INTERNATIONAL

r BICLUSIVE:

AliCALCULATOR

KIT

OCTOBER 1973

ONNCIPIM% OF

TIC LEVATION

B"IEETI

AUDIO WATTM ERTESTING THE

SHURE V15 Mk IIIHI-FI ... CONSTRUCTION ... COMMUNICATIONS... DEVELOPMENTS

Awaken to the soundof Telefon

puwri

111

boss treble I volume P

MI MI MI

Join the processionin Aida.

Smell 1812 gunsmoke.Shiver

on Bare Mountain.Awaken to the

sound of Teleton.

CT) TeletonSound Sense

(k;) TeietOnhi-fi stereo amplifier GA -2,,

aD 0hi cut loudness mono tape aux phono'I'llII

There's a new world of high fidelity in a Tesystem, with the GA 202 amplifier at its heart to bring you newstandards of purity, new heights of quality in the faithfulreproduction of the world's greatest music.

The Teleton GA 202 combines all the latest advances inhi-fi technology-calibrated slider controls for bass, trebleand channel volume, h. -cut filter, loudness contour, head-phone rocket, tape and auxiliary inputs, to give you 16 wattsper channel (RMS) at under one per cent distortion, 30-30,000 Hz-the soaring choruses and the whispers of acathedr3I inside an elegant walnut and brushed aluminiumcabinet.

Listen to the Teleton GA 202-your ears have beenasleep. Price £49.94 inc. VAT., recommended retail.

Teleton Electro (U.K.) Co. Ltd.,Teleton House, Waterhouse Lane,Chelmsford CM1 3DW.Tel : Chelmsford 62442.

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in

2 ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

electronicsTODAY

IN TT RN/VTIONALrOCTOBER

1973 Vol.2 No.10

main featuresTHICK FILM CIRCUITS 14

A technique which is growing in importanceHI-FI - THE STATE OF THE ART 20Recent trends favour both ends of the marketMAGNETIC LEVITATION 26Will Maglev replace the wheel in tomorrow's transport systems?EARLY TV CAMERAS 31A fascinating history of yesterday's developments.KILOVOLTS AND MEGAWATTS 37Valves aren't dead - just used in different applicationsVHF TRANSEQUATORIAL PROPAGATION 54VHF signals travel long distances across the equatorNUMBERS . 62The concept of number and how it evolved

projectsAUDIO WATTMETER 46Unit gives direct readings on output powerMASTER MIXER MODIFICATION 52Two IC board replaces currently unobtainable LM381EASY WAY TO MAKE PC BOARDS 66Saves messy painting and hours of timeSIMPLE LOUDHAILER 70A handful of components - a lot of power

product testsSHURE V15 MKIIIOne of the world's top cartridgesADVANCE INTERNATIONAL CALCULATOR KIT .

Preview of Great ETI offer

news & information

. . 24

. . 44

EDITORIAL -5; NEWS DIGEST -7; INPUT GATE -42;PREVIEW OF NEXT MONTH'S ETI -43; ELECTRONICSTOMORROW -72; COMPONENT NEWS -73; AUDIONEWS -76; EQUIPMENT NEWS -77; DX MONITOR -81;TECH -TIPS -82.

Cover: Thick film circuits are finding their way more and more intotoday's consumer electronics. See the article on page 14.

L_

Page 14

Page 44

Page 46

EDITORIAL & ADVERTISEMENT OFFICES36 Ebury Street, London SW1W OLW

Phone: 01-730 2136/9

Published by WHITEHALL PRESS LTD

Printed in England by: Alabaster Passmore& Sons Ltd, London & MaidstoneINTERNATIONAL ASSOCIATES: ModernMagitzines Holdings) Ltd, 21-23 BathurstStreet, Sydney 2000. Phones: 26-229622-6129. ACP, Room 401, 1501 BroadwayNew York, USA.BanchoMedia Service, 15 Sanyeicho, Shinjuku-Ku

Tokyo, Japan. Distributed by: Argus Press Ltdg) Copyright WorldwideSubscription rates per year: Home -£3.60Overseas -£4.00.

ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973 3

13IPRE-PAKSUPPLIERS OF

COMPLETE TELEPHONESEX. G.P.O. NORMALHOUSEHOLD TYPE

ONLY £1.05POST & PACKING 45p EACH

TELEPHONE DIALSStandard Post Office type.Guaranteed in working order.

ONLY 271pPOST & PACKING 164p

TESTED AND GUARANTEED PAKS

879 A 1N4007 Rec. diodes. 55p1,000 PIV lamp plastic

B131 10 Reed Switches I long 55pdia. High speed P.O. typeB99 200 Mixed Capacitators. Ap- 55prox. quantity counted by

weight. Post and packing15p.

H4BOMixed Resistors. Approx.

quantity counted by 55pweight. Post and packing15p.

H7 An Wirewound Resistors. 55p-1, Mixed types and valuesH9 . OCP71 Light Sensitive SS

Photo TransistorH28 20 ounccrdoe/j/.12-5Pcbrn Silicon

H3020 ;1.WneadtVZo;tnaegres13674e4si V. 5513

H 35100 Mixed Diodes, Germ.

Gold bonded, etc. 55pMarked and Unmarked

H38 in Short lead Transistors. 5513`, NPN Silicon Planar types1439 A Integrated Circuits. 4 5S13Gates BMC 962. 2 Flip

Flops BMC 945H40 20 BFY50/2, 2N696, 2NI613 vq,

NPN Silicon uncoded """'rTO -5

H41 2 5011rnPpowpae.rr transistorsEiil32 5513

UNMARKED UNTESTED PAKS

B I cn Germanium Transistors 5513PNP. AF and RF

B" 150 Germanium Diodes Min. CC.,glass type

B83 200 Trans. manufacturers'relents all types NPN, 55pPNP. 5,1. and Germ.

884 100 eSgiliuc.7. tDoio(dDeAs20300, -07,i202 55p886 100 ub. min. 5Spg;91'41dnedsfsh1916 typesH6

HIS

4O 250m W. Zener Diodes 5513DO -7 Min. Glass Type

20 ; s -t Rectifiers,Silicon5513;snzdvos

HI630Experimenters' Pak of

Integrated Circuits, Data 55Psupplied

H17 15 3 amp. Silicon Stud 5513Rectifiers, mixed voltsH2O 20 BYI26f7 Type Silicon

Rectifiers 1 amp plastic 55PMixed volts

H34 15 Power Transistors, PNP, CCGerm. NPN, Silicon TO -3Can

MAKE A REV COUNTERFOR YOUR CARThe 'TACHO BLOCK'. Thisencapsulated block will turn any0-1 mA meter into a linear andaccurate rev. counter for anycar with normal coil ignitionsystem.

SEMI -CONDUCTORS TO THE WORLD

OVER

1,000,000TRANSISTORS IN STOCK

We hold a very large range of fully marked,tested and guaranteed transistors, power tran-sistors, diodes and rectifiers at very competitiveprices. Please send for free catalogue.

Silicon planar plastic transistorsUnmarked, untested, factory clearance. A randomsampling showed these to be of remarkable highquality.Audio PNP, similar to ZTX500, 2N370213, BCY70etc.Audio NPN, similar to ZTX300, 2N37013;9,BC 107/8/9, BC 168/9 etc.Please state Audio NPN or Audio PNP whenordering.ALL AT 500 for L3.30. 1,000 for L5.50. 10,000 forL44 P. & P. 11p/1,000.

OUR VERY POPULAR 4p TRANSISTORSTYPE "A" PNP Silicon alloy, TO -5 can.TYPE "B" PNP Silicon, plastic encapsulation.TYPE "E" PNP Germanium AF or RF.TYPE "F" NPN Silicon plastic encapsulation.TYPE "G" NPN silicon similar ZTX 300 range.TYPE "H" PNP silicon similar ZTX 500 range.

8RELAYS FOR

VARIOUS TYPESP & P 27i 10

Our famous PI Pack is stillleading in value for money.

Full of Short Lead Semiconductors & Elec-tronic Components, approx. 170. Weguarantee ac least 30 really high qualityfactory marked Tranistors PNP & NPNand a host of Diodes & Rectifiersmounted on Printed Circuit Panels.Identification Chart supplied to givesome information on the Tran-sistors. Please ask for Pak P.1Only 55p. I Ip P & Pon this Pak.

A CROSS HATCH GENERATOR FOR

£3.83 I ! !

YES, a complete kit of parts including PrintedCircuit Board. A four position switch givesX -hatch, Dots, Vertical or Horizontal lines.Integrated Circuit design for easy constructionand reliability. This was a project in the September1972 edition of Television.This complete kIt of parts costs £3.85, post paid.

A MUST for Colour T.V. Alignment.

ELECTRONICTRANSISTOR IGNITION

Now in kit form, we offer this "up to the minute"electronic ignition system. Simple to make, fullinstructions supplied with these outstandingfeatures:-Transistor and conventional switchability, burglarproof lock up and automatic alarm, negative andpositive comparability.This project is a "star" feature in this issue.Our kit is recommended by the ETI magazine.

Complete kit including p&p £7.92Ready built and tested unit £3.02

extra

FREE CATALC'GUEFORTRANSISTORS,RECTIF ERS,DIODES,INTEGRATEDCIRCUITS,FULL NE-PAKLISTS

PLASTIC POWERTRANSISTORSNOW IN TWO RANGES

These are 40W and 90W Silicon Plastic PowerTransistors of the very latest design, a iailablein NPN or PNP at the most shatteringly lowprices of all time. We have been selling thesesuccessfully in quantity to all parts of theworld and we are proud to offer then underour Tested and Guaranteed terms.Range I. VCE. Min 15. HFE Min 15.

1-12 13-25 26-5040 Watt 22p 20p 18p90 Watt 26ip 244p 22pRange 2. VCE. Min 40. HFE Min 40.

1-12 13-25 26-5040 Watt 33p 319 29p90 Watt 384p 36ip 33pComplementary pairs matched for jg...in at 3amps. 119 extra per pair. Please state NPN orPNP on order.

INTEGRATED CIRCUIT!We stock a large range of I.Cs at very c nmpeti-tine prices (from 11 p each). These are all listedin our FREE Catalogue, see coupon be ow.

METRICATION CHARTS now availableThis fantastically detailed conversion calcula-tor carries thousands of classified referencesbetween metric and British (and U.S.A.)measurements of length, area, volume, liquidmeasure, weights etc.Pocket size 15p. Wall Chart 18p.

LOW COST DUAL IN LINE I.C.SOCKETS14 pin type at 163p each Now new low16 pin type at 18p each profile type.

BOOKSWe have a large selection of Reference andTechnical Books in stock.These are lust two of our popular lines:B.P.I. Transistor Equivalents and

Substitutes: 40pThis includes many thousands of Britisi,U.S.A. European and C.V. equivalent..The Iliffe Radio Valve & TransistorData Book 9th Edition; p. & p. 234p 75pCharacteristics of 3,000 valves andtubes. 4,500 Transistors, Diodes, Rect.-fiers and Integrated Circuits.

Send for lists of publicationsN.B. Books are void of VA-

4,--1-----Please send me the FREE Bi-Pre-Pak Cctalogue

NAME

ADDRESS

ALL PRICES INCLUDE 10% VATMINIMUM ORDER 50p. CASH WITH ORDER

OVERSEAS ADD EXTRA FOR POSTAGE.PLEASE. Add II p post and packing per order I

110Buy these goods with Access

IIII IIIII 1.1 Ell NI

BI-PRE-PAK LTD DEPT H. 222-224 WEST ROAD. WESTCLIFF-ON-SEA, ESSEX

TELEPHONE: SOUTHEND (0702) 46344

Co. Reg No. 820919

4 ELECTRONICS TODAY INTERNATIONAL - OCTOBEF 1973

$1111146..M=IMI=MIIII...A...111IMiML

HALVOR MOORSHEADEditor

ALEX MELLONAdvertisement Manager

SID GLADWINProduction Manager

Electronics Today International36 Ebury StreetLondon SW1W OLW01-730 2136

International Editions

COLLYN RIVERSEditorial Director

Australia

BRIAN CHAPMANTechnical Editor

VVENDY ROYAssistant Editor (Hi-Fi)

BARRY WILKINSONEngineering Manager

Electronics Today InternationalRyrie House, 15 Boundary StreetRushcutters Bay 2011Sydney, Australia

France

DENIS JACOBEditor -in -chief

CHRISTIAN DARTEVELLEEditor

Electronique Pour VousInternational17 Rue de BuciParis, France

kitsA FAIRLY MAJOR CHANGE is beginning to affect the homeconstruction market - the tremendous growth in the numberof kits. In some ways this is surprising for whilst kits were exemptfrom Purchase Tax, they are not from VAT.

We are in touch with several companies in the kit businessand, to a man, they have never had it so good. Ten years agokits were very popular but they declined rapidly; this we believewas due to some very shoddy kits which gave the whole fielda bad name. Today the range of kits has never been greaterand, with a few exceptions, bear little comparison to those onsale a few years ago. The housing was always a weak point butnow even inexpensive kits have a truly professional finish.

One major reason for this growth must be the difficultyin obtaining components. The range now available meansone has to try a number of component suppliers and this canbe both time consuming and frustrating: kits present no suchproblems.

The policy of ETI is to make available kits of the majorprojects whenever possible. We shall always publish completedetails in the normal way so that those who wish to go it alonecan still do so - after all some people have substantial stocksof components already.

When we arrange for a kit to be available this is done purelyas a service to readers who wish to take advantage of it. Inthese cases the designer, the supplier and the magazine workclosely together to produce what we hope is a better end product.We have no tie ups with any of the component suppliers and weare happy to consider any company who wish to take partin such a scheme.

As you will see on page 44, we have made arrangementsfor the supply of an Advance calculator kit at a remarkablylow price (but please note that this offer does not start untilthe publication of the next issue). This is the sort of thingthat we hope to do fairly often. - H.W.M.

ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973 5

S i CLOC SChooseIf

youryou need

combinationany help, please

fromfeel

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below.us.

CLOCKCHIP

Cc

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MM5311 V V V / V 28 VVVVVV 11.19 8 £11.50

MM5314 v v v V 24 V 11-19 8 £11.00

MM5316 v 4 v V V V VV 40 VVV 8-29 4 £16.00

5017AA V V VVVVV V 24 ? ? V V 5-24 8 £14.00

5017BB v y VN/ V 24 ? ? VV 5-24 8 £14.00

5017AN vV ./ ,/ VV 28 2 7 V V 5-24 8 £15.50

DISPLAYCODE0_TYPE PACK

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COSTPERDIGIT

UNITPRICEDIG PACK

DL34 LED 14 PIN 4 0.1 0.2 4 2v CALCULATOR TYPE £2.50 £10.00

TIL360 LED 16 PIN 6 0.1 0.2 6 2v CALCULATOR TYPE £2.50 £15.00

DL707 LED 14 PIN 1 0.3 0.7 1 2v SIM TO MAN 7 TI L302 £2.00 £2.00

DL62 LED 16 PIN 1 0.6 0.9 1 2v £6.50 £6.50

DG12H PH -DIODE TUBE 1 0.3 1.0 1 15v £2.00 £2.00

SP151 SPERRY FLAT 31/2 0.5 1.2 v 160v SPECIAL SKT AVAIL. £2.00 £7.50

TA8055 LIQ.CRYS EDGE 4 0.6 1.3 V V AC60v Reflective/Transmission £3.25 £13.00

D.I.Y. LED VEROBOARD 1 3" 3" 2v 21 LED LAMPS £5.00 £5.00

SOCKETS - 24 or 28 pin £1.15, 40 pin £1.35CASES - WE ARE HOPING TO HAVE CLOCK CASES SOON, PLEASE PHONE BEFORE ORDERING.KITS - 5017AA + PCB + SKT + 4 DG12s + INSTRUCTIONS. £24 - AVAILABLE NOW

5017BB + PCB + SKT + 4 DG12s+ INSTRUCTIONS. £24 - AVAILABLE NOWMM5316 + PCB + SKT + TA8055R + INSTRUCTIONS. £31 - AVAILABLE SEP/OCTMM5316 + PCB + SKT + SP151 + INSTRUCTIONS. £26 - AVAILABLE OCT/NOV

CLOCK DATA SHEETS -SAE. ADVICE - PHONE 0442-62757POST & PACKING - 10p. OVERSEAS (AIRMAIL) 50p. VAT - ALL PRICES EXCLUDE VAT.PAYMENT C.W.O. or ACCOUNT. ACCESS. ORDERS & PAYMENT BY PHONE ACCEPTED.QUANTITY DISCOUNTS ON MOST ITEMS - STATE REQUIREMENTS FOR QUOTATION.

sy tin IIBYWOOD ELECTRONICS181 EBBERNS ROADHEMEL HEMPSTEADHERTS. TEL.0442-62757.24 HOUR ANSAPHONE ON-LINE.

6 ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

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SLIMMER COLOUR TV SETSON THE WAY

Slimmer colour TV sets will soon beavailable in Britain as the UK industryswitches to new slim -line "wide-angle"cathode ray tubes. Pilkington'spressed glass division started full-scaleproduction of specially designedglassware for the new tubes in August.The new 110° angle tubes are flatterthan the existing 90 degree tubeswhich currently take up most of theUK market. They reduce the depth ofa standard 22" set by about fourinches and also give a smallweight saving bonus.

Dimensional tolerances are finerthan for 90° glassware to ensure theelectron beam - which produces theimage on the screen - is accuratelydeflected over the arc caused by thewider angle.

Wide angle tubes are common incontinental Europe, which comple-ted the switch last year. In the UK,110°set deliveries are expected toexceed £500,000 this year and thecompany envisages improved exportopportunities for TV glassware as theUK product comes into line withEurope.

RAPID INTRODUCTION OFPOST BOMB DETECTOR

In our May News Digest we gavedetails of a metal locator, the TreasureTracer Mk III produced in both a kitand ready built form by MinikitsElectronics.

Although Minikits only started atthe beginning of this year, they arealready one of the largest makersof metal locators in the country buttheir success to date has been asnothing compared to their sales of amodified version, designed for detect-ing letter bombs. All those so farfound have made use of tin foil orsilver paper for the contacts and thisis easily detected by a metal locatorat several inches.

The modified Treasure Tracer,which uses a shorter handle than thenormal unit, was demonstrated on themain news of both BBC -I and

BBC -2 TV. Immediately Minikitswere swamped with orders and nowreckon that they have supplied 60 ofthe 100 largest companies in thecountry plus the British Governmentand a number of foreign embassies.

Although the letter bomb scare wasshort-lived, production has kept atrecord levels due to re -orders fromcompanies who took only a few forappraisal. Production is running atover ten times previous levels accordingto Minikits.

The Office Metal Detector, as themodification is known, retails for£13.75 inc. VAT plus 35p carriage withex -stock delivery. Minikits, ofLangley Drive, London, Ell, areplanning to introduce two newversions specifically designed fordetecting letter bombs.

PLESSEY ABOARD HARRIER

This photograph, taken during apre-flight check, clearly shows aPlessey Weapon Control System

(WCS) installed in the cockpit of aRoyal Air Force Harrier VTOL strikeaircraft.

The WCS, designed and manufactur-ed by Plessey Avionics and Communi-cations for the Harrier, provideseffective stores management andconcentrates all the armamentselections on one panel, thus reducingto a minimum the work load onthe pilot.

Plessey has wide experience ofcomplex stores management and hasfurther systems installed in Jaguarand Nimrod.

UNATTENDED RADIOSTATION OPERATION

With the interest of radio broadcastersworldwide firmly centred on theadvantages of automated studiooperations, Britain's EMI group hasplanned a major sales drive abroad tocapture a substantial share of thispotentially large equipment market.

Initially, EMI is launching a

ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973 7

enry'sINTEGRATED CIRCUITS

VERY IMPORTANT. ONLY branded I.Ce are to the FULL manufaclurers specifications. ALL othersare not. Henrys sell on/y branded Integrated Circuits . . From TEXAS . . I . T . T. . . FAIRCHILDSIONETICS. So why buy alternatives or under spec, devices when you can purchase the gamin,article from us -el stock .. need we say morel

Type 1/1112/2930/99 Type 1/1112/2930/99 TypeCpCpCp EpCpCp

SN7400N 0.20 0.18 0.16 SN7448N 1.50 1.27 1.13 SN74142NSN7401N 0.20 0.18 0.16 SN7450N 0.20 0.16 0.18 SN74145N519740145 0.35 0.36 0.33 SN7451N 0.20 0.18 0.16 SN74147NSN7402N 0.20 0.18 0.16 SN7453N 0.20 0.18 0.16 0974148NSN7403N 0.20 0.113 0.18 SN7454N 0.20 0.18 0.16 SN74150NSN7403AN 048 048 0.33 SN74130N 0.20 0.18 0.16 SN74151NSN7404N 0.24 0.21 0.18 SN7470N 0.33 0.30 0.27 SN74153NSN7405N 0.20 0.18 0.16 SN7472N 0.38 0.38 0.34 SN74154N597405AN 0.44 0.44 0.38 SN7473N D44 0.41 0.37 SN74155N5574069 0.40 0.38 0.36 SN7474N 0.48 0.48 0.42 SN74156NSN7407N 0.40 0.39 0.35 SN7475N 0.59 0.55 0.51 SN74157NSN7408N 0.25 0.22 0.10 SN7476N 0.45 0.3E1 0.32 SN74159NSN7409N 0.33 0.33 0.28 SN7480N 0.80 0.70 0.50 5N74160NSN7409AN 0.44 0.44 0.30 SN7481N 1.25 1.10 0.95 SN74161N5974109 0.20 0.18 0.18 SN7482N 0.87 0.80 0.72 SN74162NSN7411N 0.26 0.23 0.21 SN7483N 1.20 1.10 1.00 SN74183NSN7472N 0.25 0.28 0.26 SN7485N 1.87 1.87 1.63 SN74164NSN7412AN 0.38 0.311 0.33 SN7488N 0.60 0.50 0.44 51117416514SN7473N 0.30 0.27 0.25 SN7489N 4.32 4.32 3.78 0131741865SN7414N 0.72 0.72 0.63 SN7490N 0.75 0.70 0.53 SN74167NSN74113N 0.30 0.27 0.26 SN7491AN 1.10 1.00 0.90 SN74170N5974178 0.30 0.27 0.25 SN7492N 0.75 0.70 0.53 SN74172NSN7420N 0.20 011/ 0.16 SN7493N 0.75 0.70 0.63 SN74173NSN7422N 0.28 0.22 0.25 SN7494N 0.85 0.80 0.75 SN74174NSN7422AN 0.36 0.311 0.33 SN7495N 0.85 0.80 0.75 SN74175NSN7423N 0.37 0.34 0.32 51474965 1.00 0.90 0.83 SN74176NSN7425N 0.37 0.37 0.32 SN74100N 2.16 1.89 1.89 SN74177NSN7427N 0.37 0.37 0.32 SN74104N 0.60 0.53 0.46 SN74180NSN7428N 0.43 0.43 0.37 SN74105N 0.50 0.53 0.45 SN74181NSN7430N 0.20 0.11 0.16 SN74107N 0.61 0.51 0.45 SN74182NSN7432N 0.37 0.37 0.32 SN74110N 0E37 0.57 0.50 SN74184NSN7433N 0.43 0.43 0.35 SN74111N 0.86 0.88 0.75 SN74185ANSN7433AN 0.17 0.57 0.60 SN7411619 2.16 2.16 1.69 SN74188NSN7437N 0.43 0.43 0.37 SN74118N 1.00 0.90 0.83 SN74190NSN7438N 0.43 0.43 0.37 SN74119N 1.92 1.92 1.68 SN74191NSN7438AN 0.57 0.67 0.60 SN74120N 1.05 1.05 0.92 SN74192NSN7440N 0.20 0.18 0.16 SN74121N 0.57 0.57 0.50 5574193NSN7441AN 0.85 0.79 0.73 SN74122N 080 0.80 0.70 SN74194NSN7442N 0.86 0.79 0.73 55141235 1.44 1.44 1.25 SN74195NSN7443N 1E0 1.27 1.13 SN74125N 069 0.99 0.130 SN74196NSN7444N 1.60 1.27 1.13 SN74126N 0.69 0.69 0.60 SN74197NSN7445N 246 2.15 1.89 SN74132N 0.72 0.72 0.63 SN74198N51474465 246 2.16 1.89 SN74136N 0.63 0.83 0.65 SN74199NSN7447AN 1.10 140 1.67 SN74141N 1.00 0.90 0.80

LARGER QUANTITY AND O.E.M.PRICES PHONE (011 723 3846. PRICING OF 887400 SERIES ISCALCULATED ON THE TOTAL NUMBER ORDERED REGARDLESS OF MIX. SN74 HIGH POWERSN74 . LOW POWER SERIES IN STOCK . . . SEND FOR LIST 38, FREE ON REQUEST) LOWPROFILE SOCKETS 14 PIN 159 16 PIN ... 17p 8 PIN ... 14p.

1/1112/2930 99C p

2.88 248 2.521.44 1.44 1.262.30 2.30 1.832.01 2.01 1.63230 2.30 2.011.15 1.16 1.001.09 1.09 0.952.30 2.30 2.011.15 1.15 1.001.09 1.09 1.001.09 1.09 0.952.44 2.44 2.141.513 1.58 1.381.58 1.58 1381.58 1.58 1.381.50 1.58 1.382.01 2.01 1.762.01 2.01 1.752.16 2.16 1.894.10 4.10 3.592.88 DSO 2.525.76 5.76 5.041.68 1.5e 1.451.80 1.80 1.571.29 1.29 1.131.44 1.44 1.261.44 1.44 1.261.44 1.44 1.266.18 5.18 4.631.44 1.44 1.262.16 246 1.892.16 2.16 1.896.48 5.48 5.872.30 2.30 2.012.30 2.30 2 012.30 2.30 2.012.30 2.30 2.011.72 1.72 1.511.44 1.44 1.281.58 1.68 1.381.59 1.58 1.383.15 3.16 2.772.88 2.89 2 52

TRANSISTORSAAZ I 3 10, BC1139C 14pAC107 30p 8C182 12pAC128 20p 81132 65pAC187 20p 13CY39 1.00ACY17 35p BCY55 2.60ACY39 65p 8CY70 15pAD 149 50p BCY71 20pAD161 39p BCT72 13pAD162 30p 00124 80pAF117 20p BD131 45pAF1113 50, 3E115 22pAF139 33p 8E180 33pAF186 40p 8E194 13pAF239 44p BFX 13 26pASY27 30p BFX34 66p04115 10p BFX88 22pBAXI3 6p BEY50 20pBC107 12, 6EY51 20pBC108 12p 13E1164 45pBC109 12p EIFY90 75pBC109C 14p BLY36 6.26BC113 115p 0SX20 15p80147 12p 01105 2.20

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0A81 10p0A200 eit0A202 10p0116 66pOC20 1.260128 8550C35 56P

TRIACS Sind. mountingwith eocemodee

3 AMP RANGE Price OP SC45D 400v £1.45Type P.I.V. SC45E 500v 01.85SC35A 100v 80P 15 AMP RANGESC358 200v 859 SC50A 100v £1.45SC35D 400v 90p SC500 2000 01.65SC35E 500v C1.20 SC50D 400v 01.956 AMP RANGE SC50E 500v £2.26SC40A 1000 90p TRIACS/AddltIonsaSC408 200v 1124. Type.SC40D 400v 01.20 40430 TRIACIT0661SC40E 5000 E1.150 Sep10 AMP RANGE 40589 TRIACSC45A 100v 01.05 (Plastic) 90pSC458 200v 51.15 40486 TRIAC (105175p

7101fir. 10.33 Amp1048

15 AmpT040

0C3601440C45007100720077008100830C1400C1700C200OC202OCP71ORPI 2ORP60P346ATIL209TIP29ATIP30ATIP3 IATIP41ATip42ATIS41

85p113p

18p16p25p55928p25965p25p55p90p

1.0055p45p20p25p49p58p61p74p90p28p

0405AITX1013ZTX300ZTX302ZTX5002G301286972N70628930289872N11322N13042N16132816712821472N21602N29262193053283054283055283440283442253525

25p10p14p18p15940p15p10920p46p25p22p20p1.0075p69p10p20p45p49,50p

1.1080p

293614 69p2N3702 11p283714 1.602N3771 1.75283773 2.25253790 2.26283819 35p2N3566 7692N3903 15p2N4002 1492N4126 15p284871 35p2145457 36p25001 3.0025028 641025303 70p40250 45p40361 46p40362 40p40408 50p40486 75p40636 1.0040430 85p

SILICON CONTROLLEDRECTIFIERSType

ONE AMP RON P.I.V.CRS 1/05AFCRS I/10AFCRS 1/20AFCRS 1/40AFCRS 1/130AFTHREE AMP (7041)CRS 3/05AFCRS 3/10AFCRS 3/20AFCRS 3/40AFCRS 3/60AFFIVE AMPCRS 5/400SEVEN AMP 17048)CRS 7/100CRS 7/200CRS 7/400CRS 7/600SIXTEEN AMP 00431CRS 18/100CRS 16/200CRS 16/400CRS 16/600

50v1000200v400v600v

30p30p35p45p55p

50v 40p100s 40p

200v 45p400 55p

600v 66p

400v 60p

100v200v400v600v

60p67p85p95p

100v 70p200v 75p400v 86p600v £1.10

Henry's LIMITEDEDGWARE ROAD, W2

U.Kk LARGEST RANGE OF BRANDED AND GUARANTEEDDEVICES. (Quantity Discounts 10%12+, 15%25+, 20%100+)

(Any one type except where quantity discounts show) Min. Order f1.00 please, PostlOp.,

KITS BY FREE BOOKLETAll types of

41111110UK LTD

EASY TO BUILD -EVERYTHING SUPPLIEDModel No310 Radio control receiver300 4 -channel R/C transmitter345 Superheat R/C receiver450 TC sweep generator455 AM signal generator460 FM signal generator65 Simple transistor tester

115 8 watt Amplifier120 12 watt amplifier125 Stereo control unit130 Mono control unit605 Power supply for 115610 Power supply for 120615 Power supply for 2 x 120230 AM/FM aerial amplifier240 Auto pecking light275 Min. preamplifier480 Electronic voltmeter485 0-12v 300rnA STAB. supply570 LF generator 10Hz-1mHz576 Sq. wave generator 20/.9-20Khz590 SWR meter620 NI -CAD Charger 1.2-12v630 STAB Power supply 13-110 0.25-0.14690 DC motor Speed Gov.700 Electronic Chaffinch705 Windscreen wiper timer760 Acoustic switch780 Metal Detector (electronics only)790 Capacitive Burglar alarm810 Dynamic Compressor835 Guitar preamp.840 Delay car alarm875 CAP, Discharge ignition for car engine

(-Vs Earth)80 Scope Calibrator

255 Level indicator430 3mHz Milliyoltmeter525 120-160mHz VHF Inner715 Photo cell switch795 Electronic continuity tester860 Photo timer871 Slide projector auto feed control235 Acoustic Alarm for driver465 Quartz XTAL checker

E8.00£575£6.08

£10.24£9.25£9.91£1.18f2.137£3.88£4.20E3.52£3.88£4.08£4.85E2.79£5.18£5.83

017.61£9.138

E12.60E12.137

E10.24£747E7.65E2.83£5.96£5.58E8.87E7.27E8.18E6.79E3.75£6.20

£1058£1.98£5.50

£18.23£833£6.93£3.58

£12.04£8.72E6.96£7.89

ALL KITS OFFEREDSUBJECT TOSTOCKAVAILABILITY

TRANSISTORS - RECTIFIERSBRIDGES -SCR's- TRIAGE;INTEGRATED CIRCUITS F.E.T. - LIGHT DEVICESOVER 1,500 DIFFERENT DEVICESMore MANN -Now PrIaes-Naw RangesThis is a must for all Semi -conductor Users

(ask for booklet No. 361ENTIRELY NEW 1973 EDITION

SEND FOR YOUR FREE COPY TODAY

139199wien I

TBA 800 5 WATT ICSuitable alternative to SL403D5/30 volt operated. 8/16 ohm.5 watt output.With circuitsand data51.60.

Sinaloa IC12with circuits and data. 6 waftIC with printed circuit board 28volt operated£1.80 " Is,

Wri"

ZN414 ICIntegrated circuit radio as

featured by many magazines(PW Jan. 73Reprint Ref.

No 19 for10p) C1.20

Toshiba Power and PreamplifiermodulesTH9013P 20 watt Power amp-lifier 22-0-22 or single 45 voltsoperated 04.87TO9014PStereo on twochannel pre-amplifier. ...

C1.10(circuit bookNo. 42 price 10p)

=Yam '

Ultraaonla TraradueersOperate at 4OKhz up to 100yds. Ideal remote switching andsignalling. Complete with datatransmitter and receiver new I.C.circuits. Per pair £6.90

3016E 7 SEG.LC size complete with data priceC2 each or 4for C7(digital clockcircuits ref. No.31, 15p)

BUILD YOURSELF A POCKET CALCULATOR

A complete kit, packaged in a polystyrene containerand taking about 3 hours to assemble -theta theSinclair Cambridge pocket calculator from Henry's.Some of the many features include interface chip.thick -film resistor pack, printed circuit board, elec-tronic components pack. Size 4{ long x 2. wide

wdeep.Free of charge with the kit for the more advancedtechnologist is a 32 -page booklet explaining howto calculate Logs. Tangents. Sines etc.Price 024.95 a. VAT. Also available assembledready to use 029.95 a VAT.

17.75 9

4 El°UDC.3 C7 arounmeanon

NEW RANGESBRIDGE RECTIFIERS

FEATURES SMALL SIZE AND LOW COST Sixes are approx.

2601691 QUARTER AMP VV01 100v 30p8025/05 50 PIV 16p W02 200v 32p8025/10100 PIV 16p W08 1300v 35pxi xfdia. TubularAMP 1-11 Maine 2 AMPS P.LV.

Type P.I.V. Price ea. 02/05 60v 35p1305/05 50v 20p 132/10 100v 40p005/10 100v 22p 92/20 200v 45p005/20 200v 23p 82/60 660v 50p805/40 400v 25p 82/100 1000v 55o805/60 6000 27p IFI x IL x 4- dia.LH x IL x dia. 4 AMPS P.I.V.1 AMP PLY. 84/100 1000 55p131/05 500 25p B4/200 200v 59p81/10 100v 25p 84/400 400v 65p01/20 200v 28p 84/600 800v 76p01/60 500v 30p 84/800 13000 E1.00

11 x r' dia. L.1 x 'dia.1 AMP P.I.V. 8 AMPS P.I.V.W005 50v 29p 66/05 50v 6511

86/10 100v 70p86/20 200v 80p06/40 400v 90p138/800 600v E1.00IH x dia.

ELECTRONICSFOR EVERYPURPOSESee facing pagefor addresses

AN PrIcat correct ettime of prem.

10% VAT to ha added to ellorder. (UK only).

Export end UK manufacture,./Colleges supplied.

LIVING SOUND LOW NOISE TOP QUAL-ITY CASSETTES MADE BY EMI TO IN-TERNATIONAL STANDARDS ESPECIALLYFOR HENRY'S. ALL POST PAID LESS THAN

REC. PRICES.

C 60C90C 120

3 for01.00£1.33£1.52

8 for01.60£2.67C3.15

,14.-AmmICr___ -2,r,

10 for02.60042006.00

/

25 for08.75510.25012.26

Quantity and trade enquiries, invited.LEARN A LANGUAGE -complete with phrase book. German -French-Spanish-ltalian 01.38 per course. C5 for any 4.

A SELECTION OF INTERESTING ITEMSC3025 Compact transistor testerE1300 Mono meg. cart. preernp.E 1 310 Stereo meg. can. preemp.Easiphone telephone amplifierD1203 Telearnp. Wilh PU coilLL I Door Intercornrn. and chimeChattalite (lights as you talk)1 Kw Dimmer/controller9. Twin spring unit For16.7,01 spring unit ReverbsCar Tachometer ElectronicVHF 105 Aircraft band converterVHF 205 Marine band converter82005 4 Ch. mic. mixer132004 2 ch. Stereo mixer

5.5006 p 15P1.95 p 50504415 p5 p 25p5.16 p&p25p3.6001P2OP

1145 p 5 1125013.50 p & p 20p

3.00 p p 10p2.7606 p1505.50 p & p 25p7.50 p&p 15o3.01 p 5p 15p3.060 ra Is 15p2.96 p&p 15p4.75 p 5p 150

TOP QUALITY 8LIDE8 CONTROLSnOrorn stroke high quality controls complete withknobs (post, etc 15p any quantity).Singles leg and 1.111 5K, 10K, 22K, 50K, 100K,250K, 500K, I Meg. 46p each.Ganged Log and Un 10K, 22K. 50K. 100K, 250K,55p each(Quantity discounts available) Complete with knobs.

MARRIOT TAPE HEAPS4 TRACK MONO m2 TRACK STEREO'17' High Impedance £2.00'18' Med impedance02.00R730/E73 2 track mono Racord/Erase low Imp.75p pair.Erase Heads for '17' and '18' 76p'63 2 track mono. Hi imp. £1.76

HenrysIS74C.atalo

(41 OSA OtrustsS1

Now built and used by thousandsof satisfied customers. Featuresslim design overall size in cabinet14+" x 21" x 6I". 6 -IC's, 10transistors, stabilisers Gardnerslow field transformer. Fibre GlassPC Panel, complete chassis work.Now available built and tested aswell as in kit form. HIGH QUAL-ITY & STABILITY ARE PRE-

DOMINATE FEATURES- DEVELOPED BY TEXAS EN-GINEERS FOR PERFORMANCE, RELIABILITY ANDEASE OF CONSTRUCTION. FACILITIES. On/off switchindicator, headphones socket, separate treble, bass,volume and balance controls, scratch and rumble ft-ters, mono/stereo switch, input selector; Mag. P.U_,Radio Tuner, Aux. Can be altered for Mic., Tape,Tape -head, etc. Constructional details Ref. No. 2130p. Distributed by Henry's throughout UK.FREE -Teak cabinet with complete kit. Kit price £28.50

VAT + 50p carr/packing) or built and tested £35.00( VAT + 50p carripacking) as illustrated.

