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IMINUM0111:420W:V1011*431101201WeLei

ELECTRONICS& WIRELESS WORLD

APRIL 1987 £1.95

Spectrumanalysistechniques

Developmentof an h.f.receiver

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Reducingquantizingerror

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Self calibrating

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Hard copy evidence with optional printer

Six picture stores/control setting memories

AM and FM demodulation. Built-in loudspeaker

Broadband measurement range (300kHz to 1000MHz)

Direct field strength readings in dB microvolts possible

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APRIL 1987 VOLUME 93 NUMBER 1614

LEAT.Wiri6:COVER

Marconi Instruments' 2383 spectrumanalyser. Analysis using such instruments

is the subject of this month's feature,starting on p.359

SPECTRUM ANALYSIS

359Current developments in the facilitiesprovided by spectrum and frequency -response analysers are explored and

explained

HIGH-PERFORMANCECOLOUR GRAPHICS

CONTROLLER

368Half a megabyte of memory and a new videocontrol i.c. make fast and versatile colour

graphicsby John Adams

INCREASED RESOLUTIONFROM AN A -TO -D

CONVERTER

373"Dither" and an averaging technique

provide interpolationby R.A. Beck

PIONEERS -4381

Charles Wheatstone made so manyinventions they could fill a book

by W.A. Atherton

A RADICAL APPROACH TOMICROPROCESSOR DESIGN

394Hardware details for the Novix Forth

processorby W.P. Watson

DESIGNING ACOMMUNICATIONS

RECEIVER409

Design techniques used in a new Britishreceiver, intended to out -perform Far -

Eastern competition at lower costby J.R. Thorpe

SCIENTIFIC INTERFACEFOR THE AMSTRAD PCW

454Although sold as a low-cost word processor

the PCW8256/8512 can make a usefullaboratory computer.

by Brian I Frost

Mandelbrot pattern generated by JohnAdams' graphics board described onp.368.

CLASS D AMPLIFICATIONFOR INDUSTRIAL

CONTROL

415Recent mosfet transistors bring fresh power

and performance to pulse -durationmodulation, removing historical

limitationsby Barry Friedman

THE MULTI -ELEMENTTRANSFORM

421A suggestion for overcoming the two -source limitation of the inverse square

law

by J. C. Belcher

TONE DECODING USING AMICROPROCESSOR

428A simple approach to microprocessor -

controlled tone decoding providesan excellent signal-to-noise

ratioby Christopher H. Cough

IMAGE ACQUISITIONSYSTEM

441A low-cost sensor, when used with

processing software, is adequate for use insecurity, robotics and character

recognitionby C.J. Awcock, F.W. Stone and

R. Thomas

ALCATEL AND ITT

456Alcatel and ITT combine to link IT,

computers and telecommunications.

by Adrian Morant

COMMENT 355

SATELLITE SYSTEMS 377

APPLICATION NOTES 385

UPDATE 390

TELECOMMS TOPICS 403

CIRCUIT IDEAS 407

RESEARCH NOTES 424

NEW PRODUCTS 434-439

TELEVISION BROADCAST 445

RADIO BROADCAST 446

RADIO COMMUNICATIONS 447

FEEDBACK 450

WORKFILE 458

ELECTRONICS & WIRELESS WORLD 353

This is just a sample of our

OSCILLOSCOPESHewlett Packard180 TR 100MHz Scope M/F (Mint) £15001744A 100MHz Storage Scope £2350PhilipsPM3266100MHz Storage Scope £4570PM3305P 35MHz Digital Storage £1925PM3540 Logic Anal/Scope £1500Tektronix465B/DM44100MHz Scope 2DMM £20004658100MHz Scope £1450475A/DM44 200MHz Scope/DMM £2500485350MHz Scope £4500608 Monitor £1500634 opt 1,20 DisplayMonitor £7502465 300MHz Scope £34505223 ScopeM/F (Mint) £360071041GHz Scope M/F £160007603100MHzM/F £19507704A 200MHzMainframe £28507834 Fast Storage ScopeM/F £7500R7603 100 MHz RackMINTM/F £19507904 500 MHz ScopeM/F £5500A large selection of7000 series plug -insavailable at up to 60%saving on list. Pleasecall for quotations.

ANALYSERSHewlett Packard141T DisplayMainframe £20003582A SpectrumAnalyser £75004193A ImpedanceAnalyser8552B IF Section8553B RF Section,110MHzMarconiIF 2330AWave AnalyserIF 2370 110MHz SpectrumAnalyserTF 2371 200MHz SpectrumAnalyserTektronix7L14 Spectrum Analyser P. In308 Data Analyser

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SIGNAL SOURCESHewlett Packard4204A Digital Oscillator8007B Pulse Generator8011A-001 Pulse Generator 20MHz8601A SweepGenerator8614A Signal Generator86260A Sweep Gen. Plug-in12.4-18GHz8640B 001-002 AM/FMSignal Generator8690B Sweeper MainframeMarconi2015-1 A/vVFM Signal GeneratorTF 2002B AM/FM Signal Generator

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PhilipsPM5134 Function Generator £1325PM5326AM/FM Generator £1130PM5519ITV Pattern Generator £600Wavetek1845MHz Sweep Generator £65010801GHz Sweeper £1500

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85A Microcomputer110(45710BU) The Portable'I 50B Touchscreen2673A Thermal Printer6940B Multiprogrammer7470A opt 001/002 A4 2 -pen plotter7475A opt 001/002 A3/A46 -pen plotter7910H opt 015 Disk Drive82913A 12 inch Monitor82937A HPIB Interface82938A HPIL Interface82939A Serial Interface82940AGPIO Interface86B Microcomputer9111AGraphics Tablet9121 D Single-sided Disc Drive9122D Dual Double -sided Disc Drive

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9816S Personal Computer9825A opt001-002 Desk TopComputer98256A 256K RAM board, series 2009862A Plotter9872C 8 -pen flatbed plotter9915A Computer

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GENERAL PURPOSE T & MFarnellSSG 520 + TTS 520 Transmission Test Set £4275Fluke7220AComms. Freq. CounterG. P. Industrial

MFL 373 Fault Locator. MINT £395Hewlett Packard

436A Power Meter £1200467AAmplifier £600

3403C True RMSVoltmeter £18503406A Sampling

Voltmeter £12503465A 41/2 DigitD.M.M. £3504271A 1 MHz Digital LCRmeter £25004271 B Digital LCRMeter £25005300B + 5305B 1300MHzCounter £4955381A 80 MHzCounter £225

WA8447A Amplifier £4008447D Amplifier £600MarconiTF 1246 Oscillator £500TF 1313A LCR Bridge0.1% £750TF 2173 Synchroniser

for2016 £450TF 2304 Modulation

Meter £450TF 2603 RF

Millivoltmeter £495TF 2604 Voltmeter £425

TF 2702 InductorAnalyser £950

TF 2905/8 TV Pulse .Generator £750

TF 2915 Data Monitor £1200TF 2950/5 Mobile Radio T.S. £1350PhilipsPM5580 IF Modulator £3000PM5581 RF Convertor £1000PM5582 RF Convertor £1000Tektronix520A Vectorscope (NTSC)521A PAL VectorscopeSi Sampling HeadS.3A Sampling Head1411C opt 03 TV Signal GeneratorA6901 Isolation Monitor4041 System ControllerPM 102 Personality ModulePM 107 Personality ModulePM 108 Personality Module

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All prices are exclusive of VAT and correct at time of going to press Carriage and packing charges extra A copy of our trading conditions is available on request

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COMMENT

EDITORPhilip Darrington

DEPUTY EDITORGeoffrey Shorter, B.Sc.

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Guest editorial. contributed by Bob Giddy. General Manager. NEC Electronics (UK) Ltd.

Eastern promiseIt could be argued that the British industrial machine has not always benefitted from this country'smembership of the EEC. For the UK electronics industry to succeed in Europe, the entrenchedforces of the other European multi -nationals must give up some of their long -held territory -a

gesture they are unlikely to offer voluntarily, particularly in those sectors regulated by local PTTs.In the US. hawking British electronics is a little like trying to sell sand to the Arabs - many companies

have tried it. but have not prospered.The third largest, and fastest growing, market area is the Pacific basin excluding, for the moment,

Japan. Most of this area, particularly Thailand, the Philippines and Taiwan, is part of the US capitalinvestment zone. These countries are cash -rich with low overheads and are already recipients oftechnology transfers. As such, they are heavily dependent upon United States investment and thus aredifficult market areas for British companies.

It is clear that new marketing areas must be sought in which new rules can be applied. We must findmarkets that are able and willing to absorb our products. It "necessity is the mother of invention," thenneed is the father of demand.

The UK has a good record for innovation and design. Its reputation for reliable manufacturing has not,until recently, been so good. A partnership with a nation possessing complementary skills to our ownwould surely be fruitful.

The solutions I proposed to these two problems of finding new markets and partners may seemfoolhardy on the surface, but we do have precedents.

As partners, I suggest the Japanese. There are many similarities between the countries and our people.We are islanders and consider ourselves somehow different to continentals. We are, or have been,successful in developing markets. We are monarchies, with consequent political stability. The British arefamous (or notorious for compromise - the Japanese will avoid conflict if at all possible. In bothcountries, a man's word is reputed to be his bond.

The Japanese have a truly awesome reputation for manufacturing technology. It is claimed andrecognized, even by the Japanese, that they are not innovative. Perhaps this is why they modelled theireducation system upon our own and may be why they so admire and respect British innovation anddesign skills. The Japanese need to develop strategic friendships: their spectacular successes havebrought them problems of trade friction, dumping disputes etc. They are looking for joint -venturepartners, not partners of the purely commercial kind. of which the result is just another distributor. Thepartnership must offer joint benefit, as in the British Leyland/Honda venture, where each partner's skillscomplemented the others.

As a solution to the problem of a new market area, the Comecon countries have a great deal to offer (ldid say it might appear foolhardy). The population of these countries is greater than that of Europe andabout the same as that of North America; if China is included, then it is about 2.5 times that of the US. Tocultivate the Comecon market would clearly be politically sensitive and sale of some types of equipmentwould not be permitted. It must be said that it is difficult to see how the sale of a few computers, or even acomplete communications system, is going to destabilize the military status quo. However. theseequipments, if they are to be marketed successfully, must be free of restrictions on vital components -avery real problem when a product is obtained from US companies.

The germination and growth of such a partnership. targetted at new markets, would take time toestablish. To allow for this lead-time, the next generation ofequipments should be of overriding interest.In my own field of semiconductors, for example, we should aim at the rapidly evolving field of computersand communications. As before, it will be semiconducting technology that will define the architecture ofthe equipment. Starting at the very beginning, we should explore areas of interest, be it research, design,manufacturing, or some of each. We should share the reponsibilities and agree the form in which themarketing of these future products is to be carried out. In other words, the two partners must beintrinsically locked together, thus avoiding the usual importer/exporter relationship. The partnerswould possess complementary skills which would be harnessed and directed towards working to acommon goal.

Our two nat ions are a world apart, but that does mean they are well placed to see both sides.

Electronics & W.reless World is published monthly USPS687540 Current issue price £1.95, back issues (if available)£2.10 at Retail and Trade Counter, Units 1&2, BanksideIndustrial Centre, Hopton Street, London SE1 Telephone:01-928 3567. By post, current issue £2.25, back issues (ifavailable) £2.50. Order and payments to 301 Electronicsand Wireless World, Quadrant House, The Quadrant,Sutton, Surrey SM2 5AS. Cheques should be payable toReed Business Publishing Ltd. Editorial & Advertisingoffices: EWW Quadrant House, The Quadrant, Sutton,Surrey SM2 5AS. Telephones: Editoria: 01-661 3614.Advertising 01-661 3130 01-661 8469 Telex: 892084B1SPRS G (REP, Facsimile: 01-661 2071 (Groups II & 1111Beeline: 01-661 3978 or 01-661 8986. 300 baud, 7 data bits,even parity, one stop -bit. Send ctrl -Q, then EWW to start;NNNN to sign off. Subscription rates: 1 year £18 UK and£23 outside UK Student rates: I year £11.50 UK and

£14.50 outside UK. Distribution: Quadrant House, TheQuadrant, Sutton, Surrey SM2 5AS. Telephone 01-6613248. Subscriptions: Oakfield House, Perrymount Road,Haywards Heath, Sussex RH16 31)11. Telephone 0444459188. Please notify a change of address. USA: 849.40surface mail, $102.60 airmail. Reed Business PublishingI USA ). Subscriptions Office. 21)5 E. 42nd Street, NY 10117.Overseas advertising agents: France and Belgium:Pierre Mussard, 18-20 Place de la Madeleine, Paris 75(8)8.United States of America: Jay Feinman, Reed BusinessPublishing Ltd. 205 East 42nd Street, New York, NY10017. Telephone (212) 867-2080 Telex 23827. USAmailing agents: Mercury Airfreight International Ltd,Inc., 101b1 Englehard Ave, Avenel N.J. 07001. 2nd classpostage paid at Rahway N.J. Postmaster - send address tothe above. GReed Business Publishing Ltd 1986. ISBN0043 6062


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Advances in spectrumanalysis

Undoubtedly the most versatile item of test equipmentused by r.f. and microwave engineers, the modern

spectrum analyser provides a host of functions that wouldhave been impossible a few years ago.

The origins of spectrum analysis can betraced back to the work of Frenchmathematician Baron Jean -Baptiste

Fourier in the early part of the nineteethcentury. He showed that any waveform,however complex, can be generated byadding together sine waves. The converse ofthis is also true, any complex waveform canbe broken down into individual sine waves.Spectrum analysis is thus Fourier analysis,breaking down a signal into its componentfrequencies.

A spectrum analyser is undoubtedly themost versatile item of test equipment usedby r.f. and microwave engineers. It not onlyseparates a signal into its component partsbut also measures power and frequency,determines distortion, noise and intermo-dulation, identifies spurious signals, andevaluates modulated signals.

Before studying spectrum analysis furth-er, examine more closely what a spectrumanalyser does and compare it with themeasurements that can be made by anoscilloscope. Figure 1 shows a three-dimensional graph with three mutually per-pendicular axes calibrated in terms of ampli-tude, frequency and time. The signal shownconsists of a sinewave with a second harmo-nic. The process of signal analysis is todisplay the components of such a signal.Two-dimensional displays are used, as three-dimensional displays are not practical.

A time -domain display of amplitude ver-sus time is the familiar type of oscilloscopetrace. Only a single waveform would be seenwhen the signal in Fig. 1 is viewed - thewaveform with the solid line - but there arein fact two sinusoids present, as shown bythe dotted lines. As oscilloscope shows thetotal waveform and does not therefore sepa-rate out the individual components.

Analysing the same signal in the frequen-cy domain, as would be seen on a spectrumanalyser, reveals the two separate compo-nents. The amplitude and frequency of thefundamental is represented by a single ver-tical line and the second harmonic by ashorter line, clearly seen to the right of thefundamental.

Oscilloscopes are not so widely used by r.f.and microwave engineers because the fre-quency range of oscilloscopes is limited;they are hardly ever used at frequenciesabove 1GHz.

STEVE GLEDHILL

TIME DOMAIN RitiltIENCY 00MA1N

1. Signal analysis, the relationship between frequency, time and amplitude.

Moor

-41Eimolt fieroral fOtekrs

Lot; ouroliber

cod detector

Tracking generator o/p

2. Heterodyne spectrum analyser block diagram.

The display of amplitude against frequen-cy is much more useful because spurioussignals, sidebands and noise can also bedetected. Oscilloscopes are not able to iso-late such subtleties of complex signals.

A further advantage of a spectrum analys-er is its high sensitivity; it can measure very

low level signals down to less than 0.1µVsimply because it is selective rather thanbroad -band. It can also display low-levelsignals at the same time as high-level signalsbecause logarithmic amplitude scales areused; an oscilloscope, which has a linearvertical scale, does not have this capability.


IMPLEMENTATION

All r.f. and microwave spectrum analysershave the same basic system configurationbased around the principle of a swept, tuned,superhet radio receiver. Other techniquesare encountered for very low frequencyspectrum analysis but all higher frequencyinstruments have a basic block diagramsimilar to that shown in Fig.2. In practicethe implementation is more complex andthere are many more frequency conversionstages.

Before the input signal is applied to themixer it passes through an input attenuatorso that the sensitivity of the instrument canbe changed. An input filter is generally alsoincluded at this stage to avoid i.f. feed -

through. An input amplifier may also beincorporated.

The mixer converts the input signal to afixed intermediate frequency, at which pointa range of band-pass filters can be switchedin to change selectivity. Further amplifica-tion is included at the i.f. stage to increasesensitivity. Most instruments have a verticalscale calibrated in decibels, and to accom-plish this the signal at the i.f. stage is passedthrough a logarithmic amplifier. The signalis then applied to a detector before beingapplied to the vertical scale of the display.

Video filtering may be incorporated afterthe detector. A low-pass video filter to reducethe statistical variability of displayed noisehelps to reveal coherent signals which mayotherwise be obscured by noise.

The horizontal input of the display isdriven by a variable -amplitude ramp gener-ator also applied to the voltage -controlledoscillator that feeds the mixer. As the rampvoltage is increased the receiver tunes toprogressively higher frequencies and thetrace on the display moves from left to right.A spectrum display is thus generated.

Changing the amplitude of the rampgenerator fed to the oscillator changes thewidth of spectrum which is analysed, sincethe voltage -controlled oscillator sweeps overa greater or lesser frequency range.

The applications of a spectrum analyserare greatly increased if a tracking generator

3. A modern high resolution spectrumanalyser, Marconi Instruments 2385.

Frequency analysisAn alternative method for analysing the frequencies within

a spectrum is offered by a frequency response analyser(f.r.a.) which can provide a precise measurement of gain

and phase of frequencies within a given spectrum.

The analysis of dynamic systems hasbeen of interest to mathematiciansand scientists for centuries. Newton,

Laplace and Volterra, among others, alladdressed the problem of relating theobservable behaviour of dynamic systemsto some form of mathematical descriptor.The origins of the practical approach todynamic analysis are, however, muchmore recent. The advent of radar in the1940s, and the consequent development ofthe remote -operating weapon delivery sys-tem, demanded the provision in quantity ofhigh -accuracy, fast -responding servo -controlled actuation systems. Verificationof the performance of such systems underoperational conditions was not possible;hence, complex test procedures were de-vised to determine their acceptability foroperational use. The principles of practicaldynamic analysis were founded.

In 1954 Solartron, in collaboration withthe then Admiralty Research Laboratoriesat Teddington, developed the firstcommercially -available general purposedynamic analysis instrument; the VP250

Resolved Component Analyser, the fore-runner of today's frequency response ana-lyser. The instrument is still in use in manymajor testing laboratories throughout theworld. Since then Solartron have carved aniche for themselves and are, they say, theonly producers of stand-alone frequencyresponse analysers in the world.

The f.r.a. works rather like a synthesizedradio receiver; it can sweep through thefrequencies within a range and record theamplitude and phase response of a system.This is displayed (in words and numbers)on the front panel and can also be recordedon a plotter, or transferred to a computerfor further analysis and storage.

Two new instruments have been intro-duced, one of which is aimed at reducingthe cost of the analyses; the other increasesthe frequency range and facilities.

A typical mode of operation involves theuse of an internal generator to stimulatethe system under test. The waveform fre-quency can be automatically swept be-tween user -defined limits with a logarith-mic spacing of frequency increments. A


'vernier' facility allows the operator to varythe frequency, amplitude or d.c. biasmanually in order to find a resonant peak,or a null position and then set an offset forsubsequent measurement. A modulator isincluded for the testing of transducers andsystems which require an a.c. carrier.

It is also possible to synchronize theinstrument to be triggered by an externalsignal, such as a tachometer output whentesting rotating machinery. The 1253 gain -phase analyser has two input channels withamplifiers which automatically range thesignal to ensure the best resolution andoptimum signal/noise ratios for the incom-ing signals. It operates over the frequencyrange 1mHz to 20kHz. Gain and phasemeasurement accuracies are 0.1dB and1.0° respectively. Input signals are digi-tised to 15 -bit resolution using Solartron'spatented pulse width technique, whichensures data integrity and provides a stablefour -digit display. In common with otherinstruments in the range, this analyseruses a single -sine correlation analysistechnique to provide fast and precisemeasurements of both amplitude andphase. The correlation technique rejectsthe harmonic components of a non-linearsystem response, accurately measuring thefundamental component of a signal evenwhen it is buried in noise. A commonanalyzer measures the gain and phaseresponse of the system, thus minimizingchannel mismatching problems for two -channel measurement. The process in-herently rejects harmonics. Noise is re-moved by integrating the signal over anumber of cycles. Each input can beprogrammed to demodulate signals fromsystems operating with an a.c. carrier.

The 40 -character display provides themenus for setting up the instrument aswell as measured data and status informa-tion. Data is presented in either polar orCartesian coordinates along with theappropriate variable (frequency, ampli-

tude, or bias). Results can be calibrated andscaled with a constant or vector. The vectorcan be a previous measurement and read-ings can be made relative to a referencepoint, or systematic errors can be nulled.

Measurement sequences can be storedin program files internally so that regulartests can be repeated. Keyswitch protec-tion of routine measurement sequenciesprevents unauthorized alteration. The in-ternal battery -backed memory can alsostore up to 400 measurements for outputto a printer or plotter through the RS232/423 or CP1B interfaces included. The GPIBinterface also offers automatic, remote,operation.

The instrument offers a simplified levelof frequency analysis which should findapplications in production testing, qualityassurance, the testing of goods suppliedand in educational establishments.

Solartron hopes that the comparativelylow cost of the 1253 (i4800) will open upnew markets and make the instrument ageneral-purpose tool for use by a variety oflaboratories and test facilities.

Enhanced frequency range and resolu-tion are offered by the second instrument,the 1255 (18900), which has all the abovefacilities and offers a 12 -decade frequencyrange, from 1 p.Hz up to 20MHz and a130dB dynamic range, making it ideal fortesting of video amplifiers, filters, crystals,and communications equipment, and formany applications in electrochemistry,solid state physics and mechanical testing.

The instrument features two indepen-dent channels operating in parallel andoffering basic gain and phase accuracy of0.02dB and 0.2° respectively, and a fre-quency resolution of 1:65,536.000.

In addition to frequency responsemeasurements the 1255 measures groupdelay and can modify any results usingstandard arithmetic operators. Up to nineprograms can be stored in permanenteprom storage with keyswitch protection.

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A general-purpose analyser is the Advan-test TR4131 which covers 10kHz to 3.5GHz.Input sensitivity is 116dBm with a dyna-mic range of over 70dB. Available throughChase Electronics. Tel: 01 878 7748.

is included, especially for r.f. types. A track-ing generator provides a swept signal whoseinstantaneous frequency, is always the sameas the input tuned frequency so that thefrequency response of components, devicesor systems can be measured over a widedynamic range. Figure 3 shows a modernhigh, resolution spectrum analyser withbuilt-in tracking generator.

MEASUREMENTS

When measuring distortion the harmonicsof a signal are displayed individually, asshown in Fig. 4. The amplitude of thefundamental and each of the harmonics canbe measured and the total harmonic distor-tion calculated. This figure, and the otherscreen displays mentioned in this article,was obtained by connecting a digital plotterto the instrument to obtain a high qualityhard copy.

A typical display of frequency modulationis shown in Fig.5, where a 1kHz modulationtone has been applied to a narrowband f.m.transmitter. Spectrum occupancy can bemeasured from such a display. Besse! zeroscan also be determined. A Besse! zero occurswhen the amplitude of the carrier or asideband falls to zero, a crucial measure-ment for the calibration of f.m. systems.Amplitude modulation depth, distortion andspurious f.m. can all be readily determined.

The detection and measurement of spu-rious signals is of great importance. Synth-esizers, for example, can generate a numberof unwanted products and these need to bedetermined. Spurious signals and noise canbe generated by all types of electrical andelectronic equipment, and interference maybe caused if such signals are radiated fromthe equipment, or if the noise is conductedalong mains cables or other connectingcables. Spectrum analysers are widely usedto track down such unwanted radiated andconducted signals.

OPERATIONAL ADVANCES

Spectrum analysers have become easier touse over the last 20 years. Earlier instru-ments were highly complex and the operatorhad to be skilled and needed a great deal of


THERE'S A NEW ALTERNATIVETR 4131 SPECTRUM

ANALYSER (10KHz-3.5GHz)The TR 4131 with its wide frequency range is anideal general purpose, portable, spectrumanalyser, perfectly suited for the measurementof UHF harmonic and spurious signals. With asensitivity of -116dBm, and a dynamic range inexcess of 70dB, facililties provided include:frequency and level markers, signal averaging,direct field strength readout This versatile instru-ment offers remarkable cost performance savingsFeatures not Options: as standard GP-IB interface Direct plotter dump CISPR RFI/EMC functions0- Composite video output Signal trackFor applications requiring a tracked signalthere is a choice of two tracking generators- TR 4153 (10KHz-2GHz) and TR 4154(100KHz-3.5GHz).

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SIGMA: A flexible package for signal generation, manipulation and analysis. Unique high-level language, forward and inverse Fast Fourier Transforms, time andfrequency domain convolution, multiplication etc. Features include flexible generation of signals and spectra, ioise, non-linearities, quantisation. Inclusive price f 190.

All packages have been designed for rapid interaction and flexibility and are suitable for use professionally and in teaching. Comprehensive manual and tutorial sessionncluded Details of these and other packages available on request.

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patience. It is instructive to study the areaswhere the operation of spectrum analyzershas been improved in recent designs.

When using a sweeping spectrum analyserit is essential to sweep at the correct speed.Sweeping too fast causes distortion due togroup delay variations in the filter system ofthe analyser such that the displayed signalamplitude and frequency is incorrect. Mod-ern instruments incorporatemicroprocessor -controlled sweep speed con-trols so that the instrument always sweeps atthe correct speed. Where high resolution isrequired the sweep speed may need to be asslow as 100 seconds, and it is easy toappreciate the gross errors that would occurif a sweep of 100ms for example was used forsuch a measurement. Sweep speed is also afunction of video bandwidth if video filteringis used after the detector for noise smoo-thing.

Another area where microprocessor con-trol is now used is in the selection ofsensitivity. To increase the sensitivity of ananalyser the user can either reduce the r.f.input attenuator or increase the i.f. gain.Reducing the input attenuator may overloadthe input mixer. which would cause distor-tion in the instrument. The alternative is toincrease the i.f. gain, but this could increasethe noise to an unacceptable level. Thechoice of which control to operate is notimmediately obvious and is even more in-volved when one considers that the opti-mum noise and distortion trade-off not onlychanges for different signal levels but alsowhen different bandwidth filters areselected. Automatic optimization of r.f. andIf. gain is thus an important innovation,since it prevents the operator from inadver-tently introducing distortion in the measur-ing instrument.

Older instruments initially used long per-sistence tubes to display slow sweeps. Stor-age tubes were introduced as a betteralternative but they are expensive and un-satisfactory for slow sweeps. Digital storageis now used, giving added advantages: forexample, a live trace can be compared with astored one, or two traces can be subtracted.Electronic graticules can also eliminate pa-

rallax error. A further advantage of moderndigital displays is that control settings canalso be shown on the screen for ease ofreading and interpretation.

Perhaps the three most significant im-provements that the microprocessor hasprovided are easier front panel operation,synthesized tuning and programmability.Modern instruments can be controlled froma digital keyboard so that set-ups can berapidly changed. Complete front panel con-trol settings can be held in non-volatilememory. Synthesized tuning is a greatbenefit because not only can the tunedfrequency be entered from a keyboard butthe frequency of tuning is referred to acrystal oscillator for increased accuracy andresolution with a reduction of frequencydrift. Synthesized tuning has other advan-tages: sideband noise is now significantlybetter because of the use of phase -lockedoscillators.

Programmability is increasingly impor-tant. Modern spectrum analysers can be fullyremotely controlled, usually using theGeneral Purpose Interface Bus (GP113).Screen information can be dumped forfurther detailed analysis, for archiving pur-poses or for the determination of the ampli-tude and frequencies of the individual sig-nals.

SPECIFICATION ADVANCES

Many spectrum analyser users have notnecessarily been aware of the amplitudeinaccuracy of their instruments. There aremany sources of uncertainty in the measure-ment chain from the input attenuatorthrough to the logarithmic amplifier anddisplay. To make matters worse the valueschange with temperature and frequency. Inan attempt to improve accuracy, screwdriverpre-set controls have been incorporated onthe front panel, but even when set correctlyuncertainties can exceed ±3 or ±4dB. With-out setting up, the uncertainties can be evenlarger.

Microprocessor control is now used toimprove accuracy and screwdriver pre-setcontrols can be eliminated. The self -

calibration routine which is used in theinstrument shown in Fig.3. is very compre-hensive. Pressing a key on the front panelinitiates the process which includes:- setting the amplitude and frequency of

each of the 12 resolution filters- measuring and correcting for the attenua-

tion of each of the r.f. input attenuatorsteps

- correcting the amplitude response of thesystem by sweeping through the entirefrequency range by routing the built-inprecisely levelled tracking generator intothe input.

The advantage of this self -calibration techni-que is that total level accuracy is improved toa remarkable figure of ±1dB for all levelsand frequencies and for any span or resolu-tion bandwidth.

Spectrum analysers are used to assess thepurity of oscillators by measuring close -innoise and power supply ripple. When car-rying out such close -in measurements, it isessential to use a narrow resolution filter. Afilter that is too wide will swamp low levelsignals close to the carrier; Fig.6 illustratesthis. A signal of 50MHz is analyzed with aspan of 10Hz/division; two traces are shown.The wider response was taken using a 10Hzresolution bandwidth which, up to now, hasbeen the narrowest available on most spec-trum analysers. The narrower response usedthe 3Hz filter. The 10Hz filter could notresolve the low level 50Hz component butthe 3Hz filter clearly shows it.

Improved filter resolution will obviouslybe a very important consideration whenspecifying spectrum analysers. but the shapefactor of the filter as well as the minimumresolution bandwidth is also critical. Theshape factor is the ratio of the 60dB band-width to the 3dB bandwidth.

There is a further bonus from having anarrower filter - spurious signals whichwould otherwise be obscured by the internalnoise floor can be seen. A quality spectrumanalyser typically has a noise figure ofaround 20 to 25dB and a 10Hz filter wouldthus limit the noise floor to typically- 135dBm; a 3Hz filter would reduce thenoise floor by 5dB to around -140dBm. This


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aspect may be important for measurementssuch as synthesizer purity and checking forspurs.

Many spectrum analyser users will besurprised to realise that, until recently, afirst class instrument could only claim a-70dBc or -80dBc intermodulation per-formance. Modern mixer technology andcareful r.f. design can improve this figure totypically greater than -90dBc. An additionalbenefit of a modern design is that gaincompression can effectively be eliminated sothat the operator need not normally worrywhether distortion is generated within theinstrument.

A notable facility is the ability to display asignal with two different vertical scales at thesame time. Adjusting a complex filter foroptimum pass -band ripple and maximumout -of -band attenuation can be time con-suming because adjustments can affect bothcharacteristics. A dual vertical scale, asillustrated in Fig.7, allows the operator tosimultaneously read out of the display storewith two vertical resolutions. In this exam-ple a 12.4MHz low-pass filter is analysedwith one scale of 5dB/division and the otherof 0.5dB/division.

SOFTWARE FEATURES

It has been shown how the man -machineinterface has been improved and automaticoptimization of controls has made measure-ments more foolproof. Specification pointssuch as accuracy, resolution and intermo-dulation performance have been improved.A final area of improvement is due to thesoftware features in an instrument. Thesefurther improve the man -machine interfaceand also provide a number of functions toincrease efficiency and reduce operatortime.

Steerable markers are particularly signifi-cant: a control is used to move a dot over thedisplay so that the frequency and amplitudeof any chosen point can be determined. A'delta marker' facility is particularly useful,which displays the difference in amplitudeand frequency between two points on the

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7. Dual vertical scale used to view simultaneously the overallfrequency response of a filter as well as the pass -band ripple.

screen to simplify measurements such asharmonic distortion or modulation fre-quency.

Markers can also be controlled by keystrokes from the front panel. Functionsknown as 'peak find' and 'next peak' enablethe operator to direct the marker to the peaksignal on the screen and to then identifysuccessively lower amplitude signals. This isparticularly valuable when measuring har-monic distortion, since the amplitude ofeach of the harmonics can be rapidly ascer-tained; such a facility is essential when usedin a remote control application.

The reference level and frequency of tun-ing of a spectrum analyser can be controlledwith markers. Once a marker has identified asignal of interest the operator can simplypress 'Marker sets reference level' and 'Mar-ker sets reference frequency' buttons tobring the chosen signal to the top of thescreen and to the centre of the screen. This isa great advantage over the previous manualmethod. Signal tracking, another softwarefeature, can be used to keep a signal ofinterest at the centre of the screen byre -tuning the instrument if the signal ofinterest is drifting in frequency.

Often it is necessary to make adjustmentsto a device in order to meet a particularspecification. Many operators have resortedto using a grease pencil to draw limit lines onthe screen, but modern software makes thisunnecessary, limits can now be entered fromthe keyboard and the tolerance lines display-ed electronically.

Software manipulation of a sweep is alsouseful. Modern instruments can change thetraditional linear frequency display to alogarithmic display to aid interpretation andanalysis. Software can also digitally compen-sate for the loss and frequency response ofcables and probes. One technique, whichrequires a built-in tracking generator, is toconnect the cable or probe to the trackinggenerator output socket and to carry out afrequency sweep and store the responsevalues in a digital memory. When subse-quent measurements are made the values inthe memory are used to correct the mea-sured value so that a corrected or normal-ized display is given. A further softwarefacility is A- B, one trace subtracted fromanother to assist when comparing two simi-lar signals.

The modern spectrum analyser provides ahost of functions and a specification thatwould have been impossible a few years ago.The new generation of instruments arelower in cost than their predecessors be-cause advanced manufacturing techniquesand complex automatic testing have reducedcosts significantly. A wider range of instru-ments is available now to cater for higherand lower performance and for differentfrequency ranges, so that expensive un-wanted frequency coverage can be avoided.

SJ. Gledhill, B.Sc., M.I.E.E., is product managerfor spectrum analysers with Marconi Instru-ments.

364

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Components temperature effectssupportedBreakpoints and polynominals supportedI = lo' lexpffv'q)/(rilit))-1).Resistors may have inductance etc. etc.Component characteristics can be made tovary with both time and frequencyaccording to any function Offset currentsmay be imposed

Up to 64 connections per model to maincircuit, no limit on number or sizeSignals may be sampled or injectedanywhere.

Interactive mode has powerful editing andinterrupting facilities Batch mode forheavy work allows you to come back.Sparse matrix technique allows typicallyover 500 modes in 512K memory. 8087 (or80287) coprocessors supported.A ring -bound reference manual of over 200pages is an integral part of ECA-2.If you need more convincing. ring us fordetails of money -back trial.ECA-2 costs lust 1675 + VAT, ECA-2compares favourably with well-knownmainframe simulators and is more powerfulthan any other we know available on PC's.

THOSE ENGINEERS software which is available from E99 supports IBM PC's andcompatibles and the range of 3BC microcomputers. As engineers in electronic andmechanical product and process design. we welcome enquiries for other requirements.

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DM 105 - Pocket DVM fromA meter to literally suit allpockets - including the onethat holds the wallet! ir itIts small size offers easy one hand operation, with large. clear,wide-angle display.Rut small does not mean delicate; the DM105 can withstand a 12inch drop without damage, due to its glass epoxy PC boards,shock mounted display and through thermoplastic case.overloads are handled with similar certainty; the resistancerange is protected up to 50(1 dc, AC voltage range to 800V rmsand DC voltage ranges up to 1000V.flattery life is typically 20(X) hours and a LO BATT indicatorsignals 20% battery life remaining.RangesI )C Volts: 2V, 20V, 200V, I kVAC Volts: 200V, 750VFreq Range: 45Hz 450HzDC Current: 2 mA, 20 mA.

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High-performance colourgraphics controller

External hardware is minimal using this new displaycontroller-all the timing and display manipulation is

done using programmable registers.

It is a sign of the times that one compu-ter publication recently justified its useof a less than state-of-the-art computer -

produced front cover by explaining that hadthe latest technology been used, no-onewould have recognized the cover as havingbeen computer -generated. The degrees ofresolution and hue now possible are quitebreath -taking - in cost as well as perform-ance.

Engineers need to strike a balance be-tween cost and performance and in doing soshould consider the two other vital parts ofthe system: the display device and its viewer.Consider the term high -resolution colourgraphics. Graphics, of which the display ofrecognized alphabets is just one form, is theuse of patterns to convey information. Col-our is a useful adjunct to shape in increasing

JOHN ADAMS

the information conveyed. High resolutionspeaks for itself - or does it? High resolutionof detailed shape, of colour, or of both.

Our current colour -display medium is thethree -gun shadow -mask cathode ray tubewhere three electron guns are so positionedwith respect to a mask that their respectiveelectron beams can only strike certain non -overlapping parts of a screen on the otherside of the mask from the guns. This screenis intricately patterned with three differentphosphors such that only one type is struckby the beam from one particular gun. Onephosphor glows red when struck, one greenand one blue. Early tubes had a mosaicpattern consisting of triads of phosphor dots;nowadays it is common for the screen toconsist of vertical stripes of phosphor.

Imagine a display of a series of finely

SPECIFICATIONS

Resolution Up to 640 (horizontal) by 512 (vertical) dots.Video memory 512Kbyte d -ram.Video format Analogue RGBI (Insert) with 16 levels per channel, adjustable step size.

-4 -bit digital data representing 2 or 4 -bit pel data.-8 -bit multiplexed data representing 8 -bit pel data.-4 -bit data representing one of the colour levels generated by pel data, thespecific colour selected being software programmable.

Sync. format Programmable video display window. Combined or separate syncs.Programmable period, pulse width and interlace. Can be programmed asmaster or slave for sync. purposes.

Display format Up to 16 objects simultaneously displayed. Display window for each object canbe defined to one pel vertically and to one or two pels horizontally dependingon display mode. Objects may be split horizontally and can be scrolledsmoothly in either direction. A drawing priority determines which objects areplaced in front of others. Objects may have opaque or transparent back-grounds.

Object types - Bit -mapped objects may have two, four or eight bits of video memoryrepresenting each pel depending on the colour range required. Attributesavailable are flash (programmable rate and duty cycle) and backgroundtransparency.- Character objects may access up to four programmable character sets eachwith character matrices up to 16 dots high and with widths of six, eight ortwelve dots, or with dot widths individually programmable in two -dot steps forproportional text spacing. Basic attributes are flash and background trans-parency (as for bit -mapped), one of two character sets and choice from fourcolours for foreground and background. Additionally, in full -attribute mode,character -set bank, foreground and background transparency, double width,double height, conceal/reveal, colour invert, flash, underline and full colourdefinition of both foreground and background are programmable on acharacter basis.

Colour/grey 4 from 4096, 16 from 4096 or 256 from 256 colours or grey levels, the thirdscale mode requiring external colour -generating hardware.Pixel rate Up to 25MHz, depending on chip version.

spaced red and black vertical lines on such atube. Provided that the line pitch exceedsthat of the red phosphor stripes the displaywill, from a certain distance, look quiteacceptable. When the pitch starts toapproach that of the stripes certain lines willvanish as their screen positions will notcoincide with a red phosphor stripe. Whenthe pitches are equal you may see all of thelines - or you may see none. It is thisphenomenon which limits detail resolutionto no less that the pitch of the phosphorstripes.

In practice, it is unlikely that the sense ofvertical in terms of image creation will lineup exactly with the stripes, reducing resolu-tion even further. This said, it is amazinghow much interpolation the brain can carryout, particularly with a text display. With theproviso that it is interpolation and notcertainty which is augmenting the image,resolutions down to the stripe pitch areworth experimenting with.

Standard, medium and high -resolutiontubes have stripe pitches of 0.6, 0.4 and0.3mm respectively, although the termsstandard, medium and high -resolution areoften abused in literature describing colourmonitors. For a standard 14in tube with a10% border around the display area, thiscorresponds to approximately 420 horizon-tal phosphor elements. High resolutiontubes will naturally give better resolutionbut at a cost, not just in the tube itself, but inthe entire display device from deflectionlinearity and focussing to shielding fromexternal magnetic fields.

Monochrome monitors consist of a singleelectron gun capable of striking any part of ascreen coated with a single phosphor. Detailresolution is primarily limited by the focus-sing ability of the display but monochromemonitors typically provide resolution asgood as that of the high -resolution colourdisplay at an order of magnitude lower cost.Some redress can be made for the loss ofcolour by the use of varying luminosity.

No mention has yet been made of band-width. Whichever system is chosen, it musthave a video bandwidth which is at leastequal to the pel clock rate.

There is then, a decision to be madebetween resolution, the advantage of colourover shading, and cost. Once these factorsare decided a choice of monitor must bemade. Since this design generates separatesync. and video, a monitor with these attri-


These pencils are a simple image created using 4bitipel in bit -mapped mode and acombined system and video clock of 10MHz.

butes is preferable. For colour this means amonitor with RGB and separate sync. inputs.For monochrome displays it is relatively easyto combine the signals into composite videobut the display is usually better with separatesignals. Next, the right type of input re-sponse should be chosen.

There are three types of response: non-linear (often called t.t.l.) inputs, non-linearwith an intensity control (Km) and ana-logue. Non-linear systems are designed to bedriven digitally and thus only work at onelevel of intensity for each of the threeprimary colours. They are simple and arecommon in low-cost systems. The RGBI typeis an advance in that it has a fourth digitalinput which steps display luminance to givetwo intensities for each primary colour. Thismaintains the on -off nature of the colourinputs but it provides 16 rather than 8colours. IBM colour systems use RGBI. Thedesign to be described can produce 4096distinct colours by the use of analoguesignals, and so an analogue monitor shouldbe chosen.

Finally the line -scan frequency has to be

chosen. Normally line -scan frequency is

15.625kHz but this low frequency has thedisadvantage that at a 50Hz frame rate, onlyabout 290 displayable scan lines are drawn inthe frame period, limiting the vertical re-solution. To counter this, monitors withline -scan frequencies as high as 60kHz cannow be obtained, giving a vertical resolutionof 1000 elements. The disadvantage of thesehigher performance displays is that theshorter line period leaves less time for pelconstruction and thus demands a higherperformance from the driving circuits.

This design can produce a display of up to512 lines, for which a line -scan frequency of31kHz would be suitable for a 50Hz-refreshdisplay. At this line -scan frequency, eachline lasts approximately 33p.s. A scan linecomprising a maximum of 640 horizontalpicture elements, or pets, can be producedby this system in 25.6µs, which is wellwithin the line -scan period.

Note that it is dangerous to attempt tooperate a display at a line -scan frequencydifferent from that for which it was designed.In order to minimize the drive power re-

quired most scanning systems are resonantand any significant shift away from thatresonant point increases the load on thedriving elements, resulting in their prema-ture failure.

Some systems offer extra vertical resolu-tion by using interlaced sync. and videotechniques. There is a minimum frame rate,about 40Hz, below which persistence ofvision fails to fill the gap between one viewedframe and the next. To avoid the appearanceof flicker and yet permit a slower frame rateand thus more vertical scan lines, interlac-ing makes use of an optical illusion to make areal screen update frequency appear to betwice what it actually is. It does this bydrawing all of the odd lines of the display,then the even ones alternately - and itworks, provided that the odd and evenimages are similar.

Similar odd and even images occur intelevision but not in computer displays,particularly of text. To get the greater detailin a computer display odd and even parts of abigger video memory are accessed whenconstructing the interlaced images and sothere is no guarantee that the odd part willbear any relation to the even one. Suchdisplays flicker which is very wearing, butworse, the flicker varies according to howdifferent the odd and even parts are; charac-ters E, F and s flicker far more than 1, ! and /.

An ideal colour display is a monitorcapable of operating with a range of linefrequencies such as the NEC JC-1401P3Aused for the photographs in these artiles.This monitor's screen is based upon triads ofdots rather than stripes and its dot pitch is0.31mm. Signal inputs can be t.t.l. RCB, t.t.l.RGBI or analogue and scanning and synchro-nizing to any line -scan frequency in therange 15.5-35kHz is automatic. This permitsnon -flickering displays of up to 800 by 560picture elements.

Having chosen a satisfactory display for-mat the criteria for the display controllermust be established. The number of compo-nents should be minimal and the circuitsused should be off -the -shelf, yet provide theflexibility normally associated with custom -design chips. A new integrated circuit withthese facilities is the Matra video display andstorage device (VSDD), the 82716. In itssimplest configuration this is the nearestthing yet to a one -chip colour -graphicssystem needing only the addition of a blockof dynamic memory to form a complete unitwith a microprocessor bus interface at oneend and a sync. and analogue or digital RGBIinterface at the other. Add to this thevirtually complete software programmabil-ity of the device and the ideal is approached.

Display controllers have a block of mem-ory storing bit patterns corresponding to thepatterns to be displayed. Early controllerswere little more than address generators,scanning sequentially through the memoryand producing synchronizing pulses forevery display row and screen of memorylocations scanned. These pulses would syn-chronize the display with accessing of data inmemory. Separate circuitry, if necessary,would convert the bytes of data from thememory into a bit stream for turning thec.r.t. beam on and off.

ELECTRONICS & WIRELESS WORLD369

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A very popular device of this sort is the6845. This device is fully programmable interms of memory size scanned, display ele-ments per displayed line and displayed linesper screen. As well as simple scanning ofmemory the 6845 can be made to subdivideits address bus into three sections so that thecodes being fetched from memory can betranslated into one of several possible bitpatterns depending upon the value held inthe middle addressing section. By thismeans the memory codes may be interpretedas characters, one character code generatinga sequence of complex but predefined bitpatterns stored in a character generator.

When predefined patterns such as theAscii character set are being used as de-scribed above, memory requirement is quitemodest; a 2Kbyte ram and 2Kbyte character -

generator rom are adequate. When randomgraphic plotting is required then there mustbe at least a one -for -one relationship be-tween bits in memory and picture elementsdisplayed. If one bit represents a pel thenthat pel is either on or off, precluding the useof colour or shade. Two bits make possibilefour colours and shades, four bits provide 16,etc. A display of 432 -by -288 pels with fourbits per pel requires almost 64Kbyte ofmemory.

Two schools of thought have developedover how to handle such large amounts ofmemory. One technique, as exemplified inthe NEC7220, is to have a red 'plane' ofmemory, a 'green' plane, a 'blue' plane andperhaps an attribute 'plane', the latter in-dicating whether the element is to flash, tobe bold, to be colour -inverted etc. With one

A typical example of the application is my p.c.b. design software using adisplay of 384 by 288 pels. There are four objects in use here. The main object is a twobit-per-pel graphics object of 40Kbytes in size representing the two layout sides. Ashorizontal definition is to more than 320 pe Is the high -resolution moc'e is in use, meaningthat the minimum horizontal scroll is two pels (see Object descriptor, Word 1).

So that the drawing cursor can be placed over any pel in the layout window, two cursorwindows are defined. Both have the attribute of blink and of background transparency (sothat their window outlines do not obscure layout detail). bit the actual cr )55 in the windowis displaced one pel horizontally in one of the windows.

Software selects which cursor is used depending upon whether the horizontal cursorcoordinate is odd or even, so even though the layout scrolls in jumps of two pels. thecursor may be made to move in steps of one. The fourth window hEs simple -characterattributes, is six pels-per-character wide and uses a character generator with asix -by -nine dot aspect. It reports program status to the user. Scrolling is instantaneous asit only involves rewriting a table parameter not a complete window. Likewise, switchingactive layout side is immediate. With a processor running at full speed this imageoccupies about 25% of the available construction time.

bit per plane, i.e. four bits per pel, eightcolours plus one attribute of 16 colours (ifthe attribute is bold) can be achieved.

There is a lack of flexibility in thisapproach as the number of planes will haveto match the highest number of bits-per-pelthat the system will be called on to provide,wasting memory in other modes. Newersystems tend to use one block of memory ascontinuous display data, each pel beingrepresented by n sequential bits which arefetched and then translated into one of 2"colour codes.

Neither technique appears to work wellwhen graphits and characters are mixedsince to easily fit characters into asequentially -organized graphics memorythe cell size for the character has to bebinarily related. In practice, this means an

eight -by -eight -dot matrix, resulting in thesquat characters seen in most lower -costcolour systems. Interspersing a charactergenerator rom is also a technical problem.Most systems solve this by not storing thecharacter code but expanding it into itsgraphic equivalent before sending it to videomemory. This takes a lot of time, althoughnot as long as is taken to work out whichcharacter is actually at a screen location!

The VSDD solves this, and several otherproblems, by having just one block of mem-ory and letting the host computer instructthe VSDD as to which areas are to be used forgraphic display, which for character displayand which for character generator storage.The device is highly programmable; almostall of its own registers are stored in thismemory array. These processor -like regis-

370ELECTRONICS & WIRELESS WORLD

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016

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Fig. 1 For bit -mapped objects, an object -descriptor table within the VSDD containsthe object's memory address, its width, andthe X coordinate of its left-hand side. In-formation from this table forms a pointer topel data in memory.

Width

ObjectScan n-1

ObjectScan n-2

To pixel

processor

Object

data forobjectin d -ram

Fig.3 With bit -map objects, information from the object descriptortable is fed directly into a buffer whereas with character -typeobjects, Ascii data from video memory is combined w th the slicenumber and selected character -generator base address. Thiscombined information is used to extract and pass pel data fromthe character generator to the video buffer.

Fig.2 Information on character -type objects is held in a similar wayto that for bit -map objects but used differently.

IChar 15

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Char 11 Char 10

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Char 7 Char 6

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ters indicate the memory positions of up to16 'objects' and up to four character gener-ators each containing up to 256 characters.Timing parameters, object descriptor tables,a colour look -up table and an access table arealso contained in these registers.

An object descriptor contains the '0'address of the object in the video memory,the object width and the X coordinate of theleft-hand side of the object. When describinga bit -mapped object, it also includes thenumber of bits per pel (2, 4 or 8). the quarterof the colour look -up table to be used whenusing two bits-per-pel and the object blinkand transparency attributes. When describ-ing a character object, it also includes thestarting slice of character dot row ( to permitsmooth scrolling), the character width (6.8.12, 16 dots or proportional spacing), charac-ter generator to be used, colour and mode.

In full attribute mode, where three bytesinstead of one are used to store informationabout each character, extra attributes areforeground and background colours, char-acter height, character width, underliningblinking, colour inversion, conceal/reveal


(as in Teletext), alternate character set andtransparency.

Figure 1 shows how parameters from theobject descriptor table are used to form apointer to the pel data in video memory.Character objects use a similar process asshown in Fig. 2. In the former case, informa-tion accessed is fed directly into a videobuffer. For character objects the Ascii valuedrawn from the video memory is combinedwith the slice number and selectedcharacter -generator base address: pel data isthen extracted and passed from the charac-ter generator to the video buffer, Fig. 3.

The access table is a general map of thescreen consisting of as many words as thereare to be displayed lines. Within each word,each of the 16 bits can be programmed toturn the display of an object on or off: a setbit results in toggling of the current displaystatus for that object.

A pointer to the currently -displayed line isused to get the word into the VSDD. Fromthere the word can be combined with thebase address of the object descriptor table toform a pointer to the specific object's de-scriptors. Fig. 4. By modifying the accesstable and the object's X coordinate, objectsmay be shifted around the screen or display-ed in sections down the screen as required -in tune with the window concept.

The objects have a drawing hierarchy soobjects with a high priority overwrite thosewith a low priority when they are bothmapped to appear on the same part of thedisplay screen. This priority can be easilychanged to bring objects to the foreground.

to define one of an object'scolours as 'transparent' so that a backgroundobject can still be seen in the background.

Once programmed, the VSDD takes fullresponsibility for the construction of displayof up to 640 -by -512 pels as well as arbitratingrequests for video -memory access from thehost system. There is a limit to how complexan image can be formed which is a functionof processor clock speed, display -line period,number of objects, object type (character orgraphic) and number of host requests. TheVSDD can be programmed to only allow acertain number of host high -priority accessper line -scan and has a 'construction -timeoverflow' output which can be used to signalto the host system that the VSDD is gettinginto difficulties.

For highly complex systems it is possibleto literally piggyback one VSDD and itsmemory onto another and program them toconstruct each alternate line, improvingpotential performance several -fold. Usingone VSDD, maximum processor speed, twobits per pel, eight objects and a 432 -by -288 -

line display, approximately 2200 pels can beconstructed on a line. This could be fivefull-size objects and three 8-pel ones (cur-sors for example).

Complexity depends on the image typesince the VSDD is designed to make use ofd -ram page mode. Using page mode, anumber of adjacent memory loctions - 512for a 256Kbit device - can be accessed morequickly than using normal d -ram accesses:512 adjacent locations represent 4096 se-quential pels. This mode can be used withbit -mapped images since the pel data is

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Fig.4 Addressing access and object descriptor tables. By modifying the access tableand the object's X coordinate, objects may be shifted around the screen or displayed insections down the screen.

Fig.5 Memory mapping. To the host, VSDD lookslike two memory windows - a fixed one forregisters and a variable one for data. Immediatelyafter reset, the register window appears at 400 to41F in the host memory map.

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indeed sequential in memory hut it does notwork with character displays since the d -ramis constantly switching between characterand character -generator accesses. In prac-tice, this limits the construction capabilityto scan lines containing no more than about110 plain or 96 full -attribute characters.

