THE PRACTICAL MAGAZINE WITH THE PROFESSIONAL APPROACHJuly/August 1988

Chrominance-locked clockgeneratorMicroprocessor -controlledradio synthesizerGaAs FET converter for 23 cm ATVTransmission & reception of RTTY

UK £3.00 IR £4.40 (incl. VAT)

60 -PAGE SUPPLEMENT OF CONSTRUCTION PROJECTS

\4 It I ".

A Irl

9 770268 451012

EE

July August 1988

PRINTERSBBC Micro Computer SystemBBC MASTER SERIES:AMB15 BBC MASTER 128K E356ADC06 Turbo (65C102) Card E95ADC08 512 Processor £185ADF14 Rom Cartridge £13ADF10 Econet Card £40ADJ22 Ref. Manual I £14ADJ23 Ref. Manual Pan II E14ADJ24 Adv Ref Manual £18BBC ARCHIMEDESPlease enquire about 300 & 400 serieshardware and software.

UPGRADE KITS:1.2 OS ROM £15EiNFS ROM £19BASIC II ROM (BBC B) _ _ _ £22.50AOFS ROM £261770 DES Kit £43.50Econet Kit IB&B +1 E55

(a)

Ib)(dl(dl(c)

Icl

(dl

(dl(di(dlIdl

ACORN ADD-ON PRODUCTS:Torch ZEP 100 E229 fa)512 2nd Processor £249 (b)IEEE Interface £265 (b)Teletext Adapter £95 lb)32016 Co Proc E949 lalX25 Gateway £2.175 (a)Ask for flail detalls on our furl range of software

WORD PROCESSOR ROMs:VIEW 2.1 . £35 Id) VIEW 3.0 £48 (c)Spellmaster. E49 (d) VIEW INDEX £12 (dlWORDWISE £24 (dl WORDWISE a £38 (dl

SPELLCHECKWYSIWIG= E21 (d) £31 (dlINTERWORD E46 Id) EDWORD II £43 (a)LANGUAGE ROMS:Micro Prolog E62 (c) Microtext £52 (c)ISO PASCAL £51 (al LOGOTRON E55.(c)LOGO....£46 MACROM E33 (d)USP ... £39 1, COMAL £43 (dl

Oxford Pascal £36 (c1

COMMUNICATIONS ROMS:TERMULATORMASTER TERMULATORCOMMSTAR IIMODEM MASTERCOMMAND

E25 (dl£34.75 (dl

£28£11 (dlE34 (d)

UTILITY ROMs:DOTPRINT PLUS for FX/FIX compatiblesDOTPRINT DUAL for MX rangeAcorn Graphics Extension Rom ... E28 (dlMerlin with 57 disc utilty commands100 page manual £37.50 (t)

MULTIFORM Z80 2nd Processor for the BBCThis unique 280 2nd Processor running OSIM will allow use of almost any standard CPiM soft-ware on the BBC micro. It is supplied with a number of different CPIA formats and includes atriAty to configure it to read other formats. This is particularly useful in environments where com-puters with different CP/M formats are used and the data ca -,not eas'1,- exchanged betweenthem. Mains powered includes Pocket Wordstar & MS ::05 = - £249 (b)MSAIOS Read/Write thin £49 fcl

META Version 3 ASSEMBLERAssembles 17 of the popular processors. Over 70K tong program on two routs and a disc andproVides complete Editing and Assembly facilities. It uses appropriate mnemonics for differentprocessors. Fully nestable macros. nestable conditional assembly IlF,ELSEENCOR. modularsource code. true local and global labels. 32 bit labels and arithmetic. 30 ways to send oti,ectcode and 50 directives.A ez werfi...i editor with many features. Send for deteed. leaflet. £145 1131

BBC DISC DRIVES5.25" Single Drive:I 400K 40:80T DS: TS400 £90 (b) PS400 with psu £104 RN5.25" Dual Drive:2 . 400K 401807 DS: TD800 ....E170 lal PD800 with psu E190 (a)2 . 400K 40)807 DS with psu and c_ :t in monitor stand PE1800P E209 )al3.5" Drives:1 . 400K 1307 OS TS35 1 £67 lb) PS35 1 with psu £85 IN1 e 400K 80T DS with PR/ TD35 2 E126 (b) PD35 2 with psu £149 Ibl

Combo drives (5.25" & 3.5"):P0853 with integral PSU. E165 as P0853? integral PSU £179 (al

3M FLOPPY DISCSIndustry standard floppy discs with a life time guarantee. Discs in packs of 10:

51/4 DISCS 3% DISCS401 SS DD £8.00 Id) 40T DS DD. £9.75 (dl 80T SS DD £13.50 (dl80T SS DDE12.00 (d) 80T DS DD. £12.75 (dl 80T DS DO £15.00 (d)

DISC ACCESSORIESSingle Disc Cable £6 (d) Dual Disc Cable £8.50 (dl10 Disc Library Case £1.80 (Cl 30 Dis- Storage Box E6 (ci40 Disc Lockable Box E8.50 (c) 100 D E- Lockable Box .. E13 (c)Roppidene Drivehead Cearinl Kit with 20 disnosab!e --: kits 5'ii" £14.50 ; £16 (dl

BT APPROVED MODEMSMIRACLE TECHNOLOGY WS Range

WS4000 V21/23.(Hayes Compatible,. InteEgent. Auto DishAuto Answer) £129 Ib)WS3000 V21/23 ProfessionalAs WS4000 and with BELL standards andbattery back up for memory £244 lb)WS3000 V22 ProfessionalAs WS3000 V21123 but with 1200 baud funduplex £395 (a)

WS3000 V22 bis ProfessionalAs V22 and 2400 baud full duplex £509 INWS3000/138C Data Lead E10 (dlWS2000 V21A/23Manual Modern £92 lb)WS 2000 Auto Dial Card E27 (dlINS 2000 Auto Answer £27 (d)%VS 2000 SK1 Kit £5 (dlWS 2000 User Port Lead E5 (dl(Offer Embed to current stooks,

SPECIAL OFFEREPROIVIs/RAMS

2764-2527256275126264LP-1527128-25 (12.5 Vpp)27128-25 (21.0 Vpp)

Priceson

appli-cation

PROJECTS:Junior Computer Kit £86 (b)Housekeeper kit £58 (b)Elekterminal Kit (1980) £50 (b)ASCII Keyboard kit £75 (b)J C Books 1, 2, 3, & 4E6.90 lc) eaUniversal Terminal (6502) Kit £75 (b)Elekterminal Kit (1983) . £70 (b)

EPSONLX1300FX800FX1000EX800EX1000GO 3500 (laser)1050010850 (80 toll

£179 - TAXAN KP815 180 col) E179 (a)£309 KP915 (156 coil £350 (al£419 BROTHER HR20 E349 (al£395 tai STAR LC10 £185 (a)£539 (al JUKI 6100 (Daisy Wheel) _ £295 (al

£1.290 INTEGREX (Colour) £519 lal£299 (a) NAT PANASONIC KX P 1081. £149 (a)£419 ta) NAT PANASONIC KX P 3131. £249 (a)

L01050 (136 col) £529 (a) NAT PANASONIC KX P1082 . £175 (a)We hold in stock a large variety of priwer attachments, interfaces and consumattWgease r5 -rite or !Anna fa, datogs-

ACCESSORIESBUFFALO 32K Buffer for Epson printers E75 (d); FX80 plus sheet feeder £129 Ib):EPSON Serial Interface: 8143 £30 (be 8148 with 2K buffer £65 lb).EPSON Paper Roll Holder £17 Me FX130S0e /85 Tractor Attach E37 Ib); RX/FX130Oust Cover £4.50 (dl; LX80 Tractor Unit £20 1cl:10800 Tractor Feed £47 (b).EPSON Ribbons: MkRX,FX80 E5; MXAIX.FX100 £10 tcli; LX80 £4.50 (dl:JUKI: Serial Interface £65 (dl Tractor Attach. E149 (a): Sheet Feeder £219 (al;Ribbon £2.50 lel; Spare Daisy Wheel E14 (di.BROTHER HF120: Sheet Feed £229; Ribbons - Carbon or Nylon £3; Tractor FeedElle (a); 2000 Sheets Fanfold with extra fine part. 9.5" - £13.50; 15" £17.50 lb).BBC Parallel Lead £6; Serial Le2.7 E6 (dl; IBM Parallel Lead (2m) E12

MONITORSMICROVITEC 14" RGB1431 Standard Resolution . £179 la)1451 Medium Resolution £225 (al1441 Hi Res £359 lalMICROVITEC 14" RGBIPAL & Audio1431 AP Standard Resolution £199 la)1451 AP Medium Resolution E255 (alMICROVITEC 20" RG8/PAUAurfro2030 CS std Res £380 (el2040 CS tit Res £675 (a)kfrtsubisM 14" ROB Med Res, (88C1111M)

E219 lel

TAXAN Supervision 620 £269 lalTAXAN Supervision 625 _ _ _ E319 (a)TAXAN Supervision 770

(with swivel stand) £499 (al

12" MONOCHROME MONITORS:PHILIPS:

7502 Green Screen f 69 (al7522 Amber Screen £ 75 (a)7552 E 85 la)

Al Phips Monitors supplied withswivel stand

BOOKS

LANGUAGES:

No VAT on books; Carriage (c)View 3.0 User GuideViewstore

6502 Assy Lang Prog _ £19.958086 Book E23.95Acorn BCPL User Guide . 15.00Acorn FORTH £7.50Acorn LISP E7.50Acorn ISO Pascal Ref Manual E10.00Intro to COMAL £10.00Intro to LOGO E7.50Micro Prolog Ref Manual . £10.00biteeluction to Turbo Pascal...£14.95Prog the Micro with Peeem £8.50The UNIX Book £7.50Unix User Guide E19.95Understanding Unix £18.45BBC MICRO GUIDE BOOKSBBC -User Guide Acorn . £15.00BBC Plus User Guide £15.00Drawing your Own BBC ProgramsE6.95Inside Information £8.95Math Rog in BBC Basic £7.95Toolbox 2 110.95VIA 6522 Book 4.50

PROGRAMMINGAJTIUTYAdvanced Sideways Ram UserGuide E9.95Advanced User Guide (BBC} ...E12.50Applied Ass :Lang on the SEC E9.95BBC Micro Sideways ROM's RAM'sE9.95Guide to the BBC ROM £9.95Beginners Lie to W.P E7.95

£9.00£9.00

Viewsheet £9.00Worclense Plus £9.95

SOUND & GRAPHICS:MastieMe Music E6.95

DISC DRIVE SYSTEMS:Advanced Disc User Guide _ ...£14.95Disc Book £3.50Disc Programming Tech -ewes £7.95Disc Systems £6.95Fee Handling on the BBC E6.95

APPLICATIONS:interfacing Proj for BBC £6.95BBC and Small Business E5.75

PROFESSIONAL SOFTWAREWordstar made easy E16.95Introduction to Wordstar E17.95Wordstar Handbook E11.95dBase-II for the first time user £16.95Understanding dElase.H1 £2295Multiplan Made Easy £18.95Multenate Complete Guide _ E16.95ABC of LOTUS 123 E17.451-2-3 for Business E16.95Ada Tech in dBase 111111 £2295Mastering CP;M E17.95CP ft Bible E16.50Introducing CP,'M on BBC & ZI30 £9.95MSIPC DOS Prompt £10.95

PROGRAMMED ROMS FOR ELEKTORPROJECTS

503-N Jiv. Computer Monitor 516 Talking Dice 2716... . E 7.302708 £ 4.80 521 CharGen & Video Routine for2708 E 4.80 DOS Junior .. 2732 + 2716 £16.40

522 CharGen & video; Routine for ex-tended 'prior 2732 + 2.2716E24.00523 Char. Generator .. 2732 E 9.00524 Cluantisizer 2732 E 9.00525 Universal Term._ 2732 £ 9.00526 Wind Dr Ind 2716 E 7.30527 Elabyrinth 2716 E 7.30

I .