EARN YOURSELF EASY MONEY,WITH PORTABLEDISCO EQUIPMENT

DISCO MINI A complete portable disco.fitted mixer/preamp. 2 decks all facilities £98.50100 watt amplifier for above £38.75SL100 100 watt mixer/amplifier with slidercontrols £89.00R50 50 watt mixer/amplifier £49.50DISCO AMP 100 watt mixer/amplifierchassis unit £65.85DISCO MIXER/PREAMPLIFIERS(OP for up to 6-100 watt amplifiers)SDLI (rotary controls) £49.50SDLII (slider controls) 058.50DISCO VOX (slider controls) the completedisco unit f89.50DJ100 100 watt power amplifier for above £38.75DJ3OL 3 channel 3kw sound to light £29.50DJ4OL as 30L plus built in microphone £38.75DIMANATIC 1 kw adjustable speed autodimmer £25.00SCENE STROBE £19.00. ROAD STROBE £25.00Disco anti -feedback microphone £11.95Cott 150 watt liquid wheel projector £22.50150 watt 01 liquid wheel projector £50.00

U.K's LARGEST RANGE OF ELECTRONIC COMPONENTS

AND EQUIPMENT AT BARGAIN PRICESLatest Catalogue price 55p post paid. Complete with Discount Vouchers

BUILD THE

IAN20 + 20 WATT IC

STEREO AMPLIFIERAs featured by Practical Wireless 1972

150 watt 01 cassette wheel projector £50.00Spare Effects cassettes large range of patterns £8.00Mini spot bank fitted 3 lamps £11.00Auto Trilite (mini with flashers) f17.00Mike r/Miscs/Speakers/Lighting UK's largest rangeFREE stock list ref. No. 18 on request.

SINCLAIR & MINIATURE AMPLIFIERSAMPLIFIERS (car, etc. 20014-300. 0.3 watt 9 volt104, 1 watt 9 volt304, 3 watt 9 volt555. 3 watt 12 voltE1208, 5 watt 12 volt608. 10 watt 24 volt410 10 watt 28 voltZ30. 15 watt 30 voltE1206, 30 watt 45 voltZ50. 30 watt 50 voltE1210, 24 r 2.3 watts 12 voltRE500. 5 watt IC mains operated Amplifier with controlsSAC14. 7 . 7 well Stereo with controlsSAC 13. 15 15 watt Stereo with controls

SINCLAIR UNITS (cart 2001Z30 3 57 Z50Stereo 60 PreamplifierPZ5 03.97, PZ6 £5.37 PZ8 (for 0501 £4.77 (TRANSAFU £4.45

SINCLAIR PACKAGE DEALS Post 25p2 x Z30 Stereo 60. Pzs2 x Z30, Stereo 60. PZ62 x Z50. Stereo 60, PZ8Transformer for PZ8PROJECT 605 KIT

GARRARD BATTERY TAPE DECKGARRARD 2 speed 9 volt tapedecks. Fitted record/play andoscillator/Erase heads. Wind and re-wind controls. Takes up to 4'spools. Brand new complete withhead circuits. £9.50 can. 300

1.762,202.602.854.504.104.953.579.754,375.258.309.00

11.00

4.377.97

C2.95/

15.95111-0020.25296

1995

5C202 3/6/73/9 volt 400mAHC244R Stabilised versionP5009 volt 500mAP11 24 volt 500-nA (chassis)P15 26/28 volt 1 amp (chassis)P1080 12v 1 amp (chassis/e1081 45v 0 9 amp Ichassis/P12 43-12 volt 0.4-1 ampSE101A 3/6/9/12 volt 1 amp (Stab.)RP164 6/73/9/12 I amp (Sorb./

BUILD THE NEWHENELECSTEREO FMTUNER

You pay lessVAT with Henry's

Low Prices

A completely new high stability stereo FM tuner. Features variable capacitydiode tuning, stabiliser power supply, IC Decoder, high gain low noise.IF stages, LED indicators, Tuning meter, AFC, easy to construct anduse. Mains operated. Slim modern design with fibre glass PC, teak cabinet,etc. Available as a kit to build or ready built. Overall size 8" x 2I" xProduced to give high performance with arealistic price. (Parts list and constructionaldetails Ref. No. 5 30p) Henry's are soledistributors UK and Europe. Kit price£21.00 I+ VAT) or built and tested£24.95 I VAT).

TEXAN STEREO SYSTEMPLUS PRICE SAVINGS

The Texan Stereo Systems include thehigh quality Texan Stereo amplifierassembled and ready to use. A pair ofType 200 20 watt Speaker -Tweetersystems size 21" x 12" x 10" and achoice of Garrard players built into aplinth with cover with Goldring G800magnetic cartridge. Systems 25 usesGarrard SP25 Mk III and system 76the Garrard AP76 de luxe turntable.All necessary leads are supplied.System 25 (list approx. £1091£79.50 System 76 (list approx. £1171£89.50 (plus 10% VAT and plus£1.45 carr/packing).

POWER SUPPLIES FOR EVERYPURPOSE(All cased unless stated chessisl470C 6/23/9 volt 300 MA (includes Multi-Adaotor for Tape Record.

rs. etc./ 1.95 post 20pCare Lighter Voltage Adaptors 300mA (Suite voltage Sc 73v, 9v)

1.95 each post 25p3.25 can. 30e4.25 can 30P2.90 post 20p2.90 post 20p2.70 post 20p3.25 post 20p4.40 post 20p6.75 post 3009.15 post 25p8.95 post 30p

All types offered subject to availability.

Prices correct at time of press E & OE10% VAT to be added to all orders.UK post etc. 15p per order.

Hi-Fi and Tape equipmentBig Discounts -Demonstrations.Phone 01-402 5854 for quotes onstocklist.

You can order by phone with Barclay-card or Access.EASY TERMS FOR CALLERS.

Henirv's LIMITEDEDGWARE ROAD, W2

LOW COST HI-FI SPEAKERSSPECIAL OFFERMI 13" x 8" - lull range speakers (post 20v each or 305air)

150TC-8 ohms Twin Cone 10 watt 02.20 each or£4.00 pair.450 10 watt Co Twin Tweeters 3. 8 or 15 ohms £3.50'0011 or £9.90 pair.

15 watt 8 ohms CM Tweeter £4.30 each or 07.90 pair.150 20 watt C/o Tweeters 8 or 15 ohms £7.60 each orf14.20 pair Polished wood cabinet £4.90 post 35o

8 °gnu lull range Ipowl 200FR41065 6,FR8,n23 6"

BASS & MID RANGE -B ohm (post 20p1AA12011002000139/2 13" 8"

TWEETERS AND CROSSOVERS Wow 20pl52005 10 wattrifT6 15 watt12011 30 watt127 KEF

Axcent 100 30 WW1

K4009 IkHz/5kHz5575 3k1-1, var.

SPEAKER KITS icier. etc 35020-220-3 8"LINTON 2 20 wanGLENDALE 3 30 wanDOVEDALE 3 50 wattKEF 0E2nEF KK3

5 watt10 watt15 watt15 watt

15 watt15 watt15 Watt30 wan LF

8 or 15 ohms8 ohms

ohms

8 ohms

30 watt40 watt

V s1 .1p

[4.00C5.507.80

E13.00

£3.20C5.60£6.45

E10.26

01.90[3.20£3.750425C4.90C2.0001.75

E10.00 ea:15.00 eac1C15.95 pairE29.95 pa,£42.00 pair020.40 each£32.00 each

TEST EQUIPMENTMULTIMETERS

ele 30,1200H 20K/Volt Slimline with caseTLH33DU437U4324AF 1050431304341

2K/Volt Robust with case1010/011 Steal case. AC up to 40 KHz20KiVolt with AC current ranges50K/Vo11 with Leather case20K/Volt AC curtentiSteel casePlus Skutt T transistor tester

Modal 500 30K/Volt

ectromc omponents and Equipment 01-402 8381354.356 High Fidelity and Tape Equipment 01-402 5854/4736308,PA-Disco-Lighting High Power Sound 01-723 6963303 Special offers and bargains storeAll mail to 303 Edgware Road. London W2 1BW

Open - 9 am -6 pm 6 days a week

4.954.954.958.009.50

10.5010.50

9.95

Hi-Fi and Tape Equipment BIGDISCOUNTS. DEMONSTRATIONSPhone 01-4025854 For quotes orstock list You can order by phonewith Barclay or Access Card.EASY TERMS FOR CALLERS.

All stores open a/1day Satordny

newsdigestseries of on -the -spot presentationsboth in Europe and Australasia of itsEMI Schafer automated programmingsystems which enable a high propor-tion of a radio station's daily broad-casts to be selected and presentedfully automatically, utilising pre-recorded material. Designed to meetthe full operational requirements ofany radio station, these sophisticatedsystems can provide periods of non-stop broadcasting and pave the wayfor completely unattended stationoperation.

The company's Audio AutomationDivision, of Hayes, Middlesex, isstarting these presentations inPortugal and New Zealand and,already, complete EMI Schafersystems have been airfreighted toLisbon and Wellington in prepara-tion for in-depth stereo demonstra-tions to radio station operators.

EMI Schafer automation systemsutilise pre-recorded material on bothreel-to-reel tapes and tapecartridges stored in carousels. Anynumber of tape play -back decks andcarousels can be used depending onthe level of automated operationrequired by an individual radiostation. The equipment can switchautomatically between live broad-casts and recorded material providingstation operators with full flexibilityin programme format.

In Britain, the lead in studioautomation has been taken byLondon's Capital Radio, the largeststation in the country's commercialnetwork, which has been equippedwith an EMI Schafer 903 system.

Incorporating a solid-state memory,this system selects on a time orsequential basis both live and pre-recorded 'events', including entertain-ment, commercials and stationannouncements, to provide longperiods of broadcasting. Using a key-board, an operator can insert aschedule of programmes in thememory, building up the programmeson a minute by minute basis ifrequired.

Manufactured in the United States,EMI Schafer systems are marketedexclusively, outside North Americaand Mexico, by EMI Sound & VisionEquipment.

LOW COSTAIR -POLLUTION MONITOR

A new range of portable, low-costcarbon -monoxide monitors, designed

for making quick spot-checks orcontinuous monitoring of airpollution, has been announced byAnalysis Automation Ltd of Oxford,specialists in the field of analyticalinstruments.

Six versions of this small, light -weightmonitor, called the Ecolyzer aredistributed in the UK by AnalysisAutomation and they cost less thanhalf the price of equipment ofcomparable accuracy currentlybelieved to be available.

Easy to operate and powered byintegral batteries or an a.c. mainssupply, the Ecolyzer incorporates anelectrochemical sensor which isbelieved to be unique.

!n operation the Ecolyzer drawsambient air through a detector cellwhere it passes over the catalytically -active diffusion electrode. Anycarbon -monoxide present is oxidizedto carbon -dioxide. The rate ofoxidation is related to the concentra-tion of CO, and can be read directlyfrom the meter. Humidity and watervapour in the air do not affect theperformance of the Ecolyzer.The Ecolyzer is suitable for many

different applications, including thecontinuous monitoring of urbanareas as well as restricted areas such astunnels, factories, bus depots,underground carparks and coal -mines.Industrial applications range fromwarehouses and factories wherefork-lift trucks generate carbon -monoxide to mills and foundries withCO -producing furnaces.

In the medical field, the Ecolyzercan be used by cardiopulmonary.experts to detect in the atmospheresignificant amounts of carbon -monoxide which can reduce theability of the bloodstream to carryoxygen to body tissues. The toxicityof carbon -monoxide and the highconcentrations that can occuremphasise the need for more informa-

tion on its generation and distributionin the environment, say AnalysisAutomation.

A feature of the Ecolyzer is itsportability which permits fast verticalplotting of the varying levels ofcarbon -monoxide by spot-checking atdifferent heights in cities.

PEKING SATELLITE EARTHSTATION

The Peking satellite communica-tions earth station supplied to thePeople's Republic of China by RCAGlobal Communications, Inc, has goneinto commercial operation handlingtelephone, teleprinter and othercommunications services betweenChina and the United States, it hasbeen announced by RCA.

The earth station was installedunder a co-operative arrangementwith the Chinese TelecommunicationsAdministration. In accordance withcontracts signed August 16,1972,for S5.7 million, the project includedthe supply of the Peking earthstation and the expansion of theexisting earth station at Shanghai,installed earlier in 1972 by RCAGlobcom.

The Peking station is handlingregular commercial traffic includingtelephone, leased channel, telegramand facsimile traffic, and hascapability for live television betweenChina, the United States and otherlocations in the Pacific.

The earth station is operating withthe Intelsat IV satellite, located in ageostationary orbit 22,300 miles abovethe Pacific, and links Peking with theJamesburg, California station andother countries' earth stations whichare presently operating with thePacific satellite.

The new earth station at Peking isequipped with a 98.ft diameter

10 ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

antenna and has permanent build-ings to house communicationsequipment. The Peking and Shanghaiearth stations each will be capable ofinitial operation with four otherIntelsat earth stations and have capa-city for 60 voice -grade channels.

Chinese civil and electronicsengineers and technicians wereresponsible for site preparation,building construction, and workedclosely with RCA Globcompersonnel on the antenna construc-tion and erection as well as theelectronic equipment installationat both stations.

COMPUTER AIDS INRECONSTRUCTION OF FOURTHCENTURY SYNAGOGUE

A computer at the University ofSouth Florida is helping to solve a1,400 -year -old architectural puzzle.

Using an IBM System/360 Model 65,Dr James F. Strange, an archeologist,has been reassembling a synagoguebelieved to have been levelled whenan earthquake struck the UpperGalilee in 553 AD. Until recently,the synagogue and the surroundingvillage were covered by layers of soiland wind-blown materials.

Dr. Strange, who teaches biblicalarcheology, is a member of a teamexcavating the synagogue in thecentre of Khirbet Shema - a remoteJewish community which onceexisted some 90 miles north ofJerusalem.

Restoration of the synagogue hasprogressed through three stages:excavation, planning and physicalreassembly. The final piece of thepuzzle is finding the type of roof whichcovered the structure.

Since excavation began, some 4,000artifacts including worked bone,ceramic stone, plaster, coins, and someexamples of jewelry and organicmaterials have been found.

At first, the artifacts were manuallylisted. Later, the informationconnected with each item - itsdescription and where it was found -was punched into cards and stored inthe computer. Using statisticalanalysis and comparing the data derivedfrom other excavated sites in thearea, the computer then sorts outthe data to help the team find patternsin the cultural composition of KhirbetShema. The computer has become avaluable tool in the field ofarcheology, permitting findings to bequantitive, rather than intuitive.

Not only does the computer elimi-nate those alternatives that wouldtake years to explore manually, butit also allows researchers to determinewhether their conclusions makearcheological sense.

COURTESY LAMP DELAY UNIT

Jermyn, in addition to providing aprofessional distribution service forelectronics engineers, have alwaysshown a keen interest in the consumerand are particularly adept atdesigning equipment for thismarket. Recent examples of thisability are the light dimmer, thecapacitor discharge ignition systemand the invertor which supplies240V 50Hz from a I2V d.c. input.The latest product to be added tothe range is a Courtesy Lamp DelaySwitch for use in motor cars.

It was designed around Motorola'srecently announced MC1455Ptimer integrated circuit by one ofJermyn's engineers. The unitcauses a car's courtesy light to remainilluminated for about 8 seconds afterthe doors have been closed, allow-ing the occupants to see whilefastening seat belts, switching onthe ignition, etc, at night.

The unit is potted in epoxy resin,making it mechanically virtuallyindestructible. Installation is verysimple, being limited to the connectionof four wires (earth, supply, courtesylamp and door switch) and the dis-connection of the existing lead betweenthe door switch and the courtesylight. Of course, the unit can beemployed to operate anywhere wherepower has to be interrupted a fixedtime after a pair of contacts open.The unit will cost £4.95.

ANTI -SHOPLIFTING SYSTEM'CATCHES' 35 EMPLOYEES

Installed primarily to prevent shop-lifting, the electronic security systemat Carson Pirie Scott - the Chicagodepartment store - has helped cut'back -door' pilferage, too.

Say CPS: 'The effectiveness of thesystem has allowed the security staff toconcentrate more on the problem ofinternal theft and register shortagesin particular. Their efforts haveresulted in the apprehension of 35associates since the beginning ofthe year.'

Recently, the company's Directorof Security reported the 'Firstsignificant change away from risingshortage figures' and he contributedmuch of the profitable results to hiselectronic security system whichprovides exit coverage at three storesin the Group and protects particularlyvulnerable departments in otherparts of the Chain.

Known in the UK as Senelco, thiselectronic anti -shoplifting systemconsists of an electronic scanner -cum -audible alarm at store, or depart-mental exit and small sensitisedtags fixed to the goods needingprotection. Cash -desk assistantsremove the tags at the same time asprice and swing tickets but if anyonetries to remove unpaid merchandisefrom the shop they trigger the alarm.

The CPS Security Chief has alsostated that his system has 'savedCarsons almost £60,000 over andabove the cost of the system and forthis reason it will be expanded in theChicago Retail Division.'

Shoplifting is such a problem inChicago that the city has recentlyinaugurated a special ShopliftersCourt! With UK shopliftersrelieving retailers of £200 milliongoods a year, perhaps similar measureswould be advisable this side of theAtlantic, too!

NEW UHF STATIONS

New IBA UHF transmitters haverecently been brought into service.These are Glossop, Derbyshire onChannel 25 and Weardale,Co. Durham on Channel 41. Bothare vertically polarised and will givereception to about 30,000 people.

ELECTRONICS ENGINEERS'SALARIES FALL BEHIND

The 'Survey of Salaries', published bythe Management Survey Centre thisAugust, shows that the salaries ofelectronic engineers working for largecompanies have stagnated whilst otherengineers' salaries have increased.Senior chemists have done best - theirsalaries have increased 3-4 times morequickly than the average.

For a senior professional in develop-ment (with major responsibilities) themedian salary is £4,174; for elec-tronic engineers in particular themedian at this level is £3,720.

Continued on page 74.

ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973 11

NEW VAT INCLIJSAP Series m

INTERNATIONALLY

KNOWN BRANDS

1st GRADE DEVICES AT NEW

IROCK BOT1OM PRICES(

SN 7400SN 7401SN7402SN7410SN 7413SN7420SN7447

16p16p18p17p30p16p99p

SN 74 74SN74 75SN 7476SN7490SN 7497SN 7493

This range will be increased 0.990,1.Please enquire aborii any ilexio0 no,

40p40p50p44p69p74p74p

Noce RECTIFIERS

P.I.V. 1 AMP 2 AMPI ilOV 20p 35p110V 22p 40p

i iliDV 25p 45p1000V 38p 50p

RECTIFIERSP.I.V. 1 AMP 3 AMP50 1N4001 6%p ' 15'hp100 1N4002 ThP 16%p200 1N4003 9p 17'hp400 1N4004 9P 22p600 1N4005 11p 26'hp800 1N4006 13%p 30p1000 1 N400 7 16%p 33pBY100 16%p 23pBY103 22p 55pBY105 16%11 £1.6585126 16p E1.65PY1; 161/2p 251/2p

iL

VE PRICES OVERSEAS CUSTOMERS DEDUCT

ONE ELEVENTH.

PRICE WRIER SLASNED

READOUTS14pinoil

Ref. LEO I

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OR

FILAMENT INDICATOR

MINITRON 3015F B G

16pin Oil

at RREANTRRoveRPRICE

Cheapest Opto yetCaAsp LED's

Remember

0

RESISTORS

LEO 2 0125' 263LED 3. 0175" 17p

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Vat Inclusive Prices

eroUtird

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2%" x 1" 6'hp 61/2p21/2" x 3%." 22p 18p202" x 5" 26'hp 23p3%" x 30." 26%p 23p331" x 5" 30p 30p17" x 21/2" 74p 55p17" x 3%" 99p 77p17" x 5" - -Dip BreadboardVerostripSpot Face CutterPin Insertion Tool (state 0.1" or 0.15")Terminal Pins (packs of 361 state size

Plain ExtraP&p0.15"

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DIGITAL CLOCKona

chipjust imagine, one MOSLSI I.C. eliminating 15MSI I.C.s 6 numerousother components. Either

12 or 24 hour. 4 orb digit50 or 60Hz operationleading zero supressionsingle voltage supplysimilar to DIGITRONIC inP. W, March 1973.

Only £6.99With 4 LED's £15.59With 6 LED's £1975

I electronicsRATING TYPE TOLERANCE RANGE1/16 Watt 711. L 16 v ± 5% 5112 1 i 1006121/8 Watt Cutop, f II, i 5% 61E2 iii 330KE21/2 Watt Niciai U... Iii F Ili, ± 2% 10E2 ti 1M121/2 Watt 0 2% 5612 ii i 150KE21/2 Watt C.v... I He! a 5% 1052 in 10ME21/2 Watt L ii i iiiii 1,a, ,,,,,,,, * 0.5% 2.21:: 2./1:: 3.352; 3.912; 4.702

1 Watt C II I grin CNINI ...I. 2r1 4 10% 5.652; 6.8E2; 8.2121 Watt i 0 I, . 1-1,1 6 5% f- l i. 104 ii, 10MG2 Watt - ± 5% 104 iii 10PAE22% Watt ± 10% 0.2212 ii, 0.47E22% Watt ± 5% 14 ii, 270E25 Watt 0.5E2 ' 8.2KE210 Watt 0.511 6.8KE210 Watt 0 5% 1OKS7; 156E2; 20K:l, 256E215 Watt 10'1 6.861.1

DISCOUNTS: 10%

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453 761253 2N1304fl 21 "II 09Np 7N1.107,

33p 2N I MP38p 271 I::17383 251300

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SILVERED MICA'S; TUBULARS, FEEDTHROUGHS,HIGH VOLTAGE TYPES; TANTALUM; PULSECERAMICS & MONOLITHIC CERAMICS AREALL DETAILED IN LEAFLET NO 13

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DUAL IN LINE8 pin 131/2p 16 pas 17'hp 36 pin 39%p14 pin 15%p 24 pin 26'hp 40 Pin 44p

28 pin 30%p

HEST SIMI(STV2 for TO 66 15p. 5F for TO 5TV3 for TO 3 16p. 18F for TO 18

TV4 for TO 126TV5 for TO 220

14p

[ 5'13.

DIP10 2 forSL403D

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?01#

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newstabillsed

POWER PACK CONVERTERSwitched 3, 6, 75 or 9 Volt,.

Up to 400 m4 Outpid

',a" Outran Leane 2 :3 5een plug

e FREE multi

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Unstabilised Version of above

Other Eliminators funstabilisedl6 Volts9 Volts9 Volts Iminiaturel606909

50m45OrnA50m450mA50170

4X:6; 75; 9, 12 Volts up to 04Fully Stabilised Car Battery Converter giving switched outputs of 6: 70 or 9Volts.

p on all models 16p

E2.99

E1.65E1.65[209E2.75E2.75E220E3.75

E5.49

EMIRSAll 5% tolerance

BZY88 40011120 I WailB2X70 1 51e;

1 1 p

18p2711

12 ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

INvoiciFiks ON REouEsT UNLESS

SHOPSWN

OTHERWISE

AS

Pes ON I

ORDERS OVERSE ORM RS AT r.OS T

Mulard LP1186

Varactor diode tuned. F.M.tuning heart £4.16as described in P.E. May 1973.LP1185 matching I.F. strip.

E4.85

SI MI20+20 Watt Integrated stereoamplifier Kit. Superb state-of-the-art design by engineersof Texas Instruments.

£31.36+p & p 49p

smissi EA1000

3 Watt amplifier module.Price including handbookand FREE HEATSINK(Quantity discounts/.

Our Pries £2.49

A1005S

F.M. tuner chassis, fullytransistorised. 9 voltpositive earth operation.

Our Price E6.35

A1018

F.M. tuner, similar toA1005S but in oiledwalnut case, black &silver -fascia etc.

Our Price E9.38

A1005MS

Multiplex Stereo Decoderfully built & aligned tomatch A1005S.

Our Price E5.95

AUDIO I.CVAudio I.C.Leaflet No 12 (circuit data etc.(FREE with I - 10p separately

PREAMPLIFIERSDual MC1303L £1.89

Low Noise DualMC1339P

AMPLIFIERS

1.29

250mW MFC4000A 49p

1 Watt TAA300 E1.79

2 Watt LM380 E1.59

3 Watt SL4030

Surat; TBA800 E1.59

15 Watt BHA0002E3.95

35 Watt NES4OLDrover E1.32

ref

inPut

51 decade DVMCOmPanttOr

> *splay

II

bcd to 7 see

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Maximum Display + or - 1.999V Minimum Drsplay + or - lrnv Can be sealed up to 1,999V Automatic Polarity Detection Dual Ramp Integration Automatic Overange Indication Up to 50 readings per second Chopper Output Provided

Supplied with complete data.All this on a single 16 pin DIL packaged MOS LSI Integrated Circuit.

A State -of -the-Art Digital Voltmeter I.C. for only £779

Ceikless Phese-ielreel teep

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Our Price £6.89Inc. all parts for decoder inc. Veroboard, V.A.T., p. & p. (leaflet alone 10p)

Motorola Mu 10, suppliedcomplet -with our FREEleaflet No.11

Orr Price £345

UADRISONICS

709710711723741747748

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0111k40940p45p9Bp45p

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95pE1.65E1.65E1.99E1.15E1.0566pE1.45E2.6977pB8p53pE1.10Et .10E1.59E1.69E1.75£2.420.85E1.4977p112p

78p83pE1.10

NAVIIISVIL0051NIVRI2VIL0361MORI5VIL0371NE555NE560BNE5618NE5628NE565NE566NE567SG3402NSL440TAA263TAA293TAA310TAA320TAA350TAA370TAA550TAA570TAA700TAD100TAD110TE1A550ULN21114

Er .65E1.65E16599pE4.92E4.92E4.92E3.49E2.75E3.49E3.08E2.2999p99pE1.3799pE2.54£5.1581p£1.65E4.46E1.65E1.651.65

£1.59

14- zosstos444 ftoth-Dept 7.

56, Fortis Green Road, London, N10 3HN

telephone: 883 3705

INDUCTORS

MULLARD block filler LP1175as used with TAD100now only E1.49

R.F. CHOKES 0.1pH to 19mH. For fundetails ask for List No.5 p & p 5p.

DENCOCOILS

TRANSISTOR RANGESeries 1T to 5T inclusiveBlue: Yellow; Red 8, WhiteMl 44p each.

I.F. TRANSFORMERS1E7.13; 14; 16 & 17 55p ea.IFT.15 76p. 1E7.18 73p ee.

DUAL PURPOSE RANGE.Series 1 to 7 inclusiveBlue, Yellow; Red & WhiteIII 44p each1 to 5 Green 49p each

List No.5 gives lull details.

FERRITE AERIALS Medium & Long Wavestate 300pf or 50071 tuning 87p ea.

Type C8045Pf 61p

Opt 61p15pf 61p20pf 64p25pf 61p

50pf 66p60pf 79p75pf 79p100pf 75p

Type 0365pf365 + 365pfType 00208 + 176pfwith screen &Irl TIT. -

p & p all types 10p

80p96p

99p

NEW

MOM8FS59BES60BFS618E5968E597BFS98

ZTX107ZTX108ZTX109ZTX212ZTX213ZTX214ZTX300ZTX301

15p20p20p15p23p20p

9PSp11p14p1

15p12p13p

11.:11n\-1.1The Radio I.C. in a 9 TO 18 Can - Suppliedwith our FREE data leaflet No.11 giving circuitand component details. Leaflet alone 10P-

ZTX302ZT X303IT X304ZTX310ZTX311ZTX312ZTX313ZTX314ZTX320ZTX330ZTX331ZT X341ZTX382ZTX383ZTX384

17p14p21p9p10p10plip13p31p15p16p22p13p15p18p

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DIODES25120

17p17p12p13p17p14p43p17p21p22p17p17p

811

ZS121ZS122251232512425140ZS141ZS1422517025171ZS172ZS174ZS176251782527025271

RANGE

Our Price£1.32

10p 25272 18p13p 25274 19p16p Z5276 26p18p 25278 37p25p43p KS030A33p Zener10p Series13p an16p BZY8817p Series23p 11p38p eachlip16p

CF

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3.3

10

47 Q6.8

22 614p33 Whp

ELECTROIYTICS9V 6.3V

7 bhp68100 6'hp150220 SAp330 6r4p4706801000 10p1500220033004700 29p6400100000

614pErhp

6Xp

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1218720p

10V 16V 25V 40V

67Sp

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Sp

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6 Ap6'hp 9p

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299p

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333p

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log or lin less switch 18, 1K ft lin/log or lin with switchdual less switchdual with switch 10K, 100K & 1Mlog onlyIOK log 10K antilog less switch

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PresetsVertical or Horizontal0.1 watt 5/hp 0.25 watt 7p1000 11(12 10K12 100K02500 25K0 251(12 2501(125000 51(12 501(12 500K0Cermet Type, to 16451 only

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VDR's f Therreisters82'ap GL16

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Other types obtainable upon application.

£1.49E1.6118)Sp14YspII plip18)4p1 1 p

lip1 1p11p1 1p1851p14)1p2lp29p29p

ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973 13

THICK FILMCIRCUITS

Slowly but surely, Thick Film Circuitsare finding their place in a wholevariety of electronic applications.Keith Pitt explains.

MANY OF US are now familiar withthe silicon integrated circuit. Largenumbers of them are beginning tospread from the digital world of com-puters to the field of consumer elec-tronics. Specially designed integratedcircuits are fulfilling many complexfunctions in radio and, especially, incolour television.Their uses range fromdetector and I.f. circuits to audioamplifiers. Integrated circuits can pro-duce complex digital functions cheaplyand with low power dissipation. Theanalogue circuits used in radio andtelevision are not as cheap and consumerather more power. Nevertheless bothcost and power are often less than theywould have been using conventionalcomponents.

The twin governing factors in theproduction of a piece of electronicequipment are size and cost. Althougha television set, for example, is limitedto a minimum size by its tube, there is

Cutting the ten -times full size artwork for a microelectroniccircuit. This pattern is reduced to manufacture the screenstencil. (Courtesy Middlesex Polytechnic)

still much scope for reducing thecomplexity and volume of the elec-tronics. A few integrated circuit pac-kages will replace a large number ofconventional components and simplifyand cheapen the assembly. This is oneaspect of the cost reduction, but themain scope for this is in the mass -production of a few standard buildingblocks.

However, we often find that afteras much as possible of a piece of equip-ment has been made in silicon inte-grated circuits, there are still a largenumber of components left unaccountedfor. A way of combining as many ofthese as possible into integrated pac-kages is also required. The majority ofthese components will be resistors andcapacitors.Whilst the latter do not lendthemselves so easily to integration,thereis a ready-made technology availablefor the former. This technology isknown as "thick films". It was firstdeveloped for mass production of resis-tor networks for computers by IBM.It has since found widespread use inthe automotive and professional elec-tronics industries and is now cominginto full production for radio and T.V.applications. Thick films lend them-selves readily to cheap mass productionof resistors which are rather better inquality than needed for many of theirapplications.

Manufacturers of electronic equip-ment are adopting thick film circuitryfor a variety of reasons. Decreased sizeand enhanced reliability attract theprofessional and military markets. Forconsumer and automotive users massproduction of uniform packages de-creases assembly costs. When pushedto the limit, thick films are cost com-patible with conventional components.

THICK FILMSThick film technology is based onglazes fired onto a ceramic substrate,usually alumina. The process is devel-oped from and similar to that used inpottery and china making for producingthe coloured patterns we see, forexample, on tea services. For electron-ics the glazes may be conducting,resistive or insulating. They are usuallyabout one thousandth of an inch in

ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

thickness. Like their decorative coun-terparts they are screen printed froman ink or paste and then kilned at ahigh temperature to convert the inkinto a glaze.

GLAZESThe principles involved in glaze makingare very simple but the behaviour of theinks is rather complex giving rise to anumber of technological problems.These have now been solved and theprocesses lend themselves to mass pro-duction with high yield, for both pot-tery and electronics applications. Wewill first look at the principles of theprocess and then concentrate on resis-tor glazes which, together with con-ductors, are the main application inelectronics.

Figure 1 shows the basic stages ofproducing a glaze. The ink is a com-plex mixture of glass and pigment par-ticles, an organic binder and a solvent.For resistors the pigment is generallya combination of precious metals and/or their oxides. (One of the bestavailable systems is based on the oxideof ruthenium). The conductor pigmentsare precious metals such as silver orgold, usually in combination with pal-ladium or platinum. The cheapest con-ductor which is widely used for con-sumer applications is a glaze of an alloyof silver and palladium. The pattern isproduced from the ink by the screenprinting process (we will look brieflyat this later). The ink is printed onto apiece of ceramic, usually a high gradealumina for electronics purposes, thiswet pattern dries partially in air as thesolvent evaporates, but is usually forcedried at about 150°C. The dry printcan be handled with care and further

SOME APPLICATIONS OF THICKFILM HYBRID CIRCUITS

Military and Space Equipment

Professional ElectronicsInstrumentationComputersCommunications Systems

Medical ElectronicsDeaf AidsPacemakersUltrasonic Aids for the Blind

Consumer ProductsWashing MachinesRadioT.V.Audio

Automotive IndustryVoltage RegulatorsIgnition SystemsElectronic InstrumentsBraking Control

SCREEN PRINTING AIR DRY AT ISO' CHARD DRY PRINT

300°C. ORGANIC BINDERBURNS OFF

500-700°C 750°C (GLAZE FORMATIONTAKES PL ACE

Fig.l. Principle of formation of a glaze, showing stages between ink and glaze.

CIRCUIT IN

800

600

400

200

FURNACE

300°C 500°C 760°C 760°C

.4- ENDLESS BELT .4-

GLAZEFORMING -.

FIRED CIRCUIT

\11

DRIVEROLLER

0

ELECTRICAL PROPERTIESDEVELOPING

COOLING

PROGRESS OF CIRCUIT THROUGH FURNACE

Fig.2. Principle of belt furnace for glaze making.

printing may be done at this stage ifnecessary. If not, the ceramic substrateis then put into the kiln to produce theglaze. For convenience in mass produc-tion a belt furnace is used. This employsan endless belt moving through a fur-nace which is divided into a number oftemperature zones. These are set in sucha way that the heat treatment given isof a known and controlled nature. Thisis necessary in order to produce thecorrect electrical properties. Fig. 2illustrates the use of a belt furnace forelectrical glazes.

In this article we shall only considerresistors and conductors. Dielectic andinsulating glazes are used but theirapplications are limited. When twoconductive tracks need to cross, theyare separated by a layer of insulatingglaze. (Such patterns are known ascrossovers and have applications es-pecially in complex circuitry). Beforediscussing the technology and appli-cations of thick films we will look atthe type of patterns needed for resistornetworks.

THICK FILM NETWORKSA thick film network is rather similarto our old friend the printed circuit.

Pluggable attenuator pad for digital andvoice frequency transmission equipment.Courtesy Welwyn Electric Ltd.

It consists of conducting lines or areason a board which will be used tointerconnect other components. Un-like the p.c. board, however, some, atleast, of the other components arethemselves on the board or, as it is nowcalled, the substrate. We must not takethe analogy too far, but we can addsurface components such as transistorsor capacitors to a film network in the

ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973 15

THICK FILMCIRCUITSsame way as to a board (for example bysoldering). In this case it becomesknown as a hybrid circuit. Hybrids arealso widely used in electronics and willbe examined below.

The value of a film resistor dependson a number of factors. These are,briefly, shape, thickness and chemicalcomposition. It can be shown that anysquare of a given resistor material ofthe same thickness will have the sameresistance value. This helps to reducethe number of variables and allows usto set rules for making resistors. Weproduce our patterns by screen printing(see below) and this technique gives aconstant value of thickness. As a resultwe find in practice that, using anyparticular resistor glaze, the value of theprinted and fired components is solelydependent on their geometry. In a

square the length, L, and width, W,are equal. If we make L = 2W, then L/W= 2, and the value is twice that of asingle square. If, on the other hand, wemake L = 1/2W, then L/W = 1/2 and theresistance value is half that of onesquare. By varying the ratio of L to Wwe can produce a range of resistorvalues. The principle is shown in Fig. 3.If we change the composition of theresistor, then we get a different valuefor the resistance of one square. Onceagain we can choose the exact value byvarying L/W. Since inks are available

2 =

Left. Exploded view of a hybrid data selection unit. Theunit combines thick film hybrid circuits with a double sidedplated through hole printed circuit board and a package containingan L.S.I. silicon integrated circuit. Courtesy Welwyn Electric.

Above. A thick film power resistor for use in televisionreceivers. Courtesy Erie Electronics.

R=RS

nl

-=

U.S5

IEI

21

_H

R.2Rs

Icl

R4 RSId!