To the host the VSDD looks like two

memory windows, the VSDD acting as theaccess arbitrator. The register window is to a32 -byte segment of the video memory whichthe VSDD uses to store 16 control words.These control words define the type and sizeof memory being used for display storage,the locations of the various tables andcharacter generators in the memory, system


parameters such as character dot height.interlace, priority access count etc., size andmapping of the video memory window andthe mapping of the register segment.

Size of the data window varies. Im-mediately after a hardware reset the registerwindow appears at addresses 40016 to 41616in the host memory map. This is the onlyunprogrammable feature of the VSDD;where the data window appears in a 17 -bitaddress range of the host memory map.where it appears in the video memory andsize of the data window are all pro-grammable. This mapping is process isillustrated in Fig. 5.

As access to the video memory has to bearbitrated the host may not get immediateaccess to it. Two techniques are provided tocope with this non-random access. Anactive -high ituw, active -low WAIT signal, RDY,is provided for directly driving processorswhich can extend bus cycles by testing thestate of a RDY or WAIT input pin. For those thatdo not, and must thus execute fixed -lengthbus transactions, it is possible to programthe VSDD to work in pipeline mode. In thismode the current read/write cycle reads or

SPECIAL OFFER

A limited number of VSDD display controllers is being made available to EWW readers at a specialfully -inclusive price of 139.86 as.opposed to the normal one-off price around 164.

Theses 12MHz p.l.c.c. devices, with the full part number S82716.3, can be obtained by sending acheque made payable to Thame Components to Jacqueline Cole, Thame Components Ltd, ThemePark Road, Thame, Oxon 0X9 3XD. The G82716.3 in a pin -grid array package is also available at/45.80 fully inclusive. This offer is limited to one device per reader.

writes to the video memory address used inthe previous cycle, the current address beingstored and then used during the next cycle.

What actually happens in the cycle beforethe current one is that, as soon as is possible.the VSDD reads that location and stores thevalue. If the current cycle is a read then thisdata is immediately available to the host. If itis a write cycle then the input data is

immediately stored by the VSDD and writtento video memory as soon as possible. This isfollowed by a read -and -store of the data atthe address used in the current cycle, readyfor the next one.

It would, of course, still be possible tooverrun the VSDD in this mode. Leavingtwenty VSDD video system clock cyclesbetween one pipeline access and the next will

make sure that this does not occur. Onebonus of not using the Rm . signal is that it canbe programmed to act as a free -access

indicator. This signal is active when theVSDD is idling, i.e. it has finished preparingthe next scan line of data, and thus tells theprocessor that it can have full access to thevideo memory.

Programming and hardware implementa-tion of the VSDD graphics controller aresubjects of the next article. A completecircuit interfacing to 64180 (Z80 -like) sig-nals at one end and an kGB monitor at theother will be given, as will p.c.b. details.

Increased resolutionfrom an a-to -d converter

'Dither' and an averaging process provideinterpolation between steps

Eight-bit A to D converters are com-mon and very convenient to use witheight -bit data buses. However, there

are times when it is either beneficial ornecessary to achieve a higher resolutionthan can be given directly from the conver-ter. The methods described below, in somecircumstances, enable a higher bit resolu-tion to be achieved than is directly readablefrom the converter.

METHOD

To understand how the method works, it isfirst necessary to appreciate what is meantby a converter with a particular number ofbits, and what are the implications.

An analogue -to -digital converter, as the

R. A. BECK

name implies, converts an analogue signal(which therefore has an infinite number ofdiscrete levels) to a digital number within aparticular range: it has a quantizing effect.The number of different levels which can berecognized by the a -to -d converter dependson the type of the device, but for the sake ofexample, assume that it is an eight -bit a -to -dconverter. There are therefore, 28 discretelevels, which is 256. If the a -to -d converterdigitizes voltages in the range 0 to 2.56 volts,each quantized step is 2.56/256 = 10mV.This means that in digitizing a direct volt-age, a different number is produced from theconverter for every 10mV change in level.

One can imagine the converter as being a256 -rung step -ladder lying down on theground: each rung of the ladder represents aquantization level change. The voltage that

the 'ladder' is trying to quantize can beimagined as stick being placed between therungs of the ladder. If the stick is exactly on arung, the number given from the converterat successive conversions will rapidly changeback and forth between the two levels. If thishappens one knows exactly where the stick isand therefore exactly what the voltage is. Ifthe stick now moves between a pair of rungs,a single, constant number will be given outfrom the a -to -d converter representing be-tween which pair rungs the stick lies. Thevoltage, at an instant, cannot be read moreaccurately than the width of the rungs, andin this case, it is 10mV.

If one assumes that the rungs are equallyspaced, one can read where the stick iswithin a pair of rungs provided one is able tocondition the stick movement. The method


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Measured(noise) Error

0.000 0.118 -0.004 -0.004 0.486 0.000 0.118 0.003 0.0030.100 0.118 0.104 0.004 0.043 0.100 0.118 0.118 0.0180.200 0.118 0.199 -0.001 0.121 0.200 0.118 0.205 0.0050.300 0.118 0.306 0.006 0.374 0.300 0.118 0.310 0.0100.400 0.549 0.401 0.001 0.358 0.400 0.549 0.411 0.0110.500 0.549 0.502 0.002 0.530 0.500 0.549 0.498 -0.0020.600 0.549 0.603 0.003 0.168 0.600 0.549 0.576 -0.0240.700 0.549 0.697 -0.003 0.304 0.700 0.549 0.731 0.0310.800 0.980 0.792 -0.008 0.495 0.800 0.980 0.809 0.0090.900 0.980 0.900 -0.000 0.358 0.900 0.980 0.913 0.0131.000 0.980 1.007 0.007 0.166 1.000 0.980 0.954 -0.0161.100 0.980 1.095 -0.005 0.322 1.100 0.980 1.085 -0.0151.200 1.412 1.203 0.003 0.199 1.200 1.412 1.206 0.0061.300 1.412 1.297 -0.003 0.094 1.300 1.412 1.334 0.0341.400 1.412 1.405 0.005 0.487 1.400 1.412 1.412 0.0121.500 1.412 1.499 -0.001 0.540 1.500 1.412 1.483 -0.0171.600 1.412 1.594 -0.006 0.203 1.600 1.412 1.577 -0.0231.700 1.843 1.702 0.002 0.310 1.700 1.843 1.698 -0.0021.800 1.843 1.796 -0.004 0.177 1.800 1.843 1.823 0.0231.900 1.843 1.897 -0.003 0.234 1.900 1.843 1.880 -0.0202.000 1.843 2.005 0.005 0.045 2.000 1.843 1.978 -0.022

is to move the stick randomly over a numberof rungs, making sure not to permanentlypull the stick off to one side while one isdoing so. Then, a number of instantaneousreadings are taken of the stick's position andall the readings are averaged. This reducesthe effect of the quantization. The effect issimilar to averaging the numbers 5 and 6,5+6/2=5.5. Both the numbers are integers,but the averaged result is between the two.

Provided the stick moves over at least tworungs, and a sufficient number of samplesare averaged, quite an accurate result can beachieved. In electrical terms, noise is addedto the signal to be measured and number ofreadings are taken to suit the accuracy of theresult required. Noise is, of course, noisy, somore readings must be averaged to achievean accurate result than one immediatelythinks; averaging about 100 samples isusually adequate. This method can also workfor a.c. signals. The proviso is that thetrigger must be taken from the 'clean'source. The amount of noise which must beadded has to be controlled quite closely: ifthe amplitude is not sufficiently great, themethod will not work, and if it is too large.one can get worse readings than not bother-ing with this method at all.

ALTERNATIVE METHOD

Adding noise to the signal prevents aliasingcaused by the sampling frequency of thea -to -d converter and the a.c. component ofthe input signal. Excellent results can beobtained with fewer samples by using analternative method, provided the rela-tionship between the two frequencies can beassured.

Noise, by its very nature, is difficult togenerate in a controlled manner. Wave-forms, on the other hand, are easy togenerate and control, but cause aliasingwhen they are added to a direct voltagewhich the converter tries to measure. Thesame result of reducing the quantizationeffect can be achieved by adding a controlledwaveform to a direct voltage, rather thanadding noise, provided the relationship be-tween the sampling frequency of the a -to -dconverter and the frequency of the superim-posed waveform in controlled.

Part of computer simulation of effect onreading of noise added to d.c. (a) and oftriangular wave (b). when a -to -d converterused in temperature measurement. Col-umn 5 in (b) is the difference between thestart of conversion and the start of therandomly asynchronous triangular wave.

The solution is to run the superimposedwaveform, which most conveniently couldbe a triangular wave, at a frequency whichenables a high enough number of samplesover one period of the added waveform sothat aliasing does not occur, and for thesamples to be averaged over an integralnumber of superimposed waveform periods.

An example of a configuration whichworked very well and which was im-plemented in a temperature measuring cir-cuit, was to measure temperature to anaccuracy better than 0.1 degrees over atemperature range of -40 to +70 degreesCentigrade, using an eight -bit a -to -d conver-ter. The resolution obtained by using theconverter to give a single number fromwhich the temperature would be calculatedwould be (70+40)/256=0.43 degrees.

To gain greater resolution. a triangularwave was added to the direct voltage repre-senting the temperature. The period was setto 1/64 of the a -to -d converter period, so thatfor each complete wavelength of the triangu-lar waveform. 64 samples were taken andaveraged. Where on the triangular waveformthe a -to -d converter started to take readingswas of no consequence due to the readingsbeing averaged over one complete wave-form, and the waveform and sampling fre-quencies were not required to be phaselocked.

Part of a computer simulation is shownfor the temperature range 0 to 10 degreesCentigrade, in 0.1 degree steps. The tabu-lated results show the greatest error to be0.013 degrees, a theoretical accuracy ofseven times better than that required of thecircuit.

The peak to peak amplitude of the wave-form used here was the equivalent of 10degrees or 23 quantization levels, but is byno means critical. It should be greater thanfive quantization levels and less than 20. Thea -to -d converter was set to sample at a period

of 10 ms, and the triangular waveform aperiod of 640 ms. These frequencies werechosen as they were convenient to generatefrom the frequencies available on the board.

ACCURACIES

The above discussion assumes that eachquantization level is precisely equal to everyother, and this is clearly not going to be thecase. In general, the accuracy to which thequantization levels are manufactured reflectthe bit accuracy of the a -to -d converter; i.e.the range of accuracies usually available is inthe range 1/4 to 1 bit or quantization level.

one should bear in mind that thelarger the amplitude of the superimposedwaveform, the smaller the absolute error islikely to be, as the averaging occurs over agreater number of quantization levels.

In the example, the requirement was notso much for absolute accuracy, as an accu-rate reading of temperature was not re-quired, but for the detection of relativelysmall temperature changes, which might bein the range 0.1 to 20 degrees. This techni-que provided a satisfactory solution to whatwas initially thought an insoluble problem.Since the a -to -d converter hardware hadalready been designed and it was not thenpossible to change the type of converter.

PENALTIES

The major penalty for this method is likely tobe time. To achieve the required accuracy inthe example, 64 samples must be taken foraveraging. The whole cycle time for eachsuccessive reading increases from 10 ms to640 ms (the time taken to average thereadings can be carried out in a very shorttime relative to the cycle time. However, asthe temperature changes minutely withineach 640 ms cycle time, the time penalty is ofno consequence.

Equally, in other instances where a num-ber of conversions can be averaged withoutimpairment to the operation of the system,the method can achieve very satisfactoryresults.

A little extra hardware is required, alongwith greater program length and complex-ity, but as usual, one cannot get somethingfor nothing!


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376



TSATELLITE SYSTEMSFranco-German

d.b.s.If Arianespace manages to keepto its announced programme oflaunches, both France and Ger-many will have direct broadcast-ing satellites in orbit by the endof this year. Germany's TV -Sat 1and France's TDF-1 are due to belaunched on Ariane 2 rockets andpropelled to a slot in the geosta-tionary orbit at 19°W.

These two d.b.s. spacecraft arevery similar, having been builtmore or less simultaneously by aFranco-German manufacturingconsortium. Called Euro-satellite, it was formed by Aeros-patiale and Alcatel -ThomsonEspace of France together withMBB-ERNO, AEG-Telefunkenand ANT of W. Germany. Belgianand Swedish firms are also in-volved. Overall management isby a joint committee represent-ing the French Space Agency(CNES), Telediffusion de France(TDF), the German aerospaceR&D institute (DFVLR) and theGerman Bundespost. The manufacturing programme is also pro-viding a common, spare satellite.

The photo shows TDF-1 beingprepared for tests in an Aerospa-tiale clean room at Cannes,France. The central body mea-sures 2.4m x 1.6m x 2.3mwhile the total height is 6.5m.Overall weight is 2075 kg. Whenthe folded solar panels are fullyextended the spacecraft is 19mwide from tip to tip. Power sup-plied by these solar panels is3.2kW (at the end of the satel-lite's 7 -year lifetime).

Like other satellites with thistype of structure, the TDF-1 andTV -Sat 1 are stabilized in threeaxes. An antenna position con-trol system cancels the effect ofsmall angular perturbations inthe spacecraft's orientation, sothat the 12-GHz transmittingantenna dish is always kept cor-rectly pointed (to an accuracy of0.1°). Two other antennas aremounted on the structure: a dishfor receiving the uplink signalson 17.8 GHz and a telemetry andcommand antenna.

Each satellite provides fourd.b.s. channels. In each channelthe r.f. output power from thetransponder travelling -wavetube is 230W. When the twosatellites are in operation theyare expected to broadcast with ane.i.r.p. of 63.5 dBW. Their cover-

TDF-1 satellite for d.b.s. at Aerospatiale's factory, Cannes.

age areas, or 'footprints', are ofcourse slightly different for thetwo countries but at the outeredge of these footprints (includ-ing the UK) the power flux densi-ty available to receivers will beabout - 111 dBW/m2. More cen-trally the value will be about -103 dBW/m2. For readers whoprefer to think in terms ofmicrovolts -per -metre fieldstrength contours the last-mentioned figure corresponds toa field strength of 140 µV/m.Domestic receiving dishes ofabout 70cm diameter are ex-pected to be adequate. With thiscoverage the potential audiencefor the d.b.s. services is esti-mated to be 260 million Euro-peans.

A commonsatnav receiver?A small satellite navigation re-ceiver about the size of acigarette packet, costing lessthan £700 and capable of givingposition -fixes in three dimen-sions to an accuracy of a fewcentimetres is a practical possi-bility. Such a receiver could beproduced in large quantities to aworld standardized design foruse with both the American and

the Russian satellite navigationsystems now moving towardscompletion.

This is the opinion of Dr P.Daly of Leeds University. Heoffered it to an IEE audience inLondon in the course of deliver-ing the 22nd Appleton Lectureon "Satellite navigation systemsdeveloped by the super -powers."Dr Daly's opinion is obviously avery well-informed one, as heand his colleagues and studentsin the Electrical and ElectronicEngineering Department havebeen studying the American andRussian systems intensively formany years and developing theirown receivers to work withthem.

His lecture was a survey of twopairs of satnav systems. The firstpair was the USA's Transit andthe USSR's Cicada systems,which are very similar and bothfully operational. The secondpair was the USA's Naystar (alsocalled Global Positioning Sys-tem) and the USSR's GLONASS(Global Navigation SatellitesSystem), which again are verysimilar to each other but in thiscase are both in a pre -operationalstate. Their similarities can beseen as part of the technologicalrivalry between the super-powers.

Transit and Cicada, described

in this journal some years ago,rely on integrated Doppler andwork on v.h.f. at 150 MHz. It wasbecause of their operational per-formance limitations thatNaystar and GLONASS weredeveloped, using the differentbasic principle of measuring sig-nal transit times to calculaterange and working on u.h.f. atabout 1.2 and 1.5 GHz (L band).These new systems are betterbecause they are world-wide, all-weather and continuous. As anillustration of relative perform-ance, Dr Daly mentioned thatwith Naystar the Leeds resear-chers had been able to make 125position fixes in less than anhour, whereas the same numberof fixes using Transit would takeabout a week or more. Furth-ermore, with Transit the velocityof the travelling receiver-say ona ship - must be accuratelyknown.

Whereas Transit and Cicadause satellites in low polar orbits(at about 1000km altitude) withroughly 13/4 -hour periods, thenewer American and Russiansystems have satellites abouthalf -way out to the geostationaryorbit with approximately 12 -hour periods. The GLONASSorbits are about 1000km belowthose of Naystar. Both of thesesystems will be using three orbit-al planes separated by 120°,though at present only two ofthese planes are occupied bysatellites. Naystar was intendedto have a total of 18 satellites infull operation by the end of 1988.But the Challenger shuttle disas-ter has put back this programmeand at present there are six orseven operational spacecraft.GLONASS is in a similar pre-operational phase with eightsatellites launched - which isdone three at a time, inciden-tally.

Dr Daly pointed out that 17complete orbits of GLONASSspacecraft take exactly the sametime as 16 orbits of a Naystarspacecraft. So after 17 GLONASSorbits the two systems comeback into precisely the same rela-tive positions as they had at thebeginning. He felt that this syn-chronization, along with themany other similarities, was auseful characteristic that wouldhelp in providing a commonreceiver design for civil applica-tions throughout the world.

The block diagram shows thekey sections of a Naystar GPS


[SATELLITE SYSTEMS

Itat 107MHz if .1

Built-in test equipment

Spread -spectrum signal

lock Pseudo rangemeasurement

pro codetracking loop(correlation)

Localprn codegenerator

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Simplified schematic showing key parts of Leeds University's automatic GPS satellite navigation receiver.

automatic receiver developed atLeeds. It receives the 1575.42 -MHz transmissions intended forcivil users and is suitable fornavigation in slow -movingvehicles. To understand how itworks some readers may need abrief outline of the Naystar sys-tem. The basic principle is thatthe user can fix his position in aset of X, Y, Z co-ordinates cen-tred on the Earth. To provide thisfix, his receiver measures dis-tances from itself to transmittersin satellites of known (thoughchanging) positions. The dis-tances are computed from thetimes taken by pulses to travel (atvelocity c) from transmitter toreceiver. These transit times aremeasured by means of a standardtime reference for the wholesystem -'GPS time' - establishedby caesium and rubidium atomicclocks carried in the satellitesthemselves. The receiver - say onboard a ship - doesn't need tocarry its own atomic clock be-cause it obtains the system timereference from the satellitetransmissions. Similarly the re-ceiver also obtains the positionsof the satellites in the form oforbital data sent by these trans-missions.

Thus Naystar/GLONASS isbroadly similar in principle to aterrestrial hyperbolic navigationsystem like Decca or Omega. Aconstant given difference be-tween the transit times of signalsfrom two transmitters at knownpositions means that the receiverlies on a particular hyperbola. A

third transmitter of known posi-tion will establish another hyper-bola in the same manner. Wherethe two hyperbolas intersect isthe position of the receiver.

In the satnav system the re-ceiver can work either sequen-tially (single -channel) or simul-taneously (multi -channel) fromthe satellites. The Leeds receivershown here is a single -channeltype. If the height of the receiver(z) is known, signals from threesatellites are sufficient for a posi-tion fix; if not, four satellitesmust be used. The r.f. signalstransmit digital data carrying allthe necessary timing, synchro-nization, positional, orbital andcorrection information, includ-ing an 'almanac' giving satellitepositions for months ahead tohelp the user. This 50-bit/s datais transmitted by spread -spectrum technique to counterjamming, the received signalbeing buried at least 20dB downin the noise. One pseudo-random noise (p.r.n.) code istransmitted for civil use, anotherfor military use.

Thus the receiver's job is toacquire the p.r.n. code signals,decode them and process theresulting data to calculate posi-tion fixes. It involves a mixture ofconventional r.f. engineering,signal processing and digitalcomputation. The central part ofthe computation is to solve a setof four simultaneous equations,corresponding to four satelliteinputs, to obtain distances in theco-ordinate system.

In the single -channel Leedsreceiver (see diagram) the civilsatnav signal at 1575.42 MHzwith a power of about 1046W ispicked up by a small microstripantenna and fed to a front end.Then two stages of frequencydown -conversion produce an i.f.of 10.7 MHz. This is still aspread -spectrum signal with notunable carrier in the conven-tional sense. To recover thetransmitted p.r.n. code, the sig-nal is correlated with a locallygenerated p.r.n. code obtainedthrough the action of a codetracking loop.

When correlation is achievedby the loop the spread -spectrumsignal is de -spread. The compa-ratively wide p.r.n. signal band-width of about 2 MHz is collapsedto that of the data - a few hun-dred hertz. The signal then pas-ses to a carrier tracking loop, andconventional coherent demod-ulation technique is used to re-generate a carrier and recoverthe 50-bit/s p.s.k. encoded data.

The block marked 'pseudo -range measurement' is formeasuring the time of arrival ofcertain precise data signals cal-led epochs by reference to a10 -MHz master clock in the re-ceiver. These measurements,along with the data recovered bycorrelation etc., provide thebasic information required forthe position -fixing computa-tions. All system control andcomputation is performed digi-tally by a Z8OB microprocessor,using an STD bus and the C

programming language. Naviga-tional and other data are trans-ferred via i/o devices to a v.d.u.and printer.

Normally the position -fixingaccuracy of a 'straight' Naystarreceiver is within 20m orperhaps even 10m. But Dr Dalyexplained that this could begreatly improved by the use ofadditional receiver techniques.For example, integrated Dopplerwould increase the precision toabout 1 metre. Then measure-ments of code phase could beused, and also measurements ofcarrier phase, where the period ismuch shorter. At the L -bandfrequency used, for example, thewavelength was about 19cm. Hesaid it was not difficult to makephase measurements to a tenthor twentieth of a period.

Dr Daly mentioned that cur-rent research at Leeds included arefinement called 'differentialcapability.' This has two Naystarreceivers working together. Ifreceiver A already 'knows' whereit is, it can compute any system-atic errors. It then transmits thiserror information over a com-munication link to receiver B, ina format like that of a satellitecode transmission. Receiver Bcan then receive, decode andutilize this sytematic error in-formation to correct its ownposition -fixing data to the levelof accuracy possessed by A.

Satellite systems was written byTom lvall.


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380



Pioneers4. Charles Wheatstone (1802-1875) - Master of telegraphy

'W.A. ATHERTON

Sir Charles Wheatstone and his family: this stereoscopic daguerreotype is in the National Portrait Gallery, London.

It is an irony indeed when a prolificinventor is mostly remembered for aninvention that was not his.

Charles Wheatstone did not invent theWheatstone Bridge. He did however inventthe concertina, one of the first electricalrelays, the rheostat, a solar clock, improve-ments to the mouth organ, a typewriter, abinocular 3-D viewer similar to the moderntoys, a stethoscope which he called a mic-rophone, and some of the best 19th centurytelegraph systems - amongst other things.

Born in Gloucester on the 6th February,1802, Wheatstone was the son of a musicseller. He was educated at a private schoolbut had no formal scientific education.

At 21 he was living in London where heand his brother had entered the business ofmaking and selling musical instruments.Those instruments, and the related scienceof acoustics, were to figure large in his life.

Although as yet an outsider to establishedscientific circles, he received a visit fromOersted in 1823. His first scientific paper wasread to the French Academie des Sciencesthat year by Arago and published in London,all at the age of 21.

As part of his study of musical instru-ments, in 1821, Wheatstone had demons-trated an 'enchanted lyre'. This was anentertaining application of the transmissionof sound through a solid rod. A soundingboard, in the shape of a classical lyre andapparently hanging from the ceiling,appeared to play music! It was in fact

amplifying sound vibrations conducted to itby a rod from a piano in an upper room.

This early fascination with the passage ofsound waves through a solid rod helped toturn Wheatstone's thoughts to telegraphy,the art of sending messages over a distance.He described the enchanted lyre to the RoyalInstitution of London in 1831 and reportedthat sound travelled through a solid rodabout 16 times faster than through air. Itwould, he said, travel the distance of 200miles in less than a minute - if a suitableconducting substance could be found. Histhought, even then, was to transmit mes-sages. Speech, he had already found, couldbe transmitted over short distances "perfect-ly, though feeble."

The "almost hopeless difficulty" of abreakthrough for long distances, he wrote,"might induce us to despair of furthersuccess." The answer, he speculated, laywith a mechanical speech synthesizer! Bell'stelephone was to be invented shortly afterWheatstone's death.

In 1833, however, his attention turned toelectricity, and in particular the question ofits speed of transmission. It was known to beextremely fast, so fast that no-one had beenable to measure it. Wheatstone provided thebreakthrough.

His genius lay in devising a method ofmeasuring the tiny intervals of time betweenthree sparks located at the beginning, mid-dle and end of half a mile of wire. Thismeasurement of minute amounts of time

had defied everyone else. His solution, usinga revolving mirror, was simple and effective.It became a laboratory classic. He evenattached a siren to the hand -cranked mirrorso that the tone it generated helped him togovern the speed of rotation.

Wheastone's measurement of the speed ofelectricity was much too high, but it was ofthe right order and the first to be achieved.Later with four miles of wire he revised thefigure to 192 000 miles per second, muchcloser to the present-day value of 186 000.Partly as a result of this huge success he wasappointed Professor of Experimental Phi-losophy at King's College, London, a posi-tion he retained for life.

But standing before an audience filled himwith terror and he gave few lectures. At theRoyal Institution his scientific papers wereread for him by Michael Faraday who was anenthralling speaker. It is said that on oneoccasion, when due to speak himself, Wheat-stone fled leaving Faraday to pick up thepieces.

THE TELEGRAPH

'Who invented the electric telegraph?' is, aspoliticians say, a very good question.

To the modern mind Morse's name comesmost readily; but while he was one of themost successful telegraph inventors, he wasnot the first. Wheatstone could justifiablyclaim to have invented the first telegraphsystem to be put into daily commercialoperation. In partnership with W.F. Cooke


he installed a telegraph able to send andreceive messages between London (Padding-ton) and West Drayton along the GreatWestern Railway from July 1839 and itoperated on a daily basis for 10 years, evenbeing extended as far as Slough. It was fromthis that the British telegraph systemsprang.

Even so, it was not the first electrictelegraph. Once the magnetic effects of acurrent were known (1820) several tele-graphs using magnetic needle detectorswere invented as the same idea came todifferent people in different places.

Probably the first to produce an ex-perimental electromagnetic -needle tele-graph was a Russian baron, P.L. Schilling,perhaps as early as 1825. Although he died in1837, samples of his equipment had beensent to friends abroad and one of them wasseen in Germany by William FothergillCooke. Fired with enthusiasm, Cooke re-turned to England with burning ambitionsto build telegraphs - especially for therailway companies, his first potential cus-tomers. His partnership with Wheatstoneled to commercial telegraphy.

Amongst several remembered for theirexperiments with electric telegraphy aroundthis time are the Gauss and Weber part-nership in Germany, Edward Davy and Wil-liam Alexander in Britain, and of courseMorse in America.

On his return to England Cooke soughthelp to solve the problem of how to get histelegraph to work over long distances. Over amile his results were poor. He turned toWheastone in February 1837 only to discov-er that the scientist already had his ownideas for a telegraph, and a knowledge ofelectricity, and success with four miles ofwire. Whilst Wheatstone provided the tech-nical expertise and scientific knowledge,Cooke supplied the drive and vision neces-sary for commercial telegraphy to become areality.

In April that year Wheatstone received a

The invention Wheatstone did not create

THE WHEATSTONE BRIM E

R1_ R2

R3 R4

In the early 1840s Wheatstone set out to obtaina firm basis for electrical measurements:voltage, current and resistance. This was at atime when Ohm's law was still not widelyknown in Britain. Using Ohm's work. Wheat-stone devised his own units and built a stan-dard resistance. During this work he used thebridge principle described by Samuel HunterChristie in 1833. Despite his giving Christiedue credit for inventing the bridge it wasWheatstone's name which stuck.

Fig.1. Cooke and Wheatstone five -needle tele-graph, 1837 (Science Museum).

Fig.2. A simple ABC telegraph from about 1890-1900, bought with other 'junk' in an auction. Itstill works and is now in the hands of a collector.The transmitter is on the right

visit from the great American scientistJoseph Henry, and learned of Henry's out-standing work on electromagnets and theiroperation through long lengths of wire. Amissing scientific link slotted neatly intoplace.

A partnership was formed, at times veryacrimonious and in need of arbitration tosettle disputes. Patents were acquired, andafter trials and tribulations, success camewith the Paddington to West Drayton tele-graph.

This was the famous five -needle telegraphnow in the London Science Museum. Fivewires were needed, one to each needle, anytwo of which could be made to complete abattery circuit. The current flowed out byone wire and back by the other. The choice ofwires and direction of flow was dictated by apermutating keyboard and a letter was indi-cated on the diamond -shaped dial by thesimultaneous deflection of two needles(Fig.1). The instruments were well designedand made, a characteristic of Wheatstoneprobably born during his apprenticeship as amusical instrument maker.

This telegraph was a huge technical suc-cess. In 1843 the line was extended to Sloughby Cooke, a total distance of 19 miles, usingonly two needles with codes. Two years laterit achieved fame when police in Sloughtelegraphed to Paddington the description ofa man who had just murdered his mistress inSlough. His escape by train to London tookhim into the arms of the constables.

By the end of 1845 the telegraph hadarrived and the number of lines was increas-ing. The next year the Electric TelegraphCompany was formed and Wheatstone re-ceived the healthy sum of £30,000 for hisshare of the patents. By 1870 the telegraphshad been nationalized at a cost of some £8million.

Wheatstone had meanwhile turned to thedesign of ABC or 'letter showing' telegraphs.These had a dial with letters printed aroundthe edge, only one of which would be visible.(or indicated) at any time. The first wereessentially synchronized stop clocks with aremotely -operated electromagnet whichcould be used for stopping and re -startingthe mechanism. The user simply noted downthe letter shown each time the clockstopped.

Later, however, Wheatstone made thetransmitter send multiple pulses down theline, each of which stepped the receiving dialon by one letter. Some of these devices werelittle bigger than a pocket watch and ex-quisitely made.

Although slow, ABC telegraphs were usedin a sizeable network in London from 1860.Wheatstone's were not the only versions;they were made in several countries andsome remained in use up to World War I.

Much faster than the ABCs was the Wheat-stone automatic telegraph of 1859. Its suc-cessors were in use for over half a century. Aswith computers a hundred years later, papertape was used to speed transmission, themessage being coded by hand as punchedholes which then drove a transmitter at highspeed. Wheatstone's interest in coding de-veloping into an interest in cryptographyand he even deciphered some documents forthe British Museum.

Charles Wheatstone made so many inven-tions they could fill a book. Just one sufficesto illustrate his breadth of interests; a solarclock which used the polarization of sun-light to indicate time even when the sunitself was obscured. It was used on Arcticexpeditions.

When Wheatstone died in Paris on 19thOctober 1875. a renowned scientist andinventor, he had received many and variedhonours. The medals alone are said to fill abox of a cubic foot capacity. He sat on manyimportant committees, was a Fellow of theRoyal Society, and a foreign member of theFrench Academie des Sciences. Both Oxfordand Cambridge Universities honoured himand he was knighted in 1868. He refused theAlbert Medal of the Royal Society of Artsbecause they offered the same award toCooke, his former partner. It was a bitterlegacy of the tensions and disputes betweenthem.

There was one unusual honour, though,of which Wheatstone may not even havebeen aware. In 1841, with Isambard King-dom Brunel and others, he was aboard alocomotive when Brunel set out to discoverhow fast it could go. At about 90 miles perhour Wheatstone and his companions prob-ably held the world land speed record!

Samuel Finley Breese Morse. the Americanartist and engineer, will be next in this seriesof pioneers of electrical communication.


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322 0 25- £ 89.0032100.1% True RAU £119.00

AC CLAMPMETERS With casts and leads300 300amps IS ranges'6001114 ranges! IK 0141A £32.83 ,4300 Aulmange Digital 300A

5030 cont test £85.00

DIGITAL CAPACITANCEMETER B range LCD mow to TOOOMFDPushbutton selection 160131 £55.00

STOCKISTS FOR:Logic Analysers Insulation TEsters Temperature meters Security Systems Public Address Communicalions Tools Computer Equipment TV/VideoAccessor ies (See Catalogue)

ORDER BY POST OR PHONE. OPEN 6 DAYS A WEEK FOR CALLERS.

AUDIOHEI1Rse.5 ELECTROrlICS

Sika 301 Edgware Road. London W2 16 N. 01-724 3564l 404 Edgware Road. London W2 I ED. 01-724 0323

TELEX 298102 TRANS G

CAFTALOGUREE

EHer r

SEND .lMrn11

s yrwith f E 'tam() UKx por ,end

CI 00)

EDUCATION AND ACCOUNT ENQUIRIES 01-258 1831ENTFR 26 ON RF:PLY CAROENTER 41 ON REPLY CARD


MicroProcessor Engineering Ltd21 HANLEY ROADSHIRLEYSOUTHAMPTON SO1 5AP

FORTHSFor IBM PC and CompatiblesModular Forth

Source CodeWorkforthWorkforth Extensions:

ViewtraceFloating PtWindows & GraphicsDoc Tool Pack

Workforth and all extensions

For Atari STGem Forth MetacomcoFor Vax, RSX-11, etc UniforthMPE-Forth/OS9 68K

£475.00£5,000.00

£55.00

£35.00£35.00£45.00£45.00

£145.00

£65.00£175.00£375.00

For Macintosh, Apple, C64, Amiga, OLetcMasterForth by MMExtensions: fit Pt

HIRES graphicsProforth by HMcG(Shareware, pay more to use it)MVP -Forth for C. Amiga

FORTHRIGHT

£100-£120£45.00£45.00£10.00

£150.00

Tel: 0703 780084

CROSS -COMPILERSFor CPM 80, MSDOS. PCDOS. CPM 68K,FLEX, 0S9 (needs workforth as host)Targets: PDP-11, 6502 65110, 8080/5, Z80,8086/88, Z8, 1802 8070, 6809, 6800/01/03/6303,68000, 99CO3 99000.8031/51 Bryte Forth £350.00Forth -83 Targets:Z80, 8086, 680X0 32 -bit £225.00

For RT-11, RSX-11 and VMS -11Uniforth - Prices on application

HARDWARE for PC Programmers:Gal Programmer (MPE)Pal ProgrammerEPROM ProgrammerStack EPROM Programmer

Forth Engines:Novix 5MIP BoardMVP Microcoded

Kaypro PC Clones286i (AT Clone with 20Mb)K16/2E (Luggable PC)K2000 (LCD and batteries)

Amstrad PC Clones

£450.00£350.00£145.00£795.00

£852.00£1,225.00

£2,200.00£1,450.00£1,132.00

£549-£1.069.00ENTER 79 ON REPLY CARD

[Manufacturers.

importer* and suppliers of world anions communications products584 HAGLEY ROAD WEST OLDBURY, WARLEY, BIRMINGHAM B68 OBS021-421 8201 23 CELLNET 0860 323056. PRESTEL MB% 214218216 FAX 0215614074Amateur Flado Business Rao. Rada° Telephone. Sales Service Accessories and antenna systems

riticom) YAESU AO: dot THE TECHNICALLY ORIENTATEDRADIO COMMUNICATIONS

100Khz to 950MHz IN ONE BOX!SPECIALISTS.

R. WITH:MS COMMUNICATIONS LTD

THE YAESU FRG9600 RWC Mk3 SCANNING RECEIVERNow at last a "World First'' from Ray Withers Communications Ltd. Here aresome of the unique features only available on this fine receiver.

All Band Capebility. LW MW SW. VHF Low Aeband 137sSatelitte. HF High Merely UHFlove UHF Hogh T IUHFZE1 Cellular (All Broadcast Arr. Marine. Amateur Business Radio. Ahldary. TV. Collura,. up to 950MHz) TAr.fwd. now sortable tor use in any country as all bands/channel steps are now available

All Node Capability. AM/FA4 (wile and narrow modes). LSB. USB. Video crown available INTSCPAL 5 56M5. -IF)

Selectable Frequency Steps. Most 'nodes have selectable tuning steps which allow last and eastfrequency channel selection !conventional tunrng1

100 MemonetScanning. Any trequency in the range can be enterectstored into a memory an,selected'uanned in banks priordy function allows mondonng of important channellrequency while searches:other bands channels Modes are also stored in memory

Fully Computer Compatible. Yaesu s CAT system is a standard feature and a RS232 interlace is evaders,.plus other interfaces for popular HOME computers With Mrs feature memories can be expanded and the unit Ca,be remote COMIOlkerd via a modem

Clock Function. Clock funawn allows time logging and auto switch on off of the receiver

Nigh Receiver Sensitivity. In the range 60.950MI-12 a typcal receiver senserivrty I 5uV tot 12dB SINAI:(FM) car the range r 6MHz.60 000MH2 -2uV for 12dR !EM) below 1 600MHz sensitivity es nornmally -60/ Smeter function allows nominal held strength measurement

13.8 Volt DC Operation. The unit operates at 138V DC at IA mss frehrch allows mobileportablebasyoperaho,

Matching Anlenna Options. Matching antennas for portablermobrle Axed appkCaloons are evadable eristeryincluding wile -bard drscones

Meese ask for full colour brochure and detailed specilicstions Mkt versions are available withcoverage 60-9500AHe. all units now have Prl' connectors Idled for VHF UHF and S0239 connectorsfor 1511F.

The YAESU klk2 3 RECEIVER is only available horn HWC Ltd earl., can have the extended bands all.HF module fated and receiver sensitivity S meter improved please enquire more details and paces

Export enquiries welcomeIkki. Tel: 021 421 0201 tes 1E3 qIEP I I El I 213.

Telex: 334303 G TXAGW14

ENTER 6 ON REPLY CA RI)

WWI Z:Z

iII-FIEPELITITWITH SOUND PRINCIPLESThe GATE ONE amplifier is no ordinary hobby kit. It is uncompromising in the elctronic andmechanical design, the rircuit board layout, choice of componmts and case finish. It looks andsounds as good as amplifiers in the £300 class, which is indeed what it would cost if we were tomanufacture and sell in volume through normal retail outlets.

Considerably attention has been given to the circuit layout which uses a doublesided pcbwith extensive earth plane, star supply and ground feeds. The psu is regulated. even to the TO3complementaryu output darlingtons, with secondary reservoir capacitors for each channel. Alldriver and pre.amp stages are de -coupled. All low level signals to the selector Switch are kept incoax. not sprawled acro is the pcb as in many other designs. The only power wiring is from therectifier to the pcb and directly from the output stage to the heavy duty speaker sockets.

The design uses passi,e RIAA equalisation and tone controls with a tone cancel and subsonicfilter facility. You can even introduce a subtle bass boost to compensate for loudspeakerdel I iciency. All inputs other than the MM or MC input bypass tt e front end pre -amp. The volumecontrol is placed direct') in front of the main amp. where the output overload fuse is included inthe feedback loop. The MM input sensitivity is 2mV with a 29c8 overload margin and 80d13 SINratio ref full output, which is 40 watts per channel.

The case and pcb are manufactured to professional standards. The GATE ONE kit is £139.61 incbut from 1st May this has to go up to £161.00. A fully built and tested GATE ONE is currentlyE179.86. Send for further details. PS: This is not just a well engineered design. it sounds superb aswell and offers unbeatable value for money.

GATEHOUSE AUDIO (WW)105 High Street, Evesham, Worcs. WR11 4NP. Tel: 0386 48873.


KESTREL ELECTRONICCOMPONENTS LTD.

All items guaranteed to manufacturers spec. Many other items available.'Exclus ye of V.A.T. and Post and Package'

1+ 50. 1+ 50+ 1+ 50+74LS00 0.13 0 10 682t 1.40 100 2764-25 2.70 2.6074LSO4 0.13 0 10 6502 3.30 280 27128A-25 2.40 2.5074LS08 0.13 010 6522 3.30 2.80 27128-25 2.75 2.6074LS21 0.15 0 t2 74500 0.20 0.15 27256-25 3.80 3.4074LS37 0.13 0 10 74504 0.35 030 6116LP-3 1.50 t 4074LS74 013 010 745138 0.30 0.25 62641P-15 2.40 2.2074LS86 0 t3 0 10 74S240 0.40 035 43256-15 12.00 90074LS122 020 0 18 8085A 1.40 1 20 4t64 -t5 0.90 0.8074LS244 0 40 0.32 8255.5 1.40 1 25 41256-15 2.20 20074LS245 0 44 0.32 4 meg Crystal 0.30 0 25 Z8OACPU 140 I 0074LS367 0 23 0.17 LM324 0.25 0.20 Z8OACTC 1.40 1 0074LS373 0 40 0.30 LM339 0.25 0 20 280AP10 140 1 1074LS374 0 40 0 34 LM386 0.70 0 60 8253 1.40 1 2574LS399 0 30 0 20 LM556 0.35 0 25 6845 1.90 1 30

All memory prices are fluctuating daily, please phone to confirm prices.

178 Brighton Road,Purley, Surrey CR2 4HATel: 01-668 7522



[APPLICATIONS SUMMARY

V+ or low 5

battery adj. 01 01

Reference 1voltage

Fromionization 2chamber

Chamber adj.3

V+

Bias set

V+

Eliascircuit

30ms

Tocurrent -sources

Monostablemu.ti-

vibratorTimer

200

d

12

13 Beep timer- network /

oscillator

>til Piezoelectrichorn driver

11 Alarm oscillatorenable

6 Photo/ledoutput

10k

9

V+ or output enablepiezcelectric horn feedback

Mechanical /piezoelectrichorn driver

Interconnect

Ionization chamber

Ret.

SM

Note 1

+9V

14

CA3164A

4

Nate- 1. Ins res 10311, -InA leakageC1 adjusts low -battery beep & led -

100pblink rate.

mim2. Select for sounder used.3 For intermittent alarm, ground

pin 11 through 311911

I

Pin 11 see note 3 yvvii41-*2k7 - 1

9V

62

'Piezo-electrichorn

L _ - _ J

BI

B

R315

R1..nk377

4k7

t'R

IC307

DS26LS32A

11-41 -5V_

BS 177

FBI 02(17

W7 Gill150 ii7"

7

SV

560

200 T

316

COM

is 301'

In Fig. 28 (page 302, March) the value of Et217was omitted and the connections of R308 andits associated capacitor were wrongly drawn.This amended diagram shows them as theyshould be. The author has also pointed outan error in the text: in the penultimate lineon page 302. the word advantage should readdisadvantage.

ONE -CHIP SMOKEDETECTOR/ALARMIn the 3164 detector/alarm i.c. mos circuitsform an ionization chamber amplifier whilebipolar transistors drive alarm devices. De-tector input current is sub-picoamp andalarm -output sink current is up to 300 mA.

The 3164 is designed primarily for usewith ionization -chamber smoke detectors,but it can be used with photoelectric cham-bers by adding a few components. Besidestriggering on detection of decreasing voltageat the smoke detector input, the devicemonitors battery voltage and produces abeep once every 50s when battery voltagefalls below a presettable limit.

Booklet 1139 from RCA describing theCA3164A includes circuits for a photoelec-tric detector/alarm and photographic flashtrigger.

ADDRESSES:Consumer Microcircuits Ltd

Wheaton Road. Industrial Estate EastWitham. Essex CM8 3TD, tel: 376513833.

Motorola LtdSTC Electronics Services. EdinburghWay. Harlow. Essex CM20 2DF. tel:0279 26777.

RCA Limited/Solid State DivisionLincoln Way. Windmill Road. Sunbury -on -Thames. Middlesex TW16 7HW. tel:0932785511.


APPLICATIONS SUMMARYTransmit condit ion - -I Receive

Scrambler AResetcounter (Tx)

Scrambler A

32 codes 32 codes 32 codes :odes

Secure speech

highbando/p (Tx) Tone Tone Tone Tone

scramblerreleased

Scrambler B32 codes

counter (Rx)Sync.

Scrambler Ccounter (Rx>.-A'

Scrambler C joins net Sync.

32 (-ores 32 codes I 32 codr,s I Reset

Reset l 32 codes 32 codes 32 codes Reset

No sync tone received

ROLLING -CODESPEECH SCRAMBLERIn simple speech scrambling applications,the FX204 from Consumer Microcircuitssplits the voice spectrum into high and lowfrequency bands and then inverts each bandabout its own centre.

Frequency of the split point is programm-able in 32 steps from 300 to 3000Hz. Formore secure operation, the split point can becontinually varied, as it is in this rolling -code speech scrambler/descrambler.

Because the code is continually varying,

Tx audio inTx audio out

Re audio in

Rx

11MVb

xRe audio out

'ush to MC14049talk

A

E

MC14 016

100k

L Low ban .\d /V\'o/p 2

ELow bandi/p 2

120/P

12OPKey code 'r_in Low bandselector o/p 1

Low band5n i/p 1

A

Vdd

100k

14

A4

Load/latch

High bondi/p 1

Vss

-ye

Amp

VC

VI

Tes'

Cr

FX204 CK

FE2 /2 ci

High b..0/;;

17c/Rx

High br

High h

Vdd

B

Rese

MC14011

100k

MC14C11

C-

Tone detect

Vss

Jul

MC 14011

100k n .s

MC14 093

To key codeselector

Binary counteryr

B

0

1n TAudio switch

Sync Tx switch

1

Sync Rx switch

14

MC140933

-L--4n7

Tonedetector

MC14046

100k13

11

270k<In

1M

MC14013

CK

TD n

33nI fc2

SL

14068

CK

S2/1[140713

Anti 1

glitchMC14011

. Sync

Tone gate

MC14011

Vss

CK


[APPLICATIONS SUMMARYthe receiver needs some means of synchro-nizing itself with the transmitter. For thispurpose, an f.s.k. data burst can be sent atthe start of each transmission. Alternativelya continuous tone above or below the voiceband may be sent and this tone could havephase reversals. In the circuit shown. ap.1.1. detects tones higher than 2400Hz.

Besides this and other applications, theFX204 data sheet covers specifications andoperation of the device.

400-512MHzPREAMPLIFIERElectrical, mechanical and performance dctails for a GaAs fet 400-512MHz preamplifierare given in Motorola note AN925. TheMRF966 GaAs fet used is a low-cost dual -gatdevice designed for u.h.f. applications.

In the three -page note. Smith charts shoinput/output matching networks and twgraphs show gain at noise figure and opti-mum noise figure versus frequency with thepreamplifier tuned to 430 and 480MHz. Twofurther graphs give input returnloss versus frequency; the ones shown hereare for 480MHz. Circuit board, coil windingand housing details are also given.

NIPTop of PCB

High band o/pi High bandr

High band i/P1 tiVdd

Vss

VbiasTZ/R>

XTAL/CLOCK

I CLEAR/INVERT

XTAL4

LOAD

01

Split pointprogram

Low band i/pi

Rom

032

Highband o/p 2

omp i/p

Amp o/p

- amp ip

f c 2 / 2

Test o/p

f"Thk,

ti. J

Low band o/pLi I: i/p

f ti12 o/p Low band i/p2

Low bonda/p2

r finput

E. to 10p

08to1Op

Ferritebead

OO

MRF 966

.1n <:111';'

II470p

lo11N 4001

12k

1n 1OfIr

r f outpi t

7 toI5VI« I .7. bIN 4001 1n

10p

440 460 480

FREQUENCY (MHz)520

2.0

6-°

ELL,

1 2 g

LL

14.1

084zL_

-8-9

-_a

z

-24-

-28

420 4140 460 480

FREQUENCY (MHz)500 520


HunEEDISff MSCrown Street, St Ives, Huntingdon, Cambs. PE17 4EB.

LOW COST ELECTRONICS C.A.D.Tv IF AMPLIFIER

114141

-111111Ftril

tiPUP, et

IBM PC (and compatibles). RM NIMBUS, BBC MODEL B,B+ and MASTER, AMSTRAD CPC and SPECTRUM 48KANALYSER" I and II compute the A C FREQUENCY RESPONSE of

linear (analogue) circuits GAIN and PHASE INPUT IMPEDANCE.OUTPUT IMPEDANCE and GROUP RELAY (except Spectrum version) arecalculated over any frequency range required The programs are in useregularly for frequencies between 0 1Hz to 1 2GHz. The effects onperformance of MODIFICATIONS to both circuit and component valuescan be speedily evaluated

Circuits containing any combination of RESISTORS. CAPACITORS.INDUCTORS, TRANSFORMERS. BIPOLAR and FIELD EFFECTTRANSISTORS and OPERATIONAL AMPLIFIERS can be simulated - upto 60 nodes and 180 components (IBM version)

Ideal for the analysis of ACTIVE and PASSIVE FILTER CIRCUITS. AUDIOAMPLIFIERS. LOUDSPEAKER CROSS -OVER NETWORKS. WIDE -BANDAMPLIFIERS. TUNED R F AMPLIFIERS. AERIAL MATCHING NETWORKS. TV I Fand CHROMA FILTER CIRCUITS. LINEAR INTEGRATED CIRCUITS etc

STABILITY CRITERIA AND OSCILLATOR CIRCUITS can be evaluated by"breaking the loop'.

Tabular output on Analyser I. Full graphical output, increased circuit size andactive component library facilities on Analyser II

Check out your new designs in minutes rather than days

ANALYSER can greatly reduce or even eliminate the need to breadboard newdesigns

Used by INDUSTRIAL. GOVERNMENT and UNIVERSITY R 8 D DEPARTMENTSworldwide IDEAL FOR TRAINING COURSES. VERY EASY TO USE Prices from£20 to E1 95

Full AFTER SALES SERVICE with TELEPHONE QUERY HOT LINE and FREE update service.For illustrated leaflets and ordering information please contact Ref: WW

O'NEE0.0Telephone: St Ives (0480) 61778

EN'IT ft 57 ON REPLY CARD

SOWTER AUDIO FREQUENCYTRANSFORMERSYou name it! We make it!

For the past 45 year ... .... . ,.. i:, ; in the design and manufacture of highgrade audio transformers during which period our total sold exceeds half a million. W(continually take full advantage of all the improvements in magnetic and insulatingmaterials and in measuring techniques utilising the most up to date instrumentation

We have a very large number of original designs made for clients all over the work ibut naturally there are certain types of Sowter Transformers which are in constantdemand These have taken into account the tendency towards small size withousacrifice of performance. particularly for PCB mounting, and a few of these are liste!below They can be supplied with or without mumetal shielding cans Performanc,,requirements can be modified on request (utilising our readily available questionnairi-1and generally without alteration in price

We specialise in LOW COST AND QUICK DELIVERY which means a few di,,,- ,,,,,,ex -stock.

TYPICAL PERFORMANCESUreterType No 3575 4652 3678 6499 4079 6471 6469Desr,bon Minrature

MrclarnIttransformer

line output Nutt primarymrcrophonetransformer

line output6rgh lanai fordrstortronforordal core

501.8ercombrnertransformer

Modget m.rtransformerfor BT pr...systems

Very highnualaymrcrophonetransfor me.

Ornpedanres 101.0 10k0can be fedfrom50 6000

600 or 1501/moots oroutputs

Pys 60 200or 6000Sy 511(. clownto 1081:

6000 6000 2000 Bal PyTwo 2000Secondaries

Py 600,,Sy 6001)

2000 Py for100 load.,airtlar) 8 1step up

Frequencyrange

?OH: 201.11: 20/12 20011, 30H: 20011, 20H: 20101: 20H: 204H1 30011: 3114Hz 2011, 200Hz

AO otrnance 01d8 overabove range

02508 ore,above range

0 SOB overabove range

03084011: 15kHz

05,1820111 200H:

0 SclE1 owerabove ranee

O5013 overabove ranee

0 2dB owerabove range

Maarmum:,,,, 7 75V r msor secondary

775V r rn sOn 6000

on 5.0 load340, msal 30H:

26dBrn at3011:

2 3V r msat 3011:

060, on

Pnewni2 OW ms onN al 30117

Ala wrturn1),51or6on

%Nth 10Vr rn s at4011: orny012'.

On 600(1low source?01'.

Less than01°. at IltHr

01'. al3011: al26d8m

neilrarble0 I, at

IkH:

neallarble 01'. al 20Hr

.5noelchng Electrostatrcscreens andmurnelal can

klumetal canof dewed atemtra cost

klurnetal can Toroidal can laumetal can'rind framebolts

PCBmounting

Murnetal can

Dnnensoons 33non dram- 22n1rn Pugh

36rnm men43nun33ronr

llmm dram22rnr. lug'

5Ornm dram36mrn men

33nn dram37mm NO

II Irmn Pugh19mm17mrn

33mm dram 22mm hip

Paces eachat works

1 L108350 99 77100 99 27

1 196750 18 89100 18 69

1 196750 1867100 L841

1 117 1250 11569100 LIS 35

I L145950 11337100 11308

I 138950 1355100 1329

1 111 3850 110 12100 L992

E. A. SOWTER LTD. (Established 1941) Reg. No. England 303990The Boat Yard. Cullingham Road. Ipswich IP1 2EG. Suffolk. PO Box 36. Ipswich IP1 2EL.

England. Phone 0473 52794 8. 0473 219390 - Telex 987703G SOWTER

r°0_. NEW! AFFORDABLE

PCB CADFROM

CHANNEL MICRO PRODUCTS LTD Maximum cumuli board size greater than 2' x 2'. Powerful zoom facility and fast screen re -draw. Full off -screen editing. Mouse & Trackball compatible. Hard copy al 1:1, 2:1 & 4:1 from Epson F X or R X printer. Plotter drives for most popular plotters available. Low cost BBC Micro hardware keeps system cost below £1500.

Software only £240.

Please write or telephone for full details.

