neutral density filters reduce the light

on the red and green tubes so that it matchesthe light on the blue tube. (18-7)

13. a. Reduced screen-to-target spacing

b. Improved photocathodec. A micromesh screend. Better dynode construction(18-10)

14. a. The pushbuttons on the viewfinder.b. The skew and 0 controls in addition to

the controls for three channels rather

than one on the camera.c. The colored knobs for three separate

channels, the master iris, and the master

pedestal control on the camera control

panel.(18-13-19)

15. Adjust red skew control for rectangularshape. Q control for linearity. (18-15)

16. In the color camera a dynode gain control

is provided for adjusting each 10 tUbe.(18-15)

17. The preamplifiers used in color camerasare adjustable. ( 18-16 )

18. a. Video amplificationb. Cable compensationc. Shading and gamma correctiond. Regeneration of drie pulses and blank-

ing pulsee. Generation of test signalsf. Electronic switching(18-20)

19. 1-c; 2-d; 3-b. (18-21. 22)20. They are slightly lower. (18-24)11. 3.58 mc, blanking, (18-25)22. 1-c; 2-b; 3-b. (18-23-25)23. Check your diagram with figure 96. (18-

26; Fig. 96)14. 1 and Q; matrix. (18-27)15. 1-e; 2-f; 3-d; 4-a; 5-c. (18-27, 28)76. Because the Q signal is delayed most by

its filter. (18-29)17. 57, 90. (18-30, 31)28. The output signal from the mixer unit of a

26

19.

O.

31.

33.34.35.36.

37.38.39.

colorplexer contains luminance. chromi-mince. and sync information. (18-32)Hue, luminance or brightness. ( 18-36)The chrominance demodulator. burst con-trol oscillator. and matrix sections. ( 19-;Fig, 103)Video. ( 19-3 )Check your drawing with figure 104.(19-5)Phase detector. (19-8)Bandpass amplifier, monochrome. I 19-9Synchronous. ( 19-10 )Because negative and positive 1 and (.)nals are needed as inputs to the matrixsection to form the B. G. and R signals.( 19-11)B. G. (19-13)a-1; b-2; c-3; d-4; e-5; f-6. (19-15-21)For convergence, look for color definitionat edges. For purity, look for hues of colorinstead of pure color. For temperature. ro-tate brightness control and look for back-ground change. (19-22-27)

311

1.MATCH ANSWER 2.USE NUMBER I

STOP SHEET TO THIS PENCIL.E XERCISE NUM-B ER.

30455 01 21

REVIEW EXERCISE

Carefully read the following:

DO'S:I. Check the "course." "volume." and "form" numbers from the answer sheet

address tab aeainst the "VRE answer sheet identification number" in therighthand column of the shipping list. If numbers do not match, take actionto return the answer sheet and the shipping list to ECI immediately with a note

of explanation.2. Note that numerical sequence on answer sheet alternates across from column

to column.3. Use onlY medium sharp #1 black lead pencil for marking answer sheet.

4. Use a clean eraser for any answer sheet changes, keeping erasures to a minimum.

5. Take action to return entire answer sheet to ECI.6. Keep Volumn Review Exercise booklet for review and reference.7. If mandatorily enrolled student, process questions or comments through your

unit trainer or OJT supervisor.If voluntarily enrolled student, send questions or comments to ECI on ECI

Form 17.

DON'TS:1. Don't use answer sheets other than one furnished specifically for each review

exercise.2. Don't mark on the answer sheet except to fill in marking blocks.

Double marks or excessive markings whiCh overflow marking blocks will

register as errors.3. Don't fold, spindle, staple. tape. or mutilate the answer sheet.

4. Don't use ink or any marking other than with a #1 black lead pencil.

NOTE: The 3-digit number in parenthesis immediately following each item number

in this Volume Review Exercise represents a Guide Number in the StudyReference Guide which in turn indicates the area of the text where theanswer to that item can be found. For proper use of these Guide Numbers

in assisting you with your Volume Review Exercise. read carefully theinstructions in the heading of the Study Reference Guide.

40

Multiple Choice

Note: The first three items in this exercise arebased on instructions that were included withyour course materials. The correctness or incor-rectness of your answers to these items will bereflected in your total score. There are no StudyReference Guide subject-area numbers for thesefirst three items.

I. .The form number of this VRE (or CE)must match

a. the form number on the answer sheet.b. the number of the Shipping List.c. my course number.d. my course volume number.

2. So that the electronic scanner can properlyscore my answer sheet. I must mark myanswers with a

a. number 1 black lead pencil.b. pen with blue ink.c. bIt p Ant or liquid-lead pea.d. pen with black ink.

3. If I tape. staple or mutilate my answersheet; or if I do not cleanly erase when Imake changes on the sheet; or if I writeover the numbers and symbols along the topmargin of the sheet,

a. my answer sheet will be unscored or. scored incorrectly.b. my answer sheet will be hand-graded.c. I will be required to retake the VRE

(or CE).d. I will receive a new answer sheet.

CHAPTER 1

4. (102) Which of the following is an exam-- ple of using television to monitor a hazard-

ous situation?

a. Observing personnel entering securityareas.

b. Observing the fuel-handling operation ina nuclear reactor power plant.

c. Observing vehicular movement in heavytraffic areas.

d. Observing the techniques of a highlyskilled surgeon.

5. (103) Which of the following activities re-quires an elaborate video system?

a. Monitoring a door or eate.b. Surveillance of traffic.

18

b.

c. Production of news releases.d. Weather briefing.

(103) In which application wouki closed-circuit television most likely be used?

a. Intercontinental communication.b. Photographing the moon.c. Home educational programs.d. Flight crew briefing.

7. (101) Which of the followine is un ad-vantageous use of television in the DefenseCommunications Systems?

a. Providing entertainment for all personnd.b. Providing immediate transmission of in-

formation.c. Eliminating the need for personal brief-

ings of flight Crews.d. Eliminating the need for airfield traffic

control towers.

8. (103) What is the classification of a videosystem using two or more cameras. a

switcher, and more than one monitor?

a. Fundamental.b Closed-circuit.

c. Elaborate.d, Moderate.

9. (100) If a 3-level airman is assigned to anopen 7-level position. which of the follow-ing actions is appropriate?

a. Award the airman the 7-level .AFSC ifhe passes a 7-level test.

b. Award the airman a temporary grade ofE-5.

c. Place the airman on OJT to the 5-levelAFSC.

d. Award the airman the 7-1evel AFSC af-ter 1 year's service in the position.

10. (101) Activities of the Defense Communi-cations Agency are directed b) the

a. Joint Chiefs of Staff.b. Defense Intelligence Agencyc. Communications Satellite Project.d. Defense Atomic Support Agency.

(100) Which of the following is an areaof responsibility of the technician. but no,of the repairman?

a. Use of associated test equipment.b, Installation of television systems and

equipment.

313

c. Correction of equipment malfunctions.d. Major modification of television systems

and equipment.

12. (101) Which of the following is an appli-cation of instructional televisio ?

a. Direction of aircraft ground movement.b. Monitoring of sensitive areas.c. Briefing of flight crews.d. Reconnaissance of terrain.

CHAPTER 2

13. (106) Why is regulation poor in a cascadevoltage doubler?

a. It is a full-wave rectifier.b. Its output capacitor is charged only once

per cycle.c. It develops twice the peak input voltage.d. Both input and output can have one side

grounded.

14. (105) In figure 16,B, of the text, if theload current increases, the regulator tran-sistor

a. passes more current.b. base-to-emitter bias decreases.c. emitter voltage increases.d. base voltage increases.

15. (107) The boost voltage developed in aflyback WI system is

a. produced when the HV rectifier con-ducts.

b. produced by voltage doubling.c. caused by exciting the vertical output

stage.d. produced by using a damper diode.

16. (104) What electronic components in aTV system generally require well-regulatedd-c voltages?

a. VR tubes and camera tubes.b. VR. tubes and Zener diodes.c. Receiver tubes and transistors.d. Picture tubes and rectifiers.

17. (106) For a single-phase bridge rectifiercircuit with an LC filter, what is probablythe trouble if the d-c output is low and a

29

31,

ripple having the input frequency is pres-ent?

a. An open filter capacitor.b. An open-circuited rectifier.c. A leaky filter capacitor.d. A short-circuited rectifier.

18. (104) A single-phase bridge rectifier hasan effective input voltage of 220 volts a-cat a frequency of 60 cps. The approximateoutput of the rectifier will be

a. 154 vdc with a 60-Qs ripple voltage.b. 154 vdc with a 120-cps ripple voltage.c. 308 vdc with a 120-cps ripple voltage.d. 308 vdc with a 240-cps ripple voltage.

19. (104) As compared to three-phasefiers, single-phase rectifiers

a. have a ripple of lower amplitude.b. have higher ripple frequencies.c. are smaller and less costly.d. have lower peak inverse voltage

recti-

20. (105) What occurs in the regulator shownin figures 17,C, of the text, if the outputvoltage tends to increase?

a. The forward bias on 02 increases.b. The transistor 01 conducts more cur-

rent.c. The Zener diode conducts less current.d. The collector voltage of 02 goes more

positive.

21. (107) For the regulated HV system shownin figure 27,B, of the text, what happens ifthe VOLTAGE ADJUST is moved upward(away from ground)?

a. Transistor 01 conducts longer.b. Shock excitation decreases in amplitude.c. Capacitor C1 charges to a low:1 voltage.d. The SCR fires more frequently.

CHAPTER 3

22. (109) What is the purpose of a resonantstabilizer circuit in an interlace system?

a. To insure proper count.b. To stabilize the horizontal oscillator.c. To stabilize the vertical oscillator.d. To insure proper operation of the AFC.

23. (110) The equalizing pulses have a repeti-tion rate of 31.5 kc to properly synchronizethe

a. horizontal scan frequency.b. vertical and horizontal oscillators and

produce line pairing.c. vertical oscillator .during vertical blank-

ing.d. alternate fields and produce interlaced

scanning.

24. (108) What stage in figure 29 of the textmaintains a stable output from the 60-cpsoscillator?

a. Mixer blanking buffer.b. Vertical sync buffer.c. Horizontal sync buffer.d. Blanking mixer.

25. (110) Serrations are present in the verticalsync pulse of a standard interlace sync gen-erator to insure

a. proper retrace of the beam during verti-cal blanking.

b. synchronization of the vertical oscillatorduring vertical blanking.

c. synchronization of the horizontal oscil-lator during vertical blanking.

d. proper interlace of the scan lines.

26. (108) In figure 31 of the text, if the verti-cal blanking pulses applied to the blankingmixer were too narrow, but the verticaldrive was normal, where would the probabletrouble be?

a. Squarer and peaker.b. Vertical oscillator.c. Vertical amplifier and clipper.d. Vertical blank shaper.

27. (108) The output of the vertical oscillatorof the simple noninterlace system in figure29 of the text is formed

a. in the blanking mixer and locked by the60-cps line frequency.

b. by the 60-cps line frequency and lockedby the horizontal frequency.

c. across the vertical oscillator blocking ca-pacitor and locked to the 60-cps linefrequency.

d. across the horizontal blocking capacitorand locked to the vertical frequency.

28. (109) The fixed relationship between the

30

3 Z)

3 elmaster oscillator and the coUnters in figure32 of the text maintains a

a. sequential line scan rate.b. constant number of lines per frame.c. constant number of fields per second.d. varying number of lines per second.

29. (109) What are the threecounter circuits?

a. Step-counter, blockin2multivibrator.

b. Step-counter. resonantmultivibrator.

c. Multivibrator, blockingresonant stabilizer.

d. Step-counter, resonantblocking oscillator.

basic types of

oscillator.

stabil izer.

oscillator.

stabilizer,

and

and

and

and

30. (109) What are the four basic sections ofthe interlace sync generator shown in fig-ure 32 of this text?

a. Master oscillator, HV mixer, 2:1 coun-ter, and the 525:1 counter.

b. Master oscillator, blanking mixer. 7: Icounter, and the 5:1 counter.

c. Master oscillator, 7:1 counter. 5:1 coun-ter, and the 3:1 counter.

d. Master oscillator, 15:1 counter, 7: Icounter, and the 2:1 counter.

31. (108) What are the three basic sections ofa simple noninterlace sync generator?

a. Vertical oscillator, horizontal oscillator.and sync separator.

b. Vertical oscillator. 31.5-kc oscillator. andvertical drive.

c. Vertical oscillator, horizontal oscillator,and blanking mixer.

d. Vertical oscillator. horizontal drive, andblanking mixer.

32. (108) In what section of a simple nonin-terlace sync generator are height adjust-ments generally accomplished?

a. Vertical blanking section.b. Horizontal oscillator section.c. Vertical drive section.d. Vertical oscillator section.

33. (108) In the multipulse sync generatorshown in figure 30 of the text, in 'whatcircuits are pulse width and amplitude ad-justments normally accomplished?

a. Squarer and peaker circuits.b. Clipper and shaping circuits.

c. Blanking mixer. squarer and peaker cir-cuits.

d. Blanking mixer. clipper and shaping cir-cuits.

CHAPTER 4

34. (113) What type video amplifier is used atjunction points in a closed-circuit TV dis-tribution system?

a. Isolation.b. Parametric.c. Picture signal.d. Pulse.

35. (113) Which of the following will broadenthe low- and high-frequency video band-pass of a video amplifier?

a. A decrease in the load impedance.b. Degenerative feedback.c. Series and shunt peaking.d. An increase in the load impedance.

36. (112) If the camera control scene appearsmore gray than white, which control shouldbe adjusted first?

a. Horizontal shading.b. Black stretch.c. White stretch.d. Gray scale gain.

37. (113) An advantage of transistors as com-_pared to tubes for use in video amplifiersis that transistors

a. give more gain per stage.b. have lower noise figures.c. are more adaptable to compensation.d. are more adaptable to direct coupling.

38. (112) How do the shading signals whichare added at the video amplifier (cameracontrol unit) compensate for previously in-serted horizontal and vertical shading?

a. They cancel any spurious shading siinalswhich may still be present.

b. They increase the amplitude of the hori-zontal and vertical pulse amplifiers.

c. They cancel a portion of the blanking sig-nal.

d. They reenforce the action of the dampercircuits.

31

30839. ( 111) Which of the followine best de-

scribes the function of the multistage multi-plier within the image orithicon tube?

a. To increase the intensity of the emittedelectron beam.

b. To control the position of the emittedelectron beam.

c. To increase the output current of thetube.

d. To control secondary emission from thephotocathode.

40. (112) Which of the following is not a func-tion of the image orthicon camera control?

a. To correct for shading.b. To adjust for proper blanking and black

level.c. To correct for black and white compres-

sion.d. To preamplify the signal from the target

image.

41. (111) If an imaee burn appears on thetarget screen of an image orthican tube.which of the following is a likely cause?

a. The target is being underscanned.b. The target is being overscanned.c. The alignment coil current is excessive.

d. The image accelerator voltage is exces-sive.

42. (III) What is one purpose of the videooutput stage shown in the block diagramof the vidicon TV camera in figure 43 ofthe text?

a. o amplify the output signal.b. To develop a signal which may be mon-

itored at Tp 3.c. To superimpose the picture information

onto the horizontal and vertical blankingpulses.

d. To minimize loading effects.

43. (112) In figure 50 of the text. a programoutput can be achieved and yet keep thetwo fader channels available for preview-ing. etc.. by using the

a. monitor switch.b. program transfer switch.c. sync input relay.d. alternate channel switches.

44. (111) The electron gun of a vidicon cam-era is made up of which of the following?

a. Heater, cathode, control grid, accelerat-ing grid, and shaping grids.

b. Heater, cathode, control grid, and focus-ing coil.

c. Heater, cathode, control grid, shapinggrids, and deflection coil.

d. Cathode, control grid, shaping grids, anda permanent magnet.

45. (111) If a horizontal straight line appearson the viewfinder of an image orthiconcamera, what is a likely cause?

a. Blanking output stage is inoperative.b. Horizontal damper is inoperative.c. Vertical sawtooth generator is inopera-

tive.d. Horizontal sawtooth generator receives

no input.

46. (111) Into which three sections is theimage orthicon tube divided?

a. Scan, focus, and deflection.b. Multiplier, scanning, and image.c. Image, focus, and multiplier.d. Lens, scanning, and multiplier.

47. (111) Which is an indication that the beamcontrol of a vidicon tube is critically ad-justed?

a. Small specks in the mosaic.b. An illuminated screen.c. A single vertical line.d. A single horizontal line.

48. (111) How may image burn damage tbthe photoconductive faceplate of the vidicontube be prevented?

a. By focusing the camera on a fixed spotof high intensity light.

b. By adjusting the camera scan to utilizethe maximum .area of the faceplate.

c. By adjusting for maximum vertical scanafter making all other adjustments.

d. By mounting the tube so that sunlightstrikes the faceplate at a downward an-gle.

49. (111) If, after a 10- to 20-minute warmupperiod, there is no visible display on thescreen of a vidicon tube, which adjustmentshould be made first?

3.132/

a. Centering.b. Vertical.

3017

c. Camera scan.d. Beam control.

50. (111) Which of the following statementsconcerning vidicon cameras is true?

a. A scanning beam is produced by theelectron gun.

b. Alignment is accomplished by a syn-chronizing pulse.

c. Signal output is taken from thei cathodecircuit.

d. Focus is accomplished by the accelerat-ing and shaping grids.

CHAPTER 5

51. (115) What is faulty if the display on akinescope has a black top half and a whitebottom half?

a. HV supply.b. Kinescope.c. Horizontal oscillator.d. Vertical oscillator.

52. (114) A width control is not included inthe monitor schematic shown in figure 60of the text because

a. it would adversely affect the sync sep-arator stage.

b. the H-hold control changes the horizon-tal width.

c. it would cause horizontal overscan ofthe display.

d. it would alter the horizontal output sig-nals.

53. (114) Why is a combination monitor usedin conjunction with the camera control unit?

a. It has a large screen picture display.b. It provides for signal and picture analy-

sis.c. It controls all other monitors in the sys-

tem.d. It controls the outputs from the camera

control unit.

54 (114) From what stage does the syncamplifier of a utility monitor receive itsinput?

a. Video input amplifier.b. Video output amplifier.c. Sync separator.d. Phase detector.

0.

55. ( 115) What are two noteworthy featuresthat commonly distinguish a master monitorfrom other types of monitors?

a. Direct horizontal frequency control anda separate HV supply.

b. Horizontal afc and numerous video am-plifiers.

c. D-c restoration and numerous video am-plifiers.

d. Sync separation and d-c restoration.

56. ( 115) If no raster appears on the kine-scope of a master monitor. the failure ofwhat section will cause this?

a. Horizontal section.b. Vertical section.c. HV supply section.d. Video section.

57. (114) For the TV monitor shown in figure60 of the text, the vertical oscillator is

adjusted for proper synchronization bychanging the

a. bias on 06 with the height control.b. bias on 05 with the height control.c. bias on 06 with the linearity control.d. cutoff time of 05 with the V-hold con-

trol.

CHAPTER 6

58. (116) To mechanically adjust two poly-directional microphonesone to pick upall classroom sound and the other to pickup. primarily, the instructor, you would ad-just

a. both microphones for unidirectional pick-up.

b. both microphones for nondirectionalpickup.

c. one microphone for unidirectional pick-up and the other for nondirectional pick-up.

d. both microphones for bidirectional pick-up.

59. (119 ) Where would be a likely place tofirst check for a hum which is reported onall monitors?

a.b.c.d.

All microphone cables and connectors.All preamps and mixer controls.Each cable and switch to the monitors.The hum balance in the power supply.

33

60. (118) The audio console

a. amplifies, switches, and mixes audio.b. amplifies, switches, and detects audio.c. switches, mixes, and detects audio.d. switches. mixes, and .multiplexes audio.

61. (117) Which transistor amplifier config-uration can develop the greatest power gainfor a given transistor?a. CB. c. RC.b. CC. d. CE.

62. (119) Which of the following would bethe correct signal path through an audiocontrol console?

a. Microphone, program amplifier, preamp,output, and VU meter.

b. Microphone, preamp, program ampli-fier, and output.

c. Microphone, VU meter, program ampli-fier, preamp, and output.

d. Program amplifier. VU meter, preamp.and output.

63. (116) The capacitor microphone operateswith

a. two electrodes and a variable capaci-tance.

b. two electrodes and a fixed capacitance.c. three eleetrodes and a fixed capacitance.d. three electrodes and a variable capaci-

tance.

64. (116) Which type of microphone uses the"sound cell" to produce an a-c signal?

a. Dynamic.b. Carbon.

c. Crystal.d. Capacitor.

65. (116) Which of the following microphonetypes has the best frequency response?

a. Carbon (double-button).b. Dynamic (moving-coil).c. Crystal.d. Capacitor.

66. (116) What are the most widelytypes of microphones?

a. Dynamic, carbon, crystal, and ribbon.b. Dynamic, carbon, crystal, and moving

coil.c. Carbon, crystal, moving coil. and vari-

able resistance.d. Dynamic, crystal, capacitor. and carbon.

used

3id

ef()

67. (116) Which statement best describes thedynamic microphone?

a. It generates a-c by movement of a dia-phragm which flexes a himorph unit.

b. A diaphragm moves a coil of wire be-tween the poles of a magnet.

c. It generates a-c by using two flexingelectrodes.

d. It has a moving carbon pile in a maa-netic field.

CHAPTER 7

68. (123) In a color monitor, why is oneoutput from the 3.58-mc oscillator delayed90°?

a. So the Y signal will reach the matrixat the proper time.

b. Because both +1 and 1 signals areneeded in the matrix.

c. To obtain the 0 signal frorn the chromi-nance signal.

d. This is necessary to accomplish afc forthe oscillator.

69. (121 ) In which section of a color camerachain are the color signals modified to pro-duce the proper luminance variations?

a. Sync generator.b. Colorplexer.c. Processing amplifier.d. Camera control.

70. (121) In which ways do the preamps usedin a color camera differ from the prearnpused in a monochromc camera?

a. Preamps used for color have high-fre-quency peaking adjustments.

b. Preamps used for color have low-fre-quency adjustments.

c. A monochrome preamp has both high-and low-frequency adjustments.

d. The color preamps have both high- andlow-frequency adjustments.

71. (123) What outputs from the matrix of acolor monitor are usually used for colortemperature adjustment?

a. B and G.b. B and R.

C. 1 and Q.d. Y and R.

72. (120) The Y signal has the sante band-width as which of the followine signals?

34

a. Modulated I. c. Chronainance.b. Modulated Q. d. Monochrome.

73 123) WhichIN necessary for hoth

single-input and three-input color monitors'.'

a. Color killer. c. Phase detector.Sync separator. d. Matrix.

74. (123) Which condition normally causes thecolor killer to cut off the bandpass ampii-fier?

a. No color burst sync.b. No input to the phase detector.e. No luminance signal received.d. No 3.58-mc oscillator output.

75. (122) What does the burst flag pulsetrol?

a. Duration of the color sync.b. Frequency of the color carrier.c. Width of the back porch.d. Compatibility w ith monoehro=.

76. (121) Color TV cameras differ front mon-ochrome TV cameras in that they are

a. smaller. less sensitive to light. :Ind h.three pickup tubes.

b. larger. have a different optical system.and have three pickup tubes.

c. larger. have no drive system, and ha% efour pickup tubes.

d. smaller. have a different drie system.and a different optical system.

77. (121) Which of the following purposes isaccomplished by the mirror arrangeme ntsof color TV cameras?

a. They prevent imace burn of thy greencamera tubc.

b. They prevent image burn of the redcamera tube.

c. They divide the light image into colorcroups.

d. They shift the image slichtly to preventburning of the monochrome camera tuhe.

78. (120) Why are bine. green. and red usedas the primaries in color TV?

a. They are good absorbers of eolor light.b. They are the only additive primaries.c. They are sensed equally by thc eye.d. They produce the greatest variations of

color.

3.1j

79. ( 120 ) What size images would be affectedif the Q information in a color signal wasincorrect?

a. Large. e. Small.b. Medium. d. All.

80. 120 ) What property of colored light de-scribes the amount of whitc light mixedwith a particular color?

a. Hue.b. Saturation.

c. Luminance.d. Brightness.

81. (120) What can be determined from a

chromaticity diagram?

a. Hue and saturation.b. Luminance and saturation.c. Luminance and hue.d. Compatibility and bandwidth.

82. 11201 Which signal contains the 3.58-mecolor carrier reference?

a. Chrominance. c. Modulated Q.b. Luminance. d. Composite color.

30455 02 0867 1170

. CDC 30455

TELEVISION EOUIPMENT REPAIRMAN

(AFSC 30455)

Volume 2

Auxiliary Equipments

AttVIIMIOloliteINVIIM11111111441%1111144.1~.11AWM4%%,MVO.1"%%%101%%A.WeINWIAM%\iA

woommolmm%mimvi%niAmvimviwNAWNWAIMWAMIANSIAWANVIVI

Extension Course Institute

Air University

321

Preface

MELEVISION iS no spontaneous presentation; it is a combined operationYThevideo mosaic which appcars on the monitor screen is the result of many skills.

much planning, accurate timing. and sometimes artistry. In .this course we viewthis complicated system of communications as it concerns the television repairman

and technician.

This volume is the second of a three-volume course. In Volume I we discussedequipment and maintenance requirements of the basic elements of a televisionsystem: image pickup devices at the point of origin. the means of transmittingclosed-circuit electrical signals to the intended receiving locations, and the fa-cilities for converting the signals to reproduce the images for the viewer. In

Volume 2 we will discuss the maintenance requirements and operation of

additional equipment required to support various functions of the television systems.

Included in this discussion are the equipment for studio lighting systems. intercomfacilities, special effects. prompting facilities, audio and video recording systcms.

as well as specialized equipment required for maintaining television equipment.A discussion of relay equipment in addition to television VHF and UHF trans-mitters. receivers. antennas. and associated circuitry is also presented in this

volume.

If you have questions on thc accuracy or currency ot the subject matterof this text, or recommendations for its improvement, send thcm to Tech Tng Ccn(TSOC), Kees ler AFB MS 39534.

If you have questions on course enrollment or administration, or on anyof ECI's instructional aids Your Key to Career Development. Study ReferenceGuides, Chapter Review Exercises. Volume Review Exercise. and-Course Exami-nation). consult your education officer, training officer. or NCO, as appro-priate. If he can't answer your questions, send thcm to ECI, Gunter AFB AL36114. preferably on ECI Form 17. Student Request for Assistance.

This volume is valued at 30 hours (10 points ).

ill

322

Contents

Chapter

PrefacePage

iii

1 STUDIO AND CONTROL EQUIPMENT1

AUDIO AND VIDEO EQUIPMENT 153 SPECIALIZED TEST EQUIPMENT 434 VHF EQUIPMENT 595 UHF EQUIPMENT 88

323iv

Studio and Control Equipment

INCE STUDIO lighting affects the perfor-)-.3 mance of the camera. lighting is an importantfactor in lens selection. In this chapter we dis-cuss liehting prior to describing various types ofauxiliary studio equipment and their mainte-nance, and later on. discuss the TV prompter.rear screen projector. anu special effects equip-ment. Representative distinctive circuits are an-alyzed because these circuits are required for thespecial effects generator and amplifier. We alsodiscuss essential functions and how they are ac-complished by this equipment. Finally, we discussintercom systems that may be used for TV.

I. Studio Lighting1-1. Illumination of the studio set plays an

important part in obtaining the best results froma TV camera. Since you as a maintenance manneed to understand the effect of light on cameraoperation. you should know the language of light-ing. You should also know how to obtain suitableillumination through the use of various types oflighting. With your knowledge of quality, inten-sity, levels, and sources of light, you can selectlenses and make adjustments with facility and in-telligence.

1-2. Terms. The following terms are generallyaccepted and are becoming standard throughoutthe television and motion picture industry. Theseterms are generally used for describing studio set-lighting layouts and for articles describing lightinglayouts.

1-3. Base Lighting. Base lighting is the uniformdiffused illumination (approaching a shadowlesscondition) which covers an entire set. It is oftensupplemented by other lighting, such as key andfill lighting. The intensity of base lighting de-pends upon the sensitivity of the TV equipmentbeing used; that is, the amount of light necessaryto provide a picture of technical acceptability.Because base light is a well-diffused light, weknow that it must be provided by either incan-descent floodlights or flourescent lights.

CHAPTER 1

1-4. Key Lighting. Key lightine is provided bythe principal source of directional illuminationfalling upon a subject or area. This may be na-tural light coming through a window or open door.from a fireplace. or another source; or it maybe artificial light coming from spotlights withspecial accessories. Key lighting is sometimes di-vided into two groupshigh-key and low-keyliehtingin order to facilitate discussion of sceneillumination. with respect to a gray scale of TV.High-key lighting usually results in a picture hav-ing graduat'ons falling primarily between grayand white. with dark grays and black present invery limited areas. Low-key lighting, on theother hand. results in a picture having graduationsfrom middle gray to black. with limited areas oflight grays and white.

1-5. Fill Lighting. Fill lighting is the supple-mentary illumination of portions of a scene or setto control shadow or contrast. Fill light is sometype of diffused light, supplied by any of a num-ber of sources. For example, fill light wouldilluminate the opposite side of a key-lighted sub-ject, thus bringing out the details which other-wise would have been lost.

1-6. Effects Lighting. Effects lighting is illu-mination resulting in the simulation of specialeffects such as firelight, clouds, or window light.This type of lighting may be used to simulateflashes of light from explosions, for example, inmaking military training lessons. Among otherstudio aids which we will study in the followingsection are rear screen projectors. which are some-times used to produce effects lighting.

1-7. Other Lighting. There are a number ofdesignations given to lights used for a specificpurpose. These would include cross, back, side,eye, and set lights, which are used as indicatedby the name. It is necessary for the maintenanceman to be aware of the usage of these lights, in

anticipation of limited maintenance. This mainte-nance will be determined in most cases u. theextent of light used by the production agency.

110

100

30

SOLAR RADIATION

5000 oox /COO

WAVELENGTH - ANGSTRON UNITS

Figure 1. Relative light energy.

1-8., Requirements. The requirements for goodlight are directly related to the quality of thedesired television image. In some instances theavailable light can be controlled, while in othersit cannot. If the light is to be controlled, themaintenance man will set up his TV equipmentaccordingly; if uncontrolled light is to be used.the optimum performance settings must be ad-justed to average light conditions.

1-9. It is known that spectral characteristicsof a light source should be compatible withthose the camera pickup tube used and be psy-chologically suited to the personnel in the studio.Figure 1 shows the relative characteristics of sev-eral light sources: The first curve (dashed line)represents the energy from solar radiation. Notethat this curve is relatively flat and approacheswhite light (which contains all frequencies).

1-10. The second curve shows the relative en-ergy from a typical incandescent light source.Most of its energy falls in the red region (6000to 8000 angstroms). For this reason. incandescentlamps appear yellow or slightly red to the humaneye. The response of the human eye to any lightsource is determined by the relative sensitivity ofthe human eye as represented by the third curvein figure 1.

1-11. In Volume 1 you learned that both theimage orthicon and the vidicon have responsecurves closely resembling the sensitivity curve of

2

the eye. Although both tubes will perfocm satis-factorily as pickup tubes, they are sensitive tolight levels. The spectrum of light is good forboth: but, as you know. the image orthicon ismuch more sensitive than the vidicon. Minimumlighting level for producing good pictures liesbetween 32 and 64 footcandles with an f:8 lens.The average TV installation should be capable ofproducing 200 footcandles of illumination on anygiven scene to permit flexibility in the controlof lighting and lens stops.

1-12. Again referring to figure I. we see thatwhere the energy of the incandescent lamp isweakest the sensitivity of the eye is strongest.Since the sensitivity of camera tubes and the eyecompare favorably, we can assume that the in-candescent lamp is a good light source for TV.Fluorescent lighting is weak in the red regions:therefore, skin tones appear darker. It is for thisreason that fill or key light of an incandescentsource must be used with fluorescent lighting.This kn6wledge of proper lighting techniques isimportant to the maintenance man making cameraadjustments.

1-13. Equipment Types. The control of lightintensity usually requires more than turning lightsoff ,and on in a studio area. Auxiliary equipmentis required to produce the types of lighting wehave discussed and to meet the requirements ofgood liehting. Some studios are equipped with acontrol center containing master switches, branchcircuit switches. group dimmer controls, and in-dividual dimmers to aid in control of the lighting.As an additional aid in the achievement of goodlighting, patching facilities may be included. Theiraddition permits the patchine of dimmers andswitches into various circuits to control illumina-tion at different points with a minimum of equip-ment. For convenience and to increase versatil-ity. equipment which permits horizontal andvertical movement of lighting fixtures is usuallyprovided.

1-14. You must realize that there may bestudio operations where the lighting is maintainedby a section other than the TV maintenance sec-tion. However, since lighting is sometimes main-tained by the TN' maintenance section. it is im-portant that you know the lighting requirementsand are prepared to perform maintenance if nec-essary. Some of the generally preferred liehtsources are incandescent. fluorescent, and mer-cury-vapor lamps. The most widely used is theincandescent source and it is grouped into thefollowing types: floodlights. spotlights, striplights, and dffects lights.

1-1S. Floodlights are those used to give a wide-angle general illumination or base lighting. Anincandescent floodlight consists of a lamp socket.

325

lamp. reflector. and diffuser lens. The device maybe any size from 1 0 to 18 inches in diameter andhave lamps varying from 500 to 2000 watts. Themaintenance of this type of floodlight will prob-ably consist of lamp replacement or wiring re-pair. An important part of this type of mainte-nance is the exact replacement since equipment isset up for a given light level. If a differentwattage lamp or a different size or type of re-flector were substituted. the equipment wouldhave to be adjusted accordingly. Sometimes fluo-rescent floodlights are used if light manipulationor control is not a significant factor. However,because of the weakness of fluorescent light inthe red regions, there should always be some in-candescent lighting.

1-16. Spotlights come in a wide variety of sizes(from 3 to 16 inches in diameter) and use in-candescent lamps ranging from 75 to 5000 watts.Spotlights also may have specially shaped reflec-tors to direct the light beam into a designatedgec.,netric pattern. For additional pattern control.some spotlights have iris and shutter facilitieswhich can be adjusted. In all instances, it is

important that during maintenance only exact re-placements are made due to light level require-ments.

1-17. Strip lights are useful in backgroundlighting, as base lighting, top lighting, or_ filllighting. In some applications, strip lights 'will

function as floodlights for base lighting. At othertimes strip lights will fill the need for effectslights. Since all lighting directly affects image il-lumination as seen by the camera, repairs mustbe on an exact replacement basis to insure opti-mum operation of equipment.

1-18. Operational placement of lights and

their c introls normally is not the respcnsibility ofthe maintenance section. However, you should beaware of their placement during operation so thatyou can quickly make necessary repairs. If youare required to perform maintenance on con-trols and patch panels, you should be familiar with

their location, function. and routine maintenance

procedures.1-19. Lenses. The average image orthicon

camera pickup tube (reference Volume 1) re-quires a minimum light level of approximately 50footcandles incident with a lens opening (stop)of f:8. The larger the "f" number of the lens

setting, the less the amount of light that will reachthe photocathode. The image orthicon tube doesnot have the same pickup quality as photographicfilm; lens openings as low as f:1.9 can be usedbut the technical quality will not be good. If alarge amount of light is used or is present. thelens "f" number may be as high as f:16.

3

1-20. The TV camera uses lenses similar oridentical to ordinary film camcra lenses. These

lenses are used to focus an imace of the viewedscene upon the photosensitive element in the

camera pickup tube. The image orthicon cam-eras generally use 35mm optics. while vidiconcameras use 16mm optics. The I6mm lenses forvidicon film cameras are usually of short focallengths (approximately 3 inches). The 35mmlenses used on most field and studio cameras in-clude closeup lenses with focal lengths from 35mm

to 135mm. and middle to long distance lenseswith focal lengths from 81/2 inches to 25 inches.

1-21. Most studio and field cameras have afour-lens turret to accommodate a variety oflenses of different focal lengths. With the lensespreset. they may be switched by turning the lensturret. No adjustment is necessary. Most lenseshave iris or diaphragm mechanisms built in whichwould be a part of the preset adjustments. Amaintenance repairman will be concerned with

the adjustments made during setup; from thereon the adjustments are made by the camera op-erator. Otherwise, the chief concern of mainte-nance is the cleaning of the lenses and checkingfor any damage to optical or mechanical parts.Normally, there will be no repaironly removaland replacement.

1-22. An additional lens type is the zoom lens.which is a lens assembly of continuously variablefocal length. There are a number of types of zoomlenses available and in use. Some of these typesare quite simple and may be mounted on thelens turret in addition to standard lenses. Otherversions of the lens are manually or electricallycontrolled and are the only lens on the camera;their mounting requires removal of the lens tur-ret. Again, the maintenance of this lens is usu-ally limited to cleaning or removal and replace-ment.

1-23. With the various lens configurationsavailable, it is possible to make many choices oflens units. Normally you are not required tomake this choice or selection as the equipmentis equipped with a lens. It is important that youdo not interchange lenses during cleaning, inspec-tion, or other maintenance. For this reason; youmust have a working knowledge of lenses.

2. Studio Aids2-1. In this section we will discuss two basic

groups of studio aidsTV prompters and rearscreen projectors. The basic construction andmaintenance requirements us well as some of theelectrical circuits of a TV prompter will be con-sidered. The rear screen projector portion will

include thc fundamental advintages and disad-vantages in comparison with other types of pro-

32E;

0/ '

SCROLLSECTION

SCROLLSECTION

AMPLIFIER

SECTION

REMOTECONTROL

CONTROLSECTION

Figure 2. Block diagram of a basic TV prompting unit.

jectors. General construction, maintenance re-quirements, and repair features of both groupswill also be developed in this section.

2-2. TV Prompter. TV prompting is any verbalor visual means of snpporting program scripts.Verbal prompts are usually given by a script-following prompter near the speaker. Examplesof visual prompting devices are cue cards, frontand rear screen projectors, semitransparent mir-rors, and roll or scroll type equipment. In this dis-cussion we are concerned with a typical roll orscroll type prompter which, unseen by the audi-ence, unrolls a prepared script, line by line, toaid the speaker.

2-3. A typical scroll TV prompter can beconsidered as a single unit containing severalsections. Figure 2 illustrates the sections and therelationship between them. The scroll sectioncontains a d-c motor, a gear train, two reels, andthe paper upon which the information is printed.

PWR SUP >

C1

This section is usually mounted on or near a tele-vision camera with each camera havin g. its ownscroll section. Thc control scction is comprised ofa powcr supply, control circuits. and synchroniz-ing circuits. The d-c amplifiers constitute a sep-arate section which feeds the scroll motors. Thcamplifier section contains two identical circuits.each one of which controls an individual scroll.The speed and forward-reverse controls are lo-cated in the remote control section.

2-4. Circuit analysis. The circuit diagram.shown in figure 3. illustrates the basic electronicfunctions of a prompting unit, with the exceptionof the power supply. The bleeder, R I. R2, R3,and R4, serves as a voltage divider network in-corporating potentiometer R2. Note that thebleeder network is tapped at two different points.A portion of the d-c voltage is selected at pointR2 and applied, through resistors R5 and R6, tothe grids of VI and V2. respectively. The tap be-tween resistors R3 and R4 supplies the operatingvoltage for relay K I. Both switch SI and relayK I are shown in their normal (open) positions.When SI is closed, a d-c voltage is applied to oneset of the coil windings for K I and thc relay ener-gizes (S1 also controls the relay for thc othermotor). With B + present at the center contactof K1 and the movable contacts pulled up. B+ isapplied (through the windings of motor M I ) tothe plate of VI. Amplifier VI then conducts andcurrent flows through the windings of the motor,causing the motor to run in the forward direction.The motor is reversed by simply placing switchSI in the other ON position. thus applying vol-tage to the other set of windings K I. This causesK I to energize, the movable contacts to bc pulleddown. and B+ to be applied (through the wind-

1.1111=IMIII

K 1 OFFSI

Figure 3. Diagram of amplifier and contral circuits al a basic TV prmapter.

4

327

ings of motor M ) to the plate of amplifier V2.Amplifier V2 then conducts and current flowsthrough the windings of motor M I in the oppo-site direction. thus reversing the motor. Themotor spe,,I is varied by adjusting R2 which var-ies the amount of voltage applied to the amplifiergrids (R2 also controls the other scroll motor).Resistors R7 and R8 are balance controls and are

necessary for adjusting the individual motorspeeds (forward and reverse). A start-stop sys-tem (not shown), initiated by the script paper.provides for synchronizing the scroll motors.

2-5. Maintenance requirements. The TV

prompter maintenance requirements includecleaning and inspecting the prompter and re-placing damaged or broken components. All in-terconnecting cables and connectors must beinspected periodically to insure that there are nobroken connections. Periodic inspection and clean-ing of the synchronous motors and gear trains isnecessary to prevent binding and sluggish move-ment. The relay contacts must also be cleaned atperiodic intervals to prevent arcing, sticking. poorconnection between contacts, or other undesirable

effects.2-6. Troubleshooting and repair. Trouble-

shooting the TV prompter unit is comparatively

VERTICALSTAGE

simple. The most frequent malfunctions occur in

tubes, fuses, cables, and cable connectors. Forexample, you-find that the motor runs at a normalforward speed, but runs very slowly in reversewith minor speed variations when the balancecontrol is adjusted. A possible cause of thetrouble is a weak amplifier tube in the reversecircuit. If, on the other hand, the motor runsvery slowly in either direction, the probable causeis a sluggish gear train.

2-7. Rear Screen Projection Methods. Several

types of rear screen projectors and projectionmethods are employed in television production.

You, as a maintenance technician, must befamiliar with the varied types of equipment andthe requirements necessary for normal operation

of this equipment. In many instances the famil-'iar 35mm slide projector, with increased lighting,may be used to satisfy the rear screen projectionrequirements. With this in mind, we will explainthe basic operation and variations employed inrear screen projectors.

2-8. Stages. The stage of a projector is thatportion of it upon which the object is positionedfor display. A stage may be either vertical, hori-zontal, or a combination of both (see fig. 4).Though much of the projection is accomplished

111111/11111 ammo 411110. maim

SEMI TRANSPARENTMIRROR

LENSDAr

Figure 4. Basic rear screen projector.

5

326

HORIZONTALSTAGE

by the use of transparencies, other items such asopaque objects or photographs may be pro-jected. When an opaque object is projected. thchorizontal stage is obviously preferable to a verti-cal stage; the object could simply be placed uponthe stage. On the other hand. a vertical stage isuseful when projecting a transparency or photo-graph.

2-9. Mirrors. Mirror action is governed bytwo laws of reflection. The first law simply statesthat the angle of incidence is always equal to theangle of reflection. In other words, light raysbounce off the mirror surface at the same anglewith which they strike it. This angle is meas-ured from the normal or perpendicular to themirror surface. The second law states that theincident, reflected, and normal rays lie in thesame plane. An understanding of these two lawsis necessary for alignment of projector mirrors.Figure 5 illustrates these Jaws.

2-10. Semitransparent mirrors are frequentlyused in rear screen projectors and are sometimesreferred to as half-silvered mirrors. Mirrors ofthis type have the property of reflecting from thelighted side and at the same time being trans-parent from the dark side. When both stages infigure 4 are lighted, the two displays are super-imposed. The use of this particular type ofmirror facilitates certain projection techniques:the image from one stage can be deflected throughthe lens; also, the image from a second stage canbe projected through the mirror into the samelens. The most important disadvantage of thistype of mirror is its light absorption characteris-tics. .F.,mitransparent mirrors are not very effi-cient sinci 30 percent of the light delivered is notreflected or transmitted but is absorbed by theglass and silver coating.

2-11. Depending upon design features, com-binations of front surface and semitransparentmirrors may be contained in rear screen projec-

NORMALPERPENDICULAR

ANGLE OF ANGLE OFINCIDENCEREFLECTION

MIRROR SURFACE

Figure 5. Law of reflectionangle of incidence equalsangle of reflection.

6

tion equipment. Care must be exercised to insurethat all reflected images will be projected alongapproximately the same optical axis. If the imagesare not projected on nearly the same opticalaxis, keystone effect will occur. Figure 4 is anexample of a more iiMplified projector -Using asingle semitransparent mirror to permit opera-tion from one of either of the two stages. Notethat the mirror is so aligned as to project theimage from either stage along the same opticalaxis.

2-12. Lenses. The physical assembly of lensesdesigned for projection machines differs fromthose designed for camera operation. Projectionlenses are less complicated due to the fact thatthey are required only to change the focal dis-tance of the projected image. Unlike cameralenses, they are not required to control the quan-tity of light from the projection machine.

2-13. Lighting. Lighting methods for the pro-jection of opaque objects and photographs differfrom those used for transparencies. The lightsare placed in front of the stage for opaque objectsand photographs, and behind the stage whentransparencies are used. An example of lightplacement is shown in figure 4.

2-14. The light necessary for rear screen pro-jection is much greater than for front screenprojection. A front screen projector, for exam-ple. requires only 100 watts to project a 6- x9-foot image, whereas a rear screen projectorneeds 1000 watts to project a picture of the samesize. Depending upon the studio lighting, a typi-cal rear screen projector will require more orless light energy to cover the projection screenwithout noticeable fall-off of intensity around theedges of the screen. The best general rule tofollow is to place the subject to be viewed inthe projector and adjust the lighting for the bestpicture. The exact amount of illumination willdepend on how much front lighting is used on theprojection screen, density of the transparency,type of scene being projected. screen size, anddegree of light fall-off. Studio lighting sourcesmust not be directed toward the projectionscreen. Fall-off and scene types will be includedin the discussion of rear projection screens.

2-15. Some rear screen projectors. especially16mm, employ carbon arc lights for illumination.Caution must be exercised when using this typeof lighting due to the fumes emitted. Blowers anda venting system should be installed to carry thefumes from the immediate area.

2-16. Since rear screen projectors require ahigh light level for operation, blowers are in-stalled to provide the necessary cooling. Coolingthe equipment also helps to prevent damage tothc object being projected.

32J

2-17. Other features. Many other features

can be incorporated in the rear screen projector

which would facilitate a more complete opera-

tional capability. Such features as individual light

switches, dimmer, and iris controls,will improve

the flexibility of the rear screen projector. More

complex equipment may also contain both verti-

cal and horizontal crawl mechanismsa means

of moving a film strip across the stage at an

even rate of speed.2-18. Some means of wiping an image can be

employed when using even the simplest of pro-

jectors. Wiping is the process of removing orerasing all or a portion of one displayoftenaccomplished with another display. An image

may be wiped either vertically, horizontally, dia-

gonally, or by any combination of these. If the

wiping action is accomplished vertically, the new

display will enter either from the right or left.

Horizontal wiping is done with the new display

entering from the top or bottom of the original

picture.-2-19. Screens. Commercially produced rear

projection screens are expensive and unnecessarywhen fall-off is not a problem. Many other ma-

terials are more readily available and are ade-

quate under certain circumstances. Tracing

paper, cloth, oiled canvas. white Koroseal. and

white latex are some common materials that can

be purchased from local outlets. Some considera-

tion must be given to the size of the picture to be

projected since a small picture will show the

material grain, thus destroying much of the

picture quality.2-20. The projection screen must be designed

so that it will diffuse light and still permit the

image to project through it. Since a clear screen

allows light to pass directly through it. the camera

sees only a point of light. This point of light is

referred to as a "hot spot.- Because projection

screens cannot be designed to diffuse light pro-

porflonally in all directions, light intensity de-

creases from the center toward the outer edges.

This characteristic is called fall-off.2-21. Two intrinsic properties to be considered

in selecting a projection screen are its light ab-

sorption and reflection characteristics. Both of

these properties affect the reproduction of dark

scenes since the ability of the projection screen

to reproduce dark scenes depends 'upon the nat-

ural tone of the screen when the projector is

turned off. The white projection screen reflects

much light and absorbs very little light; there-

fore. its darkest tone is milkish gray. In contrast.

a black projection screen gives excellent dark

tone reproduction; however, it has such a high

absorption factor that fall-off is rapid and notice-

ably, distracting to a viewer. Thus. both white

7

and black screens have disadvantages. A com-promise. however, has been reached with the de-

velopment of the blue projection screen. While

it absorbs much of the reflected light, the blue

screen does provide a good response with regard

to fall-off.2-22. Maintenance requirements. Rear screen

projectors require only minor maintenance;

cleaning and inspection will suffice in most in-

stances. Projectors employing blowers and similar

moving parts require lubrication at periodic in-

tervals. Alignment of projectors must be consid-

ered on an individual basis. Equipment design

and application are two principal factors deter-mining the extent and types of maintenance re-

quired.2-23. Cleaning of the mirror and lens sur-

faces is of great importance because dirt andsmudges decrease their operating efficiency. Cau-

tion must be exercised when performing thesetasks. A nonabrasive lens tissue and approvedliquid lens cleaner are recommended for use on

the mirror, lens. and other glass surfaces. Other

types of cleaning material should not be used

since any scratches or marks on these surfaces

would cause permanent damage and decreasethe efficiency of the mirror and lens components.

2-24. Lamps should be checked periodically

and any cloudy bulbs replaced. Cloudy bulbs

produce less light, thus decreasing the operatingcapabilities of the projector. Maintaining time logs

on the projector lamps aids in determining bulb

life. Changing bulbs within their expected life

period reduces the possibilitykoi equipment fail-

ure during operation.2-25. There are three important factors when

aligning a rear screen projector: (1) stability of

projector base. (2) centering relationship be-

tween the projector and projection screen. and

(3) angular relationship between the projector

and projection screen. Because the slightest

movement of the projector will be amplified on

the projection screen, the projector must be

placed upon a solid base. To permit clear focus-

ing of the display over the entire screen, the

projector must be centered in relation to the pro-

jection screen. To prevent keystone effect, all

projections must be perpendicular to the projec-

tion screen.2-26. Troubleshooting and repair. Rear

screen projectors are simple to troubleshoot and

repair compared to other equipment in a TV

system. Most of the repair is confined to the re-

placement of broken mirrors, fuses, projection

bulbs, defective power cords, and other similar

items. When peculiar problems are encountered.

the maintenance instructions for that particular

projector should be consulted.

33

A

STUDIOcAMERAINPUTS

mit

SI. PICTURE

LE PICTUREWITH SYNC

Figure 6. Relationship of special effects equipmentshowing essential inputs and outputs.

2-27. Let us, however, consider some exam-ples of troubleshooting and repair. If a low levelof illumination of the projected image were dis-covered during operation and it is judged to becommon from more than one stage, a likely causeis either dirty mirrors or a dirty projection lens.Should the problem be evident from only onestage, the probable cause is a cloudy lamp. Ineither instance correction is quite simple. If thefirst example proves to be true, cleaning the lensand mirrors twill eliminate the difficulty. Re-placement of the lamp in the second examplewill rectify the problem. These are two examplesof the most common troubles encountered in rearscreen projectors.

3. Special Effects Equipment

3-1. A multitude of special effects and pat-terns can be achieved electronically as well asmechanically. Our 'concern will be with thoseelectronically produced by auxiliary studio equip-menti.c., the special effects generator and thespecial effects amplifier. Thc effects amplifier.which receives two picturc signals, combines thcpicturc signals into a montage display that is'determined by the keying signal. Although thekeying signal can be obtained from a thirdcamera, the special effccts generator is advan-tageous whcn versatility and convenience are im-portant. Figure 6 illustrates the relationship ofthc special effects equipment to cach othcr andto a switchcr. Notc the inputs and outputs shown.The power supply (not shown ) is generally aseparate unit. It it a type of voltage regulatedsupply which you have studied previously inVolume I. Chapter 2. of this course.

A

3-2. Special Effects Generator. A few specialeffects patterns are illustrated in figure 7. Thesmall arrows indicatc the direction of thc wipc.Two pictures can be presented and wiped in awide variety of ways with differcnt keying signalsproduced by the special cffects gcnerator. Thekeying signal nceded for a particular pattern isobtained by activating a regenerative clipper cir-cuit with different waveforms. To gain a knowl-edge of how this may bc done, let's analyze thecircuit shown in figure 8.

3-3. Perhpas you recognize this circuit sinceit is commonly used to obtain rapid switchingaction. Although we referred too it earlier as aregenerative clipper, it is also known as aSchmidt trigger circuit. We have shown a transis-tor version; its operation is essentially thc sameas a circuit incorporating tubes

3-4. We have chosen an input signal whichis a sawtooth of constant peak-to-peak amplitudethat is steadily rising. This type of input is ob-tained when a sawtooth of one frequency issuperimposed (mixed) with a sawtooth of a muchlower frequency. For example, a 15.750-cps saw-tooth can be combincd with a 60-cps sawtoothto produce an input similar to that illustrated.You should realize, however, that only a fewcycles of the higher frequency are shown. More-over. these cycles are not to scale for the fre-quencies cited. We have exaggerated the inputchange per cycle to emphasize the variation ofpulse widths that results at the output. The actionof the circuit is what you need to understand toappreciate how the various outputs are generatedfor keying.

3-5. Note in figure 8 that a dashed horizontalline is drawn through the input signal. We willconsider this line a d-c reference, which is thecutoff bias (base-to-emitter) of transistor 01and is called the threshold potential. It is ap-propriately named because the circuit is acti-vated each time this potential is crosscd by theinput signal.

3-6. The circuit is designed so that when 01is cut off, 02 is at maximum conduction and viceversa. Assuming 02 is cut off, the output is low( V,.) as illustrated at to. Thus 01 is con-

Figure 7. Special effects patterns.

8

33i

1.15:

ri T2 T3

to..1"/ le-41

INPUT

-vCC

Figure 8. Regenerative clipper.

ducting and its collector potential is high (mini-mum negative). This condition will prevail untilthe input signal drives 01 to cutoff. Observe

that the input signal rises from time t0 and reachesthe threshold potential at which time 01 be-comes cutoff. Its collector voltage goes to Vand a negative signal is instantaneously coupledto the base of 02. driving 02 into conduction.Because the emitter resistor is common to 01and 02. a regenerative feedback occurs. The

conduction of 02 drives the emitter of 01 morenegative (further into cutoff). This action ac-counts for the rapid switching action that charac-terizes a regenerative clipper. The output switchesfrom its low state to its high state as shown.During time interval T1. the output remains high.

This interval is terminated when the input signalagain crosses the threshold potential. Now, how-

A.

B.

PATTERNS

02

HHHOUTPUT

ever, 01 is driven into conduction. 02 is cutoff, and the output goes low again.

3-7. The output changes from one stable stateto another every time the input crosses the thres-hold potential. In other words, the circuit is

basically a triggered. bistable multivibrator. Bycausing 'the input sawtooth to rise steadily, thepulse width of the high-level output progressivelyincreases. Notice that interval T2 is greater thanT1 and that T3 is greater than T2. Likewise,

note that the pulse width of the low-level outputdecreases proportionally since the input saw-tooth frequency is constant.

3-8. Figure 9.A. showA the special effects pat-tern produced when a 15,750-cps sawtooth and60-cps sawtooth are combined to drive the re-generative clipper. This diagonal pattern dis-plays two pictures (identified as I and 2 in the

KEYING SIGNALS CLIPPER INPUTS

......0001 mOls OWIMIlail OM OP

14.1

411111Eo

411111=

41111. 141111 mot am N. owl am-

Figure 9. Special effects keying signals for horizontal lines shown in the patterns.

9

33

.325

illustration). To the right of the pattern areshown the keying signals that correspond to spe-cific horizontal lines (scans). Each signal ismarked to indicate the amount of time pictures1 and 2 are displayed per line. Note the similar-ity of these signals. and their inputs, with thesignals of the regenerative clipper just discussed(fig. 8).

3-9. To obtain a different type pattern, sup-pose we combine a l5.750-cps triangular wave-form and a 60-cps triangular waVeform to drivethe regenerative clipper. This combination willcause the clipper input to rise to a maximum inthe center of the field. Figure 9,B. illustratesthe manner in which the clipper input changesto generate the keying signal that produces thediamond-shaped special effects pattern shown.

3-10. Sawtooth and triangular waveforms ofline and field frequency are combined in manyways to obtain scores of special effects. If youunderstand the formation of the patterns in figure9, you should be able to determine the keyingsignal and clipper input needed for other montagepatterns.