Fig.3. The principle of film resistors. Any square of the same material has the sameresistance Rs . As both a and b are squares of the same thickness, they are bothresistors of value Rs. Since c is twice as long as it is wide, it is a resistor of value2Rs and d is similarly

PRODUCE LAYOUT OFPATTERN

ADJUST RESISTORSTO DESIRED VALUE

SOLDER DIP AND

ADD LEADS

PRODUCE ACCURATEMASTER

10 U FULL SIZE-1

PRINT AND FIRERESISTOR AND

CONDUCTOR PANELS

TEST

PHOTO REDUCE TOFINAL SIZE

PRODUCE SCREENPATTERNS

COVER WITH RESINPROTECTION

Fig.4. Schematic of thick film production processes.

16 ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

Left. Focus potentiometer for colourtelevision sets. Courtesy Erie Electronics.

Centre left. Custom built thick filmhybrid assembly for the consumer market.The photograph shows from left to rightthe substrate with resistor and conductorpatterns immediately after firing. Thecomplete assembly prior to encapsulationand the module ready for assembly intoa printed wiring board. Courtesy ErieElectronics.

Bottom left. High power multiple resistorassemblies with heat sinks for the consumerelectronics market. Erie Electronics.

which produce a range of sheet resis-tances from fractions of an ohm for asquare up to several megohm/square,by choosing the correct inks andgeometry we can produce resistorsfrom about 1/2 ohm up to many meg-ohms. If need be we can print a rangeof inks in one network so that widelydiffering resistor values can be used inone circuit.

The conductor patterns serve tointerconnect the resistors and to enableelectrical contacts to be made betweenthem and the outside world. Theirdimensions are very much less criticalthan those of resistors. Some of thephotographs show typical networks.

In the next section we shall look atsome of the stages of production of athick film resistor network.

THICK FILM PRODUCTIONFigure 4 shows schematically the mainproduction stages for thick films. Aftera rough design of the pattern has beenproduced, it is drawn accurately, usuallyat ten times full size. This is photo-graphically reduced to the exact size.The resultant negative is then used toproduce the screens for the printingprocess. Fig. 5 shows the resistor andconductor patterns for a single powerresistor for T.V. use and its final shapewith pins for soldering into a printedcircuit board. (Examples of similar re-sistors may be found in most currentand recent colour T.V. sets).

In the screen printing process amesh of polyester (terylene) or stain-less steel mounted on a metal framehas most of its area blocked with anemulsion material. The only areas whichare free are those where the pattern isrequired. The substrate is held beneaththe screen and a hard rubber squeegeemoves over it, forcing ink through theholes leaving a printed pattern on theceramic; this is shown in Fig. 6.

In production, hoppers feed thesubstrates into position and automaticprinting takes place at a rate of manyhundreds per hour. The printed sub-strates are then fed onto a belt througha drying zone at 150°C before movinginto giant belt furnaces for the firing ofthe glaze. They are then ready for thenext stages of production. If the resis-

ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973 17

THICK FILMCIRCUITStor values are not very critical, thenetworks may already be within toler-ances. If so, the leads or pins used forconnection to the outside world aresoldered in place. This eliminates onemajor production stage, keeping thecost down. In general, however, it is

unlikely that a high yield of better

STRETCHEDPOLYESTER ORSTEEL MESH

'EMULSION (EXAGGERATED)

UNUSED INK

- KIK

INK..

HARD RUBBERSQUEEGEE

APERTURE IN PATTERN

(a) CONDUCTOR PATTERN (b) RESISTOR PATTERN (c) PINNED, SOLDEREDAND ADJUSTED.

Fig.5. Thick film power resistor for plugging into a TV p.c.b.

METAL FRAME

BEFORE PRINTING

WET PRINT

CERAMIC SUBSTRATE

Ib) AFTER PRINTING

than about 25% tolerance resistors willbe obtained in this way.

More commonly the resistors are ad-justed upwards in value after firing andbefore soldering. We saw earlier thatthe value depends on the ratio of lengthto width. Adjustment alters this ratioby removing part of the resistor area,(Fig. 7). This may be done in either oftwo ways. In the older, but very com-monly used process, a fine jet ofabrasive particles is fired at the resistoruntil its value reaches a target. Inproduction, machines are used which

Professional electronics industry hybridthick film module. Courtesy NewmarketTransistors Limited.

:A3,----ARREEMAOVED INADJUSTMENT

W.L R .R5

(RI BEFORE

W=22 -L

Ib) AFTER

Fig6. (left) The screen printing process.

Fig.7. (above) Adjustment of thick film resistors.

Thick film hybrid circuit for the military or aerospace market. The photographon the right is of the same unit but with four miniature transformers. CourtesyAB Electronic Components Ltd.

automatically adjust several resistors ata time to a target of ± 1% and thenstop and pass onto the next substrate.Any reject is automatically thrownout. A much faster process using lasertrimming is now taking over in massproduction, especially for consumerproducts. The capital outlay of a

computerised laser trimmer is about£60,000, but the fantastically fastthrough -put of accurately trimmedcircuits leads to a lower unit cost thanby air abrasion.

After soldering and attachment ofleads, the network is coated with aprotective resin layer and is available

to the customer after a final electricaltest.

HYBRID CIRCUITSFor many purposes a plain resistornetwork is insufficient. Many of thethick film networks in use have transis-tors and other devices mounted ontheir surfaces: these are called hybridcircuits. Some very complex circuitsare made in this way. The semiconduc-tor devices are sometimes added ascheap plastic transistor packages sol-dered in place, but are also used un-packaged as chips of silicon mounteddirectly onto the film. Special minia-

18ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

Computer interface circuit showing a pack-age which is used in large quantities byBritish computer manufacturers because itspins are dimensionally compatible withthose of the standard integrated circuitDIL package. Courtesy Erie Electronics

Right. Thick film screen printing process.Courtesy Middlesex Polytechnic,

ture capacitors are also used. These maybe ceramic chips for low values or drytantalum for high values. The photo-graphs illustrate a number of hybridcircuits with their added components.The completed and tested hybrid is

finally resin encapsulated.

APPLICATIONSSpace only permits a grief mention ofa few applications of thick films and

hybrid circuits. A vast number of resis-tor networks and true hybrid circuitsare still being used by the computerindustry. Many leading radio and T.V.manufacturers are now including thickfilms in their sets. This demand is stillgrowing and will probably continueto do so with the boom in colourtelevision. Another growth area is theautomotive market, many thick filmcircuits are now in production for use

Loading printed substrates into a belt furnace. Photo courtesyMiddlesex Polytechnic.

in cars. The pioneer for this in theBritish market was a voltage regulatormade by Joseph Lucas which has beenin production for several years. Othercar and component manufacturers areusing this new tool to produce cheapsophisticated electronic devices fortheir vehicles. Much of the newgeneration of car instrumentationcoming into use employs a combin-ation of thick film and monolithicmicroelectronics technology.

CONCLUSIONSSince the mid 1960's the consumer andindustrial electronics industries havechanged greatly in their technologies.Firstly the take-over of transistors fromvalves produced a great revolution. Thenext stage which is with us now is theintegrated package - integrated semi-conductor circuits or thick film andhybrid circuits. The fallout of mono-lithic integrated circuits from industryis now making its full impact on thehome constructor (this can be seenfrom the advertisements in this journal).These circuits are made to performspecific functions which have applicationin fields far from their original purpose.Thick film circuits and hybrids are lesslikely to hit this market because theyare very rarely made as general purposefunctions. Almost invariably they aremade for specific applications andwould have no value elsewhere. (Oneexception is a thick film hybrid poweramplifier produced by one of the lead-ing Japanese manufacturers for thehome user. This is a sophisticated andcomplex product employing the tech-nology very effectively). However, it isextremely probable that more and moreof these packages will be met in thecourse of servicing equipment. In theevent of failure they should always bereplaced with a similar module fromthe manufacturer.

ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973 19

HI-FI -thestate of the art

Editorial Director, Collyn Rivers, reports.

Photograph reproduced by courtesy of Trio Electronics, Tokyo

20 ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

HEIL AIR MOTION PRINCIPLEDiaphragm of Heil driver is a convoluted polythene membrane carrying a

continuous -foil conductor analogous to the 'voice coil' in a conventional speaker.This diaphragm is inserted between two large magnetic pole pieces.When the electrical audio signal passes through the conducting foil, the folds of the

diaphragm vary their spacing, thus altering the space between them and hence generatingthe acoustic signal.

The unusual action of the driver produces a very large air movement for a small motionof the diaphragm - thus it is very efficient - about 3 to 4 percent say Heil.

Not apparent from the drawing is that the magnetic pole pieces are in fact an open gripof parallel strips thus allowing the sound to be emitted from both sides of thediaphragm.

Practically unique in its operating principle, the Heil driver has extremely low inertiaand no resonances within its operating range.

DESIGNERS, whether of hi-fiequipment, motor cars, or evenhouses, tend to fall into two maingroups - categorised by the way inwhich they think, or are allowed tothink.

The first type of designer thinks'vertically°. He develops new devicesby building on the accumulatedexperience of what went before -examples of this are the Shure V15 MkIll cartridge (reviewed in this issue),the Rolls Royce motor car and themajority of domestic architecture.

The second type of designer thinks'laterally'. He takes advantage ofmodern technology but little heed ofthe form ii which previous generationsthought things should be. Here,examples of lateral thinking includethe Beogram 4000 turntable, the HeilAir Motion loudspeaker, the IDCitroen and the BLMC Mini, and, thefield of housing, Buckminster Fuller'sgeodesic domes. (readers interested inlateral thinking should study thenumerous books by Edward de Bono).

Until recently, the hi-fi industry hasbeen characterised by vertical designwith very few truly fresh approachesto problems:There have been a few exceptions -

such as Henry Kloss' development ofthe AR range of acousticallysuspended speakers, Ray Dolby's noisereduction system etc, but these areexamples of what one might describeas 'diagonal thinking', owing as theydo, something to both designapproaches.

The biggest problem afflicting thedesigner committed to the horizontalapproach is that he is almost invariably

competing with conventional systemsthat despite their fundamental'wrongness', have, nevertheless, beenrefined over decades of verticaldevelopment. A classic example of thisis the reciprocating internalcombustion engine, another is thedeep keel yacht.

It is then all the more to the credit ofBang and Olufsen that their newBeogram 4000 turntable is so good.

Now, all over the world, designengineers are taking a fresh look atmany areas of hi-fi equipment designand, in our opinion at least, the nexttwo or three years will see some mostdramatic developments in the recordingand reproduction of sound.

VALUE FOR MONEY

On a more down to earth level, somevery worthwhile developments havebeen taking place primarily in theupper and lower thirds of the hi-fiprice range.

A couple of years ago it was said'hi-fi starts around £200'. This is stillvery largely true today - althoughseveral companies are producingcomplete systems at £100 or evenless. One example of these is Pioneer'snew 'Prelude 500' system (sold only asa total package of amplifier, turntableand two speakers) at a recommendedretail price of about 5300. This systemis not yet available in Britain.Two years ago the optimum amount

of money to spend on a hi-fi system -judged purely on a performance/pricebasis - was somewhere between £300and £400. Surprisingly, despite inflat-ion, the best value for money is now

achieved by spending slightly less.The reason for this is the recent

introduction of a number of reallygood loudspeakers costing between£60 and £100. Many of these, such asthe smaller products from AR,Advent, Dynaco, Audiosound,Rectilinear etc, compete with theirlarger and more costly counterparts inpractically every way except powerhandling capability.

True, it is still not possible to obtainreally deep bass from a smallloudspeaker, but for the great majorityof hi-fi enthusiasts the limitation onbass reproduction is the size of theirlistening room rather than the depthof their pocket. As this is a pointrarely understood by hi-fi enthusiasts,we have included a table within thisarticle listing the lowest bassfrequency that can be realisticallyreproduced in rooms of variouslengths.

TOP OF THE SCALE

At the upper end of the price scale,recent developments include theBeogram turntable previouslydescribed - even at its selling price of£160 plus, people are queuing up tobuy it. Shure's new V15 Mk III is

somewhat of a mile stone (kilometrestone ?) in cartridge design for ittypifies what may well be the ultimatemanifestation of this type of design. Itis difficult to see what furtherimprovements could reasonably bemade whilst staying within the boundsof current technologies.

In the field of loudspeakers, the HeilAir Motion Loudspeaker may well bethe first of a new generation ofloudspeaker designs. At present it isavailable only as a midrange andtreble unit, but the manufacturers areactively developing a bass driver aswell. We have not heard this unitourselves, but authoritative sources inthe USA are lavish in their praise.Hirsch -Houck Laboratories forinstance wrote 'Even if we had neverlistened to ... this speaker, itsmeasured frequency response, alonewould invite the use of superlatives.This is one of the few speakers wehave tested, in a normally 'live' room,whose overall frequency response andsmoothness are comparable to those ofa good high-fidelity amplifier - andthat is no small achievement'.

For those who prefer a moreconventional approach, AcousticResearch's LST is probably theloudspeaker equivalent of the newShure cartridge. It is best described asthe ultimate AR3a, and for those whocan afford the room - and the price -it is well worth consideration.

ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973 21

Shure's superb new V15 Mk Ill cartridge. Trend -setting 'Prelude 500' system from Pioneer retails for less than $300.

TAPE RECORDERS

Enormous improvements have beenmade in cassette decks and it is nowpossible to buy cassette machines thathave a standard of reproductionvirtually indistinguishable from reel toreel machines. Inbuilt Dolby or othernoise reduction systems are nowstandard in all top quality cassettemachines, and the use of these circuitshas removed the tape hiss that wascharacteristic of cassette players untilrecent times.

Regrettably there is still a shortage ofpre-recorded cassettes of anyworthwhile standard and far too muchpre-recorded material is produced ontape of such poor quality that one canbut marvel at the sheer cynicism of theproducers. This is rather a pity becausesome truly excellent tape cassettes arenow readily available, and these highquality cassettes must be used if theperformance built into the top cassetteplayers is to be exploited.

The arguments and counter -arguments between protaganists of ironoxide and chromium dioxide tapesstill rages. At the risk of losing all ourgood friends in the tape business it isour opinion that there is very littledifference in listening quality betweenany of the tapes made by the leadingcontenders. It's a bit like the lightplatter versus heavy platter turntableaffair - it doesn't really matter whichtechnique is used just so it is usedproperly.

It is of course true that chromiumdioxide tape must be used with amachine for which it is specificallyintended as quite different bias levelsand erase levels are required.

Equally important is to use the taperecommended by the machine'smanufacturer, or, for those with thenecessary technical ability, to optimizebias for one brand and type of tapeand to use that tape only.

Advances in reel-to-reel machines arenow confined almost entirely to thosemachines intended for professionaluse. Excellent reel-to-reel machines arestill marketed for domestic use, buttheir sales seem to be mainly limitedto tape enthusiasts who find thatediting is so much simpler with thistype of machine.

AMPLIFIERS

Amplifier development continuesalong conventional lines, althoughthere is an increasing tendency towardhigher power outputs. Thejustification for such large amplifiers isthe inefficiency of many new types ofspeaker systems. In fact it is probablytrue to say that were it not for theavailability of multi -hundred wattamplifiers, the transmission linespeaker (and others) would not havebeen commercially feasible.Performance of top quality

amplifiers is now very good indeed -they are fast approaching the ideal of apiece of non -inductive wire withadjustable frequency characteristicsand gain.

At the lower end of the scale thereare now some excellent amplifierspriced between £100, whichare more than adequate to drive thenew generation of similarly pricedspeakers described above.

THE GREAT FOUR -CHANNEL WAR

One day in the future, battle scarredmarketing executives are going to taketheir grandchildren on their knees andtell them wondrous tales of the GreatFour -Channel War.

Now well into its third year, there isstill not the slightest sign of a

reconciliation between the competingmatrix and discrete camps, althoughthe battle lines are now more clearlydefined, for, going along with that fineold Middle Eastern proverb that 'theenemy of my enemy is my friend', thevarious matrix proponents (with thepossible exception of Sansui) nowappear to see the RCA discrete systemas their common enemy.

MATRIX SYSTEMSBasically all matrix systems are the

same in that they attempt to encodefour channels of information onto atwo channel record (or tape).Decoding circuitry built into thereceiving equipment then decodes theencoded material - aiming (but notalways succeeding) to direct eachinformation channel to its 'correct'loudspeaker.The only real difference between the

competing matrix systems lies in theproportions and phase relationships in

which the original four channels ofprogramme material are mixed downto two - and expanded out to fouragain. Following some furioustechnical battles between a dozen orso companies, there now remain onlytwo major contenders, Columbia's SQsystem, and Sansui's QS system.

The Columbia SQ system is favouredin the USA, and, according toBenjamin Bauer of CBS Laboratories,75 brands of audio equipmentproduced by SQ licencees are nowavailable, or are about to becomeavailable, both in the USA andoverseas. These 75 brands, claims Mr.Bauer, account for more than threequarters of the sales of audioequipment world-wide.

United States patent 3 708 631 hasbeen issued to Columbia coveringvarious and broad aspects of logicdecoders, and cross-licencingagreements have been signed withElectro-Voice that enables SQlicencees to take advantage ofdevelopments from both companies.

The main advantage claimed for theSQ matrix is that it is compatible withboth stereo and mono playbacksystems - and this is of primeimportance when it is realised that atleast 90 percent of record buyers listento records on mono players.

Sansui's QS matrix - which is beingadopted by an increasingly largenumber of Japanese companies - is farless satisfactory in this respect. QSencoding yields a disc that has verypoor left to right hand separationwhen played on stereo equipment andvery strange effects indeed playedmonophonically.Against this, front to rear separation

is much better than with SQ althoughthe so-called 'gain -riding' circuits thatare added to the more expensivedecoders increase the channelseparation on most programmematerial. These gain -riding circuits areavailable for both QS and SQ systems.

Actually it is slightly misleading tospeak of QS and SQ matrices, for bothsystems have been modified severaltimes during the past few months.Parameters of the two systems arebecoming closer together, and, whilstQS decoding is still not verysatisfactory for SQ discs - and viceversa - the differences between the

two systems are now relatively smalland it is more than likely that therewill eventually be a common format orone so similar as to be virtuallyidentical.

The SQ system has been chosen bythe great majority of FM broadcastingstations. These stations transmit SQrecords by conventional stereobroadcasting which are then decodedby the listeners' receiving equipment.In the US, over 200 stations broadcastfour channel programmes in thismanner.

Commercially, the cost of SQdecoders should fall substantiallyfollowing Motorola's development of asolid-state integrated matrix chip (MC1312). Two further associated chipsfrom Motorola are logic module MC1315 and power transfer module MC1314.

The MC 1314 module is technicallyinteresting in that it acts as a gaincontrol and speaker balance elementpermitting the gain of all fourchannels to be adjustedsimultaneously, with a tracking errorof less than 1 dB over a range of 80dB.

At present the highest degree ofseparation that any matrix system canachieve is 20 dB in all directions - butthis can only be obtained with themost sophisticated of gain -ridingsystems. Neither system can reproducedifferent sounds from all four channelssimultaneously.

DISCRETE FOUR -CHANNEL

Discrete four -channel sound suffersfrom few of the limitations of itsmatrixed counterpart, b,eing recorded,as its name implies, on four quiteseparate information channels.

Initially, discrete four -channelconsisted of reel-to-reel tapes andassociated tape decks, but the systemdid not meet with any noticeablesuccess until RCA's release of 8 -trackcartridges under the trade nameQuad -8. Subsequent legalcomplications caused RCA to changethe name to Q-8 and they are stillmarketed under that name.

In 1972, RCA introduced theJapanese -developed CD -4 disc. Unlikethe matrix recordings that attempt tocram channel routing information intothe two normal stereo channels, theCD -4 disc actually carries an additionaltwo channels of information. This isachieved by extending the frequencyrange to 50 000 Hz. The frequencyrange up to 15 000 Hz is used to carrythe combined front and rear signals forboth right and left channels - and thehigher frequency channels carryinformation necessary for separatingfront and rear channels.

A demodulator, operating in a verysimilar manner to decoding circuits in

TABLE I

Length of room(in metres)

Lowestreproduciblefrequency

(in Hz)

4 85.755 68.606 57.107 49.08 42.8

10 34.312 27.5

FM tuners, sorts out the various signalsrouting each (subsequently amplifiedsignal) to the appropriate loudspeaker.

Sceptics - who almost withoutexception have not heard the CD -4system in operation - doubt theability of a stylus and pick-upcartridge to operate at frequencies ashigh as 50 000 Hz. Nevertheless theShibata stylus (specifically designedfor the CD -4 system) copes admirablyand both JVC and Panasonic areproducing the necessary cartridges anddecoders.

Decoding circuitry for the CD -4system is very complex but a wellknown manufacturer of specialisedIC's will have a CD -4 decoding chipavailable in the very near future andthis will reduce the complexity of theCD -4 decoders enormously.All RCA records are now produced

in the CD -4 format as the system istotally compatible with both stereoand mono record players. The use of anew vinyl formulation for the recordshas ensured that four channelinformation is not destroyed when therecord is played on mono equipment.

Original CD -4 discs were cut at onethird playing speed, however recentadvances have enabled this to beincreased to one half playing speedand it is hoped that they willeventually be cut at normal operatingspeed.

The discrete and matrix systems aretotally incompatible. If both are toremain in use, equipment must eithercontain decoding circuitry for each -or the user must purchase twodifferent systems - or at leastdecoders.

Although a number of world famousequipment manufacturers are not yetproducing four channel equipment, itis now practically certain thatfour -channel is here to stay - the onlyremaining question seems to be thereally big one of which system will winout - or will be have two competingsystems with all the attendantcomplications?

Or, although the equipment industryneeds this like a hole in its head - willa lateral thinker come along with anew and brilliantly simple approach*

BUILD THE

TREASURETRACER

MK IIIMETALLOCATOR

Incorporates varicap tuning for extrastability

Weighs only 22oz and has perfectbalance

Loudspeaker or earphone operation(both included)

Handle knocks down to only 16infor transport

Ministry approved design

Excellent sensitivity and stability

Kit can be built using only solderingiron, screwdriver, pliers and wire snips

Drilled, tinned, fibreglass p.c. boardwith component siting printed on

Incorporates Faraday screen

Send for s.a.e. for leaflet

Complete kit £9.80with pre -built Plus 35p Postsearch coil

(inc. VAT)

Built, tested £13 75and Plus 35p PostGuaranteed (inc. VAT)

MINIKITS ELECTRONICS,35d Langley Drive, Wanstead,

LONDON Ell 2LN(Mail order only)

ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973 23

SHURE V15MK III

PHONO- CARTRIDGE

electronicsTODAY

IN!ERNAT IONAL

I product test I

Shure V15 Mk III cartridge with 1 kHzsquare wave input (7cm/sec)

FOR many years, the Shure V15 MarkII cartridge has been regarded byaudiophiles as being one of the bestcartridges that money can buy. Thereason for this is simply that in termsof the main criteria of fidelity,trackability and lack of colouration,the V15 Mark II has few peers.However, the linearity of the Mark IInever quite matched the excellence ofthe rest of the cartridge, and in thisone respect there are many cartridgeswhich are undoubtedly superior.

This clearly bothered Shure and so,over a period of seven years, they havedeveloped a cartridge which is a

worthy successor to the Mark II. Quitenaturally, the designation for the newcartridge is the V15 Mark III.

Each new cartridge that ShureBrothers have released has generallybeen a state of the art improvementover their cartridges that have gonebefore - the new Mark III is noexception.

The designers of the Mark III aimed

"One of the world's topcartridges - it is quite probablethat it is the best."

at improving several aspects ofperformance; perhaps the mostimportant of which was to flatten thefrequency response in the regionbetween 10 kHz and 20 kHz. Thosefamiliar with the design oftransformers will realise that the highfrequency roll -off of the V15 Mark IIwas primarily attributable to the lackof an optimally laminated corestructure. However, it is one thing topropose a laminated core structure andquite another to produce the type oflamination required when theminiscule size of such a transformer isappreciated.

Nevertheless, Shure have developedmanufacturing techniques that hasenabled them to build laminated coresand these are now fitted to all Mark IIIcartridges.

A second major change was that thegeometry of the pole pieces neededoptimisation in order to eliminate - orreduce - the effect of non-linearitiesin the air gap. The result of this is

improved efficiency, flatter frequencyresponse and significant improvementin cartridge output at the top end ofthe frequency spectrum.

The next area attacked was in theactual stylus and stylus assembly. Weknow from simple mechanics that alower mass is easier to move than aheavier one, hence the lower theeffective mass in the stylus, the greaterthe ease with which the stylus canfollow the record groove. But a simplereduction of mass itself is not the solecriteria. Rather it is the correctimprovement of dynamic compliancein order to be able to cope with thehigh velocities that exist on manyrecords. Whilst the V15 Mark II had aneffective tip mass of 0.45 milligrams,the Mark III is reduced to 0.33milligrams. This reduction is notdramatic, nor could it be, because ofthe need to produce a stylus leverstrong enough to work.

Having looked at Shure Brothers'design philosophy, it now remains forus to see what the V15 Mark IIIachieves in practice.

When one has for review what maywell be the best cartridge in the world,

24 ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

IB

Br uel & Kier5

Coweog.

WesurmgFRE OU E NC Y

RESPONSEOF SHUREV15 MARK IIICARTR I of1F

DIELFRFNCEAFTWFFNHPRFRialL_J (WE? CURVF5RIPPE SINT S

CHANNEL_SF PARAT 1 nN

2 5 IN AA46.4.11.4_ r

Oa.- 5/7/710 0 5, LAC 0

10

OP 1124

Potentiometer Renter -SD-dB Rectifier kja S LOW*, Lint Freq _21:1_ tia W,. Speed: _3..L.5_,Ten/ten. Paper Speed: __L.moVeec

50

MON, y Fr buena, Scar by

20 Hz 100 200

the techniques available to evaluate itsperformance are critical. The ShureBrothers' test record "AcousticalObstacle Course" TTR101 did notreally provide a good enough test forthe trackability of the Shure V15Mark II, let alone the Mark III.So howdo we evaluate the performance of theMark III? This problem obviouslyworried Shure Brothers long before itbecame our problem, and theirapproach was to develop two newrecords. The first of these, theTTR110 "Audio Obstacle Course,ERA III" was specifically developed toshow the differencebetween the V15 Mark III and other"lesser" cartridges.

This record was not available at thetime of the test, though it is now;cost is £2.97. However, cartridgesdistributed in Britain by Shure Electr-onics Ltd include a voucher for afree copy of this record.

The second record, the TT103is designed for laboratory testing andcosts £6.93 but once again was not

Shure V15 Mk III shown here in an SME tone arm.

500 1000

Zero bawl2000 10000 20000 40000 0 A B C La

11612/2112) A

available at the time we performedour tests.

Hence we were obliged to useprogramme material from standarddemonstration records such as Shure'sTTR 101. Fortunately, apart fromassessing trackability, we had nodifficulty in measuring all otherparameters, nor in subjectivelyevaluating the overall performance ofthe cartridge.

The frequency response of the MarkIII has a maximum excursion of ±1dBbetween 20 Hz and 20 kHz wheninstalled in the average tone arm, andX1.5 to an arm such asthe S.M.E. Whilst the level recordingsshow a rise at 18 kHz, this is a

characteristic of the test record notthe cartridge. This measured responseis significantly better than that of theMark II.

Cross -talk in the critical regionbetween 200 Hz and 20 kHz showed achannel separation of not less than 25dB generally, and nowhere less then 20dB. Again the limitation here is the

MEASURED PERFORMANCEOF SHURE V15 Mk IIICARTRIDGE

Frequency Response(20 Hz - 20 kHz) ±0.5 dBSensitivity(at 1 kHz at 5 cm/sec)

1.75VChannel Separationlat 1 kHz) 25 dB

RECOMMENDED RESALE PRICE:£39.60 inc. VAT

quality of the test record.

Square wave tests showed that theeffective frequency response extendsto at least 25 kHz without anysignificant resonance effects beingapparent. The square wave responseshowed less ringing than any cartridgepreviously tested.

It is in the region of trackability andlack of colouration, however, that theMark III really excels. This cartridgehas the cleanest response of any thatwe have had the pleasure of testing,and can cope with the mostdemanding programme content thatwe have in our record collection. Wecould not fault it in any way.

The Shure V15 Mark Ill is a trulyexcellent cartridge, but for its fullpotential to be realized it must be usedwith a top quality amplifier andspeakers (we used a Thorens TD125table, plus an S.M.E. arm; a PioneerSA1000 Amplifier, and JBL ControlMonitors). Top line records are alsonecessary or the results areunquestionably poor. But providedthat good quality equipment ismatched to this new cartridge, theresults will be truly superb.

The Shure V15 Mark III is one of theworld's top cartridges - it is quiteprobable that it is the best.

ELECTRONICS TODAY INTERNATIONAL -OCTOBER 1973 25

MAGNETICLEVITATIONby Dr. Peter Sydenham

Will magnetic levitation replace the wheel?

THE repulsive and attractive forcesproduced between magnetic poles havebeen experienced since magneticlodestone was discovered manythousands of years ago. But on a

comparative time -scale, our knowledgeof the electric magnet is quite recent.It was only in 1820 that Ampere,Arago, Davy and Henry laid thetheoretical and practical foundationsof the design of electromagnetsshowing that they were, in fact,analogous to the permanent magnetsalready in existence. Forces producedwith electromagnets were soonharnessed to build galvanometers,electric -wire telegraphs, generators andmotors. Few, if any, worthwhileapplications used the force as a

suspension.Theoretical considerations developed

by Earnshaw in 1839 proved that it isnot possible to site a strong magneticpole (of either kind - permanent orelectric) in a static magnetic fieldwithout added positional constraints.This was derived as the consequencethat magnetic force increases as theinverse square of the separationbetween the force source and themagnet. Since then, numerousinventions have been devisedattempting to make use of magnets toprovide stable suspension, but it is

only in the last decade that realsuccess has been forthcoming.

Like, poles attract and unlike polesrepel, so each offers the possibility ofsuspending one mass relative toanother. If the polarities are opposite(or one pole is a magnetisablematerial) the magnet hangs, usingattraction. The system, however, is

unstable, for the closer they comealtogether the greater the attractiveforce accelerating them toward eachother - they end up tightly clamped.

Like poles repel, so the suspendedmagnet would, hopefully, sit above theother magnet. However, ourexperience shows any slight imbalanceabout the central position produces anunstabilising collapsing force thatincreases as the top magnet starts toslide off the top. An alternativesuspension uses N -S and S -N pairs in ahorizontal direction, as shown with

FIXEDMAGNET

WALLOF THEVESSEL

N

S

,SUSPEN-DEDMAGNET

SUPPORTEDMAGNET

FIXEDMAGNET

FIXED MAGNETS

SUSPENDEDMAGNET

WALL OF THEVESSEL

Fig. 1. Three basic alternatives exist for suspending a mass using a magnetic field.

the other alternatives in Fig. 1. Thisalso will be unstable moving to oneend or the other.

A unique feature of the magneticsuspension is that a physical (nonmagnetic) material can exist betweenthe two magnets, a feature not offeredby bearings or air cushions.

STABILISING A MAGNETICSUSPENSION

An obvious way to produce a stablesuspension is to incorporate extradevices to obtain stability in thevertical or horizontal directions as

needed. These can be, in the repulsivesystem, low friction guides or moremagnetic pairs placed in the verticalplane.

The usual way to stabilise the

MAGNFTCONNECTION TO THE BALANCE

IRON CASING

CONTROL WINDING

NOICATOR WINDING

WALL

MSC

MAGENT

IRON CASING

OSCILLATOR

W

attractive system uses a servo -controlthat senses the relative closeness of thetwo poles (one may be induced by themagnet) using a displacementtransducer signal to control the powerof the electromagnet attracting thesuspended mass. This, therefore,maintains the distance constant andthe closed -loop feedback is, in effect,modifying the inverse square law toone having a highly stable region.

The principle is used in a recentlymarketed chemical balance withmicrogram resolution. A schematic ofthe system, having its origins in thework of Professor Gast of the WestBerlin Technical University, is

presented in Fig. 2. A permanentmagnet provides attraction for themajority of the mass of the weighingpan; a control winding provides the

FREQUENCY OUTPUT D.0 -OUTPUT

DC

AMPLIFIER

E AL DI.

MAGNET

LOAD

Fig. 2. Cross-section through the magnetic suspension used in a sensitive chemicalbalance. The schematic circuit arrangement shows how a variable frequency outputis obtained and the suspension stabilised.

26 ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

extra force required, both operatingthrough the wall of the evacuatedweighing chamber. The operation is asfollows: As the pan moves up towardthe magnet coil the copper diskreduces the inductance of theindicator/position-sensing coil. This,in turn, alters the frequency of thesensing tuned circuit providing a

variable frequency output related todisplacement. Stability of suspensionis provided by converting the variablefrequency to a direct current that thenfeeds the control winding, controllingits attractive force. If correctly phased,the feedback causes the pan to remainsuspended.

The same setup can be used tomeasure flow by passing the fluid upagainst a drag -plate mounted wherethe pan would be. It can also measuredensity if the upthrust of the pan ismonitored when it is immersed in afluid. A gravity meter has beenconstructed using a superconductingsuspension coil in this way, the featureof superconductivity being thesmoothness of the field strength.

Another instrumentation exampleusing magnetic suspension is theexperimental magnetically suspendedmotor developed by NASA staff. Therotor (see Fig. 3), consists of a

suspension cylinder, that rotates as

part of the rotor, and imbeddedmagnets that produce the motortorque when reacted against with anexternal starter winding. There is noreal difficulty with suspending the twoends of the rotor inside the suspensioncoils for it automatically aligns itselfto be in the centre, the position ofleast magnetic reluctance. Activestabilisation is needed, however, tocontrol the rotor position between thetwo coils for without it the rotorwould pull to one or the other end.Here photocells sense the end of thecylinder controlling the solenoid fieldstrengths so as to retain the rotormidway. A special design of motor wasdeveloped to reduce the radial forcesexperienced in a normal design ofmotor. The suspension is quite stiff -20kg/mm, in fact, and the powerneeds relatively small - around 10Wper bearing. This development leadsthe way to more reliable and moresensitive motors, especially ingyroscope application where thefrictional torque of normal bearingsprovides an unwanted precessiontorque.

If the inductance of the magnet coilin an ac -excited attractive typesuspension is series tuned with a

capacitor, movement of the suspendedmagnetic material alters the resonantcircuit current adjusting thesuspension force to compensate. Butthis only holds well enough for asituation where the movements occur

CONTROLLER OF COIL CURRENTS TO STABILISE END FLOAT

STEELCYLINDERFLOATS INMAGNETICFIELD

SUSPENSION SOLENOIDWINDING ROTOR OF MOTOR

STEELCYLINDERFLOATS INMAGNETIC FIELD

SUSPENSION SOLENOIDWINDING

STATOR OFMOTOR

Fig. 3. Arrangement of a motor using magnetic suspensions instead of contact bearings.

slowly or are static. Jayawant andKaplan of the University of Sussexhave continued on from earlier workon suspension design using thismethod and have researched, withworking models, ways to improve thedynamic stability. A solution proposeduses a saturable reactor as shown in aschematic of their system given in Fig.4. (Russian workers have also reportedthe use of this tuning idea, but toreduce forces, in a variable reluctanceposition sensor.)

There is a notable exception to theEarnshaw theory mentioned earlier:Braunbek showed in 1939 that theintroduction of a material having a

relative magnetic permeability (µ) lessthan unity into the field space wouldresult in stable levitation. Diamagneticmaterials have /..t less than unity -bismuth and carbon being examples.The magnetic forces exerted in thiscase are, however, only capable ofsupporting minute loads so it offerslittle real advantage in normalsituations. Superconductors, however,behave as almost perfect diamagneticmaterial (flux cannot penetrate the

skin) so it is possible to provide astable suspension in special caseswithout the need for auxiliary devices.A gyroscope, using a superconductingrotor has been built using thisprinciple. Research has also beencarried out on the use of levitatedsuperconducting rings to confineplasma.

THE GREAT INTEREST -MAGLEV VEHICLESWe have already seen some of the

proven uses of magnetic suspensionsbut these, although revolutionary, arefast becoming overshadowed by thegrowing interest in their applicationfor the support of high-speed trains.To appreciate the designs suggested formaglev trains we must first considerthe properties of magnetic suspensionswhen used as a continuous frictionlessguided slide rather than as a singlepoint stationary support.

A time varying field, such as thatproduced by an ac magnet, willproduce a counter field that canprovide lift. The so called "Foucaltrailway" devised by Bachelet in 1912

RESONATING SATURABLECAPACITANCE REACTOR

DETECTOR

400 Hzvoltagesource

LOW PASS S

FILTER DIFFERENTIATOR

DC

AMPL.

BIASCURRENTSOURCE

5

.11

SUSPENSIONMAGNET

Fig. 4. This arrangement is used to obtain dynamic stability from a tuned ac attractingsuspension.

ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973 27

MAGNETICLEVITATIONused the eddy currents, induced in athick aluminium plate by thefluctuating field, to provide a repulsiveforce between the plate and a

continuous row of fixed coils lyingalong the track of the model system.This method, at the time, had highpenalties, namely, excessive powerrequirements to provide the lift, smallgap clearance and costly magnetsystems. Consequently up to a decadeor so ago, maglev by this methodseemed to be a non-starter in a

large-scale economic situation.If, however, the magnet is moving

relative to the conducting plate it is

possible to make use of Bachelet's ideawithout the need for ac excitation ofthe electromagnet. For example, a

magnet moving over the surface of analuminium sheet will induce eddycurrents that repel it. In effect, animage magnet is produced as shown inFig. 5. (You might try mounting a barmagnet on wheels so that it just clearsthe surface and run it over analuminium rail or surface - it shouldlift off as the speed rises.) Thisprinciple is now one of the maincontenders for levitating trains.Changes in technology, from the1950s onward, have enabled magneticlevitation to become a practicalreality. Initially it was the new foundability to produce high coercivityferrite permanent magnetic materialsof relatively light weight that enableda number of groups to build and testvehicles using repulsion betweenpermanent magnets. A cross-section ofa scale -model constructed by Polgreenaround 1966 is shown in Fig. 6.