227 Canterbury Street, GillinghamKent ME7 5X8. Tel -0634 570256


Toroidal & E.I.TransformersAs manufacturers we are able to offer arange of quality toroidal and laminatedtransformers at highly competitive prices

Toroidal Mail Order Price Listprices inclusive of VAT 8 Postage15va 7.95. 30va 9.18. 50va 10.16. 80va 11.36. 120va 12.07. 160va 14.20. 225va15.21. 300va 17.04, 500va 22.10. 625va 24.66, 750va 28.75, 1000va 44.82.Also available 1 k2. 11,5. 2k. 2k5. 3k Prices on request

Available from stock in the following voltages. 6-0-6. 9-0-9. 12-0-12. 15-0-15. 18-0-18,22-0.22, 25-0-25. 30-0-30. 35-0-35. 40-0-40, 45-0-45. 50-0-50. 110. 220. 240.Primary 240 volt

Quantity prices and delivery on requestAir Link TransformersUnit 6. The Maltings. Station Road.

Sawbridgeworth, Herts. Tel: 0279 724425ENTER 21 ON REPLY ('Alt1)

388

ENTER 200N REPLY CARO


HAMEG Ltd. 70 - 78 Collingdon Street,Luton, Bedfordshire LU1 1RXTelephone: (0582) 413174.Telex: 825484.

Designed and manufactured in West Germany by HAMEG, one of the World's leading oscilloscopemanufacturers - the range of Industry's unsurpassed Price/Performance oscilloscopes.

Quality, Performance, Value... Oscilloscope Range

'For those who compare'

Dual Trace 20MHz,Component Tester,

£314.00

Dual Trace 20MHz,Component Tester.

£4 1 8. JO

Dual Trace 60MHz,1MHz Cal. Gen.rato

£583.00Dual Trace 20MHz,incl. 2 probes Type

£4 98.D0

2mV/cm, Algebraic Add,incl. 2 probes HZ36.

HM203-6

1mV/cm, Sweep Delay,

HM204-2

lmV/cm, Delay Line,r.

HM605

Digital Storage OscilloscopeHZ37.

HM205

Dual Trace 20MHz, 4 x 1k memory, plotteroutput, incl. 2 3robes Type HZ37

£1460.00 HM208

IEEE -488 Interface Version, incl. 2 probesType HZ37.

£1735.00 HM208

Price U.K. List ex. VAT2 Years Warranty, Parts & Labour


Z80 CONTROL Z80CARDMASTER CPU

46 MHz Z80 CPU

CP M compatible User transparent MULTI -TASKING

Up to 32K EPROM 8 16K RAMWatchdog crash protection

RS232 8 RS422 Comms

2' Z80a PIO (one uncommiled) On board bus buttering

i

:: r'

Ii ...:""`"

%

i

Power -on lump hardware

Euro-card constructionNOW FROM £124 VAT

CUB MICROCONTROLLER ZEO CPU 1 - Z80a PIO s (64I 0 lines)

Z80a CTC 4K Battery backed RAM (26 sup)

4K EPROM (2K MCV2.0 sup.)

Powerlul monitor (MCV2,0 Eurocard construction

NOW FROM £108

-,

y __

VAT

STARBURST V1.31A CROSS ASSEMBLER FOR

CMR16 NOW FROM£199.00

CP/M80 covers four majorfamilies of single chip uP's and

uC's* 8048 inc. 8741/2 8748/9/50 8051 inc. 8031/2 8751 8744* 6801 inc. 6800/1/2/3 68701* 6805 inc. 68705 63705

Bare PCB's Available1

C/M CPU 28.50 25.65C/M I/O 28.50 25.65CUB 23.50 21.15CMR16 40.00 36.00

Supplied with a complete set ofdemonstration files.

STARBURST V1.31 £95.00+ VAT

Requires Z80 CPU

Manuals on request

GNC ELECTRONICSLittle Lodge. Hopton Road.

Thelnetham, DISS IP22 1JN.Tel: 0379 898313


41) IC OMCommunications

pram ;;

:COM introduces the ICR7000 aavancea technology continuous coverageommunications receiver With 99 programmable memories the IC -R7000..)vers aircraft marine FM broadcast Amateur radio. television and weatheritellite bands For simplified -)peration and quick tuning the IC -R7000 featureserect keyboard entry ()recite frequencies can be selected by pushing theago keys in sequence of the frequency or by turning the main tuning knobM wide FM narrow AM upper and lower SSB modes with 6 tuning speedsI I 0. 5. 10 12 5 and 25kHz A sophisticated scanning system provides instant

,cress to the most used frequencies By depressing the Auto -M switch theP7000 atil,maticalli, memorises frequencies that are in use whilst it is in the

':[ :. vou tc recall frequencies that were in use Readout is!-.r f':,resc.- display Opii-ns includf, PC' !?

and HP iph

M3lease rush me details of the IC -R7000 and my nearest !COM dealer

Name

AddressTel

Post to: ICOM, Thanet Electronics Ltd., Dept W W. FREEPOST,L_Herne Bay, Kent CT6 8BR. (no stamp needed) Tel 0227363859. J


ENTER 12 ON It El'1.1' CARD

359

Europeanmoves fromAT&TThe American giant telecom-munications company, AT&T,are opening new sales and designcentres in Bracknell, Berkshire,and in Stockholm, Sweden.These will add to the AT&Toffices in Madrid and Munich andfurther facilities are planned forFrance and Italy.

The British branch at Brack-nell will offer basic design facili-ties as well as a sales office forAT&T products. These productsresult from research at their BellLaboratories and claim to havemany unrivalled attributes:their 32 -bit, floating-point,digital signal processor, for ex-ample, which can operate at24MHz. AT&T have also pro-duced a 32 -bit microprocessorwhich is designed specifically towork with the Unix -V operatingsystem (another Bell Labs pro-duct). Their i.c. manufacturingoffers 1.75 and 1.251.i.m geomet-ries with 0.9p.m available soon.

The company specializes incommunications equipment andcan offer a wide range of com-munication circuits and fibre -optic components.

Philips to sellPye TVT?Philips Electronics hasannounced that it is holdingdiscussions concerning the saleof its broadcast transmissionsubsidiary, Pye TVT Ltd, with apotential American purchaser,Varian Associates.

Pye TVT of Cambridge em-ploys about 220 staff in thedesign and manufacture ofbroadcasting equipment, especi-ally for tv transmission. Variansupplies communications, medi-cal', analytical and semi -con-ductor equipment with a re-ported turnover of $900 millionin 1966. The purchase of PyeTVT would be part of Varian'sprogramme to strengthen itsrole in the communicationsfield. It had already acquired in1985 the Texas -based Continen-tal Electronics Company andhas considerable strength inhigh -power broadcast and satel-lite ground -station transmitters,which would be complementedby the Pye TVT range. Varian

rUPDATEhas indicated its intention ofcontinuing the Cambridge op-erations.

In briefFor those interested in preserv-ing the history of the telephone,there has been founded the Tele-communications HeritageGroup. The group will publish aquarterly newsletter, approp-riately called 'Exchanges' whichwill include articles, and noticesfor the sale of, and requests forequipment and information.Although the group is indepen-dent of BT, the Telecom Tech-nology Showcase, 135 QueenVictoria Street, London EC4V4AT, has agreed to act as acoordinating and postage centre.This year's subscription is £3.Further information from thegroup through the Showcase.

A firm of London solicitors hasclaimed a world first by offeringlegal advice via electronic mail.Pennefather and Co. is the com-pany that has decided to breakfresh ground by opting for thisform of communication toanswer queries from clients. Theservice is being provided on Mic-rolink, a national electronic-

mail network. Clients of the soli-citors can transmit their mes-sages and receive replies usingtheir home or business com-puter.

As an introduction to this on-line service, all subscribers toMicrolink are being given thechance of a free consultation.They can receive one free replyon any legal query they wish toraise with the firm.

Philips have opened a new inte-grated research and develop-ment centre at its headquartersin Eindhoven, Holland. Its prin-cipal object will be developmentof sub -micron technology (sili-con structures with less than11.i.m width and spacing) in aresearch cooperation betweenPhilips and Siemens of Germany.

Dr Marc Faktor, who spent morethan two decades researchingthe optical and electrical pro-perties of materials, was pre-sented with BT's MartleshamMedal. His "pioneering work hashelped to put Britain in the worldforefront of optoelectronic tech-nology."

Much of his work with BritishTelecom concerned the growingof crystals from vapour; buildingup layers of semiconductormaterial no more than a mil-lionth of an inch thick - onwhich the fabrication of today'soptical devices are based. Thetechniques which he pioneered,such as metallo-organic vapourphase epitaxy are now sufficient-ly well defined as to be capable ofcommercial exploitation. A jointventure company set up in 1986between British Telecom and duPont is to develop, manufacturend market optoelectronic com-

ponents and devices which stemdirectly from Dr Faktor's work.

During the early 1970s heheaded a team which used orga-nic materials to build reliable'directly modulatable' semi-conductor lasers. He also devisedthe electrochemical technique atthe heart of the British Telecomprofile plotter, which producesan accurate profile of theelectric -current carriers in semi-conductors. This is now manu-factured under licence and soldworldwide. Dr Faktor left BritishTelecom in 1982 and is a now avisiting professor at Queen MaryCollege, London University.

The construction of two militarycommunications satellites forNato has been awarded to BritishAerospace. The Nato tv satellitewill be virtually identical to Sky-

net 4, currently under construc-tion for the British forces. Mar-coni are the principal sub-contractors for the communica-tions payloads to be launched in1990.

A report by Dataquest, of Califor-nia, on the worldwide semicon-ductor market for 1986, says thatthe three top chip suppliers,measured in US dollars, areJapanese companies.

NEC retained its number oneposition, achieved in 1985.Second and third places for 1986went, respectively, to Hitachiand Toshiba. Motorola and TIwere relegated to fourth and fifthplaces respectively. The placesare quite difficult to work outbecause of the fluctuations incurrencies; the Japaneseattained a world growth of 40%,expressed in dollars, but only0.2% when accounted in Yen.Japanese exports actually fell by8%, but this is offset by a 2.6%increase in the share of theirhome market.

IEE and IEEIE lecturesand meetings

All meetings held at the IEE,Savoy Place, London WC2:information from the Institu-tion, Tel: 01 240 7753, Ext.296 or 283, unless otherwiseindicated.

24 MarchElectronic filters: IEE collo-quium

24 to 26 MarchComputer aids for electricaland electronic engineers.Conference at the MetropoleHotel Brighton in conjunc-tion with the CADCAM 87Exhibition. Details fromEMAP, Tel: 01-606 1161.

25 MarchMulti -octave componentsand antennae: IEE collo-quium.

26 MarchThe code -breaking compu-ters of 1944: IEE discussionmeeting at 1415h.Colossus and the Germancyphers in WW2: IEE lectureby Sir Harry Hinsley. 1800h.

27 MarchEvaluation of interactive sys-tems design: IEE collo-quium.

30 March to 2 AprilAntennae and propagation(ICAP 87): IEE Fifth interna-tional conference at the Uni-versity of York.

1 AprilDigitally implementedradios: lEE colloquium.

1 to 3 AprilCommand, control, com-munications and managmentinformation systems.Second International confer-ence in Bournemouth.

2 AprilV.I.s.i. for image processing:IEE colloquium.Fibre optics in communica-tions. IEEIE lecture by R.R.Willet of Mercury. Universityof Cambridge EngineeringLaboratories. 1900h.Details from IEEIE 01 8363357 ext. 212.

6 AprilComponent tv measure-ments: colloquium.7 AprilSoftware engineering - theimportance of documenta-tion: colloquium.


RoundAustralia bymicrowaveThe commissioning of the lastlink in Telecom Australia's$lbillion round -Australia broad-band microwave network hasmeant a significant improve-ment in the security of nationalcommunications in Australia.Telecom Australia is the nationalcommon carrier, owned by theFederal Government andcharged with the development ofa modern telecommunicationssystem in Australia.

When the link across the WestAustralian/Northern Territoryborder was switched on recently.it immediately became possibleto direct Perth calls to the eastcoast of Australia, via the north.For the first time any failure inthe main trunk route across theNullarbor desert no longermeant Western Australia's com-munications could be cut offfrom the rest of Australia. Just asimportantly for people who livein the remote Kimberleys in thenorth west of Western Australia.the 455km link that now joinsKununurra to Katherine in theNorthern Territory has giventhem additional security in theevent of a cyclone disaster.

Although the towers holdingthe network's parabolic dishesare designed to withstand windsup to 225km/h, it is still possiblefor a cyclone to put a dish out ofaction. It happened with CycloneJoan in 1984, when high windstwisted an angle -iron, and a dishon a tower was edged 5° off line.On a 40km line -of -sight betweendishes the 5° was sufficient tobreak the link and bring thenetwork down for two hoursbefore the dish could be re-aligned. The completion of thefinal link means that such a faultwould no longer disable the net-work; communications trafficcould be simply redirectedaround Australia in the oppositedirection, away from the fault.

Communications HighwayOne, as it is called, began in 1959with a link between Melbourneand Bendigo. At this time, someareas were only connected bytelegraph lines and these werebeing replaced by h.f. radio links:allowing phone calls for the firsttime to the Kimberleys, for ex-ample.

[UPDATEThe completed network car-

ries telephone traffic. computerdata, telex, facsimile, tv andstereo sound broadcasts. Itstretches 11,916km in a giantcontinental loop. To provideline -of -sight communications,the 303 masts are placed at 40kmintervals in a zig-zag pattern toprevent overshooting into thenext section. Repeater equip-ment is housed at the base ofeach mast. In the northern re-gions where the temperature canrise to 50°C. the repeaters areburied in underground sheltersto keep the temperature stable,to within 5°C of the requiredambient. Remote repeaters aresolar powered.

Svi nev.

Russians ceasejammingSkywave jamming of the BBC'sRussian -language service all butceased on January 20th, and,judging from reception in Mos-cow. so too did local groundwavejamming - much beloved of theSoviet Union.

The jamming began in 1949,since when jammers have beenturned on whenever the politicalclimate has cooled. 1963 markeda temporary lull, but jammingreappeared after the invasion ofCzechoslovakia in 1968. Anotherrespite occurred in the 1970s.

At no point have the Russiansever openly admitted to jammingthe BBC; indeed last year theSoviet ambassador to Britaincountered such accusations withthe charge that Britain was itselfjamming Russian broadcasts.

Just why the jamming has nowstopped is not known. It could be

a desire for better relations withBritain following the visit toMoscow of the Foreign OfficeMinister, Timothy Renton. Thisis given more weight by the factthat (at the time of writing) otherwestern broadcasters are stillbeing jammed. The approaching1987 World AdministrationRadio Conference may also havesome bearing, allowing theSoviets to present a cleaner im-age in terms of spectral pollu-tion. Or it may turn out to beanother step in Mr Gorbachov'sliberalization policy, already de-monstrated through limitedwestern access to the country'sprint media.-.11V.

Sinclair's Z88Having sold the Sinclair brandto Amstrad, Sir Ciive Sinclairhas started a new company.Cambridge Computers. Its firstproduct is the Z88 computer: abattery -powered lap -top whichcomes with a built-in word -processor, BBC Basic, spread-sheet, database, calculator anddiary/calendar. 32K of ram isprovided but it is possible toplug in up to three ram exten-sion cartridges, of 32K. 128Kand (available later) 1Mbytes.Eproms with the same capaci-ties can be used in the sameway.

The display offers 8 lines of 80characters with an additionalarea in which every character isrepresented by a dot mapped togiven an overview of the pagelayout. There is also a menuindication and a status displayfor battery level. An RS232 out-put to a printer is provided, andthe ability to transfer files to andfrom an IBM-compatible PC.

EXHIBITIONS ANDCONFERENCES

24-26 March 1987Cadcam 87 exhibition andconference. NEC Birming-ham. EMAP Int. Exhibitions,Tel: 01-608 1161Internepcon ProductionShow and conference -'fromCAD to testing' NEC Birm-ingham. Cahners Exhibi-tions. Tel: 01-891 505125-26 March 1987Instrumentation Bristol 87Exhibition. Bristol CrestHotel. Trident Int. Exhibi-tions, Tel: 0822 467131 March -2 AprilScottish Computer Showand conference. ScottishExhibition Centre. Glasgow.Cahners Exhibitions.Tel: 01-891 50516-8 April 1987Offshore computers confer-ence and exhibition. Heath-row Penta Hotel, London.Offshore Conferences, Tel:01-549 583113-16 April 1987Acoustics '87 conference atthe Management Centre,Portsmouth Polytechnic. In-stitute of Acoustics, Edin-burgh, Tel: 031-225 214328-29 April 1987Cellular and mobile com-munications conference,Barbican Centre, LondonValue-added network services(VANS) conference. BarbicanCentre, London12-15 May 1987Automan: 4th EuropeanAutomated Manufacturingsystems exhibition and con-ference. NEC, Birmingham.Cahners Exhibitions.Tel: 01-891 505117-20 May 1987CES - Consumer Electronicsand Technology Show. EarlsCourt, London.Organized by Montbuild Ltd,Tel: 01-4861951

19-21 May 1987South -Comm 87Exhibition of the Associationof Sound and Communica-tions Engineers. BusinessDesign Centre (formerlyRoyal Agricultural Hall).Liverpool Road, Islington,London Ni. Batiste Exhibi-tions.Tel: 01-340 3291


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PYE SSB TRANSCEIVERS TYPE SSB2I0(NEW & BOXED) 60% OFF ONLY £480 EACH

Pye base stations, high band and low band AM type F401used condition and untested to clear only £75 each.

Pye TVT 35mm slide colour telecine equipment, looks new,no details available, offers invited.

Send for our government surplus catalogue.

Callers welcome by appointment only 9 am to 8 pm any day.

All prices quoted are for UK mainland and in pounds sterlingplus VAT P&P at cost.

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Programs 25 and 27 Series to 512K2516, 2532, 2564, & 2716, 2732, 2764, 27128,27256 27512 in CMOS & NMOSUses FAST Program Method.Covers all Program Voltages.Liquid Crystal Display shows EPROM type,Program -Method and Program -Voltage which are set by s Notches.also RS232 setting if presentTwo Key operation: START & RESET - pretesting is automatic- G8 reports non -blank EPROMS and correctly programmed ones.A CHECKSUM is reported if you press both keys - six hex digitsAudible output keeps you informed - you don't need to watch it.Option - A metal Case instead of a plastic case, if you prefer it.Option - A Bi-directional RS232 Serial Interface to uploadand download INTELHE X, MOTOROLA S, TEKHE X. ASCII andBINARY files

GANG -OF -EIGHT £395.00for RS232 option add £50.00for Metal Case add £35.00

Z80 ProgramDevelopment AidOn your TV screen you display program, registers and stack,using MENTA's custom -assembler you write Z80 code and try it outAn excellent int-oduction to pP programming, Designed fc r theSchool's Council to teach microsystem design, MENTA is amicrocomputer which can form the basis of an industrial -controlleror robot TV DISPLAY FULL SCREEN EDITING - MNEMONIC CODEENTRY - FAST CASSETTE INTERFACE SIMPLE DEBUGGINGSINGLE-STEP OR FULL SPEED EXECUTION WITH OR WITHOUTBREAKPOINTS DISASSEMBLER Ito external printer -term nail24 LINES FOR INPUT/OUTPUT GOOD MANUAL WITH EXAMPLEPROGRAMS, CIRCUIT DIAGRAM and FULL COMMENTED SOURCECODE LISTING Teaching modules are also available UniversalBuffer, D to A, A to D. Motor control, Variable and Switched inputsand outputs, together with Pupil Readers, Teacher's Guide andWorksheets

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SupetP0ePortable pP Bus TesterAn engineer needs more than a meter and a scope - tnese tools arehardly adequate for diagnc sing faults which afflict HP systems.SuperDOC is a diag iostic tool which you plug into the socket wherethe pP goes; using -he hardy probe you can identify address, dataand control lines in the LCD display. You can edit and keep up to225 tests, stored in batters.- backed memory and apply them tofaulty boards Each test pro duces a report on the built-in 24column printer: MEMOR y MAP - BUS SHORTS - CHECKSUM -RAM TEST - MEMORY READ - MEMORY WRITE - FILL MEMORY -INPL T - OUTPUT - ASCII PRINTOUT HEX PRINTOUT - SEARCH -DISASSEMBLY in 1:302, 8085, 6800, 6802, 6809, 6502 or Z80mnemonics. SuperDOC comes complete with a personality card foreach µP, which con-igures the probe correctly.

SuperDOC complete as above £330SuperDOC supporting only 280,6502, 6800 8 8085

Bare PCB and CableConnectivity TestingWe offer a system of CMOS custom -chips and a micro -controllercar 1, designed by DATAMAN. Using these electronic com )onentsyoc can put together your own Bare -Board Tester or Cable HarnessTester for much less than £1 per point, with no practice I limit onsize. We can also supply a complete system, with Bed -of -Nailsfixture, ready to u;e. Tell us your requirements. Ask for a c uotationand literature

Olivetti Typewriter ET221InterfacesWE can convert your ET221 to a serial or parallel compute- printer.with control of boldfacin ), underlining, justification etc. The price ofa s ngle conversion incicdes collection and delivery. IA m_ichlower price for a t ulk order) £195

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Forth processorhardware

Using the Novix processor relatively few devices are needed tomake a complete Forth computer capable of at least 4 mips.

L first article on the Novix NC4000in the February issue outlined Novixarchitecture and design philosophy.

This article illustrates how to design Novixbased hardware, looking at the criteria thatdetermine its design, and describes a

working system. This design is the basis ofthe NX4 board, a low cost Novix evaluationsystem.

A number of factors determine whichcomponents are used in a microprocessorsystem - timing diagrams, memory map,amount of rom and ram needed, choice oftechnology, and so on. But before exploringthese in detail, we need to put together a

brief specification for the system. The aim isto produce an evaluation system that willgive engineers an idea of the NC4000'scapabilities. The main key requirements inno particular order are

- Low cost- Use of readily available parts- Highest possible performance- Minimum component count- Serial i/o (RS232) for interactive

programming

Some of these criteria are mutually in-compatible (e.g. low cost versus speed) but Iwill explain how to get the best performancefrom the NC4000 for any particular com-bination of devices, whether they be ram,eprom or i/o.

The board can be used as a complete Forthdevelopment system by connecting itsRS232 port to a computer (an IBM PC orcompatible) which is then used as a terminaland pseudo disc drive. Fig. 1. Software,including the serial -link handler, Forthcompiler and keyboard interpreter for theNC4000, will be in eprom on the board, andwill be explained in the next article onsoftware. However, there are one or twounavoidable forward references to the nextarticle made necessary by software charac-teristics that have an impact on the hard-ware such as reset address, interrupt vectorsand program space.

TECHNOLOGY CHOICE

As the NC4000 is an IICMOS device. it will drivebipolar devices (standard, s, Ls and e series

NMOS and, of course, other cmos de-vices. Problems are only likely to occur if abipolar output has to be read by an NC4000input since moms inputs switch at below 1.5Vand above 3.5V whereas t.t.l. inputthresholds are 0.8V and 2V respectively. To

WILLIAM WATSON

Screen

RS232 link

PC PC compatible

Keyboard/

Disc [4-0,1-61-1

Forth programfor

disc and terminalemulation

NX4

PS212 linkNX4

single -boardNovo( computer

Fig.1. Low-cost NC4000 development The NX4 board is ideal for stand-alone real-timeapplications, but also allows interactive development of those applications. Forth PCsoftware configures the host computer to ac. as a terminal and disc drive, all down theone serial line, for the NX4 Board.

Fig.2. The memory map determines some of the eprom and ram mapping. In this design,the eprom is mapped into the middle of the ram, which can be expanded up to 24K wordsby replacing the 8Kbyte with 32Kbyte devices.

Extra paged datausing B or X port

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solve this problem, it is only necessary tointerpose an HCT buffer to perform levelconversion. Usually NMOS and cmos memorydevices have their outputs specified as beingt.t.l. compatible, but they are also implicitlyHCMOS compatible.

Output lines on the NC4000 come from

buffering is only required in exceptionalcircumstances. It is possible to load theaddress lines of a 4MHz NC4000 system with<500f I and >300pF. Resulting output drivevoltages will be within t.t.l. and mows vol-tage levels, and the system will still functionsatisfactorily. The combination of theNC4000's relatively low clock speed (com-pared with some new processors), its HCMOStechnology and its bus drive capability allhelp to reduce noise.

For the application described here, stan-dard components are used wherever possi-ble. However. memory decoding is done in'fast' t.t.l. to leave as much time as possiblefor memory access.

CIRCUIT OVERVIEW

The NC4000 is a true 16bit processor sobyte -wide memory devices are used in pairs.All addressing is in 16bit words, whether forprogram rom, ram or the two hardwarestacks. As you can see from Figs 4, 5 thismeans a minimum of eight memory devices.

Two eproms, contain a Forth oper-ating system/development environmentwith plenty of room for expansion as overhalf of it is unused. Main memory ram isprovided by IC7.8. As shown, the board has8K words (16Kbyte) of ram but, by rearrang-ing some jumpers in the decoding andchanging the 8Kbyte for 32Kbyte rams, allthe memory space not already occupied byeprom can be populated by ram.

The parameter stack uses the bottom 256locations of two 2Kbyte rams IC13.14 as doesthe Return Stack, ICH.12. Including the

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Fig.3. These timings in nanoseconds are average values based on devices with a Tas of65ns. Shaded waveforms represent an ondeterminate transitional period. Two importantfigures are Tas and I. Time Tas needs to be ready early to give as much time as possiblefor memory decoding. Time Tks has to be subtracted from overall cycle time to give theaccess time required for parameter (data) anc return stack rams.

NX4 board specification

CPUMemory

SpeedI/O

Expansion

SizePowerSoftware

NC400 3P8K words (16K bytes) eprom8K words (16K bytes) static ramSeparate parameter and retu-n stack ramsAverage 4MHz and can be uprated to .5 mips)One serial port (RS232).Novix 16bit B -port and 5bit X-oortOn -board memory expansion to 24K words (48Kbyte).Access to all Novix bus signals (except for stacks) provided on 64 -wayDIN 41612 connector pads.Single -width Eurocard0.5A with on -board 5V regulatorcmFORTH in Eprom on the board. 5'/4 in floppy disc for IBM PC/MS-DOStype host such as Amstrad PC -1512 with- Full source code for cmFORTH, utilities and demonstration,- Compiler to produce rom-based applications.- Forth Editor to run on PC host,- Terminal and disc emulation (for board) to run on host,- Documentation


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2F2530b

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6A Clock 26 27 20 14 22CK

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8A RESETRST

D- Data bus A -Address bus

Fig.4. NC4000 processor main memory eprom and ram.

1.30n

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NC4000, this already accounts for nine of the17 i.cs used. The remaining eight are forgenerating clock signals, decoding andRS232 buffering.

All major Novix signals, except for the dataand address buses for the two stacks, arebrought to a 64 -way DIN connector, PL1, sothat additional hardware can be easily added.The speed of the 4000 makes it suitable for anumber of applications including audio pro-cessing, vector graphics, robotics and com-puter vision. For maximum i/o throughputyou will want to use the two on -chip i/o ports(B and Xport) but the main memory data,address and write -enable lines also allow youto add extra memory or memory mapped i/odevices.

Referring to Fig.6, the 74F138 decoderselects memory in 4K pages, and the subse-quent And gates then give the optimummapping of eprom and ram. It also uses thelow part of the clock cycle to enable thechip -select outputs (q0_7) as a means of

synchronizing the memory access part of theNC4000 instruction cycle with the actualmemory devices. This section of the circuitalso shows the switched -frequency clockgenerator which can be made to adapt todifferent memory access times, of whichmore later.

Power, reset and RS232 drivers are shownin Fig.7, and do not need comment, exceptperhaps to note the use of a spare Or gate togive an external reset line on connector PL1.

NC4000 MEMORY MAP

On Figure 2, the memory map of theNC4000, there are five key points to note.Our first article described how the NC4000uses bit 15 to denote a 'jump -to -subroutine'instruction with the remaining bits givingthe destination address. The compiler effec-tively includes a value (the address) as part ofthe machine code instruction.

In the same way, the compiler can recog-

nize short literals and addresses below 2016and compile them with other Forth actions.As a result there is a scratch area from 0 to IFthat can be written to or read from in onemachine instruction taking, in this case, twoclock cycles.

Variable reading or writing normally takestwo instructions and four clock cycles, sothese low -memory variables are very usefulfor time -critical code. One way to regardthem is as 32 off -chip scratch registers. Thispart of low memory clearly needs to be ram.More of these time -saving software detailsare discussed in the next article.

The next landmark is 2016, the location towhich the processor jumps when it receivesan interrupt. As interrupt code can be held inram or rom, it has no impact on thehardware design - it will almost certainly bea continuation of the ram used for low-memory variables.

Prototype versions of the 4000 series,designated 4000P, have a fault in that they


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Fig.5. Stack ram and Xport hardware for the NC4000 processor.

23

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will not correctly interrupt multi -cycle in-structions. Use can still be made of theinterrupt structure but a software routine isrequired to support its operation.

The address to which the processor jumpsat reset comes next at 100016 and will almostalways be the start of rom or eprom. Thereset address is on a 4K boundary which isinconvenient given the ready availability of8Kbyte ram/eprom devices. Using 6264 ramsand 2764 eproms, the solution is to map thelower 4K ram from 0 to FFF, eprom from1000 to 2FFF and the remaining 4K ramfrom 2000 to 2FFF.

This is quite easily done by adding someAnd gates to the decoded outputs of IC5.Referring to Fig.6, Q1,2 feed the And gatewhich generates the eprom oe signal.However Al2 is inverted at 100016 (Q1 activeon IC5) so an inverter has to be inserted online Al2 between the NC4000 and the eprom,Fig. 4. This provides linear addressingbetween 1000 and 2FFF.

Because the jump -subroutine addressrange is limited to 15 bits, program spacehas to be below 32K and it makes sense tokeep that area full of ram and rom. To makefull use of this part of memory, the circuithas an expansion capability of up to 24Kwords of ram.

Links LK2 of Fig.6 allow you to selectaddressing for 6264 or 62256 type devices.Circuit IC16 maps the relevant Q outputsfrom IC5 to give acs for the 62256 option.processor can still read and write above800016 and this area is useful for data,tables, i/o devices and so on. If a full 64Kwords (128Kbyte) is insufficient, datastorage can be vastly extended by using theX or Bports to page in further 32K pages.

TIMING

A necessary area of study for any newprocessor is its timing diagram. TheNC4000's appears to be complicated by thefact that there are four of them, one foreach bus. However, each bus is easy tounderstand once you realize that everythingis timed from the rising edge of the clockinput.

Figure 3 shows how all the signals relateto the external clock applied to the proces-sor. As the clock goes high, the NC4000latches any input data or program instruc-tion, so outputs from ram, rom or i/o needto be held stable at this time (about 5ns).Propagation delay through memory decod-ing and deselect delay from standard romand ram devices is enough to cover this. Infact, the address buses are all stable for afurther 3Ons.

The chip then carries out internal actionsat maximum speed. Any output lines, forexample main memory address and datalines, become available on the chip's pinsthe moment they have been generated:

internal latching would produce delays andimpair the chip's performance. There is aperiod of transition from the previous to thenew values and these are shown as unspeci-fied on the timing diagram. The mostcrucial time on the diagram is TM sincedecoding for the next instruction can beginas soon as it is stable. Having the data readylOns after the address is fine as a memorydevice needs to be decoded and addressedbefore data can be applied to it.

Upon receiving the falling edge of theclock the NC4000 carries out no furtheractions. Instead, the designer must use thispart of the clock signal to synchronizedecoding, chip selects and so on, since thelower part of the clock cycle is for memoryaccess only. You can see from the circuitthat this synchronization is done by one ofthe se inputs to IC5.

The clock must be generated externally,and arranged so that the upper part of itscycle is at least T., (65ns) long, equivalentto 7.5MHz. Running the clock with a 1:1mark -to -space ratio at this frequency leaves

Special offer

The NX4 board has been specially designed to accoripany this set of articles and is availablefully assembled and tested. with circuit diagrams. so-tware and documentation. Availability issubject to stock and you should allow 30 days for delivery. Please send cash or cheque for£286 (fully inclusive) to NX4 offer. Golden River Ltc Churchill Road, Bicester. OxfordshireOX6 7XT.

For this offer. Novix has supplied 300 chips at a special price: the one-off price for theNC4000P alone is normally £205. Consequently numbers are limited and only one board canbe supplied per order. This off ?.r is available within the UK and Eire. Overseas readers shouldcontact Comsol.

Enqui-ies about the kit, chip and associated software should be made to ComputerSolutions Ltd at Canada Road. Byfleet. Surrey KT14 7HQ.


only 65ns for the decode and memoryaccess part of the cycle - realistically only5Ons after 10-15ns has been subtracted fordecoding. While this frequency could give acomputational performance in excess ofeight mips, 45ns ram and rom are not yetwidely available and are certainly not cheap.A low cost design forces use of lowerfrequencies.

If you now look at the lower part of thecycle and choose, say, 250ns as a practicableaccess time for readily available eproms, theclock cycle time goes up to 2 x (250+ 15)=530ns, or just under 2MHz, giving 2.4 mips.This represents a performance of aroundthree times better than a 68000 program-med using assembly language and runningat 8MHz, but it is still slow by Novixstandards.

Somewhere between lies the ideal; byarranging a suitable mark/space ratio to theclock, the processor and memory can eachbe made to work at near -optimum efficien-cy. This clock waveform could be producedby Anding the clock signal with a delayedversion of itself. An alternative is to use ahigh clock frequency and then divide it witha 74HC4017 counter, ic4.

By connecting one of the counter outputsto the master -reset line, it is possible to setup a suitable mark/space ratio. A 15MHzclock gives a convenient clock pulse of 67ns,and a division of five puts the lower part ofthe cycle at 266ns.

Further optimization is still possible. Us-ing a few extra components it is possible toreset IC4 using a cs line to give a mark/spaceratio which adapts to the speed of the devicebeing accessed. A standard crystal oscillatorfeeds the clock input of the counter, IC4.

Addition of an Or gate and two And gatesallows the decoder to select the appropriateoutput to reset the counter and give thecorrect mark/space ratio for rom or ram. TheOr gate has a spare input which is tied low.This can be used in conjunction with exter-nally generated chip selects and the i/o clocksignal to give a suitable access time forslower i/o devices.

Effective memory access time is, ofcourse, reduced by any decoding delaysthere may be. In this design, decoding takesplace through IC5,2, with a total delay ofabout 12ns. The counter gives the followingnet memory access time for its outputs afterdecoding delays are subtracted.Output stage34567

89o/c

Access time121ns188254321

388466533600

This scheme allows a free choice of ram androm access times. Outputs three and fiveprovide convenient times for 12Ons ramsand 250ns eproms, giving 5 and 3MHz clocksrespectively. Accessing any device outsidethe board's memory map without putting aWAIT signal into the Or gate causes a defaultto the slowest cycle time of 600ns.

The NC4000 is entirely static and its clockmay be stopped at any point in its clockcycle. If it is a few nanoseconds after the

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rising clock edge the c.p.u. completes itsinternal operations and then stops. Haltedlike this, the processor draws around 50µA.

STACK HARDWARE

Figure 5 shows stack hardware. Data stack,IC13.14, and return stack, IC11.12, rams do notrequire any decoding as the stack addresslines only access the bottom 256 cells. Theirtiming depends on the shortest memorycycle time taken elsewhere in the system,e.g. when addressing program ram.

Referring to Fig.2, the longest time takento output a valid stack address is Tks, orabout 75ns. Using a 5MHz clock the lowerpart of the clock cycle is 133ns, so the clocksignal itself can be used to drive the ramselect lines using 12Ons-access devices. Notethat the stack rams are accessed almostevery clock cycle; standard nmos devices canbe quite warm under these circumstances.

INPUT/OUTPUT

An important feature of the NC4000 is its i/ocapability. There are 21 programmable on -chip i/o lines arranged as a 16bit port (Bport)and 5bit port (Xport) with separate mask anddata direction registers for each port.

Ports X and B are useful in that they canoften be used to replace other hardware,with consequent reduction in componentand manufacturing costs. In this design portB is uncommitted and is available for experi-mentation. You may decide to use it for

Do 0

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16bit d -to -a

Analogue out

Fig.8. Connecting a -to -d and d -to -a converters to mainmemory. The d -to -a converter is mapped to 800016, thea -to -d converter to 880016. Latches decouple the converterfrom the NC4000 s3 that software has only to read the dataat 880016 and the n8xt conversion is automatically initiated.The analogue -to -digital converter is 12bit so the top fourinput bits are connected to ground.

analogue/digital conversion or to extend thedata storage space. The Xport gets used fortwo separate functions : serial i/o and multi-tasking hardware support.

There is no uart chip in this design - noneis needed. The Forth system supplied ineprom uses one X -port line for serial inputand another for output to form a softwareuart. During development, the serial line isused for communication with a host compu-ter such as an IBM PC, which in turn is usedas a terminal and disc drive for the Novixboard, Fig.1. Software to handle this isdiscussed in the next article; it is onlynecessary to say that for such an arrange-ment, a software-uart serial link is adequate.

If you refer to Fig.4 you will see that Xportlines 0 and 4 are used for this purpose. LinesRTS and crs are included even though thesoftware supplied on rom does not use them.

The only restriction to a software uart isthat it limits software using the serial line tosingle -tasking only. So what hardware isrequired to support multi -tasking? First, forany application that involves serial data, youwill have to add a serial device to thehardware so that data can be transmitted andreceived independently from the c.p.u. Next,the NC4000 needs to have separate para-meter and return stack areas for each task.Now it is perfectly feasible to run more thanone task in 256 words of parameter andreturn stack, but the software for each taskmay have to be restricted.

A better scheme is to give each task itsown protected parameter and return stacks

by selecting a different area of ram. ThreeXport i/o lines are available to do this, givingeight separate hardware task areas, neatlyfitting into the 2Kbyte ram chips. As shown,the circuit is set up for just one task area (asis the software supplied in eprom), but thepatch area LK5 between the Xport bus andthe Stack rams allows this to be done ifrequired.

Adding extra hardware to the main mem-ory bus is straightforward. Figure 8 showshow to add standard a -to -d and d -to -a con-verters to the memory map, which are usefulfor processing such as audio frequency ana-logue signals.

CONCLUSIONThe NX4 board illustrates how to designNovix-based hardware. A number of im-provements could be made, such as adding aproper uart and reducing component countby using pals or e.p.l.ds to replace decodingand clock hardware. Further componentreductions will be possible as 16bit-widememory devices become more readily avail-able. Even with current components aminimal system need only consist of tendevices: two roms, six rams, a clock and anNC4000.

A description of supporting software (asmall, but complete Forth development en-vironment including a compiler for produc-ing rom-compatible code) will be given in asubsequent article.

William Watson is with Computer Solu-tions of Byfleet, Surrey.


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-TELECOMS TOPICSDHSS ordersPlessey ISDX

The Department of Health andSocial Security (DHSS) hasplaced an order, worth around£3.3m, with Plessey Com-munication Systems (PCS) forISDX, digital private telephoneexchanges. This, the largest in-dividual ISDX order that Plesseyhas received, is for 57 systems forDHSS offices all over the coun-try. The systems range in sizefrom 48 to between 300 and 400line capacities. Included in theprice was a ten-year main-tenance contract.

The DHSS is currently under-taking a three-year moderniza-tion programme. Its new net-work marks a change in telecom-munications policy - purchasinginstead of renting. One of therequirements for the new net-work is to be able to switch64Kbit/s voice and data. Thisorder, according to Plessey, in-cludes some 6,700 extensionsand accounts for around 14% ofthe new exchanges required.Where there are digital trunks,DPNSS (digital private networksignalling system) is used to linkexchanges and a newly intro-duced facility known as RAS II(remote access system) will aidmaintenance.

RAS enables an ISDX to dialautomatically a special tele-phone number in the event of aproblem and connect with thePCS National Computer AidedService Centre at Nottingham.Once the telephone exchange isin contact with the computer,the two machines can analysethe problem, and very often cureit, without human intervention.Should the problem require theattention of an engineer, staff atthe computer centre can deter-mine whether the problem canbe resolved remotely or whetheran engineer must be despatched.

NATO's newsatellites from

BAeBritish Aerospace (BAe) has wonthe contract, worth in excess of1100million, to supply two com-munications satellites for NATO.They will provide secure militaryand diplomatic communications

and be virtually identical to theUK's armed forces Skynet 4series currently under construc-tion by BAe and for which Mar-coni supplies the payloads. Sky -net 4 services are voice, data andtelex to and from naval vesselsand fixed and mobile land ter-minals.

Designated NATO IV, the firstof the new satellites is to belaunched in the early 1990s. Theprevious NATO satellites werebuilt by US company, FordAerospace.

Telecomms andIT converge at

NorthernTelecom

Northern Telecom has mergedits Communications Systemsand Data Systems divisions inthe UK, the aim being to enablethe company to provide a betterresponse to market demands forconverging voice -and -data net-works.

Norwich Uniongets distributeddigital dealing

As part of its new £800,000 tele-communications upgrade, majorinsurance company NorwichUnion will be one of the firstgeographically remote financialdealing rooms to be connected toBT's City of London Dealer Inter -link exchange. Users of this ex-change system can have theirdigital private wires patchedthrough a central exchange atMoorgate in the City so thatcircuits can be added or re-allocated rapidly to matchchanging business patterns.

The network is based on aThorn -Ericsson MD110 digitalPABX and handles 2976 exten-sions plus 267 trunk lines andprivate wires. It consists of amain exchange unit at its head-quarters building in Norwichtogether with two remote sites inNorwich and one in London tohandle dealer traffic. The privatecircuits are connected toNorwich Union's own LondonPABX and then routed throughthe new corporate network to theNorwich dealing room.

Dealers are equipped with 36 -key Thorn Ericsson Courierdigital programmable tele-phones. These have built-indisplays to show each dealer theorigin and destination of anyDealer Interlink call.

Philips adoptsSiemen's ISDN

standardPhilips Electronic Componentsand Materials Division hasadopted the Siemens -developedISDN-orientated ModularArchitecture (IOM) and itsassociated interface as the stan-dard for a new range of ISDNc-mos integrated circuits. Themodularity of the IOMarchitecture is claimed to makefor easy implementation of theISDN customer basic access.

This interface is a standard4 -wire, local point-to-point du-plex interface which intercon-nects ISDN layer 1 and 2 i.cs, orlayer 1 circuits together. By con-forming to the 10M interfacestandard, the new i.cs are suit-able for use according to theCCITT I -series recommenda-tions in ISDN terminals as wellas in network terminations, linerepeaters and line cards.

Besides the 2B + D channelsrequired for basic subscriber ac-cess, a 64Kbit/s M -channel and a48Kbit/s S channel are also avail-able. They respectively transferstatus information for localcircuit control and ISDN basicaccess referred service informa-tion (such as signals for activa-tion, de -activation and mainte-nance purposes).

Boomingdatacom test

marketAccording to a report from inter-national market research com-pany, Frost & Sullivan, there wil Ibe major growth in datacom testand management markets overthe next five years. The report"Data Communications Test.Measurement and Network Man-agement Markets in WesternEurope" (No.E887) projects anaverage annual growth of 26.5%from a base of $154 million in1985 to a forecast $632 million(constant 1985 dollars) in 1991.

The study notes that the mar-ket will be driven both by userintolerance of system down -timeand by the increasing complexityand diversity of communicationssystems. F & S expect the mostexplosive growth to be in pro-grammable multi -function in-struments, which embraceanalogue, digital and protocolmeasuring and analysing func-tions. Here, from a small Euro-pean base of $4m in 1985, theyforecast the market to reach$104m in 1991.

Analogue instruments will bethe least dynamic product class,increasing more slowly as agreater number of digital trans-mission systems are im-plemented and modems phasedout. The network managementand control segment will,according to F&S, increase from$64m to $268million by 1991.

Private network owners suchas banks, insurance companies,airlines and oil companies will bethe biggest consumers of all thegroups covered in the study, withthe exception of optical time -domain reflectometers which areused more by PTTs.

In 1985, the UK accounted for28% of Western Europe's con-sumption of data communica-tions test and measurementinstruments and network man-agement systems. At that dateWest Germany absorbed 13%,while Italy and France took 12%each. By 1991, the UK's share isforecast to drop to 25% withScandinavia and the Beneluxcountries claiming 14% each.

Besides analysing and fore-casting product and countrymarkets, the report reviews re-levant technology and thecountry -by -country data com-munications environment inEurope. Individual product linesare compared and major sup-pliers profiled.

More information on the re-port. which is priced at $2,500,from Frost & Sullivan on 01-7303438

Cellular by theday

A deal between Avis car hire andCellrent, a new company offeringVodafone cellular telephones forshort-term hire, enables car ren-tal clients at London's HeathrowAirport to have the option to hire


TELECOMMS TOPICSa hand -portable Vodafone. Cell -rent has identified as a primetarget the international businesstraveller who wants instantworldwide communicationswhile visiting the UK. Leadinghotel chains and travel groupswill also act as outlets.

Basic rental is £4.95 per daywith billing being based on theMeterfone facility. This feature,unique to the Vodafone network,allows the call charge units to beread from the handset display. Itautomatically adjusts to thedifferent charge rates.

Virgin hot airsponsored by

CellnetThe Virgin Atlantic BalloonChallenge, the first attempt tomake an Atlantic crossing by hotair balloon, is being supported byCellnet, one of the two cellularnetworks. It will be providing anumber of cellphones to theorganizers of the challengetogether with Celldata equip-ment to enable them to transmitand receive technical informa-tion.

The Cellnet InternationalServicelink programme will en-able the Virgin team to use cellu-lar phones in New York as well,where there is a different cellularsystem. This scheme allows Cell -net's customers to use cell -phones whilst in the USA andHong Kong more easily andcheaply than they might other-wise be able to do.

Muirheadmoves to high

streetMuirhead. the UK's first manu-facturer of facsimile machinesand well known for the machinesused to transmit newspaperphotographs, has launched anew range of Group 3 officefacsimile machines. The threemachines, each with an increas-ing range of features, all have theability to scan A3 -wide docu-ments and have an RS232C in-terface port for linking to anencryption device or computer.

With the objective of expand-ing its customer base, the com-pany will sell through a dealer

Cel!fax facsimile system fromsheet in 11 seconds.

Muirhead, which transmits

network in addition to its estab-lished approach of selling direct.This, in the past, has been aimedmainly at the Blue -Chip com-panies, corporations, govern-ment and other public bodies -often those needing real systemsexperience.

At a time when growth isrunning at 100% per annum andthe UK population now exceeds70,000 machines, the market isgetting increasingly com-petitive. Muirhead does not in-tend to just become a "hot -boxmerchant" and aims to employits technical expertise to solvecustomers' communicationsproblems. For example, it isoffering Cellfax, an adaptation ofa standard machine. This is con-nected to cellphones via an inter-face unit fitted with a standardBT plug and socket arrange-ment, eliminating the use ofacoustic couplers which areoften unsatisfactory. Equally im-portant, the system provides fullerror correction facilities to en-sure uncorrupted transmissionregardless of line quality.

Telecom Goldimproves telex

facilityTelecom Gold, British Telecom'selectronic mail service, has in-stalled CASE Beeline equipmentto provide increased capacity formessage delivery to the telexnetwork. While users of theenhanced telex service will seefew outward changes, they willbenefit from an increased num-ber of telex lines and an even

$10 billion (£6.7 billion) in 1985and also has overseas offices inGeneva and Hong Kong. As wellas providing telecommunica-tions services in the north-eastregion of the USA, its companiesalso: offer international market-ing and consulting services;market cellular mobile tele-phone services; and sell informa-tion systems and products; etc.

Variable blocklength protocol

an A4 Microcom has enhanced itserror -correcting Microcom Net-working Protocol (MNP) with

spread of telex traffic. An addi-tional feature is the optionalonline assistance, available be-fore each prompt, to guide newusers.

The Beeline equipment atTelecom Gold combines CASE'sDCX communications exchangeand a specialized applicationsprocessor into a single electronictelex switching system. This isintegrated with TG's operationalnetwork via an X.25 packetswitching gateway. Messages in-tended to be sent by telex areentered at users' terminals, wordprocessors or personal compu-ters and are passed through thenetwork into Beeline's messagestore. Here the Beeline systemtakes over the message, trans-ferring it onwards to the telexnetwork.

Nynex acquiresBIS

Business Intelligence ServicesLtd (BIS Group) has been ac-quired by Nynex Corporation(New England Telephone andNew York Telephone) in an ex-change of shares valued at £75million.

BIS Group, a major London -based information technologyand marketing services orga-nization operating worldwide,will continue to operate under itspresent management. It providesmanagement of major organisa-tion with a range of strategicinformation and communica-tions.

Nynex is the third largest tele-communications company in theUSA in terms of sales which were

further classes which increasethe effective line throughputbeyond that provided by MNPClass 3 which has, for example,been implemented by Dowty inits Quattro dial -up modem. MNPconforms to the ISO Open Sys-tems Interconnection (OSI) net-work reference model and sup-ports interactive and file transferapplications.

The protocol efficiency of thenew MNP Class 4 implementa-tion is about 120% so that adevice employing it with a2400bit/s modem will provide athroughput of approximately2900 bit/s. It uses an adaptivepacket assembly so that whenline conditions are poor and re-transmissions are high, packetsize decreases thus minimizingthe amount of data that needs tobe retransmitted. Conversely,when line conditions are good,and retransmissions are few,packet size increases, and somaximizing data throughput.Class 5 adds a real-time adaptivealgorithm for data compressionwith a resultant protocol effi-ciency of 200% while Class 6provides a universal modem sys-tem which will operate at a fullrange of speeds between 300 and9,600bit/s and dynamically adoptthe highest speed that can besuccessfully handled.

Microcom has just receivedBABT Approval for its own AX/2400 and AX/2400c modemswhich conform to MNP Class 4and 5 protocols respectively. Ithopes to obtain approval for itsClass 6 modem by the middle ofthe year.

Telecomms Topics was writtenbyAdrian Morant.


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thandarELECTRONICS LIMITED

Thandar Electronics Limited,London Road. St Ives, Huntingdon.Cambridgeshire PE17 4HJ EnglandTelephone (0480) 64646 Telex 32250 Test

THE LOGICAL CHOICE


ENTER III ON liKPLY CARD

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PINEAPPLE SOFTWAREPrograms for the BBC models `B' with disc drive with FREE updating service on all software

DIAGRAMStill the only drawing program available for the BBC micro which gives you the ability to draw really large

diagrams and scroll them smoothly around the screen stopping to edit them at any time if requiredPineapples unique method of storing the diagram information on disc means that the size of diagrams is

limited only by the free space on disc. and not the amount of computer memory you have available IA blank80 track disc will allow up to 39 mode 0 screens of diagram}

The superb print routines supplied with the program enable large areas of the diagram to be printed in asingle print run in a number of different sizes and rotated through 90 deg if required Full use can also bemade of printers which have a wider than normal carriage available

The program is fully compatible with the Marconi Tracker ball described below

PLEASE STATE 40 or 80 TRACK DISC& WHETHER STANDARD BBC or MASTER VERSION IS REQUIRED

PRICE £25.00 + VAT

DIAGRAM UTILITIESA suite of six utility programs which add additional features to the 'Diagram drawing program The utilities

include the saving and loading of areas of diagram to and from disc The ability to display the whole of yourlarge diagram on the screen at one time ter 41,4 or 8*8 screen format) The addition of borders andscreen indents to diagrams. and the abl, ' shit a whole diagram in any direction

PRICE £10.00 ' VAT

PCBThis new release from Pineapple is a printed circuit board draughting aid which is aimed at producing

complex double sided PCB's very rapidly using a standard BBC micro and any FX compatible dot-matrixprinter

The program is supplied on EPROM and will run with any 32k BBC micro (including Master series) Alsosupplied is a disc containing a sample PCB layout to demonstrate the programs features

By using an EPROM for the program code the maximum amount of RAM is available for storing component

location and ASCII identification files etc (Up to 500 components and 500 ASCII component descriptionsmay be stored for a given layout) These is no limit to the number of tracks for a given PCB, although themaximum size of board is restricted to 8" ' 5 6"

Using a mode 1 screen, tracks on the top side of the board are shown in red, while those on the undersideare blue Each side of the board may be shown individually or superimposed A component placement screenallows component outlines to be drawn for silk screen purposes and component numbers entered on thisscreen may be displayed during track routing to aid identification of roundels

The print routines allow separate printouts of each side of the PCB in a very accurate expanded definition1 1 or 21 scale, enabling direct contact printing to be used on resist covered copper clad board

This program has too many superb features to describe adequately here, so please write or phone for moreinformation and sample pnnouts

PRICE £85.00 VAT

MARCONI TRACKER BALLThis high quality device comes with its own Icon Artmaster drawing program and utilities to enable it to be

used in place of keyboard keys. Joysticks. or with your own programs

PRICE £60.00 VAT p&p £1.75PRICE INCLUDING 'DIAGRAM' SOFTWARE £79.00 VAT p&p £1.75

CONVERTER LEADSConverter leads to enable the Trackerball to run mouse software and Inc mouse to run trackerball software

(Inc DIAGRAM) Please state which way round when ordering

PRICE £8.00 VAT

TRACKER BALL for MASTER seriesThe Pointer ROM 'S supplied instead of me Icon Artmaster disc and enabes the Tracker bal. :o work

directly with the MASTER series computers le g to use with TIMPAINT etc.) Prices are the same as for thestandard tracker ball

POINTERThe Pointer Rom is available separately for people already owning tracker balls. and comes with

instructions for use with the MASTER computer.

