pages of Electronics Features and Projects Radio 96 mat changes your every -day life! 48409 $2.50 -US Electronics $2.95 -Canada
6 174
Flat Panel Color TV Thanks to a new type liquid -crystal display, pocket -sized Color TV's are here at last! Cellular Mobile Phones All about the communications system that is revolutionizing the mobile telephone industry!
All about... Build the... PARTS SONIC MOTION DETECTOR RESISTORS AND CAPACITORS Test reports on... How to select the best type HOBBY/LAB PRODUCTS for your project
OPTOCOUPLERS What's new in... How to interface digital circuits BATTERIES to the real world
CMOS ANALOG SWITCHES Circuits for... An electrical signal replaces the knob and toggle CMOS CLOCKS
A Buyers' Guide to...GENBACKON SATELLITE TV RECEIVING What you should know about buying a satellite -TV station before you spend your first dollar!
I 65 rr Stereo Sound for TV 0 1 1 11 111 11 rr Scanner Antenna Plans rr Build a FET Audio Amplifier 71896 48409 You touch. Ir holds.
gets you the world's first It's the top model in the world cham- FROM THE WORLD LEADER 129 handheld digital/analog pion Fluke 70 Series line - the first IN DIGITAL MULTIMETERS. multimeter with "Touch Hold:' industrial quality autoranging multimeters The Fluke 77 to combine digital and analog displays. Its unique "Touch Hold"** function These tough, American -made meters fea- automatically senses and holds readings, ture a three-year warranty and 2000+ leaving you free to concentrate on posi- hour battery life. tioning test leads without having to watch So call now for the complete story on the display. the Fluke 77 with "Touch Hold:' Because Then, when you have a valid reading, it if you don't deserve the world's first, who signals you with an audible beep. in the world does? FLUKE FLUKE 75 FLUKE 77 The Fluke 77 is perfect for those test For the name of your distributor or a $85* $99* $129* Analog/digital display Analog/digital display Analog/digital display situations where accessibility is a problem, free brochure, call our toll -free hotline Volts, ohms.10A, diode Volts, ohms. 10A, mA, Volts, 3hms, 10A, mA diode test is needed for anytime 1-800-227-3800, Ext. 229. test diode test or when extra care critical Autorange Audible continuity Audible continuity measurements. From outside the U.S., call 1-402-496-1350, Ext. 229. 0.7% basic dc accuracy Autorange/range hold "Touch Hold" function 2000+ hour battery life 0.5% basic do accuracy Autorange/range hold 3 -year warranty 2000+ hour battery life 0.3% basic dc accuracy 3 -year warranty 2000+ hour battery life 3 -year warranty Multipurpose holster
* Suggested U.S. list price. effective July 1, 1984. ** Patent pending. FLUKE IN THE U.S. AND NON -EUROPEAN COUNTRIES: John Fluke Mfg. Co.. Inc., PO Box 09090, M/S 250C, Everett, WA 98206, Sales (2061 356-5400 Other. (2061 347.6100. EUROPEAN HEADQUARTERS: Fluke (Holland) BV., P0. Box 2269. 5600 CG Eindhoven. Tha Netherlands. (0401 458045, TL%: 51846 © Copyright 1985 John Fluke Mfg. co, Inc. All rights reserved Ad No 4701-77
CIRCLE 210 ON FREE INFORMATION CARD EDITORIAL AlI NUAL STAFF Hugo Gernsback (1884-1967) founder Putting Together the 1986 Edition M. Harvey Gernsback, editor-in -chief Larry Steckler, EHF, CET, publisher Art Kleiman, editorial director
EDITORIAL DEPARTMENT
Julian S. Martin, editor Brian C. Fenton, Each year I am given the task to assemble the Radio -Electronics technical editor Annual. Each year I say, "It's a piece of cake!" Each year I am totally Robert A. Young, associate editor amazed at the vast store of quality articles that have appeared in the Carl Laron, WB2SLR, previous 12 issues of Radio -Electronics. And, each year I have to associate editor squeeze my final selection of about 250 pages of top-notch articles into 96 pages that are available for me to use. Byron G. Wels, editor associate Jack Darr, CET, service editor What to do about it? Get cracking on some basic research! I chatted with the editors and discovered which articles got the biggest play in our Robert F. Scott, semiconductor editor reader mail and phone calls. Next, I spoke to our circulation chief who sorted out the compliments from the subscription orders. Of course, my Herb Friedman, communications editor personal selection had something to do with the final selection of articles. Earl "Doc" Savage, K4SDS, It all sounds easy, but the proof in the pudding is the eating. No, don't hobby editor actually chew the pages of this Radio -Electronics Annual; instead, Bob Cooper, Jr. satellite -TV editor digest the contents by carefully reading those articles that appeal to you. Robert Grossblatt, circuits editor I dare say that the bulk of those supplied will catch your interest. In fact, there's a good possibility you'll be one of those readers who writes to us David Lachenbruch, contributing editor telling us that you read the Annual from cover to cover. If you do, you'll maké my day! Mark J. Robillard, robotics editor I'm a project builder by choice, so you can expect that this issue has a Bess Isaacson, editorial assistant few projects to excite you. You will find a sonic motion detector, and my PRODUCTION favorite, the high -power FET audio amplifier. If you are a scanner buff, I DEPARTMENT have three hot antennas for you to build. Ruby M. Yee, production manager
And, I did include exciting features on "What's New in Batteries," "Flat - Robert A. W. Lowndes, panel Color TV," "Stereo Sound for TV," and a whole bunch more! Enjoy editorial production this issue of Radio -Electronics Annual 1986. I did! Karen Tucker, advertising production Geoffrey S. Weil, production traffic
CIRCULATION DEPARTMENT
Jacqueline P. Weaver, circulation director Rita Sabalis, Af. 4-.) assistant circulation director Jacqueline Allen, circulation assistant Julian S. Martin, KA2GUN Editor ADVERTISING SALES Arline Fishman BUSINESS AND EDITORIAL OFFICES MIDWEST/Texas/Arkansas/Okla. advertising coordinator Gernsback Publications, Inc. Ralph Bergen Shelli Weinman 200 Park Ave. South, New York, NY 10003 Radio -Electronics advertising associate (212) 777-6400 540 Frontage Road-Suite 325 Lisa Strassman Chairman of the Board: M. Harvey Gernsback Northfield, IL 60093 credit manager President: Larry Steckler 312-446-1444 Donna Sala credit associate SALES OFFICES PACIFIC COAST/ Mountain States Naomi Matten advertising assistant Marvin Green EAST/SOUTHEAST Radio -Electronics Stanley Levitan 15335 Morrison St.-Suite 227 Radio -Electronics Sherman Oaks, CA 91403 200 Park Ave. South 818-986-2001 New York, NY 10003 718-428-6037, 212-777-6400
1 Padin- Electronict 1986
CONTENTS PAGE
SPECIAL TVRO BUYER'S AND INSTALLATION GUIDE 49 Know before You Buy-we cover what you need to know before you go out and make your purchase 56 Installing Your TVRO-take the guesswork out of TVRO installation with this step-by-step guide TECHNOLOGY
13 What's New in Batteries-how do you use the right battery for your project? Just how good are lithium batteries? This article answers those and other questions
27 Stereo Sound for TV-here is an in-depth look at the FCC decision on multi -channel television - sound broadcasting and what it means to you in the near future 37 Flat -Panel Color TV-thanks to a new type of LCD display, pocket -sized color TV's are here 78 Cellular Mobile Telephones-all about the new system that is revolutionizing mobile telephone communications CIRCUITS AND COMPONENTS 40 CMOS Clock Circuits-a multitude of multifaceted and inexpensive CMOS squarewave generator circuits 43 Selecting the Best Resistor and Capacitor-finding the correct value for your project is the easy part-we point out how to select the type and characteristics that may make your project go 63 All About Optocouplers-a look at how to use optocouplers to interface digital circuits to the real world 67 CMOS Analog Switches-these IC's offer an excellent solution to what used to be a very complicated problem CONSTRUCTION PROJECTS
21 Tape Streamer for Your Computer-can a cassette tape be an alternative to a disk drive? 34 Sonic Motion Detector-no alarm system is complete without a motion sensor
71 Three High -Performance Scanner Antennas-pull in those signals that you have been missing with one of these easy-to -build designs
81 High -power FET Audio Amplifier-a high-performance, high-fidelity stereo amplifier
DEPARTMENTS
1 Editorial-putting together the 1986 edition Equipment Reports 4 Vidicraft Detailer Ill Image Enhancer 8 Global Specialties Model 1301 Power Supply 6 Cardco Card/? Universal Printer Interface 9 Alden Model 9321 Weatherchart Recorder
handling Radio -Electronics Annual is published yearly by Gernsback Publications, Inc., 200 Park Avenue South, New York, NY 10003. Single copies $2.50 plus $1.00 postage and for U.S.. Canada and Mexico. U.S. funds only. All other countries add $2.00 01985 by Gernsback Publications, Inc. All rights reserved. Printed in U.S.A. and technological As a service to readers, Radio -Electronics Annual publishes available plans or information relating to newsworthy products, techniques scientific and for the safe and developments. Because of possible variances in the quality of materials and workmanship used by readers, Radio -Electronics Annual disclaims any responsibility proper functioning of reader-built projects based upon or from plans or information published in this magazine.
2 We've Got It All ! Amateur Books*Funway Kits*Tools *Microphones* Multimeters Computer books*Speakers*Data Books*P A Equipment*Car Hi-Fi Amateur Books*Funway Kits*Tools Microphones* Multimeters Computer books*Speakers*Data Books*P A Equipment*Car Hi-Fi Antennas & Accessories * Batteries Fuses* Plugs*Sockets* Panel Meters*Value Pack Relays*Cables Project Boxes*Test Gear*Home Security*Ham Radio*Car Alarms PCB's* Breadboards*Computer Peripherals*Soldering Irons Heatsinks*IC'S* Resistors Capacitors* Phones *Intercoms Chokes* Filters* Power Supplies Transformers*Antenna/Rotators*CB Radar*Detectors*Scanners *Calculators All At Amazingly Low Prices! FIND OUT MORE Send S2(Plus shipping)for our huge 132 page color catalog. Includes $2 bonus coupons, redeemable off your first order.
