a-678_327309_v1.pdf - SMARTech

GEORGIA INSTITUTE OF '"TEChNOLOGY Engineering Experiment Station

. PR_OJECT INITIATION

Date June ll, ~96 3 ••••• ~ ~ ....... " ........... 4 " ........... " • • • • • • • • • • • • .. • • • • • • • • .. • • •

Project Title: Electronic Equipment Interference Characteristics - Communication Type

project No.: A..-678 :~-.:~;~~· '

.t·-- ,, Sponsor: Department of the Army 1 Signal .. Corps

Effective: ........ ?.:-:~~?} ... ~ ............................................ Estimated to run until:

., .. ~\ ... *Anticipatory Costa Permitted /;from 2-15-63 to this date.

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Amount: Estimated· Total of· $1591 880.00 of which $99,660.02 has been allotted

Reports: Monthly Letter Reports · •· ;. Quarterly Progress Reports

Final Report · .. Directory Ma.nusc,;,:i:pt __ ,_ .... ,.. .. ---·· .. -·-·-~-~·-·--~·~"·

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contact~:Pe'~son: u.s.Army Electronics Ms.terial Agency · Fort Monmouth.Procurement Office

Fort Monmouth, New Jersey

Attn: Contracting·. Offi,~~r (for admin. :matters)

U.S.Army Electronics ResearCh & Development Laboratory

Attn: '-~~j~~u~?~ New J~rsey

~chn~ matters)

· Assigned to .Communicat.ions .. .BI:an.oh, ... Ele.o.t.rnn..:l..c.~ ........................... Di v lsi on

COPIES TO:

0 Project Director Technical Information Section

0 Director

0 :;. '

Associate Direotor

0 Assistant Director(s)

. Photographic Laboratory •. ; ... 0 ;;s9Pp ., ·. ·.( , .·. . <~ .. ~/;·

~ecuri~/om~er .

D. Division Chiefs ;•' .>·' 0 Accounting '.

0 Branch Head Purchasing

General Office Services Repprt Section ·

Rich Electronic Computer Center D Library

· .: · 0 Engineering Design Services ·. ,·

S Form 400 (Rev 10-62)

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GEORGIA· INSTITU#rE OF TECHNOLOGY

Engineering Experiment Station

PROJECT TERMINATION

PHOJECT TITLE:

PROJECT NO:

PHOJECT DIHECTOR: ~ W. R. Free

SPONSOH: D.;;pt. o.f the Ar.tly, Sign~1l Corp. 9-3o-56

TEHMINATION EFFECTIVE:---------------

October 7, 19'5·S Date---------

CHAHGES SHOULD CLEAH ACCOUNTING BY: All chnrges ha.ve clettred

COPIES TO:

Project Director

Director

Associate Director

Assistant Directors

Division Chief

Branch Head

Accounting

CB, E.

Engineering Design Services

l. /' · Avl ·~'t~l':~ ofi ' /\g~(" General Office Services i i V 'i;

Photographic Laboratory

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Technical Information Section "'YJJ (llY ~ri'ty

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Form EES 402 (R 10-62)

GEORGIA INSTITUTE OF TECHNOLOGY ENGINEERING IDCPERIMENT 8TATION

ATLANTA 13, GEORGIA

3 April 1963

Department of the Army Headquarters U. S. Army Signal Research and Development Laboratory Fort Monmouth, New Jersey

ATTN: Jv'"JX. Sidney Weitz, SELRA/ SL-GFE

L.

SUBJ: Monthly Letter Report No. 1, 15 March 1963, "Electronic Equipment Interference Characteristics, Connnunication Type."

REFERENCES: (l) RFP No. AMC-36-039-63-l2L~24-9l

Gentlemen:

(2) Georgia Tech Research Proposal dated 18 February 196~ (3) Telegram dated 7 March 1963. Contracting of:'icc

SELMA-FMB-lAlB. Intention of Contracting Office·~· to authorize anticipatory cost beginning 15 February 1963 under any contract resulting from RFP No. AY~-36-039-63-12424-91.

The program of research in Electronic Equipment Interference Characteristics, Communication Type, is continuing. The work is over and beyond the work performed under Contract DA-36-039-sc-87183.

Studies are being conducted on cochru1nel CW and pulse interference to a connnunications system utilizing the .AN/TRC-29 and AN/TCC-13 sets. A GEL speech system test set is being used to determine the pattern correspondence index of a speech sample passing through the system.

Case radiation studies have been conducted on the AN/GRC-50 transmitter. The results indicate that steps should be taken to reduce the strength of signals emanating from the upper-right air duct of the high-band tuning head.

Several types of diode mixers are being tested and the resulting data are being processed and analyzed. An objective of the mixer evaluation is to try to find methods for mixer data prediction utilizing only a few measured data points.

Approved:(!

L.ttJ./({e~~ D. W. Robertson, Head Communications Branch

Respectfully submitted:

~?},p E. W. Wood Project Director

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GEORGIA INSTITUTE OF TECHNOLOGY ENGINEERING EXPERIMENT GTATlON

ATLANTA 13. GEORGiA

16 April 1963

Department of the Army Headquarters U. S. Army Signal Research and

.Development Laboratory Fort Monmouth, New Jersey

ATTN: Mr. Sidney Weitz, SELRA/SL-GFE

SUBJ: Monthly Letter Report No. 2, 15 April 1963, "Electronic Equipment Interference Characteristics, Communication Type.''

Dear Mr. Weitz:

Mr. E. W. Wood attended the 1963 IEEE International Convention at New York City on March 25-28. The paper, "-The Spectral Behavior of Spurious Responses," was presented.

}tr. E. W. Wood visited Fort Monmouth on March 29 to discuss the progress made in the research program of E.lectronic Equipment Interference Characteristics since February , 1963.

Further testing has revealed that the AN/GRC-50 receiver should meet the designed specifications on noise figure throughout the high band.

The results of analyses of the gathered mixer data indicate that incoming signal harmonics cause serious measurement problems. Additional ideas are being formulated which should lead to better. spurious response estimation.

Plans are being made to possibly include in the First Quarterly Report the results of the work done in the following areas of investigation:

1. Transmitter tests 1.1. Case radiation 1.2. pitfalls

2. Receiver Tests 2.1. pitfalls

3. Systems Tests 3.1. Improvements on the GEL machine 3.2. System S/N versus PCI 3.3. CW and pulse interference effects

·.

Monthly Letter Report No. 2

4. Mixer Evaluation

- 2 -

4.1. Effects of harmonics

16 April 1963

4~2. Comparison of data taken on several different diodes

5. Computer Techniques 5.1. Discussion of need for an automated spurious

response selection program to aid receiver design engineers 5.1.1. Crossover spurious responses 5.1.2. p = q spurious responses 5.1.3. responses in 2nd and 3rd

conversion stages

Work has been initiated to our RFI literature abstract file up-to-date. Plans are to include a second b as an appendix to the Second Quarterly

Several are being considered as possible papers at the Tri-Service Coaference. ~nong the s are: Mixer Evaluation and Systems Tests. Abstracts for at least one paper will be submitted for security approval around 15.

D. W. Robertson, Head Communications Branch


E. W. Wood Project Director

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GEORG~A T:::C~-H\!OLOGV

ENG!NEE:~ING :;:x?E~IMENT SThTION

ATLANTA 13, GEORGiA

6 June

Accountable Property Officer

Supply Officer, USAELRDL 2504, Charles Wood Area

Fort Monmouth, New Jersey

Sciences. Department, Interference Branch at Destination

Order No. 5871-PM-63-9ln

ATTN: Mr. Sidney Weitz, SELRA/GFE

SUBJ: Monthly Letter Report No. 3, 20 15 to YJ.ay 1963, Contract No., DA ) , 11Electronic

Interfere::.'1CC C!J.aracteristics' Communication Type. rr

Gentlemen:

Further receiver testing has revealed that from the AN/GRC-50 ccrMrrunications and third order intexmodulation tuned are identified to

sho\v rejection values greater including the image and IF fre

(P)/GRC receiver than 95 db second

responses near the second conversion -~1 other s~urious

db. 'rhese spectrum signature data appear are rejected more

to result from the u~ilization of a duplexer; a

preceding the first

1.-re re made on t~1.e

different C~l and ICTrJ ments -vrere J::.ade for CW interference at

and a tclei~le

system a~ciio S/N measure

and pm·rel"' levels, Index and S/N was deter

interference data exenylify and a between Pattern Corres~~on,ae:nc!e mined. The techniques used to obtain these C1,'! the need for an automatic voice is valid for both linear and nonlinear

ins trum.en t -vrlli ch interference conditions.

A and apparently reliable responses has been found which indicates

method of mixer spurious of mixer conformity to

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Monthly Letter No. 3 - 2 - 6 June 1963

existing mixer Diode mixers, regardless of the make or manufac-ture of the diode, appear to have ~ost identical relative characteristics 1dth a shift in the relative diode bias.

The First Report is being prepared and the number of draft copies \dll be forwarded in June.

Approved:

I : {) I .~ ,/:_ ,,l{i{U. v'-'



'i~)~//(;~:;r-;;;_ E. W. Wood Project Director

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I

GEORGIA INSTITUTE OF TECHNOLOGY ENGINEERING EXPERIMENT STATION

ATLANTA 13. GEORGIA

19 July 1963

Activity Supply Officer, USAELRDL Building 2504, Charles Wood Area Fort Monmouth, New Jersey

MARKED: 11For Engineering Sciences Department, Interference Branch Inspect at Destination Order No. 5871-PM-63-91"

ATTN: Mr. Sidney Weitz, SELRA/GFE

SUBJ: Monthly Letter Report No. 4, 20 July 1963, Report period 15 June to 15 July 1963, Contract No. DA 36-039 AMC-02294(E), "Electronic Equipment Interference Characteristics, Communication Type."

Gentlemen:

A quantitative study is being made of pulse-type interference on the AN/GRC-50 receiver. The HP-614A and TS-4o3/U signal generators were modified to obtain linear FM deviation up to the receiver rated deviation.

An investigation of impulse-type interference to an AN/GRC-50 receiver has shown that this receiver is not susceptible to impulse-type interference for levels up to 85 db/~v/Mc. The impulse generator used in the NF-105 NFIM was modified to obtain the impulse interference.

Multipath transmission delay of 0.25 ~sec has been achieved with the ill~/TRC-29 communications system. An effort will be made to simulate longer delays. Predicted intelligibility measurements as a function of the ratio of power levels between the direct and delayed signals will be made for various delay times and various received signal levels. The measurements will be made using the GEL machine. From these measurements, an attempt will be made to validate the predicted PCI versus S/N ratio concept presented in Quarterly Report No. 1 for this type of interference.

A statistical evaluation for determining the theoretical maximum error in predicted mixer spurious response data has been made. In addition, previously measured and predicted mixer data are being statistically analyzed to determine the accuracy of the predicted values. The results obtained by these statistical methods indicate measurement difficulties which are now

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Monthly Letter Report No. 4 - 2 - 19 July 1963

being investigated. Further measured data are needed for a complete evaluation of the mixer prediction method.

Over 14oO abstracts related to the RFI field have been folli~d in more than 50 publications. It is suggested that the second bibliography of RFI abstracts be published as Volume 9 of the Manuscript of Catalogue.

Approved:

,£, ?J, (?tj;;;j;;V\ D. W. Robertson, Head Communications Branch


E. ~-!. Wood Project Director

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ATLANTA 13, GEORGIA

16 August 1963


MARKED: "For Engineering Sciences Department, Interference Branch Inspect at Destination Order No. 5871-PM-63-91"

ATTN: Mr. Sidney Weitz, SELRA/ GFE

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SUBJ: Monthly Letter Report No. 5, 20 August 1963, Report period 15 July to 15 August 1963, Contrl\.ct No. DA 36-039 AMC-02294(E), "Electronic Equipment Interference Characteristics, Communication Type."

Gentlemen:

Two signal tests are being conducted on the R-1148(P)/GRC receivers. Pulse, AM, and FM signal generators are being used as interfering sources.

Multipath propagation studies are continuing on the AN/TRC-29 and AN/TCC-13 communications system. It has been found that for a path delay of 0.25 ~sec, the S/N ratio at the output of a multiplexer channel depends not only on the relative power, but also on the relative phase angle between the direct and delayed path RF signals. Predicted PCI measurements as a function of relative power have been made for two conditions of receiver quieting and four different relative phase angles.

Since the wavelength of the tuned frequency is approximately 5.3 inches, very small path length changes such as that caused by temperature change at any point along the delayed path cable have been found to cause significant changes in phase angles. This extreme sensitivity in the path length precludes any measur~ments with the GEL machine since they would require a constant phase angle over the length of a data run. Thus, no further data have been taken to substantiate the predicted--measured PCI relationship.

It is important to note that under every relative power level condition at both quieting levels tested, a wide range of phase angles exists at which the predicted PCI was 100 per cent. This indicates that 0.25 ~sec is not a sufficient delay to cause significant degradation of intelligibility for this communications system. Cables for achieving path delays greater than

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Monthly Letter Report No. 5 - 2 - 16 August 1963

0. 25 IJ.Sec have been acquired and further multipath te·sting will follow.

The results of the statistical evaluation for determining the accuracy of predicted values of mixer data have not been completed. The investigations of prior indicated measurement difficulties have revealed that extremely fine control of input levels and the IF response indicator are necessary for repeatable mixer measurements. Additional factors such as equipment level stability and the fact that some responses are near relative "holes" contribute to the inaccuracy and nonrepeatability of the mixer datao

Mr. Sidney Weitz and Mr. R. L. McKenzie from USAELRDL visited Georgia Tech on 16-18 July for a technical discussion.

Mr. Warren Kesselman fro~ USAELRDL visited Georgia Tech on 30-31 July to discuss project progress made during the second quarter of the research program.

Mr. J. T. Ludwig, Mr. Martin Sherman, and Mr. I. N. Mindel from IITRI, Chicago, Illinois, visited Georgia Tech on 30 July. The nonlinear effects of dummy loads and the results of current mixer studies were discussed.

The paper "The Behavior of Nonlinear Mixing" to be presented at the Ninth TRI-SERVICE Conference on RFI Compatibility has been forwarded for approval for unclassified presentation.

Plans are to prepare a paper on "The Effects of Multipath Interference on the Intelligibility of Transmitted Speech Over an FM System Employing Time Division Multiplexing" by c. w. Stuckey and E. W. Wood, for presentation at the 1964 IEEE International Convention. The abstract and summar,y for this paper will be forwarded during August for approval.

Quarterly Report No. 2 is being prepared and will be forwarded in September.

. Approved: /)

]J.f;J./(a~ D. W. Robertson, Head Communications Branch



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GEORGIA INSTITUTE OF TECHNOLOGY IINGINKDING IIXPIIJtiiiDIT IITA'nGII

ATLANTA 13. GEORGIA

18 October 1963

Activity Supply Officer, USAELRDL Building 2504, Charles Wood Area· Fort'Monmo~th, New Jersey

MARKED: "For Engineering Sciences Department, Interference Branch ·Inspect at Destination Order No. 5871-PM-63-91"

ATI'N: Mr. Sidney Weitz, SELRA/GFE

SUBJ: Monthly Letter Report No. 6, 20 October 1963, Report Period 15 September to 15 October 1963, Contract No. DA 36-039 AMC-02294(E), '~lectronic Equipment Interference Characteristics, Communication T.Y:Pe. "

Gentlemen:

A Hewlett-Packard signal generator, Model 8614A, has been evaluated at our laborator,y following a demonstration of several equipments by Hewlett-Packard's field representatives. It was found'that this generator is 'capable of linear frequency modulation characteristics up to ±3 Me over the tuned frequency range from 1600 to 2660 Me. Plans are to obtain the 8614A .signal generator to aid in further evaluation· ·tests on the .AN/TRC-29 sys.tems.

Since multiplexer e~uipments or PCM simulators are not currently available for use with the ANfGRC-50 systems, PCM signals are being simulated which approximate the known characteristics of the MUltiplexer Set AN/TCC-44. These simulated signals will be used to evaluate the characteristics of the ~/GRC-50 system when operated in the PCM mode.

Multipath interference data for delays up to 1.4 JlSec have been ·collected on the AN/TRC-29 and AN/TCC-13 system and are being analyzed. The variable parameters used in the test configuration were 1) the delay time between paths or path length differences, 2) the relative power levels between paths, 3) the absolute power level or receiver quieting, and 4) the relative phase angle between paths. The audio output S/N ratio was measured under various test conditions and used to predict the intelligibil-

. ity of received isolated monosyllabic words. Further work is being done to locate the various receiver' and demultiplexer stages where degradation of the desired signal in the presence of multipath interference occurs.

\ '

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. ' Monthly Letter Report No. 6 -2- 18 October 1963

Additional mixer data taken on germanium diode mixer configurations are being ·.analyzed. An attempt is being made to develop a technique for obtaining universal mixer parameters .for germanium mixers which are valid up to the tenth order of generation. A vacuum tube mixer is being designed

. which utilizes fer:rite-core, toroidal components to obtain the de~ired input and output impedance characteristics.

The preparation of·Volume '9 of the Manuscript of Catalogue is continuing.

Mr. E. W. ~ood visited the Electromagnetic Compatibility Analysis Center, Annapolis, Maryland, on 3-4 October 1963. Mr. Wood attended a meet·ing·on spectrum signatures and visited the technical information facilities at the center.

75°~~:~{~~ D. W. Robe.rtson, Head Communications Branch

RespectfUlly submitted:

~9 E. W. Wood Project Director

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, GEORGIA INSTITUTE OF TECHNOLOGY.

ENCIINEERING EXPERIMENT STATION

ATL.ANTA 13, GEORGIA

18 November 1963


MARKED: "For Engineering Sciences Department, Interference Branch Inspect at Destination Order No. 5871-FM-63-91"

ATTN: Mr. Sidney Weitz~ SELRA/GFE

SUBJ: Monthly Letter Report No. 7, 20 November 1963, Report Period 15 October to 15 November 1963, Contract No. DA 36-039 AMC-02294(E), "Electronic Equipment Interference Characteristics, Connnunication Type."

Gentlemen:

An Empire Devices preselector, Model PF-190C tunable from 3.9 to 7.2 kMc, has been evaluated at our laboratory. It was found that a spurious passband exists between the preselector tuned frequency and the second harmonic frequency. In addition, other spurious passbands exist between the second and third harmonic frequencies, and below the "sub-harmonic" frequency for any dial setting. The attenuation at these spurious passbands ranges from 4 to 30 db, depending upon the dial setting. This preselector was returned for factory diagnosis and reduction of the spurious passband between the fundamental and second harmonic frequencies. Two additional preselectors have been ordered and are scheduled for delivery in November: the Empire Devices Model PF-190D and the Frequency Engineering La.boratories Model 200CC. The ulitization of these and other preselectors should permit measurements of preselected signals, such as those found in intermodulation and spurious emissions tests, for improved testing limitations. A Hew·lett-Packard signal generator, Model 8614A, has been ordered and should be delivered during January 1964.

The preselector utilized in the AN/GRC-50 receiver has also been evaluated.. The measured data show a spurious passband between the second and third harmonic frequencies. 'Ihis band-pass filter, however, used in conjunction with a low-pass filter with a cutoff frequency near 1900 Me provides the spurious signal rejection reported in Monthly Letter Report Noq 3.

The analysis qf the collected multipath interference data is completed for delays up to 1.4 ~sec which correspond to path length differences up to 0.26 mile. Based on a system expected to operate over a range in excess of 20 miles, the free space attenuation of the desired and reflected signals will be essentially identical at these path length differences; therefore,

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Monthly Letter Report No. 7 -2- 18 November 1963

the relative direct to reflected (delay) path power level will depend predominantly on the efficiency of the reflecting surface{s). It was found that significant degradation in predicted intelligibility can occur for the relatively small delay times used in the multipath tests on the available FM system which ulitizes PPM or TDM.

The completion of the evaluation tests on available PPM/FM communications systems is· scheduled at the end of the fourth quarter's effort. The tests and test procedures resulting from these PPM/FM system studies will then be combined with the procedures developed during the evaluation tests on the PCM/FM systems on hand. Further knowledge acquired regarding the PCM signal requirements for the AN/GRC-50 systems necessitates additional circuitry for simulating and detecting the information pulses. The feasibility of constructing the desired circuitry and, in addition, devising an error rate detector for the system will be investigated.

An attempt to derive mixer polynomial coefficients using measured diode current versus input voltage relationships yielded similar results as those established in Report No. 1, July 1963, under contract DA 36-039 AMC-02200(E). It was found that the computer round-off of digits due to the "single-precision" computer techniques currently available and the measurement limitations prohibited the assurance of reliable computed polynomial coefficients for the method selected. This work was instigated prior to the receipt of the report, and is being abandoned at this time to avoid duplication of effort in this area. A simplified approach is expected to avoid the laborous computations necessary to obtain coefficients of responses arising from the use of an nth degree polynomia~ as a mathematical model of mixer characteristics.

Analytical studies are being made on an "envelope recovery" type mixer to determine the possibilities of this configuration for improved mixer spurious rejection. The particular mixer being examined is theoretically similar to the experimental mixer discussed in the Final Technical Report under contract DA 36-039 sc-87183. Preliminary testing on a vacuum tube mixer being designed with input and output torodial components indicates that additional shielding between components will be necessary before the mixer will be ready for a. critical evaluation.

The preparation of Volume 9 of the Manuscript of Catalogue is continuing after a delay pending the receipt of written permission from European and domestic publishers to publish their RFI related abstracts. The preparation and proof-reading of the duplication masters of the RFI bibliography, which should contain over 300 pages, are approximately 60% completed.

,


Quarterly Report No. 3 is being prepared and will be forwarded in December. The final results of the multipath interference studies on a PPM/FM system will be reported. Emphasis will be placed on the usage and importance of previously reported information regarding reduction and prediction methods for spurious signals generated in communications receivers.

The abstract and summary of the paper on "The Effect of Mul tipath Interference on the Intelligibility of Speech Transmitted Over an FM System Employing Time Division Multiplexing" by Charles W. Stuckey and E. W. Wood was submitted to the 1964 IEEE International Convention Program Chairman a:rter the receipt of the required clearance of the materials.

Mr. R. D. Trammell, Jr., and Mr. E. W. Wood attended the Ninth TRISERVICE Conference on Electromagnetic Compatibility held in Chicago, Illinois, on 15-17 October 1963. Mr. Trammell presented a paper on "The Behavior of Nonlinear Mixing 11

•

Approved:

-~ . tJ. e~]i;;;c D. W. Robertson, Head Communications Branch

RespectfUlly submitted:


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, GEORGIA INSTITUTE OF TECHNOLOGY

ENGINEERING EXPERIMENT STATION

ATLANTA 13. GEORGIA

15 ~Ta.nuary 1964


MARKED: "For Engineering Sciences Department, Interference Branch Inspect at Destination Order No. 5871-PM-63-91"

ATTN: Mr. Sidney Weitz,

SUBJ: Monthly Letter Report No. 8, 20 January 1964, Report Period December 1963 to 15 January 1964, Contract No. DA 36-039 AMC-02294(E), 11Electronic Equipment Interference Characteristics, Connnunication Type.u

Gentlemen:

A Frequency Engineering Laboratories band-pass filter, Model A200CC tunable from 2 to 4 kMc, has been evaluated for conformity to specifications. Multiple spurious pa ssbands were noted above the tuned frequency, and several lie between the tuned frequency and the second harmonic. The passband selectivity is well within specifications but rejection to the third harmonic is below specification a.t the high end of the tuning range. This filter was accepted regar<il.ess of failure to meet specifications since, in conjunction with the low·-pass filters presently on hand, the unit can be used for the desired intermodulation tests. Further delay of these tests is intolerable in view of the limited time remaining for spectrum signature investigation.

An investigation of mixer acti•rity using an exponential mathematical model has shown little promise. Neither series nor exponential solutions to mixer activity give sufficient explanation of the recurring nulls in the harmonic and spurious response levels which are evidenced by factual data. These nulls occur with respect to bias level and are adequately explained using a Fourier analysis of the output waveform. A suitable ma.thematical model of the mixer must explain these nulls and demonstrate their occurrence w·ith changes in bias level.

Attempts to show· that vacuum tube mixers follow the law'S of prediction applicable to diode mixers has thusfar been unsuccessful. The chief problem appears to stem from the difficulty of coupling 500 generator and detector sets to the high impedance vacuum tube circuits. Higher local oscillator voltages are required for vacuum tube operation than for diodes and such levels are difficult to obtain with 50D equipment. Further attempts will be made using modified circuits and techniques.

Monthly Letter Report No. 8 -2- 15 January 1964

The preselector of a typical 1.6 to 2.3 kMc FM receiver was evaluated in order to determine those frequencies most likely to create IM or spurious responses in the receiver. It was found that the combination of the duplexer and the preselector has approximately the same characteristic as the preselector itself when the interconnecting cable provided with the receiver is used to couple the duplexer to the preselector. The use of different length cables to interconnect the two units causes alteration in some of the spurious preselector peaks by as much as 40 db. The preselector-duplexer characteristic is extremely helpful in locating intermodulation products on this type of equipment.

Initial attempts to establish the spurious response levels of the receiver utilizing the preselector characteristic and mixer characteristic data previously assembled for the 1N21B diode mixer are promising. All spurious responses detected for this equipment fall in the spurious passbands of the preselector with exception of the very large mixer responses which can be detected rather far down on the preselector characteristic. The measured and calculated spurious response levels for this equipment are markedly similar over the limited range of prediction values available. This tion technique will be extended in range by data extrapolation and the values compared to the actual measured response levels. Successful prediction can cut the time required for spurious response determination on this type equipment by a considerable margin, since preselector measurement is generally less tedious than spurious response level determination.

Volume 9 of the Manuscript of Catalogue is bound in the final editor 1 s copy. The final required copies should be forwarded by 17 January 1964.

:Mr. Sidney Weitz and :Mr. Guy Johnson of USAELRDL, Fort Monmouth, New Jersey, visited the Communications Branch on 16-17 December 1963 to discuss project progress. Project effort to that date and opinions as to work required were presented by Georgia Tech personnel.

The paper on Effect of Multipath Interference on the Intelligibility of Speech Transmitted Over an FM System Employing Time Division Multiplexing, 11

has been accepted by the IEEE INTERNATIONAL CONVENTION program committee for presentation during the propagation session of the program.

Approved: /-1 , !. ' ' l t /1},·&i~ l'.:.. i '


Respectfplly,;submitted: / I '/ .,

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~ R. D. Tran:rrnell, Assistant Project Director

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ATLANTA 13, GEORGIA

18 February 1964


W.RKED: "For Engineering Sciences Department, Inter:ference Branch at Destination"

ATTN: Mr. Guy- Johnson, SEL-qA/GFE

SUBJ: Monthly Letter Report No. 9, 20 February 1964, Report Period 15 January 1964 to 15 February 1964, Contract No. DA 36-039 AMC-02294(E), "Electronic Equipment Interference Characteristics, Conrrnunication Type."

Gentlemen:

The Empire Devices cavity filter, Model PF-190C, has been received and accepted by our laboratory. The Empire Devices cavity filter, Model PF-190D, scheduled to be delivered last November, has not been received. Such filters may be used to reduce spectrum analyzer spurious responses when transmitter spectrum surveillance tests are oeing conducted.

A new delivery date for a Hewlett-Packard generator, Model 8614A, is now 1 April 1964.

A request to substitute a TVl'I1 , I''.fodel 324D, for two

cavity filters authorized under the contrac:t v1as forwCl.rded to the USAELRDL Contracting Officer on 21 January 1964. The need exists f~r such an amplifier which will deliver more energy than presently availablL ignal generators for testing spurious responses and intermodulation characteristics of the U. s. Army equipments on hand.

A request to acquire excess GSA and DoD property wh-'-c~l .:;&-r: benefit the performance of the work under this contract was forw~rded to SELRA/GFE in January. The suggested procedures for obtaining excess equipments in this manner should entail essentially no cost to the recipients and will not affect the overall contractual requirements and costs in any manner.

Quarterly Report No. 4 is being prepared and th~ appropriate number of copies will be forwarded in March. This report w·ill emphasize the importance of the receiver pre selector and du:plexer :.i..L l"bdUcing spurious

Monthly Letter Report No. 9 -2- 18 February 1964

responses and intermodulation in the U. S. Army receiver equipments on hand. In addition, the report will contain significant data and analyses on diode and vacuum tube mixers.

Tne Final Report, Volu.-ne 1, on 11 Pu.lse Code Modulation Systems" by the Raytheon Company under Contract No. DA 36-039 sc-78148 has been received and evaluated. Tnis report contains information on the PCM multiplexer sets JI.N/TCC-44 and 45 which may be used in conjunction -v;ith the AN/GRC-50 connnunications sets available at our laboratory. It -~-ras learned that the simulated PCM techniques being developed at our laboratory are not completely compatible with techniques employed in the Jh~/TCC-44 and 45 sets which are not available at the present time. This incompatibility, however, is not expected to affect the tests and test procedures derived from the use of the simulated PCM signals.

The last quarter's effort will be devoted primarily to the tests and test procedures being developed for the U. S. Army pulse type con'llunications equipments. Several volumes of the Manuscript of Catalogue are planned which will include all corr~unications equipment spectrum signature data collected during the course of the contract. A volume of the Manuscript of Catalogue is also planned which will combine all mixer investiga~~ons and analyses conducted under this contract.

Volume 9 of the Manuscript of' Catalogue was for-v;arded to USAELRDL in January. This volume was concerned with "A Second Bibliography on Radio Frequency Interference, With Abstracts," and contair·ed over 1150 abstracts, summaries, and references in the field of radio f.~equency interference.

:Mr. E. W. Wood c::ttended the "Sy:r~posium on and Applications, 11 sponsored by the U.S. Arrrry in Huntsville, Alabama, on 4-6 February 1964. NASA Marshall Space Flight Center EMC Division on 6 February 1964.

Measurements--Techniques Missile Support Command, Mr. vlood also visited the at the Redstone Arsenal

Mr. R. D. Trammell, Jr., attended the Southeastern Simulation Council Meeting sponsored by General Electric Company which was held at Cape Kennedy, Florida, on 14 February 1964.

Approved:-; ,_j ,/

~//(/; I ,• / ,-{F'i/ I if"~: , ..

~~- W. ~~be~f~on, Head o~ Communications Branch

Respectfully Submitted:

t:?_/.FLf/::1"1•• V ('';

[//, //~~

E. w. Wood Project Director

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GEORGIA INSTITUTE OF TECHNOLOGY ENQINEERINQ EXPERIMENT STATION

ATLANTA 13, GEORGIA

17 April 1964


MARKED: "For Engineering Sciences Department, Interference Branch Inspect at Destination"

ATTN: Mr. Guy Johnson, SELRA/GFE

SUBJ: Monthly Letter Report No. 10, 20 April 1964, Report Period 15 March 1964 to 15 April 1964, Contract No. DA 36-039 AMC-02294(E), ,.Electronic Equipment Interference Characteristics,

·Connnunication T.ype."

Gentlemen:

The AN/FRC-34 radio relay set has been set up and is being checked out prior to evaluative testing. New procedures will probably be required for this equipment because of the nature of its output.

Case radiation measurements in the microwave region have been conducted on the AN/TRC-29 transmitters with different planes of polarization. The results of these measurements are presently being analyzed.

The methods devised for calculating spurious responses on cavitycrystal types of receiving equipments can be extended to include intermodulation response calculation using methods originated by Steiner. These calculations will be performed and validated by measured data using the AN/TRC-29 receiving equipments. The method, if satisfactory, may eliminate the extremely time consuming intermodulation and spurious response measurements for this type of equipment. Only cavity and crystal measurements would be required.

Tests on a transistor mixer have produced inconclusive prediction results thusfar. Approximately one-half of the tests show good prediction while the other one-half are poor. Transistor damage is suspected as well as poor isolation between generators. These tests should conclude the mixer work under this project.

Monthly letter Report No. 10 -2- 17 April 1964

An effort was initiated on 1 April to construct and compute a MIC and lash-up output data to determine electromagnetic compatibility conditions for the AN/VRC-12 and AN/PRC-25 operating ~n close proximity. Spectrum signature data measured at USAEPG, Fort Huachuca, Arizona, and the computer programs reported in Volumes 6, 7, and 8 or the Manuscript or Catalogue are being utilized in this exercise.

The delivery date for the Empire Devices/Singer tunable band-pass filter, PF-190D, order in 1963 is still indefinite. The Hewlett-Packard generator, Model 8614A, due on 1 April 1964, has not been delivered to date because or klystron difficulties encountered at the factory. The new delivery date is set for 1 May 1964.

Mr. E. W. Wood attended the 1964 IEEE INTERNATIONAL CONVENTION held in New York on 23-26 March 1964. Mr. Wood presented a paper on '~The Effect of Multipath Interference on the Intelligibility of Speech Transmitted Over an FM System Employing Time Division Multiplexing.''

Mr. D. W. Robertson and Mr. E. W. Wood visited USAELRDL, Fort Monmouth, New Jersey, on 27 March 1964. A meeting was held with Mr. Guy Johnson, Mr. R. L. McKenzie, and Mr. Warren; Kesselman in which project progress and technical details were discussed.

Ap]v~~.e~ D. w. Robertson, Head Communications Branch

i:Zlf4 R. D. ~1, Jr. Asst. Project Director

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GEORGLA.. INSTITU-tE o:=- TSCHNOLOGY ENGINEERING G:XPZRIM:::,,~T ST.:...'TION

ATLANTA 13, GEOF-GIA

18 August 1964

Supply Officer, USAEL 2504, Charles Wood Area

Fort I.Corrrnouth, New Jersey

~.Jl.R:KED: "For Engineering Sciences Department, Interference Analysis and Control lu~ee."

ATTI~: Contracting Officer 1 s Designated Representative

SUBJ: Monthly Letter Report No. 11, 20 August 1964, Report Period 15 July 1964 to 15 August 1964, Contract No. DA 36-039 AMC-02294(E), "Electronic Equipment Interference Characteristics, Communication 'Iype. ~~

Gent=..emen:

?ne majority of effort during this reporting period has been concentrated in a =..iterature survey effort. Some 100 reports, papers, and references have 8een located and are being analyzed and abstracted--these references cover screen room fabrication techniQues, shielding effectiveness, anechoic chambers, absorbing materials, screen room measurement techniques, and cross-polarized antenna configurations.

Measure:nents are being conducted in a screen room (12'x8'x8') in an attempt to determine the field distribution within the room and the changes in the field distribution as a function of frequency.

An investigation of absorbing materials is in progress. A nQ~ber of absorbing materials have been obtained in sample quantities for evaluation purposes. Data and sample quantities of other materials will be obtained from a number of vendors.

P~1 investigation of cross-polarized antenna configurations is in progress. The characteristics and availability of broadband hybrid couplers, for inclusion in orthogonal antenna configurations, over the frequency range of interest are presently being investigated.

V~. E. E. Donaldson attended a meeting at the Electromagnetic Compatibility Analysis Center, Annapolis, Maryland on July 30? 1964, at the request of Mr. W. A. Kesselman, USAEL, to discuss the mixer work conducted at Georgia Tech and ECAC Special Test No. 7 (Stuqy of Receiver Mixer Characteristics).

~·_::·

1-.{onthly Letter Report No. 11 -2- 18 August 1964

TI1e program for the next repor~lng period is expected to follow the sam.e pattern ,,ri th increased effort in the a:-eas of analyzing references, screen room measurements, evaluation of absorbing materials, and analyzing antenna configurations.

Approved:

·.'- A"',-


1il. R. :Free Project Director

' /~-·--·:/_/~ ~- .. ': .

~v~ D. W. Robert?on, Head r. Co:mmunications Branch {j

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ATLANTA 13, GEORGIA

17 September 1964

Activity SupplY Officer, USAEL Building 2504, Charles Wood Area Fort Monmouth, New Jersey

MARKED: "For Engineering Sciences Department, Interference Analysis and Control Area"

ATTN: Contracting Officer's Designated Representative

SUBJ: Monthly Letter Report No. 12, 20 September 1964, Report Period 15 August 1964 to 15 September 1964, Contract No. DA 36-039 AMC-02294(E), "Electronic Equipment Interference Characteristics, Communication Type."

Gentlemen:

The literature survey has· continued during this reporting period. Over 200 references pertinent to this effort have been located and are being analyzed and abstracted.

For the purpose of analyzing the references, the project has been divided into five major tasks: (1) Case Radiation and Case Susceptibility Measurement Techniques, (2) Modeling Techniques, (3) Absorbing Materials, (4) Antennas and Probes, and (5) Techniques for Measuring and Improving Shielded Room Characteristics.

Assignments of the project personnel have been made on a task basis. Although these initial assignments were made primarily to accomplish a thorough analysis of the references, it is planned to conduct the entire program on this task basis to the extent possible.

Major emphasis is being placed on the Radiation and Susceptibility Measurement Techniques, Antennas and Probes, and Absorbing Material tasks at the present time. It is considered necessary that an optimum, standard test setup and procedure be developed early in the program, since it is felt that any improvements which are obtained in the shielded room characteristics will be highly dependent on the measurement setup and procedure being used. Hence, by adopting a standard measurement technique early in the program, it will be possible to incorporate shielded room improvement techniques which are compatible with the measurement procedure to be used. In addition, the early development of a standard measurement setup and procedure will allow open-field data to be obtained which can serve as a meaningful reference from which to determine the degree of shielded room improvement.

PAT~NT ... :~.:~1: ~'JtWBY.~ f-ORMAT ..• f.::.tl..Y.... tck.Y... BY .• ~ •••

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Monthly Letter Report No. 12 -2- 17 September 1964

The adoption or development of standard test antennas and/or probes is an integral and important part of the development of a standard measurement setup and procedure and must be accomplished concurrently with this task.

It is desirable that the types of absorbing materials to be investigated be determined and sample quanities of these materials be obtained as early as possible, since the modeling effort will be effected by these factors. It is anticipated that the modeling effort will provide the maximum advantages in the areas of evaluating absorbing materials and shielded room shapes and dimensions. ~aterials to be used in the modeling effort are presently being ordered.

A list of suggested changes to MIL-STD-449B was prepared during this reporting period at the request of Mr. Warren Kesselman, USAEL, and was submitted 15 September 1964.

The program for the next reporting period is expected to follow the same pattern with the major effort in the areas of analyzing references, development of a standard measurement setup and test procedure, selection or development of standard test antennas and probes, and selection of absorbing materials to be investigated.

Approved:

J,w ... /2~ D. W. Robertson, Head Communications Branch


lJillOL~ :fl\(tee__ W. R .. Free Project Director

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ATLANTA t3, GEORGIA

18 November 1964

Activity Supply Officer, USAEL Building 2504, Charles Wood Area Fort Monmouth, New Jersey

MARKED: "For Engineering Sciences Department, Interference Analysis and Control Area 11

ATTN: Contracting Officer's Designated Representative

SUBJ: Monthly Letter Report No. 13, 20 November 1964, Report Period 15 October 1964 to 15 November 1964, Contract No. DA 36-039 AMC-02294(E), "Electronic Equipment Interference Characteristics, Communication Type."

Gentlemen:

The analysis and abstracting of the references compiled during the literature survey has continued during this reporting period.

Two model shielded enclosures, one 2' x 2' x 2' and one 2' x 3' x 2', are being fabricated. It is planned that a 4:1 scaling factor will be used for the modeling, and hence, these enclosures will simulate a 8' x 8' x 8' and a 8' x 12' x 8' shielded enclosure. After correlation has been established between these models and the full-size enclosures, the models will be utilized to evaluate enclosure shaping factors, absorbing materials, and absorbing material placements within the enclosures.

Development of measurement techniques for measuring the VSWR of shielded enclosures over an extremely wide frequency range is in progress. A pair of ;;.rideband, four-terminal, hybrid networks for use in the 50 Me frequency range have been constructed and tested. These units vdll be used to form a bidirectional coupler to be used as a reflectometer for shielded enclosure VSWR measurements at low frequencies. Data are presently being assembled to determine the accuracy obtainable using the reflectometer for the measurement of VSWR in coaxial lines.

An investigation is presently underway to determine the feasibility of shielding the test antenna in all but the desired direction by means of a metal hood lined with absorbing material. In theory, the metal hood shields the test antenna from the reflected waves from the shielded enclosure walls, while the absorbing material prevents standing waves inside the hood. If a satisfactory "hooded" antenna can be obtained, case radiation and susceptibility measurements can be made in conventional

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screen rooms in which one wall has been lined with absorbing material.

During the next reporting period, it is anticipated that the fabrication of the model shielded enclosures will be completed and that some model measurements will be made. The fabrication of a "hooded" antenna and a preliminary evaluation of this antenna as a possible screen room measurement technique should also be completed during this period. Investigation of techniques for making case radiation and susceptibility measurements at low frequencies (below 50 Me) ~ill continue.

Approved:

l I , I /) f---h--_/\~ .. / • Vv • { r~ bt-t~ia.-Jvv



~0£rm:_ W. R. Free Project Director

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ATLANTA 13. GEORGIA

17 December 1964


MAR.KED: "For Engineering Sciences Department, Interference Analysis and Control Area"

ATTN: Contracting Offic~r's Designated Representative

SUBJ: Monthly Letter Report No. 14, 20 December 1964, Report Period 15 November 1964 to 15 December 1964, Contract No. DA 36-039 AMC-02294(E), Electronic Equipment Interference ·characteristics, Communication Type.rr

Gentlemen:

Some preliminary results have been obtained with the hooded antenna technique, discussed in the last monthly report, at frequencies above 1 Gc. These results appear promising, and indicate that virtually all effects from undesired reflections from the shielded room walls can be eliminated by proper placement of a balanced antenna in a hooded shield. Data thus far have been restricted to a few discrete frequencies where tuned balanced antennas and tuned baluns were fabricated to accomplish the desired measurements. A broadband, balanced log-periodic antenna and a broadband, tapered . line balun to cover the frequency range from 1 to 10 Gc have been designed and are presently being fabricated. It is anticipated that the use of this broadband antenna in the hooded shield will permit a complete evaluation of the hooded antenna technique over the frequency range from 1 to 10 Gc.

The anechoic chamber obtained from Western Electric as surplus equipment has been received, but assembly of the chamber has been held up due to the fact that no drawings or assembly instructions were received with the unit. The General Services Administration and Western Electric both report that they have no drawings or assembly information on the chamber. Emerson and Cuming were contacted and they have.agreed to furnish drawings and assembly instructions. This information is supposedly en route at this time.

The development of measurement techniques for measuring the VSWR of shielded enclosures at low frequencies has continued during this reporting period. Two hybrid junctions have been assembled which yield a 6 db insertion loss and a 60 db minimum isolation for frequencies in the neighborhood of 50 me. These are capable of measuring VSWR's of 1.1 and larger in coaxial lines with various known terminations.

... ... Monthly Letter Report No. 14. -2- 17 December 1964

Using tuned antennas, the hybrid reflectometer shows sufficient VSWR change between operation in'the open and in the screen room to establish the maximum VSWR within the screen room in the vicinity of the antenna. The use of non-tuned loop or rod antennas has not been successful since the line to antenna reflection coefficient is excessively large. Stub .tuning and compensation networks are being attempted as a means of reducing the high VSWR in the non-tuned antenna case in the hope that these less cumbersome antennas may replace the tuned variety. At very low frequencies, the tuned antennas cannot be placed in the screen room and the non-tuned variety must be utilized.

The fabrication of a 2' x 2' x 2' model shielded enclosure was completed during this reporting period. The evaluation of this enclosure and the use of various absorbing materials and absorbing material placements within the model enclosure has been held up awaiting a satisfactory technique for measuring the VSWR.

During the next reporting period it is planned that the broad-band, balanced L - P antenna will be evaluated as a part of the hooded antenna technique. If the antenna proves satisfactory it is anticipated that a complete set of data on the hooded antenna technique will be included in the next quarterly report.