504 Disco Eights505 Chess Intelekt . 2 x 2716 E14.60506 J C Tape Monitor . 2716 £ 7.3050744 J C Printer Mon & PME

2716 £ 7.30508 _I C Bus Control 82S23 E 4.80510 150 MHz Free Meter 2;82523

E 9.60514 Den Room Computer 2716 f 7.30

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CONTENTSJuly/August 1988Volume 14Number 158

t

!%4, t_AL7f

-.-ir

New computer system enhancestextile productionp. 64

Editorial

13 Electrical safety

Supplement

Between pages 38 and 39: a miscellany ofconstruction projects from the gamut ofelectronics

Computers

50 PROJECT: I/O extension card for IBM PCsand compatibles - Part 2

General Interest

36 PROJECT: Real-time clock patch for DCF77on the Commodore 64

64 New computer system enhances textileproduction

Radio & Television

14 PROJECT: Chrominance-locked clockgenerator

18 PROJECT: Microprocessor -controlled radiosynthesizer - Part 1

25 PROJECT: Direct -conversion receiver for80 metres

39 PROJECT: Frequency read-out for short-wave receiver

45 PROJECT: GaAs FET converter for 23 cmamateur television

55 PROJECT: Reception and transmission ofradioteletype

62 REVIEW: The Black Jaguar BJ200 Mk2

Test & Measurement

30 REVIEW: Part 8 - Function generators (2)

InformationNews: 24-44; New literature: 28; Events: 38;People: 54; Readers' services: 67; Terms ofbusiness: 68

Guide lines

Buyers' guide: 66; Switchboard: 68; Classifiedadverts: 74; Index of advertisers: 74

110 extension card for IBM PCsand compatiblesp. 50

GaAs FET converter for 23 cm ATVp. 45

In our September issue: Microcontroller-driven power supply - Final part 64 K RAM for MSX Shielding computers with metal -coated glass Microphone/line active filter/driver Inductance meter Microprocessor -controlled radio synthesizer - Final part

Front coverA robotic arm is putthrough its paces beforetaking its place in one ofBritain's industrial researchestablishments. The hand,with almost as many jointsas a human hand, andclaimed to be just as ver-satile, is capable of grip-ping up to 5 kg (11 Ib).Southampton Universityhas been researchingrobotic hands for morethan 15 years, producinga number for medicaluses. Some of these arenot only natural in ap-pearance, but also havea sense of 'touch'.This particular arm, whichhas separate controls forthe shoulder, forearm,elbow and hand, hasbeen designed for usewith dangerous materialsin special industrial en-vironments. All the move-ments are made by aseries of powerful minia-ture electric motors. Tenmicrocomputers arehooked up between thearm and joystick, effec-tively forming the 'brain'. Itis said to be capable ofmoving in a 180 degreearc in one second and tohave a repeatable accu-racy of ±0.1 mm.

4 EEJuly August 1988

READ ALL ABOUT IT!IN THE SUMMER '88Cirkit CATALOGUE

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OSCILLOSCOPESTELEGUIPMENT 083 D.124 Trace 5094112. Crt,-',...SweepL Large Tuts with rnar_rd £350S.E. LABS SM1 1 1 CliW Tra._ 18L110 Scarf State.Portable AC or External DC operation8 x 10ern de-Play with Llama' £150

SLuPtX 4010A Dsaf Trace 106110 with Kansa- - , £150

TELECHRPMENT S54A Sauk. Trace 101.'11 1. SoldState with Ltarurd

- £90GOULD/ADVANCE 05255 Dual Tr.. 7 E!..4z withManual E225

SPECIAL OFFERSCOSSOR 01-CILOSCOPE CC -115,0. EL,:sr Trace351410. Delay Sweep -Dual State Portaak 8 x 10anDispLay WO Manual NOW ONLY E180 each

P'4. Root Protection Corer. Contarting 2 Prow=s& Wewing Hood El°SOLASTROM 0501E0503K m1400 Dial Beam15,0liz with Maly ONLY £85 eachAVO VALVE TESTER C7160 ame St*. 2211,,,,, ONLY

£25each 108P £7

DM DRIVE PSL1 240V Ilk6V 1.6A & 12V 1.5Aoatt

Site W125rten.1-175rnnt 0160run- Ce=nt Urt-usedarty £10 NAP £31

°WERT! KEYBOARD (as in LYNX MICRO; push tomake Cased ES each NAP £31SWITCHED MODE PSU 5V 40A: .12V . £30 each

fp&p E41

OTHER SWITCHED MODE RE° waTat*. Pease 6'Mist- EKS4 DRIVES 5% - DPubb 'led- Dc""I0ity. 801rack From £5DensMARCONI AF Pcnver Meter TE893A 2010.3-SKHz.20.AV-IOW. Wrth Mararal (p&p t71 only E35MARCONI RF Power Mater TEl DC --500MHz. 0.5 to 25 watts 50 ohm. wan Manua(p&p £71 only E45MARCONI ALLFLI Sit Gees TFICI669 10-170400

£250MARCONI ALLEM Sig Gat W995 range from E1S0FARRELL SPIESOUARE type LF1d2 I/0 1MHzC4448acl ES°ADVA110E SG529 AM 154,Khz-220M1b. EEO

MULTIMETERSAVO 8 CorrVete with Sattercs & leads born E45AVO B MN Complete with batteries & leads . E90AVO TEST SET No. 1 flASEtary vers'on of AVO 8)COMPiele with a3Ittf&S Leads & case . .... E55TEST LEADS writable for AVO !Abreact Red & Mackwith 2 crac-caps & 2 prods fp&p r-21 E5

AVO Wader 7 .. 04750te with Batteries_ Leads &carrying case £40AVO - 72 Pocket Munirnater no AC current raveWort bartenes & leads - . . . EIOANALOGUE POCKET MULTIMETERS Riaps & Tayloreic_ With Bacteria & I ands from E10

Labgear Ova/tate, Generator CM603808.Crt-shatch.grey xt-tre Mark raves. Man or battery- unused £18: used £12 !plc/ E31

LABGEAR CoSour Bar Generate KG1. 8 Tftt PattersIP&P £41 ONLY £40 each

NEW EQUIPMENT1,!, H4.31EG OSC i 'SCOPE 6:5, Cps! Trace 66-

Darr Sweep. C'rcc...ent Testa - 2 Probes E575HAMEG OSCRIrnof 203.6 Dual Tram 20LItiz-r.m. 5 2 P.,Dbe3 (3144'll.^

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AVO TRANMSTOR ANALYSER Mkt ICT4461Suitcase Style complete with Batte4S & Opt-ratZoorwrattions a0"/ E35 itxel ;P&P 4f.

ISOLATING TRANSFORMERS 240V INPUT740V Out 500VA £15 fp&o ES) 100VA E6 ic&D E3.24V Out 500VA £6 (pap £51 200VA E4 fp&c 441

S-ACK STAR FFECIUELY COUlfrcRS P&P -./Mae 100-100MHz E OuMeteor 600-6001.00 E128Meteor 1000IGliz £175

BLACK STAR JUPITER SCO FUNCTION GUAIRA-10R.Sire.Sztoserf 0.110 500Ktez P&P £4 E110SLACK STAR ORION. PAL TVARDEO COLOUR PAT -TERN GENERATOR E199

STEPPING MOTORSType 1. 200 Steps pa rev 4 Phase (5 wire) 12/24V.

Torque 25rn inch WM run on 5V withreduced torque

Type 2. 6112 Steps per rev. 3 Huse. 1224V lrellwork on 51.). _ E2 ea. 5 off . - .. E7.50Type 3. NORTH AMERICAN 4-. _i4S 24 Stepspa rev_ 4 wire 511 1 ii: .',7:5 0-250ran0-200 PFS £6 each

Type 4. 200 Steps c: 1. ' :: . .3 .. 'r TOSCO.*25 oz ire. EA each

Type 7. WARNER 24 Stipa ;sr r..:._ 3 ,'r.2-i- t6 wire).28V- HaMneg Torque 45 oz. ash. ES each

HUNG CHANG DLIM 7030 3% digrt_ Hand held 21ranges nolluding 10 Amp ACDC 0.1%. Corrx..00with battene & leads. P&P E4 . E39.50As above DLIM 6010.0.25% E33.50c.,,,,,,,, ca,.. To, above E3

oscaaos.cons PROBES Switched 1: 10P&P £3

Used sql6Prnant - wide 30 days guarantee_ Mareafs suppled if posseThieThis is a VERY SMALL SAMPLE OF STOCK. SAE, or Telephaw foe Lists. Please dial. avalataty before

orcerhg CARRIAGE vs ur..0. i16- VAT to Os aPted to Total of Goods & Cann,:Calm rattsii-zi 9 a 7 !7: E K : 7 !!:,- -7-, .-..' F. 7., rti, Thum

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8052 -BASIC MICROCONTROLLER-KITFEATURES INCLUDE

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.4 V.'olters Kluwer CompanyManaging Editor. Len SeymourPersonal Assistant: L. VousdenTechnical Editor. J BuitingAdvertisement executive:Pauline O'Rourke

Editorial offices:1 Harlequin AvenueBRENTFORD TW8 9EWEnglandTelephone: 01-847 2618 (Nationsor +44 1847 2618 (International)Advertising: 01.847 2619Telex: 917490 (elektr giFax: 01-847 2610European offices:Postbus 756190 AB BEEK IL)The NetherlandsTelephone: +31 4490 89444Telex: 56617 (elekt nllFax: +31 4490 70161Overseas editions:Publitron Publicacoes Tecnicas LtdaAv Ipiranga 1100, 9° andarCEP 01040 Sao Paulo - BrazilEditor: Juliano BarsaliElektor sariRoute Nationale; Le Seau; BP. 5359270 Bailleul - FranceEditors: D R S Meyer:G C P Raedersdorf

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Copyright r 1988 Elektuur B.V.