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City º * * State Zip > NOW OUR 17th YEAR - OVER 60 STORES IN 3 COUNTRIES Stores at San Jose, Berkeley and Redwood City KepCbdz y Kepro Circuit Systems, Inc At Home Professional Quality Fine Line PCB's. Introducing an easy, inexpensive, step by step method for the home production of pro- fessional quality printed circuit boards without QUIPMENT a major equipment investment-KeproClad, by Kepro, makers of quality industrial equip- ment and supplies. KeproClad was designed for the home user who needs professional results with: A Simple Circuit Board; Use KeproClad unsensitized copper - clads. These boards come in 2 popular REPORTS sizes with 1 sided foil, a marking pen, all for a suggested retail price as low as $3.50. Vidicraft Detailer Ill A Fine Line Detailed Board; Use KeproClad photosensitized cop- Image Enhancer perclads. Available in 2 sizes with 1 or 2 sided foil. These copperclads use the latest technology of negative acting dry - Improve your VCR's film photoresist. This material is rug- FREE INFORMATION CARD ged, yet holds extremely fine detail. It performance with this CIRCLE 225 ON comes with a premeasured amount of versatile accessory developer and sells for as little as $3.90 (suggested retail). Other KeproClad products such as a photo reversal kit for making negative film, etch, tin IT USED TO BE THAT THE WORD "VIDEO" hance a tape of a quality over -the - plating solution and photoflood lamps are all than TV to air signal, dramatic increases in available at your local distributor. (For the meant nothing more distributor nearest you, call or write: most people. But, since the advent picture quality wil result. On the VCR, all that has changed. And other hand, used with -a third -gen- KEPRO CIRCUIT SYSTEMS, INC. of 630 Axmlnister Drive., Fenton, MO 63026-2992 with those changes has come a eration VHS tape recorded at the In MO 314-343-1630 Toll Free 800-325-3878 change in what we are willing to machine's slowest speed will pro- accept in terms of video quality. duce minimal results. CIRCLE 202 ON FREE INFORMATION CARD These days, very few are content One reason that the law of di- to "just accept" the video quality minishing returns holds so strong- provided by our home set-ups. In- ly when it comes to video is that ELECTRONIC stead, we are always seeking ways the same high frequencies that to improve the image that is dis- hold so much of the picture detail COMPONENTS played on our monitors or re- also contain much of the inter- ceivers. One way to achieve a ference that is commonly called noticeable improvement is with a snow. Thus, when you enhance video amplifier or enhancer. detail, you also enhance snow. In Those units increase picture detail order to minimize that increase in and sharpness by boosting or am- snow, most video enhancers are plifying the higher frequencies in equipped with some sort of noise - a video signal. The high frequen- reduction system. The one con- cies is where much of the fine de- tained in the Detailer III is two- tail of a video picture is located. fold. We recently looked at the One part of the noise -reduction Detailer 1/1-one of the newest system in this unit is Vidicraft's video enhancers from Vidicraft VNX circuit. That noise -reduction (0704 S.W. Bancroft St., Portland, circuit supresses certain low -am- MANUFACTURERS OF QUALITY OR 97201). plitude, high -frequency enhance- ELECTRONIC COMPONENTS ments. As such, it seems to BATTERY CLIPS 8 HOLDERS CABLE SETS CONNECTORS CAPACITORS The Detailer III perform the exact opposite of the DISPLAYS LEDs FUSES JACKS & PLUGS The Detailer III is a video en- unit's enhancement function. But KNOBS LAMPS POTENTIOMETERS the VNX system uses a different RF COILS RELAYS RESISTORS hancer that is designed to improve SWITCHES SEMICONDUCTORS SPEAKERS the performance of VCR's, video set of thresholds. The result is a TEST EOUIPMENT TRANSFORMERS 'TOOLS cameras, and videodisc players. reduction of snow at the expense WIRE & CABLE OVER 15,000 DIFFERENT ITEMS IN STOCK! As with all other such units, this of some of the increased detail, Sales and Ord., Desk Phone end Moil enhancer's performance is greatly but the overall result is an im- Open Iron, 600. m.I PST) Orden Welcome Catalogs Moiled TER MS. C.O.D.. Viso. influenced by the quality of the proved picture. MotlerCharg Oattid USA (Open ovnl. A.adobl) Send $1.00 material with which it is used. In The second noise -reduction sys- other words: The better the source, tem is "black noise reduction." MOUSER ELECTRONICS the results. When, for That system reduces the level of 11433 W00DSIDE AVE SANTEE. CA 92071 the better PHONE (619) 449.2222 TW% 910 331-1175 instance, the unit is used to en - enhancement in the dark areas of
4 CIRCLE 204 ON FREE INFORMATION CARD the picture. In those areas, in- creases in detail are not par- CABLE -TV ticularly noticeable, but increases in snow are. One interesting feature of the Detailer Ill's enhancement system is the SPLIT SCREEN function. That OR BEAT AESÁNEPRICES allows you to use a front -panel H control to split the picture into en- WE'LL MATCHAIL OR WHO hanced and unenhanced regions. That allows you to easily examine ApVERTISEp= the effect of the enhancer on the video signal. Other features of the unit in- clude a four -input switching sys- BONANZA! tem and a distribution amplifier. SINGLEUNIT Both features are capable of han- ITEM D0-UN T dling stereo audio as well as video. PRICE PRICE RCA 36 CHANNEL The unit's input and output con- CONVERTER (CH. 3 OUTPUT ONLY) 29.95 18.00 ea. PIONEER WIRELESS CONVERTER (OUR BEST BUY) nectors are all located on the rear 88.95 72.00 ea. LCC-58 WIRELESS CONVERTER 92.95 76.00 ea. panel. Included among those are JERROLD 450 WIRELESS CONVERTER (CH. 3 OUTPUT 105.95 four video ONLY) 90.00 ea. inputs, four stereo (or SB ADD-ON UNIT 109.95 58.00 ea. mono) audio inputs, four video BRAND NEW - TRIMODE UNIT FOR JERROLDS Call for specifics MINICODE (N-12) 109.95 58.00 ea. Vidicraft Detailer III MINICODE (N-12) VARISYNC 119.95 62.00 ea. OVERALL MINICODE VARISYNC W/AUTO ON-OFF 179.95 115.00 ea. PRICE M-35 B (CH. 3 OUTPUT ONLY) 139.95 70.00 ea. EASE M-35 B W/AUTO ON-OFF (CALL FOR AVAILABILITY) 199.95 125.00 ea. OF USE MLD-1200-3 (CALL IF CH. 2 OUTPUT) 109.95 58.00 ea. INSTRUCTION INTERFERENCE FILTERS - CH. 3 24.95 14.00 ea. MANUAL JERROLD 400 OR 450 REMOTE CONTROLLER 29.95 18.00 ea. PRICE/ ZENITH SSAVI CABLE READY (DEALER PRICE BASED ON 5 UNITS) 225.00 185.00 ea. ALUE SPECIFY CHANNEL 2 or 3 OUTPUT Other products available - Please Call 1 2 3 4 5 6L7 8 9 10
a }\t Quantity Item Output Price TOTAL # Geh- e Channel Each PRICE outputs, and four stereo (or mono) audio outputs. Also on the rear panel are three accessory loop input/output connectors. Those California Penal Code #593-D forbids us SUBTOTAL allow additional video and audio from shipping any cable descrambling unit Shipping Add' to anyone residing in the state 00 accessories, such as a video pro- of California. COD & Credit Prices subject to change without notice. cessor or a stereo synthesizer, to CardsCards - Add 5% be easily interfaced with the sys- PLEASE PRINT TOTAL tem. Any accessory placed in the Name loop will process any input se- Address City lected. Input selection is done State Zip Phone Number ( from the front panel. The selected 1 Cashier's Check Money Order COD Visa Mastercard input is indicated by a front -panel Acct # LED. Exp. Date Signature The Detailer III is an extremely versatile device. One indication of FOR OUR RECORDS: DECLARATION that is the number of interconnec- OF AUTHORIZED USE - I, the undersigned, do hereby declare under tion schemes presented in the penalty of perjury that all products purchased, now and in the future, will only be used on cable TV systems with proper authorization from local officials or cable company officials in unit's manual. Set-ups with as accordance with all applicable federal and state laws. many as eight permanently con- Dated nect VCR's are outlined. Signed Speaking of the manual, it does an excellent job of showing you Pacific Cable Company, Inc. how to get the most out of the 73251/2 RESEDA BLVD., DEPT. # unit. RESEDA, CA 91335 All of the numerous hook-up (818) 716-5914 schemes are illustrated in No Collect Calls (818) 716-5140 painstaking detail, and front -panel IMPORTANT: WHEN CALLING FOR INFORMATION settings are both described and Please have the make and model # of the equipment used in your area. Thank You
5 --J JAM IT! 1 -5 - shown. Newcomers to video have etc) on the unit are provided. Ad- Even the Very Best Radar Detector not been forgotten by the man- ditionally, only rudimentary trou- Can't Protect You from the Newest Radar ufacturer; sections covering such bleshooting information is basic topics as the differences be- provided. tween the various types of con- On the whole, we are very pleas- nectors used in video set-ups have ed with the Detailer III. Its flex- been included. Unfortunately, as ibility and performance should it at the top of any serious vid- THE ULTIMATE IN RADAR PROTECTION is the case with many similar put pieces of equipment, those more eo hobbyist's shopping list. The Radar Jammer: Compact under -dash unit causes speed radar guns to read out a percentage of your true speed, or technically inclined have been unit; which is covered by a two whatever speed you dial in. Or, new "SCRAMBLE" mode will re- prevent radar from obtaining any reading. Activated by Whis- overlooked; no technical details year warranty, has a suggested tler, Escort, or other detector. Best defense against instant on tail price of $349. radar. Operates on both X and K hands. WARNING; This (theory of operation, schematic, device is not legal for use against police radar, and is not FCC approved. Transmitters; The heart of the jammer is the microwave os- cillator (transmitter). ln the past, these were very expensive, and limited to only about 100 milliwatts of power. We now have our own Low Cost, High Power Transmitters up to 300 Cardco Card/? Universal milliwatts or more. Please call for prices. Radar Defectors: We highly recommend using a remote de- Printer Interface tector that is mounted so that nothing is readily visable to either the police, or thieves. (A dash mount detector is an invitation to thieves and an irritation to police!) We agree with Motor This interface lets you use Trend and Autoweek that WHISTLER SPECTRUM is the best detector available. and we know of no other remote de- almost any printer with tector that is even in the sane LEAGUE as the SPECTRUM REMOTE. Order the best for yourself now. (Our detectors are your Commodore 64. already modified for direct connection to the jammer.) ORDER TODAY -MONEY BACK GUARANTEE Complete Literature & Plans Pkg. 5 14.95 CIRCLE 228 ON FREE INFORMATION CARD D Set of Circuit Boards 40.00 D X and K -band Microwave Oscillators (Transmitters) Call Whistler Spectnun (modified for use with Jammer) 259.00 D Whistler Spectrum Remote (modified) 259.00 Modify your Spectrum for use w%jammer 55,00 BECAUSE OF ITS HIGH PERFORMANCE Card/?'s DIN connector is attached CALL or send the following information: 64 to an adapter that slips over the Items Ordered Name Shipping Address and low cost, the Commodore Payment: Check, Money Order. VISA or MC (include has become one of the most popu- computer's edge connector that card number, expiration date, and signature) SEND TO. Oregon Micrnwav, Inc.'