3-11. Figure 10 shows the sections- that makeup a special effects generator. Inputs to thegenerator are horizontal and vertical drive sig-nals. These inputs go through similar channelsto develop sawtooth and triangular signals withblanking. Note the signals at TP1 and TP2 inthe diagram; respectively identical-shaped sig-nals appear at TP3 and TP4. However, the fre-quency of the signals appearine at TP3 and TP4is 60 cps instead of 15.750 cps. Since the H-frequency channel and V-frequency channel areseen to have the same sections, we can treat bath

I4 DRIVEiNPUT

v DRIVEINPUT

M DRIVEAMPL

V DRIVEMan

KIK SQUAREWAVE

/4UL TIVISRA TOR

channels by discussing each section. Starting fromthe left in figure 10. notice mat the drir inputsare amplified by the first section to attain thesignal strength to drive the square-wavc multivi-brator and also the blanking multivibrator. Theoutput from the square-wave multivibrator is fedinto a triangular waveshaping network (active orpassive type). This network effectively inte-grates the square wave to form the desiredtriangular signal. In the same section as the tri-angular generator, mixing is accomplished to in-sert the blanking pulse. thereby giving the outputshown at TP1. Tbe blanking pulse from theblanking multivibrator also provides an input tothe sawtooth generator. This input is used tosynchronize and form the output signal from thesawtooth generator section. shown at TP2.

3-12. The relays K1. K2, K3. and K4 arecontrolled from the special effects (S.E.) selectorand mixer panel. K1 and K3 each determineswhich waveform is applied to the signal invertersection in its channel. The inverter simply makesit possible to obtain signals of opposite polarity.thereby increasing the number of special effectsavailable. Relays K2 and K4 serve to select thesignal of desired polarity for input-to-amplifierclipper sections. This section clips the blankingpulse to a prescribed amplitude, but does notalter the sawtooth or triangular waveshape.

3-13. The S.E. selector and mixer panel deter-mines the input to the regenerative clipper sec-tion. The S.E. selector and mixer panel receivessignals from the H-frequency channel. and the V-frequency channel. Selection of one or a com-bination of these two sienals. along with the H-blanking signal, is accomplished by means of

M BLANKINGMULTIVISRATOR

14 TRIANGLEGENERATOR

moult

-1114.

444

SQUAREWAVE

muLTIVIBRATOR

V BLANKINGNUL TIVIRRATOR

M SAIITCOYMGENERATOR

M BLANKING4.44PL

TP2

KI M SIGANPL

INVERTER

0 K2AmPL

CLIPPER

1111N

V TRIANGLEGENERATOR

a AuftER

TP3

v sARTooTNGENERATOR

TP4

S,E.SEL ECTORAND

MIXER

K1

REGENCLIPPER

V 516AmPL

INVERTER

Figure 10. Block diagram of a special effects generator.

10

3:33

K 4

3E.-444. GEN

OUTPUT

ANPLCLIPPER

3cP-tp

0_01 INPUT 1PICTURE 1 VIDEO

INPUT AMPLIFIERSECTION

0_41 INPUT 2PICTURE 2 VIDEO

INPUT AMPLIFIERSECTION

KEYING SIGNALINPUT1

SWITCHINGSECTION

CLAMPINGSECTION

101

OUTPUT.VIDEO

AMPLIFIERSECTION

SYNC SIGINPUT

OUTPUTMIXER

SECTION

4

NON COMPS.E. OUT

F___40 COMPS. E. OUT

Figure II. Block diagram of sections comprising a special effects amplifier.

relays which arc energized with pushbuttonswitches. The pushbuttons are mounted on theS.E. selector, mixer panel and are marked to show

the special effects pattern associated with cachswitch. The pattern, as we explained earlier, isdetermined by the input to the regenerative clip-per, which produces the keying signal. This signal

is sent to the special effects amplifier.3-14. Special Effects Amplifier. Figure 11

shows the sections that constitutc a special effectsamplifier. Thc picture inputs. 1 and 2. arc am-plified separately before being applied to theswitching section and thc clamping section. Note

that the clamping section also obtains an inputfrom thc sync generator. This input is used tosample the picture inputs at different timcs dur-ing each horizontal blanking pulse. In this man-ncr an average clamping potential is developedwhile picture channel isolation is maintained. Theclamping section functions to keep the blacklevels of the two pictures equal to each othcr au-tomatically. Thus. the picture signals to thcswitching section are properly clamped when they

arc fed into the switching section.3-15. The two pictures arc electronically keyed

(gated) in the switching section to produce a

montage d.splay. This must be done withoutpermitting the picture signals to interfere with

each other. Figure 12 shows a network which

effectively decouples onc picturc signal whcn the

other is transmitted out. This decoupling is ac-complished by means of two balanced bridgecircuitsone comprisng 03 and 04, and theother comprising 05 and Q6. Note that the cir-

cuits containing these transistors arc identical.

11

Diodes D1 and D2 are connected across onebridge circuit; there is no potential across them

when the bridge circuit is balanced. Likewise,

D3 and D4 have no potential across them Whenthe other bridge circuit is balanced Adjustmentof the potentiometers (marked "BAL" in fig.

12) and the bias applied to Q3 and 06 willbalance the bridge circuits. Assuming the ad-justments are proper, let's now investigate howthese bridge circuits operate in conjunction withthe rest of the network to give an S.E. videooutput.

3-16. Picture 1 video is applied to the baseof Ql. The collector of 01 is connected incascade to transistors 03 and 04. When no S.E.keying signal is present at the base of 04, thebridge circuit is balanced and no signal is presentacross DI and D2. Thus, the amplified picture1 video at the collectors of 03 and 04 is nottransmitted out between DI and D2. Lookingat the picture 2 side of the network, you see it isvery similar to that of the picture I side. Theonly difference is the polarity of the diodes D3and D4 with regard to the keying signal. This

is an important fact, as we will explain shortly.However, when no keying signal is applied, D3and D4 are across a balanced bridge. Because

therc is no signal developed across them, therecan be no picture 2 video transmitted out be-tween them; therefore, we see that neither a pic-

ture 1 nor picture 2 video signa is transmittedwhen the keying signal is absent.

3-17. We know that the keying signal is a

series of rectangular pulses of varying pulsewidths. To simplify, let's consider just one cycle

33g

c?-

of the keying signal and assume the high-levelalternation equal to the low-level alternation (inother words, a square wave). Applying the high-level alternatiop to the bases of 04 and 05drives these transistors to maximum conduc-tion. Their collecto voltages drop, thereby un-balancing the briC, .,:ircuits. Considering firstthe bridge circuit incorporating 04, we find thatthe collector potential of 03 is now higher thanthat of Q4. Diodes DI and D2 therefore conductand the picture 1 video signal is coupled to theS.E. video output line. Turning our attention tothe bridge incorporating 05, we have 05 at alower collector potential than 06. Note, how-ever, that diodes'D3 and D4 are reverse-biased.This action determines that the picture 2 videosignal will not be coupled to the S.E. video out-put line. The differeae that we mentioned earlierconcerning the polarity of the diodes is obviouslyquite important. The unbalance created duringthe high-level alternation of the keying signalcaused Di and D2 to conduct, but not D3 andD4. Picture I signal is transmitted; picture 2signal is blocked. Such being the case for thehigh-level alteration, should not the opPosite con-ditions occur when the keying signal switches to alow level? Using similar reasoning as before, wediscover that DI and D2 cut off, whereas D3and D4 go to full conduction. Consequently, pic-ture 2 signal is transmitted and picture 1 signalis blocked.

3-18. Depending upon the keying signal, pic-ture 1 and picture 2 signals are coupled alter-

14/CC

nately through the switching section. If a differ-ence in black level persists between the signals,it can be corrected with the balanced adjustmentwhich changes the bias on 01 and 02. The S.E.video output is shown in figure 11 as going tothe output video amplifier section. This sectionhas two outputsone that can be sent to aswitcher in the camera chain, and one that isfed into the output mixer section where it iscombined with the standard composite sync. Theoutput from this section is therefore complete andcan be distributed via distribution amplifiers tomonitors for viewing.

4. Intercom4-1. Any televisiim installation that is opera-

tional will require some type of intercommunica-tion facilities. The complexity of the intercomwill be determined by the function which theTV facility serves. In. some cases, there will bea need for simple telephone services; in othercases, requirements will necessitate the use ofan amplifying system similar to a public addresssystem.

4-2. Facilities. Installation of the televisionequipment may or may not have included inter-com facilities. In some equipment, cable circuitswill be available for intercom between camera,camera control, and control room facilities. Evenwhen internal audio circuits are included, specificexternal audio equipment will not be suppliedid conjunction with the video components. Forexample, a camera may have an intercom jack

CLAMPEDPICTURE 1

INPUT

Figure 12. Transistorized switching section of a special effects amplifier.

12

S.E.Ow VIDEO

OUTPUT

CLAMPEDPICTURE 2

INPUT

CAMERA

7STU010

CAMERA /2 CAMERA 13

PRODUCTIONMAN

CONTROLROOM

EXTRA AU010HEAOSET OPERATOR

\

PROGRAM TECHNICALOIRECTOR OIRECTOR

Figure 13. Layout of an intercom system.

but no headset is supplied. TV facilities require

an intercom system for use in conjunction with

program production or equipment maintenance.4-3, Representative System. The representa-

tive system illustrated in figure 13 includes some

of the features found in most systems. Layout

variations in a given system will be discussed

later. The illustration shows headsets (earpiece.microphone, and cord), terminal points, powersupply. an amplifier, and a speaker. The illus-

trated arrangement permits communication be-

tween the control room personnel. camera per-sonnel. production men on the floor of the studio.

dnd equipment room operators. The added am-plifier and speaker, used for conference room

monitoring, permits one-way communication

only.4-4. The maintenance requirements for a sys-

tem such as this will be eoverned mostly by its

usage and the environmental conditions. The

13

intercom system is normally trouble free; there-

fore. preventive maintenance will be the mainrequirement. This kind of maintenance consistsof keeping plugs and terminal contacts cleanreplacing broken moisture shield, and checkingfor loose screws inside the headsets and plugs.When you make visual checks, observe for broken

wires, terminals, and plugs.4-5. Although the intercom is normally trou-

ble free, a few difficulties may occur. Occasion-

ally. you will have a headset with a bentdiaphragm or broken lead. If the headset is de-signed with a throwaway insert for the earpiece.

the only repair required would be to replace the

insert. If. however, in lieu of a throwaway insert.

the earpiece is made up of separate elements.

repair of the damaod elements is necessary. The

microphone will probably be designed to useexpendable inserts. These are normally carbonunits with a moisture barrier as part of the assem-

336

bly. Sometimes the carbon in a microphone unitbecomes packed (as discussed in Volume 1.Chapter 6). You may be able to restore it tonormal operation by a slight jar t,.) loosen thecarbon granules.

4-6. Some of the simplest checks of a faultyheadset can be made with an ohmmeter. An(ohmmeter intermittently connected across theheadset terminals will cause a clicking sound ifit is good. A carbon microphone can be checkedby setting the ohmmeter to a scale that gives amidrange reading when connected. Then by talk-ing into the microphone you will observe a slightmeter movement if the microphone is good.

4-7. System Variations. There are considerablevariations from system to system This is com-monplace. However, most of the variations willbe in the quantity rather than the types of equip-ment used. These will be such refinements ascrossbar switching, which permits added cir-cuits. If the distance is great. line amplifiers

14

635may be needed. Sometimes special circuits willrequire other types of microphones. speakers.and amplifiers. You may also find priblic ad-dress systems that have been modified for inter-com use.

4-8. Other Methods. Up to this point we havebeen speaking of TV production applications ofintercom systems. However, you should realizethat some maintenance applications require meth-ods other than those described. You, as a main-tenance man. may find yourself in a situationwhere surveillance cameras are mounted on topof a building. If you are to adjust these cameraswith the assistance of someone at the monitors.you and he will need to communicate. Sincethere will probably be no audio circuit available.you may need to use transceivers. Telephonesmay also be used as intercom for making main-tenance adjustments. These two methods arccited to give you an idea of the variations youmay encounter.

3 3 ;

Audio and Video Equipment

TN THE TELEVISION field audio and video1 recording equipment are used extensively.

There are two basic methods of recording: one isrecording on magnetic tape and the other is re-cording on film. In this chapter we will discuss

and compare the audio and video tape record-ers. We will also discuss the construction andoperation of a kinescope film recorder. Becauseof the necessity to convert film-recorded infor-mation to live video or video recording. we will

discuss 16mm film projectors. slide projectors.and multiplexer units.

5. Recorders5-1. Nearly everyone today is acquainted with

magnetic tape recording in home entertainmentand business dictating machine applications. All

who arc involved with TV maintenance should be

aware of the use of maanetic tape in audio andvideo braodcasting. The magnetic recorder is amajor unit, since it plays a very large part in therecording of TV programs. The magnetic taperecording techniques have progressed from therecording of lower audio frequencies to thc re-cordine of higher video signal frequencies.

5-2. We are also concerned in this section withmagnetic tape recording of audio. and magnetictape and film recording of television programs. in-cluding the construction. operation, and maintc-nance of both audio and video magnetic taperecorders. We compare their frequencies. con-trol, tape transport, and electronic requirements.In addition this section treats kinescope film re-corders. their operation. and their maintenancerequirements.

5-3. Audio Tape Recorders. Perhaps you own

a home tape recorder and have performed minor

maintenance on it. In this section we are con-cerned with audio tape machines as they apply

to TV production. You will notice that the terms"audio tapc recorders" and "audio tape machines"

are used -interchanaeably in this material. In

the audio tape recording field there is a differcnce

in the tape machine, tape recorder. tape deck.15

CHAPTER 2

ctc. The home variety tape recorder serves three

functions: erasing, recording. and playing back

audio frequencies. A tape recorder is usually

limited to the erasing and recording of audio fre-quencies. and a tape playback machine is usuallylimited to the playback of audio frequencies. Atape machine can combine all threc functions asin the home tape recorder.

5-4. For our discussion we have divided theaudio tape machine into three main sections:transport mechanism. heads. and electronics. In

the following discussion you will find variations inthe functions of each of these main sections. Forexample. the tape heads are identified accordingto their functions of erasing. recording. or play-

back.5-5. Transport mechanism. All of the tape

machines require some type of mechanism tomove the tapc past the record and playbackheads. Such mechanisms have been given variousnamcs, but tape transport scems to be generallyaccepted as standard. Tape handlers is the tcrm

uscd to designate machincs designed for fast start-

stop operation. These fast start-stop machincsare usually a type of computer or laboratory tapetransport which require thc tape to start or stopinstantaneously. In contrast. the standard ma-chine requires about 1 sccond to rcach full speedand perhaps 5 to 10 seconds to fully stabilize.

5-6. A good quality tape transport has thcfeaturcs of thc mechanism illustrated in figure14. These fcatures include the tape supply reel.which is provided with cither a friction brake oran active back-torque. The back-torque is sup-plied by the drive system or a torque motor.Back tension (torque) is necessary to keep thetape from becoming tangled due to the inertia ofthe tape reel. The tension idler holds a ccrtainamount of tape in its loop; this spare amount of

tape is temporarily let out during quick starts.A slight delay in timc is allowed for thc supplyreel. which has appreciable inertia, to start turn-ing at operating speed. The tension idler andback-torque work together to smooth out irrcgu-

TAKEUP REEL

TENSION IDLER

TAPE GUIDE

CAPSTAN PRESSURE ROLLER

CAPSTAN

REPRODUCE (PLAYBACK) HEAD

RECORD HEADDIRECTION OF TAPE FOR RECORD AND/ORREPRODUCE (PLAYBACK)

TAPE GUIDE

ERASE HEAD

'.ROLLING TAPE GUIDE

TENSION IDLER

TORQUE

SUPPLY REEL

TAPE ON REEL

Figure 14. Tape transport mechanism.

16

33

MACH! TICCOATING

CORE

Figure IS. Construction of magnetic head.

larities caused by the rubbing of the tape againstthe supply reel sides. sticking together of tapelayers. or other causes.

5-7. Again looking at figure 14, note that thetape is drawn from the tension idler. across therolling tape guide. erase head. tape guide. recordhead. tape guide. and reproduce head. Theforce, which draws the tape across the heads ata constant speed. is provided by the capstan and

LAMINATEDCORE

WINDING

BACK GAP (CLOSED)

FWV/. =a/M OMNI. 0.0 10

the capstan pressure roller. The combination ofthe capstan. the tension idler. and thc reversetorque of the supply reel keeps the tape underconstant tension. There is friction between thetape and the stationary heads. This friction is asource of vibration. Attempts to eliminate thisvibration are included in thc design of the trans-port mechanism by using a rigid base on whichto mount the transport components. Other cause;of vibration are the amount of wrap around thehead. smoothness of head faces. tape tension.tape condition, tape composition. temperature.and humidity. The capstan may be either theshaft of the drive motor or a shaft driven througha speed-reducing mechanism. The capstan andany associated mechanism must be made withprecision or it will cause problems during bothrecord and playback. This requirement for pre-cision components includes the drive motor, as itmust drive the capstan mechanism at a constantspeed.

5-8. Immediately following the capstan andthe capstan pressure roller is another tape guide.Each tape guide serves to keep the tape in align-ment with the heads at all times. If the tapeguides permit any vertical variation of the tape,

111 .... om,

I \I \i \

I \ I \

I

t\\

1 \1 )..

"'mg- PROTECTIVE METAL MOUSING

WINDING

RECOROING TRACK

TAPE

FRONT GAP

Figure 14. Laminated core tape head.

17

34o

POLE PIECES

MAGNETIC FLUXREVERSES MANY TIMESAS A GIVEN TAPE AREA

PASSES HEAD GAP. NIt"Csltt.C130C'

995SC.MAGNETICCOATING

MAGNETIC FLUX LINESFROM CORE PENETRATINGMAGNETIC COATING OFTAPE

WEAK ERASE FREQUENCY'Nth

V

STRONG MAGNETIC FLUX . WEAK ERASE FREQUENCYAS TAPE APPROACHESHEAD GAP GAP OPENING HEAD GAP

TAPE BASE

IN AREA OF AS TAPE LEAVES

Figure 17.. Action of high-frequency erase head.

a possibility exists of attenuation of the recordedsignal during reproduction. In extreme cases thesignal could be lost entirely, or the erase headwould either fail to erase or improperly erasewhen a recording is made. The tension idlernear the takeup reel serves the same purposeas the other tension idler. The torque on thetakeup reel changes according to the amount oftape on the reel.

5-9. Heads. Three tape heads may be usedon the more expensive tape machines. Some ma-chines, such as those designed for home use, usethe same head for record and reproduce. It ispossible to use the same head for erasing thetape; however, if the same head is used forerasing as well as recording and reproducing, itwill require an additional runthrough of the tape.

MAGNUIC PuntLimes

No17:,/

Recoil:m.46 OCCURST TRAILING EOGEOf GP

TAPE MOTION

Figure 18. Flux lines in a recording gap.

18

5-10. Although,one tape head can be used forthe three purposes of erasing, recording. and re-producing. there arc some differences in construc-tion of the heads. (The head differences will bediscussed later.) The basic construction of tapeheads is the samethat is. the head consists of acore of permeable material which is wound with acoil of wire (as shown in fig. 15). This core ofpermeable material is formed into a modified cir-cular shape, with a gap at the point of tape con-tact. The core material is usually of a laminatedconstruction (as illustrated in fig. 16) rather thannonlaminated. The nonlaminated heads arecheaper to construct, but they usually producepoorer results. The laminations, by reducingmagnetic losses due to eddy currents; produce abetter response to higher frequencies.

5-11. The core of the head is wound with anumber of turns of wire, but the number of turnswill depend on the purpose for which the headis designed. The manner in which the core iswound will be dictated by the head use; also,two windings may be used. Most of the newerheads follow the two-winding design. one windingon each side of the gap. In most of the newerdesigns the two windings will be terminated ex-ternally, thus they may be connected in a parallelor series arrangement as desired. The core andwinding is inclosed in a protective metal housingto prevent the winding from picking up humemanating from motors, transformers. etc.

5-12. So far all the heads under .discussion

3 4

have been of the electromagnetic type. To fur-ther expand on the erase head. some are con-structed to use either a single permanent mag-net or a series of permanent magnets to set up amagnetic field. If a single magnet is used, thetape will be erased by the magnetic flux. How-ever, with more than one magnet. thc tape willbe erased by the changing cycles of the magneticflux fields.

5-13. The more popular erase heads are thosewhich use a high-frequency current to create ana-c magnetic flux. This current is supplied by thebias oscillator, which also provides the bias cur-rent to the record head. The magnetic flux linespenetrate the magnetic coating of the tape. asillustrated in figure 17. The a-c erase head hasfewer turns of wire than the standard playbackhead, and it passes current easier and operatesbetter at the higher frequencies. Another featureof an a-c erase head is a wider gap which per-mits the tape particles to change direction moretimes. thus giving a more complete erasure ofthe tape. You will notice that as the tape ap-proaches and then leaves the gap in the head. theerase action builds up from zero to maximum andback to zero. Thus, any magnetic pattern whichwas previously recorded is obliterated by the ac-tion of the high-frequency bias oscillator.

5-14. When an alternating current is sentthrough the winding of a record head, a magneticfield corresponding to the applied current is pro-duced in the core (see fig. 18). The magneticfield has a great deal of difficulty passing throughthe nonmagnetic gap in the core. However.when the magnetic coating of the tape closes thegap, the field can easily complete its journey viathe tape. The tape now becomcs magnetized inaccordance with the fluctuations of applied cur-rent.

5-15. The magnetic fluctuation of the tape con-tinues until the instant the tape passes the trailingedge of the gap. The magnetic orientation at theinstant of departure from the gap edge is thepattern that remains on the tape. For the bestpossible recording, the trailing edge of the gapshould be as straight and sharp as possible. Aprinciple difference between heads of poor qualityand high quality is the definition of the gap edge.The amount of electrical signal required to pro-duce a certain amount of magnetic flux on one'head may create a stronger magnetic flux on an-other head because of differences in efficiency orelements of design. The signal level that causesdistortion varies among heads of different man-ufacturers. You must take these factors into ac-count if you substitutc a different make or modelof head for the one that originally came with thetape recorder.

19

5-16. As the signal current is fed to the recordhead. the high-frequency bias eurrent is suppliedsimultaneously to this head. as shown in figure19. The residual magnetization of the tape is ac-complished by passing the signal current, plus ahigh-frequency bias current. through the record-ing head windings. This technique is referredto as direct recording.

5-11. The high frequency of the bias oscilla-tor serves to activate the head over the linear por-tion of its magnetization curve. This linear oper-ation puts the audio signal in a magnetizationarea for the most faithful recording. If, however,the bias signal is increased until the head is satu-rated. the linear operation will be disturbed. Thefinal magnetization produced in the tape is de-termined by the last flux encountered .close to thetrailing edge of the gap as the 'tape leaves thegap area. For this reason the length of the re-cording gap is not as critical, within limits, forrecording heads as it is for reproducing heads.The recording heads usually will have a gap inthe range of 0.0005 to as much as 0.001.

5-18. Certain features of the playback (re-produce) head are required to provide full re-sponse to the audio frequencies. One requirementis that the head gap be very narrow., that is,0.0001 inch or smaller. A large number of turnsof wire is required in the winding since the headmust be sensitive to the changes in flux recordedon the tape. The playback head functions in anopposite manner to the record head; that is, thetape induces a flux into the head core. The fluxpassing through the core induces a voltage intothe winding, causing current flow in the asso-ciated circuit. This signal current is amplified bythe playback amplifier for operation of speakers,headphones. or other devices.

5-19. The playback head is of prime impor-tance in the faithful reproduction of a recordedsignal. For example. if we assume that a headis good mechanically and it is playing back a sig-nal which has all frequencies recorded with equalmagnitude. we will find that the higher audiofrequencies will produce a greater voltage output.An inherent characteristic of a playback headis that the rise in output is proportional to therise in frequency. This is true up to a poitt whichis determined by the characteristics of the headand head gap. The ability of the playback headto reproduce high frequencies varies inverselywith the width of the gap. This means that anarrow gap is necessary for good high-frequencyresponse. However, remember that although anew head may have a narrow gap, as the headwears the gap will become wider, and as a result.the high-frequency response will drop off. Also,along with gap width, the definition of the edge

342

41.....14111/11.

IFFaHENCY[ BIAS ram

RECORDAMPLIFIER

/̂ \/ s9 \

/ .z'" \/ 49 \

/ cP \*,9-

TRANSPORTASSEMBLY

Figure 19. Recording with high-frequency bias.

of the head must be smooth to produce high fre-quencies. If the edges of the gap are not straightand sharp, the gap behaves magnetically asthough it were much wider than its physical di-mensions.

5-20. Other factors which affect the frequencyresponse of the head are tape speed, smoothnessof the tape. pressure of the tape against the head,and quality of the tape. The tape speed is im-portant because the more rapidly the changes influx are drawn across the hcad gap. the strongerthe voltage induced into the head windings.This added strength, in turn, gives improved fre-quency response to the recorded signal. You canunderstand this condition if you consider that aslow moving tape will cause the head to see anaverage change in the flux and not each smallchange, which is necessary to reproduce high fre-quencies. Smoothness of the tape and tape-to-head contact are directly related in their effecton frequency response as well as voltage output.If the tape is rough, the magnetic particles arenot maintained constantly close to the head.which is necessary to induce a smooth flow of fluxvariations. The rough spots or portions of thetape will move the parficies farther from thehead and cause weakening of the flux changes;thus, the high frequencies will be lost. Carryingthis thought further. you can understand thatthe same losses will be prevalent if the pressureholding the tapeagainst the head is weak.

5-21. Electronics. Typical electronic circuits

used in tape recording are indicated by figure20. There Will be certain refinements as dic-tated by performance requirements. Normally thehigher the frequency response required the betterthe overall quality of thc circuit components winbe. Even thoutth the record head requires verylittle drive power, the need for bias injection. irn-pendance matching. and possibly preemphasismakes it important w use the -correctly designedamplifiers in the recorder. In thc playback cir-cuits typical audio amplifier circuits are used. Insome recorders there is dual utilization of circuitsfor record and playback. In recorders there is arequirement for voltage equalization of frequen-cies in the output. Earlier a statement was madethat the higher the frequency the morc thc volt-age output; for the lower frequencies the oppositeis true. Therefore. the very weak low frequenciesmust be boosted. It is not cnough toincrease the

gain of thr:. amplifiers. The problem is, to..boostthe low fiequencies and limit the high fraluencies.in most instances. it k sufficient to add RC net-works to the input signal path of an amplifier.To attenuate thc high frequencies. RC networkvalues are selected that will result in bypassing amajor portion of voltage of the higher frequen-cies to ground. The reduction of the higher fre-quencies' input voltage of an amplifier results ina relative boost of the lower frequency voltage.Frequency-selective feedback circuits betweenamplifier stages may also he used w equalize theoutput voltages of the high and low frequencies.

3 4

SIGNAL AMPLIFIERS 0 a'tmpAUDIO SIGNAL

APPROXIMATELY20 THRU 20.000 CYCLES

BIAS OSCILLATORSIGNAL APPROXIMATELY

75,000 CYCLES

BIASOSCILLATOR

Figure 20. Typical record and bias oscillator circuits.

Many variations of equalization circuits are usedin both playback and record amplifiers.

5-22. Trouble diagnosis. To diagnose troublesin a tape machine, you need to remember that acombination of features can cause trouble. In atape machine you have a group of mechanicalfunctions as well as the various electrical circuits.Indications obtained from the electrical circuitswill point to most of the troubles. These troublesmay or may not be in the mechanical mechanism.but you will have to "read through" the troublesto make your diagnosis. Once you detect a mal-function you should look immediately for thecause; however, a quick mental reference to

the most common troubles and their causes shouldspeed your diagnosis.

5-23. The word "wow" is used to describe aslow variation of speed. whereas "flutter" de-scribes a fast variation of speed. If the speed isconsistently wrong, the audio signal will be off

21

RECORDHEAD

pitch. This condition is easi1y recognized with

music but can be difficult to determine withspoken words. A "wow" could be caused by cer-tain faults, such as a slipping bIlt, lack of properpressure on capstan. motor winding damage, oruneven tape surface. A "flutter," which will bemuch faster, would more likely be caused bysomething moving at a higher speed. The capstancould be out of round and give this fault withevery revolution. Sometimes a tape guide cancause a bouncing action to be repeated at a fastrate. A signal which is consistently off pitch orkey may be caused by insufficient or excessive

drag on the tape as it passes through the trans-port system. This could be incorrect action ofthe supply reel. the pressure pads, tape guides.

or improper threading of the machine.5-24. If you have an indication that the output

seems to be weak. or that it is not giving full re-sponse to the higher frequencies, you might look

341

AVERAGE STATE OFMAGNETIZATIONA TO IS = ZERO

Figure 21. Gap effect at high frequencies.

for an electrical trouble. Pause for a momentand think what would happen if you have only aportion of a track passing over a head. We knowthat the strength of the output signal is relativeto the maenetic flux recorded on the tape and thetape speed. You already know that head wear willcause a drop in high-frequency response. but ifthe track or head is misaligned, you will not getfull benefit from the recorded signal. You mayneed to check head wear. track. and head alien-ment. If these seem to be correct. then check thecircuit components. Again, you can solve manyof the tape machine problems by "reading" thesymptoms and making a logical conclusion.

5-25. For still another example of a problem.let us assume that when you make a recording'and play it back you don't eet a signal. Thereare two ways to start checkine. Use a knowngood machine to check the tape or a known goodtape to check the machine. If you determine thatthe trouble is in the record or playback portion.

SEPARTIONoF NE AOFROM ?MBE

1.1ire1°morsi

4."., NODULE

1"TRII11171-101 I in

SIGNL. DROPOUTS

Figure 22. Effect of surface defects.

HEAD CYLINDER

Figure 23. Full-helical recerder head.

VIDEO

you should proceed to check out the items inthose sections. If the trouble is in the record cir-cuits, you may check the input source or the biasoscillator; either one could cause a failure in therecord mode. If the bias oscillator is not work-ing and the machine uses this same signal toerase the tape, a recorded tape would not beerased prior to a new recording. This is onequick check of the bias oscillator. A substitutemicrophone can be used to make a quick checkof the input source. Many recorders have a mon-itor jack which can be used to determine whethera signal is being fed into the recorder. Most re-corders have a record indicator, either a light ora meter. which gives a visual indication of theinput. By checkine the circuit of the recorder inuse, you will be able. through a process of elimi-nation. to narrow the area of trouble to a limitednumber of stages. From this point it will be nec-essary to make the more routine checks of tubesand other components. To prevent head magne-tization, do not check the continuity of heads withan ohmmeter.

5-26. A trouble in the playback circuits is

most readily found b using a known good tapefor playback. With some machines you have an

21

3 4 5

NEAO CYLINDER

Figure 24. Half-helical recorder head.

intermediate output which can he checked to de-termme if the signal is reaching a given point inthe machine. Some machines have a visual out-put indicator; if you have this type. you will knowthat all circuits are good up to a point. Some-times a headset output will be provided in a

stage prior to the power output: here. all but the

last stage could be eliminated as the source oftrouble. In all cases it as a matter of taking logicalsteps toward localizing the trouble to un arca. toa circuit. and finally to a component or com-ponents.

5-27. Video Tape Recorders. The video sig-nal frequency range for television tape extendsfrom very low frequencies (approaching d-c) tothe upper limit of 4 MHz. As previously indi-cated, the size of the head eap becomes very im-portant in the magnetic recording of higher fre-

quencies. For a given gap size and tape speed.there is a frequency above which recording is

impossible. This condition occurs when the re-corded wavelength of the sienal frequency justequals the width of the head gap. In figure 21._note that the positive and negative portions of thecycle appear across the gap simultaneously andcancel each other. Maximum output is obtainedwhen the recorded wavelength is twice the widthof the head gap.

5-28. The relationship between recordedwavelength. frequency. and velocity of the tapeis expressed by the formula:

Vx = -F

where A = recorded wavelength (in). V =tape speed (in/s), and F = frequency (Hz) ofthe signal. From this formula it may be deter-mined that as the velocity of the tape increasesthe recorded wavelength also increases.

5-29. The original approach to recording thehigher video frequencies was simply to increasethe speed of the tape so that the wavelength be-came a usable size. Video recorders that useextremely narrow gap heads and very rapid mov-ing tape are called longitudinal recorders. Longi-tudinal video recorders have many drawbacks.Primarily, the picture quality (resolution) is

poor. because the active read/write speed is

limited by the tape-handling capabilities of thetransport including problems of spooling the tapeand avoiding tape- ovarthrow. Also. an excessiveamount of tape is required.

5-30. Another approach to the recordinu ofthe higher video frequencies consists of pullingthe tape at a practical speed past a rotatine head.'resulting in an increase of head-to-tape velocity.Systertfs that use thc rotating head principle also

23

apply other techniques to improve thc recordingof video signals. One of these techniques is touse frequency modulation (FM) for recordingthe signal information. The FM technique solvesthe problem of bandwidth. The largest fre-quency span that can be accommodated by directrecording is 10 octaves (15 Hz-15K Hz). Sincethe video signal has a span greater than 18 oc-taves (0-4MHz). direct recording is not practical.This difficulty is overcome by using a frequencymodulator to change the video information intoan FM signal. with a full lower sideband and avestigial upper sideband. in one application thevideo signal is frequency modulated onto a car-rier from 1 to 7 MHz wide, a span of only 3octaves. The reduction in the span of frequenciesis important in the designing of the inductors usedin the record/playback heads. The use of FMpermits the recording of the signal at a constantamplitude.

5-31. The constant level FM can be amplifiedand limited in playback to reduce the effect ofsignal dropout. Signal dropout is due primarilyto tape surface defects. These tape surface de-fects result in poor contact between the head andtape. resUlting in substantial loss of signal (seefig. 22). Another technique is to allow the headto penetrate or intimately contact the tape.

5-32. Video tape systems that use the rotatinghead principle will vary in methods used to scanthe tape physically. The traverse and helical(either full-helical or half-helical) are the princi-pal scanning methods used.

5-33. The helical method of recording videosignals utilizes 1-inch or 2-inch tape wrapped dia-gonally around a hollow cylinder. inside the cyl-inder there is a rotating head assembly containingone or two heads. Through a cutaway in thecylinder, the rotating head assembly is permittedto make contact with the moving tape. A singlerotating head is used in the full-helical methodand the tape is wrapped around the cylinder (seefig. 23). The head scans one or two fields. thenleaves the tape during or near a vertical blank-ing period. Two heads are used on the rotatingassembly in the half-hek:al method and the tapeis wrapped over halfway around the cylinder(see fig. 24). Each head records or plays backone field with sufficient overlap to allow for elec-tronic switching from head to head during verti-cal blanking. In either method (see fig. 25).the recorded video tracks are laid down at aslight angle to the edge of the tape. Audio andcontrol timing signals are recorded in longitudinaltracks alone the top and bottom edges.

5-34. Mechanical assemblies of helical re-corders include the scan heads. a transport sys-tem with takeup and supply reels. tape guides.

34

AUDIO ERASE 4EA0 AUDIO ECM HEAD

.......INTERTRACK SPACING

vioeo TRACKS

110E0

CONTROL-TRACKERASE HEAD CONTROLTRACK

RECORO HEAD

Figure 25. Track pattern laid down by a helicalrecorder.

and a tape tension control system. Signal cir-cuitry includes the FM modulator, record andplayback amplifiers, sequence switchers, FM de-modulator, and video amplifiers. Servosystemsare used to control the tension of the tape andspeed of the head assembly and the capstan.Except for the scanning method, basic operatingprinciples are essentially the same for the helicaland traverse video recorders.

5-35. Tile traverse scan video recording sys-tem uses a rotating head assembly to lay downvideo tracks transversely (across) a- 2-inch-widemagnetic tape. The rotating head assembly con-tains four small heads located at 90° intervalsaround the circumference (as shown in fig. 26).The video signal is fed to the individual headsvia a slipring and brush assembly.

5-36. The tape is pulled past the head as-sembly at a velocity of 15 inches per second andthe assembly rotates at 240 rps. A head as-sembly with a tip-to-tip diameter of 2.07 incheshas a circumference of 6.5 inches. Since thehead revolves at 240 rps, the head-to-tape veloc-

CAPSTANMOTOR

VIDEO HEADS

ity or read/write speed of the 2.07-inch diametc:.head is 1560 inches per second. As illustfated infigure 27. the tape is held concentric to the ro-tating heads .by a special tape guide.

5-37. This special guide provides for tapestretch as the head penetrates the tape (negativeclearance). Figure 28 illustrates this action.Since the position of the guide in relationship tothe heads is adjustable. the amount of tape penc-tration may be controlled. The height of theguide may also be adjusted.

5-38. Refer to figure 29 for the location of thetracks on television tape. As one head of theassembly starts across the tape, the tape willmove a small amount before the head completesits arc across the tape. These motions result inthe signal trPck being recorded with an angleslightly less than 90°. The rotating head con-tacts the tape for an arc of approximately 120°and records a track 10 mils wide. A 5-milguard band is provided between each track toprevent crosstalk. A 70-mil track across the topis erascd to provide for longitudinally recordingaudio information. A 240-cps control signal is

recorded on a separate track along the bottomof the tape. A cue track is recorded parallel tothe control track.

5-39. The head assembly rotation of 240 rpsis four times the TV field frequency of 60 cps.Thus. one rotation of the head assembly laysdown four tracks which are equal to one-fourthof a field (about 65 lines) and one track is about16 lines. In the 120° arc of a head contact, thevideo signal information is recorded in a 102°portion of the arc. Since the heads are 90°apart, two heads are simultaneously in contactwith the video recording area during a 12°overlap. The 12° overlap insures that a smooth

AUDIOERASE HEADRECORD HEAD

CONTROLTRACK HEAD

-,rj$11111111111111111 11111111W11 II 11111 11 1W 1111111111H1

r°11"1"ir411gi'l :1111 111 1111 rirrlIi un

1111

nmue.4S.thiu I III HO cUIflIUIIIItI

CUE ERASE

Figure 26. Traverse recorder head.

24 347

CUERECORD

SPECIAL TAPEGUIDE VIDEO HEI1D

Figure 27. Rotating head assembly.

continuous signal will be reassembled. Duringplayback the overlap is eliminated by an elec-tronic switching process that disconnects the headnearing the end of a track, then connects thehead that is beginning the next track. Theswitching is done during horizontal retrace.

5-40. Errors in timing may occur between re-cord and playback. For example, in the playbackposition, a head may enter or leave a trackearlier or later than it was recorded. These errorsin time will appear during playback as horizontaldisplacements of vertical lines in the picture andare known -as time-space errors or space distor-tion. One factor that contributes to space dis-tortion is incorrect alignment of the position of

SPECIALTAPE

GUIDESHOE

TAPE

Figure 28. Tape penetration by video head.

25

the tape in relationship to the rotating head as-sembly. The adjustable special tape guide deter-mines the position of the tape in relationship tothe head assembly. Provisions for adjustment ofthe tape guide include the initial (preset) me-chanical adjustments plus automatic adjustmentsduring operation by a servosystem. A type ofspace distortion known as quadrature errors re-sults from slight deviations in the spacing on therotating assembly of twp adjacent heads from atrue 900. To correct quadrature errors, somesystems provide for mechanical adjustment of in-dividual head angle. plus adjustable electronicdelay circuits. Servosystems are used to reducethe effect of other timeing errors that causdpicture distortion, flutter, and loss of snychroni-zation. Closed-loop servosystems control themotors that drive the rotating head assembly.

5-41. Like the audio tape transport, the videotape transport must have a highly stable mount-

AUDIO TRACK 170 MILS)

TRANsvemse vicmoTimm E ACN 10 MILS7/10E GUANOSANDS)

TAPE MOTION

r CUE TRACK

CONTROL. TRACK

Figure 29. Traverse tracks on television tape.

ing surface. The rigid mounting is even moreimportant for a video transport because the tapemust be held under greater tension and be ableto withstand higher speed stops on wind or re-wind. These stops are accomplished by a fail-safebraking system. (The arrangement of the com-ponents of a tape transport is shown in fig. 30.)It is important that the tape speed be accuratelycontrolled over the heads. This is done in therecord mode by using a constant speed motor todrive the capstan, which controls the rate atwhich tape is drawn over the heads. When thetape is played back the recorded speed is ac-curately duplicated by servocontrol of the re-producer capstan speed, insuring that the repro-duce heads track constantly over the recordedtracks. The capstan servo input signal is obtainedby comparing a recorded signal on a controltrack with timing pulses from the rotating headassembly.

5-42. To prevent mishandling of the tape, ortape damage, the supply and takeup reel as-

3 4

4-1

MASTERERASE HEAO

GUIDE TENSION ARm

TIMING

WHEEL

SPECIALGUIDE

CONTROLTRACKHEAD

AUDIO& CUEERASEHEADS

AUDIO& CuEREC PLAYHEADS

mOTOR

ROTATING HEAD ASSEMBLY

SLIP RINGS

SHIELD

CAPSTANSHAFT

PINCHROLLER

TENSION ARm

ROLLER

Figure 30. Tape transport.

26

34j

54:2

semblies are each driven by a separate electricmotor through a hysteresis clutch. The currentflow through the clutch is normally proportionalto the amount of tape remaining on the tape%A fitted to the assembly's turntable. A fixedmaximum current. however, is driven through thesupply reel clutch coil in die rewind mode andthrough the takeup reel clutch in the fast for-ward mode. This provides for rapid completionof either of these two modes. Tape ternion be-tween reels is maintained by arrangement ofthe drive motors in such fashion that they tendto drive the tape reels in opposite directions, witheach reel driven to take up tape. When all slacktape has been taken up and the slack takeupidlers are under tension. the tape will be held atrest, ready to be drawn over the heads by theaction of the capstan assembly. Additional con-trol of tape tension against short-term or tran-sient disurbances is provided by two slack takeupidlers which also serve as tape guides. One idleris fitted at the exit from the tape supply reel as-sembly. while the other is fitted at the entranceto the tape takeup reel assembly.

5-43. The audio and cue record/reproduceheads and audio and cue erase heads are all ac-commodated in one head assembly which followsthe rotating head assembly in the tape path.These heads function in a conventional, longitu-dinal fashion. The head assembly is mounted ona precision-machined base plate.

5-44. The electronic circuits of the video taperecorder can be grouped into two main groups.those used to control the operation of the taperecordc:/reproducer and those used to amplify orotherwise process the signal(s). Usually thetape machine will incorporate, as subassemblies.all the basic units necessaty for producing a com-patible video signal and the audio. These unitsmay include sync generators. power still:41es. anddistribution amplifiers, plus the possible inclusionof such things as built-in test equipment, andcomplete monitoring facilities. In other words.the video tape machine electronics may includeeverything necessary for a CCTV system with theexception of the camera.

5-45. As already indicated, the rotating headsand the precision movement of the tape requirea great deal of control. Therefore. much of theelectronic circuitry will have to do with servo-systems. The video signal circuits will differ fromaudio circuits (discussed previously) in fre-quency range and bandpass of circuits. Since thevideo signal has a range from near d-c to ap-proximately 4 MHz. it is necessary to apply thissignal to Ga variable oscillator to obtain an FM

27

frequency. This frequency may then be appliedto another mixer circuit or directly to amplifiersand drivers to give us a constant amplitude FMsignal for driving the video recording heads. Forplayback the signal is amplified and limited to aconstant level, then fed to a demodulator to drivethe video circuits. The actual frequencies usedand the manner in which various conversionsare made vary with manufacturer's design. Tostudy details of circuits and frequencies. you willneed to read the manuals concerning the partic-ular make and model of the tape machine youare using.

5-46. Some of the video tape machines havevarious lever controls in addition to pushbuttoncontrols. Newer models are entirely pushbuttonoperated. with provisions for remote operationduring the playback mode. In the record modethere would be few instances where the machinewould be operated remote. Some exceptionswould be when copying tapes or using the ma-chine as a training aid. in which case the tapewould be played back once before erasure andreuse. One important point is that the machineusually is designed so that you cannot start it inthe record modc without manually releasing thelock on the lever or pushbutton used to turn themachine on.

5-47. The actual number of other controlsdepends on the make and model of the videotape machine you are using. .These include thecontrols that adjust the levels. alignments, equa,lizers. deflection circuits. and others. Othermechanical controls may be located at pointsthroughout the tape machine. At those timeswhen the electronic controls will not make suffi-cient corrections. it is necessary to make mechani-cal changes. An example is the head-tip pene-tration which can cause the signal to drop outwhen there is not enough negative clearance. Ifyou have a weak signal on playback, and adjust-ment of various level controls does not result ina satisfactory signal. you should check themechanical contact between the head and thetape. If the special tape guide is adjusted in-correctly or the head tip is worn until the tapeis not stretched properly. you will have the sameweak signal symptom.

5-48. Much of the maintenance of a videotape machine consists of cleaning. lubricating, re-placing tubes (tube models only). and evaluatingoverall performance. There should be a schedule.such as the one recommended by the manu-facturcr. for oiling and cleaning. Local condi-tions will affect the cleaning routine for filters;for example. an installation in a relatively dust-free area will not require filter cleaning as oftenas a portable field unit. Do not overlubricate,

but be sure to apply enotteh oil. Tube replace-ment usually will not be a problem, except tokeep balanced drivers and amplifiers in circuitshaving multisignal paths. In transistorized tapemachines, special effort is made to work out initialtroubles at the time of installation; .consequently,they are trouble free in comparison with tube-type machines.

5-49. Whether designed for audio or videooperation, magnetic tape is a flexible plastic basematerial. The coating may be one of a variety ofmagnetic materials which cannot tolerate _roughhandling. Rough handling may erase. partiallyor completely, a recorded tape. The quality ofthe signal obtained from a tape depends uponthe smoothness of the coating and the closenessof tape-to-head gap contact. Any physical dam-

age to the recording surface then results in me-chanical distortion, thereby degrading the signal.Other considerations of tape care include thesmoothness of each surface over which the tapetravels through the tape transport mechanism. Ex-cessive temperatures during operation or storagecan cause damage to the mechanism, and tapeguides can cause edge damage. A change in

humidity or excessive dampness is another fac-

tor, and you must also watch for any sign ofbuckling, cinching, or slippage on the reels.

5-50. Troubles in video tape recorders/repro-ducers can be diagnosed in the same basic waysas in other equipment. You take any given symp-tom, check the obvious trouble sources first, thenthe less likely, and on to the least likely. Useavailable publications and follow the recommen-dations of the manufacturer whenever possible;

this practice may lead you to a quick solution.

5-51. Kinescope Recorders. The recording oftelevision programs on motion picture film is

called kinescope recording. It is a means ofstoring, on motion picture film, electrical wavescorresponding to bath the picture and the sound

portion of a television program. Kinescope re-cording equipment may be used to record atransient display where immediate' observation bytelevision is a necessary but not sufficient meas-ure of control, to record an otherwise unat-tended operation where observation is necessarybut immediate observation is impractical, and torecord televised instructional programs for analy-sis or futurc use. When a permanent recording

or many copies of the recordine of the tele-vised signal are required. film is often used inpreference to magnetic tape.

5-52. Equipment. A kinescope recorder mustbe capable of synchronization with the televisionmonitor and of resolving the timing differences

between it and the television monitor. The

camera exposure time must be controlled very

28

VIDEOINOUT

AUDIOINPUT

AUDIOAMPL

A. VIDEO RECORDER

RECORDINGAMPL

B. SOUND RECORDER

00SOUND

RECORDER

Figure 31. Elements ol a kinescope recording system.

accurately and synchronized with the televisionsystem. Special equipment has been developedto meet these requirements. Equipment requiredfor accomplishing a motion picture film recordingof the presentation shown by a television monitorincludes (1) a television monitor (a hieh-intens-

ity short-persistence cathode-ray tube), (2)a recording motion picture camera (usually16mm). and (3) the equipment for recording thesound simultaneously with the picture.

5-53. Figure 31 shows a television recordingsystem consisting of both picture and sound re-cording channels employing separate cameras

and film for each operation. The video record-ing channel consists of a suitable video ampli-fier, deflection circuits, a cathode-ray tube, and

the film camera. The sound recording channelconsists of a suitable audio amplifier, a recordingamplifier, and the sound recorder itself.

5-54. As you can see, video recording is acombination of the techniques of television elec-

tronics and photography. (Electronic techniqueswill be covered in paragraphs 5-58 through 5-67.) A brief discussion of pertinent photography

terms and techniques is considered to be ap-propriate and is included at this point.

5-55. Sensitometry is the measurement of the

light response characteristics of photographicfilm under specified conditions of exposure and

development. Gamma is the ratio of the con-trast of any two elements in the scene beingtelevised; gamma control (or correction) is ac-complished by the introduction of nonlinear out-put-input characteristics which change the ef-fective value of gamma. A good print requires agood negative with maximum gradationa grad-ual shading of one tint, tone, or color into another.

351

344

The gray scale of the negative is the result of( I ) time and intensity of exposure and (2) time.temperature. and concentration of the developer.

5-56. The same requirements must be met inorder to produce a satisfactorily bright kinescoperecording. The time of film exposure is deter-mined by the television frame rate. whereas theintensity of light is controlled by the brillianceof the scene on the face of the cathode-ray tubeand by the opening of the lens (Ustop). Theintensity of light is influenced by the region ofoperation on the characteristic curve of the

cathode-ray tube; the amount of light reachingthe film is determined by the lens opening (f/stop) of the camera.

5.-57. Development of the film is as impor-lain as its exposure and must be W;y controlled.The contrast ratio of a developed film 'is ex-pressed in terms of light transmission of the filmafter it has been developed. The determinationof optimum operating levels for contrast in filmrecording involves considerable initial testing.

Once the optimum settings are made, they areuscd continuously. However, periodic checks, offilm results should be made to determine what.if any, readjustments should be made. The teststrip method of evaluating operation is desirablebecause it permits a rapid check of the variousadjustments in the shortest period of time. Greatcare must be taken that developer concentration.age, and temperature are controlled. Operationand service manuals for the video recording moni-

vERTICLTELEvoS)ONSCANNING

I FLYBACK

FILMEXPOSURE

ANDBLANKING

T114E

Tv FIELD1,60 St C

Tv FRME1:30 SEC

tors include detailed instructions for making striptests.

5-58. Video recording. We _have discussedsome of the equipment and photographic require-ments for kinescope recording. A very importantrequisite of video recording is that the exposuretime of the recording camera ,must be very ac-curately controlled and synchronized with the

television system. Let us now discuss the syn-chronization process.

5-59. The time of film exposure is determinedby the television frame rate. This rate in theUnited States is 30 frames per second, whereasthe standard motion picture projector frame rateis 24 frames per second. This means that alltelevision recordings made on motion picture filmrequire conversion of 30 television frames to thestandard 24 motion picture frames. At the 24-frame-per-second rate, 6 television frames out ofthe 30 which occur every second must be dis-carded. The time interval represented by t)lese6 television frames may be used to provide thenecessary pulldown time in the television record-ing camera. The problem of reconverting fromthe standard 24 motion picture frame rate to the30 television frame rate. when projecting a mo-tion picture film on television, will be covered inthe discussion of 16mm film projectors (para-graphs 6-2 through 6-5 of this chapter).

5-60. Figure 32 shows a possible conversiontime relationship between television field rec-orded film frames, and film pulldown. Note thateach television field has a duration of 1;'", sec-

TV TVFIE1.0 8 FIELD A

g#FIL 4/

FRAME IFILM

FRAME 2 / FIL/4RFAME 3 / FILM

FUME 4 VSHUTTER OPEN

EXPOSURETIME

I 30 SEC

ceimo

SS=-1 FILM FRAME

TIME1,24 SEC

aLING1.120 SEC

Figure 32. Conversion time relationship between television sconnine turd film exposure.

a- 35 4

HORIZONTALSYNC

(FROm TVSYSTEM)

353Li

H-- sTARTCOINCIDENCECIRCUIT

CYCLING PULSE

PSTART

ULSE

rSHUT TER

G E NGEARTAET OR

i111--111.

(I PER F)LM FRAME24PER SECOND)

CATHODEFOLLOWER

STOPPULSE

COUNTERCIRCUIT

(524COUNT)

S24COUNT

STOPCOINCIDENCE

CIRCUlf(SU COUNT)

DEFLECTIONCOILS

vIDEOAMP I

(2-STAGE)

SHUTTERGATE

PULSE

RECORDINGCAMERA

..-I1111111111 111.1:1 111111111F--01234567

CYCLING PULSE

GRID vOL !AGE

, U STAG( OfSTART COINCIDENCE

CIRCUIT)

- ZEROPULSE

START PULSE -

S24COUNT

STDP PUI SE

II Wit

1 1 1 1 1 1 1 1 1 1 1

CLOSEDSM.) TER GA TE

I NM

OPEN

Pill I UOviN

Figtwe 33. Electronic shutter block diagram,

ond and each frame has a duration of '1 sec-

ond. whereas each motion picture frame has aduration of 1j.i second. Let's analyze the opera-tion which accomplishes the desired conversion. A

motion picture camera capable of pulling thefilm down within the available time interval is

focused upon the television image on the face of

the television monitor. With film in the cameraaperture, the shutter is permitted to open while

the picture tube beam is tracing one field ofthe television picturefigure 32 shows a TV

A field being scanned first. The shutter is per-mitted tv remain open for the rcmainder of thatA field's scanning time, plus one B field's scan-ning time, plus the portion of the next A field'sscanning timewhich is exactly equal to the lost(blanked) portion of the initial A field's scan.The shutter is then closed for second.

The motion picture film is pulled down to thenext frame while the shutter is closed. During

this interval the picture tube's scanning beam hascontinued on its way and has scanned down toapproximately three-fourths of the A field .onwhich the shutter closed. The shutter again openand the camera photographs the remaining lower

portion (approximately one-fourth) of this Afield, the whole of the next B field. and a topportion of the next A field, Note that the topportion of this last A field is equal to the pre-vious A field's scanning time minus the portionpicked up by the camera when the shutter

opened. Again, the shutter closes for 112., sec-

ond and the film is pulled down to the next

framc. The shutter again remains open for '

second (the time of two television fields) andthen closes. If you follow the action as illustratedin figure 32. you will see that two half fieldsout of every five fields scanned by the television

proccss are not photographed. This is the sameratio as 6 fields out of every 30 fields; thus. therequired conversion of 30 television frames to 24

motion picture frames is accomplished.5-61. Since a portion of one television field

is discarded during pulldown for the recordedfield, some means of preventing film exposureduring pulldown must be provided. This maybe_accomplished by eithcr a mechanical or elec-

tronic shutter which performs the cyclic steps ofstarting. stopping. and timing each film exposure.Our discussion is limited to the electronic shutter.

5-62. Shutter action and pulldown action

must be correctly timed with respcct to eachother. Figure 33 is a block diagram of the cir-cuits comprising a typical electronic shutter to-gether with a timing diagram. The diagram showsa shutter gate generator that is blanking thccathode-ray tube during a portion of thc filmcycle. The phasing and timing of the shuttcr

31

gate are established by associated electronic cir-cuits. One of these circuits opens the gate andstarts the timing action as soon as pulldown ofthe preceding exposed frame has been com-pleted. Another circuit times the. exposure. and

a third. circuit closes the gate.5-63. Counting circuits are used to time the

film exposure. Their usc is possible since eachtelevision frame contains exactly 525 horizontalscanning lines. The counting circuits blank the

cathode-ray tube after the correct number of hor-izontal lines have been scanned. The film expo-

sure may be initiated on any horizontal line.

Once started. it continued until completion of thetelevision frame and then stops until triggered by

a cycling pulse. Camera film pulldown starts af-

ter the exposure stops. When pulldown is com-pleted and the film has become stationary, thccamera generates the cycling pulse which starts a

new cycle. The cycling pulse is an electronicpulse initiated by a mechanical timing sequence.

5-64. The output of the start coincidence cir-

cuit is the start pulse. which initiates film expo-

sure. It is a two-stage stable circuit with one tubeconducting heavily and the other tube biased be-low cutoff. The cycling pulse is applied to thcstart coincidence circuit and the conducting tube

is cut off; its grid voltage instanteously reachesmaximum negative value and then begins its

buildup action. However, this action does notinitiate the actual exposure. Horizontal synchro-nizing pulses (one per horizontal scanning line)

are also applied to the start coincidence circuit.Within the time of a few scanning pulses. thegrid voltage of the cutoff tube rises sufficientlyfor one of the synchronizing pulses to trigger the

circuit. As stated earlier, this synchronizingpulse may lie anywhere in the scanning cycle: itbecomes the start pulse. which opens the shutter

gate.5-65. The shutter gate generator is a two-stage

circuit which has two stable conditions charac-terized by conduction of one or the other of thetwo tubes. It has lwo.outputs. one of which is ap-

plied to the control grid of the cathode-ray tube.Before the start pulse is received, a negative out-

put blanks the cathode-ray tube (shutter gate is

closed). The start pulse reverses thc stable con-dition of the circuit. causing a positive output tounblank the cathode-ray tube (open the shuttergate) and camera film exposure action to begin.The exposure action is continuous until a televi-sion framc is completed. Upon completion of thetelevision framc. a stop pulse from the stop coin-cidence circuit is applied to the shutter gate gen-erator and its output blanks the cathode-raytubc, thus stopping the exposure action until an-other cycling pulse is received.

j

7

5-66. The other output from the shutter gategenerator is applied to the countine circuit. Hori-zontal synchronizing pulses are also applied tothe counter circuit. The shutter gate output whichis initiated by the start pulse begins the _counteraction. Th r. counter circuit includes ten counterstages consisting of two diode sections each. Itsoperation is similar to that of a conventionalbinary counter, with combinations of connectionsbetween each reset diode and its associatedcounter diode made in such manner that, whenthe overall circuit count of 524 incoming pulsesis reached. an output pulse is generated (seeupper left. fig. 33).