ABC

_July Augus

ELECTRICAL SAFETYIn Britain, as in most western countries, we have strict legal requirements toensure that mains -operated equipment is safe as regards electric shockand fire caused by undue rises in temperature. The relevant laws andregulations apply equally to proprietary and home constructed equipmentand installations.

Also, in Britain we have one of the safest domestic electricity supplies inthe world. Yet, an average of 40 people die each year in this country fromelectricity -related accidents, while a further 2,000 need hospital treat-ment. Although these figures compare well with those of most othercountries, they are not good.

It is probably because of the high degree of inherent safety and the rel-evant legal requirements that most of us take safety for granted and areno longer (at least consciously) aware of the risks of injury or death fromelectric shock or fire caused by electrical faults. Invariably, such faults areman-made.

To increase people's awareness, the Department of Trade and Industry andthe Electrical Installation Equipment Manufacturers' Association (EIEMA)have recently launched an Electrical Safety Awareness Campaign. One ofthe aims of this campaign is to persuade people to use Residual CurrentDevices (RCDs) to reduce the risk of injury or death.

Basically, an RCD is capable of detecting an electric current that flowsanywhere other than the circuit intended for it, and switches it off rapidlyso that it can prevent electrocution or an undue rise in temperature.

The Wiring Regulations of the Institution of Electrical Engineers already re-quire the use of RCDs within an installation where hazards are recognizablygreater than normal, such as electrical equipment used outdoors.

Since an RCD provides protection that supplements the basic measuresand offers a degree of safety against the inevitable wear and tear or anymisuse, abuse or degradation of the inbuilt safety of electrical installationsand equipment, it is to be hoped that people will start making far greateruse of it, particularly, but not only, with electrical musical instruments. AnRCD Information Bureau has been established that may be contacted bytelephoning the operator and asking for 'Freephone RCD Devices.

VEVSER cs THE airEAAE.Mi O DAL-IAA:Tee%

14 EEJuly/August 1988

CHROMINANCE-LOCKED CLOCKGENERATOR

/\.

4:

A remarkably simple solution is offered to a problem almost anyconstructor of a test card or callsign generator, logomat, graphicscard, or any other video equipment must have been faced withat some time: phase synchronicity between clock pulses in the

system and the chrominance subcarrier.A PLL circuit is described that enables deriving the TV line andfield frequency, and a number of other useful signals, from the

chrominance frequency, 4.433 MHz. A mystery unravelled!

In video equipment, the beneficial ef-fects of phase -locking the central clockoscillator to the chrominance subcarrierare mainly the elimination of annoyingdigital interference and colour cross -patterning. The improvement can benoticed in the well-known colour bar testchart, in which colour transitions be-come sharply defined rather than blur-red with bands of spurious lines and ran-domly moving coloured spots whilelonger lines are moving slowly anddiagonally or horizontally across thescreen.In professional video systems andstudios, complex equipment is availableto ensure that all TV synchronizationsignals have a fixed phase relationshipwith the chrominance frequency, as setforth in the relevant CCIR specifica-tions.

by J. C. Stekelenburg PE1FYZ

This article demonstrates how somethinking on the technical background ofthe PAL (Phase Alternation Line) andNTSC (National Television SystemCommittee) TV systems, and a com-parison between these in respect of poss-ible interference, leads up to simplecomputer -assisted arithmetic and, fi-nally, the design of a circuit that achievesthe above objective of providingchrominance-locked, standard clock fre-quencies for digital video generators.

Choice of the chrominancesubcarrier frequencyThe PAL TV system is based on double-sideband modulation of the picturecolour information onto a subcarrier of4.433 MHz. This system is basically

similar to that used for NTSC TV. The Y(luminance) signal is obtained by addingthe three primary colours, red (R), green(G) and blue (B), in proportion, as

Y=0.3R-E0.59G -F 0.11B

The degree of luminance of each in-dividual pixel determines its brilliance,black corresponding to minimum, andwhite to maximum luminance. For amonochrome TV set, the luminancesignal is sufficient for producing a pic-ture. A colour receiver, however, needsthe three primary colours for mixing togive each pixel on the screen the correctcolour. The colour receiver finds twomodulated signals, R-Y and B-Y ad-jacent to the 4.433 !vIHz subcarrier.From these, the R, G and B signals areobtained by means of a number of

EE 112July August 1988

simple operations involving subtractionand addition. The R-Y and B -Y signalsare quadrature-modulated on the 4.433MHz carrier, so that the instantaneousphase provides a measure for the colourof a pixel, and the amplitude for thecolour saturation. Since the colour sub -carrier is found within the luminanceband (0...5 MHz), its sidebands will be-come visible as a pattern of thin lines. Inthe NTSC TV system, this undesirableeffect is minimized by using a coloursubcarrier frequency that is an oddmultiple of the line frequency. This givesrise to a dot pattern which is far less con-spicuous and annoying than the line pat-tern that would be formed in the PALpicture (see Fig. 1).In the PAL system, the phase of themodulated R-Y signal is inverted forevery line in the picture. This causes twosidebands adjacent to the 4.433 MHz

1

Er* HNTSC

ine Pfrl

Me N..2

Ene H43

fire N4int IN*5

cne NPAL

V* N+1

foe H-1-2

ire N.3me N -i-4

H._Ine22 -2::,-", - . :

Fig. 1. Comparison between PAL andNTSC: luminance patterns caused bychrominance information.

subcarrier, at an offset corresponding tohalf the line frequency. When the sub -carrier frequency is chosen such that it isan odd -numbered multiple of half theline frequency, B-Y information willresult in a dot pattern, and R-Y infor-mation in a line pattern. To avoid this,the chrominance subcarrier frequency isan odd multiple of the line frequencydivided by four (quarter -offset). Time-averaging of the remaining interferenceon a raster -by -raster basis is furtherachieved by adding 25 Hz (raster fre-quency) to the colour subcarrier, so thatcross -interference between luminanceand chrominance is least noticed. Sum-marizing the above, the optimum fre-quency of the chrominance subcarier,far, becomes:

far = (15,625/4) 1135 +25= 4,433,618.75 Hz

corresponding to the line frequencymultiplied by 283.7516. The deriving ofthe line frequency from the chrominancefrequency would, therefore, requiredividing this by 283.7516. This is imposs-ible by electronic means, which only

Table 1.

1 REM chrominance-locked clock generator5 REM successive approximation of clock divisors10 K=4433618.7520 INPUT"Enter output frequency ",F30 H=K/F40 P4 -1/(H-1)

50 B=160 FOR X=1 TO 1000

70 Y=P*X

80 A=AB,S(Y-RND(Y,-1)/X

90 IF A>=B; NEXT X100 IF A

16 EEJuly/August 1988

Figure 3 shows the circuit diagram of thechrominance-locked clock generator,which is essentially a discrete phase -locked loop designed around commonlyavailable parts.The 4.433 MHz crystal oscillator is setup around gate Ns, whose output signalis fed to buffer Ni and counter ICI.This, together with bistable FF1, dividesthe chrominance frequency by 910 togive 4.8721085 kHz. IC3 counts 909periods of the clock signal, while FF1delays 1 period (approx. 226 ns) duringthe resetting of the counter, giving therequired divisor and allowing sufficienttime for IC3 to reset all internalbistables.The 4 MHz L -C oscillator is a varicap-controlled Colpitts type set up aroundTi, with T2 and Schmitt -trigger gate N4acting as a buffer to obtain a digitalcompatible output signal.Division by 810 in IC4 is achieved in amanner similar to that in IC3-FF1 asdiscussed.Gate network N2-Na-N--N3 forms thephase comparator, while R4 -C3 formsthe loop filter with a roll -off of 7.2 Hz.The natural frequency of the PLL is12.96 Hz, while the hold range is of theorder of 150 kHz.

Construction and setting upThe circuit is fairly uncritical in respectof construction, and is simple to buildon a small piece of Veroboard. Connec-tions in the 4 MI-lz and 4.433 MI-Izoscillators should be as short as possiblethough, and due attention should bepaid to decoupling of the positive supplyline.The only component that requiresfurther discussion here is Li. In theprototype, good results were obtainedwith a Neosid Type 7A0 inductor as-sembly. The required inductance ofabout 22 pH was achieved by winding 60turns of 0.2 mm dia. enamelled copperwire onto the former. Do not use ready-made 4.433 MHz inductors with a built-in parallel capacitor, since this is oftentoo large to ensure the relatively high L-C ratio required in this application. The4.433 MHz crystal was a type salvagedfrom a colour TV chassis.After building the circuit, it is rec-ommended to commence testing the 4MHz oscillator by temporarily breakingthe PLL control loop. Disconnect R4from pin 4 of N3. This enables checkingthe operation of the 4 MHz oscillatorwith the aid of an external tuningvoltage obtained from the wiper of a po-

3

B11

0,

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IC3 c.4040

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2

error phasecamp.

330090 - 13

2MHz1MHz

500kHz

250kHz

4MHz

4.43MHz

8.85MHz

Fig. 2. Block diagram of the chrominance-locked clock generator for video systems.

Parts list

Resistors (±5%):RI =10MR2= 120K1:13:117:R11;R12 = 10KRd:16=100KR5= 560KRa=12KRe = 1K0

Capacitors:Cr=100pC2=40p trimmerC3= 220nC4;C5;C9;C10;C1 3 =47pC6 =68pCz;Ca;Cit =100pC12= -1n0C14;C15=100n

Inductors:Li= winding details are given in the text.Neosid Type 7A0 (Neosid Limited IcknieldWay West LETCHWORTH SG6 4AS. Tele-phone: (0462) 481000. Telex: 826405. Con-tact Mr. E. Adcott). Neosid inductors are alsoavailable from C -I Electronics.

12 = 13pH with centre tap (see text).L3= 7pH with centre tap (see text).

Semiconductors:D . . .D11 inci. = 1N4148D12 =88105D13;014=AA119ICt =4093IC2=4001IC3;IC4 = 4040IC6=4013IC6=4516Ti;T2=8F199

Miscellaneous: = quartz crystal 4.433 MHz.

It is regretted that a printed -circuit board forthis project is not available.