The next, and most relevantdevelopment, toward efficient maglevsystems was the improved capabilitywith superconducting technique -larger and more reliable refrigerationunits were developed; uniqueconducting cables were devised andmanufactured that do not lose theirsuperconducting properties until veryhigh magnetic fields are approached.

Superconducting magnets, being 100times stronger than normal magnets,have the potential advantages thatthey can produce a suspensionclearance ten times greater thannormal magnets and that, once setgoing, the superconducting currentonly needs topping up at intervals,thus avoiding the need to carry currentgenerating equipment on the train.The first advantage is very real for thecost of producing and maintaining apermanent way rises rapidly whentolerances exceed 10-50mm.

4 SPEED V

LIFT TOTAL FORCE

-41. DRAG

VEHICLE MAGNET 1 FIELD

LINES

0 0 0 0 0 0 0 CURRENTS IN SHEET Cip 0 000 0ALUMINIUM

SHEET /

f/ f [__ _ _ _ _ _ _ _ _ _ _ ,

-I \IMAGE MAGNET

Fig. 5. A magnet moving over a conducting plate produces a field as though an imagemagnet existed below.

FERRITE PERMANENT MAGNETSLA STEEL (MAGNETIC)

ALUMINIUM (NON-MAGNETIC)

D.C. LINEAR MOTORIN: TI: rEXCITATION

Li

,___ = . . . - ..,-. -,,, 4- - - -- -, . .---- -- -i-- - -5,-. B PR AA DK E

''....! GUIDANCE

N : rIs, \ NYLONROLLERS)

, MAGNETIC7 1ni-177:7M s'., SUSPENSION

-1

Fig. 6. Polgreen's maglev system using permanent magnets in a repulsive mode.

MAGLEV VERSUS AIR CUSHIONHigh speed surface transport has

become one of the engineering mustsof today. Until quite recently it wasthought that the only wayeconomically to overcome the frictionand track wear problems experiencedin high-speed rolling wheel railways(like the Japanese, 200km/h, TokaidoExpress) was to use air cushionsreacting against the inside of a tunnelor on a continuous concrete box.Indeed, much money has already beenexpended developing trains like theBritish Rail Advanced PassengerTransport (APT) unit. On the "for"side of hover trains is accumulatedexperience, with operationalhovercraft carrying from two tohundreds of people. If, however, youhave experienced a ride in one (such asthe huge SNR1) that carries 200people and many vehicles, you will, nodoubt, agree that the noise andvibration levels are hardly insignificant- ear muffs are recommended for onenewly developed air cushion vehicle!

For a while maglev lagged behind,but there is now evidence that it caneconomically provide a near noiselessoperation, as much as fifty timesreduction in operating costs of thehigh speed train, and an intrinsicallymore reliable suspension principle.

This year will see the real start ofBritish interest in it. Jayawants' groupat Sussex, and Rhodes' group atWarwick University, have receivedaround £125,000 each from theWolfson Foundation to build, to theprototype stage, both the attractiveand repulsive maglev alternatives.Already several German privateenterprises have made small, low speedsystems for evaluation. Maglev vehiclesdeveloped by Krauss -Maffei andMesserschmitt-Bulkow-Blohm areshown in Fig. 7.

At this stage in time it is clearly tooearly to say which is the best for bothconcepts are not quite as

straight -forward as appears on thesurface; one of the main problems

28 ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

Fig. 7. In Germany these two maglev vehicles have been developed by Krauss -Maffei (left), and Messerschmitt-Bulkow-Blohm(right). Both vehicles are levitated by attractive ferromagnetic forces - the lift magnets being attracted to the bottom of an in-verted U-shaped lift rail running alnnii each side of the guide -way. Propulsion is obtained via linear induction motors. Three-phase power is picked up by the vehicles, and after conversion to the required frequency and voltage, is used to drive the linearinduction motor's armature. The armature reacts against the vertical aluminium rail that can be seen in the centre of the guide -way.

being the reduction of the magneticdrag force.

THE MAGNETIC DRAG FORCEThe high field strengths available

with superconducting magnet coilsenables Bachelet's idea to beresurrected as an efficient suspensionin which a magnet is moved over afixed plate. The plate need not bethick provided it is well supported(10mm is envisaged for a 660km/htrain), for the flux is unable topenetrate very far into the surface dueto the rapid flux movement.Calculations show that a 30 000 kg.100 passenger train should be lifted'about 100mm by superconductingmagnets.

In order to exclude the field fromthe plate the eddy currents must flowto provide the reacting field. Theseproduce ohmic losses that result in adrag force being created that opposesthe motion of the vehicle along thetrack. (The eddy current damper inwatt-hour meters makes use of thedrag force to slow the movement whenpower flow ceases). It has been showntheoretically that the magnetic dragforce of a conducting sheet railreduces as the velocity Y2 and that itapproaches a limiting value. In otherwords, the faster the train goes the lessthe increase in drag forces. Even sothey are considerable. (It has beenpointed out that the aerodynamic dragat high speed could be even moresignificant). Coffey and others, fromthe Stanford Research Institute haveestimated that a 100 passenger trainmoving at 660km/h would experiencea magnetic drag of 1.5 MW. A sectionacross the maglev vehicle proposed byCoffey's group is given in Fig. 8. Notethe simplicity of the levitation andguidance walls: the wheels wouldprovide support at speeds less than100km/h.The price paid for using the simple

L-shaped track is the high drag -force.

Fig. 8. Stanford Research Instituteproposal for a train using the planesheet suspension.

Another group (Powell and Danby)evolved what is known as the"null -flux" track that consists of loops

-A

GROUNDLEVEL

of conducting material rather than asingle flat sheet. Their original scheme(1966), provided levitation from a flattrack, in which are embedded loopslying horizontally: mutual inductionprovides the repulsive lift force.Sideways control would be realisedwith the field from more loops set inthe vertical plane, but not protrudingabove the top surface. Inside thevehicle could be superconductingloops of alternating polarity. Thisscheme also must dissipate losses (as adrag force to be supplied by thepropulsion motor - the magnetstrength is not affected). Their firstidea for limiting the drag force was toreduce the loop losses by using seriesinductors. By 1969 they had realised abetter method - the "null flux"concept - which made use of othercoil configurations that providedminimized mutual inductance betweentrack and train loops. This could berealised by having the train loopexternal to the body with a fixed loop

TRAIN COMPARTMENT

HORIZONTALSTABILIZATION

CURRENT INTO PAPER

- CURRENT OUT OF PAPER

TRAIN LOOP

o TRACK LOOP

A

4 LIFT

07

Fig. 9. Cross-section through train suspended by a null -flux loop arrangement of track.

ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

MAGNETICLEVITATIONabove and below it. They alsosuggested using one group mountedloop, the pair being on the train asshown in Fig. 9.Sufficient theory has been

established for the inducting sheet andnull flux methods to be compared.Powell and Danby published curvescomparing each in 1971, see Fig. 10.Drag power is reduced to 680 kW forthe same example as stated earlier forthe conducting plate method. Thelift/magnetic drag force ratio is

claimed to be increased from nine forthe flat sheet to 63 for the recent nullflux arrangement. Tables of thecharacteristics of each are listed in amaglev review by Rhodes (see readinglist).

Now the trend seems to be pointingtoward vehicles having no powersources aboard. Reasons for this arethat it is no easy matter to carry ortransfer megawatt powers needed forpropulsion at 660km/h and that morepayload would be available. The pricepaid will be the increased cost of thepermanent way. Improved ways totransfer power include running a trainalong the focal point of a continuous

I

I

NULL FLUX

--- -CONDUCTING SHEET

3000

2000

F.F 1000

100

3 INCH TRACKCLEARANCE

-1300 400

TRA TRAIN SPEED IMPHI

CONDUCTING SHEET(WITHOUT LATERALSTABILIZATION)

NULL FLUX

1-200 300 400

TRAIN SPEED INIPHI

Fig. 10. Curves comparing expectedperformance of two possible repulsivesuperconducting maglev alternatives.(al Lift with speed. (b) Drag power withspeed.

linear microwave antenna,electromagnetic coupling between thepickup on the train and the currentcarrying conductors on the track and,of course, greatly improved brushsystems.

We have not discussed the design ofpropul6on motors that will be used,but it seems assured that they will besome form of linear motor. As bothmotor and suspension, could be

electromagnetic it would appear thatboth might be combined. Laithwaitehas done just this. In a release madeearly in 1973 he proposed a schemewherein 50Hz powered magnets liftand propel the vehicle.

It is at present uncertain whethermaglev vehicles will carry on -boardpower or not - but one thing is almostsure - that is that it will be maglevvehicles, not air cushion vehicles thatlead us into the forthcoming age ofhigh-speed ground transport.

FURTHER READING

"Magnetic Suspension forHigh -Speed Trains" R. G. Rhodes andA. R. Eastham, Hovering Craft andHydrofoil, 1971, 11, 3, 1-15.

"Superconductivity: New Roles foran Old Discovery" T. Van Duzer andC. W. Turner, IEEE Spectrum, 1972,9, 12, 53-63.

"Magnetic Suspension and Guidancefor High Speed Rockets bySuperconducting Magnets" G. A.Guderjahn and others, Jnl. App. Phys.1969, 40, 5, 2133-2140."The Development and Stabilization

of a New Electromagnetic Suspension"B. V. Jayawant and B. Z. Kaplan, Jnl.Phys. E.: Sci. Instrum. 1971, 4,301-306.

"The Development of a MagneticallySuspended Motor for Altitude ControlDevices" P. A. Studer, "SignificantAccomplishment in Science andTechnology", Goddard Space . FlightCenter, 1969, 225-229.

"Conversion of Measuring Values forMass, Density and Flow intoProportional Frequencies with the Aidof Free Magnetic Suspension" T. Gast,IEE conf. pub. No. 43. June, 1968,74-79.See also Proc. I.E.E.E. Vol 61 May

1973 (contains a number of papers onmagnetic levitation and associatedsubjects).

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30 ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

Early TV Camera TubesIt is easy to take the high qualityof today's TV for granted but 40years ago a group of young Britishengineers had to start from scratchto produce the first TV camera. Thisreport outlines the way in whichthey set about tackling the problems.

TELEVISION, as we see it today, isthe developed product of the work ofa large number of pioneers all over theworld. Despite this, however, it was thework of one team which resulted inthe start of regular broadcasting fromAlexandra Palace, London, on Novem-ber 2nd, 1936, using a system whichsurvives to this day. These early broad-casts were made using, alternately,Baird's 240 -line system with 25 -framesscanned per second and the Marconi -E.M.I. system using 405 -lines at 50interlaced frames per second.

The results of these broadcasts endedthe Baird mechanical system, and the405 -line system was adopted, and isstill used in Britain today, though it isbeing replaced completely by the 625 -line system.

Looking back, it is difficult to imag-ine the immense difficulties the pion-eers of the 405 -line system faced. Incontrast with Baird's methods whichused well -established engineering andelectronics, the Marconi-E.M.I. teamwere grappling with completely newfields at every stage of their work. Thegeneration of timebases, the synchron-isation of scanning, amplification andmodulation were all new techniques,but the most remarkable innovation ofall was the camera pickup tube.

The idea of completely electronicpicture pickup was not new. A.A.Campbell -Swinton in 1908 had out-lined a scheme for all -electronic tele-vision which visualised a camera -tubebased on the cathode-ray tubes availableat the time. The use of the cathode-raytube as the receiving device had beensuggested in the previous year byBoris Rosen, a lecturer at the Techno-logical Institute at St. Petersburg inRussia,and his ideas had been thorough-ly absorbed by one of the students,V.K. Zworykin, who emigrated to theU.S.A. in 1919 to join the Westing-house Research Laboratories. Workingthere, he extended Rosen's ideas to theproblem of picking up light signals andapplied, in 1923, for a patent on theIconoscope camera tube. This patentwas not granted until 1938, since aworking model of the tube could notbe constructed with the techniquesavailable in 1923. At the same time inthe U.S.A., Philo Farnsworth had devel-oped his dissector tube, which scanneda beam of electrons from a photoe-missive surface past an aperture leadingto an electron multiplier.

In 1932, the newly formed E.M.I.company at Hayes, Middlesex, decidedto concentrate their television effortson a completely electronic system. Thisdecision required considerable courage,because the B.B.C. and the Baird Tele-vision Company had been makingregular transmissions from AlexandraPalace since 1929, and Baird receivershad been on sale to the public sinceFebruary, 1930, at a price of just over£26.

The E.M.I. team, led by Isaac Shoen-berg, a former student of the Kiev Tech-nological Institute took the gamble ofattempting the development of an all -

electronic high definition televisionsystem, a gamble which involved, as wehave seen, a large number of untriedideas, an immense amount of faith anda great deal of money. The chanciestpart of a gamble, which paid off manythousandfold, was the camera tube.

THE EMITRONFaced with so many problems, thecompany allocated separate problemsto research teams composed of youngengineers at the peak of inventiveness.The problem of the pickup tube con-centrated on making a working modelof the Iconoscope patented by Zwory-kin, and the man in charge was Dr.J.D. McGee, now professor of AppliedPhysics at Imperial College, Universityof London.The basis of the tube was simple. An

insulating plate (Fig. la) was coated)with isolated particles of silver whichwere made photo -emissive by treatmentwith caesium vapour. Light, in the formof an image cast by a lens on thismosaic-, as it was known, caused

electronics to be emitted from eachparticle in proportion to the lightsignal, so that each particle ended upwith a positive charge (having lostnegative electrons) proportional to thelight falling on it. The electrons lost byphotoemission were to be replaced byscanning the mosaic with a beam ofelectrons, and the current caused bythis replacement process, which con-stituted the output signal, caused acurrent in the metal plate on the otherside of the insulator on which the mos-aic was deposited, just as a pulse ofcurrent on one plate of a capacitorcauses a detectable pulse on the otherplate.

This scheme of operation sounded

ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973 31

fine but was, in fact, impossible. Whena beam of electrons hits a mosaic sur-face at the voltages which were beingused in the original Emitron, the effectis not to replace electrons and make themosaic more negative, but to knock offmore electrons and make the mosaicstill more positive.

The team were faced with some-thing which worked; to develop itfurther they had to understand how itworked and find better methods ofmaking it a practical proposition. Thesituation was rather like Marconi's firsttransatlantic broadcast, which seemedtheoretically impossible until accountedfor by reflection of radio waves in theIonosphere.

The Emitron was also very much lesssensitive than had been hoped. On theoriginal idea, the exposure of themosaic to light should have been effec-tive for the time between scans (oneframe) because this was the time themosaic had to charge up by losingelectrons. Tubes such as the Imagedissector were very insensitive becausethe "exposure" was simply the timetaken to scan a small portion of imageand it was hoped that the storage of thesignal as a build-up of charge on themosaic between scans would make theEmitron much more sensitive.

HOW IT WORKEDFigures lb and 2 show simply how theEmitron was found to work. When theelectron beam scanned the mosaic, itreleased electrons so that each portionof the mosaic charged positive. Thisprocess, called Secondary Emission,could not go on indefinitely, becausethe released electrons had to end upsomewhere. The somewhere, in thecase of the Emitron was a coating ofsilver round the inside of the tubewhich was connected to earth. Becauseof the distance between the mosaic andthis silver coating (the "collector"), thevoltage on the mosaic could rise toabout 4V above earth when bombardedby electrons from the gun whose cat-hode was at minus 1,000V. When therewas no scanning, the effect of light onthe mosaic could charge up the mosaicby only 1.5V.

The action of the tube was that anarea being scanned rose to about 4V.This now acted as a collector for theareas of mosaic round about, since itwas the most positive portion of thetube and collected electrons releasedby photoemission. Since the scannedpiece of mosaic lay in the same planeas the photoemitting pieces, this wasnot an efficient process, and only thepieces of mosaic immediate round thescanned portion ever emitted. Insteadof having electrons lost through photo -emission and replaced by the beam;the electrons were simply being re-distributed as scanning proceeded.When

MICA

LIGHT

SILVER'ISLANDS'

W

JUSTSCANNED

ELECTRONBEAM

Fig.l. a) (left) Shows the silver islands on the mica. 61 (right) Wien the electronbeam scanned the mosaic, it released electrons so that each portion of the mosaiccharged positive.

LIGH

LAG

ATH

FLAT GLASSSURFACE

LENS

ELECTRON GUN

MOSAIC

SILVER COATING

CONNECTION TOBACK OF MOSAIC

TARGET

Fig.2. Overall construction of the Emitron - the first workable TV camera.

Preparing the mica sheetfor one of the earlyexperiments.

ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

the beam scanned an unlit piece ofmosaic (starting voltage = OV) and raisedit to 4V, 4V of signal could be obtained;for an illuminated piece of mosaic at1.5V the signal would be 4V - 1.5V --2.5V, so that the signal was negative,decreasing with increasing light. Theelectrons landing on the scanned por-tion would then quickly reduce itsvoltage to approximately zero again.

This action explained the insen-sitivity of the tube. The exposure timeof the mosaic was not the time betweenscans but the time for a scan to passnear that area, which was much shorter.

This,then, was the camera tube withwhich T.V. broadcasting started, andthe heart of the tube was the mosaic.It was the difficulty of constructing amosaic which so long delayed theacceptance of Zworykin's patent of theIconoscope and it was in the con-struction of this element that theEmitron mainly differed from theAmerican tube.

THE MOSAICThe mosaic started life as a sheet ofmica, 4in x 5in x 0.001 in thick whichwas specially selected for uniformtransparency and lack of blemishes.One side was silvered by coating with apaste of silver oxide in resin andheating,the other side was covered witha very thin film of silver by vacuumevaporation. When the coated micawas heated in air again to 700°C, thethin silver film started to break intosmall droplets due to the high surfacetension of silver. This process, calledagglomoration, could be closely con-trolled to produce very small drops ofsilver fairly well insulated one fromanother. In the U.S.A., these silverislands had to be produced by evap-orating silver on to the mica through afine wire mesh, but this means that thesmallest silver island was very muchdetermined by the finest mesh whichcould be obtained.

The mosaic was then fastened toanother thicker piece of silvered micawhich acted as a support. The reasonfor making the mosaic on a thin sheetrather than on a thick one was thatthe capacitance between any silverisland and the thick coating on the backhad to be high, if signals were to becollected efficiently; and the capaci-tance of such an arrangement is higherwhen the separation between the metalsis small.

After forming the mosaic and rivet-ting the pieces of mica together, thewhole assembly, now known as the"target" was rolled up so that it couldbe inserted into the tube. Using longforceps, the target was unrolled insidethe tube, and fastened in place withthe spring contact for the output socketresting against the heavily silvered thickmica of the back of the target.

THE SUPER-EMITRONBy the time broadcasting had startedusing the Emitron, the tube was al-ready near the end of its life. Every-body in television was working to theaim of televising the Coronation of thelate King George VI and Queen Eliza-beth, on May 12th, 1937. The Emitroncameras were not sufficiently sensitivefor outside broadcasting, there were nomobile units, no suitable cables - andno time!

Fortunately, work had been goingon to make the Emitron more sensitiveeven before the start of broadcasting.The Super-Emitron as the new tubewas called, could be fitted into stan-dard Emitron cameras with only a fewmodifications, and its sensitivity wasvery much greater. Fig. 3 shows theschematic of this tube. The photo-sensitive surface was no longer themosaic, but a separate surface on asheet of mica. Electrons released fromthis photocathode were accelerated bya potential of 400V towards the target,and an electron image could be focus-sed on this target by magnetic focussingcoils near the photocathode.

47 -

LENS

PHOTOCATHODE

ADVANTAGESThe Super-Emitron was about fifteentimes more sensitive than the Emitron.This improvement in sensitivity, whichmade outside broadcasts considerablyeasier, came about in three ways.

One cause was the greater efficiencyof the photocathode.The photocathodeof the Emitron was the mosaic, whichwas not a continuous surface; the photo-cathode of the Super-Emitron was acontinuous film, every portion of whichcontributed to the photo -emission. Thisfilm could also be processed to a

higher efficiency, because the caesiumvapour used to make the silver photo-cathode surface sensitive could beapplied much more generously to theseparate photocathode than it could tothe mosaic, where an overdose ofcaesium caused electrical leakage be-tween islands, so reducing resolution.

The second cause of higher efficiencystemmed from the greater use ofcaesium for the photocathode. Caesiumvapour is difficult to control, and a fairamount of it landed on the target,though not enough to cause insulationdifficulties. This layer of caesium was

MOSAICELECTRON PATH

FOCUSCOIL \

'SCANNINGCOILS

ELECTRONGUN

SILVER COATING

MOSAICCONNECTION

Fig.3. The Super-Emitron. Although similar in appearance to the basic Emitron,it worked rather differently and was much more sensitive.

The target was no longer a mosaic,but a continuous insulating sheet ofmica; the scanning electron beam andthe signal output from the silveredtarget backplate were unchanged.

The action at the target was onlyslightly different from that of theEmitron. The scanning beam chargedthe target surface positive by secon-dary emission, and this positive areaacted as an anode for electrons re-leased from other parts of the target.In this case, though, these electronswere not released by photoemission,but were released by secondary emis-sion due to the beam of electrons fromthe photocathode. Because these elec-trons had rather higher energies than theunaccelerated photoelectrons releasedfrom the mosaic of the Emitron, theycould be taken from a wider range ofthe target, and the electrons of highestenergy could end up on the silvercoating around the tube.

of great benefit to the secondary emis-sion, however, so that, for each electronreaching the target, about seven elec-trons took off again, giving the targetitself a gain of about seven times.

The third benefit was due to thehigher energy of the secondary elec-trons from the photocathode beam.As we have seen earlier, this caused anewly scanned area to gather electronsfrom a wider area of the target aroundit, and this effectively increased ex-posure time, making the tube that muchmore sensitive.

OTHER FEATURESBecause the photocathode was made ona smaller piece of mica, about 3'/tindiameter, it was easier to produce auniform photocathode. The use of themagnetic focussing close to the photo-cathode caused the electron image onthe target to be magnified about fourtimes so that conditions on the target

ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973 33

OPERATING PROBLEMS OF THESUPER-EMITRONThe bt.siness of using a Super-Emitronor Emitron in a camera was totallyunlike that of using a modern cameratube, Orthicon or Vidicon).0ne notice-able. difference was the shape of the

Trying out one of the first TV cameras. The sensitivity of thesewas so low that outside broadcasts had to wait for the Super-Emitron to arrive.

were easier for resolution. Since thephotocathode was now close to theend -window of the tube, i he cameralens could be of much shorter focallength, and the increased sensitivitymeant that lenses of smaller aperturecould also be used.

Id

An early TV transmission. The regular BBC service :tarred 37 years ago fromAlexandra Palace - long before any other country-.

34

camera which had to project forwardsunder the lens to allow for the housingof the gun tube of the Emitron. Des-pite its awkward shape, though, theEmitron and Super-Emitron cameraswere not too difficult to move aboutbecause their weight was considerablyless than that of later Image -Orthiconoutside -broadcast cameras. The reasonfor this was that the Emitrons did notuse for focussing and scanning the highmagnetic fields which are used now;much of the weight of a modern studiocamera is due to the focussing andscanning yoke used with the cameratube.

Nor was there the same requirementfor warming up the Super-Emitronswhich were ready for service almost assoon as the camera was switched on,since conditions at the target were notgreatly affected by its temperature.

The great problem with both Emit-ron and Super-Emitron was that ofgetting a picture evenly shaded. At thecentre of the target, the electronsreleased by photoemission (in theEmitron) were collected only by thenewly -scanned areas of the target in thecentre. At the edges of the target,some electrons could land on the silvercoating around the tube. In the Emit-ron, only the electrons released fromvery close to the edge could land onthe silver coating, and this caused thesignal to rise sharply at the edge of thetarget. In the Super-Emitron, the changewas more gradual due to the greaterenergy of the electrons, but in eachcase the uncorrected picture was toobadly shaded to be useful. In additionto this, the angle of the gun tube tothe target caused the beam to changein focus from one end of the target tothe other, because the distance betweengun cathode and target was changing.

The change of focus effect waseasily dealt with by using a finer beamso that defocussing had no effect, butthe shading effects were always trouble-some. Some correction could be ob-tained by adding artificial correctingsignals to the video -output. These cor-recting signals were obtained from thescans, but could be used only when theshading was proportional to the dis-tance from the edge; this was the ex-ception rather than the rule.

THE CAMERA LAYOUTThe camera used for Emitron andSuper-Emitron is shown partially dis-mantled in one photograph. The tubeshown is an early version of the super-Emitron which has used most of theold Emitron components. The lens,together with the bellows for focussingtakes up a large amount of the space inthe upper portion of the camera. Theregion under the gun arm is occupiedby the scanning stages and the powersupply to the gun, whose cathode ran

ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

Partially dismantled Super-Emitron. Despite its disadvantages it was light andwarmed up very quickly. Note the shield on top of the gun arm and thevalves at the back.

One of the early TV camera tubes.

at minus 1,000V so that the mosaiccould be operated at about earthpotential. Under the output contact ofthe tube can be seen the video amplifi-er, using pentodes run with very lowanode leads and with a high standingcurrent. In use, the bulb portion of thetube and the video ampli'ier were en-tirely screened to avoid electrostaticpickup.

Note the metal shield between thegun arm and the photocathode arm.This was to prevent defocussing due tothe varying field from the scan coilsaffecting the magnetic focus of thephotoelectrons. This field penetrationwas a weakness of the Super-Emitronlayout which was never satisfactorilysolved, though modern high -mu alloyswould have helped considerably.

THE END OF THE EMITRONTelevision transmissions from Londonceased on September 1st, 1939, forthe duration of the war. When broad-casting started again in 1946, the oldEmitron cameras were dusted off andused again. At that time the Americanswere playing with a gadget called anImage Orthicon, but the pictures ob-tained were so inferior to those from aSuper-Emitron that few people took itvery seriously at first. There is littledoubt that the picture from a goodSuper Emitron under good illuminationwas excellent; for this reason the tubewas still in use in some studios untilabout twelve years ago.

The first post-war competitor wasthe C.P.S. Emitron, an E.M.I. develop-ment of the original Orthicon concept,but the later work on the imageorthicon and the vidicon made thesetubes more and more competitive interms of picture quality until eventuallythe Super-Emitrons were withdrawn.The story of these later tubes is equallyfascinating, and is not yet finished, butmust be told another time!The Author would like to thank EMILtd, and especially Mr. Denis Farrell, for thephotographs used to illustrate this article.

ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973 35

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KILOVOLTS AND

AIEGIWATTs

Most people seem to think thatvalves died a natural death in thelate '60's; in fact we have nevermade so many. Ian Sinclair tellsus about the big valves behindthis big business.

Nowadays, when integrated cir-cuits seem to be taking over al-most every aspect of electronics,

and younger engineers confess to neverhaving seen a valve, it comes as rather ashock to learn that the U.K. productionof valves is the highest on record, andforms a major part of our exports inelectronics, whereas integrated circuitsand transistors form a major part ofour imports. This odd situation is

brought about by the steadily in-creasing industrial use of large valves,the increase in transmitters, in televisioncameras (for camera tubes are countedas valves), in cathode ray tubes and inmicrowaves, the sight of microwaveovens in roadside cafes and city pubsis now commonplate, and each ofthese represents one extra sale of amagnetron, plus spares, which did notexist five years ago. This article takesa look at the world of the large valvesand how their construction differsfrom the small valves which havealmost disappeared from everyday use.

Industrial valves each have a definitejob to do, and are required to have along operating life, to withstand awide temperature range together withindustrial atmosphere, shock and vib-ration. These considerations are im-portant, for the time needed to re-place a large valve may seriously dis-rupt a continuous process; unfortunate-ly it is less easy to make large structuresvibration proof. In most large valvesthe delicate portion is the electronemitting filament made of tungsten, anextremely brittle metal. Since thismust operate at temperatures greaterthan 2000°C, it is difficult to support,as the supports must be made ofbrittle metals and they will also con-duct heat away from the filament. Theoperating conditions also require ef-ficient cooling, and the cooling byradiation which is satisfactory for smallvalves is useable only in the smallestsizes of industrial valves. There arethree techniques used. These are forcedair cooling, where the valve anode ispart of the outer casing and finned likethe cylinder of a motor cycle so that itcan be cooled by a blast of air from afan; water cooling where water is

circulated round the anode and cooledin a radiator as in a car; and vapourcooling where the cooling is carried

Industrial heating triode with integralwater jacket.Filament 8V, 300A; Anode 13K Vtnax,10A max.

out by allowing liquid to boil and thevapour is condensed and recirculated.

CONSTRUCTIONThe construction methods used aremore reminiscent of heavy engineeringthan of electronics. The use of glass(only the high -temperature Pyrex -typeis used) is kept to a minimum byemploying it only where insulation isnecessary. Wherever possible metal st-ructures are used,and ceramic is rapidlyreplacing glass as an insulation material.Though the process of sealing metal toceramic is rather more complex thanmetal -to -glass seal ing,the ceramic body

ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973 37

sections have great advantages. Theycan be constructed to finer limits, theyabsorb less water vapour from the air,and they withstand much higher temp-eratures.

The metal parts which form themajor part of a large valve are made bya number of processes. Pressing, spin-ning and turning are the old favourites;pressing being particularly favoured sin-ce it enables large numbers of parts tobe made to good dimensional toleranceat reasonable price, once the tool costshave been paid for. Spinning and tur-ning are operations requiring humanskill; their expense makes them less

suitable for parts needed in large num-bers, but they are still widely used.The reason is that, since industrialvalves are made for specific tasks, alarge number of types is needed withcomparatively small numbers of eachtype, and the selling price is highenough to justify one -at -a -time methodslike turning.

A disadvantage of all these traditionalmethods of forming metal is that themetal has to be lubricated during theoperation and every trace of the lub-ricating material must be removedbefore the valve is assembled. Somelubricants are almost impossible to

remove completely, and valve manu-facturers must specify materials whichare known to work satisfactorily ifthey are "farming out" metal formingwork. Newer methods of forming metalsuch as explosive forming, spark mac-hining and powder sintering are muchcleaner and therefore being increasinglyused.

JOININGWhen the raw materials have beenshaped and cleaned the next problemis of joining them together. Spotwelding, as on car bodies, is a favouritemethod, since the weld can be closelycontrolled, but it has the disadvantageof leaving traces of copper behind whichmay have to be removed in an acid -wash. In addition, high conductingmetals such as copper cannot be spotwelded, and spot welding on the com-monly used molybdenum causes brittle-ness. Of the commonly used materialssuitable for valves, nickel is mosteasily spot welded, and so nickel andits alloys, many of which were originallydeveloped for jet -engine turbine blades,are extensively used.

Argonarc welding is also a much usedprocess, as it produces a clean un-oxidised finish of high strength, and isa fairly trouble free process. Manycommonly used soldering, brazing andwelding materials cannot be used invalve construction because they con-tain metals which evaporate too easilyat the temperature and vacuum used.For example, any solder or brasscontaining zinc is unusable, for thezinc will evaporate over the wholeinterior of the valve, making the in-sulators break down.

Brazing with copper, gold or a silver-

copper alloy is a useful process, butmust be carried out either in a vacuumor with the work totally immersed inhydrogen gas to avoid oxidation. Oxi-dation of metal means that elaboratecleaning is needed, because an oxidisedsurface will give off oxygen undervacuum conditions, leading to rapidfailure of the valve.

The use of nuts and bolts is avoidedas far as possible, because air is trappedin the threads inside the nut and canbe very difficult to remove. In addition,the heating and cooling of the valveduring processing and in use tends tocause bolts to slacken. If they are usedat all, they are turned from stainlesssteel.

CLEANINGBefore a valve can be finally assembledand pumped free of air,each componentmust be cleaned to a high standard.Cleaning in this case does not implymere surface cleanliness, the metalmust be free of absorbed materialswhich could evaporate during proces-sing, and it must also contain the

38 ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

KILOVOLTS ANDMEGIWATTs

Glasses and Pots. Industrial heating triodes in ceramic -metal or glassenvelopes. Filament 5V, 78A; Anode 6k V max., 2A max.

minimum of dissolved gases whichwould cause the pumping time forthe valve to be longer than necessary.Grease remaining from forming oper-ations, and volatile metals rubbed offfrom tools are the most commonsources of contamination of parts andthe most harmful. During pumping athigh temperatures, grease breaks downchemically releasing large amounts ofgases and leaving carbon behind. Vola-tile metals, zinc in particular, evaporateand coat insulators as mentioned earlier.Brass, which contains zinc, is the usualsource of this contamination; the partsmay have to be placed over a brass jigor filed with a file used on brass. Theease with which this contaminationmay occur leads manufacturers tocarry out most critical forming oper-ations themselves so that brass can becompletely excluded.

The gases absorbed by valve com-ponents include all of the gases of theatmosphere, and of these water vapourand carbon dioxide give the mosttrouble. Water vapour is particularlytroublesome when glass parts are used,as it is particularly strongly absorbedby glass and only prolonged hightemperature treatment will remove it.It is essential to remove the watervapour, as bombardment of surface

films of water by electrons causeshydrogen and oxygen (the elementsmaking up water) to be released, andthe oxygen is particularly harmful.The problem associated with carbondioxide is that it is a dense gas, andtherefore can be pumped away onlyvery slowly.

Cleaning processes must thereforebe aimed at removing surface films ofgrease and other solids, and also atmaking the job of gas removal as easyas possible. All cleaning therefore startswith washing, using pure water forceramics and glass and degreasing sol-vents for metals. The remaining cleaningoperations are carried out at hightemperature, air baking for glass andceramics, and hydrogen furnacing formost metal components. Hydrogenfurnacing consists of heating to red-hottemperature in an atmosphere of hy-drogen, and has two particular merits.Firstly, the hydrogen will combine withany traces of oxygen present; secondlythe denser gases present tend to bereplaced by hydrogen, which, as it is

the least dense gas known will be mosteasily pumped away during the finalprocessing of the valve. In a few cases,components for very specialised tubesmay be heated in a vacuum and thenstored in a vacuum until assembled,

but hydrogen furnacing is by far themost widely used treatment; the mainexceptions being the important metalsmolybdenum, tungsten and tantalumwhich become brittle when heated inhydrogen.

Other heat treatments may also beapplied at this stage. Where metals areto be sealed to glass, a thin film ofmetal oxide is needed on the metalsurface to bond to the glass, and thethickness and composition of the oxideis critical to the seal, affecting itsstrength and vacuum -holding. The mildoxidation is usually carried out in ahydrogen furnace into which watervapour is blown; the small amount ofoxygen obtained from the breakup ofthe water vapour is enough to give agood uniform oxide film on the metal.Some components require a particular-ly spongy metal surface to help retaina surface coating, and this is generallyachieved by furnacing alternately inwet hydrogen and dry hydrogen, sothat oxide films are produced andturned back to metal again.COATINGCoating of materials applied to sur-faces within a valve account for only atiny fraction of a valve's weight butoften for a large part of its performance.To take an obvious example, in thesmallest industrial valves and micro-wave tubes the electron emission isfrom a cathode coating. The cathodematerial is nickel, but no electrons areobtainable from hot nickel unless ithas been coated with a mixture of theoxides of calcium,barium and strontiumand these materials have to be appliedto the cathode at some stage in itsmanufacture. The time chosen is aftercleaning and hydrogen furnacing, whena mixture of the carbonates of thesemetals is sprayed on, in the form of apaint, to the cathodes. The sprayingtechnique is critical, much more sothan in the case of normal painting.During the valve processing, as thevalve is pumped, the heater is activatedand the carbonates release carbon diox-ide, turning to oxides. This ratherindirect method is needed because theoxide surface exposed to air absorbswater vapour, destroying the efficiencyof the cathode.

Carbon is another material much usedfor coatings, this time to destroyelectron emission. Desirable as electronemission is for cathodes, it is un-desirable from grids or anodes, andcarbon coating of the grid wire oranode cylinder is carried out to mini-mise electron emission from these sur-faces. In the case of small radiation -cooled valves, carbon coating is alsoused on the outside of the anode toincrease the efficiency of radiatingaway heat since blackened surfaces aremore efficient radiators. The longervalves use blackening on the fins (when

ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973 39

air cooled), but the need is less im-portant.

A third and most important type ofcoating is the gettering agent. Conven-tional vacuum pumping can remove afair proportion of the gases inside a

valve, but there comes a stage when nomore is being removed. At this point,or just before it, the valve is sealed andtaken from the pump, but pumpingcannot stop at this point. For long lifeeven more gas must still be removed andthere must be some way of soaking upthe gas which will inevitably be givenoff during the life of a valve. A fewhours of pumping time cannot removethe gas which will be emitted by hotcomponents over several thousand hoursof active life. A material is thereforeplaced inside the valve to 'gee this lasttrace of gas; logically enough, it is calleda getter. Smaller valves use bariumalloy getters. Because the material is sointensely gas absorbing, it cannot beexposed to air and is therefore producedinside the valve when needed. Thechemicals needed to produce the getterfilm are mixed, packed in a nickel tubeand the assembly mounted in a part ofthe valve where there is little chance ofmaterial being evaporated on to insu-lators. In smaller valves this is usuallyon top of the anode insulators or wellbelow the main assembly. When thenickel tubes are heated from outside(by induction heaters), the chemicalsreact,evaporating a thin film of bariummetal to form the familiar shiny coatingwhich will then clean up the remaininggas throughout the life of the valve.