AJ;::=a~ D. W. Robertson, Head Communications Branch

Res~ectfully submitted: ·l"'1 .11C? vJJliluw ~ '/Y"e'f_ W. R. Free Project Director

1 i t l

I ~ , f I

'

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ATLANTA 13, GEORGIA

17 February 1965


MARKED: "For Engineering Sciences Department, Interference Analysis and Control Area. If

ATT.EN: Contracting Officer's Designated Representative

SUBJ: Monthly Letter Report No. 15, 20 February 1965, Report Period January 1965 to 15 February 1965, Contract No. DA 36-039

AMC-02294(E), "Electronic Equipment Interference Characteristics-:Comrnunication Type. 11

Gentlemen:

The evaluation of the "hooded" antenna technique has continued during this reporting period. Antenna pattern measurements were made in a shielded enclosure using a "hoodedn antenna as the receiving antenna. The results of these measurements indicate that making antenna pattern measurements in a shielded enclosure utilizing the 11hooded 11 antenna technique appears to be quite feasible. The degree to which nulls in the antenna pattern can be measured repeatably seems to depend primarily on the antenna peak-to-null response ratio and the absorption characteristics of the material used on the end wall. In general, excellent results can be expected if the reflected power from the end wall is at least 20 db below the null response of the test antenna. Variations in pattern nulls of about ± 3 db can be obtained if the reflected power from the end wall is 10 db below the null responses. It appears that the "hooded" antenna technique will yield results comparable with those obtained in an anechoic chamber when the s~e absorbing material is used for both experiments; however, no tests have been made in the anechoic chamber to veri~ this at this point.

If the source under test has physical size large compared to the wavelength of the radiation, it appears that some multipath reflections may occur between the unlined end wall of the shielded enclosure and the source which could terminate on the hooded receiving antenna. Absorbing material has been placed on the other end wall to determine if better results can be obtained with the hooded antenna technique. To date, the results are inconclusive.

Monthly Letter Report No. 15 -2- 20 February 1965

An omnidirectional, balanced, log-periodic antenna was designed and fabricated to serve as a radiating source for additional testing of the hooded antenna technique over the frequency range of 900 Me to 10 Gc. A circularly-polarized, balanced, log-periodic antenna was also designed and partially constructed to operate over the 900 Me to 10 Gc frequency range as a receiving antenna within a hood.

Work has continued on the model shielded enclosure measurement program and the fabrication of the paraboloidial-section model enclosure during this reporting period. The fabrication of the paraboloidial-section enclosure is approximately 75 percent complete and it is estimated that this unit will be completed within the next two weeks.

The missing absorbing material for the anechoic chamber obtained as excess equipment has not been located and no further work on the assembly of this unit has been accomplished during this reporting period.


~s~e:tfully ~ub~ted:

~ LCJLtitcvc-~ 'r1~ W. R. Free Project Director

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.. J7::: 0?' TSC~-:~OLOGY

ATLANTA 13. GEORGIA

17 March 1965

Activity Supply Officer, USAEL 2504, Charies Wood· Area

Fort Monmouth, Nevr

:V.Lfu.1UCED: 11For Engineering Sciences Department, Interference Analysis and Control Area.n

ATTEN: Contracting Officer's Designated Representative

SUBJ: Monthly Letter Report No. 16, 20 March 1965, Report Period 15 February 1965 to March 1965, Contract No. DA 36-039 AMC-0229h(E), "Electronic Equipment Interference CharacteristicsCommunication T,y:pe. 11

Gentlemen:

The evaluation of the "hooded'' antenna technique has continued during this reporting period. Additional antenna pattern rr.easurements a better grade of absorbing material on the shielded enclosure wall have been made. Measurements have also been made the broadband, omnidirectional, balanced, log-periodic antenna as the source.

~~e broadband ferrite absorbing rr.aterial was received this reporting period and fabrication of a nhoodn for use at lower frequencies is presently under way. The ferrite absorbing material is capable of operation down to 50 Me. The effects of the hooded box configuration at these low·er frequencies are yet to be determined.

A broadband, balanced, circularly-polarized, log-periodic antenna and broadband, tapered-line balun to be operated in the ferrite-lined hood over the frequency range from 400 Me to l Gc are presentiy being fabricated.

Measurements to determine the relative merits of various types of absorbing materials and their placements w·ithin a shielded enclosure, utiliz

the antenna coupling measurement technique with the 2 x 2 x 2 foot model shielded enclosure, have continued during this period.

The fabrication of the paraboloidial-section model enclosure has been completed. Measurements to evaluate this enclosure configuration will be performed at the conc~usion of the present series of measurements being conducted on the 2 x 2 x 2 foot mode~ enclosure.

Authorization to modify the anechoic chamber, and thus mlnlmlze the effects of the mis absorbing material, and at the same time, make the chamber more compatible with our intended use, has been received from the

Monthly Letter Report No. 16 -2-

Contracting Officer. It is anticipated that the assembly of this chamber vtill be completed during the next period.

D. vl. Robertson, Head Communications Branch

i R1~;~;ul]_y su~ottc v~~~w~ <lv~ ~ \~

W. R. Free Project Director

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ATLANTA 13, GEORGIA

3 June 1965


NOTICE This dJcumcnt ; n i , used by anyone.

Prior to t -...3 -~-~-19q without !1 i :~_S2J!ch Sponsor and the Experiment SLti:)n Se;::urity Office.

MARKED: "For Engineering Sciences Department, Interference Analysis and Control Area."

ATTEN: Contracting Officer's Designated Representative

SUBJ;

Gentlemen:

A theoretical and experimental study to determine the optimum configuration(s) and characteristics of balanced, broadband, cross-polarized antenna systems for near-field RFI measurements was initiated 1 May 1965.

A literature survey to determine the state-of-the-art in broadband, balanced, cross-polarized antenna techniques has been conducted during the period covered by this report. The work on frequency-independent antennas which has been accomplished at the University of Illinois over the past ten years appears to be particularly appropriate to the present antennas requirements. A number of the antenna. configurations which resulted from this 1·mrk will be investigated as possible approaches.

A conical log-helix antenna to operate over the frequency range from 200 Me to 1 Gc has been designed, fabricated and is presently being evaluated.

A crossed-bowtie antenna for operation in the 200 Me to 1 Gc region is presently being designed. A hybrid, 3 db, orthogonal coupler, designed to operate over the frequency range from 200 Me to 1 Gc, has been obtained to feed the two orthogonal bowtie antennas. Two broadband baluns (one for each bowtie) for operation over the same frequency range are being developed for use 1.;ri th this antenna.

The fabrication of a low· frequency (400 Me to 1 Gc) ferrite-lined hooded antenna was completed in April and is presently being evaluated. The broadband, circularly-polarized, log-periodic antenna and tapered-line balun utilized in this hooded antenna assembly appear to be particularly

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Monthly Letter Report No. 17 -2- 3 June 1965

applicable to the present antenna investigation.

It is anticipated that the fabrication of the crossed-bowtie antenna will be completed during the next reporting period. The three broadband, circularly-polarized antenna. configurations (crossed-bowtie, conical loghelix, and log-periodic) will be evaluated and compared. The best configuration will be selected and the design and fabrication of lower frequency antennas will be attempted.

Approved; /)

, Q , tU .I tO~:;};:;:;;. D. W. Robertson, Head Communications Branch

Respectfully submitt~

{~~rteL William R. Free Project Director

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2

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r::::h.e 2YC.~...:_r_a-cion a:=· t~-:e ferrite lined hooded arrcenna range fro:,: .crCO

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test (?) \·Ti th the ,~

in a screen

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ies

have bc::c:..: e-:_c:o:.::.ntered in t:-.:.e S~o~dband Daluns for this

of t~e ba:u:c.s is still in progress.

COY;}-

REVIEW

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Let~e:r

It is bo-vrtie ante:c.na and the

antenna periodic) will be

D. W. Robertson, ~ead

Communications Branch

Ko. -2- 2

\·Tilliam R. F-.cee ect Director

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ATLANTA 13, GEORGIA

2 November 1965

Activity Supply Officer, USAEL Building 2504, Charles Wood Area Fort Monmouth, New· Jersey

'I

MARKED FOR: Engineering Support Services Department Electromagnetic Environment Division Interference Analysis Branch Order No. 5871-PM-63-91

FOR: Accountable Property Officer

! -•. ~ 7 .l ' '

II- ..:2-

SUBJ: Monthly Report No. 19, 5 November 1965, Report Period 1 October 1965 to 1 November 1965, Contract DA 36-039 AMC-02294(E), "Electronic Equipment Interference Characteristics-Communication Type."

Gentlemen:

A conical log-helix antenna compatible with mounting in the low frequency, ferrite lined hood has been designed, fabricated, and evaluated (unhooded). This antenna was designed to operate over the frequency

~ 1' _7

range from 300 Me to 1 Gc. To make the length of the antenna compatible with the available hood, the cone angle was increased to 30 degrees. This antenna is presently being installed in the hood, and the hooded configuration will be evaluated during the next reporting period.

A 11 short 11 crossed bow·-tie antenna has been designed, fabricated and is presently being evaluated. This antenna was designed to be one-half wavelength at 1 Gc and will be evaluated, initially, over the frequency range from 200 Me to 1 Gc. Since the antenna w·ill be equal to or less than onehalf wavelength over the operating range, the beam-splitting encountered w·ith the "long" bow·-tie (one-half wavelength at the lowest operating frequency) should not present a problem with this configuration. The evaluation should determine if the gain and impedance characteristics of the "short" bow-tie are adequate to allow· it to be used as a standard test antenna for case emission and susceptibility measurements.

..,,.-.'.•1'',•\-::><V~

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Development of a "short r! dipole antenna for evaluating the hooded antenna technique at lower frequencies is presently in progres's. Transistor emitter followers are being incorporated in this configuration to improve the gain and impedance characteristics at low frequencies.

Approved:

j).hJ./2~ D. W. Robertson, Head Communications Branch

......

submitted:

~k Williarp. R. Free Project Director

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,

ATLANTA 13, GEORGIA

3 December 1965

Activity Supply Officer, USAEL 2504, Charles 1vood Area

Fort Monmouth, ~ew· Jersey

MARKED FOR: Support Services Department Electromagnetic Environment Division Interference Analysis Branch Order No. 5871-PM-63-91


1..3--- 3

SUBJ: Monthly Report No. 20, 5 Decemoer 1965, Report Period l November 1965 to l December 1965, Contract DA 36-039 Al\1C-02294(E), 11 Electronic Equipment Interference Characteristics-Communication Type. 11

Gentlemen:

Tne evaluation of a 30-degree conical log-helix antenna, both in the open-field and mounted in the low· frequency, ferrite lined hood, has continued during this reporting period. An identical evaluation of a nshort" (one-half at the frequency of interest) bow-tie antenna has been performed in w'ith the log-helix evaluation. The majority of the measurements required for these evaluations have been completed, and it is anticipated that the complete evaluation of the tW'o antennas will be in the next quarterly report.

The evaluation of a "short 11 dipole antenna, containing transistor emitter follow·ers to improve the and impedance characteristics at low has also been in progress this period. The objective of this antenna development is to obtain small, low· frequency probe antennas which can be utilized in an evaluation of the uhooded antenna 11 technique at low frequencies and in investigations of the waveguide-below-cutoff characteristics of tunnel-like structures partially and lined w'ith absorbing materials.

A preliminary attempt was made to 11 load" a log-helix antenna with carbonyl iron particles suspended in an epoxy binder to increase the electrical size of the antenna. This preliminary attempt was unsuccessful. It is felt that the thickness of the nloading 0 layer was not sufficient to

sh the desired results, and that some additional experimentation,

Renort No 20 -2-Contract N~. DA 3tS-039 PJILC-02294 (E)

3 Decemoer 1965

will oe necessary. For the purposes of tnis the use of small antennas, which will

-r,he fabrication of the antennas and will minimize the amount of materials required, appears desirable. A small conical log-helix

antenna, de to operate over the range from 1 to 10 Gc, is fabricated for tnis pL~rpose. ?nis antenna is constructed of small, solid-shield coaxial line so that it is self-supporting not a conical form. The elimination of the form -vrill greatly o:f the antenna w·i th material.

A theoretical study of problem areas associated with near-field measurements has continued during this reporting period. Tnis study is primarily concerned with the complex field configuration in the near-field, the measurement probe re in this area, and w·hat must be measu~ed to adequately descrioe the near-field configuration.

Approved:

0 \ /'v ;

D. itJ. Robertson, Head Communications Branch

Hilliam R. Free Project Director

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ATLANTA. GEORGIA 30332

3 February 1966 . t~ or 1 c £

ifhls d:Jcument ,·:..) n t b


Prior fo

MARKED FOR:

FOR:

SUBJ:

Gentlemen:

Engineering Support Services Department Electromagnetic Environment Division Interference Analysis Branch Order No. 5871-PM-63-91

Accountable Property Officer

Monthly Report No. 21, 5 February 1966, Report Period l January 1966 to l February 1966, Contract DA 36-039 AMC-02294(E), "Electronic Equipment Interference Characteristics- Communication Type."

used by anyone·OJ

An 8' x 8' shielded enclosure and an 8' x 12' shielded enclosure have been combined to form an 8' x 20' shielded enclosure. A low·-frequency absorbing material, Emerson and Cuming HPY-72, is being mounted on one end wall of this enclosure. This enclosure will be utilized to evaluate the hooded antenna technique over the frequency range from 50 to 400 Me during the next reporting period. The larger enclosure was necessary for this evaluation due to the fact that the thickness of the low-frequency absorbing material to be utilized on the end wall is 72 inches.

The characteristics of the quadrature coupler have determined the low frequency limit of the evaluation of the "short" crossed bow-tie antenna. The broadband coupler presently being utilized with this antenna covers the frequency range from 200 Me to l Gc and is 15 inches long. It is desired to evaluate this antenna at frequencies below 200 Me, but, utilizing the present coupler technique, a coupler covering the 40 to 200 Me range would be approximately 30 inches long. In order to cover lower frequencies, the coupler would be much more unwieldy. On the basis of this, an investigation of broadband quadrature coupling techniques has been initiated to investigate the feasibility of techniques for developing shorter broadband quadrature couplers. This investigation will be continued during the next reporting period.

The investigation of loading a log-helix antenna with carbonyl iron particles suspended in an epoxy binder to increase the electrical size of the antenna has continued during this reporting period. The fabrication

Monthly Report No. 21 -2- 3 February Contract No. DA 36-039 AMC-02294(E)

of a small, self-supporting, log-conical antenna to be utilized in this investigation has been completed, and the evaluation of this antenna is in progress. It is anticipated that a small ferrite lined antenna hood for this antenna will be fabricated during the next reporting period.

A theoretical study of problem areas associated with near-field measurements has continued during this reporting period.



w~{__-t~ William R. Free Project Director

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Services

C~a~acteris0ics-Cor~~nication

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.:rt~nent

Interference

S:·he .~nstall;stion of: the material" Ern.erson & x 20 foot shielded enclosure was :v.::;;asJrerJen·cs ·co evaluate the hooded antenna tech-

rauge from 50 lv:c to 400 Me are pre in pro;;resa.

a~tenna

fabrication of a this w·eek.

--"'~n evalu&tio:c o--.:_' Jcne !-woC.ed an-':;ecna ¥till -be ir1.:. tia-,_-,ed as soon as the antenna conclusion of this the

L:on-epo:xy n-~ixture and re-evaluated.

-~ sel~:.e s ection ca2.i bratio::-1 Let-vror:~ has ·oeeE incorporated into the conical ven~a described in the lOth

Tne secoL~ helic&l utilized as ~~e series ill ·che c&:.i l/~ea.::u::::·e:;::.e:~ts -co evaluate

-oalanced conical antenna v-ras

an ar.:.d. ca_._i ~:~B.:te

results of the antenna structure.

series injection calibration :i.n progress.

Project Director

f ·~,, f \....'-'~• .: •• /----~· ... ,.-/-..;_ ....... ~

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ATLANTA, GEORGIA 30332

4 April 1966

Activity Supply Officer, USAEL Building 2504, Charles Wood Area Fort MOnmouth, New Jersey

This

MARKED FOR: Engineering Support Services Department Electromagnetic Environment Division Interference Analysis Branch Order No. 5871-PM-63-91


SUBJ: Monthly Report No. 23, 5 April 1966, Report Period 1 March 1966 to 1 April 1966, Contract DA 36-039 AMC-02294(E), "Electronic Equipment Interference Characteristics-Cormnunication Type."

Gentlemen:

The measurements to evaluate the hooded antenna technique over the frequency range from 50 MHz to 400 MHz are still in progress. It is anticipated that this measurement program will be completed by 15 April 1966. The results, conclusions and recommendations obtained from the analysis

. of the data resulting from this measurement program will be presented in the final report.

The measurement program to evaluate and calibrate the 30-degree conical log-helix antenna incorporating the series injection calibration netvrork has been completed. The analysis of the data obtained from the measurement program and the preparation of the conclusions and recommendations for inclusion in the final report are in progress.

The evaluation of the small self-supporting log-conical antenna mounted in a small ferrite-lined hood is in progress·. There are indications that the presence of the ferrite absorbing material in close proximity to the antenna is loading the antenna to some extent and shifting the operating range to lo-w·er frequencies. This phenomenon will be investigated in more detail as the measurement program progresses. It is anticipated that the measurement portion of this phase of the small hooded antenna evaluation w·ill be completed by 8 April 1966. At this point, the antenna -w·ill be loaded with a car9onyl iron-epoxy mixture and re-evaluated.



~~ William R. Free Project Director

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LIBRARY DOES NOT HAVE It is classified.

\

•

REPORT NO. 23

QUARTERLY REPORT NO. 2

PROJECT A-678

ELECTRONIC EQUIPMENT INTERFERENCE CHARACTERISTICS-COMMUNICATION TYPE

By R. D. Trammell, Jr., C. W. Stuckey, E. W. Wood, 0. H. Ogburn, and E. E. Donaldson, Jr.

CONTRACT NO. DA 36-039 AMC-02294(E) (Continuation of Contract No. DA 36-039 sc-87183) DEPARTMENT OF THE ARMY PROJECT: 3B24-0l-001

Placed by the U. S. Army Electronics Research and Development Laboratory Fort Monmouth, New Jersey

15 May 1963 to 15 August 1963


GEORGIA INSTITUTE OF TECHNOLOGY Atlanta, Georgia

RFV!E\N ~ P/l.TENT .. /!.-::.?./ ..... 19 .. ~~- BY ......... ." .......... .

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ENGINEERING EXPERIMENT STATION of the Georgia Institute of Technology

Atlanta, Georgia.

REPORT NO. 23

QUARTERLY REPORT NO . 2

PROJECT A-678


By

R. D. TRAMMELL, JR., C. W. STUCKEY, E. W. WOOD, 0. H. OGBURN, and E. E. DONALDSON, JR.


The object of this research program is to conduct a. comprehensive investigation to determine methods for measuring the interference characteristics (spectrum signature) of U. S. Army communications equipment deemed necessary for the prediction and minimizing of electromagnetic interference.

15 MAY 1963 to 15 AUGUST 1963

PLACED BY THE U. S . ARMY ELECTRONICS RESEARCH AND DEVELOPMENT LABORATORY

FORT MONMOUTH, NEW JERSEY

TABLE OF CONTENTS

I. PURPOSE .

II. ABSTRACT.

III. PUBLICATIONS, LECTURES, REPORTS, AND CONFERENCES ..

IV.

v.

VI.

VII.

VIII.

FACTUAL DATA.

A. Multipath Transmission Tests on FM Systems.

l. Introduction.

2. Common-Channel Interference Tests on a Typical Wide-Band FM System . . . . . . . . . . . .

3. Multipath Transmission Tests on a PPM/FM Radio Relay . . . . . . · · · ·

B. Mixer Study

l. Introduction ..

2 Errors in Measurement

3· Generalized Prediction Equations ..

4. Experimental Error in Prediction"

5, Analysis of the Effective Mixer Constants .

6. Conclusions

CONCLUSIONS

PROGRAM FOR NEXT INTERVAL .

IDENTIFICATION OF KEY TECHNICAL PERSONNEL

REFERENCES. . . . . . . . . . . . . . . . .

This report contains 66 pages. ii

Page

l

2

3

4

4

4

4

12

30

30

31

37

56

63

64

65

66

LIST OF FIGURES

1. Block Diagram of Test Configuration Used For Simulated Common-Channel Interference Tests on a Wide-Band FM System

2.

3·

4.

5·

6.

7·

Power Required to Give 22 db of Quieting as a Function of Frequency at a Tuned Frequency of 1550.5 Me ....

Quieting With a Signal Level of -10 dbm as a Function of Frequency at a Tuned Frequency of .5 Me ....

Block Diagram of Test Configuration Used For Simulated Multipath Interference .. o •••••••••••

Voltage Spectrum of the Direct Path Signal Showing (Left to Right) Main Lobe, First, Second, and Third Side Lobes ..

Voltage Spectrum of the Multipath Received Signal With the Relative Phase Adjusted to Give Cancellation of the Main Lobe

Upper: The Received Direct Path Signal With the Delayed Signal Attenuated 100 db . . . . . . . . . . . . .

Lower: The Received Multipath Signal With the Spectrum Adjusted as Shown in Figure 6. . . . . . .

8. Predicted PCI as a Function of Relative Power With the Relative Phase Adjusted For Maximum Voltage Cancellation of the Main Lobe at a Receiver Quieting of 39 db ...

9.

10.

ll.

12.

Predicted PCI as a Function of Relative Power With the Relative Phase Adjusted For Maximum Voltage Cancellation of the First Side Lobe at a Receiver Quieting of 39 db

Voltage Spectrum of the Multipath Received Signal With the Relative Phase Adjusted to Give Cancellation at the First Side Lobe* ............... .

Voltage Spectrum of the Multipath Received Si With the Relative Phase Adjusted to Give Cancellation at the Second Side Lobe . . . . . . . . . . . . . . . . .

Upper: Received Multipath Signal With the Spectrum Adjusted as Shown in Figure 10 . . . . . . . . .

Lower: Received Multipath Signal With the Spectrum Adjusted as Shown in ll . . . . . . . . .

(Continued)

iii

Page

5

6

9

14

17

20

22

22

22

22

13.

14.

LIST OF FIGURES (Continued)

Predicted PCI as a Function of Relative Power With the Relative Phase Adjusted For Maximum Voltage Cancellation of the Second Side Lobe at a Receiver Quieting of 39 db .

Predicted PCI as a Function of Relative Power With the Relative Phase Adjusted For Maximum Voltage Cancellation of the Third Side Lobe at a Receiver Quieting of 39 db

Voltage Spectrum of the Multipath Received Signal With the Relative Phase Adjusted to Give Cancellation of the Third Side Lobe • • • • . . • . . • . . • . • . • • • •

16. Upper: The Received Multipath Signal With the Spectrum

17.

18.

19.

20.

21.

22.

23.

24.

25.

26.

27.

28.

Adjusted as Shown in Figure . • . . . • • .

Lower: The Received Delayed Signal With the Direct Path Signal Attenuated 100 db. . . . • . . ..••.

Predicted PCI as a Function of Relative Power With the Relative Phase Adjusted For Maximum Voltage Cancellation of the Main Lobe at a Receiver Quieting of 20 db •••••

Predicted PCI as a Function of Relative Power With the Relative Phase Adjusted for Minimum Receiver Noise at a Receiver Quieting of 20 db. . . . . . . . . Test Setup For Spurious Response Measurements . Response Density Versus Prediction Error For a lN82A Diode

Response Density Versus Prediction Error For a lN82A Diode


Response Density Versus Prediction Error For a 1N82A Diode


Response Density Versus Prediction Error For a 1N82A Diode

Response Density Versus Prediction Error For a lN2lB Diode

Response Density Versus Prediction Error For a 1N21B Diode

Response Density Versus Prediction Error For a lN2lB Diode

(Continued)

iv

Page

23

24

25

25

27

29

33

Mixer. 38

Mixer. 39

Mixer. 40

Mixer. 41

Mixer. 42

Mixer. 43

Mixer. 44

Mixer. 45

Mixer. 46

LIST OF FIGURES (Concluded)

Page

29. Response Density Versus Prediction Error For a lN2lB Diode Mixer. 47

30. Response Density Versus Prediction Error For a lN2lB Diode Mixer. 48

3lo Response Density Versus Prediction Error For a lN23C Diode Mixer. 49

32. Response Density Versus Prediction Error For a lN23C Diode Mixer. 50

33· Response Density Versus Prediction Error For a lN23C Diode Mixer. 51

34, Schematic Diagram of lN82A Test Mixer

35· Response Density Versus Prediction Error Using Averaged Power Ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

36. (2, l) Response Level Versus Bias Voltage For Single Diode Mixer With No Fre~uency Discriminationo .

37·

38.

39

I.

Relative Response Level Versus Forward Diode Bias Order Responses of the lN2lB Diode Mixer. . Relative Response Level Versus Forward Diode Bias Order Responses of the lN2lB Diode Mixer.

Relative Response Level Versus Forward Diode Bias Order Responses of the lN2lB Diode Mixer.

LIST OF TABLES

SPURIOUS RESPONSE TRIANGLE FOR A MIXER HAVING A POLYNOMIAL REPRESENTATION OF THE TENTH DEGREE .

v

For Third

For Fourth

For Fifth

59

60

. 61

I. PURPOSE

The purpose of this project is to conduct a feasibility study and investi

gation to determine methods for measuring the interference characteristics

(spectrum ture) of U. S. Army communications equipment deemed necessary

for the prediction and minimi of electromagnetic interference. Emphasis

shall be placed on modulated type communications equipments operating

in the 1-10 kMc frequency range. Measurement techniques for obtaining the

required data and a format for a directory of these data shall be developed.

Computer methods shall be developed for proce these data to obtain

outputs useful in determining optimum characteristics for communications

equipments operating in prescribed interference environments.

The areas of investigation on this project are divided into two tasks

as follows:

I< The development of tests and procedures for the evaluation of the

interference ty and emanation characteristics of pulse modulated

type communications equipments.

II. The use of computer techniques for processing measured interference

data to produce outputs useful in interference prediction and control

tions.

-1-

II. ABSTRACT

Qualitative common-channel interference tests were made on a wide~band

FM The effect of simultaneous reception of two on the

understandability of the desired received signal is reported.

Two path interference tests were initiated on a radio relay system

which employs time division multiplexing. Predicted PCI as a function of

relative phase are for a delay of 0. ~sec. These data

indicate that this is not a sufficient delay to cause ficant

tion in intelli for this communications system.

Equipment limitations and the inherent errors of the tech-

nique are examined as sources of mixer prediction errors. Error-

density data are shown for fourteen diode mixer tests from which the prob-

able causes for ction errors are deduced. These data indicate that

the examined sources can produce si

tions of mixer operation.

cant errors under certain condi-

-2-

III. PUBLICATIONS, LECTURES, REPORTS, AND CONFERENCES

Mr. R. D. Trammell, Jr., attended the 5th National Symposium on Radio

Frequency Interference in Philadelphia, Pennsyl va,.nia, on 4-5 June

Mr. Weitz and Mr. R. L. McKenzie from USAELRDL visited Georgia Tech

on 16-18 July for a technical discussion.

Mr. Warren Kesselman from USAELRDL visittt:d Georgia Tech on 30- July to

discuss project progress made during the second quarter of the research program.

Mr. J. T. Ludwig, Mr. Martin Sherman, and Mr. I. N. Mindel from IIT Research

Institute, Chicago, Illinois, visited Tech on 30 July. The nonlinear

effects of dummy loads and the results of current mixer studies were discussed.

-3-

IV. FACTUAL DATA

A. Multipath Transmission Tests on FM Systems

l. Introduction

Two U. S. Army FM communications , which were de to

utilize time division to frequency modulate the trans-

mitter , were used to multipath interference characteristics

of modulated type comrrmnications A PCM simulator was not

available for one of the FM studied, and this system was tested as a

channel communications link. A PPM set and a wide-band

FM transmitter and receiver set provided a PPM/FM radio link for a

quantitative

2. Common-Channel Interference Tests on a T,ypical Wide-Band FM System

Qualitative common-channel interference tests were made on an FM

system which tunes between 1 and 2 Gc in an effort to gain some into

the multipath interference problem at these s. In these tests, two

transmitters and a receiver were used as shown in 1. Initially,

one transmitter was tuned to 1549.4 Me and the other was tuned to .6 Me

The receiver was tuned to 50.5 Me. The receiver response was approximately

6 db and 10 db down from the receiver peak response at these two transmitter

frequencies, as shown in 2.

The transmitters were modulated by tape an Ampex 601

as shown in 1. Two dual channel test tapes were

made for the study. The first tape was made by recording a local AM radio

TRANSMITTER 500 r- -----. l LOAD I I AMPEX VARIABLE

ATTENUATOR 1 I I RECORDER I I

I RECEIVER I

I REPRODUCER

I I I I TRANSMITTER son

2 LOAD L_ _ _j ---VARIABLE SCREEN ROOM

ATTENUATOR 2

Figure 1. Block Diagram of Test Configuration Used for Simulated Cownon-Channel Interference Tests on a Wide-Band FM System.

-5-

I 0\ I

e -10 ...Q -o -(.!) z 1-w ::J a ...Q -o N N

a::: 0 u.. a w a::: :::J a w a::: a::: w 3:: 0 0...

-5

0

1549 1550 1551

FREQUENCY (Me)

1552 1553

Figure 2. Power Required to Give 22 db of Quieting as a Function of Frequency at a Tuned Frequency of 1550.5 Me.

broadcast on each track of the tape with no delay time between tracks~ The

second tape consisted of the recording of a local AM radio broadcast on both

tracks with one track delayed 142 msec from the other. The delay was achieved

by recording one track from the playback of the other. Thus, the delay time

was the time req_uired for the tape to travel from the recording head of the

recorder to the playback head.

The power arriving at the receiver from each transmitter could be con

trolled by General Radio type 874-GA adjustable attenuators. The insertion

loss of these attenuators is 33 ± 2 db and the variable attenuation is con

tinuously adjustable from 0 to 120 db. The power available at the transmitter

antenna terminals of transmitters 1 and 2 was 9.5 watts and 5.6 watts, respec-

tively. With the attenuation in the line from one transmitter the

relative power levels of the two transmitters could be varied by adjusting

the attenuator in the other line.

As a first test, the transmitters were modulated by playing the undelayed

tape. Variable attenuator 2 was at 0 db and attenuator 1 was adjusted for the

maximum attenuation at which no audio from transmitter 2 was detectable

at the receiver when the modulation was removed from transmitter 1.. The result

ing relative power level at the receiver between the signals from transmitters

1 and 2 was such that the receiver exhibited complete capture on a signal from

transmitter 1. The range of relative powers over which the audio signal from

both transmitters could be detected simultaneously proved to be approximately

20 db.

The transmitters were modulated by playing the delayed tape and the result

audio signal was monitored at the receiver. Attenuator 1 was adjusted in

-7-

2 db over the 20 db range of simultaneous detection. Changing the rela-

tive power by adj the attenuator caused a corresponding change in the

relative levels of the direct and delayed audio si When the direct signal

level was greater than that of the signal) the effect was that of echo.

When the delayed signal level was greater than that of the direct signal the

effect was reminiscent of "print-througho" Under both conditions the audio

si was 100 per cent intelligible.

Some confusion arose at that relative power level at which both the delayed

and direct signal were approximately equal in level at the receiver antenna ter-

minalso Had a different audio signal been used in of the delayed signal)

the effect would have been very much like two-voice babble. The intelligibility

of this si would depend primarily on the listener's to concen-

trate on the desired signal. The range of relative power levels at which this

condition existed was less than l db.

The phenomenon of simultaneously receiving both signals over a wide range

of relative power levels can be attributed to not having sufficient voltage at

the receiver to operate the limiter. This is graphically illustrated in

3) which shows the receiver quieting obtained with a constant input signal power

of -10 dbm as a function of transmitter frequency. The two selected transmitter

) 1549.4 and 1551.6 Me) lie on the slopes of the limiting curve.

The two transmitters were retuned to the 1550.5 Me channels. The actual

resulting frequencies were 1550.3 and 15 .7 Me) both of which are well within

the limiting curve of Figure 3. Again, variable attenuator 2 was set at 0 db.

Attenuator l was adjusted through its entire range. The receiver exhibited

on the si from transmitter l until that RF si had been attenuated

-8-

I \D

I

25

20

::0 15 ~

(.!) z 1-w :J cr

10

5

1549 1550 1551

FREQUENCY (Me)

1552 1553

Figure 3. Quieting with a Signal Level of -10 dbm as a Function of Frequency at a Tuned Frequency of l550-5 Me.

such that the power at the receiver from transmitter l was about +1.5 db with

to the power from transmitter 2. The receiver exhibited on

the from transmitter 2 when attenuator l was usted such that the

power from transmitter l was about -1.5 db or less with respect to the power

from transmitter 2. Within the 3 db interval centered about equal power at

the receiver from each transmitter) the output audio was noisy. With

fixed attenuator within the 3 db interval the S/N ratio varied con-

siderably. This was probably caused by random fluctuation in output power from

the transmitters) causing the relative powers to shift about 0 db. This

same power fluctuation effect caused the attenuator setting at which capture

occurred on the two signals not to be sharply defined. The interval of incom

plete capture was measured to be from 0.5 to 4 db wide) with an average width

of about 3 db.

Because of the relative power fluctuations) it was not possible to set and

maintain the relative power levels at 0 db. Had this been ) the audio

l probably would have proved unintelligible because of the noise. However)

even when the transmitters were modulated with the ) the connected

discourse proved highly intelli although some individual words were lost

because of noise during the transitions from capture on one si to

l capture on the other. Had a different voice message been used in ce

of the delayed message) parts of the desired signal would have been lost because

of random partial capture of the undesired si

The observed of the FM receiver in the presence of two common-

channel transmitted signals was in aN~cc~c.~ with published observations

and theory. Corrington1 reported simultaneous of two FM radio stations

-10-

~hich operated on the same frequency ~hen their carrier wave voltage levels drop-

ped below the level at which the limiter in the receiver operated. This effect

was observed in the system when the transmitter frequencies were tuned

too far from the receiver tuned frequency to permit complete at the

available power levels.

Arguimbau2 ' 3 and others 1 ' 4 ' 5 through the use of mathematical models have

shown that maximum interference results from multipath and common-channel trans-

missions when the ratio of the received po~er levels is one. Further, they have

demonstrated that essentially distortion-free results should be obtained when the

2 relative power levels differ by more than 10 per cent. Laboratory measurements

latter hypothesis. Although the exact relative po~er levels were not measured,

it that distortion-free results were obtained with the present system

when the power levels differed by from at least 10 to 30 per cent.

Even with a 142 msec audio delay and the relative power levels adjusted as

equal as possible, the audio output of the receiver proved in tel-

ligible. Since a multipath delay of 10 msec requires a path length difference

in excess of 1800 miles, it would be unlikely that power for the two

received si would exist at any delay ~hich would cause the audio to be

unintelli However, it is conceivable that equal or very equal

power levels could arrive at a receiver from two (or more) paths ~hich differ

in by a few miles. The delays corresponding to these path

differences are on the order of 20 ~sec or less. While the data indicate

that the intelli ty of a signal received by the wide-band FM would

be r~latively unaffected by such , the intelligibility of a trans-

-ll-

mitted and received by a PPM/FM communications system might be

lowered as a result of path length differences of this rna

spacing on many PPM/FM systems which use time division

The channel

ranges from

3 to 10 !J.Sec. of the same order of arising from multipath

transmission could probably be expected to be a source of interference in such

a system. The work reported in the following paragraphs is part of a

investigation of the multipath transmission distortion effect on a PPM/FM radio

system time division multiplexing¢

Multipath transmission tests were initiated during the quarter on a

PPM/~1 radio relay system which utilizes time division The multi-

has independent channels and uses a sampling frequency of 8 kc. The

23 channel are separated equally by 5.2 !J.Sec. A double pulse used as a

marker or starting pulse plus the channel comprise the f-LSec sam

is 0.6 f..1Sec, time. The pulse width of both the marker and channel

The separation of the two 0.6 ~sec pulses which make up the marker is 1.25 f..1Sec.

The channel

The

deviation at 100 per cent modulation is ±0.5 !J.Sec.

fications of this indicate that audio interference

should result at the system output whenever the path lengths of two or more

multipath differ by enough to cause a relative delay of approximately

0.5 ~sec or greater, provided the

the same power. Depending upon the

from audio "noisen to random

the interference should range

and complete loss of the desired

si The ty of crosstalk between channels caused by delayed pulse

-12-

trains is also suggested by the multiplexer cations. It is the above

conjectures that the experiment outlined below will confirm or disprove.

Multipath reception tests were initiated on the PPM/FM radio relay

which is operated as shown in Figure 4. Different direct and delayed path cable

are used to obtain the experimental By viewing the recovered

pulse train (after transmitted and received) on the oscilloscope, the

degradation due to

and the adjustable line can be observed.

A analyzer Model SPA-4a, Panoramic Radio Produc can be used

to observe selected portions of the transmitted A radio interference

mea set (RIMS), Empire Devices NF-112, can be used as a comparison measur-

instrument for setting power levels at the receiver

Addition of the

DA-3FN resistance adder.

and direct signals is in a Microlab

using this device the VSWR at all in the

system is maintained below 1.50 The adjustable attenuator in the direct

is a General Radio 874-GAS2. Care is taken to always approach attenuator

from the same direction of barrel travel since this attenuator has

about l db of backlash. A General Radio adjustable line type 874-LK20 serves

to set the phase between the direct and delayed signals. A

directional coupler, Narda Model 3022, isolates (20 db) the spectrum

and the RIMS from the signal

Because of its availability, a foot length of RG-8 cable was used as

an initial delay path cable. This cable has a measured attenuation of 0.17

db/ft at the transmitter tuned or about db for the entire span.

A relative delay between the direct and delayed paths of 0.25 ~sec was obtained

at the receiver.

-13-

I f-l + I

TRANS

MITTER

SCREEN ROOM

DELAY PATH (Cable)

DIRECT PATH

I I

------, I MUL Tl

.,__....__.111111 PLEXER

DE-

l MULTIPLEXER

I L __

RECEIVER

OSCILLO

SCOPE RIMS

I I I I

SPECTRUM

ANALYZER

RESISTIVE ADDER

ADJUSTABLE LINE

Figure 4. Block Diagram of Test Configuration Used for Simulated Multipath Interference.

With the direct path attenuator of Figure 4 adjusted for maximum attenua

tion) the unmodulated signal at the receiver was measured to be -47 dbmJ which

is 20 db above the level required to produce 20 db of quieting and which corre

sponds to 39 db of quieting at the video output. Equal power could be obtained

at the receiver from the direct signal path when the direct path attenuator was

set to 20" db and the delayed path was broken and terminated at the adjustable

line"

The audio output of channel 7 of the multiplexer was monitored for the tests

reported in this section. The audio of this channel was set at approxi-

mately 1.2. A Ballantine RMS vol tmemter was used to measure S/N rat,ios at

the channel 7 output) and the S/N ratio measurements were converted to predicted

PCI" Details of the S/N ratio measurement technique and conversion of these

measurements to predicted PCI are covered in Quarterly Report No l of this

contract.

The transmitter was modulated with the pulse train from the multiplexer.

With the power levels in the direct and delayed paths set about , the

noise at the audio output of channel 7 could be varied over a considerable

range varying the adjustable line. The S/N ratios corresponding to these

noise variations ranged from +34 to -16.5 db.

With the modulating pulse train removed, it was found that with equal

power in the direct and delayed paths) the receiver quieting could be varied

from 45 db to nearly 0 db the adjustable line, This variation in

receiver quieting can be attributed to reinforcement and cancellation of the

RF direct by varying the relative phase between the direct signal

and the delayed signal when the path length of the latter is increased or

decreased. The wave length of the tuned frequency is 5·3 inches and the adjust

able line can be varied over an 8.5 inch interval; thus, it was possible to vary

the relative phase angle by more than 360°.

The RF voltage spectrum of the received direct path signal is shown in

Figure 5 'rhe corresponding video input to the demultiplexer is shown in the

upper portion of Figure 7. The voltage spectrum is made up of a main lobe and

three side lobes. For fixed relative phase angles, as the direct to delayed

po~rer ratio is changed, changes occur in the voltage spectrum, Similarly, for

fixed relative power levels voltage spectrum changes occur as the relative

phase angle is changed. Both relative phase angle and relative power changes

cause variations in the noise level at the audio output of channel 7" The

maximum noise occurred when the relative power and phase were adjusted such

that one of the four lobes of the voltage spectrum was minimized. Thus, it

was decided to determine the predicted PCI as a function of relative power in

the direct and delayed paths with the relative phase adjusted in each case to

cause a minimum voltage at the midpoint of each one of the four lobes of the

voltage spectrum.

Figure 8 shows predicted PCI as a function of relative direct to delayed

path power with the relative phase angle adjusted to give minimum RF voltage

at the main lobe. Predicted PCI is 100 for relative power levels greater than

+l db and less than -1 db. When the relative power levels are equal, the S/N

ratio becomes very small (less than db) and the predicted PCI falls to

zero. The insensitivity of the system to multipath interference under the

outlined conditions at relative power levels which differ by l db or more can

be attributed to the high quieting level (39 db) at which the data are taken.

I f-' -_;] I

l 0 G 0 B

0

• • •

-20.

• • • -· o.s

PANORAMIC RADIO PRODUCTS. INC. MODEL SPA· 40

I

r_~:-r~ 1

; l __ ! )

r I

I \

I ,.'j 111 d& •l u ".J •lflllofl ~

-0+ SWEEP WIDTH FACTOR

1.

0.1

0.6

0.4

0.2

u

v 0 L T A G E

Figure 5. Voltage Spectrum of the Direct Path Signal Showing (Left to Right) Main Lobe, First, Second, and Third Side Lobes.

L 0 G 0 B

0

• • •

-20.

•

• •

-4()41

0.5

PANORAM IC RADIO PRODUCTS. INC. MODEL SPA · 40

.. ..

l -- ' I '

I . · ···~-- ·

l J

i _,_

! l

d 111 - 0+

SWEEP WIDTH FACTOR

1.

0.1

0.&

0.4

0.2

u -

v 0 L T A G E

Figure 6. Voltage SpectrTh~ of the Multipath Received Signal with the Relative Phase Adjusted to Give Cancellation of the Main Lobe.

Figure 7. Upper: The Received Direct Path Signal with the Delayed Signal Attenuated 100 db.

Lower: The Received Multipath Signal with the Spectrum Adjusted as Shown in Figure 6 .

I f--' co I

100

90

80

70

u 60 a_

0 w 1- 50 u 0 w g: 40

30

20

10

0~--~----~----~----~--~-----L--------~----~----~----._--~~--~----~----~--~ -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 + 1 +2

POWER IN DIRECT PATH RELATIVE TO DELAY PATH (db)

Figure 8. Predicted PCI as a Function of Relative Power with the Relative Phase Adjusted for Maximum Voltage Cancellation of the Main Lobe at a Receiver Quieting of 39 db.

+4 +5

Adjusting the relative phase for minimum RF voltage at the main lobe causes

carrier cancellation between s of the modula pulse train,. The extent

of this cancellation depends directly on the relative of the direct

and delayed si and hence on the relative power. The si at the

receiver dwells at the main lobe frequency more than 70 per cent of the time

(approximately 3,7 ~sec out of every 5.2 ~sec). At equal relative power levels

the receiver is essentially not quieted during the dwell timej thus, at

powers the S/N ratio is very small. At unequal power levels, even though the

main lobe voltage is minimized and attenuated from its maximum

value, the residual power during the dwell time is sufficient to cause receiver

quieting at this relatively high signal input. Greater sensitivity to main lobe

cancellation should occur at lower overall signal levels.

Figure 6 shows the voltage spectrum of the multipath received signal with

the relative phase adjusted to give minimum RF voltage at the main lobe when

the relative direct and delayed path power levels are equal" The received video

signal under these conditions is shown in the lower half of Figure 7. The noise

between caused by carrier cancellation during the dwell time is apparent.

Th.e pulse distortion is caused by the addition of the two different simultaneous

RF frequencies in the receiver discriminator. Thus, the direct path

phase modulated in the discriminator·by the delayed signal.

is

Figure 9 shows predicted PCI as a function of relative direct to delayed

path power with the relative phase adjusted to minimum RF voltage

at the first side lobe. The lowest PCI determined by any relative power was

than As shown in Quarterly Report No. 1, the predicted intelligi-

bility corresponding to a PCI of 85 for isolated monosyllabic words is greater

-19-

I 1\) 0 I

0 a..

0 w I-u 0 w a::: a..

100

90

80

70

60

50

40

30

20

10

0 -10 -9 -8 -7 -6 -5 -4 -3


Figure 9· Predicted PCI as a Function of Relative Power with the Relative Phase Adjusted for Maximum Voltage Cancellation of the First Side Lobe at a Receiver Quieting of 39 db.

than 95 per cent. Thus no degradation in the intelligibility of transmitted

speech is to be expected at this relative phase angle. Figure 10 shows the

voltage spectrum of the multipath received signal with the relative phase

adjusted to minimum RF voltage at the first side lobe when the relative

and delayed path power levels are equal. The received video signal under

these conditions is shown in the upper half of 12.

13 shows predicted PCI as a function of relative power with the

relative phase angle adjusted for minimum RF voltage at the second side lobe.