5-67. The output pulse from the counter cir-cuit is applied to a stop coincidence circuit. Thestop coincidence circuit is similar to the start co-incidence circuit, with the 524 count pulse takingthe place of the start pulse as one of the inputs.The other input, the strine of horizontal synchro-nizing pulses. is the same. The output is the stoppulse. The stop coincidence circuit contributesthe 525 count. It stops both the exposure actionand the timing action. Again. camera film pull-down starts. When pulldown is completed andthe film has become stationary. the camera gen-erates another cycling pulse which starts a newcycle.

5-68. Sound recording. Sound recording oftelevision proerams on maenetie tape was dis-cussed earlier in this chapter. The sound portionof a television program may also be recordedon motion picture film. In kinescope recording.the sound portion and video portion of the pro-gram are recorded simultaneously. Either thesinele-film system or the double-film system ofrecording may be used. In the double-film .

method, separate motion picture cameras areused to record the video and sound portions ofthe television proeram on separate films. In thesingle-film system. video and sound are recordedsimultaneously and the audio output of a record-ine amplifier is fed to the film camera. ratherthan to a separate sound recorder. In eithersystem. appropriate conventional audio amplifiercircuits may be used. A sound track varying ineither area or density is photographed on motionpicture film. The density or area variations inthe sound track are directly proportional to theamplitude of the incoming audio sienal.

5-69. Figure 34 is a block diagram of a sinele-film system of television recording. The single-film system usually utilizes a galvanometer modu-lator unit which records a variable densityphotographic sound track on the film. A mirror isattached to the galvanometer. As the galvanom-eter fluctuates with the audio signal. the mirror'changes its position and varies the amount of light

32

CRT

FILmCAMERA

SOUND MVOPICTURE

FILM

U010AMPLIFIER

Fhmre 34. Single-film television recording system.

reaching the film. This results in a variation indensity exposure of the sound track.

5-70. Video and sound synchronization. Inthe single-film system the sound track is photo-graphed on one side of the picture track. betweenone set of sprocket holes and one edge of thepicture. The film must be stationary when videotape is exposed; however, the film must movecontinuously to expose the sound film. Eachcamera has its own film loading diagram or guidewhich must be followed for satisfactory recordine.The film loops are especially critical. Whensound and video signals are simultaneously re-corded. the sound record precedes the video rec-ord by 26 film frames. The bottom film loopis exactly 26 frames in length. This loop permitsthe film to move continuously around the soundrecording drum. Deviation from this 26 filmframe length loop results in a lead or lag ofsound in reference to the picture when the com-posite television sienal is reproduced. The upperfilm loop permits continuous motion of the filmfrom the camera during intermittent film pull-down. If this loop is too short, the video willjump or flutter when reproduced. (For furtherinformation concerning reproduction problems.refer to the troubleshooting chart for 16mmfilm projectors shown in paragraph 6-22 of thischapter.) In. the double-film system of televisionrecordine, synchronization of the video and soundsignals is usually accomplished by employing syn-chronous motor drives in both units.

5-71. Maintenance requirements. Since kine-scope recording requires critical synchroniza-tion of the television monitor and the camera re-cording equipment. it is important that optimumoperational standards be maintained for all me-chanical and electrical operations. Detailed in-structions for operational checks are included inthe manuals of operation which are furnishedwith each kinescope recorder. The instructionsshould be followed carefully.

356

5-72. The television monitor should be in-

stalled so that it is free of vibration and floatingproperly on its shock mounts to prevent distor-

tion. There never should be anything jammedunder it nor placed on top of it. Cathode-raytube and cable installation instructions should beobserved carefully. For best recording results.periodic checks are necessary to determine cer-tain optimum operating levels. Once established.the settings are used continuously. However, be-cause aging of components (particularly in the.cathode-ray tube) causes optimum settings to

change slowly with time, film results should bechecked periodically to determine which. if any.readjustments should be made.

5-73. Since critical tolerances must be ob-served in all servicing procedures other than sim-ple adjustments to the recording camera, thecamera should be returned to the factory whensuch servicing is considered necessary. For thisreason. your major responsibilities for the main-tenance of the kinescope recorder will consist ofpreventive maintenance. Neglect of camera equip-ment may cause cumulative minor damage. whichcan result in loss of operating time. The interiorof the film compartment should be cleaned fre-quently with a clean, lint-free cloth and a softbrush. All sprockets and pad rollers should beinspected for dust, nicks, and other damage. Anyforeign matter should be moved with a soft brush.Since the pad rollers must be free to rotate easily.occasional lubrication is necessary. The cam-claw mechanism requires frequent lubrication.

The lens should be removed and cleaned with alens tissue. (Procedures for cleaning lens sur-faces are discussed in paragraph 2-23. Section 2.

Chapter 1 of this volume.) Caution should be

taken to insure that the lens is returned to itsexact position and reset to the proper focus and

f/stop.5-74. The galvanometer modulator unit must

be kept clean. The coveri slfOuld- be opened onlywhen necessary and closed immediately there-after. When the unit is out of the camera, thefront lens should be covered. Under no circum-stances should the mask be exposed, because it

readily collects dirt and dust. The lamp may becleaned by breathing on it and wiping it with alint-free cloth. The lamp should be replacedwhen thc filament sags or the envelope begins to

darken.5-75. We cannot overemphasize the impor-

tance of observing proper film loading procedures.Improper loading of thb caniera film is mani-

fested in undesirable results, such as film dam-age, picture unsteadiness, and improper synchro-

nizatioq of picture and sound.33

3 5

6. Projectors6-1. Both moving film projectors and slide pro-

jectors will be discussed in this section. The

16mm and 35mm moving film projectors willbe 'compared. showing the relative advantagesand disadvantages of each machine. Conversionof the film frame rate to the television frante ratewill be included and should be of special interestto the maintenance technician. The maintenancerequirements. troubleshooting procedures. physi-cal characteristics, and other special features ofthe 16mm film projector will be explained. (Youmay wish to review Chapter 1 of this volume foran explanation of the operating characteristics ofrear screen projectors.) The more intricate fea-

tures and complex component arrangements pe-culiar to slide projectors employing dual opticalsystems will be our major concern in this sec-tion.

6-2. 16mm Projectors. The standard 16mmfilm projector and the 16mm film projector usedin television differ in three basic criteria. First.the standard projector has a frame rate of 24frames per second (fps). whereas the televisionsystem. as previously explained. operates at 30frames per second (fps). Since this differenceexists, some means of conversion from the 24frame projection rate to the 30 frame televisionrate must be devised. Second. while the stand-ard projector needs no synchronization, a projec-tor used in television must be synchronized withthe camera to insure their sequential operation.Third. the projection cycle of the television filmprojector must be adaptable to peculiar needsand applications. Some projector requirementspeculiar to television concern the lens and audio

specifications. The projector lens must have ashort throw (focal length) and moderate magni-fication factor. The sound system must be com-patible with live programming.

6-3. Flicker reduction. The standard 16mmprojector uses a frame rate of 24 fps. with eachframe being interrupted twice, once for film pull-down and once to increase the flicker frequency.This creates a flicker frequency of 48 times persecond, which is much less noticeable to the hu-man eye and gives the appearance of a constantimage. At this frequency each showing of theframe may be considered as a field. However,

as stated earlier, the television scan rate is 30frames per second or 60 fields per second; thusa conversion problem exists.

6-4. C'onversion front 24 to 30 ironies per sec-ond ( fps). One solution to conversion is the useof an intermittent film pulldown -and shuttermechanism in conjunction with a storage type

pickup tube. Light is flashed on the pickup tube

3'19

FILM MOTION

LIGHT FLASHES

TELEVISIONSCANNING CYCLE

PUL L 0011N 1 a0 SEC 20 SEC

**-11111

SCAN

FRAME 1FkAmE 2 FRAME 3

inum 1=1111111111111G=04 41.4 NEE SCAN SCAN MEM

FRAME I

1,60 SEC

VERTICAL BLANKING

4 FILM FRAMES =5 Tv FRAMES= 1 6 SEC

Figure 35. Tiow cycle of a 1.1pical projeclor.

only during the vertical retrace time, and thetube's photosensitive element retains the imagelong enough for scanning during the followingdark period. By referring to figure 35 we seethat the film picture frames are moved throughthe projector in alternate steps of 1:A and 12 sec-ond. maintaining the ncccssary I second aver-age. Actual pulldown occurs between lightflashes. and the pickup tubc is illuminated alter-nately two and threc times per picture frame.Note that the sequence of pulldown for fourpicture frames takes the same time 0,, second)as is needed for 10 television scans of 5 tele-vision frames; thus, the two systems are madesynchronousi.e.. 60 pictures or 30 televisionframes are Completed each second. while the aver-age speed of the film remains at 24 frames persecond.

6-5. Converting the 24 frame rate to the 30frame rate is accomplished with a specially de-.signed intermittent. The intermittent has a three-sided geneva movemem- which pulls the film

down for unequal time intervals. Alternateframes dwell in the film gate 11 second longerthan the preceding and following frames. Lightpulses of very short duration ( second). re-curring 60 times per second. flash twice throughthe first frame. three times through the second.twice through the third. three times through thefourth. etc. Scanning begins immediately at theend of each light flash and completes itself whilethc film is not illuminated. The action just de-scribed is possible because of the storage prop-erties of the pickup tube.

6-6. Projector synchronizing. As mentionedearlier, television film projectors require synchro-nization. To insure proper sequential operation.thc shutter and intermittent pulldown drives mustbe phased and locked together. Further. to in-sure simultaneous operation of the projector andtelevision scanning process. the projector. tele-

SCAN

9MIK:4 SCAN ga

vision camera. and synchronizing waveform gen-erator must be locked and phased together.

6-7. The synchronization process normally isaccomplished by using a unique-phase synchro-nous motor to drive the projcctor. The synchro-nizing wawform generator and the unique-phasesynchronous motor are simultaneously locked tothe a-c power supply. The unique-phase syn-chronous motor satisfies two definite require-ments: I ) it is designed to lock to the a-cline frequency: (2) the rotor and field coils arewound to permit only an in-phase line lock. Anordinary synchronous motor can bc used in lieuof the unique-phase synchronous motor. providedcare is exercised to insure its operation in phaseith the line frequency. These precautionary

measures are necessary because the ordinary syn-chronous motor can bc operated in phase with or180° out of phase with the a-c line frequency.If operation of the synchronous motor k ISO'out of phase with the a-c line frequency. theimage will be projected while the picture is beingscanned. Notice in figure 35 that the light is

applied only during vertical blanking. For boththe unique-phase and ordinary synchronous types.motor design is such that little change in torqueangle occurs under varying load conditions dur-ing film and projector operation.

6-8. Use of a unique-phase synchronous mo-tor is unnecessary when a pulsed light or flashtube is used in the projector. In this situation anordinary synchronous motor may' be used to drivethe projector because there is no shutter and thelight source is controlkd by the synchronizingwaveform generator. Since the light is controlledby the synchronizing wmeform generator and isnot dependent upon a motor or the a-c powersupply frequency. the lieht flashes are alwaysin the proper phase,

6-9. Regardless of the type of synchronousmotor used. the phase relationship between the

34

356

FilmTYPE

RUNNING TIMEMINUTES AND LENGTH

I MIN IS MIN 30 4IN 60 MIN 90 mo4

,

33mm 90 FT 1350 FT 2700 FT 5400 FT 11100 FT

I IIMM 36 FT_

540 FT 1010 FT 2140 FT 3240 FT

Figure 36. Comparison of running time length,16mm-35mm film.

projector and synchronous waveform generator is

very critical. However, this requires adjustmentonly during the original installation, unless amajor malfunction or slippage occurs.

6-10. Projector adaptability. In terms of filmcapacity the 16mm film projector is much moreadaptable than the 35mm projector and satisfiesthe needs of television to a greater degree. Acomparison of running times and film lengths(see fig. 36) readily demonstrates the advantagesof thc 16mm projector. Since much of the tele-vision programming time consists of an hour ormore in length. the 4000-foot (approximately1 hour and 45 minutes) film capacity of the16mm projector more fully meets most televisionrequirements. Other factors besides limited film

capacity restrict the use of 35mm projectorse.g.. bulk storage. weight. and city ordinancesrestricting the length of 35mm film. Safety isstill another factor resulting in thc more extensiveuse of 16mm film and 16mm projectors. All

16mm film is a safety base film.6-11. The type of pulldown mechanism may

also affect -the adaptability of thc television filmprojector. Thc sprocket or claw intermittent pull-down mechanism may be used. Selection of thetype of intermittent depends upon the featuresmost dcsired in the projector. The most signifi-cant advantage of the sprocket intermittent is its

ability to help increase film life. The claw inter-mittent. however, is thc most widely used be-cause of its capacity to handle damaged andspliced film. Also. usc ot' the claw intermittentmakes possible thc restoration of a lost film loop.

6-12. The projector optical system is designedto achieve maximum resolution (a minimum ac-ceptable resolution standard is 600 lines). Thus.the projector does not limit the overall resolutionof the television system. Light efficiency of theoptical systcm is also an important consideration.A projector designed for high light efficiency.while usine a smaller light sourcc. can producelight equivalent to a standard film projector. Theprojector should produce a uniform flat field of

light (less than 10 percent variation) over theentire picture arca.

35

3 5 j

6-13. Ease of threading, an important fea-ture to be considered when selecting a projector,is determined, to a large extent, by componentlocation. Figure 37 shows the general arrange-ment of components and the film path. Notethat ample space is provided to permit easy place-ment of the film around the sprockets and intothe film gate, thus facilitating film reel changewhen, using multireel film.

6-14. The projector selected for television useshould be both stable and reliable under con-tinuous operating conditions. Projector stabilitycovers two general areas: (1) its constructionshould be solid and free from movement in anydirection, and (2) picture stability and constantfilm speed are important factors in minimizingpicture jitter. Proper lateral guidance compen-sates for dimensional errors in the film andeliminates horizontal weave and unsteadiness.

6-15. Lens. The moving film projector; aspreviously stated. requires a lens with a shortthrow (focal length) and moderate magnifica-tion. Since the film projector casts the imagedirectly upon the camera pickup tube, the lensfocal length is determined by the distance be-tween the camera and projector. This distanceis seldom more than a few feet. The magnifica-tion factor is determined by the size of the cam-era pickup tube. which in turn dictates imagesize. These focal length and magnification re-quirements also apply when using a multiplexer.

6-16. Compatibility of the audio system. Thefilm audio must have good frequency responseand tonal quality to insure compatibility withlive television programming. To achieve thesequalities, the film is passed over the sounddrum at a. constant velocity. A pressure rolleris employed to maintain a fixed plane for thefilm while moving over the sound drum. Notethe film loop between the film gate and sounddrum in figure 37. This loop of film and tinebalanced flywheel compensate for the sporadicoperation of the intermittent pulldown mecha-nism. These features help eliminate film flutterand instability, which, if not eliminated, causewowing and fluctuation in the audio output.

6-17. Maintenance requirements. With someadditions. the maintenance requirements of mov-ing film projectors are much the same as thosepreviously discussed for rear screen projectors.However, there arc more moving componentsin a film projector than a slide or rear screenprojector; thus the lubrication procedures aremuch morc detailed.

6-18. Lubrication of motors and assemblies.such as the shutter motor. thc blower motor. thetakeup assembly. the flywheel drive assembly.and the gear boxes. must be accomplished at

35 It

REFLECTOR

/Th

PROJECTIONLAMP

SHUT *ER ,,EFO 5PROCVET

CONDENSERLENS

APERTURE

UPPER REEL

[1 IRIS Of AAAAAAAA ... -"'PROJECTION LENS

I Ills

i

I.....

PRESSURE BOLLER

Pius GATEFL TINEEL

PHOTOTURE

OPTICAL UNIT

-

CLAW OPERATINGPA TN

PuLLOOWN CLAW

SOUNO ORum

TAKE UPSPROCKET

SOLJNO OPTICALFOCUS SHIFT

GLASS

SOUNOOPTICALMIRROR

EKCITER LAMP

SNUBBER ROLL ER

vIBICON mOSA,Z

mOLOBACKSPROCKET

LOSER REEL

Figure 37. Optical principles and movement of film in 16mm film projector.

periodic intervals. Use of the proper lubricantis important. Since several types are used, themanufacturer's handbook or appropriate techni-cal order should be consulted before starting thesetasks.

6-19. Many types of cleaning agents and ma-terials are necessary for different projector sec-tions. Lens tissue must be used when you cleansuch areas as the sot.7d optical unit, the soundoptical mirror, filters, condenser lens, and theprojection lens. You must also exercise cautionwhen working near the sound optical mirror,since touching it with material other than lenstissue may cause permanent damage. Sinceother projector components, such as the rollers,sprockets, and sprocket shoes. will withstand morepunishment, you may use a brush and cleaningsolvent to clean these sections. The sound drumand pressure rollers also may be cleaned with asoft, lint-free cloth.

6-20. Several components in the moving film

projector are adjustable, but again the appro-priate instruction manuals should be consultedbefore the adjustments are performed. Adjust-ments of components such as pulldown intermit-tent, frame stop, sound optical unit, and sprocketshoe are very critical; therefore, extreme caremust be exercised when making adjustments inthese areas. Although adjustments of the idlergear, pressure roller, and damper roller are lesscritical, adjustments in these areas should none-theless be made with caution.

6-21. Because wow and flutter are inherentproblems in moving film projectors. periodic testsmust be made to prevent their occurrence. Thefrequency response and overall audio repcoduc-tion quality must be checked to insure optimumprojector operation. Specially produced filmstrips are available for performing these qualitychecks.

6-22. Troubleshooting. Many of the common

36

36 0

4,-*1

troubles. with possible causes. which may con-front you are listed below:

Luss of lower film loopTorn sprocket holein film. film bindine in the gate. dirt onclaw, or bad spices.Loss of upper film loopFilm improperlythreaded on upper sprocket.Picture unsteadyImproper threading ofprojector. emulsion on film pressure shoe.or emulsion on aperture plate.Picturejllumination lowDirty projectionlens. dirty condenser lens. or dirty reflector.No audioImproper threading. dirt block-ing light, or tube failure in amplifier.No projected imageProjection lampburned out.

Some of the more complex problems may havethe same symptoms as those indicated in the list.For instance, loss of the lower film loop can alsoindicate that the pulldown claw is out of adjust-ment. the claw and aperture plate are touching.or the cam travel is insufficient. An unsteadypicture could indicate causes other than thoselisted: for example. improper claw adjustment.worn claw teeth, worn intermittent cam, or weakside pressure springs. These two examples merelypoint out some trouble symptoms which mayindicate either major or minor problems.

6-23. Slide Projectors. Several types of slideprojectors may be employed in a single televisionsystem. Since all slide projectors operate on thesame principle, we will discuss the most versatileof these. The slide projector's versatility is deter-mined by its design and construction. In otherwords a slide projector with dual optical paths.dual slide magazines, preview facilities, and duallighting fcatures is much more adaptable tochanging requirements than a slide projector withonly a single optical path. single light source. andlimited slide capacity. In this section we willdiscuss the overall requirements. characteristics.function. and operation (electrical and mechani-cal) of the more complex slide projectors.

6-24. Function. Slide projectors. as appliedto television, are generally used to support a,

program script. This function may be accom-plished in many ways. An image may be pro-jected directly upon the face of the camera pick-up tube. or when more than one projector is

used. into a multiplexer. Other production needsmay require that the image be projected upona projection screen from either the front or rear(as discussed in Chaptcr I of this volume). How-ever, in this section we are primarily concernedwith slide projcctors which project thc imagedirectly upon the camera pickup tube.

37

6-25.-Requirements. The projector pedestalor base Must be constructed to prevent undesira-ble movement, since movement of the slide pro-jector itself will be magnified in the projectedimage. The slide projector must also be designedto permit continuous operation for extended pe-riods of time. Component size, location, anddurability are important features to be consideredfrom the maintenance viewpoint. The size andlocation of the slide projector's components willdetermine the ease with which maintenance canbe performed. The durability of each componentwill determine its failure rate, which in turn willdetermine the slide projector's reliability and con-sequently its maintenance requirements. Likethe 16mm film projector, the slide projector willprobably be located in close proximity to thecamera pickup tube. Consequently, the lens re-quirements (focal length and magnification fac-tor) are consistent with those for -16mm filmprojectors. as discussed in the previous portionof this section. Other requirements, such as uni-form flatness of the image field, light efficiency,and a minimum of 600 lines of resolution, areequally as important in slide projectors as theyare in 16mm film projectors.

6-26. Characteristics. Since many of the slideprojector characteristics are related to its re-quirerrints and were mentioned only briefly, wewill develop those areas more fully at this time.The areas we are primarily concerned with areprojector flatness of field, light efficiency, mini-mum resolution standards, lens focal length, andmagnification features. The slide projector, to becompatible with another projector, must havethe same characteristics. Since this is true, theslide projector must have the same characteris-tics as all the other projectors when they are tobe used interchangeably or multiplexed. Thus.these five characteristics must be the same forthe slide projector as those discussed for 16mmfilm projectors.

6-27. The uniform flatness of the image fieldof slide projectors like that for moving film pro7jectors should not be less than 90 percent. Thatis. light intensity through the dark scenes shouldbe no more than 10 percent less than that throughlight scenes.

6-28. Light efficiency of the slide projector isdetermined to a large extent by the condenserlens. The condenser lens collects the light andconcentrates ,it upon the slide area. Thus, theslide projector can operate satisfactorily with asmaller light source with less heat and damageresulting from high operating temperatures.

6-29. The resolution requirements for slideprojectors used in television must meet a 600-line standard. Thus the slide projector will not

36i.

be a limiting factor on the rest of the televisionsystem's resolution. The projection lens of a slideprojector must have a short throw because ofthe short distances between the projector andcamera pickup tube. Inasmuch as the image isprojectcd 'Upon the face of the: camera pickup-tube, the magnification factor uf the projectionlens must be small.

6-30. Electrical operation.- The slide projec-tor employing dual optical paths may use anelectrical means for transferring light from onepath to the other. The easiest way of accom-plishing this electrically is to use two projectionlamps, one for each optical path. When oneoptical path is in use, its projection lamp isturned on and the projection lamp for thc otheroptical path is turned off. As the optical pathsare changed the slide is also changed. The pro-jection lamp used for the first optical path isturned off and the projection lamp for the sec-ond optical path is turned on. Although the sideprojector employing a dual optical system andthis type of light transfer is much more versatilethan a slide projector employing a single opticalpath, one great disadvantage presents itself. Be-fore the second projection lamp can be turnedon, its filaments must be preheated to preventdamage. The time necessary to preheat the pro-jection lamp filaments produces a time lag be-tween slide changes; thus the program continuityis destroyed to some extent. Another electronicdevice which will improve the projector versatil-ity is a remote control switch. The projector

PROJECTIONLENS

-1

(s-.LLOVABI.E

PON' CURF ACE{LAIRROR

SLIDE DOUBL EGATE CONVE X

L ENS

operator can then remotely turn the projector onor off and change slides in either direction.

6-31. Mechanical operation. A second andmuch more efficient means of transferring lightirom one optical path to the other is accomplishedwith a sliding mirror. This method of transferringlight can be done either electrically or mehani-eally. and many slide projectors of this typewill employ both methods. The operator thenmay make the decision as to which method isbest for any given program need. The greatestadvantage of transferring light with a slidingmirror is the instant display of the new image.Figure 3R illustrates a slide projector with dualoptical paths and a sliding mirror for light trans-fer from one path to the other.

6-32. Thc two laws of mirror action asapply to rear screen projectors (discussed inChapter 1) .also apply to mirrors when usedwith projectors having dual optical paths. As wit'will probably remember, these laws simply statethat the angles of incidence and reflection areequal and the incident, normal, and reflectiverays all lie in the same plane

6-33. Maintenance. The maintenance proce-dures for slide projectors with dual optical sys-tems are similar to those pertaining to rear screen

'and 16mm moving film projectors. AF discussedin the rear screen and 16mm film projectorsections. the primary maintenance functions arecleaning. inspection. lubrication, and adjustment.These functions should be accomplished, at pe-riodic intervals in the manner prescribed by the

t-N7 ATLW ORBMG

'IL T ER

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OPTICAL PATl

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Figure 38. Slhle pruje tor dual apdcal vview

38

362

OtTht I ON x

DOUBLE CLINvEx LEN:

appropriate TO or maintenance instruction man-

ual.6-34. Cleaning of all lenses, mirrors. and glass

surfaces is accomplished with approved cleaningmaterials, since other materials may cause per-

manent clamant: to these components. Inspect

each slide projector at prescribed time intervals.

Look for damaged. broken, burned, or loosecomponents, connectors. and interconnecting ca-

bles. If you discover any discrepancies. repair

or replace immediately. All slide projector mov-ing-parts or components require lubrication. Re-fer to the appropriate TO or maintenance instruc-tion manual and use the recommended lubricant

or a suitable -substitute. Also. check and adjustthe slide projector's position in relation to thecamera pickup tube when necessary. Proper

positioning is necessary to provide the best pos-sible resolution, uniform image field..and prevent

keystoning.

7. Vidicon Multiplexers7-1. Multiplexers and multiplexing systems are

used to mix several video inputs and produce one

output tor the camera. These systems may alsoselect an input from one of several sources. Many

methods are used to accomplish this effect. Someof the methods used are swivel or track mountedcamerasand multiplexers with stationary mirrors.Movable mirrors, or prisms. The most complex

systems may employ any combination of the

methods mentioned above. Each of the systems

has its advantages and disadvantages: thg method

used depends entirely upon the requirements and

available space of the individual television sta-

tion. In this section we will he concerned primar-

ily with vidicon multiplexers which employ differ-ent types of mirrors and mirror arrangements.We will discuss the mechanical considerations. op-

eration. maintenance, and troubleshooting pe-culiar to vidicon multiplexers:

7-2. Mechanical Considerations. Since multi-plexeri and multiplexing systems are usually

permanently mounted in a fixed location. they

cannot be readily moved from place to place.The optimum performance of the multiplexer then

depends upon the mechanical requirements. com-

ponent characteristics, and component functions.

7-3. Mechanical requirements. Since the mul-

tiplexer system. unlike field and studio cameras.

operates from a fixed location, it must he bothrigidly constructed and solidly mounted to insure

proper registration and focus of the projectedimage upon the face of the vidicon pickup tube.All mountings for movable components of themultiplexer must be exceptionally rinid 6. pre-

vent ,..ibration during operation.39

7-4. The mirrors are made of heavy glass to

prevent vibration and warping. Consequently.

jitter and geometric distortion are reduced in the

output presentation. The movable mirrors aremounted on bearings to permit smooth operation.

The second surface coating of all front surfacemirrors, whether movable or stationary, must have

a low reflective quality. because high reflectionfrom these areas produces undesirable spuriousimage reflections and ghost effect.

7-5. The multiplexer mirrors must be shielded

from external linht sources. This light should notbe allowed to strike the mirrors directly sinccthis too decreases the operating efficiency of thcmirrors and produces spurious image reflectionsand ghost effect. The transmission of light be-tween any input and the output must be the same

if a free choice of projector arrangement is possi-

ble. The multiplexer and camera optics shouldbe compatible with each other. Their opticalpaths should coincide to permit proper positioningof the image on the vidicon pickup tube and aidin maintaining the proper optical focus.

7-6. Characteristics. The multiplexer spectralcharacteristics should be neutral: thus the gray-scale balance will not be disturbed between thevideo channels. Mirrors with clear, precise, planar

reflecting surfaces will not disturb the opticalfocus and uniform flatness of the image fieldbetween the camera and projector. Therefore.the characteristics of both front surface mirrorsand semitransparent mirrors, as discussed forrear screen projectors (Chapter 1) and slideprojectors (Chapter 2). also apply to the mirrorsused in the multiplexing system.

7-7. Two inherent problems are encounteredwhen projected images are not operated alongcoincident optical paths. The first, geometric dis-tortion. has the greatest effect upon the video

output. Second. jump and weave of the videodisplay are apparent. Neither of these problems

was of much importance in the original multi-plexing systems where the iconoscope was used

for video pickup. However, with the advent ofthe vidicon pickup tube, which is about ninetimes smaller than the iconoscope. they becamemajor problems that necessitated the develOP'ment of better multiplexing systems to reducegeometric distortion. jump. and weave to a mini-

mum.7-8. Function. The purpose and function of

each component. such as lenses. mirrors,- sole-noids. and precision gear trains, will determinethe versatility and flexibility of the multiplexer.The function of the field lens in the multiplexer.as illustrated in figure 39. is to form an interme-diate image between the projection lens, and the

camera lens. The projected image will then re-

3 6

PROJECTIONLENS

FIELDLENS

CAMERALENS SECOND IMAGE

PLANE

SCENE

FIRST IMAGEPLANE

Figure 39. Field lens projection system.

main true in perspective through the multiplexingunit.

7-9. Many means of selecting the optical pathmay be employed. The most common methoduses front surface full reflecting mirrors and semi-transparent mirrors. These mirrors may be eitherstationary or movable, depending upon the ver-satility and flexibility desired. Figure 40 showsa multiplexer containing a single, fixed semitrans-parent mirror which is capable of mixing twoprojector inputs and reflects one output to thecamera pickup tube. You can see from the illus-tration that the mirror directs the image from theprojector to the camera pickup tube.

7-10. Multiplexers of a more complex designwhich use movable mirrors in their operationwill also use solenoids to operate the precisiongear train. Solenoids, being electrical switches,can be operated remotely; hence, the opticalpath may be changed from a remote location.Precision gear trains are used to operate smoothlythe mirror assemblies and reduce resultant vibra-

LIGHT PATH A

SEMI-MIRROR

LIGHT PATH B

OUTPUT

VIDICON PICKUPTUBE SURFACE

tions which may otherwise destroy the align-ment of the optical paths.

7-11. Operation. The simplest type of multi-plexer may employ a single front surface mirrorto direct the projected image onto the camerapickup tube mosaic. The simple multiplexer unit.which uses a single, stationary semitransparentmirror like the one shown in figure 40. may beused when more versatility is desired from theprojection equipment. While the single frontsurface mirror is limited to single projector oper-ation. the single semitransparent mirror multi-plexer permits immediate switching between twoprojectors. The more complex multiplexing sys-

MIRROR P2

semiTRANSPARENTmiRRORS

SLIDEPROJECTOR 1

1140FM*

PROJECTOR

mIRROR

ONIIMO

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VIDICOmCAMERA

Figure 40. Semimirror optical mixing system. Figure 41. Sliding:mirror optical multiplexing system.

40

36 4

SI. IDEPROJECTOR

1414sP 'Lag

PROJECTOR2

SEW- TRANSPARENTMIRROR

4

166imFILM

PROJECTOR

YIOtcONCAme RA

Figure 42. Turnstile-tnirror optical multiplexing system.

tern5_may use sliding mirrors or mirrors that arcmounted on turnstile swivels. Complex multi-plexers arc commonly used because they aremuch more flexible. Some examples of multi-plexers which use sliding and turnstile mirrorsare shown in figures 41 and 42. Note that themultiplexer illustrated in fieure 41 employs twosliding semitransparent mirrors to direct the pro-jected image onto the camera pickup tube. When

mirror 1 is in the center or operating position. itintercepts the projected image from film projectorI and reflects that image upon the camera pickup

tubc. Selection of film projector 2 can be made

readily by simply moving mirror 1 out of the op-tical path and mirror 2 into the optical path. Thisis accomplished when both mirrors are moved

LIGHT PATH A

LIGHT PATH B

in the direction of the arrows. The slide projectorcan be used at any time because both mirrors are

semitransparent.7-12. An example of a more complex optical

mixing system is illustrated in figure 43. Notice

that it employes a stationary semitransparentmirror. as well as a movable semitransparent mir-ror mounted on a turnstile swivel. With this con-bination of mirrors any one of four sources maybe selected. It is also possible to mix inputs A,B. and C or A. B. and D.

7-13. A multiplexer which uses a single semi-

transparent mirror is illustrated in figure 42. Themirror is mounted on a turnstile swivel which canbe turned in increments of 90°. Thus, the mirroris placed alternately in the optical path of pro-jector 1 and projector 2. Since the mirror is again

semitransparent. as in the other examples. the

slide projector may be used when the mirror is ineither position.

7-14. The mirrors cannot be installed in their

proper operating positions initially; hence, somemechanical adjustments must be provided. Al-though these adjustments are made variable overa small range. they are sufficient to permit finalalignment of the optical paths.

7-15. Multiplexer complexity is determined by

the type. number, and mobility of the mirrors.Since projector design and construction are var-ied. selection of the types and their positioningare determined entirely by the individual produc-tion requirements. Consequently. the flexibilityof the entire multiplexing system is determined

by multiplexer versatility, varied selection ofprojectors. and type of camera.

7-16. Maintenance. The multiplexer mainte-nance requirements are much the same as thosefor other types of television and projection equip-

ment. Periodic cleaning, lubrication, and inspec-

LIGHT PATH D

MOVABLESEMIMIRROR

PERMANENTSEMIMIRROR c\\

OUTPUT

LICHT PATH C

Figure 43. Sonimirror optkal tnixinv sy3tein.

41

36t';

?51-

tion will suffice in most instances. Replacementor repair of broken and darnaged components 'isalso of great importance ard must be accom-plished whether discovered durine operation orperiodic maintenance.

7-17. Dirty mirrors and lenses decrease theoperating efficiency of the multiplexer. Sincethis is true, all mirrors and lenses must be cleanedregularly. Remember, as in projectors. only anapproved solvent and lens cleaning materialshould be used to clean the glass surfaces of mul-

,tiplexer components.7-18. Gear trains and other moving compon-

ents must be cleaned and lubricated at periodicintervals. Again, only an approved lubricant andsolvent or equivalent substitutes should be usedon these parts. Periodic inspection of the mul-tiplexer increases its operating efficiency, becauseall discrepancies discovered and corrected atthat time decrease the number of failures duringoperation.

7-19. Defective components should be re-paired at the time they are discovered. H thecomponent is not reparable. it must .be replaced

with an eq.iivalent part, because the multiplexermust be exact in order not to detract 'from theoverall operation of the system.

7-20. Troubleshooting. Most problems encoun-tered in the multiplexer are mechanical and arerelatively easy to locate and correct. The mustcommon problems are dirty, scratched. or brokenmirrors and lenses. and misalignment of the mir-rors.

7-21. If you discovered for example. that theimage being projected from the slide projector(see fig. 41) was out of geometric proportion.while the images projected from the two film pro-jectors were correct, the problem would prob-ably be misalignment of the slide projector. Inother words. the slide projector is not operating inthe same optical plane as the camera. Since thetwo film projectors are operating properly, themirror alignment must be correct.

7-22. In the multiplexer represented by figure41. we see that the image from film projector 1

is normal, while the image from film projector 2is washed out. The problem is likely to be a dirtymirror reflecting the image from film projector 2.

3 6

5:48

Specialized Test Equipment

ACCEPTABLE television coverage for a givenarea depends upon the operational and

transmission efficiency of the system servicing the

arca. Television, like all other electronic sys-tems, requires the use of test equipment for propercare and maintenance. In addition, to meet tele-vision color, video, and pulse standards, special-ized tcst equipment is required. In this chapterwe will discuss some of the specially designed sig-nal generators, signal analyzers. and test patternsrequired by television. The discussion of thistest equipment will include purposes. functions.

and general block diagrams. rather than specific

models. The chapter also includes a discussion

of test patterns and pulses used in making routineperformance checks and adjustments and theinterpretation of certain test pattern displays andcharts applicable to video testing.

, '10I 1.

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35'qCHAPTER 3

8. Monoseope Amplifier8-1. Since studio and film cameras arc so

costly television stations find it impractical to usethem for test pattern transmission. The mono-scope amplifier. often called the monoscope cam-era, is now used for this purpose since it is muchsmaller and less costly. The monoscope camerapermits the television station to have a single pat-tern of known quality available for display ortest purposes at all times. A block diagram ofthe monoscope camera is shown in figure 44; ourdiscussion will be concerned primarily with thepecularities of the camera and its use in genera-ting a test pattern.

8-2. Monoscope Tube. The monoscope tube

contains an aluminum plate which functions much

like the mosaic of an iconoscope tube. This

.1.1, ALLDII If

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Figure 44. Monoscope camera block diagram.

43

36 7

Figure 45. Test pattern, monoscope amplifier.

aluminum plate has a single pattern etched uponit with carbon ink. Since the pattern is etched onthe aluminum plate, the tube is limited to a singlepattern presentation. The pattern design variesaccording to the desires of the individual tele-vision station; however, its basic purposc remainsthe same.

8-3. Operation of the monoscope tube is verysimilar to that of the iconoscope tube. The clearsurface of the aluminum plate emits more sec-ondary electrons than the carbonized area. Likethe iconoscope, a collector electrode in the mono-scope tube collects the secondary electrons. Thus,by systematically scanning the target with anelectron beam. a picture signal is produced. Sincethe clear aluminum surface emits more second-ary electrons than the carbonized area. the outputpicture signal Ifas a negative white component.The standard television transmitted signal. as youalready know. has a negative black component.This means that some way of inverting the pic-ture must be incorporated in the monoscopc tubeor amplifier section. Picture inversion can beaccomplished in one of two ways. First, picture

44

inversion can be accomplished by using an oddnumber of video amplifiers in the monoscopeamplifier section to produce a 1800 phase shiftin the output signal. Second, the pattern can beprinted as a negative on the aluminum plate ofthe monoscope camera tube. In other words, thealuminum plate is coated with carbon ink and thepattern is outlined with clear aluminum. Then thepicture signal will contain a negative black com-ponent. Either method will produce an outputpicture signal which is compatible with standardtelevision systems.

8-4. The block diagram of the monoscope cam-era (fig. 44) illustrates its general circuitry andbasic operation. The drive, synchronizing. andblanking pulses are introduced from the externalsynchronizing generator. The deflection circuitsarc magnetic: thus. their operation is like thatof the image orthicon. vidicdn. and iconoscopetube-deflection circuits. Note that the mono-scope tube output presentation shows a negativewhite component. To get the signal inversionshown in the video amplifier output, an oddnumber of video amplifiers must be used.

368

8-5. Pattern Interpretation. The test patternpresentation from the monoscope tube has many

useful purposes. The puttern illustrated in figure45. for example, may bc used to accomplish sys-

tem quality checks, such as resolution capabili-

ties. low-frequency response. contrast. and de-

flection linearity. The monoscopc camera also

provides a modulated signal for transmitter qual-

ity and performance tests. When the output of an

r-f signal generator is modulated by the output of

the monoscope camera. receiver performance canbe checked readily against a known standard.

8-6. The pattern presentation illustrated in

figure 45 has five sets of wedges. one in each of

the four corners and one in the center circle.These wedges provide a reference for adjusting

the horizontal and vertical resolution of a tele-vision transmitting or receiving facility. The wedge

lines are calibrated in lines of resolutionthenumber of times a system can change from black

to white. The center line of each wedge is.dashed

to mark resolution definition; the number asso-ciated with each break in the line, multiplied by10. defines resolution for that, point. The reso-lution displayed by a given image is deterniined

by estimating the position at which definiteseparation between the wedge lines is noticeable.

The horizontal resolution can be checked by ob-

serving the vertical wedges. Since the size ofthe scanning beam is onc of the factors limitingresolution, the resolution definition is an indi-cation of the quality of focus. The corner wedges

provide a fixed reference for focusing in the areas

where defocusing is most likely to prevail.

8-7. The monoscope camera resolution is lim-

ited by the size of the scanning beam and the

maximum number of lines available for scanning.

Since the monoscope camera tube has an opti-

mum resolution of 500 lines, it cannot effectively

reproduce half-tone images. Consequently, an

alternate method of producing half tones (grayscale) had to be developed. The diagonal wedges

in the center circle of the pattern produce anillusionary standard for measuring gray-scale re-

production. By etching a series of lines at speci-

fied intervals, a simulated density range is con-

structed from light gray to black; the innermost

portions of the wedges appear 100 percent black

and the outer portions appear 25 percent black.

with graduated steps of 75 percent and 50 per-

ci-nt black separating the two extremes. When

brightness and contrast controls are properly ad-

justed, each of the steps in the density range is

separate and distinct.8-8. The horizontal lines beneath the center

circle of the test pattern are used to check the

sow-frequency response of the circuits under test.

An excessive phase shift of low frequencies re-sults in a gradual change in shadine from top tobottom of the picture. causing bright streamers, or

streaks. to follow large dark objects in the scene

of,a received picture. Thus. the amount of streak-ing following the end of the horizontal lines in the

change from black to white is an indication ofthe quality of low-frequency response. Good low-

frequency response is indicated by little or nostreak ing.

8-9. The aspect ratio of 4:3 is established

when the deflection is adjusted so as to give atrue undistorted form to the large circle, sincethis circle is three-fourths of the pattern width.The diagonal lines indicate an area equal to

one-half the picture width. Deflection linearity

may be checked by measuring the spacing be-

twccn the diagonal lines.

9. Video Test Equipment9-1. In this section we will discuss somc of the

specialized test equipment associated with tele-

vision video testing. The discussion will be de-veloped primarily around the grating generator,

dot generator. and vitleo sweep marker genera-

tor. We will describe their purpose and opera-

tion. as well as interpret their output patterns.The section will also include a discussion of thepulse cross display with reference to its useful-

ness in determining the width and amplitude of

the equalizing pulses and both the horizontal and

vertical blanking and synchronizine pulses in re-

lation to a general pattern interpretation. Wewill show some of the standard charts used for

television quality checks and briefly discuss thefunction of each pattern.

9-2. Grating Generator. The grating gcnerator

provides a convenient means for checkine and

45

36

Figure 46. Grating test pattern.

FROM SYNCGENERATOR

VERTICALPULSES

HORIZONTALPULSES

I A

1

ADDER

BLANKINGCLIPPER

ANDAMPLIFIER

VERT. FREQ.X 15

MULTIVIBRATOR

ADDER

colHORI)Z(.2F0REQ.

MULTIVIBRATOR

Figure 47. Grating generawr block diagram.

adjusting the linearity of television deflection cir-cuits. It generates a timing signal synchronizedby standard synchronizing pulses. obtained fromeither the synchronizing generator or the deflec-tion circuits of the receiver under test, and injectsthis signal into the video circuit being tested. Thepattern produced has the appearance of a grat-ing. as illustrated in figure 46.

9-3. The block diagram. ficure 47, illustratesthe typical grating generator circuitry necessaryto produce a satisfactory grating pattern. Thedesired pattern is produced by inserting the hori-zontal and vertical synchronizing pulses fromeither a standard television synchronizing genera-tor or the deflection circuits of a television re-ceiver. as previously stated. The vertical pulses ,

are then multiplied 15 times, while the horizon-tal pulses are multiplied 20 times. They are vec-

46

BLANKINGGATE

A

CLIPPER

VIDEOOUTPUT

340P-

torially added in the adder circuit and the out-put is applied to a clippet The output patternof the grating generator is determined by the biaspoint of the clipper circuit. When the bias is ad-justed so that either thc horizontal or verticalsignal extends above the clipping level, the re-sulting output is a grating pattern. Moreover, thecrating signal must be clipped at both ends of theamplitude range so that the lines will not appearblacker than black at their intersecting points.

9-4. To prevent lines from appearing duringretrace, the horizontal and vertical retrace pulsesarc combined, as shown in figure 47. Whenadded. they form a blanking pulse. and this pulseis applied to the blanking gate circuit. An outputsignal is produced only when thc incoming signalis strong enough to merride the level of the blank-ing pulse.

310

,

Figure 48. Dot test pattern.

9-5. The grating pattern is comprised 'of 14horizontal bars and 17 vertical bars. The bars.being evenly spaced, conform with both the as-pect ratio of the television system and the linear-ity chart. discussed later in this section.

9-6. The grating generator will also produceeither honzontal or vertical bars separately. By

selecting the output from either the times-I5 ortimes-20 multivibrator and applying it to the sig-nal clipper, the generator output will result inhorizontal or vertical bars only.

9-7. By injecting the grating pattern into a re-ceiver or monitor and checking the display uni-formity. you can determine descrepancies. in the

deflection circuits' linearity. The linearity is ad-justed properly if the vertical and horizontal barsare both uniformly spaced over the entire viewingarea. The grating pattern is also useful when youadjust the linearity of a camera chain. (This will

11111

-- :E7

N$ERTEo

Fieuw. 49. Sweep marker uraetular black dawram.

47

be discussed more fully in the portion concerning

chart displays.) Another valuable feature of the

grating pattern is apparent when you adjust theconvergence of a color receiver or monitor. Thisfeature is discussed further in the section dealingwith color testing.

9-8. Dot Generator. The same generator is

often used to generate the dot pattern or tilL:

grating pattern. Only the clipper bias point wdetermine which output is produced. If the signal

clipper bias is so adjusted for an output only

when the horizontal and vertical pulses are

added, a dot pattern will result. The other cir-cuits in the dot generator and their operation areidentical to those employed in ihe grating oener-,. z-

ator. Thus. figure 47 can also represent a basic

block diagram of a dot generator.9-9. The output pattern from the dot gen-

erator is illustrated in figure 48. This pattern isprimarily used when adjusting the convergenceof a color receiver or monitor and will be dis-cussed in more detail in the next section of this

%FE.1110e.

GE1460TQa141,1

CA.ER

Pe:WE*SUPL.

DE ?in. ocu ...Z5C0I.E

Figure 50. Camera amplirwr bandpass chick.

chapter. However. we can now see that a singlegenerator may be used to produce horizontalbars, vertical bars. a grating pattern, or a dotpattern as the need arises.

9-10. Sweep Marker Generator. The videosweep marker generator. shown in figure 49. isa convenient device for checking the frequencyresponse of a given amplifier. In a typical gen-ecator, the output of a fixed r-f oscillator, operat-ing at approximately 70 MHz, is heterodyned

against a sweep (variable) frequency oscillator.The sweep oscillator is being swept (varied overits frequency range of 69 to 80 MHz) at a

60-Hz rate. The 0- to 10-MHz beat frequency

is then applied to the circuit or unit being tested.and the resulting output. after detection, is ob-

served on an oscilloscope. Marker notches areinserted at 1-MHz intervals for frequency cali-bration of the beat frequency; this is accom-plished by an additional oscillator stage in thesweep generator. A more accurate means ofcalibrating can be obtained with a sweep gen-erator unit that employs a calibrated CW oscilla-

3 7 I,

5 MHz4 MHz

3 MHz

6 MHz

8 MHz7 MHz

Figure 51. Oscillosccpe presentation of camera bandpass.

tor as a marker source. This type of markersource provides either variable or fixed markersover a marker source range of 100 KHz to 10MHz.

9-11. The most useful function of the sweepmarker generator is to test and adjust the band-pass of camera preamplifiers. The equipmentlayout used to check a camera preamplifier witha sweep marker generator is illustrated in figure50. Figure 51 shows the output pattern of aproperly tuned camera preamplifer as seen onthe oscilloscope. Notice the notches inserted inthe output pattern. These markers help you ob-serve the range of frequency response of the out-put pattern from the camera preamplifier. Thesemarks are important since the frequency-responsecurve must be flat to 8 MHz for adequate band-pass of the television video information.

9-12. Pulse Cross Display. The pulse crossdisplay is one of the most important measure-ments in television and it is used to determinewhether the synchronizing generator is producingthe proper pulse sequel-we. width, and amplitude.The pulse cross display, along with its correctinterpretation. is a convenient means of conduct-ing operational measurements of the output pulsesproduced in the synchronizing generator. Other.types of more detailed pulse analyses and ad-justments may be necessary at periodic intervals:

48

!!:

however, these functions will require the use ofspecialized test equipment. Thus the pulse crossdisplay is more practical for routine operationalmeasurements because this test simply requiresthe usc of a modified video monitor. This moni-tor is usually available in any television broad-casting station.

9-13. In normal video transmission the hori-zontal and vertical synehronizng pulses occur atthc end of each scanning line and cach field.respectively. Thus, the front porch of the hori-zontal synchronizing pulse occurs at the rightedge of the picturc. whereas the back porch oc-curs at the left edge. On the other hand. thevertical blanking interval occurs during verticalretrace. We see then that the information con-tained in the vertical blanking pulse occurs atthe top and bottom of the viewing screen. Sinceall of the synchronizing and blanking informa-tion occurs at the edges of the picture arca, itsinformation is hidden by the picture tube mask.

9-14. Though detailed information may bedifficult to distinguish. the general shape of thevertical blanking interval can be observed on moststandard receivers and monitors by rotating thevertical-hold control until the vertical blankingbar is located in the viewing area. The hori-zontal synchronizing and blanking pulses. occurr-ing at the end of each scan line. arc much more

372

4-61)

difficult to observe: however, with the modifica-tions normally .provided, the standard television

monitor will eliminate any definition, vertical

displacemem. or horizontal displacement prob-

lems. Thus the pulse cross display can be ob-served instantly or monitored continually for

extended periods of time.9-15. The individual lines can be seen more

readily if thc horizontal and vertical scanningprocess is expanded. As a result, the pulse crossdisplay information is seen in more detail. Ex-pansion of the picture tube swecp circuits willpermit the horizontal and vertical synchronizingand blanking information to be placed in theviewing area of the picture tube.

9-16. Interpretation of the pulse cross displayis relatively easy when you understand that theindividual pulse amplitudes are indicated by light

intensity. In the pulse cross display. shown infigure 52. the horizontal dimensions. of the lightintensities are relative measures of time or pulse

widths. Use figure 52 to identify the followingpulse group patterns:

Athe horizontal synchronizing pulse duration.(0.075H-0.098H )

Bthe horizontal blanking pulse duration. (0.1651[0,18H)

Cthe vertical synchronizing pulse interval. (0.4211-0.44H)

Dthe vertical blanking interval. (13.IH-21.0H)E and Fthe equalizing pulse intervals.Gthe six dark lines which show vertical synchroniz-

inn pulse duration.1the equalizing pulse duration. (0.05 horiz sync

width IJthe horizontal blanking and synchronizing pulses

that continue to occur at the end of each horizontalvideo scan line until the beginning of the next verticalblanking interval.

Kthe front porch of the' horizontal blanking pulse.

(0.02H)Lthe back porch of the horizontal blanking pulse.

(0.05H)Mthe pulses which occur during the remaining

vertical blanking time.

F l-es A`4=01111/1

VIM

1

Figure 52. Pulse cross disphi..

49

37,3

p

a

,PIA'ic.,V,Y 44,44414, -144":"."0.7.4c1:1

r%%,-)44,, 4ctrig :4'414," 0:41.4A'

It

[f'r4

4

ta7t9i ,1

c

k 411114

ic-.4.1e t;IV'

1 4

.

4

Each pulse width may be compared to its normalduration. You may desire to review portionsof Sync Generators. Chapter 3. Volume I. par-ticularly figure 40. Table uf TV Pulse Svmdards.After you have had some experience in usingthe cross pulse display. you may devise a rulercalibrated in normal pulse widths to check thepulse cross display. Of course this ruler wouldapply only to a particular monitor. You can alsouse the pulse cross display to check the numberof lines in the equalizing and vertical pulses.

9-17. The quality of detail in the reproducedpicture is called resolution. or definition, anddepends upon the number of basic picture ele-ments that can be reproduced. A picture withgood resolution requires as many picture elementsas possible. Good resolution of a picture is in-dicaied by sharply defined objects and no blur-ring or running together of closely spaced linesor points. Horizontal detail and vertical detailmust be considered separately in a 'televisionpicture. The maximum vertical resolution is de-termined by the number of active scanning lines.The horizontal resolution is determined by themaximum number of changes in voltage that canoccur in each line that is scanned. This numberof voltage changes depends directly upon thefrequency respoviSe of the system. the resultingsignal bandwidth, the size of the pickup. andthe picture tube scanning spots.

9-18. Test Patterns. Standard test charts havebeen developed which permit more comprehen-sive testing of system performance than the testpattern produced by the monoscope amplifier(discussed in Section 8 of this chapter). Theresolution chart shown in figure 53 can be usedfor making system quality tests for geometricdistortion (linearity), aspect ratio. resolution.shading uniformity, frequency response. streak-ing. interlace, gray-scale reproduction (contrast).brightness. and r-f or other high-frequency inter-ference.

9-19. When making a geometric distortioncheck. position your camera and focus on thetest chart. The resulting picture display will ex-actly cover the visible portion of the receiver ormonitor screen. A picture free from distortionhas linear scanning and correct aspect ratio.Check vertical linearity by comparing thc spacingbetween the short horizontal bars at the top.bottom, and center of the picture. If the spacingis equal in each set of horizontal bars. verticallinearity is satisfactory. You can check hori-zontal sweep linearity by comparing thc spacingof vertical bars at each side of the picture andin the center square. If the spacing is equal ineach set of vertical bars. horizontal linearity is

satisfactory. The circles located in each corner

51

and at the center of the chart are a further checkfor geometric distortion. Circles that are non-linear or distorted in shape indicate incorrectadjustment of the vertical. horizontal, or bothhorizontal and vertical sweep linearity. You cancheck aspect ratio by measuring the large portionof the picture formed by the four gray-scale barsto determine if it is square. Aspect ratio is correctif the pattern is square and the scanning is linear.

9-20. A resolution check is made only afterthe set is adjusted for minimum distortion. Youmeasure resolution horizontally and vertically byobserving the wedges in the large circle at thecenter and the small circles at the edges of thepicture. The wedge lines are calibrated in linesof resolution in the same manner as those of thetest pattern produced by the monoscope ampli-fier discussed in paragraph 8-9 of this chapter.Resolution of the system under test is numeric-ally defined on the chart at the point where theseparation between these lines is no longer dis-cernible. You judge horizontal resolution by ob-

.serving the vertical wedg%s at the top and bottomof the circles, but in the case of vertical resolu-tion. you observe the horizontal wedges at theright and left of the circles.

9-21. To check interlace, you observe the di-agonal lines in the center square of the picture.Interlace is correct if the lines appear similar tothose in figure 53. Jagged diagonal lines indicatepartial pairing of the lines. The diagonal lineswill not appear jagged if complete line pairingoccurs. Under this condition, total line pairingcan be determined by the resolution wedges.since vertical resolution cannot exceed 250 lines.

9-22. The quality of gray-scale reproductionis judged by the number of distinguishable stepsin each of the four gray scales which form thelarge square in the center of the picture. Thequality of reproduction is related directly to thenumber of steps that are distinguishable. Youcheck shading uniformity by observing the back-ground of the test pattern presentation. An evengray background indicates satisfactory shadinguniformity.

9-23. Tie dominant white quality of the chartmakes it necessary at times to adjust the con-trast and brightness controls to obtain a picturepleasing; to the eye. The picture should be pleas-ing to the eye for the average televised programif you adjust the receiver for optimum perform-ance with the chart.

9 ,24. R-f or other high-frequency interferenceis sometimes introduced into the video amplifierscanning circuits. R-f interference in the hori-zontal sweep circuits from the power supply isindicated when the verticai lines in the test pat-

0.075 H

0.165 H

ASPECT RATIO IS 4,1HORIZONTAL BLANKING 17.5%VERTICAL BLANKING 7.5%EL ECTRICAl GRATING PAT TERN GENERATOR FREOUENCIES:

315 KC HORIZONTAL, 000 CYCLE VERTICAL 0 065 V

_o A o A o

o o o ooB0 0 0 0 0 it 0 0 0 0 00 075 V

00 0 0 00 0

2 3 4 5

0 00 0 0 00 0 0 00 0

2 3 4 5

c 0 0 c 0 00 D 0 0 0 0 0 D 0 0 0 0 0

E 0 0 E 0 06 7 8 9 10 11 12 13 14 15 16

F 0 0 . F 0 01OGO 0 0 0G0 0 0 0 0

. H 0 0 0 0 0 0 0 0 0I 0 0 I 0 0

6 7 8 9 10 11 12 13 14 15 16

O 0 J 0 0 J 0 0O 0 0 0 0 K 0 0 0 0 0 K 0 0 0 0o 0 0 0 0 0

LIHEARTY CHARTO 0 0 0 0 IA 0 0 0 0 0 0 0 0 0 0V 0 7 0 I 0CIRCL ES OUTER RADII fo.