PRICE £12.50 + VAT

MICROSPICEA new addition to our range of engineering software Microspice is a very powerful DC and AC analogue Circuit

Simulator package for any model BBC computerAs well as all the usual facilities available with this type of program non-linear effects small signal, noise

measurements and sweeps may be performed Component values may be swept allowing component tolerances to beinvestigated as well as thermal performance etc Comprehensive transistor modelling is incorporated using a 20parameter Ebers Moll description The program is supplied on disc with a very comprehensive 49 page manual

Please write or phone for more information

PRICE £99.00 VAT P&P FREE

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Telex No: 312242

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ERS LANE, HALL GREEN, BIRMINGHAM B28 OTB. ENGLAND.TRANSISTORS: VALVES:TYPE.

2N33752N35532N36322N37332N38662N44162N44272N50902N5109211451602N55892N55902N55912N56412N56422N56432N59132N59442114594521%159462N60802N60812N60822N60832N60842SCI7292SC19452SC1946A2SC19472SC19692SC19702SC19712SC197.7

LIST: TYPE: LIST.f f

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AH21 lAAH2511AH2532BT5BTSBBT17BT17ABT95C3JC3JAE55LE8OCCE801E 88CCE9OCCEl 30LEB91EBC91EBF89EC90ECC32ECC81ECC82ECC83ECC85ECC88ECC91ECC189ECF80ECF86ECF801ECH81ECL82ECL86EF80EF85EF86EF89EF9IEF92EF93

LIST

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21 251 351101 3 .1 253 251 901 901 903 802 002 002001 501 651 802301 931 601 703003002 302 952 201 50

TYPE:

EF94EF95EF183EFt 84EK90EL34EL36ELB4EL86EL519EL803SEL821EN32EN9EZ80EZ81EZ90FG17FG105GXuiGXU4GZ34KT66KT77KT88ML8536M18741NL SERIES00V02-600V03-10OVO3-120Y3-650Y3-1250V4.250RG1-240ARG4.3000XG1-2500XG5-500SRI .3200xR1-64000A2

LIST:

2001 601 90i 80I 403 902 303.002.107 709.95

13 7516 252001 901 501 50

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120 002 00

TYPE:

0A30B20830C32C39A2C39WA2D2I2E2621(253.400ZE IN3-500ZEIM38283C453CX100A54.65A4.125A4-250A4-400A4-400B4.400C48324C35A4CX250BEIM AMP4CX250BNAT4CX350A4X150A5AR45AS4A5R4GYA-E5U4GB5V4GA6AH66AK5W6AK66AL5W6A05A6A05W6AS66AS7G

LIST:

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39 9042 00

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114 0099 0099 0015 0024 5070 0052 5060 0076 00

110 00110 00110 00

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5 352 103502 102 502302 501 951 801 75

802404 30

TYPE:

6AU5GT6AZ86BA66BE66BH6613J668K4C6BN86BZ66C46CB6A6CJ36CW46DC66E56EA8601(66HF56HS66JB6A6JE6C6.156CEK 761X116I<D66K1386L6GC6L0660116SL7GT6SN7GTB6U8A

2AT612AU612AV612BA612BA712BE612BY7A12BZ612DW7

LIST:

3 703 80I 701 952152004503502 501 951 802.308002 454 202 252504 253 954506256652502 256 402004.106 252252.253052001 901 902001 952 352002.703.703.75

81393493520502050A554455455557555957275867A58795965599161306146A6146B6360A6550A6883869737027A719972477262A7360758675877591A 4.65781 5AL.GE 48007815R 53.008122 120 008906AL 55 00150132 650572B CETRON 55 00807 290810 82 00812A 36 85

TYPE: LIST:

30 0018 0041 20480480

81 0095 0024 5052 50

29514000

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32.0024 509509504 957908 703.956 504203.20

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CIRCUIT IDEAS

FREQUENCY MULTIPLIERI needed a cheap but accurate way of display-ing frequencies from 350 to 800Hz with aresolution of better than 0.5Hz. This designmultiplies by 1000 over a 100Hz to 1 kHzrange and locks onto input changes veryquickly -a standard counter would require agate time of about lOs to give the sameresolution.

Output of the 4046 phase -locked -loop6

v.c.o., which is used to drive the frequencymeter, is 1000 times the input frequency. CiTThis output frequency is divided by three 7

decade dividers to provide a signal for thephase -comparator input. Phase of the di-vided v.c.o. output is compared with phase ofthe input signal and the difference outputdrives the v.c.o.

Changing the number of dividers changes vssthe multiplication factor, but bear in mindthat the v.c.o. only works up to just over1MHz. Response time is controlled by thelow-pass filter.Damon HoggettCarlisleCumbria,

Signal n

Vdd +15V

12

2 10k11 16 14

Frequency countermodule

4 046 pHV C out

Phase compLI

v (r) in out in

8 9 13

3 10k

4P7

Low pass filter

3

ILV34 TOOn

14

NLClock

15

Vdd +15V

16

12

16

Carry ci/t4017

124017

14

113 I8 115 13

VSS

12

+15V

4017

VSS

15 13

Divide by 1000

CLOCK CIRCUIT FOR ASYNCHRONOUS DATA TRANSFERBesides being simpler than a p.1.1, this clockcircuit with synchronizing inputs can beused in systems receiving asynchronous datafrom several sources.

Async.inputs

*RI

inputsAsync.

0

Normally a fixed squarewave clock is

produced but if there is a transition on anyinput, a short output pulse occurs. If outputlevel is high a negative pulse is added and

Clockoutput

Clockoutput

vice versa so positive and negative clockedges are produced for each input transition.

Operation of the oscillator is similar tothat of the two -inverter type so its clockperiod is

Tini(2 -101 I +k)]

k(1-k)

where T is RC. is threshold voltage for alogic -level transition, VD!) is supply voltageand k is Vti,ND1).

Both a simplified circuit and a c-mosversion for three asynchronous inputs areshown. With no input, clock frequency is atits lowest so the design is useful for battery -

powered equipment.He man TaccaBuenos AiresArgentina

Further readingCMOS Linear Applications, G. Taajes.National Semiconductor application note88, 1978 (two -inverter oscillator).Nuevo circuito de reloj para maquinassecuenciales sincrenicas, H. Tacca. RevistaTelegrafica Electronica No 831, July 1982.Nuevo metodo de proyecto en circuitossecuenciales. E. Capdevile, A. Barragan, N.Vergani and R. Ahumda. Revista TelegraficaElectronica No 821, July 1981.

EI.F.(1120NICS(C, lia.1.1 WI I 407

FCIRCUIT IDEAS

MULTIPLE -CORECABLE TESTERA string of leds powered from a constant -current source is used in this simple multi -way cable tester to check for broken orshorted conductors and crossed wires.

To test for short circuits, the cable isplugged into connector A. A short between,say pins 2 and 5 extinguishes diodes 3, 4 and5. Open conductors are found by connectingthe cable to both connector A at one end andconnector B at the other. A lit led indicatesthat its corresponding line is open.K. DvorakCanadian Standards AssociationRexdaleOntario

-10V

DUAL -OUTPUTREGULATOROne part of a quad single -supply op -ampforms a regulator both for its own supplyvoltage and other circuits. A secondary lowervoltage output with better regulation isavailable for references, etc.

Despite its simplicity, this circuit isadequate for many applications. Perform-ance is better than circuits using just ahigher -voltage zener diode and trimming ispossible using the op -amp feedback net-work. Note that the two voltages verytogether when the feedback network isaltered.

Current output is about 500mA using the2A ZTX650. If more current is needed, it maybe wise to buffer the op -amp with a secondtransistor.Robert BainesJesmondNewcastle-upon-Tyne

44 4

140Vd.c

8k2

OTS 423

1N960

2 I 3

15mA

44 44

-÷14*-}-189 90

820

5k6W

Constant current source1 2 3 4 5 89 90

0 0 0

A B

Cableundertest

90 89 6 5 4 3 2 1

0 0 - - - - 0 0 0 0

AMPLIFYING SMALL VOLTAGESCommon practice when amplifying smalldirect voltages is to use a bandpass amplifierwith switches at its inputs and outputs. Thisproposal is based upon simulation of aresistor by a switched capacitor.

The first op -amp functions as an amplifierand d.c.-to-a.c. converter, so the secondop -amp amplifies an a.c. signal. Attenuationis provided by the third op -amp, which alsoacts as a switch for removing switchingeffects.

Two inverting and one non -inverting op -

R1

Vin -"\/\/`

Vindo

Amplifier & FVIswitch

amps are used. Resistance Req is simulatedby a capacitor C (10-11to 10-1°F) given byReg= 1/Cuf where f it switching frequency so

V1= -VulfRiCu,V2 = KV'

and\cut = -RiCufV2=KVin

where K is 1+ R3/112.Kamil KrausRokycanyCzechoslovakia

AmplifierVy Attenuatort vout

switch

vout


Designing acommunications receiver

This new British -made receiver aims to outstrip far -easterncompetition in both price and performance. John Thorpe of

Lowe Electronics outlines his design approach.

Most modern communi-cations receivers adopt adual -conversion super-

heterodyne design (Fig.1.). Themultiple -conversion receiverprovides several advantages: A high first i.f., higher than

the highest frequency receiv-ed, distances the mixer con-version image from the re-quired coverage, and allowsits rejection by a low-passfilter at the input. Also thelocal oscillator tunes througha sub -octave range.

A low -frequency final i.f. canprovide selective filters withgood shape factors, and ampli-fiers for the bulk of the receiv-er's gain.

Each i.f. section must have a sufficientlynarrow bandwidth to remove image respon-ses from the subsequent section. With theavailability of monolithic crystal filters forthe first i.f., a dual -conversion h.f. receiverwill be able to offer more than 80dB of imagerejection for its second i.f.

The r.f. filters at the receiver input areusually arranged as a bank of fixed band-passfilters, an appropriate one being selected tomatch the receiver's tuned frequency. In

J.R. THORPE

earlier receivers these filters would have abandwidth typically less than 100kHz andwould be mechanically tuned, either by aganged tuning device or separately as a pre -selector. In electronically -tuned receiversthis is uncommon: with a few exceptions,there is no tracked r.f. tuning and filters areconsequently wider.

If the filter bandwidth is less than one oc-tave the receiver system will be protectedfrom strong signals that can produce even

order intermodulation productswithin the receiver's tuning range.A set of suboctave filters iscommonly found for frequenciesabove 1 or 2MHz, but below thislimit fewer and wider filters are used.

A very important function ofthe input filters is to attenuatefrequencies close to the first i.f.of the receiver and in the imagetuning range. A separate 30MHzlow-pass filter is often includedto ensure good attenuation. Asecond requirement is low inser-tion loss, since signal losses heredirectly worsen the receiver'ssensitivity.

The need for an r.f. amplifierstage will depend on the type ofmixer and on the sensitivity re-

quired. With a useful sensitivity, an h.f. re-ceiver would produce an output signal-to-noise ratio of 10dB for an input signal ofabout 0.20 (p.d. into 50 ohms) in s.s.b.mode. This corresponds to an input noisefigure of around 10dB, a noise level whichwill be exceeded by antenna noise in most loca-tions using fixed aerial systems. If the receiv-er is intended for portable use with a whipantenna it should be more sensitive, andnoise figures of around 3dB are appropriate.

Fig.1. Dualconversion superhet for general h.f. coverage. First i.f. is commonly between 40 and 75MHz; second i.f. is oftenat 455kHz because of the wide range of standard filters available for this frequency.

0 to 30MHz

45MHz1st. mixer

r. amplifier 1st i f amplifier

1st. i.f. filter15kHz bandwidth

r f input bandpass filters

amplifier

2 ld if filter25kHz b -w for ssb6kHz b/w for a m

Local oscillator Conversion oscillator45 to 75MHz 44 545 MHz

Tuning

a m udio

Product detector

ssb audio

Carrier re-injection oscillator455kHzs 1.5 kHz


FREQUENCY

Fig.2. Reciprocal mixing may reduce receiver sensitivity when a strong, unwantedsignal is present Noise at h originatingfrom the local oscillator b is mixed into thereceiver's i.f. passband a; this noise mayalso be modulated by unwanted signal g.c noise sidebands due to phase noise in

oscillatord wanted signal (weak)e unwanted signal (strong)f wanted signal after mixing, including

local oscillator noise.

Fig.3 (right). First mixer and i.f. filter. Abalanced output from the SL6440 mixerhelps achieve maximum gain and dynamicrange.

Tuned to 494Hz

r fsigrLH

r

(011-0Cr

SL6440mixer

/ pin

45MHz if

3gc from

Local oscillatorsignal I -

Below: layout of the main p.c.b., showing signal and control paths. Manufacture is greatlysimplified by avoiding the need for inter -board wiring, connectors and screening.

Antenna input I

f amplifiersand detectors

f filters

C[

p s u

a f amp

a f pre- Receiveramp and control

istersswitching...wiem.

J LrIs b carrierinsertion osc

2nd mix list i f filterI

LJConversionoscillator

1stmix

r f inputfiltersO=:1[

1

C]Ij

p l system Local oscillator

Signal path through receiver

Internal signals

Control information

Data from control uniton front panel

4

4

4

detector

FIRST MIXER

The first mixer and first i.f. filter mustwithstand the effects of potentially manystrong signals over quite a wide range offrequencies; the performance of these stageswill directly affect the receiver's ability toresist overload.

Double -balanced mixers are findingfavour with many designers for severalreasons:-a useful 30 to 40dB of attenuation of the

local oscillator signal fed into the i.f. filteris obtained by using a balanced mixer, withconsequently less noise fed into the i.f.system.

- good isolation between the local oscillatorport and the mixer input port means lesssignal fed back towards the antenna.

- sensitivity of the receiver to signals at theintermediate frequency is reduced by 30 to40dB.

- even -order intermodulation performanceis usually very good, and consequent sav-ings can be made in the r.f. input filterswithout sacrificing overall performance.

The first i.f. filter serves two purposes: firstlyto attenuate signals at the image frequencyof the conversion to the second i.f., andsecondly to reduce the number of signalsthat can reach, and may overload, the secondmixer. Filter bandwidths are in the range 12to 18kHz, but this is more chosen byavailable filter elements than by receiverrequirements, which would call for a nar-rower filter.


Matching the first mixer to the filter isoften a problem. Many mixers require aconstant impedance at their output across awide frequency range if they are to give goodintermodulation performance.

SECOND MIXER

The second mixer generally has only to copewith in -band signals: the majority of out -of -band signals are removed by the first i.f.filter. It is often selected as a low -noisedevice or is preceded by a low -noise amplifierstage. But if there is excessive gain before orin the mixer, the receiver's third -order inter -modulation performance usually suffersbadly at signal separations of 10 or 5kHz.

Cain up to the selective filter (followingthe second mixer) should be kept as low aspossible whilst preserving adequate receiversensitivity.

Amplifier and detector stages followingthe selective filter have much more effect onresolved audio quality than on receiver r.f.performance. The a.m. envelope detector'slinearity is critical for good quality, especial-ly since some broadcasters now use modula-tion levels approaching 100% with heavilycompressed signals.

The response of the a.g.c. system can havea marked effect on audio quality. For a.m.reception the average (i.e. carrier) level ofthe signal is best used, and the a.g.c.response should be slow enough to stop lowfrequency modulation causing excessive sig-nal distortion via the a.g.c. feedback path.With s.s.b. signals, a.g.c. must be derivedfrom peak signal levels. The attack (gainreduction) time needs to be fast enough toprevent i.f. amplifier clipping, but not so fastthat the receiver is deafened by impulsenoise spikes. Slow release times improvequality, but can be inconvenient for searchtuning and for monitoring two-way trafficwhen the signals are of different strengths.

OSCILLATOR PROBLEMS

The local oscillator can have a considerableeffect on the r.f. performance of a receiver.

Modem designs, with cheaper digital inte-grated circuits, favour electronically -tunedoscillators and frequency synthesis systemsbased on quartz crystal references. Thesecan provide excellent frequency stability butsuffer from a number of other problems: receiver tuning is not continuous as with

a mechanically -tuned oscillator, butoccurs in discrete tuning steps. For s.s.b.reception the steps must be small enoughto resolve signal frequencies correctly; astep size of 10Hz is considered adequate.

the oscillators and digital dividers pro-duce quite large quantities of signals at avariety of frequencies. These can affectreceiver operation in two ways: signalspicked up by the sensitive input circuits ofthe receiver appear as spurious signalswhich can mask stations being received orproduce annoying heterodynes; and sig-nals may alternatively appear as sidebandsto the local oscillator output, causing thereceiver to have spurious responses atfrequencies other than its tuned fre-quency.

HF-125 SPECIFICATION

Coverage: 30kHz-30MHz (150kHz-26.1MHz for German market)Modes: a.m.. s.s.b. (u.s.b.. 1.s.b and c.w.)Tuning: by spin -wheel, in 15.6Hz steps (step size increases with faster tuning rate); megahertzquick selection by up/down push buttons.Memories: 30. with lithium battery back-up1,1 filter bandwidths: 2.5/4/710kHz; 400Hz audio filter for c.w.Sensitivity (typical values for frequencies above 500kHz): (s.s.b.) 0.31, V for 10dB s n

0.71J.V for 10dB s -n at 70°i modulationR.I. attenuator: user -selectable. 20dBNoise blanker: permanent operation. 0.4ms blank p sriodDynamic range: 90dB at 50kHz from tuned freq iency. 80dB at 20kHz (both intermodula-tion distortion and reciprocal mixing)Image and spurious responses: 80dB rejectionAudio output 0.75W into internal loudspeaker 1.25W into external 411 loudspeakerConnections: antenna. 5011 (S0-239 socket) or 6301! earth terminal; jack sockets forheadphones. recorder, external loudspeaker. d.c. it put (12V at about 250mA)Options: f.m. and synchronous a.m. modes; internal NiCd pack, charger and active whipaerial; keypad frequency controller.

Electronically -tuned oscillators used infrequency synthesis tend to have quitelow -Q tuned systems and as a resultproduce an output with significant phasenoise. By a process known as reciprocalmixing (Fig.2) this phase noise worsensthe selectivity of the receiver. With alow -noise oscillator and a good qualitys.s.b. filter, selectivities of -105dB at20kHz, improving to better than -110dBat 50kHz from the tuned frequency areobtainable, but more typical values are-85dB and -95dB.

THE HF-125

At the design stage, the HF-125 communica-tions receiver was required to have adequateperformance to operate well on the short-wave broadcast and communication bands;but an overriding objective was to produce areceiver which could sell on the UK marketin the £300 to £400 price bracket. Designingwith a fixed price but a flexible specificationproduced the following initial guidelines: Standard parts and components should be

used whenever possible; specialized partsshould be producible with minimal tool-ing costs. As a direct result of this, thedesign does not require large volumeproduction to maintain a low price.

Assembly should be as simple as possible.A single p.c.b. design was desirable, avoid-ing wiring and connectors. Mechanicalassemblies should be avoided in favour ofan all -electronic design.

As much circuit as possible should re-quire no alignment, and necessary adjust-ments should be straightforward and in-dependent. Testing and alignment proce-dures should be provided in the controlsystem.

CHOICE OF MIXER

For the first mixer, a double -balanced devicewas required to overcome performance de-ficiencies in the necessarily economical r.f.filters. A choice of three types was available:diode ring, active ring (using fets) andintegrated circuit (a transistor tree mixer.The transistor tree mixer, in the form of aPlessey SL6440 integrated circuit appearedto offer significant advantages over the othertypes: It could offer a small amount of gain and

so removed the need for an amplifier stagein the first i.f.

No broadband r.f. transformers wereneeded at the input and local oscillatorports of the mixer, significantly reducingcosts. Also, the local oscillator powerrequirement was small.

Mixer performance was relatively un-affected by the impedance seen at itsoutput, allowing direct connection to thefollowing crystal filter.Operating current of the SL6440 mixer

can be extemally controlled, allowing abalance between power requirement, inter -modulation performance and mixer noisefigure. In the HF-125, the mixer is operatedwith about 10dB of gain; a mixer noise figureof 8dB is achieved with an input third -orderintercept point of +10dBm. This perform-ance fits the specification very well.

The gain of the mixer is dependent on itsoutput impedance, and with a gain of 10dBperformance is limited by the output stages.The 45MHz first i.f. crystal filters are of thefundamental type, with an input impedanceof about 500 ohms matching the mixer'soutput directly. With no i.f. amplifier, a.g.c.action is provided by a p-i-n diode whichreduces the mixer load impedance, decreas-ing its gain and at the same time raising itsintercept point.

INPUT FILTERS

The input impedance of the first mixer isaround 600 ohms, and since this is a conve-nient value for a high impedance input to thereceiver, all the input filters were designedto match it. A 50 ohm input, also provided onthe receiver, is transformed up to 600 ohmsby a broad -band transformer.

Five selectable filters cover frequencyranges 18 to 30MHz, 10 to 18MHz, 4.2 to10MHz, 1.6 to 4.2MHz and below 1.6MHz.Although there are too few filters to providesub -octave coverage for much of the h.f.spectrum, an attempt has been made toseparate broadcast bands containing strongsignals from communications bands. Par-ticular attention has been paid to removingmedium wave signals (below 1.6MHz) fromthe higher frequencies. The appropriatefilter is switched into the input circuit byp-i-n diodes; the high filter impedance helpsreduce signal currents through these diodesand so prevents intermodulation.


2 5k Hz filter

Conversionsignal

4kHz filter

a g c

amdetector

Productdetector

0

Fig.4. Second i.f. stage includes a cascaded series of amplifiers and filters. Filters are diodeswitched for different i.f. bandwidths.

The filters consist of five -pole high-passand low-pass sections constructed from fixedvalue inductors and capacitors. There are noadjustments; to cope with component toler-ances the filters are designed to be widerthan their required bandwidth. Even sothere may be a variation of several decibels inreceiver sensitivity at the extreme edges ofthe filter bands. The alternative type of filterusing over -coupled tuned circuits was re-jected because of the difficulty of productionalignment.

SECOND I.F. SYSTEM

The first i.f. filters feed directly into theinput of the second mixer. This is also anSL6440, although it operates at a muchlower current than the first mixer. Con-figured to give about 4dB of voltage gain, itstill has quite good intermodulation per-formance; and this, coupled with low gain inthe first i.f. (about 8dB allowing for filterlosses) ensures that the receiver's overalldynamic range is maintained above 70dBalmost to the edges of the selective passband.

Because there is little room for worseningthe noise figure from the first mixer, thenoise figure of the second mixer is, ofnecessity, very low. The receiver as a wholeachieves a noise figure of about 12dB (0.28ILV sensitivity for 10dB s/n in s.s.b. mode).which is quite adequate for nearly all ap-plications except perhaps for optimum 10metre amateur band listening.

The remainder of the second i.f. stage isbased upon the Plessey SL6700 integratedcircuit, intended for a.m. receivers. It con-tains two a.g.c.-controlled amplifiers, ana.m. and a.g.c. detector, and an i.f. conver-sion mixer which in this receiver is used as aproduct detector. Use of this chip means thatthere are only three active devices in thewhole of the r.f. and i.f. sections of thereceiver.

Multi -element ceramic filters are used inthe 455kHz i.f. for the receiver's mainselectivity. Because the small four and six -element filters cost little morethan a tunedi.f. transformer, they were used for allcoupling between amplifiers and detectors.The result is an i.f. system with good filtershape factors and excellent stop -band atte-nuation, that requires no alignment inproduction. In addition four different i.f.bandwidths are available by bypassingselected filters.

The 2.5kHz filter used is an expensive14 -element device; but it gives a 6:60 dBshape factor of better than 1:2, and isespecially suitable for reception of a.m.signals in s.s.b. mode where a degree ofcarrier attenuation is required. Careful filtermatching to achieve a flat i.f. passbandresponse, coupled with a linear detector inthe SL6700 produces good audio quality ina.m. mode. The 10kHz filter immediatelybefore the detector improves the s/n ratio byremoving broadband noise generated in thefinal i.f. amplifier.

P.L.L. SYSTEM AND TUNING

The easiest way to achieve the requiredfrequency stability is to use a phase -lockedloop synthesizer to produce the receiver'slocal oscillator signal. Several I.s.i. devices -programmable dividers and phase detectors- make the single loop synthesizer astraightforward and economical circuit. Un-fortunately it is not generally suitable forreceiver use, because the frequency steps(i.e. tuning increments are equal to thereference frequency; and for the loop tocontrol a wide -range voltage controlledoscillator (v.c.o.) adequately the referencemust be greater than the required 10 to20Hz tuning increment.

Two approaches are commonly used toovercome this problem:-a controlled phase slip within the p.1.1.

system, where a higher frequency refer-ence is used with fractional division im-plemented by dividing by integers N orN + 1 for varying proportions of time.Because the v.c.o. is divided by a numbereither above or below the required value(although the average value is correctthere is a gradual phase change betweenthe oscillator and the reference, and thishas to be made up by some form ofcontrolled phase shift.

-a multiple loop system, using two, three,or even four separate p.l.ls to control thefinal output frequency. The loops share acommon reference, but the output fre-quency of each loop is divided by a fixedvalue before being mixed into the nextloop.The cost advantages of a single loop p.1.1.

were so great that the system was consideredvery carefully to see if its problems could beovercome. In a dual conversion receivertuning is affected by both the local oscillator

Table 1: i.f. filter selection (frequencies in kHz).

i.f. bandwith 1st filter 2nd filter 3rd filter2.5 2.5 4 104 7 4 107 7 bypassed 10

10 500(1.p.f.) bypassed 10

and the conversion oscillator frequencies;so, provided that the first i.f. is kept withinthe bandwidth of its filter, the conversionfrequency can be tuned. This allows the localoscillator to tune in steps larger than therequired tuning increments, and the conver-sion frequency to fill in with the fine tuning.

In the HF-125, the conversion frequencyis about 44.5MHz, and a crystal oscillator isthe obvious choice to generate this. Thisoscillator can be electronically tuned over asmall frequency range of a few kHz by thecontrol system, and although the resultantfrequency is not locked to a reference oscilla-tor, the stability is good. In practice thetuning range was restricted to kHz becausebeyond this range the linearity of controlsuffered unless thermal stability was sacri-ficed. The control voltage is derived from ad -to -a converter to allow digital tuningcontrol.

By tuning the conversion oscillator therequirements of the local oscillator are easedsomewhat: it is now required to tune in kHzincrements. A synthesizer producing 45 to75MHz from a kHz reference is feasible, butseveral problems will arise: the phase detector and loop filter require

very careful design to reduce sidebands onthe output (at 1 kHz intervals) to anacceptable level.

tuning response of the loop will be slow. the p.1.1. system will not be able to correct

frequency fluctuations in the oscillatorcaused by noise or mechanical vibrationto any great extent.

To offset these points, low cost of the systemand a low component count produces acompact design; and with a c-mosdivider there is virtually no spurious signalradiation and no need for screening.

PHASE DETECTOR

An important part of the p.I.I. system is thephase detector and low pass loop filter. Theoutput from the phase detector will changeat the same frequency as the referencesignal, in this case at I kHz. Signal compo-


nents at this frequency must be removed bythe loop filter to ensure purity of the localoscillator signal. Here, a digital phase detec-tor has the advantage that when the oscilla-tor and reference signals are in phase there isvirtually no signal output from the detector.Also, the capture range of the p.I.I. is notdependent on the response of the loop filter.The digital phase detector consists of a seriesof edge -triggered latches.

To achieve the necessary reduction of1kHz signal in the v.c.o. control voltage, thtloop filter has a long time constant. As aconsequence the lock time of the loop isconsiderable - about 600ms for a largefrequency change. This is not normally aproblem in a manually tuned receiver, but toalleviate unpleasant noises after, say, keypadentry of a new frequency, the receiver outputis muted until the system achieves lock.

The p.I.I. is implemented with a single -chip Motorola device containing a pro-grammable divider, a reference frequencydivider and a digital phase detector. Thenecessary division range is from 45 000 to75 000, and an additional dual -modulusprescaler (divide by 128 or 129) provides a17 -bit counter.

LOCAL OSCILLATOR

A fundamental i.c oscillator provides thelocal oscillator signal over a frequency rangeof 45 to 75MHz.

The varicap tuning element provides arather lossy capacitance, and to include it asa major part of the tuning reactance wouldresult in an oscillator with a poor phasenoise performance. To overcome this prob-lem receiver designers often use severalseparate oscillators to each cover part of therequired frequency range: three -oscillatorsystems are common. By this means therequired capacitance change from the vari-cap element is reduced, and its Q can beimproved by a small series capacitor com-bined with a fixed capacitor to provide mostof the Lc reactance. In the HF- 125 a similareffect is produced without the expense ofseveral oscillators: the inductance is switch-ed to give four frequency ranges: 45 to51MHz, 51 to 57MHz. 57 to 66MHz and 66 to75MHz.

Performance is quite satisfactory for alow-cost receiver. The 1kHz sidebands onthe oscillator output are below -45dBc,below -60dBc at 2kHz, and at or below thenoise floor further from the carrier. Peakf.m. deviation is about ± 5Hz at the lowerend of the tuning range, rising to about± 10Hz at the higher end. The latter isaudible when a pure tone is resolved, but isnot detectahle on s.s.b. voice signals. Oscil-lator phase noise results in a receiver selec-tivity of about 85dB at 20kHz. and 95dB at50kHz, corresponding to oscillator noiselevels of -120dBc/Hz and -130dBc/Hz re-spectively.

CONTROL SYSTEM

The control system provides the interfacebetween the user and the internal workingsof the receiver. It needs to be designed at twolevels: the electronics required to control

H.F. RECEIVER DESIGN

Recent years have seen a trend towards more expensive and more feature -laden short-wavecommunications receivers on the domestic marke:. Unfortunately. many new designs haveachieved little or no improvement or have even worsened, the ability of a receiver -- toreceive.

This article looks at the design criteria, and necessary compromises, in producing alow -cos: communications receiver with good performance.

To quantify that performance, we can consider some of its aspects

Sensitivity: the input signal level required for the receiver to produce. say. a 10d8signal-to-noise ratio at the output under ideal conditions with no othersignals present

Selectivity: the ability to extract a wanted signal from a band containing many signals.Selectivity assessment would include measuring filter shape factors andtheir degradation by reciprocal mixing.

Dynamic range the level of rejection of effects die to strong unwanted signals, includingblocking, crossmodulation and intermodulation.

Stability: the extent of frequency changes with time and temperature.

Signal cuality: the quality of resolved signals, d stortion, signal-to-noise ratio, frequencyresponse. Also the characteristic of the a.g.c. system.

Facilities: for example, reception modes. available filter bandwidths, noise blanker,notch filter, memory channels. external connections etc.

Ease of use: methods of tuning, frequency disk lay. selection of modes and filters etc.

A successful design should balance the d fferent performance requirements so that thereceiver is neither lacking in any one respect nor excessively expensive because of the costof mak ng one aspect outstandingly good. Features offered will depend very much on theintended market area and the projected price.

the parts of the receiver and the user'soperating procedure. The latter forms a veryimportant part of the receiver's specifica-tion, and in a domestic market is oftendominant over r.f. performance in estab-lishing sales potential.

To minimize costs and to keep the frontpanel uneuttered, many receiver functions,such as a.g.c. time constant and r.f./i.f. gain,are left to automatic control with no manualover -ride. This approach helps the less ex-perienced user to operate the receiver.

For the control system a microprocessorusing prom for program storage was chosenso that mask programming would not benecessary, and devices could be program-med as required for production.

Software holds the microprocessor in astatic condition when the receiver's controlsare not operated, and with the exception ofthe clock oscillator all signals in the controlsystem remain at a steady d.c. level. Thiseliminates nearly all radiation from thecontrol system and allows screening to beeliminated without affecting performance.The microprocessor clock also serves as thep.I.I. reference oscillator, reducing the num-ber of signal sources within the receiver.

The microprocessor is supported by aliquid crystal display driver chip and a c-mosram chip with lithium battery supply backupfor the receiver's memories. These are inter-faced through the processor's i/o portsrather than being connected to the c.p.u.data bus for reasons stated above. Thereceiver is controlled via a three -line syn-chronous serial data bus, which is wellfiltered to remove low level signals emanat-ing from the c.p.u. A serial bus was chosen tominimize filtering and simplify connect ions.

ASSEMBLY

All components are mounted on two printedcircuit hoards. A small board behind thefront panel contains the microprocessor andmemory circuits, the display and all thefront panel controls. It is connected to themain board by two right-angled connectors,a total of 15 connections for power andcontrol lines. The main board is mounted inthe bottom of the case, and connections onthe rear panel of the receiver mount directlyon to this p.c.b. There is no wiring in thereceiver with the exception of a cable to theloundspeaker mounted in the top of the case.

The main p.c.b. is double -sided: the com-ponent side is mostly covered with a groundplane. This. with a careful component lay-out, reduces interaction between separatesections of the receiver: no additionalscreening is required.

The local oscillator and p.I.I. system havea separate ground plane from the rest of thereceiver circuit to eliminate circulating cur-rents in the ground system and the metalcase. Splitting the ground plane was effec-tive in reducing local oscillator radiationfrom the antenna input. An aluminium casescreens the receiver circuits from externalsignals.

John Thorpe read engineering and computerscience at Cambridge University. with spon-sorship from Lowe Electronics. Since gra-duating in 1983 he has been with Lowe atMatlock where he is head of development.One of his spare -time interests is hell -ringing.


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414



Modulated -pulse amplifiersrevived

Recent m.o.s. transistors remove historical limitations topulse -duration modulated amplifiers and bring new power and

performance to industrial applications.

A'

dvances in m.o.s. power transistortechnology, plus fresh circuit think-ng, have propelled pulse duration

modulation power amplifiers from technolo-gical backwaters to the forefront of sophisti-cated power deployment. Modulated -pulsetechnology provides a new level of compati-bility with a surprising range of applications.Besides competing against s.c.rs at the up-per levels of 'smart' power, and providing analternative to linear amplifiers where size,weight, heat dissipation and efficiency areissues, p.d.m. devices span an impressiveapplication range. outlined on page 416.Pulse -duration modulated power sourcesnow provide off -the -shelf answers for fast -response four -quadrant d.c. supply needs.shrink the size and heat dissipation ofvariable -frequency a.c. sources and line con-ditioners, and contribute high efficiency andease of voltage stabilization to u.p.s.s. Theyalso provide new solutions to magnet coilenergization in nuclear accelerators andhigh energy physics research, plus freshresponsiveness and power ratings for d.c.motor drives.

Low distortion, excellent linearity, andbandwidth of 12kHz, plus improvementsthat are in the offing, add audio and publicaddress systems to the expanding roster ofnew p.d.m. power amplifier applications.The technology's inherently high efficiency- upward of 90% is standard, 98% is notunknown - maximizes operating life andminimizes heat generation in mobile equip-ment for robots, in -plant vehicles and re-search submarines. Small size and lowweight promote mobility and portability,and enable electronic control to be packedinto tight spaces without the cost andcomplexities of water cooling.

Applications that demand a combinationof power and what might be called electronicagility are particularly compatible withp.d.m. High power function generators arewidely used in nuclear research, vibrationtesting, sonar excitation, and automatic testequipment, where subtle computer prog-ramming must be capable of choreog-raphing kilowatts, or even hundreds of kilo-watts, of electrical power, and in many casesp.d.m. amplifiers do a significantly better jobthan any other technology.

A linear amplifier is inherently inefficientbecause of the balance of power supplyvoltage not applied to the load is developed


Comparator

_FL

BARRY FRIEDMAN

10y

Modulationinput

Set V./for

a e

VM

VR

ve, VR 2

Solenoid-opens valve I 1,

LI for VR V5

Lower Vez settingopens valve forsh ter intery I

Solenoid -controlled valve

Fig.l. Simple open -loop system adjusts air flow by controlling the solenoid -poweredvalve's on/off duty cycle in accordance with flow rate voltage VR set by potentiometer. Solong as modulation voltage VM is less than flow voltage VR the comparator switches to+10 volts output, energizing relay and solenoid, hence opening valve for air passage.When modulation triangular waveform VM exceeds flow voltage VR, comparator outputswitches to zero, releasing relay and solenoid to halt air flow. Waveforms show howhigher values of flow voltage VR produce longer valve -open periods.

Highly compact p.d.m. amplifier develops 4,50C watts heat dissipation (98% efficiency)and is smaller than a telephone directory.

-at

q\keila : 1 1.°1-%-fr/

i

415

across the output transistors. In essence,whatever the load does not recieve thetransistors dissipate. Pulse modulationamplifiers skirt this fundamental difficulty,rather than confront the heat dissipationissue head on.

The panel on p.419 shows how the effi-ciency of the simple circuit rises to a

theoretical 100% when an ideal transistorhandles rectangular wave signals. This is theprinciple that p.d.m. amplifiers harness: thepower output stage is arranged to handleonly rectangular waves - hence apply fullpower supply voltage to the load - regardlessof the kind of signal that the amplifierprocesses. Accordingly, even though thep.d.m. amplifier might deliver 50kW ofsinusoidal energy to a vibration transducer.efficiency is not limited to the theoretical78.5% efficiency ceiling of ordinary linearamplifiers under the same circumstances.Instead, by arranging for the power transis-tors to switch rapidly between fully on andfully off conditions, the output stage pre-serves a close approximation to the ideal.

In other words, ideal transistors operatingin this mode would exhibit zero dissipation,hence provide 100% efficiency, regardless ofthe input waveshape. This is the essence ofclass D operation. The design task faced bycircuit engineers is to arrange for the outputpower transistors to handle only rectangularwaves at full power supply voltage, whileadjusting their conduction periods to vary inaccordance with input signal amplitude. Thefixed -amplitude, fixed -frequency pulses areadjusted in duration and polarity so thatwith output filtering, the amplifier developsan accurate amplified replica of the input.

WHAT TOOK SO LONG?

What's new is today's generation of m.o.s.power transistors, which remove the histor-ical limitations imposed by early bipolardesigns. Today's m.o.s. power transistorsprovide current and voltage ratings compa-rable with bipolar types, but the feature thatdistiguishes them most for modulated pulseamplifiers is their speed, leading to widerbandwidth operation, which puts the tech-nology into the mainstream of industrialusage. In addition, with today's switchingfrequencies far above the human hearingrange, audible noise at the modulationfrequency has been completely eliminated.

In absence of output filtering, p.d.m.amplifiers feed the load with fixed-

frequency, variable -width pulses whose am-plitude is equal to the supply voltage. Natur-ally, only a limited number of applicationscan handle raw output pulses: they need tobe smoothed into a continuous but highpower copy of the input.

Early p.d.m. amplifier designs made out-put filtering difficult, owing to their lowswitching frequency. A typical bipolar ampli-fier designed a decade ago switched at 500 to5,000 Hz: consequently, inductors capableof full -load filtering become enormous. Theinability to build such filters into the ampli-fier, along with the bandwidth limitationimposed by low switching frequency, hasconfined bipolar amplifiers to servomotordrive systems, where the motor's inherentinductance and mechanical inertia provides

10y

Set flow rate

Min.

Error amp

-G[VR-VF].VE

"Ddulation input

Air f lc

C)

Vol

For V I setting

TUFor Vi2 setting

VE1

E2

Pressure tank smooths\-ISensel-pulsed air flow f I V/ 7

Flow rate feedback/ v

Fig.2. Introduction of feedback reduces air flow's dependence on linearity and amplitudestability of modulation voltage. Instead. flow rate depends on gain stability of thehigh -gain error amplifier - determined by the three external resistors - and thecalibration accuracy of the flow sensor. Comparator develops positive pulses for drivingthe power mosfet into conduction whenever error voltage (which has negative polarity),is more negative than the negative -going modulation voltage. Pressure tank's ability tosmooth the air flow depends on tank capacity, modulation frequency. and rate at whichpressure control voltage is varied. Flow control system mimics the electrical p.d.m.power amplifier. which develops a pulsed output in absence of filtering circuits.

AMPLIFIER COMPARISONS

Traditionally modulated -mike amplifiers have been confined by bandwidth and output -distortion limitations to a niche market powering servomotors. Availability of recent m.o.s.power transistors has eliminated historic performance limitations, enablihg p.d.m.amplifiers to compete with a wide range of linear and thyristor power sources. In addition,they can function as bipolar four -quadrant programmable supplies, variable frequencies a.c.sources and line conditioners. as well as high -power function generators.

Comparison between commercial linear amplifiers. p.d.m. amplifiers. and thynstor power sources

First generationp.d.m. units

Linearpower units

Thyristorsystems

Second generationp.d.m units

Power ceiling 20 kW 100 kVA MW MWSwitching frequency 5 kHz 60 Hz 80 kHzBandwidth 500 Hz 50 kHz 5Hz 10 kHzLinearity. d.c. 5% 0.10/0 0.05 - 0.5%Distortion 5% 0.5% 0.1- 0.5%Efficiency 80% 30 - 60% 90% 90- 98%Watts per pound' 200 - 500 5-50 15-50 500 - 1500Dollars per watt 2.00 3-0.6 1.00 - 0.25 0.50 - 0.30Watts per cubic inch 5.00 0.15- 0.5 0.7- 2 15-30

' Excludes power supply; varies with cooling method. Thyristor systems don't require separate supply.

a natural filtering effect.Indeed, because most servomotors de-

mand modest amplifier performance, there'sbeen little incentive for servo system manu-facturers to exploit new m.o.s. transistortechnology. As a result, much of the currentferment in p.d.m. amplifier design comesfrom firms outside the servomotor field,where entrepreneurial manufacturers seekmarkets far removed from the restrictedniche of motor powering.

Today's m.o.s. power transistors give

creative circuit designers the wherewithal toextend pulsed amplifer capability to per-formance levels previously the sole provinceof linear amplifiers. The upshot is anindustry -wide upgrading of amplifier speci-fications, where an order -of -magnitudehigher switching frequency raises noise farbeyond human hearing, achieves 12kHzbandwidth, and permits a built-in filter tohold switching frequency ripple below 1% ofthe output voltage.

Growing compatibility between


modulated -pulse amplifiers and music re-production will probably lead to distributedmusic systems with an amplifier built in toeach loudspeaker. Instead of using a largecentralized power amplifier, low-level musicsignals will then be piped, probably in digitalform, to the widely dispersed speakers. Byadding address information to each digitalmusic word, a jukebox -like music sourcewill then be able to send individual musicselections to self -amplified speakers in eachseparate location.

LOW HEAT GENERATION

Reduced heat dissipation leads to lowertransistor junction temperature hence en-hanced m.t.b.f. In addition, heat removal issimplified, room air conditioning require-ments are eased, and the amplifier's bulk andweight are significantly decreased. Watercooling, necessary with many linear ampli-fier applications, is also eliminated. In turn,these attributes lead to notable applicationbenefits: equipment mobility for instance, orintegrally mounted electronics instead of aseparate equipment rack. Another is drasti-cally reduced operating cost.

If a linear amplifier delivers 50kW ofsinusoidal power to a vibration transducerfor on-line reliability testing, it is very likelyto convert another 50kW into waste heat,and total power consumption will be in the100kW range. Ideally, of course, the linearamplifier should operate at 78.5% efficiencywhen handling sinewave signals (Page 419).In reality, real rather than ideal transistors,imperfect load matching and the need toprovide a safety margin of supply voltagebring the efficiency nearer this 50% figurethan the theoretical 78.5%.

Replacing the 50% efficient linear ampli-fier in this application with a 90% efficientclass D amplifier (whose efficiency is inde-pendent of signal waveform), reduces totalenergy consumption from roughly 100 to55kW. The benefit: a tenfold reduction inwaste heat; the amplifier can pay for itself inenergy savings alone, without the simplifica-tion of heat removal, air conditioning, andother support needs.

PULSE DURATION MODULATIONREFRESHER

A mechanical example of pulse modulationprobably affords a more graphic and intuiti-tive introduction to p.d.m. principles than adirect electrical one. Figure 1 simply out-lines basic principles, rather than extol pulseduration modulation as a superior methodfor air flow control.

Assume for explanation's sake a frequencyof 2Hz for the triangular modulation wave-form, VM, so that the solenoid -controlledvalve has an opportunity to open and closetwice per second, with the control circuitdetermining the duration of the intervals.The comparator energizes the relay andholds the valve open for as long as theinstantaneous value of triangular modula-tion voltage VM is less than flow voltage VR.Viewed differently, so long as the compara-tor's inverting input terminal is negative tothe non -inverting input terminal the com-parator output remains at 10V. When the

Vin

F

0Off '

RF

AeFilter averages pulsedourput to developfeedback voltage

vi

Load voltage

Unfiltered output

Remoteload currentreadout

001n

Fig.3. Early p.d.m. power amplifiers were constrained by available bipolar transistorperforrrance to operate at modulation frequencies in the 500-5000 Hz range, whichmeant that filter circuits capable of smoothing significant load currents would be largerthan the amplifier itself. Servomotors. which present highly inductive loads to theamplifier, provide an inherent filtering effect, eliminating the need in many instances forany series inductor -capacitor network. This compatibility between p.d.m. amplifiers andservomotors has probably led the indust-'ial world to overlook application possibilities in

the mainstream of power usage.In this simplified p.d.m. amplifier con'iguration. which only handles positive inputs, a

mosfet develops a positive output across the external load, a fraction of which is tappedoff and filtered to form the error -correcting 'eedback signal. The output transistor isdriven into conduction by the comparator's negative going output; in turn, thecomparator's output goes negative whenever the error voltage is more negative than thetriangular modulation voltage.

Drive pulsesfromcomparators

Load

T T

JL

Fig. 5. Full -bridge output circuit, based on pairs of series connected transistors A B and

C D, permits bipolar operation from single -polarity d.c. supply. One constraint lies in

the need for a floating (non -grounded) load, although this drawback disappears whena.c.-only applications permit a transformer to be interposed between amplifier andgrounded load. Modern amplifier designs minimize power transistor switching losses bysophisticated circuit design that confines pulse modulation to only one transistor in each

active pair. For instance. if a positive inout signal activates series transistors A and B, it is

only necessary to apply modulated pulses to transistor A; transistor B in this pair canremain fully on for the duration of the positive input. Likewise. transistor D can be heldfully conducting for negative inputs, while transistor C provides the pulse modulation.

ELECTRONICS & WIRELESS WORLD '117

modulation waveform exceeds the flow vol-tage, the inverting input is positive relativeto the non -inverting terminal, which dropsthe comparator's output from 10V to zeroand closes the valve.

Different levels of flow voltage establishedby the control potentiometer, produce com-parator triggering earlier or later in themodulation cycle. Higher VR values meanthat the modulation voltage exceeds VR foronly brief periods at the tip of each modula-tion cycle.

Comparators may have an open -loop gainof 100,000:1 upwards. For 10V operation,this means that a 10V/100,000 = 0.1mVpotential difference between the compara-tor's input terminals will develop maximumoutput. If the comparator is operated fromdual -polarity d.c. supplies, the output canswing to maximum in either direction,depending on whether the inverting inputterminal is more positive (negative output),or more negative (postive output), than thenon -inverting terminal. It takes a 0.2mVdifference between VR and VM to switchoutput polarity from -10 to +10 V.

CLOSING THE LOOP

Feedback, VF, from the flow sensor intro-duces sensor calibration as the system para-meter responsible for flow rates commensu-rate with potentiometer setting, Fig.2. Inthe open -loop arrangement, Fig.1, systemaccuracy depended on the linearity andamplitude stability of the triangular mod-ulating voltage VM, as well as comparatord.c. stability, potentiometer supply voltagestability, and so forth. A whole collection oferror sources get into the act.

Use of feedback eliminates most errorsources did ties performance to the flow -meter reading. Feedback also accelerates thesystem's response to a change in flow set-ting, btause increased flow setting im-mediately produces an exaggerated errorvoltage and an overcompensating initial flowrate. As the tank pressure builds up andforces a faster flow through the sensor,increased feedback reduces the excessivevoltage until equilibrium is attained at thehigh flow setting.

The pressure tank smooths out air flowpulsations, but also prevents the output flowfrom responding immediately to new flowsettings. One can visualize computer con-trolled applications in which a digital -to-analogue converter replaces the manualpotentiometer for generating flow voltage.For rapid computer -commanded changes inflow rate, tank capacity becomes an impor-tant factor in the system's responsiveness.Modulating frequency is another crucialingredient in responsiveness.

Since air flow control is analogous to ap.d.m. amplifier's power control, these con-flicts between responsiveness and outputsmoothness also arise in amplifier designand application. Modern p.d.m. amplifiersminimize the effect of this conflict by usingmodulating frequencies in the 100 kHzregion. Doubtless, future mosfet circuitswill push the switching frequency higher,and useful bandwidth with it.

Vin± 10y

Summing amplifierreverses error -

signal's polarity

5V-5V I.

,--LErr:7

+150V

o o o

I

-150y

Fig.4. A half -bridge output circuit, using complementary p -channel and n -channel powertransistors. enables the p.d.m. amplifier to handle both positive and negative inputsignals. including the sinusoidal waveform shown. The drawback to this simple outputcircuit is its requirement for a costly dual -polarity d.c. power supply. The full bridgeoutput circuit of Fig.5 permits bipolar operation from a single -polarity d.c. source.Modern amplifiers incorporate internal converters to provide the various operatingvoltages required by the amplifier's signal handling circuitry.

Upper transistor A develops positive output pulses in response to positive input signals(and negative error voltage), while transistor B develops the negative output pulses inmirror image fashion. The waveforms show how the amplifier's internal filter smooths thevariable width output pulses to produce a sinusoidal replica of the input. Actualwaveforms shown are representative (for the sake of explanation) of an unfilteredresistance load. A choke input filter alters the voltage pulses and causes a phase lag inthe sinusoidal output. Modern p.d.m. amplifier designs operate at high modulationfrequencies so that a relatively small filter can reduce the output component atmodulation frequency to acceptable levels.


SIMPLEST PDM AMPLIFIER

The simplest p.d.m. amplifier handles onlypositive inputs, and develops a train ofoutput pulses having the same polarity asthe input - Fig.3. The non -inverting ampli-fier operates much as the feedback -controlled air flow system. Fig.2, but re-quires an inverting amplifier to develop anegative -going feedback signal from theamplifier's positive output. The feedbackvoltage then opposes the amplifier's input toproduce error voltage VE, which adjusts theduration of output current pulses. The com-parator develops negative drive signals forthe power transistor whenever error voltageamplitude exceeds (is more negative than).the modulation voltage. For ease of intuiti-tive circuit understanding, the sawtoothmodulation waveform is presented in bothFig.2 and Fig.3 with negative -going polarity:the idea is to maintain the appearance ofcompatibility with the error signal's invertedpolarity. In reality, the sawtooth modulationvoltage would ordinarily vary uniformly ab-out zero, and the error amplifier wouldautomatically adjust its output to producewhatever transistor drive pulses were neces-sary for the desired on -off duty cycle.

For description's sake, this primitiveamplifier incorporates no output filter. In-stead, a small internal RC filter smooths afraction of the pulsed output for use asfeedback. Remote current readings are pro-vided by a low value resistance in series wihthe load: a highly stable d.c. amplifier feedscurrent signals to a remote indicator.

Fancy footwork is necessary to create apower amplifier capable of developing ± 150volts output. Fig.4, output p -channel mosfetA operates during positive amplifier inputsignals and develops a positive train of 150Voutput pulses in response. Conversely, thesecond power transistor B, an n -channelmosfet. responds to negative amplifier in-puts with -150V output pulses. The filtersmooths the pulsed output to. create anamplified replica of the original input.

One disadvantage of the half -bridge poweroutput circuit of Fig.4 is the need for twopower supplies, which adds considerably tosystem cost and bulk. Another drawbackoccurs when driving highly reactive loads:reactance can cause a transfer of powersupply to the other, building up excessiveand damaging power supply voltages.

Commercial amplifier designs may usemany output transistors connected in para-llel to achieve desired power levels. A fortun-ate attribute of m.o.s. power transistors istheir positive temperature coefficient foron -resistance. This characteristic aids loadsharing between transistors. A negativecoefficient would decrease resistance withtemperature, causing the hottest semicon-ductor junction to hog most load currentand immediately launch into a self-destructspiral of ever -worsening temperature riseand current imbalance.

Biasing the comparators (one positive.one negative) and using a modulating vol-tage with peak -to -peak amplitude slightlyless than the sum of the bias voltagesensures that each comparator responds onlyto its assigned error voltage polarity. (Note

EFFICIENCY DEPENDS ON WAVESHAPE

Chart shows how efficiency of an amplifier circuit depends on the waveshape being amplified: a fact ofphysical reality that prevails even though ideal transistors are used. A varying fraction of the power supplyvoltage is developed across the transistor, leading to transistor energy dissipation in the form of heat but for arectangular wave signal. the entire power supply voltage is developed across the load. permitting a theoretical100% efficiency.

In normal operation, many factors conspire to reduce linear amplifier's efficiency below the theoreticalceiling established by signal waveshape. For instance. less-thanideal transistors introduce resistance into thecircuit contributing loss of output voltage and internal heat dissipation. Also, it is necessary to provide a safetymargin between peak output voltage and the power supply voltage; this too violates the conditions formaximum theoretical efficiency. Operating linear amplifiers at reduced power - equivalent to using a largeramplifier than the application requires - is another source of efficiency degradation. Driving low resistanceloads is no problem for p.d.m. amplifiers, which can feed short circuits without efficiency degradation or lossof stability: linear amplifiers suffer extreme efficiency losses when driving low resistance values - most of thepower supply voltage is developed across the output transistors rather than the load.

Instantaneous power dissipation

Load power, WI - V2 X k CR,

Total power, WT = VS X Ic - MLA

Averaged over time. T

TLoad power = V2i/RE dt

1

0

T

Total power - !i VsVoVIIIIL dt

0

VZ

Amplifier efficiency is ratio ofuseful power ± total power x 100% -

1IT0W dt

fr dt0

T IW7

dt1 I VSVL dt

0-17.