11 shows the voltage spectrum of the multipath received signal corre

sponding to this phase adjustment when the relative power levels are equal.

1rhe lo""..rer half of 12 shows the corresponding received video signal. No

degradation in the intelligibility of transmitted speech is to be at

this relative angle.

Figure 14 shows predicted PCI as a flinction of relative power with the

relative phase angle adjusted for minimum RF voltage at the third side lobe.

Figure shows the spectrum of the multipath received signal corresponding to

this phase adjustment when the relative po-;;..rer levels are equal. The upper half

of Figure shows the corresponding received video signal. As seen from Figure

15, when the relative phase is adjusted for cancellation of the third side

lobe, the main lobe voltage is greatly attenuated. As seen in Figure 16 random

noise results between because of reduced receiver quieting during the

dwell time. Thus, Figure 14 is essentially the same as Figure Sj however, the

S/N ratio at equal power levels is less when the main lobe is completely can

celed than when partial cancellation occurs as a result of third side lobe can

cellation, The S/N ratios which correspond to Figs. 6 and 15 are -17 and -12 db

-21-

I 1\) 1\) I

PANORAMIC RADIO PRODUCTS. INC .

• •

v L • 0 ~-+-4~··"--~.,., --+---+---; 0. 6 0

l T A

G -20 ............... ~-+--· +>•• · •••r•···-' ·~······--

~ .~W-~m --+--.......,__--; 0.4 G E

-40-

0+ ~· SWEEP WIDTH FACTOR

Figure 10. Voltage Spectrum of the Multipath Received Signal with the Relative Phase Adjusted to Give Cancellation at the First Side Lobe.

ll iO G -20. ;[) :e

•

PANORAMIC RADIO PRODUCTS. INC. SPA·40

v .. ._ .... ,..-~.-..... f-.-f------1---t--......... 0. 6 0

l T

--+--......,._--1 0.4 ~ E

~s -o+ SWEEP WIDTH FACTOR

Figure 11. Voltage Spectrum of the Multipath Received Signal with the Relative Phase Adjusted to Give Cancellation at the Second Side Lobe.

Figure 12. Upper: Received Multipath Signal with the Spectrum Adjusted as Shown in Figure 10.

Lower: Received Multipath Signal with the Spectrum Adjusted as Shown in Figure 11.

0 a.. Q w 1-u 0 w ~ a..

I f\) w I

100

90

80

70

60

50

40

30

20

10

0~--_.----~----~--_.----~----~--~----~----~--~----~----~--~----~----~--~ -10 +2


Figure 13. Predicted PCI as a Function of Relative Power with the Relative Phase Adjusted for Maximum Voltage Cancellation of the Second Side Lobe at a Receiver Quieting of 39 db.

I 1\)

+ I

u c.. 0 w 1-u 0 w 0:: c..

100

90

80

70

60

50

40

30

20

10

0 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 +1 +2 +3


Figure 14. Predicted PCI as a Function of Relative Power with the Relative Phase Adjusted for Maximum Voltage Cancellation of the Third Side Lobe at a Receiver Quieting of 39 db.

+4 +5 +6

I f\) \J1 I

l Q G 0 8

0

• . •

-20. . • • _.,.

0.5

PANORAMIC RADIO PRODUCTS.INC. MODEL SPA - 40

i l

I I

1 dl ~ 11 ,l J

-0+ SWEEP WIDTH FACTOR

I.

0.1

0.6

0.4

0.2

u --

v 0 L T A G E

Figure 15. Voltage Spectrum of the Multipath Receiver Signal with the Relative Phase Adjusted to Give Cancellation of the Third Side Lobe.

Figure 16. Upper: The Received Multipath Signal with the Spectrum Adjusted as Shown in Figure 15.

Lower: The Received Delayed Signal with the Direct Path Signal Attenuated 100 db.

A visual comparison of Figures 7 (lower) and 16 (upper) shows the

difference in the video waveform resulting from complete and partial main lobe

cancellation. The lower half of Figure shows the received video si when

the direct path si was attenuated 100 db. This signal is identical with

that of Figure 7 (upper) that it is delayed 0. ~sec.

From the foregoing data, it can be concluded that for a delay of 0. ~sec

between the direct and reflected paths, multipath interference will degrade the

transmitted intelli over this communications system at 39 db of

when the relative powers are within ±l db and the relative angle is adjusted for

cancellation or near cancellation of the carrier frequency. The degradation in

intelli lity under these conditions can be attributed to greatly reduced

receiver quieting between the modulating pulses.

A variable attenuator was inserted in the delayed path at the transmitter

end and 20 db of fixed attenuation was removed from the delayed path at the

adder, The variable attenuator was adjusted to. dbm at the receiver

when the direct path adjustable attenuator was set at 100 db. This power

level corresponds to 20 db of receiver Equal power could be obtained

at the receiver from the direct path when the direct path attenuator was

set at 41.5 db and the delayed path was broken and terminated at the adjustable

line.

shows predicted PCI as a function of relative power with the

relative se angle adjusted for maximum voltage cancellation of the main lobe

of the voltage spectrum. The data which were taken at a power level which gives

20 db of quieting correspond to those shown in 8, which were taken at

39 db quieting. As expected, the range of relative power levels over which the

-26-

I 1\) -J I

u a.. Q w 1-u 0 w a::: a..

100

90

80

70

60

50

40

30

20

10

0 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1


Figure 17. Predicted PCI as a Function of Relative Power with the Relative Phase Adjusted for Maximum Voltage Cancellation of the Main Lobe at a Receiver Quieting of 20 db.

predicted PCI is less than 100 is much for 20 db ~uieting than for 39 db

~uieting. At slightly relative power levels when the main lobe voltage

is minimized, complete voltage cancellation of the main lobe does not

occur; however, at this reduced overall power level (20 db of ~uieting) the

residual power available during the dwell time is insufficient to cause suffi

cient ~uieting for a PCI of 100. The nonsymmetry of the curve of Figure

can also be attributed to receiver ~uieting. For direct-to-delayed

path relative power ratios, attenuation is removed from the direct path, and

fur ratios attenuation is added to the direct path" Thus, at positive

ratios more power is available at the receiver than is available at the corre-

sponding negative ratios. The ~uieting at any given ratio is therefore

greater than it is at the corresponding negative ratio, and the predicted PCI

curve rises from zero more for positive ratios than for ratios.

Figure shows predicted PCI as a function of relative power at 20 db of

quieting with the relative phase angle adjusted for minimum interference. Pre

dicted PCI does not fall below 64 at any relative power. Predicted

bility corresponding to PCI of is greater than per cent for isolated

monosyllabic words. Thus, it is possible to adjust the relative phase

under these conditions such that there is essentially no degradation in intel

ligibility of a transmitted voice message.

It is to note that for every relative power condition at both

levels tested, it is possible to adjust the relative phase so

that than 90 per cent predicted ty can be achieved on

isolated monosyllabic words transmitted over this communications system. Fur

ther, the range of phase angles for which such noise free transmission is

u a.. a w 1-u a w

I e::::

[\) a.. \0

I

100

90

80

70

60

50

40

30

20

10

0 -10


Figure 18. Predicted PCI as a Function of Relative Power with the Relative Phase Adjusted for Minimum Receiver Noise at a Receiver Quieting of 20 db.

possible is wide compared to the range of se angles at which degradation of

intelligibility takes This conclusively indicates that 0.25 ~sec is

not a sufficient delay to cause ficant degradation of intelligibility for

this communications system.

Approximately 1000 feet of RG-l7A/U cable has been acquired. Since meas

ured attenuation of this cable is only 0.07 db/ft, it should be possible to

obtain delays in excess of l ~sec at workable RF signal levels. Several spe-

cific delays between 0.25 and l. ~sec will be studied; the results of these

tests will be evaluated with respect to the time division multiplexer specifica-

tions to determine if dia c techniques can be to predict desired

si degradation at specific delays.

B. Mixer Study

l. Introduction

The mixer prediction scheme established in Quarterly Report No. l

as the most acceptable method of prediction among the several presented was shown

to be accurate within 4 or 5 db. 6 Further accumulation of data and associated

prediction have indicated that the scheme may yield predicted values with con-

siderably errors. One cause for such errors presently appears to stem

from the measurement difficulties discussed subsequently.

Another source of prediction error may result from the basic assumptions

made in establishing the entire method for determining the mixer characteris-

tics. The generation similarities peculiar to members of a common generating

order may be sufficiently different to produce ficant errors with large

input levels.

-30-

2. Errors in Measurement

In any study the need for accurate and reliable data, the

investigator is often plagued with measurement errors which prevent data repeti

tion and correlation of measured and calculated values. Since the validity of

the results of an investigation is dependent upon substantiating data, the re

searcher must either eliminate these errors, or else recognize their si

cance by their source. Numerous errors may be found to be associ-

ated with improper eQuipment operation or calibration. Others can be elimi

nated by a change in measurement techniQUe. One source of error that cannot

be completely eliminated, however, is that due to eQuipment limitations.

Because of this, allowances must be made for data variations depending upon

the particular eQuipment and test used.

Specifications of accuracy, stability, etc. on most commercial test eQuip

ment available today are very conservative, and operation of the instruments

will normally be well within the limits imposed by the manufacturer. However,

an instrument cannot be assumed to accurately except within the range

of its limits, and thus any measurements made should be considered only as

accurate as the measuring of the instrument.

To date, the studies of mixer action have resulted in the accumulation of

large amounts of data, not only for the purpose of show similarity of

operation between different mixer types, but also to substantiate theoretical

calculations of mixer action. The deviation in measured data and predicted

mixer action has been sufficient in some cases to warrant a study of the

effect of measurement errors upon correlation of measured and calculated

results. To illustrate the variations in results that may occur due to

-31-

measurement errors, a typical measurement procedure is given below, along with

the errors that may occur. Only errors associated with equipment

limitations are considered.

shows the test involved in the measurement of spurious

responses of a lN82A diode mixer. The sequence of pertaining to the

measurement of a response are listed, along with the error associated

with each

a. Calibrate radio interference measuring set for a standard response.

Error e + 2e l 3

b. Set local oscillator to desired level. Error = +

c. Set signal generator to standard response as measured on

radio interference mea set. Error

d. Monitor signal to mixer using radio interference measuring

set. Error = e3

e. Measure signal input to mixer by signal substitution method.

Error + 2e 3

error in db associated with stability/accuracy of

used for signal substitution measurements.

error in db associated with stability/accuracy of local

oscillator.

= error in db associated with dial

Total error + + 7e 3

I w w I

LOCAL

OSCILLATOR

SIGNAL

GENERATOR

RADIO

INTERFERENCE -

MEASURING

SET (

(~ ,.. GENERATOR

DIODE INPUT

J - DIODE IF

-- MIXER

RADIO

INTERFERENCE

MEASURING

SET

Figure 19. Test Setup for Spurious Response Measurements.

It is seen that the cumulative effect of errors associated with each step

can result in quite a large error in the measured response. The absolute value

of the error will be dependent upon accuracy, while variations in

repeated data depend upon equipment stability. Since the errors e1

, and

are established by the particular equipment being used, no great improvement

is possible in the measured data.

Consider the absolute errors associated with a measured response for

±l db, = ±l db, and ±0.1 db, These particular values of and

are those associated with the accuracy of the equipment used in the mixer

studies, and is an estimation of dial reading error. For these values, the

total error possible in a given response is .7 db. The differences in mea-

sured data for independent investigations could therefore be spread over a

range of 7.4 db. Next consider the effects of instrument stability upon

repeated data. For = ±0.3 db, e2 ±0.3 db, and ±0.1 db, a range of

3.2 db could exist in a repeated measurement for this particular test con

figuration. Although not of unreasonable magnitude, this error is

considerably in spurious response calculation, and its effect upon

mixer action can become intolerable.

The above illustration not only emphasizes a particular problem encountered

in the measurement of spurious responses, but also indicates a general measure-

ment associated with equipment limitations. Added to errors from other

sources, errors resulting from instrument accuracy and stability can eliminate

the validity of measured data. Only if the investigator understands these

limitations can he make the fullest use of experimental data obtained by

measurements.

-34-

3. Generalized Prediction Equations

The entire mixer response system can be expressed as a

zed equation the ection value of any chosen response:

R ::::: ection to the (p, p,q

M l,l

Measured value of (l,

M2,l == Measured value of (2,

~,2 ::::: Measured value of (l,

M (n-l),l == Measured value of

n = P

K p,q

+ q

(cp,q - c(n-l),l)/q

q, ±) responses in db.

l, ±) responses in dbm.

l, ±) responses in dbm.

±) responses in dbm.

[(n-1), l, ± J responses in dbm.

Response constant from Table I for (p, q, ±) responses.

(l)

c (n-l),l =Response constant from Table I for [(n-1), l, ±] responses.

The generalized equation can also be written to express the absolute response

level for the system sensitivity:

A p,q

2 M q 1,2

A Absolute response value in dbm. p,q

M + ~ M - 2 p,q q 2,1

can be written in terms of the measurement accuracy, ±e db:

-35-

(2)

(3)

0

2

3

4

I w 5 0\ I

6

7

8

9

10

a +

a..

t

TABLE I SPURIOUS RESPONSE TRIANGLE FOR A MIXER HAVING A POLYNOMINAL REPRESENTATION OF THE TENTH DEGREE

10 9 8 7 6 5 4 3 2 0 2 3 4 5 6 7 8 9 10 Q- P--....

~ vo ' "~~/ ' v/

---""

'" "" / f), v...., .. ~ 0 [>( 0

~ I" / ..;>

[<« _'\ 6 ~ 0 [X 6

v ~ ~0 ~ l" / '(

":::-.!.:::> ' [>( [>( [X l/ sr v~ ~~ f'.. 12 2.5 2.5 12 /

O,.e..

/- ~\ 18 ~ 6 [>( 2.5 [X 6 [>( 18 /~s 9~

b !".

~ ~ [>( [>( [>< r:i

' 24 10 4 4 10 24 v '\ " /

.> '\ 30 [>( 14.5 [>< 6.5 ~ 4 [X 6.5 [>( 14.5 [>( 30 IL

co "' / t:9

' 36 [>( 19.2 [>( 9.7 [>( 5.2 [>( 5.2 [>( 9.7 [X 19.2 [X 36 v ~ ' / .P

' 42 X 24 )( 13.2 X 7.2 >< 5.2 [X 7.2 X 13.2 [>( 24 C>< 42 v

,~ 1\. / ' 48 [>< 29 [X 17 X 9.7 L( 6.1 >< 6.1 [X 9.7 )( 17 [X 29 ~ 48

" / I 52 I [X 34.2 X 21.2 X 12.6 ~ 7.8 ~ 6.1 [X 7.8 X 12.6 [>( 21.2 )< 34.2 [X 52 I

I CHART VALUES ARE IN db BELOW INPUT LEVEL

/ /o

1i 0

u 0 ·e 0 c >. 0

a..

E p,~

± e ± ~-l e + 2 ~-l e + 1 e. ~ ~ ~

(4)

In the limit as~ ~oo, the maximum possible error is ±4e db, Lower values of

~yield successively less error. Actuall~, the absolute maximum

possible error is only ±3e db since the error in measuring the absolute response

level is considered in e~uation (3). The limiting case for e~uation (3) indi-

cates the maximum differences to be expected between measured and predicted

values.

Considering the maximum measurement error possible and the error

function for the ction scheme, outside errors of as much as 6.4 db may

be obtained. However, the likelihood of occurrence of the maximum possible

error is not very hi and the average error should lie considerably within

these outer bounds.

Fourteen sets of mixer data were collected to check the accuracy of the

prediction method. The tests were conducted different conditions of

local oscillator sensitivity level, and mixer output These

data are plotted as prediction error versus response density as shown in

20 through 33. The diode type and the conditions imposed during the

tests are noted on the individual figures. 34 shows the circuit used

to obtain the various response measurements through the tenth order of

generation.

It is noted that for large local oscillator levels and for conditions of

tuned diode output, the prediction error is displaced in the negative

direction by a considerable amount. The peak of the rough density integral,

~7-

15

14

13

12 DIODE: 1NB2A L.O. LEVEL: + 2 dbm SENSITIVITY: - 95 dbm

11 I.F. FREQUENCY: 1 Me TUNING: None

10 L.O. FREQUENCY: 10 Me

>-CROSSHATCHED: True Density 1-

9 v; DASHED: Density Integral z ,...,

w I I 0 I I w 8 I I V') r-' L1 z 0 0... 7 I I V') I I w I I a::

6 I I I I I

w I I OJ

5 I I I

4

3

2

PREDICTION ERROR IN db

Figure 20. Response Density Versus Prediction Error for a IN82A Diode Mixer.

15

14

13 DIODE: 1N82A

12 L.O. LEVEL: + 2 dbm SENSITIVITY: - 95 dbm I.F. FREQUENCY: 3 Me

11 TUNING: None L.O. FREQUENCY: 10 Me

10 CROSSHATCHED: True Density

>- 9 DASHED: Density Integral 1-in .-..rl z w

8 I I a I I w I I V) I I z 7 0 I I a.. I L1 V) I w 6 .-.J L, a:::

I L, I

I 5 I L-----, VJ r.J \.0 I I I

4 I L, I .-.J I

I 3 L1

I I

2


Figure 21. Response Density Versus Prediction Error for a lN82A Diode Mixer.

I -r::-0 I

15

14

13

12

11

10

~ 9 v; z ~ 8 w II)

z 0

7 a.. II)

w 6 0::

5

4

3

2

,.-"'1 : ... _, r-.J I I I

r-' I

! L-1 r-~ L-1 I I I I i L-,

'--, I I I

DIODE: L.O. LEVEL: SENSITIVITY: I.F. FREQUENCY: TUNING: L.O. FREQUENCY:

CROSSHATCHED: DASHED:

-., I '----,

I L-, L_,

I

1N82A + 9 dbm - 95 dbm 1 Me None 10 Me

True Density Density Integral

0~----~--._~--~~~~~~L-~~~~~~~~~~~~_._.~~---r----~----~._~~----~

-13 -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 +2 REDUCTION ERROR IN db

Figure 22. Response Density Versus Prediction Error for a 1N82A Diode Mixer.

15

14

13

12

11

10

>- 9 1-;:;; z 8 UJ 0

UJ 7 !./')

z 0 a.. !./') 6 I UJ

-!=" a:: 1-l I 5

4

3

2

-17 -16 -15 -14 -13 -12 -11 -10 -9 -8 -7




-6 -5

1N82A + 2 dbm - 95 dbm 1 Me Output to 1 Me 10 Me


-4 -3


-2 -1

15

14

13

12

11

10

>-t- 9 v; z UJ 0 8 UJ V')

z 7 0

a. V')

UJ 0::: 6

I .f:"" 1\) I 5

4

3

2

-9 -8 -7

Figure

-6 -5 -4 -3

r-.... _ I I

I : r-' --1 I I I

I f I -~

I L--,

I I I .._.,.

I -, I I

-2 -1 0

-1 ._, I

+1


DIODE: 1N82A L.O. LEVEL: - 5 dbm SENSITIVITY: - 102 dbm I.F. FREQUENCY: 1 Me TUNING: None L.O. FREQUENCY: 10 Me

CROSSHATCHED: True Density DASHED: Density Integral

+2

Response Density Versus Prediction Error for a 1N82A Diode Mixer.

+7

15

14

13

12

11

10

>- 9 1-ii') z w

8 0

w II)

z 7 0 a.. II)

w 6 l ~

.f.:"'" w I 5

4

3

2

-8 -7 -6 -5 -4 -3 -2

DIODE: L.O. LEVEL: SENSITIVITY: l.F. FREQUENCY: TUNING: L.O. FREQUENCY:


,...., I I I L..., I I

~- I I L--1 I I I I I I

~~ ..... .., I L..,

-..J L.., I_J L---, I I

-1 0


L, I I

+4

1N82A -5 dbm - 102 dbm 3 Me None 10 Me


+6


+7 +8

15

14

13

12

11

10

>-1-

9 ;:;; z w 0

8 w ..,., z 0 7 a.. ..,., w 0::

6 I + + I 5

4

3

2

-9 -8 -7 -6 -5 -4


CROSSHATCH ED: DASHED:

-3 -2 -1 0 + 1


1N21B + 2 dbm - 95 dbm 1 Me None

10 Me

True Density

Density Integral

+4

Figure 26. Response Density Versus Prediction Error for a 1N21B Diode Mixer.

+6 +7

15

14

13

12

11

10

>- 9 1-v; z LU 8 a LU V')

7 z 0 S;

I LU 6 + 0::

V1 I

5

4

3

2

-8

DIODE: L.O. LEVEL: SENSITIVITY: l.F. FREQUENCY: TUNING: L.O. FREQUENCY:


1N21B + 2 dbm - 95 dbm 3 Me None

10 Me


-2 -1

,..-... ,.._ .. : I I I '--.,

: I ,.-J '----., I I I '--, I I I I I I

,..-~ L-~ I I I I I I I I

r•J ~-~ I I I I I I I I

.---' '--, I I

r-" '--, I I I I ,.---""

I

0


Figure 27. Response Density Versus Prediction Error for a lN2lB Diode Mixer.

+8

15

14

13

12

11

10 >-I-v;

9 z w 0

w 8 (/)

z 0 Q_

7 (/)

w 0:::

6

I + 5 0\ I

4

3

2

-10 -9 -8

r r.J

r------J r.J I

-7 -6 -5

,., I -, I ._, I I

,-..J I I 1 I I I I I

r.J L, ,-.J L, I I I I

r----J L, I I I I I I I I

DIODE: 1N21B L.O. LEVEL: + 2 dbm SENSITIVITY: - 95 dbm I.F. FREQUENCY: 1Mc TUNING: Output to 1 Me L.O. FREQUENCY: 10 Me



---,

-4 -3 -2 -1 0


L, L,

L--, '-----------

+1 +2 +4

28. Response Density Versus Prediction Error for a 1N21B Diode Mixer.

+5 +6

15

14

13

12

11

10 >-I-Vi 9 z w 0

w 8 V)

z 0 CL 7 V)

w 11':

I -f::"" 6 -...:] I

5

4

3

2

-6 -5 -4 -3 -2 -1

,..., I -, I I I I

r----' .... ., f I f I I I I .._,

r.J ; I .... ,

,...J I I I I ~~

,..~ L~ I I

~.J I __ ,.,

0




+5

1N21B -6 dbm - 95 dbm 1 Me: None 10 Me:


+7 +8

Figure 29. Response Density Versus Prediction Error for a 1N21B Diode Mixer.

+10

15

14

13

12

11

10

>-t-

9 v; z w Cl

8 w V')

z 0 7 a.. V')

w a::

I 6 + (X) I

5

4

3

2

-8 -7 -6 -5 -4 -3

r--. r-J I I I I I

r .. J I l..-,

I I I Li

I I



1N21B -9 dbm - 95 dbm 1 Me None 10 Me

True Density

Density Integral

NOTE: Many Responses are not Measurable Under these Conditions.

r--' I

L-- --1

I r~J I I

'

I

' I I

-2 -1 0 + 1 +2


+3 +4 +5

30. Response Density Versus Prediction Error for a 1N21B Diode Mixer.

+7 +8

15

14

13

12

11

10

>- 9 1-v; z w

8 0

w II)

z 7 0 I ll..

II)

+ w 6 \0 0::

I

5

4

3

2

-9 -8 -7 -6 -5 -4

r, I

r-' ,......J

I I

r.J • I I I I

r-' I I I I

1 I I I I I -----. L,

L, L--,

DIODE: LO. LEVEL: SENSITIVITY: I.F. FREQUENCY: TUNING: LO .• FREQUENCY:


1N23C + 2 dbm -95 dbm 1 Me None

10 Me

True Density

Density Integral

L-------,

-3 -2 -1 0 +1


+2

L-----, I

+3 +5

Response Density Versus Prediction Error for a 1N23C Diode Mixer.

+6 +7

15

14

13

12

11

10

>-1-v; 9 z w 0

w 8 V')

z 0 7 c..

I V')

\.Jl w 0 0:::

I 6

5

4

3

2

-8 -7 -6 -5

Figure

r-i : I

r--~ ... _, I t I I I t I t I .__-:

I I I t I I ,..... .

I I

: L., I I

r-~ 1 I I ,._ ..

I ,._,., I I • I r-----"'

I

r-"' I

r-"' I

r-" I

-4 -3 -2 -1 0 +1 PREDICTION ERROR IN db



+2 +4

1N23C + 2 dbm - 95 dbm 3 Me None

10 Me


Response Density Versus Prediction Error for a lN23C Diode Mixer.

+7 +8

-14 -13 -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 +1 +2 PREDICTION ERROR IN db

Figure 33· Density Versus Prediction Error for a lN23C Diode Mixer.

I \Jl [\) I

BNC NO.2 INPUT TEST OUT

·-------, I ~n I

- I VARIABLE I

BIAS I SOURCE I

I I I L _______ J

Figure 34.

1N82A

Schematic Diagram of 1N82A Test Mixer.

BNC NO.4

TEST OUT

BNC NO.5

TEST OUT

indicated by the dashed encirclement, lies in the center of the distribution

and indicates the distribution mean. The position of the mean with respect

to the overall distribution is similar fdr all tests made. This would indicate

that the calculation procedure is satisfactory in all the test cases. The

displacement of the mean indicates an error in the value of local oscillator

to signal power ratio.

The latter fact is verified by utili many measured responses to cal-

culate an average power ratio. This average power ratio is used in the pre

diction calculation instead of the power ratio determined by the (2, 1) and

(1, 2) responseso The result is the return of the distribution mean to the

vicinity of the 0 db error position. Figure 35 shows the response density

versus prediction error chart for the same data used to abtain the chart of

Figure 22 that an average power ratio was utilized.

Since the power ratio of local oscillator to input signal is normally

determined using the (2, 1) and (1, 2) responses, an error in either response

measurement could cause the distribution mean to shift. Errors in these meas-

urements appear to be the chief cause for the errors in prediction which

are associated with a shift in the distribution mean.

A consideration for the cause of measurement errors in the ( 1) and

( 2) responses is the fact that both of these responses lie near or in

response nulls for the normal bia conditions of the diodeo7 Small

changes in local oscillator absolute level may result in response level

variations since the slopes of response curves are very steep near response

nulls and the bias point is chiefly determined by the local oscillator level.

Figure 36 shows the curve of the (2, l) response level versus diode bias

where a sharp null is seen to exist near the point of zero bias.

15

14

13

12

11

10

>- 9 1-Vi z

8 w 0

w 1,/) 7 z

I 0 Vl 0... + 1,/)

I w 6 ~

5

4

3

2

-8 -4

r-"' I I I 1..-, I I I I

r-.J I I I I L---, I I

r-~ L-, I I

r-~ 1 I : L.,

,...J L-, I I

r-J L., I '

DIODE:

L.O. LEVEL: SENSITIVITY: I.F. FREQUENCY: TUNING: L.O. FREQUENCY:


L--,

+1


'--; ' 1..-~

I '----, I ._ __ _

+4

1N82A + 9 dbm - 95 dbm 1 Me None

10 Me


Figure 35. Response Density Versus Prediction Error Using Averaged Power Ratio.

I \Jl \Jl I

-D -o

_J w > w _J

~ z 0 1J:; w 0::

w 2: t-<{ _J w 0::

! 10 db

• • •

1N21B

1N23C

1N82A

• •

0

0

0

0

-0.6

-0.6

-0.5

-0.5

Figure 36.

BIAS VOLTAGE

(2, 1) Response Level Versus Bias Voltage for Single Diode Mixer with no Frequency Discrimination.

L.O.: lO Me, ' 13 dbm

-- 1N21B DIODE MIXER

0 1N23C DIODE MIXER

• 1N82A DIODE MIXER

p ·- 2, q 1

0

The averaged local oscillator to signal power ratio offers the most

accurate solution but suffers because of the large data sample necessary to

resolve the average. Examination of the data has indicated that the value of

local oscillator to input si power ratio obtained from the (3, 1) and (1, 3)

responses follows the average power ratio, It is reasonable that such is

h th . t h 11 1 t th b . . t 8 Th t e case since lS response se , as no nu s c ose o e zero las poln . e

use of these two response levels rather than the (2, l) and (1, 2) response levels

may yield better prediction values when the diode is operated near the zero bias

condition.

5. Analysis of the Effective Mixer Constants

The large errors in determining the average power ratio may not be

entirely due to measurement error. The problem may lie in the inherent error

of the computation method used to predict response levels The entire system

is based on the fact that members of a common order follow very similar curves

when their levels are plotted versus changes in diode bias. 9 The relative

It is assumed that each member of a order of generation has as a factor

the same identical constant as all other members of the order and that this

constant is a function of both the order and the diode bias. The constant is

not necessarily the same as that of the like ordered term of the mixer polynomial.

An example of this is ea

10 response:

k + (15 e 2 eb 3 8 a

constructed using the coefficient of the (2, 1)

4 ) +

-56-

( e a 4 3

2 5 . 105 + eb + 64 ea

+ 945 e 6 3 315 + 64 64 a

6 eb) 2 e 7 + 63

b 32

+

e a

8

4 e 5 b

(5)

In the prediction scheme, only the first term of the coefficient is considered. 11 , 12

The sample response measurement determines a value for the constant, k3

, and this

value is assumed to be the same as that in the (1, 2) response coefficient~

3 2 ( e 3 2 +2 eb4) k5 + ( 105 3 4 '4 eb k3 + a eb 4 16 eb

105 5 2 105 eb6) ( 315 5 4 + 32 eb + 64 + 16 eb

945 3 6 + 315 e 7 2 63 ebB ) (6) + 64 ea 64 a eb + 32 +

of which again only the first term is considered.

In reality, the constant determiped by the sample response measurement is

not a constant, but that sum of terms which remains after the response

coefficient by its first term ...._ .... ~.-.... ..LJ.Jf'> k . Thus the constants, K , determined n n

by the sample response measurements of the

and (1, 2) responses:

K I

3

k + 3 (

2e2 3 a

+ (lO, 2

(2e2 2 a

+ ( 4

+ 2 e 2) 2 b

+ e a

5 2 ) + 3 eb

+ e a

+

4 +

+

2

-57-

ction scheme are, for the ( l)

( 35 e 2 e 2 + 35 e 4 + 35 e 4) k 4 a b 16 a 8 b 7

e a

( 3~

6 + +

+

+ (8)

The differences in the value of K3

and the value of K3

' are manifested in the

constants of corresponding terms since the same type and number of terms appear

in both. The differences are ordinarily slight but increase readily with larger

signal levels.

The sl difference in the constants, K , is evidenced in the shi n

of the response or harmonic generation nulls for a common generating order.

Figures 37 through 39 show curves of common generation orders taken on a lN2lB

diode with a +2 dbm local oscillator level at the diode. It is noted that the

of these curves are somewhat but that the nulls consistently

shift to the with increa q. The shapesof the harmonic and the q = l

response curves are often so similar that the differences might be attributed

to measurement error. The plots of q responses, however, indicate a

definite trend of shift with increasing q. The effective mixer con-

stant is therefore only a semiconstant and not identical for all members of a

common order. With the exception of operation in close proximity to

however, the assumption is valid and good results are obtainable.

6.

Mixer response prediction errors may be the result of several factors

in conjunction or any single factor alone. Measurement accuracies are greatly

affected by equipment limitations and the response prediction system is sensi-

tive to measurement error. The assumptions upon which the prediction system is

based are imperfect to a which may be sufficient to produce rather

errors under certain conditions of mixer operation. Sli alterations of the

ction procedure appear to greatly reduce the prediction errors.

-58-

.....J

~ 50 w .....J

w > ~ 40 .....J w 0::

30

'::l-

+"+I+

' 1+-+

I+ .

Figure 37.

'' u ~"-r+-

++~-'+':r

FORWARD BIAS VOLTS

Relative Response Level Versus Forward Diode Bias for Third Order Responses of the 1N21B Diode Mixer.

-59-

z 60 ~

~ w > w ~

50 w ~ ~ ~ ~ w ~ 40

0.0 0.1 0.2 0.3

FORWARD BIAS VOLTS 0.4

38. Relative Response Level Versus Forward Diode Bias for Fourth Order Responses of the 1N21B Diode Mixer.

-60-

80

Ld 50 > UJ _J

UJ > ~ 40

g ·······-30

20

10

0.0 0.1 0.2 0.3 0.4 0.5 0.6

FORWARD BIAS VOLTS

Figure 39. Relative Response Level Versus Forward Diode Bias for Fifth Order Responses of the 1N21B Diode Mixer.

-61-

0.7

Further analysis is necessary to determine which of the several factors

is the predominant cause for prediction error. Subsequent quarters will be

devoted to such analysis and to the gathering of data for other mixer types.

-62-

V. CONCLUSIONS

The observed performance of the FM receiver in the presence of two common-

channel transmitted si was in general agreement with published observations

and theory. Corrington reported simultaneous reception of two FM radio stations,

which operated on the same frequency, when their carrier wave voltage levels

dropped below the level at which the limiter in the receiver operated. This

effect was observed in the present system when the transmitter frequencies were

tuned too far from the receiver tuned frequency to permit complete limiting at

the available power levels.

The multipath study made on the PPM/FM communications system indicated

that for every relative power condition at two direct path signal levels, it

is possible to adjust the relative phase so that greater than 90 per cent

predicted intelligibility can be achieved on isolated monosyllabic words trans-

mitted. In addition, the range of phase for which such noise free

transmission is possible is wide compared with the range of phase angles at

which degradation of intelligibility takes place. It is concluded that 0.25 ~sec

is not a sufficient delay to cause significant degradation of intelligibility

for the PPM/FM communications system which was investigated.

The prediction of mixer response levels suffers from errors due to measure

ment inaccuracies and to inherently imperfect assumptions in the prediction

calculations. These errors may be reduced by substituting certain responses

for those normally used to obtain the local oscillator to input signal power

ratio. Reliable prediction is obtainable for ordinary mixer operation.

-63-

VI . PROGRAM FOR NEXT INTERVAL

Additional interference susceptibility studies will be conducted on avail

able communications sets.

The effects of several delays between 0.25 and 1.25 ~sec on multipath

interference conditions will be studied the PPM/FM communications system

described in this report. The results of this investigation will be evaluated

with respect to the time division multiplexer specifications to determine if

diagnostic techniques can be applied to predict desired signal degradation at

specific delays.

Further analysis will be made to determine which of the several factors

is the predominant cause for prediction errors of mixer data. The

of data for different mixer configurations will continue.

An RFI bibliography) with abstracts) should be completed during the next

interval.

-64-

VII. IDENTIFICATION OF KEY TECHNICAL PERSONNEL

Title Approximate Hours

R. M. Cook Grad. Research Assistant 81

H. w. Denny Research Assistant 14

E. E. Donaldson, Jr. Grad. Research Assistant 343

0. H, Ogburn Research Assistant 516

D. w Robertson Head, Communications Branch 61

c. w. Stuckey Asst. Research Engineer 499

H. D. Trammell, Jr. Asst. Project Director 513

J. R. Walsh, Jr. Research Engineer 69

Wo B. Warren, Jr. Research Engineer 41

E. W, Wood Project Director 371

Mr. Cook accepted a position with the Federal Communications Commission

on 3 June 1963.

Approved:

~. /J, {Gtdl;co D. W. Robertson, Head Communications Branch

-65-



lib-sascan

Rectangle

lib-sascan

Rectangle

VIII. REFERENCES

l. Murlan S. Corrington, "Frequency Modulation Distortion Caused by Connnonand Adjacent-Channel Interference,'' RCA Review, Vol. 7, pp. 522-545, ( 1946).

2, L, B. Arguimbau and J. Granlund, ''The Possibility of Transatlantic Connnunication by Means of Frequency Modulation, t1 Proceedings NEC, Chicago, pp. 644-653, (November 1947).

3 L. B. Arguimbau and J. Granlund, "Sky-Wave F-M Receiver, 11 Electronics, pp. lOl-103, (December 1949).

4~ Harold A. Wheeler, "Connnon-Channel Interference Between Two FrequencyModulated Signals, f! Proceedings IRE, pp. 34-50, (January 1942).

5 Elie J. Ba ghdady, !!The FM Random-Noise Threshold, '' Frequency, pp. 12-17, (March-April 1963).

6. Eo W, Wood, R. D. Trammell, Jr., C. W. Stuckey, H. W. Denny, E. E. Donaldson, Jr., and R. M. Cook, t!Quarterly Report No. l, Project A-678, 11 Electronic ~quipment Interference Characteristics-Communication pe, Contract No. DA 3 -039 AMC-0229 E , Georgia Institute of Technology, Engineering Experiment Station, pp. 91-95, (15 February 1963 to 15 May 1963)

7" R. N. Bai R. D. Trammell, Jr., J. R. Walsh, Jr., and E. W. Wood,

8.

9o

10,

ll.

12"

°Final Technical Report, Project A-543, 11 Electronic Equipment Interference ,Characteristics-Communication Type, Contract No. DA 36-039 sc-87183, Georgia Institute of Technology, Engineering Experiment Station, pp.77-78,

February 1963).

Wood, op. cit. , p. 78.

Bailey, op. cit., pp. 63-83.

Bailey, op. cit., p. 129.

Bailey, op. cit., pp. 80-89.

Wood, op. cit., pp. 81-102.

-66-

No. of

1

1

1

3

10

1

1

1

2

1

1

1

1

1

1

DISTRIBUTION LIST

To

OASD (R&E) Rm ' Pentagon, Washington ATTN: Technical Library, The

, D. C.

Chief of Research & Development, OCS1 Department of the Army, Washington , D. C.

Commanding U. S. Army MBteriel Command, ATTN: R&D,Directorate, Washington 25, D. C.

Commanding General, U. S. Army Electronics Command, ATTN: AMSEL-AD, Fort Monmouth, New

Commander, Defense Documentation Center, ATTN: TISIA, Cameron Station, . 5, Alexandria,

Commanding General, USA Combat Developments Command, ATTN: CDCMR-E, Fort Belvoir, Virginia

Commanding Officer, USA Communication and Electronics Combat Agency, Fort Huachuca, Arizona

Commanding U. S. Army Electronics Research and Development Activity, ATTN: Technical Library, Fort Huachuca, Arizona

Chief, U. S. Army Agency, Arlington Hall Station, Arlington Virginia

Deputy President, U. S. Army Security Agency Board, Arlington Hall Station, Arlington 12,

Director, U. S. Naval Research Laboratory, ATTN: Code , Washington, D. C. 20390

Commanding Officer and Director, U. S. Navy Electronics laboratory, San Diego 52, California

Aeronautical Division, ATTN: ASAPRL, Wright-Patterson Air Force Base, Ohio

Air Force Research Laboratories, ATTN: CRZC, . G. Hanscom Field, Mass.

Air Force Cambridge Research Laboratories, ATTN: CRXL-R, L. G. Hanscom Field, Bedford, Mass.

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Rome Air Development Center, ATTN: RAALD, Griffiss Air Force Base, New York

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Commanding Officer, U. S. Army Electronics Materiel Support Agency, ATTN: SELMS-ADJ, Fort Monmouth, New

Director, Fort Monmouth Office, USA Communication and Electronics Combat Development Agency, Fort Monmouth, New

Corps of Research

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Commanding Officer, U. S. Army Electronics Research and Development Laboratories, ATTN: SELRA/NRL, Fort Monmouth, New

Commanding Officer, U. S. Army Electronics Research and Development Laboratories, ATTN: SELRA/GFR, Fort Monmouth, New Jersey

No. of Copies

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To

Commander, Rome Air Development Center, Griffiss Air Force Base, New York, ATTN: RAUMA (C. R. Miller)

CommEnding Officer, U. S. Army Electronics Research and Development Activity, ATTN: Sig Corum Department, Tech Division, Fort Huachuca, Arizona

Chief, Bureau of Ships, Department of the Navy, Washington 25, D. C. ATTN: 8lld(E. G. Nucci)

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Chief, Bureau of Aeronautics, Department of the Navy, Washington 25, D. C.

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Commanding Officer, U. S. Army Electronics Research and Development Activity, ATTN: FC-05, White Sands, New Nexico

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AFSC Scientific/Technical Liaison Office, U. S. Army Electronics Research and Development Laboratories, Fort Monmouth, New Jersey

REPORT NO. 24


PROJECT A-678


By C. W. Stuckey, E. W. Wood, R. D. Trammell, Jr., E. E. Donaldson, Jr., and 0. H. Ogburn


Placed by the U. S. Army Electronics Research and Development Laboratory Fort Monmouth, New Jersey

15 August 1963 to 15 November 1963



ENGINEERING EXPERIMENT STATION of the Georgia Institute of Technology

Atlanta, Georgia

REPORT NO. 24


PROJECT A-678


By

C. W. Stuckey, E. W. Wood R. D. Trammell, Jr., E. E. Donaldson, Jr.,

and 0. H. Ogburn

CONTRACT NO. DA 36-039 AMC-02294(E) (Continuation of Contract No. DA 36-039 sc-87183)

DEPARTMENT OF THE ARMY PROJECT: 3B24-0l-00l

The object of this research program is to conduct a comprehensive investigation to determine methods for measuring the interference characteristics (spectrum signature) of U. S. Army communications equipment deemed necessary for the prediction and minimizing of electromagnetic interference.

AUGUST 1963 to 15 NOVEMBER 1963

PLACED BY THE U. S. ARMY ELECTRONICS RESEARCH AND DEVELOPMENT LABORATORY


FOREWORD

This report was prepared at the Georgia Tech Engineering Experiment Sta-

tion on Contract No. DA 36-039 AMC-02294(E). The report covers the activity

and results of the third quarter's effort on a project to conduct a feasibil-

ity study and investigation to determine methods for measuring the interfer-

ence characteristics (spectrum signature) of U. S. Army pulse modulated

type communications equipment deemed necessary for the prediction and minimiz-

ing of electromagnetic interference.


ii



lib-sascan

Rectangle

lib-sascan

Rectangle

TABLE OF CONTENTS

I. PURPOSE

II. ABSTRACT . .


IV. FACTUAL DATA .

A. The Effect of Multipath Interference on the Intelligibility of Speech Transmitted Over an FM System Employing Time Division Multiplexing

l. Test Procedure . 2. Data Evaluation

3· Test Results . . 4. Discussion . . 5· Conclusions

B. Mixer Testing and Evaluation

1. Introduction ....

2. Prediction and Mixer Operating Conditions

3. Prediction and Mixer Driving Circuitry .

4. Prediction and Mixer Design

5· Considerations for Receiver Design .

6. Conclusions

C. A Method for Determining Response Coefficients .

1. Introduction .....

2. Development of Method

3. Procedure

4. Conclusions

(Continued)

iii

Page

l

2

3

4

4

4

7

10

19

23

24

24

24

29

31

33

34

34

34

34

39

42

TABLE OF CONTENTS (Concluded)

V. CONCLUSIONS

VI. PROGRAM FOR NEXT INTERVAL

VII. IDENTIFICATION OF TECHNICAL PERSONNEL

VIII. REFERENCES . . . • . • • . . . . . . .

This report contains 48 pages. iv

Page

44

45

46

47

1.

LIST OF FIGl.JRES

Block Diagram of Test Configuration Used For Multipath Interference Tests . . . . . •

2. Predicted Intelligibility of Isolated Monosyllables as a Function of S/N Ratio at the System Audio Output

3. General Electronic Laboratories Scoring Curve

4. PCI as a Function of S/N Ratio at the System Audio Output

5. Predicted Intelligibility as a Function of Direct to Delay Power Level Ratio For a Relative Delay of 0.2 ~sec







12. Predicted Intelligibility as a Function of Relative Delay Time For Five Quieting Levels . • . .

13. Photographs of Demultiplexer Pulse Trains

14.

15.

16.

17.

Response Density Versus Prediction Error For a 1N82A Diode Mixer With +0.1 Volt Bias . • • ••.••••

Response Density Versus Prediction Error For a 1N82A Diode Mixer With -0.1 Volt Bias . . . • . .•.

Response Density Versus Prediction Error For a 1N82A Diode Mixer With +0.2 Volt Bias . . . . • ..•..

Response Density Versus Prediction Error For a 1N82A Diode Mixer With +0. 2 rna Bias • . • . • • . . . • . .

(Continued)

v

Page

5

5

8

8

11

12

13

14

15

16

17

20

21

26

26

27

27

18.


Response Density Versus Prediction Error For a lN82A Diode Mixer With Tuned Output • . . . . . • • • . .

19. Response Density Versus Prediction Error For a lN82A Diode Mixer With Unfiltered Input Signal •••...

20. Schematic Diagram of Double-Diode Mixer Test Circuit

21.

22.

Response Density Versus Prediction Error For Two Cascaded lN82A Diodes . • • . • . . . . .