ARE 2% OFPICTURE HEIGHT

Figure 54.

CIRCLES INNER RADII'ARE 1% OF

PICTURE HEIGHT0.175 H L. 0.165 H

Fl7

. uE

Figure 55. Co1or-bar l''enerator output taveforms.

tern become modulated and take on a ripple ap-pearance. R-f or other high-frequency interfer-ence in the video amplifier is indicated by amoire pattern over the whole picture.

9-25. The standard linearity chart illustratedin figuie 54 is used when you make cameralinearity adjustments. This chart has an aspectratio equal to that of the grating pattern (shownin fie. 46). Furthermore. the circles occur atthe same positions in the linearity chart that thelines intersect in the grating pattern The twotest patterns are superimposed on a monitorscreen when you focus the video camera on thelinearity chart and simultaneously transmit it andthe pattern from a grating generator. A camerawith linear scanning produces a picture uniformlydistributed on the screen. Therefor,: you canadjust the linearity of thc camera by adjustingthe camera linearity controls so that the circlesof the linearity chart coincide with the intersec-tions or the grating pattern (within the accepta-ble 2 percent tolerance).

10. Color Testing10-1. Since color television requires more crit-

ical standards of operation, some types ofspecialized test equipment are necessary to main-tain these standards. In this section we willdiscuss the purpose and usefulness of some of thetest equipment used to maintain these criticalstandards. The function of such test equipment asthe linearity checker. color-bar generator, colorsignal analyzer. vectorscope. and grating genera-tor will be discussed. We will also interpret theoutput patterns produced by this equipment anddiscuss their oscilloscope presentations.

10-2. Linearity Checker. The gain and phaselinearity in a-color video signal must bc main-tained at an established level. A composite colorsignal consists of a luminance component on

53

which is imposed the 3.58-MHz color subcarrier.The subcarrier is modulated in such a mannerthat the amplitude determines the degree of satu-ration of the reproduced colors and the phaserelationships produce the hue. The typical line-arity checker provides a means of measuringthe differential gain (system gain variation atdifferent light levels) and differential phase dis-tortion (phase shift at different light levels) ofvideo amplifiers and transmission systems. Initeneral. linearity checkers are signal generatorsproviding a simulated color video signal.

10-3. Color-Bar Generator. The color-bar gen-erator is produced in two basic models. The firstis a compact. lightweight instrument primarilydesigned for portability. The second is designedfor standard 19-inch rack mounting and is usedprimarily in television broadcast station opera-tions. In both units the operation is much thesame and the desired outputs serve the samebasic purpose.

10-4. The color-bar generator serves manyuseful purposes. such as checking the operationof color television ;.eceivers and monitors. adjust-ing color phase. checking and adjusting colormatrix systems. supplying'a color reference signalto the signal analyzer, and supplying a colorreference signal zo the colorplexer.

10-5. The color-bar generator supplies rec-tangular pulses which are applied to the red. blue.and green input circuits of the colorplexer toform a color-bar test pattern at the cclorplexer

,

w

Q WHITE

I YELLOW

WHITE

CYAN

GREEN

BLACK

PURPLE

RED

BLUE

Figure 56. Location of burs on color-bar pattern.

3.440

FROMSYNC

GENERATOR vERTICALDRIVEINPUT

1

RED,AU

,tBF A TCR

SluEMUL T1.

VIBRATOR

«NIT EMUL TI-

vIBRA TOR

mUL T -OBRA TOR

G,ODE

DIODE

n,ODE

O`ODE

:IBRA,DPmtjt. TI- DIC.DE

Figure, 57. Color-bar generator block (Ii(lerani.

output. Provisions are also incorporated to pro-duce a split-field pattern with the standard colorbars making up the top portion and the specialQ. I, and a white bar making up the bottomportion. Figure 55 illustrates the red. blue. andgreen pulse shapes and duration. These pulsesare produced in the color-bar generator. Figure56 illustrates how the special Q. I. and whitebars are placed in relation to the output colorbars.

COLORBURST

'

10-6. Figure 57 shows a basic color-bar gen-erator. Note that the input pulses are receivedfrom the synchroni7int: generator. In the case c;a portable color-bar generator. these pulses arereceived from the deflectkm circuits of the re-ceiver or monitor under test. The blanking pulseis used t6 form thc wawsshape. amplitude. andduration of the pulses illustrated in figure 55.The keing multivibrator is free-running at 60Hz. The input vertical drive pulse from the

Figure 58. Sunerimpos,,,l col wptexer output vicnalr-

54

3 7 d

I!

7°

At:7)

COLORBURST

=1

116.

TOP HALF

G.

COLORBURST

BOTTOM HALF

Fimure PO. 0,10,plcxer output 3ignals (top half, bottom halh.

synchronizing generator keys this multivibrator.producing a split screen pattern. The vector addi-

tion of the red, blue. .uid green pulses generated

in the color-bar generator will produce the colorbars. as shown at the top of figure 56. The

special Q and I signals are derived from theblanking pulse and are produced as separate out-

puts. The white bar is produced when the I

multivibrator output kcys the white .multivibra-

tor. The output of the %%hitc multivibrator

applied to the three primary color outputs in

equal amounts. As seen in figure 56 the pulsew.dth of the special Q. I. and white bars are ad-

justed for onc. one.. and two bar w idths. re-

speetiel>. When the output sinals are coupled

through regulating diodes, the output luminance

55

is stabilized. When these signals are applied to.the appropriate section of the colorplexer. the

output composite signal. with top and bottomhalves superimposed (bars at 75 percent level).looks like fieure 58. The individual output sig-

nals for the upper and lower portions of thepicture area appear much like those in figure

59.

10-7. Color Signal Analyzer. A color signalanalyzer is a test instrument used to study thecomponents of a composite color video and sub-carrier signal. (A block diagram of a basic colorsigaal analyzer is illustrated in fig. 60.) Whenused in conjunction with a color-bar generatorand oscilloscope, it permits measurements of thephase relationships bctwccn the subcarrier burst

3 7j

37)

0 -2 MCEll TER

VIDEO INPU TCOLOR

2-5 MCFILTER

sib

ADDER

3 6 MC CALIBRATEDRLFI R FNCE 360°>-10. PHASE

SHIFTER PHASEDET

SHIFT

I

PHASE1 - 10°

SHIFT

15°PHASESHIFT

LOWPASSFILTER Pa

30°PHASESHIFT

leePHASESHIFT

5o

PHASESHIF T

tooPHASESHIFT

20°PHASESHIF T

L BLOCK DIAGRAM OF 360° PHASE SHIF TER

Figure 60. Color signal analyzer block diagram.

900PIIASESHIF T

OU IPU1TO

OSCILLOSCOPL

3 8

aittrArlfoli

Figure 61. Colorplexer output, modulated 1.

reference and the various components of a com-posite xolor signal. It may be used also withlinearity checker to make differential phase meas-urements.

10-3. Notice in figure 60 that the 360° phaseshifter consists of several fixed and variablephase-shifting circuits; thus, the input signal canbe shifted a full 360°. in increments of 1°. Thisis possible because the individual phase shifterstotal 360° and one 10° shifter is adjustable inincrements of I °. The capability of being ableto shift the incoming signal 360' is necessarybecause phasing of the individual color com-ponent signals is critical if an acceptable com-posite color signal is to be achieved.

10-9. When the colorplexer is operated in thecolor-bar mode, some representative oscilloscopepatterns as they appear at the input of the colorsignal analyzer are modulated I (fig. 61) andmodulated Q (fig. 62). respectively. When theoutput signals are demodulated. they can bephased properly with minimum problems. Inaddition. the phase relationship between any ofthe input sienals and the subcarrier or betweenthe individual input I. Q. red. blue. and greensignals can also be checked. Usine the color sub-

COLORvIDEO

2.5 mCFILTER

MOD

carrier as a reference. you see that the signalscan be phase shifted in the 360° phase-shiftingnetwork. The I signal must be 90° out of phasewith the color subcarrier. To do this, insert themodulated I color signal component (fig, 61)intO the color signal analyzer. In the color signalanalyzer the I signal is demodulated to simplifythe phase adjustments. Next, select a 90° phaseshift and adjus. the I phase control on the color-plexer until all the pulses rest on the referenceline. After removing the inserted phase shift.phase the color signal component properly inrelation to the color subcarrier. Employ the sameadjustment procedure when dealing with the Qsignal component. However, since it is only 33°out of phase with the color subcarrier, it requiresonly a 33° phase shift when making the necessarytests and adjustments.

10-10. The phase relationships between in-dividual input pulses can be checked if you firstplace one signal on the reference line (color sub-carrier) and then place the second input signalon the reference line. You can determine theamount of phase shift between the two inputsigna/s by finding the difference between thetwo phase insertions which were necessary toplace the two signals on the reference line. Inother words. if the first pulse signal was 90°out of phase with the reference line and the

Figure 62. Colorplexer output, modulated Q.

mOD

BURSTCONTROLL EDOSCILLATOR

IMm

LPFILTER

90°SHIFT

_J.

LPFIL.TER

Figure 63. Block diagram of a typical vector display oscilloscope.

57

382

Ic-

D-CCATHODE-RAYOSCILLOSCOPE

MM/00

vECTOR DISPLAYOSCILLOSCOPE

Fisture 64. Typical t.ector tli pluv oscilloscope pattern.

second pulse signal 33° out of phase. the differ-ence would be 57°. The first pulse signal wouldthen be 57° out of phase with the second pulsesignal. You can now see that the color signalanalyzer has many useful purposes for insuringthe proper operation of the color-bar generatorand colorplexer.

10-11. Vectorscope. One of the newer testequipment items developed for close inspectionof amplitudes and phases of subearricr signalsis the vector display oscill'O'Scope. commonly calledthe vectorscope. A block diagram of a typicalvector display oscilloscope is shown in figure 03.Generally. this equipment uses a pair of quad-rature demodulators, The demodulator outputs

applied to the X and Y plates of a d-c oscillo-,.'ope. Most designs incorporate a burst-con-trolled oscillator to generate a reference sub-carrier from the synchronizing burst o; the signalunder test.

10-12. When used v. ith eolor-1,.ar signals, thevectorsegpe produces a pattern ok lines anddots which indicate th: vectors corresponding tothe various colors. The pattern appears as brightdots linked by relatively faint lines. As illus-trnted in figure 64. boxe3 may be drawn on theoscilloscope face to indicate phase and amplitudetolerances.

10-13. By comparing our discussion- of thevectorscope and the color signal analyzer. wefind that the two pieces Of equipment performmany of the same functions. Furthermore, weknow that both have their athantages and dis-advantages. Future planning seems to indicatemore varied uses for the vectorscope, includingfacilities for monitoring the camera nut signalsat the camera.

10-14. Grating Generator. The purpose andoutstanding features of the grating generator, asit applies to black and white television, weredeveloped earlier in this chapter. Now we willexamine its operation and functions as they per-tain to color television testing.

10-15. The cross-hatch pattern generated bythe grating generator is extremely useful whenmaking adjustments in the convergence of a colorreceiver or monitor. When viewing the picturearea of the receiver. with the grating patternapplied. look for proper alignment of the verticaland horiz..,,ital bars. The convergence is prop-erly' adjusted if the bars are placed over oneanother and no color fringing is apparent.

10-1(1. Dot Generator. The dot pattern pro-duced by the dot generator is also very usefulfor testing and adjusting color receiver and moni-tor convergence. As with the grating generator.place the dots one upon the other; if no colorfringing is apparent. the convergence is properlyadjusted. Though either the grating or dot pat-tern may he used for convergence adjustments.the dot pattern is usually. preferred since it showswhich direction the correction must be applied.

38358

VHF Equipment

MHIS CHAPTER concerns transmitters, an-tennas. and receivers. However, since very-

high-frequency (VHF) equipment is the lowestin frequency used by TV, the VHF equipmentis discussed prior to ultra-high-frequency (UHF)equipment. In this chapter you will study theVHF equipment necessary to create. amplify.modulate. and radiate a carrier frequency. Also

CHAPTER 4

discussed is the equipment necessary to pick up.amplify, and reproduce both visual and auralsignals.

11. VHF TransmittersI l-I. VHF transmitter principles employ

many of the basic transmitter circuits. Normallythese circuits will consist of an oscillator. fre-

9D

Figure 65. Master oscillator power amplifier tMOP.4) transmitter.

59

38,4

quency multiplier, modulator. and r-f amplifier.The first part of our discussion win be devotedto basic transmitters.

11-2. Tranimitter Principles. You will recallthat the basic transmitter consists of an oscillatorconnected directly to an antenna. Because ofcertain limitations, this circuit is unsatisfactoryas a means of transmitting communications. Thereare two main drawbacks in connecting the oscilla-tor directly to the antenna. First, the poweroutput is limited because there are no stages ofr-f amplification between the oscillator and theantenna. The second limitation of a variablefrequency oscillator transmitter is its lack of fre-quency stability. The frequency of an electron-tube oscillator is, of course, controlled by theinductance and capacitance of its frequency-de-termining circuits. Coupling a loading device,such as an antenna, to the output of the oscillatorhas a great effect on its frequency stability. Theload impedance of the oscillator is the reflectedimpedance of the antenna. This reflected im-pedance contains both resistive and reactive com-ponents. The resistive component lowers the Qof the tank circuit and the reactive compc,,-ntalters the resonant frequency.

11-3. Another problem. frequency stability.arises in the use of VHF and UHF transmitters.Although the frequency of an oscillator can bestabilized by use of a crystal, transmitters mustoperate at much higher frequencies than a crystalcan be cut to operate. The crystal oscillator,therefore, must be followed by frequency multi-pliers to provide the desired output frequency.

11-4. The oscillator determines the frequencystability of a transmitter. An unstable oscillatorwill cause an unstable signal to be radiated bythe antenna. A master oscillator power amplifier(MOPA) circuit can be used to overcome theinstability of the antenna-coupled oscilllator. (Anexample of a MOPA circuit is shown in fig.65.) The output of the series-fed Hartley oscilla-tor is coupled through C4 to the power amplifier(PA) stage. The oscillator stage is isolated fromthe antenna by the PA and will not be affectedby changes in antenna-to-ground capacitance.Changes in the plate impedance of the PA will

A LOOSE COVP:iNGCRIT.CEE COUPLING

PEO:ENCY

E',5,3:10..1;`47.,CLCSE ENO LOOSECOUPLING

Figure 66. Coupling response curves.

nut be reflzcted into its grid circuit and backto the oscillator. The signal applied to the gridof the PA from the oscillator v. i11 cause'the platetank of the PA to oscillate at the frequency ofthe oscillator. The MOPA circuit normally is notused with crystal oscillators, but generally is usedin conjunction with one of the common variablefrequency types such as Colpitts or Hartley oscil-lators. Selection of the type of oscillator willdepend on thc purpose for which thc transmitteris intended. If the frequency must be variableyet stable, an electron-coupled oscillator may byselected.

11-5. Stages are coupled by one of threemethodscapacitive, inductive, and link. In fig-ure 65. C4 is a coupling capacitor and providesa low-impedance path for the r-f energy from theoscillator tank to the grid of the power amplifier.It also acts as a blocking capacitor by prevent-ing the high d-c potential on the oscillator platefrom reaching the grid of the amplifier tube.Capacitive coupling is simple and is used fre-quently in low power amplifier stages. However.it has some disadvantages that limit its use inthe higher frequency ranges,

11-6. Inductive coupling is used extensivelyin transmitters. This type of coupling is possthiebecause magnetic lines of force set up by thecurrent in one coil will induce a voltage intoanother coil. The extent to which the lines offorce of the energized coil (primary) cut theother coil (secondary) is measured in henrys.This is called mutual inductance (M). In figure66. notice the various response curves resultingfrom the different degrees of coupling. In thecurves shown, the input voltage applied to theprimary is held constant in amplitude while itsfrequency is varied. If each circuit is independ-ently tuned and the coupling kept loose, theoverall frequency response assumes the formshown by curve A. The double-humped curveshown by curve C results from a coefficient ofcoupling that is greater than critical coupling.As shown in curve D, it is possible to work outa compromise between very loose and very closecoupling and arrive at a uniform response to asmall band of frequencies.

11-7. Link coupling is actually a special formof inductive coupling and is commonly used intransmitters. The link consists of a low-imped-ance line terminating in a coil at each end. Thiscoupling is made at a point of low potential.called the nodal point. The nodal point occursat the ground end of the tank in single-endedstages and at the center of the coil in balancedcircuits such as the push-pull amplifier. By op-erating at a point of low voltage. link coupling

60

38,4

THECAMERA CHAIN

THETRANSMISSION CHAIN

&LIKE

IMMO CON TROt ROOm

VIE WFINDER

CAMERA

viDEO

1

AUDIOAMPS

AUDIOCON TROL

COMPOSITEVIDEO

DISTRIBUTIONEQUIPMENT

MONITOR

H AND VDRIVE

CAMERACONTROL

vIDEO

FILM CHAIN

SWITCHINGEQUIP

POwERSUPPL Y

H AND v DRIVEBLANKING

SYNCGENERA TOR

COMPOSITEVIDEO

I

1ADDITIONAL

CAMERACHAINS I

COMPOSITE ISYNC

DISTAmP

EQUALIZERSR-F GENCOA XIAL

CABLEMICROWAVE

COmPOSIT EVIDEO

COmPOSI TEviDEO

TO ADDITIONAL CAMERA CHAINS.MONITORS, FILM CHAINS.

NOTES

I. SYNC IS ADDED TO THECAMERA-CONTROL IN SOMECASES IN LIEU OF THE SWITCHER.

BROADCAST TRANSMIT TE RSYSTEM

VIDEO (Am)TX

FILTERISIDEBAR()

I I

1 I

I I

AUDIO

T X PLEXER "---1I

i

AUDIO IFM1 DI- BALUN iI

I

AUDIO

_CLOSED-CIRCUIT REPRODUCTION

APPLICATIONS

MAPS

SWITCHINGEQUIP

I

SPEAKERS

H_ MONITORS

Figure 67. Basic elementsbroadcast and closed-circuit television transmission.

386

can eliminate harmonics which might our....rv..;s.be transferred hy capacitive coupline.

11-8. Transmllter SignaIs. The transmissionchain of a television system. as shown in figur267, includes equipment tor transmittmg the tele-vision signal through spine or coaxial-cable. Com-merical broadcast TV informatiorris, of course.transmitted by radiated signal through space tothe reproducing devicesthe TV receivers OtherTV applications, explained earlier, utihze coaxialline to transmit TV information between thecamera chain and the reproducing devices,.The type of auxiliary equipment used for videodistribution between the camera chain and eitherthe transmitter (broadcast) or video display units(dosed-circuit applications) depends on the loca-tion and the distance to be covered. The videoand sound in the broadcast system must be trans-mitted by electromagnetic radiation to the TVreceivers. In closed circuit systems, however.raw video may be used for direct production ofthe televised scene on the screens of specific TVmonitors.

11-9. The audio chain (fig. 67) is parallel tobut separated from the video chain. In closed-circuit application the audio system wiH fre-quently be composed of stock audio componentssuch as the microphones. amplifiers, and speak-ers found in an ordinary public address system.For a television broadcast studio. however, mostaudio components will be chosen because of theiradaptability to FM operation,

11-10. The visual transmitter takes the videosignal from the camera chain and passes itthrough the amplification and modulation processto produce an amplitude-modulated r-f output.

xTAL MULTIPLIER AMPLIFIER

Also inciucied the equipment components:o form the proper bandpas ..:har,ic-

teristics to meet FCC standard. The aural trcn.%-mir:(7 takes the oricinal audio silmals and irc-quency-moi:ul.,tes and amplifs the NI* signal toohtd.r. the filml modulated output. We can f.eefrom thk description and figure 67 that there at:two separate transmitters.

11-11. The television transmitter operatingband rekrs to the frequencies at which the trans-mitter may be operated. A low-band VHF trans-mitter may be tuned and operated in channels 2to 6, or at frequencies of 54 to 88 MHz. A high-hand VHF transmitter may be used to operatein channels 7 to 13, or at frequencies of 174 to216 MHz. Some types of VHF transmitters redesigned to operate in any one of the channds2 through 13. A UHF transmitter (discussed inthe next chapter) operates in channds 14 to 83.or at frequencies of 470 to 890 MHz.

I 1-12. Visual transmitter. T he functionalstages of a visual transmitter are indicated inure 68. The composite video signal from thccamera chain reaches the transmitter throughthe various ways already mentioned. The videomodulator and d-c restorer function to modulatethe r-f Signal in accordance with the incomingvideo information and to maintain the blankingand sync peak levels at fixed values. The r-fstages of the transmitter usuaHy contain a cryst:il-controned oscillator. foHowed by frequency-mul-tiplier stages to attain the desired operating fre-quency. The r-f signal strength is then increasedby amplifier stages to a level desired for modula-tion. Modulation of the r-f carrier takes place ata driver or power amplifier stage. Linear power

MODULATED LINEAR-AMPLIFIERAMPLIFIER SIDEBAND

ANTENNASYSTEM

OUTPUT

aDIPL EXEROSCILLATOR

VIDEOFROMCAMERACHA IN

STAGES

STABILIZINGAmP

STAGES

VIDEOAmP.

VIDEO mODUL ATOR- - - - -11-r"

STAGESSTAGE (IF USED)

MODULATOROUTPUT

FIL TER

FREQUENCYPOWER. MOD-ULATION, AND

PICTURE mONITORSFROMAURALTRANSMITTER

0-CINSERTION

Figure 68. Block iliagrrunvisual transmitter functional stages.

62

1.0

RELATIVE 0.3OUTPUT

LOWER

e....VIDEO CARRIER

UPPER

VIDEO SIDEBAND(IN MEGACYCLES)

VIDEO SIDEBAND(IN MEGACYCLES)

PORTIDN OF SIGNAL USEDIN VESTIGIAL SIDEBAND

TRANSMISSION

5 -4.0

44

4.0 4 5 4.75

41 4.0 MHz --*/4.5 MHz

5.70 MHz

6.0 mHz

Figure 69. Distribution of signals on a standard television channel.

amplifier stages, including the output power stageof the transmitter, are used following the modu-lated stage.

11-13. The visual signal must be maintainedwithin certain tolerances. The visual carrier fre-quency of a station must be held stable within atolerance of ±1000 Hz. The aural carriermust bf, maintained at 4.5 MHz zt..-1000 Hzabove the visual carrier frequency. Televisionchannels of 6 MHz are necessary to transmitboth the audio and picture information. You

can appreciate the space occupied by a TV chan-nel by comparing the AM broadcast band with asingle TV channel. The 106 10-KHz channels inthe AM band extend from 540 to 1600 KHz. All106 radio stations occupy much less frequencyspace than a single TV station.

11-14. Higher bands of frequencies are allo-cated to TV stations than those used for standardradio broadcasting so that there may be a reason-able number of channels available. The overallallocations for TV channels are split into twobands in the VHF range (as already indicated)and one more band in the UHF range. In allbands of VHF and UHF, every channel is 6MHz wide. The VHF channels by number andfrequency are allocated as follows (the UHFband will be listed in the next chapter):

Channel Nuniber

23

Frequency Range in MHz

54-6060-66

63

MO CARRIER WITH25 KHz SWING

VIDEO CARRIERATTENUATED 20 DB

A T THIS POINT

Channel Number Frequency Range in MHz

4 66-725 76-826 82-887 174-1808 180-1869 186-192

10 192-19811 198-20412 204-21013 2 10-2 16

11-15. The frequency gaps between the TVbands are Used for other purposes. One TVbroadcasting channel can be used concurrentlyby many TV broadcasting stations, provided thestations are separated by at least 150 to 225

miles. This separation is necessary in order tominimize the interference between these stations.They are known as co-channel stations. Stationsthat use channels adjacent to one another in fre-

quency are termed "adjacent-channel stations."To minimize interference between them, adja-cent-channel stations are not assigned to the samecity but are separated by at least 50 to 75 milesor more. However, channels consecutive in num-ber but not adjacent in frequencies, such as chan-nels 4 and 5 or channels 6 and 7, can be assignedin one local area. The standard TV channel(shown in fig. 69) consists of both the pictureand sound carriers plus their corresponding side-bands. Notice that the picture carrier .and its sig-nal sidebands occupy approximately 5.75 MHzof the 6-MHz bandwidth. The sound carrier,

however. which is frequency-modulated, with arnaxirnum.deviation of .t---25 KHz, occupies the re-mainder of the bandwidth. (Fig. 69 is scaled toshow a channel width of 6 MHz.) To calculatethe distribution of signals for any specific chan-nel, consider the 1.25 point as representingthe lower frequency extreme in MHz and the4.75 point the upper frequency extreme in MHz.To find the picture carrier frequency of channel5, add the low sideband of the picture carrier1.25 MHz to 76 MHz. This will result in apicture carrier frequency for channel 5 of 77.25MHz. To find the sound carrier frequency, addthe upper video sideband of the picture carrier4.50 MHz to 77.25 MHz. The sound carrier fre-quency for channel 5 will be 81.75 MHz.

11-16. You can see in figure 69 that thehigh-frequency sideband of .the picture carrier is4.5 MHz wide, while the low-frequency sidebandis only 1.25 MHz wide. This unsymmetrical dis-tribution permits transmission of a picture withbetter definition while using only a 6-MHz chan-nel. This method is called vestigial sidebandtransmission. Using this method will provide agreat savings in the TV frequency allocations inthe frequency spectrum. The picture carrier fre-

INPUTFROM

VISUALTRANSMITTER

C1

quency is located az the 0-MHz. point in the chan-nel. The high-frequency sideband cf the picturecarrier is flat to the 4.0-MHz point and thendrops off to almost zero at 4.5 MHz. The low-frequency sideband ( 1.25 to 0 MHzi of thepicture carricr is flat for 0.75 MHz and thendrops off to almost zero in the remaining 0.5MHz. These 0,5-MHz dropoff areas arc thevideo guard bands whose purpose is to preventinteraction between thc video and audio signals.

11-17. Vestigial sideband filter. There arevarious methods of attenutating the unwantedportion of the lower sideband. The transmitterusing low-level modulation may provide someattenuation of the lower sideband by tuning thebroadband linear r-f stages toward the desiredupper sideband. An advantage of this mode ofoperation for sideband suppression is thc ability

'of being able to adjust the transmitter for anychannel within its tunable range without usingthe sideband filter. In most cases a sidebandfilter is incorporated in the system to furnish ab-solute sideband attenuation.

11-18. Absolute sideband suppression is ac-complished by placing a sideband filter betweenthe output of the final stage and the antenna load

e 01

so. 'ARO

Figure 70. Vestigial sidehand

64 3 8

°

AUDIOFROM -.-SwSTUDIO

AUX. LINEAMPLIFIERS

FMMODUL ATOR

OSC.FREO.

MULTIPLIERSPOWERAMP.

Figur!7). Block diagramaural transmitter functional stages.

system. All final-stage modulated systems must

use a filter, since stagger-tuning is not possibleas used in the case of prefinal-staee modulatedsystems. The entire ,sideband suppression in

final-stage systems is accomplished by filtering.with the power being dissipated in the foiln ofheat. A disadvantage of this system is that aseparate filter must be designed and used foreach operating channel.

11-19. In order that the power-handling ca-pability may be made less severe, the filter unitmay be placed between the modulated stage and

a class B linear amplifier stage. The physicalsize of the sideband filter is determined by itsfrequency of operation and power-handling capa-

bility. Sideband filters used for UHF trans-mission are made considerably smaller than those

for VHF.11-20. A theoretical schematic of a vestigial

sideband filter systcm is shown in figure 70. Thesideband filter is made up of suitable lengths ofcoaxial line which are used to simulate the induc-tive and capacitive elements as required. The

filter output must have the characteristic outputimpedance equal to the antenna resistance

R, is the antenna radiation resistance. and Rais a dissipating resistor which removes the energyof the unwanted frequencies. The tuned circuits.formed by coaxial lines, determine the frequen-cies to be passed to and radiated by the antennaand the unwanted frequencies to be passed toand dissipated by R.I.

11-21. The series-resonant circuit L3-C3 is

tuned to a frequency slightly lower than the car-rier frequency. At this frequency and higher,

the impedance of L3-C3 will be zero (1,1); thiseffectively moves ground to the bottom of LI and

short-eircuits Ra. At the same time, the circuit

components L2-C2 appear as an inductive reac-

tance X 1. The effective filter 'circuit for this fre-

quency will be a pi type filter as shown by LI-C1

and X 1 of figure 70. All the available powerfor the video sienal at this frequency and higher(depending on the designed bandpass) will befed to the antenna represented by 12.1. The

effective circuit represents a high-pass filter.

11-22. The series-resonant circuit L2-C2 is

resonant to the desired cutoff frequency (thatpoint of the lower sideband frequencies at which

65

3

TO DIPLEXERANDANTENNASYSTEM

attenuation will start to take place). At this fre-quency and lower, the circuit impedance ofL2-C2 is zero (1), resulting in an effectiveshort circuiting of the antenna (Lin). At thesame time, L3-C3 will appear as a capacitivereactance, X,.. The effective filter circuit at

this frequency and lower will be a pi type filteras shown by Xe, LI. and CI of figure 70. In

this case all the energy will be dissipated by theresistor Ra. This effective circuit represents alow-pass filter.

11-23. As a result of the foregoing action, thehigh frequencies of the operating band are passedmore easily to the antenna and the low frequen-cies to the dissipating resistor, to form the fre-quency band-pass response of the signal requiredby FCC. The resistor Rd is designed to handlesufficient power dissipation. Even so, the greatestpart of the total energy to be transmitted is found

at the carrier frequency and near the carrier fre:

quencies in the sidebands. This indicates that

the resistor receives only a small amount of thetotal power.

11-24. Because the frequency response of afilter begins to rise again at frequencies belowthe desired cutoff point, the vestigial sidebandfilters actually used are designed more elabor-ately than .the one shown in figure 70. Addedsections of eoaxil line provide more absolute

attenuation of the unwanted lower sideband fre-quencies. If a vestigial sideband filter is insertedafter the final r-f stage (as shown in fig. 68),the output of the filter will feed a diplexer. If

the filter is used at an earlier stage, the outputof the final r-f stage will feed the diplexer. Thediplexer is usually employed to permit the visual

and aural transmitters to feed into a common an-

tenna system.

11-25. Aural transmitter. Figure 71 represents

a block diagram of the functional stages of theFM aural TV transmitter. The audio signal ar-riving from the studio is usually reamplified toproduce operating levels. Amplification is ac-

complished with a line amplifier inserted at thetransmitter end of the studio-to-transmitter line.

A compression amplifier is often used after theaudio signal has been amplified to Orevent over-modulation of the transmitter. The compression

3 5 I

amplifier also permits settintis of average modu-lation levels close to the allowable limits.

11-26. The audio frequency is applied to theFM modulator tinit where frequency-modula-tion takes place and the center frequency of theaural signal is initiated and controlled. The FMsignal is controlled either direetl), by a crystalfollowed by multiplier stages, or through the com-parison of two frequencies derived from a masteroscillator and a crystal oscillator. In the lattermethod, a difference of frequency produces acorrected voltage which is applied back to thcmaster oscillator to provide frequency stability.The frequency control of the initial signal mustbe highly stable in order to provide the properfrequency difference (4.5 MHz) between thevisual and aural carrier signals for application ofthe intercarrier principle.

11-27. The number of frequency multiplierstages depends on the initial frequency producedin the modulator-oscillator section and the opera-ing band for which the transaf r is designed.The general principles found in TV au-al trans-mission are almost identical with those used inFM radio broadcasting. The main difference isthat FM radio is designed with a center fre-quency deviation of 75 KHz. whereas the devia-tion in TV is only 25 KHz. Monitors are used torecord the carrier frequency (center frequency)and modulation deviation readings continuously.A loudspeaker is provided in most cases for auralmonitoring of the signal. and provisions are madefor noise and distortion measurements. The tol-erance for the aural center frequency undermonochrome standards is set at =1000 Hz. Dis-

N-5E-w RADIATORSRADIATORS

AURALTRANSMITTER

OUTPUT

VISUALTRANSMITTER

OUTPUT

A

tortion must he held to current FCC standards.'Nith =25 KHz being defined as 100 percentmodulation, measurements are made at '100, 50.and 25 percent. Maximum distertion ranges from2.5 to 3.5 percent, depending on the modulationfrequency. The power output of the aural trans-mitter cutout must meet minimum and maximum.FCC standards. These standards are expressed asa relationship between the aural and visual trans-mitter outputs. For example. the standard mayrequire that the aural output be from 80 to 110percent of the visual output. The signal from theaural transmitter is passed on to the diplexerthrough coaxial cable, which connects to anantenna system common to the visual transmitter.

11-28. f he diplexer. A diplexer unit is em-ployed by TV systems using one antenna for thetransmission of both the aural and visual signals.Besides connecting the two separate transmitteroutput sienals to a common antenna system, thediplexer also prevents intercoupling between thetwo signals. A tee-diplexer used in VHF bandtransmission is shown in figure 72.B, along witha schematic of the equivalent circuits fed by thetwo signals (fig. 72,A).

11-29. As you can see, the diplexer schematicshows the use of the familiar Wheatstone bridge.This principle achieves the desired isolation be-tween the two transmitter inputs. The arrange-ment also permits the symmetrical feeding of thetwo transmitter outputs to the TV transmittingantenna system. The output of the visual trans-mitter is applied across one pair of bridge points

. TO ANTENNA 61-5,RADIATORS RADIATORS

Fiqure 72. Dipfrxer and equivalent circuit.

66

3 9

abi

Nommal,

VISUAL INPUT

3

while the aural transmitter is applied across the

other pair, The two antenna outputs constituteadjoining arms of the bridge while split sleeves

form the bridge arms opposite the antennas. Ifthe arms of the bridge are in perfect balance, the

energy applied to one pair of bridge points will

not appear at the other pair. Crosstalk. there-

fore, will be eliminated by carefully balancingthe bridge arms. The diplexer must be designed

and built for specific operating frequencies. For

UHF frequency 'application, of course, the di-

plexer is much smaller in size than the types

used in the VHF bands. Notice in figure 72.A.

that the antenna load presented to the aural

transmitter is unbalanced to ground (single-

ended). whereas the visual transmitter output

load is balanced to ground (double-ended).

The output of the visual transmitter is normallysingle-ended (coaxial line). To convert the vis-

ual output to match the double-ended load of the

bridce diplexer. a device known as a balun is

used. (The theory of baluns will be discussed in

the next section.) The construction of the bridge

diplexer is based on the split balun (fig. 72.C).

in which the outer conductor of a coaxial line is

split for a quarter-wavelength (inductor L in fig.

72.A).11-30. Transmission Polarity. In the United

States negative transmission is standard for the

TV picture carrier. Negative transmission is a

carrier which is modulated so an increase in pic-

ture brightness results in a decrease in signal

amplitude. In a negative transmission the- tips

of the synchronizing pulses represent maximum

carrier level. The highlights in the picture cor .

respond to the maximum carrier amplitude. Anadvantage of negative transmission is that it

makes use of the nonlinear transmitter modula-

tion characteristic sometimes encountered. Be-

cause of the rectangular shape of the synchroniz-

ing pulses. any compression or saturation taking

place during the modulation process only reduces

the amplitude of the pulses; otherwise. their

shape is not materially affected. It is also

possible to compensate for compression by

preemphasizing the synchronizing pulses before

modulation. In this way a correct ratio of picture-

to-synchronizing pulse amplitudes is maintained.

In a positive transmission system the highlights

of the picture correspond to the maximum car-

rier; however, any nonlinear region of the

modulation characteristic cannot be used without

compression of the white portion of the picture

signal. A large portion of the low end of the

modulation- curve (which is usually completely

linear) is used up by the synchronizing pulses.

11-31. Negative transmission has the advant-

age that noise peaks will produce black spots or

67

streaks rather than white in the reproduced pic-

ture. For this reason black "noise" is generally

less objectionable than white "noise." especiallyif the amplitude of the white noise is great enough

to produce blooming of the picture-tube scanningbeam. The picture tube, therefore, serves as a

partial noise limiter in a negative transmission sys-

tem because the interference cannot become any

blacker than black.11-32. Normally. negative transmission sys-

tems will have an average power rating of thetransmitter. This is less than that for a positivetransmission system because the duty cycle ofthe synchronizing pulses is small as compared to

the average picture waveform. This means thatthe average transmitter power requirements are

less when the synchronizing pulses (negative

transmission). rather than the picture waveform

(positive transmission), determine the maximum

peak power needs. Negative transmission also

offers advantages in TV receiver design with re-

spect to automatic gain control and the inter-carrier sound system.

11-33. General Maintenance. Finding troublesthat develop in a transmitter is relatively quickand simple if you follow a few definite rules.There is a general procedure that can be fol-lowed in troubleshooting which, with a few spe-cific rules. can be made to apply to any particu-

lar transmitter. In most transmitters practicallyall troubles can be isolated to a stage by using

meter indications. The following normal indica-tions listed are those where the meter is located

in the cathode circuit.11-34. Oscillator. The meter will indicate

total oscillator tube current. When the plate cir-

cuit is tuned, the meter reading will "dip" if theoscillator is functioning normally.

11-35. Doubler. The meter indicates doublertube current and the reading will dip when you

are tuning the doubler plate circuit if all the pre-ceding stages are operating normally. Care mustbe taken to obtain the lowest dip in this positionor the stage will be tuned to the wrong harmonic.

11-36. Tripler. The meter indicates total trip-ler tube current; when the plate circuit is tuned,the meter reading will dip if the tripler is re-

ceiving drive from the preceding stage and isworking normally. Again, care must be taken to

obtain the lowest dip or the stage will be tuned

to the wrong harmonic.11-37. Power amplifier. The meter indicates

power amplifier tube current and will dip when

tuning the plate circuit. This will be true onlyif all the preceding stages arc operating normally

and the grid circuit is properly tuned.

11-38. If a transmitter is designed to use grid

readings in addition to cathode readings. remem-

.31)

ber that a grid reading will be for maximumcurrent rather than a dip. The meter actu,Illindicates the grid drive of a stage. This drive orreading should increase as the plate circuit of theprevious stage is tuned to resonance.

11-39. When troubleshooting a transmitter,start with the oscillator and continue until youreach the stage giving an abnormal meter readingor no meter reading. This should,.of course, bethe defective stage. Most maintenance will con-sist of cleaning filters, cavities, and other com-ponents. The other major maintenance items wilt..prisist of tube and fuse replacements. The prob-lems to be solved will be easy if you will "read"the symptoms and reason them out.

11-40. Color Transmitters. Many of the trans-mitters used by commercial companies were de-signed before color requirements were completelystandardized. As a result, because of initial in-vestments, modifications have been developed toadapt these transmitters to color operation. Wecan conclude from this statement that TV trans-mitters are fundamentally the same for mono-chrome and color. The main factor to be con-sidered, relative to color transmission. is thereduced tolerance limits. Some specific problemsare the filters and clampers of the various trans-mitter circuits which tend to distort the burst sig-nals and the "whiter-than-white" overshoots.

11-41. The new transmitters being designedand used are able to meet the FCC standards inthe sections dealing with permissible subcarrieramplitude and phase errors. There are certainauxiliary units designed to be used with a colorTV transmitter. These units include stabilizingamplifiers, phase and amplitude equalizers. timedelay precompensation sections, and linearitycorrectors. Parts of these units are passive net-works, while others are units with circuits ofsolid state or tube design. The vestigial sidebandfilter for color transmission must be adequate tokeep the burst signal radiation to the 60-dblevel specified by the FCC.

12. VHF Antennas

12-1. The antenna system is the link betweenan individual transmitting station and its receiv-ing station or stations. Regardless of the form ofthe TV antenna. its main purpose is to radiateor receive signal-bearing r-f energy. An antennasystem can be considered to include the antennaitself, the feed line, and any coupling devicesused for transferring power to the line and fromthe line to the antenna. In this section we willconsider the characteristics of transmission linesat various frequencies, the propagation and radia-tion characteristics at various frequencies, the re-quirements of VHF television antennas, and the

physical anJ electrical characteristics of :annespecial types of HF television anteimas.

12-2. Transmission and Propagation. Thetransmission line provides the path for transferr-ing signal energy tront the TV transmitter to itsantenna and for delivering the signal energy re-ceived by the antenna to a IV receiver. Propa-gation refers to the way the electromagneticwaves. representative of the TV signal. travelfrom the transmitting antenna to the receivingantenna. A knowledge of the characteristics oftransmission lines and propagation i:, very im-portant in TV work.

12-3. 1/1-IF television transmission require-ments. The transmitter's frequency of operationdepends upon its channel alloca0on ( VHF chan-nel allocations were discussed in Section 11 ). Atransmission line must be capable of ,--nsferringsignal energy from one point to a..,,her withminimum attenuation and without introducingany reactive componeots which would vary thecharacteristics of its input or output circuits. Also.a transmission line whould have negligible pickupalong its length so that it will not introduce sig-nals into the receiver other than those receivedsignals coming from the antenna.

12-4. Transmission lines. An efficient '.rans-mission line must be selected with great care withrespect to dimensions, length, and irnpedancematching. Failure to secure optimum conditionsresults in a noticeably pronounced decrease inpicture and sound signals and an increase innoise interference. Two general types of trans-mission lines, the parallel-wire type and thecoaxial cable, are used extensively in VHF TVinstallations.

12-5. A transmission line can be describedin terms of its characteristic impedance (Z),determined by the diameter of the conductorsand the spacing between them. You will recallthat Z is the same regardless of the lengthof the line and is defined in electrical terms asZo = Zo is in ohms. L is the inductance per

Cunit length in henrys. and C is the capacitance perunit length in farads.

12-6. A line terminated in a resistive loadequal to Z is nonrcsonant. transfers maximumpower, and contains no reflected energy. On theother hand, a line terminated in opens. shorts.capacitances. inductances, or resistances unequalto Z is resonant and has energy reflected backinto it causing standing waves to be set up onthe line. You have no doubt already noted thatthe measurement of standing waves on a trans-mksion line yields information about its effi-ciency of operation.

68

3 9 3

5/5(-fr

12-7. Of the three types of inherent losses ina lineresistive, dielectric, and radiationtheradiation loss is likely to be the most variable: Itis very important to notc that radiation loss varieswith frequency. A VHF or UHF transmissionline is efficient only at the frequency for which itis designed. When used at frequencies higherthan those for which it is designed. a line hasgreater losses.

12-8. Radiation and propagation clurracteriA-tics. You will recall that the creatiVe manner inwhich electromagnetic waves travel throuehspacc is called propagation. The direct-wavecomponent of a VHF or UHF radiated field tendsto travel in practically a "line-of-sight" manner.with minor rcfraction due to the lower atmos-phere. A portion of the wave strikes the earthat some distance from the antenna. however, andis reflected upward. Increasing the height of areceiving antenna tends to decrease signal-volt-age cancellation caused by ground-reflectedwaves.

12-9. VHF Antennas, General. The electricaland physical features of VHF antennas areuniquely determined and vary with operating fre-quency. power-handling capability, plane of po-larization. and the desired radiation field pattern.The physical size of an antenna is determinedprimarily by its operating frequency and power-handling capability, whcreas its shape and heightarc determined by the desired radiation field pat-tern. Since the effective authorized area of serv-ice. local tcrrain conditions. and power outputlevel of transmitting equipment vary from in-stallation to installation, the antenna system usedis almost always custom designed and custombuilt.

12-10. Function and requirements. The func-tion of the VHF television transmitting antennais to radiate with essentially uniform efficiency atthc frequency range of the channel it serves. Toperform this function. the antenna must meet cer-tain physical and electrical requirements.

12-11. The physical requirements of any VHFantenna systcm include adequate structuralstrength to withstand wind, snow, and sleet loads;low wind-resistant radiating elements; immunityto damage from lightning; and deicing facilitieswhcrc needed. The most important electricalconsiderations of the VHF transmitting antennainclude horizontal polarization of the radiatcd,...aves, omnidirectional horizontal radiation pat-tern, wide = bandwidth. high gain, adequateinsulation to har.dle peak voltages that will beapplitNI to it, and vertical directivity to obtain therequired effective radiated power in relation tothc transmitter output. Satisfactory signal re-ception by VHF TV antennas is obtained by

69

considering such antenna factors as broadbandresponse, directional characteristics, eliminationof unwanted signals and reflections, and an-tenna location. In our introductory discussion ofthc various properties of TV antennas, we arctaking the simple dipole as the basic reference.

12-12. Resonant wavelength. The electrical(resonant) wavelengths of TV antennas differfrom those of radio waves in free space. As thefrequency of operation increases, radiation resis-tancc and thc effect of capacitance at thc end ofthc antenna effectively rcducc the resonant wave-length of an antenna. It is therefore necessary tocut TV antennas with a correction factor (usually0.94). For example. let us assume we are design-ing an antenna for television channel 3. 60 to 66MHz. using the midfrequency (63 MHz) in thedesign formula.

12-13. You will recall that a formula describ-ing r-f propagation in free space is:

(feet)984 feet

F (MHz)

Using the correction factor. 0.94, we can deter-mine the physical length of the antenna whichwould operate with an effective wavelength equiv-alent to that of a 63-MHz signal:

984 feet x 0.94(feet) 63 MHz

A = 14.5 feet

A dipole antenna designed fon channel 3 opera-tion. therefore, should be 7.25...feet in length. Itis often desirable to calculate thc length of a di-pole in inches. Here is a practical 'form of theformula (including a correction factor) com-monly used for this purpose:

5540 inches-F (inches) F (MHz)

12-14. Impedance. Thc impedance at anypoint on an antenna is simply equal to the voltageat that point divided by the current at the point.A half-wave dipole antenna usually has an im-pedance of approximately 72 ohms at the center(input impedance). but its impedance may beseveral thousand ohms at the ends. with intcr-mcdiate points having intcrmediatc ohmic values.These values are valid only for the resonantfrequency; for frequencies off resonance, thecenter impedance is greater.

12-15. Folded dipole antennas can be used tofacilitate impedancc matching with Aransmissionlines. Each additional conductor of a folded di-pole antenna increases the input impedance. If

1)5

MAL,MUM

41.

'Neu,

Z\-

: \'; S,,

/r Y.\ 7.1°)11:17:

am NUL I eoq.

\

< I?IC

o.

MA XIMUM

;

Figure 73. Radiation pattern of a horizontally mounteddipole antenna.

two conductors are used, the current is reducedto one-half its original value and the input im-pedance of the antenna increases to four times72 ohms, or about 300 ohms. Therefore, a 300-ohm transmission line can be connected to thefolded dipole and a correct Z-match will occur.If the added conductor has a larger diameter thanthe conductor to which the transmission line is

connected. the impedance stepup produced bythe folded dipole is further increased.

12-16. Polarization. You will recall that thepolarization of a propagated electromagnetic wavedepends upon the direction in which the electricfield travels.with respect to the earth. A verticallymounted antenna radiates a vertically polarizedwave, whereas a horizontally mounted antennaradiates a horizontally polarized wave. Horizon-tal mounting of the transmitting antenna in theclear at a high altitude substantially reduces theeffects of the earth on the propagated wave.Better reception is usually obtained from a hori-zontally mounted receiving antenna because itis less susceptible to noise pickup.

12-17. Directivity. Antennas which radiate inall directions are referred to as omnidirectional.Since radio waves are electromagnetic in nature,they can be directed so that radiation either oc-curs in specific directions or is concentrated into anarrow band. The polar-coordinate graph is gen-erally used in studying signal intensity or radia-tion patterns. Figure 73 is a polar representa-tion of a horizontally mounted dipole antenna.The pattern may be used to interpret transmittingor receiving directivity characteristics.

12-18. The antenna characteristic that causes

70

the antenna to radiate or receive morc k,owercertain directions than in others is dirt.:livit.There are severai method.. obtaining Lifts:et:analcharacteristics in an anterma. One method Uheheither driven or parasitic multiclement arrays.Driven arrays are bidirectional. whereas para-sitic arrays are unidirectIonal. Another mohoduses reflectors and directors. Still another uses anumber of individual antennas connected to-eether. A combination of methods may bc usedto achieve highly directional antennas. Such di-rectional antennas form an important part ofpoint-to-point communications. microwave link.and radio relay systems. Many TV systcmsa microwave link between the studki and trans-mitting antenna. Microwave signals travel instraieht lines. It is therefore possible to reflectand focus them in a manner similar to light waives.The use of highly directive antennas permits asmall amount of energy at a transmitting point toproduce a satisfactory signal at a distant receivinepoint.

12-19. The VHF TV broadcasting antenna iseenerally omnidirectional: howoer. the receiv .

ing antenna is generally directional and is orientedto have maximum sensitivity in the direction ofthe transmitting station. The directional receivingantenna has better sensitivity and less noisepickup than the omnidirectional antenna. In-creasing directivity increases antenna sensitivityand tends to eliminate unwanted ,,ignals. wavereflections, and interference. Horizontal direc-tivity can be achieved by placing one or more re-flectors behind thc antenna and directors in frontof the antenna. Vertical directivity can be achievedby stacking antenna arrays one above the other.Some specific military applicatkm may require adirectional transmitting antenna

12-20. Gain, The gain of an antenna dependsupon its total radiation pattern and is a functionof directivity. The gain of onc antenna over thatof any other antenna can be determined by ob-serving the field streneth of both antennas at aparticular point. Generally. the basic half-wave(dipole) antenna is the standard aeainst whichother antennas arc measured. When not ,4peci-fled otherwise, the figure expressing the gain ofan antenna refers to the gain in the direction ofmaximum radiation, or reception. Gain is ex-pressed in terms of decibels, with zero decibels(0 db) the standard for the gain of 'a dipole.

12-21. Bandwidth. For optimum service. thetransmitting antenna should have a constant fre-quency response over the 6-mc bandwidth of itsassigned TV channel. A single receiving antennaarray is often used to receive many VIII' TVchannels. Reducing the 0 of an antenna win in-

3 9 t)

crease it bandwidth. A reduction in Q also willlower thc gain of an antenna. Methods employedto provide a wideband response and maintaingam may include:

Folding elements.Increasing size and/or number of elements.Intricate phasing of elements.End-fire arrangements.Stacking of arrays.

12-22. Factors Affecting Efficiency. If antennasare to produce or collect electromagnetic energyin an efficient manner. they must be designed andmounted in a fashion which permits efficient op-eration. Let us now discuss some of the factorswhich are considered in the designing and mount-ing of VHF antennas.

12-23. Design considerations. The field pat-tern of a given antenna is the same for receptionas for transmission. The functions of the trans-mitting and receiving antennas are. however.quite different. Transmitting antennas are de-signed for high efficiency in radiating energy.whereas receiving antennas are designed for theefficient pickup of energy. Some of the majorfactors considered in the design of antennas are(1) frequency of operation. (2) power-handlingcapabilities. and (3) desired beam pattern. Spe-cial types of antennas designed for specific pur-poses will be discussed in the last part of thissection.

12-24. Mounting considerations. Since hills.buildings. and trees affect propagation and de-crease efficicncy, surrounding areas must be con-sidered when installing antennas. Transmittingsites should be chosen to provide minimum bend-ing of direct-path energy. Receiving antennasites should be chosen to provide minimum re-flections. shadow losses. absorption losses, andinterference. The line-of-sight distance can beextended by increasing the height of either orboth of the transmitting and receiving antennas.To assure optimum service to the maximumnumber of people, transmitting antennas are us-ually placed atop a high tower or mast which isitself on top of thc highest building. mountain.or hill available. Sincc field strength dependsupon height, increasing the height of receiving an-tennas results in stronger signal reception.

12-25. It is desirable to concentrate verticalradiation at small vertical angles to provide bestcoverage of the service area. VHF energy radi-ated at ,-ngles considerably higher than the line-of-sight path is wasted because it does not returnto the effective path of signal transmission. VHFenergy radiated downward toward thc earth is

either absorbed by the earth ur reflected back toreducc signal strength or cause ghosting in the re-

71

ceiver. Vertical directivity can be readilyachieved by stacking identical antenna arrays oneabove the other and feeding them in phase.Stacking antenna arrays concentrates sensitivityat smaller vertical angles. This arrangement alsoreduces noise pickup from the top and bottom ofthc antcnna. thus improving reception sensitivityin the desired direction.

12-26. Power-Handling Capabilities. In orderto assure the best possible TV service to themaximum number of people. the FCC limits boththc maximum and minimum power which may beradiated by each broadcasting station. The an-tenna system must be capable of handling thepeak power output of the picture and soundtransmitters ( peak power input of the antenna).Meeting this requirement demands considerationof power-handling capability when selecting atransmitting antenna. It should be understoodthat antenna input power and effective radiatedpower (ERP) are not the same. Basically, ERPis the product of the antenna input power andantenna gain. In other words, a relative medium

. antenna input applied to a high-gain antennamay be as effective as a high power output ap-plied to a low-gain antenna. The maximum ERPfor a TV station is established with reference tothe visual transmitter. Channel assignment andantenna height become factors in ERP standard.The transmitting antenna must be properlyinsulated to withstand the peak voltages of thetransmitters it serves. However, insulation of thereceiving antenna presents no problem becausereceived signal strength is never over a fewmicrovolts.

12-27. Impedance Matching. The impedance ofthe transmission line serving an antenna systemmust be matched to the antenna it serves. Youwill recall that there is a maximum transfer ofenergy only when the impedances of toad andgenerator circuits are both resistive and equal.Transmitting antennas are designed to radiatewith uniform efficiency over the frequency of therange of the assigned channel. With proper im-pedance match to the transmission line, an an-tenna will radiate all of its input power. exceptfor the portion dissipated thermally in the antennaconductors. Defective termination causes reflec-tions to occur at the antenna terminals and stand-ing waves on the transmission line. Since thestanding-wave ratio for any given sidcband com-ponent is a function of frequency. the signalreaching the antenna suffers from frequency andphase distortion in addition to attenuation.

12-28. Matching of the charcteristic imped-ance of the transmission line with the input im-pedance of the receiver is important from thestandpoint of maximum sienal transfer. This is

3 9 6

especially true in weak signai areas. In additionto attenuating signal strength. reflections due tomismatching at the receiver input terminals pro-duce double image effects on the picture screen(ghosts). Matching at the receiver input (usu-ally 72 or 300 ohms) is done by using a trans-mission line with a corresponding value of char-acteristic impedance. In strong signal areas, closematching of the antenna to the transmission lineis not as important because the mismatch resultsmerely in a slight loss of sienal strength; how-ever, in this case, the transmission line and re-ceiver input impedances should be matched.

12-29. Baluns. There are two types of linesor circuitsbalanced and unbalanced. The twoconductors of a balanced transmission line haveequal resistance per unit length and equal imped-ance from each conductor to eround and to otherelectrical circuits. Antennas are usually balanced;that is, they are symmetrically constructed withrespect to the feed point. Twin lead transmissionlines are balanced. The use of shielded twinleads does not disturb the balance because theshield does not act as a conductor for the signal

1-1

,s

CYLINDER-0.

SHOR1 ED TOSHIELD

2

I

I

I II

I I

I s

I

72OHMCOAX

A BAZOOKA

72 OHMSBALANCED

B TRANSFORMER

Figure 74. Ilazno4a 1)(111111.

72

72OrtAS

Figure 75. Coaxial balun.

energy. A coaxial cable transmission line is un-balanced. Its outer conductor has a much largersurface area than the inner conductor, causingthe line to be inherently unbalanced. The con-nection between the coaxial line and the antennamust be made without upsettine the symmetry ofthe antenna itself. This requires a circuit thatwill isolate the balanced load from the unbal-anced line while providing efficient power trans-fer. The device which performs this function ofconverting balanced to unbalanced feed systems.or vice versa, is called a balun. The word is acontraction of balanced-to-unbalanced.

12-30. Bazooka Galan. A satisfactory connec-tion can be made with a bazooka. or line-balanceconverter, as shown in fieure 74. In the coaxialline, the center conductor corresponds to the hotlead; that is, it has a hieh r-f potential and is atsome impedance to ground. The purpose of thebazooka is to raise the outer conductor to a highimpedance above ground. Through the use of aquarter-wave shorted cylinder, the impedance be-tween the outer conductor and ground can be in-creased to the required value (fig. 74, A). Thisquarter-wave cylinder is connected directly to theouter conductor of the coaxial line and is shortcircuited at this point as shown. Since the cylin-der is a quarter-wavelength long, it presents ahigh impedance at the open end. Therefore. theshield is isolated from ground (electrically one-quarter wavelength) and can be connected to onewire of a balanced line or antenna. The action ofthe bazooka is similar to that of the transformershown in figure 74.B. The primary is groundedat one end. while the secondary is grounded atthe midpoint of the winding.