Large valves work at such high inter-nal temperatures that barium getterswould re -evaporate, causing insulationproblems, so other materials must beused. A favourite metal is zirconiumwhich, again, cannot be used directly.Anodes and grids of large valves arecoated with zirconium hydride, oftenmixed with carbon, and this emitshydrogen during valve pumping toleave a coating of pure zirconium as thegettering material. Unlike barium, zir-conium works better hot and so thecoating can be formed while the valveis on the pump.

PUMPINGAssembly ends with the sections of thevalve being sealed together ready forpumping. A large triode would consistof an anode, with glass or ceramicinsulator as one unit, and a filament andgrid mounted on a base unit with glassor ceramic seals. The final operation istherefore a glass or ceramic seal. Inother cases there may be several seals,or the final operation may be that ofargonarc welding metal flanges. Oncethis is carried out, the valve is ready tobe pumped.

Pumping is never merely an operationof removing air from a valve; many of

Checking the alignment of the grid assembly for a power triode.

the activation processes are carried outat this stage. During pumping, thevalve must be heated to a temperaturehigher than it will normally attain inuse, and this temperature must be helduntil most of the absorbed gases havebeen pumped away. In addition, thevalve will usually be operated; sosupply voltages need to be laid onready for connection to the filament,grid and anode.

The schedule of operations for pum-ping a valve will vary from one type toanother, but the principles are roughlysimilar.Two pumps are used, a mechan-ical pump which provides a 'backing'vacuum, removing about 99.9999% ofthe air (this is a poor vacuum!), andproviding conditions good enough forthe second pump to take over. Thesecond pump uses the principle ofdiffusion - that a stream of rapidlymoving dense gas such as mercuryvapour or silicone oil will carry alongwith it molecules of less dense gasesand so move them from one place to

another. In the diffusion pumps usedfor valve pumping, the stream ofvapour carries gas from the valve to thebacking pump, and the backing pumpthen carries it away.

In action, the valve is sealed to thevacuum system. Rubber or similarjoints are unusable, as they can standneither the vacuum nor the temperature.The backing pump is started up and avacuum gauge switched on. When thepressure of gas in the valve is lowenough (about 1/100,000 of normalair pressure) the diffusion pump isswitched on. As the diffusion pumptakes over, the pressure falls rapidlyand an oven is drawn down over thevalve and switched on. As the ovenheats up, the gas absorbed in the valvecomponents is released and pumpedaway by the diffusion pump.

After a few hours or so, depending onthe size of the valve and the speed ofthe pumps, the pressure will be lowenough to start the activation of thevalve. The smaller valves are the most

40 ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

KILOVOLTS ANDMEG4WATTSdifficult to deal with at this point,because the operation of the heaterreleases very large quantities of carbondioxide from the cathode and this hasto be pumped away before electronscan be &awn from the cathode. Thelarger valves have the emitting wire(tungsten or thoriated tungsten) runat a higher temperature than will beused in practice. Then current is takento the anode, often using the valve asa rectifier.

For the large valves this may requiresubstantial power supplies at the pump;for example it is not unusual for a largetransmitting valve to need 115V at400A on the filament, and 30-50kV on

the anode at currents of 1A or so.Photoelectric devices such as TV

camera tubes and photo multipliers re-quire very specialised pumping schedulesat this point, since the photosensitiveand multiplier stages are formed insidethe tube during pumping. Microwavevalves also require specialist treatmentas they can seldom be operated normallywhile on the pump.

When activation is complete and thevalve is behaving normally, coolingstarts, and this should be accompaniedby a steady drop in pressure as gasceases to be emitted from the internalcomponents. Once the valve is coolenough, it is removed from the pump.Where a glass seal has been used this iscarefully heated until the glass tubingcollapses and can be drawn out into thefamiliar tip so sealing off the valve. Forthe metal pipe seals, more common inthe large valves, the pipe is simply

High power transmitting triode being prepared for high voltage testing.

squeezed flat and then cut. Using a softcopper pipe, this is sufficient to ensurea vacuum seal owing to the 'coldwelding' which takes place betweenclean copper surfaces when pressedtogether at high pressures. At this stage,the small valves, phototubes and smallermicrowave tubes will have their bariumgetters activated.

CHECKING AND TESTINGAn industrial valve is a high cost item,and its packing and transport is expen-sive; it is important that each valve sentout should have been properly checkedand tested. The first checks are forelectrical leakages between electrodes.since the valve is to be used at highvoltages, a high voltage tester is usedwith the valve cold. Traces of conduc-ting films on insulators can be sparkedaway until the insulation is of a satis-factory standard. This cannot be meas-ured with a conventional megohmeter,as its test voltages would be too low.For example, a gap of 1mm betweenconducting films would register as

open circuit on a megohmeter, butwould spark furiously at anywherenear operating voltage. The valves arethen slowly run up to normal operatingconditions, during which time thegetters are working hard and the elec-tron emission is building up. Testing thevalve during this period is useless, asthe characteristics will alter continuallyuntil the valve has settled. This period,the ageing period, can often be speededup by operating the valve at rathermore than its normal ratings.

Testing follows when ageing is com-plete, and can vary from a simple testin an oscillator to the complete measure-ment of every parameter of the valve,depending on the price and the appli-cation. In some cases, a valve whichfails to meet one specification maymeet another one, and will be stampedaccordingly, but usually the uses oflarge valves are so specialised that thereis no outlet for a 'near -pass. Thesuccessful valves are booked into storesfor sales, the failures are broken up andthe most valuable components salvaged.

This, then, is one of the bright spotsof our Electronics industry, the regionof megowatts and kilovolts, phototubesand microwaves. The design of some ofthese devices has hardly changed in40 years; others are novel both in con-cept and engineering. Lumped togetherthey form a formidable part of theelectronics components industry whichis hardly known outside professionalengineering circles. It seems likely thatthe achievements of this sector ofelectronic engineering will continueto grow and yet will continue to beunnoticed.

(The author is grateful to STC ValveDivision for the provision of the photo-graphs illustrating this article).

41

r.

1111111I-%Ili4

THE LADIES REPLY

Having only recently discovered yourmagazine, I was intrigued by theplea in the 'News Digest' section forany ladies who are interested in elec-tronics to write to you. My interestin electronics is fairly recent (withinthe last couple of years) since itwas so badly taught at university(London, Westfield College) that theword transistor made me shudder.I decided that this was a very badsituation in view of the increasinginfluence of electronics on everydaylife, and ended up at the local collegedoing a City and Guilds eveningcourse.

At present I am employed bya local firm, Erie Electronics Ltd.,as a 'Filter and Suppressor DesignEngineer' (albeit a rather fledgelingengineer).

I hope this letter is of interestto you, if only to convince youthat there are members of the gentlersex who show an interest in elec-tronics.

Joyce A. Farnese,Gt. Yarmouth, Norfolk.

Mrs. Farnese was the first lady readerto write to us and has been givena free three months subscription.

With reference to your appeal in ETIfor lady electronics enthusiasts towrite to you, I felt that you may beinterested to hear of my involvementin the electronics field.I am 21 years of age, recently married,

and employed by the Ministry ofDefence (Air) as a radio technician.I received my training for this positionat the Royal Air Force MaintenanceCommand Civilian Technical TrainingSchool at R.A.F. Sealand, Deeside,Flintshire. It is at Sealand that I worknow doing all the same jobs as mymale counterparts. I have obtainedmy final certificate in the City andGuilds of London Institute Telecom-munications course and, although I

am extremely happy at my work,

my only regret is that should myhusband (who is a serving memberof the Air Force) be posted it mayprove very difficult, as a woman, toget another technical position in theelectronics field.

Mrs. J. Sayce, Mold, Flintshire.

As one of your female readershipI was full of good intentions aboutanswering your "C.Q. Ladies" callin May. As usual, a second call wasnecessary to kick me into action,and I hope you will receive a goodlynumber of replies this time. I lookforward to reading about my contem-poraries in other places.

I must confess it is my hubbywho buys the magazine but I enjoy"second read".

My entry into electronics wasfairly accidental - first job being as atechnical trainee in PYE's Radio andTV design lab at Waihi, New Zealand.I eventually gained a New ZealandCertificate of Science (Chemistry) -

had a spell on radio and TV alignmentand did a radio apprentice's corres-pondence course.

After four years with PYE, thentwo years testing milk, cheese andwater with the makers of "Anchor"products, I joined the staff of theTechnical Institute in Hamilton, NZ.I found myself doing a wide varietyof things; drilling holes to put upshelving, sexing fruit flies, buildingelectronic test gear and even a bitof teaching.

When we came to England twoyears ago I decided, if possible,I wanted to work for someone whomade scientific instruments. I startedas a junior electronic engineer withVacuum Generators who producevacuum chambers, associated controland measuring instruments andsystems such as electron spectro-meters.

By the way, I'm not a "Women'sLibber". I haven't yet met sexdiscrimination that isn't to my advan-tage.

Mrs. M. Donald, Lingfield, Surrey.

LETTERS FROMOUR READERS

BOOM! BOOM! BOOM!

I was watching colour television inthe Tokyo YMCA in November 1964,which is more than "about six yearsago". Even a remote farm in NikkoProvince had colour television whenI stayed there in February 1968, whichis more than "two years ago".

One can but wonder where wewould be today if the developmentcontract for Concorde had beenplaced with Japanese industry!

R. G. Simmons, Pinner, Middx.

ELECTRONICS TOMORROW

May I congratulate you on your newseries electronics tomorrow. Thisis the kind of article we want tokeep us in touch with the latestproducts, and of equal importancewhere to get data and (we hope)applications sheets. Where to buyone-off components is also very help-ful.

D.G., Stanmore, Middx.

LIQUID GAS?

The enjoyment of the article on'Cryogenics and Superconductivity'was considerably lessened for me bythe repeated references to 'liquid gas'.One expects technical publications todo better than this especially as thereare references in the article to lique-fied gas.If you or your contributor can show

me some liquid gas I will present himwith an empty box of matches!!

J.R.T., Colwyn Bay.

The Editor does not necessarilyagree with the views expressed onthis page.Letters intended for publicationshould be addressed to:

Input GateElectronics Today International36 Ebury StreetLondon SW1W OLW

42 ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

WHAT TO LOOK FOR IN

SPECIAL SUPPLEMENT:

DIRECTORYofHiFi AMPLIFIERS

EXCLUSIVE OFFER TO ETI READERS

THE Amnia InaPORTABLE CALCULATOR HIT (as

FOR ONLY f26'95

HI -H -The state of the artThings are happening in Hi-Fi with entirely newapproaches being taken by some manufacturers.The Quadrophonic War is only one of the itemsdiscussed.

Unreasoning radiationIt took some years to appreciate the dangers ofradioactivity and now a similar danger is seen

for microwaves. ETI reports on disturbing newevidence.

ON SALE MID -OCTOBER -20p

ETI TAKES A PRIDE IN BEING REALLY UP-TO-DATE, SO WE OURSELVES DO NOT ALWAYS KNOWWHAT WILL BE IN THE NEXT ISSUE SO THE FEAT-LRES MENTIONED ON THIS PAGE ARE ONLY SOMECF THOSE THAT WILL BE INCLUDED.

the next issue we shalllisting the specificationsabout 100 of the most

commonly available Hi-Fi

amplifiers available in theUK. Where possible thespecifications will all beshown in the same formto enable instant compari-son of performance.

described in this issue )

Product test: Beogram4000

This revolutionary turntable is now becoming avail-able. It uses completely new techniques and theseare tested by ETI's audio consultants.

Automatic batterychargerAn ETI project which en-

ables you to connect thebattery charger and forget it. The unit will evenoperate into a short circuit and is regulated forboth voltage and current.

electronicstoday INTERNATIONAL

- -

``Aik The ADVANCE\, 44, International

sk§ Portable Calculator

"A KIT FROM ADVANCE?....surely they're test and laboratorygear people?'

Correct Sir, but they're alsopretty big in calculators; theAdvance Executive is one of the bestsellers in this country and also thiscompany have quite a bit ofexperience in calculator kits. Theyproduced some time back the firstcalculator kit known to us (featuredin Wireless World) and for sometime now they have been exportingthe Executive in virtually kit formfor assembly overseas.

Our calculator competition in theJuly issue which had three of theExecutives as prizes attracted over2000 entries - an exceptionally highresponse and so when we heard thatAdvance were thinking of introducingthe Executive as a kit we were on tothem like a shot.

Your Editor already had one of thebuilt versions and was very pleasedwith it. Now, for most mechanicallyor electronically minded chaps theguts of a machine of this type havean overpowering fascination, even ifit is just a few components. Withthe maker's agreement, this wasopened to see what a kit wouldinvolve. '!.The inside can be seen inone of the photographs.

THE INTERNATIONALAdvance will be launching this kit

known as the International onOctober 19th but we were suppliedwith a prototype kit and a set ofbasic instructions and allowed to geton with it.

Now we have all heard about thedanger of soldering CMOS I.C.'sand we mentioned this to Advance.This is more critical in this kit thanmost as the main chip is soldered indirect: there is no room for asocket. Advance say, and theyshould know, that if reasonableprecautions are taken troubles aremost unlikely. These precautions

include leaving the chip on itsconductive foam until the last minute,avoid handling the pins, use a smallbit soldering iron and make certainit is earthed. There are one or twoother simple rules but they areclearly described in the instructions.If these rules are followed, Advancewill replace the chip free of chargeand they can tell what has causedthe thing to blow!

BUILDING THE KITAt the time we received the kit the

instructions were not completed andso we were provided with theinstructions for the overseas assemb-lers which were far more basic. Evenso, after reading them carefully, wechecked that the earth on our mainssocket was connected (they aren'talways) and plugged in the solderingiron (which must have a bit of 1mmor 2mm).

The kit has been well thought out.The correct solder is included andthe fifteen or so wires from thekeyboard to the main circuit boardare all cut to length, stripped and

tinned.Component siting is printed on the

p.c. board and is virtually foolproof.The p.c. board has plated throughholes and only requires solderingon the underside.

After about 2% hours we wereready to switch on but not before athorough check had been made toensure that there were no solderbridges and that everything was theright way round.

Success! On came the little LEDzero and we were underway.

We have since seen the instructionswhich will accompany the kit andthey are excellent. It would havesaved us some time if we had themavailable. The instruction bookswhich accompany calculators havealways seemed to us to be rather poorbut that which comes with theInternational is pretty good and showshow best use can be made of yourcalculator.

There is a Mains Unit which alsoacts as a desk stand and recharger(rechargeable batteries come withthis); this is extra. We also built up

44 ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

- * .....miniommminIIIMININ Ole

111,

wt.*11_ Mbl'Asevese

As tho photograph shows, there are relatively few components to the AdvanceInternational Calculator kit. It can be built in under three hours.

this with no problems.Both kits are beautifully thought

out - there is even a plug with themains unit!

CALCULATOR FEATURESThe Advance International is

identical to the Executive except thatyou build it up yourself and sonaturally it has the same features.

In addition to the usual functionsof addition, subtraction, multiplica-

tion and division, the calculator willperform chain operation, a series ofconsecutive instruction and constantoperation in the multiply or dividemode. A useful fixed or floatingdecimal point function is included,the fixed decimal point being veryuseful for monetary calculations.

The 'International' is based on aTexas chip and incorporates a ninedigit, LED, seven segment display. Ithas one of the best keyboards thatwe have come across - having a pleas -

The main circuit board, the key board and the battery holder of the kit built by ETI.

ant, positive 'click' action making italmost impossible to enter incorrectdata.

NEXT MONTH'S OFFERThe regular selling price of the kit

will be £29.95 including VAT andpostage, making it one of the bestcalculators available at about thecheapest price. However, ETI havemade arrangements for an evenlower price to our readers -

£26.95 including VAT and postage.Please note, however, that theInternational will not be availableuntil October 19th and the low priceonly applies to those using thespecial coupon which will appear inthe next issue.

CALCULATOR COMPETITIONWINNERS

Over 2000 entries were recei-ved for the Advance CalculatorCompetition in our July issue.Surprisingly only about onethird were correct. The firstthree drawn were from

G. W. Horrocks,Nantwich, Cheshire.

F. Birchall,Levens, Westmorland.

S. McLuckie,Coatbridge, Lanarkshire.

A number of readers pointedout that question 5 was ambig-uous. For this reason weaccepted both answers:53.17581 and 30.14279although very few entries werereceived with the formerfigures.

The correct answers were:1. At present a man is earning E1,875 per annum. If his

salary increases by 8.5% each year for five years and7.6% per year for a further five years, what will hissalary be after 10 years? The rises are compound;give your answer to the nearest 1p.

E 4066-41p

2. decimalplace:

(187.63250.485 23250.647.531 8.437

3. What is the square root of 789 (to five decimal places)28.08914

4. If we take the population of England, Scotland andWales as 54,022,410 and the total area as 88,763square miles, what is the population density per acre?Give your answer to five decimal places.

0.95096

5. What is 1.76413 to the power of six (multiplied by'itselfsix times)? Give your answer to five decimal places.

= 30.14279

6. The resonance of a tuned circuit is given by the formula:

f = 10x kHz2rNTr_C

Where L is in microhenries and C in picofarads; take nas 22

7

If L is 97pH and C is 109pF, what is f? Give youranswer to four decimal places.

f = 1547.1993

ELECTRONICS TODAY INTERNATIONAL - OCTOBER 197345

AU i III IVATIMETE

PROJECT

BY B. GRAVES.

THE MOST COMMON method used forchecking audio power levels is first tomeasure the r.m.s. voltage (V) across agiven load resistance (R) connected tothe amplifier output and from V2/Robtain the r.m.s. power in watts. Testgear requirements are an audio signalvoltmeter that will operate over a fre-quency range of at least 10 to 100,000Hz (+1dB), a load resistance of accur-ately known value and an oscilloscopefor monitoring the signal output. Thelatter is essential for (a) checking thatthe signal output is not distorted byoverloading at the amplifier input stagesand (b) for verifying the onset of clip-ping when measuring maximum r.m.s.output power. If power level differencesare to be expressed in decibels, whenplotting power bandwidth for example,then the ratios must be connected by10 log10 P2/P1 (or by a decibel cover-sion table or chart).

The advantage of a direct readingaudio wattmeter is that instant powerreadings in watts (r.m.s.) and leveldifferences in decibels can be obtainedat any frequency within the normalaudio range. This facility is particularlyuseful for example, when carrying outtotal harmonic distortion checks atdifferent power levels and frequencies.An instrument of this nature could beparticularly advantageous in a busyservice department dealing mainly with

amplifiers of various kinds and to thosewho like the writer, are frequently en-gaged in testing hi-fi amplifiers and thelike for performance to manufacturer'sspecifications.

The audio wattmeter described here

was designed and constructed expresslyfor checking the r.m.s. power output ofamplifiers operating into standard loud-speaker loads of 4, 8 and 15 ohms.

Three power ranges are provided, 0 to0.5W, 0 to 5W and 0 to 50W withminimum levels on each range of 0.01

0.1 and 1W respectively. The lowest

level that the meter is capable ofindicating with reasonable accuracy is

0.01W (10 milliwatts). Absolute maxi-

mum on the 0 - 50W range is 56 wattsfor the meter f.s.d.The audio frequencyrange of the meter is 10 to 200,000Hz ±1dB.The 4, 8 and 15 ohm load resistors

are incorporated within the meter butnote that the meter will not indicatetrue wattage readings with loads ofvalues other than 4, 8 or 15 ohms.

THE CIRCUITThe meter circuit is shown in Fig. 1

and consists simply of the dummy loadresistors R1, R2 and R3, the attenu-ation and correction networks RV1 toRV6 and the two stage audio volt-meter Q1 -Q2. The input impedance tothe meter circuit is never less than 100k

ohms, the value of R4, and imposes noload on the dummy load resistors R1,R2 and R3. From R4 signals are fedvia RV1, R V2 or RV3 which providesignal level correction according to thedummy load in use. For instance 20Winto 8 ohms will produce a lowerr.m.s. voltage than 20W into 15 ohms,so correction must be provided in orderthat one wattage scale only can be usedon the meter itself.

The pre-sets RV4, RV5 and RV6set the wattage ranges to either 0 to0.5, 0 to 5 or 0 to 50W, the signalsacross these being taken to the meteramplifier 01-02. The meter operatesfrom a bridge rectifier D1 to D4 withnegative feedback applied via RV7 toensure a uniform frequency response,from 10 to 200,000Hz, and also to setthe initial sensitivity of the meteramplifier. The meter circuit is poweredfrom a 24V stabilised supply, the cir-

cuit of which is shown in Fig. 2.

CONSTRUCTIONThe prototype, as shown in the photoswas housed in a mild steel case withlouvres in the base and rear (HomeRadio type BX5 12'/4 x 71/2 x 51/2ins).

If any other, ready made or home made,

case is used it must have holes orlouvres in the base and rear to allowair circulation around the dummy load

46ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

NETEP

!V°LINK

LOAD

COMME 0

OSCILLOSCOPEMONITORSOCKETS

R1

4n

GANGED

/ I /Ra

/ 100k // /

LOAD

Sla CV Sib

R280

15

R31511

R1,R2,R 3 (See text)

110RV1

resistors. Details for the panel layoutare given in Fig. 3a and for the chassisin Fig. 4. The chassis is attached to thefrort panel as in Fig. 3b.

There are four circuit boards, onefor the power supply, one for the meterampl if ier,one for the meter rectifier andone for the pre-sets RV1 to RV6.Details for these are given in Figs. 5, 67 and 8. The two larger boards, meteramplifier and power supply, are moun-ted on the chassis on stand-off pillars inthe positions shown in Fig. 9. The pre-sets board is mounted upright on apiece of aluminium angle and the meterrectifier board is secured under themeter terminals (see also Fig.5).

THE DUMMY LOADS

These must be accurate to within aboutDne tenth of an ohm, if the meteritself is to give accurate readings. Theload resistors are made from spiralalectric fire elements rated for 1,000watts and which can be purchasedread ly from electrical goods retailers.The frame for the resistors is madefrom paxolin (not less than 1/16th in._hick.) as shown in Fig. 10a. The 4 ohmload is made from three lengths ofspiral element connected in parallel asin Fig. 10b.

Each length is approximately 11ohms but the best way of being sure toobta n the right amount in each pieceand then arrive at the final 4 ohms, isto cut three pieces each of say 12 ohms.Join them in parallel on the frame as inFig. 10c and trim each piece by a turnor two of the spiral at a time untilexactly 4 ohms is obtained. The pre-liminary cutting can be done with theohms range on an ordinary multimeterbut the final adjustment must be doneby measuring voltage and current withaccurate meters.

A supply voltage can be obtainedfrom a transformer capable of deliveringsay 6V at 1A or by tapping a carbattery. The test set up is as shown in

- - -GANGED- - - - 7

1WATTS 1

7 E5ow

/ 6 o5W,, S2 a

00.5w

S1c(11..5

RV410k

R5100k

RV5

10k

Fig. I. Complete circuit of the Audio Wattmeter.

Fig. 2. Power supply circuit.

R910k

C3

50yF

01BC108

R8 +1.2k

C41000F

Rear view of the prototype. Various sub -assemblies can be seen thoughthe load resistors are hidden underneath.

STABILIZEDC6 SUPPLY500)..,F

C5

ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973 47

PARTS LIST

R1

R2R3R4R5R6R7R8R9R10R11R12R13R14R15R16R17R18

C1

C2C3C4C5C6C7

RV1RV2RV3R V4RV5RV6RV7

Resistor

Capacitor

made from 1000W electricfire spiral element (2 required)See text100k100k100k

12k1.2k

10k120k

12k1.2k

10k100ohms

5.6k8.2k8.2k

220k

10uF250uF

50uF100uF

50uF500u F

2,500u F

Miniature Pre-sets

5%lAW

25V min. electrolytic

40V min. electrolytic

10k

1k

D1 Diode 0A91

D2D3D4

Z1 Zener Diode 24V, 1W

Q1 Transistor BC 108

Q2BC 108

S1 Switches 3 pole 3 way

S22 pole 3 way

BR 1 Rectifier BY164

T1 Transformer Primary 230V; Secondary 12V + 12V, 50mA(Eagle MT12)

Meter 0 - 100uA f.s.d.; Anders KM118

Case 121/4 x 71/2 x 5Y2 ins. (BX5, Home Radio)

On/off Swtich; mains panel neon; 2 pointer knobs; 3 insulated panel terminals;

2 insulated sockets; four 0.15 in. matrix circuit boards (1 x 33,, in., 3 x 11/2 in.,

5 x 31/2 in., 4 x 3 in.; Aluminium sheet (16 s.w.g.), 16Y4 x 4% in. for chassis,

2 x 1/2 in. for link; Aluminium angle, 3/8 x 3/8 in. (2 pieces, 3 in. long and one11/2 in.; Paxolin sheet 5 x 3 3/4 x 1/16 in; 4 stand-off pillars.

Needed in setting up

For load resistors: 6V, 1A supply; meters for 1A and 6V; 20 ohm, 1A variable

resistor (see text)

For Calibration: Signal Generator; Audio millivoltmeter.

Fig. 11 and requires a heavy duty vari-able resistor in addition to the voltagesupply and meters. The 4 ohm load

resistor (R1) can be adjusted for truevalue with a current of say 0.5A at 2V.

Do not use higher voltage and hence

higher current, as the resistor will heat

and give a false value. Even at 0.5Asome heat will be produced but notenough to effect the readings. If a

heavy duty variable resistor is notavailable a temporary one can be made

from about 6 inches of spiral element(as used for the loads) and a couple ofcrocodile clips. The 8 ohm load (R2)is adjusted the same way but this timewith 0.25A (250mA) at 2V and the 15

ohm load (R3) with say 0.2A (200mA)at 3V.

Considerable care must be takenover this operation as the accuracy ofthe meter depends on it. The resistorsare arranged on the frame as in Fig. 10cand the frame is finally mounted spacedoff by about half inch on the undersideof the chassis as shown in Fig. 12. Notethat leads from the load resistors con -

104

ALUMINIUM ANGLE(EACH END)

716 s.w.g. ALUMINIUM

FRONTPANEL

4- -4-

(T220)

Fig. 4a) Details of the chassis.b) How the chassis is bolted to thefront panel.

48ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

32

7'

L

METER

4

.

0V/// A K

,

40r7.

\\24'A

\WIN\

lelK4171

CUT OUT(METER BODY)

ON -OFF PILOT NEON

CHASSIS LINEBEHIND PANEL

nectmg to the load input terminal andto S1A should be heavy flex or 18s.w.g. covered wire.

THE METER

The meter used for the prototypeshown in the photos was an Anderstype KM118 0-100uA f.s.d. The meterscale can easily be removed for re -

calibration in watts and decibels to thescale given in Fig. 12. The figures onthe meter scale will come off with anordinary India rubber leaving a plainwhite surface. The new scale, which isSuitable only for the meter specified,can be drawn on with Indian ink andthe figures transferred from Letraset.Again accuracy is important and greatcare must be taken to avoid damage tothe meter movement and the pointer.

CALIBRATION

The new meter scale must be drawn onand the meter itself connected in cir-

PANEL

C5

D1

D3 D4

PR7

S1a-S1bLOAD

O

7,8

S2a-52bWATTS

OSCILLOSCOPE

LINK

METER LOAD

;

COMMON E

2-;

Fig. 3a) Front panel layout and drilling details. b) Position ofchassis at rear of front panel.

/ METER

CIRCUIT BOARD 3-4 x 1

CLAMPED UNDERMETER TERMINALS

Fig. 5 (above). D1 -D4 are fittedto a board which mounts on themeter terminals.Fig. 6 (right). Circuit board forthe presets.

BOARD 3"xPLAIN 0.15' MATRIX

RV1 RV4

I

// RV2 RV 5

RV3 RV6

'x l'ALUMINIUM8 8 ANGLE 67)IFP

ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973 49

AUDIO

tt

ON/OFF

MAINS

WATTMETER

PANELNEON PILOT

C72500 yF40V wkg

-veye

+24V+24V

CIRCUIT BOARD5X 3:11 PLAIN 0.15'MATRIX

Fig. 7. Layout of the power supply board.

cuit. A signal generator (sine -wave)capable of 10V r.m.s. output and anaudio millivolt meter are required forthe adjustment of the attenuator pre-sets RV1 to R V6 and the feedbackcontrol R V7.

The signal generator is used at 1,000Hz and is connected to the input of themeter amplifier at C1 and with the leadbetween C1 and S2b common discon-nected. The audio millivolt meter is

8 8 ^ 8 8 8

58

11

4

-0- -0-

4 BA CLEARANCEHOLES

THK PAXOLINFRAME

-0- -0-

-0- 413' 4 A3

8 3 34

8

8

BOARD 4'x 3' PLAIN 0.15"MATRIX

/7/7CHATS S(E) D4 -D3 D1 -D2

Fig. 8. Layout and wiring of the meter amplifier.

PRESET VR1 TO VR6

POWER SUPPLY

METERMETER RECTIF

METERAMPLIFIER

24V

V!

Fig. 9. Layout of circuit boards on the chassis.

Sla

8 15

Sla

411 811 1511

LOAD RESISTORS (See text)

Fig. 10a). Frame for the dummy loads RI, RZ R3. b). The circuit of the dummy loads. c). Assembly of dummy loadresistors on the frame.

50ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

HEAVY CURRENTVARIABLE ABOUT 2011

SUPPLYAC OR DC(See text)

VOLTS

AMPS

Fig. II. Measuring set up fordetermining values of the dummyload resistors.

R BEINGMEASURED

O

Fig. 12. Meter scaleshown actual size.This will only fit theAnders KM118.

10

15

connected across the output from thegenerator, i.e. between C1 and earth.Set the generator to provide exactly50 millivolts output and adjust RV7 toobtain full scale reading on the powerlevel meter, that is to point X, Fig.I2. TABLES FOR CHECKING CALIBRATIONAt this stage the meter amplifier canbe checked for frequency response bykeeping the generator output constant Range 1, 0 to 0.5W V = \,( P0 x Rat 50mV and running through thefrequency range from about 10 or Power level watts 4 ohms 8 ohms 15 ohms20Hz to at least 10,000Hz. (volts) (volts) (volts)

Now reconnect C1 to S2b common 0.5 1.414 2.00 2.739and disconnect the common of S2a0.4 1.265 1.789 2.449from Sic. Couple the audio generator,

with the audio millivolt meter in 0.3 1.095 1.599 2.121parallel, to the common of S2a. Set 0.2 0.894 1.732S2a to the 50W range and adjust RV6

0.1 0.632 0.394 1.224to obtain meter f.s.d. (to point X)from a 600mV signal from the gener- 0.05 0.447 0.532 0.866ator (all these tests are at 1000Hz). 0.01 (0dB) 0.200 0.282 0.383Now set S2a to the 5W range andadjust RV5 to obtain meter f.s.d. (to Range 2, 0 to 5W V =N/P0 x Rpoint X) from 180mV signal from thegenerator. Finally, set S2a to the 0.5Wrange and adjust RV4 to obtain meter Power level watts 4 ohms 8 ohms 15 ohmsf.s.d. (to point X) from 68mV input. (volts) (units) (volts)Again accuracy is important.

Reconnect the common of S2a with 5 4.472 6.325 8.660S1c. Couple the audio generator with 4 4.00 5.357 7.746the audio millivolt meter in parallel 3 3.464 4.399 6.708between the main input terminal mar-ked 'METER' and the common E 2 2.828 4.30 5.477terminal. The "link" to the loads must 1 2.00 2.328 3.873be disconnected. Set S2 to the 5W 0.5 1.414 2.30 2.739range and S1 to 15 ohms. Adjust RV3

0.1 (0d6) 0.632 0.394 1.224to obtain a meter reading of 5W witha signal input (at 1,000Hz) of 8.66V.Check with S2 on the 50 watt range to Range 3, 0 to 50W V = .\,/ P0 x Robtain meter reading of 5W.

Reset S2 to the 5W range and S1 to8 ohms. Adjust RV2 to obtain meter Power level watts 4 ohms 8 ohms 15 ohmsreading of 5W with a signal input of (volts) (volts) (volts)6.32V. Check with S2 on the 50W 50 14.142 2C 27.386range to obtain reading of 5W.

40 12.649 17..889 24.495Reset S2 to the 5W range and S1 to4 ohms. Adjust RV1 obtain meter 30 10.954 1E.492 21.213reading of 5W with 4.47V input signal. 20 8.944 12.649 17.321Check with S2 on the 50W range to

10 6.325 E.944 12.247obtain a meter reading of 5W.5 4.472 .325 8.660

Continued on page 80 1 (0d B) 2.00 2.828 3.837

ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

Master Mixermodification

This simple two IC board replaces the LM381 dual preamplifier which is currently unobtainable.

The replacement board is mounted, component side down,as shown. A small wooden block spaces this board from themain board. Note that Cl and C3 mounted on the copperside of the board.

OFig. 1. Circuit diagram of the replacement unit. The ICs areNational LM301.

PARTS LISTIC1 integrated circuit LM301

(mini -DIP pack preferred)IC2 integrated circuit LM301

(mini -DIP pack preferred)R1 resistor 1 OM 1/4 or 1/2 watt 5%.R2 resistor 1 OM Va or 1/2 watt 5%.R3 resistor 10M IA or 1/2 watt 5%.R4 resistor 1 OM 1/4 or V2 watt 5%.C1 capacitor 5.6pF ceramicC2 capacitor 220pF ceramicC3 capacitor 5.6pF ceramicC4 capacitor 220pF ceramicPC board ETI 414dThe LM301 is available from Elect-rokit, 8 Cullen Way, London N.1N.10at 49p plus 10p postage.

THE component shortage strikesagain! After being assured by NationalSemiconductor that they had plentyof LM381s for our Master Mixerproject, stocks dried up completelyand efforts to find fresh stocks hereand overseas have been unsuccessful -to both National's and ourembarrassment. Even worse, deliveriesof LM381's cannot be reasonablyexpected until the end of 1973!

The LM381 was chosen for theMaster Mixer because it has excellentlow noise characteristics, andunfortunately, there is no directreplacement.

Partially to overcome this problemwe have designed a small printedcircuit board conversion carrying twoLM301's (and associated components)that may be substituted for theLM381's on the main preamplifierboard.

Due to the wide gain variationsrequired in the mixer, most availablelow -noise ICs will either not remainstable, or will not have the requiredfrequency response (-50 dB to +55

HOW IT WORKSExcept for biasing, theoperation of

the LM301 is identical to one half ofthe LM381 (LM381 is a dualamplifier).

The LM381 is designed foroperation from a single -ended powersupply whereas the LM301 requires adual power supply. The LM301therefore requires resistors to splitthe power rail by providing anartificial centre tap (R, R2 and R3,R4).

The 390 kohm biasing resistors forthe LM381, R7 and R8, are thereforeno longer used and must be removedfrom the main board.

A 5.6 pl: capacitor is connected

across pin 6 to pin 2 of each IC, asfeedback, to reduce the highfrequency gain beyond 20kHz, thusreducing high frequency noise. Withthis capacitor in use the gain whenset to maximum drops 3 dB at 20kHz. At lower gain levels theresponse is flat to well beyond 20kHz.

Frequency compensation is appliedto each amplifier by means of the220 pF capacitor connected betweenpins 1 and 2. This mode ofcompensation is known as "Feedforward" and is used to extend thefrequency response of the LM301which would otherwise be 3 dB at 1kHz and maximum gain.

14d

kgir-ONACFig. 2. Foil pattern of printed circuitboard shown full size.

Fig. 3. Component overlay

52 ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

Cl

cn <

co

rn

1- 33 33 33° «cri cr:

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dB gain at 10 kHz). We haveestablished however that the LM301,when used with feed -forwarda)moensation, does provide thenecessary stability and frequencyresponse over the required gain range.

The LM301 is not primarily a

low -noise amplifier however, and thenoise level of the mixer will be 10 to15 dB worse than with the LM381.This however will not be a problem fornormal ive work. It may however,(but not necessarily) be a problemwhen the unit is used for recording.

As the noise performance of theoriginal unit was very good indeed, 1010 15 dB degrading is not as serious asit might at first seem, and for normallive work, will cause no problems. Theincreased noise level may (but notnecessarily) be a problem when theunit is used for recording purposes instudios with low ambient levels.

Apart from the noise increase, thismodification will not degrade theperformance in any way. Both gainand frequency response will remain asspecified, and the mixer will operatesatisfactorily for all but the mostexacting applications.

OV

Fig. 4. Position of the printedcircuit board with respect tothe preamplifier board. Notethe positioning of Cl and C3.

Fig. 5. The completed PCboard is connected by meansof wire links from the re-maining holes to the LM381socket on the preamplifierboard.

CONSTRUCTIONMount the components onto the

printed circuit board as shown in Figs.3 and 5. Ensure that the IC's arecorrectly orientated. The dot or notchon the IC should be to the left whenthe board is orientated as shown in thephotograph. Note that capacitors C1and C3 are mounted on the copperside of the board as shown in Fig. 4and the photograph.

Remove existing R7 and R8 from thepreamplifier board (390 kohm) andusing a small wooden block as a spacer(1/2" x 1/4" x 3/4")position the smallboard over the LM381 socket in thepreamplifier board as shown in thephotograph and in Fig. 4.Small straight pieces of

tinned -copper may be used (eg,. endsof resistors previously cut off) to jointhe two boards together. Note that thesmall printed circuit board is designedas a pin -for -pin replacement for theLM381 but pins 3, 5, 6, 10, 11 and 12are not used. Thus the pieces of wireare passed through the holes in thesmall board to the corresponding holein the LM381 position. Solder the wireto the copper pads on both boards andtrim the excess wire.

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Swan Works, Bank Square, Wilmslow,Cheshire SK9 IHF.

ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973 53

VHFTRANS -EQUATORIALPROPAGATION

Magnetic field- alignedBULGE i rregutorities

CREST

NC

Geomagnetictot it ud

Geomagnetic 01

Equator /Geographic

equator

Lines of equalCREST electron density.