Change in Spurious Response Rejection With a Change in IF Sensitivity .......•

23. Triangle of Constant Coefficients

24. Responses Generated from the Power Series Representation of a Mixer Characteristic When the Input is Two Summed Sinusoids

25. Table of Binomial Coefficients ..

26. Response Coefficient in Triangular Form

27.

28.

Numerical Coefficients (k. 1 s) of the Terms in the (2, l) Response Coefficient . . ~ • • • • • • • . • .

Triangle for the (3, 2) Response Formed from the Table of Binomial Coefficients . • . • . • . . . • • .

vi

Page

28

28

30

30

32

35

36

38

40

41

I. PURPOSE

The purpose of this project is to conduct a feasibility study and investi

gation to determine methods for measuring the interference characteristics

(spectrum signature) of U. S. Army communications equipment deemed necessary

for the prediction and minimizing of electromagnetic interference. Emphasis

shall be placed on pulse modulated type communications equipments operating



Computer methods shall be developed for processing these data to obtain




as follows:

I. The development of tests and procedures for the evaluation of the

interference susceptibility and emanation characteristics of pulse modulated



data to produce outputs useful in interference prediction and control applica

tions.

1

II. ABSTRACT

The effects of multipath interference on the intelligibility of speech

transmitted over an FM system employing time division multiplexing are reportedo

Predicted intelligibility measurements based on audio output ratios indi-

cate that significant degradation in intelligibility will exist for the FM/TDM

system tested when multipath signals of strength are received over paths

which differ in length by as little as 0.15 mile (0.8 ~sec delay). The prob-

ability of significant multipath interference in FM systems which use TDM

is expected to be greater than that for ordinary wide-band FM systems.

The accuracy of mixer spurious response level prediction is demonstrated

for variations in mixer operating and drive conditions. Utilization of the

prediction techni~ue in the design of mixers is discussed. Several signif-

icant facts concerning the design of radio receiving e~uipments as illuminated

by the mixer studies are presented for future guidance.

A simplified method of obtaining the series describing a given response

amplitude using only the Pascal triangle of binomial coefficients is presentedo

Any single term or the entire series coefficient for any response of a mixer

th represented by an n degree polynomial may be readily obtained.

2

III. PUBLICATIONS, LECTURES, REPORTS,AND CONFERENCES

Mr. J. F. Chappell and Mr. N. R. Castellini from USAELRDL, Fort Monmouth,

New Jersey, visited Georgia Tech on 15-16 August 1963. The results of current

mixer studies were discussed.

Mr. R. D. Trammell, Jr., visited USAELRDL, Fort Monmouth, New Jersey,

on 28 August 1963. A meeting with USAELRDL and industrial personnel was held

for the purpose of discussing mixer and spurious response theories.

Mr. R. D. Trammell, Jr., and Mr. E. W. Wood attended the Ninth TRI-SERVICE

Conference on Electromagnetic Compatibility held in Chicago, Illinois, on 15-17

October 1963. Mr. Trammell presented a paper on uThe Behavior of Nonlinear

Mixing.u

Mr. E. W. Wood visited the Electromagnetic Analysis Center, Annapolis,

Maryland, on 3-4 October 1963. Mr. Wood attended a meeting on spectrum

signatures and visited the technical information facilities at the Center.

3

IV. FACTUAL DATA

A. The Effect of Multipath Interference on the Intelligibility of Speech Transmitted Over an FM System Employing Time Division Multiplexing

Multipath interference occurs in wide-band FM systems when two or more

signals of approximately equal strength arrive from the same transmitter over

paths which differ greatly in length. 1- 5 In contrast, the specifications of

FM systems which employ T.DM suggest that such systems may be subject to multi-

path interference when the path lengths differ by less than one mile. Since

equal power levels are more probable at reduced path length differences, the

incidence of multipath interference might be expected to be greater for FM

systems which use TDM.

1. 'I'est Procedure

Two path interference tests were made on a typical FM system which

employs TDM. The PPM multiplexer video specifications for this system are as

follows:

Sampling Time: 125 ~sec

Channel Pulse Separation: 5.2 ~sec

Sampling or GatiEg Sig~al: Two pulses separated by 1.25 ~sec

Pulse Width: 0.6 ~sec

Figure 1 is a block diagram of the test configuration used for data

collection. Tne variable parameters of the experiment were (1) delay time

between paths or path length difference, (2) the absolute power level or

receiver quieting, (3) relative power level between the two paths, and (4)

the relative RF phase angle between the two paths.

4

t=:' 80

z w u 0:: w ~

>- 60 t: ..J co § ..J ..J w 1- 40 ~

0 w 1-u 5 w 0:: Q_ 20

SYNC-MASTER GATE OUTPUT

1.

SCREEN ROOM r ------------------, I I I I 1

I I I I I I I I I I I L---- --------------..J

OSCILLO· SCOPE

DELAY PATH (CABLE)

FIXED

ATTENUATION

Block Diagram of Test Configuration Used for Multipath Interference Tests.

S/N RATIO (db)

2. Predicted Intelligibility of Isolated Monosyllables as a Function of S/N Ratio at the System Audio Output.

5

Three lengths of RG-17A cable were cut to correspond to relative delay

times of 0.2, 0.4, and 0.8 ~sec, respectively, when connected between the

transmitter and adjustable line. Relative delays of from 0.2 to 1.4 ~sec

could be achieved in 0.2 ~sec intervals by interconnecting the three cable

lengths appropriately.

Receiver quieting was made continuously variable by using an adjustable

attenuator in the delay path. The total attenuation along the delay path

consisted of the delay path adjustable attenuator insertion loss (33 ± 2 db),

the adjustable attenuation, the delay path cable loss (0.07 db/ft. at the

transmitter tuned frequency), and the dela~ path fixed attenuation. Receiver

quieting was measured using an unmodulated signal; for making this measure

ment on the delay path signal, 120 db of attenuation was used in the direct

path adjustable attenuator. The delay path adjustable attenuator was set

to give the desired receiver quieting. Data were taken at each of the relative

delays at 20, 25, 30, 35, and 40 db of receiver quieting. To achieve high

quieting levels at the longer delays, it was necessary to remove the delay

path adjustable attenuator and set the receiver quieting with selected fixed

attenuators. Fine adjustments were made under these conditions by slightly

altering the transmitter power output level.

The relative power levels between the two paths were controlled with the

direct path adjustable attenuator. After the receiver quieting level had

been established for the delay path signal, the delay path cable was temporarily

disconnected at the adjustable line and replaced by a 50 ohm termination.

Equal direct to delay path power levels were achieved by setting the direct

path adjustable attenuator to give equal receiver quieting. After the direct

path cable was reconnected, the relative power levels were made positive or

6

negative by decreasing or increasing the attenuation of the direct path

adjustable attenuator. All relative power readings were made on the latter

attenuator with respect to the reading for equal power. At each of the delay

time-quieting level combinations, the relative power level was adjusted in

0.5 db steps over a range centered about 0 db which included receiver capture

of the direct and delayed path signals as end point limits.

The relative phase angle between the direct and delay path RF signals

was controlled by varying the adjustable line. The wavelength of the trans

mitter tuned frequency is 5.3 inches and the adjustable line could be varied

over an 8.5 inch interval; thus, it was possible to change the relative phase

angle by more than 360~ For each delay time-quieting level-relative power

level combination, the relative phase angle was adjusted to give both the

maximum possible interference and the minimum possible interference.

2. Data Evaluation

The measure chosen to reflect the extent to which interference is

produced at the audio output of the communications system by the presence of

the multipath signal was the predicted intelligibility of transmitted isolated

monosyllabic words. Figure 2 shows the predicted intelligibility or predicted

average articulation score that would be obtained by a trained listening team

using a test vocabulary of 1000 Harvard Phonetically Balanced (PB) words6

as a function of system output S/N ratio.

The relationship of Figure 2 was derived from two calibration curves

which permit approximate articulation scores to be predicted for certain linear

interference conditions. The first of these curves is the General Electronic

Laboratories scoring curve shown in Figure 3, which relates the composite

7

t=: 80 z UJ u 0:: w e:. >- 60 1-:J iii Q ..J ..J w 1- 40 = 0 UJ 1-u a UJ 0:: 0.. 20

PCI

Figure 3. General Electronic Laboratories Scoring Curve.

u 0..

S/N RATIO (db)

Figure 4. PCI as a Function of S/N Ratio at the System Audio Output.

8

listener test results from five independent articulation studies7-11 to Pat-

tern Correspondence Index (PCI) for a speech system to which random noise

was added. The PCI measure of intelligibility is obtained as the output

from the General Electro~ic Laboratories Speech System Test Set, an electro-

mechanical test apparatus which measures the degradation in understandability

of a speech sample that passes through a noisy intelligence channel. Details

of the theory of the test set and PCI measure of intelligibility can be

found in reference 12. An extensive investigation and evaluation of the

test set verified that the PCI measure of intelligibility is valid for random

noise and a limited number of other linear interference conditions. 13

tl'ests on the FM system shown in Figure 1 showed that noise generated

in the receiver discriminator produced random gating by the demulti-

14 plexer gate. This resulted in noise with a positive and/or negative tilted

spectrum at the demultiplexer audio output. Since these noise types are

examples of the limited interference conditions for which the test set can

be used to provide a synthesized listener score, the test set was used to

evaluate the performance of the FM system in the presence of CW interference.

A study revealed that PCI is a linear function of S/N ratio measured at the

demultiplexer audio output. This relationship is shown in Figure 4 and is the

second curve from which Figure 2 was derived. The curve of Figure l~ was used

to predict PCI measurements from S/N ratio measurements for a nurr.Lber of CW

interference conditions. Extremely close agreement was found between the

predicted PCI and the corresponding PCI measured with the test set. Details

of these tests and test results can be found in reference 14.

While no evidence yet exists to validate the general application of a

predicted intelligibility-S/N ratio relationship for every system using T.DM,

the experimental results reported above give creditability to the use of the

9

curve of Figure 2 in evaluating the performance of the particular FM system

used in these multipath interference tests. At each delay time-quieting level

rela.ti ve pow~er level-relative phase angle combination tested, the S/N ratio a.t

the audio output of a. channel of the multiplexer set was determined as outlined

in equation (l) of reference 14. Briefly, this consisted of the following

measurements. The audio input (Figure l) was adjusted to give the maximum

vol ta.ge a.t w~hich the peak amplitude excursions of the speech waveform w·ere

not clipped by the multiplexer. The gain of the external amplifier system

was set for a convenient listening level. The peak rms speech voltage

ratio at the rms voltmeter was determined in db with respect to a. l volt

reference when the system was operated with no delay path signal. For each

of the test conditions the rms noise signal voltage ratio was determined in

db with respect to a. l volt reference when the system was operated with no

speech input. The S/N ratios corresponding to those on the abscissa. in Figure

2 ~<7ere formed by algebraically subtracting the noise signal ratio from the

speech signal ratio. Predicted intelligibility corresponding to each S/N

ratio was read from the ordinate.

Since the audio input and external amplifier were held constant

for all tests, it was necessary to measure the speech ratio only once.

:Maximum possible interference a.nd minimum possible interference attainable a.t

each delay time-quieting level-power level combination were readily obtained

by shifting the phase with the adjustable line to give a. maximum and minimum

noise reading, respectively, on the rms voltmeter.

3. Test Results

Figures 5 through ll show the predicted maximum and minimum attain-

able intelligibility as a. function of relative direct to

level for seven delays and five quieting levels.

10

path power

DELAY .. 0.2 p.sec

CMETING- 40 db

DELAY .. 0,2 p.uc

QUIETING- JS db

RATIO OF DIRECT TO DELAY PATH POWER LEVELS (db) RATIO OF DIRECT TO DELAY PATH POWER LEVELS (db)

DELAY- 0.1, .. ,

QUIETING • 30 db

-1 -6

(B)

-8

RATI() OF DIRECT TO DELAY PATH POWER LEVELS (db) RATIO OF DIRECT TO DELAY PATH POWER LEVELS (db)

Figure 5 (a-e) .

(C)

DELAY • 0.1 ,.,.,

QUIETING " 10 db

-2 -4

RATIO OF DIRECT TO DELAY PATH POWER LEVELS (db)

(E)

-6 -8

(0)

e MAXIMUM INTERFERENCE

X MINIMU.~ INTERFERENCE

Predicted Intelligibility as a Function of Direct to Delay Power Level Ratio for a Relative Delay of 0.2 ~sec.

11

DELAy ... 0, 4 ,ILSI!iC

QUIETING • 40 db

4 2 0 -2 -4 RATIO OF DIRECT TO DELAY PATH POWER LEVELS (db)

DELAY- 0.4 p.SOC

QUIETING- 30 db

(A)

-4

RATIO OF OIRECT TO DELAY PATH POWER LEVELS (db)

(C)

DELAY • 0:.4 ~!Sec

~UifTING. 2U db

-6 -a

DELAY .. 0.4 ~sec

QUIETING • 35 db

-2 -4

RA TID OF DIRECT TO DELAY PATH POWER LEVELS (db)

DELAY ... 0.4 i<sK

QUIETING. 25 db

I B)

4 1 0 -2 _j


(0)

-6 -8

-B


X MINIMUM INTERFERENCE

6( a-e). Predicted Intelligibility as a Function of Direct to Delay Power Level Ratio for a Relative Delay of 0.4 ~sec.

12

40

20

DELAY .. 0.6 ,~~.sec

OUtETtNG ~ 40 db

DELAY"' 0.6 ~o~.-sec

QUIETING • 30 db

4 ~ ~

RATIO OF DIRECT TO OELAY PATH PO~ER LEVELS (db)

(A)

2 0 -2 -4 RATIO DIRECT TO DELAY PATH POWER LEVELS (db)

(C)

100

~80

DELAY .. 0. 6 fl"~c:

QUIETING • 20 db

DELAY"" 0.6 f"SitC

QUIETING • 25 db

4 0 -2 -4


(El

4 ~ ~


-x'x x \I X

-2 -· RATIO OF DIRECT TO DELAY PATH POWER LEVELS (db)

-6 -8

(D)

• MAXII.IUM INTERFERENCE

X MINIMUM ·~TERFERENCE

Figure 7(a-e). Predicted Intelligibility as a Function of Direct to Delay Power Level Ratio for a Relative Delay of 0.6 ~sec.

13

100

ao

60

40

20

100

BO

60

40

20

DELAY "" IU! ).I.$CC

OUIETIHG • 40 .Jb

DELAY - 0.8 trsec

I;!UIETING-30db

RATIO DIRECT TO DELAY PATH POWER LEVELS (db)

IAI

-2


(Q

DELAY .. 0.8 psec

QUIETING • 20 db

lOO

80

60

DELAY ..-O.S:".sec

QUIETING. 35 db

1i)

-8

-2

RATIO OF DIRECT TO DELAY PATH POWER LEVELS (dbl

(E)


IBI

RATIO OF DIRECT TO DELAY PATH POWER LEVEU {db)

(!)}

-8


X MINIMUM JHTERFERENCE

8( a-e). Predicted Intelligibility as a Function of Direct to Delay Power Level Ratio for a Relative Delay of 0.8 ~sec.

14

DELAY -1.0 J<SK

QUIETING< 40 db

DELAY - 1.0 ""' QUIETING~ 30 db

~2

RATIO Of DIRECT TO DELAY PATH POWER LEVELS

(A)

_, -·

-8

-6

DELAY .. l.O ~sec

QUIETING • J5 db

DELAY. 1.0 ,,..c QUIETING- 15 di>


(0

100

DELAY .. l.OJ.sec

QUIETING • 10 db

4 ~ ~


[E)


(BJ

-1 -4 -6 RATIO OF DIRECT TO DELAY PATH POWER LEVELS (db)

(D)

-6



Figure 9(a-e). Predicted as a Function of Direct to Delay Power Level Ratio for a Relative Delay of 1.0 !J.Sec.

15

DELAY .. 1.2 puc

CUIETING • 40 db

OELAY .. 1.21tSoc

QUIETING. Jl) db

4 0 -2 -4 RATIO OF DIRECT TO DELAY PATH POWER LEVELS (db)

(A)

X

4 2 0 -2 -~ RATIO OF DIRECT TO DELAY PATH POWER LEVELS (db)

(C)

DELAY • 1.2 ,.sec

QUIETING • 20 db

DELAY -1.2 "'"" QUIETING • 35 db

j 2 0 -2 -~ RATIO OF DIRECT TO DELAY PATH POWER LEVELS (db)

(B)

100

\ 80

\ 60

DELAY· U" .. ' QUIETING • 25 db

jQ

• 2 0 -2 -4 -8 RATIO OF DIRECT TO DELAY PATH POWER LEVELS (db)

(D)

o MAXIMUM lt!TERFERENCE


4 2 0 -2 -~


(E)

Figure 10( a-e). Predicted Intelligibility as a Function of Direct to Delay Power Level Ratio for a Relative Delay of 1.2 ~sec.

16

100-

80

60-

20

100

20

DELAY .. 1.~ fA.NC

QUIETING • 40 db

j

4 1 0 -2 -4 RATIO OF DIRECT TO DELAY PATH POWER LEVELS (~b)

(A)

DELAY • 1.4 ,...,

QUIETING • 30 db

DELAY • 1.4 pH<

QUIETING • 20 db

I I

DELAY. 1.4 pH<

QUIETING • 35 db

DELAY ... \. .. pSK

QUIETING -15 db

• 1 0 -2 -4 -6 RATIO OF OIRECT TO DELAY PATH POWER LEVELS (db)

{Dl

4 2 0 -2 -4 RATIO OF DIRECT TO DELAY PATH POWER LEVELS (db)

(E)

-6

• MAXIt.IUt.l INTERFERENCE


Figure ll(a-e). Predicted Intelligibility as a Function of Direct to Delay Power Level Ratio for a Relative Delay of 1.4 ~sec.

17

1~e curves of Figures 5 through ll show the general characteristic shape

that would be expected for wide-band FM systems in the presence of multipath

interference. Specifically, predicted intelligibility is a minimum at equal

direct to delay path power levels and increases monotonically with increasingly

positive and negative relative power levels. Higher quieting levels generally

give rise to higher predicted intelligibility; lower predicted intelligibility

is prevalent at longer delays.

Differences also exist between the curves of Figures 5 through ll and

those intuitively expected for wide-band FM systems. One difference of

potentially great importance is the significant degradation in predicted

intelligibility that exists at the relatively small delay times used in

these tests. A delay of 1.4 ~sec corresponds to a free space path length

difference of only 0.26 mile. Based on a system expected operating range

in excess of 20 miles, the free space attenuation of the desired and reflected

signals will be essentially identical at this path length difference. There

fore, the relative direct to reflected (delay) path power level will depend

predominantly on the efficiency of the reflecting surface(s). The absence of

a difference in the free space attenuation of the direct and reflected si&lals

should enhance the probability of equal or nearly equal power levels, and

hence should increase the probability of multipath interference in FM systems

which use T.DM.

The nonsymmetry of the curves can be attributed to the method used in

forming direct to delay power ratios. For positive ratios, attenuation was

removed from the direct path, whereas for negative ratios attenuation was

added to the direct path. Thus, at positive ratios more total power was

available at the receiver than was available at the corresponding negative

ratios.

18

4. Discussion

The data are summarized in Figure 12 which shows the predicted maxi

mum attainable intelligibility as a function of relative delay time between

paths for each of the five quieting levels at direct to delay path power

ratios of 0 db and 1 db. These curves can best be interpreted from the stand

point of system operation.

Under interference-free operating conditions, a pulse position modulated

pulse train such as that shown in Figure 13a is detected and fed to the

demodulator. The double pulse is the gating signal, and the single pulses

each correspond to a multiplexer channel. Each channel demodulator operates

to convert a position modulated pulse (PPM) to a width modulated pulse (PWM)

which contains the audio component and when filtered gives the audio output.

The instantaneous width of the latter pulse corresponds to the instantaneous

amplitude of the original modulating signal. The instantaneous width of

the PWM pulse is determined by the length of time between the gating signal

and the PPM pulse.

Video signal distortion is produced at the receiver output (demultiplexer

input) when the equipment is operated in a multipath enviror~ent. This

distortion is caused primarily by the following:

(1) Limiter noise due to absence of the carrier,

(2) Noise produced by amplitude modulation due to the absence of

effective limiting action at low signal levels, and

(3) Phase modulation of the direct signal by the delayed signal.

The distorted video signal generates sampling or gating pulses in the demulti

plexer in addition to those transmitted. This condition is called random

or false gating, and results in the generation of random noise at the audio

19

100

~ "' IJ.J "-,... .... :i ai i3

:3 ~ § u fii !f

100

~ u

"' w "-

~ 60 :J 1ii i3 :J ..J

~ frl .... u

~

0

~ db u

"' IJ.J "-,... .... :i 1ii i3 :i u:l ~ 0 UJ .... u

~

0 0.2 0.4 0.6 0 0.2 0.4 0.6 0.8

RELATlVE DELAY TIME ("sec) RELATIVE DELAY TIME ("sec)

(A) (B)

100

~ 80

QUIETING LEVEL 30 db "' w "-,... .... :::; Cii i3

~ 0

b ~ "-

0 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 0.2 0.4 0.6 0.8 1.0

RELATIVE DELAY TIME ("sec) RELATIVE DELAY TIME (l.sec)

(C) (D)

100 ±1 db

~ 80

u

"' w QUIETING LEVEL , 40 db "-,...

60 .... :::; ai t5

~ ~ 40

fil t ~ "-

20

0 0 1.0

RELATIVE DELAY TIME ("sec)

(E)

Figure l2(a-e). Predicted Intelligibility as a Function of Relative Delay Time for Five Quieting Levels.

20

f\) 1--'

t t '' 1 ' '' 1 rt' t rt't • t r• 'y • t l' ' t , ' ·1 ', ', , ' ' • ~ -·· ~! f ~ ~:~ ·~1 . •

I i i I I ~ I j u i I i ' l I l i i l i • i ' I j i i I j i j i ,. ' ' ' • .

(a) PPM PULSE TRAIN UNDER INTERFERENCE - FREE CONDITIONS

'f

(c) LOW DENSITY FALSE GATING (Note: Time Exposure)

I I . 1r .. •

(b) GATING PULSES UNDER INTERFERENCE - FREE CONDITIONS (Note: Time Exposure)

a 'f - ~ -- ~· -·' - ~ - ........ ..... .L .

(d) HIGH DENSITY FALSE GATING (Note: Time Exposure)

f.' ... y ' !1 • • • ' • '' ' ' • t 1 t ~ t lr~ 1 ..

(e) PPM PULSE TRAIN UNDER A CONDITION OF BLANKING

Figure l 3 (a -e). Phot ographs of Demultiplexer Puls e Trains .

output by causing the PWM pulse following the false gate to exhibit a false

instantaneous width. Figure l3b shows the gating pulses under interference

free conditions and Figures l3c and l3d show two conditions of false gating

caused by multipath interference.

1~e S/N ratio at the system audio output is a function of the density

(number per unit time) of the false gating signals: a high false gating

density results in a low S/N ratio and a low false gating density results i~

a high S/N ratio. A very high density of false gating signals arose from

video signal distortion caused by limiter noise in the receiver when the

relative phase angle of the direct and delay path signals was adjusted to

give carrier cancellation between channel pulses. This generally resulted

in the lowest S/N ratios at each delay time-quieting level-relative power

level combination; this condition could easily be avoided in the field by

antenna relocation or rotation, and hence is not reflected in the curves

of Figures 12.

For a fixed relative delay time, the density of the false gating signals

resulting from noise in the video signal produced by amplitude modulation

would be expected to decrease with increasing quieting levels. Figure 12 shows

that this did occur, as evidenced by increased intelligibility for fixed delay

times as a function of increased signal level. Increased effectiveness of

amplitude modulation limiting at high signal levels also accoQ~ts for the

larger increase in intelligibility predicted at higher signal levels when the

delay to direct path power ratios are changed from 0 db to ±1 db.

The density of the false gating signals resulting from distortion of the

video signal caused by phase modulation would be expected to increase as the

22

relative delay time increased. Occurrence of this phenomenon is evidenced by

the decrease in predicted intelligibility with increased relative delay times.

In addition to the three general causes of video signal distortion listed

and discussed above, a fourth type of distortion occurs at 40 db of quieting.

At relative delay times of 1.0 and 1.2 ~sec at this quieting level, the video

pulse train appears as shown in Figure 13e when the direct to delayed path

power ratio is 0 db. The pulse train consists primarily of the transmitted

gating pulses; the channel pulses are "blankedrr or highly attenuated. Under

blanking conditions, neither noise nor desired audio signals can be heard at

the system audio output. This condition does not exist at any of the other

delay time-quieting level-relative power level combinations used. Blanking

accounts for the discontinuity of the 0 db curve of Figure 12e. The cause

of the blanking effect may be related to gating pulse reinforcement since

the delay times involved are close to the desired gating pulse separation time

(1.25 ~sec), but the relationship is unclear as of this writing.

5. Conclusions

When the FM/TDM equipment was operated in a multipath environment,

video signal distortion was produced at the receiver output. The distorted

video signal produced false gating signals in the demultiplexer, resulting in

the generation of random noise at the system audio output. Predicted intel

ligibility measurements based on audio output S/N ratios indicate that signifi

cant degradation in intelligibility ca~ be expected for this system when

multipath signals of equal or near equal strength are received at a level cor

responding to 35 db or less of receiver quieting over paths which differ in

length by as little as 0.15 mile (0.8 ~sec delay). At normal operating ranges,

23

the free space attenuation of the desired and reflected signals will be essen

tially identical for path length differences of this magnitude. This should

enhance the probability of equal or near equal power levels, and hence should

increase the probability of significant multipath interference in FM systems

which use TDM as compared to ordinary wide-band FM systems.

B. Mixer Testing and Evaluation

1. Introduction

Quarterly Reports Nos. l and 2 have established and partially

evaluated a technique for predicting the spurious response rejection data

for single diode mixers. The technique generally yields predicted values

within 6 db of the measured rejection data but occasionally errors in excess

of 10 db are obtained. These errors in prediction appear to stem from

certain imperfections inherent to the prediction technique as well as inac

curacies in the measurement of the actual mixer response levels. Better

prediction can come only at the expense of complexity in the methods of

measuring and calculating response levels.

2. Prediction and Mixer Operating Conditions

Although the prediction technique previously discussed is not

highly accurate in all cases, its simplicity and relative accuracy render

it useful in determining a mixer characteristic with a minimum of measured

data. It has the further advantage that the data may be taken with the mix

ing element connected into ap~ desired mixer circuit. Since all previously

assembled data demonstrating prediction accuracy were obtained under conditions

24

of zero de bias, a question concerning the effect of diode bias on the accuracy

of prediction was raised.

It is known that for a given local oscillator level, the relative rejec

tion of a spurious response is dependent on the relative diode bias as well

as the associated generating order. The diode bias must therefore be set

to the designed operating value prior to prediction measurements or the pre

dicted rejections will be in error for the conditions of operation within

the equipment. It is desirable therefore to ascertain whether or not the

prediction accuracy is significantly affected by the relative bias level at

which the mixer data are obtained. The prediction error data obtained with

three constant bias voltages and one constant bias current for a 11~2A diode

are shown in Figures 14 through 17. These data indicate little significant

degradation in prediction accuracy with change in diode operating point or

bias level.

Previous data have indicated large prediction errors when the mixer

diode output termination is tuned to the intermediate frequer-cy rather than

being almost entirely resistive. These errors are manifested by a shift

in the response density mean and spreading of the error range about the

mean. It was noted that a shift of the mean also occurred with local

oscillator overdrive and that perhaps a reduction in the level of the local

oscillator input would improve the prediction. The data shown in Figure 18

tend to validate this assumption in that the density mean remained near the

zero error point. The error spread, however, was not improved by a reduction

in the local oscillator input level. It should be observed that the local

oscillator level was not reduced below the level required for satisfactory

conversion efficiency.

25

15

14

13

12

11

10 >-~9 z w 0 8 w ...... ~ 7 c.. ...... Mt 6

r, I I

J I I I I L1

L., I I I ... ,

DIODE: 1N82A LO. LEVEL: -5 dbm SENSITIVITY: -102 dbm I.F. FREQUENCY: 1 Me TUNING: None L.O. FREQUENCY: 10 Me


0 4---~----------~--~--~+-~~~~~~~~~~~~--~---U4~---~~~--~~~ -8 -7 -6 -5 -4 -3 -2 -1


Figure 14. Response Density Versus Prediction Error for a 1N82A Diode Mixer with +0.1 Volt Bias.

>-1-;:;; z w 0

!!:l :z: 0 S; w

"'

15

14

13

12

11

10

7

5

.. -, I I I .. _,

: L, I I I I I I

I ~-,

I I I I ......

I -., I ... __ ,

L., 1..

DIODE: 1N82A L.O. LEVEL: -5 dbm SENSITIVITY: -102 dbm I.F. FREQUENCY: 1 Me TUNING: None L.O. FREQUENCY: 10 Me


04---~----..----~--~~--~~-..-~~~~~~~~~~--~~~~~-----~--~--~ -3 -2 -1 0 10 11 12 13


Figure 15. Response Density Versus Prediction Error for a 1N82A Diode Mixer with -0.1 Volt Bias.

26

15

14

13

12

11

10

>-1-Vi z w 0

~ z 7 ~ V')

w 0::

-11 -10 -9 -8 -7 -6 -5

r, I I I l..1

: : I L,

-3

~...,

I I I I I

-2 PREDICTION ERROR IN db

-1



Figure 16. Response Density Versus Prediction Error for a 1N82A Diode Mixer with +0.2 Volts Bias.

15

14

-10 -9 -8 -7 -6 -5 -4



-3 -2 -1 0 PREDICTION ERROR IN db

Figure 17. Response Density Versus Prediction Error for a lN82A Diode Mixer with +0.2 rna Bias.

27

15

14

13

12

11

10

>-.... 9 ;:;; z ~ 8 LIJ

~ 7

~ M:! 6

r.,_, r.J ~...,

I I I I I I

I L.--,

L, I I

DIODE: L.O. LEVEL: SENSITIVITY:

1N82A -5 dbm -102 dbm

I.F. FREQUENCY: 1 Me TUNING: Output to 1 Me L.O. FREQUENCY: 10 Me

CROSSHATCHED: True Density DASHED: Density lntegrol

L--, I L---.,

L-----

0+-~~---~~~~------~~~~~~~~~~~~~~--~L-,--L~L-~~---~~~---~

-9 -8 -7 -6 -5 -4 -3 -2 -1 0 PREDICTION ERROR IN db

Figure 18. Response Density Versus Prediction Error for a 1N82A Diode Mixer with Tuned Output.

15

14

13

12

11

10

r.J r--- ___ ..J

r--..J ----...J

-28 -26 -24 -22 -20 -18 -16 -14 -12 -10 -8 -6 -4 -2

r1 I I I I

: I


DIODE: 1N82A LO. LEVEL: -5 dbm SENSITIVITY: -102 dbm I.F. FREQUENCY: 1 Me TUNING: None L.O. FREQUENCY: 10 Me

CROSSHATCHED: True Density DASHED: Density lntegrol

10 12 14 16 18 20 22

Figure 19. Response Density Versus Prediction Error for a 1N82A Diode Mixer with Unfiltered Input Signal.

28

3. Prediction and Mixer Driving Circuitry

A study of the effect of injecting signal and local oscillator har

monics into a mixer was presented in Quarterly Report No. 1. 16 The effect of

injected signal harmonics on response level was shown to be significant. The

resultant effect on prediction error is also significant as illustrated in

Figure 19.

No significant shift in the density mean is observed but the error spread

increased almost threefold over the normal error spread obtained using filtered

inputs. This fact severely limits the utilization of the predictio~ technique

to receiver spurious response prediction when there are amplifiers without low-

pass filters prior to the mixer. The possibility of harmonics being generated

within such amplifiers is distinct, especially with the high signal levels

required to obtain responses with large values of q.

The prediction technique was originally developed as a means to evaluate

receiver spurious response rejection data using a.:minimum of receiver measure-

ments. The assumption inherent in applying the technique to receivers is that

the prediction error for a device containing ma~~ cascaded nonlinear elements

will not be significantly larger than the corresponding error for a device

containing only one nonlinear element. The data obtair.ed with injected signal

harmonics tend to invalidate the above assumption conclusively. For complete

assurance of result, two diodes were connected within the test circuit as

shown in Figure 20. The prediction error data obtained with this cascaded pair

of diodesa.re given in Figure 21. It is obvious that the prediction error

spread is many times larger than normal and there is a significant shift of

the distribution mean. O~ly if the premixer circuitry is entirely linear can

the prediction method be utilized with any assurance of accuracy.

29

BNC NO. 1

SIGNAL

BNC NO.2

INPUT TEST

L.O.

Figure

15

14

13

12

11

10 >-1-;:;; z w 0

w "" z 0 7 0.. ..,., w e::::

5

1N82A 1N82A

TEST OUT

20. Schematic Diagram of Double-Diode Mixer Test Circuit.

DIODE: 1N82A L.O. LEVEL: -5 dbm SENSITIVITY: -102 dbm I.F. FREQUENCY: 1 Me TUNING: None LO. FREQUENCY: 10 Me


0+-~~-r--~~--~--~UT~~~~~~~~~~~~~~~~~~4-~~--,-~~~~~~-34


Figure 21. Response Density Versus Prediction Error for Two Cascaded 1N82A Diodes.

30

14 16

4. Prediction and Mixer Design

The prediction technique has perhaps its greatest utilization in the

design of equipments using mixers. The effect of changes in mixer operating

conditions on the overall spurious response rejection can be found with only

a basic set of measurements at each operating point. The test mixer setup

need not have the same IF sensitivity as the intended equipment since conversion

to the equipment sensitivity level is automatically accomplished in the predi

tion calculations. The measurements must be made with the mixer element in

the final circuit using the same operating levels as expected in the end

equipment.

Mixer spurious response rejection is dependent upon the IF output level

at the mixer and is thus a function of the gain or sensitivity of the IF ampli

fier. Furthermore, the effect of the IF sensitivity on spurious response

rejection is a function of the value of q for the response in question. This

is the case since the response level is proportional to the response input

voltage raised to the qth power. It follows that the relative rejection to

responses having a unity q value will remain constant for all values of IF

sensitivity and that all other spurious response rejections will increase with

increasing IF sensitivity. The percentage increase in the rejection to a

spurious response of given q for a known decibel increase in IF sensitivity

may be obtained from the envelope curve shown in Figure 22. If the ratio of

local oscillator level to input signal level is increased by the exact decibel

increase in IF sensitivity and the prediction of response rejections is calcu-

lated using this corrected ratio, the predicted spurious response rejections

will conform to those expected at the higher IF sensitivity. 17

31

1.0

0.9

::0 ::!:!..

z 0.8 0 i= u w ., w 0.7 c:t::

w cl)

z 0

0.6 0.. cl)

w c:t:: cl)

:J 0.5 0 n: :J 0.. cl)

z 0.4 VJ w 1\)

(.!) z <(

0.3 J: u 1-z :J

c:t:: 0.2

w 0..

0.1

0

0 2 3 4 5 6 7 8 9 RESPONSE Q VALUE

NOTE: This Curve Shows the Envelop of the Rejection Change Versus q Since q is an Integer.

10 11 12 13 14 15

Figure 22. Change in Spurious Response Rejection with a Change in IF Sensitivity.

5. Considerations for Receiver Design

Several factors concerning receiver design have been illuminated

by the mixer studies and resultant prediction techniques. Though this facet

of communications equipment is not specifically covered by the present studies,

it is felt that facts pertinent to design should be stated for future guidance.

Harmonics of the local oscillator and especially those of the input signal

can cause excessive generation of spurious products within a mixer, particularly

whe~ spurious product generation by the mixer alone is very slight. Both the

signal and the local oscillator inputs should be isolated from the mixer using

suitable low-pass filters with at least a 3 db pad between the filters and the

mixer proper. Amplifiers preceding the mixer require a high degree of low-

pass filtering prior to the mixer. At high spurious signal levels, these units

exhibit clipping which generates considerable harmonic content and which is

perhaps the largest single contributor to receiver intermodulation product

formation. The preponderance of the band selectivity filtering should occur

prior to any amplification in order to prevent out-of-band clipping in the

first stages of the amplifier. This consideration should apply to both RF and

IF amplifiers.

Spurious response rejection values are increased by maintaining the IF

gain at the maximum level consistent with the mixer noise figure. AGC action

and similar automatic or manual control systems should not alter the gain of the

IF amplifiers. The AGC control should act prior to the RF amplifier, if at all

possible, and certainly prior to the mixer. Control of the mixer conversion

efficiency by alteration of the local oscillator input level may also provide

a method of AGC consistent with the reduction of spurious responses.

33

6. Conclusions

Mixer response prediction by simple means is limited in accuracy

and in utilization. The present technique is useful in mixer design and

for certain cases of receiver spurious response prediction. The technique

is too sensitive to harmonic interference for receiver prediction where non-

linear elements precede the mixer. Significant improvement in prediction can

be realized only through more complex techniques for the measurement and cal-

culation of spurious responses. A more reasonable approach appears to be

that of concentrating future effort toward eliminating the cause rather than

trying to predict its results.

C. A Method for Determining Response Coefficients

1. Introduction

The purpose of this section is to present a method for determining

the coefficients of the responses arising from the use of an nth degree poly-

nomial as a mathematical model of mixer characteristics. The laborious com-

putations necessary to obtain these coefficients from the binomial expansions

of the summed input signals indicate the desirability of such a method, and

previous mixer studies have provided the basis for its development. 14, 18 The

triangle of constant coefficients shown in Figure 23 and the response coeffi-

cients listed in Figure 24 are taken from reference 18. These coefficients

and the mixer theory presented in references 14 and 18 furnish the foundation

from which the following method evolved.

2. Development of Method

The representation of the mixer characteristic by the power series

"' /

"' / """

/

" /

""' /

""' /

1 l l 2 2 2

" /

""" /

""' /

""" /

.!. 3 1

4 4

4"'-~

.. +

" /

""" """ /

""' / / "'(':

"j¢ ~eo. "Q

,, l .!_ 6 4 I '1:>~

o"" 8 8 8 8 8 o,-

«/''- "' /

""' /

""" /

""" /

""" /

""' / ~

/ 1 5 lQ. lQ. _!L _l ~ 16 16 16 16 16

16 ""' "' /

""' / /

""" /

""" /

""' / /

1 .i 11 20 15 ~ 1

32 32 32 32 32 32 32

"' ""' /

""' /

""" /

""" /

""" / /

""' /

w I 7 1!_ ~ ~ 1l L ..!.

\Jl 64

64 ""'

64 64 64 64 64 64

"' /

""' / /

""" /

""" /

""" / /

""' /

""' /

1 8 56 56 _!_ 2 - rn i2a 128 128 128 128

"' /

""' ""' / /

""" /

""" /

""' /

""" /

""' / /

1 36 ~ 126 ~ 36 I 10 10 - 2~ 256 256 256 256 256

256 ""'

"' /

""' /

""' /

""' / / /

""' /

""" /

""" /

""' / /

1 45 210 210 10 1 ll 11 512 ill m ill 5!2 512

" / ""'

/

""" /

""' /

""" /

""' / /

""" /

""" /

""" /

""' /

""' /

1 11 55 ~ 462 ~ 330 165 11

1o2i 1024 1024 1024 1024 1024 1024 1024 1024

Figure 23. Triangle of Constant Coefficients.

w 0\

1575 e 5e 5 + 525 3 7) J + -- a b - ea eb K 10 + 1 I.+

61J 61J

Figure 24. Responses Generated from the Power Series Representation of a Mixer Characteristic when the Input is Two Summed Sinusoids.

expression

i = K 0

+ K1 e i + K2 e~ + · · · + Kn e ~

involves the binomial expansions through degree n of the input signal

e. = e cos a+ ebcos b. 1 a

This expansion yields a multitude of response terms of the form C cos p,q

(pa ± qb), and harmonic terms of the form C cos(pa) or C cos(qb). Each of p q

the response coefficients, cp,q' is in the form of a series, and Figure 24

indicates that this series is one comprised of modified binomial expansions.

This is not unexpected, since each term in the series arises from a binomial

expansion of the input signal. Thus it should be possible to derive this

series from an inspection of the operation of the power series expression on

the binomial expansions of the input. It will be shown that the generation of

response coefficients is possible through the use of only the table of binomial

coefficients, Figure 25, and the triangle of constant coefficients, Figure 23.

From Figure 24, it is noted that any given response may be written

[cos (pa + qb) J [ k0 e~ ~ Kptq + (kl e~+2 ~ + k2 e~ er) Kp+q+2

e~ ~+J Kptq+4

er-6 ~ + k7 er-4 ~+2 + kg er-2 ~+4 + k9 e~ er? Kp+q+6

+ ... + J

37

VALUE OF p ~ VALUE OF q

6 7 8 9 10 11 12

1

+1

3+ 1

+4+1

10 + 5 +1

+15+6+1

35 + 21 + 7 + 1

+56+28+8 +1

126 + 84 + 36 + 9 + 1

+ 210 + 120 + 45 + 10 + 1

0

2

3

4 w ::>

5 <1. > ....

6 m z; 0

7 ~ w

8

9

10

462 + 330 + 165 + 55 + 11 + 1 11

220 + 66 + 12 + 1 - 12

Figure 25. Table of Binomial Coefficients.

where the k. 's are dependent upon the particular response under consideration. l

This may be represented in triangular form as shown in Figure 26. With the

exception of the k.'s, this triangle will then generate the response coefficient l

for any given (p, q) response.

To illustrate the method of finding the k. 's, consider Figure 27 which is l

a triangular representation of the k. 's for the coefficient of the (2, l) l

response given in Figure 24. The k. 'shave been factored such that the tril

angle is expressed as the term-by-term product of two different triangles, one

of which may be recognized as composed of odd-ordered terms in the triangle of

constant coefficients. The sides of the triangle formed by the bracketed

terms are seen to be the p = 2 and q = l columns in the table of binomial

coefficients. The values within this triangle are merely the product of the

side values at their diagonal intersection. The k. 's for the (2, 1) response l

are thus uniquely determined by multiplication of the appropriate terms in

these two triangles, and in general the k. 's for any response coefficient l

can be computed from the triangle of constant coefficients and one formed from

the table of binomial coefficients.

3. Procedure

The procedure for obtaining a response coefficient may best be

illustrated by an example computation. If the (3, 2) response is of interest,

its series form can immediately be written from the triangle of Figure 26.

[cos (3a + 2b)][k0 e~ e; K5 + ~k1 e~ e; + k2 e~ ~~ ~

+ G3 e ~ e; + k 4 e~ ~ + k 5 e~ ~ K9 + • • · + J

39

p+2 q p q+2 k lea eb -- k2ea eb ------------------------ Kp+q+2

Figure 26. Response Coefficient in Triangular Form.

-r=-1---1

I), /

" / + .)..

.; 3 ~ 00 - [1] !!'+: ;r ~ 4 ..} :.00

~ " / ""'- / ")$

~0 "'"' ~0 o,. «7

5 10 ~

/ - [4] 16 [3]

~ b 16 .s

" / "' / "' / 7 35 [ 12] 21 [ ,

co 64 [ 15] 64 64 10J

.>

" / ""' / "" / ""'- /

9 84 126 36 '(':)

256 [56] 256 [45] 256 [401 256 [35] .J)

" / ~ / ~ / ~ / ~ / 11

1024 [ 210] 165

1024 [ 168] 462 1024 [ 1501

330 1024 [ 1401

55 1024 [ 1261

Figure 27. Numerical Coefficients (k. 's) of the Terms in the (2, 1) Response Coefficient. l

th To determine the k. 's, first form a triangle whose sides are the p l

th and q columns of the table of binomial coefficients, in this case the third

and second columns respectively. Inside terms of this triangle located at

the intersection of the diagonal rows are obtained from the product of the

side values in these rows. Figure 28 shows the completed triangle.

The value of k. associated with a given term in the (3, 2) response l

coefficient can now be computed by multiplying the particular (x, y) value in

the triangle of Figure 28 by its corresponding (x, y) term in the triangle

of constant coefficients. For example, to compute k4

, note that k4

is

associated with the term whose exponents are x = 5 and y = 4. The (5, 4)

values in Figure 28 and 23 are (20) and (126/256) respectively, and their

product yields k4

= 315/32. Sample calculations for other k. 'sin the (3, 2) l

response coefficient are given below.

k = (1)~ = ~ k3 = (21) 36 = 189 0 256 E)4

(5)~ 105 84 315 kl = b4 k5 = (l5 )256 = E)4

k2 = (4)~ = fi

The generation of the response coefficient through the desired number of

terms is thus complete.

