PAL: ". . . 20% bette r in transmission andreceptionthan my 5/8 wave Pal Firestik. "-John A. Blum, Box 446, Z e ~ e n o l p l e , PASHAKESPEARE: ".. . I'vebeena CS'er forthreeyearsandtheK40 iothebest I've everhad. Setter inreceptionandtransmission thanmy Shakespeare."- H. Bachert Jr... 15 King Rd., Park Ridge, NJHUSTLER: "ComparedtomyHustlerXSLT-4, the K40 can consistently transmit 40 %further and the reception was better. The K40isthe perfect way to complete a CS system."-Jerome R. Brown, 7800 S. Linder, Burbank, IL.. . Here'swhat CB'ers allacrossthecountrysaid.3. It'sprovenbest!. .. Here'swhat theleadingCBpublicationssaid.ANTENNASPECIALISTS: ". . . truckdriver and CS' er for10 years . . . 50 % furtherthan my M410 'Sig Momma' ."-J.H. Collett 20 7 McFee, Bastrop, LAAVANTI :"I'man electronic tec hnician witha Second ClassFCClicense. . . I wasabletotransmit 70%furtherandtunethe SWR 75 % lower than my Avant i."- H.R. Castro,VRB, MonssrranteD-67, Salinas, PuertoRicoCB TIMES: ". . . it'snot oftenthat a product burstsontothe mar-ket scene, dominates and improvesCS'ing foreveryone. Ameri canAntenna and the K40 are doing it- repeated testsshowed the K40couldout-performthe major competitive brands."RADIO-ELECTRONICS: " Theresultsof our tests showedthat, in three different positions of the monitoring receiver, themodel K40 equaled or out-performed the competitive antenna.Apparently, Amencan Antenna' s advertISing IS not merelyMadIsonAvenue showmanship."PERSONAL COMMUNICATIONS: "... an impressive95 % of the trials, the K40out-performedthe existingmobile anten-nas. We had to try one for ourselves ." . . .inevery case, theK40 either equaledor out-performeditscompetitor." Noifs, ands, orbuts! TheK40AntennafromAmeri can Antenna wouldhavetobe just about the best antennaaround.CBMAGAZINE: "Introducedin October,1977, theK40quicklybecamethetopsellerand in mid 1978, becamethe number oneselling antennain the nation."IIIt's madebetter...In one year our K4Q. antennahas become the largest sellingCB antenna inthe world!2.' Includingoption-al mountsat extracost.MORE PERFORMANCE:The K40 is guaranteed totransmit further or receiveclearer than any antenna itreplaces. We know it will .We've tested it with 771CS'ersjust likeyoufor oneyear.... ThisAntennais soDYNAMITE,"OUreoeiveaMORE QUALITY:It's not imported. It's notmade in Taiwan, Korea orJapan. It'sAmericanmadeinanAmericantown. It'smadewit h better materials thatcost more and by profession-al peoplewepaymore. Andwe designed it righthere in the U.S.A.MORE FLEXIBILITY:Youcanfit your K40 toanymounting surface . It will fitanyvehicleyou'll ever own!That incl udes choppers, dunebuggi es, gutters, mirrormounts,luggageracks,trunks,hatchbacks, through roofs,semis, pick ups and RV's.542.50suggested retailAnd when youpay more,you expectmore!1. It'smoreexpensive ...Magnacox modcl4012.;-- - - - - - - - - - - - - - - - - - - - - - - 9-il/ch diagollaimcasllrcmclll- - - - - - - - - - - - - - - - - --------!AC/DC color portabletoith electronic IlIlIill$ wheel!- and dial scale indicator. -\- VI I N Y.Magnavox sees the nextstage of televiewing with--""';youas the participant aswell a the recipient.-------;For mat, you will needthe mo t reliable colortelevision possible.