Geomagnetic X..latitude

03 t's

Fig. 1. The propagation modes of class land class II TEP.

RECEPTION of VHF signals oververy long paths that cross more -or -lesstransversely to the equatorial zonehave been frequently reported in thelast 25 years. The frequenciesinvolved are generally far inexcess of the predicted maximumuseable frequency, and signal strengthssometimes approach free -space values.Path lengths reported are usuallygreater than 5,000km - with a few upto 18,000 km. These signals aregenerally regarded. as having arrived by"anomalous" transequatorialpropagation.

Throughout the remainder of thisarticle the letters TEP are used todenote this form of propagation.

A SHORT HISTORYThe . first intercontinental VHF

contacts were reported in QST by EdTilton in "The World Above 50 Mc",May and October 1947 but thediscovery of TEP by radio amateursdid not receive a great deal ofattention in the scientific world untilthe late 1950's (and the IGY in1957/58).

Contacts *between Australia andHawaii, Mexico and Argentina, and theU.S.A. and Peru were fairly commonbetween 1947 and 1951. There wasthen a sharp decline during thesunspot minimum but new reportsbegan to appear again in 1955,

reaching a maximum during 1957 -1960, and again during 1968 - 1971.Some contacts were reported overextremely long paths, ranging from9,860km to 18,760 km.The first scientific paper to appear

on TEP was by Ed Tilton, published inthe Proceedings of the Second Meetingof the Mixed Commission on theIonosphere, in Brussels 1951.Observations made between 1950

and 1966 of the characteristics andpropagation modes of TEP along withresearch into the equatorialionosphere, brought to light a lot ofvery interesting information. Inaddition to collecting amateurobservations, a number of experimentswere set up involving HF and VHFscatter soundings, oblique incidenceionosondes, observation of beaconsand TV and FM stations - in Korea,Japan and Russia, and topsideionospheric sounding by satellites.This led to a better understanding ofthe structure of the equatorialionosphere and to suggestionsregarding the various modes thatsupport TEP.

GENERAL CHARACTERISTICS OFVHF TEP SIGNALS

There appears to be two distincttypes of TEP, distinguished by timesof peak occurrence, fadingcharacteristics, path lengths, and

By ROGER HARRISON

principal mode of propagation.One mode, designated Class I,

exhibits the followingcharacteristics:-

(a) a peak occurrence aroundmid -to -late afternoon (1200to 1900 local mean time,measured at the point wherethe path crosses the magneticequator).

(b) normally strong, steadysignals with a low fading rateand, more specifically, a smallDoppler spread (around ± 2to 4 Hz).

(c) path lengths of 6,000km to9000 km and sometimeslonger.

The proposed propagation mode forClass I TEP is generally termed the"super -mode" or FF mode. As can beseen from Fig. 1, the ray, transmittedfrom A, "skips" from the crest in theequatorial ionosphere at X, across thecrest at Y and is refracted down toearth at B. These "crests" are a featureof the equatorial ionosphere (aboutwhich I shall have more to say later).The other mode, designated Class II,

shows the following characteristics:-(a) a peak occurrence around

2000 hours to 2300 hourslocal mean time

(b) high signal strengths but withdeep, rapid fading (typicalrates are 5 Hz to 15 Hz)accompanied by a Doppler

54 ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

0°

10'

-20° \_

20e/

30

.'30° //

Ao

Cap et',wr

/--

E 20°

. I.30 40 50 0

31r°ap° 50' 610

40

fele

40

20'

40

Fig. 2. The African -Mediterranean Sector of theworld showing terminal zones for class 1 TEP(20° to 400 geomagnetic latitude) and class 11TEP (100 to 30° geomagnetic latitude).

spread much greater than forClass I, generally in the orderof ± 20 to 40Hz (i.e. tentimes that for Class I).

(c) path lengths are usuallyshorter than for Class I, beingaround 3,000km to 6,000km.

The propagation mode or mechanismfor this class of TEP is not fullyunderstood, but it is believed thatirregularities (dense "clouds" ofelectrons having a certain specificshape) in the equatorial ionosphere -aligned with the earth's magnetic field- are responsible for "ducting" orefficiently "scattering" the signal such

that the path geometry looks like thatin Fig. 1. (from C to DI.

Additionally, Class II will supportmuch higher frequencies than Class I,signals have been observed up to 102MHz.

THE EQUATORIAL ANOMALYThe equatorial ionosphere does not

have an even distribution of electrondensity. As can be seen from Fig. 1.,the F -region iso-electronic contourlines (lines of equal electron density)show a depletion of electrons, togetherwith a rise of the F -region height,above the magnetic equator. Roughlysymmetric, north and south of the

geomagnetic equator, are two "crests"that represent an increased electrondensity in the F -region. These crestsare located between 10° and 20°(geomagnetic latitude) north andsouth of the geomagnetic equator. Thelocation of these regions are shown inFigs. 2, 3 and 4.

This region of the ionosphere (withinapproximately ± 20° geomagneticratitude) is generally referred to as theequatorial anomaly region. It is a

regular feature and not a transientphenomena.

If the electron density within thecrests increases sufficiently, it will bepossible for a signal, incident upon onecrest at a very small angle, to berefracted across the geomagnetic andgeographic equators to the oppositecrest and hence to earth as illustratedin Fig. 1.

DIURNAL VARIATION OF THEEQUATORIAL ANOMALY

From what little data is available, itappears that the equatorial anomalystarts to develop between 0800 and1000 LMT, the crests moving awayfrom the magnetic equator between0900 and 1500 LMT.When the sun sets on the base of the

equatorial ionosphere (about 11/2 hourslater than ground sunset, i.e. 1930hours LMT, the base of the layergenerally rises and the equatorialanomaly begins to break up into large"blobs". This does not always happen,the base of the layer may notnecessarily rise and, on occasion, isfound to fall or remain at thepre -sunset height. Sometimes theanomaly does not break up intodistinct blobs and the electrons appearto diffuse back over the magneticequator. The ionosphere is generallylike this during early morning and lateevening. The detailed behaviour of thedecay phase of the equatorial anomalyhas not yet been fully established.

SEASONAL VARIATIONS OFTHE EQUATORIAL ANOMALY

The crests lie very nearlysymmetrically either side of themagnetic equator at equinox andasymmetrically at solstice. Theelectron densities of the bulges aregreater at equinox than at solstice andthis, combined with the anomalysymmetry at equinox, favours Class I

TEP at the equinoxes. The separationand overall width of the crests variesseasonally also, being greatest atequinox.

"Tilts" in the base of the F -layer areknown to be associated with the crestsand are most pronounced between1200 and 2000 LMT and at equinox.These tilts which are departures of the

ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973 55

VHFTRANS -EQUATORIALPROPAGATION

somewhere within these limits. Thepeak occurrence times coincide withthe stable phase of the equatorialanomaly which is generally welldeveloped after 1100 LMT and beginsto decay around 1900 LMT.Occasionally it remains stable afterthis time, particularly at equinox atsunspot maximum and observationsbear this out, signals remaining stablefor several hours after 1900 LMTbefore experiencing the flutter fadingof Class II TEP.

Paths that are normal (or nearly so)to the geomagnetic equator andsymmetrically located either side arefavoured, experiencing earlier starttimes, longer durations and a greaternumber of occurrences - especially atsunspot minimum.

I might add that TEP can occur atany time of the night or day but it ismost infrequent between 0400 and0800 LMT for either Class I or Class IITEP.

Occurrence times are generallydependent on:-

(a) Suitable path geometry,including tilts which allowsupermode propagation.

(b) Build up of sufficientionisation density in thecrests of the equatorialanomaly such that foF2 ofeach crest is sufficiently highto increase the maximumusable frequency above thatnormally expected.

(c) Sunspot number - (b) is

obviously dependent onsunspot number but this is

not the only factor involved.This dependence is not as

great as one would imagineand is much less than forClass II.

(d) Season.

PATH CHARACTERISTICSAs class I TEP is propagated via a

supermode (Fig. 1.) the path geometrycan be determined for the maximumand minimum range possible for theobserved parameters of the bulges ofthe equatorial anomaly. Theparameters affecting the pathgeometry are the height and locationof the virtual reflection points, foF2for these points and incidence anglesto those points. Knowing these, itbecomes possible to predict themaximum and minimum ranges. Thesework out to be between 5000 and9000 km. This was calculatedassuming that the path and equatorial

anomaly were symmetrical about thegeomagnetic equator.

The 'best' paths are those which arelocated symmetrically about andnormal (or nearly so) to thegeomagnetic equator and the terminalsof which lie in areas between 20° and40° geomagnetic latitude north andsouth of the geomagnetic equator.These areas are marked in Figs. 2, 3and 4 (cross hatched to the right).These paths tend to experience Class ITEP more often than oblique orasymmetrical paths.

Very long paths (greater than 10 000km) are always oblique and someother form of propagation appearsnecessary to assist the signal in beingfavourably incident on the bulges ofthe equatorial anomaly. Sporadic E(Es) is the most likely cause but thishas yet to be confirmed.

TEP over paths which are fairlyoblique to the geomagnetic equator(65° or less) tend to be reasonablylong (greater than 8000 km), rare,short lived and tend to occur mainlysome weeks after the equinoxes. Manyof them are asymmetrically situatedwith regard to the geomagneticequator but this bias is probably dueto observer station distribution. Verylong range TEP is generally observedone to two years after a sunspotmaximum and rarely, if ever, duringthe sunspot minimum.

RAY TRACINGIf a series of rays from a transmitter

in one hemisphere is traced, usingcomputer simulation through a modelof the equatorial ionosphere, it is

found that much of the low angleradiation travels via the supermode ofpropagation and experiences a largedegree of focussing at the receiver.

In Fig. 7., a computer printoutillustrates this ray -focussing effect.The inset shows the variation of foF2with geomagnetic latitude assumed forthe particular circuit. The printout isreproduced by kind permission of Mr.B.C. Gibson -Wilde of the James CookUniversity of Ndr-th Queensland.

Ray focussing is a very importantcharacteristic of Class I TEP as itprovides the strong signals and "areaselectivity" (signals being heard in onenarrowly defined area and not inothers) that is often noticed as beingassociated with afternoon type TEP.

SEASONAL CHARACTERISTICSThere is a maximum number of

occurrences around the equinoxes forall sectors of the world. This is due tothe' more favourable conditions thatexist in the equatorial anomaly at theequinoxes.

It is well known that the

sunspOt number affects the maximumuseable frequencies of the F -layer andpeak electron density for the crests ofthe equatorial anomaly follow a

similar pattern. However, the greatestnumber of occurrences of Class I TEPlags behind the sunspot maximum byone to two years. The reason for thisis, as yet, unknown.

SIGNAL CHARACTERISTICSApart from the frequencies involved,

the most extraordinary characteristicsof Class I TEP signals are their strengthand steadiness (absence of fade).Signal strength can sometimesapproach free space values, and thefading rate is normally quite low andnot very deep. This is explained by thefact that rays strike the tilts associatedwith the crests of the equatorialanomaly very near to tangency and areefficiently refracted; this, combinedwith ray focussing, and the sameabsorption for a one -hop path, leads tovery little signal loss.

Many amateurs report good resultsrunning only medium to low power(under 20 watts) and small antennas.

The frequencies involved in Class I

TEP will always be above thepredicted maximum useablefrequency, for the path involved, by aconsiderable factor. Thus Class I TEPaffects the HF region as well as thelower VHF region. Contacts on the HFbands via Class I TEP have beenreported, but are not often recognisedby amateurs.The MUF for oblique paths is

generally lower, owing to unfavourable"look" angles on the equatorialanomaly, and consequently the MUFfor these paths exceeds 50 MHz lessoften than for paths which are morenearly normal to the magneticequator.

Although Class I TEP provides fairlystable signals, wideband system willsuffer distortion due to multipatheffects (see Fig. 7). Voicetransmissions will not appreciablysuffer, especially narrow band FM, buttelevision picture signals will be ofvery poor quality.

It must be understood that Class I

TEP is not a "normal" F2 mode ofpropagation as many VHF amateursseem to think, but it is certainly not"anomalous" within the definition ofthe word. The maximum useablefrequency of the F -layer for 1F or 2Fmodes in general rarely exceeds 50MHz so that Class I TEP cannot beclassed as "normal" F2 skip on thesegrounds alone. Secondly Class I TEPtravels via a two -hop ionospheric modewithout intermediate groundreflection. This supermode orFF-mode is sometimes referred to as"chordal -hop" propagation.

58 ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

Fig. 7. A copy of a ray tracing printoutshowing the focussing effect obtained whentransmissions are propagated via the super -mode. The inset shows the theoreticalsymmetric anomaly assumed in the ray -tracing program that produced the printout.(Reproduced with the kind permission ofB. C. Gibson-Wildel.

CREST (17.0 GEOMAO LAT.)

TAKE OFF ANGLESe-12. IN 2° INCREMENTS

TX AT SEOUL35.5°N GEM LAT.

MAO E0

3000

CLASS II TEP - CAUSESAND CHARACTERISTICSThe characteristics of Class II, or

evening -type TEP, are generally wellknown but the mode of propagation isnot yet known or completely defined.Several different explanations havebeen put forward, based on thecorrelation observed betweehnight-time TEP observations and theoccurrence of equatorial spread -F.Experimental results, when applied tothe various theories, have shown themto be incorrect, but it is wellestablished that there is some definiteconnection between spread -F alongthe paths considered and theoccurrences of Class II TEP.

The higher frequencies propagatedby Class II TEP offer some interestingpossibilities to the communicator.There is a maximum occurrencebetween 2000 and 2300 LMT with apronounced peak somewhere in thisrange for different seasons andparticular paths. This means that justabout every circuit has an individualpeak occurrence time for differentseasons but it will be somewherebetween 2000 and 2300 LMT. Thiscoincides well with the occurrence ofequatorial spread -F, but the durationof TEP signals is usually less than theduration of spread -F. This is probablydue to the reduction of peak electrondensity in the F -layer after midnight.

Class II TEP has been observed tolast until the early hours of themorning, but only on lower VHF. Theoccurrence of Class II TEP openings isgreatest during the equinoxes as is

spread -F - this is more pronouncedthan in the case of Class I TEP. Theseopenings are fewest during the wintersolstice over the magnetic equator.

4000

10

SYMMETRIC ANOMALY G7

NORTH0 -10

0(064.46. LAT

CRE5TI-17.0 GEOMAG. LAT I

6000

RANGE (km I

This occurs during December -January for the Asian and Africansectors and June - July for theAmericas (7).Start times for openings via Class II

TEP are less dependant on pathgeometry than for Class I TEP as alsoare the times of duration. Class II ismuch more tolerant of asymmetricalpath geometry than Class I.

Usually contacts are dependent on(a) Appearance of equatorial

spread -F at an appropriategeomagnetic latitude.

(b) Season of the year, i.e. proximityto the equinoxes.

(c) Sunspot number.

PATH CHARACTERISTICSPath lengths for Class I TEP are

generally from 3000 km to 6000 kmand terminals are quite oftenasymmetrically and obliquely situatedwith regard to the magnetic equator.Some very long night-time paths havebeen observed but these can beexplained by the occasionalcontinuance of the Class I TEP modeafter sunset, or another mode ofpropagation assisting in extending therange of signals. Again, sporadic -E islikely to be the reflector at the lowerend of the VHF range. Troposphericducting could extend the range in asimilar fashion at the higherfrequencies but little work has beenreported irt this direction. Nielsonmentions Es in this regard in his paper.There is a zone where stations (or

circuits) will experience both modes,and zones where stations will onlyexperience one or the other. The areabetween 20° and 30° geomagneticlatitudes (Figs. 2, 3, 4) is common

SOUTH

ground for both Class I and II TEP.Stations located in these areas willencounter both modes from time totime with perhaps a gradual transitionfrom Class I to Class II (evidenced byan increase in flutter fading after 2000hours) or a signal dropout of up to anhour's duration.

Stations north and south of about30° geomagnetic latitude will tend tosee only afternoon -type TEP whilethose stations closer than about 20° tothe geomagnetic equator will tend tosee only evening -type TEP.The westward movement of contacts

via Class II TEP is not generally notedas it is for Class I TEP. Theirregularities that occur in the base ofthe F -layer, are certainly known tomove westward but their longitudinal"spread" is usually considerably widerthan for the equatorial anomaly. AsClass II TEP appears to depend to alarge extent on these irregularities, thewestward movement may be maskedby their longitudinal width and thetolerance to asymmetrical paths that isnoted.

SEASONAL CHARACTERISTICSThere is a marked dependence of

Class II TEP on the equiinoxes andsunspot number. The samedependence is noted for equatorialspread -F.

Class II TEP has a maximum numberof occurrances which lags the sunspotmaximum by a year or so - as is notedfor Class I. The reasons for this are notyet clear but further research shouldelucidate the causal mechanisms.

Similarly to Class I, contacts can behad almost every night around theequinoxes during peak occurrence

ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

VHFTRANS -EQUATORIALPROPAGATION

years. There is a rapid drop off in thenumber of occurrences after this time,few contacts being noted during thesolstices and the years spanning thesunspot minima. Observations carriedout using oblique sounders and beacontransmitters also bear this out.

SIGNAL CHARACTERISTICSThe most surprising aspect of Class II

TEP signals are the high frequenciesthat it will support and the high signalstrengths that are recorded.

Beacon transmissions on 102 MHzfrom Darwin have been recorded insouthern Japan on many occasions,but, as yet, there have been no reportsof higher frequency signals. No upperfrequency limit has been proposed forClass II TEP as the mechanism bywhich it is reflected or refracted in theionosphere is not yet known.

Here is an opportunity forenterprising amateurs who would liketo try for some exotic DX on 144MHz - and make a contribution to abody of scientific knowledge on aphenomenon about which we knowlittle. Unfortunately 144MHz contactsmight have to wait till the nextsunspot maximum. But don't let mediscourage anyone from trying.

Generally speaking, high signalstrengths are experienced having a

considerable amount of flutter, Theflutter rate is mostly between 5 and15Hz and Doppler shift is mainlybetween ± 40Hz. This means that, attimes, A3 (DSB or SSB) signals will beseriously degraded. The effect onwideband systems (FM or PM) wouldbe much less but TV would sufferowing to the spread of time delaysexperienced.

Paths whose terminals are magneticconjugates (have the same angle ofmagnetic dip but the opposite sensei.e. 25°N and 25°S) experience thehigher frequencies more often andwith greater reliability. The signalstrength for these paths is higher thanfor the less favourable asymmetricpaths and path lengths are generallyshorter.

As Class II TEP is probablysupported in some way by field guidedionization, the closer a ray can belaunched to tangency with themagnetic field, the more favourableare its characteristics, i.e. higherfrequencies will be supported, highersignal strengths will be guaranteed andgreater reliability will be obtained thanfor less favourable rays.

Many people refer to class II TEP as

transequatorial scatter. This is quitewrong for a number of reasons. Scatterpropagation involves incoherentreflection from tropospheric orionospheric irregularities of a sizesmaller than the wavelength in use.Signal strengths are weak and have aconsiderable flutter component.Transmitted and received angles ofelevation from the ground are muchgreater than for a field guided modeand signals are not necessarily receivedover a great circle route. Ranges forscatter propagation are much less thanfor Class II TEP. It appears that theconsiderable flutter component oftenobserved on evening -type TEP leads toa confusion involving the modes ofpropagation. Class II TEP is dependenton many factors (season, sunspots,geomagnetic latitude, etc.) that seemto have no bearing on true scattermodes.

CURRENT RESEARCHThe Ionospheric Prediction Service

(Australia) is currently conductingresearch into TEP, particularly theevening -type or Class II. Equipmenthas been set up to examine the signalcharacteristics of VHF beacons locatedin Japan' (JAI IGY) as part of thisresearch which is aimed at elucidatingthe propagation mechanism of theevening type TEP and eventuallypredicting its occurrence. Theionosonde located at Vanimo, NewGuinea, is almost ideally situated tostudy the equatorial ionosphere. It hasbeen equipped with an interferometersystem to assist in studying theirregularities that cause spread -F.

REFERENCES1. Tilton, I.P., "The World Above

50Mc", QST, 31, May, 1947, page61

2. Tilton, E.P., "The World Above50Mc", QST, 31 October, 1947,page 56.

3. Tilton, E.P., "Long DistanceCommunications over north -southpaths on 50c/s", Proc. 2ndMeeting Mixed Commission onIonosphere, Brussels, 1951, page119.

4. Ferrell, D.P., "Enhancedtransequatorial propagationfollowing geomagnetic storms",Nature, 167, 1951, page 811.

5. Yeh, K.C. and Villard, 0.G., "Anew type of fading observable onhigh frequency radiotransmissions propagated overpaths crossing the magneticequator", Proc. I.R.E., 46, 1958.

6. Yeh, K.C. and Villard, O.G.,"Fading and attenuation of highfrequency radio waves propagatedover long paths crossing theauroral, temperate and equatorialzones", Journal of Atmosphericand Terrestrial Physics, 17, 1960.

7. Southworth, M.P., "Night timeequatorial propagation at 50Mc/s.Final report from an IGY amateurobserving program",Stanford Elec-tronic Labs., Final Report, Con-tract AF -19-604-5235, May 1960.

8. Villard, O.G., Stein, S. and Yeh,K.C., "Studies of transequatorialionospheric propagation by thescatter sounding method",Journal of Geophysical Research,26, 1957, page 399.

9. Bowles, K.L. and Cohen, R.,"Studies of Scattering Phenomenain the Equatorial IonosphereBased upon VHF Transmissionsacross The Magnetic Equator",Some Ionospheric Resultsobtained during the IGY, ed.W.J.G. Beynon, ElsevierPublishing Co., 1960. page 192.

10. Gibson -Wilde, B.C., "Aninvestigation at Townsville intoanomalous long-rangetransequatorial VHF propagation(1961-1966)", Research ReportNumber 2., Physics DepartmentUniversity College of Townsville,June, 1967.McCue, C.G., and Fyfe, D.F.,"Transequatorial Propagation:Task, Bridger IntroductoryReview", Proc. I.R.E.E. (Aust.)26, Jan. 1965, page 1.

12. Nielson, D.L., 'A Review of VHFTransequatorial Propagation",Stanford Research Institute(unpublished).

13. Eccles, D., and King, J.W.., "AReview of Topside SounderStudies of the EquatorialIonosphere", Proc. I.E.E.E. 57,June, 1969, page 1012.

14,McNamara, L.F.,"Range -Spreading andevening -type transequatorialpropagation", Nature, PhysicalScience Vol. 234, Nov. 22, 1971.

15. Ratcliffe, J.A., "Sun, Earth andRadio -an introduction to theionosphere and magnetosphere",World University Library,published 1970.

16. Jamieson, E., "VHF", AmateurRadio, January 1970 to June,1971.

11.

60 ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

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ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973 61

"God made the integers: all else is the work of man" - Leopold Kronecker

THE concept of number belongs tosocieties which have reached a certainlevel of sophistication. Certain veryprimitive and illiterate societies - theearly Australian aboriginals or theKalahari bushmen for example, go nofurther than - ONE, the individual(me) - TWO, the two sexes (us) - andMANY. Even the ancient Greeks, withtheir insatiable curiosity about theworld around them, stopped theirnumbering system at 10,000, allgreater numbers being consideredinfinite!

It is probable that the evolution ofhighly organized societies, where taxesand revenue (in terms of corn, animals,gold, etc.) made necessary some formof accountancy, and man began to beaware of numbers and of the necessityof recording them. The ancientEgyptians, the Babylonians, the Mayaand other such civilizations evolved, ata very early state in their evolution, asatisfactory system of recording thenumber of things, but did not evolve asystem of recording that was adaptableto arithmetical operations on thenumbers thus recorded.

An important step forward was madewhen it was realized that numberscould be used not only to record butalso to calculate. Since the systems ofrecording numbers did not permitdirect arithmetical operations, it wasnecessary to invent a calculatingdevice. This gave rise to the firstcomputer - the abacus. Inventedindependently in Rome, China andJapan, in slightly differing forms, thissimple device of beads on wirespermitted the operations of addition,subtraction, multiplication anddivision. Even today a skilled abacusoperator can add up a column offigures more rapidly than can be doneon an electric desk calculator, and ifone considers the time taken inpunching cards and preparing an

appropriate program, much morerapidly than an electronic computer!

The Roman abacus merits closerstudy as it demonstrates severalprinciples common to all methods ofcalculation.

The Romans had no numericalsymbols, but used letters of thealphabet to represent numbers: I, V,

X, L, C, D, M, C . It will be seen thateach symbol is alternately five times aslarge and twice as large as the onepreceding it: 1, 5, 10, 100, 500, 1000,5000. This apparently clumsy systembecomes clear if it is realized that theletter symbols represent the positionof the beads on the abacus, as shownin Figure 1.

A feature of Roman numbers thathas puzzled many is the use of thecombinations IV, IX, XL, XC, CD,CM, etc. to represent 4, 9, 40, 90, 400,900, etc. This is because in carryingout additions and subtractions on theabacus, it is simpler to add, say 4, byadding 5 and subtracting 1, than bythe direct operation.

The Roman system of numeralstherefore is well adapted to recordingthe results of calculations performedon a computer (the abacus) but doesnot, of itself, permit any arithmeticaloperations upon the numbers thusrecorded.

The ancient Chinese numerals aresimilar in concept; they represent theresult of operations on the Chineseabacus, which differs from the Romanin certain details. The numerals are:

" "

1 2 3 4 5 6

7 8 9 10 100 1000 10 000

To write any given number,combinations of these signs are used,for example, the date 1973 would bewritten:

or (1 x 1000) + (9 x 100) + (7 x 10) +3Here again direct arithmetical

manipulation of these numbers is

impossible.The great breakthrough in numbers

was achieved by the ancient Hindus,who realized two fundamentalparameters of any numbering system:

- the use of a sign to indicate zero- a radically new conception thatnone of the earlier systems hadconsidered;

- the concept of positional notation,that is to say, that one can expressany number by a very small numberof signs (in fact 10) the signs beinggiven a significant value by theirposition.The original Hindu signs were:

R.Yk9 6'r°1 2 3 4 5 6 7 8 9 0

which are sufficiently close to our ownfigures that several of them can berecognized at once. Here, the year1973 would be written

Vk9exactly as we do.

From India these numerals weretaken over by the Arabs, who wrotethem:

Triol VAA7 8 9 0

and it is from these characters that our"arabic" figures that we use todaywere derived.

With the invention of the arabic (orHindu) numerals, man was enabled tocarry out arithmetical operationsdirectly on numbers as written,without the intervention of anymechanical assistance.This state of affairs continued right

into the seventeenth century, when,evolving scientific knowledge requiredcalculations of greater complexity tobe performed than were practicable(though still possible) without theassistance of some device - hence theevolution of logarithms, the slide -rule,mechanical calculators, and now theelectronic computer.

Inherent in any numerical systemusing positional notation is that of a"base".

62 ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

Fig. 1

the abacus can beextended in thisdirection to coverthe size of thelargest numberrequired

DL V

TTT

C X I

This is the number that correspondsto the number of different numericalsigns used. Since man has ten fingersand ten toes, it has been usual to usethe number ten as a base, sincecounting on the fingers is one of themost primitive and fundamental waysof expressing numbers.As we have previously shown (using

as a base the number 10) the digits inany number beyond 10 are given asignificant value by their position inthe number.

Thus by using the nine numeric signs,1, 2, 3, 4, 5, 6, 7, 8 and 9, togetherwith the zero, we can express anynumber we like. For example 1973 =(1 x 1000) + (9 x 100) + (7 x 10) + (3x 1); we know that the 1 represents1000 solely because it has three wholedigits to its right.

livith this principle established, wecan carry out any desired arithmeticaloperation upon our numbers. It must,however, be borne in mind that

basically there are only twoarithmetical operations possible -addition and subtraction.Multiplication, division and theextraction of roots are all, in theultimate, dependent on addition andsubtraction. We cannot multiply twonumbers together without having firstcommitted to memory a

"multiplication table" which gives theresults of all possible combinations ofmultiplication from 1 x 1 to 10 x 10.The expression 5 x 7 = 35 is merely aconvenient shorthand version of

5+5+5+5+5+5+5 = 35or

7+7+7+7+7 = 35Note here the principle of

commutation, it does not matterwhether we write 5 x 7 or 7 x 5, theresult is the same. For some types ofcalculation, however, this law is notvalid and care must he taken toperform the operations in the correctorder. This aspect, however, is outside

the scope of this article and may beignored.The smallest base that can be used is

2. Here only two symbols, 1 and 0, areused. But with just these two symbolswe can express any number no matterhow big.

In this system, known as 'binarynotation', each successive symbol tothe left of the first digit - which canonly be a '1' or a '0' - is increased bya factor of two.

Thus the binary number 1011 is

represented by 11 in decimal notation.Starting from the left, the first digit

represents 1, the second 2, the third 0,and the fourth 8, hence binary 1011equals decimal 1 + 2 + 0 + 8).

Were the binary number to be 1110then the decimal equivalent would be14, (0 + 2 + 4 + 8).

Table 1 shows b inary/decimalequivalents from decimal 0 to decimal15. The table can be extendedindefinitely. Just remember that eachdigit to the left has twice theweighting of its neighbour to the right.Thus the weighting of succeedingdigits are from the right to left, 1, 2, 4,8, 16, 32, 64, 128, 256, 512, 1024 etc- the number 1024 would in binarynotation appear as 10000000000,1025 would be 10000000001.

The date 1973 becomes11110110101 in binary notation(1x1) + (0x2) + (1x4) + (0x8) +(1x16) + (1x32) + (0x64) + (1x128) +(1x2561 + (1x512) + (1x1028).

There is no absolute reason why 10(or 2) must be chosen as the base forour numbering system. For certainpurposes, a system based on 8 (octalsystem) has distinct advantages. Such asystem would give us the numbersequence shown in the octal column ofTable 1. (The octal system is describedin greater detail later in this article).

It is important to realize thatalthough the number recorded mayappear strange, the number of objectsit represents remains the same.

At this point, many readers will beasking why anybody in their rightmind would willingly forgo theconciseness of decimal notation forthe apparant obscurity of the binarysystem.

ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973 63

NUMBERS

R IlliP SWITCHES

o

0 LAMPS

Flq. 2. This arrangement of four switches may be used to represent the decimalnumbers 0 to 15 in binary notation.

TABLE 1

Table 1. Comparison of decimal numbers from 0 to 15 in binary andoctal. Letters A to D refer to switches shown in Fig. 2

DECIMAL BINARY OCTAL

One switch 0 0 0 0 01 0 0 0 1

Two switches 2 0 0 1 0 2

3 0 0 1 1 3

4 0 1 0 0 4Three switches 5 0 1 0 1 5

6 0 1 1 0 67 0 1 1 1 7

8 1 0 0 0 109 1 0 0 1 11

10 1 0 1 0 12

Four switches 11 1 0 1 1 1312 1 1 0 0 1413 1 1 01 1514 1 1 1 0 1615 1 1 1 1 17

Weight 10' 100 23 22 21 20 8'80

The answer to this lies in thecapabilities and limitations ofelectronics to perform mathematicaloperations.

At present the simplest and leastambiguous device that is suitable forour requirements is a basic on/offswitch. It has two stable states - it is

either 'on' or it is 'off'.

A device such as this fits in perfectlywith the binary system, the 'on' staterepresenting a '1', the off state '0'.

Four switches, interconnected as

shown in Fig. 2 may be used torepresent the (decimal) numbers 0-15in binary form.

Each switch represents one binarydigit - thus decimal '0' would berepresented by all switches being inthe 'off' (0) positions. Decimal 5would have switch D at '0', Cat '1', B at '0', and A at '1'.(note that the '0' lamps shown in thecircuit are only necessary to avoid

possible ambiguity - i.e. the '1' lightneed only be off to represent a '0' -but there is always the possibility thatabsence of light is due to a blown bulbrather than an intentional '0')

The number of switches may beincreased as desired to cover any rangeof numbers. Thus five switches willcover 0-31, six switches 0-63. in otherwords, where 'n' equals the number ofswitches the range of numbers coveredequals 2n-1

For example when n = 82n = 28 = 256

i.e. eight switches will representnumbers from zero to 255.

In a computer these switches arereplaced by transistors which performthe same function electronically.Transistor switches may be packedinto an amazingly small area (5000 persquare millimetre), they require verylittle power and are very fast acting.

The computer may therefore beconstructed to handle vast quanties ofdata in a very short space of time.

The binary numbering system is

essential to electronic computationbecause at present there are no knowndevices or circuits which exhibit morethan two stable states and are as

simple and unambiguous in operationas the transistor switch.

Although it is possible to construct acomputer working strictly in binarynotation, such a device would beunnecessarily complex and occupy toomuch space. What is more suitable is asystem of numbering based on a

number which is an integral power of2. Such a system is the octenary. Itsbase, 8, is sufficiently close to ourusual base 10, to give numbers of areasonably concise format and, at thesame time, the numbers 0 to 8 caneasily be expressed in binary form,thus:

0, 1, 10, 11, 100, 101, 110, 111,10000, 1, 2, 3, 4, 5, 6, 7, 8For an octal number, the weighting

for successive positions are:1, 8, 64, 512, 4096, 32768, .. .

So that we can have a numbercomposed of, say:

80, 81, 82, 83, 84, 85Each position of which can easily be

expressed in binary notation using amaximum of three binary .numberseach position.

Taking the date, 1973 as ourexample, we get, in octal notation:

1973 = 3665or

(3x83)4-(6x82)+16x811-1-(5x80)which can be transcribed into binary -octenary notation as:

1973 = 011 110 110 101.It may be thought that such a system

is cumbersome, but although forrelatively small numbers it is morecomplex than other forms of notation,when dealing with very large or verysmall numbers, such as are frequentlymet with in computer calculations, aconsiderable economy in memory cellsresults.

The foregoing analysis shows that therepresentation of a physical numbermay differ according to the system ofnumeration employed, however it is

the number itself that is fixed and notthe group of numerical signs by whichit is represented.

So far we have considered numbersin the abstract as being the numericalrepresentation of physical magnitudes.However, as will be seen below,numbers have an independentexistence of their own with some oddand surprising properties.Henceforward in this article we shallonly consider numbers written in ournormal decimal notation.

64 ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

Let us first of all consider wholenumbers (integers) only and see whatkinds of numbers may exist. The firstcategory is that of odd and evennumbers. Starting from unity thenumbers are alternatively odd (that is,cannot be divided exactly by 2, butalways leave a remainder of 1) andeven (which can be divided exactly by2). Simple manipulation of thosenumbers show the followingproperties.- the sum of two odd numbers is an

even number, e.g. 9+5 = 14;- the sum of two even numbers is an

even number, e.g. 8+6 = 14;- the sum of an odd and an even

number is an odd number, e.g. 9+4= 13;

- the product of two odd numbers isan odd number, e.g. 7x9 = 63;

- the product of two even numbers isan even number, e.g. 8x6 = 48;

- the product of an odd and an evennumber is an even number, e.g. 9x8= 72;

- the division of two odd numbers, ifan exact solution exists, will be anodd number, e.g. 63/9 = 7;

- the division of two even numbers, ifan exact solution exists, may beeither an odd or an even number,e.g. 48/6 = 8; 72/8 = 9;

- division of an odd number by aneven number, will not give an exactsolution.

It can thus be seen that straight awaywe have found some regular patternsin the relationship between the oddand the even numbers.

A second division of numbers is thatof prime and factorial numbers. Aprime number is a number whichcannot be divided exactly by anyother number except unity. Thus1,2,3,5,7,11,13,17,19,23,29,31are all prime number.Since the prime numbers cannot by

definition be divided exactly by 2 theyare all, with the exception of 2 itself,odd numbers, but all odd numbers arenot primes, e.g. 9 = 3x3; 15 = 5x3; 21= 7x3, etc.

Since Leibnitz in the seventeenthcentury mathematicians have tried toestablish two formulae:- a formula permitting one to

determine whether a given largenumber is a prime or not;

- a formula permitting the calculationof the series of prime numbers up toany desired value.

So far neither of these goals havebeen reached and the problem, whichappears so simple at first sight, hasresisted all attempts at solution.

The series of numbers, 0, 1, 2extends up to infinity, since no matterhow large a number we may choose,

there is always the possibility ofaugmenting its value by 1 and thusobtaining a new and larger number.

If we now consider numbers such as1 1 1

10 100 1000 etc a whole infinity ofsuch numbers can be inserted betweenany two integers in the series 0, 1, 2,3, ... These numbers also have theirpeculiar properties and may be dividedinto two main categories:- decimal fractions which have a

definite and exact value. Thus 10/4= 2.50000 ... with no doubt as toits exact equivalence;

- recurring decimals, which, no matterhow far the process is extended afinal and exact result is neverreached:

e.g. 10/3 = 3.33333 ...10/9 = 1.11111 ...10/7 = 1.42857142857142857 ...

and so on for ever.It must be realized that between any

two consecutive whole numbers thereare a whole infinity of numbers whichcan be represented exactly, andequally a whole infinity of recurringdecimals.

Finally, in our classification ofnumbers there come the real "wildmen". These are called "irrationalnumbers" or "surds" and arerepresented by decimals that neithercome to a final result nor recur. Thismeans that we can approach the valueof the number to any desired degree orprecision by taking into account anappropriate number of decimal points,but can never reach a final result. Tocomplicate the issue, many of thesenumbers represent physicalmagnitudes which have a realexistence.