. 9515 S.W. Baróar Blvd. MI095 lar computers for home -and -fam- provides power and signal I/O for Portland, OR 971,19 ORDI,R LINE, 1503162bó764 the Datassette (cas- Po i Design Cn. ily and school use. Unfortunately, Commodore its matching line printer leaves a sette) tape recorder. The wire CIRCLE 212 ON FREE INFORMATION CARD lot to be desired when it comes to provides the 5 -volt power supply word processing of any kind. In for the interface and still allows the fact, there is no low cost formed - Datassette to be used. Be an FCC character (daisy -wheel type) or The interface plugs directly into high -quality dot-matrix printer the Centronics type connector on presently available for that com- the printer. (An earlier version of LICE N SED puter. the Card/? interface-called the ELECTRONIC TECHNICIAN! The way to get high quality Model A; the model we are de- printouts from the Commodore 64 scribing is the Model B-was (or VIC-20) is to use one of the larger and had a ribbon connector Earn up to inter- between the cabinet and the $30 an hour better printers and a Card/? and more! face, a device that lets you use a printer connector.) Its operation is Centronics -type parallel printer in completely automatic. When the
Learn at honte in spare time. place of a Commodore printer. computer is told to output to the No previous experience needed. printer, the interface converts the The Card/? Commodore's unusual ASCII out- No costly school. No commuting to class. ASCII of the The Original Home -Study course pre- The Card/? interface from put to the standard pares you for the "FCC Commercial Radio- Cardco, Inc. (313 Mathewson, printer. As far as the computer is telephone License". This valuable license Wichita, KS 67214) is priced at $69. concerned, it "sees" a simulated of exciting is your "ticket" to thousands The unit consists of a small, light- Commodore printer. jobs in Communications, Radio-TV, Micro- measures To avoid problems caused by dif- wave, Computers, Radar, Avonics and weight plastic box that more! You don't need a college degree to approximately 31/8 x 3 x 7/8 inches ferences in response to ASCII con- qualify, but you do need an FCC License. with a Centronics -type connector trol codes between the computer No Need to Quit Your Job or Go To School on one end and a cable on the and the printer, the interface auto- This proven course is easy, fast and low other end that terminates in a DIN matically makes the required con- S, cost! GUARANTEED PASS - You get your when rn FCC License or money refunded. Send for connector that matches the serial versions. For example, FREE facts now. MAIL COUPON TODAY! output connector on the Com- listing a program, the Com- modore computer or its disk drive. modore's CHR$(19) "home cursor" ZcommanD PRODUCTIONS (When using a disk drive, the command would stop an Epson FCC LICENSE TRAINING, Dept. 90 is dead in its tracks because w P.O. Box 2223, San Francisco, CA 94126 printer connection moved from printer tr Please rush FREE details immediately! the computer to the disk drive.) A CHR$(19) is the Epson -printer NAME single wire trailing from the command for "stop printing." To ADDRESS CITY STATE .ZIP 6 J avoid that hassle, the interface au- Ca rdco Card/? CHR$(15) functions is because tomatically changes the listing Commodore uses CHR$(15) to OVERALL from CHR$(19) to an "[HM]" PRICE cancel the expanded print mode, (home cursor). Other ASCII codes EASE but other printers use CHR$(15) from 1 to 31 and 128 to 160, that OF USE for condensed print with might be inconsistent with the INSTRUCTION CHR$(20) used to cancel the ex- MANUAL non -Commodore printer com- panded mode. By automatically mands, are similarly PRICE/ designated VALUE swapping CHR$(15) for CHR$(20), within brackets. For example, 1 2 3 4 5 6 7 8 8 1Q the Commodore command to CHR$(150), which is the Com- "cancel expanded print mode" modore command for the color e°°` ie 0°6 will work properly with just about "light red," is listed as "[LR]". any non -Commodore printer cur- The interface normally defaults rently on the market. to the "normal printing mode," that can function with non -Com- For listings, user written pro- which is upper case only with au- modore printers, and that can ac- grams, and word processing, the tomatic linefeed after carriage re- cess the advanced graphics fea- Card/? works as claimed, doing an turn. A short software command tures of certain printers. A semi- effective job of emulating a Com- can be used to temporarily or permanent selection of the graph- modore printer, while providing "permanently" lock (until power ics mode can be made by an inter- the enhancements of the higher - reset) the interface to provide up- nal DIP -switch on the printed - performance printers. The few per case only with no line feed, circuit board. problems that arise, such as upper and lower case with no line Three other DIP switches on the dropped spaces between words feed, upper and lower case with PC board are used to automatically and stepping of the printer automatic linefeed, graphics exchange the function of CHR$(15) through each blank space (no mode with line feed, or graphics and CHR$(20); enable or disable character) on a line comes about mode with no line feed. software selection of automatic through some off-the-wall pro- The graphics mode has the abil- linefeed after carriage return, and gramming used in some commer- ity to pass any character string to enable or disable the ASCII correc- cial programs -even some better the printer unchanged. It's pri- tion described above. quality software. Fortunately, pro- marily intended for use with word The reason for the automatic ex- grams for the Commodore com- processors and other programs change of the CHR$(20) and puters are in BASIC, so it's
Pots -1 Meg, Linear Taper . 5/1.00 74SC374-D Type Flip -Flop. Non/Inv Motion 506 Central Ave. Detector Bds (Inc IC-$2) 7/10.00 745C533 -Transparent Latch Inverted Mot Det (IC Only-UL N22324) 3/82.20/10.00 74SC534'D Type Flip -Flop. Inverted Westfield. N.J. 07090 Project Box/Lid For Detector 1.95 74SC540-Octal Buffer/Line Driver -Inv (201) 6544008 A Miniature Speaker For Detector ..25 74$C541 -Octal Buffer/Line Driver -N/1 Extensive Construction Article For Oct. Si 74SC563-Transparent Latch. Inverted N Knobs 15/1 00 74SC564-D Type Flip -Flop. Inverted ÄRTO Ammeter (0-15 A.0 Amperes/. 4.95 74SC573'Transparent Latch Non/Inv M Volt/OHM ter.MeVMN MT 10-1K OHM, 74SC574'D Type Flip Flop Non/Inv O -300y.. 2 95 Cods For Radio Elec's Feb. 84 7 Data Book For All Above 's 2 50 TV Segment Display) 3 CommonCathl 15 6V Miniature Gear Motor Project, Toko 8'S T-1, T-2, L1 (/2uH) 7 Segment Display(.6" .50 Common Ann) 65 RFChokes-1.8uh, 8.2uh, 12uh, IV 8 L-2 (.071 uH) Complete Set Of All Te State LED's 3/1 00 22uh-10/1.00 Cypher Micro -Controller Kit -$119.50 22/44 Pin Edge Card 4 MHz 8 -Bit Microprocessor Jumbo Red LED's -Diffused Lens, Prime (T4 Connector 50 34 Pin Connector(For Drives) (NAT 1 NS8073) MC 1330- Prime (Moto) 2/1 00 All 100% Prime -15/51,100/$6. 1,000/$57 50 W/Hood... 75 BNC "T' Connector (UG-274) .. 95 Control Basic Interpreter On -Chip BFO-85 Transistor 1 50 LED Mounting Clips & Rings. 15/1 00 Mixed Connector Asst . 10/1.00 Auto -Start Operation At Power -On Disc Caps .001 of . 20/1 00 Texas Inst/s9944 Keyboard-Inc/Data For 1 SAMP 50V Bridge G1, TO -5 Pkgl Fast 16 74123 -Prime (Nat) 3/1 00 Pins Made When Each Key Depressed 4.95 . 50 -Bit Multiply And Divide 470uf 35V (Radial). 3/1.00 Dip Switch -12 Position 25AMP 200VBridge(Sdder Lug Term) 1.50 RS -232. Supports CRT 8 Serial Link 2/1 00 Zenith TV Replacement Special Bi -Directional 470uí 16V (Axial) 4/1 00 Dip Switch -8 Position 4/1 IC $1 Each 24 I/O Lines 18255Aí 00 221-42. 221-43, 221-45, 221-48. 221-69, RAM Memory -2K Expandable To 16K 2N3904 . 10/100 Keyboard Push Button Tops 30/1 00 221-79, 221.87.221-96, 221.104, 221.105. Eprom Memory -Expandable To 16K 2N3906 10/100 Audio . Cable. 30 Feet/1 00 221-106, 221-140 Built In Eprom Programmer. 1N914 . 40/1.00 22AWG Wire 50 Feet/1 00 2SD900 1 (Horiz Output W/Damper Diode)-2.95 Parr (Centronix) Printer Interface N4148 . 40/100 27AWG Wire 50 Feet/ t 00 2SC 1 1 728 (Toshib-Honz Output Trans) -1.95 Optional Real -Time 1 N5231 B (5.1 Clock W/Backup V.Zener Diode 5/1 00 Mini Lubricator (& Lubricant) 1 00 Winegard Voltage Regulators) Prame TO-220) 7805, Soldering Iron (20W) 4 Bay Bowtle UHF Antenna -19.50 5.50 IC Storage (Bug) Box (Holds) 30 IC's -1.75 Pay TV Hardware Installation Kit Blow Out 7812,7824.7905.7912 . -Mix or Match -3/1 00 Solder Sucker 6 50 As Low As $2.95 + $3.50 Shipping Per Unit Mica Insulators For TO Pkg. PrecisionMKFH Pots121 -220 20/1 00 Molex Pins (7 Pin/Strip)100/52. 500/$4,11986 All Kits Contain 5 F Connectors. 300 to 75 Voltage Regs 60% Prime) May Clock -Crystal 500 OHM. 2K 10K. ÓK (Unmarked. Module Controlled. Green 50K, 100K, 200K. OHM Balun. 300 OHM Terminal Block 2 Ft '5 Include Positive/Ne9 & Adjust 15/100 Display/ 12VDC/Time 500K 1M-.85 Each -3/$2 Set Switches/Data-4 95 Plher PT-t OV Hor Mt (SingleTum) Tdmmers 75 OHM Patch Cord 2 Ft 300 OHM Twin Lead. 78L08 Voltage Reg (DM 106.70-92).20/ 1 00 Rotary Switch (5 Position. 