12-31. Coaxial &dun. Another method ofconnecting a coaxial cable to a balanced trans-

397

3-b's

mission line or a balanced antennawhile at thesame time having a 4-to-1 impedance stepupisshown in figure 75. Equal and opposite voltages,balanced to ground. are taken from the innerconductor of the main transmission line and half-wave phasing sections. Since the voltages at thebalanced end arc in series while the voltages at theunbalanced cnd are in parallel, there is a four-to-one step down ratio in impedance from the bal-anced to the unbalanced side.

12-32. VHF Antennas. Special Types. An im-portant principle in the study of antennas is that

DIRECTION OFSIGNAL RECEPTION

DIRECTION OF SIGNALR EC E P T ION

the characteristics of an antenna used for trans-mitting arc much the same as when the antennais used for receiving. Some of the practical dif-ferences between them are directional character-

power-handling capabilities, weather pro-tection. and elevation. A VHF TV transmittingantenna should be omnidirectional and radiate abroadband signal. Somc factors which affect thechoice of receiving antennas are direction andrange of the station or stations to be received,channel frequency of the transmitting station,noises and interferences prevalent in the sur-rounding area, and relative signal strength.

DIRECTOR

A

INSULATED BLOCK

TRANSMISSIONLINE PHASING SECTION

B

Figure 76. Yag: antenna.

73

396

LEADIN

INSULATING BLOCK

A

INSULATINGBLOCKS

DINECTION OfSIGNAL ACCEPTION

Figure 77. Conical antenna.

a

12-33. The choice of an antenna is sometimes'a matter of compromise. Many types of anten-nas, ranging from the modified basic dipole tomore complex wideband arrays, are used today inTV. Our discussion of the characteristics ofVHF TV receiving antennas will include thcYagi, conical, and log-periodic types. whereas thediscussion of transmitting antennas will includethe turnstile, traveling-wave (slot type), andhelical types.

12-34. Yagi antenna. The Yagi antcnna is oncof the most popular TV receiving antennas. Itscharactcristics are high gain, sharp unidirectionalresponse pattcrn, good front-to-back ratio, andrelatively narrow bandwidth. The Yagi antennais an array consisting of a driven element (di-pole) with one reflector and two or more direc-tors. The radiator may bc either a simple orfolded dipole, Additional reflectors do not im-prove reception. The more directors used. thegreater thc min; however, thc eain does not in-creas.e directly with the number of elements.

Also, adding elements will decrease the imped-ance of the array.

12-35. The simplest Yagi, such as the cneillustrated in figure 76,A, is most effective fora single channel (6-mc bandwidth). Becauseof its high gain and high front-to-back ratio, it is

particularly effective in a weak signal area. Inmany locations, however, thc sinele-channel an-tenna is outmoded because of the greater numbcrof TV channels occupied. Wideband-Yaei an-tennas have been developed for use in areaswhere several distant stations that are close infrequency lie in the same general direction.

12-36. The basic plan for thc widcband Yagiis illustrated in figure 76.B. The driven elementsare folded dipoles which may be the samc ordifferent overall lengths. However, they mustbe properly spaced and fed to make the systemresonant and maintain a constant impedance overa very broad band of frequencies. The length ofthe elements must be properly measured andspaced to provide widcband service. A typicalwideband Yagi employs two folded dipoles ofdifferent lengths which are fcd by a transmis-sion-line phasing section between the dipoles. Adouble reflector is used to obtain the most suita-ble front-to-back ratio over the wide hand offrequencies to be received.. A group of two tofour directors can be placed in front to obtainpeak gain and good front-to-back ratio at thehieh-frequency end of the band to bc received.An additional parasitic element may bc insertedbetween the driven dipoles to act as a reflectorat the high cnd and as a director at the low endof the frequencies to be received. It is possibleto cover the entire TV spectrum with three orfour wideband Yagis.

12-37. Fanned type conical antenna. One ofthe most effective of all VHF channel TV re-ceiving antennas is thc fanned type conical. shownin figure 77.A. Thc low 0 needed to obtainbroadband characteristics is obtained in this an-tenna by thc lame cross-sectional area producedby spreading or fanning out the elements. Thesix-element conical with reflector has an im-proved gain at the high ends of the low- andhigh-band channels. In general, the conical typeantenna must be oriented carefully on the lowband to prevent picture smear and on thc highband to prevent echoes in the picture. High-bandorientation is critical because of the sharper di-rectional antenna lobes and the presence of strongminor lobes that introduce refkction or signalinterference. The gain of thc conical type an-tenna can be raised and the vertical directivityp'attern imprmed by stacking two to three com-binations of the basic type. as shown in figure77,B.

74 3 9

12-38. Log-periodie antenna. The log-peri-odic antenna is a recently developed broad-band. high-gain, highly directive antenna. Theoperational and design characteristics of a log-periodic antenna are such that input impedance.radiation pattern, and the active elements mustrepeat periodically as a function of the logarithmof frequency.

12-39. Design parameters for a planar typelog-periodie dipole are shown in figUre 78. Thetwo half structures are fed onc against the otherin a horizontal plane. A balanced-line feeder isused in the illustration. The length of each suc-cessive dipole element forms a geometric pro-gression with a common ratio of less than one.This common ratio is usually referred to as tau(7). Tau. called thc scale factor. determines theperiodicity (spacing) and the number of ele-ments. As the number of elements is incredsed.the directivity. front-to-back ratio, gain, and inputimpedance increase. The longest element. 1,,.

492is approximately 1/2 wavelength. . at the

ir me

lowest operating frequency. and the shortest ele-ment is :Vs wavelength at the highest operatingfrequency.

In

12-40. The limiting factor of tau is the anglephi (0). Angle (6 defines or limits the lengthof each succeeding dipole element since di is de-pendent upon the length of the longest element.the length of the shortest element. and tau. As

the angle (6 increases, the directivity, front-to-back ratio, gain, and input impedance decrease.Therefore. in the design of the log-periodic an-tenna. the angle (6 and the geometric ratio tauare a compromise for directivity, front-to-backratio, gain, and input impedance. The anglealpha (a) is 1/2 the angle 4 and is used in thedesign charts for a log-periodic antenna. Sigma(a) is the spacing factor and is the ratio of thedistance between two adjacent elements totwice the length of the longest element. Thegeometry of the log-periodic antenna relating

si2ma to tau and alpha is a = 7) cot a.

12-41. Turnstile antenna. In both low- andhigh-band VHF applications, the transmittingantenna usually consists of several individualradiating elements arranged one above the otherto obtain the necessary gain. directivity, and de-sired bandwidth. The superturnstile arrangement.shown in figure 79. is an example of this type

UNEXCITED ACTI VEei'RANSMISSION

REGION --1/14-- REGION REGION -401.

1 n+2

1

VERTEX

n-1

dn

2In- Cr

DIRECTIVITY

(1r) cot aa- =

4

Figure 78. Log-periodic antenna.

75

BALANCEDLINE

Figure 79. Superturnstile antenna.

76

of antenna design Each stacked array providesadditional signal gain for the TV system. Gainfor low-band VHF antennas is usually limited to10 db or less, whereas high-hand VHF antennasare designed for gains as high as 20 db. A TVsystem utilizing an antenna having a gain of 10db can realize an approximate ERP of 50 kwwith a video transmitter output of 5 kw.

12-42. The turnstile antenna receives its namefrom its physical shape. The basic turnstile an-tenna consists of two horizontal half-wave an-tennas mounted at right angles to each other inthe same horizontal plane. When these two an-tennas are excited with equal currents 900 outof phase, the typical figure-eight patterns of thetwo antennas merge to produce to the nearly cir-cular pattern shown in figure 80.A. When twopairs (bays) are stacked 1/2 wavelength apartand the corresponding elements excited in phase.as shown in figure 81, a part of the verticalradiation from each pair cancels that of the otherpair. By stacking a number of bays. the verticalradiation pattern can be altered to obtain sub-stantial gain in all horizontal directions withoutaltering the overall horizontal directivity pattern.Figure 80.B. compares the circular vertical radia-tion pattern of a single-bay turnstile with thesharp pattern of a four-bay turnstile array. Athree-dimensional radiation pattern of a four-bay turnstile antenna is shown in figure 80,C.

12-43. Superturnstile antenna. As previouslymentioned. the superturnstile antenna, shown infigure 79, is a popular VHF transmitting antenna.Its radiating elements are constructed to producehorizontal .polarization of the radiated signal.Since the radiating elements are slots, slot radia-tion theory is the fundamental principle involvedin the operation of the antenna system. Let usconsider slot theory by examinng a flat sheet ofmetal in which a narrow slot has been cut; theslot is the width of a half-wave dipole and is aquarter-wavelength long (fig. 82,A). The radia-tion pattern produced by the antenna (slot) cutinto an infinitely large metal sheet and that ofthe complementary dipole antenna are the same.However, it is interesting to note two importantdifferences between the slot antenna and its com-plementary antenna. First, the electric and mag-netic fields are interchanged. In the case of thedipole antenna shown, the electric lines are hori-zontal. while the magnetic lines form loops inthe vertical plane. With the slot antenna. themagnetic lines arc horizontal and the electriclines are vertical. These electric lines are builtup across the narrow dimension of the slot. Asa result. the polarization of the radiation pro-duced by a horizontial slot is vertical. whereaspolarizatiOn of a radiated wave produced from the

40i

IR)

PATTCRN OF A-A'

A

VERTICAL PATTERNOF SINGLE BAY

VERTICAL PATTERNOF BAYS

RESULTANT OF HORIZONTALPATTERNS OF DIPOLES

A-A AND B-B'

PATTERN OF El-B.

00 mooLUZ0; 17Kc.4 610 0°

..."""REAT/VEOUTPUT

15.5.

10°IS°

Figure 80. Turnstile antenna radiation pattern.

vertical slot is the same as that produced by ahorizontal dipole. The plates may be considered

to bc a horizontal dipole. 1/2 wavelength wideand 1.14 wavelength long, being fed at the center.When energy is applied to the slot antenna. cur-rents spread over thc entire sheet and flow in adirection parallel to the small side of the plates.Radiation then takes place from both sides of the

metal sheet as in the case of the horizontal dipole.

Sincc radiation resistance causes the magnitudeof thc currcnt to decrease rapidly from the slot.the plates need be cut only 1/4 wavelength long.The radiation current becomes negligible 1/4

wavelength from the slot.12-44. The actual form in which the elements

are generally constructed is shown in figure 82.B.

Thc open construction shown has no effect onthe electrical characteristics of the antenna butis very advantageous in reducing wind resistance.

The norizontal conductors are made smaller at

thc center (giving the batwing appearance) to in-

Figure 11$. Stacked turnstile antennas.

77

crease the current at the top and bottom in rela-tion to that at the center of the radiating sur-face; thus. horizontal directivity of the radiation

pattern is increased. At the same time, the impe-

dance characteristic is broadened, making itmore constant over a wide band of frequencies.Horizontal coverage of the serviced area is in-creased by feeding the antenna pairs 900 apartin phase. The 900 phase difference is achievedby feeding one group of antenna elements (E-W or N-S) with a transmission line 1/4 wave-length longer than the transmission line feeding

the opposite group.12-45. Traveling-wave antenna. The trans-

mitting antenna. shown in figure 83, also usesthe slot radiation principle. The design is similarfor high-band VHF and UHF TV transmission.The name "traveling-wave" comes from the waythe slots in .the antenna are fed. Through thetraveling7wave method of feeding the slots, highantenna gain is obtained without using a largenumber of feeder lines. Because the physicalsize of the slots in relation to wavelength is much

smaller at the higher frequencies, it is possible todesign these antennas for gains of 9 to 60. de-pending upon the frequency of operation. AnERP of 1 million watts may be achieved in UHFpractice with an r-f carrier of 25 kw driving a60-db antenna. The maximum radiated powerauthorized for UHF transmission is 5 millionwatts.

12-46. The radiating elements consist of aseries of 1/2-wavelength slots, four to a layer.equally spaced at 90° intervals around the cir-cumference of the mast. Additional layers of slots

may be added at 1-wavelength distances, meas-uring from the center of the slots. Each layerof slots is rotated 450 with respect to the pre-ceding layer to achieve the necessary horizontal

4 04:,

omnidirectional radiation pattern. The rumherof lacrs ot slots. a:, in the ease of supertastile batwings. will deternii!: the appiw.::..,at.:gain of the antenna system.

12-47. A copper tnbe, mount,:d coax iallywithin the...steel tube. acts ;n coniunctioI withthe steel tube as the center conductor ofline. Probes mounted inside the steel tube at oneside of the center of each slot are oriented towardthe conductor in a manner that will cause excita-tion of the slots. The traveling-wave method offeeding thc slots is accomplished by capacitivelyfeeding the r-f energy from the center conductorto the slots by way of the probes. The excitationfrom the slots forms the radiated signal patternnecessary to service a given area. Broadbandrequirements arc met by placing additional probesbetween each layer of slots.

12-48. Helical antenna. Another specially- de-signed TV transmitting antenna is the helicaltype, consisting of a coil quite similar to a large-size air-core inductor. It can be made to havemaximum radiation either in the axial dircctionor in a direction normal (perpendicular) to theaxis, depending upon the circumference of thehelix and its pitch. If the helix is constructedso that the length of one turn is approximately1 wavelength and the spacing between turns is

approximateiy 1/4 wavelength at the center ofthe operating frequency band, the radiation pat-tern will be like that shown in figure 84.A. Aradiation pattern in the normal mode, like that

\ 2

'A. 4 --I

SLOT

A ASIGNALFROmFEEDER SYSTEM

CURRENT WAVE SHOWINGMAGNITUDE ACROSSTHE RADIATING PLANE

ss.

A

shci.i in figure occurs if the hehx dimen-s:ons are small in comparison with a l% li,vekngth.

12-49. Helical antennas ar.: generally usedon the high VH/- band and UHF channels. TheVIP' helical antenna in its popular form is es-sentially a coil of uniform pitch wound arounda circular mast section of uniform outside diam-eter. A typical VHF helical antenna is shownin figure 85.

12-50. When excited w hh r-1 energy. a V. aveis established which travels between the helixw ire and the ground plane formed by the mast.The wave travels around the circumference of themast. and. because of ,the pitch of the helix.progresses up or down the axis of the helix.This causes the entire length of the helix to serveboth as a radiator and as a feeder for successiveportions of the antenna. The radiated beam ismaximum at right angles to the helix axis. Suc-cessive turns of the helix work together to pro-duce side-firing fields ,that form thc radiatedbeam. Because of structural considerations. a

2-wavelength turn is most commonly used. Helicalantennas for channels 7 to 13 are huilt in a stand-ard series having gains of 4 to 25, dependingupon the number of bays used. A one-bay an-tenna can be used with transmitter powers up to

10012-k571.. Color Television Antenna Require-ments. The requirements of an antenna for colorreception are quite similar to those for blackand white reception. In general. an antenna

FOuR INSIDE CORNERSGROUNDED TO MAST

COAXIAL LINE FROMFEEDER SYSTEM

Figure 82. .Suprrturnstile element characteristics..

78

40J

Figure 83. Traveling-wave (slot type) antenna.

79

4u1

which delivers a clear sharp picture. free of inter-ference. reflections. and noise on black andwhite. will provide an excellent color picture.Almost all standard designs of broadband an-tennas have more than adequate bandwidth if

properly installed. However, a narrowband an-tenna, such as the Yagi. will have sharp dips inthe response curve at certain frequencies whichwill alter color reception on the channel involved.

12-52. The directivity requirement is the

same for color as for black and white reception.The narrow beamwidth is required as an aid indiscriminating against reflections. Reflections

cause hues and shades to vary in the color pic-ture, and may also cause partial or complete can-cellation of the color subcarrier "burst" if the

reflected path is an odd multiple of a half-wave-length at the transmitted subcarrier frequency.Good directivity can reduce interference pickup.

AXIAL MODEOF

RADIATION

(A)

;;-:1117"111.-

.11.4

fi44-0.

(B)

NORMAL MODEOF

RADIATION

Figure 84. Helical antenna showing ef fect of pitch and

diameter on direction of maximum radiation.

12-53. The gain and impedance matching re-quirements are also the same as those for blackand white. Sufficient gain to produce a noise-

free picture as required and the impedance mustbe matched between the transmission line andthe receiver.

13. VHF TV Receivers

15-1. Since VHF TV receiver circuits are likethose you find in other kinds of high-frequencyequipment. you can apply much that you alreadyknow to this subject. For example. y3u alreadyknow about amplification and detection of AMand FM signals. Your study of TV transmission

1-11

(Tm

Figure 85. Center-fed helical antenna.

SO

irtaciples si:owed ou that thc cornposue videosignal amplituue modulates the TV tr.tnsiniueroutput.. Also. ou learned how the sound infor-mation frequenty-modulates the separate soundtransmitter output. Considerine the different com-ponents that make up the composite video signaliid he fact that amplification and detection of

both video and sound information must be donesimultaneously. you can easily see that the TVreceiver is more complex than a radio receiver.

13-2. Sections. The TV receiver consists often distinctive sections, as shown in figure 86.These sedtions are the r-f. i-f, video, sync sepa-rator, vertical sweep. horizontal sweep. high volt-age, low voltage, automatic gain control (age),and audio. The antenna picks up the video andsound signals and applies them to the r-f section.Since the combined signals have a bandwidth of6 MHz, the r-f section and antenna must delivera linear response to the wide band of frequen-cies.

13-3. The composite signal is applied to amixer stage where it is combined with a signalfrom the high-frequency oscillator. The resultantsignal conversion will produce the desired inter-mediate frequency (i-f) signals. From this pointthe path of the signal will differ. depending onwhether the receiver is of the converuiona/ orintercarrier type.

13-4. In the conventional receiver the videoand sound signals are separated after the mixerstage and are fed to their respective i-f amplifiers.The sound signal goes to an FM detector. com-monly known as a discriminator. The video sig-nal goes to an AM detector, the output of whichis amplified by the video amplifier stage andthen sent to thc picture tube.

13-5. In the intercarrier receiver the videoand sound signals are separated after passingthrough a common i-f amplifier system. A soundi-f of 4.5 MHz is taken off at some point pastthe video detector, then coupled through a band-pass filter network to the input of the sound i-for FM detector.

13-6. The video signal consists of the picturesignal with blanking pulses and synchronizing(sync) signals. (You should be familiar withthese signals from your study of TV monitors inVolume I. Chapter 5, of this course.)

13-7. Tuner section. The r-f section (tuner)has several important functions to perform. Thissection must select the desired TV channel. con-sisting of the sound and video carriers. lt mustconvert these signals to an i-f signal for amplifica-tion. In most receivers an r-f stage is used toincrease amplification of the signal before itrcaches the mixer. The r-f amplifier acts as abuffer between the oscillator and antenna and

403

prevents thc retransmitting of extraneous signals.This typc of extraneous retransmission can. ofcourse. cause interference to other local TV re-ceivers.

13-8. The r-f section must be of widebanddesign if it is to provide linear response over a6-MHz range. Sincc the circuits must be wide-band. thc efficiency will bc low, and the properchoice of parts and values is essential if we areto have satisfactory results. Thc layout of thechassis and components. the inductance andcapacity of leads, plus the interelectrode capaci-tancc of tubes become important factors in wide-band circuits. The use of miniature tubes. care-fully positioned parts, and all leads as short anddirect as possible satisfy the wideband circuitrequirements to somc extent.

13-9. The r-f tuners have band switching cir-cuits which are used for channel selection. Al-though thcre are many methods of band switch-ing, the turret type and various switch types arethc most popular. The r-f tuner is controlled bythe channel selector switch. As we turn the chan-nel selector switch, we select the proper tunedcircuits, r-f mixer, and local oscillator for each

AGC.e.

RF SEC

MIX

OSC

,11 4111116 WNW.

individual channel. In addition, wc also have afinc tunin2 control in the r-f section. This con-trol varies the local oscillator frequency for propercentering of the video and sound signals in thei-f. bandpass.

13-10. 1 -1 section. The i-f output of the mixerstage will be increased in amplitude by severalstages of amplification. The i-f frequency maybe anywhere from 19 MHz in some models to45 MHz in others. The sensitivity and selectivityof the TV receiver arc determined mainly by thenumber of stages of amplification. Once again,as in the case of the r-f section, the i-f amplifiersmust have wideband characteristics. The i-f re-sponse must be flat over at least a 3-MHz rangeand should be flat over .a 4-MHz range. Al-though there is a sacrifice of gain for the wide-band requirement, three to five stages of i-f am-plification will produce thc necessary gain.

13-11. Video and sound separation is accom-plished with resonant circuits in the output ofthe mixer or in one of the earlier i-f stages inthe conventional receiver. In the intercarrier re-teiver, the video and sound separation is ac-complished in the video detector or video ampli-

FIAGET

AUDIO SEC

AUOIO EAmP

AUOIOPA

CONVENTIONAL RECEIvERSOUNO SEPARATION

1 rl-41.11 O.NNO .11111 MIMED MIMS

+11.

/I F SEC

-J

SPF

IF IF

4111111. ,11 41.11101.

AGC

1111,

AGC

r

7c:E7E0 rLOm-E I IRECT

I I

L_JH

MIM ,11 =111 ,11 ,11

SYNC SEP SEC

SYNCSEP

SYNCAmP

MONO 01111111 ,11 *MO ,11

r1

VERT SWEEP SEC

Ilr -

rwow. omma .11M

....INTERCARRIER RECEIVERSOUNO SEPARATION6 J

I OET -L-11.01 VIOE0OUTPUT

I I

I i VIDEO SEC16.

INTEGRATORj L.- ami

HORIZONTAL SWEEP SEC

MOMAFC

NORIZOSC

I

VERTOSC

AGC I.AGC SEC

VERTOUTPUT

NORIZOUTPUT

1NI-ERECT

I L. HIE SEC

,11

CAMPER

Figure 86. Television receiver Huck diagram.

81

406

IMMIN

T I

01

C3

OSCILLATOR SIGNALINPUT

11.

SIGNALINPUT

TI

RI

R3

AAA

Figure 87. Mixer stage.

T3

vcc

I-F SIGNALOUTPUT

_.

T2

01

RI

R2

C:

Figure 88. Canverter stave

82

4 0/

T3

1-F SIGNALINPUT

4)

Figure 89. Basic oscillator circuits.

fier stage. In the latter case, the video andsound i-f carriers are amplified together througnthe i-f 3ection. Automatic gain control tagc:. iS

applied to all the i-f amplifier's except the last(normally). Also, agc is applied to the r-f ampli-fiers to control variations in signal strength.

13-12. Transistor r-f and i-f arnpli9e:s haveto take into consideration the internal capaci-tances of transistors which provide feedbackpaths for high frequencies. For this reason. thereare certain features peculiar to transistor r-f and

amplifier configurations which must be consid-ered. The common-emitter (CE) amplifier offersthe highest power gain, better than 10 db abovethe common-base (CB) type. The CB amplifiercannot be discounted because its power gain issubstantial and often adequate. Because powergain is usually a majJr requirement for high-frequency applications, the relative low-powergain of the common-collector (CC) amplifierdetracts greatly from its usefulness. Since theCE amplifier has more feedback than the CBamplifier, the CB amplifier is preferred wherestability, accurately controlled gain, and inter-changeability are required.

13-13. All things considered, the CE config-uration is generally selected for r-f and i-f am-plifiers. The CB configuration is used when feed-back must be kept to an absolute minimum.

13-14. Mixer section. A schematic diagramof a mixer stage with typical component arrange-ment is shown in figure 87. The r-f injected intothe base circuit and the oscillator frequency in-jected into the emitter circuit are heterodyned inmixer 01. The intermediate frequency is se-lected by the colleczor tank circuit. The inter-

INPUT

mete frcquene!. is then coupled through trans-formzr T3 to the following stage. As ru cansee. this is a relatively simple circuit comparedto tube stage.

13-15. Converter section. The converter stagediagram is shown in figure 88. The r-f signalinjected into the base circuit and the oscillatorfrequency generated by converter 01 are hetero-dyned in the converter. The parallel-resonantcircuit, consisting of capacitor C3 and the pri-mary of transformer T3, selected the desir.:d i-ffrequency. The i-f is then :oupled through trans-former T3 to the following stage.

13-16. Capacitor CI and the pri-nary of trans-former T1 form a parallel-resonant circuit forthe r-f which is coupled through the transformeito the base circuit of converter 01. Resistor R Idevelops the emitter-base bias, and resistor R3is a voltage dropping resistor. Resistor R2 is theemitter swamping resistor. and capacitor C4 is abypass for the r-f. Capacitor C2 and the primaryof transformer T2 provide the required feedbackfor the oscillator portion of converter Q1, Capaci-tor C3 and the primary of transformer T3 forma parallel-resonant circuit for the i-f which iscoupled through the transformer to the followingstage. The primaries of transformers T2 and T3are tapped to obtain the desired selectivity.

13-17. Oscillator section. Illustrated in figure89 are basic circuits which show componentarrangements and polarity applications for p-n-ptype transistor oscillators. N-p-n type transistorsmay be substituted in any of the circuits as longas the d-c polarities are reversed. Each circuitprovides 'amplification. regenerative feedback.and inductance-capacitance tuning. Exact bias

A

6

Vo

B

Figure 90. Diode AM detector.

84

410

OV

Oo

Q

F SIGNALOUTPU T

C2

T 1

Vcc

C3

Figure 91. 1-1 amplifier and discriminator.

aad stabilization arrangements are not illustrated.However, the relative transistor d-c potentials re-quired for normal functioning of the oscillator

are shown.13-18. The circuits in parts A and B of figure

89 are similar. In both cases feedback is coupledfrom the collector to the base by a transformer(tickler coil). The circuit in B is a shunt-fedversion of the circuit in A. Since the feedbacksignal is from collector to base in each case. thenecessary feedback signal phase inversion is ac-complished by the transformer which. when prop-erly connected. provides a 180° phase shift.

13-19. The circuits in parts C and D are also

tickler-coil oscillators. In C. regenerative feed-back with zero phase shift is obtained in thetuned collector-to-emitter circuit by the properconnection of the transformer. In D. since thefeedback is from collector to base. a 180° phaseshift is required. The signal in the untuned col-lector winding is coupled and inverted in phaseto the tuned base winding.

13-20. The circuits in parts E and F are tran-sistorized versions of the Colpitts type electron

tube oscillator. In E. the signal from the tunedcollector is coupled to the emitter in phase. In F.the signal from the tuned collector is coupled tothe base 180° out of phase.

13-21. The circuits in parts G and H aresimilar to those in E and F except that a splitinductance is used to provide the necessary feed-back in place of the split capacitance. These aretransistorized versions of the Hartley type elec-

tron tube oscillator. In each of these circuits.the collector is tuned. Since each coil functions

as an autotransformer. feedback in proper phaseis accomplished by induction. In G. the feedback

85

signal is coupled from collector to emitter with

no phase shift. In H, the feedback signal is

coupled from collector to base with a 180°phase shift.

13-22. AM detector section. The circuitsshown in figure 90 select, rectify, and filter,thereby detecting the amplitude variations of aspecific AM signal; in TV the video signal is

AM. The selectivity is, of course. accomplishedby the tuned tank circuit. The tank is maderesonant to the desired center frequency, andit is designed to have a Q that allows the desiredsideband frequencies to be accepted. Thesemi-conductor diode rectifies the accepted signal.A p-n junction diode is commonly used, but apoint contact diode can be used for low currentapplications. The diode may be placed in serieswith an RC filter (fig. 90,A) or in parallel withan RL filter (fig. 90,B). The latter arrangementis more suitable for a current-driven, low inputimpedance device such as a transistor. This doesnot mean, however, that the circuit shown infigure 90,A. is not also designed for transistorinputs.

13-23. Diode detectors are simple and willhandle relatively large signals. They give high-fidelity detection for signals of sufficient ampli-tude. For small signals (less than about 1 volt),square-law detection occurs; some detectors aredesigned to take advantage of this type of detec-tion.

13-24. Two drawbacks of diode detectors are:(1) they provide no power gain, and (2) selec-tivity is affected by loading. Since a rectifyingdiode is not an amplifying device, we know therecan be no power gain realized. Loading affectsselectivity because the input tank "sees" the load.

41'

Consequently. the Q of the tank is lowered whenthe load increases and increased when the loaddecreases.

13-25. FM derector section. Since v.e refer todemodulation in an FM receiver cf the ircoiningaudio carrier signal as detection, in TV FM de-tection is also necessary in additon to AM detec-tion. Figure 91 shows a transistorized version ofan i-f stage and a discriminator, a circuit usedfor detecting FM signals. Amplifier QI ampli-fies the i-f signal applied to the discriminator.Resistor R1 is the emitter swampine resistor, andcapacitor Cl is an i-f bypass. Capacitor C2 andthe primary of transformer T1 form a parallel-resonant circuit for the i-f signal which is coupledthrough the transformer to the discriminator. Ca-pacitor C3 couples the i-f sienal to the secondaryof transformer Tl for phase shift comparison.The i-f signal, coupled across capacitor C3. isdeveloped across coil Ll. Capacitor C4 :and thesecondary of transformer T1 form a resonant cir-cuit for the i-f signal coupled through the trans-former. The top half of transformer T1 second-ary. diode CR1, coil Ll. load resistor R2, andfilter capacitor C5 form one half of the compari-son network. The bottom half of transformerTl secondary, diode CR2, coil LI, load resistorR3, and filter :capacitor C6 form the second half

1F SIGNALINPUT Cl

.46of the comparison network. I he audio output ofthe discriminator circuit is taken from jhe top ofcapacitor C5 and the bottom of capacitor CO.The audio output is coupled throueh capacitorCi to the primary of transformer T2. The audiosignal. coupled through transformer T2. is appledto the following stage.

13-26. The slope detector is also used to de-tect FM signals by converting the frequencychanges of a carrier signal into amplitude chan-ges. The amplitude chanees can then be detectec:by an AM transistor detector. The input and out-put waveforms of a slope detector and an AMdiode detector are shown in figure 92. The i-fsignal with frequency deviations is applied toslope detector 01 . The output of slope detectorQl, the i-f signal with amplitude and frequencydeviations, is applied to diode detector CRI. Theresultant output is an audio signal which is equiv-alent to the frequency deviations of the i-f in-put signal.

13-27. The i-f signal coupled through trans-former TI is applied to the base circuit. Theresonant circuit. consisting of coil LI and capaci-tor C2:(tuned slightly off the carrier frequency).develops a large amount of i-f signal when thefrequency deviation is 'near the resonant fre-quency. As the frequency diviation of the i-f

L2

AUDIOOUTPUT

Figure 92. Slope defector aad diode dereck,r,

86

412

signal becomes lower than the resonant frequency

of the resonant circuit, a smaller amount of i-ts

signal is developed. A large amount of i-f signal

added to the bias voltage developed across re-

sistor R I increases the emitter-base bias and a

small amount of i-f signal decreases the emitter-

base bias. The emitter-base bias is therefore in-

creasing and decreasing as the frequency of the

i-f signal increases and decreases, respectively.

Since the bias of slope detector 01 changes at thefrequency deviation rate. the output of the slope

detector is an i-f signal that is changing in ampli-

tude and frequency. The i-f signal applied todiode detector CR I is rectified, filtered by coilL2. and developed across resistor R4. The out-put of the current output type diode detector is

an audio signal.13-28. Maintenance. Maintenance of the TV

receiver consists of cleaning and tube replace-

ment (tube type equipment). We use the term"maintenance- as meaning care and upkeep of

the TV receiver. However, we can extend ourmeaning to include the repair of the equipment.

which immediately leads to troubleshooting.Troubleshooting a TV set to locate defects is

done by a systematic step-by-step analysis. Thelogical procedure is to:

Locate the trouble in a particular circuitgroup or section.Isolate the stage or circuit at fault.Locate the faulty component.

13-29. To be technically competent in servic-

ine TV receivers, you must be able to understand

the correct function and operating principle of

each circuit. Your ability to analyze and rapidly

87

diagnose troubles is not developed merely by

studing a chapter on troubleshooting. You must

realize that success in troubleshooting is a result

of understanding the principles of TV receivers.keeping informed on new developments, and

learning specific methods of recognizing faults.13-30. The TV receiver, monochrome or

color, can be used to localize its own trouble. You

can localize the trouble to one section of the re-

ceiver if you analyze the visual and audio indica-

tion. Test equipment plus your knowledge of TV

principles will enable you to isolate the fault to aparticular stage, circuit. or component.

13-31. Color TV Receivers. Color TV re-ceivers are different from monochrome receivers

in only three sectionscolor synchronizing, de-

modulation (chrominance), and matrix. The

luminance channel corresponds to the video

channel section of the black and white receiverand therefore is new in name only. It should be

noted that all sections must be operated under

closer tolerances than monochrome receivers, and

the technician must follow correct practices whenworking with and adjusting color receivers.

13-32. The three sections just mentioned asbeing different in the color receiver were dis-cussed in Volume I. Chapter 7. At this point.therefore, you should review the referenced sec-

tion to reinforce your understanding of mono-

chrome and color receiver differences. The color

receiver will be more complex due to the addi-

tional circuits involved; thus the maintenance will

be restricted to precision quality workmanship.'You must follow the same logical procedure whentroubleshooting because the basic principles ofoperation are the same.

413

/4-

CHAPTER S

UHF Equipment

BECAUSE OF co-channel and adjacent-chan-IJ nel broadcasts, the limited number. of VHFchannels available created a problem. Since onlyVHF channels 2 through 13 were available, morechannels were needed. This need led to thedesignation of the UHF broadcast channels 14through 83. In this chapter a comparison ofUHF to VHF transmitters, antennas, and receiv-ers will be given. Also, you find material ex-plaining microwave relay applications plus theassociated transmitters, antennas, and receiversused to accomplish signal relay.

14. Transmitters

14-1. The transmitters used for TV broadcastand TV relay are of many designs and sizes. Thefrequency range, the intended operating charac-teristics, and the manufacturing techniques in useat the time of design will determine many of thephysical and electrical characteristics of the finalproduct. Within all of these variables, there arecertain principles which will appear in each trans-mitter no matter how different the techniquesemployed to obtain them. The transmitter con-sists basically of an oscillator. a modulator, andan r-f amplifier; it also contains such additionalrefinements as frequency multipliers and auto-matic frequency control.

14-2. Characteristics. Many similar character-istics are found in VHF equipment which oper-ates in the 54-MHz to 216-MHz frequencyrange and UHF equipment which operates in the470-MHz to 890-MHz range. You will also findthat the same characteristics are included in mic-rowave relay equipment. Like VHF. UHF radiowaves are propagated throueh the atmosphereand are not effectively returned to the surface ofthe earth at usable receiving levels. This limitsthe effective range of TV communication topoints on the surface of the earth not far beyondthe optical horizon as seen from the transmittingantenna.

14-3. As the frequency is increased throughthe VHF/UHF range. the radio waves become

88

shorter in physical length and are comparable insize to the component parts of the equipment.This tells us that much consideration must begiven to circuit design and component selection.You will recall that the formula for computingwavelength is:

Wavelength __frequency

velocity

With this formula and a knowledge of the fre-quencies used, we can compute some componentdimensions. The VHF broadcast frequencieswere listed in the previous chapter: therefore. tocomplete your knowledge of the broadcast fre-quencies used. the UHF channels and respectivefrequencies are listed as follows:

ChannelNo. Frequencyljnaualik)

14 470-47615 476-48216 482-48817 488-49418 494-50019 500-50620 506-51221 512-51822 518-52423 524-53024 530-53625 536-54226 542-54827 548-55428 554-56029 560-56630 566-57231 572-57832 578-58433 584-59034 590-59635 596-60236 602-60837 608-61438 614-62039 620-62640 626-63241 632-63842 638-64443 644-65044 650-656

Channel Nu. Frequency Limits (MHz)

45 656-66246 662-66847 668-67448 674-68049 680-68650 686-69251 692-698

52 698-70453 704-71054 710-71655 716-72256 722-72857 728-73458 734-74059 740-746

60 746-752'61 752-75862 758-76463. 764-77064 770-77665 776-78266 782-78867 788-79468 794-80069 800-80670 806-81271 812-81872 818-82473 824-83074 830-83675 836-84276 842-84877 848-85478 854-86079 860-86680 866-87281 872-87882 878-88483 884-890

14-4, Remember also that we will be usingadditional bands of frequencies for microwave re-

lay purposes. For commercial TV relay use,there are three bands for video use and one addi-tional band for audio relay. The three videobands arc:

1990 MHz to 2110 MHz (2000-MHz band)6925 MHz to 7050 MHz (7000-MHz band)13.025 MHz to 13,200 MHz (13,000-MHz band)

The additional audio carrier band is 890.5 MHzto 910.5 MHz (900-MHz band). This audiocarrier band is not as widely used as are land-lines. Otherwise, multiplexing equipment is used

and the audio is carried with the video in theprimary frequency band. When these bandsarc used for TV. it is only necessary to use a 6-

MHz channel to carry both the video and audiosignals.

14-5, Comparisons. The UHF transmitter will

have the same basic oscillator. multiplier, andamplifier circuits at the lower frequency levels as

the VHF transmittcr. The differences in compo-nent sizes and arrangements of UHF and VHF

.^

89

become evident at the higher frequency powerlevels. To help you understand the operationalcharacteristics, complexity, and components used.

we will study representative power amplifiers..14-6. VHF power amplifier. A modern r-f

power amplifier designed for operation in the 54-MHz to 216-MHz frequency range is shown infigure 93. Although this amplifier uses a type4X150A (see fig. 94) coaxial tetrode tube. theremainder of the circuit is made up of conven-

tional lumped-property components. Referring

to the left portion of figure 93, we see that thesignal to be amplified is applied to the gridthrough inductor L5 which matches the input im-pedance to the grid-circuit impedance. CapacitorC17, resistor RI, and inductor L6 from a loadingcircuit for the grid with amount of resistive load-

ing being determined by the setting of variablecapacitor C17. Inductor L6 balances the straycapacitance of resistor RI. The tube is biasedfor class C operation by the voltage drop acrossoathode resistor R6 (lower center of fig. 93) andby the voltage drop caused by the grid currentflowing through inductors L5 and L3 and resis-tors R3 and R2 when the grid is driven positiveby the incoming r-f signal. Capacitors Cl andC2 serve as r-f bypasses for resistors R3 and R2.The voltage developed across R2 is applied to thegrid meter. The meter reading is an indication ofthe amount of signal applied to the control grid.

14-7. The cathode current, which is the com-bined plate and screen-grid current, flowsthrough bias resistor R6 which is bypassed forr-f currents. Resistors R5 and R7 form a voltage-divider network for the cathode meter.

14-8. The screen-grid potential for this stagecan be adjOsted by changing the setting of resistorR12 (extreme right, fig. 93). Adjustable screen-grid voltage is a refinement which is not foundin all r-f amplifier stages. The exact screen po-tential must be determined from the operatinginstructions for the stage. Resistor R8 and capac-itors C9 and C16 form a decoupling network toprevent any r-f signal from entering the powersupply.

14-9. The amplified signal voltage appearingat the plate of the tube is developed across a pi-s,e,ction network consisting of inductor LI. capa-Eiiiir C13, and capacitor C14 (upper center, fig.

93). The circuit is tuned to resonance byadjusting CI3 and L I. The amount of r-f signalcoupled to the antenna through capacitor C15(upper right, fig. 93) is controlled by the adjust-ment of capacitor C14. Inductor L2, resistorsR9 and R 10, and capacitors C10 and C12 forman r-f decoupling network to prevent any of ther-f signal from entering the 750-volt power sup-ply.

415

RFINPUT

CI170

L30.12

Li0 . 1 - 3. 6 C115

Ell"gUrTPUTCIA2G-220 2000

1.2

C12:00

RIO22

C10500

4)1150APLATERING

LS0.12 BASE

KEYRI

C9500

TOGRID me

METER

R3AK

C 1 73.7-52

R212.1

3250

R6 RS200 IIK

R13I6K

1701.6 RI

0.111 110R7

211.7K

Ce170

Figure 93. VHF power amplifier circuit.

14-10. UHF power amplifier. A coaxial cav-ity type r-f power amplifier designed for opera-tion in the 470-MHz to 890-MHz range is shownin figure 95. Not shown in this drawing is the

4X LSOG

A

CONTROLGRID

CATHODE ANDFILAMENT

FILAMENT

wiATe

SCREENGRID

TOOw CATHODE

METER

RI225K

.750

.350

mechanical linkage used to adjust the tuning ofthe cavities.

14-11. This amplifier is an excellent exampleof the use of distributed properties in an operat-

4X150A

FILAMENT

CATHODE

Figure 94. Coaxial tetrodes.

90

41 6

FILAMENT

CONTROLGRID

RF INPUT

r6(teik, tsS 1,1r

TO R I 3

TO FIL SUPPLY 410

TO R15

C20

NYI ."61'0,40101*S.I,

Cill**C24

C22

P2 PLATE TUNING

4t A roy AN, tkt:

e3

*C i4e "sq. ,

*C13

Nett.ra

GRID TUNING PI -'*

411

C if

TO R23 40

I 1

e-v4A0

dtio,s4. 41, yo'i 1;".1,10,11,-r,;.41V70.5,0401, *14",,Er.'414101404.1..

\\N:

et+, iif-vP r ,in'Ot"qt..1.".r s,

ovr1, S1b r1r2.,l, 114 ta

THIS CAPACITOR IS A STRUCTURAL PART AND IS NOT OFTHE CONVENTIONAL TYPE.

MIS CAPACITOR IS OF THE FEED THROUGH TYPE.

11. 12. 23, AND 24 ARE TUNED CONCENTRIC CAVITIES.

4)1130G CONNECTIONS1 CATHODE2 CONTROL GRID3 SCREEN GRID4 PLATE

17.

PLATE TUNING P2

7t.0 rs ^.. *00140 ;I)g. N,C14

'\$%1"Ak-' -r,4.4,4.3 A.. 0: v1.4., v444, kC

C25 RF OUTPUT

Figure 95. Cutaway view of coaxial cavity type UHF amplifier.

TO RII

C13

RPINPUT

L16 43130G

L 13

C13SS2700

L IS allrrrYY''W/--406 6750

C14 711711"4311.1300

330

1030

C201000

C31

1000

LIDR1611K TO

CATHODENETER

Cal1457 011

26.1K

TOGRIO

METER

Figure 96. UHF power amplifier circuit.

ing circuit. Plate coupling capacitor C13 (ex-treme lower right, fig. 95), screen-grid decou-pling capacitor C14, and grid decoupling capaci-tor C23 are all distributed-property capacitances.The capacitance in each case is formed by themetal ring connected to that tube element, thesupporting dielectric, and the wall of the cavitysupporting the dielectric. The insulating mate-rial, besides serving as the dielectric of the re-spective capacitors and as part of the tubesupport, prevents the high voltage on the plateand screen-grid elements from being shorted toground because the cavity structure is at d-cground potential.

14-12. There are four coaxial cavities in thisamplifier. Grid cavity Z4 is formed by rod Mand the inner surface of cyclinder N. Input cav-ity Z5 is formed by the smaller branch of rod Mand the associated cavity walls. Tuning cavityZ6 is formed by the larger branch of rod M andthe surrounding .cavity walls and is tuned byplunger PI (extreme left. fig. 95). Plate cavityZ3 (lower portion of fig. 95) is formed by theouter surface of middle cylinder 0, tuningplunger P2, and outer cyclinder R.

14-13. The amplifier input circuit consists ofthree coaxial cavities of a different characteris-tic impedance; in the upper left portion of figure96, we see these cavities represented as L9. L12.and the combination of L16 and stray capaci-tance C32. Coaxial line Z5 is short circuited atone end and the input power is fed into a tapon this line. Line Z6, consisting of inductaneeLI2 in series with grid capacitor C19. tunes the

03

.40.OUTPUT

input to the operating frequency. These two linesare joined in parallel to the cathode-grid struc-ture of the coaxial tetrode by means of Z4 (L16and C32). This circuit may be looked upon asa three-quarter waveline in which variable capa-citance loading (C19) has been added so as toreduce the physical length of the line. One endof line Z5 is at r-f ground and is connectedthrough bypass capacitors C16 and C23 to thecontrol grid and through capacitor C14 (middleportion of .fig. 96) to the screen grid; thus, thccontrol and screen grids are held at r-f groundpotential and the circuit functions as a grounded-grid .amplifier. The other end of input line Z5isconnected through line Z4 to the cathode andcauses the cathode voltage to vary at an r-f ratewith respect to the grid. When the grid voltagedecreases, capacitor C23 discharges slightlythrough a length of wire, represented as L14, andthrough resistors R13. R22, and R14. The r-fplate current is coupled to plate cavity Z3 (ex-treme right, fig. 96) through blocking capacitorC13. Cavity Z3 (inductance L11 and capacitorC31) is tuned to the same frequency as the inputcircuit by means of shorting plunger P2 whichchanges the physical length of the cavity to corres-pond to one-quarter wavelength at the operatingfrequency. The voltage across cavity Z3 iscoupled to the output circuit through capacitorC25.

14-14. The d-e cathode circuit is formed byL16. L9. and L 10. The r-f energy is containedon the top side of L 10 ( the lead inductance) andis thus isolated from the d-c circuit. Cathode

4 1 j

ge)

bias is developed across resistor R 15 (lower left.fig. 96) which is'bypassed by capacitor C22. Ca-pacitor C16 preyetits _the d-c cathode voltage

from being shorted to ground through cavityZ3. A voltage divider. consisting of resistors RI6

and R 17. is connected across the cathode bias

resistor. The voltage across resistor R17 is pro-portional to the total tube currcnt and is applied

to the cathode meter.14-15. When the cathode becomes more nega-

tive than the control grid, grid current flows in

pulses which are smoothed out by capacitor C23.

The average d-c grid current flows through alength of wire, represented by r-f choke LI4. andthrough resistors R13. R22. and R14. which arebypassed by capacitors C20 and C2I. The volt-age across R14 is roughly proportional to the

amount of drive to the cathode and is supplied to

the grid meter whic: !ovides an indication ofthe amount of excitation applied to the amplifier.

14-16. The d-c screen-grid circuit is isolatedfrom the r-f circuit by the inductance of a length

of shielded wire. L13. Capacitor C18 provides

additional decoupling to prevent r-f from enter-

ing the power supply. Inductance L 15 (upperright, fig. 96). a length of shielded wire, isolatesthe d-c power supply from the r-f plate circuit.Resistor R 1 I provides additional decoupling for

the +750-voit power supply.

14-17. The circuits shown in figures 93 and96 indicate the similarities of VHF and UHF cir-

cuits. while figure 95 gives us an idea of the

physical differences. since we know the VHF uses

conventional lumped-property components as

compared to the UHF distributed properties of

the amplifier structure.14-18. UHF Relay (Microwave). The Air

Force makes wide use of two wideband trans-mission systems used to relay communications.They are the microwave and tropospheric scatterrelay systems and both can be used to relay TV.Microwave relay, however, is the primary systemused with TV. A number of models of microwave

equipment are in use throughout the Air Force.Some of this equipment is of military design and

some is of commercial design.14-19. Although the design of microwave relay

equipment varies, all the equipment is similar in

basic design. Some of these similarities are asfollows:

Klystrons. Klystrons are used extensivelyfor generating the microwave r-f signal (at fre-

quencies above 6000 MHz) in the transmitter.and they are used as local oscillators in microwave

receivers.Waveguides. Waveguides are used for

transmission lines in many microwave systems. es-

93

4 2

pecially those operating at frequencies higher

than 3000 MHz.Antennas. Most microwave systems use

highly directional paraboloid reflector antennas.

or paraboloid reflector and plane reflector an-tennas in combination.

Microwave receivers. Most microwave re-ceivers will be similar in design; i.e., they require

a large number of i-f amplifiers and the same type

of discriminator.

14-20. &sic microwave system. A two-waymicrowave system consists of two complete mi-crowave terminals, both of which will have capa-bilities for transmitting and receiving microwavesignals. Normally, microwave terminals are sep-

arated by a distance seldom exceeding 30 to 55

miles. If a greater distance between microwave

terminals is involved, repeater stations become

necessary. Repeater stations are two terminals

connected back to back.14-21. A basic microwave system. as shown in

figure 97. includes a microwave transmitter, a di-

rectional transmitting antenna system. a direc-tional rc:eiving antenna system. and a microwave

receiver. The main parts of the system in figure97 are designated A through H.

14-22. Point A shows the microwave transmit-

ter. B transmission line, and C and D show the

microwave transmit antenna system at the west

terminal. Point E shows the plane reflector atthe east microwave terminal. The plane reflec-tor at the receiving terminal is aimed at the trans-mitting station's plane reflector and directs themicrowave beam downward toward the parabo-

loid reflector. The paraboloid reflector (point

F) directs .the beam to a particular focal pointthe waveguide aperture. Thus, the microwaveenergy is directed into the waveguide. as shown

by point G. Point H shows the microwave re-ceiver. The receiver contains circuits for in-

creasing the signal-to-noise ratio; this increasesthe signal level for subsequent detection by adiscriminator. Microwave receivers use conven-

tional superheterodyne receiver principles. Areflex klystron is used as a local oscillator; itssignal is combined with the incoming signal in adiode type mixer arrangement to produce an i-f

signal.14-23. Velocity modulation. The klystron be-

longs to a class of tubes known as velocity-modu-

lated tubes. In a conventional vacuum tube, an

electron beam is modulated by varying the num-ber of electrons. In a velocity-modulated tube.

the electron beam is modulated by varying theelectron velocities.

14-24. The behavior of a velocity-modulatedelectron beam can be shown on a graph known as

MuL TIM. EXCOMPOSITE

SIGNAL

muL TIPL EXCOMPOSITE

SIGNAL

4-

wEST TERMINAL

Figure 97. Basic microwave system.

an Applegate diagram (fig. 98,C), In figure98,A, the distance traveled by an electron isshown as a function of time. Figure 98,B, showssimilar plots for electrons that leave the givenpoint at intervals after the zero time. Supposenow that the beam is velocity modulated. Asshown in figure 98,C, some electrons will travelfaster than others. The plots for these electronsare more nearly vertical than the plots for theslower ones (the slower plots being more nearlyhorizontal). Figure 98,C, shows the points wherebunching occursthat is, where the faster elec-trons overtake those traveling at normal velocitiesand the slower electrons fall back to those travel-ing at normal velocities.

14-25. Figure 99 shows an example of a reflexklystron. It consists of a heater, cathode. resona-tor cavity with two grids, drift tube. and a re-peller plate. The cavity, as well as the body ofthe tube, is usually (not always) operated atground potential. The cathode is operated at anegative potential so that the first cavity grid-serves as an accelerator. The second cavity grid,on the side away from the cathode, velocity-modulates the electron beam. The repeller plateis operated at a potential slightly more negativethan the cathode, and it serves to turn the elec-trons back toward the cavity.

14-26. Operation of the reflex klystron de-pends upon the proper relation between the cath-ode voltage, repeller voltage, and cavity tuning.Note the arrangement of the electrodes and thevoltages involved for operation of the reflex ye,locity-modulated tube shown in figure 100.

94

EAST TERMINAL

tho

TIPL ExCOmPOSI IF

SIGNAL

muL TIPL E XCOMPOSITE

SICNAL

Electrons are emitted by an indirectly heatedcathode. These electrons arc attracted by thecavity grids. The grids are more positive thanthe cathode by the amount of voltage E. Theelectrons emitted from the cathode travel towardthe cavity erids at a velocity determined mainlyby voltace E.

14-27. Most of the electrons pass throusth thecavity grids and continue on toward the repellerplate. After passing the cavity gries they come tothe drift tube. Since the repeller plate is negativewith respect to the cathode, the electrical field inthe drift tube opposes the electrons' motion. Thestrength of the electrical field is determined byvoltage Er. Thus, the electrons stop. reverse direc-tion, and pass back to the cavity erids. They arecollected by either the shell of the tubc or by thecavity grids which arc connected to the tube shell.

14-28. When the electrons return to the cavitygrids, the voltage across the cavity grids againacts upon the electrons. Since they are now trav-eling in the opposite direction, they will be de-celerated if they return when the grid voltage ispositive and accelerated if they arrive when thegrid voltage is negative.

14-29. Reflex klystrons are capable of beingtuned across a band of approximately 300 MHz.The resonant cavity of a klystron can be me-chanically tuned to a desired frequency in sev-eral ways. Three tuning methods are shown infieure 101. Figure 10I.A. shows how the reso-nant frequency point of the cavity may bechanged by use of a capacitive tuning slug. Fig-ure 101.9, shows how the resonant frequency

421

point may be changed by the use of an induc-

tive tuning slug. Both of these tuning methods

are somewhat ,..:quivalent to conventional tank cir-

cuit tuning. where the resonant frequency point

is changed by a variable capacitor' or inductor.

Whether or not the resonant cavity tuning slug is

inductive ur capacitive depends upon the position

of thc slug in relation to the electric and mag-

netic fields within the cavity. Figure 101,C, shows

a third technique for tuning the resonant cavity.

This tuning method involves physically changing

the dimensions of the cavity. With this tuning

technique. the cavity is designed so that it may

be compressed or expanded. The cavity is

squeezed when pressure is applied. This causes

the upper cavity grid to move closer to the lower

cavity grid. This change in grid spacing increases

A. SINGL E EL ECTRON

A

DISTANCE

10. TIME

NORMAL-VELOCITYPLOTS

the capacitance and lowers the resonant fre-

quency of the cavity. All of these mechanicaltuning methods are considered to be coarse fre-

quency adjustments.14-30. A slight change in repeller voltage is

sufficient to change the klystron frequency sev-

eral megahertz or more. Thus, it is a method for

fine tuning of a klystron. When the repeller is

made more negative in relation to the cavity

grids, the repelling force on the electrons is in-

creased. Therefore, an electron passing through

the cavity grids on its way from the cathode will

return sooner and the frequency of oscillation

will be raised. There is. of course, a limit to the

amount of frequency change that can be obtained

by changing the repeller voltage. The frequency

will change approximately 1 MHz for a 1-volt

0B. NUMBER OF ELECTRONS

FAST-VELOCITYPt OTS

SLOW-VELOCITYPLOTS

BUNCHING OCCURS AT INTERSECTIONS OF PLOTTED LINES

AT DISTANCES INDICATEDBY DOTTED LINES (- - -) AND AT

TIME INTERVALS INDICATED BY DASHED LINES I ).

Figure 98.

C. APPLEGATE DIAGRAM

Applegate diagram.

95

COOL I NG,F !NS

FIL AMENT

CAVITYTUNING SCREW

Es

0:L1111+

Figure 99. Reflex klystron.

114//CAVITYGRIDS

%MP

RESONANTCAVITY

DRIFT \REC.ION

REPELLER

OUTPUT IINDUC TIVE L OOP)

Figure 100. 12, flex klystron want voltages.

96

CAVITY

changc in the repeller voltage. In general. bychanging the repeller voltage and retuning the cav-ity, a reflex klystron can be tuned over a rangeof about ±5 percent from thc center of its oper-ating band. Whcn the repeller voltage is changed.it can be frequency-modulated over a range ofabout ±0.5 percent of its operating frequency.Remember, however, that thc frequency modu-lation is accompanicd by some amplitude modu-lation when the frequency shift is accomplishedby variation in the repeller voltage.

14-31. Frequency modulation of the klystronsignal is accomplished by feeding thc modulatingvoltage to the repeller of thc klystron. The modu-lating voltage frequency modulates the internalklystron signal by makinc the repeller voltagemore or less negative. The amplitude of themodulatine voltage determines thc amount of kly-stron frequency deviation. and the frequency ofthe modulating voltage determines thc rate of kly-stron frequency deviation. For many klystrons a1-volt change in repeller voltage produces a I -MHz change in klystron frequency. The amountof repeller voltage change required to producea I-MHz chance in klystron frequency is corn-

423

OUTPUT

INDUCTIVECOUPLING

OUTPUT

CAPACITIVECOUPLING

.1.1711m1;

CAPACMVETUNING

SLUG

INDUCTIVETUNING

SLUG

111..1 NO .11 Mb

.

..qt-6--1111111r1.1111.111111.111

RESONANTOWED 410 8=6 41= .=1.11110

WINDOW -IN'

Et

PthATUNINGSCREW

PRESSURESPRING

011111=6 ONININI 41=1 =No

Fieure 101. Reflex klysiron cavity uthine methods.

monly referred to as the klystron modulation

sensitivity. Thus, a modulation sensitivity of1v/MHz implies that the repeller voltage mustehange 1 volt to change the frequency 1 MHz.You may encounter slight differences betweenindividual klystron modulation sensitivities.