EE 111July/August 1988

tentiometer connected between +12 Vand ground. To begin with, adjust Li sothat oscillation is achieved around 4MHz. Check that the oscillator can betuned with the potentiometer. The out-put of Ni should supply CMOS-compatible clock pulses. It is essentialthat these pulses have the full CMOSswing of about 12 Vpp when the oscil-lator is tuned around 4 MHz. Do notadd too much capacitance to the paralleltuned circuit when its resonance fre-quency is found to be too high: instead,ensure more inductance by increasing thenumber of turns on Li.Next, adjust trimmer capacitor C2 togive 4.43362 MHz at the buffered out-put. Measure the frequency at pin 2 ofN2 - this should be 4.8721085 kHz.Similarly, measure the frequency at pin Iof N2 to check the operation of IC4-FF2.Tune the oscillator to obtain about 4.8kHz here.When these tests check out, it is time toclose the loop by removing the poten-tiometer, and connecting R4 to the out-put of N3. Connect the frequency meterto the 4 MHz output. Some re-adjustment of Li may be required to getthe PLL to lock.The oscilloscope photographs of Fig. 4may be used as guidance if difficultiesare encountered in the setting up. Theupper two traces show the 4.8 kHzsignals at the inputs of the phase com-parator, i.e., pins 1 and 2 of N2 (or N6),the lower trace the phase comparatoroutput (pin 4 of N3). Although the lat-ter signal is different in the photographs,the PLL was locked in both conditions,with only Li set differently within thehold range of the oscillator. It is clearlyseen that the phase comparator is essen-tially an exclusive NOR function: theoutput goes low only when the two inputsignals are different.The operation of the PLL can be check-ed by carefully adjusting Li whilemonitoring the phase comparator out-put with an oscilloscope. It will be foundthat the PLL loses lock when the pulsesbecome significantly narrower thanthose in the lower trace of Fig. 4b. Whenthe PLL is locked, Li can be adjustedover a small span while the output fre-quency remains stable at 4.000002 MHz(7 -digit resolution).Finally, switch the power to the circuiton and off a few times to verify that thePLL starts and locks properly. All drifton the 4 MHz output is, of course, caus-ed by drift of the quartz crystal fre-quency. It is, therefore, recommended tomake the final adjustment of C2 and Liafter a warming -up period of about 10minutes.

Multiplier for TEA1002The circuit described is used by theauthor as part of a digital test chart andcall -sign generator for amateur tele-

4

a

Fig. 4. Oscillograms showing the operation of the XNOR phase comparator.

Fig. 5. Frequency multiplier circuit for driving the Type TEA1002 colour generator.

vision. The system incorporates aTEA1002 colour generator chip (Ref. (")which requires an input signal of 8.86MHz. The circuit of Fig. 5 multiplies thebuffered crystal oscillator output of thechrominance oscillator by two to obtainthis frequency. The multiplier is essen-tially a double -phase rectifier with aparallel -resonant L -C output filter.Suggested diode types are AA119 or0A95 (in any case, germanium typesshould be used). L2 and L3 are woundas 30 and 20 turns respectively of 0.2mm dia. enamelled copper wire,'with acentre tap. It is also possible to useready-made inductors provided they are

known to have a centre tap and the cor-rect inductance (use a grid -dipper tocheck the in -circuit resonance fre-quency). Both L2 and L3 are simplypeaked for maximum amplitude of the8.86 MHz output signal. Du

Reference:t" Video combiner. Elektor ElectronicsFebruary 1984, p. 2-36 ff.

For further reading:Principles of PAL Colour Television. H.V. Sims, London Iliffe Books Ltd. 1969.Phase -lock techniques. E M. Gardner,John Wiley & Sons Inc. 1966.

18 EEJu y Augu 988

MICROPROCESSOR -CONTROLLEDRADIO SYNTHESIZER 1

The addition of a microprocessor -controlled synthesizer to acontinuously -tuned receiver greatly improves tuning accuracyand provides several additional facilities that have become

available in recent years.The versatile synthesizer described has a 6 -digit LCD or LED

display and a 16 -position keyboard which allows direct frequencyentry, channel or frequency increment or decrement, as well asthe storing and recalling of 30 frequencies. The MW, SW and FM

band are covered each with a choice of IF offsets.

Most recently designed quality-, radiosemploy synthesized local oscillators con-trolled by a microprocessor. These com-plex designs should not discourage theadvanced home constructor, however, ascomponents are currently availablewhich enable similar facilities to beeither incorporated in individualdesigns, or added to existing radios.Synthesis of the local oscillator (LO) ina superheterodyne receiver providesmany advantages over the more tra-ditional mechanical tuning. The mainbenefits are improved tuning accuracy,stability and the possibility to store oftenused frequencies. Accuracy and stabilityresult from the fact that the local oscil-lator is phase -locked to a referencecrystal oscillator. Before synthesizersbecame available, crystals were used toobtain a good degree of accuracy. This

by P. Topping

has the disadvantage of requiring aseparate crystal for each frequency.Using a phase -locked loop (PLL) syn-thesizer, similar performance can beachieved at an unlimited number of fre-quencies from only one crystal. Ac-curate, drift -free, tuning is particularlyimportant for stand-by use of a receiverwhen nobody is on hand to provide finetuning.A synthesizer can be incorporated intoalmost any receiver simply by replacingthe tuning capacitor with a variablecapacitance diode (varicap) as shown inFig. 1. The voltage biasing this varicap issupplied by the synthesizer, which thustakes over the RF tuning. A simplersolution is to retain the RF function ofthe existing tuning control as a preselec-tor to avoid tracking problems in multi -band designs. The current trend is to

1

Display

Microprocessor

Controller

add varicap removecircuit I tuning capacitor

Keypad

Synthesize:

Pre cater.10

(IF REO D.)

On

Sutter

(IF REO D.)tOn

*see test

8S0120 -10

EXISTINGLOCALOSCILLATOR

Fig. 1. A local -oscillator synthesizer can easily replace mechanical tuning to provide crystal -controlled accuracy and many other improvements in performance and convenience.

eliminate front-end tuning altogether,and employ only a wideband filter be-tween the RF input and the first mixer.

Synthesizer MC145157The Type MC145157 CMOS synthesizerfrom Motorola is one of a series offeringa variety of options including serial orparallel interfacing, and single or dualmodulus prescaling. In the synthesizerdescribed here, only single modulus

MULTIBAND RFSYNTHESIZER

Features:

Coverage of MW, SW and VHF FMbands.

Variable step size in accordance withstation spacing.

II CMOS design allows battery back-upwhile minimizing power consumptionand RF interference.

11 switch -selected bands with a var-iety of IF offsets, including nought.

Power -down mode for display andprocessor.

Easy to operate keyboard. RIT (receiver incremental tuning)

control provided.MI Choice of three 6 -digit displays: 7 -

segment LED, static LCD ormultiplexed LCD.

Memory function for up to 30 often -used frequencies.

Last used frequency automaticallyrecalled at receiver power -on.

MI Simple to incorporate in almost anygeneral-purpose receiver.

Direct synthesis up to 16 MHz with-out prescalers.

Prescalers for up to 60 MHz and upto 150 MHz.

III IF offset can be customized toindivual requirement.

Fig. 2. The MC145157 synthesizer includes two 14 -bit shift registers, one each for the refer-ence divider (top) and the variable (LO) divider. Their loading is controlled by the value ofa trailing 15th bit. The outputs of these dividers are compared in respect of phase to controlthe frequency of the local oscillator.

3 +10y(RECEIVER)

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880120 -12

EE

July/August 1988prescaling is used. Serial interfacing waschosen to minimize the number of inter-connections between the synthesizer andthe microprocessor.The block diagram of the MC145157 isshown in Fig. 2. There are two 14 -bitlong counters, which are loaded by shiftregisters, starting with the most signifi-cant bit (MSB). After loading the 14databits, a 15th control bit is loaded,and the information is transferred to theselected latch using LE (latch enable). Ifthe control bit is a logic one, the refer-ence divider latch is loaded; if it is alogic zero, the variable (LO) divider latchis loaded.The reference counter divides the crystaloscillator down to the reference fre-quency (in this case 1 kHz), at which thecomparison is made with the (also div-ided down) local oscillator frequency.The error signal from the phase com-parator is filtered, and forms the tuningvoltage for the local oscillator. Thenumbers chosen as the divide ratiosdetermine the frequency at which thisoscillator stabilizes. The equation belowshows the relationship between thevarious frequencies, where P is the LOprescaler, N is the reference divider ratio,and Q is the LO divider ratio. The re-ceived frequency can be changed byaltering the LO divide ratio. The micro-processor takes care of the decimal tobinary conversion, IF offset, and theother required arithmetic.

fLo= RF IF = P(fxto/1V)Q

The practical application of theMC145157 is shown in the circuitdiagram of Fig. 3. The output signal ofthe synthesizer's 10 MHz crystal oscil-lator is divided down by 10,000 to obtainthe reference frequency at which thephase comparator operates. A com-promise is required when deciding onthis frequency. Filter design is relaxed bychoosing a high reference frequency, butthe disadvantage is that the minimumstep size of the synthesizer is determinedby the reference frequency, as thesmallest change which can be maderesults from a change of 1 on the LO div-ide ratio (see the above equation). A ref-erence of 1 kHz is a reasonable com-promise for most broadcast receivers.The MC145157 is specified to operate upto 20 MHz, so prescaling is required onFM (VHF) and SW. Shortwave banddivide -by -5 prescaling is used, and forFM divide -by -10. This increases theminimum step size to 10 kHz on FM,which is ideal for this band, and to5 kHz on SW, which is suitable for mostbroadcast receivers but too large forsome shortwave applications. Fortunate-ly, however, this can be alleviated by theuse of an RIT (receiver incremental tun-

Fig. 3. The synthesizer module contains the MC145157 phase -locked loop chip and its ing) control, formed by external poten-opamp-based active low-pass filter. It also includes a RIT control and a microprocessor reset tiometer PI. The low -IF (455, 468 andcircuit, which makes it possible to resend the last used frequency in stand-by applications. 470 kHz) SW bands do not use prescal-

20 EEJuly August 1988

Keyboard

7 8 9 UPSI 55 59 513

4 5 6 STORE

52 56 510 514

1 2 3 EXECS3 57 511 515

0 MODE CISTEP DCYrai54 58 512 516

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'lg. 4. Circuit diagram of the microprocessor -based controller and the keyboard.

ing, and thus have a step of 1 kHz, buta maximum frequency of just under 16MHz. (2'4-IF).