Figure 3 shows two examples ofthese numbers. Figure 3(a) shows asquare, the side of which is 1 unit,with its diagonal. Now, according tothe theorem of Pythagoras concerningright-angled triangles, the length ofthis diagonal is given by d = 12 + 12 =

2. But although the diagonal of thissquare has a physical existence, there

Fig. 3

is no finite number capable ofrepresenting 2, the best we can do isto write 2 = 1.4142 ... out toinfinity.This means that although the length

d on the figure is a definite physicalmagnitude it is not possible to expressits value exactly in our system ofnumeration.

Again, in figure 3(b) we have a circleand its radius. The length of thediameter D. is known, and thecircumference C of the circle is a

physical magriitude which has a realexistence. However, if we wish toexpress the ratio of the circumferenceC to the diameter D. we obtain thewell known relationship:

C=7rDwhere rr = 3.14159 ... and to infinity.

This number can never be expressedexactly in our numerical notation butcan only be expressed to a desireddegree of accuracy by taking intoaccount the appropriate number ofdecimal points in the expression for 7r.

It will now hardly come as a surpriseto know that between any twosubsequent numbers in the series 0, 1,2, ... there can exist a whole infinityof such surds, none of which is capableof exact representation using ournumbers.

Other categories of numbers exist:negative numbers, imaginary numbers,complex numbers, vectorial numbers,which are not dealt with .n this simpleexposition. Nevertheless, it is hopedthat it has been made clear that aseries of conventional signs, designedinitially to represent simple physicalmagnitudes have come to have a

curious life of their own, divorcedfrom their primitive functions, thestudy of which provides a fascinatingfield to the inquiring mind.

ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973 65

.33.133o pee .43.3snpuoonues .343343jod 43,3344:3umotts 34uouorltocoo oyi 4.3.4 pee .uwaopNOJ.43 3.44 4.A. F...4 043 .1,34

Fig. 1. Place the Letrafilm over the diagram.

Easier wayto makeyour ownPC.boards

Now you can do away with all thefuss and bother of conventional

printed circuit preparation, says A. J. Lowe

Fig. 2. Trace around the copper areas on the diagram. Mark hole positions and corners also.

,iiri7C?,1

At last! Here's a quick, cleanmethod of preparing printedcircuit boards for etching - and

it's for the home constructor.Photographic methods are fine if you

want to produce a large number ofidentical boards, but far too slow,expensive and involved for the'one-off' man who simply wants tomake one board - usually from adiagram in a magazine.

The standard method, for theexperimenter, involves the use oftracing paper, carbon paper, and aresist paint. Sure, it works - but thosewho have used it know how hard it isto get narrow clean -edged lines withpaint. Sometimes the paint is thin andporous and lets the etchant through,and sometimes it runs across narrowgaps, leaving short circuits to becleaned up later. Sometimes the paintis thick and hard to manage. Besides, ittakes ages for the paint to dry.

This new method requires no tracingpaper, no carbon paper, no paint, nobrushes, no solvents - and you canhave a printed circuit board ready inan hour or so.

It depends on the use of a cut-outcolour film used in the graphic artsfield, called LETRAFILM. Made bythe manufacturers of the widely -usedLetraset stick -on letters, it is

obtainable from artists' shops anddrawing office supply houses.

Letrafilm is a thin sheet of filmavailable in a range of 50 colours,tacky on one side and 'toothed' on theother. The tacky side is backed with atranslucent paper support. Thetoothed side can be written or drawnon with ease. The film is quiteimpervious to etchants and so makes

Fig. 3. Separate the Letrafilm from its backing support.

Fig. 4. Place the film down on the copper side of the p.c. board.

Fig. 5. Press the film down gently

Fig. 6. Cut around the copper areas with a sharp craft knife.

Fig. 7. Remove the unwanted film, leaving film over the areas where copper is to remain.

an ideal resist. It is available in sheets10" x 15" and is quite inexpensive.Only a few pence worth will cover thetypical printed circuit board. A lightcolour, such as pale yellow, is ideal forthis application.

Here's how to use it:1) Cut a piece of Letrafilm, complete

with its backing, about 3/8" or solarger all round than the printedcircuit board.

2) Place a sheet of aluminium, orphenolic board, or even printed circuitboard, below the diagram of theprinted circuit. This gives a hardsupport for the next few operations.

3) Lay the Letrafilm over thediagram (see Fig. 1) and hold it downat one side with sticky tape. It will befound that the diagram can be seenquite clearly through the Letrafilm.

4) Trace around the copper (i.e.black) areas in the diagram with apencil. (Fig. 2), making sure that thecorners of the board are marked aswell. The position of holes for thecomponent leads should be markedwith a pencil dot. This is anotheradvantage of this method over thepaint method, in which hole positionshave to be gauged later.Many diagrams prepared

professionally, using stick -down circlesand lines, have lots of fine curves andindentations where none is reallyrequired. There's no need to followunnecessary detail and it may beeliminated as tracing proceeds.

5) Remove the Letrafilm from thediagram and carefully separate the filmfrom its backing sheet (FT. 3).

6) Lay the film, tacky side down, onto the thoroughly cleaned coppersurface of the printed circuit board,using the corner marks as a guide (Fig.4).

7) Press the Letrafilm gently downon to the printed circuit board. (Fig.5). Do not press too hard, as this willmake later removal of the unwantedfilm portions unnecessarily difficult.Small air bubbles need not besqueezed out.

8) Cut around the pencilled outlinesof the copper areas with a sharp craftknife (Fig. 6). This process is mucheasier than painting, and quicker -and clean sharp lines are automatic.

Do not, at this stage, do anythingabout the dots marking componentlead hole positions.

9) When cutting is complete,carefully peel away the unwanted film

67

from the board - that is, the filmwhich does not cover areas wherecopper is required. This is done bygently lifting the film at one cornerand easing it back. It will break as youprogress, but that's no disadvantage(Fig. 7). Watch that none of the'islands' lifts, due to bad cutting alongthe pencil lines. If one does lift, pressit back and cut around it once again.

10) When all the unwanted film hasbeen lifted, lay a sheet of paper overthe board and press down firmly allover it. This bonds the film to thewanted copper so that it acts as aneffective resist (Fig. 8). Make sure thatno air bubbles are near the edge of anisland. In the middle they don'tmatter.

11) Etch the board. This can be donein your usual etching bath. For thosewho have never made a printed circuitboard before, an effective etchingsolution is 4oz. of ferric chloridedissolved in 10oz. of hot water. Thiswill etch a typical board in 20 to 30minutes. Protect your eyes and hands- the solution is corrosive.

12) When etching is complete,remove the board from the etchingbath and wash it clear of etchingsolution under running water. Dry theboard by dabbing it with a rag.

13) With a scriber, mark thepositions of the holes for componentleads by pressing through the film intothe copper (Fig. 9). The pencil dotsalready made (see introduction 4above) give the positions.

14) Remove the remaining Letrafilm.This can be peeled and rubbed off(Fig. 10).

15) Clean away any residual adhesivefrom the film by cleaning the boardwith an abrasive domestic cleaningpowder and, if needed, some steelwool. The board is now clean andready marked for drilling (Fig. 11).

16) To prevent the copper oxidising,it should be sprayed with a specialprinted circuit board lacquer.Alternatively - and much morecheaply - it can be brushed with a

Fig. 8. Press down hard, to bond the remaining film fo the board.

Fig. 9. After etching away all unwanted copper, mart hole positions with a scriber.

rosin solution (one lump of rosindissolved in a little methylated spirit).This makes a first-class flux andmaintains the shiny look of the board.

Well, there it is - a simple, clean,efficient and cuick method ofdoing -it -yourself and, at the sametime, saving money.

Fig. 10. Remove remaining film from theboard.

Fig. 11. The board, cleaned and ready fordraing.

J. T. EDEN ELECTRONICSTRANSISTORS 85Cc 10.12 BFX 37 10.30 25 1613 10.20

AC 107 10-20

,185:

BC 16910120.13

BFX 848FX 85

0.250-30

25 163125 1711

0-250.20

AC 113 0.20 8C 170 0.12 BFX 86 0.25 2N 1893 0.35AC115 0-20 BC 171 .0-12 EIFX 87 0.25 25 2147 0.75AC 117 0.20 BC 172 0.12 BFY 50 0.20 25 2148 0-60AC 117K 0.20 BC 173 0.20 BFY 51 0-20 29 2160 0.80AC 121 0.15 BC 175 0.23 BFY 52 0.20 25 2192 0.40AC 122 0.15 BC 177 0.17 BFY 53 0.150 252193252194 0.40AC 125 0.18 BC 178 0.20 8FY 64 40 0.25AC 126 015 BC 179 0.20 EIFY 90 0.80 25 2217 0.25AC 127 0.15 BC 182 0.10 BRY 39 0.30 25 2218 0.20AC 128 0.15 BC 1132L 0.10 858 19 0.15 252219226 0.20AC 132 0.15 BC 183 0.10 BSX 20

22211954

0.20AC 141K 0.25 BC 1831 0.10 BSY 27 0.15 2N 2220 0.20AC 142K 0.25 BC 184 0.10 BSY 28 0.15 25 2221 0.20AC 151 0.20 BC 1841 0.10 BSY 38 0.15 2N2222 0.20AC 154 0.20 BC 186 0.25 BSY 39 0.15 21522224 0.20AC 155 0-20 BC 187 3.21 BSY 52 0.25 2N 2368 0.18AC 156 0.20 BC 207 0.1P BSY 95A 0.10 25 2369 0.12AC 176 0.18 BC 208 0.11 BU 105 2.25 2N 2369A 0-15AC 187 0.20 BC 202 0.10 BU 105/2 1.75 25 2646 0.45AC 187K 0'20 BC 212L 0.12 C111 0.50 25 2711 0.15AC 188 0.20 BC 213L 0.12 C 407 0.20 25 2712 0.13AC 188K 0.22 BC 2141 0.14 C 424 0.20 25 2714 0-20ACY 17 0'25 BC 258 0.10 0425 0.35 2N 2894 0-35ACY 18 0.20 BC 259 0.13 C 426 0.25 2N 2904 0.20ACY 19 0.20 BC 268 0.15 C 428 0.25 2N 2904A 0.25ACY 20 0-20 BC 300 0.42 C 449 0-30 2N 2905 0-25ACY 21 0.20 BC 301 0.35 C 450 0.20 2N 2905A 0.25ACY 22 0-15 BC 302 0.25 OC 16 0.00 2N 2906 0.18ACY 28 0.20 BC 303 0.50 OC 19 0.40 2N 2906A 0.25ACY 39 0.50 BC 304 0.40 OC 20 0-65 25 2907 0.20ACY 40 0.20 BCY 30 0:25 OC 22 0-40 2N 2907A 0.12ACY 41 0-20 BCY 31 0.30 OC 23 0.40 2N 2923 0.12ACY 44 0.30 BCY 32 0.50 OC 24 0.80 2N 2924 0.12AD 140 0.50 BCY 33 0.25 OC 25 0.35 25 2925 0-12AD 142 0.45 BCY 34 0.30 OC 26 0.30 2N 292811 0.10AD 143 0.45 BCY 39 0.65 OC 28 0.40 2N 29260 0-10AD 149 0.40 BCY 42 0.20 OC 29 0.40 2N 29260 0.10AD 150 0.65 BCY 43 0.20 OC 35 0.42 2N 2926Y 0.10AD 160 0-35 BCY 70 0.16 OC 38 0.50 2N 29206B 0.10AD 161 035 BCY 71 0.20 OC 41 0.20 2N 3053 0.20AD 161/2 0.55 BCY 72 0.15 OC 42 0.25 2N3054 0.50AD 162 0.35 BCZ 11 0.40 OC 44 0.15 2N 3055 0.50AD M/PR 055 80 115 0.75 OC 45 0-15 25 3133 0.30AF 114 0.20 BD 121 0.65 OC 57 0.50 2N 3391 0.20AF 115 0.20 BD 123 0.80 OC 70 0.12 2N 3390 0.25AF 116 0.20 BD 124 0.60 OC 71 0.15 2N 3393 0.15AF 117 0.20 BD 130 0.50 OC 72 0.20 2N 3394 0.12AF 118 0.45 BD 131 0.75 OC 74 0.30 2N 3404 0.25AF 124 0 25 BD 132 0.75 OC 75 0.25 25 3405 0-25AF 125 0.20 BD 133 0-65 OC 76 0.15 25 3414 0.10AF 126 0.20 BD 135 0.40 OC 77

90:4920 33 4

0.10AF 127 0.20 BD 136 0.45 OC 81 r5 41169 0.15AF 139 0.40 BD 137 0.45 OC 8113 0.20 25 3417 0-20AF 178 0.45 80 138 0.55 OC 82 0.25 2N 3440 0.85AF 179 0.55 80 139 0.130 OC 82D 0.20 2N 3563 0.15AF 180 0.50 BD 140 0-75 OC 83 0.23 2N 3564 0.18AF 181 0.42 800 20 1.00 OC 84 0.25 2N 3565 0.13AF 186 0.45 BF 115 0.25 OC 139 0.25 2N 3566 0.20AF 239 0.43 BF 117 0-45 OC 140 0.55 2N 3572 0.96AL 102 0.65 BF 119 0.58 OC 169 0.25 2N 3892 0.17AL 103 0.80 8F 121 0.25 OC 170 0.25 2N 3702 0.10ASY 26 0.30 BF 123 0.27 OC 171 0.30 2N 3703 0.10ASY 27 0.30 BF 125 0.25 OC 200 0.40 2N3704 0.10ASY 28 0.30 BF 127 0.27 OC 201 0.75 2N 3705 0.10ASY 29 0.30 BF 152 021 OC 202 0.80 2N3706 0.10ASY 50 0.20 BF 153 0-30 OC 203 0-50 2N 3707 0.10ASY 56 0'25 BF 154 0-16 OC 204 0.40 2N 3708 0.10ASY 57 0.25 BF 158 0.15 CIC 205 0.75 2N 3709 0.70ASY 58 0.25 8F 159 0.30 OCP 71 1.00 2N 3710 0.10BC 107 010 85180 0.23 oRP 12 0.50 25 3711 0.10BC 1078 0.10 BF 161 0.35 ORP 60 0-40 2N3713 0.10BC 108 0.10 13F 163 0-20 ORP 61 0.40 2N 3773 3.00BC 10813 010 BF 166 0.35 2G 301 0-20 2N 3790 2.00BC 109 0-10 BF 167 0.20 2G 302 0.20 2N 3794 0.15BC 1098 0.10 BF 173 0.20 2G 303 0.20 25 3819 0.258C 113 0.15 BF 177 0.25 2G 306 0.35 2N 3820 0.50BC 114 0.15 BF 178 0.25 2G 309 0-35 2N 3866 0-65BC115 0.15 8F 179 0.30 2G 371 0.15 2N 3903 0.208C118 0.15 BF 180 0.30 26 374 0.15 2N 3904 0.18BC 117 0.15 8F 181 0.32 2G 381 0.20 2N 3905 0.20BC 118 0.10 BF 182 0.35 2G 417 0.20 2N 3906 0.20BC 119 0-30 BF 183 0.40 2N 404 0.20 2N 4033 0.75BC 125 0.15 BF 184 0.20 2N 696 0.15 2N 4058 0.12BC 126 0-20 BF 185 0-20 2N 697 0.15 2N 4059 0.12BC 132 0.25 BF 194 0.15 2N 698 0.25 2N 4060 0-12BC 134 0.20 BF 195 0-15 2N 699 0.30 2N 4061 0.12BC 135 0.12 BF 196 0.15 2N 706 0.10 2N4062 0.12BC 1313 0.15 BF 197 0.15 2N7066 0.12 25 4143 0.25BC 137 0.15 BF 200 0-35 2N708 0.13 25 4236 1.35BC 138 0.25 BF 224 0.35 2N709 0.40 25 4248 0.10BC 140 0.30 BF 244 0.18 25 718 0.20 25 5172 0.10BC 141 0.40 BF 257 0.40 2N 7184 0.30 2N 5457 0.30BC 142 0.25 BF 258 0.45 2N 916 0.18 2N 5458 0.33BC 143 0-20 BF 259 000 25 918 0.30 2N 5459 0-35BC 144 0.25 BF 270 0.25 2N 929 0.15 2S 301 0.50BC 145 0.20 BF 271 0.20 2N 930 0.15 2S 302 0.42BC 147 0.10 BF 272 0.50 2N 1131 0-20 2S 303 0.55BC 148 0.10 BF 273 0-25 25 1132 0.20 2S 322 0.50BC 149 0.12 OF 274 0.29 25 1302 0.16 2S 324 0.95BC 153 0-20 BFS 61 0.27 25 1303 0.76 25502 0.35BC 154 020 8FS 98 0.25 2N 1304 0.20 40360 0.45BC 157 0.13 BFW 10 0.25 2N 1305 0.20 40361 0.50BC 158 0-13 BFX 13 0.25 2N 1306 022 40362 0.45BC 159 0'13 BFX 29 0.25 25 1307 0.22 40408 0.50BC 160 0.12 BFX 30 0-60 2N 1308 0.25 40836 7.10BC 167 0.12 BFX 34 0.70' 25 1309 0.35

ORDERS TO

DIODES AND RECTIFIERS INTEGRATED CIRCUITSN 34 10.08 BA 154 10.15 7400 10.18 7488 11250N 34A 0.08 BA 155 0.16 7401 018 7489 5.50N 914 0.08 84 156 0.18 7402 018 7490 0.70N 916 0.08 BAY 18 0.20 7403 0.18 7491 1.109 4001 008 BAY 31 0.10 7404 0.18 7492 0.7054002 0.06 BAY 38 0.30 7405 0.18 7493 0.70N 4003 0-07 BAX 13 0.10 7408 0.35 7494 0-80N 4004 0.07 BAX 16 0.15 7407 0-35 7495 0.8054005 0.12 BY 100 0.15 7408 0.20 7496 0.9054006 0.13 8Y101 0.15 7409 0.20 7497 6.5054007 0.15 BY 103 0.25 7410 0.18 74100 1.80N 4148 0.05 BY 105 0.20 7411 0.25 74104 1.005 021 BY 114 0.15 7412 0-40 74105 1.00544 0.15 BY 124 0.15 7413 0.30 74107 0.45S 113 0-15 BY 126 0.15 7416 0.40 74110 0-60S 120 0.15 BY 127 0.20 7417 0.40 74111 1.30S 121 0-11 130164 0.65 7420 0.18 74118 1.10S 130 0.11 BYX 10 0.35 7421 0.25 74119 1.403 131 0.11 BYX 38/30 0.45 7422 0.50 74121 0.45S 132 0.13 BYZ 10 0.35 7423 050 74122 1.50S 4148 0.07 BYZ 11 0-35 7425 0.50 74123 2.85

920 0.10 802 12 035 7426 0.35 74741 0-805 922 0.10 BYZ 13 0.30 7427 0.45 74145 1-605 923 0-15 BYZ 16 0.45 7428 0.60 74150 3.505 940 0-06 BYZ 17 0.40 7430 00i4185 7744115531 1.10S 951 0-08 BYZ 18 0-40 7432 1-30AA 119 0.10 80219 0.30 7433 0.80 74154 2 00AA 120 0.10 BZY 78 1.00 7437 0.80 74156 1.5044129 0.10 OA 5 0.25 7438 0.60 74157 1.50AAY 30 0.12 0A9 0.12 7439 0.60 74160 2.00AAY 42 0.15 04 10 0.20 7440 0.18 74161 2.00AAZ 13 0.12 06 47 0.10 7441 0-70 74162 3.7544215 0.15 06 70 0.08 7442 0.70 74163 3.7544217 0-15 0A79 0.08 7443 1.20 74164 2.50BA 100 0-15 OA 81 0.10 7444 1.20 74165 2.50BA 102 0-25 OA 85 0.10 7445 2-00 74166 4.00BA 110 0.25 OA 90 008 7446 1-20 74187 7.00BA115 0.08 OA 91 008 7447 1.20 74170 5.00BA 118 0.25 04 95 0.08 7448 1-20 74174 2-50BA 126 0.25 OA 200 0.10 7450 0.18 74175 1.50BA 141 0.35 OA 202 0.10 7451 0.18 74176 2-00BA 142 0.35 SD 10 0.06 7452 0.23 74177 2.00BA 144 0.15 SD 19 0.06 7453 0.18 74180 1.80BA 145 0.25 T1V 307 0-25 7454 0.18 74181 6.00BA 148 0.15 7460 0.18 74182 2.25

7470 0.30 74184 3-007472 0.30 74185A 3.007473 0.40 74190 2.207474 0.40 74191 2.20

ZENER DIODES 7475 0.50 74192 2120

All preferred voltages from 2.0 to 33.0.74767480

0.440.70

7419374194

2.252.75

5% Tolerance 400 MW (DO -71 12p.; 1.5W (SO -16120p: 10 W (S0-10) 30p.

748174827483

1.301.001.10

741957419674197

2.001.751.75

7484 1.00 74198 5.00.485 3.00 74199 5.00/486 0.35

RESISTORSCracked carbon. Metal oxide. 5% Toler-ance. i watt all values 1 p. each.

I. C. SOCKETS14 pin, 14p.16 pin, 16p.

Please send your remittance with order: cheques, P.O.'s, M.O.'sshould be made payable to J. T. EDEN ELECTRONICS andcrossed. Cash should be sent by registered post. Add 12p. forpost and packing charge; orders are despatched by first classpost. If an item is temporarily out of stock and is not expected infrom our supplier for more than a week, a credit note is issuedfor the value and should be included with your next order. We canalso despatch the item to you when it arrives and not charge youfor the post and packing. If you would prefer, we can also refundthe amount to you. Please let us know what you would like usto do.As V.A.T. is chargeable, please add 10% of the total value (thatincludes the 12p. post and packing charge). In order to try andkeep prices down we have decided to charge only 5% to ordersof £5 and over, so if you just include 5p. in the pound, we willpay the rest in the form of a discount to you.Finally, if you think there are any significant omissions or linesyou like us to stock, we will try to include them in our newcatalogue which will include capacitors, potentiometers, meters,kits and more semi -conductors.

J. T. EDEN ELECTRONICS, P.O. Box 5, LANCASTER LA1 3HZ.

ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973 (39

SIMPLELOUDHAILER

PROJECT

This cheap and simpleloudhailer can bebuilt in a few hours

HERE's a simple device to saveyour voice at sports meetings,large picnics or any other

occasion that requires you to raiseyour voice above the surroundingnoise.

It needs a minimum of components,all of which are easily obtainable; it ischeap and can be built in a very shortspace of time.

THE CIRCUITThe circuit is shown in Fig. 1. A

single transistor (01) is arranged as anamplifier with resistor R2 providingthe necessary bias. The resistance ofthe carbon microphone will vary assound is impressed upon thediaphragm, thus varying the voltageacross R1.

Resistor R1 is ac coupled to the baseof the transistor 01. This transistoramplifies the signal and drives thespeaker.

CONSTRUCTIONAll the minor components are easily

mounted on a single tagstrip (as shownin Fig. 2). This tagstrip may be boltedto one wall of the loudhailer enclosureand wiring taken to the microphone,speaker, pushbutton and battery.

Any suitably enclosed box of theright dimensions, may be used tohouse all the components includingthe battery and the speaker.

Generally, the larger the speaker thebetter, but remember this is a

loudhailer not a public address system!The back of the carbon must be

enclosed to prevent feedback from theloudspeaker - if this is not done thesystem will oscillate. (See over)

CARBONMICROPHONE

R2

47012

47µf 10V

R1

3352

LLOUDSPEAKER

0-

01

1111 SVV1

-4-

6 TO 12 VOLTBATTERY

FIG. 1 CIRCUIT DIAGRAM

LOUDSPEAKER

Gi

TAG STRIP/Th /Th

CARBON MICROPHONE

FIG. 2COMPONENT CONNECTIONS

70 ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

SIMPLELOUDHAILER

A sketch, showing one suggestedarrangement for mounting thecomponents, is shown in Fig. 3. Thelayout is not critical however.Practically any arrangement that isconvenient to you will worksatisfactorily.

The unit is surprisingly effective -and quality is excellent - despite thebias caused by some dc energization ofthe loudspeaker voice coil.

PARTS LIST

R1 resistor, 33 ohm, '1/2 watt, 5%R2 resistor, 470 ohm, 1/2 watt, 5%SW1 small push -to -make switchC1 capacitor 47 AF,10 Volt electrolytic01 transistor type 2N 3055, 40250,2N 3054, SE 7010 or suitableequivalents.

Loudspeaker - 3" to 8" diameter, 4ohm to 15 ohm impedance.Batteries - two type 509 lantern

batteries.Carbon microphone.

One seven lug tagstrip, connectingwire, box, etc.

CARBONMICROPHONE

BATTERIES

PUSHBUTTON

HANDLE

SPEAKER

VENT FORSPEAKER

J -BEAM F.M. 6S THE OUTSTANDING BRITISH ENGINEERED F.M. AERIALSTILL UNRIVALLED IN*PERFORMANCE*QUALITY* AND PRICE *

20 Mil 4 Radius

Professional In allation Service

We also stock the new broadband J -Beam F.M.4S, 1, 2, 3, element F.M. arrays high performance A.M. vertical rod aerials, .all U.H.F. T.V.aerials, Stolle Memomatic and Automatic aerial rotators, balanced twin feeder, coaxial cables, masts, fixings, amplifiers, baluns, and a hostof other accessories. Please send large S.A.E. for catalogue to:APOLLO AERIALS, STATION FORECOURT, GUILDFORD STREET, CHERTSEY, SURREY

TEL CHERTSEY 60320 and BYFLEET 43151

electronicstomorrowHAVE YOU EVER wondered how the BBCmanage to get sub -titles up on the televisionscreens so quickly and accurately duringsports events and similar programmes? Nexttime you see one of their captions comingup, watch the speed that it flashes across thescreen, much too fast to be typed in but notinstant as if it were a pre-printed captioncard. Of course they could be prepdred on acomputer but this would be extremely ex-pensive and would involve recording on amagnetic disc or drum as paper or magnetictapes would not give fast enough access times.The answer apparently is a record, not anormal record but a disc of magnetic recor-ding tape material layed out (oxide facedown) on a Garrard 401 turntable rotatingat the good old speed of 78 r.p.m. A singleread-write head it carried across the disc onan arm controlled by a stepping Motor, thishead has sixteen positions across the disc thusgiving sixteen tracks or 'grooves'. Eachtrack is logically divided into sixteen spaceswhich are identified by the equipment usinga LED -photocell system activated by sixteenequally spaced holes drilled around theturntable. Thus, by activating one control toselect the track and another to select thesegment of that track one can assess the datain that storage space in less than one second.

Each of these segments holds about 400bits (a bit Is a logical 1 or logical 0) if eachcharacter is defined by eight bits, as instandard ASCII or EBCDIC codes, thisgives enough for start and finish codes, line -return, etc codes and 32 characters per line,thus each disc segment defines one displayline. All of the required data is preparedbefore the event and consists of playersnames, tittles, placings, countries, etc.

For anybody interested in building mini-computers or suchlike and requiring 100Kbits (12K bytes) of slow random access thissort of system seems to be ideal but checkwith the BBC fast as the system (calledAnchor by the way) is probably patented.

SHIFT REGISTERSIf you don't require 100K bit data storage,you could always try using a shift register. Ashift register is a small storage device whichcan be likened to a conveyor belt with npositions on the belt, n is the number of bitsin the register. When the clock controlling theshifting of the belt is pulsed, the belt movesalong one position allowing the acceptanceof a new one or zero bit at the input andproducing an old one or zero at the output.One obvious use of a shift register is a divideby n counter; if we are using an 8 bit registerwe use the signal we wish to divide as theclock and press the start switch. This switchcauses a logical 1 to be entered at the input

COUNT

Fig.]. The basic arrangementof the 8 bit shift register.

CLOCKINPUT

8 BIT SERIALSHIFT REGISTER

DATAINPUT

DATAOUTPUT

during one clock period, the switch will thenrevert to entering a logical 0. Our logical 1 isnow in bit 1 of the register and, as the clockpulses, it is shifted through the other bitsuntil it reaches bit 8, in the meantime ourswitch has ensured that logical Os follow itand thus at any stage our register onlycontains one logical one. When the 1 reachesbit '8 it is transferred to the output and fromthere passed on to the rest of the countchain and also passed back into the registerat bit 1. The layout of the register is shownas Fig. 1. If the output is Only inverted oncethen a 0 output will produce a 1 input andvice -versa, this means that our output willbe low for 8 clock pulses and then high forthe next 8 and so on, this means that wenow have a divide by 2n counter.

Next question - why are we telling youall about shift registers? Answer - becausethey are our special offer this month, whatbetter reason. We have discussed an 8 bitregister above such as the 7491, our specialoffer is for a triple 66 bit register theEMIHUS EDSR3166, three 66 bit registers,2 clocks, TTL compatible, wire -OR capabilitywith speeds from 10Hz to 10MHz. All this ina TO -92 ten pin package, but be warned,this is one of those devices which dies if thepins are mishandled as do a lot of MOSdevices so use a socket.

This special offer to ETI readers is beingmade by BI-PAK components of Ware,Herts who normally sell this device at £3.50the special offer price is £2.00 inclusive ofVAT, post, etc. The offer is limited to 2000devices and each order must be accompaniedby the coupon.

Fig.2a. A simple phono amp-lifier using only eight comp-onents.

CRYSTALCARTRIDGE

AUDIO CHIPOne problem with the available audio ampICs such as the IC12 and SL403 types is thenumber of additional components requiredresulting in an amplifier a lot larger than theIC used and thus losing one of the mainbenefits of using an IC. Also the poweravailable from these ICs is wasted in mostapplications such as radio output stages,intercoms, etc, the smaller audio ICs beingnot quite powerful enough. National Semi-conductors have an amp designated theLM380 designed to give 2.5W r.m.s. into an8 ohm load. Supply voltage range is 8-22V ata max of 1.3A, input voltage for maximumoutput is 500mV although the LM380produces a good output from only a 50mVinput, the quiescent current is only 7mAand the input impedance is 150k. Package is14 pin D.I.L.

All very well,but what about the externalcomponents? Fig. 2 shows the LM380 in twotypical applications, count the componentsfor yourself! Data from (2), LM380 from(3) price £1.50 plus VAT.

DIY PCB'SThat stands for Do -It -Yourself Printed CircuitBoards. Quite a few kits are available toenable you to draw and etch your ownPCB's but most of these kits work on theone-off principle, that is you have to draweach board required, one mistake and back tosquare one. Professionally boards are drawnup on drawing paper or film, photographed,exposed on photosensitive boards and etched,any mistake can be rectified on the master

'BV Continued on page 85

72 ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

component news

SURGE ARRESTER

A special surge voltage arrester has been des-igned by Vitality to protect Post Office linesfrom high voltage transients generated inequipment connected to the lines. Thisprotective device, type XSA 2, is the onlyprotector approved and specified by thePost Office for use where signals exceed±6V.

The two principal applications for thesurge arrester, which is a miniature gas -filled tube, are in the Post Office's mandatorygeneral purpose barrier for speech bandcircuits (for signals up to 80V a.c. or 120Vd.c.) and the barrier for wide band circuits(for use on wide -band and coaxial circuitsup to 5.5MHz.)

The gas -filled tube, 6mm diameter and23mm long, has a breakdown voltage of150V and is designed to blow a 200mAfuse within 20mS when a transient voltage inexcess of its breakdown voltage appears onthe line.

Vitality Ltd, Beetons Way, Bury St Ed-munds, Suffolk.

LOW INPUT CURRENT OP AMPThe SSS112 series are precision monolithicoperational amplifiers featuring extremelylow input offset and bias currents, madepossible through use of 'Super Li" inputtransistor circuitry.

This unit from Precision Monolithics Inc.is suitable for battery operated and otherlow power applications due to the low supplycurrent drain and ability to operate at ex-tremely low supply voltages, while the lowoffset and input bias current provide ex-cellent performance in high impedance cir-

cuits such as long period integrators, sample -and -holds, low frequency active filters, log-arithmic amplers and with piezoelectricand capacitive transducers.

Features include: Low Offset Current,200pA max; Low Bias Current, 2nA max;Low Power Consumption, 18mW max. Sup-ply Voltage can be plus or minus 20V. Theunit also has internal frequency compen-sation, compensation overvoltage protectionand balanced offset nulling.

Bourns (Trimpot) Ltd, Hodford House,17/27 High Street, Hounslow, Middx.

AUDIO WARNING DEVICE

When lamps are used for warnings theyare only useful if the right person happensto be looking the right way at the righttime. A range of warning devices basedon audible alarm signals is now available.They vary in size and in the volume of thealarm signal.

A.P. Belson Ltd., St. Joseph's Close,Hove, Sussex, BN3 7EZ.

MICROCIRCUIT FORELECTRONIC ORGAN

Manufacturers of low cost electronic organsand electronic music enthusiasts can nowobtain, in a single microcircuit package,all the circuitry needed to generate fromone frequency source a full 12 note chro-matic music scale.

The new AY -1-0212 microcircuit, manu-factured by General Instrument Micro-electronics, significantly reduces the numberof components needed in the manufactureof an electronic organ. Today, most massproduced electronic organs employ 12separate master tone generators, nor-mally manufactured in discrete components,to generate every keyboard note.

GIM's master tone generator can beused with a quartz crystal oscillator orwith a high stability electronic oscillatoras the master tone generator. From its

12 -note chromatic scale output all otherkeyboard notes can be generated by simplefrequency division using MOS dividers. Thismeans that the entire keyboard can betuned by a single adjustment to the masteroscillator during manufacture and will notdrift out of tune with time or temperature.

The cost of the AX -1-0212 is £4 andfor a six stage binary divider to interfacewith the master tone generator (the AY -1-6721/6) the cost is £1.10 (both in 100 -upquantities).

General Instrument Microelectronics,57/61 Mortimer Street, Londor. WIN 7TD.

LONG DISTANCE PHOTOCELLRELAYThis is a new self contained, long distancephotocell relay from Photain Controls. Theunits are contained in weatherproof housingssuitable for all outdoor operating conditionsand can be used for a wide variety ofapplications (Conveyor Control, PaperBreakage Alarm, Machine Gtard, Auto-matic Spraying, Automatic Door Opening,Level Control, Height Gauge, Burglar Alarmetc.)

Each set of equipment consists of aProjector Unit and a Receiver Unit. TheProjector Unit is complete with its ownpower supply, low voltage lamp and opticalsystem which provides a concentrated lightbeam over any distance up to 30 metres.The Receiver Unit has its own pcwer supply,photocell and optical system and is com-plete with an operational relay with two setsof changeover contacts (5A mains).

If the power supply fails or a componentfails then the relay is immediately de -energised, providing a "fail safe" operation.

The price is £30.00 per set plus V.A.T.Photain Controls Limited, Randalls Road,

Leatherhead, Surrey.

METAL CAN BC107/BC108Despite the enormous shortage of metalcan BC107 and BC108 transistors, GothicElectronic Components announce that theyare able to source supplies and maintaindeliveries. Buyers experiencing difficultiesin obtaining regular supplies of these de-vices are requested to contact them.

Gothic Electronic Components, BeaconHouse, Hampton Street, Birmingham 19.

ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973 73

newsdigestContinued from page 11.

(Development chemical engineers get£4,303, electrical engineers £4,270and mechanical engineers £4,221.)

At the bottom two rungs of theprofessional ladder (for engineers intheir first four yearscif experience) thesalaries are: electronic engineers£1,800 & £2,066; chemical engineers£1,808 & £2,175; electrical engineers£2,054 & £2,373; mechanical engineers£1,784 & £2,273.

NEW ELECTRONICIGNITION

From the makers of GuntonElectronic Ignition, comes a newproduct called Sparkrite. Thishighly developed electronic igni-tion system incorporates a shortcircuit proof inverter to preventSCR lock on, improved radiointerference suppression filter and

a trigger circuit with a positivefeedback clamp circuit from out-put of the unit, as well as theusual benefits of electronic igni-tion, which when fitted (can bedone in 15 mins) produces ahigher energy spark and therebycreates more efficient combustiongiving faster acceleration, highertop speed, continual peak perfor-mance, reduced fuel consumption,longer spark plug and contactbreaker life etc. Designed for allpetrol engines, the unit costs£11.55 incl. VAT and carriage andis guaranteed for 5 years, or£9.35 including VAT and carriagein kit form.

For further details onSparkrite Electronic Ignitioncontact: Electronics DesignAssociates, 82, Bath Street,Walsall, WSI 3DE.

TRANSVERSE PHOTON DRAGDETECTOR

Having developed a range of detec-tors and monitors based on the'conventional' Photon Drag prin-ciple in which the momentum fromthe photons in the beam of light istransferred to free carriers in a dopedcrystal, further research has nowresulted in the development of a newinstrument which takes advantageof the transverse component of theenergy transfer and enables a voltagegradient to be measured across thecrystal instead of at both ends.

The result of this developmentpermits the manufacture of detectorscontaining crystals of very largeaperture but very short length. Thelight passes through what lookseffectively like a window and creates avoltage gradient across the crystaland this can be fitted to an outputsocket. In the new Model 7412Transverse Photon Drag Monitor,attenuation of light passing throughthe crystal is between 3% and 5% andthis permits output measurementsto be made from pulsed CO2 lasersduring normal operation. As thefaces of the monitor crystal are veryflat, virtually no distortion isintroduced to the beam and thedetector can be said to give littlemore effect on the laser beam thanthat of a window. With respon-sivity of 10mV/MW an aperture of1" the monitor has a rise time ofapproximately lns, operating at roomtemperature and will withstand veryhigh peak powers.