54 12531-3/1 00 100 OHM, 1K 10K 25K, 50K, 100K 4/$1 Nylon Cable Ties. And UHF Antenna PN2222A 20/1.00 Giant Alpha Numeric Display 1-1/2 X 2' Heat Sensitive Switch/150' C. 10/1 00 Model x4124-$2.95 Includes A1101 2N3055 . 50 7X5 (35 Total) Red LED Matrix/Specs-4 95 Mixed Switch Asst 10/1 00 The Above Plus 25 Feet Coaxial Cable And . 20/1 00 11 LED Bar Graph Display -2-3/4' . Rect Mixed 1 Mounting Hardware For Indoor Wall'Ceihng 15 Cent (.15) Per IC TTL Coil Ass'/ 10/ 00 LED's(Specify Red,Grn,Amb) Specs 269 Rubber Feet ..... 10/t 00 Installation 7403 7440 7495 Seven Amp(7)Tapped Transformer-Can Be All Buzzers . Model 8488642.95 Includes 01 7410 7442 74107 Wired For(7.9V,15V.18V) Reg 3/1.00 Shpg 8.95 Chip Resistor (6.8K) 20/1.00 The Above Plus 25 Feet Coaxial Cable And 7436 7450 74151 Wall Plug Transformer -24V 525mA 1 50 For Chip Resistor (470K) . _ 20/1.00 Attractive Expandable Poie'U Bolt 7437 7474 74163 6.3V 1.24 Transformer .. 1 20 7438 Chip Cap(3309f) 20/100 Easy Indoor Installation 7476 74393 12V Center Tap Transformer 2.50 Model x484543.95 Includes Ail 15 Jumbo Red LED W/Built In Resistor -30/$1 Of Cent (.15) Per IC 74LSXX Mini Audio Transformers. 10/ 1.00 MRF901(HobbyGrade-60%Good The Above Plus 65 Feet Coaxial Cable An . 10/1 00 74LS10 74LS86 74LS174 1 N4ó07 . 20/1 00 De-Soldering Braid (3S-Wickl 5 Ft 90 Ali Necessary U -Bolt Hardware 74LS20 74LS153 74LS257 1N5059 ``200V 1 Amp) 15/1 00 IC Asst ( Hobby Grade, Some Marked( -30/$1 74LS74 74LS158 74LS273 1N5060 (400V 1 Amp) 10/1,00 20 Cent (.20) Per IC CMOS Zener Diodes-20V 1W 30/1 00 MODEL 705 Digital Multimeter 4001B. 4011B, 4050B Zener Diodes -13V 1W Glass 30/1 00 20 Cent (.20) 74SCXX MC838(DTL) . 10/1.00 25600KC Crystal 50 DC Voltase 100MV to 1000V
OptoIsoiator(H11G2-6PINDIPI I Specs 40 3.579545 Color Burst Crysta I HC -181 50 Series Special AC voltage 100n, to 750V 2716 Eprom 1.45 10 Mhz Crystal . 1.95 DC Current 0.1 MA lo 10A
. AC . Current 2732 Eprom 1.95 60 Mhz Crystal 1 95 Octal Interlace Circuits 0.les to lox $519s 2764 Eprom 2.45 TO -5 Heat Sinks (Bern) 10/1.00 Equivalent To 74LSXX Series MI -Lo Resistance 0.14 to 20544 256K Dram 150ns Prime Hitachi (Ideal For TO -1B Heal Sinks (Bern/ 10/1 00 Low Power ISO-CMOS Technology Capacitance 1pF to SOME Mac Plod, Test toned voltage teasing Upgrades& Expansion Projects). 4.95 Super Sub -Mini Ceramic Caps (All 100 Short Propagation Delay NEE test translator testing 8243(1/0 Espander IC) W/Sppeeccss. 2.95 .0015uí í00V(152.. 30/1.00 Improved Noise Margins UDN 6118 (Display Dover IC -Specs) 85 00220 100V 182 30/1.00 High Current, Sink/Source Capability r UDN 6128 - 95 0027uf 100V 272 30/1.00 74SC137-1 018 Inverted Decoder. Latched UHF-TV PREAMP UCN 41 16B-OsclFreq DIV Clock IC -Specs-5/1 00330 100V 3320 30/1.00 74SC138.1 Of8 Inverted Decoder (As featured in Radio Electronics March/ IJCN 4801 (8 Chan BrMos Latch/Driven-1.00 0039uí 100V 1392 .. 30/1.00 74SC139-1 Of4 Inverted Decoder May articles, 1982) LM339 .. 45 0056uí 100V (562 30/100 74SC237-1 01 8 Non -Inverted. Latched This inexpensive antenna mounted pre. LM380(UL N2280) . 45 0082uí 100V 111822 30/100 74$C238 -t Of 8 Non -Inverted amp can add more than 25 dB of gain fo 555 Timers (TI 00 4/1 4 7uf 40V Lytic (Radial) 20/1 00 74SC239-1 Of 4 Non -Inverted your System. Lots of satisfied customers NE556 (Dual Timer -Moto) . 47 50 of 25V Lytic (Radial) 10/100 74$C240 -Octal Buffer/Line Driver -Inv repeat for high quality kit, 741 J Op Amp(Mini Dip Hi Rel Pkgl 4/1 00 1000uf 745C241 -Octal Buffer/Line Dnver N/I and orders this 185V Twist Lock 1.00 which includes all parts. PC LM1310 (Unmarked, Tested Primel 50 3200uí 50V For Power 74SC244-Octal Buffer/Line Driver-N/I component (Ideal Supplies)-1.00 BD. Case. Power Suppl yand Balun LM1889 95 5600uí 25V (Comp Grade 3-5/8 X11-3/1 00 74SC245-Octal Bus Transceiver -Non I $34.50 Assembled Version $5750 LM3900 45 1 of 50V Monolithics 10/1.00 74$C373 -Transparent Latch-Non/Inv AM/FM Radio IC W/Specs-Hobby (x2204 22uí 50V Monolithics . 20/1.00 15/1 00 Chip Caps -Set of 4, 2 Each 2 7 8 3.3pf-1 00 Tams: MICRO -MART accepts Visa MC IC Sockets .33uf 100V Dip Mylar. 10/1.00 and telephone COD's Minimum order $10.00 Shipping - U S orders, 8 Pin/ 07, 14 Pin/ 13. 16 Pin/ 15, .022 of 20011 Wrapped Mylar. .. 15/1.00 $2.00 Canada and other countries 63 50 (Includes ins) Shippnlg rate adiusted where applicable 18 Pin/ 17 24 Pin/ 22, 28 Pin/.24 1 of 50V Wrapped Mylar. .. 15/1.00 NJ residents add 6% sales tax TO-5 Transistor Socket 7/1 00 1,000 PC Resistor Ass' t(30 Values) 1/2W-$3 MICRO-NIA11T 501 CENTRAL AVE., WESTFIELD, NJ 07000 (201) 05M-1001 7 CIRCLE 211 ON FREE INFORMATION CARD possible to get into the listings and Overall, the Card/? interface is make whatever changes are neces- the way to go for "professional sary to provide rational printer op- quality" printouts from the eration. Commodore 64 and VIC-20.
Global Specialties Model 1301 Power Supply
A DC power supply for both analog and CIRCLE 233 ON FREE INFORMATION CARD digital applications.
AS ANY ELECTRONICS TECHNICIAN OR supplies can be floated to different hobbyist knows, one of the most levels if desired. important instruments on any If an earth -ground reference is workbench is a stable, depend- required for an application any of able DC power supply. And that's the six binding -post terminals can true whether you work with ana- be connected to the front -panel log or digital circuitry. But if you "earth -ground reference" binding work with both, often you will post. Also, if required, one termi- need two such supplies. That's be- nal from one, two, or all three sup- cause a supply intended for use plies can be simultaneously con- with analog circuitry, often is un- nected to the earth -ground termi- suitable for digital circuitry, and nal. vice versa. One supply that nicely bridges Using the unit both worlds is the Global Spe- The supplies can be used inde- cialties (70 Fulton Terrace, PO Box pendently, or can be intercon- CIRCLE 209 ON FREE INFORMATION CARD 1942, New Haven, CT 06509) model nected to accommodate different 1301 DC power supply. That's be- voltage and current requirements. MULTI -PURPOSE cause that supply is made up of For instance, the two variable sup- SHEET METAL WORKER three independent supplies-a plies may be connected in series fixed 5 -volt supply rated at 1 -amp to provide a variable 10- to 36 -volt, maximum, and two variable 5- to 0.5 -amp power supply. For a high- 18 -volt supplies rated at 0.5 -amp er voltage, the 5 -volt supply can be maximum. also combined in series with the two variable supplies, yielding a The 1301 15- to 41 -volt, 0.5 -amp supply. The The model 1301 power supply two variable supplies can also be can be used in a wide variety of paralleled, using equalizing re- applications. Priced at $219.95, it is sistors, to yield a 5- to 18 -volt, 1 - equally at home in industry, ser- amp supply. vice shops, schools, or on a hob- Other interconnection schemes byist's workbench. are also possible; those are out- 24"& 30" SHEAR -BRAKE -ROLL Housed in a functional, yet at- lined in the unit's instruction man- tractive, black aluminum case, the ual (more on that later). unit measures 4 x 14 x 7 inches. It Aside from the binding posts, SHEARS ROLLS BENDS weighs 5 pounds. Power (117 -volts TRIOK-A multi -purpose sheet metal worker where all func- AC) is supplied to the unit via a tions operate simultaneously. There are NO special set-ups Global 1301 not otherwise required on single -purpose machines. three -wire cord; a 240 -volt AC ver- TRIOK-The heavy duty shearing and forming machine that sion of the power supply is also OVERALL can be in your engineering or maintenance shop, ready to PRICE finish a job at minimum cost, in minutes instead of weeks. available for use abroad. EASE TRIOK- Now available in two sizes with new male 6" dies and The three supply outputs are OF USE removable female "V" dies for deep boxes and maximum versatility. available from the front of the unit INSTRUCTION TRIOK-A complete sheet metal shop in one unit, at less than via three sets of color -coded bind- MANUAL a third of the cost of the individual machines it replaces. ing posts. Those three supplies are PRIG Telephone or write for literature today. VALUE isolated, and can be floated to a PACIFIC ONE CORPORATION 8 8 la 513 Superior Avenue, Suite 580 DC level from any other supply, or Newport Beach, CA 92663 (714) 645-5962 from the equipment to which it is f TELEX 4996168, P00 NPT connected. In addition, all three 8 CIRCLE 206 ON FREE INFORMATION CARD and the potentiometers used to supply is well -regulated. Under a set the output levels of the variable 25%-100% load, the output of the supplies, the dominant feature of variable supplies is stable to within the front panel is the two meters ±150 mV; the output of the 5 -volt used to monitor the voltage and supply is stable to ±50 mV. Ripple current outputs of the three sup- for the variable supplies is spec- plies. Since only one of the sup- ified as less than 10 -mV P-P; for the plies can be monitored at one 5 -volt supply it is less than 5 -mV DESCRAMBLER PARTS time, a front -panel MONITOR switch P-P. We stock the exact parts and PC Board for Radio is Electronic's February Article on building your own used to select which of the sup- The documentation that accom- Cable TV Descrambler. plies is monitored. panies the unit is brief, but it is well #701 PARTS PACKAGE $29.95 hhe 1301 uses current limiting to illustrated and does a more than Includes all the original resistors, capacitors, diodes, transistors, integrated circuits, coils and IF trans- guard against damage due to short adequate job of describing the formers (BKAN-K5552AXX). circuits. If the output should be unit and how it is used. #702 PC BOARD $12.95 shorted, the voltage drops to zero Our impressions of the Original etched 8 drilled silk-screened PC Board used Model in the article. and the current is limited to about 1301 power supply are that it is sol- #704 AC ADAPTOR 2.5 $12.95 amps for the 5 -volt supply, and idly built and that it performs reli- (14 volts DC @ 285MA) 1 amp for the variable supplies. ably. The unit is backed by a one- Both #701 & #702 $39.00 As mentioned previously, the year warranty. FREE!! Reprint of Ruh Electronics Article on Building Your Own Cable TV Dencrintbler with elry'llrlehiU.