14-32. The multiplexed aural and visual signal

must be sufficient in voltage amplitude to be

applied to the kystron repeller. In some cases the

signal will consist of a visual signal only and theaural signal is relayed by another method. Whenthe multiplexed signal is used, the necessary sig-

nal strength is achieved in the input combiningand amplification circuits.

14-33. Transmitter Maintenance. After equip-ment is installed and in an operational mode for

97

424

vt

a period of time with all initial discrepancies cor-rected, you still have the task of maintaining per-formance. To maintain UHF equipment in asatisfactory condition requires a slichtly differentapproach from the way low-frequency equipmentis maintained. With UHF. especially microwaveequipment, it is not enough to "dip" the plate and"max" the grid. Also you do not just peak-up thetuning of a stage as in equipment with narrow-band tuning. With widc-bandpass equipment. youmust be extremely careful of any voltage changeas this could change the operating bandpass andresonant frequency. Any dirt, lint, or other par-ticles carried into a tuning cavity by the coolingsystem could change its capacitance and cause afrequency shift. Along this same line, with hiehvoltaees and close tolerances, arcing can be aproblem with foreign particles in cavity areas.Cleanliness, precision adjustments stable power.and avoiding unnecessary touchups are some ofthe things to remember when maintaining UHFand microwave equipment.

15. UHF Antennas

15-1. As stated in Section II, the UHF band470-890 MHz, is assigned to television channels14 through 83 by FCC. Assignments of hieherfrequencies are made for portable, mobile, andpoint-to-point TV service. The frequency assign-ment for a particular piece of equipment is madeby FCC in accordance with the locality and thepeculiar needs of the equipment.

15-2. Television stations receiving .allocationsin the higher frequency ranges fall into the fol-lowing categories; (1) remote-pickup stations.(2) studio-to-transmitter link stations. (3) inter-city relay stations. (4) broadcast translator sta-tions. and (5) broadcast booster stations. A re-mote-pickup station transmits proeram materialand related communications from a remote site tothe primary TV broadcast station. A studio-to-transmitter link station transmits program and re-lated communications from a fixed-base remotestation to the primary TV broadcast transmitter.Intercity relay stations retransmit the programand related communications between two TV sta-tions. A broadcast translator station retransmitsthe initial TV program on a different frequencycarrier. A broadcast booster station retransmitsthe signal of a primary broadcast station by am-plifying and reradiating the incoming signal onthe same frequency carrier.

15-3. UHF Transmission and Propagation.Propagation characteristics for UHF and higherfrequencies are less favorable than for VHF. At-mospheric absorption of signal energy is in-creased. Likewise, shadow effect is more severebecause the hieher frequency wave passing over

an obstacle dces not disperse itself in back ot theobstacle (shadowed area) as does a hewer fre-quency wave. The transmission range of UHFand higher trequencies is limited to short dis-tances.

15-4. In TV microwave links, thinsmission isusually required netween a transmitter and onlyone receiving station. Therefore. it is desirablethat both the transmitting and receiving antennasbe highly directional. The general requirementsfor receiving and transmitting antennas are thatthey have small energy losses and that they bcefficient as receptors and radiators.

15-5. UHF Receiving Antennas. Many typesand designs of UHF receivine antennas are avail-able on the commercial market. Our discussionwill be limited to some of the more popularonesi.e., corner reflector, V-type, bow-tie, andparabolic reflector.

15-6. Corner reflecwr. The corner reflectorgives good results under adverse conditions. isrelatively directional, and has excellent euin overa major portion of the UHF spectrum. It consistsof u half-wave radiator set in the plane of a linebi,..ecting the corner anele formed by two flatmetal reflector shcets. Construction of a typicalcorner reflector is illustrated in figure 102.A. Forhorizontal pohirization, the radiator and reflector

334

30

.10

10

A

01 3 1 33 OA

SPACiNG OF DIPOLE FPOu COANE IN WA rELENGTHS

Fiwure 102. Curlier rt. fleen.w antorna.

0 5

Fiver 103, Basic V-antenna.

are mounted in the horizontal plane. This mount-ing arrangement results in a very narrow verticalradiation pattern with maximum signal radiatedin line with the bisector of the corner angle. Thedirectivity in the horizontal plane is approximatelythe same as for any half-wave radiator having asingle-rod type of reflector behind it. .

15-7. Both gain and radiation resistance of the

antenna are affected by the reflector cornerangle B. the spacing between the radiator andthe corner A. and the size of the reflector. Fig-

ure IO2.B. shows the gain (expressed as a powerratio) between the dipole with a reflector and abasic dipole antenna for corner reflector anten-nas having different corner angles. In some ap-plications. the driven element is made in the formof a folded dipole to increase input impedance.The reflector often consists of a sereen with open-ings spaced approximately one-tenth wavelength

apart.15-8. V-type antenna. The V-type antenna

is another version of the dipole antenna. Each ofthe quarter-wave elements of the dipole is slantedforward to form a V-shape. (Fig. 103 illustratesthe construction of a basic V-antenna.) The Vis formed at such an angle that the main lobesreinforce along the line bisecting the V to make a

very effective bidirectional antenna.15-9. The V-antenna has a broad bandwidth

capable of covering the VHF as well as the UHFstations that serve an area. As the frequency ofthe received signal increases, the antenna ceasesto be a 1/2-wavelength structure. Each leg grad-

ually becomes a wavelength relative to the fre-quency of the arriving signal. For example, ifeach of the two legs of a V-antenna is cut for1/4 wavelength at channel 2 (54-60 MHz), theybecome 34 wavelengths at 180 MHz, almost 21/2wavelengths at 600 MHz, and approximately 31/2wavelengths at 840 MHz. The gain of this typeof antenna is dependent upon its leg lengths andupon the anele which ,the two legs make with

each other. Sincc gain is almost directly propor-tional to the leg length, it would seem advisable

to make each leg as long as possible. However.there are structural limitations. With excessive

99

extension of leg length. the antenna becomes un-wieldy and readily breaks when exposed to wind,ice, or snow. This problem is partially overcomeby using antenna elements of sufficient diameter

(3/8 to 1/2 inch) to provide additional strength.

Design variations include adding or stacking V'sto increase gain and directivity.

15-10. Bow-tie antenna. The bow-tie antenna(sometimes called fanned dipole) is still anothervariation of the dipole. In order to achieve thebroadband characteristics necessary to receive all

signals within the TV UHF band, triangularsheets of metal are used instead of rods (see fig.104. A). The array is normally designed with acorner angle of 70 to achieve an input impe-

dance of approximately 300 ohms. The radia-tion pattern of a bow-tie antenna is a figureeight; however, if a screen is placed behind thedipole (as shown in fig. 104.B), the field be-comes unidirectional.

15-11. The gain is only slightly greater thanthat of a rod dipole; therefore, these units providesatisfactory reception in strong signal areas where'there are relatively few ghost signals. Bow-tie

antennas. however, can be stacked two and fourhigh to provide increased gain and better discrim-ination against ground-reflected signals. Notice

that the reflector in figure 104,B, is a wire screeninstead of the rods usually used at VHF. Screens

are as effective as solid metallic reflectors, pro-vided the openings are no larger than 0.2 wave-length at the highest operating frequency. Re-flector dimensions are not critical, but the edgesshould extend for a short distance beyond thedipole elements. As shown in figure 104.C, thecorner reflector is also used with the bow-tie an-tenna.

15-12. Parabolic reflector. Parabolic reflectors

are generally used in TV microwave relay sys-tems. They are used in both transmitting andreceiving antenna systems. The principles of

operation of antennas designed for operation inthe super-high-frequency range are the same asfor the lower frequency antennas. However, be-cause of the small physical size of the radiatingelements, full advantage can be taken of directivearrangements for efficient line-of-sight operation.

15-13. Focusing microwave energy is a rela-tively easy task, because the radiation propertiesof microwave frequencies approach those of lightwaves. Figure 105 shows how this focusing ofenergy is accomplished in many microwave relaysystems. Energy is radiated from the apertureantennas into a paraboloidal-shaped reflector(parabolic reflector). This reflector concentratesthe microwave energy into a tight beam. Asshown, a plane reflector intercepts the beam ofenergy. The plane reflector is tilted at an angle

426

A. BOWTIEANTENNA

CORNERANGLE

C. BOWTIE ANTENNAWITH CORNER REFLECTOR

Figure 104. . Bow-tie antenna.

sufficient to direct the beam tdward the distantstation. The angle of tilt depends upon the posi-tioning of the parabolic reflector, plane reflector.and distant station.

15-14. In most microwave antenna systems,the parabolic reflector and the aperture antennaassembly are constructed as one unit. The wave-guide is fed through the rear at the center of thereflector. The aperture antennas arc positionedat a point above the reflector.

15-15. Figure 106 illustrates the beaming ac-tion of a microwave parabolic reflector. Notethat all parts of a wavefront leaving point Aarrive at line BC simultaneously. Thus, the para-bolic reflector forms the energy from the wave-guide into a beam in the direction of the planereflector which, in turn, reflects the microwavebeam toward the distant station. The receivinecharacteristics of a parabolic reflector are also

B. BOWT1E ANTENNAWITH FLAT REFLECTOR

such that r-f energy striking thc surfacc of aparabolic reflector forms a well-defined focalpoint. Hence, energy received from the distantstation is directed into the waveguide at point A(the aperture antenna).

15-16. UHF Transmitting Antennas. In com-parison with a VHF system, the UHF antennasystem must generate a higher signal gain in or-der to service a given area. The complicatedfeeder system and stacked element array methodsused with VHF systems would introduce lossesif further advanced to accommodate the highergains necessary in UHF systems. The higherfrequency and shorter wavelengths of thc UHFsignals require a new approach.

15-17. The loop antcnna in its basic form issimply a coil of wire uscd to radiate energy. Theshapc of the radiation pattern varies with varia-tions in thc diameter of the loop. If the diamctcr

1004 2

is less than 0.585 A. the field of maximum radia-

tion is in the plane of the loop. Radiation atright angles to the plane of the loop is nil.

15-18. The slotted loop (slotted ring) an-

tenna. a modification of the basic loop antenna.is an effective high-band VHF and UHF trans-mitting antenna. It consists of a series of slotted

rings mounted on a channel, as shown in figure107. The rings are lenticular in cross section with

the long axis in the plane of the rings. This con-figuration results in an antenna structure that has

Figure 105. Microwave antenna system.

a minimum resistance to wind forces. Two paral-lel rods are mounted to the rings, one along eachside of thc open portion. This arrangement forms

a continous slot and acts as a balanced trans-mission line. Figure 108 shows a section of this

type of antenna mounted on a supporting mast.A basic slotted ring antenna is a bay consisting oftwo radiating elements (called half bays) ar-raneed one above thc other and fed with a singlerigid coaxial transmission line.

PARABOLOIDAL -SHAPIDREFLECTOR a

Figure 106. Paraboloidal-shaped reflector.

15-19. We can best understand the operationof the slotted ring antenna by considering it as abalanced transmission line shunted by a numberof loops, or rings. The phase velocity at which avery-high-frequency wave is propagated alongthe transmission line can be substantially variedby properly arranging the separation and cross-sectional area of the rings. Figure 109 shows aloaded transmission line short-circuited at oneend and fed with r-f energy at the other. Stand-ing waves having an apparent wavelength areset up along the line. When the number of ringsalong the balanced transmission line is approxi-mately 12 per free-space wavelength and the dia-meter of each ring is approximately 0.14 of thefree-space wavelength, the apparent wavelength

RING SUPPORTS

MOUNTING CHANNEL

Figure 107 Section al slotted ring anienna.

101

Ab

Figure 108. Slotted ring antenna mounted on pole.

102

will be about twice that of the irec-space wave-iength.

15-20. When the same arrangement is shortcircuited at both 'ends and fcd at the centerthrough a length of transmission line (as shownin fig. 110). a wave propagates from the cen-ter feed point toward each of the short-circuited.ends. The reflected wave from the ends sets upa standing wave, and thc difference of potential

'between the conductors of the antenna and thebalanceti..transmission line is distributed approxi-mately as shown: The phase of this potentialdifference is essentially constant over the entirelength of line. The difference of potential exist-

1Xa

LANCEDSIGNAL

GENERA TOR

Figure /09. Balanced transmission line loaded withshunt rino

4 2,.)

'1713

COAXIALTRANSMISSION

LINE

SIGNALGENERATOR

Figure 110. Unbalanced transmission line loaded with

shunt rings.

ing between the balanced conductors causes cir-cumferential currents to flow in the shuntingrings.

15-21. Gain is proportional to the number ofbays used. Each transmitting bay is approximately3.4 wavelengths at the operating frequency andhas an average power gain of approximately 4.As many as five bays may be stacked one abovethe other. High-gain antenna configurations arcpractical for use at the high-band VHF and UHFchannels because of the short physical antennalengths.

15-22. The slotted ring antenna is capable ofhandling high input power. Rigid coaxial trans-

103

4 30

mission lines running to each bay permit the useof approximately 35 kw in the high VHF band.

15-23. The impedance of the slotted ring an-tenna is a nominal 50 ohms. Since the antenna isfed by a single rigid coaxial transmission linehaving a nominal impedance of 50 ohms, noimpedance matching problems exist.

15-24. The horizontal radiation pattern of thisantenna is essentially circular. Directional hori-zontal radiation patterns are achieved by addingpattern-shaping members to the basic antenna. A

common method is to connect two beam-shapingmembers to each alternate active ring. The ringsto which these members are attached direct asubstantial portion of the antenna current into

the beam-shaping elements.15-25. UHF and VHF Antennas Compared.

Although UHF antennas actually can include anyone of the VHF antennas previously discussed,the UHF antenna will be considerably smallerin physical dimension. It has a lower length-to-diameter ratio; hence, it has a lower (..) and wider

bandwidth response than the VHF antenna.Sticked arrays and other complex systems have

much less wind resistance, less weight, and arenot as massive. The UHF antenna is less subjectto interference from the surrounding area than isits VHF counterpart. Even when tin roofs, rainpipes, or other metal objects which might in-fluence antenna performance are nearby. theUHF antenna is farther away from these influen-ces in terms of actual wavelengths. Some VHFantennas can be converted to VHF/UHF anten-nas by modifying 'their mounting arrangements.Among those that can be made suitable for bothVHF and UHF reception are the VHF conicalanterina and the VHF V-type antenna.

15-26. IMpedance matching at the antenna

and, more importantly, at the receiver requiresmore careful attention in UHF installations. Mis-matching at the receiver results in energy beingreflected back along the line with resultant stand-ing waves. Attenuation characteristics of a linemay be increased substantially over its normalrating when standing waves are present. In strongsignal locations, the additional loss may not beserious; however, in moderate and weak signalareas, it can mean the difference between usableand unusable pictures.

15-27. Waveguide. A special type of trans-mission line, the waveguide. is used when greatertransmission efficiency is required that can be ob-tained from coaxial lines. Electromagnetic fieldstransfer the energy in a waveguide without theuse of a center conductor. The waveguide maybe considered a hollow pipe and may be.round,square, rectangular, or elliptical. Waveguides

have certain advantages over the transinission

lines. Radiation losses are very small in a wave-guide because the fields are contained whollywithin the guide. Since a waveguide has a largesurface area and does not have a center conduc-tor. the copper losses are less than those in othertypes of lines, cince the absende of a center con-ductor also e: ..,ates the netA for a solid dielec-tric support, dielectric losses are less. The power-handling capability of a waveguide is greaterthan that of a coaxial line having an equal sizebecause the distance between the conductors ofthe waveguide is greater. Waveguides are alsosimplier to construct than coaxial lines.

15-28. Waveguides are used in UHF TVtransmission systems when greater power-han-dling capacity and lower signal attenuation is de-sired. Waveguides may also be employed in themicrowave relay system. Two of the sizes oftypical rectangular waveguides are 53/4 by 111/2inches (650- to 1000-MHz range) and 71/2 by15 inches (450- to 750-MHz range). Thewaveguides are formed using copper-clad steelor aluminum. The installation of a waveguidesystem for UHF is much the same as with coax-ial lines and the same precautions should be fol-lowed. Transition or coupling devices must beused if the system requires a change from wave-guide to coaxial line or from coaxial line to wave-guide along the transmission route.

16. UHF Receivers

16-1. In the preceding section, only the VHFTV channels (2 through 13) r-f tuners using thesuperheterodyne principle were discussed. Inmany areas it is possible to receive ultra-high-frequency (UHF) TV channels. In the past,TV receivers were manufactured with combinedVHF/UHF tuners or with the VHF tuner only.Separate UHF tuners are available for VHF setsoriginally manufactured for VHF only.

16-2. UHF Conversion. There are severalmethods of heterodyning the UHF signal downto the i-f signal range. One method. direct heter-odyning, shown in figure 111.A, employs aUHF local oscillator whose frequency is equal tothe total of the desired i-f and the UHF incomingsignal. If a UHF signal is being received on chan-nel 31 (572-578 MHz), the UHF oscillator willbe set on 619 MHz to heterodyne with the videocarrier frequency of 573.25 MHz. The differencefrequency will be the i-f video carrier frequency.45.75 MHz.

16-3. Another method of UHF heterodyning.shown in figure 111.B. uses an external conver-ter that can be connected to a standard TV re-ceiver having only a VHF tuner. This methoduses the double superheterodyne principle where-by the UHF signal is heterodyned two times be-

420fore it is reduced to the i-f range Of the TV re-ceiver. In the example illustrated in figure111.B. UHF channel 21 is to he received. TheUHF local oscillator will be set on 430 MHz forchannel 21 ( 512-518 MHz) reception. Hetero-dyning the UHF oscillator frequi:ncy with thevideo carrier frequency (513.25 MHz) of chan-nel 21 will produce an 83.25-MHz signal in theoutput of the external converter. The frequency83.25 MHz is the video carrier frequency ofchannel 6. Injecting the output of the externalconverter into the antenna input terminals of theVHF TV receiver and with the channel selectoron channel 6. the VHF local oscillator will beset to 129 MHz. The second heterodyning step.mixing 129 MHz with 83.25 MHz. will resultin a difference frequency of 45.75 MHz. Withthe external converter set on channel 21 and theVHF receiver set on channel 6. the .pieture onchannel 21 will be produced on the screen of theVHF receiver. An additional i-f amplifier in theoutput of the external converter is usually usedto step up the first heterodyned i-f signal into theVHF receiver.

16-4. A third method of UHF heterodyning.as shown in figure 111,C, uses a harmonic gene-rator (frequency multiplier) to produce the de-sired UHF oscillator frequency. The harmonicgenerator usually consists of a crystal circuitwhose output is selective to the desired harmonicfrequency range (in this case. the third harmo-nic). No UHF local oscillator stage is needed be-cause an output is taken from the VHF localoscillator (139.75 MHz) and applied to the har-monic generator. The output of the harmonicgenerator (three times 139.75 MHz) is mixedwith the incoming UHF signal to produce thedesired i-f signal.

16-5. The direct heterodyning system. as

shown in figure 111.A. is usually used with re-ceivers that contain a combination VHF/UHFtuner. The external converter method is usedwith TV receivers that have only the VHF tuner.The harmonic-crystal mixing method is mostoften used with receivers in which the tuner de-sign provides plug-in channel strips, as withturret type tuners.

16-6. Maintenance. Receiver maintenance forUHF receivers will be increased by the additionof one tube and associated circuiti One veryimportant difference is that the tuning section ofa UHF tuner contains some very delicate tabs.These tabs are adjusted to obtain the correct capa-citance for proper tracking of the tuner. For thisreason it is a good idea to avoid inserting any-thing into this tuning section, because even astrong blast of compressed air can damage ordetune it. Also. rough handling. moisture. ex-

104

43i

CHANNEL 31VIDEO SIGNAL

573.25 MC

UHFLOCAL OSC.

SET TO 619 MC

A

UHFMIXER

CHANNEL I21

1UHF

LOCALOSC.

CHANNEL 21

HIGH IFAMP

1

83.25 MC

430 MC

EXTERNAL CONVERTER

UHFMIXER

ANT.TERM.

HARMONICSELECTOR

HIGH IFAMP

45.75 MCIF AMP TO 45.75 MC

IF STRIP

VHF RECEIVER

MIXTO IF STRIP45.75 MC

VHFLOCAL OSC.

129 MC

X 139.75 MC

VHFMIXER

-4*-tViREVANTIEF4-:-*--419.25 MC

Figure III. Methods of UHF conversion.

105

1 32

VHF LOCALOSC.

139.75 MC

TO IF STRIP..45.75 MC

tre,.'s of hzat or cold, etc.. should he avoided.Here also. as stated previously. precision com-ponents require precision maintenance. This isespecially true of the microwav:: receiver whichmust maintain a broad frequency response. 'withthe same amount of gain.

16-7. Microwave Receiver. The microwave re-ceivers must be capable of receiving weak signals(sometimes as low as 100 dbw): At VHF fre-quencies it is possible to increase receiver sensiti-vity by the use of r-f amplifiers. Thus far, ampli-fication of low-level microwave signals has notbeen practical. except by the use of the paramet-ric amplifier. Microwave receivers, therefore, donot provide amplifications at the received signalfrequency. Basically, microwave receivers areFM superheterodyne receivers with sufficientstages of i-f amplification to boost the first de-tector (mixer) output signal to the desired level.In these receivers the noise generated within theinput circuits (first detector and first two i-fstages) is the factor which limits the receiver'ssignal-to-noise ratio. Normally. a signal-to-noiseratio of 15 db is considered satisfactory for re-liable reception. Figure 112 shows a typicalmodern microwave receiver. Note that this re-ceiver bears a resemblance to an ordinary low-frequency FM receiver except that r-f amplifierstages are not used in the microwave receiver.

16-8. Basically, the microwave receiver oper-ates as follows: The microwave energy is re-ceived by the antenna system, radiated down the

MIXER

LOCALOSCILLATOR

KLYSTRON

IFAMPS

AGC

LIMITERS

waveguide to the receive bandpass filter, passedthrough the filter, and fed to a mixer,stage. Alocai oscillator klystron, operating at a frequencyapproximately 70 MHz removed from the re-ceived signal frequency, is also fed into the mixerstage. The mixer stage produces- a number offrequencies at its output. The difference fre-quency is selected, amplified by a number of i-famplifiers, and fed to one or more limiter stages.The limiter stages clip the noise from the FM i-fsignal. The i-f signal is detected by a discrimina-tor stage. The output of the discriminator con-sists of the original baseband signal. This signalis then fed to a number of baseband amplifierstages. (Baseband amplifiers are sometimes re-ferred to as video amplifiers or as dropout am-plifiers.) The amplified signal is then distributedto the multiplex equipment and to any otherappropriate equipment. A portion of the signalat the output of the discriminator is fed to fre-quency correction circuits. These circuits are usedto keep the local oscillator klystron tracking 70MHz (or the i-f frequency) removed from thefrequency of the incoming microwave signal.

16-9. As already mentioned, the microwavereceiver uses a klystron oscillator to produce afrequency to mix with incoming r-f. Since this is adifferent tube from those ordinarily used in re-ceivers, we can assume that probably the UHFfrequency receivers will also use specialized tubes.In the UHF receiver the input signal is weak andneeds amplification for mixing and detecting.

.10. DISCRIMINATOR

VTO LOCAL

OSCILLATORFREQUENCY

CORRECTIONCIRCUI TS

Fipure 112. yicroware receiver block diagrom.

106 A-I

TO RECEIVEALARM CIRCUITS

COMPOSITCSIGNAL TOMULTIPLEXEQUIPMENT

However, in most UHF tuners there will be amixing of the kiput signal and local oscillatorwith subsequent amplification of the i-f signal.Again, the reason for not amplifying the inputr-f is that there will be too much noise amplifiedalong with the signal. This noise factor is evidenteven_thongh tube elements being closely spacedarc designed for high-frequency operation. Thespacing between the cathode and grid is as smallas 0.001 ineh and the cathode-to-plate spacingas small as 0.005 inch. Other design considera-tions that have been incorporated are smallerelements and multiple tube pin connectionswhich reduce coupling effects of the tube ele-ments. .Engineering factors have been extendedto consider such items as decreasing the size ofthc elements, using very short leads between thetube elements and the base pin, using multiplepin connections. making the connecting pins ofspecial material such as chrome iron, using nickelfor thc connectors between the tube elements andthe base pins, and plating the base pins withsilver or copper to reduce the resistance factor.

16-10. The transistor r-f amplifier presents

similiar problems to those encountered in tubetype counterparts. For audio-frequency transitoramplifiers, it is permissible to disregard the effectsof transistor internal capacitances and transittimes, since these effects are negligible in thelow-frequency range. Such is not the case, how-ever, in the upper frequency ranges. Transistorinternal capacitances provide feedback paths forhigh frequencies. Unless this feedback is con-trolled or eliminated, the operation of a high-frequency amplifier may be seriously impaired.Transmit times cause a falloff in gain which be-comes more pronounced with increasing fre-quency. These effects must be taken into accountwhen dealing with r-f and i-f amplifiers.

16-11. The transistor design has a great dealto do with high-frequency response; its alphacutoff frequency and internal capacitances arelimited factors. Desirably, it should have verylow internal capacitances and its alpha cutofffrequency should be well above the requiredupper limit of response. Special high-frequencytypes such as these are available and more arebeing developed.

*U.S. GOVERNMENT PRINTING OFFICE: 1173-640-065 / 660

AUGAFS, AL (753152) 660

107

434

aura

adapting this ma erial for inclusion in the "Trial Implementation of a

Model System to Provide Military Curriculum Materials for Use in Vocational

and Technical Education." Deleted material involves extensive use of

military formS, procedures, systems, etc. and was not considered appropriate

for us,, in vocational and techdical education.

MODIFICATIONS

40Whkj9of this publication has (have) been deleted in

/71,2/-/-

41 3 5

30455 02 21WORKBOOK

AUXILIARY EQUIPMENTS

C-- KIT-ItMAINGCegt viZz.

SRG

This workbook places the materials you need where you need thcm while youare studying. In it, you will find the Study Reference Guide, the Chapter Review

Exercises and thcir answers, and the Volume Review Excrcisc. You can easilycomparc textual references with chapter exercise items without flipping pages

back and forth in your text. You will not misplace any one of these essentialstudy materials. You will have a single reference pamphlet in the proper sequence

for learning.These devices in your workbook arc autoinstructional aids. They take the

place of the teacher who would bc directing your progress if you were in aclassroom. The workbook puts these self-teachers into one booklet. If you willfollow the study plan given in "Your Key to Career Development," which isin your course packct, you will bc leading yourself by easily learned steps tomastcry of your. text.

If you have any questions which you cannot answer by referring to "YourKey to Carccr Development" or your course material, use ECI Form 17, "StudentRequest for Assistance," identify yourself and your inquiry fully and scnd it to

ECI.Keep the rest of this workbook in your files. Do not rcturn any other part

of it to ECI.

EXTENSION COURSE INSTITUTE

Air University

436

TABLE OF CONTENTS.

Study Reference Guide

Chapter Review Exercises

Answers to Chapter Review Exercises

Volume Review Exercise

Ea Form No. 17

4 3 7

STUDY REFERENCE GUIDE

I. Vse this Guide as a Study Aid. It emphasizes all important study areas of this volume.

2. Use the Guide as you complete dw Volume Review Exercise and for Review after Feedback onMe Results. After each item number on your VRE is a three digit number in parenthesis. Thatnumber corresponds to the Guide Number in this Study Reference Guide which shows you wherethe answer to that VRE item can he found in the text. When answering the items in yourVRE. refer to the areas in the text .indicated by these Guide Numbers. The VRE results will besent to you on a postcard which will list the actual IRE items you missed. Go to your VRE

booklet and locate the Guide Number for each item missed. List these Guide Numbers. Then goback to your textbook and carefully review thz areas covered by these Guide Numbers. Review

ilw entire VRE again before you tail: the closed-book Course Examination.

3. Use the Guide for Follow-up after you ctnnplete the Course Examination. The CE results will

be sent to you on a postcard, which will indicate "Satisfactory" or "Unsatisfactory" completion.The card will list Guide Numbers relating to the questions missed. Locate these numbers in theGuide and draw a line under the Guidc Number, topic. and reference. Review these areas toinsure your mastery of the course.

GuideN umber Geide Numbers 200 through 224

200 Studio and Control Equipment; StudioLlght-ing, pages 1-3

201 Studio Aids, pages 3-8

202 Special Effects Equipment, pages 8-12

203 intercom, pages 12-14

204 Audio and Video Equipment; Recorders:Audio Tape Recorders, pages 15-18

205 Recorders: Heads; Electrmics; TroubleDiagnosis, pages 18-23

206 Recorders; Video Tape Recorders, pages23-28

207 Recorders: Kinescope Recorders, pages28-33

208. Projectors: 16 MM Projectors, pages 33-37

200 Projectors: Slide Projectors, pages 37-39

210 Vidicon Multiplexers, pages 39-42

211 Specialized Test Equipment; MonoscopeAmpliffers, pages 43-45

212 Video Test Equipment: Grating Generator;Dot Generator; Sweep Marker Generator,pages 45-48

213 Video Test Equipment: Pulse Cross Dis-play; Test Patterns, pages 48-53

1

GuideN umber

214 Color Testing, pages 53-58

215 VHF Equipment; VHF Transmitters: Trans-mitter Principles, puges 59-62

216 VHF Transmitters: Transmitter Signals,pages 62-68

217 VHF Antennas: Transmission and Pmpaga-tion; VHF Antennas, General; Factors Af-fecdng Efficiency; Power-Handling Capa-bilities; Impedance Matching, pages 68-71

218 VHF Antennas: Baluns; VHF Antennas,Special Types; Color Television AntennaRequirements, pages 72-79

219 VHF TV Receivers, Pages 79-87

220 UHF Equipment; Transmitters: Compari-sons, pages 88-93

221 Transmitters: UHF it el ay (Microwave);Transmitter Maintenance, pages 93-98

222 UHF Antennas: UHF Transmission andPropagation; Receiving Antennas, pages98-100

223 UHF Antennas: UHF Transmitting Anten-nas; UHF and VHF Antennas Compared;Waveguide, pages 100-104

224 UHF Receivers, pages 104-107

43'6

CHAPT''.R REVIEW IZERCISES

The following r are study your auswer.s in pincil in th, sp;tc, prm.idc,/ ;et, rexercise. Immediately after cmnpletng each se! of exercise:N. chuck yflur resi)onses illflt th,answers for dm! set. Do not submit y..ur imsweu, to. ECI for grading.

CHAPTER 1

Objectives: To identify types, sources, and methods of controlling studio lighting; and to determmemaintenance and repair procedures for such studio aids as prompters. projectors, special effects, andintercom equipment.

1. Match the descriptions in Column B to the terms in Column A by writing the alphabetical designa-tors of Column B in the blanks of Column A.

Column A Column R

1. Base lighting. a. General overall diffused illumination.Key lighting. b. Additional illumination of a principal subject from it gtven

3. Fill lighting. c. Added diffused illumination tc reduce shadows.4 Effects lighting. d.

.Lighting which simulates a :ealistic scene.

(1-3-6)

2. Does the incandescent lamp have a stronger or weaker energy output at the greater wavelengil(1-9, 10. fig. 1)

3. Which of the two common camera pickup tubes would be more suitable fur use with low-intensztvlighting? (1-11)

4. is tht incandescent or fluorescent lighting preferred for TV studio illumination% (1-12)

4 3 J

5. t spotlight with an adjustable iris and shutter would be an aid toin a studio. (1-13, 16)

h. Which one of the folltming lenses-81: inch, zoom, or 25-inchwould be the best substitute for a90mm lens on a studio camera? (1-20. 22)

7. Name several types of equipment which are often used for TV prompting. (2-2)

8. Name the basic sections of the scroll type of prompting unit. (2-3)

9. Name the components contained in the scroll section. (2-3)

10. What are the primary maintenance requirements of the TV prompter unit? (2-5)

11. During operation the d-c synchronous motor runs very slowly in the forward direction, but reversespeed is normal. Later checks disclose that V2 plate voltage is normal and the plate voltage ofVI is low. What is a possible trouble? (2-6. fig. 3)

3

440

A/a

12. The stage is aore practical than theprojecting opaque objects. (2-8)

- ---,stage when

13. The first law governing mirror action states that the - angle andangle are . (2-0)

14. What disadvantage is characteristic of a semitransparent mirror? (2-10)

15. All projected images must operate along the same 0-11)

16. What is the primary functional difference between projector and camera lens assemblies? (2-12)

17. Lighting methods differ according to the application; pictures are lightA from theand slides are lighted from the ____-- _ _ .. (2-13)

18. List the five factors which determine the amount of illumination required for a rear screenprojection. (2-14)

4 4

4

19. Why must the projection screen diffuse light? (2-20)

20 When selecting u projection screen, two properties that you should consider are its light

and characteristics, (2-21)

11. Give the symptom for each of the following discrepancies.

i. Dirty mirror.b. Open fuse.

Cloudy lamp.d. Open lamp.t. Rroken mirror.

1. Too much angle between projector and screen.

g. Dirty tens.h. Shorted dimmer control.(2-22-27)

22. Why is it so Important to keep the lens and mirror surfaces clean? (2-23)

21 The special effects generator provides a signal which determines the

video signal produced by the

24. Name the inputs to a special effects generator. (3-1, fig. 6)

5

442

(3-1)

25. What change(s) in figure 8 are tiecesry if a regenerative clipper incorporates n-p-n jrcinsistorsconnected for C-E operations? How is the output signal affected? (34-7, fig. 8)

26. Describe the input to a regenerative clipper that is needed to produce the special effects patternillustrated in figure 7, A, and 7, D. (3-8-10, fig. 7)

27. Identify four pertinent signals that are formed in the special effents generator. (3-11)

28. What waveform is absent if the pattern of figure 7, B, is seen when the pattern of figure 7,C; isselected? Name some checks that can be rnade to locate the trouble in the special effects system.(3-11, 12, 18, figs. 7, 10, 12)

29. Sketch a block diagram showing the principal sectionS of a special effects amplifier.(3-14, fig. 11)

30. From figure 12 determine whether each component named below is conducting or cut off when thekeying signal is at its low level.

a. Q1b. D2c. D3d. Q5e. Q3(3-15-17, fig. 12)

Explain how the black level balance corrects for undesirable differences between the picture 1

and picture 2 side of the switching network shown in figure 12. (3-18, figs. 7, 12)

32. A headset is working, but you find that an internal spring contact is weak. You replace the

contact. What type of maintenance would this be? (4.4)

33. A normal repair procedure for repair of an earpiece or a microphone is to

the insert. (4-5)

34. Draw a diagram and name the parts of an intercom system necessary to provide two-way

communication between offices. This would be used by maintenance personnel for adjusting

CCTV systems. (4-8, fig. 13)

CHAPTER 2

Objective: To describe and analyze the principles and procedures required to operate, align, and

adjust audio and video equipments to include recorders, film projectors, and multiplexers.

1. The three functions of audio tape recorders areand of audio frequencies. (5-3)

2. The , and are the three

main sections of an audio tape recorder. (5-4)

7 444

3. Explain why a braking facility is necessary in the tape transport mechanism of an audjo taperecorder. (5-6)

4. Explain why a laminated core is preferred over a nonlaminated one in the construction of audiotape recorder heads. (5-10)

5. Why is a bias oscillator used in many audio tape recorders? (5-13, 16, 17)

6. Describe the purpose of equalization in an audio tape recorder. (5-21)

7. If the bias oscillator in figure 20 of the text failed, what would be the audio indication on are-recorded tape? (5-25)

8. A basic difference in audio and video heads is that the is a moving headassembly. (5-30)

9. Much of the electronic circuitry of a video tape machine is concerned withsystems. (5-34, 40, 41, 45)

44,

8

it5

10. The video tape transport must be more rigid than a tape transport for audio only, because the

video tape is under and it must withstand high

stops. (5-41)

11. The variable oscillator is controlled by a video frequency of to

which results in an FM recording. (5-45)

12. Sometimes the cause of a weak signal on playback can be corrected by mechanically

increasing the clearance of the special tape guide. (5-47)

13. A.video tape could be partially erased through of the recorded tape. (5-49)

14. List the basic equipment required for kinescope recording of a television program. (5-52)

15. With reference to kinescope recordings, what are the conversion requirements for synchronization

of the motion picture camera with the television system? (5-59)

16. What is the cycling pulse which controls the synchronization process in kinescope recording?

(5-63, fig. 33)

94 4

17. Differentiate between the single-film ...stem and the double-film system of television.recording.(5-68)

18. Maintenance of kinescope recordilg equipment consists chiefly ofthan maintenance. (5-73)

ri.thor

19. What are the basic requirements which must be met before a 16mm film projector is consideredcompatible with the television system? (6-2)

20. The scanning sequence 2-3-2-3 is common for each ----- - film frames andtelevision frames. (6-4, 5)

21. If the shutter were found to be operating when pulldown is taking place and the image is beingprojected during vertical blanking, what is a possible cause of the trouble? (6-6, 7)

22. The intermittent is best for use with damaged film while theintermittent extends film life. (6-11)

23. Explain why various cleaning materials must be used in different sections of the 16mm filmprojector. (6-19)

4 410

24. Why would a slide projector with dual optical paths be preferred to a slide projector with a singleoptical path? (b-23)

25. What is the most efficient method of transfetring light from one optical path to another in thedual path slide projector? (6-31)

26. Explain why periodic maintenance functions are important for slide projectors. (6-33, 34)

27. Name the primary functions of a vidicon multiplexer. (7-1, 11)

28. What two majoi components make up the optical path of the multiplexer? (743, 9)

29. If you cannot move the mirror illustrated in figure 41 of the text, what is a possible cause of theproblem? (7-8, 10, 1.1)

30, Name some of the major maintenance requirements of a multiplexer. (7-16)

CHAPTER 3

Objectives: To define the purpose of certain specialized television test equipment and to Interpret thepattern..presentations of each.

1. The monoscope amplifier is actually a special item of test equipment. however. its ctrruits arecomparable to those of a (8-1)

2. A monoscope amplifier can be used in a TV system to provide a standardized(8-1)

3. List the quality checks which can be accomplished by using the monoscope pattern presentation.(8-5)

4. What part of the monoscope test pattern is used to check streaking? (8-8)

5. What circuits are checked and adjusted with the aid of the grating generator? (9-2)

6. You are using a grating generator to check a monitor and notice that the aspect ratio is compressedat the top and stretched at the bottom. This will require adjustment of the(9-7)

44j

//V7. What adjustment of a color monitor can be made with the aid of a grating generator? (9-7; 10-15)

8. Adjusting the signal clipper bias so an output occurs when the vertical and horizontal pulses

cross will result in a pattern. (9-8)

9. What piece of test equipment, in addition to a scope, would be most useful when checking the

frequency response of a linear amplifier? (9-10,11)

10. Which item of test equipment would you use to make an operational check of a sync generator?

(9-12)

11. Look at the pulse cross display of figure 52 and determine how many lines of video are

represented by F. (9-16, fig. 52)

12. Which would have the greater picture resolutiona 3-Mfiz or a 4-MHz video bandpass system?

(9-17)

13. List the items which can be checked with the aid of the standard resolution chart. (9-18)

4 513

14. Which standard chart would you use in conjunct:on with tne gruting generator pattern tio adjust

linearity and aspect ratio? (9-25)

15. Match the item of test equipment to the associated stem.

Linearity checker.Color-bar generator.Color signal analyzer.Vectorscope.

(10-2, 4, 8, 12)

1. Provides a means of measuring the differential gainand phase distortion of transmission systems.

2. Provides a reference signal which can be used tocheck many aspects of color receivers and monitors.

3. It has an adjustable phase-shifting network providinga 3600 (in 10 increments) shift.

4. Produces a pattern of lines and dots corresponding tocolors.

CHAPTER 4

Objectives: To recognize and specify the requirements of a VHF television transmitting system

including signal characteristics, transmitter components, special filters, transmission lines, andantennas; to identify the maintenance requirements of VHF television transmitters; and to identify,

analyze, and state the maintenance procedures of certain sections of VHF television receivers.

1. A basic transmitter is nothing more than an (11-2)

2. What does the abbreviation MOPA stand for? (11-4)

3. List the three methods of coupling. (11-5)

4 5

14

4. To achieve a uniform response to a small band of frequencies, would you choose loose coupling,

close coupling, or a compromise between the two? (11-6)

5. Identify the transmitter(s) necessary to initiate a complete TV broadcast. (11-10)

6. Once a visual transmitter is modulated, all the following amplifier stages must bein operation. (11-12)

7. How many MHz wide is a broadcast TV channel that carries both the aural and visual signals?

(11-13)

8. What are the stability requirements for visual and aural carrier signals? (11-13)

9. State the difference between co-channel and adjacent-channel stations. (11-15)

10. What equipment is used between the final r-f stage and antenna system to suppress the unwanted

sideband of a TV signal? (11-17)

11. What is the difference in center frequency deviation used for FM radio broad::asting avid TV auralsignal? (11-27)

12. State the basic function of a diplexer. (11-28)

13. One advantage of negative transmission is that "noise" produces streaksor spots. (11-31)

14. If you are tuning a stage and cannot get a "'dip" on a cathode meter, what would you check first?(11-33-37)

15. What one term would best describe the difference between a monochrome and a color transmitter?(11-40)

16. Why is a transmission line which is efficient for low-band VHF operation not also efficient forUHF operation? (12-7)

17. Compare and analyze VHF TV transmitting and receiving antennas with respect to the followingcharacteristics: (a) polarization, (b) bandwidth, (c) directivity, (d) gain, and (e) insulationrequirements. (12-11-26)

453

16

18. Explain how the center input impedance of a folded dipole antenna compares with that of a basicdipole antenna. (12-14, 15)

19. How may the bandwidth of a dipole antenna be increased? (12-21)

20. -Why is it generally desirable to mount TV transmitting and receiving antennas as high as iseconomically and structurally practical? (12-24)

21. Although it is desirable that the antenna impedance equal the impedance of the TV receiver, it ismore important that the characteristic impedance of the transmission line match the impedance ofthe . (12-27, 28)

22. A balun is a device used to convert to feed

systems, or vice versa. (12-29-31)

23. Describe the electrical characteristics of a Yagi antenna. (12-34)

24. The fanned type conical antenna is a popular (broad/narrow) band VHF TV (transmitting/receiving) antenna. (12-37)

5417

25. What makes it possible to predict the rnperatie;:al characteristics of a log-periodic ant:nna for

many frequencies ii ;he characterisitcs of one period of frequency are known% (12-38)

26. What are the advantages of the supetturnstile antenna compared to the basic turnstile antenna?

(12-41-44)

27. The antenna shown in figure 83 in the text uses the slot radiation principle. Flow does it get the

name "traveling wave"? (12-45, 46)

28. Assuming that a radiation pattern in the normal mode (perpendiculat to the antenna axis) is

desired from a helical antenna, the helix dimensions should be (large/small) in comparison with

a wavelength. (12-48)

29. Generally speaking, the requirements of an antenna for color TV reception are quite (different

from/similar to) those for black and white TV reception. (12-51-53)

30. List the sections of a VHF TV receiver. (13-2)

31. State the function of the fine tuning control. (13-9)

450

18

32. Which would normally be the best configuration for r-f and i-f frequency modulation: a common-base (CB). a common-emitter (CE), or a common-collector (CC) amplifier? (13-12)

33. If you substitute an n-p-n type transistor for a p-n-p type transistor, what else must alsobe changed? (13-17)

34. What are the undesirable characteristics of a diode detector? (13-24)

35 A discriminator circuit is used in conjunction with what signal? (13-25)

36. Maintenance of a TV receiver means its care and upkeep; also included is the(13-28)

37. Give a logical procedure for finding a faulty component in a TV receiver. (13-28-30)

38. List the basic differences in monochrome and color TV receivers. (13-31)

CHAPTEP 5

Objectives: To describe the requirements of a UHF transmission system including transmitters..antennas,,microwave relay and special receiver compcnents; to identify and state the...maintenancerequirements of UHF transmitter; and receivers.

1. UHF equipment used for TV broadcast covers what range of frequencies% (14-2)

2. List'the microwave frequency bands available to be used in conjunction with TV signal relay(14-4)

3. What is the distinguishing chatacteristic of an amplifier which makes use of distributedproperties? (14-11)

4. List the basic microwave equipment necessary to relay TV signals from a studio to a remotetransmitter. (14-21)

5. The electron beam in a klystron is modulated by varying the electron(14-23)

6. What causes an electron to reverse its direction of travel in a reflex klystron? (11-27)

4 5 /

20

7. Fine tuning of a klystron can be accomplished by a slight change in

(14-30)

8. Where would you apply the multiplexed aural and visual signal to a klystron? (14-32)

9. Why is UHF and microwave equipment sometimes more difficult to maintain than equipment

operating at lower frequencies? (14-33)

10. Give a possible cause for a change in cavity resonance during normal operation. (14-33)

11. Describe the directivity and gain characteristics of a corner reflector antenna used for UHF TV

reception. (15-6)

12. The basic V-type antenna is a (broad/narrow) band, (omnidirectional/bidirectional/unidirectional)antenna capable of covering both VHF and UHF bands. J15-8, 9)

13. The bow-tie antenna is a (broad/narrow) band, unidirectional antenna which provides satisfactoryUHF TV reception in (weak/strong) signal areas. (15-10, 11)

4 5021

14. Why are parabolic reflectors generally used in TV microwave relay systems rather than,en VHFand UHF TV systems? (15-12, 13)

15. The slotted loop (slotted ring) antenna is generally used as a high-band VHF and UHF TV(transmitting/receiving) antenna. (15-18)

16. How can the gain of the slotted loop antenna be increased? (15-21)

17. How do UHF and VHF antennas compare with respect to size, bandwidth, and impedancematching requirements? (15-25, 26)

18. Explain the various ways in which the use of waveguides increases the efficiency of microwavetransmission. (15-27)

19. When using the double conversion method with UHF TV, how many oscillators are necessary?(16-3)

20. How is the capacitance changed during alignment of a UHF tuner to insure proper tracking?(16-6)

4 5

22

/0/1.21. Give a basic description of a microwave receiver. (16-7)

22. How is the noise removed from the microwave receiver? (16-8)

23. What type of tube is frequently used for a local oscillator in a microwave receiver? (16-9)

24. A common consideration when selecting tubes oftransistors is their time.

(16-10)

2346

ANSWERS FOR CHAPTER REVIEW EXERCISES

CHAPTER 1

1. 1. a.2. b.

3. c.4. d.(1-3-6)

2. Stronger. (1-9, 10, fig. 1)

3. Image orthicon. (1-11)

4. Incandescent. (1-12)

5. Control the lighting. (1-13, 16)

6. Zoom. (1-20, 22)

7. Front and rear screen projectors, semitransparent mirrors, scroll, and cue cards. (2-2)

8. Scroll, d-c amplifiers, control section/power supply, and remote control. (2-3)

9. D-c synchronous motor, gear train, reels, and paper. (2-3)

10. Clean and inspect the equipment, and replace or repair all defective components. (2-5)

11. Dirty relay contacts, K 1. (2-6, fig. 3)

12. Horizontal, vertical. (2-8)

13. Incidence, reflection, equal. (2-9)

14. Absorption. (2-10)

15. Optical axis. (2-11)

16. Projector lenses are not required to control light quantity, whereas camera lenses do control lightquantity. (2-12)

17. Front, rear. (2-13)

18. a. Front light.b. Slide density.c. Type of scene.d. Screen size.e. Fall-off.(2-14)

19. So light will not pass directly through the screen and into the camera lens. (2-20)

20. Absorption, reflection. (2-21)

21. a. Low light level.b. No power.c. LOW light level.d. No light from that stage.e. No image from that stage.f. Keystone effect.

g. Low light level.h. Maximum light with no Control over brightness.(2-22-27) 4 61

24

22. Dirt decreases efficiency. (2-23)

23. Keying, montage, special effects amplifier. (3-1)

24. Horizontal and vertical drive signals. (3-1, fig. 6)

25. Polarity of biases must be changed to positive if n-p-n transistors are employed in figure 8. The

d-c reference level of the output signal becomes positive, but the waveforms and phase relation-

ships are unaffected. (3-4-7, fig. 8)

26. To produce the keying signal (square wave) for the pattern in figure 7,A, the regenerative clipper

is driven with a sawtooth having the horizontal scan frequency. For the pattern in figure 7,D, a

triangular signal having the horizontal scan frequency combined with a sawtooth having the field

scan frequency must be used as the input to the regenerative clipper. (3-8-10, fig. 7)

27. a. Triangular 15.75-kc signal.b. Sawtooth 15.75-kc signal.c. Triangular 60-cps signal.d. Sawtooth 60-cps signal.(3-11)

28. The pattern in figure 7,C, needs both a horizontal and vertical sawtooth signal to produce the

keying signal, whereas the pattern in figure 7,B, is produced when only a vertical sawtooth is

used. For these reasons, the trouble described indicates the absence of the horizontal sawtooth

input to the regenerative clipper. To locate the trouble, select on the S.E. generator panel the

pattern in figure 7,A. If pattern appears, the selector circuit for figure 7,C, is faulty. If pattern

is blank, check the keying signal input to the special effects generator. A normal signal locates

the trouble in the switcher section of the S.E. amplifier; no signal means S.E. generator trouble.

Observe waveform at TP2 in figure 10. If normal, check output of K1. No signal at TP2 localizes

the trouble to the H-sawtooth generator. (3-11, 12, 18, figs. 7, 10, 12)

29. Check your sketch with figure 11. (3-14, fig. 11)

30. a. Conducting.b. Cut off.c. Conducting.d. Cut oft.e. Conducting.(3-15-17, fig. 12)

31. The black level balance adjust (fig. 7) changes the bias of Q1 and Q2 oppositely until both

conduct equally. (3-18, figs. 7, 12)

32. Preventive maintenance; an actual breakdown has not occurred. (4-4)

33. Replace. (4-5)

34. See figure 13 and use only one headset and microphone in each place or use the telephone which

would be the same circuit. (4-8, fig. 13)

CHAPTER 2

1. Recording, erasing, playing back. (5-3)

2. Transport mechanism, heads, electronics. (5-4)

3. To keep_the tape from becoming tangled. (5-6)

4. Reduction of magnetic losses due to eddy currents, thus better response to high frequencies.

(5-10)

25

S. To provide a high frenuency for tape er.1n:-.,1 and t serve as a rource of bias current forainerecord head so 6E1: it w:ll operate on pot ion of i!s :.:urve. (5-13. 16, 17)

6. To equalize the voltages of high and :o.v fre.quencre.s. (5-21;_-7. The old signal would not be eras.:d. The r,,v, signal would be weak and distorted. to-25)

8. Video. (5-30)

9. Servo. (5-34. 40. 41, 45)

10. Greater tension, 3peed. (5-41)

11. D-c to 4 MHz. (5-45)

12. Negative. (5-47)

1.3. Rough handling. (5-49)

14. a. A television monitor.b. A motion picture camera.c. A sound camera or recorder.(5-52)

15. Conversion of 30 television frames to 24 motion picture frames. (5-59)

1.6. An electronic pulse from the recording camera. (5-63, fig. 33)

17. a. Single-film system: sound and picture recorded on same camera film.b. Double-film system: sound and picture recorded by separate cameras.(5-68)

18. Preventive, corrective. (5-73)

19. Conversion, synchronization, and adaptability of the projection cycle. (6-2)

20. 4, 5. (6-4, 5)

21. A defective synchronizing waveform generator or a defective unique-phase synchronous motor.(6-6, 7)

22. Claw, sprocket. (6-11)

23. Some sections and components are delicate, while others are very sturdy. (6-19)

14. Provides more versatility. (6-23)

25. A sliding mirror. (6-31)

26. To prevent malfunctions and thus insure optimum operation. (6-33, 34)

27. Select or mix the output from several inputs and thus provide more versatility. (7-1. 11)

28. Field lens and mirrors. (7-8, 9)

29. A defective solenoid or gear train. (7-8, 10,11)

30. Clean, lubricate, and inspect. (7-16)

1. Film camera. (8-1)

2. Test pattern. (8-1)

CHAPTER 3

26

4 6

3. a. Resolution capabilities.b. Low-frequency phase shift.c. Contrast.d. Deflection linearity.c. Transmitter quality and performance tests.1. Receiver performance.(8-5)

4. Horizontal lines beneath the center circle. (8-8)

5. Deflection Circuits. (9-2)

6. Vertical linearity. (9-7)

7. Convergence. (9-7; 10-15)

8. Dot. (9-8)

9. Sweep marker generator. (9-10, 11)

10. Pulse cross display. (9-12)

11. Three (since a video scan is 1H and F represents 3H). (9-16, fig. 52)

12. 4 mc. (9-17)

13. a. Resolution.b. Geometric distortion.c. Aspect ratio.d. Shading uniformity.e. Streaking.1. Gray-scale reproduction.g. Interlace.h. R-f interference.i. Frequency response.j. Brightnesl.(9-18)

14. Standard linearity chart (by focusing the camera on this chart and superimposing the grating

pattern on the presentation). (9-25)

15. a. 1.

b. 2.

c. 3.

d. 4.(10-2, 4, 8, 12)

CHAPTER 4

1. Oscillator connected to an antenna. (11-2)

2. Master oscillator power amplifier. (11-4)

3. a. Capacitive.b. Inductive.c. Link.(11-5) _

4. Compromise of the two methods. (11-6)

5. Itsxs necessary to have an AM visual transmitter and an FM aural transmitter. (11-10)

6. Linear. (11-12)

7. 6 MHz. (11-13)

8. Visual. is .4:1000 Hz and the aural is :1000 Hz. (11-13)

9. Co-channel stations are two stations on'the same frequency, while adiaceri channel stationsare two stations adjacent in frequency. (11-15)

10. Vestigial sideband filter. (11-17)

11. 50 KHz. (11-27)

12. A diplexer enables the transmission of multiple signals by one antenna. (11.28)

13. Black. (11-31)

14. Check to see if you have drive from the preceding stage. Then, if necessary, , check the stagewhich you are tuning. (11-33-37)

15. Tolerance limits. (11-40)

16. With an increase in frequency, transmission line losses increase. (12-7)

17. Characteristic Transmitting Antenna Receiving Antenna

a. Polarization. Horizontal. Horizontal.b. Bandwidth. 6 mc. Minimum of 6 mc (often much

wider).c. Directivity. Omnidirectional. Unidirect ional.d. Gain. Good. Excellent.e. Insulation requirements. Critical. Not a matter of concern.(12-11-26)

18. The center input impedance of the folded dipole is greater than that of a basic dipole; eachadditional conductor of a folded dipole further increases the center input impedance of theantenna. (12-14, 15)

19. By using antenna wire with increased diameter, by stacking dipoles one above the other, or byusing a folded dipole. (12-21)

20. a. By mounting transmitting and receiving antennas at increased heights, the line-of-sightdistance between them can be extended.

b. Increasing the height of a receiving antenna generally places it in an area of stronger heldstrength. (12-24)

21. Receiver. (12-27, 28)

22. Balanced, unbalanced. (12-29-31)

23. The electrical characteristics of a Yagi antenna are high gain, unidirectional, good front-to-backratio, and relatively narrow bandwidth; it is also used as a TV receiving antenna. (12-34)

24. Broad; receiving. (12-37)

25. Because its input impedance, radiation pattern, and active elements repeat periodically as afunction of the logarithm of frequency. (12-38)

26. The stacked radiating elements of the superturnstile antenna have higher gain. increased verticaldirectivity, and wider bandwidth than has the basic turnstile antenna. (12-41-44)

27. From the way the slots in the antenna are fed. (12-45, 46)

28. Small. (12-48)

29. Similar to. (12-51-53)4 6 J

28

30. a. R-f.

b. I-f.c. Video.d. Sync separator.e. Vertical sweep.I. Ho:izontal sweep.

g. High voltage.h. Low voltage.i. Automatic gain control (agc).j. Audio.(13-2)

31. The fine tuning control varies the local oscillator frequency, thus centering the incoming signalfor proper bandpass. (13-9)

32. CB is generally preferred due to stability, controlled gain, and interchangeability. (13-12)

33. The d-c polarities must also be reversed. (13-17)

34. No power gain and selectivity are affected by loading. (13-24)

35. This is the detector for the FM signal which is the audio portion of TV broadcasting. (13-25)

36. Troubleshooting and repair of equipment. (13-28)

37. a. Determine' if visual, aural, or both are affected.b. Determine the section or circuit group.c. Isolate to a specific stage or circuit.d. Locate the faulty component.(13-28-30)

38. a. Color synchronizing section.b. Demodulation (chrominance) section.c. Matrix section.(13-3 1)

CHAPTER 5

1. 470-MHz to 890-MHz range. (14-2)

2. a. 1990 MHz to 2110 MHz (2000-MHz band).b. 6925 MHz to 7050 MHz (7000-MHz band).c. 13,025 MHz to 13,200 MHz (13,000-MHz band).d. 890.5 MHz to 910.5 MHz (900-MHz band for audio only).(14-4)

3. The amplifier is so designed that the materials used in its construction make up circuitcomponents. (14-11)

4. a. A microwave transmitter.b. A transmitting antenna system.c. A receiving antenna system.d. A microwave receiver.(14-21)

5. Velocities. (14-23)

6. The electron which leaves the cathode approaches the repeller plate which is more negative thanthe electron; the like charges repel and the electron travel is reversed. (14-27)

7. Repel ler voltage. (14-30)29

3. Apply the signal to the klystro:i repeller and thus 71,..:dulatt- the output. (14-32)

9. UHF and microwave equipment is more diff'cult t...) maintain because the circuits are morecritical and may be influenced by such things as dust, lint, temperature changes, and voltagevariations. (14-33)

10. The tuning cavity can have its capacitance and thus its resonance changed by any particlecarried into it by the cooling system. (14-33)

11. The UHF comer reflector antenna is unidirectional, with maximum signal radiated in line with thebisector of the corner angle. It has excellent gain over most of the UHF spectrum. (15-6)

12. Broad; bidirectional. (15-8, 9)

13. Broad; strong. (15-10, 11)

14. Microwave transmission is usually between two points; therefore, it is directive. The propertiesof microwave energy approach those of light waves; therefore, microwaves can be easilyconcentrated into a tight beam. Also, antenna structure is bulky for the lower frequencies.(15-12,13)

15. Transmitting. (13-18)

16. By stacking identical bays one above the other. (15-21)

17. UHF antennas are smaller. UHF antennas have broader bandwidth. (They are shorter in length;therefore, they have a smaller length-to-diameter ratio.) Impedance matching should be morecarefully considered in UHF antenna systems because, transmission line losses are greater atthe higher frequencies. (15-25, 25)

18. Microwave transmission efficiency is increased when waveguides are used because radiationlosses are less, copper losses are less, dielectric losses are less, and power-handling capabilityis greater. (15-27)

19. Two. (16-3)

20. By bending the tabs located in the tuner. (16-6)

21. A microwave receiver is basically an FM superheterodyne receiver with several stages of i-f

amplification. (16-7)

22. The i-f signal is passed through clipper stage(s) to remove noise. (16-8)

23. Klystron. (16-9)

24. Transit. (16-10)

30

4 6 ,

S T 0 PI. MA TCH ANSWER

SHEET TO THISEXERCISE NUM-BER.