------.:;anowMagnavoxStatSSy terncolor ------itelevision ets combineadvancedde ignconcepts,high technology andnewmanufa .ng systemstodeliver the highest level __of reliability in Magnavoxhistory.Magnavox.Television --;as visionary as tomorrow.Witha picture as reliable__as it is bright andclear.Time after time.Magnatox. ApictureyO Ilcall relyon lime after lime.Magnaoo model 4265.19-i llchdiagonal measurement---Star Slste m. All Star System -setsgiue you infrared remotecontrol;lOS-chO/mel capability:;...-__automaticsioitching betweentwochannels. display limeof day and channel numberall TV screen.Magnaooxmodel 5260.25-inchdiagonalmeasurement:---- - - - - - - - - - - - - - -SlarSyslem. This set even has expandedrangehigh-fidelity sound.. , , .,. The brightest ideas in the world arehere toda>:; 1981NA P CONSUMERELECTRONICSCORPCIRCLE30 ON FREE INFORMATI ON CARDiI iII I-iaTHEMAGAZINEFOR NEWIDEASIN ELECTRONICSElectronics publishers since 1908 NOVEMBER1981 Vol. 52No. 11SPECIALFEATURE 43 VIDEOTEXHow your TV will be able to supp ly you wit h all the informat ionyouneed. when youneedit. RichardLarrattONTHECOVERBUILDTHISTECHNOLOGY47 LOW FREQUENCYFILTEREliminate t he effects of annoyinglow-frequencyrecord" noise" withthis simp le ci rcui t.JosephM. Gorin52 EXPANDEDSCALEVOLTMETERHere's a wayforyoutoaddsuper accuracytoyouranalogvoltmeter. T.J. Byers66 SYNTHESIZED RF GENERATORPart 3. Howtocomplete. calibrateanduse t heProgr amma-2. GaryMcClellan4 HOMEELECTRONICSTomor row' s newsandproductsint hisquicklychangingindustry. DavidLachenbruch22 SATELLITEITELETEXT NEWSThelatest happeningsincommunicati onstechnol ogy . GaryArlenTelevision has already revolu-tion ized the way we live. A secondTVrevolut ion isnowunder waywith the introducti on of video-tex. Videotex will allowyou touseyourTVset toreceivei nfor-mation on almost any subjectyou desire-news of all sorts.local special events , and evenrestaurant menus. Inaddition. itwill permit youtotransact muchof yourpersonal business-shop-ping , banking , etC.-fromhome .For a look at what 's in sto re, turntopage43.57 ELECTRONIC TEMPERATUREMEASUREMENTWhat youneedtoknowtobui ldyour own electronict her mometers. JosephJ. Carr60 SUPERSCOPE'SPIANOCORDERThe pl ayer pi anoisn't dead-it' s nowelectro nic! WarrenBaker78 HOBBYCORNERRemot e weat her-sensi nginstruments.Earl " Doc" Savage,K4SDS90 NEW IDEASA batterysaverfor your car.VIRTUALLY ALL STEREO records contain very -low-frequencysignalsthatcanbeannoyingtolisten to and , potentially, can damage yoursound system. A low-frequencyliIter will re-movethosesignals, and plansfor such ade-vicebeginonpage47.COMPUTERSVIDEOAUDIOEQUIPMENTREPORTS82 COMPUTERCORNERLookingfor a computer. Kathy Tekawa72 ONE VCR-MULTIPLE TVSETSHowtouse anMATV system todi stri but e programs fromyour VCR. JamesE. Kluge92 SERVICE CLINICNewshutdowncircuits. JackDarr93 SERVICE QUESTIONSR-E'sServi ceEditor solves technician'sproblems.63 CBS' CX NOISE-REDUCn ON SYSTEMHowCBSproducescompandedrecordsthatcanbe pl ayedwith or without a decoder. LenFeldman26 Creat ive Electronic sESR Meter26 RealisticModel TV-20High-FidelityTV Tuner28 ChromaticsChromaChimeElectronicDoor Chime36 UngarModel 4000 Hot VacDesolderingSystemSOMETIMES IT'S DESIRABLE to connect severalTVsets tothesame VCR. If youhavea master-antennasetup, youcanuse it for that purpose.Several methodsfortak ing advantageof yourMATV facilities are described, start ing onpage72.Radio-Electronics, (ISSN 0033-7862) Publi sheo monthl yby GernbackPubli cat ions. Inc.. 200 Park Avenue South .NewYork. NY10003. Second-ClassPostagePaidatNewYork. N.Y. and additio nal mailin g offi ces. One-yearsub scripti onrate: U.S.A. andU.S. possessions. $13.00.Canada . $16.00. Ot hercou ntries. $20.50. (Cashordersonly. payable i n U.S.A. currency.) Single copi es$1.25. 