Alden Model 9321 Add $4.00 Postage b Handling
Weatherchart Recorder TOLL FREE 1-800-227 8529 (Orders Only) 1-617-339-5372 Keep an eye on the weather (Information) with this chart recorder. it's 36W available in kit form, too. ELECTROIIICS,ICIC. P.O. Box 800 CIRCLE 237 ON FREE INFORMATION CARD Mansfield, MA 02048 40 CIRCLE 208 ON FREE INFORMATION CARD DOES YOUR MIND COME TO ATTENTION when you hear weather reports of storms brewing at sea? If you are an avid sailor, or you're just into weather forecasting as a hobby, you need to know all there is to A defense know about what's happening against cancer can be cooked up "out there." in your kitchen. One way to keep track of the There is evidence that diet and cancer are related. ocean's surface weather, ice for- Follow these modifications in mations, your daily diet to reduce the condition of the Gulf chances of getting cancer: Stream, or anything else having to 1. Eat more high -fiber foods such as fruits and vegetables do with the "big ponds," is and whole -grain cereals. 2. Include dark green and through the Alden model 9321 deep yellow fruits and vegeta- Weatherchart Recorder (Alden bles rich in vitamins A and C. 3. Include cabbage, broccoli, Electronics, Washington St., West- brussels sprouts, kohlrabi and An ETCHED cauliflower. borough, MA 01581.) 4. Be moderate in consump- circuit board The Alden Weatherchart Re- tion of salt -cured, smoked, and nitrite-cured foods. from a corder is a facsimile printer specif- 5. Cut down on total fat in- take from animal sources and ically designed to recreate the fats and oils. Printed PAGE charts broadcast on shortwave fre- 6. Avoid obesity 7 Be moderate in consump- in just 3 Hours quencies by marine radiofacsimile tion of alcoholic beverages. stations throughout No one faces cancer alone. the world. AMERICAN Gomm SCOUT The North and South Atlantic and Ad No. 1284.0 (r s s) Pacific oceans, the Indian ocean, Created as a public service by D arcy. MacManus Masius, Inc. The ER -4 PHOTO ETCH KIT gives you the tools, materials and chemicals the Antarctic, the Red Sea, the Per- to make your own printed circuit boards. The patented Pos-Neg'" process sian Gulf, and coastal waters are all copies artwork from magazines like this one without damaging the page. Use the circuit patterns, tapes and drafting film to make your own 1X served by the radiofacsimile artwork. Or try the Direct Etch' system (also included), to make single broadcasts. circuit boards without artwork. The ER -4 is stocked by many electronic parts distributors, or order direct, postpaid. The charts are broadcast on ER -4 PHOTO ETCH KIT (NJ and CA residents add sales tax) $37.00 many different frequencies, from 4 DATAK'S COMPLETE CATALOG lists hundreds of printed circuit products MHz to and art patterns. Also contains dry transfer letter sheets and electronic title approximately 20 MHz. (A sets for professional looking control panels. WRITE FOR IT NOW! The DATAK Corporation 65 71st Street Guttenberg, NJ 07093 CIRCLE 203 ON FREE INFORMATION CARD 9 directory of the stations, frequen- powered by 117 -volts AC. The input ALDEN 9321 of operation is sup- to the recorder is 600 ohms bal- cies, and time OVERALL plied with the recorder.) The anced, available at a terminal strip PRICE accessory facsimile signals, which are easily located on the rear. An EASE recognized by their distinctive matching transformer is provided OF USE ding -dong sound, can be received for unbalanced receiver outputs, INSTRUCTION .n MANUAL on any shortwave receiver capable such as a headphone jack. The However, we connected the re- PRICE of upper-sideband reception. VALUE ® tones are converted to hard -copy corder's 600 -ohm input directly to printouts by the Alden a receiver's 4 -ohm headphone out- Weatherchart Recorder. put and had no difficulty of any The chart recorder is housed in a kind in driving the recorder. It is plastic cabinet that measures 17í/1e possible that some receivers might a budget -priced "shortwave radio" x 35/8 x 101/4 inches. It weighs a require the matching transformer, shade over 10 pounds. It is but we tried several, ranging from to a top -of -the -line communica- tions receiver, and always got good results without the matching transformer. The top of the recorder has the BOOKSTORE main power switch, the start Radio -Electronics. switch, two LED's that serve as tun- ing indicators, and a framing 7 Radio -Electronics back issues (1985) $3.00 Special Projects #4 (Summer 1982) $4.50 switch that centers the pictures on Write in issues desired Special Projects #5 (Winter 1983) $4.50 the paper. Radio -Electronics back issues (1984) $3.50 Special Projects #6 (Spring 1983) $4.50 (January 1984 not available) Special Projects #7, #8, #9 ... NOT AVAILABLE The charts are created on a roll $4.50 Write in issues desired Special Projects #10 (Spring 84) of 11 -inch wide electrosensitive pa- back issues (1983) $3.50 E Radio -Electronics Annual 1983 $3.50 3 Radio -Electronics that is supplied in a cylindrical (January, February 1983, May 1983 not available) Radio -Electronics Annual 1984 $3.50 per Write in issues desired Radio -Electronics Annual 1985 $2.50 cassette that mounts near the front 3 Radio -Electronics back issues (1982) $4.00 How td Make PC Boards $2.00 of the machine. (You tear off the Write in issues desired All About Kits $2.00 -driven Radio -Electronics back issues (1981) $4.00 E Modern Electrics (Vol. 1. #1 $2.25 charts as needed.) Motor (Jan., Feb., March, Dec. 1981 not available) April 1908) rollers located in front of the cas- Write in issues desired Electro Importing Co. Catalog $4.95 sette feed the paper out. The im- Etch your own PC boards $3.00 (1918) (176 pp) a Hands On Electronics #1 $4.00 Low Frequency Receiving Techniques $6.00 age is traced on the paper by Hands On Electronics #2 $4.00 Building and using VLF Antennas stylus assembly located between $3.50 Hands On Electronics #3 $3.50 New ideas - 42 circuits for experimenters the cassette and the rollers that Hands On Electronics #4 $3.50 Descrambler (Jan., Feb., 1981) $3.00 VCR Repairs $3.00 Descrambling (Feb.,1984) $2.00 "burns" the image into the paper. El IBM Typewriter to As you would expect from the $3.00 Computer Interface method of creating the image, the issue we is because it contains To order any of the items indicated above, check off the If you need a copy of an article that is in an paper damp from ones you want. Complete the order form below, include indicate is unavailable you can order it directly us a conductive fluid. The electric your payment, check or money order (DO NOT SEND We charge 50e per page. Indicate the issue (month & in current representing the image CASH), and mail to Radio -Electronics, Reprint Depart- year), pages and article desired. Include payment ment, 200 Park Ave. South, New York, NY 10003. full, plus shipping and handling charge. passes through the paper and the Please allow 4-6 weeks for delivery. stylus, causing a burn where they touch. The recorder responds to FSK ARTICLE (Frequency Shift Keying) frequen- cies of 1500 Hz ("white") and 2300 Hz ("black"). While the machine can be started and stopped man- MONTH YEAR PAGES ually, it also operates under tone control, broadcast from the radio - facsimile stations. TOTAL PAGES @50e each TOTAL PRICE How it works is first pretuned to MAIL TO: Radio -Electronics The receiver funds Reprint Department, 200 Park Ave. South, New York, NY 10003 All payments must be in U.S. the desired station by adjusting Total price of order S the receiver's tuning control until Sales Tax (New York State Residents only) $ Shipping & Handling (U.S. & Canada only) (Includes FIRST CLASS POSTAGE) $1.00 per item S the "white" tuning indicator All other countries ($2.00 per item, sea mail) S flickers most of the time and the ($4.00 per item, air mail) $ "black" indicator flickers occa- Total Enclosed $ sionally. The actual tuning adjust- ment isn't critical; as long as the Name tuning indicator lights appear to Address (continued on page 91) City State Zip
10 Mail -Order Electronics Worldwide NEM; Since 1974 ELECTRONICS 1jam 2 MILLION PC. IC CLEARANCE - CALL FOR QUANTITY DISCOUNTS - RED-HOT RAM & EPROM PRICES NEW EEPROM Pan No. Pins Price Part No. Description 7400 Part No Pins Price Price Pert No. Description Price Part No. Pins Function Price aO9N 4 29 59 2415'133 1 1 95 s9/1111N 4 29 21C14 SNI4/4N 4 39 120076) CMOS SRAM .99 2816A 24 2048x8 16K 533741611 6 59 6264LP-15 115015) L.P SRAM 7.49 E2PROM 350ns. . . 12.95 W710311 4 29 5N74)5N 6 4S 533/416133 6 59 CMOS USES LESS POWER Features: ' 07/40.rá Addreee/Date Latches Auto-limed Byte Write SN/403N 4 29 9047611 ton 6 9 513/41621 6 chip timer) SV Erase/Write/Read Optional High Voltage Erase/Program 'X/4040 4 35 513l479N 4 95 MC146818 HEAL TIME CLOCK & RAM 5167416133 fi 1050741 7.95 (12422V) Power Up/Dawn Write Protection Auto Erase 54/4UN4 4 27C16 CMOS EPROM 9.95 before Write 49 5517413061 4 89 SN1419413 The 2816A is an Ideal nonvolatile memory 8144417g at system allerabilily :M/106N 4 59 5104826 1 517417533 with 27128-25 250761 EPROM Me same ease and with the same features as 2918 Static RAMS 9174076 4 59 5N)403N 5.95 6 ss 4164N-200 DRAM) 94740811 4 9/9.95 29 50748504 6 59 5N1409t9 1 )5 5N14440 1 39 41256-150 150751 DRAM Digitalkea 611741004 6.49 1 29 56/4096 6 275 5N7417N 6116P-4 1200791 9RAM 4 M 581749011 4 3.49 DT1050-ApRg60n148461n1 Ws webs= eM4M. aAen6lx. Ialwmna1Ma11i. 5674120 4 49 5174916 68764 1450ns) 21V EPROM 1 79 6 12.95 h puye swains IOSO a 313631ara rt DIGITALKER . 