Complex multiple loops are used insome commercial designs to achieve bet-ter resolution, but this can also beachieved with the previously mentionedRIT control. With reference to Fig. 3,the adjustment is made by slightlychanging the synthesizer's reference fre-quency. This can be accomplished by re-placing the usual combination of a fixedand a trimming capacitor on the crystalpins of the MC145157 with varicapdiodes (Di -Di). Adjustment is thus by adirect voltage, taken from the wiper ofpotentiometer PI, which can be fittedremote from the synthesizer.This type of adjustment necessarily givesa control range which depends on thetuned frequency, but the relatively highIF ensures that this is not too significant.For instance, using an IF of 10.7 MHz,the circuit shown gives the requiredrange of ±2.5 kHz at the lower end ofthe SW band (1.6 MHz), and just overtwice this range at about 15 MHz. If anRIT control is not required, pins 1 and 2

should have a 47 pF capacitor and a 30pF trimmer to ground respectively, thetrimmer being adjusted to provide a ref-erence of 1 kHz. If a frequency meter isnot available, this adjustment can easilybe made by tuning into a strong broad-cast of known frequency, and adjustingfor optimum reception and symmetricoff -channel response.An important part of any phase -lockedloop is the loop (low-pass) filter. The ac-tive filter set up around opamp IC2 isdriven from the double -ended phasedetector output of the MC145157. Anactive filter has the advantage of increas-ing the available voltage swing beyondthe supply rail (5 V) of the synthesizerchip. The supply voltage on the activefilter determines the maximum voltageavailable to the varicap diodes in theRIT circuit - 10 V is suitable for theType KV1235 triple varicap from Toko.The 10 V supply is conveniently takenfrom the receiver which incorporates thesynthesizer.The combination of active filter anddouble -ended phase detector outputsmakes it simple to select the correct rela-tionship between voltage and LO fre-

quency. Usually, one side of the varicapdiode is grounded, so that increasing thereverse voltage on it increases the fre-quency of the local oscillator. In someoscillator designs, however, the fixed sidemay be taken to the supply rail, so thatincreasing the tuning voltage decreasesthe frequency. With the filter designshown, the choice can be made simplyby interchanging the connections to pins15 and 16 on the MC145157.Resistors R7... Rio incl. may need to beadjusted empirically to stabilize the loopand eliminate any trace of the referencefrequency from the output of the radio(remember that LO phase noise isdemodulated together with the wantedsignal).

Microprocessor and keyboardThe next module in the synthesizer is themicroprocessor circuit - see Fig. 4. Themicroprocessor used is the CMOS TypeMC146805E2 from Motorola, which of-fers powerful bit manipulation instruc-tions, useful for this type of application.It also has a stand-by (power -down)mode in which the clock is stopped. This

has the double advantage of savingpower in battery applications, andeliminating interference problems withthe radio. When a key is pressed, the mi-croprocessor 'wakes', performs the re-quired function, and then goes back intothe stand-by mode.The MC146805E2 has a multiplexed busfor data and low -order addresses. Thisarrangement saves pins but requires anexternal address latch, IC4, to interfacewith the system EPROM, IC5. This is aCMOS Type 27C64 so that the wholesystem consumes only a few milliwattswhen active, and a few microwatts instand-by. Although the control programin the EPROM could have been accom-modated in a 27C16 (2K x 8) with roomto spare, an 8 Kbyte EPROM was chosenbecause this is currently less expensiveand generally better obtainable; the2716, and its CMOS version, 27C16, isnow rapidly becoming obsolete.After performing the initializationroutine at power -on, or following areset. the microprocessor is programmedto switch lines PA4...PA7 of pore A tooutput, and PAO. ..PA3 to input. Theoutput lines are set logic low before theCPU is software -switched to the power-down state. Any subsequent action onone of the keys Si . S16 incl. drives theprocessor's interrupt request (IRQ) linelogic low, ending the power -down state.Instructions in the EPROM cause theCPU to start scanning the keyboard withthe aid of outputs PA4...PA7 and in-puts PAO. .. PA3, to determine which key

was pressed, execute the appropriatecommand or load the pressed numberon the keyboard, write serial data to thesynthesizer via PM, PB1 and PB2, andupdate the display read-out via PB3-PA7, PBO-PB2, or PB1-PB3-PA7 (theport lines used depend on the displaytype - this will be discussed later).The EPROM -resident control programis located in address ' range 1800H toIFFFu. This is the top of the CPU's ad-dress space (it can address 8 Kbyte ofmemory), and includes the reset and in-terrupt vectors. These vectors reside be-tween 1FF6H and 11-1-1-H with theprogram itself starting at 1800H. TheMC146805E2 microprocessor has a 112 -byte on -chip RAM area in page zero.The CPU bus is demultiplexed by octallatch IC4 using the address strobe (AS)pulse.The 5 V supply to the controller shouldnot be switched off if the stationmemories are to survive. The supplydoes not need to be regulated, and four1.5 V zinc -carbon or Ni-Cd batteries willdo. With the static LCD on, the currentdrawn in stand-by is about 50 pA, with-out it, less than 1 ?IA. Eight 100 kQ pull -down resistors on the multiplexed buslines of the CPU are used for ensuringminimum stand-by power dissipation.When the display is switched on, it willshow random data, but will be written towhen any key is pressed (use of the EX-Ecti-rE key restores the display to itsprevious data), or automatically by thereset circuit shown in Fie. 3.

EE 1111July/August 1988

Using the keyboardThe 16 -key keypad performs the follow-ing functions:

0-9 These keys are used for both directfrequency entry and recalling (or stor-ing) the ten frequencies available in eachband.UP Increment by one channel (5 KHzSW; 9 kHz MW; 50 kHz FM) or 1 kHz(10 kHz on FM, not applicable to 10.7MHz SW).DOWN Decrement by one channel (5KHz SW, 9 kHz MW, 50 kHz FM) or 1kHz (10 kHz on FM, not applicable to10.7 MHz SW).STORE Next key (0-9) stores currentfrequency at that key (indicated by adecimal point on the left -most digit).CLEAR Clear display (direct frequencyentry). Also toggles between channelsteps and 1 kHz steps (indicated by adecimal point on the second digit fromthe right).MODE Change between frequency andstation mode.EXECUTE Go to frequency, but stay incurrent mode.

The leftmost digit in the display in-dicates which mode is current: Display blank: direct frequency entry

mode; Number: last station stored or recall-

ed - station mode; Small square (LC display) or a single

lit horizontal centre segment (LED

5

Tsv

5

HEM107RT2...T7 = BC182 *see text

SIR 1.15157 P55 P82

*S22 R31

V

13

R32

0

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0

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DATA CLK

h

418

IC8 eMC14499P m

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LD1 L02

LI13 10 11

15

14 R408.2700

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L03.1=L

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L05

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841 13 124 DATACLA trt

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77

945*8.2700

TS

10 11

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IS (i)

883512_-15

Fig. 5. Six -digit multiplexed LED display.

121 EEJuly August 1988

6

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DINSEGMENT OUTPUTS

1C9

MC144115P

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24 13 12

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11

12. 41 10 11 35 34 16 17'36

15 16 17 18.19 2182 3 4 5 6SEGMENT OUTPUTS

IC10MC144115P

CLK Eli

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17 18 19

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22 4

24

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24 13 2 12

23 1

DIN

SKP

SEGMENT OUTPUTS

IC11MC144115P

CLK EN

Dotrr

OSC

24

T0 0 rt

13 2 12

00

TR53

23

Fig. 6. Static liquid crystal display for the synthesizer.

display): the current frequency has notbeen written into or recalled from mem-ory.

A choice of two modes permits theminimum number of keystrokesregardless of method of use. In thestation mode, previously memorizedstations can be recalled by pressing onlythe required key - there is no RECALLkey. Storing a frequency requires two keyactions, viz. STORE (indicated by adecimal point on the left -most digit) fol-lowed by the memory number.

If direct frequency entry is required,MODE is pressed followed by the fre-quency. There is now a choice: pressMODE again to jump to the new fre-quency, and return to the station mode.Alternatively, press EXECUTE to jump tothe selected frequency but stay in the fre-quency mode - new frequencies canthen be selected with only the EXECUTEkey required after each new frequencyentered. The store facility also works inthe frequency mode.

If it is desired to change back from fre-quency mode to station mode withoutretuning the radio, press STORE, thenMODE, and to display current frequencypress EXECUTE. In station mode, EX-ECUTE updates the synthesizer and thedisplay with the current frequency. Thiscan be used when the receiver is newlyswitched on to retune the frequencywhich was in use when it was switched

off, even if that frequency was notstored. Returning to the circuit diagramof Fig. 3, it is seen that this is achievedby Ti resetting the microprocessor whenthe radio is switched on - when the10 V supply rises, Ti momentarily pullsthe CPU's reset input low.

Bands and IF offsetsPort B lines P134...PB7 incl. are usedfor providing band selection infor-

mation to the CPU. These lines can betied to the appropriate logic level if onlyone band is required (one band can con-stitute all the bands which use the sameoscillator, but select frequency range byswitching inductors). If, however, morethan one oscillator has to be tuned, orthe step size has to be changed (e.g. be-tween MW and SW), the port lines canbe set to the appropriate logic level bymeans of a set of switches (as shown in

Table 1

Band PB 7(S18)

PB6(S19)

PBS(S20)

PB4(S21)

IF

offset(kHz)

Step(kHz)

Memory Use Prescaler

0 0 0 0 0 455 5/1 1 SW -1 0 0 0 1 468 5/1 1 SW -2 0 0 1 0 470 5/1 1 SW -3 0 0 1 1 10,700 5 1 SW ÷ 54 0 1 0 0 -10,700 50/10 2 FM ± 105 0 1 0 1 0 50/10 2 FM + 106 0 1 1 0 -70 50/10 2 FM ÷ 107 0 1 1 1 10,700 50/10 2 FM ÷ 108 1 0 0 0 455 9/1 3 MW -9 1 0 0 1 468 9/1 3 MW -