1981 by Gernsback Publi cati ons. Inc. All rightsreserved . Print edinU.S.A.Subscription Service : Mail all subsc ription orders.changes. co rrespo ndence and Postmaster Noticesofundelivered copies (Form3579) to Radio-Electr onicsSubscript ionService. Box 2520. Boul der. CO 80322.Astamped self-addressedenvelope must accomp anyall submitted manuscripts and/or artwork or phot o-9raphs if their returnis desired should they be rejected.We disclaim any respo nsibil ity for the loss or damageofmanuscripts andl or artworkor photographswhil einOUf possessionor otherwise.24 Letters102 Market Center96 NewLit84 NewProducts6 What'sNews16 Advertisi ngandSal esOff ices136 AdvertisingIndex98 Books104 ComputerMarket Center16 Edit ori al137 Free InformationCardDEPARTM NTSzo0-60100200 l K 2KFREQUENCY-Hz___ RECORONOISE- 1 1J1J 1IH111111 1/3 OCTAVEBANO SPECTRUM _1\ -- AWEIGHTING(APPROXIMATE30PHON LOUONESSCONTOUR)' I,~It.:~.....0,-equ al tothat of aconventi onal (unen-cod ed) record. Ifanencodedrecordisplayed back wit hout the benefit ofacorresponding expansion circuit.changes in the dynamic gain of themaster tape ' snoi setendtobemaskedbv the continuo us record-surfacenoise.making themall but inaudible to thelistener. That effect is aided bycare-fully choosingthe time constants thatareusedinthe controlcircuitryof thesyste m' (moreon that later).Figure 2also shows t he expans ioncurve of the system. That curveis com-plementary to the compression curvesothat asignalthat undergoestheen-tireprocess of compress ion and expan-sion will match the original programsource closel y. but with 20-dB lessnoi se. For proper operation. the sys temrequi res reasonabl y acc ura te trackingby the phono stylus . Not all phonocartridges deli ver exactly the samelevel of output for a given stylus velocityin a record grooveand for that reason itispossibleforthereproducedsignal todiffer somewhat from the sourcematerial.Acc ording toCBS. however. that ef-fect hasbeenfoundtobevirtuallyun-noticeable for mismatches of up to 6 dBbetween the ex pansion and compres-sion curves. Some of the ex expande rsonthemarket offer a-calibra tion adjust-ment sothe y can beusedwit h virtua llyanystereoca rt ridge.50INPUT- dB-80 -60 - 40-120FIG. 2-COMPRESSION AND EXPANSIONcurves for the CBS noise-reduction system.Thecurvesarecomplementarysothat apro-cessed signal will closely match theoriginalprogramsource.FIG. 1-WHILERECORDSURFACE-NOISEIsgreater at bassand treble frequencies, the sen-sitivityof thehumanear Isreduced Inthoseranges. The overall subjective response Isessentially flat.ce 40"CIu:30>W....l 20w>f= 10:s~ 0(/JoZoa:I-oUJ...JUJ6is-ca:64042N3906R1910K-'Wor-Rn4.7K- ISVRI6 03IS0K 2N3904IC2-b1/4LF347 DBC40"1 '1SVRIS... IS0KVH16r - --- - - - - --- -- - - - ,'SIIC3.b I-"'-........- , SVI 1/2 LM13700 1 R4B141 I 68K-----'-'-;- 1 - Ir-_ _1R29 1 I C9 RIGHTIK L - - - - - - - - - - - - J6.B.F OUTPUT12 10 9 R31 R41S. IKlOOK- ISVR9