33 SI 047dle 98 741381 1 3.1 5674926 4 45 ott 66693 036311 lane 587414N 6116LP-4 20075) LP SRAM Ì and 5 a. Me 70196 and Ines YamPm 4 4'1 3I/4911 4 45 3.69 01.363336 sale, 951,861e 16 .91901 6.13 31974fiN 1 68766 (3507s) 25V EPROM 14.95 fl9 59/ 4176 1 a O31050 Mn h el ä Spee0 Processor 7N 10654104 5804270 (10 041 sot av (21 Speerh ROW 49 1015215 10.6111 ind N052164060212 l 4444 34111 1 Axtler Md M 1M 4174t IN MICROPROCESSOR wemn. 01464 15 doomo 35 COMPONENTS Ax pplqb sheet_ 1126 á 5 MICROPROCESSOR i7/142:0 CHIPS DYNAMIC RAMS Wr 83 Pint40 DT1050 Digitalker' 9N741811 16 Funch4u Pr $29.95 ea. 9174250 111 SH/4185N Ifi 11 MM54104 5N/426N 39 Processor Chip $12.95 ea. 004 t909 139 16 91/42/0 1 40 54l41919 16 DT1057-E.Pnds Oa 011050 wºapa4R lrom 117 t4 dm 260 amp IMI. 2114174 44 specs 5x112811 39 5N/4/929 16 -Z80.Z80A. 180B. ZBDDO SERIES .N/1314 1 35 Part No. DT1057 , $21.95 t. 56141936 16 ea. SN24314 39 49 961/11909 16 SN 334 49 51041959 16 49 9V/417N 25 9174/96N ?me II 7' 4 0 N/438N 19 40 d O,a,LCD 63046.14 /211IPL 5874197N II 75 A :3IrMIPL 9974395)97440N 19 M 1 I/IaIlCI,Omen la'1'I6A"'fi îN741979 21 119 49 28 CO297/s, 1,1,0/ SN/41996 119 30 24 SI>pwalc^ 7442N 6 99 19 28 Cn:p %11 1Eralu,un,ntN 395 SN'11216 16 46 J A1/7000 SN/442N 45 SN/4143N 10 :IIa10u 04734: 5/741517. 16 38 10 IC 6.141.1 Board Dosplav 'Evalwpnn K,Oo >67443N 6 125 5N74/46N STATIC RAMS á111N 20 to N 3', 019n ATI9E1111rIw. 611744413 6 125 5N14145N fir) 7 2/NI 20 a0 40 C Cocoa Board 11a86614 dv4l,eo57 NS 5674456 65 6674 /478 199 40 1''0,9n 870 LCD 000 5147427'rN 16 40 0.6 5674469 75 91/4 148N 40 Pm Bag, Vna I,Mnulol 9474283N 16 ' 22 fi i150 24 (N1447N SN/4/.50N 149 ns1005 249 CMOS lE05naevxcnTee. 149- 50/42940 16 1. B r450ns1 - 0/995 24 Slanyalr:la 71.6 %Tl 1Ev31uataen Kn, 1695 047441313 ]5 5104 t5-10 49 9N/4285N 16 6 1450m, /P 165-76r--1393 012,07434 95 16 lone Generale, 514/454N 40 495 19 51414/5/1, 49 120Ons1 54743656 16 40 16 61m Generaro^CA4p XILIEvanlnllnn 611 8 P SR/ 4504 35 5474151N 102444 1200n1s1 I Ry - 9.i)49 14 99 01143660 16 pNlayr Ca'Irplar S 999 5104609 8 409641 r7Onsl 39 5/1741546 149 10 II Beg Cana, Ohp %11 ifva4ualen Krll SN/436219 16 A 1024.4 r Onsl . 567170N 39 5N74155N 40 411yn LCD pl.plry OecraenOrlsv ITTL 56114368N 16 1054045 1 1024.4 ,450/,S, companmel :N7472N 40 11).0 LCD Dnp.ry Donee Oo, IMoepmc. SN/4156N 59 5N)439W 6000 6800 10540117.45 re 102444 7450ns1 mmpnl 16 58000 SERIES 21 ne CMOS 9.874/IN 39 SN/415/6 5101 n 256.4 15ons1 CM05 Stomper Cat 611143936 II 4 e 409611 7450n04044 24 rap Swamalan cnm 511_ 17 r ,.6 741500 1 2048.8 1120ns, CMOS tB b 0'a,1 0,r fn,na, C 1 1120ns10P 74LS 7345144 t 29 1049.9 CMOS 70 9 Dual N+I Cnumer Cl 74LS01 0 40 19257 2ó 1 20408 050m, CMOS 28 7474/902 35 10 2405131 65 /4L0251 15 59 ; 2a6.8 150ns,1PC5105 503 29 74L9133 59 1á1S253 16 59 11Wns1CM05 741564 39 s0 'aN1 12W"s1 L P CMOS 741.5136 39 105257 16 59 741505 6911.' 10 Mlv,/- 11101slCMOS /415130 59 7415256 16 8p 741506 11802 B - 99 0 C91 . 60 11211ns1LPCMOS /á15139 59 t415266 11 sá 130009 1983 INTERSIL Dala Book ,..cm _. $9.95 74/507 99 6809E B 3:92.3 115O15ICMOS LS145 6 I 19 741.608 /4/5266 14 8 3/9248 P 35 741514/ 8.6009E I 50411 l CM,.3 6 19. 15278 20 746509 6 156.1 180ns/ LP 74HC HIGH SPEED 35 7416148 6819 24 128.3 CMOS 6 13 1.51/.1 16 6 16.4 15pn513101 741510 35 11,., .V 7469151 6 N 00 /49L14' 59 1/S2/.í1 11 59 7496133 1 95 20 241511 0 750.4 CMOSInsI 35 /41915;1 10 4a,.MC:1. 744/251 ]ILS11 6 59 7 .6222 20 0 024.1 125Ong CMOS I51191 59 /46C147 129 16 59 74051U 10 asp-pm welt. e Aaalne 4'15 715189 /44C251 1 1(9 ,415323 20 ZMHZI 6 16.4 /35,5193405 XCW 99 /4MC151 99 18 109 741520 29 745289 7415155 6 9 /415323 20 995 6 16.4 r35ns11101 '1µC04 59 710C151 lO/ 14xC151 15 141521 35 02510 1024v1 709156 6 09 7425.34/ /495 6 1580s10C 1934151 nµCUUa 69 /410,15.1 265 /aMC159 16 741526 ! 82525 6 6.4 50n4/0C 17452091 Lsr,; 6 59 16 46c07 59 r1MC15! 99 744C266 14 741527 35 7d1515P. 1.010 6 -9 /41511.1 20 PROMS/EPROMS 59 701015t 99 740C223 20 741528 39 /415160 6 69 7.6365 1995 1329 4 256.8 pap :I4Cn 69 74NC167 139 /SC2b0 II 70930 39 9:1n.I.1 lµ52516 7405161 4 2048.8 1 :IMC14 6 119 /4L5366 16 do 995 50ns, 09 7411016: 139 /0X7299 20 70532 39 15152532 7415163 26 : 4 409640 2450,51 14XC366 6 69 /asw7 16 49 695 C20 59 /4X7162 139 16 99 7aL537 35 76162564 8/92,8 /450nS, 115163 6 N 49 I 1,1C17 59 74XC16.3 139 /4X736/ 16 219 741630 1538 16 8000 89000 SERIES ne126611 2708 Je /4LS164 7487323 20 89 740537 20 149 40 1 uUwR4M810 09 7010164 35 269 7á1542 89 129- 1052156 4 tÓi8.6 150nsI3 705165 6 19 241. /4X7374 20 89 7415314 1 49 10 711 C165 269 20 - 4 r5 2716 4 2040.8 1458nsI L547 89 7415168 74µC2M 6 1. 74153/6 16 69 10 uns 84112801s RAM) 27016 é /4XC'66 49 16 59 '41.551 29 1 0046.0 CMOS 1415169 6 149 749C3Y' 11 59 7415386 11 39 40 - ' Pr 1716-1 1 1048,9 10HCq1 29 5'3 39 85405 JS 1350np /d,/n 6 45 89 7435393 11 10 .,, M3 r7lnlerpretea 2935 27760,5 1 204858 1550,s1 749C114 39 MK,20 fi I69 74L537rv 16 10 11312 1 096.8 r45OnM 79 7aCl/5 09 289 45 3 35 6 69 /415990 15 1132470 1 4096.8 ItWns/ 21V 79 1407/90 I59 16 319 39 21324.15 4096.8 6 69 /415533 20 e1158.1/: / 250ns121V 99 /4MCr9i 159 H9 17324 45 4096,8 5Da5,1N 119 741SS34 24 -63 9 /4XCeC' 333 1/032 4096.0 LMOS 6 79 7415540 20 69 /4µC193 1x3 '/731030 1 409601 13005/51 1107CMO51 6 09 ]4155.41 /5 /407194 15 1/µ..O 20 81976 1200,512+V 9 7x5.10 20 40 79 2áI1C195 15 20 8/92.8 7150,1 21V 41.5641 19 !'1 7.17C77 16 28 819703 50, 6 ;45C21/ 11 ',9 /x5644 20 p 8192.8 i150, , 6 41.º,45. 4HC240 II 59 5µ 20 1 49 28 8/92.0 CMOS " 20 1 89 20 6 195 706670 16 149 40 26 /0381.6 /250, ' '140141 24 119 7415680 20 26 16381.3 1250n: 1 447212 11
77 16 6 10'.1 8'2595 20 iá' 16 - 28 32160.8 /25005,246.i4N: '40C:13 14 959 20 1w 611596 149 11 24 8192.8 /450nº1 1/V 1 11 3/5 B/92.5 1175...o25v m 59 6491 m 16 YI 11 109 6 3566 ónsv/ 20 28 20 195 I6 256,4 1 20 195 15241 I6 22.8 20 28 20 29 74S/PROMS' 45141 11 0 14 Pe 14 45 '.v25/ 16 PRUNI 79 71508 11 45 MP, I/ 40251 1 16 2e 57.812.8 PROM IS 7008152950 11 59 /4509 11 39 45257 29 r PP10 16 5/1,7 0 C 763401 11 ]4510 II J5 73 16 N 11 7511 /1 35 213 64515 20 219 21 28 35 75180 6 112.14 11 1 89 40 26 95 745211 11 35 4S1fi/' 2. 6 16 40 la 522 11 35 1024.: 19 6 Sr Ifi 40 21 q5 74630 11 35 I@4.; 6 20 2A 2i 3 49 74532 11 : 8 51.0 18 45 6 99 20 28 74537 93 5256H 20 95 19 20 40 Ifi 5 95 7á.528 1á 89 e 2,e 40 6 ,i5,1133 6 256.4 ai 18 5 95 564 39 5n/t p í29 16 69 14665 11 39 45411' 10 29 3779 10 -15130 6 5i].4 ÚC i17572, 9 9 740221 6 71574 11 55 16 69 15 74547N 20 "i279.5 10 -15185 8 2048.4 PROMIS 1169249811. 14595 /8 199 74551r 16 8282 Nï191 1 '018.0 180ns1 1 flfi 11 55 '.1S52.' 16 9S 8184 UM815181N 1 024.6 OMIS /8251811 1995 IL071CP LIICN10 L5124/N II 69 /45112 16 55 149 14591' 11 495 0210 649 IL02CP LM74BN 1 59 /IS114 16 115 DATA ACQUISITION NY 1F155N 109 20 1455/3" 1e 4ºs 8267 :170º73./1 I/074C0 95 995 6 49 DCIG Mos/ee DC DC Convener r-51/ m -9V 195 1L0817v LEI56N 109 8188 20 He: '395 A000001 20 08a1 All Gnvener 11/IL561 1495 59 5 195 11 59 74ALS130 15 125 110358N M1 74ALS 8289 20 But Amp,.I 2495 RDCU001 20 865 A/0 Cansener/'1 20581 495 11081[4 1 19 ''9 /M4 14 59 4015240 20 225 LM1458CN 0 59 8141 40 004 U,I:v :'.:.' 6971.31 1995 04 20 9784 AN Commie 11IlS81 319 IL084CN 195 1MJ59N 1 1/9 14AtSO4 14 59 /401532 74415244 21 IMIIBR4 11 69 225 8749 91 AD7000809 20 8 Rol Cow lAnala9 40 1-15105 (PIP_ MM'. 1995 0N wr6G 995 lMIW6 595 0031UN 1 495 744.36013 11 59 I4AL514 11 /9 14415245 21 259 ADCW09 21 8 Convener LM1489N II 99 8749 40 A1PU B BI (PROM el 1995 BI N0 18Sn Mum I 449 LM1U6x 39 tempt 804 LM3/3N 1 195 14ALS10 1/ 59 /4/139109 16 79 74015371 A070816 20 25, 40 1 LM1096N 8751 40 CPU 6+MOW790M EPROM 8 118.8 RAM9 Lµ302H 149 II 95 744/$30 14 2995 LMJ21N I 195 59 4015111 16 69 74015374 20 259 A0x0P12 00 81 ÑpCoNnvenwe1 6/ CO Muñ,W 1949 8755 M 167 EPROM won , 0 1995 6 LM004H 91 L51/600(0 995 0400806 15 3.04 O,A ConvMe/ LM380CN L09 7.011 80186 55 Hon Intry, 16 1018%Lo, 195 103050 u 69 a7 MR/ 1995 LI_L 10 740240 75 0000902 113 295 20 8.011D,A Cam7ener/MC1408-/I 49 LM3N4 I 89 /4E02 11 75 54 4ph Integra 16x8, 7n0,8 Bo Kai Bust -n ' 0M3D1CN /41744 m 349 OAC0808 16 Contents063071 1µC1400--81 225 LMIB/26 10 74504 80287 W Numeric Processor Era LM3110CN 69 lMJli/N I I 79 14 89 74686 1 19500 00(0830 I/ I5 74115.3 16 1 79 20 6-13,/ W 0/4 Cony / 054 Lin I 5 95 L51187069 14 1031196 749 /4F08 11 ]5 74E109 16 DAC0631 20 8-011 upu MA Cow 11 LM382N I 95 740257 16 179. /754401545445,45 1/0': do1 449 LM18.99N II 195 74710 11 74F139 (MCI 000 21 Cont. LM31WN 75 I6 169 141280 14 169 495 f0 -at Macro C31360 1005'51 795 .C3.°'/8 159 74120 11 DAC1008 20 10.04 OA Cons. LM311CN 8 5'J LMIfl9/N II 69 74F139 1 Mom Como 0y I6 49 MM5311N 16 iRV 10.20%1 695 L19 M,J06N 3 I '4I.173 00 489 Barge, 740,/41,, 995 DAC1022 16 I0.550 Co,y I LM3120 195 74732 14 19 74E157 I6 I6 155 MM5816/AN 24 0,pop/ocecsn Real Nrre 04 1020%lin 595 20 Clad 895 DAC1222 LM:01N 13 74E74 14 II 1264 OM Cony 1020'M Lon I 695 lMJ1/1 119 85 747158 Ifi 6. 4.374 16 199 0058//400 IB MILT, Cmtal/ble nee Clod, üN2WJ7A IB 9 b45 29 12.134 /44)8944 I 119 Up D.A Cam 1054o 1m1. ;495 LM3116 49 xR220fi 00536907'0 8 679 194/2i, a'O,noer160071 1 79 16 395 D4: 1,rJ OAC11J 20 1261/ Op 5A Cony Lin) It 1A091N801 C04/MB 29 f 6 24.1 MM5369E51- P.,9 11044 1395 L0318C33 1 I59 8 Osoll41w7prv,cer /1B341/I 195 01.3 1015D 10 258 Baud PART Ir/ eR23o2 11 249 1.304001 CO-CMOS 16 9 125 LM329N 11 149 LM391N 159 29 MC1461318 24 Real Tome C,pa nus RAM 795 %R1108 Ny.5,1013A 40 30 Baud BA(11- Ifi 1 79 '15/e Ifi ' 'Y 1771602, 395 CD.M12 694941 69 LM3WN5 45 11 119 L0J21411 I35 112211 11 195 9n7.á2 69 020 Wnp 1M3398N 395 1M11'ì.4 24 7 95 gal 1.032011 15 i 35 M28nP 95 9943 6 9 1M399X e' CD15:6 16 65 Socket LMJ2g121 35 LM28]8P 295 195 ]1 OK, .11 16 85 L0J2015 BS LE112CH I40161 Leael #3 LM2901N 11 79 546 6 89 611451' 16 85 1.513201 12 .e5 IL491CN I 279 14 Suldertil 1G0101 Standard LM2902N 11 89 7D4042 89 C114' 21 119 Lox Profile RH Socket M IN. 19 1099 IW.y 103X0115 85 i1496C: 159 24 49 P0n 11 19 1099 IOOup 1M29p]N 14 249 074748 6 59 8 4,9 NM 55 49 10320124 85 NFS]IV 29 NO Ile. /0 1099 I1016 45 Header Plugs (Galdl I/9 6,14516b0` 16 89 000216 I/ 149 LM2917N 0 195 Ca4619 39 10 an WW .69 65 59 NE540MIC54 HI 195 áhlx 16 B 15 14 15 14 PM N4. 1 8 10 99 100.0 LM323K W 71719 nn SC de 45 39 14 on WW 75 69 GS 1y5 /1 59 W4050 6 39 I 195 9 5 ' NE5a41, 16 59 It me LP 17 t5 14 16 pm SG 55 45 16 pIn WW 14 on HP 65 59 55 /M32aN 11 110490(0 C04051 79 72 89 29 45): 16 69 16 pro LP 19 1/ 16 18 NE550A I 19559 p,n SG 59. 6 HP 69 0MJ2902 65 65 51 18 p,n WW 95 85 IS Dan 65 59 LA43909N 0 C04/070 6 89 16 18 pm LP 26 24 39 /0 10 pm 1 LM334N 145 NE55SV DP 5G 15 65 59 20 pc 01W 1.19 109 95 24 HP 15 99 89 35 IM3914N II CD1053 /9 01/4525 16 201 LP 30 27 25 21 SG 19 L0331Z 119 49 an 5, 740711%9179 119 1 MAL555 05 69 IM3'115N 16 CIM056 6 71,152P 15 119 21 p1 LP 3/ 78 26 24pmSG 19 24 pal W1Y130 t19 Header Corers M3J52 i,'M3 79 35 - 1H LM556N 1 79 p19 0M3916N IA 16 .59 24 IP 40 30 18 28 per 9, 28 prit LM336 418 ( 04059 w WW 16_ 1 55 139 M 395 13 405531 1 /9 /0 60 RC,1136N 0545r 28 LP 40 37 35 125 : LM331MP R 11 99 36elnSG 364/006/7/ I 79 169 19 49 114W0 6 09 6 In el 17 NE564N 40 pm LP 49 46 43 40p1nSG 139 .f0 tor' 03311 189 I ta-5 R¿4151NB CMI5 36 16 WW229 195 1 79 11224 ply el 22 0 UPON. 16 l' LM339K 695 LM565N I 99 6.0454' II RI:dIS'/NB 1 C04058 4 19 S OMinimum Order-LLS. Funds Only CA Residents: LM3394 11 65 1056604 6015./á 15 Add 66,% Sales Tee Spec She-els- 304 each nC4.1,,,TN 4 35 S ipoing. Add 5% plus $1.50 Insurance M34065 135 Send61 Postage for FREE late Jameco Catalog Prices 9933,133 LMS6N LM42SOf,N a On5\3 16 1 96 Send stamped. self-addressed Change `0340011 135 29 envelope to receive a Monthly Sales Flyer - FREE' NE5/(W I 195 NE