10 1 0 1 0 470 9/1 3 MW - 111 1 0 1 1 10.700 5 3 SW ÷5

Table 2

0000: 2E 01 80 CD 18 4D 24 23 5F B7 28 A6 27 B7 2D A60010:- OE B7 2E D6 18 71 B1 28 27 0A Al 77 27 OD 5C 5C0020: 5C 5C 20 EF 5C DD 18 71 CD IA E2 80 A6 FO B7 040030: A6 OF B7 05 3F 01 3F 00 3F 2F A6 27 B7 2D A6 OE0040: B7 2E CD 19 63 10 2F CD lA E2 8E 20 FD A6 F7 480050: 24 12 B7 00 2F F9 98 B6 00 AD 0C 2F 07 2E FE AD0060: 06 2E FA 99 3F 00 81 AE FF 21 FE 21 FE 5A 26 F90070: 81 EE CC 18 B1 DE CC 18 Bl DD CC 18 B1 DB CC 180080: Bl BE CC 18 B1 BD CC 18 B1 BB CC 18 Bl' 7E CC 180090: Bl 7D CC 18 B1 7B CC 18 B1 ED CC 19 91 D7 CC 1900A0: 3D E7 CC 19 12 EB CC 19 A2 B7 16 2F 81 77 CC 1900BO: 05 9F 44 44 00 2F IE 06 2F 1B P7 24 05 2F 05 150000: 2F CD IA C2 CD IA D9 BE 22 E6 01 F7 5C B3 23 2600D0: F8 B6 24 F7 81 97 B7 2E D6 lA CF B7 2D 9F 4C OF00E0: 01 04 AB 14 20 05 0D 01 02 AB 0A 48 97 07 2F OB00F0: B6 30 E7 30 B6 31 E7 31 17 2F 81 E6 30 B7 30 E60100: 31 B7 31 20 5E AD lA 3C 30 26 02 3C 31 5A 26 F70110: 20 51 AD OD 3D 30 26 02 3A 31 3A 30 5A 26 F5 200120: 42 AE 02 02 2F OD AD OC Al 03 27 07 AE 0A OF 010130: 02 AE 12 81 P6 01 A4 70 44 44 44 44 81 00 2F 230140: CD 19 B6 AE 10 BF 2B CD 1A 5B AD E8 Al 03 26 100150: AE 10 BF 2C CD lA 5B AE 05 E6 OF E7 10 5A 26 F90160: CD IA OB CD IA 91 AD CC Al 03 26 19 AE 10 BF 2P0170: BF 2C AE 16 CD IA 5B AE 16 BF 2B AE 10 CD IA 5B0180: AE 10 CD IA 5B CD 19 B6 AE 10 BF 2B 14 2F CC IA0190: 42 06 2F 02 AD A7 17 2F 01 2F 04 11 2F 20 06 1001A0: 2F 81 00 2F 05 -CD lA C2 20 09 02 2F 04 12 2F 2001B0: 02 13 2F 17 2F 81 CD 19 34 48 B7 22 48 BB 22 AB01C0: 05 B7 23 A6 06 B7 2A BE 23 D6 19 DB 3A 23 BE 2A01D0: E7 15 3A 2A 26 Fl AE 16 BF 2C 81 00 00 00 04 0501E0: 05 00 00 00 04 06 08 00 00 00 04 07 00 00 01 0001FO: 07 00 00 09 09 08 09 03 00 00 00 00 00 00 00 090200: 09 09 09 09 03 00 00 01 00 07 00 3F 30 3F 31 5F0210: B6 30 48 B7 22 39 31 B6 31 P7 23 B6 22 48 39 310220: 48 39 31 BB 22 B7 30 P6 31 B9 23 P7 31 5C E6 100230: BB 30 P7 30 4F P9 31 B7 31 A3 05 26 D3 38 30 390240: 31 81 BF 26 BE 2C A6 06 B7 24 A6 09 E0 05 E7 050250: 5A 3A 2A 26 F5 3F 29 3C 29 20 04 3F 29 BF 26 A60260: 06 B7 2A BE 2B BF 24 BE 2C BF 25 BE 24 E6 05 3A0270: 24 BE 25 EB 05 3A 25 BB 29 3F 29 AD OF BE 26 E70280: 05 3A 26 3A 2A 26 E4 81 AO 0A 3C 29 Al 0A 24 F80290: 81 B6 31 B7 23 B6 30 B7 22 AE 1C BF 2B AD 25 3C02A0: 21 AD 1F A6 OE B7 27 34 23 36 22 34 23 36 2402B0: 06 AE 10 BF 2C AD A4 AE 1C BF 2C AD 9E 3A 27 2602C0: EA 81 AE 10 A6 06 B7 2A 7F 5C 3A 2A 26 FA 81 EB02D0: 60 C7 E5 6C AD AF EO EF ED A6 10 B7 22 AB 05 B702E0: 23 81 AD F5 AE 1C AD DC BE 22 5A 5C B3 23 27 0302F0: F6 27 F8 5A BF 27 A6 05 B7 25 BE 23 F6 BF 26 970300: D6 lA CF BE 25 E7 1C 3A 25 BE 26 5A B3 27 26 EC0310: OD 01 05 OE 01 02 18 1F B6 1C 01 2F 02 P6 2D 070320: 2F 02 AA 10 P7 1C CD 19 34 Al 03 27 05 03 2F 020330: 18 20 AE 05 E6 IC BF 24 1F 00 AE 08 44 24 02 1E0340: 00 16 01 17 01 1F 00 5A 26 F2 BE 24 5A 2A E5 A60350: FF B7 IF P7 20 B7 21 A6 OF B7 1D 3F 1F BE 23 F60360: B7 22 CD 1C 05 B7 23 A3 15 26 04 B6 23 B7 IE A30370: 14 26 04 P6 22 B7 1D B6 21 A3 13 26 06 A4 F0 BB0380: 22 B7 21 A3 12 26 06 A4 OF BB 23 B7 21 B6 20 A30390: 11 26 06 A4 F0 BB 22 B7 20 A3 10 26 06 A4 OF BB03A0: 23 B7 20 5A B3 27 26 B7 OD 01 05 OE 01 02 10 1F03B0: 01 2F OE B6 20 A4 OF B7 20 P6 2E AD 48 BB 20 B703C0: 20 07 2F 02 16 1F CD 19 34 Al 03 27 05 03 2F 0203D0: 1E 1D A6 FF AD 39 A6 FF AD 35 A6 FF AD 31 B6 3103E0: AD 28 B6 30 AD 29 14 01 15 01 5F E6 1D BF 24 AD03F0: 1E BE 24 5C A3 05 25 F3 A6 4E AD OE A6 21 AD OF0400: 14 01 3F 01 81 48 48 48 48 81 48 AE 07 20 02 AE0410: 08 48 24 02 12 01 11 01 10 01 13 01 5A 26 F2 810420: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF

07F0: FF FF FF FF FF FF 18 2C 18 2C 18 00 18 2C 18 2C0800: 00

880120

Table 2. Hexadecimal dump of the EPROM contents. EPROM address range .043011 to07EFil is purposely not shown because it is left unprogrammed (addresses read FFii). just asthe remaining 6 Kbyte in the EPROM (080011-1FFFH).

EE

July/August 1988the circuit diagram), or, if available,spare contacts on the band selectionswitch in the receiver. Additionally, thelocal oscillator feed to the MC145157synthesizer may need to be switched withthe aid of RF relays or PIN diodes. Thedirect tuning voltage will not normallyneed to be switched as it can be fed to allvaricaps in parallel.

The relationship between the bit combi-nations on the four MS lines of Port Band the selected band plus IF offset isshown in Table 1.

Bands 0, 1 and 2: single -conversionSW receivers;

Band 3: dual -conversion SW receivers(external prescaler P=5);

Band 4: 'oscillator -low' FM receiversor front ends such as the LP1186 (ex-

ternal prescaler P=10); Band 5: FM band without IF offset;

intended for seeine the actual oscil-lator frequency on display in experimen-tal configurations using a purpose-builttest oscillator (external prescaler P=10;no prescaler in band 13); Band 6: low IF (70 kHz) FM radio

ICs (e.g. TDA7000); Band 7: 'oscillator -high' FM receivers

or front ends such as the Toko 5803/4or 5402, or Larsholt 8319 or 7254; Bands 8, 9 and 10: single -conversion

MW receivers (9 kHz steps); Band 11: dual -conversion SW

receivers (external prescaler P=5).

It is seen that bit combination 0112 inPB6, P13.5 and PB4 will select 10.7 MHzIF shortwave reeardless of the state ofline PB7, so two banks (1 and 3) ofmemory givine a total of 20 stations canbe used, provided that the third bank isnot being used for medium wave. Afront -panel button connected to PB7 isrequired to utilize this feature. This willalso work for the low -IF shortwave op-tions in which the raising of PB7 selectsmedium wave with the same IF offset.The IF offsets can be modified inEPROM if required. They are in 6 -digitunpacked BCD format, starting at mem-ory address 1E05n with neaative offsetsappearing in 10 -complement form. FMoffsets are in tens of kHz, all others inkHz. For medium wave, starting at band8, the same series of offsets is used againstarting at band 0's 455 kHz. Only thefirst three are meaningful for mediumwave, and at band 11 the software auto-matically repeats a selection of band 3 asdescribed above. Beyond this there areno useful bands except, perhaps, band13 which, like band 5, has a zero IF off-set.The software does not include anyrestrictions on the frequencies which canbe used in each band. This maximizesthe versatility of the synthesizer. Forexample, the shortwave bands can beused for MW in the USA where the

24 EEJulyAugust 1988

7

P250k

22

LCD 3200-365.920

14 ISIS 17

11 11 rln n4 3 7 6 10 9 13

13 11 10 9 8 7 6

12

5

16

4

15

3

20 19

2

Tara_ 2

C26101,16V

3 2 12 11 10 9 8 7 6 5 40 up FP

1C12

MC145000DATA UK

3 2 1 OSC

OSC

1154

PA7 P53 817120-15

J

Fig. 7. Multiplexed liquid crystal display. P2

channel spacing of 10 kHz means thatthe SW step size of 5 kHz is more usefulthan the 9 kHz provided on MW for usein Europe.

Select your displayThe display indicates the current fre-quency and memory number, and assistswith the entry of commands and newfrequencies. The user is offered a choiceof three types of 6 -digit display for thesynthesizer:1. LED display; this has the advantage

of probably being the least expensivethanks to the use of common 7 -segmentLED displays. The disadvantage of thiscircuit is its relatively high current con-sumption.2. Static liquid crystal display.3. Multiplexed liquid crystal display.

All three displays are driven with onlytwo or three lines from the processorboard to simplify wiring, and they workwithout any change in the software. It is,of course, possible to omit the displayaltogether, or use two displays simul-taneously.The multiplexed LCD is definitely themost elegant of the three options

is used for setting the contrast.

available, since it enables building acompact display unit with only onedriver chip and few connections betweenthis and the LCD. Unfortunately, how-ever, the display required in this appli-cation proved very difficult to obtain,and it was, therefore, decided not to sup-port this option with a printed -circuitboard. The circuit diagram will, how-ever, be discussed below.

LED displayThe circuit diagram is given in Fig. 5. Inline with the rest of the design, the LEDdisplay driver is also based on low -powerCMOS LSI chips from Motorola, in thiscase two Type MC14499 displaydecoders/drivers set up in a multiplexedcircuit with four and two common -cathode 7 -segment LED displays. Theanode resistors, Rm... RA incl. and1141....Ras incl. should be dimensionedto give the required compromise betweenbrightness and power consumption. IC7and ICs share their clock and latch en-able (LE) lines with the synthesizer(ICI), and receive their data from itsshift register (S/R) output, pin 12.As the current consumption of the LEDdisplay unit is of the order of 100 mAusing 270 Q anode resistors, the module

cannot be left on with the microproces-sor in battery -backed up applications,but should be switched off with the re-ceiver. As the data to the drivers is sup-plied by the MC145157, the displayshould not be switched off while theMC145157 is still powered, unless thedata line (SR) from this is also discon-nected by opening S.