+lSV+ISV012N39D4+15V02IN4S803lN4S804lN4S8- ISVR4633KR4901 lMEGl N4S8 FEEO.THROUGHr+--.t.... R710Kr----:--:=--4R8 0510K IN4S8R2410K I KR3210KFIG. 4-THE OUTPUT of the time-constant circuit is buffered by IC2-c, and t hen summed by IC2-d and04, avoltage-to-current converter.Thecontrol current for thevarlable-galnamplifiers(IC3-a andIC3-b)Is takenf romthecollector of 04.not removed, audible distortion willoccur inthe t ransient. Listening testshave confirmedthat the humanear isnot particularly sensitive tosuchdis-tortion if its duration is less than 30milliseconds. So filter 3 passes only thefirst 30 milliseconds of the attack-transient. If the signal continues forlonger than 30 milliseconds, filter Itakes over.It is a low-pass filter with a30-millisecond time constant. When asudden transient signal occur s, thatfilter will ignorethesignal for thefirst30 milliseconds, but will allowwhatcomes after that lengthof time to pass.It will also remove nearly all of theripplefromsuchsignals.Filter 4 is usedto controlsudden de-cre asesin signal levels. If such suddendecreases werenot controlled , pumpingor "breathing" would be heard. It' sbeendemonstrated that thehumanearis not sensitive to pumping during arapiddecay of not morethan 200 milli-seconds . Filter 4allows thecircuit totrackthe dec ay for that length of time.Afterthat period, at thetimewhen thelistenerwould begin to notice the decay.control is takenove rbyfilter 2. Thatfilter. thank s to its two-second timeconst ant,keeps the noise-level relati ve-ly steady.According to CBS engineers, theoverall combination of the four filtersallows their systemto operat e effec-tivelywithmusicsignals thatwouldbecon siderably more difficult for ot hernoisereduction or companding systemstohandle.Anobvious advantageof thesystemis thecompatibility claimed for it. If theencoded version of a given piece ofmusic isindeedvirtuallyindistinguish-ablefromtheconventionalpressing ofthe same materi al , CBS Record s, oranyoneelseusingthe exsystem, willhave to produce only one type ofrecording in the future . The casualmusic listener canthen listen to thatrecordingonhisordinaryphonographor hi-fi component- systemas he nor-mally would . The more seriousaudio-phile. on theother hand, will be able toadd a relati velyinexpensiveexpanderaccess ory to his stereo systemandenjoy thefull benefit of an additionaldBofnoisereduction .It is inter estingtonote that CBShasproposedthat its new companding sys-tembeincorporatedin any multi-chan-nelTV-audiosys tem that mightbe ap-pro ved by the FCC in the futur e.Transition to stereo audio (or multi-lingual audio), regardless of whichofthe proposed sys tems is chosen. isboundtoresult in some degradationofaudio signal-to-noise ratios for manyviewers wit hinaTVstation' s servicerange. The incorporati on ofa compand-ingsys tem at theoutsetwouldhelptooffset that degrad ation. Furthermore .sincetheCBSsys temis claimedtobecompatible, those viewers who con-tinue towatchthefuture " stereo"TVprograms over the ir mono TV receiverswould not not ice any difference inaudio quality . Other noise reductionsys tems that have been suggestedforTV stereo-audio include a modified,compatible formof thelinear dbx com-pandin g system and the newly de-veloped Dolbyenoise-reductionsys-tem(see the MayissueofRadio-Elec-tronics) fromDolbyLaboratorie s. R-Ezo