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Box 240, Massapequa Park, NY 11762-0240 Total Price of Books $ I Name i Sales Tax (NY State Residents) Address *Shipping in U.S. only I City State Zip ($1.00 1st two books, 400 ea additional) i *Canadian Shipping ($1.50 1st two books 50e ea. additional) tTOTAL ENCLOSED $ Isgoß THERE'S NO ULI ONU AROUND THE FACT that as modern electronics becomes more and more sophisticated, batteries have be- come an increasingly important part of the electronics world. The development of CMOS and all the other low -power tech- nologies have changed even the way we buy batteries-these days, it isn't as easy as just zipping down to the supermarket and pulling the right -sized blister pack from the rack. Modern batteries come in a mind bog- gling array of configurations so there are are lots of ways you can categorize them. Probably the most basic categories are "throw -away" and "rechargeable." There can be a major difference in cost, capacity, and characteristics between those two types. Deciding which one is best suited to your particular application requires a good understanding of each. This month, we'll look at the throw-away or disposable battery. Before we go any further, though, we should point out what we mean by the words "battery and "cell." A cell is the basic building block of a battery. A bat- tery is generaly thought of as a single, What's New in BATTERIES Ever since electricity was first discovered, people have been working on ways to store it. Let's take a look at today's battery technology and how you can choose the right battery for your application. ROBERT GROSSBLATT 13 integral unit made up of one or more cells. a battery in a short-circuit situation, we the electrolyte, the battery will explode. If a single cell is packaged with termina- felt that it would be a good starting point It's as simple as that. tions and insulation (such as a "D" cell), for understanding just how much elec- The outer cases of all batteries are made it can be correctly called either a battery or tricity we're talking about. out of steel because the gas creates pres- as in Fig. a cell. Of course, Table 1 doesn't list all avail- sure. (Alkaline batteries, shown able battery sizes and chemistries, but the 2 also have an inner case.) If the jacket Disposable batteries batteries listed are the most commonly warps and destroys the seal of the case, the Disposable (non -rechargeable) bat- used. The figures for other battery sizes, electrolyte will dry out and that will be the teries are available in a huge range of such as "AAA" and "N" will be less than end of the battery. But that's not the only sizes. And as if that wasn't confusing those listed for "AA" cells since they're problem, Some of the chemicals used in enough, every one of those sizes is avail- smaller and, consequently, their energy the cell are dangerous and a blown seal lot able with a variety of electrochemical sys- capacity is less. means that they'll leak. Since a of tems (what we'll call "chemistries"). And There are two main things that stand out battery changing is done by children, it even if the voltages of two batteries with when you look over Table 1. The first is pays to make sure that you don't abuse the different chemistries are the same, just that the amount of energy stored in any of battery. other characteristic-from the batteries is surprisingly large. Sec- about every Battery life the power capacity to the price -can be ond, you can see that the chemistry of the different. Like most things, you get what cell makes a tremendous difference to the The short-circuit current shown for the you pay for-more power means more total amount of energy that you can pack batteries in Table 1 is, unfortunately, bucks. into a battery. nothing like the working current. Re- bat- So far I haven't said anything earth- member that the unit for measuring shaking, but let me give it a shot: For Battery construction tery capacity is the amp -hour-a product some applications, batteries that use the The internal construction of most of current and time. And as mentioned more expensive chemistries won't per- throw -away batteries is very similar: before, the rate of discharge is going to form any better than cheaper batteries. As Basically you have two electrodes sepa- have a major influence on the useful life of we'll soon see, battery life isn't always rated by an electrolyte. The construction the battery. As a general rule for all dis- dependant on the battery type. of a typical disposable cell is shown in posable cells, the more current you pull its life is going to be. The voltage of a disposable battery, no Fig. 1 and the chemicals used in the vari- from it, the shorter matter what the chemistry, is always ous cells are listed in Table 2. The elec- There's a fixed amount of energy available stamped on the package. What is (almost) trolyte used in all the cells has two basic in a new battery and the lower the current never stamped anywhere is the other es- purposes. drain, the more efficiently the battery can sential piece of information you need to be First and foremost, it is the current - convert its stored energy into electricity. able to make an intelligent choice about conducting medium between the elec- Heavy drain means that some of the ener- which battery to use: that is the amp -hour trodes of the cell. But the chemical reac- gy is going to be transformed into heat, capacity. tion that produces the current also the conductivity of the electrolyte is going The amount of energy that a battery can generates gas as a by-product. The second to decrease, and other factors are going to deliver (sometimes called its service ca- main job of the electrolyte is to absorb the all contribute to a significantly shortened pacity) is usually expressed in amp -hours, gas. The warnings on the side of batteries battery life. or milliamp-hours. It would be nice if the about excessive drain, recharging, and so Figure 3 is a graph showing the dis- amount of power available from a battery on are all related to the gas. If gas is charge rates for both a carbon -zinc and was a fixed amount, kind of like a pail of produced faster than it can be absorbed by alkaline "C" cell. To obtain data for the water. Unfortunately, things aren't that graph, an appropriately sized resistor was simple and when you're dealing with bat- CATHODE used to load the cell and the time for the teries of any kind, linearity is usually out cell voltage to drop one volt was mea- METAL both the window. OUTER sured. The graph clearly shows that How much current you can get from a CASE types of cells are more efficient at lower It also shows that at low throw -away battery depends on a number PAPER current drains. of things: SLEEVE current drains, the efficiency of carbon - 1. The temperature of the battery. zinc and alkaline cells is pretty much the 2. The rate of discharge. INSULATOR same. 3. The chemistry of the battery. Translated into more practical terms, 4. The frequency of use. the less current your circuit needs to oper- 5. What you call a dead battery. ate, the less of a difference there is be- 6. stuff. Other ANODE tween the efficiencies of carbon -zinc and In order to give us a starting point, we alkaline cells. So unless your device current of decided to find the short-circuit ELECTROLYTE METAL draws a lot of current (like a photo flash, disposable batteries of different sizes and BOTTOM etc.,) there's no reason to spend the extra 1, lists short- chemistries. Table which FIG. 1 -ZINC -CARBON CELL CONSTRUCTION. money for alkaline cells. circuit currents, is the result of sacrificing This cutaway view shows that the standard cell and elec- Don't forget that the graph was plotted a bunch of new batteries on the alter of consists, basically, of two electrodes trolyte. by putting the batteries under a constant science. Even though you would never use TABLE 1 -TYPICAL DATA Size AA C D 9V Type Zinc Alkaline Mercury Zinc Alkaline Zinc Alkaline Zinc Alkaline Mercury Rated voltage (volts) 1.50 1.50 1.40 1.50 1.50 1.50 1.50 9.00 9.00 8.40 Measured voltage 1.49 1.56 1.46 1.50 1.55 1.48 1.58 8.90 9.20 8.41 (volts) Short-circuit current 4.40 7.70 10.3 5.50 9.70 6.80 11.8 0.60 1.40 1.70 (amps) 14 TABLE 2-ELECTROCHEMICAL SYSTEMS - Cell type Anode Cathode Electrolyte o_ Zinc -Carbon Zinc Manganese Dioxide Ammonium and Zinc Chlorides c160- Alkaline Zinc Manganese Dioxide Potassium Hydroxide 1-140 cc120 ZINC OXIDE -- - Mercury Zinc & Mercury Mercuric Oxide Potassium Hydroxide & Zinc "22100 Oxide 80 r, 60 40 MERCURY INSU LATO R ci=c) 20 expect your usable battery life to be more LL 0 than twice as long. 0 10' 30` 50' 70° 90° 110° 130° z TEMPERATURE -°F OUTER Temperature is a major consideration in