Static LC display6 -digit static displays are currentlyavailable with standard pin -outs from anumber of manufacturers, with onlyminor differences in the use of colonsand other signs, which are not used here.Figure 6 shows the circuit diagram of thestatic LC display unit set up arounddrivers Type MC144115P. The suggesteddisplay from Philips Components (for-merly Mullard/Videlec) gives good con-trast while requiring very little power -the total current consumption of thisdisplay module is about 50 ,uA. Non -used segments in the display are tied tothe backplane.

Multiplexed LC displayThe software can control a display unitcomposed of a 6 -digit multiplexed LCDand a single driver chip as shown in Fig.7. The benefits of a multi -plane displayare immediately apparent from a com-parison of the number lines between thecontroller and the display in this circuitdiagram and that of Fig. 6. The con-troller, a Type MC145000, is fed seriallywith 48 bits corresponding to 6 digits of8 segments, including the decimal point.It formats this data into the fourbackplane and 12 front -plane waveformsrequired to drive the LCD. Preset P2 isused for setting the contrast. To avoid in-terference with the radio owing tomultiplexing pulses, the complete dis-play module should be fitted in a metalenclosure.

Part 2 of this article will deal with theprescalers and the construction of thesynthesizer.

COMPONENT NEWS

Mullarcl no moreAfter 68 years in the forefront ofBritain's electronics industry, `Mullard'has ceased to exist, at least the name.The company, acquired in 1927 by theDutch Philips Group, is now tradingunder the name 'Philips Components'.The new name has also been adopted byPhilips's world-wide component oper-ation, formerly known as `Elcoma'.

Optical shaft encoderAn optical shaft encoder, made 1)Sharp, is now available from Greemt eldat a very competitive price.Producing two phase -shifted outputsand a sync pulse once every revolution, itis ideal for use in robotics applicationsor, in fact, anywhere where the positionand speed of a rotating shaft need to beknown.The encoder costs £8.50 incl. VAT and issupplied with comprehensive data sheet.See p. 10 for Greenweld's address.

DIRECICONVERSION RECEIVERFOR 80 METRES

What better occasion to present an ultra -simple 80 m receiver than this month'sissue devoted to amateur radio and TV?An ideal project for the holidays, thisCW/RTTY/SSB receiver is inexpensive,yet has good sensitivity and selectivity.You will have it ready in no time, and itonly requires headphones, a set of bat-teries and' a long-wire aerial to bring inthe 80 metres band, popular amonghams around the world for its reliablepropagation characteristics.

The tuning range of the receiver dis-cussed here is about 3.5 to 4.0 MHz, asection of which is assigned to licencedradio amateurs. In most areas in theworld, the 80 m amateur band extendsfrom 3.5 MHz to 3.8 MHz. Predominantmodulation methods are single-sideband(SSB), continuous wave (CW) and FSKRTTY (radioteletype based on frequencyshift keying, using an SSB transmitter).The 80 m band has some interestingproperties as regards propagation.Daytime range is usually of the order ofa few hundred kilometres, while in theevening and at night field -strength in-creases, and stations up to 2,000kilometres away can be heard. Occasion-ally, American stations are received inEurope in the early hours of the morn-ing.

Direct -conversion receiverThe operating principle of the direct -conversion (or homodyne) receiver issimple: the received signal is mixed withthat of a local oscillator to give a beatnote, which is at once the AF output (seeFig. 1). In a direct -conversion receiver,

1

band-pass fillet wiser fosrpus filler

0L I

Rena -13

Fig. 1. Basic direct -conversion receiver.

the degree of selectivity is determinedalmost exclusively by the AF low-passfilter. The present design uses an activemixer which doubles as a linear detector,obviating the need for a prestage andproviding the necessary high audio am-

plification thanks to a special feedbackcircuit.The practical circuit of the receiver isshown in Fig. 2. The circuit looks rela-tively complex at first, but is basicallynot very different from the blockdiagram.The aerial signal is fed via coupling ca-pacitor CI, to a parallel tuned circuit,LI-C2-C3-C4-D1. This band-pass filtercan be tuned by applying a direct voltageto variable capacitance diode (varicap)Di. Coupling capacitor Cs feeds signalspassed by the filter to operationaltransconductance amplifier (OTA) ICI,a Type CA3080. An OTA differs from anoperational amplifier in supplying anoutput current rather than an output

voltage. In the present application, am-plification of the CA3080 is controlledby the feedback circuit and the voltageon pin 5, which is provided by the localoscillator, to achieve the desired mixingeffect. The feedback network is com-posed of C,, Clo, Ti, Rs, R6, R4 andC6. It is a relatively complex circuitbecause it functions as a current -to -voltage converter in conjunction withFET Ti, and at the same time as a low-pass filter whose roll -off frequency is de-termined mainly by the capacitanceacross Rs, i.e., CI! (100nF; CW/RTTY)or Cii-FC12 (57011F; phone).The oscillator set up around T2 is avaractor-tuned Clapp type withpolystyrene capacitors to ensure opti-

2

P2

0Ltr -

P10S

R12

L

I

I

L

12V

Cr)

C2

16Y

02

R11

R2

R3

CS

C MNS C11 SONMT.9.970.

= munition * = styrenes D1, D2 = 85212

0 see test

Tt

uv

CO.,'

_i nRTTY attars

CU

12V

0

®

Fig. 2. Circuit diagram of the direct -conversion receiver for the 80 metres band.

26 EEJuly/August 1988

Fig. 3. Track layout and component mounting plan of the double -sided printed circuit boardfor the direct -conversion receiver.

Parts list

Resistors (±5%):;Re= 220K

R2;R3=15KR4=100RRs:Ra t =100KR7 = 27K

Re=2K2

Rs=47KR1o;R12=4K7Pt =10K multitum presetP2=10K linear multitum potentiometerP3=10K multitum presetP4=100K logarithmic potentiometer

Capacitors:CI =10p trimmerC2=330p

C3=470pC4=40p trimmerCs;Cti;C2o=100nC8=4p7; 16 VC7=1n0Ce = 390pCs;C12 =470nCto=1n5C13=47nC14;C18=470p÷Cts=220p+C16=1p5 MKTC17=270p+Cts=1n5+

polystyrene (Siemens: styroflex! ) capacitor5% (available from Cricklewooti Electronics).

Inductors:Li;L2= Neosid assembly 7A1S; winding detailsare given in the text. Neosid part no.06955500. Neosid Limited lcknield WayWest LETCHWORTH SG6 4AS. Telephone:(0462) 481000. Telex: 826405. Fax: (0462)481008 (contact Mr. E. Adcott). Neosidinductor assemblies are also available from C -IElectronics P.O. Box 22089 6360 ABNuth The Netherlands.

Semiconductors:D1;02=89212 (Cirkit stock no. 12-02045)Tt =BF256BT2=BF494ICI =CA3080E

Miscellaneous:St = miniature SPST switch.PCB Type 886034X (see Readers Services

page).

mum stability. The common tuningvoltage for the oscillator and the inputbandfilter is obtained from multiturnpotentiometer P2. Presets Pt and P3form part of a potential divider, and en-able accurate setting of the receiver'stuning range. Since the capacitance of avaricap is inversely proportional to thereverse voltage across it, the received fre-quency increases with the voltage on thewiper of P2. With this in mind, it isreadily seen that Pi and P3 set the upperand lower band limit respectively.

ConstructionThe direct -conversion receiver is con-structed on the double -sided, but notthrough -plated, printed circuit boardshown in Fig. 3. The component side ofthis board is left largely unetched to en-able it to function as a ground plane.Commence the construction withsoldering 15 mm high tin plate or brassscreens onto the component side - thelocations are shown in dashed lines onthe overlay. Use soldering pins at thecorners to aid in positioning and, ifnecessary, bending the screens. Drillholes to ensure access to the spindles ofmultiturn presets Pt and P3 later.Inductors Li and L2 are home-madeand identical. They are composed of 20turns of 0.2 mm dia. enamelled copper

wire wound on the plastic former of aType 7A1S inductor assembly fromNeosid. Remove the three pins on oneside of the base, and use the remainingtwo pins for connecting the winding.Scratch off the enamel coating with apen -knife, pretin the wire end, removesolder flux by scratching again, and thenwind the wire end two times around thepin. Tighten the winding and move it uptowards the base to prevent a short-circuit with the ground plane. Solder fastto prevent the base melting and the pinbeing dislocated. Now close -wind 20turns of the wire upwards on to theformer, right up to the rim. Adjustmentof the inductor is facilitated when thegrounded (`cold') end of the inductor isnear the rim on the former. Secure thewinding with a few drops of glue or wax,and check continuity at the pins.Carefully mount the inductor on theboard, and solder the pins at the trackside. Fit the ferrite cup, and insert thecore. Finally, mount the screening can,and solder the tabs to ground at bothsides of the PCB.The mounting of the remaining compo-nents on the board is a matter of routine.One terminal of the following compo-nents is soldered to ground at both sidesof the PCB: R2, Rs, Rio, C2, C3, -C6, Cs,C14, C15, C19, C20, DI, D2, P4 and Si. Thetwo rotor terminals of foil trimmer Cs,

and the two ground pins (supply and AFoutput), are soldered likewise. In thecase of the trimmer, take care not todamage the PTFE material byoverheating it with the iron.Unfortunately, there is a small error onthe ready-made PCB for this project:facing the flat side of varicap Di(BB212), the right-hand side terminal ofthe device should not be inserted in thehole provided. Instead, it is soldereddirect to the ground surface. PCBs sup-plied through our Readers Services areaccompanied by a note advising of thisdesign error.Capacitor C16 is preferably an MKTtype. When this is not available, a low -leakage electrolytic type may be used in-stead. The photograph of Fig. 4 shows aprototype of the receiver. Note that anumber of ceramic capacitors are fittedin positions that should have polystyrenetypes. Unfortunately, these were notavailable when the photograph wastaken. The previously mentionedgrounded terminal of Di is clearly vis-ible to the left of the device. It is essen-tial that the receiver is fitted in a metalenclosure. Figure 5 shows a suggestedfront -panel layout.

Setting upThe following items are required for set-

EE FZIJuly/August 1988

t_I 3a ;51,1 ;.4),...'.7)

is)

Fig. 5. Suggested layout of the front panel.

Itt

%.../

f1/4:i

Prototype of the receiver hoard.

ting up the receiver: a nylon trimmingtool, a multimeter and a frequency meter(or a good -quality 80 m receiver).Temporarily power the completed re-ceiver from a regulated 12 V supply.Connect the AF output to an amplifier.Turn P2 to the centre of its travel, andmeasure the voltage at the wiper. AdjustPi and P3 to obtain 4 V. Connect thefrequency meter to the emitter of T2,and use the nylon trimming tool to ad-just the core in L2 until the oscillatorproduces 3.65 MHz. Turn P2 fullycounter -clockwise, and check that theoscillator frequency decreases. Exchangethe wires to the outer connections of thepotentiometer if the frequency increases.