4. Conclusions

The above method provid·es a simple approach to the problem of

generating response coefficients. The triangles necessary for numerical

computations are easily obtained from the table of binomial coefficients.

Although the above discussion and examples are concerned with response co-

efficients, the method works equally well for harmonic coefficients.

42

1287 1320 1260 1176 1050 792

Figure 28. Triangle for the (3, 2) Response Formed from the Table of Binomial Coefficients.

V. CONCLUSIONS

This report contains the concluding results of two quarter's study on

multipath interference for FM systems which employ TDM. Multipath inter

ference data were taken at receiver input levels corresponding to 20, 25,

30, 35, and 40 db of receiver quieting. The delay path time was adjustable

in 0.2 ~sec steps from 0.2 ~sec up to 1.4 ~sec and the relative phase angle

was variable over 360~

Multipath interference was found to cause several interference producing

conditions in the receiving system. These are: (1) random multiplexer gating,

(2) video signal blanking, and (3) distortion of the video signal caused by

phase modulation of the direct signal by the delayed signal. Predicted intelligi

bility results indicate that significant intelligibility degradation can be

expected for the FM/TDM system tested when multipath signals of equal strength

are received at a level corresponding to 35 db or less of receiver quieting

over paths which differ in length by as little as 0.15 mile (0.8 ~sec delay).

Serious effect of multipath interference is felt to be more probable in FM

systems which utilize TDM than in ordinary wide-band FM systems.

Higher accuracy in mixer prediction can be realized only at the expense

of increased mathematical complexity .. The simple technique of the mixer pre

diction method concluded in this report is useful under limited conditions,

but is unsuitable for accurate receiver response prediction.

The coefficient series of any mixer response or harmonic can be easily

calculated from the Pascal triangle of binomial coefficients regardless of

the order of nonlinear representation.

44


The completion of the evaluation tests on available PPM/FM communications

systems is scheduled at the end of the fourth quarter's effort.

Further kno1-rledge acquired regarding the PCM requirements for

available PCM/FM systems necessitates additional circuitry for simulating

and detecting the information pulses. The feasibility of constructing the

desired circuitry w·ill be investigated.

Band-pass filters and preselectors on order will be evaluated when

received.. The utilization of these a.nd other filters should permit improved

testing limitations at the frequencies involved.

Volume 9 of the Manuscript of Catalogue which w·ill contain a. second

general RFI Bibliography will be published in the next interval. A delay

wa.s encountered in the receipt of wTitten permission from publishers to

publish their RFI related abstracts.

Data. on transistor a.nd vacuum tubes mixers w"ill be collected a.nd analyzed.


Name Title Approximate Hours

E. E. Donaldson, Jr. Grad. Research Assistant 316

0. H. Ogburn Research Assistant 495

I. E. Perlin Research Professor 6

D. w. Robertson Head, Communications Branch 78

P. T. Spence Grad. Research Assistant 150

c. w. Stuckey Asst. Research Engineer 501

R. D. Trammell, Jr. Asst. Project Director 466


w. B. Warren, Jr. Research Engineer 26

E. w. Wood Project Director 376

Mr. Spence ha.s been associated -with the Engineering Experiment Station

since September 1963. He received a. B.E.E. degree in 1960 at Auburn University.

He is currently pursuing an M.S. degree in E.E. a.t the Georgia. Institute of

Technology. His previous experience includes two years as a. Factory Test

Planning Engineer and one year as a.n Equipment Engineer for the Western

Electric Company.

46

VI I I • REFERENCES

1. Murlan S. Corrington, "Frequency Modulation Distortion Caused by Commonand Adjacent-Channel Interference," RCA Review, Vol. 7, pp. 522-545, (1946).

2. L. B. Arguimbau and J. Granlund, ''The Possibility of Transatlantic Communication by Means of Frequency Modulation," Proceedings NEC, Chicago, pp. 644-653, (November 1947)~

3. L. B. Arguimbau and J. Granlund, "Sky-Wave F-M Receiver," Electronics, pp. 101-103, (December 1949).

4. Harold Ao Wheeler, "Common-Channel Interference Betw·een Two FrequencyModulated Signals," Proceedings IRE, pp. 34-50, (January 1942).

5. Elie J. Baghdady, ''The FM Random-Noise Threshold, 11 Frequency, pp. 12-17, (March-April 1963).

6. J. P., Egan, "Methods of Articulation Testing, '' Laryngoscope, 58, pp. 955-991, (1959)"

1. Egan, Miller, Stein, Thompson and Waterman, "Studies of the Effect of Noise on Speech Communication," Harvard University, Psycho-Acoustic Lab. PB22907, (November 1942).

8. G. A. Miller, "The Masking of Speech,'' Psychol. Bull., 44, 105-129, 1947; also, Harvard University, Psycho-Acoustic La.b. PNR 23, PEL 80873, (March 1947)"

9. J. C. R. Licklider, "The Influence of Interaural Phase Relations Upon the Masking of Speech of White Noise," J. Acoust. Soc .. .Amer., 20, pp. 150-159, (1948).

10. J .. C. R. Licklider and G. A .. Miller, "The Perception of Speech," Handbook of Experimental Psychology, John Wiley and Sons, Ne-vr York, pp. 1040-1074' (1951) ..

11. J. C. R. Licklider and N. Guttman, "Marking of Speech by Line Spectrum Interference," J .. Acoust. Soc • .Amer .. , 29, pp .. 287-295, (February 1957).

12. Instruction Book for Speech Systems Test Set, General Electronic La.boratories, Inco, Cambridge, Ma.ss., ContractDA36-039-SC-72788, (1958).

13. DG W. Robertson, and C. W. Stuckey, "Investigation a.nd Evaluation of the GEL Speech System Test Set, '' Engineering Experiment Station, Georgia Institute of~ Technology, Contract AF-30(602)-2150, (1961).

14. E. W .. Wood, R .. D. Trammell, Jr., C. W. Stuckey, H .. W. Denny, E. E. Donaldson, Jr., and R. M. Cook, "Quarterly Report No.1, Project A-678, 11 Electronic Equipment Interference Characteristics-Communication T,ype, Contract No. DA 36-039 AMC-02294(E), Georgia. Institute of Technology, Engineering Experiment Station, pp. 24-49, (15 February 1963 to 15 May 1963).

(Continued)

47

15. R. D. Tra.mmell, Jr., c. W. Stuckey, E. W. Wood, 0. H. Ogburn., and E. E. Donaldson, Jr., "Quarterly Report No. 2, Project A-678., u Electronic Equipment Interference Characteristics-Communication T.ype, Contract No. DA 36-039 AMC-02294(E), Georgia. Institute of Technology, Engineering Experiment Station, pp. 38-51, (15 May 1963 to 15 August 1963).

16. Wood, op. cit., pp. 64-73.

17. Wood, op. cit., pp. 91-99.

18. R. N. Bailey, E. W. Wood, R. D. Trannnell, Jr., and J. R. Walsh, Jr., "Final Technical Report, Project No. A-543, 11 Electronic Equipment Interference Characteristics-Communication T.ype, Contract No. DA 36-039 sc-87183, Georgia. Institute of Technology, Engineering Experiment Station, pp. 58-59, and 117-134, (1 September 1961 to 15 February 1963).

48

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~-------------------------~~~~'---

REPORT NO. 25


PROJECT A-678 . . ...... ~ ..... ..........


By 0. H. Ogburn, E. E. Donaldson, Jr., P. T. Spence a nd C. W. Stuckey

CONTRACT NO. DA 36-039 AMC-02294(E) (Continuation of Contract No. DA 36-039 sc-87183) DEPARTMENT OF THE ARMY PROEJCT: 3B24-0l-00l

Placed by the U. S. Army Electronics Research and Development laboratory Fort Monmouth, New Jersey

15 November 1963 to 15 February 1964


1964


lib-sascan

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ENGINEERING EXPERIMENT STATION of the Institute of Technology

Atlanta, Georgia

REPORT NO.


PROJECT A-678


By

0. H. Ogburn, E. E. Donaldson, Jr., P. T. , and C. W.

CONTRACT NO. DA 36-039 AMC-02294(E) (Continuation of Contract No. DA 36-039 sc-87183)

DEPARTMENT OF THE ARMY PROJECT: 3B24-0l-001

The object of this research program is to conduct a invest to determine methods for measuring the interference characteristics (spectrum

) of U. S. Army communications equipment deemed necessary for the pre-diction and of electromagnetic interference.

NOVEMBER 1963 to FEBRUARY 1964

PLACED BY THE U. S. ARMY ELECTRONICS RESEARCH AND DEVELOPMENT LABORATORY


FOREWORD

This was at the Georgia Tech Engineering Experiment Sta-

tion on Contract No. DA 36-039 AMC-02294(E). The report covers the

and-results of the fourth quarter's effort on a project to conduct a feasibil-


ence characteristics (spectrum

conrrnunications

interference.


ii

of U. S. Army modulated type

submitted:


of

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Rectangle

lib-sascan

Rectangle

TABLE OF CONTENTS

I~ PURPOSE

II. ABSTRACT

IIIe PUBLICATIONS, REPORTS AND CONFERENCES

IV. FACTUAL DATA

Ao Receiver Tests

lo Intermodulation

a 0 The Receiver Preselector and its Importance in Intermodulation Interference

Techniques

2. Spurious Responses •

a. The Preselector Techniques ..

Selectivity, Sensitivity, and Noise Figure

Mixer Te and Evaluation . . • . • . . .. •

Introduction .,

Calculated and Measured Data

3. Conclusions

c. Response Prediction of Triode Mixers

1 .. Introduction

2. Triode Mixer Theory

3. Data Evaluation

4. Conclusions

v. CONCLUSIONS



VIIIo REFERENCES ., o .. • .. • .. .. .. • .. • • •

This report contains 45 pages.

iii

1

2

3

4

4

4

6 9

12

13

18

19

32

34

34

37

39

42

43

44

1 ..

2.

3.

4 ..

6 ..

LIST OF FIGURES

Preselector Insertion Loss as a Function of for a PPM/FM Receiver. • .. • .. .. • .. .. ..

Block Diagram of Suggested Test Configuration for Receiver Intermodulation Evaluation • .. • • • • •

Block Diagram of Receiver Spurious

Test Configuration for Evaluation .. .. .. .. • ..

Test Configuration for Measurements ......... .

Block of sted Test Configuration for Receiver Sensitivity Measurements ..... " ... e ..

Block Diagram of Test Configuration for Noise Figure Measurements

7.. Ideal Diode Operation for Sinusoidal. Input Plus Bias

8. Calculated Level of 2nd Harmonic Versus B/A Where B = Bias Voltage Input and A = Peak Amplitude of Sinusoi.dal Input .. .. .. .. .. ., ., . .. • • ., ., ~

9. Calculated Level Harmonic Versus Where

10.

B = Bias Sinusoidal Input

and A = Peak Amplitude of

Calculated Level of 4th Harmonic Versus Where B = Bias Voltage Input and A = Peak Amplitude of Sinusoidal Input e ., • .. • .. $ • • .. • • • • • • •

Calculated Level of 5th Harmonic Versus Where B = Bias Voltage Input and A = Peak Amplitude of Sinusoidal Input • • • .. • .. . • • • .. • • ••

12. Diode Current Versus Bias Voltage for IN21B Diode

14.

in the Circuit of 13

Diagram of Test Mixer Circuit

I Measured Level of 2nd Harmonic Versus B;A Where B = Bias Voltage Input and A = Peak Amplitude of S:inusoidal Input .. .. • • .. • .. • .. .. . . ..

(Continued)

iv

7

10

10

16

20

22

26

28


Meas~red Level of 3rd Harmonic Versus B/A Where B = Bias Voltage Input and A = Peak Amplitude of Sinusoidal Input o " o ., • • • • • • .. • • • .. •

Measured Level of 4th Harmonic Versus Where B = Bias Voltage Input and A = Peak Amplitude of Sinusoidal Input • • .. . . . . • • • • • • o • •

Measured Level of 5th Harmonic Versus B/A Where B = Bias Voltage Input and A = Peak A~plitude of Sinusoidal Input • • • • • ., • • • .. • • o

Response of the Mixer Circuit in Sinusoidal Input .

Mixer Schematic

to a

20., Time Transconductance Between the Grid and

22 ..

Plate of a ~riode Mixer Tube • a • • • • • • •

Block Diagram of the Test Configuration Used to Measure Triode Mixer .. • . • . • .. . • •

Density Versus Prediction Error for 6J4 Triode Mixer • • • • .. . . • • .. •

v

Page

30

35

I_ PURPOSE

The purpose of this project is to conduct a fea and investi-

gation to determi.ne methods for measuring the interference characteristic


of interference. sis for the prediction and

shall be placed on modulated type communications equipments operating


data and a format for a directory of these data shall be

Computer methods shall be for these data to obtain

""''" . .,....,,.,.,... s useful in optimum characteristics for communications

in interference environments.


as follows:

I. The development of tests and

interference susceptibility and emanation characteristics of pulse modu.lated

communications equipments.

II. The use of techniques for proces measured interference

data to outputs useful in interference and control

tions.

1

II. ABSTRACT

sted derived from standard spectrum

tests conducted on U. S. Army microwave communications receivers are o~tlined.

The of the receiver in the receiver evaluation studies

is sized.. Common encountered in the procedures are

discussed and alternate test methods are presented.

A fini.te mathematical model of a mixer characteristic is

the use of the Fourier series. Calculated harmonic levels based on the mathe-

matical model were found to approximate the measured levels from

a diode mixer circuit. Modifications of the model which 10rill more

closely realize actual diode nonlinearities are considered.

Mixer is discussed for a vacuum tube triode mixer. Data taken on

a 6J4 triode mixer are compared to responses computed a previously

prediction

that the

tested.

applicable for diode mixers. This comparison indicates

is valid for vacuum tube mixers of the

2

III. PUBLICATIONS, LECTURES, REPORTS AND CONFERENCES

Mr. W. L. and Mr. E. W. Wood attended a field service seminar

sponsored oy the Hewlett-Packard Company on 20 Novemoer 1963 in Atlanta,

Mr. Guy Johnson and Mr. Sidney Weitz of USAELRDL, Fort Monmouth, New

Jersey, visited the Tech Experiment Station on 16-17 Decem-

progress and effort to that date were discussed.

Volume 9 of the Manuscript of Catalogue was forwarded to USAELRDL in

1964. This volume was concerned with "A Second Bioliography on Rad:io

Interference, With Aostracts,n and contained over aostracts,

su.nnnari.es, and references in the field of radio interference.

Mr. E. W. Wood attended the ''Symposium on Measurements- and

11 oy the U. S. Army Mi sile Command, in

Huntsville, Alaoama, on 4-6 Mr. Wood also visited the NASA

Marshall Space Flight Center EMC Division at the Redstone Arsenal on 6

Mr. R. D.

on 14

ities at

Jr. attended the Southeastern Simulation Council

the General Electric

1964. Mr. Trammell

3

at Cape Kennedy, Florida,

in a tour of the NASA facil-

IV. FACTUAL DATA

A. Receiver Tests

The following receiver te techniques and test resuJ..ts are di.scussed

in this intermodulation, spurious response,

and noise The tests descri.bed are the generally a quality

for most receivers but some are conducted using approaches which differ from

those employed. attention is given to the role of the re-

ceiver

tion of a

in receiver characteristics evaluation. With the excep

preselector curve, little data from receiver tests are

published in this sectionj rather, sis is on the

ed and on to avoid v.rhen the tests are conducted. The data for

the

be

and PCM/FM receivers used in the verificati.on of these tests wili

in volumes of the of Catalogue.

1. Intermodulation

Receiver intermodulation is the production of a spurious in

a receiver by two or more RF which differ in frequency from the

receiver tuned frequency. Upon reaching the receiver mixer (or other non-

linear elements), the or their harmonics mix. An unwanted and inter-

intermodulation response may be generated if the mix

at either the receiver intermediate frequency, the tuned

a signal

or the

image If the nonlinearity produces a at any other fre-

quency, the receiver intermodulation is generally of no consequence$

The intermodulation responses are identified by their order, i.e.,

total of the harmonic number the response. For

harmonic of one combines with the third harmonic of the other to

4

response, a fifth order intermodulation product resuJ..ts. Other

are s follows:

Let f = lower signal frequency a

f = tuned 0

(local oscillator - IF), or

= tuned image (local oscillator + IF), or

= IF

Then f = fb - f is 0 a a second order (primary mix) intermodu:ation

response;

= 2f a

is a third order intermodulation response;

f = 0

is a fourth order intermodulation response;

= is a fifth order intermodulation response.

intermodulation responses above the fourth order are not

to be of any consequence.

It is conceivable that the above type intermodulation mixes are not the

only ones These are based on the receiver mixer pro-

a difference rather than a summation when

on the two off-channel One su~ation type product was observed in

the laboratory on an FM test receiver which utilizes modulated tech-

The which excited this response were = 4939.88 Me and

= Me.

In this receiver the local oscillator frequency was measured to be

2160.01 Me.

+ = 4939. + 8136. = 13076.63 Me

5

(LO

The intermediate

) X 6 =

12960.

.01 X 6 =

.57 Me

.06 Me

of this wideband FM receiver ranges from

to .,5 Me; therefore, it appears that the sum of the two input

with the sixth harmonic of the local oscillator to a

mixed

in the

IF passband. The order of this intermodulation response is not defined by

the conventional methods of identification~

It should be noted that in order to "track" a difference type inter-

modulation it is necessary to both

in the same direction. With an additive type product it is necessary to

increase the of one signal and correspondingly decrease the fre-

quency of the other in order to track the response.

a. The Receiver Preselector and its Inter-

modulation Interference. A most important element in the of

i.ntermodulation responses is the receiver The

should have an insertion loss at the receiver tuned of

a few decibels and a loss than 70 db at all other frequencies~ As with

most microwave filters, this is not the case. The measured pre-

selector response of a PPM/FM receiver tuned to

18 The response to

maximum attenuation at 4.9 Gc. Secondary

to exist in the response curve at

ence of the spurious passbands in the

of intermodulation responses is enhanced.

6

Me is presented in

above 4 Gc increases to

passbands are seen

Because of the exist

response, the probability

0

5

10

::0 3 15 V') V')

0 _j

z 20 Q 1-0:: UJ 25 V')

~

0:: 0 30 1-u UJ _j

UJ 35 V')

UJ 0:: a...

40

45

50

55

60 0.1 0.2

TUNED FREQUENCY: 2040 Me

0.4 0.6 0.8 1.0 4.0 6.0

FREQUENCY kmc

1. Preselector Insertion Loss as a Function of Frequency for a PPM/FM Receiver.

8.0 10.0

From the curve it can be seen that there is an i.ncreased

possibility of a primary (2280 Me) intermodulation mix at

= 5000 Me and = 7280 Me. An intermodulation response was meas·urable

when these signals were at the receiver antenna terminals. A

number of such combinations resulting in intermodulation responses may be

observed to coincide near the spurious passbands in the preselector curve.

The fact -!:.;hat an intermodulation combination is possible does not

mean that the response will exist. However, the measured data were

found to indicate the most combinations giving rise to inter-

modulation responses in the receivers tested for a given signal

level.

At the the most reliable and accurate method known for plotting

a preselector response curve is that of by point data

and a response indicator such as a spectrum or

radio interference mea set. Swept oscillator and noise offer

faster but less accurate means of obtaining response data on filters wi.th

w:ide variations of attenuation.. It was found to be sufficient to plot only

the major variations in response as function of frequency in

order to its influence on intermodulation interference~

It should be noted that when such devices as were inserted in

the receiver antenna circuit, the input characteristics slightly;

however, the

desired i.n

was the dominating element. If extreme accuracy is

the (input) response, it would be advan-

tageous to connect all circuit test components to conducting this

test.

8

Two of the communications receivers of the same type which were examined

were found to be susceptible to intermodulation interference for 0 dbm input

ls. Two receivers of another type were found to reject intermodulation

interferences greater than 90 db under the same testing conditions. The lat-

ter receivers utilized low-pass filters which had a cutoff above

the maximum tuned frequency in the band, whereas the former receivers utilized

no low-pass filters. inserting low-pass filters in the antenna circuits of

these receivers, it was determined that the intermodulation rejection was more

than db at all greater than 100 Me from the tuned frequency in

the frequency range of 1 to 10 Gc. The receiver sensitivity was reduced less

than 1 db during this experiment.

b. Testing Techniques. The test configuration used to evaluate

the intermodulation characteristics of laboratory receivers is shown in

Figure 2. As indicated in the paragraph, it is advantageous to

study the preselector response curve to determine which intermodulation pro-

ducts are more to exist and over what range of frequencies. When

a response is detected the general

range and record~f:

is to "track" it over a wide

and the equal power setting for f a

and necessary to produce a standard receiver response. A sufficient

number of data points should be taken to plot a smooth curve of ~f as a func

tion of the power required to produce the response. The power levels

should be corrected for cable and other losses in order to yield the result

ing power at the receiver antenna terminal. The standard receiver response

for the present laboratory measurements is 6 db of receiver quieting.

(with an unmodulated input 1) as measured with a Hewlett-Packard Model

9

QUIETING INDICATOR

CW (VOLTMETER) SIGNAL

GENERATOR j

VIDEO (fa)

COAXIAL SWITCH OUTPUT ~---~-, RESISTIVE

I • I ADDER FM

I • I - RECEIVER

I u I ANT UNDER TEST

L. --- _ _I

CW SIGNAL

GENERATOR (fb)

FREQUENCY COUNTER

Figure 2. Block Diagram of Suggested Test Configuration for Receiver Intermodulation Evaluation.

QUIETING FREQUENCY - INDICATOR

COUNTER

'

COAXIAL SWITCH VIDEO 0 UTPUT r-- ..... ---, I 4~ I

SIGNAL - LOW-PASS I ... - I TEST GENERATOR FILTER I ; ANT RECEIVER

I L ____ ..J

Figure 3· Block Diagram of Suggested Test Configuration for Receiver Spurious Response Evaluation.

10

voltmeter. The 6 db of quieting level does not agree with the 20 db of

level in MIL-STD-449B; in order to obtain a refer-

ence for the receivers tested, the 20 db of reference was found to

be an ctical for the maximum output levels of the generators

used in the laboratory tests. However, it must be pointed out that the rejec-

tion ratios of ordered intermodulation products will differ when measured

with different reference levels.

Care must be taken to be certain that the observed intermodulation is

actually place within the receiver and not in the external circilit

components, such as

for the

confirm

generatorso A hybrid ring or directional

generators is one method commonly used to prevent or

intermodulation. It was found that an ar•r><..:>F'\'T'-l

method is that of placing appropriate filters in the external eire-edt -vrhen

the two differed more than a few hundred mega

As an example., suppose an intermodulation mix of 7000 Me and Me to pro-

duce a tuned of 2000 Me is to be A high-pass 3000 Me

filter in the :receiver antenna line would reduce any

2000 Me intermodulation product which inters the receiver. At many

generator frequencies

for use in the

combinations of filters can be obtained

and/or receiver antenna leads to prove the existence

of receiver intermodulation responses. It appears sufficient to show that

a response is actually caused by receiver intermodulation at only one or

two points along a given tracking range

modulation is found.

Each time an intermodulation response is

no trace of external inter-

it is necessary to

ascertain that the response is not a receiver spurious response to one of

11

the signal fre s. This can be checked noting whether the level of

the response changes with power level changes on both generators. A true

intermodulation response will be affected by power level changes in either of

the signals, whereas a spurious response level will be affected by a change in

level of only one generator. For this reason it is advantageous to conduct

receiver response measurements prior to intermodulation tions

in order to determine the range of a frequency in which spurious responses

are most

2.

responses are unwanted receiver responses caused by the

local oscillator or its harmonics mixing with an external l or its bar-

moni.cs to prod"U.Ce the receiver intermediate frequency. The harmonics of

the external 1 are not present at the receiver antenna terminal but

are in some nonlinear element within the receiver, such s the re-

ceiver mixer. Genera spurious response are given the fol-

relation:

f sr

where f , r1

, f.f are spurious response sr o l local oscillator fre-

quency, and intermediate respectively. The symbol (p, q,

represents the order of the harmonics of the local oscillator and external

l and conversion process which produces the intermediate

a. The Preselector. As in an intermodulation response investiga-

the receiver preselector was found to an important role in

12

response evaluation for the receivers tested. An examination of the

of a response. Initially, it is advantageous to search for

responses '\vhere there are passbands rather than scan-

ning a very large frequency range.

Since the receivers tested had no RF amplification to the mixer

stages, the response rejection depended on the

response, response and mixer conversion loss at the in

question. Therefore, for the (2, 1, ±) response which may have a

2 conversion loss of only 9 db, the and must contribute

the ma attenuation characteristics. For one receiver the (2, 1, +)

response rejection was 46 db, and the combined and

attenuation was measured to be db at the spurious

In many cases, the spurious responses could be predicted within 6 db with

of mixer behavior and attenuation characteristics of the

the mixer

b. Testing Techniques. The test configuration for

response meas~rements is shown in 3. A low-pass filter should be used

as shown in order to eliminate harmonics of the spurious response test

that are at the output. It is desirable to

mea sure the frequency response on the lo-vr-pass filters used in the mea sure-

ment setup to determine if spurious passbands exist in these filters which

could cause false spurious responses. Many low-pass filters have attenuation

characteristics, as near the filter cutoff but exhibit

low and fluctuating attenuation characteristics at

13

The and power to produce a standard response should

be recorded i.n this test. The standard response level used in the laboratory

tests wa 6 db of receiver since a maximum of +2 dbm of signal

power was available over the frequency range from 1.25 to 10 Gc.

The spurious response ection data 20 db of is

to different results because of the difference in the nonlinea order

of each response. For two receivers tested at a tuned frequency there

were only six spurious responses that were measurable between 0.

l.O Gc with the following power levels available:

Frequency range Available

o. - 65 Me + 23 dbm

- 450 Me + 13 dbm

- 1250 Me + 7 dbm

1.250 - 10 Gc + 2 dbm

Me to

These receivers utilized a and low-pass filter to achieve these

results. The image response, 120 Me from the tuned frequency, was not

detected. For each of two other receivers tested, over spurious response

data points were recorded for a given tuned frequency under the same condi-

tions. The

frequency.

A TWT

response wa db at 240 Me from the tuned

has been ordered which will provide sufficiently

power to excite the other spurious responses at frequencies where the pre-

selector attenuation effects.

The l shape of the spurious responses should also be known

to measuxing the spurious responses of wideband receivers. The

is useful in the identification process.

and Noise

is a measure of how well a receiver is able to

undesirable ls which are very near the tuned The selectivity

characteristics of a receiver are primarily by the res-

ponse and the bandwidth of the intermediate amplifier. The the

the greater the rejection of off channel ls; however,

in a frequency modulation receiver the

must be ma i.nta ined wide enough to

modulated carrier ..

cover the

response and IF bandwidth

excursions of the

In the receivers the receiver passband was not flat, and detailed

measurements were necessary to define the The active AFC circuits

were disabled these measurements. The influence of the presence of the

counter was found to be

The test configuration used for ma selectivity measurements is shown

in 4. For the receivers tested, readings were made of the difference

between the nominal tuned frequency and the test frequency, and of the power

to produce a standard response at the test frequency. It was neces-

sary to measure all

was limited. A

necessity.

accurately since the selectivity passband width

with a vernier frequency dial was found to be a

Receiver sensitivity is a measure of the minimum signal required at the

antenna terminal to produce a given response at the receiver output. This

test is conducted at the tuned frequency.

15

FREQUENCY COUNTER

SIGNAL GENERATOR

r--~--,

I u I I _ _ I I - - I I I L ____ ..J

COAXIAL SWITCH

QUIETING INDICATOR

VIDEO 0 UTPUT

TEST ANT RECEIVER

Figure 4. Block Diagram of Suggested Test Configuration for Receiver Selectivity Measurements.

QUIETING INDICATOR

VIDEO 0 UTPUT

SIGNAL TEST GENERATOR ANT RECEIVER

Figure 5· Block Diagram of Suggested Test Configuration for Receiver Sensitivity Measurements.

TERMINATION

r{ I NOISE ~ SOURCE

'---NOISE

FIGURE ANT"- TEST

METER IF RECEIVER

Figure 6. Block Diagram of Suggested Test Configuration for Noise Figure Measurements.

16

The test used for making receiver sensitivity measurements

i.s shown in 5. This test should be made at several in the

tuning range of the receiver. The power, corrected for losses to the antenna

terminal, necessary to produce the standard response should be recorded. Care

should be taken to adjust the signal frequency to the center of the

passband since the passband may be multipeaked with the

response levelso

having different

The receiver noise figure is defined as the ratio of the available input-

to-output l to noise power ratios. It is measure of the degradation

in ratio of a signal with a receiver. Noise generated in the

first or second RF stages in the receiver contribute most to the noise

since noise generated in these is more than noise

in later

The noise figure measurement configuration used is shown in 6.

Measurements have been made on wideband communications receivers using an

Airborne Instruments laboratory Automatic Noise-Figure Indicator. It was

found that the comparison of noise figure data and sensitivity data showed

that poor noise data were obtained at where poor sensi-

tivity data were recorded and better noise figure data were recorded at fre

where the receiver was more sensitive. The input to the receiver

was made at the antenna terminal and the output was taken from the pre-IF

amplifier. Any convenient point in the IF amplifier stage is satisfactory

for the output since additional stages of IF amplification will not appre-

ciably affect the noise figure. The shortest cable should be used

from the noise source to the receiver since cable attenuation will yield an

17

erroneous noise reading. An a:pproxi:rnate attenuation correction can 'be

made subtracting the cable attenuation in decibels from the noise figure in

deci.bels as read from the noise figure meter.. This is a good approximation

for cable attenuation values less than 10 :per cent of the noise figure meter

reading~ Measurements with the receiver tuned to several different channels

should be made. The instruction manual should be consulted for

instructions for the noise meter ..

B.. Mixer and Evaluation

1~ Introduction

The search for a method which the spurious responses in receiv-

may be accura calculated usually results in the

'ing problem. of obtaining a usable mathematical model which will represent

the mixer characteristic. Since no finite model has been found which

will adequa represent the of a nonlinear device, the investi

form of infinite series to express the mixer gator is forced to resort to

cu.:rve mathematicallyo

Considerable effort has been in :previous of

mixer the :power series .3-5

+ "" .. + + ....

as a :mathematical model of the mixer characteristic. The :prediction method

developed was derived from this approach, and so far has proved to

be a simple and means of predicting spurious response formation

in the particular experimental mixer circuits tested. However, efforts to

calculate the absolute values of responses using this representation have not

been successful, primarily because of difficulties in obtaining the proper

coefficients of the terms in the expansion. Experimental data on various mixer

configurations have shown that the amplitudes of the harmonics and responses

are a function of bias voltage, and no approximating polynomial has been

found which will yield this phenomenon.

Ah alternate approach to the problem of expressing mixer action mathe-

matically is that of representing the mixer characteristics by a trigonometric

or Fourier series. Since previous studies have indicated that spurious response

formation is a function of harmonic generation in the mixer, efforts have

been expended toward the derivation of a mathematical harmonic generator.

Agreement between the experimental data and the calculated harmonic values

when using an ideal diode as a basic model indicate the possibilities of

this approach as a means of representing mixer operation.

2. Calculated and Measured Data

The characteristic curve of an ideal diode is shown in Figure 7.

For the input e. = B + A sin rnt, the output will be a series of current ln

pulses whose amplitude is dependent upon the bias voltage B and slope of

the ideal characteristic k, and whose width is dependent upon B. If one

expresses this waveform as a Fourier series, the amplitude of the coefficients

of the harmonic terms may be represented by:

c = p

2k.A 1(

sin pa cos a - p sin a cos pa

p(p2 - 1)

where a= ; T, T T -1 -B

= rr cos A

19

[\) 0

I I

ein = B + A sin ((t)t)

\ I \ I \ It \ I \ I \ I

\ I \ I ..... ,

Figure 7. Ideal Diode Operation for Sinusoidal Input Plus Bias Voltage.

\ \ \ \ \ \

' '

and p = 1, 2, 3, · · ·

Figures 8 through 11 represent the calculated power level of various harmonics

as a function of the ratio of bias voltage to peak sinusoidal input, for A= 0.3

volts and a value of k = k1

on the curve of a 1N21B diode as shown in Figure 12.

The calculated power level is expressed in dbm which excludes the phase relation

of C , the harmonic output voltage. The curves are symmetrical about the point p

B/A = 0, the point at which the odd order harmonics are zero and the even order

harmonics are at a maximum. The curves are nonexistent for IB/AI ~ 1, which is

expected in view of the representation in Figure 7. Considering the points

jB/AI = 1 to be nulls, it is seen that the number of nulls appearing in a partie-

ular harmonic C is equal to p. For a given sinusoidal and bias voltage input, p

the amplitude of the output harmonics are entirely dependent upon the slope of

the ideal diode curve, and the change 6k in this slope results in an identical

change in the amplitude of each harmonic. Thus the relative amplitude between

successive harmonics does not change with variations in k.

Figure 12 represents the E versus I curve of the simple 1N21B diode mixer

circuit shown in Figure 13. Data for this curve were taken with an applied

sinusoidal peak voltage input of 0.3 volt which results in the characteristic

having a nonzero value for zero bias. The measured harmonic levels as a func-

tion of bias for this mixer are shown in 14 through 17. Except for a

shift in the abscissa scales, these curves are very similar to those obtained

by calculation, with the absolute amplitudes and the distances between null

points being approximately the same in both cases. However, it should be noted

that the close agreement obtained here is not only dependent upon the slope

selected for the ideal diode curve, but also requires a knowledge of the shift

in abscissa scale. No logical basis for deriving these values has been

determined.

21

e ...0

~

..J w > w ..J

0 w t-<(

l\) ..J l\) :::::J

u ....J <( u

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

-0.6 -0.4 -0.2 0

B/A

+0.2

Figure 8. Calculated Level of 2nd·Harmonic Versus B/A Where B = Bias Voltage Input and A = Peak Amplitude of Sinusoidal Input.

+ 1.0

-10

-20

-30

-E -40 ..Q

~

_J w > -50 w _J

0 w -60 1-<(

/\) _J

\.N ::J u _J -70 <( u

-80

-90

-100

-1.0 -0.8 -0.6 -0.4 -0.2 0

B/A

+0.2 +0.4

9· Calculated Level of 3rd Harmonic Versus B/A Where B = Bias Voltage Input and A = Peak Amplitude of Sinusoidal Input.

-10

-20

-30

-E ...Q -40 3 ...J w > -50 w ...J

0 w

-60 t-< ...J ::J u ...J -70 < u

-80

-90

-100

-1.0 -0.8 -0.6 -0.4 -0.2 0

B/A

+0.2 +0.6

Figure 10. Calculated Level of 4th Harmonic Versus B/A Where B ; Bias Voltage Input and A; Peak Amplitude of Sinusoidal Input.

+0.8 + 1.0

-10

-20

-30

-E ...Q -40 3 _J w > --50 w _J

0 w

-60 1-<( _J

[\) ::::::> Vl u

...J -70 <( u

-80

-90

-100

-1.0 -0.8 -0.6 -0.4 -0.2 0

B/A

+0.6

Figure 11. Calculated Level of 5th Harmonic Versus B/A Where B = Bias Voltage Input and A= Peak Amplitude of Sinusoidal Input.

+0.8 + 1.0

1\) 0\

--0.6 -0.5

I (ma)

-0.4 -0.3 -0.2 -0.1 0 +0.1 +0.2 +0.3 +0.4

BIAS VOLTS

Figure 12. Diode Current Versus Bias Voltage for 1N21B Diode in the Circuit of Figure

+0.6 +0.7

GENERATOR 10 Me

BIAS

1N21B

FILTER H

Figure 13. Diagram of Test Mixer Circuit.

RADIO INTERFERENCE MEASURING SET

-10

-20

-30

e ...0

-40 3 _J w -50 > w ....J

0 -60 w Q:

I\) :::> 1.1)

m <( w -70 :E

-80

-90

-100

-0.8 -0.6 -0.4 -0.2 0 +0.2 +0.4 +0.6 +0.8 +1.0 B/A

Figure 14. Measured Level of 2nd Harmonic Versus B/A Where B = Bias Voltage Input and A= Peak Amplitude of Sinusoidal Input.

+1.2 +1.4

-10

-20

-30

e -40 ..a ~

...J w -50 > w ...J

Q -60 w

~ :::>

1\) V)

<( \.0 w -70

~

-80

-90

-100

-0.8 -0.6 -0.4 -0.2 0 +0.2 +0.4 +0.6 +0.8 + 1.0 B/A

Figure 15. Measured Level of 3rd Harmonic Versus B/A Where B = Bias Voltage Input and A = Peak Amplitude of Sinusoidal Input.

+ 1.2 + 1.4

-10

-20

-30

'E -40 ..0

3 ..J w -50 > w ..J

Q -60 w

0::

\.N ~ V')

0 ..q: w -70 ::E

-80

-90

-100

-0.8 -0.6 -0.4 -0.2 0 +0.4 +0.6 +0.8 +1.0 B/A

Figure 16. Measured Level of 4th Harmonic Versus B/A Where B = Bias Voltage Input and A = Peak Amplitude of Sinusoidal Input.

+1.2 +1.4

-10

-20

-30

e -40 ..Jl

3 _J w -50 > w _J

0 -60 w

a::: :::l

\J.J tl)

f-' <( w -70 ::E

-80

-90

-100

-0.8 -0.6 -0.4 -0.2 0 +0.2 +0.4 +0.6 +0.8 + 1.0 B/A

Figure 17. Measured Level of 5th Harmonic Versus B/A Where B =Bias Voltage Input and A= Peak Amplitude of Sinusoidal Input.

+1.2 + 1.4

As discussed previously, the value of k used in the har-

monic levels was selected from the E versus I curve of 12. The

value k1

was used in the actual computations, while k2 was determined to be

the value which calculated harmonic amplitudes equal to the measured

amplitudeso The significance of this particular value of k2 has not been

and further investigation is being conducted in order to deter-

mine its upon diode parameters and/or signal levels.

It can be seen from 12 that the larger the sinusoidal

signal the more closely the diode curve approaches an ideal characteristic

to the signal input). as the signal level is decrea

the nonlinear portion of the curve is predominant. 18 shows the

response of the ci.rcuit in Figure to a sinusoidal It is seen that

this response is more approximated by (coswt)2 pulse or a (coswt) 3

rather than a (coswt) A study of this waveform by the Fourier

series approach has been initiated in order·to determine its value as a rrillthe-

matical model of mixer operation. A mixer study6

the modified

Bessel function of the first kind has also been reported.

Conclusions

The Fourier series approach to the of ana mixer

action has yielded a mathematical model, the operation of which can be

clo correlated with that of a 1 diode mixer. the finite

model used was only an approximation of the actual mixer characteristics,

the promising results obtained warrant further investigation using this

approach, and effort has begun toward the derivation of a model which will

also realize the nonlinearity of the diode curve.

-TT

A cos wt

-rr/2 0 +rr/2

Figure 18. Response of the Mixer Circuit in Figure 13 to a Sinusoidal Input.

wt

+rr

Ca Response Prediction of Triode Mixers

1. Introduction

toward a study of diode mixers. An accurate technique to predict the

spurious responses of a diode mixer with a minimum amount of labors-

tory measurements has been demonstrated. 7 During the current quarter this

has been evaluated for applicability to triode mixers.

2 Q Triode Mixer Theory

The mixer circuit used in the is shown in

The local oscillator which has an

to the control grid of the 6J4 tube. This voltage,

19.

rn is sup~ o'

with

the bias voltage it produced grid is suffieient to reduce

the current to a smaJ..l value or even cut it off for an appreciable

part cf the cycle" The oscillator voltage thus controls the

grid-to-plate transconductance, g , in the manner shown in Figure 20~ The m

transcond~ctance between the and is therefore a time va

quantity that varies periodically at the oscillator frequency.

In the mixer of the voltage is supplied in the cathode

circ;J.it; thus, the current is proportional to the signal

difference between the grid and the cathode. Since the signal voltage e s

is much smaller than the oscillator voltage, it has no appreciable

effect on the instantaneous value of g • The varying component of the plate m

current produced by the simultaneous presence of the oscillator and l

voltages is given approximately by:

\.)'J \.n

PLATE

VOLTAGE o--------..J TEST POINT

L.O. O.lpf

INPUT ~ son

S6n

TEST POINT son

SIGNAL INPUT son

l 0. lpf

330k

1820flflf

6J4

390n

660

6.3 V AC.

Figure 19. Mixer Schematic.

0. lpf 5.6k

O.lpfi

I.F. ~OUTPUT

son

PLATE

lOOk BIAS

OSCILLATOR ELECTRODE VOLTAGE

E m

w u z

w< t-t<(u ...J:::J

a..~ oO t-~ oz _<( ~~ <.:>t-

Figure 20. Time Varying Transconductance Between the Grid and Plate of a Triode Mixer Tube.

here both e and g are functions of time. s 'lll

If the oscillator voltage is represented as a cosine wave in Figure 20,

the transconductance is an even periodic function and may be

the Fourier series:

= a + 0

cos (1) t + 0

cos 2w t + · • • 0

The signal voltage may be represented as a pure cosine wave:

e = A cos w t s c

where w is the carrier angular frequency. The varying component of the c

current is then:

i = a A cos w t + A cos (w - w )t c 0 p 0 c

2

2

a2 A cos (rn + w )t + -- A cos (w - 2w )t

c 0 2 c 0 +

2 A cos (rn + 2w )t + •·•

c 0 +

by

The plate current equation for triode mixers is characteristic of the

equations presented in earlier reports for diode mixers. Although differences

exist in the absolute values of the coefficients of the terms, the predic-

tion technique makes allovrances for these differences s.ince the predicted

response levels are computed relative to selected measured response levels.

3. Data Evaluation

The test configuration used in obtaining the response data is

illustrated in Figure 21. The responses were first measured without the

10 db pad in the signal input. Several measured responses differed from their

37

SIG. GEN.

LOCAL osc.

RADIO SWITCH INTERFERENCE - MEASURING SET

SWITCH 10 db LOW-PASS IF OF 1 Me RADIO MIXER INTERFERENCE

PAD FILTER MEASURING SET

~

10 Me AT + 20 dbm LOW-PASS PLATE

FILTER VTVM VOLTAGE TEST

DC BIAS

SOURCE

Figure 21. Block Diagram of the Test Configuration Used to Measure Triode Mixer Responses.

predicted values by more than 7 db. This was found to be caused by inter

modulation products which were eliminated by the addition of the 10 db pad

between the signal generator and local oscillator. Figure 22 shows prediction

error as a function of response density with the 10 db pad inserted. All

responses through the tenth order of generation were predicted and found to

be within 3.5 db of the measured value except the (1, 8 ±) and (1, 9 ±)

responses. The signal input frequencies necessary to these two

responses are 1.375 Me and 1.22 Me, respectively. With the oscillator of

21 disconnected and the signal generator set for the standard response

level at 1.22 Me, an output of -108 dbm was obtained on the Radio Interfer

ence Measuring Set when the latter was tuned to 1 Me. An output of -120 dbm

was obtained in a similar manner for 1.375 Me. This indicates that the

signal input frequencies necessary to generate the (1, 8 ±) and (1, 9 ±)

responses are within the passband of the Radio Interference Measuring Set

when it is tuned to 1 Me, thereby causing excessive errors for these two

responses.

A 6J4 triode grounded-grid mixer was constructed and an attempt was

made to collect data. This mixing technique did not prove satisfactory

because the signal generators used to supply oscillator and signal voltages

in the cathode circuit were not capable of developing an adequate voltage

difference between the grid and cathode to produce proper mixing action.

4. Conclusions

Although extreme case was exercised in obtaining the data, it is

believed that errors of as much as 3 to 4 db exist between the measured and

calculated responses because of possible accumulation of equipment and

39

13

12 TRIODE: 6J4 L.O. LEVEL: + 20 dbm SENSITIVITY: - 110 dbm

11 I.F. FREQUENCY: 1 Me TUNING: Output to 1 Me

10 L.O. FREQUENCY: 10 Me PLATE VOLTAGE: + 100 v

9 CROSSHATCHED: True Density DASHED: Density Integral

>- 8 t-v; z w 7 0

w V')

6 z 0 a..

+:- V')

w 5 0 c::

4

3

2

-11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 +1 +3 +4

PREDICTION ERROR (db)

Figure 22. Response Density Versus Prediction Error for 6J4 Triode Mixer.