1 fRLTV2sin2uit dt

100%x

RLTV' sin 2 wtdt

1

= 100% x2T -100%xRiT

Far sinusoidal signals (consider only halfcycle signals because simple amplifier willnot handle complete cycles) maximum effi-ciency becomes

S

For sawtooth signals

Vc TVs

so maximum efficiency becomes

11fT

O

(1Vsy dtT 3RiT

- 67%1 12dt

TVs 2IILT

2T 3T

For square wave signals the ideal transistorwould dissipate no power because it wouldapply the entire power supply voltage to theload.Efficiency is therefore 100%.

Inputsignal

Wave

shapeRatio

WI /WrPercent

efficiency

Sir.e f N.Y.\ Tr/4 78-5

Sawtooth AA 2/3 66.7

Square J -La 1 100

VS

T

toy


DC SERVO AMPLIFIERMODEL 217

Off -the -shelf p.d.m. modules with 500Wcontinous rating 1500 peak. provide ele-gant solution to control c.c.t.v. camera'sillumination.

that the error amplifier produces an errorvoltage of opposite polarity to the amplifierinput). The waveforms of Fig.4 illustrate thebiased comparator operations, which areperhaps less readily understood than theconfigurations of Fig.2 and Fig.3.

A full -bridge power output circuit reducespower supply cost by permitting bipolaroperation from single -polarity supply, Fig.5.Each comparator in this basic configurationnow commands the operation of two series -connected power transistor pairs A+ B andC+ D. In high power amplifiers, of course,many parallel -connected transistors are rep-resented by each single transistor.

Today's new levels of p.d.m. amplifierpower and performance expand applicationsinto the full spectrum of industrial usage,where they provide compact economicalalternatives to linear amplifiers on the onehand, and fast -response competition tothyristor power systems on the other. Figure6 outlines the basic schematics for coildrives, function generators, and smart pow-er sources, in addition to traditional motioncontrol applications. Once the rebirth ofp.d.m. technology is widely appreciated.further innovative uses will enlarge theroster of p.d.m. problem solving.

Barry Friedman is vice-president of market-ing at Copley Controls Corp, 375 ElliotStreet, Pewton, Maryland. USA.

Seven p.d.m. power amplifiers are paralleled tofeed fast -rise computer -contoured 160 -ampcurrent pules into magnetic resonance imagingsystem's 500 µH. 50 ml.! gradient coils. Datacompiled by magnetic resonance imaging byequipment manufacturer compares new designbased on p.d.m. technology with earlier systembuilt around linear amplifiers. Size and weightreductions permit development of compact.mobile imaging system. Figures show results forsingle -axis gradient coil supply; entire systemuses three identical supplies.

E-0-5 +0

60HzDec

men

d -to -a

Opt -interface

Current feedoack

COIL DRIVER

MOTOR CONTROL

Corn

AC POWER SOURCE

+ 0 (Floating)

Loadroil

0'

LJ

o Output'o deviceunder test

0Corn

FUNCTION GENERATORS

Tin*

VIns

115

V

Line input

Time

Output

rFig.6. Four basic schematics illustrate use of p.d.m. technology in different application categories:coil drive: motion control: power delivery and function generation. Each category spans manydifferent kinds of amplifier uses and power levels.

NMR DRIVE VOLTAGE

MASTER

DRIVE SLAVE 1

160 AMP PULSE

GRADIENT COIL N1

SLAVE 6 VDRIVE SEPARATE AMPLIFIERS

DRIVE ADDITIONALGRADIENT COILS

420 ELECTRONICS (Sc WIRELESS WORLD

Multi to single-elementtransform

A suggestion for overcoming the two -source limitationn of theinverse square law by resolving complex force situations, both

those involving non -point sources and those involving anynumber of point sources.

The concept of force is by way of beingthe most important concept in phy-sics, simply because it is the basis of all

natural phenomena. Moreover, it is the onefeature common to the three main types ofphenomena - gravitational, electrical, andmagnetic. It is embodied in the classic forceequations of both Newton and Coulomb,normally expressed as FG = GM1M2/d2, andFE = QIC)2/e0d2, respectively.

These equations describe particular situa-tions involving two sources of force. In moregeneral situations involving three or moresources of force, these particular equationsor concepts are not applicable. The difficultywhich this brings about is exemplified bywhat are variously described as the many -body problem, the three -body problem andthe three -charge problem.

Be that as it may, the general problem canonly be overcome by arriving at a high -orderconcept of force, which is to say a generalconcept as distinct from the particular con-cepts of the force equations.

The thinking used in scientific researchtoday has its basis in inductive logic, atechnique notoriously prone to error. Thus,whereas some progress can be made fromthe level of fact to the level of theory - on alevel with a first -order concept - any de-velopment toward higher -order conceptsbecomes well nigh impossible. It is for thisreason that scientific theories in generaltend to be particular concepts describingparticular situations.

The application of recursive logic, bycontrast, enables a researcher to develophigh -order concepts at will, and in consequ-ence it has been found possible to arrive at ahigher -order, more general concept offorce'.

In what follows, an introduction to thisconcept is made by way of a transform, adevice which literally transforms the many -body situation to its more recognisabletwo -body form. In use, the transform issubject to a certain imposed discipline, oneaspect of which is the recognition of a zerothelement or body, known as the referenceelement. Because of this, the two -body situa-tion becomes a single -element situation,involving a reference element and a singlesource element.

To illustrate the potential value of thetransform in research, an examination is

BYJ.C. BELCHER

made of simple configurations of elements,chosen for the short computer programswhich describe them. The use of the trans-form in arriving at the centre of force of abody is also demonstrated, and the oppor-tunity is taken to effect a convincing intro-duction to cataclysmic force!

MULTI -ELEMENT TO SINGLE -ELEMENT TRANSFORM

The force exerted on a reference element, A0,by a number of elements N is defined as

Fn= kA0AE/RE2 1

where k is a constant of proportionality, Aothe magnitude of the reference element,typically unit mass, unit charge, or unitpole, AE the resultant magnitude of the Nsources which equals A icos0, +A2cos02 ++ANcosON, RE the resultant distance be-tween AE and A0 in the direction of thereference vector, which equals x

x ...RNAcosfts/AL (A is the magni-tude of the xth source, R the radial distanceof A from Ao, and O the angle subtended byR, to the reference vector.

This general equation simplifies to themore particular equation expressed by theclassical equations when N = 1, which is tosay when it involves two sources Ao and Ai ,

AE = A1cos 01RE RiAlcoseibq = RI

from which

Fi = kAoAl cos01/R12. 2

Two important features of this equation are- The presence of the direction cosine, cos 0,

which correctly describes F1 as a vectorquantity, a feature not normally brought

SUMMARY

The multi -element transform effectively ex-tends the application of the two -source basicforce equations to the solution of morecomplex force situations involving any num-ber of sources.

In practical terms, it also provides a usefulapplication in the determination of the certre of torce or centre of gravity of a body orsource of force. whether of regular or irregt.-lar profile. In certain source configurations talso predicts the existence of a new form cfforce. potentially thousands of orders cfmagnitude greater than the force normallypredicted by the basic force equations.

to light in the customary expression of theclassical force equations (apart from onenotable exception, the definition ofCoulomb's equation in Harnwell's text 2).

- The implication that Fi is the force exertedon Ao by the presence of AI, and not viceversa. In more complex applications ofequation 1, in which A0 is itself a multi -element array, there are occasions whenthe force exerted on Al by A0 is not equal tothe force exerted on Ao by Ai .

In the general analysis of arrays of elements,the presence of the constant k becomes anirritating accompaniment. The conventionadopted, therefore, is to make units of suchvalue that becomes equal to unity and can bedisregarded.

In the general case, therefore, when Ao =I and k =1, equation 1 simplifies to

FN = AE/ 11E2

ARRAYS OF ELEMENTS

Any array of point sources, simulating amassive body or charged body, is conve-niently represented by an array of elementsof unit magnitude, each occupying unitvolume of space or unit volume of area, asthe case may be. In this manner, eachelement is located in two or three dimen-sions relative to the centre of the array, thiscentre being ideally the centre of force of thearray, or more often its geometric centre. Atypical arrangement involving a circulararray is shown in Fig.l.

The analysis of array characteristics isessentially an analysis of the array's forcecharacteristics, followed by its proximity -profile characteristics*, each set of charac-teristics being divided into the externalcharacteristics, common to all arrays, andthe internal characteristcs, often peculiar tothe type of array in question.

In this short article, only the force charac-teristics of arrays are examined, because ameaningful study of proximity effect and

Sources of force in the basic force equations areessentially point sources, having no linear dimensions.and taking up no volume in space. When such sourcescan no longer be regarded as point sources - when theyale in close proximity - then the basic equations nolonger hold true. What happens is that the force equationis subject to a qualifying factor, the 'proximity -profile'factor, the value of which depends on the proximity to thesource, and to any irregularity in its profile.


profile effect calls for a detailed analysis ofmany types of different arrays of elementsand constitutes an article in its own right.

The force characteristics of a sphericalarray of elements - simulating the classicalspherical body - in which distance is mea-sured in terms of radius, are found to be asfollows.

- Magnitude AE is essentially equal to theintrinsic magnitude Al, the arithmeticsum of all the magnitudes of the elementswithin the array.

- Distance RE is essentially equal to the truedistance between the reference elementand the centre of the array.

- Force FN is AE/RE2.

The internal characteristics of such an array,although essentially in agreement with clas-sical theory, nevertheless give a more de-tailed explanation of the factors involved:

1. Magnitude varies directly with the dis-tance d from the centre, being maximum atthe surface and zero at the centre, i.e. AF =Aid.2. Distance is unity, i.e. RE = 1.0.3. Force is FN = AE/12 = Aid.

The force characteristics are, of course,modified by proximity effect. This effect ismost noticeable over the range defined bythe two inverse points of the array, d = 2 xradius and d = 0.5 x radius, and reaches amaximum value at the surface or perimeterof the array. Its effect can be determined.however, at distances as great as 1000 xradius, and as small as 0.001 x radius.

RING ARRAY OF ELEMENTS

The force characteristics of a ring array ofelements are exceptional in that they de-monstrate a capacity in natural phenomenato combine a pleasing simplicity of formwith a mathematical complexity of struc-ture. More to the point, these characteristicsare entirely open to discovery by even themost casual researcher.

The analysis is conveniently undertakenby the use of program 1*, a self-containedprogram in BBC Basic which both simulatesthe necessary array of elements, and carriesout the required analysis. On running theprogram, it calls for an input of the numberof elements, N, and then goes into a repeatcycle for the input of the distance in terms ofthe radius along the x-axis between thereference element and the centre of the arrayitself. Within the repeat cycle two for -nextloops determine the value of AE usingpeoccalc 1 and of RE using peoccalc2, whichtwo procedures essentially carry out therequired transform.

Because the simulation of a uniform ringis effected by a series of discrete pointsources, simulation error is likely to beencountered if the value of N is very small.By contrast, if the value of N is very large,then the analysis calls for the calculation oftrigonometrical functions involving verysmall angles and computing error becomesprominent. Thus a value of N = 100 is anoptimum figure to input on running theprogram. Pressure on space led us to hold back these simulationprograms - they are available from the editorial office inreturn for an s.a.e.

Ao3

e3 ArdiReference vector =Mr

1.1110"Distance

Fig. 1. The simulation of any non -pointsource of force of uniform material isconveniently effected by dividing it intounit or partial areas or volumes with apoint source of unit charge or magneticpole at each centre of gravity. Each pointsource is identified by its value. A3 forexample, and located relative to the originby coordinates. X3, Y3, and Z3. (Dimensionsare in terms of the effective radius of thebody which is of unit -length.) The analysisof the array of elements thus simulated iscarried out relative to the reference ele-ment. Ao, conveniently located on thex-axis at a distance measured in terms ofthe radius. The reference vector is normal-ly concurrent with the x-axis, although thiscan be rotated in steps over a full 360 toprovide data for a polar diagram of theforce exerted on the reference elementRelative to the reference element. an ele-ment is located in terms of the polarcoordinates. R3, 1)3, where cos o3 is thedirection cosine relative to the referencevector.

In the print-out, the relationship betweenthe computed results and the theoreticalresults for AE and RE are given at the side asan assessment of the accuracy of the simula-tion and computation.

At d = 10,000, the value of AE = 100,showing no sign of proximity error. Thevalue of RE < 10,000, and this shows thepresence of computing error. At = 100, bothvalues properly show the presence of prox-imity error, and computing error is essen-tially absent. Proximity error is predictablygreatest at d = 1, and this is seen to be thecase.

At d < 1, the value of AE varies directlywith half the distance. The value of RE, onthe other hand, is essentially equal to thebase of natural logarithms, RE = e' =2.7182818. This becomes most obvious at d= 0.001, whereas at smaller distances, i.e.0.0001, computing error once again becomeprominent.

It is interesting to compare the followingresults internal to the array perimeter, withstatements 1, 2 and 3:4. Magnitude varies directly with half thedistance from the centre, being maximum atthe perimeter, and zero at the centre, i.e. AEand Ai cV2.

5. Distance is equal to the base of naturallogarithms, i.e. RE = e' = 2.71828 etc.6. Force is FN=Aid/2e2.

SHELL ARRAY OF ELEMENTS

The hollow enclosed spherical shell, orequipotential surface, is an important fea-ture in contemporary physics. Since, byassuming the validity of the inverse square

law, an attempt is made to demonstrate thatthe force on a reference point source withinsuch a surface must be zero everywhere.Conversely, proof that such a force is indeedzero thence confirms the validity of theinverse square law.

This reasoning would appear to be basedon a misconception of the three -body prob-lem and its rigorous solution. Since, itargues, a source of magnitude 9 units at adistance of 3 units, exerts the same force as asource of 4 units at a distance of 2 units. Inisolation, the. two sources do indeed exert a

force of 9/32 = 4/22 = 1 unit. Takentogether, however, this simplicity no longerapplies, and use of the multi -element trans-form will show that, where the two sourcesare opposing, the resultant force is0.290389882 units in the direction of thelarger source. It is at this point, therefore, atwhich the transform comes into disputewith contemporary theory.

Be that as it may, the success achievedwith the simple ring array of elements leddirectly to similar research on the shellarray, where the problem has been one ofarray simulation, since poor simulation pro-duces not only incorrect results, but entirelymisleading results. The simulation of theshell array itself suggests something on thelines of locating dimples on golf balls, butthe spherical trigonometry involved doesnot make for easy calculation where uniformdistribution of surface area is to be achieved.

The final simulation had its basis in aregulation pattern, drawn with a felt-tip penon a six-inch rubber ball and composed ofeight 90° spherical triangles, each with threequadrants of radius 45° drawn at eachright-angle together with a smaller sphericaltriangle at the centre, making a 36 -elementarray. Although composed of a small num-ber of elements, this array is neverthelessexceptionally accurate in its representationof a spherical surface.

The simulation and analysis of the shellarray is embodied in program 2, the simula-tion details being held in the DATA state-ments. Because the number of elements isfixed at 32, the user need only input therequired distance. In numerical terms, theintrinsic magnitude of the array is set at A1 =1.0, which makes for ease of analysis.

As el/2 = 1.648721271, and it appearsfairly obvious that, in the general case withinthe surface of the shell, RE = el/2. Undersimilar circumstances, AE = (2/3)AI d.

The internal force characteristics of theshell array of elements, therefore, may beexpressed as

7. Magnitude varies directly with two-thirdsof the distance from the centre, being max-imum at the surface and zero at the centre,i.e. AE=2/41(1/3.

8. Distance is the square root of the base ofnatural logarithms, i.e. RE = 1.658721271.9. Force FN = 2d/3e = 0.245253338 dis-tance.

CENTRES OF FORCE OF HALF -SHELLARRAYS

A useful facility afforded by the use ofMulti -element Transform is the determina-tion of the centre of gravity, or in more


general terms the centre of force, of anygiven body or array of elements. In the caseof symmetrical arrays, of course, such acentre is at the geometrical centre of thearray itself. A problem arises, however, whenthe profile of the body or the array is highlyirregular in outline, since under these cir-cumstances a formal solution presents diffi-culties.

This particular use of the transform can beconveniently demonstrated by calculatingthe centre of force of a half -shell array.

The simulation of the shell array is effec-tively that of two half -shells in close juxtas-position. If the reference element is at somedistance greater than the radius, then thehalf -shell adjacent to it is composed solely ofelements having negative x -ordinates, andthe half -shell remote from it is composedsoley of elements having positive x -ordinates. The convention adopted here is torefer to these two half -arrays as the adjacentarray and the remote -array, respectively.

To determine the centre of force of theadjacent array, run program 2 after havingdeleted lines 80 and 100, thereby exculdingthe elements having positive x -ordinates.Enter the program with distances of 4000,and 1000. The results are

Matinee RE (distance-RE)4000 3999.464226 0.5357742311000 999.4644563 0.5355436802

Reload the program, this time deleting lines70 and 90, thereby simulating the remotearray. Thence repeat the above sequenceobtaining the following results

distance RE (RE - distance)4000 4000.535907 0.5354071000 1000.53616 0.53616

The mean value of these four differencevalues is 0.5357, and it follows from this thatthe centre of force of a half -shell in generalterms is at a point approximately 0.5357radius from its centre of curvature.

'CATACLYSMIC' FORCE

A significant development arising from earlystudies involving the transform, it is unex-pected prediction of the existence of aparticular type of force of extreme magni-tude. Over the years, this force has beenidentified with a certain type of force inNature which gives rise to events of cataclys-mic proportions, and has been called acataclysmic force. That the predicted forceand the actual force are indeed one and thesame thing, would appear to have becomewell established. This is confirmed in par-ticular by the application of the transform tothe analysis of gravitational tidal forcesobtaining within the Sun's core, in which itsprediction of solar phenomena is in excellentagreement with recorded observation.

Which is to say 'cataclysmic' force ex-erted essentially by a configuration of slow -moving planets over a period of weeks ormonths, coincides with the occurrence oflarge sun -spots or eruptive prominences.The same force, on the other hand, exertedby a configuration of fast-moving planetsover a few days, coincides with the presenceof minor sunsports and minor prominences.In complete contrast, a notable period of

IR p

1

I

Fig. 2. The negatively charged electron isnormally bound to the group by virtue ofthe electrical attraction of the two positive-ly charged protons, and by the gravitation-al attraction of their combined largermasses, causing the electron to orbit thepair about their commoitaxis in a state ofequilibrium. In the absence of the electron,the two protons would normally experi-ence mutual repulsion and fly apart, butthe 'cataclysmic force' set up by the pre-sence of the electron in this the three -charge situation effectively guards againstthis.

little of no solar activity, the period of thecontroversial Maunder Minimum, is seen tohave taken place during a time when theapplication of the transform points to a nearabsence of planetary configurations found tohave given rise to cataclysmic tidal force.

An examination of 'cataclysmic' force, onpaper at least, suggests it to be the outcomeof some form of mathematical chicanery.This is understandable, since it has its basisin a certain mathematical paradox, thedominant negative direction cosine. Undernormal circumstances, negative directioncosines exhibit no abnormal behaviour whenpaired off with their counterparts, the posi-tive direction cosines, and we have seenevidence of such normality in the simulationand analysis of both the ring and shell arraysof elements. If, however, a hollow array isopened out at one side to produce an openhollow array, the balance between positiveand negative direction cosines becomes lost.In consequence, should the negative direc-tion cosines predominate, the resultant dis-tance, exhibits a net negativeindex, so muchso that, in the ultimate, RE = zero, and bythe same token, FN = infinity. This, then, isthe essential basis of 'cataclysmic' force.

A demonstration of this force, entirelyinnocent of any form of chicanery, canconveniently be arranged by running prog-ram 2 in an adjacent array mode, inputtingvalues of distance in incremental steps fromd = 0 to 0.5837 x radius.

THE THREE CHARGED -BODY PROBLEM

Careful examination of the multi -elementtransform, in its association with 'cataclysmic' force, shows the resultant distancewill exhibit a negative index if the magni-tudes of the sources or elements themselvesexhibit negative signs. Although not a fea-ture of gravitational force involving massivebodies, it is nevertheless perfectly obviousthat such a condition can obtain whenelectrical charges or charged Bodies of oppo-site polarity are involved.

The ultimate example of the threecharged -body problem is perhaps the bestrepresented by the simulation and analysisof the forces obtaining within the atomicnucleus. In this demonstration it will beassumed that the nucleus consists of twonucleons, a positively charged proton and aneutron exhibiting a net charge of zero.Because a neutron can be likened to apostively charged proton orbited by a nega-tively charged electron, this substitutionwill be assumed, giving rise to three chargedbodies, two positive and one negative.

It seems likely that the negatively chargedelectron will see the two positively chargedprotons as being a single composite source,having twice the mass and twice the positivecharge of a single proton. Under thesecircumstances, the electrons is likely toorbit the two protons in combination, asshown in Fig.2, from which it is seen that atany given time the three elements are likelyto form an isosceles triangle in space, withthe electron at the apex of the triangle, andthe protons at its base.

The forces exerted on one or other of thetwo protons can be determined by runningprogram 3 and inputting selected values ofthe apex angle in the range, 0 - 180°.

The force exerted by the opposing protonis shown as F+ and is normally repulsive innature as indicated by the negative sign. Bycontrast, the force exerted by the electron,F_, is attractive in nature as indicated by thepositive sign.

Predictably, when the angle is zero, thetwo protons are infinitely close together andthe Coulombian force is a repulsive force ofinfinite magnitude. Thus the two protonssuffer mutual repulsion. When the angle is158° or more, however, the 'cataclysmic'force experienced between each proton andthe solitary electron is one of mutual attrac-tion of infinite magnitude. Hence, the twoextremes of force. That the forces on theprotons are zero when the angle is 180°, isnot a serious restriction, because the orbitalmotion of the electron will immediatelyrestore the status quo.

The cataclysmic energy involved in theatomic nucleus is, of course, well recognisedas nuclear energy. A potentially less hazar-dous form of cataclysmic energy, however,would appear to be a feature of the cataclys-mic array, and, editor willing, this will formthe subject of a further article.

References1. Belcher, J.C. Unit radius and the resolution ofinverse square law forces. International Journal ofTheoretical Physics, vol. 15, no. 10 1976, pp755-771.2. Hamwell, G.P., Principles of Electricity andElectromagnetism. McGraw-Hill, New York,1949, 2nd Edition. pll.

John Charles Belcher, MIERE, retired fromBritish Telecom in 1984, but since 1967 amajor concern has been research into re-search techniques, particularly successful,he says in the case of the powerful thinkingtechnique, recursive logic, which led to an"extensive and detailed understanding ofnatural phenomena in general, described bysome 300 original equations."


RESEARCH NOTES£2.5 million foradvanced vision

systemA major research project toproduce a prototype AdvancedVision System is to involve fourUK organizations:

Thorn -EMI Central ResearchLaboratories;Laser -Scan Laboratories(Cambridge);Royal Signals and RadarEstablishment (Malvern);andUniversity College London

The project cost is £2.5M to bespread over three years. TheAlvey Directorate is providing£1.6M, the remainder being metby the non -university collabor-ators.

The vision system's principalfunction is to process stereo im-ages of a scene to produce anarray of depth values, which arethe distances from the viewpointto surfaces of objects. Like thehuman visual system, themachine will utilize stereo paral-lax to calculate depth, havingdetermined the correspondencebetween points in the differentimages. The depth arrays consti-tute 2.5D representations ofscenes providing important, butnot full, information on the 3-Dshape of objects present. Themachine will employ photo-grammetric techniques, includ-ing the recognition of controlfeatures, so that absolutemeasurements can be obtained.

There are numerous applica-tions for such a system. Oneexample is industrial inspection,where images are produced bytwo or more television cameras,and the 2.5-D representationforms the basis for automaticallymeasuring shape variations.Another example occurs in thepreparation of maps and terraindata bases, where images areobtained from spacebome or air-borne sensors in two or moreviewing positions. Here the 2.5-D information can form the basisfor a relief map. Both these ap-plications are to be used in theresearch programme, the datacoming from an industrial in-spection cell for the first exam-ple, and from the French SPOTsatellite for the second.

The market potential for a2.5-D vision system is considered

to be substantial - provided thatit is accurate and fast. To achievethe necessary accuracy, furtherdevelopment of existing stereomatching techniques is re-quired, and is included in theresearch programme. To achievethe necessary speed, the systemis not being implemented on aconventional single -processorcomputer but on a network ofprocessors running in parallel.In this way, the intensive com-putation required can be speededup by a factor approaching thenumber of processors in the net-work. The processors in the net-work will be transputers, manu-factured by Inmos. The complete2.5-D vision system, running inreal time, is to be operational bythe end of the three-year project.

Star wars laser?Formerly classified details haverecently emerged of a develop-ment in free electron lasers thatcould become a front runner inthe race for a directed -energybeam weapon. An 11 -membergroup from the LawrenceBerkeley and Livermore Labor-atories has demonstrated amirror -less laser amplifier thatuses an electron beam from anaccelerator to boost the energyfrom a 50kW magnetron to near-ly 1.9GW. The 4kA electron beamis pulsed once per second andcomes from an experimental testaccelerator (ETA).

Energy transfer from the elec-tron beam to the microwavebeam takes place in an 'undula-tor' (also called a 'wiggler'). Thename derives from the interac-tion which takes place along anoscillating path. The undulatorconsists of a linear array ofpulsed, air -cored electromagnetsgenerating alternating dipolefields. If the dipole field, theelectron energy and the inputmicrowave radiation are in step,then lasing action occurs. Formaximum energy transfer (up to40%), the laser outputwavelength is related to the un-dulator period divided by thesquare of the electron beamenergy.

Extending the laserwavelength from microwaves tothe more militarily useful near -infra -red therefore demands aconsiderable increase in beamenergy. Increasing the overallpower demands also an increase

in the electron beam pulse re-petition rate, something whichvarious US teams are workingon.

The Los Alamos NationalLaboratory are, for example,developing a radio -frequencyelectron injector with a signifi-cantly increased 'brightness'.This is important because thelaser output can be no greaterthan the power of the beam thatpumps it.

To produce an effective SDI-type infra -red beam weapondemands not only that theseproblems be solved: there areother fundamental physicalconstraints. Microwaves of thefrequency used (around 35GHz)can be kept parallel by means ofwaveguides using well knowntechnology. Shorter wavelengthinfra -red radiation will dependfor its guidance on focussingeffects which, as yet, are still atthe theoretical stage.

SDI, it seems, still has someway to go.

BiocomputersJapanese style

Japan's Ministry of InternationalTrade and Industry's Agency ofIndustrial Science and Technol-ogy (MITI/AIST) is planning tolaunch a biochip research pro-ject that will cost an estimated110M yen for the first two yearsalone. It's an attempt to circum-vent what the Japanese see as theinherent limitations of silicontechnology itself and of vonNeumann architecture. The aimof the MITI project is to design anartificial intelligence capabilitybased on the information proces-sing principles employed in thenervous systems of relativelysimple animals. As yet, MITI aresaying little about which organ-isms they have in mind or indeedwhat biomolecules or modellingtechniques they'll be employing.

To begin with, scientists willdevelop non-invasive means ofanalysing the workings of animalnervous systems to try and dis-cover how memory and learningare accomplished. The resultingdata will then be used to designmodels that mimic these proces-ses. Later in the project they'll belooking at how living moleculesand cells organize themselves tocarry out highly complex func-tions.

Ultimately the intention is todevelop chips based on biologicalprinciples that can circumventthe limitations of today's sys-tems. MITI gives no indicationsof what architecture might beemployed - or even what fabrica-tion technology. But, howeverfuturistic this approach mightseem, the prospect of ultimatelydeveloping a highly intelligent,low -consumption computer,based on relatively slow activedevices, isn't as far-fetched at itmight seem. Each of us alreadyhas one sitting inside our skulls!

BiocomputersRussian style

According to G. Ivanitskiy,Director of the Institute ofBiophysics of the USSR Academyof Sciences, microtechnologybased on organic substances willbecome a major force in compu-ter research and development inthe next 10 to 15 years. Ivanitskiystarts from the basic premisethat living systems employhighly efficient energy conver-sion processes that operate atroom temperature. Soviet effortsare therefore being directed to-wards a biocomputer based onenergy -efficient 'organicallygrown' sensors and switchingdevices.

Many such devices, says Ivan-itskiy, already exist in primitiveform. Molecular biology hasmade it possible to design trans-ducers with high sensitivity andselectivity. At the Institute ofBiophysics, protein -based de-vices have already been de-veloped to measure tiny changesin chemical reactions. Opticaltransducers based on biolum-inescence are also the subject ofresearch that could extend to thedevelopment of new non-volatilebiological memories. For exam-ple, the bacterium Halobacter-ium halobium uses a pigmentcalled bacteriorhodopsin to con-vert light into electrochemicalenergy. It's a process very similarto that which takes place in theretina of the human eye.

According to Ivanitskiy, bac-teriorhodopsin could be used notjust as a transducer but as thebasis of a memory device. Scien-tists at the Institute of Bio-physics have discovered that de-hydrated bacteriorhodopsin canbe stopped at one stage of the


RESEARCH NOTEStransduction process withoutlosing the image printed on it.Films based on bacteriorhodop-sin could thus, in principle, beacted on by lasers to record, readand erase data. The Russiansbelieve that the contents of alarge library could be stored onone 30cm 'biochrome' disc.

As for processing data, Ivanits-kiy predicts that systems basedon discrete bits will give way tobiological films in which data isprocessed through waves ofchemical reaction. He speculatesthat protein crystals could act asmedia through which movingplane waves could perform theequivalent of 1012 operation/s inthe space of 1cm2

Compute -a-

drugDr Lindsay Sawyer is one of ateam from the Department ofBiochemistry at EdinburghUniversity who is using 3-Dcomputer graphics to performwhat amount to conjuring trickswith complex protein molecules.Anyone who has seen even sim-ple biochemical molecules mod-elled with coloured sticks andballs will know immediately howcomplex these structures are.When it comes to larger mole-cules of the sort that abound inour bodies this 'meccano'approach is hopelessly in-adequate.

Dr Sawyer has been attemp-ting to study the reactions of amilk protein, beta lactoglobulin(BLG), using an Evans andSutherland PS300 vector displaydevice in conjunction with a hostcomputer and a Leeds I.c.d.stereopsis viewer. The viewerconsists of a pair of spectacleswith l.c.d. shutters in place of theusual lenses. This enables alter-nate frames (which correspondto each half of the stereo image)to be presented sequentially tothe right and left eyes.

Using a molecular graphicspackage called FRODO,developed by Alwyn Jones of theUniversity of Uppsala, it is possi-ble, using any input device suchas a keyboard or a mouse, tomanipulate the images in realtime. It's possible, for example,to turn a 'molecule' around andsee how it best fits with anothermolecule. Using this approach,Dr. Sawyer has been able to

A of W4748411 1

Stereo pair of molecular graphic. To see in 3-D these pictures should ideally be cut out and placed in abinocular viewer. Alternatively the illusion may work if the pictures are separated by a sheet of thin

card, normal to the paper.

provide an 'intelligent guess' asto the structure of the chemicalcomplex that forms when BLGbinds to certain other moleculessuch as vitamin A. This is valu-able because such complexes arenot always easily amenable toX-ray crystallographic analysis.The images, if viewed in 3-D,display all the atoms in theirdifferent colours.

The value of this research isn'tjust in its ability to speculate oncomplex molecular processes.Given the structure of one pro-tein, it should be possible intheory to design another mole-cule that would fit onto or into itto modify the protein's prop-erties in predictable way. That inturn is a possible route to newdrugs. There remains of coursethe job of actually creating thenew molecule using some sort ofgenetic engineering. And whenyou have created it, it may turnout to be toxic when tested onanimals. Ah well, back to the(3-D) computerized drawingboard!

Magnetic fields- the health

risksAn international meeting heldlast summer at the A.N. MarzeevResearch Institute of Generaland Communal Hygiene in Kievexamined the biological effects ofexposure to static and time -

varying magnetic fields at ex-tremely low frequencies of up to300Hz. The job of this task groupwas to produce a final agreedversion of a document initiatedby the International RadiationProtection Association (IRPA)and commissioned by the WorldHealth Organization (WHO).

The document, which issummarized in a paper publishedby the National Radiological Pro-tection Board (Bulletin No 78),provides an extremely clear andconcise overview of what is pre-sently known of the dangers ofmagnetic fields.

Of static fields, the group con-sidered that there is no evidenceof any adverse effects on humanhealth due to short-term expo-sure to static fields of up to 2Tesla(T) or to chronic exposureto fields of less than 100mT.However, it is felt that there isinsufficient knowledge of possi-ble effects in certain key areas: long-term exposure to thenervous system and the car-diovascular system: certain metabolic reactionsthat involve radical pairs; and the use of magnetic reso-nance systems for medical diag-nosis involving fields over 2T.

More studies, says the group,should be carried out into thecellular tissue and who e bodyresponses to such static fields.

Turning to alternating fields,the task group was particularlyconcerned about reports of anincreased incidence of cancer inthe vicinity of a.c. power lines.

Such fields are commonly nogreater than 0.1-1.0µT. Thegroup concludes that studies sofar have been inconsistent andraise more questions than theyanswer. Further well -designedepidemiological studies aredeemed necessary.

Laboratory studies, however,show no adverse clinical or phy-siological changes in subjectsexposed to 50Hz fields of up to5mT. At greater flux densities,people sometimes report seeingflashing lights - magnetophos-phenes - caused by induced cur-rents in the retina of the eye. Atextremely high e.l.f. fields of0.5T or greater, acute healthhazards, such as heart fibrilla-tion exist. It isn't known, howev-er, whether the hazard is a directresult of the magnetism or of theelectrical currents which are in-duced as a consequence.

In respect of alternating fields,the task group concludes thatcomprehensive new studies areneeded to assess the risk, if any,of cancer; also the risk toembryos in the case of exposureduring pregnancy and finally theeffects of induced currents onnerve tissue.

What seems to emerge overall,however, is the extreme difficul-ty of demonstrating any phy-siological effect at all, let alone ahazard, of the sort of magneticfields that are likely to be en-countered in the average labora-tory or workshop.

Research Notes is written byJohn Wilson.


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C??? (a)£279 (a)

£229 (a)F X800 £329 (a)FX10(30 £449 (a) BROTHER HR20 £329 (a)E x800 £409 (a) COLOUR PRINTERSL0800 (80 col) £439 (a) Integrex Jet Printer £525 (a)L01000 £589 (a)

Dotprint Plus NLO Rom forTAXAN Epson versions for FX, RX, MXKP815 (160 cps) £269(a) and GLP £28 (d)KP915 (180 cps) £369(a)

PLOTTERSJUKI Taxan A3 (6 col. flat bed) £679 (a)6100 (Daisy Wheel) £259 (a) Hitachi 672 £459 (a)

Graphics WorkstationNATIONAL PANASONIC (A3 Plotter) £599 (a)KX P1080 (80 col) £159 (a) Plotmate A4SM C450 (a)

PRINTER ACCESSORIESWe hold a wide range of printer attachments (sheet feeders, tractor feeds etc)in stock. Serial, parallel, IEEE and other interfaces also available. Ribbonsavailable for all above plotters. Pens with a variety of tips and colours alsoavailable. Please phone for details and prices.Plain Fanfold Paper with extra fine perforation (Clean Edge):2000 sheets 9 5' x 11' £13(b) 2000 sheets 14 5' x 11' 8.50(b)Labels per 1000s Single Row x 1 7/16. £5.25(d) Triple Row 2-7/16' x 1 7/16' £5.00(d)

Single Disc Cable £6 (d)10 Disc Library Case £1.80 (d)50 5' 2 Disc Lockable Box C9.00 (c)

3M FLOPPY DISCSIndustry Standard floppy discs with a lifetime guarantee. Discs in packs of 10

51/4- Discs 392" Discs40 TSSDD £10.00 (d) 40 T DS DD E12.00 (d) 80 T SS DD £20.00 (d)80 T SS DD £14.50 (d) 80 T DS DD £15.50 (d) 80 T DS DO £25.00 (d)

FLOPPICLENE DRIVEHEAD CLEANING KITFLOPPICLENE Disc Head Cleaning Kit with 28 disposable cleaning discsensures continued optimum performance of the drives. 5',)" £12.50 (d)

31/ £14.00 (d)

DRIVE ACCESSORIESDual Disc Cable £8.50 (d)30 x 51/2" Disc Storage Box f6 (c)100 x 51'2" Disc Lockable Box £13 (c)

MONITORSRGB 14"1431 Std Res £179 (a)1451 Med Res C225 (a)1441 HI Res £365 (a)

MICROVITEC 14' RGB/PAL/Audlo1431AP Std Res C199 (a)1451AP Std Res £2591(a)All above monitors available in plastic ormetal case.

TAXAN SUPERVISION 62012" - Hi Res with amber/green options.IBM compatible C279 (a)Taxan Supervision III £319 (a)

MITSUBISHIXC1404 14" Med Res RGB. IBM & BBCcompatible £219 (a)

MONOCHROMETAXAN 12" HI-RESKX1201G green screen £85(a)KX1203A amber screen C95 (a)

PHILIPS 12 HI-RESBM7502 green screen £75 (a)BM7522 amber screen £79 (a)8501 RGB Std Res £139 (a)

ACCESSORIESMicrovitec Swivel Base £20 (c)Taxan Mono Swivel Base withclock C22 (C)Philips Swivel Base C14 (c)BBC RGB Cable £5 (d)Microvitec £3.50 (d)Taxan £5 (d) Monochrome £3.50 (d)Touchtec - 501 £239(b)

MODEMSAll modems carry a full BT approval

MIRACLE TECHNOLOGY WS Range

WS4000 V21/23 (Hayes Compatible,Intelligent, Auto DQUAuto Answer) £149 (b)

WS3000 V21/23 Professional As WS4000and with BELL standards and battery back upfor memory £295 (b)

WS3000 V22 Professional As WS300 V21/23but with 1200 baud full duplex £495 (a)

WS3000 V22 bis Professional As V22 and2400 baud full duplex £650 (a)

WS3022 V22 Professional As WS3000 butwith only 1200/1200 £395 (a)

WS3024 V22 Professional As WS3000 butwith only 2400/2400 £570 (b)

WS2000 V21/V23 Manual Modem £95 (b)DATA Cable for WS series/PC or XT £10 (d)

DATATALK Comms Package If purchased with any of the abovemodems 'C70 (c)

PACE Nightingale Modem V21/V23Manual £75 (b)

(Offer limited to current stocks)

RT256 3 PORT SWITCHOVERSERIAL INTERFACE3 inputil output or 1 input/3 outputmanual channel selection Inputoutput baud rates independentlyselectable 7 5018 bit. odd/evervnoneparity Hardware or softwarehandshake 2568 buffer mainspowered 0375 OH

PS BUFFERInternal butler for most Epsonprinters Easy to install InstsuppliedPB128 1288 V39 (c)

UVERASERSUV 1T Eraser with built, timer and mains indicatorBuilt-in safety interlock to avoid accidental exposureto the harmful UV raysIt can handle up to 5 eprorrts at a time with an averageerasing time of about 20 mins C59 + C2 p&p.UV1 as above but without the timer £47 + £2 p&p.For Industrial Users we o'ter UV140 A UV141 era-sers with handling capacity of 14 eproms UV 141 hasa built in timer Both offer full built in safety featuresUV140 C69, UV141 £85, p&p 0.50.

EXT SERIAL/PARALLELCONVERTERS

Mains powered convertersSerial to Parallel £48 (c)Parallel to Serial £48 (c)Bidirectional Converter £105 (b)

Serial Test CableSerial Cable switchable at troth endsallowing pin options to be re-routed orlinked al either end - making it possibleto produce almost any cableconfiguration on siteAvailable as M/M or MiF C24.75 (d)

Serial Mini Patch BoxAllows an easy method toreconfigure pin functionswithout rewiring the cableassay Jumpers can be usedand reused £22(d)

Serial Mini TestMonitors RS232C and CCITTV24 Transmissions.indicating status with dualcolour LEDs on 7 mostsignificant lines Connects inLine 'f22.50 (dl

CONNECTOR SYSTEMS

I.D. CONNECTORS(Spoodblock Typo

No of Header Receo Edgeways Plug acie Conn

10 110p 11Sp 120920 14Sp 125p 195926 1750 1S0p 240p34 2009 1609 320p40 2 1 340p50 2230pSp 201113p0p 360p

SOFTY IIThis low cost intelligent eprom programmer can program 2716 25162532. 2732 and with an adaptor 2564 and 2764 Displays 512 bytepage on TV has a serial and par allel I/O routines Can be used as an emulator cassette interfaceSofty!! C195.00 (b)Adaptor for 27642564 025.00

SPECIAL OFFER2764-25 £2.50 (d);

27128-25 £2.75 (d);6264 LP -15 £2.80 (d);

D CONNECTORSNo of Ways

9 15 25 37MALE:Ang Pins 120Solder 60IDC 175FEMALE:St Pin 100Ang Pins 160Solder 90CC t95St Hood 90Screw 130Lock

18085

275

230 350125 170325

140 2t0210 275130 195325 37595 100

150 175

380440290

120

2 8 -way Icornmodorei2. 10way1 x 12 way (rite 2012 n 18 way2 x 23 way i2X8112 x 25 way2 x 28 way iSpectru,2 x 36 way

x 43 war2 x 22 way2x 43 way

v 77 way2 n 50 wayiS100co,,,,

EDGE

CONNECTORSOr 0 156- 30091SOp

i 75p725p200p250p260p1510p

395p400p600p

350p140p220p220p

500p

AMPHENOLCONNECTORS

36 way plug Centronics(solder 500p (IOC) 475p36 way ski Centronics(solder) 550p (IOC) 500p24 way plug IEEE (solder)475p IDC) 475p24 way ski IEEE (solder500p IDC ) 500pPCB Mtg Skt Ang Pin24 way 700p 36 way 750p

10 -way

I6 -way20. way

26. wa y

RIBBON CABLEigreyirneirei40p 34 -way 160p

tOp 40'way 110p660 50way 2009

1209 64 -way 210p

TEXTOOL ZIFSOCKETS 14 -pm 07.5028 port [9.10 40 pint12 10

EURO CONNECTORSDIN 41612 Plug Skt2 x 32 way St Pin 230p 275p2 x 32 way Ang Pin 275p 320p3 x 32 way St Pin 260p 300p3 x 32 way Ang Pin 375p 400pIDC Skt A + Sr 400pIDCSktA+C 400p

For 2 x 32 way please speedyspacing (A + B, A + C).

GENDER CHANGERS25 way D type

Male to MaleMale to FemaleFemale to Female

10£10C10

14 pin16 pin18 pin20 pin24 pin28 pin40 pin

DIL HEADERSSolder IOC

40p 100p50p 110p60p75p100p 150p160p 200p200p 225p

RS 232 JUMPERS(25 way Di

24 Single end Male24 Single end Female24 Female Female24 Male Male24" Male Female

CS 00ES 25

01000CO 50[950

MISC CORNS21 pin Scarf Connector 200p8 pin Video Connector 200p

DIL SWITCHES4 -way 90p 6 -way 105p8 -way 120p 10 -way 150p

ATTENTIONAll prices in this double pageadvertisment are subject to

change without notice.ALL PRICES EXCLUDE VAT

Please add carriage 50punless indicated as follows:(a) £8 (b) £2.50 (c) £1.50 (d)

£1.00

TECHNOLINE VIEWDATA SYSTEM. TEL: 01-450 9764 Using 'Prester type protocols. For informationand orders - 24 hour service, 7 days a week


11111=111 74273 2.0074276 1.4074278 1 7074279 0 90'4283 1 0574742 3 2074290 0 9074293 09074298 1 8074351 200743654 0 80743664 0 8074367A 0 8074376 16074390 1 1074393 1 20'4490 140

7400 0.307401 0307402 0.307403 0 307404 0367405 0.307406 0.407407 0.407408 0307409 0.307410 0.307411 0.307412 0307413 0.507414 0.707416 0.367417 0407420 0307421 0607422 0.367423 0 367425 0607426 0.407427 0.3274213 0.437430 0.307432 0.367433 0.307437 0.307438 0607439 0607440 0.407441 0.9074426 0 7074434 1.007444 1107445 0.7074464 1.130

74474 1.007448 1.007450 0.367451 0.157453 0.387454 0.387460 0.557470 0.507472 0.457473 0.457474 0.507475 0.607476 0.457480 0.657481 1.8074834 1.057484A 1.257485 1107486 0.427489 2.1074904 0 557491 0 7074924 0.707493A 0.557494 1.1074954 0.607496 0.807497 2.9074100 19074107 0.5074109 0.7574110 0.7574111 0.5574116 1.7074118 11074119 1 7074120 1.0074121 0.5574122 0.7074123 01074125 0.6574126 0.5574128 0.5574132 0.7574136 0.7074141 0.9074142 2.5074143 1.3074144 2.7074145 1.1074147 1.7074148 1.4074150 1 75741514 07074153 0.8074154 1 4074155 0.8074156 0.9074157 0.8074159 2.2574160 11074161 0.8074162 1.1074163 1.1074164 1.2074165 11074166 1.4074167 4.0074170 2.0074172 1.2074173 1.4074174 11074175 1.0574176 10074178 1.5074179 1.5074180 10074181 34074182 14074184 1 80741854 1.8074190 1.3074191 1.3074192 11074193 1.1574194 11074195 0.8074196 1 3074197 11074198 2.2074199 2.2074221 1.1074251 1.0074259 1.5074265 0.80

74LS SERIES

74L00'741002741S0374100474100574L508741$0974151074LS1I74151374LS1474LS1574L52074LS2I74LS2274LS24741_52674LS2774LS28741S3074LS3274LS3274LS33741S3774153874LS4074542741543741048741049741051741S54741055

0 240 240.240.240 240 240 240 240 240 240 340 500 240 240 240 240 500 260 240 240 240 240240 240 240.240.240501 500901.000 240 240 24

7410734 0307415744 0.35741075 06570.5764 0.36741578 06274L583A 0.7074L585 0.75741586 0.35741590 0.4874LS91 0.90741092 0.35741_593 0.5474159513 0.7574L596 0.90744.5107 04074LS109 04074LS112 0457415113 aas7015114 0.4574LS122 0.70741S123 0.807410125 0.50741S126 0.507415132 0.65741S133 0.557416136 0.457415138 0.5574L5139 0.557415145 0.957415147 1.7574L5148 1.407415151 0.657410152 2.00'415153 0.657415154 1.60745155 0.6574L5156 0.6s741S157 0.507410158 0.65'41516001 0 65"41.01674 075401624 0 75'4151634 0757415164 0.75'4LS165.4 11074151664 1.5074L5168 1.3074LS169 1.007410170 1.407401734 1007410174 0.757415175 0.757415181 2.007415183 1.9074LS190 0.757410191 0.757415192 0.80-4151944 0.7574/51954 0.757415196 010741S197 0.80741S221 0.907410240 0.80745241 0.80740242 0.904415243 0.9074L5244 0.707416245 0.9074LS24] 1.107410248 1.1074LS249 11074L5251 0.757 415253 0.757410256 0.90'41524574 0.70-452584 0.7074LS259 1.207415260 0.75741S266 0.60

7410273 1.257415279 0.707415280 1.907415283 0.807410290 0.8074529214.007415293 0.807410295 1.40741029/14 00741S298 1.007410299 2.207410321 3.7074153226 3907410323 3.007415324 1207413348 2 00741S352 1 20741S353 1 207415356 2107410363 1.807410364 1.80740365 0.50741S366 0.50740367 0.527415368 0.507410373 0.70740374 0.70740375 0.757410377 1 307410378 095741S379 1.307410381 4.507410385 3.257410390 0.60740393 1 0074LS3954 1 007410399 1 407410445 1.807415465 1.207410467 1.20740490 1 507410540 1.00740541 1.007410608 7.007410610 25.00745612 25.007415624 3.507410626 2.257410628 2.257415629 1.257413640 2.007410640- 3007415641 1.507415642 2.507415642-1 3007415643 2.50745643- 3007410644 3.507415645 2 00745645-, 4007410668 0.907415669 0.907415670 1 707410682 2 507410683 1007415684 3.507415687 3.507415688 3 507415783 16.00

74C SERIES

74C00 0.7074C04 0 5074C08 07074C10 0.7074C I 4 05074C20 0.7074C32 1.0074C42 1.5074048 1.5074C73 10074C74 1.2074076 1.0074083 2.0074085 2 2574086 0.5074090 1.9074093 1.5074C95 1 60740107 7.00740150 00074C 151 2.00740I57 2.5074C160 1.8074C 161 11074C162 1.8074C163740173 1.00740174 1.50740175 1.5074C 193 1.50740I94 1.5074C195 1.50740221 2.50740214 2.00740245 2.25740373 2.25740374 2.25740902 1.207409II 9.00740912 4.5074C922 6.00740923 6.5074C925 600740926 7.50

7441.0 SERIES

7441000 0.457441002 0AS744004 0.5074A1508 0.507441510 0.457441020 aos7441632 0.457441074 0.707445138 1.507440139 1.5074410244 400744102/5 4.7574ALS573 2.6074615574 4.5074810580 260

74S SERIES

740007403274SO47450574S087401074S11740207402274S3074S32740377403874040740517406474074740857408674011274011374011474012474013274013374013874013974014074515174015374015774015874516374016974517474017574018874018974519474519574519674S20074S20174022574S24074024174024474325174325774025874026074526174S28374028774328874028974029974S37374574.