'10

Adjust P3 until the frequency meterreads 3.4 MHz. Turn P2 fully clockwise,and adjust Pi for an oscillator fre-quency of 3.9 MHz. Turn P2 to thecentre of its travel, and check that the os-cillator frequency is about 3.4 MHz. Ifnecessary, re -do the adjustments of Piand P3 until P2 covers the full tuningrange of 3.4 MHz to 3.9 MHz.As a matter of course, the function ofthe frequency meter can be taken over bya calibrated 80 m receiver, which shouldhave no difficulty picking up stray radi-ation from T2. The oscillator frequencycan then be read from the dial of theauxiliary receiver.Connect the aerial to the input of the

direct conversion receiver. Tune to aweak transmission at the lower bandedge (3.4 MHz), and peak C4 for opti-mum reception. Then tune to a station atabout 3.9 MHz and similarly adjust thecore in Li. Repeat the adjustment of C4and Li to optimize sensitivity across theband.

Power supply: beware ofadaptorsThe receiver is preferably fed from awell -regulated 12 V supply, or a set ofbatteries that gives the same voltage. Inmany cases, however, it will be con-venient to power the receiver from anavailable 12 VDC mains adaptor. Whenthis is used, it is likely to cause hum inthe receiver, a problem which can oftenbe solved by fitting an additionalsmoothing capacitor of 470 or 1000 pFacross the adaptor's output terminals. Ifhum persists, it is probably caused bycapacitive coupling of the receiver andthe mains. When the rectifier diodes inthe adaptor are reverse -biased, theybehave as capacitors. This is not nor-mally a problem, but the oscillatorsignal, via the supply wires, can thusfind a path to these diodes, which causeamplitude modulation of 50 (60) Hz(single-phase rectifier) or 100 (120) Hz(double -phase rectifier). This modulatedsignal is radiated by the mains wires, andis picked up again by the receiver. In this,the oscillator frequency equals the re-ceived frequency, so that hum is pro-duced as the AF output signal.The supply connections of the receivershould be decoupled by fitting chokesbetween the terminals of the 12 VDC in-put socket and the relevant solderingpins on the board. Both socket terminalsare decoupled to ground with a 100 nFcapacitor. The L -C networks prevent theoscillator signal being superimposedonto the supply lines. If hum still per-sists, try winding the supply wiresthrough a ferrite ring core, or around aferrite rod. A final tip is to solder a100 nF capacitor across each rectifier inthe mains adapter.

28 EEJuly August 1988

NEW LITERATURE

CIRCUITS, SIGNALS & DEVICESby Michael JulianISBN 0 582 99467 5515 pages - 238x 164 mmPrice £14.95 (soft cover)Circuits, Signals & Devices is a textbookintended for first- and second -yearundergraduates and diploma students inelectrical and electronic engineering. Itwill also be of value to students studyingsystems and electronics in otherengineering and scientific disciplines.The mathematical content is broadlyconsistent with the intended readership.The text is written for readers meeting atopic for the first time. To meet the needsof an evolving technology, the bookexamines not only the more traditionalareas of circuits and devices, but alsocovers important aspects of signalanalysis which are often omitted fromintroductory books.Consistent with its title, the book is div-ided into three sections. The first, Cir-cuits, starts with basic principles andprogresses through circuit analysis andtechniques to time and frequency re-sponse.The second section, Signals, commenceswith Fourier Series and proceedsthrough modulation techniques to noisein transmission systems.Although the first two sections deal withthe subject matter in a clear and directmanner, the third section, Devices, is,for me at least, the most fascinating partof the book. It gives a wealth of infor-mation on all kinds of semiconductordevices - from materials and bipolartransistors to microprocessor systems.The book is well illustrated and indexed.Each chapter ends with a useful selec-tion of exercises, answers to which aregiven at the end of the book.A clear, useful textbook that will nodoubt find its way to many a college oruniversity library and also to students'own bookshelves. The very reasonableprice is an additional bonus.Longman Scientific & TechnicalLongman HouseBurnt MillHARLOW CM20 2JE

Mobile Radio Telephones inthe UKby Dr R.C.V. MacarioISBN 1-85181-182-6194 pages - 225x 155 mmPrice £9.95 (soft cover)This lavishly illustrated book, written byone of the UK's authorities in the fieldof mobile radio telephones, provides aclear guide to this topical subject. DrMacario deals with the subject in a man-ner that will enable the reader to get to

grips with the technical, social, andlegislative aspects of mobile radiotelephones in an enjoyable way.The technology is described and placedin an historical context, enabling thereader to appreciate the sources of tech-nical innovation and understand thesteps that have led to the present revol-ution in communications. The geo-graphical aspects of both transmissionand reception are covered and the limi-tations of the available spectrum dis-cussed. The various technologies avail-able for radio telephone usage are ex-plained and future possible develop-ments described.The regulation and licensing of the radiospectrum are covered and an appendixoutlines the present allocation of fre-quencies.The text is confined to UK allocations,activities, and developments in mobileradio, unless a common European policybecomes applicable (as, for instance, incellular radio).This book is in no way meant to be atextbook, manual, or system guide. Itsprimary intention is to be a text that canbe read easily, say on a train, or late atnight, to give added awareness to theremarkable engineering achievements ofmobile radio. It should please many ofthe tens of thousands of radio mobileusers who want to know a little moreabout their equipment and itsbackground.Glentop Press LtdBath PlaceBARNET EN5 5XE

VIDEO TECHNIQUESby Gordon White, CGIA, CEng,MIEREISBN 0-434-92290 0496 pages - 220x145 mmPrice £30 (hardback)This second edition of Video Tech-niques, which provides a comprehensivetreatment of the many aspects of videofor the engineer or technician working intelevision or associated industries, hasbeen updated throughout and enlarged.Amply illustrated (235 diagrams and 100half -tones), Video Techniques does notdescribe circuitry or individual pieces ofequipment, unless it is to illustrate aprinciple, as these change rapidly.Rather, it describes the principles of tele-vision and shows how the equipment isdesigned and functions in the completesystem and, with present technology, itscapability and limitations. These prin-ciples generally remain the same ir-respective of the model, which usuallyinvolves only modifications to the per-formance or operation.Contrary to so many other books onvideo, it does not ignore different trans-mission systems, such as SECAM, andNTSC. It is right up to date with descrip-tions of the MAC system, direct broad-

cast satellite (DBS), and high -definitiontelevision (HDTV).Other contents include standards con-vertors, CCD cameras and telecine,camera tubes, broadcast video recorders,ENG cameras and recorders, domesticrecorders and cameras, video tape, videodiscs, interactive video, conference tele-vision, fibre optics, television receiversand displays including FST, broadcastmonitors, teletext, large screen projec-tion, world standards, digital tech-niques, and graphics and digital effectsgenerators.A book that nobody involved inwhatever aspect of video engineering,production, or management can affordto be without.Heinemann Professional Publishing22 Bedford SquareLONDON WC1B 3HH

BRITISH STANDARDSBS 2011:Part 2.1 Ea:1988IEC 68-2-27:1987This revised standard, Basic en-vironmental testing procedures,supersedes BS2011: Part 2.1 Ea:1977. Itdescribes the tests applicable to compo-nents, equipments, and other elec-trotechnical products.

BS 6840:Part 12:1987IEC 268-12:1987This part of'. BS 6840, Sound systemequipment: specification for appli-cations of connectors for broadcast andsimilar use, supersedes BS 5428:Part5:Section 5.3.

BS 5310: Part 3AThis additional Part of BS5310, Specifi-cation for hand crimping tools for con-tacts of electrical connectors, gives detailrequirements for such equipment, incor-porating a system of multiple indentorsfor use with removable male and femalecontacts complying with BS 9521, elec-trical connectors complying withBS9210, and components that meet boththese standards.

BS 5070:Parts 1 & 2This standard, Engineering diagramdrawing practice, has been revised andpublished in a fresh format. It com-plements BS 308: Engineering drawingoffice practice, which last yearcelebrated its diamond jubilee amid con-siderable professional acclaim.

BS 5783This revised standard, Code of practicefor handling of electrostatic sensitivedevices, has now been published. Itdescribes practices which, if adopted,will reduce the risk of inadvertentdamage to the components. It providesrevised definitions and workshop layoutdrawings and includes revised recom-mendations.

BS 9530This is a new standard giving a Specifi-cation for cable fitting accessories ofassessed quality for circular electricalconnectors: generic data, methods oftest, and rules for the preparation ofdetail specifications. The specification isintended primarily for use in telecom-munication and allied electronic equip-ment.

BS 6513:Part 5: 1987BS 6513:Part 6: 1987These parts of the multipart standardfor 1Videband cabled distributionsystems cover (Part 5) Recommendationsfor one-way and interactive data ser-vices, and (Part 6) Specification forsafety requirements.

CECC 52000This generic specification for the testand measurement procedures of Mer-cury wetted change -over reed contactunits mechanically biased has been for-mally approved by the CENELEC Elec-tronic Components Committee (CECC).CENELEC is the European Committeefor Electrotechnical Standardization.

International certification and approvalschemesA third edition is now available of thepopular publication International Cer-tification and Approval Schemes fromBSI Technical Help to Exporters. Thisedition presents revised data on ninemajor technical certification schemeswhich relate to a wide range of productsin more than 90 countries.These schemes, which have been exten-sively revised (hence the need for a newedition) include the CB scheme for thesafety of electrical equipment; theCENELEC Certification Agreement;the CEN Certification System; theCENELEC HAR Agreement: the CECCHarmonized System; the IECQ System;the ECE Harmonization and Conform-ity Scheme; EEC schemes under 'Article100' Directives; and schemes co-ordinated by EFTA.

British Standards may be ordered fromThe Sales DepartmentBSILinford WoodMILTON KEYNES MK14 6LE

Readers should also note that eachcounty in the UK has at least one largePublic Library where complete sets ofBritish Standards are kept for generalconsultation.

Available free from Hitachi New MediaProducts is CD-ROM Directions, aquarterly journal which reports on thelatest developments, standards, software,and available databases for CompactDisk -Read Only Memory optical disk

drives. Apply to Nick Rogers HitachiNew Media Products Hitachi House Station Road HAYES UB4 3DR

Telephone 01-848 8787.

Introducing Digital Audioby Ian R. SinclairISBN 1-870775-05-8112 pages - 216x138 mmPrice £5.95 (soft cover)This non -mathematical introduction toCD, DAT, and sampling is intended pri-marily for students, technicians, and en-thusiasts. But, although the mathemati-cal background and theory are omitted,the principles and methods of digitalaudio are explained in detail. These prin-ciples (and practices) owe little ornothing to the traditional linear circuitsof the past, and are much more com-prehensible to today's computerengineer than the older generation ofaudio engineers.Digital recording methods have existedfor many years and have becomefamiliar to th