. 8 t measurement errors. The da a in 22 indicate that the

is highly accurate for triode mixers of the type shown

in Figure However) other vacuum tube configurations should be examined

before a statement can be made about all vacuum tube mixers. Ap-

plicability of this technique to mixers of multigrid configurations and to

mixers transistors and tunnel diodes will be investigated as a part of

41

V. CONCLUSIONS

The verificati.on test results of standard tests conducted on available

U .. S. Army cormnunications receivers show that powered signal generators

are required to excite and measure spurious and intermodulation responses at

where the receiver exhibits high attenuation effects.

On the other hand, preselectors on certain receivers exhibited many spurious

passbands which cause these receivers to be highly vunerable to spurious re-

sponse and intermodulation interference above the tuned These pro-

blem.s were reduced in other examined receivers which ulitized low-pass filters

witb cutoff above the receiver tuning ranges. The spurious response

data co~ld be closely estimated from the measured preselector response charac-

teristi.cs and recorded mixer conversion loss data.

The Fourier series approach to the ana of mixer action has

a mathematical model, the operation of which compares with that of a

1 diode mixero The results obtained indicate that a similar approach

whi~h would incorporate the nonlinearity of the diode curve may be promising.

The mixer response prediction technique for diode mixers discussed in

previous reports was used to predict the responses of a vacuum tube

triode mixero The results indicate that the technique is equa valid for the

mixer type examined. However, other vacuum tube configurations such as multi

' as well as mixers using transistors or tunnel diodes,

should be tested before the general application of the prediction technique

can be evaluated.

42

VI • PROGRAM FOR NEXT INTERVAL

The next quarter's effort will be concentrated on the completion and

documentation of all previously examined equipment interference tests and

test procedureso

The tests, test procedures, and testing techniques and pitfalls for

obta interference characteristics of U. S. Army communications equipments

which utilize modulation techniques will be submitted in a volume of the

Manuscript of Catalogue.

Several volumes of the Manuscript of Catalogue will be published

which will contain the data collected in the verification tests conducted

on the AN/TRC-29, AN/TCC-13, AN/GRC-50, and AN/FRC-34 communications equip

ments ..

All pertinent mixer data, a , and materials during

the course of the contract will be combined in one volume of the Manuscript

of Catalogue. Work on transistor and vacuum tube mixers during this quarter

will also be included in this volume.

43



E. E. Donaldson, Jr. Grad .. Research Assistant

J. H. Jv18ckay Research Mathematician 2

0. H. Ogburn Research Assistant 416

I. E. Perlin Research Professor 2

w. L .. Research Assistant 420

D. w. Robertson He a Connnunications Branch 48

P .. T. Grad. Research Assistant

c. w. Stuckey Asst. Research 418

R. D. rr'r a:mme 11 J Jr. Asst. Project Director 414

J .. R. Walsh, Jro Research Engineer

w. B. Warren, Jr. Research Engineer 12


44

VIII . REFERENCES

le Measurement of Radio Frequency Spectr·wm Characteristics, Military Standard7

MIL-STD-449B_, (1963) ~

2. E. We Wood, R. Do Trammell, Jro, C. W. Stuckey, H. W. Denny, E. E. Donald-son, Jr .. J and R. M. Cook, "Quarterly No. 1, Project A-678, '' Elec-tronic Equipment Interference Characteristics-Communication Type, Contract No. DA 36-039 AMC-02294(E), Georgia Institute of Technology, Engineering Experiment Station, p. 90, ( February 1963 to May 1963)8

3. R. N. Ba Ec W. Wood, Ro D. Trammell, Jr., and J. R. Walsh, Jr., l. Technical Report, Project A-543," Electronic Equipment Interference

Characteristics-Communication Type, Contract No. DA 36-039 sc-87183, Georgia Institute of Technology, Engineering Experiment Station, pp. 58-89, (l 1961 to 15 February 1963).

4. Wood, et al, loc cit.

5. E. Jo Lefferts and W. M. Rise, Report No. 1, Interference Reduction Techniques for Nonlinear Devices, Contract DA 36-039 AMC-02200(E), Martin Company, (l April 1963 to 30 June 1963).

"Intermodulation 2, PPo 173-179, (

of Crystal Mixer, 11 Proc. 1964)., ----

7Q R. D. Trammell, Jr., C. W. Stuckey, E. W. Wood, 00 He Ogburn, and E. E. Dona Jr .. , "Quarterly Report No.2, Project A-678," Electronic Equip~ ment Interference Characteristics-Conrrnunication Type, Contract No. DA 36~039 AMC-02294(E), Georgia Institute of Technology, Engineering

Station, pp. 35-37, (15 May 1963 to 15 August 1963).

8. Trammell, loc cit.

No .. of Copies

1

1

1

3

20

1

1

1

2

l

1

l

l

l

l

DISTRIBUTION LIST

To

OASD (R&E), Rm 3El065, ATTN: Technical Library, The Pentagon, Washington 25, D. C.

Chief of Research and Development, OCS, Department of the Army, Washington 25, D. C.

Commanding General, U. S. Army Materiel Command, ATTN: R & D Directorate, Washington 25, D. C.

Commanding General, U. S. Army Electronics Command, ATTN: AMSEL-AD, Fort Monmouth, N. J.

Commander, Defense Documentation Center, ATTN: Cameron Station, Bldg. 5, Alexandria, Virginia

TISIA, 22314

Commanding Officer, U. S. A. Combat Developments Command, ATTN: CDCMR-E, Fort Belvoir, Virginia

Commanding Officer, U. S. Army Combat Developments Command, Communications-Electronics Agency, Fort Huachuca, Arizona

Commanding Officer, U. S. Army Electronics Research and Development Activity, ATTN: Technical Library, Fort Huachuca, Arizona

Chief, U. S. Army Security Agency, Arlington Hall Station, Arlington 12, Virginia

Deputy President, U. S. Army Security Agency Board, Arlington Hall Station, Arlington 12, Virginia

Director, U. S. Naval Research Laboratory, ATTN: Code 2027, Washington 25, D. C.

Commanding Officer and Director, U. S. Navy Electronics Laboratory, San Diego 52, California

Aeronautical Systems Division, ATTN: ASNXRR, Wright-Patterson Air Force Base, Ohio 45433

Air Force Cambridge Research Laboratories, ATTN: CRZC, L. G. Hanscom Field, Bedford, Massachusetts

Air Force Cambridge Research Laboratories, ATTN: CRXL-R, L. G. Hanscom Field, Bedford, Massachusetts

No. of Copies

l

1

l

l

l

1

l

l

1

4

l

1

1

DISr:f.1HIBUTION LIST (Continued)

To

Hq, Electronic Systems Division, ATTN: ESTI, L. G. Hanscom Field, Bedford, Massachusetts 01731


AFSC Scientific/Technical Liaison Office, U. S. Naval Air Development Center, tTohnsville,

USAELRDL Liaison Office, Rome Air Development Center, ATTN: RAOL, Griffiss Air Force Base, New York

Commanditlg Officer, U. S. Army Electronics Materiel Support Agency, ATTN: SELMS-ADJ, Fort Monmouth, New Jersey

Director, Monmouth Office, U. S. Army Combat Developments Command, Communications-Electronics Agency, Fort Monmouth, New

Commanding Officer, Engineer Research and Development Laboratories, ATTN: Technical Documents Center, Fort Belvoir, Virginia

Marine Corps Liaison Office, U. S. Army Electronics Research and Development Laboratories, Fort Monmouth, N. J.

AFSC Scientific/Technical Liaison Office, U. S. Army Electronics Research and Development Laboratories, Fort Monmouth, New

Commanding Officer, U. S. Army Electronics Research and Development Laboratories, ATTN: Logistics Division, Fort Monmouth, New Jersey, (MARKED FOR: GUY JOHNSON)

Commanding Officer, U. S. Army Electronics Research and Development Laboratories, ATTN: SELRA/DE, Fort Monmouth, New Jersey

Commanding Officer, U. S. Army Electronics Research and Development Laboratories, ATTN: Technical Documents Center, Fort Monmouth, New

Commanding Officer, U. S. Army Electronics Research and Development Laboratories, ATTN: SELRA/GF, Fort Monmouth, New Jersey

No. of Copies

l

l

1

l

1

1

l

DISTRIBUTION LIST (Concluded)

To

Commander, Rome Air Development Center, Griffiss Air Force Base, New York, ATTN: EMCVR (C. R. Miller)

Chief, Bureau of Ships, Dept. of the Navy, Washington 25, D. C. ATTN: Code 452 (Mr. Roman)


Commanding Officer, U. S. Army Electronics Research and Development Laboratories, ATTN: SELRA/GFA, Fort Monmouth, New

Commanding Officer, U. S. Army Electronics Research and Development Laboratories, ATTN: SELRA/GFR, Fort Monmouth, New Jersey

Commanding Officer, U. S. Army Electronics Research and Development Activity, ATTN: FC-05, White Sands, New Mexico

IIT Research Institute, ATTN: Mr. J. T. Ludwig, 10 W. 35th Street, Chicago 16, Illinois

REPORT NO. 26


PROJECT A-678

ELECTRONIC EQUIPMENT INTERFERENCE CHARACTERISTICS-CO~JICATION TYPE

C. W. Stuckey, R. D. Trammell, Jr., and E. W. Wood

Contract DA 36-039 AMC-02294(E) (Continuation of Contract DA 36-039 sc-87183) DEPARTMENT OF THE ARMY PROJECT: lG6-2050l-D-449

15 February 1964 to 15 July 1964 Issued 15 July 1964

Prepared for U. S. Army Electronics Laboratories Fort Monmouth, New Jersey



REVIEW~ P·".-,- .·-;· IT {)- ~('./ ,, ; ::,\, ... 6 ..... 1. ..... 19 .. (e;'!.': BY .. 7li:. ........ _ ..... . F·Q· OI\ ,-''T ~l· .-K /t

t\ 11J ) /"1 u " .. , ................... 19 ....... BY ................••

lib-sascan

Rectangle

GEORGIA INSTITUTE OF TECHNOLOGY Engineering Experiment Station

Atlanta, Georgia

REPORT NO. 26


PROJECT A-678


By

C. W. Stuckey, R. D. Trammell, Jr., and E. W. Wood

CONTRACT NO. DA 36-039 AMC-02294(E) (Continuation of Contract No. DA 36-039 sc-87183) DEPARTMENT OF THE ARMY PROJECT: 1G6-2050l-D-449

The object of this research program is to conduct a comprehensive investigation to determine methods for measuring the interference characteristics (spectrum signature) of U. S. Army communications equipment deemed necessary for the prediction and minimizing of electromagnetic interference.

15 FEBRUARY 1964 to 15 JULY 1964 Issued 15 July 1964

Performed for U. S. ARMY

ELECTRONICS LABORATORIES FORT MONMOUTH, NEW JERSEY

FOREWORD

This report was prepared at the Georgia Tech Engineering Experiment Sta-

tion on Contract No. DA 36-039 AMC-02294(E). The report covers the activity

and results of the fifth quarter's efrort on a project to conduct a feasibil-


ence characteristics (spectrum signature) of U. S. Army pulse modulated type

communications equipment deemed necessary for the prediction and minimizing of

electromagnetic interference.

Appro~ed: ./J

~.?J.,ca~ D. W. Robertson, Head Communications Branch

ii



lib-sascan

Rectangle

lib-sascan

Rectangle

TABLE OF CONTENTS

I. PURPOSE •

II. ABSTRACT


IV. FACTUAL DATA

A~ Pulse testing of a typical FM/PCM system

1. Error detection system

2. Effects of receiver tuning on error rates •

a. Test procedures ••• b. Test results

3. Effects of interference on error rates

a~ CW interference tests • b. AM interference tests • • c. FM interference tests

4. Conclusions •

B. Spurious response and intermodulation predictions in cavity-crystal receivers • • • • . •••

1. Introduction

2. Measurement techniques

3. Calculation techniques

4. Experimental results

5. Simplification measures •

6. Advantages and disadvantages of prediction

7. Conclusions and recommendations

C. Summary of publications during the contract period from 15 February 1963 to 15 July 1964 •••••

1. Report No. 22, Quarterly Report No. 1, 15 February 1963

Page

l

2

3

5

5

9

9 L3

15

17 29 36

47

48

48

49

52

57

66

70

71

72

to 15 May 1963, (Confidential) • • • • • . • 72

(Continued)

iii

2.

3.

4.

TABLE OF CONTENTS (Continued)

Report No. 23, Quarterly Report No. 2, 15 May 1963 to 15 August 1963, (Unclassified) ••••

Report No. 24, Quarterly Report No. 3, 15 August 1963 to 15 November 1963, (Unclassified) ••••

Report No. 25, Quarterly Report No. 4, 15 November 1963 to 15 February 1964, (Unclassified) ••

5. Manuscript of Catalogue, Volume 9, "A Second Radio Frequency Interference Bibliography, With Abstracts,"

Page

73

73

74

1 December 1963, (Unclassified) • • • • • • 75

6. Manuscript of Catalogue, Volume 10, "Methods for Measuring and Processing the Interference Characteristics of Communications Equipments Operating in the 1 to 10 kMc Range," 15 July 1964, (Unclassified) • • • • • • • • 75

7. Manuscript of Catalogue, Volume 11, "Mixer Interference Characteristics," 15 July 1964, (Unclassified) • • • • • 76

8. "Manuscript of Catalogue, Volume 4oo, "Interference Characteristics of Radio Set AN/~C-29 and Multiplexer Set AN/TCC-13,'' 15 July 1964, (Secret) • • • • • • • • • • 77

9. Manuscript of Catalogue, Volume 401, "Interference Characteristics of Radio Set AN/GRC-50," 15 July 1964, (Confidential) • • • • • • • • • • • • • • • • • • 77

10. "Manuscript of Catalogue, Volume 402, "Interference Characteristics of Radio Set AN/FRC-34,1! 15 July 1964, (Secret) • • • • • • • • • • • • • • • • • • • • • • • 77

11. "Mutual Interference Chart (MIC) (AN/VRC-12 Transmitter and AN/PRC-25 Receiver), 11 submitted to the Electromagnetic Environment Division, USAEL, 15 April 1964, (Unclassified) • • • • • • • • • • • • • • • • • 77

12. "Lash-Up Output Data (AN/VRC-12 and AN/PRC-25 Equipm~nts)," submitted to the Electromagnetic Environment Division, USAEL, 15 April 1964, (Unclassified) • • • • 78

13. "Mutual Interference Chart (MIC) and Lash-Up Exercise," submitted to the Electromagnetic Environment Division, USAEL, 24 April 1964, (Unclassified) • • • • 78

(Continued)

iv

14.

15.

TABLE OF CONTENTS (Concluded)

"The Behavior of Nonlinear Mixing," Proceedings of the Ninth Tri-Service Conference on EMC, Chicago, Illinois, pp. 59-81, October 1963, (Unclassified) ••••••••••••• . . . . . . . . "The Effect of Multipath Interference on the Intelligibility of Speech Transmitted Over an FM System Employing Time Division Multiplexing," 1964 IEEE International Convention Record, Vol. 12, Part 6, pp. 305-319, New York, N. Y., 23-26, March 1964, (Unclassified) •••••

V. CONCLUSIONS . . . . . VI. PROGRAM FOR NEXT INTERVAL


VIII. REFERENCES •

IX. APPENDIX • •

This report contains 85 pages. v

.

. . . . . . .

Page

79

80

81

82

83

84

8~3

LIST OF FIGURES

Page

l. Block Diagram of Error Detection System •••••••• 6

2. Schematic Diagram of Pulse Delay and Shaping Circuits • 7

3. Block Diagram of the Test Configuration Used in Tuning Tests • • 10

4. Error Rate as a Function of Receiver Quieting for Three Tuning Methods • • • • • • • • • •••••• 12

5. Block Diagram of Test Configuration Used in System Interference Tests • • • • • • • • • • • • • • • • • • • • • • 16

6. Error Rate as a Function of Desired to Interfering Signal Power Ratio for CW Interference. Condition l .••••••••••• 18

7. Error Rate as a Function of Desired to Interfering Signal Power Ratio for CW Interference. Condition 2 • . . . . . . . . . . . 19

8. Error Rate as a Function of Desired to Interfering Signal Power Ratio for CW Interference. Condition 3 . . . . . . . . . . . . 20

9. Error Rate as a Function of Desired to Interfering Signal Power Ratio for CW Interference. Condition 4 • . . . . . . . . . . . 21


ll. Error Rate as a Function of Desired to Interfering Signal Power Ratio for CW Interference. Condition 6 . . . . . . . . . . . . 23




15. Error Rate as a Function of Desired to Interfering Signal Power Ratio for CW Interference. Condition 10 . . . . . 27

16. Receiver Sensitivity with Active AFC as a Function of Input Signal Frequency . . . . . . . . . . . . . . . . . . . 30

(Continued)

vi

LIST OF FIGURES (Continued)

Page

17. Error Rate as a Function of Desired to Interfering Signal Power Ratio for AM Interference. Condition 1 . . . . . . . . . . . 31

18. Error Rate as a Function of Desired to Interfering Signal Power Ratio for AM Interference. Condition 2 • . . . . . . . . . . 32


20. Error Rate as a Function df Desired to Interfering Signal Power Ratio for AM Interference. Condition 4 . . . . . . . . . . . 34


22. Error Rate as a Function of Desired to Interfering Signal Power Ratio for FM Interference. Condition 1 . . . . . . . . . . . 37









31. Error Rate as a Function of Desired to Interfering Signal Power Ratio for FM Interference. Condition 10 . . . . . . . . 46

32. Equipment Setup for Measuring Mixer Harmonic Generation . 51

(Continued)

vii


Page

33. Spurious Response Prediction Error for a Cavity-Crystal Receiver 58

34. Third Order Intermodulation Power Prediction Errqr for a Cavity-Crystal Receiver ••••••••• 58

35. Second Order Intermodulation Characteristics 64

36. Change in Spurious Response Rejection with a Change in Receiver Sensitivity • • • • • • • • • • ••• 67

37. Asymptotic Limit Curve for Responses with p = 1 69

viii

I. PURPOSE

The purpose of this project is to conduct a feasibility study and inves

tigation to determine methods for measuring the interference characteristics


for the prediction and minimizing of electromagnetic interference. Emphasis

shall be placed on pulse modulated type communications equipments operating



Computer methods shall be developed for processing these data to obtain




as follows:

I. The development of tests and procedures for the evaluation of the

interference susceptibility and emanation characteristics of pulse modulated



data to produce output! useful in interference prediction and control appli

cations.

l

II. ABSTRACT

During the previous quarter, systems tests have been made on a wideband

FM system which will utilize a multiplexer that employs pulse code modulation.

To evaluate the system in a PCM environment it was necessary to provide pulse

modulation which simulates that which will be used by the multiplexing equip

ment. This was achieved by modulating the transmitter with a continuous binary

pulse train at the pulse repetition frequency (PRF) of the multiplexer. The

pulses consisted of alternate zeros and ones. The system performance under

various interference conditions was measured by an error detection system which

determined the total number of transmitted pulses which were received incor

rectly. The fraction of total pulses received incorrectly was determined, and

this fraction, or error rate, was used as a measure of system performance.

The effects of various methods of receiver tuning were evaluated. Interference

tests included CW interference, AM interference, and ~4 interference.

The techniques of predicting the spectrum signature of cavity-crystal

receivers are presented and the results of an experimental prediction on a typical

military receiver are reported. Results indicate that prediction of the spectrum

signature for spurious response and intermodulation data is reliable and pro

vides more information on the receiver interference characteristic than previous

direct measurement methods.

A summary of all publications and work accomplished on the contract

during the period of 15 February 1963 to 15 July 1964 are presented in this

report. The contents and classifications of the fifteen reports and papers

published during this period are described.

2


Mr. E. W. Wood attended the 1964 IEEE International Convention held in

New York on 23-26 March 1964. Mr. Wood presented a paper on "The Effect of

Multipath Interference on the Intelligibility of Speech Transmitted Over an

FM System Employing Time Division Multiplexing."

Mr. D. W. Robertson and Mr. E. W. Wood visited USAEL, Fort Monmouth,

New Jersey, on 27 March 1964. A meeting was held with Mr. Guy Johnson,

Mr. R. L. McKenzie, and Mr. Warren Kesselman in which project progress and

technical details were discussed.

The following reports were prepared during the 5th Quarter of the research

program. The classification and contents of these reports are summarized in

part C, section IV of this report.

1. "Mutual Interference Chart (MIC) (AN/VRC-12 Transmitter and AN/PRC-25

Receiver)," 15 April 1964.

2. "Lash-Up Output Data (AN/VRC-12 and AN/PRC-25 Equipments)," 15 April

1964.

3. "Mutual Interference Chart (MIC) and Lash-Up Exercise," 24 April 1964.

4. Manuscript of Catalogue, Volume 10, "Methods for Measuring and Process

ing the Interference Characteristics of Communications Equipments Operating

in the 1 to 10 kMc Frequency Range," 15 July 1964.

5. Manuscript of Catalogue, Volume 11, "Mixer Interference Character

istics.''

6. Manuscript of Catalogue, Volume 400, "Interference Characteristics

of Radio Set AN/TRC-29 and Multiplexer Set AN/TCC-13," 15 July 1964.

3


of Radio Set AN/GRC-50," 15 July 1964.


of Radio Set AN/FRC-34,u 15 July 1964 ..

4

IV. FAGI'UAL DATA

A. Pulse testing of a typical FM/PCM system

During the previous quarter, systems tests have been made on a wideband

FM system which will utilize a multiplexer that employs pulse code modulation.

The multiplexer unit is not yet operational and was not available for testing.

To evaluate the system in a PCM environment it was necessary to provide pulse

modulation which simulates that which will be used by the multiplexing equip

ment. This was achieved by modulating the transmitter with a continuous binary

pulse train at the pulse repetition frequency (PRF) of the multiplexer. The

pulses consisted of alternate zeros and ones. No other pulse coding was

attempted.

The system performance under various interference conditions was measured

by an error detection system which determined the total number of transmitted

pulses which were received incorrectly. The fraction of total pulses received

incorrectly was determined, and this fraction, or error rate, was used as a

measure of system performance.

The effects of various methods of receiver tuning were evaluated. Inter

ference tests included CW interference, AM interference, and FM interference.

1. Error detection system

Figure 1 shows a block diagram of the error detection system used in

these tests. Figure 2 is a schematic diagram of the pulse delay, shaping and

filtering circuits.

The operation of the error detection system consists of inverting the

shaped pulse in the received channel and adding it to the shaped pulse in the

direct channel. If the FM system is operating in an interference-free environ

ment, this type of pulse addition ideally yields pulse cancellation, or no

5

0\

RECEIVED CHANNEL

OUTPUT .. PULSE

FROM -----~~~~~ SHAPER RECEIVER

DIRECT CHANNEL

INPUT TO TRANSMITTER

·~

PULSE _ PULSE H.P. 211A SHAPER .... _11----a DELAY ... -:-........ ---..SQUARE WAVE

CIRCUIT GENERATOR

INPUT INPUT ---- ~------------------------4- -----NO. 1 •• ~~ NO. 2

•r

VARIABLE GAIN

INVERTER

TEKTRONIX 545 OSCILLOSCOPE

- LINEAR ADDER

VARIABLE GAIN

--• VERTICAL

OUTPUT

I FILTER I ~

OUTPUT TO COUNTER

Figure 1. Block Diagram of Error Detection System.

CHANNEL NO.2 PULSE SHAPER

AND DELAY

Figure 2.

1N54

39k

3.3 k

INPUT~TTO ERRO/~~TMECTOR t. gg~~~ER -!- ~30 ~~ -!-

FILTER

Schematic Diagram of Pulse Delay and Shaping Circuits.

voltage at the adder output. If a pulse is detected in the received channel

at a time when no pulse exists in the direct (transmitted) channel, an output

or error voltage pulse is produced. Similarly, if no pulse is detected in the

received channel at a time when a pulse exists in the direct channel, an error

voltage pulse is produced.

In actual operation, some error voltages are produced when the system

is operating in an interference-free environment. These errors result primarily

from slight instability in the Hewlett-Packard 211A square wave generator and

differences in the attack and decay times of some corresponding RC networks

in the direct and received channel pulse shaping networks. These residual

error voltages are of shorter duration and/or lower amplitude than are the

true error pulses. The residual errors were eliminated by low-pass filtering

of the error detector output.

The amplitude of the output voltage of the error detection system is

continuously variable over a 50 db range. By using an attenuator at the counter

input, it was possible to choose a number of arbitrary threshold voltages above

which the counter detected error pulses and below which it did not. Varying the

error voltage threshold was found to affect significantly the total number of

errors recorded under a given interference condition. This was expected since

the output filter caused residual errors to be attenuated rather than eliminated;

by increasing the vertical output voltage (figure 1) and decreasing the counter

input attenuation various numbers of residual errors could be detected. The

most reliable results were obtained when the error detection system output

voltage was set 3 db higher than the minimum output at which the counter counted

the PRF correctly when the input to the received channel pulse shaper was

grounded. For simplicity no attenuation was used at the counter input.

8

Under these conditions the results proved very repeatable. No residual errors

could be detected when the received power was sufficient to yield 20 db or more

of unmodulated receiver quieting.

2. Effects-of receiver tuning on error rates

It was necessary to determine error rate as a function of receiver

quieting in order to choose suitable power levels at which to operate the

receiver during external interference tests. The degree of receiver quieting

at a given input signal level is determined by the "closeness" of receiver

tuned frequency to the transmitter frequency. Three methods of tuning the

receiver were investigated to discover a repeatable tuning method which would

produce a high degree of receiver quieting at input power levels which might

reasonably be expected under field conditions. The three methods investigated

were (1) optical tuning, (2) tuning for maximum quieting without the use of

AFC, and (3) tuning for maximum quieting with the use of AFC. The latter

method is the suggested method of field tuning when the received signal is audio.

The test configuration used in the tuning tests is shown in figure 3.

a. Test procedures. The optical tuning method consisted of dis

abling the receiver AFC and tuning the receiver to give a desired PCM output

waveform as viewed on an oscilloscope at the receiver PCM output terminal.

The desired PCM output, as determined by the specifications of the pulse

shaping circuit, consisted of a waveform at least 0.1 volt peak-to-peak in

amplitude and as nearly sinusoidal as·possible. This tuning method relies

ultimately on an observer opinion and has the drawback of being mostly

qualitative. The obvious flaw of the nonrepeatability of the optical tuning

method was quickly verified. Two curves of error rate as a function of quieting

9

CIRCUIT CONFIGURATION ,-------------------------1 I SCREEN ROOM NO. 1

600

I H.P. 211A OHM .& :: SQUARE OUTPUT r

I WAVE 75 PRF =288 kc

I GENERATOR OUT~~~ f--,! I ~--------~-,

I

SIMULATED PCM PULSE CIRCUIT

DIRECT CHANNEL I ... -11---------. PULSE SHAPER I RECEIVED CHANNEL -

AND DELAY I PULSE SHAPER

r ,, DIFFERENCE CIRCUIT AND

ERROR DETECTOR

( PCM OUTPUT

I RECEIVER

I ANTENNA I FILTER TERMINAL

I ,--~- J .-----. I

6 db TS-403/U

I l r 10 db _ MATCHED ~o~~~::1----t PAD ..... --1 SIGNAL

I BERKELEY MODEL TEE CONNECTOR ._ GENERATOR

7370 COUNTER I ·~

'----------~ jSCREENROOMN0.-2--~l

I IN~3~ +- I I ANTENNA I

I TRANS~I~·;~·;L I l _______ l

H.P. TYPE 400D VTVM

(QUIETING METER) -

I I J

GENERAL RADIO TYPE 874-GA

VARIABLE ATTENUATOR

..

Figure 3· Block Diagram of the Test Configuration Used in Tuning Tests.

50 OHM DUMMY LOAD

for this method are shown dotted in figure 4. These curves represent the "best"

and "worst" conditions of tuning which might reasonably be expected using the

optical technique. It should be re-emphasized that nonrepeatability is the

major objection to the optical tuning technique, since the better results from

this method could never quite be equaled using the nonobserver techniques

discussed below.

Tuning the receiver for maximum quieting without AFC consisted of dis

abling the receiver AFC and tuning the receiver to give maximum quieting at a

given unmodulated transmitter signal level. To determine if the input signal

level affected the final tuning, the receiver was tuned at five different input

levels ranging from -61 dbm to -100 dbm.

Nearly equal results were obtained for all five levels tested. All of

the error rate-quieting curves compared favorably with the results obtained

using the optical tuning technique, with the additional advantage of much better

repeatability for the maximum quieting technique. When the input power level

was in excess of -75 dbm, it was found that the tuning range over which maximum

quieting existed was quite wide. Consequently, it was difficult to determine

when maximum quieting was reached. This "flat topping" is the result of complete

receiver limiting action and could be avoided by tuning at input power levels

of less than -75 dbm. When the input power level was small, it was extremely

difficult to find initial tuning settings which would deflect the quieting meter.

Once the initial settings were obtained, however, the quieting level was very

sensitive to small tuning changes, thereby producing good selectivity.

As a compromise between too much and too little power, a level of -80 dbm

was chosen at which to evaluate the maximum quieting without AFC tuning method.

Eight curves of error rate as a function of receiver quieting were made. The

11

100

80

60

40

20

30

--- OPTICAL TUNING METHOD -o-o-o- MAXIMUM QUIETING METHOD WITHOUT AFC

• • • MAXIMUM QUIETING METHOD WITH AFC

20 QUIETING

(db)

7 /

/~EST OPTICAL RESULT

I I

10 0

Figure 4. Error Rate as a Function of Receiver Quieting for Three Tuning Methods.

12

receiver was detuned and retuned prior to each run; two operators were used in

the tuning tests. Figure 4 shows a curve derived by averaging the data from

th,:se eight curves. The maximum deviation of any of the eight curves from the

average curve was found to be less than 10 per cent, thereby indicating that a

high degree of repeatability could be obtained using this tuning technique.

Eight error rate versus receiver quieting curves were also made using the

maximum quieting with AFC tuning technique. The test procedures for obtaining

these eight curves were identical to those used for tuning without AFC; however,

the AFC circuit was switched on after the receiver was tuned. Error rate as

a function of receiver quieting for this tuning method obtained by averaging

the results of the eight curves is shown in figure 4. The maximum deviation

of any of the eight curves from the average curve was less than 7 per cent.

b. Test results. At a receiver quieting of 0 db, essentially no RF

power exists at the receiver antenna terminals. Hence, the PCM output of the

receiver consisted of unquieted noise. Intuitively, one would suspect that

under these conditions the error rate would be approximately 50 per cent, since

the receiver channel pulse shaper would produce pulses from the received noise

that would be equally likely to be more in phase or out of phase with the desired

pulses in the direct channel. However, the curves of figure 4 indicate that

the measured error rate at 0 db receiver quieting was 40 per cent.

To investigate this apparent discrepancy, a Hewlett-Packard 1490A random

noise generator was used as an input to the received channel. Band-limited

random noise with an amplitude of 0.1 volt rms was introduced at the. received

channel pulse shaper input terminals and the resultant error rate was recorded.

When the noise was limited to a 20 kc upper frequency limit, the error rate was

found to be 72 per cent. When the upper frequency limit was raised to 500 kc,

13

the error rate dropped to 30 per cent. Raising the upper frequency limit to

5 Me produced an error rate of 26 per cent.

A detailed study of the pulse shaping circuit shows these results to be

compatible with the circuit design. Primarily, the results show that the

bandwidth of the error detection system is limited. If the instanteous voltage

at the input terminals never dropped below the threshold at which the circuit

detects a pulse (de "noise"), the output of the received channel would always

be "on". Thus, the difference circuit would always detect a pulse from the

received channel and compare it to the input from the direct channel. An

error would be detected each time the direct channel pulse did not exist; this

would occur at the PRF and an error rate of 100 per cent would be recorded.

As the upper frequency limit of the noise is increased, the error rate

would continue to decrease, as was observed when the random noise generator

was used as an input.

The nominal bandwidth of the PCM output of the receiver is 250 kc. Based

on the findings of the random noise input tests, an error rate of 40 per cent

for unquieted noise is reasonable for this bandwidth.

The maximum quieting method of tuning proved to be highly repeatable

either with or without AFC. As indicated in figure 4, the results of this

method with AFC were superior to the results without AFC for quieting levels

better than 15 db. As a result of the tuning tests, the maximum quieting

with AFC tuning techniques was adopted for tuning the receiver for the remainder

of the FM/PCM system tests.

The decrease in error rate shown in figure 4 as quieting decreased from

10 db to 0 db for the maximum quieting method with AFC was apparently caused

by an upward shift in the noise spectrum. The average time required for a half

14

cycle of noise at -10 db of quieting was approximated by observing a number of

single noise sweeps on an oscilloscope. At 0 db of quieting the average time

decreased noticeably, thereby indicating an increase in high frequency com

ponents in the noise. Hence, the error rate was lower at 0 db than at 10 db

of quieting. This is in agreement with the noise spectrum effects on error

rate noted above.

3. Effects of interference on error rates

A number of interference tests were made on the FM/PCM system to

examine their effects on error rate. These were CW interference tests, AM

interference tests, and FM interference tests. Each test was repeated at five

interference frequencies. The interference frequencies used were the trans

mitter tuned frequency, 0.5 Me above and below the tuned frequency, and 1.0 Me

above and below the tuned frequency. The rated peak-to-peak deviation of the

transmitter is 0.75 Me. At 20 db quieting, the power response of the receiver

is 3 db down at 0.8 Me above and below the tuned frequency. Hence, the fre

quencies chosen cover the receiver band adequately.

Figure 5 shows a block diagram of the test configuration used for the

interference tests. Under each test condition, the total number of errors

occurring in 1 second were counted 10 different times. No less than 15 seconds

elapsed between successive 1 second counts. Each data point shown on the in

terference tests graphs in the section was derived by averaging the 10 error

rate observations made under that test condition.

a. CW interference tests. Error rate as a function of desired signal

level to CW interference signal level power ratio was determined at two receiver

quieting levels at each of the five chosen interference frequencies. The

interference signal source used was a TS-403/U signal generator.

15

,------, I

SCREEN ROOM I NO.2

I I I TRANSMITTER I I PCM ! I

INPUT ANTENNA L TERMINAL

-- ----------------1 I ---------. I ANTENNA I

750 H.P. 211A TERMINAL

I SQUARE l

BERKELEY COUNTER

MODEL 7370

BERKELEY TRANSFER OSC.

MODEL 7580

SIGNAL SOURCE

WAVE RECEIVER I I GENERATOR ._4---~~ j 6oo n I

H.P. 400D VTVM

(QUIETING METER)

I I I SIMULATED PCM PULSE CIRCUIT I I DIRECT CHANNEL ,' RECEIVED CHANNEL I I

PULSE SHAPER PULSE SHAPER I AND DELAY

I I I DIFFERENCE CIRCUIT I I AND I

ERROR DETECTOR

I I I I I SCREEN ROOM

I NO.1

L__ _________________ J

BERKELEY COUNTER

MODEL 5570

Figure 5. Block Diagram of Test Configuration Used in System Interference Tests.

Figures 6 through 10 show the results of the CW interference test when

the desired signal level is set to give 30 db of (unmodulated) receiver quieting.

Figures 11 through 15 give the results of 40 db of receiver quieting.

Figures 6, 10, 11, and 15 graphically depict the characteristic shape

of the capture curve of an "ideal" FM receiver. However, when the interfering

signal frequency is at or close (±0.5 Me) to the transmitter tuned frequency,

as in figures 7, 8, 9, 12, 13, and 14, error rate does not increase monotonically

with interfering signal to desired signal power ratio. The points of inflection

in the curves were found to occur either when the noise spectrum of the receiver

output shifted or when the overall noise level decreased.

The rms noise level of the receiver PCM output was monitored and the

tests were rerun as the CW power level was increased, the noise level was found

to first increase, then decrease as equal RF power was approached, then increase

to the previous level, and finally to decrease as the CW signal was captured.

Further tests revealed that this phenomenon was caused by the receiver dis

criminator, which was always referenced to the signal with the highest power.

At nearly equal power, the discriminator was referenced between the signals,

and relatively little discriminator output was present. When the discriminator

was referenced to either of the signals (when one was greater than the other)

the PCM output contained noise which was interrupted at the rate of the dif

ference frequency between the desired and interfering signals.

The decrease in error rate that occurs at desired to interfering signal

power ratios just above that ratio required for capture of the undesired signal

is the result of decreased discriminator output. All other points of inflection

on the curves were traced to noise spectrum shifts, and result in relatively

minor error rate decreases as compared to the above effect.

17

lOO

80

60 w 1--<(+-a:: ~ a::U 0 ... a::~ a::-w

40

1--J (J:J

20

DESIRED SIGNAL FREQUENCY: 1825.50 Me INTERFERING SIGNAL FREQUENCY: 1824.50 Me QUIETING LEVEL: 30 db RF POWER AT 0 db: -73 dbm

40 30 20 10 0 -10

DESIRED SIGNAL TO INTERFERING SIGNAL POWER RATIO {db)

-20 -30

Figure 6. Error Rate as a Function o~ Desired to Inter~ering Signal Power Ratio ~or ~N Inter~erence. Condition 1.

-40

100

80

60 w 1--<(-~ i ~u 0 .. ~cf. ~-w

40

I-' \0

20


40 30 20 10 0 -10 -20 DESIRED SIGNAL TO INTERFERING SIGNAL POWER RATIO

(db)

-30

Figure 7. Error Rate as a Function of Desired to Interfering Signal Power Ratio for CW Interference. Condition 2.

-40

100

80

w 60 ..... _ <(+-IX ~ IXU 0 ... IX u IXe:. w

40

!\) 0

20


40 30 20 10 0 -10 -20

DESIRED SIGNAL TO INTERFERING SIGNAL POWER RATIO (db}

-30

Figure 8. Error Rate as a Function of Desired to Interfering Signal Power Ratio for CW Interference. Condition 3·

-40

100

80

60 w 1--<C'E 0:': G)

D:':u 0 t 0:':0.. 0:':-w

40

1\) 1--'

20


40 30 20 10 0 -10

DESIRED SIGNAL TO INTERFERING SIGNAL POWER RATIO {db)

-20 -30

Figure 9· Error Rate as a Function of Desired to Interfering Signal Power Ratio for CW Interference. Condition 4.

-40

100

80

w 60 t-..-.. <(+-et: ~ et:u 0 ... et: 41 et:~

1\) w 1\) 40

20


40 30 20 10 0 -10 -20 DESIRED SIGNAL TO INTERFERING SIGNAL POWER RATIO

{db)

-30


-40

w 1-.-... <(-0:: ~ o::U 0 .. 0::~ 0::-w

I\) w

100

80

60

40

20


0~--~--------_.--------~--------~~~~~ .......... ._._ ________ ~--------~--------_. __ ___ 40 30 20 10 0 -10 -20

DESIRED SIGNAL TO INTERFERING SIGNAL POWER RATIO (db)

-30


-40

100

80

w 60 ..... -:;::-<( 1: ~ 4) u ~ ... 0 4) O!Q._ ~-w

40

1\)

+

20


40 30 20 10 0 -10 -20


-30

Figure 12. Error Rate as a Function of Desired to Interfering Signal Power Ratio for GW Interference. Condition 7.

-40

100

80

60 w 1-_ <C-0:::: c

G)

a:::U 0 ... 0:::: G)

a::!::. w

40

1\) \.Jl

20

0


40 30 20 10 0 -10 -20


-30


-40

100

80

w 60 1--<C'E 0::: Q)

o:::u 0 Q; a::: a.. a:::-w

40

f\) 0\

20


40 30 20 10 0 -10 -20


-30

Figure 14. Error Rate as a Function of Desired to Interfering Signal Power Ratio for CW Interference. Condition 9·

-40

100

80

w 60 I--;:-<t 1: ~ 4) u ~ ... 0 4)

~a.. ~-w

40

1\) --.:j

20


40 30 20 10 0 -10 -20


-30


-40

The major difference between the data taken at 40 db of quieting and the

data taken at 30 db of quieting is that the curves of.the latter data show

wider, more pronounced excursions than the curves of the former data.

The frequencies to which the interfering signal was tuned were chosen to

be equally spaced with respect to the tu~ed frequency. However, the results

of the tests do not show this symmetry.* For example, capture of the undesired

signal occurred at a desired to interfering signal power ratio of -9 to -10 db

when the interfering signal was tuned to 1.0 Me below the desired signal. The

corresponding ratio for capture of the undesired signal was 0 db when it was

tuned 1.0 Me above the tuned frequency. Thus, approximately 10 db less inter-

fering signal power was required for capture 1.0 Me above the tuned frequency

than was required 1.0 Me below the tuned frequency.

Figure 16 shows receiver quieting as a function of frequency as a signal

generator with a constant output power was tuned across the frequency range of

interest. It is immediately apparent from this figure that the transmitter

tuned frequency was not in the center of the receiver passband. Further, it

is detuned in the direction to explain the nonsymmetry observed above. Retuning

the receiver in accordance with the adopted tuning procedure produced essentially

no change. It was not determined if this effect was the result of the tuning

*All tests reported herein were made by initially having the receiver captured on the desired signal and increasing the undesired signal strength until capture of the undesired signal occurred. The undesired signal strength had to be increased significantly greater than 0 db for capture of the undesired signal using this procedure. However, when the receiver was initially captured on the undesired signal and the undesired signal strength was reduced until capture of the desired signal occurred, the opposite effect was noted; in this case the undesired signal strength had to be reduced significantly less than 0 db for capture of the desired signal. In this respect, symmetry was observed for the two methods.

28

technique adopted or the result of a slight tuning defect in the AFC of the

receiver used. The latter is suspected.

b. AM interference tests. Error rate as a function of desired signal

level to AM interference signal level power ratio was determined at a 40 db

quieting level at each of the five chosen interference frequencies. The AM

interference source used was a Hewlett-Packard 8614A signal generator 100 per

cent externally modulated by a 288 kc sine wave. This external modulation

frequency is nominally equal to the pulse modulation PRF of the desired signal.

Figures 17 through 21 show the results of the AM interference tests. The

effect of capture of the interfering signal is less pronounced for AM inter

ference than for CW interference. This indicates that even with the limiter

operating at a level to give 40 db of receiver quieting (unmodulated), some AM

is allowed to pass. It is expected that this effect would be more severe with

less limiting.

The nonsymmetry of the results at frequencies above and below the tuned

frequency caused by receiver detuning is apparent for AM interference, just as

it was for CW interference. Complete capture occurs at a desired to interfering

signal power ratio of -9 db with the interfering frequency 1.0 Me below the

tuned frequency and at a ratio of -5 db with the interfering frequency 1.0

Me above the tuned frequency.

c. FM interference tests. Error rate as a function of desired signal

level to FM interference signal level power ratio was determined at a 40 db

quieting level at each of the five chosen interference frequencies. The FM

interference source used was a Hewlett-Packard 8614A signal generator externally

modulated with a 288 kc sine wave to give peak-to-peak frequency deviations of

29

(.!)

~ 1-IJj

::> cr f:t:Jl UJ~

w ~ 0 IJj

u IJj

r::t:

-40

TRANSMITTER TUNED FREQ. 1825.50 Me

-30

-20

-10

0~~._----~--------~--------._ ________ ._ ________ ._ ________ ._ ________ ._ ________ ._ ________ ._ ______ ~ 1824.0 1824.5 1825.0 1825.5 1826.0 1826.5 1827.0

SIGNAL GENERATOR FREQUENCY (Me)

1827.5 1828.0

Figure 16. Receiver Selectivity with Active AFC as a Function of Input Signal Fre~uency.

1828.5 1829.0

100

80

w 60 t--. <C1: 0:: Cl)

a::U 0 .. 0::~ 0::-w

40

w ~

20


40 30 20 10 0 -10 -20


-30

Figure 17. Error Rate as a Function of Desired to Interfering Signal Power Ratio for AM Interference. Condition 1.

-40

100

80

w 60 1--<( .... 0::: ~ o::;U 0 ... 0::: Q)

0:::~ w

40

w 1\)

20

DESIRED SIGNAL FREQUENCY: 1825.53 Me INTERFERING SIGNAL FREQUENCY: 1825.03 Me QUIETING LEVEL: 40 db RF POWER AT 0 db: -62 dhm

40 30 10



100

80

60 w t-,-... <'E 0:.: Q)

e::.:u 0 Qi a::.: a. 0:.: .._.. w

40

w w

20


40 30 20 10 0 -10 -20


-30

Figure Error Rate as a Function of Desired to Interfering Signal Power Ratio for AM Interference. Condition 3·

-40

100

80

60 UJ 1-..-.. <( .....

~ i ~u 0 ... ~.f. ~-UJ

40

w +:-

20


40 30 20 10 0 -10 -20


-30


-40

100

80

60 UJ 1--<C'E 0!: G)

O!:u 0 ... O!:cf. 0!:-UJ

40

w \J1

20


40 30 20 10 0 -10


-20

Figure 21. Error Rate as a Function of Desired to Interfering Signal Power Ratio for AM Interference. Condition 5·

1.0 Me and 2.0 Me. Figures 22 through 26 show the results for a 1.0 Me

deviation and figures 27 through 31 show the results of a 2.0 Me deviation.