Carefully read the following:

14: :

2. USE NUMBER IPENCIL.

30455 02 21

VOLUME REVIEW EXERCISE

1. Check the "course," "volume." and "form'' numbers from the answer sheet address tab against

the "VRE answer sheet identification number" in the righthand column of the shipping list. If

ra;mhers do not match, take act lin to return the answer sheet and the shipping list to ECI immedi-

ately with a note of explanation.

.2 Note that numerical sequence on answer sheet alternates across from column to column.

.3. Use oalt medium sharp l black lead pencil for marking answer sheet.

4. Use a clean eraser for any answer sheet changes. keeping erasures to 0 minimum.

5. Take action to return entire answer sheet to EC1.

6.. Keep Volume Review Exercise booklet for review and reference.

7. If ..,;annuhuilll enrolled student, process questions or comments through your unit trainer or OJT

supervisor.If i ,iluntartlu enrolled student, send questions or comments to F.C1 on EC1 Form 17.

Don't use answer sheets other than one furnished specifically for each re%iew exercise.

2. Don't mock an the answer sheet except to fill in marking blocks. Double marks or excessive

markings which ,',.ertliiw marking blocks will register us errors.

Don't fold, spindle, staple, tape, or mutilate the answer sheet.

4. Don't use ink or any marking other than with a l black lead pencil.

. The .3-digit number in parenthesis immediately following each item number in this Volume

Review Exercise represents a Guide Number in the Study Reference Guide which in turn Indicates

the area of the text where the answer to that item can be found. For proper use of these Guide

Numbers in assisting you with your Volume Review Exercise, read carefully the instructions in

the heading-of the Study Reference Guide.

31

466

21

MuLpie Choiceit,

Note: The first three irerns in this exercise r,re based on instructions that were included with vc!ircourse materials. The correctness or incorrectness of your answers to these items will be reflected inyour total Score. There are no Study Refererr-e Guide ,t:b.iect-area numbers for these first three items.

1. The form number of this VRE (or CE) must match

a. my course number. c. the foim number on the answer sheet.b. the number of the Shipping List. d. my course volume number.

2. So that the electronic scanner can properly score my answer sheet, I must mark my answers with a

a. pen with blue ink. c. number 1 black lead pencil.b. ball point or liquid-lead pen. d. pen with blue.< ink.

3. If I tape, staple or mutilate my answer sheet; or if I do not cleanly erase when I make changes onthe sheet; or if I write over the numbers and symbols along the top margin of the sheet,

a. I will receive a new answer sheet.b. my answer sheet will be unscored or scored incorrectly.c. I will be required to retake the VRE (or CE).d. my answer sheet will be hand-graded.

Chapter 1

4. (202) What is the purpose of the special effects generator?

a. To produce a montage display.b. To produce a keying signal.c. To make it possible to receive two picture signals simultaneously.d. To combine the picture signals and montage display.

5. (200) What are the four major types of lighting used in television?

a. Base, key, fluorescent, and incandescent lighting.b. Base, fill, fluorescent, and effects lighting.c. Base, fill, effects, and incandescent lighting.d. Base, fill, key, and effects lighting.

6. (202) How do the waveshapes and frequencies of the signals at TP3 and TP4 of the specialeffects generator compare with those at TP1 and TP2?

a. The waveshapes and frequencies are the same as those at TP1 and TP2.b. The waveshapes are the same as those at TP1 and TP2. but the frequency of the signals is

different.c. The waveshapes are different, but the frequencies are the same as those at TP1 and TP2.d. Both the waveshapes and frequencies are different from those at TN and TP2.

7. (201) What sections make up the scroll TV prompter?

a. Scroll, control, power supply, and gear train.b. Scroll, power supply, amplifier, and gear train.c. Scroll, control, amplifier, and remote control.d Scroll. amplifier, power supply, and control.

32 4 6 L.)

8. (202) What components conduct on the high-level alternation of the special effects keying signal

in the special effects amplifier?

a. Q4, Q5. DI. and 02. c. Q4, Q1, D3, and D4.b. Q4, Q5, D2, and D3. d. Q4, Q5, Q3, and P3.

9. (200) How is the TV light source effectively controlled?

a. By placement of the lights, size of the lights, and individual dimmers.b. By individual dimmers, individual switches, placement, and patching of the light facilities.

c. By individual and group dimmers, individual and master switches, and size of the lights.

d. By individual and group dimmers, individual and master switches, and patching facilities.

10. (201) What operating controls could make the rear screen projector more versatile and flexible in

its operation?

a. Dimmers, crawl mechanisms, light switches, iris controls , and semitransparent mirrors.

b. Dimmers, wipus, light switches, and semitransparent mirrors.c. Dimmers, crawl mechanisms, light switches, iris controls, arid wipers.d. Diramers, wipers, light switches, and semitransparent and front surface mirrors.

11. (201) Why are the troubieshooting and iepair functions encountered in the rear screen projector

relatively simple in nature?

a. Because.few components become defective.b. Because all of the components are stationary.c. Because few of the components are movable.d. Because of its design simplicity.

12. (202) What determines the regefterative clipper's rapid switching action?

a. The input signal. c. The collector voltage.b. The threshold potential. d. The regenerative feedback.

Chapter 2

13. (207) The basic equipment required for kinescope recording of a television program must include

a. TV monitor, video camera, s mind camera recorder.

b. TV monitor, video amplifier, video camera.c. TV monitor, video amplifier, audio amplifier.d. TV monitor, video camera, audio aliplifier.

14. (207) When the shutter of the kinescope recording camera is controlled electronically, what is

the duration of the blanking pulse output from the shutter gate generator?

a. `,. second.b. second.

C. t,,, second.d. second.

15. (210) What unit provides for mixing several video inputs to produce one output for the camera?

a. Dual-optical slide projector.b. Vidicon multiplexer.c. Video recorder-reproducer.d. Video distribution system stabilizing amplifier.

33

4 70

/-/5-1

16. (204) The erase head of an audio tap.: rt :orde f i1ore the previous rcf-oziling wh,:nrecording is made. Which of the follow:ng a possible cse?a. Tape and heads are out of alignment.b. Capstan aFtd capstan pressure roller are out o: alignment.c. Transport mechanism is inoperative.d. Record head is inoperative..

17. (206) Which of the following represents a major maintenance problem of a traversevideo tape recorder?

a. Lubrication. c. Head tip wear.b. Tube replacement. d. Equalization.

18 (206) The relationship between wavelength, frequency, and tape velocity is expressed by theformula A r- . What occurs to the wavelength if the frequency increases ivL the l'elocitt' remd:nsconstant?

a. It decreases.b. It remains the same.

c. It increases in length.d. It disappears.

19. (210) Which of the following is a maintenance requirement of a rnultiplexer

a. Lubrication of focal throw. c. Inspection of optical plane.b. Adjustment of mirror transparency. d. Cleaning of mirrors.

20. (207) When the shutter of the kinescope recording camera is controlled electronicall. what thefrequency of the cycling pulse?

a. 30 pulses per second.b. 24 pulses per second.

c. 60 second.d. It:, second.

21. (205) Which of the following features is employed in the construction of tape heads tu reducehigh-frequency losses?

a. Laminated core.b. Circular shape.

c. Magnetic filled gap.d. Hard steel.

22. (209) The more efficient way to transfer light from one optical path to another in a dual-opticalslide projector is to use

a. two projection lamps. c. a rotating slide magazine.b. a sliding mirror. d. an adjustable pnsm.

23. (206) What circuitry is used to maintain constant tape arld rotating head speed and to ;educetiming errors?

a. Closed loop servosysterns. c. Elec:mnic delay.b. Quadrature overlap. d. Initial presets.

24. (207) In a single-film system, the sound of a reproduced composite tele...ision signal precedes thepicture. What is a possible cause?

a. The top loop of the camera film is too lor.g.b. The top loop of the camera film is too short.c. The bottom loop of the camera film is too short.d. The bottom loop of the camera film is too long.

34

4 7 .1

Avo

25 (204) la audio tape recorders, erasing, recording. and playing back are functions of which of the

jemmying'

a. Transport mechanisms. c. Tape heads.b. Electronic circuits. d, Tape handlers.

26. t 208) In addition to the specially designed intermittence of the projector. what is required to

convert the film frame rate to the TV frame rate?

a. .A low persistent type pickup tube.b. A pickup tube with storage properties.

c. Pickup camera synchronization.d. Light flaShes from the pickup tube.

27. 1205) The high-frequency bias current insures that the signal to be recorded will fall on thelinear portion of the hysteresis curve. What is another use of this bias current?

a. Audio amplifier fixed bias. c. Frequency equalization.b. Head current erasure. d. Playback bias.

28. (205) In tape recorders it is standard practice to overcome the loss of high frequencies in the

record amplifier. and to overcome the loss of low frequencies in the playback amplifier. Which of

the following terms best describes this practice?

a. Preemphasis.b. Deemphasis.

c. Equalization.d. Attenuation.

29. (208) What special feature of the film projector permits moving the film in alternate steps of

1, and `... seconds)

a. An ordinary synchronous motor. c. Pulses from synchronizing waveform generator.

h. A unique phase synchronous motor. d. Intermittent with a 3-sided Geneva movement.

30. (205) Which of the following statements best describes the purpose of equalivation circuits in an

audio tape recorder)

a. To prov ide the same output level for low and high frequencies.b. To permit full-track or half-track recording.c. To provide automatic gain control.d. To maintain constant tape speed.

31. (204) Which of the following components of a tape transport mechanism reduces the effect of tape

speed variations)

a. The pinch roller. c. The rolling tape guide.

b. The tension idler. d. The capstan.

32. 1208) If there is no image from the film projector. the trouble might be caused by

a. a burned out projector lamp. - c. loss of the upper film loop.

b. loss of the lower film loop. d. a broken intermittent claw.

33. (208) What is a desired characteristiC of the moving film projector lens?

a. Short focal length. c. Long throw.

b. High magnification. d. Automatic zoom.

35

Chapter 3

34. (213) The output of the synchronizing generator rniT be observed as a pulse cross display on amodified television monitor. Which of the folloyLing hc.st describes the rneasuretnents that can bemade with this output display?

a. Linear amplifier frequency response and bandwidth.b. Horizontal and vertical deflection frequency rates.c. Dynamic and static convergence.d. Equalizing, sync, and blanking pulse widths.

35. (211) What is the purpose of the calibrated markings associated with the verticid and horizontalwedges in test pattern presentations?

a. To measure grayscale reproduction. c. To evaluate low-frequency response.b. To calculate aspect ratio. d. To determine the resolution capability.

36. (213) A modified television monitor is being used to observe a pulse cross display. What checkcould be in progress?

a. A resolution check. c. A vertical blanking check.b. The deflection linearity check. d. The geometric distortion check.

37. (214) Which test equipment could be used to adjust the convergence of a color TV monitor?

a. Grating or dot generators. c. Color analyzer or linearity checker.b. Color-bar or rainbow generator. d. Vectorscope and color-burst generator.

38. (211) Which of the following units can be used to replace a camera for te.rt pattern transmission.'

a. A grating generator. c. A linearity checker.b. A monoscope amplifier. d. A resolution chart.

39. (212) Which of the following statements best describes one of the purposes of the videoequipment known as a grating generator?'

a. To generate a pulse cross display.b. To provide equalizing pulses.

c. To check the linearity of deflection circuits.d. To check the blanking interval.

40. (213) A monitor displays a grating pattern superimposed on a standard linearity chart presentation.Which of the following statements is correct if the grating lines intersect w!th;n the circles?

a. Geometric distortion is less than 2 percent.b. Resolution is 500 or more.c. Correct gray scale is present.d. Correct interlace condition is present.

41. (211) What part of the monoscOpe test pattern is used to check low-frequency response?

a. The wedge lines. c. The station identification letters.b. The upper right corner wedge. d. The horizontal lines beneath the center circle.

4 7,i36

42. (214) Which combination of test equipment can be used to adjust the phase of the 1 and Q signalsin a colorplexer?

a. Color linearity checker and colcr analyzer.b. Color-bar generator and color analyzek.c. Rainbow generator and color linearity checker.d. Color-bar generator and chromatron.

Chapter 4

43. (219) In most TV receivers, the output of the tuner section is

a. an i-f signal.b. an r-f signal.

c. an oscillator frequency signal.d. a raw video signal.

44. (216) Which of the following TV stations are adjacent-channel, but may be assigned to the samecity?

a. 7 and 8.b. 5 and 6.

c. 4 amd. 3 and 4.

45. (219) What is a logical procedure for TV receiver troubleshooting?

a. Isolate the stage and locate the circuit group.b. Locate the circuit group and then locate the component.c. Locate the circuit group, isolate the stage, and locate the faulty component.d. Locate the faulty cumponent, isolate the stage, and locate the circuit group.

46. (217) The length of a dipole antenna designed for channel 10 operation (192-198 mc) should beapproximately how long?

a. 4:7 feet.b. 2.4 feet.

c. 14 inches.d. 42 inches.

47. (219) Which transistor amplifier configuration is preferred for stability and interchangeability clcomponents?

a. CA. c. CC.b. CS. d. CE.

48. (217) Which of the following is a major purpose of a reflector placed behind an antenna?

a. To increase signal gain.b. To increase vertical directivity.

c. Tr) increase input impedance.d. To increase bandwidth.

49. (216) Suppose there is no output from a transmitter whose stages are V1 (oscillator),V2 (doubler). V3 (tripler), and V4 (power amplifier). In what order would you "read"the symptoms?

a. V4, V3, V2, and V 1. c. V4, VI, V3, and V2.b. V4, V3, and V1, V2. d. V1, V2, V3, and V4.

SO. (216) How much visual carrier frequency deviation is permissible in a television system?

a. -1000 Hz.b. 1000 Hz.

c. +1000 Hz.d. ±-100 Hz.

37

31. (219) What is the function of an AM ae,ector ci:ruir in r: 1V receiver?

a. To select, rectify, and filter the aural siqnal.b. To select, rectify, and filter the video signId.c. To select, rectify, and fill:er only the video sync pulses.d. To select, rectify, and filter out unwanted AM stations.

52. (218) Which of the following best describes the log-periodic antenna (LPA) used in VHF TVsystems?

a. A high-gain, wide-band, unidirectional receiving antenna.b. A high-gain, wide-band, omnidirectional transmitting antenna.c. A high-gain, narrow-band, unidirectional receiving antenna.d. A high-gain, narrow-band, omnidirectional transmitting antenna.

53. (219) Normally, what amplifier sections of a TV receiver have agc voltage applied?

a. All i-f sections and r-f sections.b. All i-f sections except the last (normally) and r-f sections.c. All i-f sections and r-f sections except the second (normally).d. The i-f sections only.

54. (217) Which characteristics greatly determine the physical size of a VHF TV antenna?

a. The operating frequency and desired radiation pattern.b. The polarization and desired radiation pattern.c. The operating frequency and power-handling capability.d. The polarization and power-handling capability.

55. (218) Which of the following serves most efficiently as an omnidirectional VHF TV transmittingantenna?

a. Th fanned conical antenna with reflector.b. The three-bay log-periodic antenna.c. The Yagi antenna.d. The helical antenna.

56. (216) When using a meter in the cathode circuit to tune an amplifier plate circuit in a TVtransmitter, the meter should show

a. maximum plate current. c. maximum grid drive of stage being tuned.b. minimum grid drive of following stage. d. minimum plate current.

57. (215) Which of the following are basic types of coupling in VHF transmitters?

a. Capacitive, link, and inductive. c. Inductive, link, and chain.b. Link, capacitive, and chain. d. Capacitive, chain, and inductive.

58. (218) What is the chief function of a balun?

a. To:match impedances.b. To balance asymmetrical circuits.

c. To balance antenna impedance.d. To increase antenna.gain.

59. (219) What is the purpose of the fine tuning control in the r-f section of the VHF TV receiver?

a. To trim the r-f amplifier. c. To change the frequency of the local oscillator.b. To vary the i-f amplifier. d. To select the proper tuned circuit.

47u

60. (210) What stages are replaced by use of a converter section?

a. R-f amplifier and mixer stages. c. Oscillator and r-f amplifier stages.

b. Oscillator and mixer stages. d. Mixer and i-f amplifier stages.

61. (216) When troubleshooting a TV transmitter, if V3 grid meter indicates grid drive and thecathode meter indicates no tube current, you should check the components of

a. the previous stage (V2).b. the following stage (V4).

,c. both the previous stage (V2) and the following stage (V4).

d. the stage in question (V3).

62. (219) What signals are amplified by the r-f section of a TV receiver?

a. AM video and FM audio signals. c. AM audio and sync signals.

b. Composite video and AM audio signals. d. FM video and sync signals.

63. (219) What is the necessary bandwidth of the r-f section of a TV receiver?

a. .25 MHz.b. 1.25 MHz.

c. 4.50 MHz.d. 6.0 MHz.

o4. (217) The transmitting antenna serving a VHF TV broadcast station is usually

a. bidirectional. c. omnidirectional.

b. vertically polarized. d. narrow in bandwidth.

65. (218) Which of the following will increase the gain, directivity, and bandwidth of a turnstile

antenna used for VHF TV transmission?

a. Increasing the height of the antenna.

b. Increasing the size of each radiating element.

c. Vertical stacking of individual radiating elements.

d. Balun coupling of antenna and transmitter.

66. (217) A TV antenna which has a low Q will possess

a. a high gain. c. a narrow bandwidth.

b. a broad bandwidth. d. an excellent directivity.

67. (217) The insulation requirements of an antenna serving a VHF TV transmitting station would

most likely be reduced by increasing the

a. height of the antenna.b. bandwidth of the antenna.

c. video transmitter output.d. video transmitter ERP requirement.

Chapter 5

68. (22W What is the normal transmitting range of VHF and UHF equipment?

a. Both systems have an infinite range.b. A range of 54 MHz to 216 MHz.

c. A range of 470 MHz to 890 MHz.

d. Both systems are limited to line-of-sight transmission.

39

476

69. (223) Which of the following best describes the UHF slotted loop (slott9d rin7:1 tntenn

a. High-gain, balanced conductors. c. Low-gain, high-power-handling capL,biliiv.b. Low-gain, unbalanced conductors. d. High-gain, low-power-handling capability.

70, (222) Which of the following is a proper comparison of UHF and VHF propagauon characteristics*"

a. VHF propagation characteristics are less favorable.b. UHF shadow effect is less severe.c. UHF line-of-sight distance is shorter.d. VHF line-of-sight distance is shorter.

71. (224) What is double conversion in a UHF receiver?

a. The reception of two TV signals simultaneously.b. Two stages of heterodyning to develop two i-f signals.c. A tuner with two r-f paths.d. Detecting two r-f signals with one i-f stage.

72. (224) How does a tricrowave receiver differ from a TV receive('

a. It uses fewer i-f stages. c. It has a narrower bandpass.b. It uses r-f amplifier stages. d. It uses a klystron local oscillator.

73. (220) Under what conditions, if ever, will the UHF transmitter have the same basic circuits asthe VHF transmitter?

a. The transmitters never have the same basic circuits.b. The transmitters have the same basic circuits at the higher frequency levels.c. The transmitters have the same basic circuits at the lower frequency levels.d. The circuits are the same when transmitting video signals only.

7 4. (223) Why are waveguides more efficient than transmission lines for microwave transm1ssior0

a. Waveguides have less signal attenuation.b. Waveguides have no standing waves.c. Waveguides present no impedance matching problems.d. Waveguides permit the antenna to be more directive.

75. (221) What is velocity modulation?

a. A variation in the number of electrons.b. The speed of an electron beam.

c. Electrons striking a resonant cavity.ci A variation in the speed of electrons.

76. (223) UHF antennas are less subject to interference from the surrounding area than VHFantennas because the

a. VHF antennas are longer. c. UHF antennas are shorter.b. VHF wavelengths are longer. d. UHF v.avelengths are shorter.

77. (221) Why does a UHF microwavL transmitter require more careful matntenance than a standardAM transmitter?

a. It has wide-band circuits that are sensitive to changes.b. There is more heat generated that causes circuit changes.c. The circuits use lar-3.47r component tequiits comit out tunity4.d. Standing waves are constantly changing iind must he !tined out.

40 4 7

78. (222) Which of the following is a characteristic of the UHF TV bow-tie antenna?

a. Narrow bandwidth.b. Broad bandwidth.

c. Omnidirectional.d. Vertical polarization.

74. (220) From the information in the text, what does a UHF power amplifier have that a VHF power

amplifier does not have?

a. Four coaxial cavities. c. Larger capacitors.

b. Two more coaxial tetrodes. d. Larger inductors.

80. (222) The input impedance of a corner reflector antenna can be increased by

a. using a balun between the antenna and nsmission line.

b. mounting the antenna in the vertical plane.c. using a folded dipole for the driven eiement.d. increasing the height of the antenna.

41

4 76

30455 03 0867 1170

CDC 30455

TELEVISION EQUIPMENT REPAIRMAN

(AFSC 30455)

Volume 3

Systems Maintenance

//0

AVM W W. WWWI" %%%%%% WWN Wit.WHAMIWIWI WAWNWRIMW1W111

Extension Course InstituteAir University

Preface

THIS FINAL VOLUME of CDC 30455 contains information necessary for theproper maintenance of television systems. Chapter I deals with operational re-sponsibilities. more specifically. publications, types of inspections, and quality

checks. as well as thc dutics and responsibilities of inspection teams. In Chapter 2,we develop troubleshooting and repair procedures as they apply to both testequipment and television 'equipment. In addition, proposals for correcting re-curring equipment malfunctions are discussed. Finally, the responsibilities forrepair, calibration, and certification of precision-measuring equipment are stated.Television system troubles are described and the symptoms diagnosed in Chapter 3.Our final chapter is devoted to C-E planning, programming, and the related PCand PCSP documents. A discussion of siting. installation, and the various types ofaccepiancc tcsts necessary for new television systems is also included. Finally,the need for modification is discussed.

If you have questions on thc accuracy or currency of the subject matter ofthis text. or recomnwndations for its improvement, send them to Tech Tng Cen(TSOC). Keesler AF13, MS 39534.

If you have questions on eourse enrollment or administration, or on any ofEn's instructional aids I Your Key to Career Development. Study ReferenceGuides. Chapter Review Exercises. Volume Review Exercise, and Course Exami-nation). consult your education officer, training officer. or NCO, as appropriate.It' he can't answer your questions. send them to ECI, Gunter AFB, Alabama36114, preferably on ECI Form 17. Student Request for Assistance.

This %olunw is valued at 15 hours (S points). .

Contents

Page

Preface iii

Chapter

1 OPERATIONAL RESPONSIBILITIES 1

TROUBLESHOOTING AND REPAIR 8

3 DIAGNOSING SYSTEM TROUBLE'S 18

4 INSTALLATION AND MODIFICATION 25

s,

1d7

MODIFICATIONS

of this publication has (have) been deleted in

adapting this material for inclusion in the "Trial Implementation of a

Model System to Provide Military Curriculum Materials for Use in Vocational

and Technical Education." Deleted material involves extensive use of

military forms, procedures, systems, etc. and was not considered appropriate

for use in vocational and technical education.

CHAPTER 2

Troubleshooting and Repah.

IN THIS CHAPTER wc will discuss the typesof test equipment uscd at a television installa-

tion, as well as their purpose. use. and commonfailures. When test equipment failures are en-countered. alternate testing methods must beavailable; therefore, we will discuss some ofthese alternate testing methods. General tele-vision system troubleshooting methods and pro-cedures that arc needed to maintain a systemin proper operating condition will be diseussed:in addition. television equipment alignment andcalibration procedures are developed. We willalso describe the advantages of using bcnch mock-ups over other testing methods. Finally, the re-sponsibilities for the repair. calibration, and cer-tification of precision measuring equipment areexplained.

4. Television Test Equipment, Types, Use,and Malfunctions

4-1. This section states the types of testequipment necessary to maintain various telei-sion system configurations properly. In addition.we will identify some alternate systcm testingmethods and describe how each is accomplished.Likewise. alternate transistor tests and precau-tions are discussed. Finally, we will identifysome test equipment malfunctions and describethe related symptoms,

4-2. Television Test Equipment. The normalprocedure of troubleshooting closed-circuit andr-f television systems is through tests made todetermine the character of the video and audiosignals; to evaluate the performance of the tele-vision equipment: to maintain and repair theequpmcnt: or to determine peculiarities of in-dividual equipments. The majority of these func-tions and tests can be made with standard shoptest equipment. such as tube checkers. watt-meters. voltmeters, ohmmeters. tnilliammeters.and dummy loads. However. the oscilloscopeand video sweep generator are particularly ap-plicable to television testing. while the multiburstgenerator. grating generator. monoscope aniplifier

8

(camera). and waveform monitor re gener-ally eonsidered as speciali/ed test equipment k-sitned television system quality testing.

4-3. Ohmmeters. t,,huwters, and minium-mewrs. These general pet, of metered testequipment are normally used in :*tnal sZagcsof ir,..ubleshooting. This ma} entail ::nding thefailed component of an inoperative circuit. Hoe,ever. the %oltmeter milliammeter nix, alsobe used whik you niaL sonw relatively simplesystem maintenance checks. These checks usu-ally consist of monitoring the output of the reg,u-lated power supplies ni.! similar operatkms. Inaddition. they are used to make some types ofoltage and current measurements during PMI's.where metered measurements arc required. It

must be understood that oscilloscope voltagemeasurements are much more accurate: thus.they are more desirable for critical readings.

4-4. Tube checker. A tube checker is nor-mally used during PMI's and when a tube'scondition is doubtful. Somt tete% ision equipmentpeculiarities extend the ustiiness of the tubechecker be}ond locating defective tubes. Tele-vision equipment using balanced modulator cir-cuits is an example. inasmuch as the tubes mustbe closdy matched under such conditions. 1here-fore. the tube checker can be used to -niatdi-tubes in pairs from the bench stock. thereb)saving a oonsiderable amount of money. Tubesthat are purcliased in matched sets are much moreexpensive.

4-5. Dummy loadv am! wattmeters. Whenperforming PMI's and troubleshOdting functionson transmission equipment. dummy loads andwattmeters are often needed. Their use will pre-vent r-f interference with other operations which

may be going on at that time. The dummyloads and wattmeters selet:ted for television main-tenance must have adequate power handling capa-bilities to handle the hieli-power output of the%idol transmitter satisfaetoril.

Catho(fr_rw osohvovro In% A cathode-rayoscilloscope suitable for television application is

specifically designed for maintenance. alignment.and adjustment of that equipment. It must pre-sent accurately all of the video waveforms thatare employed in a television broadcast installa-tion.

4-7. By using an oscilloscope designed fortelevision, you can observe any portion of thetelevision picture waveform, from, complete tele-vison picture frames to small segments of individ-ual scanning lines, as well as waveshape, width.and amplitude. The oscilloscope thus provides anaccurate means of measuring both amplitude andtime of television signals. in addition to present-ing a detailed representation of the picture sig-nal. Consequently, the oscilloscope is adaptablefor both troubleshooting-and system maintenance.

4-8. Video sweep generator. The video sweepgenerator is used to inject a signal through acircuit under test. Thus, the oscilloscope meas-urement of signal amplitude is possible. Theoverall response of the tested circut with respectto its frequency characteristic can be obtained.Use a vkleo sweep generator when adjustmentof camera preamplifiers and bandpass of othervideo circuits is necessary.

4-9. Multihurst generator. The multiburstgenerator is primarily used for complete televi-sion broadcast facility operational checks. How-ever. while it is limited when used to test in-dividual components or circuits, it can be usedlike the sweep generator in some respects. suchas providing the signal to a circuit under testand for measurement of the circuit output am-plitude versus frequency response. The advan-tage of using this instrument is that no testedcircuitry need be disabled or disconnected. Thegenerator will apply test signals, simulating ac-

0.51130-

0-40--

.1111, 'MIMI.

1.5

I I

tual teie..;sion signal frequencies. and feed themdirectly into the television facility for an opera-tional response. The multiburst generator pro-vides an output consisting of bursts. or group-ings, of various frequencies superimposed on thepedestal, with standard blanking and synchroniz-ing signals added. As shown in figure 1, allbursts must be of equal amplitude for applica-tion to the input of the television broadcastfacility. Changes of waveform amplitude, asobserved on an oscilloscope connected at eitherthe facility output or other convenient check-point. will indicate circuit or network frequencyresponse deviationi at particular frequencies.However, this check does not isolate a mal-functioning circuit; it only indicates a malfunc-tion of the system.

4-10. Grating generator. The grating gener-ator provides a pattern which is a convenientmethod of testing and adjusting both the hori-zontal and vertical linearity of the television de-flection circuits. This test provides checks fordeviations in picture characteristics, such as pic-ture compression or expansion resulting fromnonuniform scanning velocity that may be causedby the deflection circuits.

4-11. Monoscope amplifier (camera). Themonoscope amplifier (camera) unit, as you al-ready know. is a suitable means of checking res-olution, low-frequency phase shift, contrast, anddeflection linearity of the television broadcastequipment. It also provides a modulating signalfor transmitter tests and receiver performance.

4-12. Waveform monitor. The waveformmonitor is a specialized type of oscilloscope whichprovides detailed and varied video information.It is capable of presenting many video combina-

APPROXIMATE FREQUENCY (MC)

2.0

I

iii

3.0

I

ONE LINE-63 1.1SEC

3.6

I

Figure I. Multiburst generator output test signal.

9

48 4

tions from a complete television frame to a sing'esegment of a desired line or even a single pulseshape or edge. Consequently, the waveform mon-itor is much more adaptable to tele% ision testingthan is the average oscilloscope. Its UF(*ti arcmuch the iame as other types of oscilloscopes:however, it is more suitable for system tests thanfor individual circuit or circuit component troub-bleshooting.

4-13. Color Television Testing. In addition tothe previously mentioned items of test equipment.the proper maintenance of a color televisionbroadcast system necessitates the use of morespecialized and refined test equipment. Suchequipment as the dot generator. color bar genera-tor. vectorscope, color signal analyzer, and linear-ity checker are used to provide the proper testsignals.

4-14. Dot generator. The dot generator pro-vides a pattern which is prirnariy used for con-vergence and registration checks of color tele-vision monitorS and receivers. However, it is alsoused for system maintenance checks.

4-15. Color bar gewrator. A color bar gen-erator provides rectangular pulses for applica-tion to the red, blue, and green input circuitsof a colorplexer. This will produce a color bartest pattern at the colorplexer output. The pat-tern is used to check the color quality of anentire color television system.

4-16. Vectorscope. The vectorscope permitsinspection of the amplitudes and phase relationsof the color subcarrier signals. A vectorscope isparticularly valuable for checking the phase am-plitudes of the color outputs from the colorplexcr.Again, the vectorscope is p .imarily used to checkthe color quality of the system.

4-17. Color signal analyzer. This test instru-ment is used to study the components of a

composite color video and subcarrier signal. Whenthe typical color signal analyzer is used in con-junction with a color bar generator and oscillo-scope, you can measure the phase relations be-tween the subcarrier burst reference and thedifferent components of the composite color sig-nal. In addition, the color signal analyzer usedin conjunction with a linearity checker will pro-vide a method of obtaining differential phasemeasurements.

4-18. Linearity checker. Lincarity checkersare primarily signal generators which provide asimulated color video signal. The typical linearitychecker is used to measure both the differentialgain and differential phase distortion of videoamplifiers and transmission facilities. The linear-ity checker is more valuable since the gain andphase linearity of color television signals must bemaintained at a hiah level.

10

Test Equipment NIaliunctions and De-tection. Test equipment malfunctions ar c. usuallydiscovered during operaticn since test equipmentis not normally maintained in a-continuou oper-wing. condition. Beeause of !he differences intest equipment. indications of equipment failureswill manifest themselves in %:irious wa. '1 hemost reliable means of isolating test equipmentproblems, as in other types of electronic equip-ment. is through substitution of a like item. Thu,.if the alternate unit operates properly. thz:

original unit is faulty. Many of the problems en-countered in television test equipment will hevisually apparent since the primary funetion ofthis test equipment is video alignment and test-ing.

4-20. O.seilloscopes und waveform moniton,The most obvious problems in oscilloscopes andwaveform monitors are lack of vertical or hori-zontal deflection, unstable display, no video dis-play, and loss of operating-voltage.

Loss of vertical deflection is indicated whenthe visual display has no height: consequently.the problem is most likely in the vertical deflec-tion circuits.

Loss of horizontal deflection is indicatedwhen the video display has no width: thus, theproblem will probably be located in the horizontaldeflection circuits.

An unstable display usually indicates a lackof triguring pulses. The trigger pulses may bederived either internally or externally. depend-ing upon which mode of operation is being used.When the trigger pulses are derived externally,the problem is probably a defective test lead. Ifthe trigger pulses are derived internally, thetrouble is probably in the 1000-kc oscillator cir-cuit.

When no video display is visible. the usualcause is a failure in a video amplifier circuit ordefective test lead.

Loss of operating voltages indicates a failureof the power supply or line fuse.

4-21. Remember that substitution is the bestmeans of determining if the test equipment or theunit being tested has failed.

4-22. Video sweep generator. Video sweepgenerator problems usually consist of no outputor an unstable output. Either of these conditionscan be checked with an oscilloscope.

When there is no output from the videosweep 1.!enerator. the cause may be in any oneof several areas: pow er supply, oscillator. am-plifiers, or test leads.

An unstable output is usually caused bythe failure of a component in the oscillator circuit.

kki5

4-23 Vultiburst venerwor. Since the mufti-burs( generator is a type ot signal generator. itsoutput can he checked. or monitored, with an)scillosLope. If an portion of the output wave-

form is missing or distorted. determine which cir-cuits are concerned. then troubleshoot,

4-24. Gratinv L,' enerator. The most noticea-He problems occurring in the grating generatorare the loss of horizontal bars or vertical bars.

fhe loss of the vertical bars indicates a

failure of the I S times multiplier or adder cir-cuits.

The loss of the horizontal bars indicates afailure of the 20 times multiplier or adder cir-cuits.

4-25. Dot venerator. A possible problem inthe dot generator is the appearance of hori-zontal or vertical bars. This indicates a failure ofthe clipper circuit or misadjustment of the clipperbias.

4-2o. Color bar enerator. The color bar gen-erator produces a series of rectangular pulses.rcd. Hue. green. special -I.- special "Q.- andwhite. used tor color quality testing. The bestInethod of detecting discrepancies is to observethe output on a color monitor. A failure in oneof the color bar generator circuits will cause asso-ciated problems in the output. Since the colorbar generator produces pulses. an oscilloscopecan be easily used to trace the pulses throughtheir associated signal paths.

4-27. The most common problem encounteredin the color bar generator is low amplitude of theindividual pulses. This problem may be causedby a defective amplifier circuit.

4-2S, Vectorscope. The vectorscopes opera-tion is much like that of an oscilloscope andany problems encountered in it will be similarto those found in the oscilloscope or waveformmonitor.

4-29. Color signal mwlyzer. Indications ofproblems in the color signal analyzer are inabilityto demodulate the color subcarrier signal or aninability to check the phasing of the color sub-carrier.

When you are unable to demodulate thecolor subearrier signal. the malfunction will prob-ably he in the demodulating circuits. Using nor-mal troubleshooting procedures. the circuit mal-function can be rapidly located.

Phasing problems will be found in the as-sociated phasing network or circuit.

4-30. Monoseope wnplifier (camera). Thefailures encountered in a monoscope amplifier(camera) are similar to those found in a simpleclosed-drcuit television camera chain: therefore.

the trouble symptoms are also similar. The onemajor difference between the monoseope ampli-fier (camera ) and other types of televisioncameras is the pickup tube design. as you knowfrom Volume 2. Because the image is etchedon the target of the rnonoscope tube. defects inthe coating material will cause errors in the outputvideo signal.

4-3 1. .Alternate Quality Testing Methods. Whenthe test equipment fails, an alternate means oftesting system frequency response. picture quality.and color fidelity is necessary. Some of the al-ternate testing methods may not be as accurateor complete. while others may be more complexthan the desired methods. They are. however.acceptable on a temporary basis.

4-32. Frequehey response. The two items oftest equipment generally used for checking andadjusting the television system frequency responseare the video sweep generator and the multi-burst generator. The video sweep generator. asyou know, is used to check and adjust individualcircuits and system components: whereas. themultiburst generator is designed to check theoverall system frequency response.

4-33. Should the multiburst eenerator fail, themonoscope amplifier (camera) unit or the EIAresolution chart may be used to check the overallsystem frequency response. The frequency re-sponse checks are accomplished in the samemanner when either of these alternate methodsbecomes necessary. However, you must insurethat the camera is properly positioned and focusedon the E1A resolution chart when it is used.

This is not -necessary when the monoscope unit isused since its display is permanently positioned.

4-34. When .the E1A resolution pattern is usedfor frequency response checks, spurious peaks orsharp cutoff of the characteristic response fre-quency will disclose themselves as irregularitiesin the video presentation. The irregularities ap-pear as closely spaced. horizontally displaced.positive or negative, delayed or advanced repeti-tions of the original signal and will.appear in thevideo output of the television system. These dis-crepancies are called "ringing". The verticalwedges in the pattern are used to determine hori-zontal resolution. The point in the wedgeswhere the lines appear to blend together indi-cates the limits of resolution. By referring to thecalibration adjacent to the bars. the resolutionmay be read directly in terms of lines. The maxi-mum horizontal resolution is approximately 80lines per megahertz of bandwidth. To obtainhorizontal resolution in terms of bandwidth.- di-vide the number of lines by 80. To evaluatethe frequency response of the system. compare

the bandwidth figure obtained with the normalbandwidth figure of the system.

4-35. Picture quality. Again, the monoscopeamplifier (camera) unit as well as the EIA reso-lution teu patterns arc used as an alternatemethod of testing the overall picture quality of atelevision system. In addition, the. EIA linearitytest chart can be used to test i.he deflection line-arity. which in turn will determine the quality ofthe video signal.

4-36. Since the monoscope camera and EIAresolution patterns are similar, their picture test-ing capabilities are much the same. As previouslydiscussed (Volume 2), most aspects of the videosignal can be analyzed and adjusted while usingeither of these patterns as a standard. The com-ponents of the video signal that may be checkedwith these patterns are: gray-scale rendition.shading, uniformity, streaking, interlace, aspectratio, geometric distortion, horizontal and verti-cal resolution, and irregularities in the responsefrequency characteristic. All of these items willhave specific relations to the picture quality.

4-37. The grating generator pattern may alsobe considered a picture quality check since it is acheck of the deflection linearity. However, it is

normally used in addition to the EIA linearitytest chart

4-38: Color fidelity. All of the items discussedin the picture quality and frequency responseareas will have a determining effect on the colorquality. One of the most important things incolor reproduction is to first derive a good blackand white picture. In addition, other specializedtesting procedures have been developed to pro-duce the best quality color picture possible.

4-39. As you know from previous discussion of

specialized test equipment (Volume 2), boththe vectorscope and color signal analyzer are used

as a method of testing the color subcarrier phas-ing and amplitude. Thus, they may be consideredas alternate methods for each other when colorsubcarrier phase and amplitude tests arc required.Likewise, the grating generator and dot generatormay be considered as alternate methods of testingconvergence of a color receiver.

4-40. The color bar generator produces a

series of pulses which, when vectorially added.produce color bars covering the color spectrum.These bars are then used to test the system'sability to reproduce those colors. An alternatemeans of checking color fidelity is by observinga video presentation. Look for proper shadingand color fringing around objects. These willgive some indication of the color quality andproper camera setup.

4-41. Transistor Checks. The usual trouble-shooting practices also apply to transistors. It is

recommended that transistor checkers be used toevaluate transistors whenever possible..,Howel,er.if a transistor tester is not available, a goodohmmeter may be used for this purpose. Theohmmeter slected must. however, meet estab-lished requirements sincc damaai to transistors-may result when improper test equipment is used.The damage is usually the result of accidentallyapplying too much current or voltage to the tran-sistor.

4-42. Test equipnwm. Tcst equipment with itransformerless power supply is one source of

excess current. This type of test equipment canbe used by employing an isolation transformer in

the powei iffle. Damage to the transistor mayalso result from too much line current, eventhough the test equ'pment has a power trans-former in the power supply, if the test equipmenthas a line filter. This filter may act as a voltagedivider and apply half of the line voltage anda portion of the line current to the transistor. Toeliminate this trouble situation, connect a groundwire from the chassis of the test equipment tothe chassis of the equipment under test before

making any other connections.4-43. Another cause of transistor damage is a

multimeter that requires excessive current for ade-quate indications. Multimeters that have sensi-t;vities of less than 5000 ohms per volt should notbe used. A multimeter with lower sensitivity will

draw too much current through many types oftransistors and damage them. The use of 20,000-ohm-per-volt meters or vacuum-tube voltmeters is

recommended. Check the ohmmeter circuits(even thwe in VTVM's) on all scales with anexternal, low.resistance milliammeter in serieswith the ohmmeter leads. If the ohmmeter drawsmore than 1 milliampere on any range, this rangecannot be used safely on small transistors.

4-44. Finally, always use fresh batteries of

the proper value for the equipment under test.Never use battery,eliminators because the regula-tion of these devices is poor at the current values

drawn by transistor circuits. Be certain aboutidentification of polarity before attaching the bat-

tery to the equipment under test; polarity re-versal may damage the transistor.

4-45. When troubleshooting transistor circuits.be sure the test probes are clean and sharp. Manyof the resistors used in, transistorized equipmenthave low values; therefore any additional resis-tance produced by a dirty test probe will make agood resistor appear to be out of tolerance.

4-46. Ohtnmeter test of transistors. To cheeka p-n-p transistor. connect the positive lead ofthe ohmmeter to the base and the negative lead

to the emitter. Use caution when connecting thetest leads to the transistor, ince the red lead is

4 i

not necessaril y. the positive lead on all ohm-meters. Generally. a resistance reading of 50.000ohms Or more should be obtained. Connect thenegative lead to the collector: again a reading oi50.000 ohms or more should he obtained. Recon-nect the circuit with the negative lead of theohmmeter to the base. With the positive leadconnected to the emitter, a value of resistance olapproximately 500 ohms or less .should be ob-tained. likewise. with the positive lead con-nected to the collector, a value of 500 ohms orless should be obtained.

4-47. Similar tests on n-p-n transistors willproduce the following results. With the negatieohmmeter test lead connected to the base and thepositive test lead connected to the emitter. thevalue of resistance should be high. Then connectthe positive test lead to the collector: the valueof the resistance should again be . high. Withth; positive ohmmeter test lead connected to thebase and the negative test lead connected to theemitter, the value of the resistance between thebase and emitter should be low. Likewise, whenthe negative test lead is connected to the collec-tor the %utile of the resistance should be low.

4-48. If the readings in either instance do notcheck out as indicated, the transistor is probablydefective and should be replaced. If a defecti etransistor is found. make sure that the cricuit isin good operating order before inserting the re-placement transistor. If a short circuit exists inthe circuit. plugging in another transistor mostlikely will result in another burned-out transistor.Do not depend upon fuses to protect transistors.The transistor is very sensitive to improper biasvoltages: therefore, a short or open circuit in thebias resistors may damage the transistor. For thisreason. do 'not troubleshoot by shorting variouspoints in the circuit to ground and listening forcl icks.

5. Troubleshooting and MaintenanceProcedures

5-1. In this section we will outline systematictroubleshooting procedures and identify whateach step entails. A description of how intricatealignment, calibration, and maintenance proce-dures are written and used is included with a fewexamples. Finally we will propose some coursesof action to take should you be faced with re-curring equipment malfunctions.

5-2. Elements of Troubleshooting and Repair.When troubleshooting a television system, thereare basic steps which should be followed. Thesesteps should- be accomplished in a systematic se-quence such as: symptom recognition, symptomanalysis. trouble localization, trouble analysis.and trcluble correction. In the following para-

graphs we will discuss each of these steps andenumerate the things to be considered as thetroubleshooting process develops.

SYmplom recognition. The symptom mayhe defined as a trouble indication. Some ex-amples of symptoms are: no video, no raster.unstable synchronization. weak picture, and anyother indication of trouble in the television sys-tem. Most trouble symptoms indicate malfunc-tions in either the transmission or receiving equip-ments. As an example. unstable synchronizationcart be a symptom of trouble in the synchronizinggenerator. pulse distribution amplifier, video dis-tribution amplifier, video transmitter. or receiver.Once you have detected a trouble from a partic-ular symptom. analy ze that symptom.

5-4. Simptom analysis. Symptom analysis is

the process of determining in what area or areasa trouble. with a particular symptom. could origi-nate. Again referring to the symptom of unstablesynchronization, analyze that symptom, determinethe trouble possibilities. and then isolate the mal-function.

5-5. Trouble bicalization. After determiningthe possible troubles, through symptom analysis.isolate the malfunction using systematic trouble-shooting procedures. Where the symptom indi-cates that the trooble may originate in either thetransmission or receiving equipment. isolate theproblem to one or the other. In either area, thetrouble can be further localized through signaltracing. When the failed unit is located, a com-bination,of signal tracing. voltage readings. andresistance measurements may be used to isolatethe faulty circuit and finally the failed component.

5-6. Trouble witilysis. When the malfunction-ing unit is located, an analysis of the trouble mayindicate which circuit has failed. An analysis ofthe signal at various points in the unit will indi-cate possible circuit and component failures.Thus. trouble analysis is the process of evaluat-ing signal discrepancies and relating them to pos-sible circuit malfunctions.

5-7. Trouble correction. When the failed cir-cuit component has been located, the final stepof correction is necessary. At this point, completeany disassembly. replacement. repair. and reas-sembly deemed necessary to place the equipmentin proper operating condition.

5-8. Recurring Malfunction Correction. Usually.malfunctions that recur regularly indicate one oftwo things: another faulty component or circuitwhich is causing the more obvious problem orfaulty design of the malfunctioning circuit. Cor-rection of the recurring malfunction demandsthat you locate the basic cause of the problem.If the cause is another faulty component or cir-cuit. simply replace or repair that item. However,

13

4 86

if the reeurring miaunction caused by fault:circuit design. recommendations for modificationof that circuit will be necessary.

5-9. Prescribed Nlaintenance Procedures. All

prescribed maintenance procedures should be

written in a logical sequence. Nlaintenance pro-cedures are written and used to eliminate the

possibility of forgetting to accomplish assignedtasks. Failure to complete a specified task mayresult in an operational malfunction. Preventivemaintenance instructions (PMI's), alignment.and calibration procedures arc examples of pre-scribed maintenance procedures.

5-10. Alignment and calibration procedures'.Alignment and calibration procedures must beaccomplished upon installation of all new equip-ment to insure its proper operation. They mustalso be performed after replacement of circuitcomponents. after certain system maintenance hasbeen completed. and immediately prior to opera-tion. This last requirement is necessary at leastdaily, twice daily, and sometimes on a more fre-quent basis, depending on the type- of equip-ment and the operational requirements of thetelevision system.

5-11. Examples of transmission equipmentalienent and calibration requirements are cam-era setup. synchronizing generator adjustments.pulse and video distribution amplifier gain ad-justments, audio output checks. and transmittertuning. In addition, color transmission alignmentand calibration procedures will include the color-plexer setup. a more detailed camera setup, andthe alignment of other units as necessary for

proper color production.5-12. The most common alignment procedures

performed on color television receivers and moni-tors are convergence, purity, and white balance(temperature adjustments). These proceduresmay need to be accomplished each time the com-ponents affecting their circuit operation arc re-placed.

5-13. Written alignment and calibration pro-cedures. Alignment and calibration proceduresshould be written in a straightforward, logical se-quence of events. Consequently. the steps arewritten in such a manner that even the mostcomplex alignment and calibration procedurescan be easily followed. An example of some ofthe more complex procedures are those requiredfor adjusting convergence. purity, and tempera-ture of a color television receiver.

6. Systematic Repair6-1. In this section we will discuss the prac-

tices, procedures. and precautions necessary toperform logical and systematic repair of televisionequipment. The advantages of using bench

14

mockups tor ,clevision equipment checkvt andalienment will also by identified and comparedto alternate che,:',e,ut proeedures. Finally, we,ill ,,pecif tile :e5pon3ibilities for repair. calibr4-lion. and certification of various categ-ories of pre-ci3ion measuring equipment.

n-2. Equipment Repair. In ordei to repair tele-vision equipment there are four necessary func-tionsdkassembly. replacement. repair. and re-assemblywhich must be done. There are also

certain pro,:edures. ;7!.actiees. and precautionsw hich must be observed and followed when wudo these tasks. We now describe the procedures.practices, and precautions as they relate to thefour repair tasks.

6-3. Disassembly. Daring disassembly of tele-

vision equipment it is most important ' t you

follow the recommended procedures contained inthe appropriate technical order or manufacturer'shandbook. If no disassembly instructions arcavailable, proceed with the most direct approach.taking care not to disassemble any more thannecessary in this phase of the equipment repair.While disassembling the equipment. place all

component parts. in orderly fashion, in a de;,11and convenient location. Place all small com-ponents, nuts. and bolts in containers. This willprevent the parts from being scattered and lost.Soldered and other types of mechanical wiringconnections should be labeled during disassembly.Labeling will permit their proper reconnectionduring reassembly.

6-4. Replacement. This action is necessarywhen the malfunctioning component requires re-placement. When replacing parts, insure thatonly like items or suitable substitutes are used toreplace circuit components. Unsuitable replace-ment parts may do further damage to that equip-ment or other equipment in the television system.

6-5. If solder connections are used. insure thatthey arc properly made: cold-solder joints andloose connections will decrease the equipment'soperating capabilities.

6-6. Repair. If it is possible to repair the failedcomponent without decreasing the equipment op-erating efficiency, by all means do so. On theother hand, some breakdowns lend themselvesmore readily to repair than others. Failures suchas broken connections. cold-solder joints, andother similar defects should be repaired ratherthan replaced. ,When dealing with broken con-nections. consult schematic and wiring diagrams if

there is any doubt about where the connectionshould be made. Failure to consult the necessarydiagrams, and a resulting wrong connection, maycause serious damage to the equipment and therest of the television sstern serviced hy thatequipment.

48J

6- 1-,-.Reassembly. Remember that reassemblyis simply the reverse operation of the diassemblytask: however, you must insure that all partsand components arc replaced in their originalpositions. Care must also be exercised when re-placing such items as screws, nuts, and bolts: hesure that they are not cross threaded or otherwsedamaged during reassembly. All electrical con-nections must be replaced in their proper pla.:eand good solder connections made when appro-priate. A final visual check of the equipmentshould be made to insure that no shorts, brokenwires, loose solder. washers, or other discrepancesare found before returning the equipment to op-eration.

6-8. Advantages of Bench Nlockups. There aremany advantages in using bench mockups andtheir related test equipment for final checkout oftelevision equipment. Bench mockups facilitatealignment. calibrating, and final checkout proce-dures before the equipment is installed or rein-stalled in the television system. Consequently.the equiptnent is known to he in good operatingcondition prior to use. Since bench mockups arepermanently set up. they are available for promptequipment checkout at all times. Therefore. spareequipment can be readily maintained in goodoperating condition and placed in operation at amoment's notice if needed.

6-9. Alternate Checkout Nkthods. When benchmockups are not avaiiable, the equipment mustbe checked with test equipment similar to thatused in bench mockups or placed in an opera-tional facility for final checkout, alignment, andcalibration. These alternate testing methodscreate some disadvantages. The test equipmentmust be set up each time it is used. and theoperating facility is not always available due toscheduled programming. Consequently. delaysand increased timc outages may be encountered.

6-10. Quality Checks. Quality checks are finalinspections to insure that the equipment is inacceptable condition prior to being placed in op-eration. The quality inspector must make surethat all repairs were completed and had met thehighest standards. Any defects found should henoted and brought to the attention of those re-sponsible. as this could be a basis for additionaltraining. This may also require reaccomplish-ment of the repair task: poor workmanship couldcause damage to other system equipment and ex-tended outage of the system.

6-1 I Precision Measuring Equitiment (PMELPrecision measuring equipment consists of toolsand test equipment required for repair. inspec-tion, calibration, or adjustment of operatingequipment. major assembly. or components.whose* normal function is to measurcs or provide

15

a known reference of comparison for perfor-mance characteristics.

.6-12. PME categories. PME categories are

established to identify -.stem. subsystem, andequipment calibration requirements. and to facili-tate assignment of responsibility for calibration.certification, and repair.

6-13. Category I equipment is operationalequipment installed in systems. subsystems. orequipment whose performance parameters arc tobe measured. verified, or tested

6-14. Category 2 equipment is peculiar PMEused to check. maintain, and calibrate category 1equipment.

6-15. Category 3 equipment is commercialand military standard PME used for mainte-nance. troubleshooting. testing. verification, andcalibration of cati:uory I and 2 equipment.

6-16. Category 4 equipment consists of stand-ards and accessories used to calibrate category2 and 3 equipment.

6-17. Calibration and certification of PME.Calibration is a comparison between instruments;one is a standard of known accuracy used to de-tect and correlate or adjust any variation in theaccuracy of the instrument being compared.

6-18. Certification is the act of designatingthat the PME has been calibrated and meets theestablished standards.

6-19. Economy. mission. and combat effec-tiveness demand that maximum calibration beperformed at the lowest practical organizationalelement. Maximum emphasis must be placed atall levels on fast. high-quality, base-level supportand TO compliance. The calibration and certi-fication of PME are performed as prescribed inthe TO 33K series calibration procedures.

6-20. The maximum interval for recalibrationof PME is specified in TO 33K-1-01 except forthose intervals prescribed in Calibration Measure-ment Summaries for PME, as applied to a speei-fie system. Calibration intervals prescribed inCalibration Measurement Summaries take prece-dence over all other TO's. Items designated"schedule calibration as necessary" (SCAN) willnormally be recalibrated at unscheduled inter-vals unless the using organization elects to es-tablish a scheduled interval based on system ap-plication. When an interval or SCAN is notprescribed in TO 33K-1-01. thc maximum cali-bration interval is 180 days.

6-21. There is no minimum time interval be-tween calibration periods of PME. When it hasbeen determined that PME requires calibrationor is known to have been subjeCted to roughhandling, overload, or other conditions detrimen-tal to the capabilities of the equipment. it must beconsidered questionable. Recalibration of equip-

46)0

ment falling into this cateLzory is mandatoryPME that has .exceeded the prescribed ealibr-don interval or has not been calibrated will nothe used.