0.500.500500.500.500500 750.500.500.500600600.600.500600.050706581001.501201203.001000601801.801001501502.002.003.005503003.201801803.003.003504503205.204.004.004.002.502.502501.003.002.702.252.002.254504 004002 25

4000 SERIES

400040014002400640074008400940104011401240134014401540164017401840194020402140224023402440254026402740284029403040314032403340344035403640374038404040474042404340444045404640474048404940504051405240534054405540564060406340664067406840694070407140'2

0200 240 250 700 250.600450600.240.250 360.600.700.360550.600000.800.600.700300.440 240900.400.600 750.351.251.001.252.500.702.501.101 000600 550 500 600601 000.600.600550360 350.650.600600 800.800.850 700850 402 300 250 240 240.240.240.240.24

4076407740784081408249854006408940934094409540964097409840994501450245034504450545064507450845104511451245134514451545164517451845194520452145224526452745284529453145324534453645384539454145434551455345554556455745604566456845694572458345844585472414411144121441614419144901449514500014$9922100221012210240014400854009740098401004040'401024010340104401054010640107401084010940110401144014740163401734017440175401924019340194402444024540257403734037480C956009780C98

0650 250 250 240 250600 751 200 350900 950902 700 750990360 550360953600900351 200.550 550 551.501.101.100 557200480 320601 15

0 BO0 700 800 65I 000 750 653802500 750 750900 701 002400 360501 401 401 402 40I 700.450.900.480.601.507507503.002.604204506502.003 507007000 48i 200 360401 501 25

ao2001.201 500 480 553200 802 252 25280

00200000000000SO

50808060

0 750 750.75

LINEAR ICs 447+:112.004000808 1190804791000 25 00AN'03 290AN -1.5050 10044.11350 35044-3-8910 4.904.3-8912 500CA30194 1.00CA3020 3.50CA3028A 110C43046 0 70CA3059 3 25CA3060 3.50CA30801 0.70CA3085 1.50CA3086 060C43089E 2 50C4309040 3 75CA3130E 0.90CA31301 1.30CA3140E 0.45CA31401 1.00CA3146 2.25CA3160E 1.50CA31611 2.00CA3162E 6 00C43189E 2 70C53240E 1.50C43260G 300D7002 60011401408.8 3 000400800 3 0006008083.0000308 3 00HA 7366 190CL7106 6 75CL7611 0.95

1_7650 40017660 2 50

018038 400M7555 0.90

CM7556 1.40LC7120 3 OCLC7130 3.00LC7131 150LC7137 3.501F347 1 2C16351 0601F353 0.9016355 0.90LF 35614 1 ICLF357 1 OCLF 398 400LM1OCLH ISO1.1413014 0.3014307 0.45LIA308CN 075LM310 2 2514311 060101318 1.5014319 1 BOLS1324 0451843341 1151613352 1.30L61336 160LM339 040161348 0.60LM358P 050LM377 3.00L938041.8 1.5011438014 1.50L4381ANI.73LMRIN . 100LM383 3.25LM384 2 201143865 1 ICC116387 2 73LM391 1 BOLM392N 1.10LM393 08511.13940-. 4001 M704 035

LM710 0.4804711 1.00LA1723 0.60LM725CN 100LM733 0.65LM741 0.22LM7747 0.70101748 0.30L611011 4.80LMI014 1.50L1311801 1001641830 2.501611871 3.00LM1872 3.001611886 6.00111.11889 4.50LM2917 3.00LM3302 0.90LM3900 0.80LM3909 1.00LM3911 1.80LM3914 3.50LA13915 3.40

M3916 3.40LMI3600 1.5064515131 2.30M515161 4.506103712 2.00MC1310P 1501413 0.751.4C1458 0.45MC1495 3.00MC1496 0.70MC3340P 2.006403401 0.70MC3403 0.65MF IOCN 4.10610502409.00611902 5.00611922 4.006462216 300NE529 120NE 531 12014E544 190NE555 0.22NE556 0.60NE 564 4.00NE565 1.20NE566 1.50NE567 1.25141570 4.00NE 571 3.00NE592 0.90NE5532P 1.50NE55338 1.60

NE5534P 1 20

14E55346P 1.50OP -07E P 150PLL024 5.00RC4136 0.55RC4151 2.00RC4I95 1.50RC4558 0.55550240 9.005441900 16.00S3396364 60051490 3.005976013N 3.0051760231 3.0051760114 3.005176115N 2155076489 4.005N76495 4.005076660 1.20560256412 7905P8515 7.50T47120 1.70747130 1.40167204 1 50747205 0.90TA7222 1.50TA7310 1.50

1134231 1.20

'86800 1110

'134810 /90'8820 0031848209 0.751134920 1001134950 2.251C9109 5.001CA210 1501C/1220 3.50TC4270 3.507CA940 1/510410044 5001041010 2.25TD41022 4.501041024 1.1010611705 1001042002 3.2511342003 1101042004 2.40TDA2006 3.201042020 3.2011342030 2.5011347593 5.007 082653 7.001DA3560 7.50IDA3810 7.501047000 3.501E41002 7.0011_061CP 3.4011062 0.601L064 3901L071 3.4011072 3 7011074 11011081 0 3511082 0 5511083 0 7511084 10011094 2.0011430C 1.2034759 3.20342240 1.20

41.1C.4 6.0001520010 0.7551520028 0.7514192003A 0.75L1920044 0.75ULN2068 2.9031142802 1.9031142803 1.80UL N2804 1.90UPC575 2.75uPC59213 2.00080115613 3.0008011858 500X9210 4.00492206092207092211092216X92240114404ZN4141144198ZN423EZN424EI542568 3.501N426E8 3.0011427E86.0025428684.50Z542918 2.25114447E 0.0019448 I 7.50154491 3.00IN450E 7.50IN459CP 3.00I510341 2.00Z541040 6.60

2100/54234E9.50

4.503.755.755.751.201.003.801.751.30

COMPUTER COMPONENTS

1802CE 6.5026504 10.506502 4.5065CO2'2MH,

12 0065024 6506502B 8 006800 2506802 3 006809 6 506809E 10.0068809 10 00686091 12 0068000.1.6 3600

8035 35080035 6008039 4.2080039 70080804 7 408065A 3.00800854 7 508086 22.00

80878087.8808887418748

3206030.82802808/80828071

120016017.5015 0012 0012 0014 5018 0010.0010.002.502.905.507.50

1454503 14.00TMS99C1 S007459902 500100999 11 001M5914 14 00

Z8OPIO 2.5028061.10 2.75180C 1: 2.50280401: 2 752130DAP 7 650ZBOADART 700

280016.4 7 00ZBOADNA 7.50

280/S1040129700

2808P10 5.001808C1C 50028013D6R1 9.00

MEMORIES

VOLTAGE REGULATORS

IA FIXED VOLTAGE PLASTIC 10220 VE VE

5V 7805 0.45 7905 0.506V 7806 0.50 7906 0.506V 7808 0.50 7908 0.50I2V 7812 045 7912 0.5015v 7815 050 7915 0.15189 7818 0.50 7918 05024V 7824 0.50 7924 0 50

IA FIXED VOLTAGE PLASTIC 70925V 78105 0.30 5V 79105 0456V 78106 0.30 12V 791.12 0.50BV 78108 030 150 79115 05012V 78112 0.3015V 78115 0.30

SUPPDEVICORTES

2651 12 032816.30 20.003242 8003245 4 506520 3006522 3506522A 5 506532 48065514 600682168B21682968406884068506885068526854680546875

815481558156

8205821282168224

822882438250

2 5012 503 756.001 802502 506 508005.00

850380380

2 252 001.60

P 0 A

5.502.6012 DO

82514 3 258253C-5 3.50825545 3208256 re 009257C.5 54 00

8259C-5 400

8275 290087790-5 4808282 400

332848287828808755A

4603.80650

16.00

2101 4.00

21078 50021114435 4.002114 15021142 250

2147 4.06

4116 2.004116-20 1.50

41256-15 300

4164 T1 300

4416-15 3.504532-20 2.50

510115501 4.065514/5,14 4.005516 400551758 4.00

61I68-3 3.506116LP-3

62641115 3.40

651445 4.006810 2007451E83 1 BO7452119 2 25

93415 6.00

93421. 100

I PROM,

2516.5V 3.502516-35 5.502532 4.502532.30 5502564 11 00

2708 4.502716+59 3.502716.35 5.502732 4.5027324.2 9.50

2732410 6.0027324-35 550276425 2.002706475 6.00

27126-25121027256-25 400

27512 P.0.82 7512 25 14.00TMS2716 5.00

CONVCIALER

_81502' 18 00CR1503' 12.00CRT6545 000669364 800199365 2000EF9366 25.00EF9367 36.00'719369 1100MC6845 650MC6845SP 650MC6847 6.5053 F96364 8.00TM59928 10.00

PPOM111

28122 4.0024610 7.50185030 2.001864830 2.00740168 1 807452.17 2.25745248 1.807453437 2.2582523 150825123 150825129 1.75

EP PROM

2816-30 150026+8 30.009306 75668s1167'61 4.50

OTHER REGULATORS

1613098 IA5V 1401.843238 3A 5V 3 SC78H0513C 5A 5V 5 40783412 SA 124 64C78805 10A 5V 900VARIABLE REGULATORS1443054H 2 50143171 10-220 170143170 703 2 40/01337T 2 25184350T 1043. VAR 4.00164396K MA 4. VAR 15 00L16723N 0 5078383058C SA 5V 5 7578t4GKC 56-3 VAR 6.5078GUIC IA+VAR 2217061013C 54 -VAR 6 7579GU1C IA VAR 2 SC

SWITCHING REGULATIONSIC17660 250503524 30011494 300it 497 2.25

2501 50

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Tone decoding using amicroprocessor

A simple approach to microprocessor -controlled tone decodingresults in excellent performance in noisy conditions.

Land -mobile radio telephones usuallyoperate through a repeater site over-looking the service area. So that many

user groups can use the same r.f. channelthrough a particular repeater, it is commonfor user groups to be allocated a certainsub -audible tone which is continuouslytransmitted along with the speech. Thiscontinuous tone -controlled suppressedsquelch, abbreviated t.c.s.s., enables the f.m.receiver output only for that particular usergroup. In this way, users are not subjected toa torrent of unwanted transmissions. Thesystem commonly uses one of about thirtytones in the band 67 to 250.3Hz.

Because decoder input noise comes froman f.m. receiver, the noise characteristics aredifficult either to calculate or to measure.This article discusses measurement of f.m.noise characteristics of a typical f.m. mobilereceiver and specific microprocessor techni-ques used to produce a useful decoder.

Two basic approaches to implementationare period measurement which is capable ofmodest s -to -n ratio performance for tonesup to around 10kHz, and correlation filter-ing giving excellent s -to -n ratio performancefor tones up to around 500Hz.

Quality of the output voice channel ismeasured by means of a sinad meter givingsignal + noise + distortion/noise + distortionand this measurement is done at I kHz.Sensitivity of an r.f. receiver is commonlydefined as that r.f. level which gives a 12dBsinad reading on the audio output. A charac-teristic of any f.m. receiver is that output

Noisyinput Reference

wavesh ape

C.H. COUCH

signal quality degrades slightly towards the12dB sinad point as r.f. input level is de-creased, but then degrades very rapidlybelow that point. Further, the output noisecharacteristic is 'dicky' or 'raspy' and quitedifferent to Gaussian noise.

For a mobile receiver, signal level variesrapidly by perhaps 20 or 30dB as the vehicletravels down the road. Any decoder must berelatively immune to noise bursts from thisvariation, and yet capable of detecting thepresence or absence of tone within about250ms. Further detection bandwidth may be

ut

Clock

d

Sampled analoguedelay line with

n taps

limited to ±2.5% or less. References one andtwo partially define the characteristics ofsuch a decoder.

Usually decoders like this are preceded byan analogue filter, then a hard limiter toremove decoder dependence upon the audiosignal level. However, this process is verynon-linear - it removes some noise spikesand emphasizes others. Also the analoguefiltering never completely suppresses voice -channel signal and the hard limiter canemphasize this problem.

With the introduction of microprocessorsinto f.m. land -mobile radio telephones, it isnecessary to design an optimum tone decod-er using a microprocessor. Reference 3describes one attempt at a practical imple-mentation.

111111kitteredoutput

Referencewaveshape

lock

Quad at urereferencewavesh ape

dt

2

Peak leveldetector andcomparator

d.c output

dc levelcomparator

Fig.1. Two basic implementations of acorrelation detector -a matched filter attop (a) and a quadrature correlator atbottom (b).


GENERAL CORRELATION

Two basic approaches to the detection of atone are shown in Fig. 1.1n (a), the matchedfilter uses the complete stored replica of thereference waveform after each shift throughthe shift register to determine correlationbetween the reference and the incomingsignal. Between each sample, n multiplica-tions and n additions must be performed. InFig. 1 (b), after each sampling, only twomultiplications and two additions into theintegral are required.

This approach however inherently in-creases decoding time. At the end of theintegration period, the integrators are resetto zero. If the incoming sinusoid started atthe middle of the integration period, it isunlikely to be recognized for 11/2 integrationperiods; worst -case delay approaches twointegration periods.

A matched filter gives optimum detectorperformance in the presence of Gaussiannoise". Figure 2 gives the basic frequencybehaviour of such a filter and Fig.3 showstypical amplitude response as the normal-ized input frequency is swept from zero to 2f.

There are two important features of Fig.3:

- For low values of n the output is skewed,which is quite correct. As n becomes large,the integral approaches the Fourier trans-form, the curves approach sinx/x and theasymmetry disappears.- If a sinusoid is cross-correleated withanother sinusoid, frequency selectivity ispoor unless many cycles are used.

As the number of cycles cross -correlatedis pushed up, so is filter selectivity. However,two other factors are important. Firstly thenumber of taps along the delay line is notinfinite, because finite time is required forgeneration of the integral. Secondly, thefilter can respond to multiples of the fun-damental because of aliasing.

From the Nyquist criterion at least twosamples per cycle are required at the max-imum frequency. However for equal sam-pling at two samples per cycle, the relativephase of the reference and the incomingsinusoid is important, since a phase shift of90° makes the difference between full outputand no output from a matched filter.

Referring to Fig. 1(a), output samplesequence E(k) from the stepped delay line is

= (f(k-n)h(n))n=0

where k is output sample number, incom-ing sinusoid f(k) is cos((k2/r/M)+0), filtercorrelation pattern h(n) is cos(ln2w/M)+ 8),and 0, 8 are relative phases.

t4-1 -2 n)E(k)= 1/2cos[(k 2ir + 0 -8] +n=o

1/2COS [-k27r+ 0 +8]

j2icos[4r+0+8]+

cos [(k -2n) 27r+k-o]n

Input signal

Tapped analogue delay lines

c. -A very largenumber of tapsRe

Vout

(a)

At 0= 0

I = Icost cos f't dt

where r is the normalized frequencydifference between the incoming andreference sinusoids

I =Incos(1-flt 2

cos(1.f')t dt2

_ 1- sintl-fltc FITT) sin11.nrt-1

it f'=1,-1

At 9 = 0

in cos nt cos oft dt

where n is the number of cycles used byth'? matched filter

I=I

I cosli-Ont cos (14")nt-Tt 2

sin(1-r)nrc sinitnntt 041,-1n (1- n (lf)

I = Tt r. 1,-1

Fig.2. Tapped delay line detector using a single sinusoid cycle (a) and using multiplesinusoid signals (b).

Cycles Half - power bandwidth1 0862 01.366667

0 2210 8666666E-02

NORMALIZED I P (FREQUENCY)

2

Fig.3. Peak output and half -power bandwidth for the detector of Fig.2 (b) using 1,2,4 and10 cycles.

The first term is desired output, while thesecond is an error term. If M,3, then thesecond term is zero so the minimum integersampling rate is three samples per cycle.

Figure 4 gives plots of proportional band-widths versus number of cycles in thematched filter for a number of waveshapes.As the waveshape used for cross -correlationprogresses from a sinewave to a 1:1 square -wave then to a 16:1 rectangle wave (all ofzero mean value), fewer and fewer cycles arerequired to achieve a given bandwidth. Thelimit is reached when the waveshape used isreduced to an impulse; in this case, barelymore than one cycle is required to determinefrequency of the incoming waveshape.

Such selectivity is bought at a high costsince a correlation detector like this willrespond to almost any incoming signal ornoise. A sinusoid waveshape gives excellentnoise immunity and rejection of harmonics,but from Fig. 4, a bandwidth of 5% (i.e.±2.5%) requires 16 cycles for correlation.

Figure 4 includes the curve for the commonanalogue filter approximation for rise time.

If incoming signal flt) consists of N cycles,each cycle with period T, then energy in theensemble, E, is

f 1th:it= J.NTI2(t)dto

=NT2n1IP

Table 1 shows this evaluated for four particu-lar waveshapes. If it is accepted that filteringover a number of cycles will reduce noise to a

Table 1. Sine and squarewave zero means.

Waveform,zero mean

Energy inwavetrain

Scalingfactor K

SineRectangular 1:1

1:71:15

IT TNA2 1

2TrTNA2 20.28577 TNA2 0.28570.1333177W 0.1333


T

10 20

NUMBER OF CYCLES (Ncyc)

Fig.4. Numerically calculated graph showing the relationshipwaveshape and normalized bandwidth.

near -Gaussian noise characteristic, thenstandard matched filter theory may be used.

Average s -to -n ratio for a sinewave plusnoise is

A2/2SNRAV= NT,

Standard matched filter theory gives thepeak -output s -to -n ratio as

n 2E 2E 2EBSNnpk=1= -(NA)- N

where 1 is noise spectral density with whitenoise characteristic, N. is total noise powerand B is noise bandwidth. Substituting fromTable 1, then for the previous equation.

SNRo(pK)=21f37) rTNA2K=41rB.TNK.SNRoavi

Design of a tone decoder for the t.c.s.s.application revolves around a trade-off be-tween bandwidth given in Fig.4 and factorsT, N and K in the previous equation.

If limited spurious response to odd har-monics can be tolerated, then the square -wave has a clear s -to -n ratio advantage overother waveshapes.

However, for the t.c.s.s. application, thereference may be rectangular but the in-coming signal is merely a hard -limitednoisy sinusoid. For low s -to -n ratio opera-tion, the reference waveshape shouldemphasize the signal where the peak of thesinusoid is.

In practice the reference waveform is notcritical; a rough three -level or five -levelapproximation to a sinewave is quite accept-able.

30

between correlation

PERIOD MEASUREMENT

If the incoming signal is relatively noise freebefore hard limiting, a microprocessorequipped with a hardware timer can readilymake a period measurement to an accuracyof the maximum instruction execution time.

Thus, an incoming sinusoid period can bedetermined accurately to within a few mic-roseconds if the sinusoid is guaranteed to befree of any d.c. or transient offset. This ismost easily implemented if the microp-rocessor is given an interrupt pulse on eachpositive (or negative) zero crossing; this isapproximately equivalent to the incomingtone being reduced to an impulse.

For a high s -to -n ratio, probability densityof zero crossings can be found if someapproximations are made:

- If the noise passband extends beyond thefrequency of the sinusoid to be decoded,then distribution in time of one zerocrossing is statistically independent of theprevious zero crossing.

- Around the point of the zero crossing, thesinusoid may be approximated by astraight line of slope Aw.

- The noise voltage has a Gaussian distribu-tion.

- There is only one zero crossing per half -cycle.

This requirement implies a high s -to -n ratioand a relatively low upper cut-off frequencyfor the bandpass filter.

A noise voltage sampled infrequently withrespect to the upper cut-off frequency of apassband filter has this Gaussian amplitudedistribution

2

p(y,ti)= exp - (tr1

where a is the r.m.s. voltage and p. themean direct voltage.

At the point of zero crossing of a sinewave,the amplitude distribution of sinewave plusnoise can be scaled to give a distribution intime at the instant of zero crossing.

13. CT-Y =Ato A27r

when normalized to a frequency of 1Hz.Input s -to -n ratio should be such that the

instant of zero crossing is within a certainerror bound A. For example, a t.c.s.s. systemmay require a 5% bandwidth so A is ± 0.025in this case. Since the point of interest is atthe zero crossing of the noise -free sinewave,the mean p. is zero and the error limit on thetime axis is:

Za A ZAZir cr -2.TrA

A)2SNR= 1/2(0. SNR; = 1/2g_)2.

7r

However, if the decoder averages the periodsover each cycle, then the required SNR,reduces by Nrcl where N is the number ofcycles:

1 ZA21Ti 12SNR.=VF1 1

For the example of a 5% bandwidth, SNR,reduces to 5.5 for 16 cycles. This derivationis not suitable for use when s -to -n ratio isless than four. It does however indicate thatat modest s -to -n ratios fast decoding ispossible. Further, using a small timerinterrupt -service routine it is possible for amicroprocessor to directly decode a 10kHztone without use of aliasing techniques.

DISTRIBUTION OF ZERO CROSSINGS

Figure 5 shows the arrangement used tomeasure the period between adjacent posi-tive zero crossings of the output signal froman f.m. receiver. It is necessary to eliminateall noise contamination from mains fre-quencies for these results to be valid.

Figure 6 shows normalized distribution ofperiods between successive positive zerocrossings. The normalized measurement in-tervals were 0.05 and 1000 samples weretaken for each curve. These graphs show thata received tone is more likely to be con-taminated by a spurious zero crossing if it islow in the analogue -filter passband.

For the particular receiver, the 12dB sinadsensitivity is -118dBm. At this level, prob-ability of correct detection of a tone byperiod measurement, i.e. correlation withan impulse -like reference, is poor, particu-larly when the tone is low in the filterpassband.

These results indicate that best decoderperformance is achieved when the mostanalogue filtering is done before hard -limiting the signal.

To be continued.


References1. EIA RS220-A Minimum standards for land

mobile communication continuous tone -controlled squelch systems (CTCSS), Electro-nic Industries Association 1979.

2. MPT1306 Code of Practice, Continuous tonecontrolled signalling system (CTCSS) for use inthe land mobile services, HMSO, London 1978.

3. Labedz G.P., Continuous tone -coded squelchsystem implemented in an eight bit micro-computer, International Conference on Com-munications, Denver, Colorado, June 1981.

4. Introduction to communication systems, F.G.Stremler, Addison-Wesley 1982.

5. Communication Systems, S. Haykin, Wiley1983.

6. Turin G.L., An Introduction to Digital MatchedFilters, Proc. IEEE vol. 64 no 7, July 1976.

7. Rice S.O., Mathematical analysis of randomnoise, BST.123 (1944) pp.282-332 and 24 (1945)pp.46-156.

8. Rice S.O., Statistical properties of a sinewaveplus random noise, BSTI..

9. Rice S.O., Noise in f.m. receivers in the syrripo-sium proceedings of time series analysis, ed. M.Rosenblatt, pp.395-422, Wiley 1963.

10. Roberts J.H., Angle modulation: The theory ofsystem assessment, [EE TelecommunicationsSeries 5, Peregrinus 1977.

11. Tozer T.C. and Kollerstrom J., Penalties ofhard decision in signal detection, ElectronicsLetters, vol.16 no 5, 28 Feb 1980.

Chris Gough works as a design engineer withTait Electronics in New Zealand. Before thathe worked as an electronics technician forthe DSIR, and in 1984 he gained his BE(Hons) from the University of Canterbury.His interests include r.f. design, signal pro-cessing and instrument design.

Signalgenerator

Modulated atrate f.m.

f.m.receiver

qcdtir)Ci

Butterworth 4th order50Hz to 325Hz

LM 324

200mV to 5V p -p(must not clip)

CK

RST

20x fmSquarewave

generator

CK

RST

MC 14013

- DoCK

EN

RST

Personal computer

CK

RST

MC 14520

.41. D0 -D7

Fig.5. Hardware test arrangement for measuring the period between adjacent positivezero crossings.

Fig.6. Normalized distribution of periods between adjacent zero crossings in a noisy f.m. signalusing 1000 samples for each curve and 0.05 measurement intervals.

500-

400-

_

300-

_

200 -

100-,

0-

0

...... 70Hz- - - 130Hz

250Hz

SNRIF = 2 dI3

.....

20 26

100

No carrier present

1 II T I I I I I I

10 20 30(d)

400

303-

200-

100-

0

SNRIF .0dB

0 10

( b)

20 26

300-

200-

100-,

.0 -10

I T

SNRIF. -2d8

I

10 20

c)

T I I26


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Used Test E ouiprrserd

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01-943 4477


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12K7GTI 2K8GT

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UABC80 0.75UBF80 0.70

6AK6 2.856AL5 0.60

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85A2

85A2*1A0255ECC82 0.95 E 786 87 060 UBF89 0.70 6AL5W 0.85 66E16 7.40 807 220

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POSTAGE AND PACKING CHARGES: C1 -E3 50P. E3 -E5 60P, E5 -E10 80P. E10 -E15 C1.00, C15 -C20 Cl 50.. l,er 1201' 00 bur helovr :',.0 Parcels over ;No at Cost

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ENTER 71 ON REI'I.Y CAM )

532



LOW COST DESIGN TOOLSFOR ENGINEERS

Why should EPROM Programmers and similar devices be so expensive?We have found two products which beat all the price barriers.

OCTAGON EP -8 8 GANGEPROM PROGRAMMER £499This highly acclaimed German product measures only270 mm x 170 mm x 30 mm high. Its strong metalconstruction and simplicity of operation makes it equally-___suitable for a production or development environment

8 -gang simultaneous copying-- fl

all popular EPROM makes and sizes

32 character alphanumericdisplay RS232 down -line -load fa (ity

The first truly professional Ethe £500 price barrier!

' 112: ,

OCTAGON EP -1EPROM SIMULATOR £399Turn your IBM PC into an EPROM Simulator and developprograms for any microprocessor system - withouttedious EPROM burning and without the high cost of anGr-circuit emulator.

add -in card simulates Jp to 64K bytes of EPROM

ribbon cable connects to your target microprocessor'sEPROM socket

accepts binary or hex oad files

Fiet_ qn also supply most cross-assemblers/compilers torr k -a complete low cost development system.

Programmer: Enter 43 on Reply Card

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Racal Solid State Communication Recelvent - RA1217 - Mechanicil digit readout 1

3OMC S C300 Racal RA17L Communi-cation Reosivers 500KGS to 30MCiS in 30bands 1MC/S Wide - C175 - All receivers are airtested and calibrated in our workshop -

supplied with dust cover - operationinstructions - circuit - in 'air used conditionRacal Synthesisers (Decade frequencygenerators) MA250 - 1 6MOS to 31 6 MC/S -C100 MA1350 for use with RAI7 receiver -C100 MA2S9G - precision frequency standard5MCiS - 1MC.JS - 100KHz - f100 to 0150 RA137and RA37 - LF convenors 10 to 980KC/S - £40to C75 RA98 SSE-ISB convertor - C50 RA121SSB.ISB convenor - £75 Plessey PR155GSolid State receivers - 6OKC/S - 30MCiS - C300Transtel Matrix Printers AF1IR - 5 levelbaudot code - up to 300 bands - for pnnt out onplain teleprinter paper C50 Army Field

Telephone sets type F L and J - large quantityn stock - C6 to C15 depending on type andquantity P 0 R Don 10 Telephone Cable -half mile canvas containers £20 NightViewing Infra -red periscopes - twineyepiece 24 volt DC supply - C100 EAOriginal cost to Government over C11.000 EAStatic Invertors - 12 or 24 volt inpi.t - 240 voltAC sinewave output - venous wattages P 0 RXI' Plotters and pen recorders - venous -P 0 R Signal Generators - various - P 0 RTF 893A - Power meter - '.150 Racalfrequency counter type 836 - C50 Tektronlcplug -Ins Al1 C50 1A2 C40 1A4 0100 M C50All items are bought direct from H MGovemment being surplus equipment Price isen works S A E for enquiries Phone forappointment for demonstration of any itemsalso availability or price change VAT andcarriage extra

EXPORT TRADE AND QUANTITY DISCOUNTSJOHNS RADIO, WHITEHALL WORKS,

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SYNCHROS ETC. RECEIVING AND TRANSMITTING EQUIPMENT

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New software for existing owners of Acorn GPIB controllers whi.:;h offers compatibilitywith the new IEEE 488 2 standard. C28

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needed and is compatible with new devices using IEEE 4::.2 fo-mat comnands.

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DIPL.-ING FRANZ BRAUNSCHMIDInzersdorferstr. 119/23, A-1100 VIENNA, AUSTRIA




ANEW PRODUCTSHigh -resolutionmonitorDesigned for use as the basis of agraphics workstation, the CBT Ultra-high resolution monitor will finduses in cad/cae, electronicpublishing, document storage andretrieval and the like. The monitorhas a rotatable screen which can beused in the upright - 'portrait', orhorizontal - 'landscape' modes andthe housing includes tilt and swivelfor ease of use.

The monitor has a 300MHz videobandwidth and a raster format of2301 lines with 1728 pixels/line. Thisworks out at about 8 pixels/mm (or200 per linear inch) and thecompany, Consolidated BusinessTechnology, claim to be the onlymonitor manufacturers who keep amagnifying glass in their showroom!

The monitor includes a frame -store memory for four images(16Mbit). The refresh rate is 100Hz(2:1 interlace); line rate is 125kHzand the video rate is 288Mbit/s. Thevideo ram has 8 -bit direct memoryaccess with a data rate of up to5Mbit/s. It is possible to read to orwrite from any byte in the four pagesand to dump any of the pages to aprinter.

The company tells us that theirdesign goals were (a) no compromiseon the image quality and (b) ease ofinterfacing to other equipment. Theybelieve that they have achieved bothof these. There is a wide range ofoptional peripherals, mainly for

memory storage (e.g. optical discs),input (document digitizers), output(high -resolution plotters) andcommunications includinginterfaces for VME, facsimile andEthernet. There is to be an adaptorcard for IBM AT -like computers, and

a larger monitor able to display A3documents with 8Mbits/image.Consolidated Business TechnologyLtd, 14 Parkside, RingwoodIndustrial Park, Ringwood, HantsBH24 3SQ.Tel: 0425 47014.

Analogue c.a.d.New from Hi-Tek CAE is the DaisyAnalog Design series of advancedc.a.e. tools which make the analoguedesign cycle faster and easier.

The system is based aroundDspice, Daisy's circuit simulator,which provides a fully -functionalanalogue simulation which is easy touse and takes all its parameters fromthe entered circuit diagram.

During analysis, Dspice canperform the functions of voltmeters,ammeters, multi -channeloscilloscopes, network analysers,and other familiar laboratoryinstruments. Engineers can performd.c. time and frequency domainanalyses, including a wide range ofcommon subanalyses such as d.c.transfer curves, Fourier analysis, andnoise analysis. Dspice can also beused for sensitivity analysis,providing key information on criticaldesign elements that cannot beobtained through traditionalbreadboarding.

The Daisy Analog Design seriesalso includes ChipSim, an optionalhigh-speed circuit -level simulatorfor transient analysis of digital i.s.i.and v.I.s.i. designs. ChipSim usesadvanced relaxation algdrithmswhich are optimized to deliverdetailed circuit information at speedssignificantly faster than multi-function DSPICE algorithms.

Hi-Tek CAE. Beadle TradingEstate, Ditton Walk, Cambridge, CB58QD. Tel: 0223 215055.

NEXT MONTHLogic analysis. A logic analyser isone of the essential tools in thedesign, testing and monitoring

di of digital equipment. Our feature'discusses the use and applicationof the instrument.

IMarx generator. An inexpensivemethod of generating unipolarpulses of several million voltsamplitude at very high currents.

The incredible Scophony.Mechanical systems of television did

Inot come to an end after the 30 -lineBaird transmissions in 1935. TimVoore describes the Scophony backprojection system that provided a33 in -diagonal picture in 1938.

Current, or voltage? Joules Watt, asserts that nothing is pure and veryV little ever simple, so that there is

II

ELECTRONICS& WIRELESS WORLD

Logicanalysers andanalysis

Experimentalhigh -voltagegenerator

Very lowfrequencymeasurement

Coprocessorsfor the 68020

Comparingpower mosand bipolardevices

Morse - theAmericanLeonardo

often confusion over whetheramplifiers amplify voltage orcurrent, or a mixture of both.

Building blocks in activecompensation. Single op -amp, first-order blocks for the realisation ofactively -compensated amplifiers andintegrators.

Power mos v. bipolar. It is possiblethat power mos will gradually replacebipolar power devices. This articleoffers a comparison of the twotechnologies.

Colour graphics controller. JohnAdams discusses interfacing theVSDD colour -graphics controller toproduce a high resolution graphicsboard with RCB output at one endand microprocessor -bus signals atthe other.


[NEW PRODUCTSSOLDERING

Soldering to solderThe problem of solderingmetalcomponents to an existing pre -soldered joint has been solved by theuse of a bismuth -tin alloy with amelting point well below that ofordinary solder. Melting at 137°C,the alloy is used in an extruded wireform to ensure the accuracyfrequently necessary when solderingcomponents for electronicequipment. The manufacturers canadjust the composition of the alloysacross a wide range of low meltingpoints, anywhere between 20° and300°C. MCP 137 - one of the mostpopular alloys in the MCP range - hasthe further advantage, unlikeconventional solder, of having nolead content. Mining and ChemicalProducts Ltd, Alperton, Wembley,Middlesex HAO 4PE. Tel: 01-9021191.

Conveyor system forautomatic solderingClosed -loop conveyor lines are thespeciality of PAF Ltd. Each of thelines, in a typical installation, is on asingle level in the shape of arectangle, and uses PAF's twin -tapeconveyors to transport the cardswhich are fitted in jigs on carriers.This highly -efficient closed -loopsystem incorporates PAF's 90° twin -tape transfer units at three corners,automatically synchronized with thecarriers, and an Electrovert flow -soldering and board cleaningmachine.

To facilitate the processes involvedin flow soldering and cleaning, theboards are raised as they passthrough the machine, and a higher -level conveyor takes the carriers ashort distance to a PAF twin -tape liftand transfer unit.

The component inserters sit alongthe outside of each line and are ineasy reach of the parts, which areheld in 10 or 20 tray, foot -operatedPAF rotary carousels locatedopposite them on the inside of theline. PAF Systems, Sanders Road,Fineden Road Industrial Estate.Wellingborough, Northants NN84NL. Tel: 0933 222195.

SolderingequipmentA range of tools, machinery andmaterials for soldering is availablefrom Solbraze Ltd. They produce awide range of soldering irons from 30to 500W; flame, induction andresistance heating tools; and a largenumber of different solder pots fordip soldering. The companyspecialises in tailoring machines andjigs for specific applications.Solbraze Ltd, Bilton Road, Erith,Kent DA8 2AN. Tel: 0322 341411.

Robot for solder maskingA low-cost robot has been developedfor the application of solder -resistmaterials to printed -circuit boards.The Polar Robot comes fromCrantech Robotics. The machine canbe programmed easily and quickly onthe production line to deal with anyspot -masking configurationrequired, in any combination ofmask patterns - lines, dashes, dots,squares, etc. as intricately as theapplication requires.

In batch production, the machinecan recall a number of presetprograms at the touch of a button.Even different combinations of headthickness can be incorporated intothe same program by use of aninbuilt device known as the speedmultiplier. The Polar is claimed tocarry out its task far more accurately.

swiftly and economically than ispossible by hand application.

As the robot can deal accuratelywith solder masking, it can atso beused for other applications, such asthe dispensing of solder paste.adhesives and encapsulatingmaterials. All that is needed is achange of dispensing valve andproduct feed line; the substitution ofsolder paste (or adhesives orencapsulant) for solder mask; andcalling up of the appropriateprogram. At its basic installed priceof around113 000, payback isbetween six and eighteen months,depending on the type of application.Crantech Robotics IndustrialSystems Ltd, Unit D3. Gedding Road,Hoddeston Herts EN11 ONT. Tel:0992 445935.

Soldering thermometerWhere the temperature of a solderingiron may be critical. it is possible touse the WSI 500 thermometer. It hasa built-in sensor mounted on the

ELECTRONICS St WIRELESS WORLD

front panel, surrounded by a bit -cleaning sponge, with a liquid -crystal readout. The instrument hasa temperature range of - 50 to+750°C. with an accuracy of 0.5%( ± 1 digit) calibrated to BS4937.West Sussex Instruments Ltd, 12ACorc nation Buildings. BroughamRoad, Worthing, W. Sussex BN112NW. Tel: 0903 212303.

Static -freedesoldererA low-cost static -free desolderingtool has been added to the anti -staticrange of OK Industries. It has beenmanufactured in accordance with ULand MIL standards and satisfies MIL/B/817025 2nd barrier electrostaticfree material requirements. It isprovided with a bayonet typeconductive tip which is easy to cleanand change.

The DP3 is available ex -stock andcosts £5.751+ tax & delivery). Tipsare 95p. OK Industries UK Ltd.Dutton Lane. Eastleigh, Hants S054S1.. Tel: 0703 619841.

Hot-air resolderingDesigned for repairing surfacemount boards, the new System 1000uses directed hot air exhaust todesolder and resolder s.m.ds anddual -in -line components. Thesystem features an X and Y board -holding mechansim on linearbearings, with a panel size from 0 to600 by 400mm and two hot air tubeswhich can be individually extendedor retracted by means of a controlknob. Additionally, the temperatureof either of the tubes can beindividually controlled, for aparticular application.

The System uses a blower fan topass air through both the upper andlower tubes, each of which isequipped with a heat controller to

monitor the temperature of the air asit passes through the tube. Once thetubes are extended forward, hot air isdirected through a special disc platefitted to the tube's end and onto thesubstate for repair. The system hasbeen designed to be portable, andweighs only 10kg. Sohlberg-SurtechLtd. Intec 2. Wade Road,Basingstoke, Hants RG24 ONL. Tel:0256 470848.

Wave solderingGood soldering is combined withpleasing design and good, soundmanufacture in the lemme Italiarange of wave soldering machines;according to Electrautom Ltd, whoare the UK agents.

The IM range is well established inEurope but is newly imported to theUK. Their design has improved theimage of such machines which aretraditionally dirty and smelly.Electrautom Ltd. Etom Buildings.Quarry Wood, Aylesford, Kent ME207NA. Tel: 0622 70188.

435

LANGREX SUPPLIES LTDClimax House, Fallsbrook Rd., Streatham, London SW16 6ED

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I erms of business: CWO. Postage and packing valves and semiconductors LI .0111 per order. CRTs £1 .511. Prices excluding VAT. add I('rice ruling at lime of despatch.In some cases prices of Mullard and USA valves will he higher than those advertised Prices correct when going to press.

.1111 lu Sites available to approved companies with minimum order charge 1111 I .111i.0, .01.1 4,0 k 0nr ( I 71/011 credit order.I types of valves, tubes and semiconductors in stock. Quotations for an, 1. I ' 1

Telephone: 01-677 2424/7Telex: 946708E. 8 O.E.Open to callers Monday-FrIday 9 a.m. -5 p.m. VVW



FATEW PRODUCTSSPECTRUM ANALYSERS

HP portableAlso from Livingston TechnicalSales, comes the The HewlettPackard 8590A RF SpectrumAnalyser, offering features previouslyfound only in high-performancemodels, but it comes in alightweight, sturdy packageweighing only 13.5kg. It is equallysuitable for bench applications, inr.&d. manufacturing environmentsand for field use; for stand-alone orsystems applications. It has theversatility to handle virtually any r.f.signal measurement requirement.

The instrument covers the 10kHzto 1.5GHz frequency range (1.8GHzoptional), with -115 to +30dBmamplitude range. Designed for easymanual operation, the 8590A is thefirst HP spectrum analyser to haveboth dedicated pushbuttons, forfrequently -used functions, andmenu -based softkeys, with access tomore than 80 additional functions.Most measurements require onlyfrequency, span and amplitudeselection, the analyser automatically

adjusting remaining parameters foran optimized c.r.t. display. OptionalHPIB, HPIL RS232c interfacesenable fully programmable, anddirect output of results to printer orplotter.

More than 100 built-in functionsaid measurement and data handling.including signal track and markerfunctions, automatic performance ofcomplex measurements. tracearithmetic and trace storage.

Coupled with the HP 8444Atracking generator, the HP8590Aperforms evaluations such asstimulus response measurements,e.g. frequency response andinsertion loss. Further addition ofthe HP 10855A broadband amplifierand the new HP 11940A close -fieldprobe yields a swept, broadbandsysem for e.m.i. troubleshooting.

The unit is available for sale exstock from Livingston TechnicalSales or on short term rental fromsister company. Livingston Hire. at£200 a week.

Portable analyser forsatellite receptionEspecially designed to cope withtv.r.o. installation and serviceproblems, the Avcom PSA-35 is alightweight portable instrument,which operates from a.c. mains orinternal rechargeable batteries. Thefrequency coverage is from under 10to over 1500MHz and from 3.7to4.2GHz in 6 bands (including thecurrent 12GHz for 1.n.bs. Theinstrument has a built in powerblock and power for 1.E.as and b d csIt will accurately measure wide bandsignals commonly used in the tv.r.o.industry, and is ideal for accurate andrapid testing and alignment ofsatellite equipment.

Optional extras include a signalsampler, a terrestrial interferencesurvey horn and a carry case. Forfurther details contact FieldtechHeathrow Limited, Huntavia House,420 Bath Road, Longford. Middlesex,UB7 OLL. Tel: 01-897 4446.

Synthesizedspectrum analyserUp to 3.6GHz from 10khz with aninput sensitivity of -131dBris and aminimum resolution bandwidth of30Hz are provided on the TR4135synthesised spectrum analyser fromAdvantest.

The increased use of the upperu.h.f. band a tighter control offrequency harmonics have created ademand for measurements to bemade up to and beyond 3GHz. Thisanalyser costs less than £16,000

An in-built frequency counter with1Hz resolution is included, together

with adjustable marker display offrequency and level. Log. frequencydisplays are possible with a directhard -copy capability. Facilities areprovided for field -strength andCISPR interference measurementsfor ATE applications. GPIB controlsare available with an optionaltracking generator to 3.5GHz.

Advantest products are availablefrom Chase Electronics Ltd, St.Leonards House. St Leonards Road,Mortlake. London. SW14 7LY.Tel: 01-787 7748.

1GHz analyser fromFarrellFrom Famell comes the 352Cportable spectrum analyser.designed for ease of use inmonitoring spurious radiations inteh range 300kHz to 1GHz. Fivesweep ranges have threemeasurement bandwidths from2MHz on the widest range to 9kHz onthe narrowest, (3MHz) range. Theinstrument may be used as a fixedtuned receiver over the fullfrequency range and both a.m. andf.m. demodulation is provided withan internal loadspeaker for output.

The display has long persistencegreen phosphor with 488 lines on ac.r.t. screen. All control functions,including error reduction andsystem monitoring aremicroprocessor controlled. Up to sixfront -panel settings can be sored andcontrolled. The internal picture storecan be output to a printer for hardcopy. Famell Instruments Ltd.Sandback Way, Wetherby. W.YorksLS22 4DH. Tel: 0937 61961.

Portable Tek analyserTektronix has introduced a newgeneration v.h.f./u.h.f. spectrumanalyser priced at around £7 500; the10kHz to 1.8GHz TEK 2710. Theinstrument provides a 5MHz i.f.bandwidth filter, 10 5 frequencyaccuracy, four -trace digital storage.full marker/delta marker control, acomprehensive time domainmeasurement capability; and many"built-ins" not available on currentlower cost spectrum analyzers.

The standard TEK 2710 hasresolution bandwidths down to3kHz: there is an option for 300Hzresolution. Frequency accuracy is105 or ±10kHz at 1GHz centrefrequency on the standard 2710. withan option for accuracy of 5 x 10' or±500Hz at 1GHz centre frequency.An optional built-in frequencycounter provides readout resolutionto the nearest hertz and rapidfrequency measurement when inwide spans: any signal 10dB abovedisplayed noise will he counted.When the counter is used in zerospan (time domain). it will measure

the frequency content of thedemodulated signal e.g. modulationfrequency.

On -screen dynamic range is 80dBand vertical scaling is selected from10.5 and IdB/div with reference levelunits of dBm, dBmV. dBV, dB/µvdBp.W, and dBµV/m available. TheTEK 2710 accommodates both 5011/dBm and 7511/dBmV operation.

Sensitivity is -117dBm at 3kHzresolution. A built-in preamp may beswitched into the conversion chainwhich will boost sensitivity to- 129dBm. An additional 10 dB ofsensitivity is available if the 30011zresolution option is included. Thecomprehensive time domaincapability of the instrument makes itof particular value in makingcommunications measurements.Included are 1µs to 2 seddiv sweep ina 1-2-5 sequence for maximumflexibility in expanding the display.Analogue display for gray -scaleenhancement and 5MHz systembandwidth (including c.r.t.) thatminimizes amplitude measurement

distortion. A.m./f.m. detectors withaudio amplifier, built-in speaker andheadphone jack permit listening todemodulated audio.A new, optionalvideo monitor mode permits viewingthe demodulated, rasterized video onthe c.r.t. of the TEK2710.

The instrument includes marker/delta markers with front panelcontrol for peak find, next right andnext left manoeuvres. Other marker -related functions are available via afrequency/marker menu. Markersfunction in both the time andfrequency domain and include off -screen measurement capability.

Digital storage display includes afour -trace capability. A,B and Cdisplays may be stored and viewed,with the D display always remainingcurrent. This results inenhancement of signal comparison.Acquisition of the analogue signalmay be on the basis of positive/negative peak processing wheresignals "buried in the noise" may bediscerned; or positive -peak -onlyprocessing that provides best

horizontal -scale display resolution.Ensemble signal averaging may beselected between min, max. mean ormin/max values. Ease of use isenhanced by logically grouped:dedicated front panel controls forprimary functions. The TEK 2710includes comprehensive secondarycontrol capabilities that are accessedvia a set of five clearly marked menukeys. A user -definable key providessingle keystroke measurements thatare programmed and executed fromthe front panel. Operation is furthersimplified by an auto calibre routine,and automatic resolution, sweep andr.f. attenuation modes whicheliminate operator traps and keep theanalyser in a calibrated state.

Additional options availableinclude Centronics interface, batteryoperation and rackmountconfiguration. GPIB and RS232interface and a tracking generatorwill he available at a later date.Tektronix U.K. Ltd.: Fourth Avenue,Globe Park, Marlow, Bucks. SL71YD. Tel: 06284 6000.


The Archer Z80 6bCThe SDS ARCHER - The Z80 based single boardcomputer chosen by professionals and OEM users.* Top quality board with 4 parallel and 2 serial ports,

counter -timers, power -fail interrupt, watchdog timer,EPROM & battery backed RAM.

* OPTIONS: on board power supply, smart case,ROMable BASIC, Debug Monitor, wide range of I/O &memory extension cards.

from £185 + VAT.ENTER 32 ON REPLY CARD

The 5owman 68000 61)CThe SDS BOWMAN - The 68000 based single boardcomputer for advanced high speed applications.* Extended double Eurocard with 2 parallel & 2 serial

ports, battery backed CMOS RAM, EPROM, 2 counter -

timers, watchdog timer, powerfail interrupt, & anoptional zero wait state half megabyte D -RAM.

* Extended width versions with on board power supplyand case.

from £295 + VAT.ENTER 33 ON REPLY CARD

6herwood Data 6y6tern6Sherwood House, The Avenue, Farnham Common, Slough SL2 3JX. Tel. 02814-5067

HART - The Firm for QUALITYLINSLEY-HOOD 300 SERIES AMPLIFIER KITS

Superb integrated Mosl- et amplifier kits with an unbeatable pedigree,circuit design by John Linsley -Hood and engineering by HARTUltra easy assembly and set-up with sound quality to please the mostdiscerning listener Ideal basis for any domestic sound systems ifquality matters to you Buy the complete kit and save pounds off theindividual component priceK300-35. 35 Watt. Discount price for Complete KitK300-45. 45 Watt. Discount price for Complete KitRL H485 Reprints of Original Articles horn HiFi News

LINSLEY-HOOD SYNCHRODYNE AM RECEIVERVery high quality kit for this recent design featured it Wireless World Advanced Lonstrucfionsystem approved by the Author uses 3 double sided PCBs in a stacked layout for total stability. easeof construction and minimal wiring This module will form the AM section of an ultra high qualityAM/FM switched bandwidth tuner to match our 300 series amplifiers Power supply and tuning gangwill be included with the FM sectionK450 JLH Synchrodyne Kit Special Price £59.95

LINSLEY-HOOD SUPER QUALITY FM TUNERThe long awaited ultra high quality FM companion to the Synchrodyne AM receiver Novel circuitfeatures ready built pre -aligned front end phase locked loop demodulator and advanced sample andhold stereo decoder Circuits featured in Electronics Today International magazine February andMarch 1987 Complete kits for FM only or combined with the Synchrodyne are cased to match our 300Series amplifiers Send for details

HIGH QUALITY REPLACEMENT CASSETTE HEADSDo your tapes lack treble. A worn head could be the problem Tapeheads are constantly improving and fitting one of our latestreplacement heads could restore performance to better than new.Standard mountings fit most decks and our TC I Test Cassette willmake it easy to set the azimuth spot on As we are the actualimporters you get prime parts at lowest prices All our heads aresuitable for Dolby machines

HC20 Permalloy Stereo Head Good quality standard head fitted as original equipment on manydecks £7.66HS16 Sendust Alloy Super Head Quite simply the best Longer life than permalloy higher output thanferrite. fantastic frequency response £14.86H0551 4 -Track head for auto -reverse or quadrophonic use Full specification record and play head E14.60Special Offer Stereo R/P Heads £2.494 -Track Auto -Reverse Play Head £3.50HS9510 2/4 Stereo DC Erase Head £6.70H0751 E 4/4 Erase compatible wdh H0551 £39.70Full data on these and other heads in our range are contained in our free list

HART TRIPLE -PURPOSE TEST CASSETTE ICIOne Inexpensive lest cassette enables you to set up VU (Dolby) level head azimuth andtape speed without test equipment Vital when fitting new heads Complete with instructions £4.66

JLH QUALITY AM RADIOSets of Parts available now including Short Wave coils Full kits ready later Send for list

Send for your FREE copy of our lists with full details of our complete range of Kits. Components,PCBs, Cassette Heads and Decks Overseas please send 5 IRCs for Airmail Post

Ploa, ..-14-1 VAT to all prices Postage on orders up to f 10 50p f 10 to f49 f 1 Over f50 f 1 50

£98 79£10236

£f 05 no VAT

,40

ELECTRONIC KITS LTD1, Penylan Mill. Oswestry. Shropshire SY10 9AF24 hr SALES LINE (0691) 652894 Please add VAT

IN VIEW OF THE EXTREMELY RAPID CHANGE TAKING

PLACE IN THE ELECTRONICS INDUSTRY, LARGE

QUANTITIES OF COMPONENTS BECOME REDUNDANT.

WE ARE CASH PURCHASERS OF SUCH MATERIALS AND

WOULD APPRECIATE A TELEPHONE CALL OR A LIST IF

AVAILABLE. WE PAY TOP PRICES AND COLLECT.

R. Henson Ltd.21 Lodge Lane, N. Finchley, London, N12 8JG.

5 mins. from Tally Ho Corner

Telephone: 01-445 2713/0749

ENTER IRON R1.1'1.1 f \1311

- TARGET ELECTRONICS16 Cherry Lane. Bristol BSI 3NG. Telephone: 0272 421196Telex No 946240 CWEASY G. Quoting. 19013485 Easylink No. 19013485

D type plugLO1111, (,old platedcontacts Solder bucket

terminals

one ten 1009 -way mak:9 -way female

38p40p

28p30p

251,

9 -way hood 34p 25p 22p15 -way maie 44p 33p 29p15 -way female 48p 36p 32p15 -way hood 38p 28p 25p'5 -way male 60p 48p 38p25 -way female 65p 95p 45p25 -way hood 42p 32p 27p

v

£1 .55

crrr-2

£2.05

RS232 WALL PLATESWith 25 pin '0' sockets

25

.5732

£3.15

on.IBM/PCAmstrad/ 1 BM 750Tandon 3 OM 850 Si,Amstrad6128464 12M 795 6

BBCCentroncs 10M 450CentronicsCentronics IBM 550 40

Ommal ,woew, welcomedGovernment Fdirniwr, Detsvirnonw CGx

438



riNTEW PRODUCTSSPECTRUM ANALYSERS

Analyser for test and educationPart of the Lab -Volt analoguecommunications training system isthe 9405 Spectrum analyser. It hasbeen designed for the study of audioand r.f. signals in the frequencydomain. Combined with anoscilloscope, the power levels of thefrequency components of an inputsignal can be displayed on theoscilloscope screen.

The analyser can display frequencycomponents from 0 to 30MHz. or

from 85 to 115MHz, with the centrefrequency being displayed on adigital readout. The input signal levelis from - 70 to +30dBm. The outputspectrum can be directed to theoscilloscope or a recorder/plotter.

The input impedance is switch -selectable between 50 and IMS1 andinputs can be attenuated in five stepsfrom 0 to 40dB. The bandwidthresolution is set automatically to theoptimum for the range selected,

between 100 and 50kHz.The analyser incorporates a digital

memory for the oscilloscope displaywith a refresh rate of 30Hz.Frequency scan is selectable between2khz and 1MHz/volt. With theoscilloscope set to 1V/div, a total spanof 20khz to 10MHz can be displayed.A 'no scan' position can also beselected. Lab -Volt UK, Unit 6,Cromwell Mews. St. Ives, CambsPE17 4BH. Tel: 0480 300695.

111111111M IM1 MNMMVAMMN.\ \\\\W\1.IMM

Analysis of power -line spectraA new disturbance waveformanalyser from Dranetz is claimed tobe the first of its kind to featurescreen-based operation. The touch -sensitive screen displays self-explanatory menus for easyoperation, and full disturbancewaveform detail derived from high-speed sampling detectors.

The Series 656 not only monitorspower line disturbances on fourchannels but also offers the option ofan eight -channel environmentanalyser enabling monitoring oftemperature, humidity, r.f.i. etc. Bycapturing, displaying, analysing andstoring vital information, theinstrument helps to eliminate the

hazards that threaten reliableoperation of sensitive electronicequipment.

Setup and report parameters aresimply programmed using the screenor keyboard, and an RS232c interfaceis provided for remote operation. Thedisturbance waveform is stored innon-volatile memory for analysis anddisplay, mass storage being providedto allow an extended period ofdisturbance monitoring.Disturbances are analysed on -screen,stored on a disc, or printed out usingthe integral thermal printer. A zoomfacility enables areas of thedisturbance waveform, selected onthe touch -sensitive screen, to be

expanded for further analysis. The656 can also be programmed to selectdisturbances with user -definedcharacteristics for investigation.

Software support includes avariety of standard report formats forthe generation of records, includingeasily -interpreted summaries andrelevant disturbance waveforms, tohelp production of site histories.

The eight -channel environmentalinput board accepts 0 to 10V or 4 to20mA inputs from external probesand transducers.

Livingston Technical SalesLimited. 2-6 Queens Road.Teddington, Middx TWI 1 OLR.

Tel: 01-977 0055.

Analyser and DSOcombinedHaving the functions of both aspectrum analyser and a digitalstorage oscilloscope, theScopadaptor 9060 is used with a'host' two -channel oscilloscope. Theinstrument is a two -channel digitalsignal processing unit with inputattenuators-amplifiers, anti -al iasingfilters and a -to -d converters. Itprovides analogue outputs to theoscilloscope together with a trigger.

In the FFT mode it acts as aspectrum analyser with a bandwidthof 40kHz. The high-speed monolithicd.s.p. allows updating the display, atthe slowest frequency, every fourseconds and at high frequencies,every second. Averaging in binarysteps from 1 to 128 is provided,which is useful when testingequipment using white noise. Otherfeatures include the ability tocompare, or subtract the signals.

The instrument will also convertan oscilloscope into a digital storagedevice. The Scopadaptor has 512-bytes/channel. Memory is readcontinuously by the screen refreshcircuitry at the sweep rate of theoscilloscope.

Both functions can be combined inone display fora single signal. Thiscan be used for a continuous signalbut is particularly useful for single -shot capture and analysis. DataAcquisition Ltd, Electron House.Higher Hillgate, Stockport, CheshireSKI 3QD. Tel: 061 477 3888.

Analyzer in softwareStructured Software's SpectrumAnalyser II runs on the BBCmicrocomputer and providesfacilities previously found only onexpensive dedicated hardware.Typically, a waveform is displayed,windowed if necessary, and itsspectrum computed and displayed inapproximately 15 seconds using FFT.Digital readout of waveform andcalibrated spectrum are availableunder cursor control.

For transfer function andtransmission loss measurements,input and output waveforms areconsidered together: both theamplitude ratio (in dB) and therelative phase can be displayed.

The analyser software is disc -based, and is easily adapted toprocess files in any format generatedby the user. As supplied, it is directlycompatible with the Data HarvestVELA data recording system: thecombination provides a completeanalyser working from analogueinput signals.The price of the Spectrum Analyser IIsoftware is £200. Further detailsfrom Structured Software. 15Athelstan Close, Bromborough,Wirral, Merseyside. L62 2EX.Tel: 051 334 3290.


Hitachi Oscilloscopes leading the way from £299in performance and pricing! +VAT

The highest qualityThe Hitachi name is synonymous with quality and reliability andis backed by a 2 year or 3 year warranty on every oscilloscope.The keenest pricieg

ith prices start ng at only £299 for a 20MHz dual -trace modelHitachi's price -performance ratio can not be bettered.The largest rangeNow totalling If models the Hitachi range covers bandwidthsfrom 20MHz to 150MHz and digital storage models to 60MHz.The fastest serviceWe can supply ary Hitachi 'scope immediately from stock and weback it with full c ilibration and after -sales service.