The results show approximately the same degree of system sensitivity to

FM interference as they do to CW and AM interference. At 2.0 Me of FM devi

ation (figures 27 through 31) the receiver interfering signal was of sufficient

amplitude to trigger the received signal pulse shaping network. Thus, instead

of capture of the undesired signal being represented as an error rate of 100

per cent, it is represented as the average error rate produced by two signals

of the same nominal frequency being added with a random and continually changing

phase relationship. The average resultant error rate was about 70 per cent as

indicated in the figures. This phenomenon resulted in the apparent capture of

the undesired signal at a higher desired to undesired signal power ratio for a

2.0 Me deviation than at a 1.0 Me deviation. Since complete "capture" at a 2.0

Me deviation occurs whenever the received undesired pulse voltages exceed the

noise voltage, and complete capture at a 1.0 Me deviation occurs when the noise

disappears, the observed result does not seem to be significant.

4. Conclusions

Pulse testing of a typical FM/PCM system yields results which indicate

that the system is almost equally susceptible to CW interference, AM inter

ference, and FM interference. Tests on methods of receiver tuning showed that

the suggested methods of field tuning for audio (tuning for maximum quieting

with the use of AFC) also proved to be the most repeatable method of tuning

for pulse reception. Although the pulse tests made were comprehensive in

scope, it is felt that they are of limited value in predicting the performance

of the pulse code modulated multiplexing system. When the multiplexing equipment

36

w t--<(1; 0:: G)

o::u 0 :u o::a.. o::w

100 .--

80 !-

60-

40 !-

20 !-

DESIRED SIGNAL FREQUENCY: 1825.48 Me INTERFERING SIGNAL FREQUENCY: 1824.48 Me QUIETING LEVEL: 40 db RF POWER AT 0 db: -60 dbm FM DEVIATION: 1.0 Me

o~--~'------~~------~------~~~--,---Hl~~-~~--~~----~------~------~---40 30 20 1 0 0 -1 0 -20


-30

Figure 22. Error Rate as a Function of Desired to Interfering Signal Power Ratio for FM Interference. Condition 1.

-40

LU_ r--4 c: ~d a::: .. 0 II)

a:::E:. ~ LU

w (X)

100

80

60

40

20


o~------------_.--------~~---------~~ .... ~._--------~--------~--------~--------~-----40 30 20 1 0 0 - 1 0 -20


-30


-40

w 1-<("';:" 0:: c

Cl) o::u 0 ... 0:: Cl) o::CL w-

w \.0

100

80

60

40

20


0~------------~----------------~~~r-------*-------------------~--------~---------------40 30 20 10 0 -10 -20


-30

Figure 24. Error Rate as a Function of Desired to Interfering Signal Power Ratio for FM Interference. Condition 3·

-40

w 1-,........ <(+-~ ~ ~u 0 ... ~ G)

~e::. w

+ 0

100

80

60

40

20


o~------------_.--------~--------~~~~-----~--------._ ________ ._ ________ ~--------~----40 30 20 10 0 -10 -20 -30 -40



100

80

60 w 1--<( .... Ct: ; et:u 0 ... Ct:~ Ct:-w

+ 40 f--J

20

0


40 30 20 10 0 -10 -20


Figure Error Rate as a Function of Desired to Interfering Ratio for FM Interference. Condition 5·

-30 -40.

Signal Power

100

80

w 60 ....... _ <(-et: i et:U 0 ... et: II)

et:e::. w

40 + [\)

20

0


40 30 20 10 0 -10 -20


Figure 27. Error Rate as a Function of Desired to Interfering Ratio for FM Interference. Condition 6.

-30 -40

Signal Power

w ............ <(c 0::: ., o:::u 0 ~ 0:::0.. o:::w

100

80

60

40


40 30 20 10 0 -10 -20


-30


-40

100

80

60 w 1--:;::-<( c .:t: G:l u .:t: ... 0 G:l .:t:O.. .:t:-w

40

..p-

..p-


40 30 20 10 0 -10 DESIRED SIGNAL TO INTERFERING SIGNAL POWER RATIO

(db)

-20 -30

Figure Error Rate as a Function of Desired to Interfering Signal Power Ratio for FM Interference. Condition 8.

-40

w 1-..-.. <(+-0:: ~ o::U 0 ... 0:: " o::f::. w

100

80

60

49


40 30 10 10 0 -10 -20


-30


-40

100

80

60

40


40 30 20 10 0 -10


-20 -30


-40

is available, it is recommended that the tests be repeated using the techniques

outlined in this report.

47

B. Spurious response and intermodulation predictions in cavity-crystal receivers

1. Introduction

Mixer studies conducted at Georgia Tech have shown that certain mixer

types are reliably predictable with regard to their level of spurious product

t. 1 genera 10n. The excellent results of the prediction technique have encouraged

its use in the calculation of the spurious response rejection levels for an

entire communications receiver. Harmonic pollution problems encountered with

cascaded nonlinearities render the technique useless for ordinary receivers

which employ RF amplification prior to the mixing element, or which utilize

multigrid tubes as multiplying mixers. The receiver which achieves preselection

in an entirely passive or linear manner and mixes with a singularly nonlinear

device (a device which may be represented by a single Taylor series) may be

reliably predicted using mixer and preselector data alone. Cavity-crystal

receivers, i.e. receivers which employ a tuned cavity preselector immediately

prior to a crystal diode mixer, fall into this category and thus are predictable

within the accuracy limitations of the method.

The spurious response prediction technique developed by Georgia Tech in

conjunction with a method by Steiner2 may provide an accurate means of evaluating

both spurious and intermodulation product rejection with a minimum of receiver

measurements. The Georgia Tech spurious response technique is known to be

accurate using a measured set of q = 1 responses for the calculation base and

should be equally or more precise using a harmonic set of measurements. Once

the response rejections are calculated using this method, the IM rejections

can be obtained for the necessary orders. The preselector characteristics may

then be measured and the total receiver rejection calculated. Since most of

48

the computations can be programmed for computer solution, the entire spectrum

signature for the receiver would be rapidly attainable after the initial pre-

selector and mixer measurements had been obtained.

2. Measurement techniques

In order to predict the spectrum signature of a cavity-crystal receiver,

the insertion loss of the cavity preselector must be known over the entire

frequency spectrum of interest. In addition, a mixer product level representing

each of the required orders of mixer nonlinearity must be obtained. These

measurements together with receiver sensitivity and signal-to-local oscillator

ratio are all that are required for the calculation of the entire spectrum

signature of the receiver in regard to the antenna input port.

Receiver sensitivity is obtained in the normal manner specified for the

type of receiver under consideration. In the case studied, the signal-to-local

oscillator power ratio was accurately obtained by the following procedure:

1) Remove the local oscillator connection to the receiver mixer unit.

2) Connect an RIMS (radio interference measurement set) to the antenna port and tune it to the receiver tuned frequency.

3) Connect a signal generator to the local oscillator input port to the mixer and tune it to the receiver tuned frequency.

4) Set the signal generator level for an IF Mixer meter reading as specified for the equipment.

5) Record the level indicated on the RIMS.

This measurement establishes the local oscillator reference level as it

is normally established during ordinary usage of the receiver.

6) With a directional coupler, connect two generators to the local oscillator port of the mixer.

7) Tune generator No. 1 to the normal local oscillator frequency and establish the specified IF Mixer meter reading.

49

8) Tune generator No. 2 to the receiver tuned frequency and set the level for the standard response indication used in establishing the receiver sensitivity.

9) Record the level indicated on the RIMS.

This measurement establishes the signal level relative to the local

oscillator level and the difference of these two readings expressed in db is

the signal-to-local oscillator power ratio required for prediction. The

validity of this measurement may be dependent on the exact configuration of

mixer design and therefore may not represent a universal means for obtaining

the indicated power ratio.

The entire mixer characteristic can be calculated from the set of local

oscillator harmonics generated by the mixer. In order to avoid variable

coupling effects, all measurements are made at the receiver tuned frequency

and the local oscillator level is established at subharmonic frequencies by

obtaining the specified IF Mixer meter reading. With sufficient power avail-

able, this can be accomplished by inserting the subharmonic signal through

the mixer local oscillator input port to obtain the specified IF Mixer meter

reading. The desired harmonic output level is obtained with an RIMS at the

receiver tuned frequency through the receiver antenna port. Since relative

levels are of interest, the various insertion losses can be neglected. In the

case tested, the power out~ut of the available generators was insufficient to

always establish the required IF mixer reading through the mixer local oscillator

input port. The setup shown in figure 32 was substituted to establish the set

of harmonics using an identical technique and a commercial mixer mount.

Determining the preselector insertion loss characteristics for the sig-

nificant spectrum is somewhat difficult in that the mixer is usually mounted to

the cavity and no cavity output port is readily available. In the case at hand,

50

SUBHARMONIC OF

TUNED FREQUENCY SIGNAL .. LOW-PASS .- - 3 db - _j l- -- MIXER GENERATOR - FILTER - - PAD - - uT'' - - MOUNT

n ••

RECEIVER IF

AMPLIFIER

RECEIVERTUNED FREQUENCY HIGH-PASS RIMS - --- FILTER - ,, RECEIVER METERING

Figure 32. E~uipment Setup for Measuring Mixer Harmonic Generation.

the mixer local oscillator input port was used to detect the signal level

passing the preselector. This port is padded internally with 250 ohms and

the mismatch causes some VSWR problems in the measurements as well as a

sensitivity loss. The problem of measuring the preselector may be eased by

dismounting the mixer and attaching a specially built 50 ohm coupling loop to

the preselector for the output port.

Ideally, the preselector should be measured while it is loaded by the

mixer because this is the situation encountered under ordinary operation. The

measurement could be accomplished with high available power and two generators

in each band. One generator functions as the local oscillator and the other

provides t~e test signal. The two generators are tracked at the IF difference

frequency so that the receiver may function as the standard response indicator.

The local oscillator level is set for the specified IF mixer meter indication

at each datum point and the signal level required for a standard response

indicates the relative preselector insertion loss. This technique is lengthy

but includes the frequency admittance characteristic of the mixer diode in

the preselector insertion loss characteristic. The result should be a higher

overall accuracy in the prediction of the spectrum signature.

3. Calculation techniques

The calculation procedure for the mixer spurious response levels has

3 4 been adequately covered in previous quarterly reports. ' In this case, however,

a harmo~ic set is used to establish the expanded mixer response triangle instead

of the p = n, q = 1 response set. The procedure is identical except.that the

calculation begins in the q = 0 diagonal instead of the q = 1 diagonal. A

rejection value of zero is established in the p = 1, q = 1 position and the

harmonic set is normalized to this value by back-calculation from the p = 1,

52

q = 1 position to the p = 2, q = 0 position using the measured signal-to-local

oscillator power ratio. The normalized harmonic set is then used to expand

the spurious response rejection triangle. The response constants or weighting

functions required for expanding the triangle through high orders of non-

linearity are most easily generated using the digital computer.

Fvr the tests reported herein, a set of response constants was generated

through the 40th order using the Burroughs 220 computer and the ALGOL program

outlined in the appendix.

Calculation of the mixer intermodulation rejection values is a new

technique developed from the work of James W. Steiner of the ITT Federal

Laboratories.5

According to Steiner, the level of an IM response is:

where: A = product level,

N = product order,

n = number of input frequencies,

P. = power level of jth term in product, J

P f . th . t f i = power o l lnpu requency,

W = weighting function for the product

~ = order constant.

( 1)

If the sum of all input powers is very nearly that of the larger signal alone,

the second term in (1) becomes equal to the power level of the larger signal

in dbm. This is the normal condition found in a mixer where the injected local

oscillator power determines the input power level and (1) becomes:

53

N ~w J A( dbm) =I Pj (dbm) - NP LO( dbm) + 20 1og10 [ 2

N_1 • (2)

j=l

The Georgia Tech method employs ratios in determining a response rejection

and since the local oscillator power is constant, the second term in (2) drops

out. The third term in (2) can be broken down into two terms, one containing

the weighting function and the other containing the order constant divided by

N-1 2 • If the ratios used are all in the same order, the second of these terms

drops out. The remaining terms establish the ratio of two products of like

order:

~ N Pj [w J 10 1og10 A_ = 10 log10 TI P

1 + 20 1og10 w1

2. or,

--c j=l j2

~_( db ) - ~ (db ) = f [ p j 1 (db ) - p j 2 (db ) J + w 1 (db ) - w 2 (db ) '

j=l

N

~(db) = ~ (db) + \ [ P. (db) - P. (db)] + w1 (db) - w2 (db), ~ Jl J2 J=l

The Georgia Tech method for two signal IM (spurious responses) is a form of

this equation where:

N

\ [ p. (db ) - p. (db )] ' ~ Jl J2 J=l

(3)

(4)

(5)

(6)

reduces to the power ratio in db of the two mixed signals for adjacent responses

within the same order. It should be remembered that these equations are based

on constant-input-variable-output power levels.

54

As an example of how this equation can yield IM data, consider the spurious

response (1,2,+) and the IM response (f1 - f2 - fL 0). The spurious response

rejection is desired. It will be assumed that f1 and f2 have equal power levels,

though this may not necessarily be the case.

Equation (5) becomes:

= -100 + 2Pf f - 2Pf - 9.5 + 15.5 , (8) 1 2 SR

= -1 00 + 6 + 2P f f - 2P ( 9) 1 2 fSR

With constant input power, 2Pf f = 2Pf and AIM(db) = -94. Converting to 1 2 SR

constant output power level is accomplished by dividing the resultant by the

number of input frequencies other than the local oscillator:

94 RIM(db) = ~ = 47 db , ( 10)

where RIM is the IM response rejection. This quantity represents the number of

decibels above the desired input signal level required of the two intermodulating

signals in order to obtain a standard response.

A more generalized form of the equation may be arrived at by transposing

the sum of input power levels of the IM response to the left and equating it to

the remaining terms. The resulting equation is:

(11)

55

where the lower case p and q are the harmonic multipliers as defined for spurious

responses.

Since a full set of spurious responses is easily calculated, the term

containing PLO can be eliminated by choosing PsR = PIM

(12)

The sample IM rejection calculation now becomes:

(13)

= 2(50) + 9.5 - 15.5 (14)

= 100 - 6 = 94 db • (15)

Thus, the sum of the input power levels of the two intermodulating fre-

quencies in decibels must exceed the power level of the desired signal by 94 db

in order to obtain a standard response. For equal IM power levels, the resultant

47 db rejection level is obtained.

It should be noted that the weighting functions employed by Steiner and

carried through in the above equations are divided by 2N-l to obtain the Georgia

Tech response constants. This enables relationships to be carried out between

adjacent orders with the same set of constants. The difference in weighting

functions produces no alteration in the above outlined procedure for the deter-

mination of mixer intermodulation response rejections. The intermodulation

response constants utilized in this study were obtained from the charts given in

reference 5.

56

Total receiver spurious response rejection values are obtained by summing

the mixer response rejection and the preselector insertion loss at the response

frequency for each response of interest. The calculation of receiver intermodu

lation rejection is somewhat more involved in that the total input power rejec

tion is added to the sum of the insertion loss values of the preselector at the

several intermodulating frequencies. The resultant sum is then divided by (N-p),

i.e. the number of external intermodulating powers, to arrive at the equal power

intermodulation rejection of the receiver for the frequencies chosen. The equal

power input level in dbm can be obtained by adding this rejection value to the

receiver sensitivity in dbm. When dealing with intermodulating orders in which

the input powers carry multipliers, the preselector insertion loss must carry a

multiplier of the same value as its associated frequency's power multiplier.

4. ExPerimental results

In order to test the validity of the foregoing techniques and to pro

vide sample calculations, the spectrum signature of a typical military, cavity

crystal, FM receiver was predicted. Comparison of the calculated and measured

data for the receiver indicates a relatively high degree of successful pre

diction. Figures 33 and 34 show the response density versus prediction error in

db for the measureable spurious responses and third order intermodulation prod

ucts respectively. The ultimate accuracy of the method is not indicated by

these histograms since the preselector data were averaged to eliminate VSWR

problems and frequency errors in the preselector measurements.

Sample calculations for the first three orders of receiver spurious

response and intermodulation rejection are presented below.

Receiver Sensitivity: -70 dbm for 20 db quieting

Signal to L. 0. ratio: 68 db at 20 db quieting

Rejection of (1,1) response: 0 db at 20 db quieting

57

Vl CD

15

14

13

12

11

10

Figure 33·

-10 -9 -8 -7 -6 -5 -4 -3 -2 -1 4 PREDICTION ERROR (db)

STANDARD ~ESPONSE: 6 db QUIETiNG SENSITIVITY: -79 dbm

TRUE DENSITY: CROSSHATCHED MEAN DENSITY INTEGRAL: DASHED

10 11 12 13 14

Spurious Response Prediction Error for a Cavity-Crystal Receiver.

Vl \.0

15

14

13

12

11

10

II 1- I

I '-, I I_, I I I I

11 L

1

STANDARD RESPONSE: 6 db QUIETING SENSITIVITY: -76 dbm

TRUE DENSITY: CROSSHATCHED MEAN DENSITY INTEGRAL: DASHED

I ~__,

1_1 1 ___ 1

r----~ L-, ~~ ~ I I r- 1

-12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 10 11 12

Figure 34.

PREDICTION ERROR (db)

Third Order Intermodulation Power Prediction Error for a Cavity-Crystal Receiver.

(16)

= 0 - 0 - 68 + 6.0 , (17)

= -62 db ' (18)

where: R . (2,0) =Constant input rejection of the L. 0. second harmonic. Cl

R (l,l) = Constant output rejection of the (p = l, q = l) responses. co

= Weighting function or response constant of the (l,l) responses.

=Weighting function or response constant of the (2,0) response.

With the normalized rejection level of the local oscillator second har-

monic now calculated, the remaining harmonic set is easily normalized. The

measured level of the (2,0) harmonic is added to the normalized rejection level

and each measured value in the remaining harmonic set is subtracted from this

value to yield the corresponding normalized rejection values for the set.

Thus:

R( 3,0) = -62 + (-28.5) (-34.0) = -56.5 db ' (19)

R( 4,0) = -62 + (-28.5) - (-38.5) = -52.0 db , (20)

Returning to the spurious response calculations and continuing with corre-

sponding symbols and definitions:

R (0,2) co = Rc 0 (l,l) - w(l,l) + 68 + w(o, 2 )

2

0 - 0 + 68 + 6.0 = 2

60

(21)

(22)

R ( 1, 2) co

74 = ~ = 37.0 db '

= -56.5 - 12.0 + 68 + 2.5 '

= 2.0 db '

= Rei (3,0) - w( 3,o) + 2(68) + w( 1, 2 )

2

-56.5 - 12.0 + 136 + 2.5 =

2

= 7 ~· 0 = 35.0 db

R (O 3 ) = -56.5 - 12.0 + 204 + 12 , co ' 3

= 147•5

= 49.2 db ' 3

R (3,1) = -52.0 - 18.1 + 68 + 6.0 , co

= 3.9 db '

-52.0 - 18.1 + 136 + 2.5 R (2,2) = co 2

= 64•8 = 34.2 db 2

-52.0 - 18.1 + 204 + 6.0 R (1,3) = co 3

= 13

;·9

= 46.6 db '

61

(23)

(24)

(25)

(26)

(27)

(28)

(29)

(30)

(31)

(32)

(:33)

(34)

( 35)

(36)

(37)

R (0, 4) = -52.0 - 18.1 + 272 + 18.1 , co 4 ( 38)

220.0 = -4- = 55. 0 db • (39)

This concludes the mixer rejection for the second through the fourth orders

of nonlinearity. To obtain the total receiver rejection for these responses,

the relative preselector insertion loss at each response frequency is added to

the mixer rejection for the response.

Thus:

SR (0,2) = 37.0 + > 65 = > 102.0 db ' (40)

SR (0,3) = 49.2 + > 65 = > 114.0 db ' (41)

SR ( o, 4) = 55.0 + > 65 3 > 120.0 db ' (42)

SR (1,2,+) = 35.0 + 45.0 = 80.0 db ' (43)

SR (1,2,-) = 35.0 + 57.0 = 92.0 db ' (44)

SR (1,3,±) = 46.6 + > 65 = > 111.6 db ' (45)

SR (2,1,+) = 2.0 + 65.0 = 67.0 db ' (46)

SR (2,1,-) = 2.0 + > 65 = > 67.0 db ' (47)

SR (2,2,+) = 34.2 + > 65 = > 99.2 db ' (48)

SR (2,2,-) = 34.2 + 37.0 = 71.2 db ' (49)

SR (3,1,+) = 3.9 + 65.0 = 78.9 db ' (50)

SR (3,1,-) = 3.9 + 44.0 = 47.9 db • (51)

62

It is noted that for several frequencies the preselector insertion loss is

greater than the measurement sensitivity and that the spurious response

rejection can only be recorded as greater than a given value. Furthermore, it

is evident that the prediction .technique will yield data that are below the direct

measurement sensitivity under ordinary circumstances. Thus, prediction yields

a greater knowledge of the spectrum signature than can be obtained through direct

measurement.

Second, third, and fourth order intermodulation are calculated as shown

in the following examples for each of the above orders:

Second order (fa,fb) intermodulation is calculated from the (0,2) mixer

response rejection since no local oscillator power is utilized. Substituting

into equation (12) for 20 db quieting:

Pa + Pb = 2(37) + (-6) - 0 = 68 db, (52)

above -70 dbm at the mixer input. Adding the relative preselector insertion loss

at the intermodulating frequencies, fa and fb, one obtains:

Pa + Pb = 68 + 34.5 + 44.0 = 146.5 db, (53)

above -70 dbm at the antenna port. For Pa = Pb the rejection is:

146.5 = ---2-- = 73.3 db . (54)

Curves of this type of intermodulation are shown in figure 35.

In cavity-crystal receivers, second order intermodulation exists only

when the sum or difference of fa and fb is equal to the receiver intermediate

frequency. This and other variations from the normal intermodulation order

designations are phenomena of the mixer element occurring as the first

nonlinearity in the receiver RF section.

63

DESCRIPTION: f0

- fb = INTERMEDIATE FREQUENCY

ORDER: SECOND

o~---o MEASURED IM

..,__ __ .... CALCULATED IM

E" ...a 3 0::: w ~ 0 a... 1-::::l a... ~ _J <( ::::l

0'\ 0

-5 w +

-4

-3

-2

-1

0

10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160

Figure 35. Second Order Intermodulation Characteristics.

Third order (fa,fb,f10) intermodulation is calculated from the (1,2) mixer

response rejection since the local oscillator term appears once in the inter-

modulation product. This type of intermodulation, normally designated second

order, exists when the sum or difference of fa and fb is equal to the tuned or

image frequency of the receiver.

Substituting into equation (12) for 20 db quieting:

p + a

= 2(35) + (-2.5) - 3.5 = 64 db ' (55)

above -70 dbm at the mixer input. Adding the relative preselector insertion

loss at the intermodulating frequencies, fa and fb' one obtains

Pa + Pb = 64 + 17.5 + 50.0 = 131.5 db, (56)

above -70 dbm at the antenna port. For Pa = Pb the rejection is:

(57)

The error density distribution of the predicted third order intermodulation is

shown in figure 35.

Fourth order (2fa,fb,f10 ) intermodulation is calculated from the (1,3)

mixer response since the local oscillator term appears once in the intermodulation

product. This type of intermodulation exists when the sum or difference of 2f a

and fb is equal to the tuned or image frequency of the receiver.

Substituting into equation (12) for 20 db quieting:

2Pa + Pb = 3(46.6) + (-6)- 3.5 = 130.3 db

above -70 dbm at the mixer input. Adding twice the relative preselector loss at

fa and the actual relative preselector loss at fb' one obtains:

65

2Pa + Pb = 130.3 + 2(17) + 65.0 = 229.3 db ,

above -70 dbm at the antenna port. For

=229.3= 3

the rejection becomes:

76.4 db •

(59)

(60)

No data were collected on the receiver for this type of intermodulation. This

case is presented as an example of the calculation procedure and indicates that

any desired type of intermodulation can be claculated for a receiver of this type.

The actual data collected from the test receiver were taken at a standard

response level of 6 db of quieting rather than the normal 20 db of quieting

because more responses could be measured at the lower sensitivity level. The

comparison between predicted and measured spectrum signature values was enabled

through the use of the curve shown in figure 36 and a knowledge of the 6 and 20

db sensitivity levels of the receiver. Using this curve, spectrum signature

values may be obtained for any desired level of quieting. It is worthy to note

that rejection tends to decrease with an increase in quieting level. Conse-

quently, a receiver operating in the field at greater than 20 db of quieting

has less rejection to spurious interference than its spectrum signature indi-

cates. It is true, however, that the actual power level required for inter-

ference will always increase with increased quieting regardless of the decrease

in ection.

5. Simplification measures

The entire technique of prediction may be simplified through the use

of computers and a theoretical approach to mixer prediction which eliminates

the necessity for a response representing each order of nonlinearity.

66

1.0

0.9

::0 ~

z 0.8 0 1-u w ..., w 0.7 a:::

w V)

z 0 a.. 0.6 V) w a::: V)

::::> 0.5 0

iX ::::> a.. V)

0\ z 0.4 -.J

w (.!) z «( J: 0.3 u !-z ::::>

a::: 0.2 w a..

0.1

0

0 2 3 4 5 6 7 8 RESPONSE Q VALUE

9

NOTE: This Curve Shows the Envelop of the Rejection Change Versus q Since q is an Integer.

10 11 12 13 14 15

Figure 36. Change in Spurious Response Rejection with a Change in Receiver Sensitivity.

It has been recognized for many years that the magnitude of spurious

responses falls off asymptotically toward a finite limit as the order of the

response increases. If a maximum-upper-bound style of prediction is contem

plated, the null points6 of responses can be ignored and a value which is always

equal to or greater than the actual response level can be utilized. This

approach leans slightly toward the generation of pessimistic spectrum signa

tures, but is probably more reliable since two or more receivers of a given

type will not necessarily exhibit null positioning of the same orders.

Throughout the mixer study conducted at Georgia Tech, the marked similarity

of the asymptotic approach of the p = 1, q = n responses was noted. No means

for utilizing this phenomenon was deduced because the order had not been carried

out sufficiently far to determine the asymptotic approach limit. By carrying

the order to 33 in the receiver prediction attempt, the asymptote was disclosed

to be the signal-to-local oscillator power ratio expressed in db. This is the

separation factor used to expand the spurious response triangle and is easily

obtained through proper measurement. The rejection values for the p = 1, q = n

responses are plotted in figure 37 and the asymptotic approach is indicated by

the smooth curve.

The fact that the asymptotic limit appears to be the separation of the

signal level producing a standard response and the local oscillator level is

further substantiated from consideration of the classical limit theory for mixers.

Variation of the amplitude of the larger signal presented to a mixer has little

effect on the amplitude of the output signal. As the small signal level is

increased, the output increases until the level approaches that of the larger

signal, whence the signals reverse roles and the output ceases any further incre~se.

Since the separation factor represents the maximum power increase of the smaller

68

0

5

10

15

20

25

:::a ""0

; 30 Q 1-

~ 35 -, w 0:::

0\ 40 \0

45

50

55

60

65

68

0 2 4 6 8 10 12 14 16

NOTE: THIS CURVE SHOWS THE ENVELOPE OF THE REJECTION VARIATION WITH q SINCE q IS AN INTEGER.

18 20 22 24 26 28 30 32 34 VALUE OF q

Figure 37. Asymtotic Limit Curve for Responses with p 1.

36 38 40

signal, i.e., it then becomes the larger signal; the upper limit of rejection

is realized when this value is approached.

The asymptotic limit thus establishes one end of the envelope of the p = 1,

q = n response rejection values and, since the other end is represented by the

(1,1) response, it is automatically established at zero. The curve may thus be

normalized between zero and an asymptote of unity such that for any given value

of separation, the entire mixer characteristic can be obtained. Calculation

would proceed from the p = l diagonal in both directions along the triangle rows

to expand the spurious response triangle as a maximum-upper-bound rejection set.

Hopefully, all mixers of a given class will exhibit asymptote approach

curves of sufficient similarity to enable the use of a single curve to represent

the entire class. No effort has been extended in this direction to date but

the noted similarity of silicon diode behavior holds high promise for a suc

cessful investigation. If such curves were established and all computations

were programmed for computer solution, the only measurements required WJUld

include sensitivity, separation factor, and preselector insertion loss for a

rapid and accurate assessment of the receiver spectrum signature.

6. Advantages and disadvantages of prediction

The one outstanding advantage of spectrum signature prediction thus

far is the great wealth of information attainable. The complexity of measure

ments is not substantially smaller than in the direct measurement approach since

the preselector characteristic must be measured over the entire frequency spectrum

of interest. The measurement complexity can be reduced through the use of

normalized mixer curves and some means of rapidly sweeping the preselector to

obtain an 80 db limit insertion loss characteristic.

70

With the use of standard zero dbm signal generators, the rejection to

spurious responses can be predicted to levels some 50 db higher than attainable

by direct measurement techniques. The problems encountered in eliminating

generator intermodulation are practically nonexistent in the prediction tech

nique since only one two-generator measurement is required. These advantages

allow the equipment user to establish mutual interference information with

combinations employing high power transmitters since the rejection levels are

known for an equivalent input power of 50 dbm. Responses with such high rejec

tions cannot be detected using standard signal generators.

7. Conclusions and recommendations

The reliable prediction of cavity-crystal receiver spectrum signatures

is a reality. The spectrum signatures so obtained contain far more information

on the receiver interference characteristic than can be obtained by the standard

direct measurement approach. The entire prediction calculation can be programmed

for computer solution such that rapid expansion of the entire characteristic can

be obtained from the measured data.

The establishment of normalized mixer curves according to class should be

undertaken in an effort to reduce the required receiver measurements. In

addition, computer programs should be written for the computation of the expanded

receiver characteristic. In the light of improving measurement techniques,

studies should be initiated to develop sweeper detectors with at least -80 dbm

sensitivities such that accurate preselector characteristics may be rapidly and

automatically obtained. Prediction techniques for other receiver types should

be further investigated.

71

C. Summary of publications during the contract period from 15 February 1963 to 15 July 1964

This section contains a summary of the contract work accomplished to date

under the Electronics Command Technical Requirements SCL-4187, ELECTRONIC

EQUIPMENT INTERFERENCE CHARACTERISTICS, COMMUNICATION TYPE, dated 27 August

1959. The summary is presented in this report since subsequent work will be

done in accordance with Amendment no. 1 of SCL-4187, dated 7 April 1964. The

classification and contents of fifteen publications are listed and discussed

below. In addition, ten monthly letter type reports were submitted to the

U. S. Army Electronic Laboratories, Fort Monmouth, New Jersey.

1. Report No. 22, Quarterly Report No. 1, 15 February 1963 to 15 May 1963, (Confidential)

Many useful spectrum signature measuring techniques are discussed in

this report. Results of several tests and test procedures evaluated using the

AN/GRC-50, AN/TRC-29, and AN/TCC-13 communications sets are presented. The

spectral behavior of spurious responses for wideband receivers is shown to be

instrumental in identification procedures for spurious responses.

Tests were conducted on the AN/TRC-29 and AN/TCC-13 PPM radio relay com-

munications system to determine system susceptibility characteristics in the

presence of CW and ICW interfering signals. A modified General Electronics

Laboratories speech system test set was used to evaluate the degree to which

the running power density spectrum of speech was preserved when the system was

subjected to CW interference at various selected frequencies near the tuned

frequency. Tape recordings were made of the system audio output for 260 dif-

ferent CW and ICW interference conditions.

The effects of injected harmonics on mixer activity and measurements are

presented. The measured data for three different diode mixers show that the

72

diodes behave in a similar manner for a particular bias condition. The results

of diode mixer response prediction methods which indicate proof of conformity

to current mixer theory are presented.

2. Report No. 23, Quarterly Report No. 2, 15 May 1963 to 15 August 1963, (Unclassified)

This report contains qualitative common channel interference tests

made on a wideband FM system. The effect of simultaneous reception of two

signals on the understandability of the desired received signal is reported.

Two path interference tests were initiated on a radio relay system which

employs time division multiplexing. Prediction PCI as a function of relative

phase angles are presented for a delay of 0.25 ~sec. These data indicate that

this is not a sufficient delay to cause significant degradation in intelligi-

bility for this communications system.

Equipment limitations and the inherent errors of the prediction technique

are examined as possible sources of mixer prediction errors. Error-density data

are shown for fourteen diode mixer tests from which the probable causes for

prediction errors are deduced. These data indicate that the examined sources

can produce significant errors under certain conditions of mixer operation.

3. Report No. 24, Quarterly Report No. 3, 15 August 1963 to 15 November 1963, (Unclassified)

The effects of multipath interference on the intelligibility of speech

transmitted over an FM system employing time division multiplexing are reported.

Predicted intelligibility measurements based on audio output S/N ratios indi-

cate that degradation in intelligibility will exist for the FM/TDM system tested

when multipath signals of equal strength are received over paths which differ

in length by as little as 0.15 mile (0.8 ~sec delay). The probability of

73

significant multipath interference in FM systems which use TDM is felt to be

greater than that for ordinary wideband FM systems.

The accuracy of mixer spurious response level prediction is demonstrated

for variations in mixer operating and drive conditions. Utilization of the

prediction technique in the design of mixers is discussed. Several significant

facts concerning the design of radio receiving equipments as illuminated by the

mixer studies are presented for future guidance.

A simplified method of obtaining the series describing a given response

amplitude using only the Pascal triangle of binomial coefficients is presented.

Any single term or the entire series coefficient for any response of a mixer

th represented by an n degree polynomial may be readily obtained.

4. Report No. 25, Quarterly Report No. 4, 15 November 1963 to 15 February 1964. (Unclassified)

Suggested testing techniques derived from standard spectrum signature

tests conducted on U. S. Army microwave communications receivers are outlined.

The importance of the receiver preselector in the receiver evaluation studies is

emphasized. Common pitfalls encountered in the testing procedures are discussed

and alternate test methods are presented.

A finite mathematical model of a mixer characteristic is developed through

the use of the .Fourier series. Calculated harmonic levels based on the mathe-

matical model were found to approximate the corresponding measured levels from

a simple diode mixer circuit. Modifications of the model which will more closely

realize actual diode nonlinearities are considered.

Mixer theory is discussed for a vacuum tube triode mixer. Data taken on

a 6J4 triode mixer are compared to responses computed by a previously developed

prediction technique applicable for diode mixers. This comparison indicates

that the prediction technique is valid for vacuum tube mixers of the type tested.

74

5. Manuscript of Catalogue, Volume 9, "A Second Radio Frequency Interference Bibliography, With Abstracts," 1 December 1963, (Unclassified)

This bibliography, with abstracts, is the result of a continued liter-

ature search which is being conducted in conjunction with the measurements

portion on a research program for developing tests and test procedures for

determining the interference characteristics of U. S. Army pulse type communi-

cations systems. The bibliography contains over 1150 titles, summaries, and

abstracts of published works related to radio frequency interference and electro-

magnetic compatibility during the period from January 1960 to June 1963. In

essence, the bibliography is a continuation of the materials contained in the

first general RFI bibliography, with abstracts, initially published under

Contract DA 36-039 sc-74855 and later published in the IRE Transactions on

Radio Frequency Interference, Vol. RFI-4, No. 1, February 1962.

The accumulated references from more than 50 sources should be useful in

all phases of RFI investigations ranging from the practical elimination of TV!

to a theoretical discussion of signal detection for various interference envi-

ronments. An author index and a subject index containing 68 categories are

included to aid the researcher in finding pertinent subject information.

6. Manuscript of Catalogue, Volume 10, "Methods for Measuring and Processing the Interference Characteristics of Communications Equipments Operating in the 1 to 10 kMc Frequency Ranqe,"l5 July 1964, (Unclassified)

This report is a compilation of measuring techniques developed during

the contract period which can be helpful in establishing interference character-

istics of communications equipments. Methods for establishing the interference

characteristics of U. S. Army radio relay systems are described. System common-

channel, ICW, and multi th interference tests are outlined along with methods

for avoiding pitfalls in existing spectrum signature tests.

75

Emphasis is placed on the receiver preselector in evaluating receiver

susceptibility to spurious response and intermodulation interference. A com-

puter program is presented for use in spurious response measurement and iden-

tification procedures.

The limitations of test equipment are illustrated with data and graphs

depicting the characteristics of filters, generators, radio interference

measuring sets, couplers, and hybrids. In general, it is shown that test equip-

ment exhibits various characteristics such that false spectrum signature data

can be obtained unless these undesirable characteristics are realized.

7. Manuscript of Catalogue, Volume 11, nMixer Interference Characteristics, lr (Unclassified)

This volume is a compilation of mixer interference characteristics

investigated under the Electronic Command Technical Requirements, SCL-4187,

ELECTRONIC EQUIPMENT INTERFERENCE CHARACTERISTICS, COMMUNICATION TYPE, dated

27 August 1959. There are three major categories of mixer and nonlinear inves-

tigations described in this report: 1) the effects of mixer characteristics of

spurious responses, 2) response prediction techniques, and 3) mixer mathematical

models.

Experimental and measured data show the effects of harmonic test results

and mixer data. Curves and graphs are presented which illustrate the variation

of response and harmonic levels versus bias conditions for mixer orders up to

ten. Experimental and theoretical results are compared and discussed.

A method for predicting the levels of spurious response data has been

developed. Steps leading to the development of this method are described in

detail. Expected errors in mixer measurements are outlined. Comparison of

measured and predicted data show promising results within 10 db. Data are

presented on triode, transistor, diode, and multigrid vacuum tube mixers.

76

A mixer mathematical model is described in detail. Fourier analysis and

other mathematical techniques are used to describe mixer term coefficients.

B. Manuscri of Radio

This contains data taken on two R-418/G receivers and two

T-303/G transmitters. System test data on one Radio Set AN/TRC-29 and one

Multiplexer Set AN/TCC-13 are also presented.

9. Manuscript of Catalogue, Volume 401, "Interference Characteristics of Radio Set .AN/GRC-50, 11 15 July 1964, (Confidential)

T~is report contains interference test data on two R-ll48(P)/GRC

receivers and two T-893(P)/GRC transmitters. Interference test data are pre

sented for the AN/GRC-50 operating as a system.

10. Manuscri Characteristics of Radio

This report contains interference test data for one 4UR2B2 receiver

and one 4UT2B2 transmitter.

11. "Mutual Interference Chart (MIC) (AN/VRC-12 Transmitter and AN/PRC-25 Receiver)," submitted to the Electromagnetic Environment Division, USAEL, 15 April 1964, (Unclassified)

This report contains a complete MIC for the AN/VRC-13 transmitter and

AN/PRC-25 receiver. Approximately 200 pages of computer printout contain all

compatible anj noncompatible frequencies for the conditions imposed by the

measured spectrum signature data which were used in the exercise. The computer

programs contained in Volumes 6 and 7, Manuscript of Catalogue, form the basis

for the computer techniques demonstrated in this report.

12.

Unclassified

to

This report contains a computer printout of compatible frequencies for

the AN/VRC-12 and AN/PRC-25 equipments operating push-to-talk or relay. A set

77

of available operating frequencies were used with measured spectrum signature

and antenna coupling data as input to the program written for the Burroughs 220

computer. The simplified modifications of the computer program presented in

Volume 8, Manuscript of Catalogue, and the transmitter spurious emission and

receiver spurious response programs presented in Volume 7, Manuscript of Cata-

logue, emphasize the versatility of modular computer program construction.

13. "Mutual Interference Chart (MIG) and Lash-Up Exercise," submitted to the Electromagnetic Environment Division, USAEL, 24 April 1964, (Unclassified)

This report contains a summary of the exercise at Georgia Tech to

establish MIG and lash-up capabilities for determining the electromagnetic

compatibility operation of the AN/VRC-12 and AN/PRC-25 equipments operating in

close proximity. Limitations and comments regarding the existing computer

programs and data presented in parts 11 and 12 above are discussed. This exer-

cise demonstrated the flexibility of the lash-up program as it appears in

Volume 8, Manuscript of Catalogue. Because of its modular construction, it is

necessary only to add library procedures to this existing program to accomplish

different equipment lash-up tasks.

This exercise brought out many problems which could not be fully resolved

regarding the measured spectrum signature data. For close proximity EMC appli-

cations, it is felt that adequate tests are not being conducted on receivers to

determine strong signal effects on 1) spurious response data, 2) two-signal

(adjacent channel) selectivity data, and 3) RF selectivity data. In addition,

improved methods for measuring and identifying the spectrum output from fre-

quency synthesizer type transmitters are needed.

14. "The Behavior of Nonlinear Mixing," Proceedings of the Ninth Tri-Service Conference on EMC, Chicago, Illinois, pp. 59-81, October 1963, (Uncla ssi fi ed)

The purpose of this paper is to discuss the basis for the formation

of spurious products and to show methods for prediction of troublesome spurious

78

responses. Considerable research has been expended toward these goals for a

period in excess of ten years. Many investigations in this field begin with

the normal binomial expansion of two summed sine or cosine functions and eventu

ally attempt to show that the mixer rigorously follows these equations in the

formation of spurious products. Many devices and methods have been employed

for demonstrating that mixers behave according to the assigned mathematical

model, and more recently researchers have accurately predicted the amplitudes

of the spurious products generated by certain mixer types up to about the fifth

order of generation.

The majority of experimental evidence demonstrates that, for the conditions

established during the experiment, the mixer will follow the mathematical model.

Unfortunately, devices for reducing spurious products based upon the theories

so established do not always function as intended. In fact, the data presented

by any given investigator may not agree with the data extracted by another, even

though the conditions for both experiments were believed to be established in

the same manner.

This paper discusses the effects of injected local oscillator and input

signal harmonics, emphasizes their relative importance in producing responses,

and demonstrates their experimental effect on mixer measurements. Possible

sources of such harmonics are outlined.

The absolute response level is shown to affect the relative spurious

response rejection measurements for responses having large q values.

A reliable mixer response prediction method based on sample response

measurements is presented. Its application to receiver spurious response pre

diction is discussed along with associated pitfalls and limitations. The basis

for the method and the v2rious relationships for its use are examined. Experi

mental results illustrate the accuracy of the prediction procedures to the

tenth order of generation.

79

15. uThe Effect of Multipath Interference on the Intelligibility of Speech Transmitted Over an FM System Employing Time Division Multip1exing,u 1964 IEEE International Convention Record Volume 12 Part 6 • 305 -319 New York N. Y. 23-26 March 1964 Unclassified

This paper reports the results of two-path interference tests on a

typical FM system which utilizes TDM. The variable parameters of the test con-

figuration used were the delay time between paths or path length difference, the

relative power levels between paths, the absolute power level or receiver quiet-

ing, and the relative phase angle between paths. The audio output S/N ratio

was measured under various test conditions and used to predict the intelligi-

bility of received isolated monosyllabic words. It was found that the video

distortion produced was primarily assignable to the following causes:

(1) limited noise due to absence of the carrier,

(2) noise produced by amplitude modulation due to lack of effective

limiting action at low signal levels, and

(3) phase modulation of the direct signal by the delay signal.

The distorted video signal produced random gating in the demultiplexer, result-

ing in the generation of random noise at the audio output.

It was found that at approximately equal relative power levels, the pre-

dieted intelligibility fell to zero for a delay of 0.8 ~sec at absolute power

levels corresponding to 35 db or less of receiver quieting. In general, the

data indicate that degradation in the intelligibility of transmitted speech

can be expected from the effects of multipath interference on this system for

path length differences of a few tenths of a mile.

80

V. CONCLUSIONS

Pulse testing of a typical FM/PCM system yields results which indicate

that the system is almost equally susceptible to CW interference, AM inter

ference, and FM interference. Tests on methods of receiver tuning show that

the suggested methods of field tuning for audio (tuning for maximum quieting

with the use of AFC) also proves to be the most repeatable method of tuning

for pulse reception. Although the pulse tests made were comprehensive in scope,

it is felt that they are of limited value in predicting the performance of the

pulse code modulated multiplexing system. When the multiplexing equipment is

available, it is recommended that the tests be repeated using the technique

outlined in this report.