INTEGRATED CIRCUITS FORTELEPHONE COMMUNICATIONS

Plessey Semiconductors have announ-ced a new family of bipolar inte-grated circuits (designated SL1000series) primarily designed to enable PostOffice contractors to offer a morecompact Channel Translation Equip-ment. However, these devices willalso appeal to wider markets andalready several other applications have

been evaluated within the telephonecommunication system.

Basically, there are two devices inthis new family, which has beendeveloped in co-operation with theBritish Post Office. The channelamplifier SL1020 is designed to meetrequirements of the Post Office for anaudio amplifier with a gain whichmay be varied from a remote pointvia a single wire. The device is acomplex monolithic circuit whichhas to meet many of the constraintsplaced upon the translation equip-ment in which it is used. Themodulator/demodulator (SL1001A/B)is designed to require the additionof only three external components tocouple into a normal balanced linesystem.

Both of these devices are applic-able to overseas equipment and PlesseySemiconductors expect to see consid-erable sales into these markets.

The SL1001A/B modulator/demodulator is designed for a minimumexternal component count when usingbalanced signal and balanced carrierinputs. Two coupling capacitors anda resistor are sufficient to realise anF.D.M. modulator/demodulator. Theintegrated circuits exhibit signaland carrier suppressions at the outputof typically 40dB without anyadjustment, a conversion gain of I,and a bandwidth up to IMHz. Noise,weighted in the speech band and witha 600 ohms load is typically -112dBm0p.The package is a 10 lead T074, andquiescent current is 6mA (SL1001A)or 4mA (SL1001B)

The SL1020 channel amplifierincludes a d,c. controlled attenuator.Hence the overall gain of the amplif-ier may be varied from a remotepoint. The control system is unaffec-ted by the reactive components ofthe control wires and by noise andcross talk induced into them. Thedistance over which the remotecontrol system may be operated islimited only by the d.c. resistance ofthe control wires and exceeds320 metres for 0.4mm copper con-ductor. A typical application of thecircuit gives a gain of 26dB variableover a range of 7 4dB, Class Aoperation up to +13dBm output andnon -interactive adjustment ofabsolute gain, gain range andreturn loss. Noise into 600 ohmsis typically -81dBm0p.

ANTI-SKID CONTROL

The first standard i.c.'s designedspecifically for the automotive markethave been announced by Fairchild.Both are complex linear circuits devel-oped over the past two years as'custom' circuits before being addedto the standard product line.

74 ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

Typical applications include thecontrol of anti-skid systems, fuelmetering and the generation of eitherdigital or analogue tachometerdisplays. Both are subsystems thatwill be used as components of largerautomotive electronic systems.

The UA 7350 includes a tachometerpulse generator, an operational ampli-fier and two comparators on a singlechip, in a 16 -pin dual -in -line package.The tachometer section producesfixed -width pulses at the zerocrossings of a ground -referencedalternating current input signal. Thissection is a common emitter NPNtransistor with an uncommittedcollector. The output stages of theop -amp and comparators are Class -APNP amplifiers with uncommittedcollectors. This allows the system tobe used with a variety of loads forgeneral applications. It will operatewith either single or dual powersupplies and includes built-in shortcircuit protection.

The UA 7350 has a variety of non -automotive applications, includingmotor speed control, frequency -to -voltage conversion and tone decoding.The on -chip op amp can be used as anintegrator to provide a dc outputproportional to speed (input fre-quency) or to amplify digital pulses.

The UA 7351 is a triple operationalamplifier, a general purpose circuitalso specifically designed for auto-motive operation, with single 4 toI6V or dual 2 to 8V power supplies.The circuit contains three identicalop amps on a single circuit chip in a16 -pin DI L package. Each two stageamplifier has a Class -A PNP commonemitter output stage with an uncom-mitted collector, enabling the circuitto be used with a variety of loads.The op amps can be connected in the'wired -or' mode for logic blocks,such as dual or tri-level comparators.Slew rate is one millivolt a micro-second.

Typical applications for the UA 7351include tri-level sensors, biquad statevariable filters (low pass, high passor band pass), voltage to frequencyconversion and peak detectionwithout an external diode.

IMPROVED SHORT RANGETELEMETRY SYSTEM

An improved version of their generalpurpose short-range telemetry systemis now available from I.E.C. Limited.The modifications result from appli-cations knowledge gained since 1966

when I.E.C. Limited, who pioneeredthis type of equipment, first intro-duced the system.

The well proven principle ofoperation - transferring transducerinformation from moving componentsby the use of capacitive transmissionand an F.M. pulse carrier has beenretained but the transmitter circuitis now housed in a stainless steelcasing. Together with its batterysupply it is fixed to a shaft(measurements from rotating shaftsbeing the major requirement) usinga special clamping bracelet. Thebracelet, which is made up fromstandard transmission chain linksinterspaced with special carriers andtensioners, combines great strengthwith easy adjustment over a widerange of shaft sizes. This technique ofmounting the transmitter assemblydoes away with the need for specialclamps and is the subject of worldwide patents.

Further improvements in thesystem specifications include adifferential operational -amplifierinput stage in the transmitter. Thispermits adjustments of the inputcharacteristics to suit a wide rangeof transducers and input levels.Typical applications of the equipmentinclude torque and strain measure-ment in drive shafts and temperaturemonitoring from rotating kilns anddryers.

BOMB ALERT

When Castle Associates introducedtheir new Falling Ball Calibrator theydid not bargain for the problemsrecently encountered. Produc-tion problems, staff problems, compo-nent problems, test problems arenormal day to day occurrences formost companies but a product mis-taken for a bomb is unusual. This isexactly what happened to Castle ontwo recent occasions. The PSQ 101AFalling Ball Calibrator is manufac-tured by Castle Associates for thecalibration of their range of soundlevel meters. It is a mechanical devicewhich operates rather like an egg -timer. When turned upside down6,000 tiny steel balls fall onto a micadiaphragm creating a fixed randomnoise of 96 dB which is used as areference level.

Even in a well designed postal packthe loud noise escapes and hasgiven several postmen quite a shock

A recent delivery to a well knowncity insurance company resulted inthe bomb squad being called out. As aresult all future deliveries to thiscompany have to be by special arrange-ment...a rather unwelcome addition-al overhead cost on a unit selling atonly £19.

The latest problem was w th alarge shipment of PSQ 101A's toBoston, U.S.A. Castle Associates'Air Shippers declined to handle thepackage for fear of a bomb ;care atLogan airport, so once agair specialarrangements had to be mace.

If a scared customer receiving aPSQ 101 throws it into water think-ing it is a bomb, Castle could wellend up with another problem -RUSTY BALLS.

JAPAN'S ELECTRONIC PARTSINDUSTRY

A recent report by the Fuji 3ankBulletin contains a summary of theresults of a survey on the presentconditions in Japanese industry andthe prospects for April -September 1973.

Despite the large upvaluat on ofthe yen in December 1971, Japan'sindustry made a satisfactory recoveryfrom the 1970 recession in the latterhalf of 1972.

The comments on the electronicparts industry are as follows:

Present situation and outlook

Production of TV sets and radioreceivers will decrease butstronger demand for electronicequipment for industrial use andlarger exports will expand productionby almost 10%. The low inven-tories may push unit price; up by10%-15%.

Exports and imports

Overseas demand is brisk and nosignificant slowdown in theexpansion of exports of parts isexpected.

Equipment investment

The main emphasis is on investmentfor strengthening the productionof integrated circuits; investmentis also large for rationalisation andthe installation of labour-savingmachinery.

Remarks

The quantitative increase in theproduction of circuits and semi-conductors has lessened theimpact of the change to integratedcircuits but in 1974, the effectswill be rather pronounced.

ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973 75

AUDIO NEWSQUADRAPHONICDECODER/AMPLIFIER

Designed specifically to complement theSony '8' family, the Sony SQA 100 Decoder/Amplifier is compatible with any Sonysystem or in fact most amplifiers with a tape/monitor selector switch. The amplifiersection is designed to provide the rearspeakers of the system with 6W r.m.s.Recommended resale price is £40 plus VAT.

Sony (U.K.) Ltd., Pyrene House, SunburyCross, Sunbury -on -Thames, Middx.

PROFESSIONAL TAPE

Users of machines which accept large reelssometimes get trouble from the unevenwinding of tapes, causing overlapping andpossible consequent damage. We have newsof two new tapes with anti -static matt back-ing a feature which ensures uniform windingto overcome these problems (even whenusing sideless tape hubs or single -sidedspools).

BASF have announced a double playversion, DPR 26LH, of this tape, previouslyavailable only in long play. Prices start forthe double play tape, at £5.60 for a Tin.spool.

EMI's new range is called Emitape 817, andis available in four widths. This tape is low inbias and modulation noise and EMI claim itcan be used on multi -track machines with-out need for any noise reduction system.

BASF U.K. Ltd., P.O. Box 473, 197Knightsbridge, London SW71SA.

EMI Electronics & Industrial Operations,Blyth Road, Hayes, Middlesex.

TUNER AMPLIFIERS

Latest additions to the Eagle range ofaudio equipment are two new tuner ampli-fiers, AA.28 and AA.30. Both units aresaid to be compatible with transcription

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88 102 95 Ir. 100 104 105 mH,

008000000080000000000+810080040000000000118M154 80 AI 80 ' AO 170 $40 160

OUSE EWER" CONTROLS

RA 88 02 96 i100 104 108

1114111111M1111111141111111111111111111111111111111111111111.1.111111111111101111111111111

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turntables and cartridges and high qualityor monitor type speakers.

Standard features on both amplifiersinclude main/remote speaker switching,loudness control, and normal bass, treble,volume and balance controls. In additionto these the AA.30 incorporates a SoundEffect Control system.

The tuner section on both units usesa FET front end together with a tuningmeter and switching for AFC and inter -station muting. Output power is 30W perchannel.

Eagle International, Precision Centre,Heather Park Drive, Wembley, Middlesex,HAO 1SU.

RC 430 CASSETTE RECORDER/PLAYER

The new Siemens RC 430 cassette recorder is for recording and playback withC60 or C90 compact cassettes. It includesmany advanced technical features; auto-matic switch -off and automatic volume con-trol guarantee fault -free tape recordings.For manual control the automatic volumecontrol system can be disconnected. A V.U.meter indicates the recording level andcan also be used to check battery voltageduring playback. The normal functions arecontrolled by press -buttons. Insertion of thecassette is facilitated by guide bars inthe cassette compartment cover.

The reproduction from the loudspeakersis good. There is a 20 cm speaker anda high frequency tweeter, 4 cm in diameter.

The frequency range 80 - 9000Hz and

the output is 700 mW.The recommended retail price is £41.09

(inc. VAT).

Interconti Electronics Ltd., AlbanyHouse, Petty France, London, S.W.1.

76 ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

EQUIRMENr NEWS

MORE CHARGE CURRENT

The Electroplan automatic constant currentcharger now has a maximum charge currentof 750mA. The charger provides a transistorregulated constant charge current and isspecially designed for rapid re -charging ofnickel cadmium batteries and cells.

A 'Set Current' control allows the chargecurrent to be varied up to the 750mA maxi-mum. A 'Set Hours' control gives quick

setting of the required charge period. Thecharger has a useful power output of approx-imately 17 watts which allows the chargingof up to 15 cells in series at the maximumrate of 750mA.

This newly designed charger costs £25.00Electroplan Limited, PO Box 19, OrchardRoad, Royston, Herts SG8 5HH

SIMPLIFIED TRANSISTOR TESTER

The TT169 Transistor Tester offers simple"go/no go" testing of p -n -p and n -p -n signalor power transistors without having to un-solder them from circuit. Good or baddevices are indicated by lights on the frontpanel working in conjunction with a cali-brated control; intermittent illuminationgiving immediate indication of 'good' devices.

The instrument is hand held, and suppliedwith insulated colour -coded probes for col-lector/emitter/base connections. It operatesfrom three internal 1.5V cells, which are

sufficient to provide 90 minutes continuousoperation. Where bench testing over extendedperiods is required, an external 4.5V sourcecan be applied.

Diodes and thyristors can also be testedby suitably connecting the probes andwatching the lights. Made by AVO Ltd., it issupplied with all necessary leads and con-nectors in a compact plastic case. Price is£15 plus VAT.Gothic Electronic Components, BeaconHouse, Hampton Street, Birmingham 19.

SPECTRUM ANALYZER

Model 8558B, a new 0.1 - 1500MHz Spec-trum Analyzer from Hewlett-Packard, comesas a plug-in module for their oscilloscopes.Although simple to operate, the instrument'sperformance is lab grade, with ±1dB fre-quency response and greater than 70dBdistortion -free dynamic display range.

Ease of operation has been emphasizedin the design. For most measurements onlythree controls need be used; TUNING setseither the centre -frequency or the start -frequency of the display, which is indicatedon a 31/2 digit LED readout. FREQUENCYSPAN sets the width of the frequencywindow to be viewed. Span range is 1000MHzto 50kHz. REFERENCE LEVEL (amplitude)directly calibrates the display in absolutepower units. The range is -115dBm to+30dBm.

When the FREQUENCY SPAN controlis set, the analyzer automatically selects theoptimum resolution bandwidth and sweeptime. If the operator chooses to override theautomatic selections, resolution bandwidthsfrom 1kHz to 3MHz can be chosen. Theanalyzer also indicates optimum and maxi-mum input level for the chosen amplitudecontrol setting, which minimises the pos-sibility of overloads that could cause er-roneous measurements or even equipmentdamage.

It was interesting to use this equipment to see what radio signals could be picked upby a small aerial. Using just a door key heldto the input socket, ETI staff could see at aglance what frequencies were being used bylocal radio and TV stations. The whole ofthe LW, MW, SW, VHF and UHF bandswere monitored in one picture and then weanalysed the bands one by one.

The equipment is beyond the pocket ofthe amateur, however, at £1,675 (L2,133with oscilloscope).Hewlett-Packard Limited, 224 Bath Road,Slough, Bucks. SL1 4DS

ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973 77

EQUIP/MEN' NEWS

NEW CLAMP AMMETERElectronic Brokers Limited have introduceda new clamp type ammeter having 6 currentranges plus 2 voltage ranges for use on 50 to60Hz alternating current supplies. Known asthe AMPERTEST 690, the new instrument ismanufactured in Italy by Industria Construg-ioni Ellectro-meccaniche.

The Ampertest 690 uses the familiarclamp or 'pincer' system to measure thecurrent flowing in a conductor withoutbreaking the circuit. The meter, has 6 currentranges from 3 to 600 amps f.s.d. with thefirst division at 100mA. The current rangesmay be extended by use of a 10 to 1 currenttransformer which is supplied with the instru-ment providing ranges from 300mA to 60Af.s.d. with the first division at 10mA. Inaddition there are two a.c. voltage ranges,250V and 600V f.s.d. The connections forvoltage measurements are made by twoleads and probes which plug into the base ofthe instrument.

The Ampertest 690 is supplied withvoltage measuring leads and probes andcombined twin wire adaptor/current trans-former in a solid leather carrying case.

The Ampertest 690 is available at a priceof £37.50 complete.Electronic Brokers Ltd., 49/53 Pancras RoadLondon NW1 2QB

PRINTING CALCULATORThe Meritronic is the latest addition to theDiehl range of advanced printing calculators,and is designed to fill the need for a robust,reliable office machine for day -in, day -outcommercial calculations.

One of the features of the Meritronic isthe simple, functional keyboard, equippedwith full-size colour -grouped keys. Officemachines must be designed to standards thatallow the inexperienced operator every facilityclearly. Thus the numerics are centrallygrouped, and electronically buffered so thatit is practically impossible for an operator to

key too fast. The function keys include thefour basic rules of arithmetic, and allowchain operations, automatic constants, auto-matic decimals,and accumulation of productsand quotients. A useful feature is the abilityto accept a floating decimal input to give afixed decimal output.

Every keyboard action prints out as it ismade, giving a ready check that figures havebeen correctly entered and the appropriatefunction performed. Provisional figures can

be readily re -checked, or final calculationsfiled for future reference - of special value toVAT bearing services. Cost is £168 complete.Calculating Systems Limited, 956 High RoadFinchley, London N12.

DIRECT READING 30kV METERComplementing their range of power suppliesthis direct reading 30kV d.c. meter designedand developed by Brandenburg Ltd., providesan highly accurate tool for both field orlaboratory use.

It is the only one of its type currentlyavailable. It is compact and portable and ishoused in a lightweight rigid new style caseincorporating an easy -to -read 4.5in. scalemeter.

Operated by internal 9V battery, linkedwith a built-in checking facility, the instru-ment is flashover and transient proof andprovides an accuracy of 1% fsd over thecomplete range of 0-30kV d.c. High inputimpedance of 30,000M0 ensures that cur-rent drain is negligible at less than 1µA andpositive or negative ground is easily selectedby a switch mounted in the front panel.

The meter, only 178 x 114 x 127mm issuitable for a temperature range of 5-35°Cand has a battery life of 800 hours.

AUTOMATIC DISTORTIONANALYZERRadiometer A/S of Copenhagen have justannounced a new fully automatic program-mable Distortion Analyser, known as theModel BKF 10. This instrument can beconnected to any signal source and willinstantly and automatically indicate its fre-quency and the percentage distortion with-out balancing or any further adjustment.Furthermore the BKF 10 has a built-in lowdistortion sweep generator and an amp-litude input/output response ratio meter,the combination of which can be used toobtain complete and fully automatic fre-quency response and distortion analysis ofamplifiers, tape recorders and similar LowFrequency equipment.

A voltage proportional to the logarithmof the frequency is available as a recorder

output and can be used as the X input forX -Y recordings.

The fundamental frequency range is from20Hz to 20kHz and the harmonics range from10Hz to 150kHz. For distortion measurementthe fundamental frequency is automatically

suppressed by a band -stop filter circuit but anautomatic level control circuit enables eitherthe fundamental input or the output fromthe apparatus under test to be held constantand thus it is possible to measure distortion asa function of frequency at a constant outputpower. The signal-to-noise ratio can beautomatically shown on the meter by merelypressing a front panel button, and if thesignal should include a high hum content,this can either be suppressed or measuredby using the high-pass or low-pass filterswhich are built-in the instrument. Thedistortion range of the BKF 10 is from0.02% to 10% and the accuracy ± 1dB.

Radiometer A/S market their equipmentin the UK through International InstrumentsLtd., Cross Lances Road, Hounslow, Middx.

SYNTHESIZED SIGNALGENERATOR

The Farrell Modular Signal Generator rangehas now been extended to include synthesizedversions of two existing AM/FM signalgenerators, M1 /ACM and M2/ACM, whichcover the frequency ranges 100KHz to12MHz and 10MHz to 108MHz respectively.

In the new systems the frequency is con-trolled by a six decade bank of thumbwheelswitches with an accuracy of ±5PPM and aresolution of 1KHz.

Although the oscillator module usesseveral frequency bands to cover the range,the digital control selects the correct rangeautomatically so that the only adjustmentnecessary is to set the thumbwheel switchesto the required frequency. The correct rangeis automatically selected and a search lampextinguishes to indicate that the correctfrequency has been reached.Farnell Instruments Limited, Sandbeck Way,Wetherby LS22 4DH, Yorkshire.

78ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

From ITT.

A completely new kindof changeover relay.

Don't let its sizefool you.

We've recently developeda changeover relay quite unlike anyother on the market. It's called adiaphragm relay and offers almost exactlythe same performance as a mercury -wettedrelay yet is smaller in size. And a lotsmaller in price !

Distributor quantities availablefrom ITT Electronic Services. Harlow 26777

Take a look at theseoutstanding features.* Hermetically -sealed precious metal

contacts.* Switching capability of 30W.* Max. current and voltage contact

ratings are 500mA and 150V. a.c./d.c.respectively.

* Coil voltages (d.c.) 6, 12, 24 and 48V.* Withstands high levels of shock

and vibration. From 50Hz to 5kHzand acceleration of 100g.

* Pins provided for direct -mountingonto 0,1 in. module printed circuitboards.

* Dimensions:26,25mm x 12,5mm x 11,5mm.Phone Harlow 26811 Ext. 642 now

for more information.ITT Components Group Europe,

Electro-Mechanical Product Division,Edinburgh Way, Harlow, Essex. CM20 2AQ.Telex : 81146.

Components_ITT

cEnmonic

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photon emitting and detecting devices. Centronic, nowsole U.K. Agents for OKI Electric Industry Co Ltd, of Japan,

introduce a new and very competitive range which includes

Solid state numeric displays

*lmm to 6.8mm character size*Numerals 0-9 and decimal point* Bright red displays* Low current consumption*Flat -pack mounting in sticks of 8 and 12 digits* Dual in -line pack 1 or 4 digits*Circuit board mounting option

Light Emitting Diodes

* Red, green and I.R. emitters* 100,000 hours life*Small lightweight and rugged construction* Low voltage and current operation,

transistor and TTL compatible* High light output efficiency* Pulse operation facility giving

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Write now for full details on these newcomers.You'll be impressed!

TWENTIETH CENTURY ELECTRONICS LTD King Henry's Drive, New AddingtonCroydon, England. Telephone Lodge Hill 2121. Telex 896474

ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973 79

AUDIO WATTMETERContinued from page 5/

Some further checks can be madeas follows:-Set S2 to 0.5W range and S1 to 15ohms. With the audio generator at2.73V output the power level metershould read 0.5W. Now set S1 to 8ohms and the audio generator to 2.0Vin which case the power level metershould again read 0.5W.

Providing all the pre-sets have beenadjusted as already described the cali-bration for different power levels andfor the three load ranges of 4, 8 and 15ohms can be checked simply by coup-ling known audio signals into the metercircuit via the 'METER" terminal on thefront panel and common E. The loadlink must be disconnected. The tablesprovide a number of spot checks forvarious power levels and for each of thethree load values.

It will be seen that the tables havebeen worked out from V---VP0xR tothree decimal places. In practice, meterreadings to this accuracy are almostimpossible but if readings to onedecimal place only can be achieved,then providing everything else has beenadjusted to the same degree, the audiowattmeter will be accurate enough forall practicalthe finished prototype is shown in

the photograph.

IN OPERATION

The prototype was finally checkedagainst laboratory standard instrumentsand found to have a high degree ofaccuracy. The loads of 4, 8 and 15ohms were chosen because these aremore or less standard. The load rangesand even the power ranges could beextended with additional attenuatorsand correction networks. In operationthe load resistors will run warm at highpower levels but these should not besustained for longer than is necessaryto take a reading. The loads have noinductive effects and the material usedfor them was chosen because it is

readily available and fairly cheap. Highwattage load resistors of precise valuesare difficult to obtain and the one ortwo firms who do manufacture themwere not prepared to supply other thanbona -fide trade users. In any case theywere very expensive.

When a meter of this nature is usedit is essential to know when the maxi-mum output of an amplifier has beenreached, i.e. at the point just beforeclipping occurs. It is for this reason thatan oscilloscope monitoring point hasbeen included to check the waveformacross the load. Maximum power out-put must always be checked with an

Fig. 13. Al Clippedoutput B1 Sine waveat maximum power,just before clipping.

The dummy load resistors mounted under the chassis.

oscilloscope monitor and the usualprocedure is to set the amplifier gaincontrol at maximum and then bring upthe input signal (sine wave) to thepoint at which clipping occurs as on theupper trace in Fig. 13a. The inputsignal is then reduced until clippingjust ceases and the amplifier outputsignal resolves into a sine -wave as inthe lower trace Fig. 13b. Even atlower power levels, i.e. well belowmaximum power output,a check shouldalways be made on the amplifier outputwaveform as clipping can occur atamplifier input stages if the inputsignal is too high. Do not connect thepower meter to an amplifier unless theload link is connected between the'METER' terminal and the "LOAD"terminal. This link may be a piece ofwire or a thin plate with slots to fitunder the terminals as shown in Fig.3b. Finally please note that the decibelscale is for power dB related to 10Logi 0P2/111.

Ala

BACK NUMBERS

A limited quantity of back ,um-bers of Electronics TodayInter-national are available at 25peach plus 7p postage (32p inall). Requests for these shouldbe addressed to:

BACK NUMBERS DEPT.,Electronics Today International,36 Ebjry Street,London SW1W OLW

80 ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

DXmonnoCompiled by Alan Thompson

No reader of this feature will need me to point out that the days ofsummer are past for another year, and that in just a few weeks weshall be huddling together at the bus -stop or on the station (why,oh why, are they always located in the windiest spots in the region?)sheltering from the icy blasts - or else, joy of joys, turning thestarter of the car for the umpteenth time when we know darn wellthat the so-and-so battery is as flat as the proverbial pancake.There's no problem in recognising the DXer amongst the winter -battlers: he's the one with an inner warmth and a smug, complacentsmile! DXers, of course, are somewhat schizophrenic about theseasons; as others long for the warm summer days, so DXers longfor those endless winter nights when the DX is coming in thick andfast, there's a healthy (?) fug in the shack and there's always thechance of another new country going into the logbook. Truly,DXers are something of a strange breed of men (and women,because there are a few YLs in the fraternity too) and their waysmust seem rather strange to the rest of the world!

The approaching winter gives promise of being one of the moreabsorbing for DXing for quite a few years. Currently we are on thedownward side of Sunspot Cycle No. 20 which means that thenumber of sunspots is getting steadily less and less and theminimum ought to be reached about 1975. Fewer sunspots meansless atmospheric noise and that means that there will be a betterchance of hearing some of the weak stations that the real DXer isalways searching for. However, there are a few minuses in all this -firstly, it is likely that the signal strength of stations will, generally,be lower than it has been whilst the sunspot cycle was nearer themaximum; next, there will certainly be added congestion in theinternational broadcast bands between 49 and 19 metres asnumerous stations are forced by propagational factors to give uptransmitting in the 16, 13 and 11 metre bands and will be forcedto look for some clear spot in the already over -crowded lowerfrequency bands; lastly, there has certainly been a great increasein the a;nount of man-made interference since the last time wewere at this point in a sunspot cycle (11 years ago) and that isn'tgoing to make hearing the rarer stuff any easier!

Whenever cute goes into print, or on the air, on any subject,there is always a quiet little man lurking somewhere who is goingto read what you have said and who will then carefully demolishyour arguments just because he is THE authority on that subject.So, my dear Sir, please don't take issue with my statement thatwinter is the time for hearing Australasia and the Pacific Islands -I do know that it is (just) possible to hear some of them at othertimes of the year when propagation windows are open for briefperiods, but explaining the whys and wherefores of thoseopenings is rather beyond the scope of "DX Monitor". Right -if Australasia and the Pacific Islands are the targets for your DXingthis winter, a good place to start will be with Radio New Zealand.RNZ is never the easiest of catches in the U.K. since it usestransmitters of only 7.5W and non -directional aerial arrays(for most of the time). Best reception is usually noted in the 31metre band around 0800-0930 GMT and once you've heard the verydistinctive interval signal of the New Zealand Bell Bird you'll besurprised just how often you'll hear it on other channels throughoutthe years ahead. As this is being written, precise details of RNZ'swinter sked are not to hand, but it is a fair bet that either 9520 or

9540kHz will be the 31 -metre band frequency used.Another nice Pacific catch is ORTF's station in Tah ti: the

channel that usually gives the best reception in the U.K. is15170kHz, where ORTF uses a 20kW transmitter and is

frequently a really good signal at sign -on at 0300 GMT, althougha couple of times a week it begins at 0230 GMT with educationalbroadcasts. At that time of day, the language used is Tahitianchanging into French at 0500 if the signal is still audible, as itoften is. One that has not been reported over here for a few yearsis Noumea, in New Caledonia: the frequency for this 20kWtransmitter is 7170kHz where it is on the air from 220C until 0600GMT each day.

Radio Australia's Overseas Service is one of the easiest long -haulDX stations to hear with its characteristic Waltzing Matida intervalsignal at the start of each transmission. If you want to try for thispart of the world in a more difficult way, why not try L920kHzwhere ABC's Domestic Service station in Brisbane ofter puts inremarkable strength signals around 0800-0900 GMT on a cold winter'smorning. Radio Australia, too, operates a number of stations inPapua and New Guinea with most of these Domestic Servicesbeing of low -power in the 90 metre band: a couple of cutlets wortha try are 3925 and 4890kHz where you stand a fair chance ofmaking your catch either at 2000 GMT sign -on (not on Saturdayevening UK time!) or just before sign -off which comes shortly after1400 - with irregular later operation on Saturday afternoons ourtime when it may be heard carrying sports features. The transmittersare located at Port Moresby, by the way.

Moving over towards the Far East, Laos is a country that manyDXers find difficulty in logging - best channel to try is 6130kHzwhere the Domestic Service outlet is often quite fair until sign -offat 1430 GMT. One of the more difficult countries in th s generalarea of the world is Burma with Rangoon transmitting tvvo HomeServices on 5040 and 4725kHz until around 1500 GMT: even whenyou have managed to log this one your problems are not over if youare a OSL collector - OSL's from the Burma Broadcast ng Serviceare anything but easy to get. My own was the result of come dozenreports and something like another dozen follow-ups before therequired card was added to the collection.

Last station to be mentioned in this round -up of some of thegoodies that should be available through the winter is Azad KashmirRadio, the official voice of the Pakistani -controlled porlon ofKashmir. This station operates on a somewhat irregular schedulesigning -off around 1800 to 1900 GMT at the end of it's day'sprogrammes, with a once -heard, never -forgotten, vocal 'anthem'in which the words "Azad Kashmir" are repeated over and overagain. Frequencies, too, are somewhat variable but a favouriteoutlet is around 4730kHz, and in the 90 metre band it can oftenbe heard on or about 3390kHz. Recently, OSL's have startedto come from this station after years in which it refused to answerany reports and I was delighted to obtain the very first in theworld for this station - the address is simply Azad Kashmir Radio,Muzzafarabad, Azad Kashmir, Pakistan.

A few general words on DXing the Far East may not be out ofplace. The stations mentioned above should all be audible at sometime between now and the beginning of March but it is veryunlikely that all will be heard on any particular day. Especially

ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973 81

DXMOIIITORon the lower frequencies, afternoon reception will normally notstart until the days are very much shortened, and the peak periodfor reception of stations like ABC Port Moresby and Laos in theafternoon 'slot' therefore tends to be between the end of Octoberand mid -February. Similarly, ABC Brisbane isn't likely to appear onthe 60 metre band until the same part of the year. However, it isworth keeping a sharp look -out for these stations as they may wellshow up at times when they are not normally to be expected.

Far Eastern languages are not easy for European ears tocomprehend since many of them are of the 'tonal' variety. If oneis interested in getting to grips with them, a lot of progress can bemade by tuning to either the B.B.C. or the Voice of America'sservices to the Far East, as both these broadcasts start theirtransmissions with an English announcement that "the followingprogramme is in Chinese" (or whatever). However, reporting isn'ttoo difficult since the vast majority of stations will acceptEnglish reports, although French is to be preferred in the case ofboth Laos and Cambodia.

I hope that this short introduction to some of the delights of FarEastern and Australasian DXing will have fired some of our readerswith a wish to get in on the band wagon. If anyone has any questionsI shall be very glad to do what I can to assist and you can write directto me at 16, Ena Avenue, Neath, Glamorgan SA11 3AD: if you wanta personal reply I am afraid that a self-addressed, stamped envelopeis a must. If you feel that there are any aspects of DXing that youwould like to see given the treatment in this feature I shall be verypleased to hear what they are and I shall try and include them infuture articles in this series. "Feedback" letters should, if possible,reach me by about the 10th of the month for inclusion in this page.Until we meet again in a month's time, all good wishes for a verysuccessful autumn and winter of DXing - I'm just off to bring mylist of wanted countries up-to-date and I'm hoping to add a few moreto the list of those I've heard before 1974 arrives. My fingers arecrossed!

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82 ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

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If you find a programme scheduled incon-veniently you merely set the clock and leaveJONAN "FAB" to its job and return to hearthe recorded version whenever you wish.JONAN "FAB" can also be used as anordinary radio, cassette -recorder or clockradio.Two simple controls preset the recorder; onedial selects the time, a second dial sets pro-gramme length. Sixty minutes can be recordedon one cassette. JONAN "FAB" receivesmedium wave and FM on battery or mainsand is fitted with automatic level control,socket for external speakers, microphone (ofcourse, there's one built-in as well) or tele-phone pick-up.

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andPeacock Cross Industrial Estate,Burnbank Road, Hamilton.Tel Hamilton (06982) 29511

GETTING BORED WITH ELECTRONICS?Some things are repetitive, once you have built an astable multivibrator, they tend to get boring-tried a 555timer ? It works in mono or astable modes for long or short pulses (95p). How about building a radio tuner foryour record player, the ZN414 chip makes this simple (£1.10). LEDs? We have a fantastic choice-LEDlamps-TIL209 or HP4480, 4 for £1.50, 50 for £10; large lamps (HP4480), 35p each. 50 for £15, RED andGREEN LEDs £1 per pair. LED displays-TIL302 (or similar) £2.50 each. TI L312 (similar to MAN4) £2 each-limited quantity. TIL360 6 digit package £18, DL34 four digit package £15. DL62 (I") £6.50.Phosphor diode displays DG12 £2 each.CLOCKS CLOCKS CLOCKS CLOCKS Bywood is now foremost in the LSI clock chip market (who elsehas four different clock chips in stock with two more on order?) MM5311-the original -01.50. MK5017ANwith alarm or and radio controls £15.50. MK5017AA with alarm or MK5017BB with calendar, either ofthese two is offered with a PCB, socket and suitable displays (4DG12s) at £24.Don't get bored, if none of the above fascinate you how about liquid crystal displays, DVM chips etc?This technology is here to stay. Bywood have got it or can get it-give us a try.VAT. All prices above EXCLUDE VAT, add 10%. P. & P. Please add 10p post and packing.You can have clock data sheets for a S.A.E. or our 1973 catalogue (2nd issue) for 16p. (And we haven'teven mentioned our calculators yet- but they are in the catalogue.)You may phone us for help on 0442 62757 and you can use your ACCESS card for phone or personalpurchases-Service from Bywood

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84 ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973

ELECTRONICS TOMORROWContinued from page 72drawing, rephotographed, etc. Not muchsaving, you might comment, except that thedrawing stage is the most time consumingand expensive part of the system. The costof getting one prototype board say 3 x 4incontaining 60 components or 10 TTL ICs isabout £80, board £3, photographic charges£3, ancillaries £4 (each twice allowing forone set of corrections) design and layout £45,corrections to design and layout £15. Thesefigures as a matter of interest were basedroughly on the board produced for theclock in the September issue, a simpler orrougher board may be a lot cheaper. Thepoint is that a large proportion of the cost isin something which the average amateurcould tackle himself with the right equipment.

The equipment required is drawing filmand 0.1 inch graph paper from a drawing orart show, layout tapes (lx size for contactexposure), photosensitive boards (positivesensitivity, the developer will wash off theclear areas of the original and leave the blackareas), developer, Ferric Chloride etchant,drill.

Layout tapes - Mecanorma Electronic(press on tapes).

Photosensitive resist and developer -Kodak Autopositive from Kodak.

Positive -20 from Electrovalue.Ferric Chloride - Electrovalue or some

chemists.Drill - Mini Drill and bits from Model

Shops.Ideally you will also require an ultra-

violet lamp for exposure. The Kodak chem-icals cost about £15 but these will dohundreds of boards. Positive -20 costs 50p and

Fig.2b. An intercom usingonly seven components

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covers about 10 boards, a good range oftapes will cost another £15. Your first boardwill cost you about £80 but the boardsafter the first will cost less than 10p eachand you end up with artwork suitable forsmall production runs. The boards producedmay not be up to professional standards butthey will be better than etch -resist pen orpaint boards and more customised thanmatrix type breadboards.

REFERENCES

1 Bi-Pak Components, P.O. Box 5, Ware,Herts.

2 National Semiconductors, The Pre-cinct, Broxboume, Herts.

3 Bywood Electronics, 181 EbbemsRoad, Hemel Hempstead, Herts. 0442-62757

4 Mecanorma Electronics, 49-51 CentralStreet, London EC1. 01- 253 1102

5 Electrovalue Ltd., 28 St. Judes Road,Englefield Green, Egham, Surrey. Egham3603.

6 Kodak Ltd., Resists Dept., Swallow -dale Lane, Hemel Hempstead, Herts.

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ELECTRONICS TODAYINTERNATIONALOctober 1973

REMOTE

ME 1

I would like to take advantage of thespecial offer of the EDSR 3166 ShiftRegister as mentioned in the articleElectronics Tomorrow. I enclose acheque/P.O. made out to BI-PAKComponents to the value of £2.00

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Orders should be sent direct to:BI-PAK COMPONENTSP.O. Box 5,Ware,Herts.

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Research in Electrical EngineeringApplications are also invited from similarly qualified persons who wishto pursue a course of research leading to the Degree of M.Phil. orPh.D. in any of the above subjects.Application forms and further particulars from the Hear of theDepartment of Electrical Engineering (Ref: M.Sc. 8), The l'niversityof Aston in Birmingham, BIRMINGHAM B4 7PB.

THE UNIVERSITYOF ASTONIN BIRMINGHAM

ELECTRONICS TODAY INTERNATIONAL - OCTOBER 1973 85

MI NMI MINN MB MN - OM -INDEX TO ADVERTISERS

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Apollo Aerials 71

BI ET Cover iii

BI-PRE-PAK 4

BN RS 82

Bush & Meissner 83

Bywood Electronics 6, 83

Chromasonic Electronics . 12,13

Centronic 79

Decon 61

Gerald Myers 30

Henry's Radio 8, 9

ITT 79

J T Eden 69

Minikits Electronics 23

Ramar 83

RCS Electronics 61

Sansui Cover iv

Teleton Cover ii

Trade Disposals 83

University of Aston 85

Wilmslow Audio 53

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86 ELECTRON ICS TODAY INTERNATIONAL - OCTOBER 1973

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