For colour brochu-e giving specifications and prices ring (0480) 63570Thurlby Electron es Ltd., New Road, St. Ives, Cambs. PE I7 4BG


The world's most advanced low-cost bench multimeter!Thurlby 1905a £349, VAT

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Image acquisition systemG.J. AWCOCK, F.W. STONE AND R. THOMAS

A low-cost solid-state sensor, coupled with suitable image -processing software, is more than adequate for many

applications in robotics, security and character recognition.

In many cases the broadcast tv format isselected as the basis of an image process-ing system for no better reason than its

familiarity, or ease of display on standardmonitors. However, the quantity of data re-quired to represent a high -resolution imageis a major factor contributing to the inacces-sibility of computer vision; and so it is essen-tial that very careful consideration of the thesystem requirements should result in asensor specification which is adequate, andno more.

A conventional tv camera produces ananalogue video signal which is continuous inthe horizontal axis but discrete in the vertic-al axis, by virtue of the raster scan method ofpicture reconstruction. The maximum re-solution in the vertical axis is approximately574 lines, with interlace, and because thehorizontal:vertical aspect ratio of a standardtv screen is 4:3 this implies a horizontalresolution of approximately 765 picture ele-ments (pels, or pixels). Thus the number ofpels required to represent a full -resolutionpicture is 574 x 765 = 439 110.

lf, in addition, each pel is represented asone of 64 grey levels, i.e. a grey -scaleresolution of six bits, the quantity of datawhich must be acquired for each picture willbe a grand total of 2 634 660 bits for a mono-chrome signal! Thus the scale of the problemof acquiring images and storing them in apersonal computer becomes obvious.

In addition, a new picture is generatedevery 40ms, leading to a throughput re-quirement which makes real-time camera/computer interfaces both complex and cost-ly. This problem has been tackled to someextent for static or slowly changing imagesby the development of slower multi -frame tvinterfaces, which build up their images overa number of consecutive frames. This eli-minates the problem of video -rate a -to -dconversion and considerably reduces thecost of an interface, but it does nothing to

Fig.1 (above). Raw image acquired by the1532 sensor: the picture shows light fallingon another IS32.

ease the problem of storing this quantity ofdata within the computer.

Solid-state image sensors should offerhope of a simpler interface, since the data isinherently discrete in both the horizontaland vertical axes. Generating distortion -freeraster scan video is then a relatively simpleproblem for digital electronics.

Unfortunately, the best known of solid-state sensors, the charge -coupled device(c.c.d.), does not have many advantages overconventional vacuum tube cameras in low-cost applications.

In general, c.c.ds have been designed withthe full tv standard specification in mind,offering spatial resolution of typically380 x 488 pets with continuous grey -scaledynamic range of typically 1000:1. Thus theydo very little to ease the problem of excessiveimage data; and a sensor free of blemishedphotosites (i.e. light-sensitive cells that aredefective in some way) costs considerablymore than a complete normal tv camera.

There is, however, a relatively new solid-state image sensor which is ideally suited toexperiments with computer vision. The de-vice is the 1S32 optic d -ram (Fig.2) fromMicron Technology, which is based upon a64K dynamic ram and thus offers 65 536pels, each having a one -bit grey -scale. Thepets are organized into two banks of128 x 256, separated by a thin dead -zone,which effectively makes one of the banksredundant for use with normal optical sys-tems. Hence the working resolution of thedevice is 128 x 256, making it well suited tothe high -resolution screen modes of manypopular computers. The one -bit grey -scalemaps well on to the limited range of coloursusually offered in such modes.

The hardware interface to be describedhere uses only half of one bank of pels (a

Fig.2. Micron Technology's IS32 optic d- 128x 128 'quadrant), because the elongatedram: a 64K memory device with a tra nspa- shape of each pel (13.6 x 8.8 microns) makes

rent lid Price is about L40. this resolution match the aspect ratio of the


your

Fig.3. The raw image (top) can be en-hanced by software (middle) and proces-sed further (bottom) into a form suitablefor character recognition purposes.

computer monitor screen most accurately.Image data from a quadrant may conve-niently be stored in 16K -bits (or 2K -bytes).

The binary grey -scale of the system may atfirst seem a limitation, but it should beremembered that many image processingschemes 'threshold' their grey -scale data atan early stage to produce binary images fortheir descriptor extraction algorithms towork on.

However, this system should not bethought of merely as an educational toy,since many applications such as robotics,security and character recognition (Fig.3.)etc., are perfectly well served by binaryimages. Indeed, with the careful use oflighting to emphasize the features in thescene, some industrial inspection taskscould be undertaken by systems making useof this sensor. In addition, the small physicalsize of the IS32 opens up some unique andexciting applications: for example, in thefield of robot vision, with the sensormounted in the end -effector of a robot arm,the so-called eye -in -hand mode of opera-tion*.

OPERATION OF THE OPTIC D -RAM

A 64K d -ram consists of 65 536 memorycells, which, for reasons of economy ofsilicon and efficient access. must be orga-nized as a matrix; or, as in the case of theIS32, two matrices, each of 128 rows by 256columns (Fig. 4). Thus when row and col-umn addresses are supplied to a d -rammatrix the row address is responsible, in-itially, for selecting the bank of cells to beaccessed and, ultimately, for selecting whichof the rows of cells is connected to the set ofcolumn data input/output lines. Each ofthese lines is terminated by a bidirectional

Pugh. A.. Second generation robotics and robot vision:Robotic Technology pp. 1-9. Peter Peregrinus Ltd onbehalf of the IEE. 1983.

sense amplifier; and the column addressmust meanwhile select which of these senseamplifiers is connected to the data in and/ordata out buffers during read and write cycles.

Each photosite in the IS32 is one d -ramcell, consisting of a small capacitor con-nected to a fet analogue switch, which allowsthe row -selection of its associated capacitoras the target for write or read operations.When row -selected, all the cells in this rowwill be connected to their column datain/out lines, but only one sense amplifier willbe activated and connected to the outsideworld. Then the process of writing to thetarget cell involves storing a voltage on itscapacitor, whilst reading it involves conduc-tion of the charge stored there to theselected sense amplifier for regeneration.

In isolation, regeneration would not be adifficult task, but since the cells are con-nected in a matrix the output of eachselected cell switch is connected to a columndata in/out line along with 127 other cellswitches in their off -state. This results in aconsiderable capacitive loading upon thedata line, of the order of 20 times the cellstorage capacitance. Thus, when a cell capa-citor is connected to the data line, the chargeit stores must be re -distributed betweenitself and the line capacitance now con-nected in parallel, this results in an attenua-tion of the voltage used to represent the data

by a factor of approximately 21. The speci-fication of the 1S32 states that in the normal,memory, mode of operation a voltage grea-ter than 2.1V on the cell capacitor will beinterpreted as a logic 1 ; and assuming anattenuation factor of 21, this implies athreshold for the sense amplifier of 100mV!

There is a further task, related to re-generation, to be dealt with by the d -ram'sinternal circuitry: that of refresh, if thecapacitor in the cell were totally loss -freethere would be no need for refresh. since anyvoltage stored on the capacitor would re-main constant for ever. However, capacitorleakage is inevitable, and it is necessary toprovide a mechanism that can read thecontents of each cell and, upon re-generation to the required logic level, writeit back into the appropriate capacitor. This isa job that the sense amplifiers are well able toperform, and indeed their design ensuresthat refresh takes place automatically whenany cell is read. Alternatively the user mayinitiate a refresh -only cycle which performsthe same function but without enabling thedata output buffer.

It is left to the user to ensure that therefresh operation takes place sufficientlyoften to avoid loss of data in normal memoryapplications. To reduce the problem of timeoverhead due to refresh, a read or refreshcycle to any address in a row will cause

Fig.4. Block diagram of 64K d -ram. showing basic memory cell configuration.

Row

addressbuffers

Column

addressbuffers

CAS Timing and control

Row

decode

half memory array

Dummy cells

Column decode

Senseamplifier

contrOl

256 Sense/ Refresh a mpi f fr''-

Column decode

Dummy tells

Row

decodeoaif memory array

PI

imp

A 0 -A 7

Data IN

register

Buffer Data OUTregister

Read f Write selecttransistor

Row select

10 127

other cells

Storage

capacitorColumn data

IN fOUT line

To 255

other cells


refresh of that whole row to take place, inaddition to accessing the particular cell asdesired. This thoughtful aid to normal d -ramapplications proves to be rather less thanhelpful when the device is used as an opticalsensor, as we shall see later.

Loss of charge on the cell capacitor is anuisance with regard to data storage, but istolerated because of the significant spaceand power savings that d -rams offer overother, static, memory cells. However, arelatively recent development has allowedthis same mechanism to be exploited as alight sensor, since it can be shown that whenthese capacitors are subjected to light ener-gy. the rate of discharge becomes pro-portional to the intensity of the incidentlight, as well as time elapsed since re-generation. Light sensitivity is well knownin other applications of silicon and is due tothe generation of an electron when a photonis absorbed in the bulk of the material.

In the case of d -ram cells, the plates of thecapacitors are fabricated in silicon and theelectrons which result from photon absorp-tion serve to reduce the charge stored there.Thus the decay of capacitor voltage withtime exhibits a characteristic such as thatshown in Fig.5: it is clear from this that thetime taken to decay below the logic 1 /logic 0threshold is now dependent upon the level ofincident illumination.

Conversely, a fixed time delay betweeninitialization (or re -generation) of the celland its subsequent interrogation will effec-tively set a threshold level of illumination. Ifthe incident light is above this thresholdthen the cell voltage will be interpreted as alogic 0; if below, the sense amplifier willread, and re -generate a logic 1.

The net result is two -state, or binary,detection of illumination, provided that norefresh operation has been performed in theinterim. Extreme care should be taken toavoid reading or refreshing any cells in thesame row of the matrix as those undergoingexposure. and careful thought must be givento the initialize -expose -interrogate cycle tobe employed.

It is also necessary to be aware of somepeculiarities of the 1S32, which stem from itshaving been designed primarily as memorydevice, rather than as an image sensor.Firstly, the two banks of cells store their datadifferently, so that the least significant, orupper bank (rows 0 to 127), must be initial-

Vss CAS Dour A6 A3 A4 A5 A7

f-1 f-1

112

Y19i

Y257

Quadrant 1

UPPER ARRAY

1

LOWER ARRAYI

X513 Spatial grid coordinates Xc

Ll LI Li LI LIAnalogue Din Write RAS AO Al A2 Vcc

threshold

Fig.7. Layout of the 1S32 device. A dead -zone between the upper and lower arraysmakes half the device unusable in mostoptical systems. Only one quadrant is usedin this design: it gives a working resolutionof 128 x 128 picture elements.

Fig.5. Characteristics of storage cells in the IS32 optic d -ram. Decay time of the capaci-tor depends on the incident light level.

ROW address COWMN address

Counter IS32 Counter IS32

A0 (51 07 A0 IS)07

A3 (12106 06 A3 (12)

A1161 Q5 (6)05 Al

A2 (71 ( 7)04 Qt. A2

A41111 03 A4(11)3

A5110)2 02 A6 ( 13)

A6(13) giQ1

A5(10)

A7(91 go A7 (9)a 0

Fig.6. The 1832 chip is designed primarily as a memory device, not as an imagesensor. To correct image distortions caused by the irregular layout of its photo -sites, a two -stage linearization process is required. The first step consists of manipu-lating the row and column addresses.

ized to logic 1, whilst the most significant,lower bank (rows 128 to 255), must beinitialized to a logic 0. Thus, after exposure.if the cell remains in the same state as that lowhich it was initialized, then the pel must beinterpreted as dark (black); if it has changedstate, it must be treated as white.

If data from the 1S32 is to produce a

Fig.7b. This close-up of Quadrant 1 illus-trates local scrambling of addresses whichremains after the hardware address de -scrambling of Fig.6. Software correction isneeded to eliminate it and so linearize theresulting image. Blank cells representpcints having no light sensitivity, such asthe fet associated with each photosite.

X256 X255 X254 X253 X252 X251 X250 X249 X248 X247.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

Y120 R119C127

R120C125

R119C125

R120C123

Y121 R121C126

R120C126

8121C124

R1200124

R121C122

Y122 R121C127

R122C125

R121C125

R122C123

Y123 R123C126

R122C126

R123C124

R122C124

R123C122

Y124 R123C127

R124C125

[R123C125

R124C123

Y125 R125C126

R124C126

R125C124

R124C124

R125C122

Y126 R125C127

R126C125

R125C125

R126C123

Y127 R127C126

R126C126

R127C124

R126C124

R127C122

Y128 R127C127

I R127

IC125

. . .


meaningful picture, the screen pels must bemapped with exactly the same spatial inter-relationship as the photosites on the surfaceof the chip. Unfortunately, this is not a trivialtask because the logical addresses of the cellsof the IS32 do not correspond directly totheir physical positions: consecutive addres-ses applied to the device will not necessarilyaccess adjoining cells on its surface. Thismakes it necessary to apply a two -stagelinearization process, of which the first stageconsists of the application of the addressde -scramble logic recommended by theIS32's manufacturer (Fig.6).

The mapping that results is shown inFig.7(b). Notice that there is still an elementof local scrambling and also that only halfthe surface area of the chip is available forphotosites, the rest presumably being occu-pied by the switching fet that each cell needs.Thus, the second stage involves generating amapping scheme which has twice the resolu-tion in the column axis to accommodate'space-pels' which represent the inactiveareas of the chip surface, since these must beincluded for a picture of the correct aspectratio.

Additionally. an algorithm must be ap-plied to sort out the local scrambling evidentin Fig.7, and, furthermore, a slightly differ-ent algorithm is required for each of the two

qDR

Serialinterface

TOR

Table 1: characteristics of 1532 quadrant

Number of active pelsLayoutArray dimensionsPel dimensionsArray aspect ratio

16384256 x 128 grid2210 x 876.8 microns6.4 x 6.4 microns2.52: 1

In the next article, the authors introduce a- - hardware interface for the IS32 which en-

ables it to be driven via a personal computerover an RS -232 serial link.

cell banks. In the picture which emergesfrom this process, 50% of the pets representactive photosites in the 1532 and can takeeither black or white states, whilst theremainder are space-pels which may bedisplayed in the user's chosen backgroundcolour. The use of an enlarged mappingmatrix with the inclusion of space -pets re-sults in subjectively pleasing images with anabsence of the annoying 'cogging' at straightblack/white boundaries that would other-wise be present.

If required, simple picture pre-processingmay be carried out to cause the 'space-pels'to agree with the majority oftheir nearest neighbours.

This type of enhancementwill be essential if theimage is to be used forfurther work such asedge detection, andhas been applied inFig. 3 (middle).

Corn manc

decoder

V.Z.k7

Craeme Awcock is a lecturer at BrightonPolytechnic and is reading part-time for adoctorate in computer vision techniques forlow-cost robotic systems. Previously heworked as a senior design engineer at Com-puting Devices. which he joined after gra-duating from the polytechnic in 1979.

Bill Stone designed the prototype imagingsystem as his final -year project at BrightonPolytechnic. Since graduating he has beenworking as a development engineer for MELat Crawley and is currently involved in thedesign of electronic support measure sys-tems.

Ray Thomas gained his Ph.D. researchinginto high -permeability magnetic materials.Subsequently he spent seven years in theelectronics industry before joining BrightonPolytechnic as a lecturer in 1977. His in-terests are in microprocessor applicationsand computer vision systems.

1532 Optic

Dram and suppore

ClocK

controller

Fig. 8. The hardware, to be described inthe next article. occupies two boards: adouble Eurocard for the control systemand a small p.c.b for the 1832 sensor.

Sensor p c b

Main board

Address multiplexers

Address descrambler

Row

counter

Var able delaygenerator

STOP

Shift

register

Buffer

Tide

store Iran


TELEVISION BROADCAST

Digital tvThere is a deep-rooted beliefamong broadcasters, includingsome engineers, that televisiontechnology is changing at a fas-ter rate than ever before. It isforgotten that d.b.s. has beenunder development since 1965(and was implied in Arthur C.Clarke's 1945 article in this jour-nal); that digitalization ofbroadcast -quality video was firstdemonstrated in the mid -sixtiesat Bell Telephone Laboratories;and the concept of "The digitalfuture of television studio cen-tres" was propounded by JohnBaldwin (IBA) as long ago as1972. He suggested then thatwhile the time when domesticreceivers wou!d receive tv signalsin digital form was still some wayoff, and not likely to have signifi-cant practical impact "before ab-out 1990", studio complexesbased on the use of digital tech-niques would be possible "now"(i.e. 1972) and that it could wellbe that "by 1976 the cost of adigital studio complex would beless than its analogue equiva-lent."

By 1987 it is possible to buildexperimental component digitalproduction units (such as theITCA one at Thames Television,Teddington described in theFebruary "Update" column,pages 197 to 198) using the by nomeans low cost Sony DVR1000recorders now in production anddue to be delivered to customersvery soon. There are also inwidespread use many "digital is-lands" within studios includingthe special effects and picturemanipulators that, in order tojustify their cost, now seem to beused (over -used?) on every possi-ble occasion.

But the large all -digital studiocomplex at comparable cost tocurrent analogue "productionfactories" still seem as far awaytoday as they did at IBC72!

What has happened is thatanalogue systems have con-tinued to develop and, indeed,analogue -component systemspromise to provide most of thepromised advantages of digitalvideo at substantially less cost.The industry is buzzing withspeculation as to the future roleof the 1/2 -inch all-purpose M.IIcomponent v.t.r. machines

rather more than about the over -£100,000 DVR1000 machines,though these, offering superbquality even after 20 genera-tions, will certainly fill post -

production role in studios pro-ducing high -cost commercials. Amajor problem with digital v.t.r.machines is that their high pow-er consumption largely rules outtheir application in portablebattery -operated machines.

Communication engineers inthe early 1970s were in the habitof suggesting that if valves hadbeen developed after transistorsthey would have been hailed asthe answer to all problems. To-wards the end of a well -attendedIEE colloquium, TV studios fromA/D, Brian Scott (Thames Televi-sion) echoed this by comment-ing that if analogue televisionhad just been discovered wewould all be hailing it as a mar-vellous system with a big future.He added that new technologyhas improved the stability of ana-logue systems, although we willstill need digital techniques,even where they remain moreexpensive, for some things thatcannot be done analogue. Thepressure for more digits is nowcoming more from productionteams than from engineers.

Better picturesThere remain engineers who be-lieve that the first priority, aheadof h.d.tv, should be to ensurethat the pictures transmitted onthe existing 625 -line 50Hz inter-laced standard are of the highestpossible quality. In due coursethis could be followed by theimprovements possible with"component" rather than "com-posite" working, MAC transmis-sion on d.b.s. and steady, flicker -free displays with progressive(sequential) scanning madepossible by digital processing inthe receivers, and, later, ford.b.s. wide-screen pictures bymeans of compatible, enhancedsystems.

In recent years, despite manyimprovements, the quality of thetransmitted pictures, particular-ly with material acquired fromoverseas, has tended to fall, part-ly due to distribution on multi -generation tape rather than on

16 or 35mm film. Similarly, UKproducers have strained after"realistic" mood lighting thatoften results in "noisy" pictureswhen compared with program-mes produced in well -lit studios.

Bits all roundAn interesting three-part pre-sentation by BBC research en-gineers (A. Oliphant, J.T. Zubr-zycki and N.H. Gilchrist) showedhow digital signals couid berouted in a flexible manneraround a large studio complexusing optical -fibre cables and acombination of time -divisionand frequency (wavelength) divi-sion multiplexing. There is norequirement to "switch" theoptical cables, since all sourceswill be available at all destina-tions.

It became clear that this is stilllargely a "paper" design thoughvirtually all of the technology iscurrently being developed else-where for broadband telecom-munications applications, in-cluding local area networks,c.a.tv etc. The BBC work is seenas meeting a possible require-ment for the BBC TelevisionCentre in the mid -1990s.

Essentially the system usesoptical fibres in conjunctionwith distributed feedback (d.f.b.)lasers. Each laser would be mod-ulated by a 2 Gbit/s stream andwould produce a narrow line -width output at a specific opticalwavelength. The d.f.b. laser is asemiconductor laser diode with adiffraction grating etched overthe active region, resulting incoherent light output at only theone wavelength strongly re-flected by the grating. This optic-al part of the system follows thework of Olson et al at Bell Labs.At present d.f.b. lasers are com-mercially available for only thetwo main optical wavelengthsnow being used or advocated fortelecommunications.

It was claimed that the system,though conceived as being usedto route 4:2:2 digital signals,would be capable of carryingh.d.tv signals. These would usethe capacity required for four orfive 4:2:2 channels, but could bemultiplexed into the 2Gbit/s bitstreams.

Television inbits?

Certainly the IEE colloquiumbrought forth many expressionsof continued faith in digital tech-niques in the studios and post -production areas. Duncan Tho-mas (BBC) while showing him-self by no means fully committedto bits, stressed that it was nowtoo late to put the clock back andthat eventually digital tv will winthrough.

Most of the papers describedsystems based firmly on CCIRRecommendation 601, the 4:2:2component -digital standard withan initial bit -rate of 213 Mbit/s.While this system includes provi-sion for hierarchical systems.both upwards and downwards,the basic system, as severalspeakers pointed out, imposes a"brick -wall" filter on luminanceat 5.5 MHz and would require acomplete re -think for h.d.tv.(higher -definition television).There was, however, nothing butpraise for the trend to digitalsound. This is seen as an entirelypractical means of removingmany of the traditional degrada-tions of analogue sound.

What could have been fore-seen as a confrontation betweencomponent and composite digit-al v.t.r. machines was the juxta-position of a paper by CarlosKennedy (Ampex) on his com-panies development of theACR225 composite "cart"machine - and the proposed useof this composite system for stu-dio and transportable machines- with the paper by John lye(Sony) on the DVR1000. But thesparks did not fly. Indeed, CarlosKennedy made a convincing casethat, because of the strained eco-nomic situation of many US pro-duction companies, it is certainthat composite 525 -line NTSCwill remain in use for manyyears. Composite machines canfit comfortably into compositeenvironments without dis-couraging Ampex from con-tinuing development of 4:2:2component machines.

Television Broadcast was writtenby PAT HAWKER.


RADIO BROADCAST

Portable stereoThe difficulty of receiving "noise -free" stereo from v.h .f./f.m.broadcast transmissions withoutthe aid of a reasonably goodroof -top aerial array is well-known. The problem has beenwith us for a long-time. The BBCis in process of an expensiveconversion to mixed (circular)polarization in order to improvereception with portable tele-scopic aerials and car radio whipaerials, but there remains thebasic 12dB or so difference be-tween what is needed for monoand that required for goodstereo.

The growing popularity oflarge stereo portable receiversand walk -about headphone setsincorporating radio as well astape -cassette facilities hastended to highlight the problem.

A couple of years ago, CBS, incollaboration with the USNational Association of Broad-casters, began testing their com-patible FMX system. This wasclaimed as permitting goodstereo reception (on sets fittedwith a special decoder) over vir-tually the same coverage area asthe mono transmissions. CBSpromoted the system in Europe.Some engineers were doubtful asto the performance of FMX andits effect on conventional receiv-ers in severe multipath condi-tions, but the BBC undertook toinvestigate the system providedthat CBS would loan FMX encod-ing and decoding units. Manymonths went by, however, withno sign of the experimentalequipment reaching the UK. Thesituation has been further com-plicated by the reported closureof the CBS laboratories con-cerned with FMX, although pre-sumably CBS still holds the pa-tents. The prospects for any earlyUK trial, let alone operationaluse, now seem remote.

Some listeners are suggestingthat the UK national and localv.h.f. services should be replan-ned with extra transmitters toprovide much stronger signals inthe centres of towns. This wouldnot only be a horrendously ex-pensive undertaking but wouldalso upset the current frequencyplanning under the 1984 WARCallocations.

More realistic are the sugges-tions that receiver front -ends

should be made more sensitiveby reverting to the use of at leastsome discrete transistors along-side the integrated -circuit de-vices. It would also be sensiblefor portable receivers, if provid-ing stereo, always to have co-axial sockets fitted to permittheir use with effective externalaerials. There also still seems tobe a need to get the messagethrough to more listeners that ittakes a great deal more signal toprovide good stereo receptionthan is necessary for mono.

A listener in Paignton sug-gests that the problems faced byv.h.f. broadcasting in the UK goback a long time, with littleserious effort by either broadcas-ters or Government to promote"superior" v.h.f. as the main ser-vice, but rather only as sup-plementary to m.f. services. Inmany areas v.h.f. (even mono) istoo weak for good reception on alot of portable radios, althoughthe increasing use of circularpolarization helps (unfortunate-ly it can in some areas increasemultipath distortion on high-fidelity equipment). Manufactur-ers, he suggests, aim at sellingportable radios as cheaply aspossible with little regard totheir sensitivity or audio quality.When coupled with "unfriendly"tuning arrangements and un-clear tuning dials this all servesto discourage v.h.f. listening bythe general public. Part duplica-tion, part splitting of the m.f. andv.h.f. transmitters confuses thepublic with few broadcasterswanting to risk losing audiencesby encouraging them to moveaway from the m.f. outlets. In alocal survey he found 10 per centof homes with an external v.h.f.aerial, presumably mostly forstereo. Compared with SouthLondon this is a very high figure.There are still more old BandI/Ill television aerials to be seenthan aerials for Band II!

Copyrightreform delayed

Whether the marketing of R-DATcassettes and machines willfinally get under way in Europethis spring, as the Japanese in-dustry hopes, or whether it willbe further delayed by the con-tinuing arguments about the

need to incorporate anti -copyingdevices to protect the CD indus-try, is only one of the problemsthat continue to accumulateover the whole field of intellec-tual property and patent legisla-tion.

A recent unannounced trial inthe UK by the Werner videosoftware company of the "Mac-rovision" anti -copying systemfor VHS video tapes seems tohave done little to inspire confi-dence in an anti -copying systemthat can be rendered largely in-effective by relatively simplemodification of existing VHSmachines and is not designed toprevent copying on Betamaxmachines.

The trial did not produce sig-nificant evidence of any large-scale copying by video libraries.Macrovision, developed by JohnRyan, formerly with Ampex, isintended to stop the copying ofvideos or the programmes onpremium cable channels by theaddition of phase -modulation tothe colour -burst reference sig-nal. This results in fuzzy pictureswith spurious or no colourswhen tapes are copied and thenreplayed on VHS machines.

Japanese industry continuesto resist the appeals of the inter-national recording industry,concerned at the possible impactof R-DAT on the CD digital discs,that an anti -copying chip shouldbe built into all R-DAT machinesand different sampling rates, etc.should be used. The recordingindustry is still hoping to obtainbetter copyright protection bymeans of EEC and US legislation.The problem is heightened bythe likelihood of blank R-DATtapes becoming readily obtain-able at a time when pre-recordedtapes may be very limited inchoice.

The 1986 Government WhitePaper prepared by the DTI ("In-tellectual property and innova-tion" Cmnd 9712) proposedradical changes which the DTIsaw as being necessary to en-courage industrial innovation, tokeep abreast of the new copyingand recording technologies andto simplify and reduce the cost ofobtaining patent and design pro-tection. One of its many propos-als was to legalize home taping ofaudio (but not of videos or com-puter programs) while introduc-ing a compensating 10 per cent

levy on blank audio tape cas-settes.

However although the WhitePaper was generally welcomed,the proposed levy ran into a lot offlak from tape manufacturers -as did some of the proposals forrestricting to the original manu-facturers the supply of specialspare parts.

The White Paper has not beenfollowed up by the expected Gov-ernment Bill. There was no men-tion of any new copyright legisla-tion in the Queen's speech at theopening of Parliament last au-tumn. This virtually ensures thatno bill based on the DTI propos-als will appear before the GeneralElection, if ever, and the wholequestion could become en-meshed in EEC directives andthe extremely complex web ofthe very different intellectualproperty legislation in differentcountries.

Meanwhile further significantadvances seem likely to be madeduring the next decade over thewhole field of magnetic record-ing. Progress in packing density,access times, transfer rates andmagneto -optical recording mayincreasingly come to overwhelminformation -storage and record-ing systems based on optical andphotographic techniques. It isforeseen that before very long itwill be possible to record as wellas play back compact discs byusing magneto -optical tech-nology.

In recent years, the US hasencouraged more university re-search and education in magnet-ic recording with specialist cen-tres at Carnegie Mellon Universi-ty, Pittsburgh and the Universityof California at San Diego(UCSD).

Radio Broadcast was written byPAT HAWKER.

Guide toBroadcasting

StationsThe 19th edition of CBS isnow available at £6.95 or£8.70 by post from book-shops or from HeinemannNewnes, Freepost 10, LondonWIE 7YZ.


RADIO COMMUNICATIONSCB, RIS and the

Home OfficeIn November 1981, followingseveral years of public con-troversy, the first 27/934 MHzCB licences were issued in theUK. The initial response, thoughmore muted than forecast,quickly raised the number oflicences to over 450,000, despitecontinuing protestations thatthe licences ruled out the use ofamplitude modulation (a.m. ands.s.b.) and that the 27 MHz chan-nels did not coincide with thosewidely used elsewhere. Thegrowth of both illegal and legalCB was reflected in a massivesurge in the number of com-plaints of interference to tv re-ception made to the old RadioInterference Service, still thenoperated by British Telecomteams and providing free inves-tigation of interference to radioor television.

The number of CB licencesbegan to fall after the first yearand currently are down to122,920, about one-third of thepeak figure. RIS became theDTI's own Radio InvestigationService with a significantly re-duced staff and a £21 fee wasintroduced during 1985. This re-sulted in a dramatic falling off ininterference complaints made tothe DTI (from about 1900 to 375per month). Many viewers havebeen seeking assistance from thebroadcasters, who have neitherthe resources nor the legalpowers/experience/diplomaticapproach of the DTI. One resulthas been to increase personalantagonisms and conflicts be-tween the parties concerned,particularly where the CB oper-ators and radio amateurs areoperating in full accordance withthe terms of their licences andthe problem arising primarilyfrom the lack of 'immunity' ofmany consumer -electronics re-ceivers and appliances.

The smaller RIS has concen-trated its activities primarily onattempting to close down illegal'pirate' broadcasters, though ithas proved more successful attracing and seizing transmittersthan catching and prosecutingpeople.

According to a recent reply byLord Lucas, ParliamentaryUnder -Secretary of the DTI, 83land -based unlicensed UK broad-casting stations were active dur-

ing 1986, most of them onlyintermittently. RIS raided 70 ofthese on 209 occasions, with 74prosecutions (only about oneprosecution for each threeraids). DTI are satisfied that theyhave adequate resources to keepthis problem under control.With Radio Laser back on the air,there are three unauthorized sta-tions broadcasting from twoships off the UK coast, with RISnow proposing to allocate furth-er resources to coping with thisproblem.

CB is one of the services forwhich the Home Office is re-sponsible for policy, the DTI forspectrum regulation. It is ex-pected that the UK governmentwill adopt, during 1987, a recom-mendation (T/R 20.02) by theConference of European Postsand Telecommunications(CEPT) that there should be acommon (harmonized) Euro-pean allocation between 26.965and 27.405 MHz for frequency -modulation only. The UK gov-ernment is continuing to resistpressures from "a few" CB enthu-siasts to permit the use of single-sideband, on the grounds that itis more likely to cause interfer-ence to other users of the radiospectrum.

The Merriman Committeecommented on the need for im-proved monitoring and policingof the air -waves and it is perhapsunfortunate that in many Euro-pean countries the "pirates" (CBand unauthorized broadcasting)have shown that persistenceoften brings the reward of licens-ing or toleration. Would CB everhave been authorized on 27 MHzin the UK otherwise? Commun-ity radio, which has a genuineplace in the broadcasting spec-trum if finally it comes, will oweits existence to the pirates - justas the origins of IndependentLocal Radio can be traced to thepirate ships of the 1960s.

The Spanish authorities areplanning to spend some £26 -million over the next few years inpolicing the radio spectrum, in-cluding establishing main sur-veillance centres in Madrid, LaCoruna, Barcelona and Valencia,50 smaller monitoring units, 14mobile units and a satellite sig-nal sampler. The fixed andmobile units will use modern d/fsystems to trace illegal transmis-sions, although it seems unlikelythat any great effort will be madeto close the several hundred "pri-

vate" radio broadcasting stationsthat have existed for many yearsin Spain.

Mobile safetycodes

The inclusion in the new editionof The Highway Code of therecommendation against usinghandheld microphones or tele-phone handsets while driving,together with the injunction that"you should only speak into afixed, neckslung or clipped -onmicrophone when it would notdistract your attention from theroad" is clearly putting increasedresponsibility on the users ofmobile radio. What does or doesnot "distract attention" tends tobe a highly subjective judge-ment, on which the parties toany legal dispute are unlikely toagree.

But the new recommendationhas served to concentrate mindson the general problem of mobileradio safety. The independent BTRoad Safety Committee has recently drawn up a new and stifferCellphone Safety Code which isbeing sent to all existing Cellnetcustomers and brought to theattention of other cellular radioservices. More stress is beingplaced on the not -always -appreciated need to avoid trans-mitting while refuelling or whileon the forecourt of a petrol -filling station. Unlike conven-tional mobile radiophones,where the user has direct controlover his transmitter, cellularradios are subject to frequent"interrogation" of the mobileunit by the base station to checkthat the vehicle is still within thesame "cell" area. Most cellularradios stay "on" as long as theignition switch is turned on; the

fact that the user is not making acall does not mean that there areno transmissions, since thetransmitter automatically re:plies to the interrogations.

The new Cellnet code includesthe recommendation: "Alwaysswitch off your Cellphone whenat a refuelling point even if youare not refuelling your own car."Whether this practice has beenobserved fully in the past is opento doubt. Some installations arewired to be switched indepen-dently of the ignition.

In papers presented in 1975 atIEE and IERE conferences, aBradford University team includ-ing Dr Peter Excell, G.H. Butch-er and D.P. Howson reportedthat "practical tests" had shownthat a potential hazard existsduring the fuelling of a vehiclecontaining an operating trans-mitter, or parked close toanother vehicle containing one.This arises from the possibility ofa spark occurring at the mosthazardous point, between thefuel nozzle and the tank inlet.They wrote: "Existing injunc-tions not to operate a transmitterwhile fuelling a vehicle contain-ing it need to be strengthened:transmitters should not be oper-ated anywhere within fuellingstations. Possibly electro-mechanical interlocks could beapplied to advantage here."

It is recognized that sparks aremore likely in the case of thehigher -power mobile h.f. trans-mitters as used by a few radioamateurs but this hazard haslong been recognized and co-vered in their safety codes. It isless likely to be known by thelarge number - now well over100,000 - of users of cellularradio.

Radio Communications wascompiled by PAT HAWKER.


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HEAT SINK LONIPUGND 1.00FREEZE IT aosSOLDA MOP 0.64SWITCH CLEANER 0.65WD40 1.75

POSH PULL MAINS SWITCH(DECCA GFC RANK THORNETC I 1.02PVE IF GAIN MODULE 6.90ANODE CAP 127601 0.69


PHONE0474 60521

P. M. COMPONENTS LTD TELEXSELECTRON HOUSE, SPRINGHEAD ENTERPRISE PARK 966371

4 LINES SPRINGHEAD RD, GRAVESEND, KENT DA11 8HD

A SELECTION FROM OUR3.50400

051213 5.000S1215 2.10

XC24 1100C25 0.50

mow4CO2506 49.00

5C1313GA 4.506CF6 1.50

6060 1.256V6GT 1.50

STOCK OF BRANDED VALVESM14 4.50MP25 195.00

051218 600OU37 9.50

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4052506 EIMAC5910

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AirmacOne of our readers, who wasassociated with the firm Airmec(not Airmac) telephoned to tellus that the receiver taken toPoland by Mr Bar (February let-ters) was probably made by thatcompany, which was a subsidiaryof Radio and Television Trust.They exported sets under theAirmec name, but used the namePhilco, under licence fromAmerica, for export. The Airmecname is no longer used.

Our informant still possesses a1947 -vintage Airmec receiver,which works well, having neededonly a replacement electrolyticin 40 years of service. - Ed.

Police radioThe article by Jack Davies (Janu-ary 1987 issue), brought back aflood of memories as I was one ofthe ETE/Mullard/Philips teamthat installed and commissionedthe synchronous f.m. system forthe Lancashire police.

The system was based on thePhilips IGO (impulse governedoscillator) concept used for fre-quency and audio locking of a.m.broadcast transmitters operatingon the same frequency. The de-sign and development of the sys-tem started in 1947 when PhilipsElectrical was approached by thelate Inspector Frank Gee whohad read a paper describing thePhilips IGO work. Philips Trans --mission Equipment Ltd., inBalham did the initial study forthe Lancashire police. The de-velopment work was handled bya small group of engineers led bythe late Christopher Bailey work-ing in a makeshift laboratory in adisused laundry in Wandsworth.Frank Gee and Eric Jones. thenthe commercial manager of theMullard/Philips communica-tions activities, were the drivingforce behind the project. Many ofthe team in Wandsworth andLancashire were licencedamateurs.

Jack has a good memory as,apart from one or two minordetails, his description of thesystem is correct. The originaltwo -station arrangement at Bil-linge and Barnacre was a crudelash-up to prove the system. Apreset variable delay was in-cluded to equalise the differentpath lengths between the wire -

[FEEDBACKlinked base station and the radio -linked slave transmitter. Afterthese intitial tests a more sub-stantial set of prototypes wasproduced for installation in theForce HQ, Hutton. This was alsoa single -frequency system andwas designed to work with up tosix remote slave transmitters.Initially only four slaves wereused, as it was found that theyprovided full coverage of thecounty.

The updated master unit useda more sophisticated variable -lock system to provide the neces-sary audio delays and the fre-quency off -set facility mentionedby Jack. It was never intendedthat those prototypes would havean extended life, and develop-ment work continued both inLancashire and at Wandsworthto provide multi -channel opera-tion and many other facilitiesthat were likely to be required forfuture expansion of the system.

From the experience gainedwith the Lancashire units, Geeand Bailey produced a compre-hensive specification for a set ofproduction equipment to replacethe prototypes. In 1950 Mullardhad formed a new company Mul-lard Equipment Ltd, (later MEL)which merged with ETE. AMobile Radio Division of MELwas established at the same timeunder Christopher Bailey andtook over the responsibility forthe Lancashire units. In early1953 contracts for the replace-ment production system werebeing negotiated between Lan-cashire and Mullard when, forpolicy reasons, Mullard decidedto discontinue v.h.f. mobileradio activities. As reported, theLancashire Police Wireless De-partment continued to use andsimplify the system to providegreater reliability and ease ofservicing before it was finallyclosed down in 1968.R.L. Glaisher (G6LX)Croydon

Planck and thefine structure

It is unfortunate that the deeprelationship that is 'thought' toexist between Planck's constant,h and the so called atomic finestructure constant, a as was sug-gested by Ove Tedenstig (EWWFeb. 1987) is not really new.Already this relationship is corn-

mon knowledge and has beenwell established since the earlydevelopment days of quantumphysics. Most general text bookson the subject show that a isgiven by

27re-a =

ch (1)

However, the classical restradius of the electron r, is de-rived from the following:

-= m c -re e (2)

where e is the charge of theelectron and m, is its rest mass.Therefore, substituting for e2 in(11 and re -arranging results in

h = 27rmerecla -11This leads us nowhere new ex-cept, perhaps, to that of compli-cating furthermore the subject.M. Zaman AkilRegent's ParkLondon

InsanityMr W. Scott really ought tostraighten out his wife for talk-ing about the insanity of en-gineers (Feedback, January,1987).

All these standards are in-flicted on us by desk -pilots with alack of imagination and arro-gance that I associate with civilservants, despite Bernard Joneshaving taken me to task forcalling them such (November.1986).

The most recent of the mainswiring codes is so baffling andsilly that it has earned a send-upin Punch (30th July, 1986. p.29).

Shortly after the end of thewar, a committee of intelligentmen (obviously engineers) sat atWhitley and worked out a colourcode for circuit wiring in RNSSequipment. In 1951, when a sci-entific assistant, I was told toclear out a lot of files and saw theword "secret", which naturallypersuaded me to look into them.I found the Whitley code andhave used it ever since in every-thing I have built, also puttingtiny numbers beside every wirein my diagrams to indicate itscolour in accordance with theresistor colour code. No onesmote me with the Official Sec-rets Act, even after I sent thecode to WW (May, 1960, p.256).

Yellow. Signal: Red. Steadypositive potential: Orange, signal

at a positive potential; Blue,steady negative potential: Green,signal at a negative potential:Black, earth; Brown, signal atearth potential; White, pure a.c.(any frequency): Mauve, any-thing needing distinguishingfrom the above.

Although one colour some-how got lost in transmission(grey) the meaning of it could bededuced from the other nine.This was the only code I haveever seen that was able to makethe transition from valves totransistor circuitry unaltered.

It may not have been the ori-ginal intention, but from thiscode comes naturally the onlythree colours for wiring a mainsplug that will offer protection topersons handicapped by allknown types of colour-blindness:

white livegrey neutralblack earth

A colour code for mains wiringthat can be safely used under thelight of sodium lamps calls for alevel of intelligence that I fearmay prevent it from ever becom-ing an officially ratified standard.John C. RudgeHarlingtonMiddlesex

Hands-onEngineers

Regarding 'Hands-on En-gineers', by R.E. Young, therecannot be many engineers whowill disagree with his thesis that"engineers should have had leng-thy shop-floor experience withworking plant and equipment".But what about the corollary thatthey should continue to havethat experience no matter whatlevel or sharpness of specialitythey attain? Maybe, like militaryreservists. they should be calledup for their annual refreshment.

The element of snobberyshould not be overlooked, either.Could anything be more absurbthan. for example, the sight of anExperimental Officer walkingalongside the quite lightly -loaded trolley of instrumentsbeing pushed by a Shopman(new -style 'labourer'). And whatabout the Technician's ( new -

style 'craftsmen') mate - possiblyalso styled Shopman - who iscondemned by fortuitous cultu-ral and economic circumstancesto be forever a fetcher and car -

450 ELECTRONICS dr WIRELESS WORLD

rier? And then there is the pathe-tic reluctance of 'qualified' en-gineers to seek help from theirsupposed juniors, because thatwould be demeaning; or to payadequate attention to their sug-gestions, of which the mostdamaging variation is the 'not -invented -here' syndrome.

Service in a warship in war-time is the place to experiencethe results and the sometimesfatal consequences of these atti-tudes and practices: doubtlessother Services could claim simi-lar suitability. And not only war-time, for I recall vividly the pre-war loss of the new submarineHMS THETIS with most of itscrew and some of its builders,within Liverpool docks, becausea test -cock on a torpedo -tubeinner door was blocked withpaint: and because the Davisescape apparatus would not workunless the ship was on an evenkeel.

I recall, too, my own weaknes-ses arising from excessive 'chalk -and -talk' learning - partly, itmust be conceded, from wartimeshortages of time and equipment- and from my unscientificjumping to conclusions withoutexperimental verification ofthem. For .example: having abso-lutely no hands-on experience ofthe use and care of lead -acid (orany) batteries, I used to keep agyro -compass alarm batterytrickle -charged by the ingeniousdevice of a torch bulb connectedbetween the charging terminaland the battery, when the alarmsystem was in use at sea. I couldtell that the battery was fullycharged by the colours of thepositive and negative plates inthe glass battery case. However,when the alarm system was cal-led for when a gyro -compassbroke down, the battery wouldnot sound the heavy -currentalarm bell though. fortunately, itwas able to light a red warninglamp on the bridge of the mainescort vessel on the Russian con-voy. But (and I am not sure of therelevance of this to my argu-ment) nobody recognized it as analarm! I was called from myhammock to "get this damnedred light switched off': it wasirritating the Officer -of -the -Watch! In direct contradiction toMurphy's Law, it was the sparecompass that had broken down.

It was 20 years later that I

learned that lead -acid batteriescannot be continuously trickle -

[FEEDBACK 1

charged, or regularly lopped -upafter only slight use. but must beoccasionally discharged fully ifthey are to retain their capacity.It seemed that the battery manu-facturer learned this at the sametime as I did, for his engineershad approved my chargingarrangements. Their alarmsounded when a large number ofexpensive teak -encased auto-mobile batteries were returnedunder guarantee within only afew months. It was another 15years or so before research hadperfected lead -acid portable bat-teries that could be continuouslytrickle -charged.

Very likely the relatively'junior' engineering grades whonormally looked after the ship'sLow Power System batterieswould have made a better jobthan I did of 'my' alarm batteries.My point is that I thought I knewabout them because I had beentaught about them. You have tolearn through your finger endsand through the consequences ofyour mistakes and incorrectassumptions - which necessarilyentails lots of opportunities tomake mistakes.

Finally, in supporting R.E.Young's plea that a "managingengineer's" career demands thatat least the classical seven yearsshould be spent under appren-ticeship conditions", I believethat Sir George Stapledon wasright to urge the value of every-one doing an apprenticeship insome form of craft. Apart from itsvalue in inculcating a real feel formaterial and process, it would, Ibelieve, reduce the appallingtrend towards full-time con-sumerism that is making most ofus little different from the unfor-tunate geese who are forciblystuffed to make pate de foie gras.Ronald GillAl lestreeDerby

RelativityAlthough I haven t read W.A.Scott Murray's relativity articlein your December issue. I havefollowed the resulting corres-pondence with some interest.

There is a fundamental errorin everybody's thinking here, asto why the Earth is designed asan oblate spheroid. As everyschoolboy knows, the Earth isthis shape due to the constantpressure applied by the wing

nuts situated at each polar cap. Aquick glance at any model of theEarth on our readers desks willconfirm this fact.R. ThomasDorkingSurrey

The main thrust of Dr Murray'sinteresting article "If you want totell the time ..." (E&WW, Dec.1986) hinges on the statement inthe last sentence in the box.However he does not tell us whywe must "not identify" the twoterms with each other. Nor isthere any reason why we shouldat first sight, since although STRis recognised to be a special caseof GTR. so that any STR effectmust necessarily be a GTR effectas well, the opposite is by nomeans always true. We may haveone of these "one-way" caseshere.

It seems hardly necessary tofollow in detail how Einsteinreaches his conclusion of a rate -change of 1/2v2/c2 seconds persecond in his 1905 paper. Heuses the well-known device oftreating a curved path as a suc-cession of instantaneous linearpaths in order to apply a linearequation to a curved case. Weshould now consider the situa-tion from the viewpoint of theaccelerated, GTR case.

The moving clock is con-tinuously accelerated towardsthe fixed clock, with an accelera-tion of w2r. GTR tells us that aclock under acceleration has itsrate altered by a factor whichequals its "acceleration poten-tial" divided by c2. In this case,the acceleration potential of themoving clock relative to the fixedone will be seen to be:

=rt. IAPotential 2 r v2w2R2

(since when R = 0, P = 0 and theconstant of integration therefore= 0). We now have:

Rate change = 1/2,02R2/c2

= V9v2/c2where v = wR.

We have to conclude that farfrom "not identifying" the twoterms with each other, we can-not avoid it. They are the sameterm, merely derived by differentroutes. In my opinion, Dr Mur-ray's argument therefore fails.

In passing, I think that thisalso finally disposes of the "Ding-le Question". Viewed from the

GTR standpoint. one clock is

under acceleration and the otheris not, so there was never anysymmetry in the situation. andhence no question.

On a quite different tack. I ammost grateful to Prof. Waldronfor his very authoritative over-view of the present 'state of play'on the second postulate (Feed-back. December. 1986). It seemsthat I can go on breathing for alittle while yet, hoping for anexplanation of split spectra togallop to the rescue, because inmy simple-minded fashion I havealways had the idea that, since itappears to describe precisely thecharacteristics light possesses inthe aether. its disproof would notonly scupper the theory of re-lativity, but blow a nasty hole inthe only other theory I knowabout as well. Of course, I willstill have to come to some sort ofterms with the 'resonance'theory Dr Aspden espouses(Feedback, Nov. 1986). In orderto get the arithmetic right, I findthat his c' (>c) has got to be thespeed relative to the aether. Thismeans that we have an entirelynew aether to deal with, capableof supporting an infinite numberof different light -speeds. I con-fess that my mind boggles madlywhen I try to define its character-istics. It mucks up relativity -and everything else - with avengeance!Alan WatsonPollencaMallorca

Your correspondent Lee Coe(January 1987) seems not to beaware of the relativistic Dopplereffect, the theory of which maybe found in any undergraduatephysics textbook.

According to the relativisticmodel, the Doppler effect arisesfrom the Lorentz contraction ofthe space and time coordinates.and not from a change in wavepropagation velocity as isassumed in the classical model.

The classical and relativisticresults differ by the Lorentzfactor

V1 - v2/c2

and for ordinary speeds the re-sults are virtually identical.H. PurseyNew MaldenSurrey


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Scientific interface for theAmstrad PCWThe Amstrad PCW8256/8512 is marketed as a low-cost

word -processor, but it can also make an excellentcomputer for the laboratory.

Athough marketed for small businessapplications, Amstrad's PCWmachines are supplied with powerful

CP/M and Basic software, a large internalmemory (256K or more) and the ability tohandle graphics on screen and printer.

This design exploits the features of the8256 to provide a simple, general-purposeinterface that can be used to generate.record, analyse and plot complex waveformsor voltages without the need to purchaseextra peripherals. It offers both analogue anddigital input and output and uses modularcircuitry which can perform as a complexfunction generator, waveform recorder, pat-tern simulator, or general purpose measur-ing system for software measurement orcontrol of analogue or digital real -worldparameters.

Its facilities also allow the investigation ofsuch techniques as digital signal processing,network analysis, speech and music synth-esis, and can help in the teaching of elec-tronic theory.

The unit was first designed to allow simpleprogrammable measurement and waveformgeneration for applications in the d.c. toupper audio -frequency range: for example.battery discharge curves, speech and musicwaveform synthesis and capture or monitor-ing and storage of one-off events that other-wise are not suitable for an oscilloscope.

However, it became apparent that signifi-cant power came from the inclusion ofanalogue output as well as input, thuspermitting waveforms to be replayed, editedor created directly from software.

With the ability to use over 85% of theprocessor memory for data storage (exclud-ing the large memory disc within the com-puter), the unit has been used for

digitizing or synthesizing music andspeech

waveform capture measuring voltages waveform storage, plotting and manipula-

tion replay from waveform library to oscillo-

scope, chart recorder etc. controlling or monitoring t.t.l. logic measuring network transient response.

A block diagram of the scientific interfaceis shown in Fig.1. The processor bus avail-able at the rear of the computer is bufferedand decoded to communicate with five sepa-rate modules: two analogue to digital con -

BRIAN J. FROST

- ve supply fora- to -d converters

and i/o

Analogueprotection

& conditioning

31,2 digitdual -slope-to-d

converter

8 -bit lOpssuccessive--approxconverter

a -to -dinputData

Address

d -to -odecoding Card

andbuffering

bus'8 -bit lasd - to- a

converter

output

Address

(Fig 2

8 -bit ttloutput

8 -bit ttlinput

Amstrad 8256 or 8512 computer

Fig.1. System block diagram. For versatility, the interface is modular in design.


verters, one digital to analogue converterand a simple digital input and output.Circuitry between these functions and theoutside world provides conditioning andprotection against damage, an importantpoint that has often been considered trivialin other designs.

To keep the design as simple as possible,software control has been adopted for alldata transfers. For example, waveform gen-eration is performed simply by outputtingdata bytes via the eight -bit d -to -a converter.Such data can be created by Basic programs,derived from user -written functions thatgenerate sine, square, triangle or even 'fun-ny' shapes, or supplied by replay of previous-ly recorded data captured by the a -to -dconverter and stored in the disc waveformlibrary. The interface's versatility resultsfrom the large memory available.

Although they provide greater speed,more hardware -intensive techniques such asd.m.a. were not considered here since theaim was not primarily to exceed the upperaudio band but rather to provide circuitrythat would interface easily to existing lan-guages, besides being simple and flexible inconstruction and use.

ANALOGUE I/O DEVICES

Despite certain performance restrictions im-posed by the software approach, the choiceof devices used for the analogue i/o is stillfundamental to the design and so it is worthidentifying the trade-offs available.

It became clear that for analogue input nosingle a -to -d converter would allowmeasurement to be made at high-speed,with good resolution and at reasonable cost.It is a point of interest that there is no othersemiconductor sector where the trade-offbetween performance and cost is moremarked than in analogue data converters.

Despite continuous improvement in valuefor money, popular converters are still of twomain types: successive approximation andintegrating. Each has advantages and dis-advantages. A successive approximationconverter is fast (often less than 50ps con-version time) and is readily available from 8to 12 bit resolution. In contrast, an integrat-ing is much slower (often less than 25conversions per second) but easily providesgreater precision with the equivalent of 12 to16 bits resolution. Integrating convertersalso have a certain inherent immunity tonoise and mains pick-up and in many casesoffer auto -zeroing and dual -polarity logic.

To offer good precision and yet high-speedmeasurement, a low-cost device of each typehas been included in the design, with switch-ing so that the final choice can be decided bythe application. The devices selected are ahigh-speed eight -bit successive approxima-tion converter sampling at up to 100ksamples per second, and a low-cost 31/2 -digitb.c.d. dual -slope integrating converter thatprovides 0.05% resolution as well as dual -polarity, auto -zero and noise rejection, at aspeed of around 15 conversions per second.

Choosing the digital to analogue conver-ter is rather easier since an eight -bit deviceallows good waveform resolution and a speedof operation limited only by software. De-spite this software speed limitation, sine

-1- Vc c

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Fig.2. Address decoding and buffering module plugs into the Amstrad bus connector.

waves well into the kilohertz region can begenerated. High -frequency waveforms areeasily cleaned up using simple RC filteringsince the sampling harmonics do not appearuntil around 30kHz.