6-22. PME., especially that of- a general-pur-pose nature. is designed to operate over a widerange. This equipment may be used only over aportion of the range. or at certain points in therange, When this is :he case. there is no need to

--certify the entire range. You should calibrateonly at the points or in the ranges where usedif the calibration range is clearly indicated on theinstrument. It is the using activity's responsibilityto specify desired calibration points or ranges onAFTO Form 211. Maintenance Discrepancy Pro-duction Credit Record.

6-23. PME having ancillary equipment suchas cables. probes. test leads, and other accessorycomponents must be delivered to the PrecisionMeasuring Equipment Laboratory (PMEL) in acomplete package. The PMEL may return with-out action any item that is not sufficiently com-plete to allow full calibration and certification,

6-24 At installations where AF standards arenot maintained. PME is calibrated by the closestPMEL subject to support agreements negotiatedbetween the site or base and the supporting ac-tivity. Remote sites and bases are required toinvestigate this type of calibration support priorto requesting command van assistance.

6-25. Items in storage do not require periodiccalibration. Items which are overdue for calibra-tion may be shipped as set.% iceable. Activitiesreceiving such items should have the reSponsiblePMEL calibrate them before placing the_ itemsin use.

6-26. Activities involved in evaluation of tech-niques and procedures or collection of data forprototype calibration equipment may not haverequirements for scheduled periodic calibration ofits PME. These equipments may be identifiedwith an AFTO Form 108, Certification Label.marked "this equipment is used for andneed not be periodically calibrated." The AFTOForm 108 must be signed and dated by the own-ing organization supervisor. In the event equip-ment status changes. it is to revert back to aperiodic calibration schedule. Under no circum-stances will PME being used to determine serv-iceability or acceptability of systems or otherequipments be released from the requirement ofperiodic calibration.

6-27. Calibration and certification responsibili-ties. The basic requirements and assignment ofresponsibilities for calibration and certification ofPME are outlined ir AFR 74-2. Repair. Cali-bration. and Certification of Preiision ,tittoure-ment Equipment. This regulation is applicable to

16

all isersonnel ;neagcd on orgai.and depot-ievc1 maintenanc.: ofcision measuring equipment.

PMEI . established

Air Force pre-

n act:ordaneewith AFR 74-2 as the base focal point in theAF single integrated calibration sstem. will heresponsibk for:

Operating and maintaining th; highestechelon of calibration reference standards as

signed to the base.The ealibration and certification of eat.:gory

3 general-purpose AF and comthercial test equip-ment.

The calibration and certification of general-purpose AF and commercial test equipment usedas component parts of category 2 equipnmitwhich does not require calibration in place andcan be removed to the PMEL for the work to beaccomplished.

Participating with other base-assigned ortenant activities in calibration of category and2 equipment that must be calibrated in place andwhich requires skills ur equipment available onlyat the base PMEL. Base reference standards wnot be removed from the PMEL for this purpose.

Calibration and certification of selected cat-gory 2 items specifically kkntified in TO 33K-1-01.

6-29. In addition to responsibilities for normalmaintenance, activities having responsibility formaintenance of weapon and support systems andequipment will be responsible for:

Calibration of category I and 2 equipmentand certification of category 3 equipment.

Return of AF and commercial general-pur-pose test equipment. including any category 4-type items in their possession. to the basePMEL on a scheduled basis for calibration.

Requesting assistance from the base PMEL.on category 1 and 2 items on which such as-sistance is specified in thc applicable 33K seriesweapon system TO.

Requesting command assistance throughchannels for calibration of category 2 equipmentbeyond the base PMEL resource capabilit!'.

6-30. Any category 1 and 2 items on whichthe PMEL has participating responsibility forcalibration will be identified during thc weaponsystem calibration review and indicated in theapplicable 33K series TO.

6-31. Those types of category 4 equipmentauthorized to activities other than the base PMELwhich are used for support of athanced systemsand equipment are referred to the base PMELfor ciAibration. The base PMEL will either cali-brate or will have these devices calibrated by

49i

an echelon capable of meetine the required ac-curacy.

6-32. While thc above responsibiilties arc di-rected generally to systcm support where cate-gories can be readily determined, thc same

principles can be applied to "nonsystcm" equip-ment.

6-33. Calibration responsibilities for specificitcms of equipment are published in TO 33K-1-01 and the systcm calibration mcasurementsummary. Activities requiring clarification Of

equipment categories and calibration responsibi-lities not listed in these TO's should submit thcirrequirements to the Calibration and MeteorologyDivision.

6-34. The using organization is responsible forcompiling an accurate list of all tools and equip-ment which require calibration. inspection, oradjustmcnt by PMEL or the calibrating work cen-tcr. This list will be used by Data Systems toestablish thc PME scheduling master file. Theusing organization will also notify Data Systemswhenever the owning work ccnter. building num-ber. or phone number used to identify the loca-tion of equipment is changed. This is necessaryin order for Data Systems to prepare accuratescheduline reports.

6-35. It is the responsibility of the using or-ganization to process a new item of equipmentthrough the PMEL or calibrating work center toverify calibration of the item. This action is takenin accordance with procedures established forscheduled calibration. The input forms will serveto establish a scheduling card for the master fileto control future calibrations.

6-36. The organizational equipment custodianwill be responsible for immediately notifying thePMEL or calibrating work center of all changes(quantity. serial number. etc.) to the inventory ifmanual instead of mechanized records are main-tained.

6-37. The AFTO Form 211 initiated by theowning organization must contain the followingcntries.

a. The owning organization will enter the Fed-eral Supply Class Code for thc item in block lc.

b. The owning activity will cnter thc part num-bcr for the item as listed on the data plate or in

17

thc parts catalog in block 2c. If an item does nothave a part number. the manufacturcr's modelnumber will be recorded in this block. If theitem has neither a part number nor a modelnumber. thc Federal Item Identification Number.which consists of all digits following thc Federalstock class, will be recorded in this space.

c. Thc owning activity will enter the manu-facturer's or AF serial number in block 3c. Ifno manufacturer's or AF serial number is as-signed. a local numbcr will be assigned by thePMEL or calibrating work center and this num-ber will be used as long as the equipment is as-signed to the base. Locally assigned serial num-bers will not exceed eight digits.

d. The PMEL or calibrating work center tech-nician or the owing organization will enter theappropriate "when discovered" code from TO00-25-06-4-1, Field Maintenance Shops WorkUnit Code Manual, Precision measuring Equip-ment, or TO 00-25-06-2-2, Field MaintenanceInstructions, Work Unit Code Manual, AerospaceGround Equipment, that identifies scheduledor unscheduled calibration or repair of the equip-ment being processed. This information is enteredin block 9 of AF Form 211.

e. The owning activity will enter a brief de-scription of the work required in block K.

f. The owning activity will enter the work cen-ter code. building number where the equipmentis located, and the phone number of the re-sponsible office in that order. This informationis recorded in Block L of AFTO Form 211.

6-38. All four copies of the AFTO Form 211will be attached to the item by the owning activitybefore it is delivered to the PMEL or calibratingwork center workload scheduler. Upon receipt.copy 1 of the form will be siened by thescheduler and dated in the last line of block K.Copy 1 of the AFTO Form 211 will then serve asa receipt by the owning organization.

6-39. When the necessary action has been com-pleted on the PME and the workload schedulerhas properly completed the forms. the equipmentwill be returned to the using activity. The work-load scheduler will obtain the AFTO Form 211,copy 1, at this time and destroy it.

4 9

CHAPTER 3

Diagnosing System Troubles

IF THE TV equipment and systems arc tooperate in accordance with applicable speci-

fications. you must maintain the equipment andsystems to meet certain standards. In this chapterwe will discuss some of the procedures for diag-nosing system troubles and the general mannerin which diagnosis is accomplished. The follow-ing system troubles are not intended to familiar-ize you with one specific system. but rather toacquaint you with the general nature of an sys-tems. In addition to discussing a number oftroubles. we will discuss symptoms of troubles.symptom analysis. and associated circuit per-formance.

2. Troubles of the transmission system willbe discussed first and the receiving system lastin this chapter. However, remember there willbe interrelated symptoms. Yet. with cumulativeexperience. it will become easier to recognizein which of the systems or unit of a system atrouble exists. The major units of the transmis-sion system wiltse problems can arise are powersupply. sync generator. camera, switcher, distri-bution amplifiers, monitor, exciter, and transmit-ting antenna. The major units of thc receivingsystem are subdivided into two groups: however.this is only an arbitrary subdivision as othercombinations are possible. For our purposes wewill divide the receiving equipment in the fol-lowing manner: antenna. cable, and receiver:tape machine, distribution amplifiers, and moni-tor.

3. To communicate by television, we necd onlya few items of equipment. However, if equip-ment problems are studied in a complete system.you will be able to understand these problemsin a simple system. The symptoms presentedand reasoning used to locate the unit at faultare intended to help you become proficient indiagnosing system troubles. The symptoms andproblems form a pattern for diagnosing systemtroubles. which may be similar or different. yetthe analysis process is the same.

18

7. Transmission System Troubles7-I. We must he able to eliminate either the

transmitting system or receiving system as thefirst step toward locating the trouble. Wc shouldhe able to recognize interkrence due to spurioussignals. ghost signak. adjacent channd or co-channel signals. and local oscillators whidi areradiating signals. plus many more signal sources.Incidenmlly. these interfering signals nta bc pre-sent in both cable and radiated systems. Insystcm maintenance when we are locating trans-mission system trouble. we would. in a sense.use a split system analysis. In a radiated ss-tem: for example. we would simply select an-other channel to determine if the receiver wasfunctioning properly. In cable -broadcast wecould do the same; however, in most closedcircuit systems, we woukl only need to feed in atest signal from installed test equipment. In anycase. after insuring that the receiver is workingproperly, we assume the transmission system to hefaulty. Whcn the preliminary analysis is com-pleted and the transmission system is found to beat fault. the ensuing steps are to locate andrepair thc trouble or troubles.

7-2. The following troubleshooting and troubleanalysis procedures for a television system arebased upon system operation. Faults can he iso-lated. to some extent, during preliminary testsetup operations by observing the results of theseoperations on the \lewer monitors and the main-tenance monitor. Normally, operating units eanbe .eliminated as a source of trouble by switdi-ing between cameras and monitors and observ-ing all units before starting trouble analysis ofthe system. For example. a malfunction in oneof the camera units could indicate a possibletrouble in the monitor. the switching and distri-bution circuits, or the camera. By switching themonitor to use another camera. the monitor andthe switching and distribution circuits are elimi-nated as thc cause of trouble.

7-3. The procedures in this section are limited

49j

I0 diagnosing troubles of a complete system be-cause you have already studied troubleshootingand trouble analysis of the individual units in

the system, In some instances a reverse proce-dure is used; that is. the trouble k given for aunit of thc system. The following discussion con-cerns thc symptoms as they appear throughoutthe system.

74, Power Supply. In our first exaniple wewill take a known trouble and list the symptomswhich will he found throughout the system. Re-member. this is a prirwiple-centered study andnot a specific power supply. Assume you havea power supply which pros ides unregulated volt-ages. regulated voltage. and centering current.We will assume that thc unregulated output volt-ages and the centering curr,.....t are normal. butthe regulated voltage outpu. 's zero. In someinstances this trouble can be found by a voltagecheck with the mcter built into the power supply.In other cascs it will bc necessarY to find thctrouble, through analysis of thc equipment symp-toms, which would require verification by theuse of an external meter at checkpoints.

7-5. When thcre is a failure of the regulatedvoltage output. the symptoms would be rasteronly on utility monitor and camera control moni-tor: the eamcra view findcr will not have a raster.and the waveform monitor will have a traceline without any video modulation. However.these symptoms could also be present in a cam-era control unit which uses a free-running oscil-lator driven by the sync generator. For example.if thc sync generator drive failed. you would losethc oscillator output and thus the signal.

7-6. A note of caution when looking at thereverse of thc preceding analysis symptoms:Never grasp at a quick conclusion when an imagedisappears from a screen. With thc disappcaranccof an image on onc monitor or viewfinder, cross-check with other monitors. If the presentationis from a live camera and it is in a closed circuitsystem. there will probably bc a voice circuit toaid in making thc suggested checks. if the pre-sentation is from a tapcd sourcc, there will bc amonitor on the tape machine or in the tape room.thus enabling cross-ebecks with the initiatingpoint.

7-7. Again referring to the power supply as asourcc of trouble, you can examine the symptomsfor a clue to thc actual power supply trouble,As previously stated. you do not have regulatedvoltage; therefore. there is no image pickup butthcrc is a raster on'camera control monitor. Thisindicates there is some high voltage present: thus.it can be assumed that the control relay of thepower supply is functioning. On the othcr hand.if you do not have any voltage present. you

19

4 9

would assurne that a relay could bc at fault.Most powcr supplies are equipped with time-delay devices to permit adequate warmup timc.If thc time-delay device (relay) should fail. thiswill eliminate thc various output voltages, and itwill also eliminate any centering current output.The exact nature of thc trouble as to its symptomswill also depend on the power supply itself. Ifthc heating element of the tic delay is opcn. thcnthe pilot light probably will not light. If thefuse is blown, this will give thc same indication.Through this reasoning you will probably checkthc fuse and pilot light beforc checking the time-delay relay. Again, it is a matter of reading thcsymptoms correctly and being able to make aquick diagnosis of thc possible troubles. Con-sequently a faster repair can be madc and thesystem will be returned sooner to operationalstatus.

7-8. Sync Generator. Assume that you have aclosed circuit system in which the monitor inyour room is tearing horizontally. This is notthe even displacement. such as the venetian blindeffect. but represents thc loss of scanning linesor portions of lines anywhere in thc picturedue to something which affects synchronization.Normally, your first assumption is that the hori-zontal oscillator of the monitor in question is

not operating properly. Again. it is important thata cross-check with other monitors be made wherepossible. If a cross-chcck is not possible, thena check with monitors at the point of origin ofthe signal is the next step. A check in thisinstance reveals that ail monitors are giving thesame indications of tearing.

7-9. If. in a given instance, a cross-check didnot give the same indications but rather onlyone set had thc indications and this was con-nected to only one distribution amplifier, thenyou would check the distribution amplifier or themonitor. A substitudon of a distribution ampli-fier or another monitor would localize thc troubleto the given unit of a system.

7-10. Going back to the original set of symp-toms. cross-check with othcr scts. and then pro-ceed on to the sync generator. Here you againsubstitute. if possible, to localize to the syncgenerator. If you do not have a spare syncgenerator. you would probably use a scope tocheck the 15,750 signal. If this signal is nt tstable. you will find the symptoms as indicated.Another method of checking frequency stabilityis to use a frequency counter with a short-timeconstant. sincc it will indicate the frequency driftby recounting thc frequency each time it changes.

7-11. Camera. in this instance, assume thesituation of a live camcra presentation with anumber of monitors in use simultaneously. The

e64

following symptoms appear: you have a normalpicture and the presentation is normal; suddenlythe normal presentation is interrupted and thereis only a rastcr on the monitor in question. Im-mediately a cross-check is made to determine ifthe same indications are to be found on othermonitors. In this instance all monitors are thesame; that is, a raster but no picture. After across-check of monitors. a check to see if thecamera has an output is in order. The nextlogical step is to use a substitute camera to makethe final determination of a faulty camera.

7-12. Another camera trouble which happensquite frequently is the (white) high-peaker ad-justment. The symptoms of this trouble are whitestreaks to the right of an object as it appears onthe monitor screen. When this symptom appears,and if a cross-check is made. the same indica-.tions will appear on the other monitors. A sub-stitute camera should eliminate this trouble, un-less the second camera would have the sametrouble (which is unlikely). The actual troublein the camera is the high-frequency compensatorsout of adjustment. This trouble can usually becorrected by adjusting the hig.h-peaker controlwhile observing the monitor screen.

7-13. There is another very similar troublewhich occurs in the black regions or the signal.Since this is in the dark portions of the picture,it is not so noticeable. The dark streaking willbe most noticeable when a test pattern is beingpicked up by the camera. The blacks will havetrailing streaks to their rieht as observed on themonitor screen. This can be adjusted by chang-ing the setting of the low-frequency peaking con-trol, while observing the monitor screen. Whena major realignment of these circuits is necessary.a sweep generator and a scope must be used toobtain the correct envelope presentations.

7-14. Switcher. A symptom which will appearas a result of faulty switcher contacts is a lossof sync. This will be evidenced by the verticalroll and the horizontal flopover of the picture.These symptoms may appear together or individ-ually. This trouble can be quickly checked ona live progam by checking the line monitor atthe immediate output of the switcher. The linemonitol compared to the camera-ready monitorsand preview monitors will immediately localizethe trouble to the switcher.

7-15. Another trouble which will be evident tothe switcher operator is the loss of picture afterpunch up. This is where there is a picture whilethe switcher button is pushed down; but whenthe button is released, the picture on the line'monitor disappears. This is a fault in the switchbuttons of the switcher panel. These troublesmay be further localized by punchine up another

20

camera to cross-check with another seleeter but-ton on the switcher control panel. In this waythe trouble may be localized to thc exact push-button at fault. Use an oscilloscope to circuittrace in the switcher. when locating the exactset of contacts at fault. or in some cases therelay at fault.

7-16. Distribution Amplifiers. There are twobasic types of distribution amplifiers: the pulsedistribution amplifiers and the video,distributionamplifiers. They are similar in their constructionand use; however, the pulse distribution amplifieris designed to handle more power than the videodistribution amplifier. The pulse distribution am-plifier also has more adjustments; thus it is setup in a different manner. These two basic typesarc not to be interchanged in an installation. lfthey arc inadvertently interchanged during in-stallation, there will be problems in the initial ad-justments of the system. If during checkout of anew system this difficulty of adjustment is ex-perienced by personnel, the first items to look atwould be the distribution amplifiers to see if thccorrect units are installed.

7-17. Pulse distribution amplifiers. The pulsedistribution amplifiers can be responsible for anumber of symptoms in a live camera system.Individual pulse distribution amplifiers can beresponsible for loss of sync pulses. vertical drivepulses. horizontal drive pulses. and blankingpulses. This would be indicated by failure of therespective picture elements as they appear on amonitor screen. Another factor is the actualsystcm location of the pulse distribution ampli-fier; this location will determinc the overall effectand symptom indication.

7-18. Assume that the system is a live camerapresentation and suddenly the picture disappearson a room monitor. Immediately upon making across-check of other monitors in the system. youfind there are no images on any monitors, butthere are rasters present. However, when themonitor on the camera (view finder) is checkedit does not have a raster. This symptom couldbe an indication of a failure of either the verticalor horizontal sweep signal. The failure of eitherof these signals will result in the activation ofthe camera protection circuit to prevent burnineof the camera tube or the picture tube. Sincethere are separate pulse distribution amplifiersused to drive the horizontal and the verticalsweep, it can be concluded that a failure of eitherof these distribution amplifiers would cause thesystem to give the indicated symptoms.

7-19. As you will recall. there is also a sepa-rate pulse distribution amplifier for thc blankingpluse. Consequently. if this distribution amplifierfails, then the blankine pulses would not bc pre-

4 9,

sent to eliminate the retrace lines. Thus. in thcpicture presentation there would be retrace linesvisible on thc systcm monitors. A word of cau-tionin some monitors if thc brightness is in-correctly adjusted. retrace lines may also be visi-ble. This emphasizes the value of making across-check with other monitor units of the sys-tem.

7-20. If thc pulse distribution amplifier whichis used for the sync pulse fails, then there willbe a loss of both vertical and horizontal sync.This is evidenced by vertical roll or horizOntalflopover in the video presentation. Since individ-ual monitors in many cases have adjustments forthis. it is important that a cross-check with othersets be madc before any conclusions are drawn.

7-21. Video distribution amplifiers. The videodistribution amplifier is designed to pass eitherthe blanked video only. composite video, or syncsignal. Its actual use depends upon its location inthe system. Therefore. any symptom that is to betraced to a video amplifier must be thought of inrelatkm to the amplifier's location. If it is in thesystem prior to thc sync being added. the com-posite signal will have sync but it will not havevideo. Suppose you have a loss of compositesignal. but on a cross-check you find that thesync and the blanked video signals are presentin the system. This combination of symptomsindicates that the distribution amplifier responsi-ble is located in the system following a point atwhich the composite signal was formedproba-bly at the switcher output. Most of the systemtroubles that may be traced to a video distribu-tion amplifier will neycr occur. Or it can be said.they should not occur because during the preop-erational test all normal problems will be recog-nized and repairs will be made.

7-22. Assume that a tube weakens in a videodistribution amplifier used to amplify the com-positc output signal and a dimming of picturesignal is apparent. A cross-check also revealsthe identical symptoms on all monitors: includ-ing thc line monitor in the control room; how-ever. it would not include the preview monitorand thc individual camera monitors located alongwith the line monitor. Again it is the situation ofreasoning out thc most likely problem from thcsymptoms presented. and keeping this idea in

mind, you will find most of the trouble sourcesrapidly.

7-23. Monitor. Sincc thc monitor isin a man-ner of speakingthe end of a systcm. there willbe few troubles inserted into thc system fromthe monitor. The monitor is thc termination foreach output of thc video distribtuion amplifiers.

7-24. Assume there is a sudden loss of signalat a particular monitor. With a cross-check youfind there is a signal present at the other moni-tors connccted to the same video distribution am-plifier. The distribution amplifier would not be atfault, in this instance unless there was an openin-the output for the specific monitor. Now if youhave the symptom of no signal at a monitor, andon a cross-check you find there is no signal atthe associated monitors connected to the samevideo distribution amplifier, the first suspectedfault would be the video distribution amplifier.

7-25. Exciter. The term "exciter" is used toidentify the r-f signal generator used in either thecabled closed circuit or the radiated signal sys-tem. In the case of the cabled system. with avideo r-f carrier. if the exciter were to fail therewould be a loss of the video signal. In some ofthe more elaborate cable systems the exciter isused to generate a carrier for both the videoand audio; an exciter failure results in a failureof both video and audio signals. This is assum-ing that the failure is of a nature that wouldcause a loss of power to the entire unit. Therewill be instances where only a tube fails andthus only one signal will be lost.

7-26. Assume the situation of a cabled closedcircuit system which uses an r-f carrier for boththc video and audio. In this instance 't will berather easy to find the part of the system thatis at fault when a failure of the exciter unitoccurs. For example, if suddenly the monitor'svideo image is lost and the audio is good, manypossible troubles are eliminated immediately.Reason it this way: If a cable breaks or powerfailure occurs. all signals will be lost. By makinga cross-check, it is dctermned the other monitorshave the same symptoms; therefore, you willknow the trouble is at a point in the system com-

21

4 9

mon to all monitors. A furthcr check revealsthat the line monitor at the input of the excitermodulator section has a video signal prescnt.Thus. all of the sections arc eliminated as a

sourcc of trouble except the modulator portionand the exciter stages. It is assumed that the r-fcarrier is common to both the video and audiostages; therefore if the audio is being receivedand the video is not, the r-f section of the exciterunit must be good. This would leave the sourceof trouble as the video modulator portion of theexciter unit.

7-27. If the system being used is of the typewhich uses an r-f carrier for video, and the audiois transmitted by conventional wire. the techni-que will be simpler. In this instance. therc willonly be one sigial (video) to be affected by thefailure of the exciter. In this case. it will bemerely a matter of elimination to determine thepoint at which the video signal is no longerpresent.

7-28. The exciter becomes a very importantpart of the radiated system. both broadcast andrelay. In the case of the relay systeni the excitercan be used as a carrier for the video only or itcan be used for a carrier of video and audio.The broadcast system does not use the sameexciter for both the video and audio carrier.As you will recall from earlier volumes, thevideo is AM and the audio is FM.

7-29. This tells us that the relay system willhave a complete failure of both signals whenone common carrier is used. However, in theinstance where the relay system uses a video r-fcarrier and the audio is carried by wire. therewill be only one signal failure as a result of ex-citer failure.

7-30. The broadcast system will also experi-ence separate exciter failures. That is, the exicterfor video will not affect the one for the audiounless it causes a complete power failure, aswould be true in case the audio exciter causeda power failure. Where the exciter units or as-sociated modulator units fail in the broadcastsystem. it will usually require more extensivetroubleshooting to find the source of the trouble.The failure of the video will give more symptomsthan the audio because of the fact that it is AM.This means there can be a carrier signal presenteven though the video modulator fails. This iseVidenced by the gray raster but no image is

present on the picture tube.7-31. Transmitting Antenna. Transmitting an-

tennas are in two basic categories: the broad-cast antenna and the microwave relay antenna.Therefore. there are two basic types of problenisas related to the use of the antenna. For exam-ple, the broadcast antenna failure will be noted

22

on ail receiv;ne set.F. whereas ia a closed circuitsystem with a microwave link, a relav'antennafailure will be noted only on the closed circuitreceiving system. Tbe overall effect of anv an-tenna failure will of course bc indicated tirston the receiving sets. The indications on thesets will be any variation from a weakening ofpicture to a complete loss of picture. Also. sincethe audio carrier is fed in from a separate trans-mitter in the case of the broadcast unit. therecould be a weakening or loss of audio whiL Iiwoud be directly attributable to the antenna sys-tem.

7-32. Broadcast. In most instances the main-tenance personnel will recognize trouble symp-toms associated with a broadcast antenna just asquickly as those using receiving scts. There willbe instances whcre those using receivers willnotice problems first: however, unless they 'aretrained maintenance personnel. they will not heable to recognize the difference in receiver prob-lems and transmitter problems. If the transmit-ting antenna becomes damaged or the coaxialcable becomes damaged. there will be an alarmsignal. This may be either audible or visual. hutit will indicate thc failure of the antenna system.Then by analyzing the associated meters. the ex-act type of failure can be determined. In thistype of trouble there L not a great problem infinding the part of the system at fault. It willrequire more extensive analysis to determine theexact cause of the trouble. but the system hasbeen located and repair action can be initiated.

7-33. Microwave relay. The failure of a micro-wave relay antenna will be more of a go or no-gosituation. This is due to the limited power anddirectivity of the antenna because if power weak-ens or alignment is changed. there will be nosignal. As stated earlier, normally there willbe only one receiver unit affectedthe Micro-wave receiver. However. thc receiver will beconnected to a monitor system which may containone or more monitor units. The monitors willnot receive a signal and the video and audiowill be- lost. Those using the monitors will beaware of a failure but will not know its exactlocation. Both the microwave receiver and trans-mitter will alarm when thc signal is lost. Thereis little effort required to locate the systcm caus-ing.the trouble. The problern_will be in findingthe trouble in the system by using test equipment..

8. Receiving System TroublesAs already stated. the receiving equip-

ment mav be divided into a number of combina-tions. Also the receiving equipment may becombined into one large system in which all thedifferent types of units arc used, even to the

49,

i/t7

J

UHF-VHFANTENNA

OFF THE AIRUHFVHF RECEIVER

MICROWAVE MICROWAVERECEIVER

D A

ANTENNAD A

UHFVHFUTILITYTUNERMONITOR

D AIN

POWER SUPPLY

OUT

VIDEO TAPEMACHINE

UTILITYMONITOR

Figure 2. Receiving equipment combinations.

extent of duplicaton of many of .the units. As.already implied, there will be a large number ofmonitors or receivers in most systems. Logicalreasoning will lead to the conclusion that wherethe most equipment is involved in a system therewill be morc system problems. In contrast therewill bc a minimum number of antennas. cables.tape machines. and distribution amplifiers. Fig-urc 2 illustrates an overall combination of re-ceiving equipment. Any given installation couldinclude part or all of the equipment shown in theillustration.

8-2. Simple System. Thc term "simple system"is uscd here only as a means of separating sys-tems. The simplest systcm thcn includes an an-tenna. a cable from the antenna to thc receiver.and thc receiver. In this system if you lose thevideo and audio. but still have a lighted screen.you would suspect the incoming signal. Thequickest check is to change channels. if thcrcstill is no signal, the ncxt stcp is to check theimmediate systcm. This includes the cable con-nections. thc cable. and the antenna. If a visualinspectton reveals thc conncctions and cable to

23

4jo

UTILITYMONITOR

UTILITYMONITOR

be in apparently good condition. the next stepis to use test equipment. When more than onereceiver is available, substitution of receivers willlocalize to one specific cable or antenna. Insome installations, one antenna will serve morethan one receiver. Where this type of installa-tion is used. a simple cross-check of receiverswill be sufficient to localize the trouble.

8-3. There will be installations where the sim-ple system is a part of a large system. Where

this is true. there will be a variety of checksthat can be made to determine if the antenna.cable. or reciver is at fault. Again look at figure2 and you will see that in the large installationthe simple system is connected to the overall sys-tem; thus. an overall check is possible with moni-tors or built-in test equipment to localize troubleareas.

8-4. Complex System. The term "complex sys-tem" is uscd to have a point of reference. Thccomplex system can be represented by figure 2or it could have fewer units as well as more unitsto make up thc overall system. Logical reason-ing tells us that there is litne interaction between

units of tit:: simple system to complicate any sys-tem analysis. In the cornpin system this is r..nthe case. as a trouble in one arca can affect thcentire system.

8-5. Assume that only a per: :on of the sys-tem is in operationthe tapc machine, the di-tribution amplifier, and monitors. In this instanceif a video image is not obtained on a nwnitor.the trouble could be in the cables. switclwr.distribution amplifiers, or tape machine. Anopen cable between the switcher and the monitorwould cause a loss of image; however, this trou-ble could be checked by using a known goodmonitor. Also a faulty distribution amplifier couldcause the same symptom, but substitution wouldaid in localizing the faulty unit. If the tape ma-chine were faulty. then when video on a monitorwas lost, all monitors would have the same indica-tions. A check with the tape machine video moni-tor and the tape machine waveform monitor willquiekly indicate that the tape machine is the_

trouble source.8-6. The distribution amplifier unit can be

affected by a monitor in such a manner to cause

24

!r biow a ruseznc system. This

and thus affect the rest ofwould be the s,anc as

ctscd in the previous section im transmissiond;-.;ribution o.mplifiers. The distribution ampli-,k1 power suppiy unit lailure would have th::same effect. in that would affect more than oneLiistribution amplifier. This v..ould also ;Weer allmonitors attaehe to thc distribution amplifierunits the same as would be revealed by cross-check of monitors.

8-7. The complex system will enable a morycomprehensive stud\ of system troubks. Whentroubleshooting a system tdways renwmher touse all available symptoms. learn to read thes)mptoms. and analyze them to deterrnine theunit which is faui:y. Never fai! to compare sys-tem symptoms as this will lead to a rapid repairand thus keep a system on the air. If a signaldoes not reach its destination. regardless of thecause. then efficiency is lost. Therefore all partsof the system are important. as you wiil see fromthe planning involved in system installation, ascovered in the next chapter,

4 9j

ebqaE")

MODIFICATIONS

Arlof this publication has (have) been deleted in

Mo

adapting this material for inclusion in the "Trial Implementation of a

Model System to Provide Military Curriculum Materials for Use in Vocational

and Technical Education." Deleted material involves extensive Use of

military forms, procedures, systems, etc. and was not considered appropriate

for use in vocational and technical education.

30455 03 21

WORKBOOK

TELEVISION EQUIPMENT REPAIRMAN/TECHNICIAN

Ire.T--ItP\CAING/SRGCRE VdR

This workbook places thc materials you need where you need thcm while youare studying. In it, you will find thc Study .Reference Guide, the Chapter ReviewExcrciscs and thcir answers, and the Volume Review Exercise. You can easilycompare textual references with chaptcr exercise items without flipping pagesback and forth in your text. You will not misplace any one of these essentialstudy materials. You will have a single reference pamphlet in the proper sequence

for lcarnino.Thcsc devices in your workbook are autoinstructional aids. They take the

place of the teacher who would be directing your progress if you wcre in aclassroom. The workbook puts these self-teachers into one booklet. If you willfollow the study plan given in "Your Key to Carccr Development," which isin your course packet, you will be leading yourself by easily learned stcps tomastery of your text.

If y ou have any questions which you cannot answer by referring to "YourKcy to Career Development" or your course material, use ECI Form 17, "StudentRequest for Assistance," identify yourself and your inquiry fully and send it toECI.

Keep the rest of this workbook in your files. Do not return any other partof it to ECI.

EXTENSION COURSE INSTITUTE

Air University

50,

TABLE OF CONTENTS

Study Reference Guide

Chapter Review Exercises

Answers to Chapter Review Exercises

Volume Review Exercise

Ea Form No. 17

STUDY REFERENCE GUIDE

I. Cse this Guide as- a .Stady Aid. It emphasizes all important study areas of this volume.

2. 1 se the Guide (1)111plete the VI,Iffine Review ExerriAe and for Review after Feedhack

the Results. After each item number on your V RE is a three digit number in parenthesis. That

numbcr correspomk to the Guide Number in this Study Reference Guide which shows you where

the answer to that VR E item can he found in the text. When answering the items in your

VRI:, refer to the areas in the text indicated by these Guide Numbers. The VRE results will he

sent to you on a poocard which will list the actual I'RE items you mi.s.sed. Go to your VREbooklet and locate the Guide Number for each item missed. List these Guide Numbers. Then gohack to your textbook and carefully review thz areas covered by these Guide Numbers. Review

the entire VRE again before you take the closed-book Course Examination.

3. I e the Guide for Follow-up after you complete the Cours.e Examination. The CE results will

he sent to you on a postcard. which will indicate "Satisfactory- or "Unsatisfactory- completion..1 he card will list Guide Nunthers relating to the questions missed. Locate these numbers in the

Guide and draw a hue under the Guide Number, topic, and reference. Review these areas toinsure your mastery of the course.

GuidcNumiwr Guide Numbers 300 through 315

300 Operational Responsibilities; Sy stem s,pages 1-2

301 Inspection: Daily; Weekly; Monthly, pages2-4

302 Inspection: Two Months (60 Days); ThreeMonths (90 Days); Semiannual; Annual; In-spection Teams; Evaluation of InspectionReports, pages 4-6

303 System Quality Checks, pages 6-7

304 Troubleshooting and R ep al r; TelevisionTest Equipment, Types, Use, and Malfunc-tions: Television Test Equipment; ColorTelevision Testing, pages 8-10

305 Television Test Equipment, Types, Use, andMalfunctions: Test Equipment Malfunctionsand Detection; Alternate Quality TestingMethods; Transistor Checks, pages 10-13

306 Troubleshooting and Maintenance Proced-ures, pages 13-14

307 Systematic Repair, pages 14-17

GuideNumber

308 Diagnosing System Troubles; TransmissionSystem Troubles: Power Supply; Sync Gen-erator; Camera; Switcher, pages 18-20

309 Transmission System Troubles: Distribu-tion Amplifiers; Monitor; Exciter; Trans-mitting Antenna, pages 20-22

310 Receiving System Troubles, pages 22-24

311 Installation and Modification; C -E Program-ming: C-E Requirements; Planning; Plan-ning Qualitative and Quantitative C-E Re-quirements; Programming; ProgrammingQualitative and Quantitative C-E Require-ments, pages 25-28

312 C-E Programming; Programming Televis-ion Requirements; C-E Program Manage-ment; Implementation; Implementing Quali-tative and Quantative C-E Requirements;C-E Schemes; C-E Implementation Sched-ule; Implementing Television Requirements,pages 28-30

313 Installation Phase, pages 30-32

314 Installation Testing, Inspection and Accep-tance, pages 32-35

315 Modifications, pages 35-38

*NOTE: Pages 494 and 495 are missing due to deleted material. No pertinentinformation was omitted.

1

2. Match the follw.ving items of test equirri.-:it wit' the apprqpriate staten't'nt. 41,

Tube checker. 1. Used fo7 regulated pov.er suppl% t-sts.

Wa; tmeter. 2. Checks Jefleti ion Iirienritv.Voltmeter:: and mill iamrneters.Ohmmeter.

Prevents r-t inter'crenee dunng rr.insinittettesting.

Grating generator.,Dummy load.

4. Provide!, modulating signal tor transmittertesting.

Multiburst generator. 5. Provides accurate voltage rnew-urements.

Video sweep generator. h. Checks transmitter output power.-h.Oscilloscope. 7. Checks video circuit bandwidth.

Monoscope amplifier. 8. Checks system pulse widths.

Jc Waveform monitor. 9. Produces video and other timed pukes.10. Check for matched tubes.11. Alternate transistor test.

3. Identify the test equipment specially designed for color testing. (4-13)

4. What is the best method of troubleshooting a color bar generator? t 4.26)

5. Give the best alternate method of testing the frequency response of a television system the

multiburst generator should fail and describe how irregularities are identified. I 4-33..1-1)

6. Name the video quality tests that can be made using the E1A resoiutton test pattern. 14. f),

5u,t

7. How do you check a p-n-p transistor with an ohmmeter? (4-46)

3. Name the steps associated with troubleshooting and repairing television equipment. (5-2)

9. Describe the similarities of symptom analysis and trouble analysis. (5-4, 6)

10. What conditions may result in recurring circuit malfunctions? (5-8)

11. Why are intricate maintenance procedures written? Give three examples of these procedures. (5-9)

12. How are alignment and calibration procedures written? (5-13)

13. What precautions should be taken during disassembly of television equipment? (6-3)

14. What are the advantages of using bench mockups for equipment checkout? (6-8)

5

5 u

/MI15 What are the dist,dvantages of not,usine bench mockups for equiPMent checkout? (6-9.0

16.. Why are quality checks desirable? (6-1G)

17. Who is responsibk for the calibration of precision measuring equipment? (6-27)

18. Who is responsible for processing new items of precision measuring equipment through the PMEL?(6-35)

CHAPTER 3

Objectives: To desc,ribe the procedures used in analyzing system symptoms to determine the'malfunc-tioning units in the system.

1. Number the following events in their proper sequence as they relate to systems maintenance.(7-1, 2)

Isolate trouble.b Recognize symptoms.c. Cross-check symptoms.d. Verify symptoms by substitution.e Localize symptom to unit of system.

Analyze symptoms.g Verify unit at fault by substitution.

Repair or replace unit at fault.

506

6

eier

2. Which of the following items can be matched to the associated statement(s)? (7-44)

...a. A fuse. 1. Can be bad and there will not be any power to the pilot light.

- -----b. A time-delay device. 2. Malfunctioning will cause a loss of current and voltage output.

A control relay. 3. Working improperly; could cause voltages to be applied too

quickly.4. Could possibly be a cause of the pilot light not working.

11;0

3. In a closed circuit cable system, a monitor indicates erratic horizontal tearing of the image. List

the system units which could cause this. (7-8-10)

4. If you have high-frequency loss in a camera preamplifier, what would be the symptoms and what

would be adjusted to compensate for the loss? (7-12)

5, What unit of the system would cause an instantaneous video presentation, but would also cause

the presentation to drop out just as quickly? (7-15)

6. Three monitors have lost thei signal but the other monitors all have good signals. What is the

most likely cause of the trouble? (7-16-22)

7. What would be the symptoms if a monitor input becomes shorted? (7-24)

8. List the various methods of using an e.:citer unit as related to the various types of r-f

transmissions. (7-25-30)

9. If you were told that a slight misalignment of antennas had caused a complete loss of signal.what basic category of antennas would this probably be? (7-31-33)

10. Which signals would be affected on a TV receiver if the antenna cable is broken? (8-2)

11. How would a simple system, installed as part of a complex system, be an aid to trouble analysis?(8-3, 4)

5 d

8

66/

6adapting this

13

MODIFICATIONS

of this publication has (have) been deleted in

material for inclusion in the "Trial Implementation of a

Materials for Use in Vocational

involves extensive use of

Model System to Provide Military Curriculum

and Technical Education." Deleted material

military forms, procedures, systems, etc. and was not considered appropriate

for use in vocational and technical education.

5 d

ANSWERS FOR CHAPTER REVIEW EXERCISES

CHAPTER 2

1. Multiburst generator; grating generator; monoscope amplifier; and waveform monitor. (4-2)

2. 1, c; 2, e; 3, f; 4, j; 5, i; 6, b; 7, h; 8, k; 9, g; 10, a; and 11, d. (4-3-12, 46)

3. Color bar generator, dot generator, vectorscope, color signal analyzer, and linearity checker.(4-13)

4. Signal tracing. (4-26)

5. The EIA resolution test pattern. Characteristic response frequency irregularities appear in theoutput presentation as closely spaced, horizontally displaced, positive or negative, delayed oradvanced repetitions of the original signal. These discrepancies are called ringing. (4-33, 34)

6. Gray-scale rendition, shading, uniformity, streaking, interlace, aspect ratio, geometric distortion,horizontal and vertical resolution, and characteristic response frequency. (4-36)

7. Base to emitter and base to collector front to back ratio. (4-46)

8. Symptom recognition, symptom analysis, trouble localization, trouble analysis, and troublecorrection. (5-2)

9. Both are evaluations of known factors. (5-4, 6)

10. Faulty circuit design and unrepaired component or circuit defects. (5-8)

11. To remember all necessary steps. Alignment, calibration. and PMI's. (5-9)

12. In r.imple, logical, straightforward steps. (5-13)

13. Do not perform more disassembly than necessary, follow TO's and manufacturer's handbooks, donot lose components and other parts, and label wiring as it is disconnected. (6-3)

14 5 I o

6-o2

14. They are permanent4set.up. they are available at all times, they permit easy alignment,

calibration, and final checkout of equipment. (6-8)

15. Possible checkout delays and test equipment must be set up each time it is used. (6-9)

16. To Insure that repair is properly completed to locate need for additional training, and to prevent

equipment and system damage. (6-10)

perEonnel in organizational, field, and depot level maintenance of precisionn-::.:75. ring equipment. (6-27)

18. The using organization. (6-35)

1. a. 7.

h. 1.

d. 3.

s.f. 4.g. 6.h. 8.(7-1, 2)

CHAPTER 3

2. a. 1.

b. 3 and 4.(.. 2.

(7-4-7)

3. Monitor (horizontal oscillator), distribution amplifier, and sync generator. (7-8-10)

4. The symptom would be white streaks in the video presentation, and the adjustment of the high-

peaker should correct the problem. (7-12)

5. The switcher would cause this symptom if iti switch contacts are bad. There would be amomentary video presentation due to the pressure of the operatbr pushing the button. (7-15)

6. A video distribution amplifier used as a line amplifier for the three monitors. It could be a line

going to the distribution amplifier, but this is a less likely problem. (7-16-22)

7. There would not be a video presentation on that particular monitor or other monitors connected to

the same distribution amplifier. A short on a monitor input will cause a distribution amplifier fuse

to blow due to the excessive current at the distribution amplifier output. (7-24)

8. Cable video only, r-f carrier; cable video and audio, r-f carrier; relay radiated video and audio, r-f

carrier; broadcast radiated video, AM carrier; braodcast radiated audio, FM carrier. (7-25-30)

9. Microwave relay antennas, because they are a highly directional low-power antenna; thus a slight

misalignment can cause complete loss of power. (7-31-33)

10. Both the video and audio signals as they are separated internally; thus a broken cable will cause

a loss of all signals. (8-2)

11. The simple systerr could be used to insert a test signal, and it can be used to receive and thus

compare signals. This enables the checking of inputs to the complex system. (8-3, 4)

*NOTE: Pages 504 and 505 are missing due to deleted material. No pertinentmaterial was omitted.

15

51i

S T 0 P -I. MA1CII ANSWER

SHEE1 10 THISEXERCISE NUM-BER.

Carefully read the following:

bo'S:

2. USE NUMBER' IPENCIL..

30455 03 21

VOLUME ,REVIEW EXERCISE

1. Check the "course.- "volume.- and "form- numbers from the answer sheet address tab againstthe "VRE answer sheet identification number.' in the righthand column of the shipping list. Ifnumbers do not match, take action to return the answer sheet and the shipping list to ECI immedi-ately with a note of explanation.

2. Note that numerical sequence on answer sheet alternates across from column to column.

3. Use only medium sharp ::1 black lead pencil for marking answer sheet.

4. Use a clean eraser for any answer sheet changes. keeping erasures to a minimum.

5. Take action to return entire answer sheet to EC1.

6. Keep Volume Review Exercise booklet for review and reference.

7. If ntantiatortlu enrolled student, process questions or comments through your unit trainer or OJT

supervisor.If roluntarilu enrolled student, send questions or comments to ECI on ECI Form 17.

DON'TS:

1. Don't use answer sheets other than one furnished specifically for each review exercise.

2. Don't mark on the answer sheet except to fill in marking blocks. Double marks or excessivemarkings which overflow marking blocks will register as errors.

3. Don't fold, ,::pindle, staple. tape, or mutilate the answer sheet.

4. Don't use ink or any marking other than with a I black lead pencil.

Note: The 3-digit number in parenthesis immediately following each item number in this VolumeReview Exercise represents a Guide Number in the Study Reference Guide which in turn indicates

the area of the text where the answer to that item can be found. For proper use of these Guide

Numbers in assisting you with your Volume.Review Exercise, read carefully the instructions in

the heading of the Study Reference Guide.

181 .")

61

f0(49

Multiple Choice

Nott.: The first three Items in this exercise are based on instructions tha t were included with your

course materials. The correctness or incorrectness of your answers to these items will be reflected in

your total score. There are no Study Reference Guide subject-area numbers for these first three items.

1. The form number of this VRE (or CE) must match

a. mv course number. c. the form number on the answer sheet.

b. the number of the Shipping List. d. my course volume number.

2. So that the electronic scanner can properly score my answer sheet, I must mark my answers with a

a. pen with blue ink. c. number 1 black lead pencil.

b. ball point or liquid-lead pen. d. pen with black ink.

3. If I tape, staple or mutilate my answer sheet; or if I do not cleanly erase when I make changes on

the sheet; or if I write over the numbers and symbols along the top margin of the sheet,

a. I will receive a new answer sheet.b. my answer sheet will be unscored or scored incorrectly.

c. I will be required to retake the VRE (or CE).d. my answer sheet will be hand-graded.

5

Chapter 2

10. (306) What functions are involved during the trouble correction phase of troubleshooting and

repair of TV equipment?

a. Disassembly, replacement, repair, and reassembly.b. Disassembly, replacement, repair, evaluation, and reassembly.c. Disassembly, repair, reassembly, and inspection.d. Disassembly, replacement, reassembly, and inspection.

11. (304) What unit of TV test equipment is used for contrast, deflection linearity, low-frequencyphase shift, and resolution tests?

a. The waveform monitor. c. The grating generator.b. The monoscope amplifier (camera).. d. The multiburst generator.

12. (306) What steps (not necessaiily in logical order) are it:volved in the systematic process of

troubleshooting and repair of TV equipment?

a. Trouble localization, trouble analysis, disassembly, correction, and reassembly.b. Disassembly, replacement, repair, and reassembly.

c. Symptom recognition, correction, trouble localization, symptom analysis, and trouble analysis.

d. Symptom recognition, trouble analysis, disassembly, repair, and reassembly.

13. (304) Which of the following units of test equipment are used for color testing?

a. The vectorscope, color signal analyzer, and lenearity checker.b. The vectorscope,.color signal analyzer, and multiburst generator.

c. The ve:.torscope, monoscope amplifier, and color-bar generator.d. The vectorscope, video sweep generatot, and linearity checker.

14. (305) What video quality tests can be made using the EIA resolution test pattern?

a. Streaking, interlace, aspect ratio, and color fidelity.

b. Gray-scale rendition, aspect ratio, streaking, and geometric distortion.

c. Interlace, aspect ratio, frequency response, and color fidelity.

d. Aspect ratio, shading, vertical resolution, and horizontal amplitude.

15. (307) Who, is responsible for processing new items of precision-measuring equipment through the

PMEL?

a. The PMEL.u. Base supply.

I. (307) Why are quality checks necessary?

a. To prevent equipment damage.b. To complete repairs.

c. The using organization.d. The Calibration and Meteorology Division.

c. To discover poor workmanship.d. To increase training needs.

rJ ki20

5o ?

a 561:-

17. (305) What is the best method of troubleshooting a color-bar generator?

a. Voltage checks. c. Resistance checks.b. Signal tracing with an oscilloscope. d. Pulse amplitude checks with an oscilloscope.

18. (307) Why are alternate checkout methods less desirable than bench mockups?

a. Increased time outage of the operational equipment.b. Increased repair time.c. Scheduled programming is interrupted.d. Test equipment must be set up when it is used.

19. (306) Why are detailed maintenance procedures written?

a. To complete proper alignment and calibration of the equipment.b. To complete the proper PMI's.c. To insure completion of all necessary maintenance tasks.d. To complete all necessary alignment procedures.

20. (306) What conditions do recurring malfunctions usually indicate?

a. Faulty circuit design and modification.b. Unrepaired circuit components and excessive equipment failures.c. Unrepaired circuit components and modifications.d. Faulty circuit design and unrepaired circuit components.

Chapter 3

21. (308) A monitor has erratic tearing of the horizontal image. Which of the following groups is mostlikely the cause?

a. Monitor (horizontal oscillator), transmitter, and sync generator.b. Distribution amplifier, camera, and sync generator.c. Monitor (horizontal oscillator), distribution amplifier, and sync generator.d. Monitor (horizontal oscillator), power supply, and sync generator.

22. (309) What would be the most correct symptoms if a monitor input were to become shorted?

a. No video presentation and a blown fuse in the distribution amplifier.b. No video presentation on one monitor, but all others would be normal.c. There would probably be a weak video signal present on the monitor.d. The video signal would have a vertical roll due to change of impedance.

23. (310) How would the incoming signal to a color TV receiver be affected if the antenna cableconductor is broken?

a. The video will become weak. c. Only the color burst signal will be lost.b. All incoming signals will be lost. d. The audio will become weak.

24. (309) Which of the following systems would normally use an r-f exciter unit to generate a carriersignal to he modulated by video?

a. Sin Oe camera and monitor, used for doorway surveillance.b. Studio camera to tape machine for making tapes.c. Studio-to-transmitter relay.

Switcher to tape machine for making Wises.

21

513

616

MODIFICATIONS

elf o2c3-0,)4 of this publication has (have) been deleted in

adapting this material for inclusion in the "Trial Implementation of a

Model System to Provide Military Curriculum Materials for Use in Vocational

and Technical Education." Deleted material involves extensive use of

military forms, procedures, systems, etc. and was not considered appropriate

for use in vocational and technical education.

7s.LIST OF CHANGES

COURSENO.

30455EFFECTIVE DATEOF SHIPPING U.ST7 Apr 76

CAREER FIELDS. POLICIES. PROCEDURES AND EQUIPMENT CHANGE. ALSO ERRORS

OCCASIONALLY GET INTO PRINT. THE FOLLOWING ITEMS UPDATE AND CORRECT

YOUR COURSE MATERIALS. PLEASE MAKE THE INDICATED CHANGES.

. CHANGES FOR THE VOLUME WORKBOOK: VOLUME lA

e. Page 35, Special Situation instructions preceding question 64, line 1:

Change "test" to "text." Line 2: Change "as folloWb" to "initially for each

question."

f. Page 36, Special Situation instructions, question 68: Change "up as

follows"%o "initially for each question."

g. The following questions are no longer scored and need not be answered:

32 and 36.

8. CHANGES FOR THE VOLUME WORKBOOK: VOLUME 2

a. Page 30, Chapter Review Exercise, answer 11: Change "radiated" to

"received."

b. The following questions are no longer scored and need not be answered:

24 27 and 67.

9. CHANGE FOR THE VOLUME WORKBOOK: VOLUME 3

The following questions are no longer scored and need not be answered:

22, 40 and 45.

NOTE: Change the currency date on all volumes to "15 December 1974."

51

rage 4 of 4 )

L

LIST OF CHANGES

COURSENO.

30455

EFFECTIVE DATEOF SHIPPING UST

7 Aor 76

CAREER FIELDS, POLICIES, PROCEDURES AND EQUIPMENT CHANGE. ALSO ERRORSOCCASIONALLY GET INTO PRINT. THE FOLLOWING ITEMS UPDATE AND CORRECTYOUR COURSE MATEFIIALS. PLEASE MAKE THE INDICATED CHANGES.

1. CHANGES FOR THE TEXT: VOLUME 1

a. Preface, page iii, line 2: Change sentence to read ". . . achievement of5-level proficiency." Lines 4 and 5: Delete sentence which reads "If you aretraining to . . . in additign to this course." Lines 7 and 8: Change sentenceto read "Such items are contained in CDC 30000 for 5-skill level training."

b. Page 6, Fig 1: At the 5 skill level, change "1098" to "2095." At the7 skill level, change "1098" to "2096."

c. Page 51, col 1, line 3: Change "you will" to "possibly."

d. Page 90, Fig 83: Change secondary of input transformer to center tapped.Label upper transistor Ql and lower transistor Q2. Add tie point at the junctionof the emitters of both transistors and ground.

2. CHANGES FOR THE CHANGE SUPPLEMENT: VOLUME 1 (30455 01 S01 0569)

a. Page 1, col 1, lines 8 and 9: Change °Tech Tng Ctr (TSOC), Keesler AFB,MS 39534" to "USAF School of Applied Aerospace Sciences (TTOX), Lowry AFB, CO80230."

b. Page 1, under "Workbook" changes: Beginning with page 18, changes shouldbe reflecte under Changes for the Text.:

c. Page 1, Changes for the Workbook, line 5: Delete "Change CDA to DCA."

3. CHANGE FOR THE TEXT: VOLUME lA

Page iii, lines 24 and 25: Change "Tech Tng Ctr (TSOC), Keesler AFB, MS39534" to "USAF School of Applied Aerospace Sciences (TTOX), Lowry AFB, CO 80230."

I. CHANGE FOR THE TEXT: VOLUME 2

Page iii, lines 20 and 21: Change "Tech Tng Ctr (TSOC), Keesler AFB, MS39534" to "USAF School of Applied Aerospace Sciences (TTOX), Lowry AFB, CO 80230."

5. CHANGE FOR THE TEXT: VOLUME 3

Page iii, lines 15 and 16: Change "Tech Tng Ctr (TSOC), Keesler AFB, MS39534" to "USAF School of Applied Aerospace Sciences (TTOX), Lowry AFB, CO 80230."

6. CHANGES FOR THE VOLUME WORKBOOK: VOLUME 1

a. Pdge 7, Chapter Review Exercise, question 10, line 3: Change "(7; Fig. 31)'

(Page 2 of 14 )

COURSENO.

LIST OF CHANGES

30455

EFFECTIVE DATEOF SHIPPING UST

7 Apr 76

CAREER FIELDS, POLICIES, PROCEDURES AND EQUIPMENT CHANGE. ALSO ERRORS

OCCASIONALLY GET INTO PRINT. THE FOLLOWING ITEMS UPDATE AND CORRECT

YOUR COURSE MATERIALS. PLEASE MAKE THE INDICATED CHANGES.

6. CHANGES FOR THE VOLUME WORKBOOK: VOLUME I (Continued)

to "(7-9; Fig. 31)." Question 11, lines 2 and 3: Change "I6-17-Kc" to "16.7Kc.".

b. Page 8, Chapter Review Exercise, question 13, line 1: Change "31" to "30."

c. Page 11, Chapter Review Exercise, question 21, lines 3 and 4: After "no"

add "horizontal."

d. Page 14, Chapter Review Exercise, question 22, col B: Change "grid" to

"heater" in choice b.

e. Page 18, Chapter Review Exercise, question 16: Change "How can the color

camera TO be adjusted?" to read "What provision is made to equalize the gain of

the TO tubes in a color camera?"

f. Page 22, Chapter Review Exercise, col 2, answer 10: Change "(7; Fig 31.)"

to "(7-9; Fig 31.)"

g. Page 24, Chapter Review Exercise, answer 12, line 3: Change "(at TP3)"

to "(at TP6)." Answer 17, line 2: Change "oscillator" to "monitor."

h. Page 34, question 69: Change "(121)" to read "(122)."

i. The following questions are no longer scored and need not be answered:

9, ul and 63.

7. CHANGES FOR THE VOLUME WORKBOOK: VOLUME lA

a. Page 7, Chapter Review Exercise, question 25: Change "(10-10)" to

"(10-15)." Question 26: Change "(10-15)" to "(10-13)."

b. Page 20, Chapter Review Exercise, answer 26: Change "control" to

"management." Answer 29: Change "310E" to "210E."

c. Page 21, Chapter Review Exercise, answer 40: Change "213" to "187."

Answer 43: Change "extra copy" to "a shop."

d. Page 24, Chapter Review Exercise, answer 23: Change " 10 " to

104.73 X 105

4.73 X 10 Answel, 29: Change "TO 33K-1-01, Calibration Procedures and

Responsibilities" o "TO 33K-1-100, Responsibilities and Calibration Measurement

Areas."

(Page 3 of 4 51 J

cc'