The reliable prediction of cavity-crystal receiver spectrum signatures

is a reality. The spectrum signatures so obtained contain far more information

on the receiver interference characteristic than can be obtained by the standard

direct measurement approach. The entire prediction calculation can be programmed

for computer solution such that rapid expansion of the entire characteristic can

be obtained from limited measured data.

The establishment of normalized mixer curves according to class should be

undertaken in an effort to reduce the required receiver measurements. In addi

tion, computer programs should be written for the computation of the expanded

receiver characteristic. In the light of improving measurement techniques,

studies should be initiated to develop sweeper detectors with at least -80 dbm

sensitivities such that accurate preselector characteristics may be rapidly and

automatically obtained. Prediction techniques for other receiver types should

be further investigated.

81


The next quarter's effort will initiate investigations in determining

the interference characteristics of U. S. Army communications equipment to

include the near-field emission and su lity characteristics which are

important in intra-system and lash-up compatibility. The study will be con

ducted in accordance with the Electronics Command Technical Requirements

SCL-4187, ELECTRONIC EQUIPMENT INTERFERENCE CHARACTERISTICS, COMMUNICATION

TYPE, 27 August 1959, Amendment no. 1, 7 April 1964. The scope of the pro

gram is to conduct a study for establishing a controlled electromagnetic envi

ronment for measuring near-field radiated and susceptibility interference

characteristics of electronics equipments. The objectives are to conduct a

mathematical and experimental study to determine the most economical and practi

cal means for measuring and reducing the VSWR and other undesirable effects of

anechoic shielded rooms.

The specific efforts for the next quarter will include a literature

survey of existing anechoic shielded room design and measuring techniques appli

cable to this study. Methods will be investigated for improving existing and

developing new measuring techniques utilizing screen rooms which are presently

available.

82



E. E. Donaldson, Jr. Assistant Research Engineer 325

N. T. Huddleston Graduate Research Assistant 605

s. P. Lenoir Special Research Engineer 70

w. L. Reagh Research Assistant 628

D. w. Robertson Head, Communications Branch 140

P. T. Spence Graduate Research Assistant 424

c. w. Stuckey Assistant Research Engineer 776

R. D. Trammell, Jr. Assistant Project Director 841


R. D. Wetherington Special Research Physicist 9


Mr. Lenoir is a staff member of the Georgia Tech Computer Center and has

been associated with Georgia Tech for fifteen years. He had been responsible

for the design, construction, and operation of special purpose data logging

and analyzi-ng equipment using both analog and digital techniques. He has

provided extensive analyst and programmer services on several of Georgia Tech's

radio interference and frequency assignment projects.

Mr. 0. H. Ogburn accepted a position with Civil Service in April 1964.

83

VIII. REFERENCES

1. R. D. Trammell, Jr., E. E. Donaldson, Jr., and P. T. Spence, "Manuscript of Catalog~J2, Volume 11, Mixer Interference Characteristics, Project A-678," Electronic E ui ment Interference Characteristics-Communication T e, Contract No. DA 36-039 AMC-02294(E , Georgia Institute of Technology, Engineering Experiment Station.

2. J. W. Steiner, "An Analysis of Radio Frequency Interference Due to Mixer Intermodulation Products,'' IEEE Transactions on Electromagnetic Compatibiiity, Volume EMC-6, pp. 62-68, (January 1964).

3. E. W. Wood, R. D. Trammell, Jr., C. W. Stuckey, H. W. Denny, E. E. Donaldson, Jr., and R. M. Cook, "Quarterly Report No. 1, Project A-678," Electronic Equipment Interference Characteristics-Communication T e, Contract No. DA 36-039 AMC-02294 E , Georgia Institute of Technology, Engineering Experiment Station, pp. 81-101, (15 February 1963 to 15 May 1963).

4. R. D. Trammell, Jr., C. W. Stuckey, E. W. Wood, 0. H. Ogburn, and E. E. Donaldson, Jr., "Quarterly Report No. 2, Project A-678,,. Electronic Equipment Interference Characteristics-Communication Type, Contract No. DA 36-039 AMC-02294(E), Georgia Institute of Technology, Engineering Experiment Station, pp. 35-62, (15 May 1963 to 15 August 1963).

5. Steiner, op cit.

6. Trammell, Donaldson, and Spence, op cit.

84

2 corviMEriT BOB's FOLLEY 2 INTEGER N,K,I 2 FLOP.TING OTHERWISE 2 ARRAY S(4l),T(41) 2 OVERFLOW (5) 2 N=O 2 PPl .•

IX. APPENDIX

2 K=l $ N=N+l $FOR I=(O,l,40) $BEGIN S(I)=l $ T(I)=l END 2 PP2 •• 2 =0 2 PP3 .• 2 S(K)=S(K).(N-I) 2 T(K)=T(K).(I+l) 2 I =I+ 1 2 IF I LSS K $ CD TO PP3 2 IF K LSS N $ BEGIN K=K+l $ GO TO PP2 END 2 FOR I=(O,l,K) $ S(I)=S(I)/T(I) 2 IF N LEQ 20 BEGIN FOR I=(O,l,K) $ S(I)=S(I)/(2*(N-l)) 2 IF N GTR 20 BEGIN FOR I=(O,l,K) $ S(I)=S(I)/(2*20) 2 FOR I=(O,l,K) $ S(I)=S(I)/(2*(N-21)) END 2 FOR I=(O,l,K) $ S(I)=((LOG(S(I)))/2.3026) 2 FOR I=(O,l,K) $ S(I)=20.S(I) 2 WRITE($$DATAl,DATA2) 2 OUTPUT DATAl( FOR I=(O,l,K) $ (N,S(I))) 2 FORMAT DATA2(I3,B5,Fl2.6,W2) 2 IF N LEQ 39 $ GO TO PPl 2 FINISH

85

:t $ $ $

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General, U. S. Army Materiel R & D Directorate, Washington 25, D. C.

U. S. Army Electronics ATTN: AMSEL-AD, Fort Monmouth, N. ,J.

Cormnander, Defense Documentation Center, ATTN: Cameron Station, • 5, Virginia

Commanding Officer, U. S. NrTN: CDCMR-E, Fort Belvoir,

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Officer, U. S. Army Combat Developments. Command, Communications-Electronics Fort Huachuca, Arizona

Commanding Officer, U. S. Army Electronics Research and Activity, ATTN: Technical Library, Fort

Huachuca, Arizona

U. S. Army Security Arlington Hall Arlington Virginia

Deputy President, U. . Army Security Agency Hall Sta.tion, Arlington

Director, U. . Naval search 25, D. C.

Commacding Officer and Director, U. S. Electronic San , California

Aeronautical Systems Divis terson Air Force Base, Ohio

ASNXRR, Wright-Pat-

Air Force

Air Force

Research Laboratories, ATTN: CRZC, Bedford, Massachusetts

Research Lc:tboratories, CRXL-R_, Bedford, Massachusetts

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AFSC Scientific/Technical Liaison Office, U. S. Naval Air Center, Johnsville,

USAELRDL Liaison Office, Rome Air Development Center, ATT~: RAOL, Griffiss Air Force Base, New York

Commanding Officer, U. S. Electronic Materiel Support Agency, ATTN: SELMS-ADJ, Fort Monmouth, New

Director, Monmouth Office, U. S. Army Combat Command, Communications-Electronics Fort Monmouth, New Jersey

Commanding Officer, Engineer Research and Development Laboratories, ATTN: Technical Documents Center, Fort Belvoir, Virginia

Marine Corps Liaison Office, U. S. Electronics Research and Development Laboratories, Fort Monmouth, N. J.

AFSC Scientific/Technical Liaison Office, U. S. Army Elec-tronics Research and Laboratories, Fort Monmouth, New

Commanding Officer, U. S. Electronics Ree.earch and Development Laboratories, ATTN: Logistics Division, Fort Monmouth, New (MARKED FOR: GUY JOHNSON)

Commanding Officer, U. S. Army Electronics Research and Development Laboratories, ATTN: SELRA/DE, Fort Monmouth, New Jersey

Commanding Officer, U. S. Army Electronics Research and Development Laboratories, ATTN: Technical Documents Center, Fort Monmouth, New

Commanding Officer, U. S. Electronics Research and Development Laboratories, ATTN: SELRA/GF, Fort Monmouth, New ,Jersey

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Bureau of D. C. ATTN: Code

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Director, Compatibility ATTN: ACX (Lt. Col. John A. Gahr), U. S.

Laboratory,

Officer, U. S. Army Development Laboratories, ATTN: New Jersey

Research and Fort Monmouth,

Commanding Officer, U. S. Electronics search and Development Laboratories, ATTN: SELRA/GFR, Fort Monmouth, New

Commanding Officer, U. S. Army Electronics Research and Activity, ATTN: FC- , White New Mexico

IIT Research Institute, ATTN: Mr. J. T. Ludwig, 10 W. 35th Street, 16, Illinois

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D"~:r int"; th~· p1·~v1ou ~ ::;yot c·m~ te sLR hrtVf' been !Jlll.dd (Hl ·"l widc-"bo.nd Fi.-f ;,yst?.m whi ch will ut. i l i:z.c a thaL ~m_~1 l oyc pulse code modul~tion . ':'c eval uat e '!..he in a 1-'CM r:nv l~ · (H"Uncnt it wa~ m:~P.ssary t u provide pul s e mn(lu 1FJ.tion ~o:: Gir.lU..L-1-te s that whit:h •·•ill l H! 1J Gcd by the mu 1t.1 ,.:.. .i ,e ; . ""; . 'l'his was

~~~: i ~~~~~0. :):l' (' 'i . t - ~l .. . ~ - ,~ ' :: (r~ :\·~. w~ ~~ ~u~~~i:~~~~~ 11·~~~l·;Lir~;~e r.~~:~ ~t:~ uf ttlt. ._-~r no.t c z • ' 1 :-e-rfo nrmnr.(' und e r va!'iou::. int crfc1·enef:' C'owli -:ion:. wJ.;.::; r:lf:' n:)~J'l"C'i t::r ·;.n '! r ror • •• • • e sy::;tcll". wh i ch dP ' t• l \. • •.•f tra n;.rr.1t.tr:::i pu .!. .>f:' S \.;hi C' h "-'C!' t" r• •h r d i !'lcurrec:Lly . r ~ : • ~·:. 1 :."', 1':::; r cc~i •:f:>d i r1r:O'!"r ~ c tly w~w •' • _ne d , A.nd t.hi ~ fr u. ; • 1 , f" r n r • .. , uzert :1 :.; ~t :nt:a::;urc c f ~ , ' •-· 'TI:c ct'i'cc t ::; of var i ous methode-{ o f receiver tt tniniJ "''~r t'! e valu :tLrJ•l - l ~ renr P tp::;t n included CW i nter f ere ncP , AM inter f e r -l.ncc , :tr.d FM intr.l 'f'f!!"ence.

f.)f !'r ed ict ine t he ::.pe rt. r nm sir;nature of cavity- e!)·::; tal r ..:cei ve r-s n..n1: t he re ~ ul t..r:; of an e xt: r -·ntal prP.dic tion <m A. typic -3.1 m1lt tnry

' ~ · i ndil·H. t • - t pre dlc tlCJn of the :-; pe(~t..rum !;;ip;na.-l"-; ~; :.e and i ntr:rmoc:). J.el. ~m 1lat a is r elin.b lr: and pruv i r.ie ::; more

r .. ver i.nt<"rfc renc -\ l ' Fl.ct e ri ~th~ lhan previ ous direct rr..ec.f;>tu' f.! Jne n t me:tho,js.

t, c-..unma:·y of nl l puolic ~J.t.lon ::; and -work . - p l 1 shed on \.. he contract during t he period of 15 ~ ·ebruary 1965 t o 1) ,July 1964 n.re present~rl i.n this report. 'L'he r·nnt • A .. ; :.. • l "' . .. :. c- : of tht'! fifteen r epo r t. c. a nd paper ~ publ i !:hed dur ing Lh ( ::; p0.:·i od a::-f:' :k .sc ribed .

/\D Acee::;.::;ion No. .Enp; lw:eri.ne; :Sxperi!nc Et fl"l.o. t ion, fi;>orgia ! n::o Li t ute of 'l'P.r::.-.:-h,::::lo"lo:::gy=:-, "At"l"""nn:.t::-a,---,;:Ge::-:o-::crg071-=-a, ."' , VI . !:'tlle key , :-: . n. T'!'r.l.ITII!le ll , •. 1r ., :tw'! L W. WooJ .

Ho . 5, J5 Fr:bru:'try 1 • ' C. ·'·•Y l?t., , I - ued (lontrnct No . DA )i-:': _.. .f 1"-tll...·- - · ).( ) , ::' '"1 inun

l:> i.: - 8718.) , Departmt:nt ur t he Army Pro,icct: lGG-

Jt:ri n,_: tr:r c.J· •'vl r. ~l .J ·:uf1.r 1.Pr 1 t:;( <:-:le r> l:; 1 . ~ hav e~ beeu ma tlc: o n ;'I -w1<kband FM sy::; t em ·.:tt l .·t "-'il.l 1:1.il iz. c- a lw1i.ipl('x c•r that • lly~ pulsP r:od12 modu]o.tion . To evnlua l~ · r ,,., :-:yGte! ~: ir t ::c. \-""";1.1 r-' nv i ron:w:.•o.t. it wa : • · ~:scary to prov ide pu l se modulati o n .....-tti :- 1! s im1Jl a. "'... e ~ t..~l · Jt '.o.'h i ··l• w1 !:. t e w;c thf-! mul ti plexinc; e quipmP.nt . 'llJ"ll n -wns

t h~ t r r.nmnitt eJ • l l h ·'l c1.mt t l ' • ..,. pul s e Lr ain at (!'~F) r~ ': f,e mult..1pl pul :,;e r. ~onsif:>t €> 11 o i'

"o r'l'll ance a. • r a.r! • 1 i nt e rfe r encc condi -t.iun~; w·:J.::: tru-, ~1r ·1 ~· e ·..:. l ·y :,n c ! 'l'or c.ystem ,,:h i 1"""' .r 'cot I .c'l the t.ot;ll munb er nf tr:t:wP. i ~t ~- · - "-'hh ·"l", wc r (• l"l?f 'f-'1V(':d incorrect -( . 7'1 \ C Lion of t otal :1;,,.:. !: • - r~ r ~·: c- P(: t t:r ... , ... u . .; and t ld J #" ~= · ! 1 , or t: rr or· r ate, wah

• y~tem ef le0. t!l oi' va.riou~ lile i.. hn<l G of r·eec iver ~unl n1~, we ~ • · ~ ~.. t e st~ include-d CW j nt e rfere ncc , A.M. intP.rfer-

un•j

( •f ':""'TC:di ct..i nr; t he ~p~ctnun ::ol gnn.ture of ~~n.vity- cryntnl rer.: ei v~:r!-3

n.nc-1 ... Uw rr.~ ult :·; of em expi:'T'imental predictio n on a i..ypl cFLl mili tr..ry n.re r·epm·tc-d . ~P:;u1t~ indicat e thRt. :.-r-1.1 ~ 1 o :r U tf.' spectrum c.igna-

Lurr· fo r ~'f!ll rio'.t~ !'( ... nr1 i nte.rmo<lu l ation · ' t r eliable and provides more i:t1'onw.J.Lion e-n i..l1P r - ,.~ • r i n t erf f:'rf'nce d ttt.r a • .j .I than prev1ou ~ di rE>r.t.

• 1 .. , ~ :. meL hods .

~~ suwmo.t·y of' Hll put ... • ~ and work accomp.l \ J r he c.; o utra.ct duri ng the p·t·iocJ Ul' 15 FclJruaJ 1 "t' \. 0 15 ,?" 'Jly 1964 ar E' _ , .:<T,t i j n thi~ r eport. The ':':Onten t~.; a n:l -:la3 t.d fl.:o::r~ lt ot' thE;;! fift een r·Aports and paper s publ i~hed Uur ine;: t.t1i :s pcri.od are dA::.cribed.

' 'NC' M J<;lfiF.D HEron-r l . :tadi.o c()lTCTI\lnicai.. lons

?. • Int e r f f: rene !;;!

.; . 11a diu Frc q-..1enr:y I nterfr.r enc!.:

I . c. w. St.. ·.H~ kc·y , n. D.

IV .

Tr ammell , ,_rr . 1 a. ud 1:: . W. Wood

:t '"'< ~ No . 2G, Q- -ly RPport i'-!o .

C ' ,. .:- t ~io . D/1. ;.O .. OYJ A ' . ~ !<)I , (E ), Dent. of L• .rrt.:; Pro~~P-ct l "':6-2 • • ~-41< 9

r:AEL , Fort Mon!IlO':.lth, New ,Jerse-y

l JNC LJ, !"" '! RE RlR'f 1 . Rad it1 ~ A 1i c ation~

; . !~adio f're>qut:ncy l nte r fercn c e

r. C . W. Stu c.·key, H. D. ·· --, J r., a nd

} • -·. -..:;.od

I T. t " n . 26, ~ • t - . y R•port No .

TTl. :•· : • t1o . DA 36-03') •. : -..IJI(f-) 1 DeJ:'t . nf

-J Proje ct 116-20501- D- l>i19

I V. IJ::iA.E[J, For t Monmouth , New .TP.r ~ey

AU Ac ce::;n1on j;o . EVneP.-r i nti r.::-r ~ rL C . w. Stw: !:ey,

' "' t i on , Ge-org i li ! nstl t..utc of Tec;:;:hn:-::o""1o::-:gy::-,.......,.,At".l "'an'"'.t-=-a ,--o-0e-=-o ..,.,r g"'"1a,.--, - .11 , ..: r ., 9.nd i': , W. Wood.

Report ~,Jo . ) 1 15 Fetr .JD.ry 196!1 to 15 ,Ju l .y 19(>4 , .i.::;:::; ue:d illuo , ( Cont,·ae t. ~io . !JA 36 - 0 )9 AMC- 022<)11(TC) , r.ontinu~

oc - 13' (1(1), !Jc,po.rtmenl o f th~ Army Pro j ect: 1 -~(,-

DJri ng t t,e _ ~ .- r , :;yst r:ms t <::> ~ U~ have been rnac1i'! on ~ wi deln'l.nd FM cystf:!m whi c!1 '"' l ll ;:. ~Ju.lt. irlc~xc·r tbat 1:>mp l oys pulst> r: otk r.todul ni.. i o n . J'o evalu~Le t.~e:- sy'Jt.elf! in n l?Cf·~ envtronm..:nt i i. wus n r~ <:c-ssary to provi de p~lh>e modt1la.ti o n w·r.l ·.:h .>1tl~-1te s Lktt. whio:h \./i ll b€' used by Lhe lnul• 4r:..r I 1' 1t. . Tid::; was n r ·hin·('·.~ "!..y )'llCJ.:lu \ :"l t inp, · " · t · er -wtth n cont . • ..... ~'1'""";_1 r ~ t rn in at tht: pt;: .• e •·r·p(•t itlon f l' • \ i) of' t he mu1Llp1t:xcr. '!.he _! lu l::;c::; cunsi si..e d f")f :~.P•r 'r .. <# l - ~ -e :~y:> tt7lll perfo n:1.:=t.ncc unde r va riCJllS i nterfer-eiH~ t: condi -1. i on ::; ·w::.~ ::te :!.~llr<"'fl ty ~c f:' !Tnr det ec t ion ;,y ;, tt:m -wh l:.:b de t t:t-::: i ned t. he tot;-:.;_ :1tur:ber cf' t ::an::;;·1i t tctl r-uls e :::; wh~r: h '-'ere rec· ei vt~d i ncorrect1 y· . 'lhe frac· t. ion of' tolal rul ~ ~:> s n~c~ i vo<? 'i l;. t·on'(.-ct ::..y w~~ -:lt:t.~mir.ed, .'ln rl thi ~ fraeLion, or t t .. r r A.t r: , ·w.':ls : .:a~ , : .?.S ·.~ :ne a.:w : t: o i' zy:.;Lf:'! 'i< - ; ·-:-- l:, nf vn.r i ous methoci ::; of' re o:.·e i VL'l'

-. .:r r: eY:~..lu:;. l fo:.O · l . Tt~ .. : .. • • • · · - ! I C\o.' interfererK:r~ , Nv1 int..f:'rfr.r -~·t ; N .l. rt i...t.~r ~'t":rc nce .

rli quc·:::. of th'= ~>pPc trum ::.ien~-l.i..ure of' cavity - e ry::;t n.l reeeiver G ... ~nted H.n~l m~ FJ.n e x peri:uent.al predi c J ' ~"" ~ on i1. typlt.:a.l mi li tary

l • - •-- :'l,rr. r eport •· .. . t ~ ~ "• , . • • r ·; •!._ I~ of the spr.ctrum ~ignn-l . spu:-l r. 1.l:l r ))""~ r- 1 .1 'f; : ! t·e ] iablc and prCJvides mor<~ -'•: ".. ion Or t the r e r.eive r 1r,tr::=-f'erence dl.r.tracte rist i r: than prev i ous d i rec t ~- · r~ent mt: thod::;..

.D. :>1ml!l1ilry <.> .:. ... :-t11 pub l icat ion:> ann -w or k ft <:c· #" t ~ on th('; contract. Uur inr,- th e Pf~riod of 1 ; h .... b r uary 1963 t o 1) .Tuly 196L. - ..1. rt nt c d in Lhi:; rr:port . The cor.te nLn nnd c.:. • .! '" 1 t l l of t.hc fift ee r. r eport::; n.nd paper:; publ i sh e d nuri ng t h i :'"> ~'r--rioti ar t

Al) Ac·cc:ssi on :'!CJ . f,n[)ineer : ng .!:;xve r tr~cnt :itation, ·}eorn ia Tn s t1t ute of 'T't - -;-:-:::-:---=-::--.-:--,.....,=-:::-~·. W. 2tucK(:'y, ~,. D. ':-'r nr.1Il1ell, ,· ~. 1 an.-1 :: . w. Wnon .

f.h1 ri r.:: C 1 whi c!1 w1. l

.( l\~olS ' fll I t 1

~ 1 z. c a i'r • ~ • \ - ..

1~)6!1 to l) r. ;~ly 1964 , i s sne<l 3G-G)9 ANC- ~---).4 (1!:) , Conti. nua

Del;artmr:!lt tlf t he A11n.y Pro jec t: 1:;6-

w • have beer1 made. on n videbo.nd Fl-1 ~W!-3tem

· oyr:. rul.:;C' r:ode :nodulat ion . rr'CJ c va.l mti.P. "l 1't''·~ >:'rt ' • r~s sa.ry to pTuvldc pulse modu l ati o n ~ 1.b Jt, ~o.•J1i. ·.· !t \·:i l i be ~I :;r:d l'Y Lhc multi!)l P.xinp; ea ~d l t. ~1::; Wa !i

':!'lr.- t:·ar:mn:.tt e~ wit.!". n. t:or JL inuou.s b1nrtry ~,. oe t rain at (r~:r ) nf' the nt Jlf' t ... ~ t" Xer. The pul s er; con:.il;,tcd of

• :- §O r ~ .. tc::r var i ou ::; i.nterf~;> rP.nce cowli --:i ~.m~; ·wo.r : ·~t'' .. :; uro:-:. 1:/ Errol ~ . • \::' , de>tt:>"l"~ined t.. he tot .:tl nn.mb r.r 0 f !. .. ..... Jl~.cs -...:h l ·:b ·,...'r:!'c .:: · ~(:civcd in(·CJrT'.,..._,. - ,i . The f'r.'3.ction o f totr.t l

~ U: '."UI"I" I-". ·-r-ly HT·; rlr-: t e rmlm.! cl, ·'3.11d ... f'rnc l l , < .,,.,. ... r flte , wa ::; 1\.-H"d ac ·~ mcn~·Jre nf r;yzte ::J 'n:e e f .. _•-;.;, of v ••lp~ I s of r~ceiver :un.i.r4,.; w'<'::.·r- E:'V ~Ll lln ~-::· :1 . tr~ .. ~ ts tnclOJded CW int e r f ere nce, AM intcrfer -f'~ l<..' l' 1 :l1Xl. H / 1nt€'l' fercncc:,

'T1K· t~:• .. :i·,nio ue ::; of :- r -: :.et.i ng thf~ ::;p r.c tnun ~ignntui'e of cavity - ~rystal r~cc:ivers

c.:n pn :senl.P•l nne. Ute r c:r.u ltg m"""' n.n experimenta] predic:Li • •• ' I y· , ,. _1 mi l itnry l"Ci.:eiVe "!' nr e n"pcrted. ~c ::;ult s J!·,r11cr:.te t..lt r.Lt p!.·edi ~.·t.. ion ! L ..... 1 .m oip;mt-r~u~· t: 1'or :-.r-ur iou1,: r PSl"Xmse a 'lr • tr - ~ · t ic .. .. i '"'P. l i a ble D.nU provi(lP. ::; more inf'Qr"mal i011 Uri. \., b1; receiver ..... . ~ rl ) al'" •• ( ,, 1 than prP.Vi OU!-3 dli'CCt

. t method ~;.

fo. ~wrrrnnt·y oi' :-~ . ll pu bl i r: r:tt. ionz and work accom~ I~ 1 ,.,.. ";he cCJ n• . '. du.r inp; t he [..'E:'r ll'•tl of 15 Fr:b!' UM-r y 196"3 t o 1) ,,l u l y 1964 ar. ;.r-nt 1 in thi:-; rr~port. The Nmt enV> n.rul c l assif' icatlo n c of thP. "fi ftee n r ,.~ r• I paper s p ubl i shP.tl c'luring this !Jf:> t' iOd ~1' 1:' Ucscribed.

lTI'lC LA:J~~l V.!.ED REPOnrr l. n.a ctlo Communi cat i o ns.

2 . Tntcr f e rP-nce

I. C. W, !: tuck (-;y , R. D. T'ra.mmf:! l 1 , •. •r . 1 and E . W. Wood

iT. ·,.· ~ ·· ·· t ~0 . 261

./u:l!'f.f:' !' l y Report ~·Io ,

TT1 . Contnn~t No . Dfl ; G- O _.'"I~ .A.MC- ri2294( F. ) , !Jt>1 ·L, of t h E> Amy Proje- ct 1 ~;G .. 20)01 - D- 44 y

IV . lj:::A£T,, Fort Mo runouth , New ."!"ers~y

'JNCTA S~~;H'lED RF.FOR': 1 . Ra.Uio Communi r.Ation~

_. Interf' t:r e nce

.. , . :1iid i o Prequen(:y I nterferenc e

T, C . W. Stuckey, R. D. 'Prnmme ll, ~T r ., nnd F.. w. woo(l

TI. Report No . 26, Qua.r t e r ly R0.port I': a . 5

ITT. <~ tr ' No. DA 36- 039 •4(E) , Dept . of

lhc fu:m.y Proje ct F;6-205C1- D- 449

TV . U:iAF.T . -·..;;rt ~ '1 ,

New ... r 1

AD A<;ce ssj on rio. J::n6'1 [u:·ering Experime nt fJtat ion , Georgia l n;;ti tut e of Tec···""hn"'o""lo"'r;;:r"",---.:J\t"l-::c~ =o:.-,--.,. __ .,-_.,.;-r:""'l-, .~ . \J , ~Luc.: key, 11 . D . ·j'r Jl J J r., and E . w. Wo od.

ihe Pl' cv i o u.~ ': • \. •- 'HlVF:> bee n TIK-I.d( ~ on ':l w1. rl o l'l d .F'M r;y~;tem 1vi l l ut i l ize ~ .... · : : . • s -:. ~'-'J" G pu]se l'Ode rnCi<lula tion. 'l_·u e vn lu::t.ie

U:e system ln a PCM e n vironmr.n1' I w·- sary t o pr uvid r. lhJ. lt.i e mo lat ion ~·f if'll <!i_mJJ.l ·.:d t-> <-:. t ha.t whL· l! wi l l be l~ S ed by the mult t plE;!xi np; ~ ~ .~ r:-:. '!ld ~ wa.s

! · ' 1 • J1 'i.L l ne the l rant>mi tt P.r "W i t h a conli nuous hi.. nary train A..t

.. •• i tion fr e auenc:y (PRF) of t he multipl exe r . ':lH:! ... <'Ons i ~t ed nf •t • • .':lnd ~n p::; . 1'hc ., ' ~~r:t'orma.nce ;.mtler va r i ot .. .,.. rf'c:ruw:e ccndi -

Li v:::::. ;,; :;~. ::; men.r.ure·l by <ln (~ :·r IJ l' • '"' • t n "'y:::. t r:m wliic h d~tennit~ t ut a.] numbE;!r o; r Lran;;m t t l ed whi ch -..:pre T""-~ , l: ":-rP.c-tly . •nw [ ! ~--~ of Lotal :;:. ~ ;.e-.c; W·'lG 11 • _ \ , • thl.G f n~xtion , • • -ror raL~ J was

; l'ormnnt:- e. l'he ef f e cts o f vario u.G me lhods of rece i ver • • .. -. rf:'n ~:f' t c":~l:; .incl ~ded CW intcrf':!rence , AM lnter f{":l" -

o f' r• r ed. h·Ling the spectrqm :.,; i r;nn t.u re of c avity - t•r;ys tnJ receiver::. ;.;.nd. t he r~!mlt f-i of an exper jmenLal prcdh:L l on IJn <t t ypic ."l l rnill t. a ry

io:c GuJ ind i c:nte 1. h..-.~-t predi ction of ihe spcctrtlln ~ • .. --:-.· ).Xm:;t! a nd int. e nnodulat i on do.ta is rel iab le a nd provi :'l~s more

.:. nl 'm•mn Ll ~;.• •. r .:ei v0r lnteri"c: rc~ H t·e chilra0.ter i o.ti c than prev1 o u :=; d i rec t t:~e af.:urcmcm L r:~.et hoil:; .

J.. s·.1r.1nary of r:1 l .Publ i cnt1ons a nd 'WOl'k 1:\.t'C'ompl :1 :;hed on th~ cont r act. duri np; thL" ; :e r i oc"l ()f 1 5 YP.bru ~try 1~)63 tc; 15 .)u l y 1961. :~.re present ed in t h is r eport. 'i'he ~~(HI !. ""( .....

1 - •!r' ('al l ont> o f t.he f iftr:en r-epor ts a nd pa pen; pqbli~hed clur i ne

th1 ~ J r _.;.t lr : ,..··· i hed .

~:~f, incc~ ri. ng Expe!'i:ncnt st'iit 10n, _ :~ Inr;~~~:~=i~~ ~~:~-. ,...hn-o-,-lo-gy-,~J\t-,-ln-n.,--t~ , Geur e; i a J ~ . W. S i..~lC J.:c~:r , ::· . TJ. ·i'~ .. -:..mm.~ ll , ,,Tr., <'l n d E . W. Wood .

.. ~.eport No . 5, l) Yc brunry 1961..1 to 1~ ,Ju l y l~ , isGucc.l il h t>' . (Ccmt i·acL No . !JA )6- 059 AMC- 02294 ( •. : , Cont i nuo.-

~: : - L1"(185 , Dep rt&=nt of thr.• A.nny Pro,)cct : lG()-

trH~ ar·tc: r·, :>.v:~L-::rn:; t c ::;tr. hi'tv e bteen ma rlc on "1. wide bnnd Ff4 systtem \Vl ll • ultipim: P•' t.hnt empl oyG puls e ._:ode rnodu l<l i..ion. ·ro cvnlua Le

t ho:- :.;:;~t.cr.. ~ .. v i ro!Uncnt. i L w~:~.:; ne t'e55nry t o provide puJ ::. c mo<lulati on · . ·b :> l r::q_;.J~.~ec tt. ·:t wb i"l! .. · lJ..L ue ·..1:::. ~ · 1 lJy lhe :nul ti plcx Lug equipment . 'T'hiR W<l f:;

.r~l l r~\'cll~'Y th(.t.r·r-""' ' ' l•r•.!.~}- n· · · ,~ , .. .,....1 ~ · t.r;,.lr ·. ~111 .' ! : ~ll..>e repetit i otr '" II .o.t•rt, • r.,. "'J.;. · • . -,.1 of ~: .. t. crnf!LP ;;- p .:\nJ. c-r.c ;:.: . ~;y ::. L em pcrfor"Manr.-e under vari ou ~; l nt erfr:r~n<~ t:' l"Ondi -~i<. · n ~: w.:l::· mc ;-,::;:.n·(:1 L~t ··.n C'l'YOl" ·lf>tec:l l un !:>ystcm .. ,.:hi<:h determin~ cl t h e t t1tal number .. 1 1~ L:· :., ~ ll. • r •• 1 ., 1 ! . -:"r-t J . Th e f r .3.(:tion of Lotal r·.l..:.:::~":G .r : · •~"""':~" ... ~ · 'II! f::-a<."'t i on , or e r ror rfit ~ , wah (l,"!f.•·! a:.. n l:K·a.::.urc c:f ~..; y::; Lem pe1· ·,.. '!'· of" variouG nu~t.hods-; of rec e ive turJ.inu wc:r·e e~.·:;o,l u·:t r:d . Tnt. P r·rer~?nr:c t cstl3 lneluded CW inl€rferenc e , J\M t nl!::!Tf e r':" t t ·: ~, ~Ln ~t ]" ~··1 i nt.r .. r· f'f~'· e nc e .

t:l ' rr(: r1i ,~ t. i ng t h e ~-;:pectrum .slgnatur 0. of' cav1 t.y-crysta. l rccc l ver· :, n.nt1 Lhe res ults cf a n t 1.1"'r:· ~· ~ ,... "'1 t~c.n on a t..yp l t·al militn.ry

~r· ··· r·er:o!~te •l. !1o~ull::> i ndi c- a • "' • .u · : ' t"< .. Lhe ~pectrum sl~nR-

spur i ou:::; re::;ponse nnr1 1 ntP.rrnodu1atio n (l atH ls reliablP. <1nd provi de s mor e l nfor ::1n Lion t't1 the '!''P.I'f> Lver i r.t ert'crcnce cha racteri ct. i r: t han previ ou~ U:l: r e~.: L

•..., nt !'JPihud.s.

fl. c ... uronfJ.ry of Pwll pu.bli r: ~li. i Ci rJS -3.nd work - ~: 'r 1 c r- , ,.., • 1 r • .... ing ihe pe r ll}rt or' J ~~ FP1>ruary 1963 to 15 J ul y 1 /( ..,._, ; ...... , ... J • t.r ! · ',., r• _' or-.. . 'i'he contPnt.s ~nd c lnccif icallon~ of' t he f1 ftf:>en re portr. a wl pnper s pub l 15hP.d dur i ng t hi s p1 :r·lod are deccr H)t'!d,

'JI·;C .:...ASSlf'I.J::D REIDR~ 1 . ~adio Communi c a t ions

RaJ i o FT , ! nt ~~·fe't" 0.nc:0.

T. C' . W. Sluckey 1 H. D. l'ramm0.11 , ,Tr . , ~nd

E . W. Wood

TT . ~Ppo r·t No . ?6, Qua.rtc r l y Report. f·!o . 5

J! I . Contrn.ct t:o . ll.~ )6- 0)9 AMC- 02294( E), D<·nt . o f L.he A.rmy FTc: t 1 ·,c;_ 20)01- D- 41;9

IV. lS/I.ELJ Fort Mm:1mo·.tthJ H~w· ~7~ n:;!:'y

l~\C J:ASSHTJ::D Rl\FDR~

1. ;~ ad 1 o Cormnunicn.t t ons

2. TnL t> r f erence

) . Ra d io ~ ·re qucncy

Int e r·f er l::! nce

T. C . w. 8tuckcy , R. D. ':'rrumncl1, J r. 1 anil E. w. wooa

II . Rf·port No . 26, Quart!"'r 1y Report No. 5

TE. Contro.ct No . DA 36- 039 AMC - Or'20)4 (E ), Tle pt. oi' th~ M111Y Project lr.6-?0')0l - D- 4h9

IV . I TSAEL, fort _· uth, N0.'W ,Jersey

J\D Acc(':::.r>ion :~o . ~"\:· ·..i.ne Exrx=r l ment Stcil t on, Georgi a Tnst i t ut c of Tec·"'h=-=nocclo-:-:g.r- , ...,.At'""l-.>n--,-ti, ('.eorgia, C . W. 3tur:.>\ey, .:L D. 'Pr·Rl1ltlel l J ,· r ., ~;~.nd t: . W. Wood .

H~port No . 5, ~ 5 Feb r uar .{ 19611 to 1) .Tuly 1~64 , i. nsued i llus . (Contrn0.t No . DA 36- 059 AMC - 02294(E) , Conttnua

r. ~- 8718), IJ<··partment of the Arm,y Projec t : lG6-

Duri ntj t h(o> Il: ·e,.; :.ou;:; qu<.u· t eT .~ • lr t e sts li~ ve be en ma(le on~'!. wid~h.md i"t-1 ~y:.t~m whlch ¥,ril l. utl llze a mulli p:..,("Jr• '1 :. L , .. ~ 1 1 ~ ll!l) dul ~;~.t ion . ?o cvr...lual~ ! llt> i r. q PCM e n vi r·onrnent 1. t. w·:t.s ~ • f' ,. ·'- ;;:- _ i (le l)U lsc rno(l u. l;:.t ion

S lia~~ lntr:5 l ht L 'oo,'hi ;;h Wi l l be UGC:'l ·uy t h t=! M1ll'tipl eXil'lf2: ! ,. .: _ r • . - • wa£: c~d:i c.·vc: J l:,y r::•Yiul :Jting the t2·an::.::~.l Lt er wi th ::t. cont inuous b inary pulse t1"~ in al t be .i :. r '1 queney ( f'H F) of the ~~ll..i.pl exer. lhe pul::.c ::::; r: l":n:;i 5tP.d o f .1l t c 'rtie system pe :·furmanc: r. under variou::i i nter ff' r e>ne t- condi -t ion~ 'W~:~• mea~.; ·.Jr('~~ Ly <in e r - ~ ~ ~ - ... 1 ' ·.. 1 ~ • Ue Lermi nerl thf? t ot al m unh:-.: n i' lrans~itted pulGc ~ -....l ,L· ~ ~ or •• • •· r~-;· -.i · 7h e f.., ... ! 1~ Lot<ll ;>ul:-: ,... s re ~·e ivr: : i i rwvr r e..::tJ:v '<::-~. ·; detcnnjr~ed , (!. tV~ th is :fra·~t ic J r r • "" rate, wa~ u::.cd o.~ "! mea~ur r. of sy :..;ten pcrfor me.nce . Ti te effect s of var i ou:. methods of n ·•. :eiver t.1 :: i ue wer .. ,.. I . TrtLerl'err:nce Le . .;tc inc ·, ude d '..:W 1 nt e r f erenct: , Ar-t interfer -~"'11..!~ , n.n(l ! - • r enee .

o f t h.r! :; pJ:>c trum ~ign ~t Lure of' ~avt ty- c ryct <J.l re (..: e i vers D.r11l of an c xpt:!rlrne ntn.l p rJ:> dlctio n on 1:t Lypi cn1 military

n~J..lo r tecl . ~ e:-:·.:.;. 1 t~ indicttte thnt pl~edi ct ion of the spe~trum s i e n o. -t. -.- r - _ .. rl..:J"~ .._ r• ~ :·and lntermociu1at hm Uat<: is reliab le a nd provi d(':5 more inl'<.n·rnat. ion tm the r et·ei ver int(:- r .... opor ... ~., chl:i.!'a ct erist i ~ than prcvi ous direct rne :?..S'..l.rcmc:ni !rte thods .

A s ununary c: f .:-~ll pu'ulicationr; a nd \o" t~rk a ccomplit>heil on i he c~ L dur i nr, t he : < ... • • ' l - r 1 ' - j to l ) : tJly 1964 an:- presented i n lhi~ report.. '!11<7

' .. r-~·· t lo') n ::; o f t he fifte e n r eports and pa~r:> publ i~hcd Uuring

/ , !..:;

Eng ineering 1,

(' . ·'i<: . Sl l't"!-.ey;

,. lN't,

t o 15 •.'uly 1964 , i ooue<l AMC- - -- )4(~ ), Conti nun

Army Pr o ,i " <'t : l GG-

~~t!~ i n(' t !t~"' tW"V i nu. ;.; uu:t !~ter , ~yct ct:t r> le lj ll:i. llav~ b~0.n -:nadP on :t wi dcbnn<l F'M sy;,tern ..... h Ld! "'' .:.:.1 ~ti ..:.i z c· a. wul l l plex"!'r that i!mpl\)ys fl'..ilse c-od e rnoliu1n.l lon . 'J'o ~valuate 1 L•: ...... :.;t ee: in ·., :•cJ.l Pnvi •·c,nr: 1 i t W"·:'cti :ll'!CC . r • ·.. t .c pll1 :i.e :nodul at ion .... ~.i.;:: :;i:notl:tl"':; lb:.tt ;,;hi :h \. , l c u :;~d 'JY .. ,... • · · 1 1 f' ~l ~ equi pment . Tlti::; wn.s

lJlt' L~·am~mitt cr y.•ith 1 ~!- ~ .... inary pul .... ' .e~t.

( n~F) of the: mult i plexer . 'ihe pulst'!s l'Onsist ed of a l tc.:::-r.ctt t: zcrn.s <;,nri cme s . ~y:;t(:m perfo rmance tm<1P. r var i ous i nterference c ondi-t j,·>nr: '>rt :· r::ea.-:. ·.lr c~c by <"n c n ·or 'let.e o:- t i on ::;y s t e tr1 wh ic h det r.r mi ne<l Lb e t otal numbP. r c :"' t r rm;,mille·l \...'hie:h 'W("l" f:' ;e ·:~ ! ,.. 1 ---~·ectly . 'I'he fra.~t ion of total

~l ;~:; ~~.~ r. ·t mP.:~:.; ~Ir:11 ~:~.!·~~~~ :.~~ ~~Q~ dct.0.r- ~ \ ,1A "~.r~~~~ s f:;(=:~~~~u~\~=~~~~s r ~~ ; ~ •. t Lr.;,nlnr: w·z. r c C\'fl ~ u -,. L ~ :l. Le s t s included CW inler .ference 1 AM 1 n L~? r r t:>rcnc c: , <lntl ? !.: lnterfr.r~n c· A .

'!'h.: techni que ;; of p·e cti •1 .. •• I,... 1~ · • . t'l .,r . Lty- cr;ystal re~P.lve~·s ~re pr c:lt:!ttle c.t a.nd the r • • ~· t c t r \ ' • . r" • c "'tr n on a t.ypica l rnili t <ll""Y J e ~..·~lver nr0. r er,.m· Led . Hcsult:::. jndl eale that pr0.dict. ion of t he 8pectrwn r, 1

turr~ t' nr :·.;purlou s resp:msc and l ntermodulat1 on dr'lt.:t is reli ~b lc .1.nd provide;:, mvr e it- --.: te r e e eiver i nLPrference c har a ctc:'!·i cl lc Unm previous d1ref't

r.~ _ .. .. ·-l)ds .

A ctunm<lry of tt ll publi t•a iionG ancl work ·~ • r t - ... ,.. t he JA.:rlod t}f 1 ·.~ ~cDruary 196) t.o 15 .. :uly J • rt ; :~ & ... & • r -. 1.. The ·.:ont(~nt~ ~nd r·lass i f i cations of t he fiftee n re port.:=; A..nd pF!.pers publ ished duri ng thi :;. pcrioJ an: de :5 l"r i bed.

ll'NC TAfl f: J FTF.D TtF.PCJRIT' l. Ra.JJ.Ci Conmrun i ea. Ll on G

? . I nterferen r. e

Had io fre r;,uency I n t e rference

. • C: . W. :itu~k~y , fL D. • 11, .Jr. 1 a nd

~ ... ,.; .,. Wuod

n . ~:o. 26 , . .. rl rly Re port ~:o . 5

IT! . r l' t No . DA ~~G - 039 AMC - 02291< (!\), Tlt.':>l . <>r t.hr. A1'7fr.;/ Pro,ie ct l ~ ti -20C,01-D- 44')

T'V . !l fiAFL , ForL Monmouth, New .rc:rsr.y

IINCT.Af.f,IF'IED REIDRT 1. Radio Corrommieat ion z

2 . Tnt.P. r rerence

' . Pa.dio Fre quency lnt0.r:t" f" r ene e

T . C. W. Stuckey, n. D. 'l'rammc11, ,Tr· . J and E. W. Wood

TT. ~,...f'O,...t. Nl"'l, ?h t . t r .. 7 , .... ... t r.:o . )

ITT . Coutr·o.c· t No . DA )6- 03~1 AMC- 0??')1: (E), Dent . or t he JlrTI\)' Project l >;G-20501-D- 449

A f. r•l'rt ut h , New Jer zc:y

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