To be continued.

Brian Frost, C.Eng., M.I.E.E. graduatedfrom Bangor University in 1974 with adegree in electronic engineering. Until re-cently he was in charge of the design ofautomatic test and manufacturing equip-ment at STC; now he is with Deltest Systemsworking on advanced analogue specific a.t.e.

His spare -time interests include writingand an involvement with Remap, a UK -widenetwork of engineering working voluntarilyto make special aids for the disabled. In thisfield he is working on radio communicationaids for the deaf. He is also a licensed radioamateur. G6UTN.

COMPONENTS

The interface is available fully assembledanc- tested at £139, or in the following kitstages:Kit A: printed circuit board with connectorfor address decoding circuitry of Fig.2,

£16.50.Kit B: address decoding circuitry of Fig.2,inciuding p.c.b, connector, and all compo-nerts fully assembled and tested. £31.50.Kit C: complete interface including case,p.c bs, components. connectors, switchesand interconnecting cable. £117.50.

Prices include postage and packing butplease add v.a.t at 15%. Orders or enquiriesshculd be addressed to Placepower Ltd. Unit24, Longs Industrial Estate, Englands Lane.Gorleston. Norfolk NR31 613E; telephone0493 603771.

ELECTRONICS & WIRELESS WORLD '155

Alcatel and ITTconverge on IT

January 1 saw the start of a new era withthe establishment of a new telecom-munications company, Alcatel NV. This

new alignment will be instrumental in plac-ing greater stress on information technologyand the convergence of telecommunicationsand computing. A joint venture consisting ofthe telecommunications activities of the ITTCorporation worldwide and all of Alcatel ofFrance and Cables de Lyon activities underthe management of the Compagnie Generaled'Electricite (CGE), the company is active in110 countries, with annual sales of $12billion and some 150 000 employees. CGEgroup controls 55.6% of the company andITT owns 37%.

At the same time as bringing togetherthese resources the new company will makeexisting and prospective customers (includ-ing PTTs and thus, effectively, governments)re-examine their procurement policies andis therefore a realignment of the industry.This is especially so in public switching,where a country rarely has more than two orthree suppliers, and so this can be seen asanother step in the rationalization in themarket -place. In other areas it could wellbring the benefits of economies of scale.

In the short to medium term, the out-come will probably be less than the sum ofthe individual parts. This is due to thedifficulty of merging two companies which.because of their very size, overlap in anumber of product areas. Thus, an amountof rationalization will be required - some ofwhich will no doubt be traumatic. Evenbefore this occurs, it will already havechanged the centre of gravity of the telecom-munications industry.

With sales forecast to reach $12 billionthis year, the new organization becomes theworld's second largest telecommunicationssupplier with a broad spread of activitiesincluding public switching, business sys-tems, cables and a variety of consumer andindustrial products. It claims to be theworld's largest international supplier of pub-lic network equipment and to have marketleadership in digital switching and transmis-sion equipment, including advanced fibreoptic systems. However, while in the fullnessof time Alcatel will have a higher profile,many people in the UK will not even recog-nise the name even though many more willknow ITT.

ITT has occupied an important place inthe UK for many years. Probably most widelyknown in the High Street are the tv setsbearing its name and STC (once StandardTelephones & Cables) was one of its UKsubsidiaries. Even though it no longer hascontrol, it still holds 24% of STC's shares.

Last year Alcatel and ITT had total sales inpublic telecommunications of around $5billion and, in digital public switching

ADRIAN J. MORANT

together they have 37 million lines eitherinstalled or on order in 76 countries. Thenew company will develop and market boththe Alcatel El° and ITT's System 12. Alcatelis a pioneer of digital switching, havingsupplied the world's first digital public tele-phone exchange, which was commissionedin France in 1970. Since then, with 765 EIOexchanges in service, over half of the Frenchnetwork is already digital while the whole ofthe country can benefit from the 64k-bilisswitched bearer service to transmit data andimage. Fully compliant with the latestCCITT standards, the system will allow forsmooth migration from PSTN to ISDN.

ITT entered the business much later.Nevertheless, almost two million equivalentlines of System 12 have been handed over toPTT customers in 14 countries while thetotal order book has now reached 14 millionequivalent lines for 21 countries over thenext 10 years.

Today five subsidiaries of the new com-pany (SEL in West Germany. BTM in Bel-gium. FACE in Italy, Standard Electra inSpain and STK of Norway) are principallyinvolved in production and development ofSystem 12 under the central co-ordinationof a public switching headquarters based inBrussels. These companies are involved intechnology transfer to other manufacturingsubsidiaries of the new company, in directexport to world markets and in joint ven-tures and licence agreements for local pro-duction in countries which include China,Turkey and Yugoslavia.

It has been announced that developmentwill continue on enhanced features for Sys-tem 12 (which in recent times has involvedR&D expenditure in excess of $100M perannum) to meet PTT requirements forISDN-related services. However, System 12deliveries have been running late and theview has been frequently voiced that thedesign is flawed. While ITT could not denythat there were delays, it, and now Alcatel,assure everyone that these problems arethings of the past.

In West Germany. the Deutsche Bundes-post has started Europe's first large-scaleISDN field trial. This trial includes a System12 exchange in Stuttgart to which 400full-ISDN subscribers will be connected. InBelgium, the PTT is the first one in Europeto introduce CCITT No.7 common channelsignalling links between exchanges forhandling both signalling and call charginginformation. This feature is being im-plemented on System 12s throughout thecountry. Other systems include a combinedexchange in Denmark handling trafficequivalent to a 40 000 line local exchange

and a group of exchanges in Norway, equip-ped for 70 000 lines. which interconnectlocal and toll exchanges with remote sub-scriber units. It does appear, therefore, thatSystem 12 is getting over its early problems.

In radio links Alcatel is Europe's largestand the world's second supplier with over100 000km of equipment already in service.In submarine cable links, it holds 25% of theworld market outside the USA. This amountsto some 31 000 nautical miles of submergedcable containing 3 400 repeaters.

In addition to conventional copper cable ithas a new generation of digital optical fibresystems. These activities stem from Cablesde Lyon together with the fibre optic activi-ties of ITT in the USA. This is possibly one ofthe reasons that STC has been excluded fromthe joint venture, even though ITT owns alarge proportion of its shares. After all, STC'sexpertise in submarine cables - includingoptical - is in direct competition.

In terms of subscriber services, Alcatelswitches are central to the French videotexservice. The growth of this network, whichnow serves over three million subscribers: isin part due to the French government'selectronic telephone directory project. Thisensured that there was a large installed basethat would attract information providers.

Similarly in mobile communications, thegroup manufactures both u.h.f. and v.h.f.network equipment and mobile units andhas joint agreements with different Euro-pean manufacturers to develop a 900MHzdigital cellular radiotelephone system whichit hopes will be adopted as the futureEuropean system.

In business systems the new company willhave sales of around $3.2 billion (i2.5G). Aswell as producing over 10 million telephoneinstruments, Alcatel has its existing range ofp.a.b.xs and telephone key systems while ITTbrings its Office 2000 system. This latter isbroken into three basic elements essential toa user's information management system:telecommunications (orientated towardsprivate systems): data communications(host/computer orientated systems) andcomputing where ITT has a family of smallbusiness computers. It encompasses a com-plete range of hardware and software rang-ing from telephone handsets and peripheralslike facsimile machines up to powerfulsuper -minis that link to mainframe compu-ters.

Altogether, this is enough to make a verypowerful group with enormous resources.However, success in many of its areas ofoperation is not only determined by tech-nical and direct commercial considerations- politics and even national aspirations areinvolved. The broad spread of product mix intelecommunications and IT will providemany opportunities but only time will tell.


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Editorial Feature ListMAY 1987Logic analysers are clearly indispensable tothose working on digital system design ormaintenance. This feature presents thecharacteristics of those available and discussesapplications.

JUNE 1987Batteries. Recent developments in battery designmean that an investigation into the new typesavailable is needed. We discuss design andapplications and characterize the types on themarket.For further advertising details please ringAshley Wallis on: 661 8641

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457

46

WORKFILEuality can't be put in at the end:you've got to build it in from thebeginning," seems to be the con-

ventional wisdom behind Quality Assurance(QA). New government standards may beencouraging this attitude, but if there's a"revolution" taking place in the QA world, itshappening slowly.

"A cultural change is taking place in QA,and it's not before time," according to MikePerry from the British Standards Institute,"the next five years should be very exciting."Perry says the move to higher quality iscoming from the top downwards. The newcorporate philosophy, according to Perry, is'Total Quality Management' (TMQ). TMQ, anAmerican phrase with its roots firmly inJapanese management practice, calls forproductivity to go hand -in -hand with quali-ty. The idea is to involve all members of theworkforce to keep the customer satisfied atevery level. In some Japanese plants, forexample, production line workers have beenable to send components back to the pre-vious work station when they are not satis-fied with the quality of the piece.

The British government is seen to bepromoting TMQ with the introduction threeyears ago of BSI 5750. Made up of threeparts, BSI 5750 introduces the art of statis-tical process control, so that any flaws canreadily be identified and put right. The ideabehind BSI 5750 is for major companies -such as British Aerospace (BAe) and BritishTelecom (BT) - to put pressure on theirsub -contractors to conform to quality stan-dards. Quality becomes the responsibility ofthe sub -contractor. The government istherefore using the purchasing power ofthese giant corporations to bring smallercompanies into the quality line.

Parallel with the commercial develop-ments have come a new set of militaryprocedures. The new NATO AQAP standardsreplace the old 0251 MoD standards. Again,the responsibility for maintaining standardslies with the sub -contractors. When certifiedby MoD inspectors, the company is thenvisited around four times a year to make surethings are up to scratch, according to anMoD spokesman. The MoD also has a veri-fication workshop where more detailed in-spection work can be undertaken.

So what sort of people are being taken onin the QA business? The general standardseems to be an HND followed by three to fiveyears of experience. The favoured age rangeseems to be 24-38 but, as with all theseguidelines, they're only approximate. Theaverage pay package for a suitably qualifiedand experienced engineer is around112,000.

Steve 011erton from Data EngineeringRecruitment said that, while they prefer twoto three years experience, a shortage of goodQA engineers means they'll take somebodywith 12 months under their belt - so long asthe experience is directly related.

Quality assuranceQA is big business at BAe's Stevenage

plant, with a staff of 850 out of a totalworkforce of some 6 500. These people coverall aspects of the spectrum from techniciansto engineers. These include calibration en-gineers using proprietary test equipment.BAe recently passed through its AQAPSprocedures with "flying colours" accordingto personnel manager Richard Aubigne.Aubigne says AQAPS covers all areas of theplant including quality planning. "AQAPStakes the skill away from people," saidAubigne. "You can't do things your own wayand that's no bad thing as you can't missanything out this way." BAe currently has avacancy list for 20/30 QA people - rightacross the board. Officially, for engineersBAe requires an HNC with six years ofexperience. However, with such good train-ing facilities, the company is willing to takepeople on with the right qualifications andthen train them up themselves.

Aubigne said calibration engineers seemto be the hardest to come by "Some takemonths to recruit - others take a couple ofyears," he said. With such a specialized areaand modest salary, Aubigne said BAe isfinding recruiting the right engineers verydifficult indeed.

David Hunt from Interlord - aWimbledon -based recruitment company -said there's a large demand for QA engineers,not just in this country but in NorthernEurope as a whole. Hunt maintains thedemand for British QA engineers persistsbecause of their high reputation for gettingthe job done. Providing the engineer isfluent in that country's language, a wellqualified person is widely sought after. Huntadded that the change to BSI 5750 andAQAPs standards has led to more work forthe QA engineer. "As companies carry onpicking up new standards there's an in-creased requirement for quality personnel,"he said. There seems to be a shortage ofexperienced people in all engineering fields.QA engineers are in especially short demand,according to Hunt, because of their loyaltyto one particular company. Hunt puts thisdown to QA being regarded as a highlydesirable and interesting occupation.

At Plessey Semiconductors, QA personnelcome from the general graduate trainingprogramme which takes on 25 to 40 peopleeach year. Vacancies are then filled as theyappear. A small proportion of engineerscross over from electrical engineering. APlessey spokeswoman said it isn't any moredifficult to find QA's than any other type ofengineer- but that's hard enough!

Mark Wright from the IndependentBroadcasting Authority agreed with Huntinsomuch as he has a very low turnover ofQuality Control staff. The IBA employs Qual-ity engineers to monitor the technical quali-ty and broadcasting standards of local sta-tions. They also make sure broadcastingequipment is up to specifications. Wright

said the IBA looks for degree -educated peo-ple with two to three years experience. Whenit does have vacancies it can't fill internallythe IBA advertises through the trade press.

While degrees are preferred by some largecompanies, it seems most QA engineers takethe HNC/HND route. According to GrahamSmith from the Southampton Institute ofHigher Education, the courses are very"hands on" practical courses, with thetheory to back it up. At HND level thestudents, most of them on day release fromelectronics employers, have 6/7 assignmentsto complete. Smith said these assignmentsare very sophisticated and a lot of emphasisis placed on presentation with people beinggroomed to become QA managers. Afterfinishing the HND, some students go on totake the Engineering Council Part Twoexams, which on completion give charteredengineer status. Smith said these examsrequire six passes which can take up to threeyears part-time study to complete.

Southampton also runs courses for thosepeople who work in QA on a day-to-day basisat the technican level. This is a City andGuilds 743 course, teaching Quality Controltechniques to mature people who are oftentrying to be upgraded to inspector level.With the introduction of the new standardsthere is increased company demand fortraining. To meet this demand South-ampton is running courses specifically de-signed for each company, either in-house orat the company's premises.

BSI 5750 will eventually affect all manu-facturing companies. Many larger ones,such as BT, have already come into line andare applying pressure on their sub-contractors to do the same.

Mike Perry said the job of the QA engineeris bound to change quite dramatically. Pre-viously a works engineer given the qualityhat, as well as many others, the QA manageris adopting an ever more important role. TheQA manager needs to be able to gain therespect of all departments within the orga-nization as quality becomes an all-pervadingissue. The QA manager also needs to be ableto bend the ear of the chief executive officer,who alone can authorize the required levelsof expenditure.

QA engineers are therefore going to haveto be of senior management status. Payscales seem slowly to reflect demand forhighly skilled personnel. With a large num-ber of companies seeking to adopt the BSI5750 standards the demand is set to in-crease. However, it seems unlikely mostcompanies will be able to offer the salariescurrently on offer to some QA consultants.According to Perry, figures of £35 000 arenot unheard of. As I said, a revolution may betaking place but it's certainly happeningslowly.

Workfile is written by Stephen Horn, Em-ployment Editor. Electronic Weekly.


APPOINTMENTSAdvertisementsaccepted up to

12 noon March 27for May issue

DISPLAYED APPOINTMENTS VACANT: £23 per single col. centimetre ( nun. 3cni ).LINE advertisements (run on): £5 per line, minimum £40 (prepayable).BOX NUMBERS: £11 extra. (Replies should be addressed to the Box Number in theadvertisement, co Quadrant House, The Quadrant, Sutton, Surrey SM2 5AS).PHONE: SUSAN PLAITS, 01-661 3033 (DIRECT LINE)

Cheques and Postal Orders payable to REED BUSINESS PUBLISHING and crossed. 1

Design ElectronicCommunications Equipment

Progress from initial concepts through prototypeconstruction to the pre -production phase using CA DMATtechniques. Analogue and digital circuitry, incorporatingmicroprocessor systems, is designed and developed by ourengineers who are involved with both hardware and softwareconsiderations. The broad field of activity means that engineerscan expect to move to challenging new projects every few .earsaccording to their interest and aptitudes.

Working conditions are pleasant, the surroundings areattractive and the support facilitiesare superb. Relocation expenses arcavailable and shared ownershiphousing schemes may be negotiatedin the nearby city of Milton Keynes.

HER MAJESTY'S GOVERNMENTCOMMUNICATIONS CENTRE

HANSLOPE PARK -

We are now looking for young men and women who haveelectronic engineering degrees and relevant experience (2 yearsminimum). Appointments will be made on a scale ranging fromV.10,302 to :13,642 per animin but substantial improvements tothis scale are agreed and will lead to a minimum upper salarylimit of i'14,458. The career prospects in the longer term areexcellent including opportunities for promotion in the salaryrange ,,:14,264) to %:17,84(1.

For an application tinin or further details pleasewrite to:The Recruitment Officer.1-1M Government CommunicationsCentre, Hanslope Park,Buckinghamshire MK I') 7BH.

Electronic Engineers-What you want, where you want!TJB Electrochemical Personnel Services is a specialised appointmentsservice for electrical and electronic engineers. We have clients throughoutthe UK who urgently need technical staff at all levels from Junior Technicianto Senior Management. Vacancies exist in all branches of electronics andallied disciplines - right through from design to marketing - at salarylevels from around £8,000 - £25,000.

If you wish to make the most of your qualifications and experience andmove another rung or two up the ladder we will be pleased to help you.All applications are treated in strict confidence and there is no danger ofyour present employer (or other companies you specify) being made awareof your application.

TJB ELECTROTECHNICALPERSONNEL SERVICES,12 Mount Ephraim,Tunbridge Wells,Kent. TN4 8AS.

Tel: 0892 510051(24 Hour Answering Service)

Please send me a TJB Appointments Registration form.

Name

Address

ilea Working inEducation

Electrical/ComputingTechnicianPADDINGTON COLLEGE25 Paddington Green. W2Tel 01-723 8826

To provide a full Technicalservice in the Electrical/ElectronicLaboratories and to providetechnical support for the CollegesComputer Centre at SaltramCrescent. Includes preparation ofmaterials for all levels of practicalclasses £8,643-f9,957 inc.

Applicants should have at leastONC. OND, BTEC/TEC HigherCertificate. Advanced City 8 Guildsor equivalent qualrfications inappropriate subjects, plus aminimum 8 years relevantexperience (including training(

Application forms and furtherdetails are available from theschool or college concerned.Completed application formsshould be returned to:PER/PS5b, Room 336a, TheCounty Hall, London SE1 7PB.

Closing date: 30th March 1987.


APPOINTMENTS

ilea Working inEducation

Electrical/ComputingTechnicianPADDINGTON COLLEGE25 Paddington Green. W2Tel 01-7238826

To provide a full TechnicalService in the Electrical/ElectronicLaboratories and to providetechnical support for the CollegesComputer Centre at SaltramCrescent Includes preparation ofmaterials for all levels of practicalclasses £8,643-C9,957 inc.Closing date: 30th March 1987.

Computing &Micro -ElectronicsTechnicianWESTMINSTER COLLEGEBattersea Park Road SW 11 4,IRTel 01-720 2121

GRADE 5: responsible for theday to day provision of a technicalservice in relpon to the collegesComputing and InformationTechnology facilities on all sites ofthe college Duties include settingup checking and ensuringsatisfactory functioning and firstline maintenance of computingequipment £8.613-£9.957 inc.Closing date: 3rd April 1987.

Applicants should have at leastONC. OND. BTEC/TEC HigherCertificate. Advanced City 8 Guildsor equivalent qualifications inappropriate sublectsi plus aminimum 8 years relevantexperience Including training)

Application forms and furtherdetails are available from theschool or college concerned.Completed application formsshould be returned to:PER/PS5b, Room 336a, TheCounty Hall London SE1 7PB.

Inner LondonEducationAuthorityitif A IS AN EOUAL

OPPORTUNITY EMPLOYE R

IP sTYPE -SETTING SYSTEMSRepair and service of digital andcommunication systems Experience of28000 useful£12,000 Car E.C. LondonBROADCAST EQUIPMENTTest and service of multi -processorvideo systems£9,000

CELLULAR RADIORepair of R F Communicationsequipment Analogue experience useful£9,000 CamberleyRADIOCOMMSDevelop and support a wide rangedigital communications£12,000 MiddlesexRADAR SYSTEMSRepair of microwave communicatioilinks£10,000 EssexSECURITY SYSTEMSRepair of analogue and digital signallingsystems.£9,000

MIddlese.

Berks

Hundreds of other Electronic andComputer vacancies to £15,000

Phone or write:Roger Howard C.Eng. M.I.E.E. R.I.E.R.E.

CLIVEDEN RECRUITMENT92 Broadway. Bracknell,

Berkshire RG121ARTel: 0344 489489

COMMUNICATIONSCONSULTANT/

ENGINEERHFNHF/UHF/RTTY

BASE AND MOBILE PABX/PAGERS

Widely experienced Afria andMiddle East.

If you need communicationsyou need reliability whetherits installation, maintenance

or advice, get an expert.Contact:

FREMARCONSULTANTS ONTEL (0722) 742284 orTLX 477019 ASR -G

ATTN FREMAR CONSUL382

ELECTRONICS RESEARCHAT THE

UNIVERSITY OF ESSEXGraduates who have (or final year students who expect to obtain) a first or upperiiecond class honours degree are invited to apply for research leading to a higher

Sc M Phil. or Ph D l in the following areas

Audio EngineeringComputer Systems - Information Systems

- Man -Machine InteractionComputer -Aided DesignDigital TransmissionDisplay SystemsImage ProcessingOptical CommunicationsPerformance EngineeringRadio and Satellite Systems

Further information and application form available from. Professor D E Pearson.Chairman. Department of Electronic Systems Engineering (EWW) Iln ver5:tv ofEssex. Wivenhoe Park, Colchester C04 3SQ

r t

TRAINEERADIOOFFICERS

Are you looking for o secure shore -based loba rewording career in the forefront of r

communications technology...Cher

pining GCHQ os o Trainee Radio 0"Training involves o 32 week residentia

course, (plus 6 weeks extra if you connottouch type) after which you will be

appointed RADIO OFFICER and undertakeo variety of specialist duties covering the whole

We offer you: Job Security GoodCareer Prospects Opportunitiesfor Overseas Service AttractiveSalaries... and much more.

to obtain on MRGC or riNC: in oTelecommunications subject withan ability to read morse of 20wprn.

Anyone with PMG, MPT or 2 years relevant radio operating experience is also eligible.The Civil Service is on equal opportunities employer

Salaries: Storting pay for trainees is age pointed to 21 years. For those aged 21or over entry will be at £6,572. After training on RO will start at £9,758 rising by 5

ncrements to £14,387 inclusive of shift and weekend working allowance

Write or telephone for on applicationform to:-

EEEEEEEEEEE

laCHQ THE RECRUITMENT OFFICE. GCHQ. ROOM A/1108OAKLEY, PRIORS ROAD. CHELTENHAM. CLOS GL52 5A1

OR TELEPHONE (0242) 32912 :t

PART-TIME TUTORS,ENGINEERING. Part-time tutorsrequired in the following subject areas:Basic electronic skills; Digital andanalogue electronic engineeering. Postsavailable throughout the UK.Attractive rates of pay and ideal! suitedfor College Lecturers interested in

enhancing their pay, or recently retiredprofessional persons anxious to retaincontact with their subject areas. Pleasewrite to Academic Consultants, coGroup Four Marketing Services, 138High Street, Eton, Near Windsor,Berkshire SI.4 6AR. 386

Ha rdwa re/So ftwa re/ Systems£9,000-05,000

As a leading recruitment consultancy we have a wide selection of opportunitiefor high calibre Design, Development, Systems and supporting staff throughout the UK

If you have experience in any of the following then you should be talking to us It,your next career move

ARTIFICIAL INTELLIGENCE IMAGE PROCESSING ANALOGUE DESIGNMICRO HARDWARE 8 SOFTWARE GUIDED WEAPONS C PASCAL

ADA RF MICROWAVE ELECTRO- OPTIC 5 SIMULATION C'lREAL TIME PROGRAMMING SYSTEMS ENGINEERING ACOUSTICSSONAR RADAR SATELLITES AVIONICS CONTROL ANTENNA

VLSI DESIGN

Opportunities exist with National, International and consultancycompanies offeringexcellent salaries and career advancement

To be considered for these and other requirements contact John Spencer orStephen Morley or forward o derailed CV complete confidence auotrng Ref. WW/66.

Q-4Recruitment

STS Recruitment, 85 High Street, Winchester,Hants S023 9AP. Tel: (0962) 69478 (24 hrs).


MAINTENANCE

Outside Broadcasts

SUPERVISORCommunications

inBBQWe are an equal

opportunities employer

I

I

I

I

I

II

rs

1

..... MMMMMMM

We are looking for an Engineer equal to the challenge of runningthe Maintenance and Test Area of our largest centre of MobileRadio Links in the country.

The equipment ranges from Satellite ground station and Radiolink control vans, trrough SHE UHF and VHF video and audiolinks to radio telephones and digital audio equipment.

You should hold an HNC. B/Tech Higher Diploma or Degree inElectronics Engineering and have some experience of one ormore of the types ol equipment listed.

Good opportunities for promotior will exist for the rightapplicant.

Salary: £13,194 - £16,796 plus an allowance of £597 p.a.The job is based in West London and relocation expenses will

be considered.For further information contact John Sewell on 01-992 5344

Ext. 316.For application form contact (quote ref. 5580/WL) BBC

Appointments, London W1A 1AA. TeL 01-927 5799.Completed application forms should be returned by 10 April 1987.

r MI 11111 Ell ME OM ENO OM MI MMMMMMCAPITAL APPOINTMENTS LTD I

THE UK's No. 1 ELECTRONICS AGENCY IIf you have HNC/TEC or higher qualifications and are

looking for a job in design, test, customer service. technicalsales or similar fields

Telephone now for our free lobs listWe have vacancies in all areas of the UK

Salaries to £15,000 pa

01 8083050(24hours)

CAPITAL APPOINTMENTS LTD76 WILLOUGHBY LANE, LONDON N17 OSF

ARTICLES FOR SALE

I

I

KING'S COLLEGE LONDON (KOC)University of LondonDEPARTMENT OF ELECTRONIC & ELECTRICAL ENGINEERING

ELECTRONICS TECHNICIAN- GRADE 6Requred for interesting and varied work for Electronics researchand teaching including prototype design and development andservic ng and maintenance of a wide range of commercialelectronic equipment. Experience and qualifications inElectronics (particularly digital) at an appropriate level areessential.Salary E9.708 to £11.424 per annum inclusive (under review).Further details and application forms from Mr M. E. Cane.Departmental Superintendent, King's College London (KIDC).Department of Electronic & Electrical Engineering. Strand.London WC2R 2LS or telephone Mr Alan Dimes, 01-836 5454.ext 2736.

TO MANUFACTURERS, WHOLESALERSBULK BUYERS. ETC.

LARGE QUANTITIES OF RADIO. TV ANDELECTRONIC COMPONENTS FOR DISPOSAL

SEMICONDUCTORS. all types. INTEGRATED CIRCUITS. TRANSISTORS.DIODES. RECTIFIERS. THYRISTORS. etc RESISTORS. C/F, M/F, W/W. etc.

CAPACITORS. SILVER MICA. POLYSTYRENE. C280. C296. DISCCERAMICS. PLATE CERAMICS, etc.

ELECTROLYTIC CONDENSERS. SPEAKERS. CONNECTING WIRE, CABLES,SCREENED WIRE, SCREWS. NUTS. CHOKES, TRANSFORMERS, etc.

ALL AT KNOCKOUT PRICES - Come and pay us a visit ALADDIN'S CAVE

TELEPHONE: 445 0749/445 2713R HENSON LTD

21 Lodge Lane. North Finchley, London. N.1215 minutes from Tally Ho Cr, e, 11 6 I 3

VHFFM BROADCASTEQUIPMENT

A special range of high quality

Transmitters. power amplifiers. stereo

encoders. UHF repeater links.

compressors, antennas. Powers 10w to

1kw. Built to high specifications at an

economic price. Meets IBA & Full

Broadcast specifications.

Phone now for prices and delivery

Cyberscan International,3 Eastcote View, Pinner.

Middx HAS lAT. Tel: 01-966 33003%

INVERTERSDC -AC High PowerGardners sq wave type GR75108I,P 50V DC 85ACYP. 240V 50Hz 4kVA £300Also 2kVA E200 - IkVA £150

H&D Sinewave 600WUP, 24V DC0/P: 230V 50Hz 600VA £240

CVT.s: Cetronic Reguvolt 6kVA £290.5kVA £250. 4kVA £220. 2kVA C160

GREEN WELD ELECTROMCS LTD443 Millbrook Road, Southampton.

SO1 OXH. TeL (0703) 772501/783740

TEST EQUIPMENTFOR SALE & WANTED

Buyers and Disposal Officers contact.COOKE INTERNATIONAL

Unit 4. Fordingbridge SiteMain Road. Barnham.

Bognor Regis.West Sussex P022 OEB

Tel 0243 68 5111 2

G.W.M. RADIO LTD4042 Portland Road. Worthng, Susstx.

Tel: 0903 34897Constantly c hang strxn of interestingitems for callers Receivers test equipmentcomponerts etc Pye pocketIone PFI TXunits with battery and circuit; C12 Inc p&pMeters survey radiac No 2 portableradiation detectors untested noinformation available C15 inc p&p RacalDecade Frequency Generator MA 35013 TxDrive Unit MA79 synthesizer for caller,

Radiotelephones,Terminal Units, TestEquipment, Ex -RAFRadar and Instruments.

Brent Electronics 8 Camms.49 Seaview Street. Cleethorpes.South Humberside DN35 8EL.Tel: 0472 690383.

LIGOLLEDGEI

IELECTRONICSI

QUARTZ CRYSTALSOSCILLATORS AND FILTERS ofall types. Large stocks of standarditems. Specials supplied to order.Personal and export orders welcomed -SAE for lists please. OEM support thru:design advice, prototype quantities,production schedules. GolledgeElectronics, Merriott, Somerset VA 165NS. Tel: 0460 73718. (24721

BRIDGES wavelormn transistoranalysers. Calibrators. Standards.Millivoltmeters. Dynamometers. KWmeters. Oscilloscopes. Recorders.Signal generators - sweep, lowdistortion. true RMS. audio, RM.deviation. TeL NO 376236. (2616)

SEMI CUSTOM IC DESIGN. Verylow cost power. fast delivery. eraseable.Spectal i.c.s. standard logic, PA I.replacement. protoyping,microprocessor peripheral application.Design changes easily carried out. Alldesigns copy protected. Price starts atas little as CAL Glenavon Electronics at0733-733385. 388

WSLI: - SIEMANS - S T Ccommunications & cable testequipment. Level meters -generators -receivers etc. S.A.E. lists: J.B. Pattrick191 193 London Road, Romford, EssexHM791)10708 44473. 415


ARTICLES FOR SALE

TEST EQUIPMENTFOR SALEAll equipment in period condition includes88K 20101902 superhet analyserB8K 2305 level recorder with 4 pots1389 4440 gating system

BAK 2971 phaserneter

88 K 2206 precision sound level meter withcapsule

88K 2426 auto range milivoltmeterEnquire for full list of BAN

HP86. 3 25 disc drive. bindata microlink Ill.HP7475A 6 pen plotter other accessoriesTektronics computer 31. 152 and 2 DM501millimeters HP3580A spectrum analyserSound technology 17005 distortionmeasurement system Philips 6652programmable high res timer counter Dacron1065 aulocal DMM Sennheiser universal UDM550 ACidEl meter Kerno VBF /14 band pass,stopfilter Technon I M D analyser Wayne Kerr 8221universal bridge

Please call Angus McKenzie for rue list -01-349 0511 strictly 9.30am-5.00pm. 422

Component Testing Bridges - Avo. 138K£97 Portable Variable 15A DC stabilisedPSU. £85 Portable oscilloscope. £45 B&K2603 Microphone Amplifier. £55 NashtonCoulometrtc Plating Gauge. £65 2KVstabilised PSU. £49 BTL ElectrolyticAnalysis Apparatus. £120 BTL KarlFischer water content analyser. £98Electrothermal Melting Point Apparatus,£79 Optical Pyrometer. £89 LaboratoryThermostatic Heated Bath. £69 TektronixOscilloscope dual trace. E135 PortableBradley oscilloscope. operates from mains.internal/external 12V batteries. auto -chargerwith boost. 20MHz. £179 AmocoPhotomultipher Micropholometer. E65High Power White Light Stroboscope. dualtube. £135 Tektronix 'a plug-in fortransducers. strain -gauges etc. £35 AlnorVelometer. meter & two range selectors forprecision air velocity measurement. £95Avo EHT meter. 0-15Kv. 0-30Kv. £35Record Chart Recorder. £65 CentrifugeE49 Electrostatic EHT Meter. 0-15Kv. £20Stablished variable PSU. 6V metered. £20Leak Detector. £25 Marconi SignalGenerator Tektronix plug -ins L £35. B£25. TEL: 040-376236

SERVICES

WANTED

STEWART OF READING110 WYKEHAM ROAD.

READING RG6 1 PL.TEL: 0734 68041

TOP PRICES PAID FOR ALLTYPES OF SURPLUS TESTEQUIPMENT, COMPUTER

EQUIPMENT, COMPONENTSetc. ANY QUANTITY

WANTED FOR CASH,SURPLUS AND

REDUNDANT BROADCASTEQUIPMENT

Particularly medium -wavetransmitters, FM transmitters.

studio links (STL), studiofurniture, affects: cartmachines, AA3 carts.

COMP SHOP HI -TECH311 LONDON ROAD

CAMBERLEY, SURREYTel: 0276 29219

WANTED: Who has experience acidcan develop a radar receiver with thefrequencies 9,41 and 34,36 GHz forradar car speed control detection"WALLFASS, P.O. Box 1244, D -4( r,Moenchengladbach, W -Germany. Tlx852582. tel 2161-88555. 380

I'LATINUM, GOLD, SILVERSCRAP, melted assayed and paid forwithin 24 hours. Relay contacts, p.c.b.s.thermocoupoles, crucibles, plugus.connectors, etc. Totally free samplingservice. Send samples or parcelsregistered postI or contact Eric

Henderson, 0773 760661. SteinbeckRefineries (UK) Ltd, Anchor House.Anchor Road. Eastwood. Notts. 406

CIRCOLECTHE COMPLETE ELECTRONIC SERVICE

Artwork, Circuit Design, PCB Assembly, Test & Repair Service, Q.A.Consultancy, Prototypes, Final Assembly. Full PCB Flow SolderingService.Quality workmanship by professionals at economic prices.Please telephone 01-646 5686 for advice or further details.

TAMWORTH MANOR302-310 COMMONSIDE EAST, MITCHAM

11391)

IE11 POR I S EXPORTS of all kinds ofElectronics and Computers. Please sendyour enquiry or product details toDEDICATED MICROPROCESSORSLTD. 299A Edgware Road. London W2IBB. England, or Telex 945922GLADEX-G for the attention of Mr.C.Paps. 1300)

PRINTED CIRCUIT BOARDSsingle and double sided manufacturedto your specifications. We offer qualityand fast service (same day onprototypes) at very keen prices. Wesupply copperclad material cut to size.Artwork service available. MondoCircuits Ltd. 35 Grosvenor Rd,Twickenham, Middx. 01-891 5412. 413

ARTICLES WANTED

TURN YOUR SURPLUS i.cstransistors etc. into cash, immediatesettlement. We also welcome theopportunity to quote for completefactory clearance. Contact COLES-HARDING & CO, 103 South Brink.Wisbech, Cambs. 0945 584188. (921

P.C.B's DESIGNED. Artworkcapacity available for single/doublesidod, P.T.H. and multi -layer P.C.B's.also silk screens, solder masks, labelsetc. For C.A.D./photoplot, artwork &photography, contact Mr. Williams, 49Westbourne, Honeybourne, Evesham,Worcs. WR11 5PT. Tel: 0386 832152.409

When replying to

I classified advertisements, I

I readers are recommended

to take steps to protect

their interest before

sending money

WANTEDTest equipment, receivers,valves, transmitters, com-ponents, cable andelectronic scrap and quan-tity. Prompt service andcash. Member of A.R.R.A.

M & B RADIO86 Bishopsgate Street

Leeds LS1 4BB0532 435649

EVENTS

SWINDONRALLY

OAKFIELD SCHOOL, MARLOWE AVE., SWINDON

Sunday 10th May, open 10.30am, adm. 50p.

Radio & Electronic Equipment, Components,Computer Equipment & Software. Refreshments,Entertainment for the Whole Family.

DETAILS: GSSFY1 (yrtiR. I'LL. 1)66689-307

ARTICLES FOR SALE

HV capacitors. Pulse Generators. TektronixTime/Mark Generator. £79 PlasticPackaging Heat Sealer. £29 Tektronixprobes. £12.50 HV Stablished PSU.stabiliser may be series or parallel. I 7Kv.7A, 14A. C95 Aircraft Radio Test Set. £35.Densitometer. £35 Ignition Analyser. C39.Blue Steel Missile Electronic section. andothers, (collectorsmuseums) 5 for £50Vacuum pump assembly. £125Stereoscopic, binocular, prismaticmicroscope. £195 Precision C 8 R boxes.Precision Capacitance Bridge. E49 PSU svarious. Linear audio sweep generator. withvariety of facilities, £69 Advance 50Kc sGenerator. sinecsquare. £35 Wayne -KerrSource 8 Detector for RF Bridges. £69 ea20A steel cased variable resistance. £40Micro -spot Welding Head. C59 KentChromalog Recorder Marconi Frequencymeter/counter timer. E75 pH electrodes.Specific -Ion Electrode. Fluorine. £20Laboratory Hydrometers ES ea. variousPye Gas Pressure and Flow Controller. E45Portable Oxygen Cylinder (6 oxygen) withcontrol valve. £35 Modulation meter (FMAM). E69. etc etc 040-376236

TEST EQUIPMENT FOR SALE. 3pallets, as one lot, including Tektronix:7633 scope. 4 graphic display units.8002 development system + ICE for Z80and 8085 incl. 4024 terminal incl. SWdiscs + doc, 611 storage screen. C12camera, 6046 cliff. probe HP 140A scope+ 3 plug -ins, Prowest PMA7 22" PAL/RGB colour monitor. Philips LDK 65telecine periscope + electr. SMS 3000dev. system for 8 x 300 micro controller,Zilog Z80 development system.complete Bryants A3 X -Y recorder.Culton 147 L -R -C bridge, narda highdirectivity -10 db couplers, etc... etc.

Viewing at Peaks Store House, 135Ditton Walk, Cambridge. Any time9-1600 hours weekdays.

DISH AE Radar dishes 32 ilia 5 deep new.06 50 RX AD94 24v DC PR 2. L W and 4 SW2 18 5Mc,s with arc E85 VEHICLE NAV TS bySperry see list £95 RAPID DISCHARGE CAPS2150 2 5Ky Pk ex photo tlauti £14.50 Wraps etcavailable MONOC SIGHTS 5. 27 5 £750VARIACS 240v at 8 amps £36 REC PAPER pressink Inci teed 8 wide Gould £6.50 BIRD METERSspares for thro liner 30Ua new E12 50 AUDIOTAPE 1 14" die new El 4 50 BLOWERS med size',Ingle ended 115v new E14 50 CAPS 270001250v £4 50 33 0000 60v 2 to E6 50 ROT INV18v DC ids 230v 180w Serfs GP £45 CT471 ELECinultmeters with RF probes £75 RX AE PREAMPS 162/174 MOs 4 0/Ps 12/24v DC £16 50PHILLIPS PM5508 TV Pall Gen £85 COAX TESTA CONNEC LEADS see list MULTI TRACK FMRECORDER WITH H.Elks £165 Prices are,nelusive List 39 available on request

A H Supplies. 122 Handsworth Road.Sheffield S9 4AE Tel 107421444278

381

BUYING OR SELLING TEST

EQUIPMENT OR COMPUTERSFor our free monthly cataloguecontaining an up-to-date list

equipment write to or phone:David Maxfield on 048 641 3000

Albury House. Albury= = - = 7= Guildford GU5 9BP

395

SPECTRUM ANALYSERS - H/P 140S/8552B/8553B 1KHz-110MHz - £2,500:8553B RF - £995, 182T/8558B0.1-1.500MHz - £4,950, Singer SSB-50-20Hz-40MHz (160MHz with external sig-gen). Single sideband analyser - 10Hzresolution £1,175, Marconi G.C.H.0Surveillance Receiver - Superb specs -10KHz-30MHz, fully synthesised, 1Hzresolution - Type 2540 - £1,495.Matching HF Drive Unit. Type 1540 -synthesised. all modes £850.Microwave power meter (10MHz-12GHz 1uW-10mW - £495. BWOTube for H/P 8551B spectrum analyser -£395 (tested 50mW co) EddystonePanoramic Adaptor 1061 (new( 2395.All above equipment is in excellentcondition, with manuals. Tel: 01-8663300 3 Eastcote View. Pinner.Middlesex HAS 1 AT.* Stop Press: 2Kw FM BroadcastLinear (cancelled order) £4,500.

SILLY PRICED T.T.L.OWING TO DISCONTINUED

PRODUCTION WE HAVE ON OFFER300 74LS123 60 74LS1384,000 74LS165 80 74LSOO100 74LS163 1,500 5 Volt Reg+50 74LS74 3,500 74LSO515 NT28 3,100 74LS365100 74LSO4

PRICE GUIDE! HALF OF YOURLOWEST NEW PRICE

WILL SELL SEPARATELY

PHONE: 0276 29219 (SHOP)Comp Shop Hi -Tech.

311 London Road, Camberley.Surrey GU15 3HE 403

FOR SALE. 2 Boards and 18MB HardDisk Drive for Olivetti M40 ringGraham Ledger 01-647 4747. 385

HONEYWELL VIP 7700RTERMINALS, used, reconditionedwith manual £125 each. Tel: Gary 0268419523 or Phil 04024 45676. 399

BOX NosBox number replies

should be addressed to:

Box Noc/o Electronics &Wireless World

Quadrant House.The Quadrant,

Sutton,Surrey SM2 5AS


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SURPLUS COITT soma III WORD PROCESSING SYSTEM.Professional system originally selling at around E6000without printer Now offered with software Included 8 avariety of different options available This system isavailable from us ALL BRAND NEW at the cost of currentbudget systems. but with offIca-quality performance 8featuresSOFTWARE INCLUDED'DATABASE - allows information storage 8 retrieval by

user -selectable criteria'EDITING - including easy reformatting, global search 8replace. save 8 move. cursor control etc

'AUTOMATIC LETTERWRITING - with merge, glossaryfife for much used phrases etc

'MATHS FUNCTIONS - screen maths allows addition ofrows. columns 8 complete tables

'PROGRAMMABLE COMMANDS - allows formatchanges, accessing record block files, prompts etc

'HELP FILES - quicker to use than the comprehensivemanual supplied

'BASIC COMPILER.

HARDWARE INCLUDED'SCREEN/WORKSTATION - dual processor 116 bitTI 9995 8 Z80hll with 128K memory. 12" green screen25 x 80 character display with slow scrolling. OUMEprinter interface

'KEYBOARD - lowprofile keyboard additionally has 43clearly marked dedicated function keys

'DISC DRIVES - dual SHUGART 5.4- °SDI) driveseach 4.30K capacity formatted

C295.00OPTIONS tOmbyte MiniScribe WINCHESTER disc drive ((195).'NEC Model 3500 35cps daisy wheel printer (E295).'NEC Model 7700 55cps daisy wheel printer 1E3951. 128K additional memory with spelling check software

1E40)

'Communicationshardwaresoftware 1E951

"COLOUR LEAFLETAVAILABLE

2kt.Y9= 7M61

(m

MPtJTER HARDWAREHITACHI Model 3058 r Wee drives. With SHUGARTcompatible interlace 134 way edge connector) 8 suitablefor 88C with DFS. AMSTRAD 664/6128, TATUNGEINSTEIN 8 many others 250K (double densityunformatted) per side reversible, 40 track, standard powerconnector for 12V 8 5V, overall power consumptionIYOKally 3.7W Supplied BRAND NEW with connector w-ool details etc but uncased. Data cables only are availablefor AMSTRAD 8 BBC 1E7 50) and TATUNG 1£10001

1:29.95

HITACHI Model 3050 double sided 3' Mee drives.As above. but double sided 1500KB unformattedaccessible without turning disc over) Not suitable forAMSTRAD 664/6128*Over 2000 Model 305 drives already sold by us

039.95

-I

MATMOS PC. Available without disc drrves only 64KBZ80A based keyboard sized machine with RGB.composite video outputs 8 UHF modulator Serial, parallel,cassette 8 peripheral bus interlaces are provided, togetherwith a ROM port MICROSOFT BASIC is in ROM. Officequality machine originally sold at £350 by its big -namemanufacturer. BRAND NEW.'Over 1000 already sold by us 049.00

MATMOS TERMINAL. MATMOS PC as above but withadditional plug-in menu driven terminal emulation ROMoftenng RS -232 communications up to 9600 Baud (ROMis available separately at E20

059.00

s.1."pt.""

arms & COMPUTER APPRECIATION

TOSHIBA Model T300 ISM compatible PC system.With 6mHz 8088 processor 256KB RAM. single hat+height 5'! floppy disc drive (640KB), high resolutiongreen display, serial 8 parallel interfaces Included are MS-DOS Ver 2. MICROSOFT T -BASIC 8 comprehensivediagnostic disc Available options include a high resolutioncolour monitor, graphics cards etcBRAND NEW 0325.00

AS ABOVE but with dual floppy disc drives.0396.00

TOSHIBA Model 7100 CP/M Briton. With 64KBRAM, dual 500K 5'. floppy disc drives, serial & parallelinterfaces 8 high resolution green display.BRAND NEW. C199.00

DEC POP 11/73 system. With I MB RAM. twin 20MBWINCHESTER disc drives, single 8" floppy disc dnvesDLV1 1-J quad serial interface

C4600.00

DEC PDP 11/23 system. With 256KB RAM. single20MB WINCHESTER disc drive, single 8' floppy disc drive8 XENIX operating system

01800.00ITT Model 3500 FACSIMILE machine. Very compactGroup II machine allows document transmission 8 receptionover phone line. EX DEMO

cass.00-"N

Please note'VAT 8 CARRIAGE must be added to all items Carriage isf3 00 VAT for 3" disc drives. and f 10.00 + VAT for mostother items'SAE please, for further details of any item and completestock list

MATMOS Ltd., 1 Church Street,Cuckfleld, W. Sussex RH17 5JZ.(0444) 414484/454377COMPUTER APPRECIATION, 111Northgate, Canterbury, Kent CT1 1BH.(0227) 470512. TELEX 966134 COMPAP

1.NTI-11 25 ON HF:1'1.1. CARD

INDEX TO ADVERTISERSAppointments Vacant Advertisements appear on pages 459-463

PAGEAdcola Products Ltd 357Aden Moore Ltd 380Advertising Standards Author 457Airlink Transformers Ltd 388Anritsu Europe Ltd 358Bamber B Electronics 392Brigden Technology 383Carston Electronics Ltd ....367,432Caracal Power Products 380Channel Micro Products Ltd 388Chase Electronics Ltd 362Cirkit Holdings PLC 366Clark Masts Ltd 356Colomor Electronics Ltd 432Computer Appreciation 464Conquin Software 401Crotech Instruments 440Crouzet Ltd 379Cybernetic Applications 405Data Acquisition Ltd 358Dataman Design 393Dipl-ing Franz Braunschmid 433Display Electronics 452/453

PAGEElectronic Brokers

Ltd. .354 Advert Card Back CoverEMS Manufacturing Ltd 401Engineering Solutions 375,433Essex Electronic Centre 366EWW Edit Feat. List 457EWW Wall Chart 400Farnell Instruments

Inside Front CoverField Electric 379Fieldtech Heathrow 365Fluke (GB) Ltd Advert CardGatehouse Audio 384Global Specialist Corporation 402GNC Electronics 389Golten & Verwer Partners 362Hameg Oscilloscopes 389Happy Memories 432Harrison Electronics 402Hart Electronic Kits 438Henry's/Audio Electronics 383Henson Ltd (R) 438Hilomast 392

PAGEIan P Kinlock 380Ines Gmbh 376JDR Sheetmetal 366Johns Radio 433Kestrel Electronic 384Langrex Supplies 436Level Electronics 380Lloyd Research Ltd 432Marlow Marketing 366M&B Radio (Leeds) 401McKnight Crystal Co 414Micro Concept 362,402Microkit Ltd 414Micromake Ltd 383Microprocessor Engineering 384Monolith Electronics Co 376Moordene Assoc 433Number One Systems 388Olsen Electronics 392Pineapple Software 406P M Components Ltd 448,449Raedek Electronics 406

PAGERalfe Electronics 376Semicon Indexes Ltd 432Sherwood Data Systems 438Stewart of Reading 414Structured Software 365Surrey Electronics 402Sowter E.A. 388Target Electronics 438Taylor Bros (Oldham) 356Technomatic Ltd 426/427Telonic Instruments

Ltd Inside Back CoverThandar Electronics 375,405Thanet Electronics Ltd 389Those Engineers Ltd 365,457Thurlby Electronics 440Triangle Digital

Services 379Valradio Power 392Webster Electronics 362West Hyde Development 432Willesden Transformers 457Withers Communication (R) 384

OVERSEAS ADVERTISEMENT AGENTSFrance and Belgium: Pierre Mussard. 18-20 Place de la Madeleine. Paris 75008.United States of America: Jay Feinman, Business Press International Ltd, 205 East 42nd Street, New York, NY 10017 - Telephone (212) 867 2080- Telex 23827.

Printed in Great Britain by E.T. Heron (Print) Ltd, Crittall Factory, Braintree Road. Witham, Essex CMS 3Q0, and typeset by Graphac Typesetting, Imperial House, 108The Broadway, WimbledonSW19, for the proprietors, Reed Business Publishing Ltd, Quadrant House. The Quadrant, Sutton, Surrey SM2 5AS. © Reed Business Publishing Ltd 1987. Electronics and WirelessWorld can beobtained from the following: AUSTRALIA and NEW ZEALAND; Gordon & Gotch Ltd. INDIA: A. H. Wheeler & Co. CANADA: The Wm, Dawson Subscription Service Ltd., Gordon & Gotch Ltd.SOUTH AFRICA: Central News Agency Ltd; William Dawson & Sons (S.A. i Ltd. UNITED STATES: Eastern News Distribution Inc., 14th Floor, III Eighth Avenue, New York, N.Y. 10011.


Simply Superior.Meet COM 7000.

Technologically superior oscilloscopemeasuring systems from Kikusui.

With all the wavefo'm measurement dataright where you need it.

Right where you're looking - on the C.R. T.

Screen text display of sensitivity settings,timebase speeds, delay times, plus voltageand frequency read out

Teloric Instruments Ltd., Boyn Valley Road,

Maidenhead. Eerks SL6 4EG

Tel (0628) 739:.3Telex: 849131.

With band w dths of 60, 100 or 200 MHz.

built-in digital storage and G.PI.B. capability,

depending on model.Simply superior oscilloscopes you have

to see.Ask for data or demonstration.

OSCILLOSCOPE MEASURING SYSTEMS

KIKUSUI

2955 Radio CommunicationsTest Set £5,750

II test functions, including full duplex radio test Revolutionary design: fast and easy to use High clarity CRT shows all settings plus

measurements in digital or analog forms Tones encode/decode facilities 38 instrument settings in non-volatile memory Spin -wheel frequency/level control in addition to

front panel buttons Single and two -port operation.

2305 Modulation Meter 500kHzto 2GHz £5,418 smut/. to 2GHz frequency range Outstanding 0.5% basic accuracy Exceptionally fast autotuning, with low noiseIII Modulation analysis including frequency and power Non-volatile memory to store user settings Excellent stereo separation Automatic self -calibration. advanced diagnostics.

2382/80 Spectrum Analyser £13,470and Display £5,480 Audio to UHF coverages: I(5)Hz--l(N)MHz Outstanding resolution, with 3tiz minimum

resolution filter bandwidth 0.025dB amplitude resolution Superb les-el accuracy ± Id11, with auto calibration Frequency response better than ± Fully GPM programmable capabilityIN Two steerable markers tOr levels and frequenciesIN Self calibration for I, peatability of measurements.

6960 Option 001 Digital RFPower Meter £1,900 Simple push-button or systems application Unparalleled accuracy through sensor correctionIN Non-volatile storage of frequently -used settings W or dB readings, plus offset capability Single -key auto -zero operationII Average factor selection to reduce noise or improve

resolution, advanced GPM facilities.

2022 AML/FM Signal Generator10kHz to 1GHz £2,950

Wide frequency cover: 10kflz to 1000MHz Compact, rugged and lightweight Comprehensive modulation: AM/FM/PhMIN Simple push-button operation, large LCD display Non-volatile memory for I(S) settingsMI The perfect MT\

2440 Microwave Counter 20GHz£3,650 Wide frequency coverage: 10Hz to 2(Xillz High sensitivity and resolution Fast acquisition time: only 200ms typical High -stability ovencontrolled crystal oscillator OVerload capability up to 27dBm High AM/FM tolerance Built-in GPIB. ENTER 3 ON REPLY CARD

throughELECTRONICBROKERS

Electronic Brokers are nowdistributors for a full range of MarconiTest Instruments including SignalGenerators, Microwave Counters.Rover Meters, Modulation Meters,

Spectrum Analysers, Radio Communication lest Sets and othergeneral test and measuring equipment. For further informationand a colour brochure please contact our Sales Office.

The first name in test equipment distributioni 11 U H c- Electronic Brokers 140-146 Camden Street, London, NWI 9PBo u

Fax: 01-2677363 Telex: 298694 Tel: 01-267 7070Electronic Brokers 0 All prices exclusive of VAT Prices corms t at tonic ot going to press I Is tints coi slalom available on rivit

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