U NICKLE-PLATED judging battery life. It's also one of those CASE W things that everyone has a tendency to G. SLEEVE ignore. Every data sheet I've ever seen FIG. 4-EFFECT OF TEMPERATURE ON CELL lists acceptable temperature ranges for the CAPACITY is shown for zinc-oxide and mercury INNER batteries. You can draw more current from a CASE operation of various devices and every- battery at high temperatures, but, of course, the body I know pays almost no attention to battery won't last as long. INSULATOR the information. (Maybe it's because we don't have any control over the weather.) and lithium cells. In any event, since a battery produces The most common use for silver -oxide electricity as a result of a chemical reac- cells is in digital watches and small cal- tion, STEEL BOTTOM PLATE the lower the temperature, the slower culators. Although their energy density is the reaction, and the less electricity the FIG. 2-ALKALINE high, they are usually packaged as small CELLS are built with an inner battery is going case, making them more rugged than zinc -car- to produce. The effects of button cells and the available current is, to bon cells. that are often quite dramatic. Once again, be generous, limited. all of us with cars are familiar with what All the batteries we've discussed so far starting the car is like on a cold winter use some form of zinc as the anode mate- morning! rial. By changing the cathode and the The effect of temperature on the capaci- electrolyte, cells with different energy < 160 ty of a battery varies with different cell densities and other characteristics can be 140 chemistries. Again another general rule: e 120 ALKALINE made. Recently though, batteries have 100 The more constant the voltage of the bat- been introduced that have a different tery under load, the less effect tem- anode material and are the result of more ¢ 60 ZINC CARBON perature will have on the ability of the cell than a decade of research and develop- 40 to z 20 deliver current. ment. The devices I'm referring to are cc 0 Figure 4 is a graph that compares the cc 250 450 lithium cells. 0 50 150 350 550 600 two extremes among the common dis- TIME -HOURS posable batteries, carbon -zinc and mercu- Lithium cells FIG. 3-ENERGY DISCHARGE CURVES for typ- ry. ical alkaline and carbon "C' -sized cells show It's immediately obvious that the zinc - Since lithium is the element with the that for low -current applications. there is not carbon cell is extremely sensitive to tem- highest oxidation potential in the periodic much difference between the two types. perature-a 30°F rise in temperature will table, cells with lithium anodes will have raise the capacity of the battery by more the greatest open -circuit voltage. Just as it current drain. So the battery life time than a third! Mercury cells, on the other is with zinc -based cells, lithium cells can shown is for a worst -case situation. A hand, are much more stable: The same be made with a variety of chemistries and more realistic test might include rest time 30°F rise (from 70°-100°) will have only a the composition of the cell will determine for the battery. The amount of rest time 6% effect on the cell. Don't forget that the operating characteristics of the bat- would have a large effect on the life of the while increasing the temperature will tery. Table 3 is a list of the possible lithium battery. raise the capacity of the cell, we've al- cell chemistries and the open -circuit volt- The more rest time the battery has, the ready seen that heat will shorten the life of ages they produce. longer it's going to last. There's nothing the cell as well. Put another way, a hot Lithium-thionyl chloride cells have an really surprising about that and anybody battery will put out a greater amount of open circuit voltage of 3.7 volts (3.4 volts who owns a car is familiar with the occa- current, but it won't last as long as a when connected to a 1 kilohm load) and sionally miraculous recuperative powers a cooler one. (There's no such thing as a more than ten times the energy density of battery will exhibit when it has a bit of free lunch!) the lead -acid battery in your car. They time off. Treat the information in Fig. 3 as Mercury cells have a slightly lower have a shelf life of over ten years and a a guide rather than the gospel. The data open -circuit voltage than carbon -zinc or battery that is packaged in a standard "D" there reflects constant current draw- alkaline cells, but the voltage is almost size provides an energy capacity of 14 worst case operation. You can only do constant over the life of the cell. As a amp -hours! better. matter of fact, the voltage is so constant The energy -discharge curve of those In Fig. 3, we chose a cutoff point of one that mercury cells used to be used in cir- cells is so flat that they come in packages volt. If your circuit can operate with less cuits as precision voltage references. They that are made to be soldered directly to voltage, your results, naturally enough, are still used in equipment, such as smoke circuit boards to provide semi-permanent will be better. If you're feeding raw bat- alarms, where a constant voltage and high backup systems for CMOS circuitry and tery voltage into a regulator, what your energy capacity are important considera- low-power memories. Specially made cutoff point is will depend on how far the tions. Two newer chemistries have been cells are surgically implanted in the battery voltage is above the regulated volt- developed that have produced batteries human body to provide long-term power age. If you can live with a cell voltage of with even more stable voltages and higher for cardiac pacemakers. .5 volt, for example, you can reasonably energy densities. Those are silver-oxide Battery engineers have known for years 15 vious question is which battery should TABLE 3-LITHIUM-CELL CHEMISTRIES you use. Well, we don't have a definite answer: Which battery you need depends Cell chemistry Open circuit voltage on what you want to use it for. Make a list (volts) of the parameters of your circuit and then Lithium-Thionyl Chloride 3.7 see which battery comes closest to satisfy- Lithium -Vanadium Pentoxide 3.4 ing them. Lithium -Silver Chromate 3.3 very Lithium -Manganese Dioxide 3.0 If your requirements aren't strict, Lithium -Sulfur Dioxide 2.9 you can use one of the less expensive Lithium -Carbon Monofluoride 2.8 batteries such as zinc or alkaline. More Lithium -Iodine 2.8 exacting needs almost always mean more Lithium -Lead Copper Sulfide 2.2 expensive batteries. Lithium -Copper Sulfide 2.1 In general, the more expensive the bat- Lithium -Iron Sulfide 1.8 tery, the more predictable its charac- 1.8 Lithium -Copper Oxide teristics. Zinc batteries are cheap, but the number of factors that go into determining exactly how the battery will behave is about the potential advantages (no pun mind boggling. As you go upmarket in al B2 83 intended) of lithium -based batteries. The price, things become more scientific and clearer. The only advice I can give you is development of a working cell, however, RINTERNAL RINTERNAL RINTERNAL has involved overcoming the kind of prob- that whichever ones you decide to use, - + buy the best constructed lems that are usually associated with the -. make sure you development of any high -energy -density throw-away batteries you can. Every bat- system. tery uses and produces highly corrosive LOAD battery In its simplest terms, a battery is a de- chemicals. A poorly constructed and any vice that stores a quantity of energy and can't withstand a lot of abuse POLARITY REVERSED ON the secret of a successful design is the BATTERY adverse conditions will cause the cell to IF NO CHARGE IS LEFT IN regulate 82 rupture-with highly unpredictable and ability to provide some means to THE CELL AND B1 AND 83 ARE STILL GOOD. the release of the energy. The more energy frequently disastrous consequences. REVERSE -VOLTAGE CONDITION oc- more danger FIG. 5-A Let's next turn our attention to re- there is in the battery, the curs because all batteries of the same type do chargeable batteries such as nickel -cad- there is from a sudden, uncontrolled re- not discharge at the same rate. Above, battery lead - lease of that energy. High current de- B2 has discharged, and a negative voltage is mium and, yes, they're still around, mand, spikes, heat, physical damage, developed across it. acid batteries. charging current, and overvoltage are a The rechargeables few of the conditions that can lead to po- tentially dangerous situations. be completely exhausted while the others The history of battery development is squeeze more into Heat, as we've already seen, is one of are still producing power. As you can see the story of trying to the major enemies of any battery. Lithium in Fig. 5, current will still flow through the less. Research is constantly being done to has a melting point of 180° C and thermal circuit and the dead cell will be acting as a develop schemes and electrochemical runaway in the cell caused by physical resistor. A reverse voltage will be present systems that will increase the energy den- damage, environmental or circuit condi- at the terminals of the dead battery. Heat sity of the cell and make the energy-dis- In other tions can lead to a situation where the will be produced and chemical reactions charge curve as flat as possible. entire energy of the cell is released in a will take place that can lead to explosive words, the primary goal of every battery split second. That causes what is known in venting. The higher the reverse voltage, company is to make a battery with the then at scientific circles as a big problem. Rapid the more potentially dangerous the situa- capability of lasting, if not forever, generation of gas will make the battery tion is. Battery engineers have designed least a very long time. explode and spew out highly corrosive several methods to handle that hazardous The two basic approaches to the prob- material and 180° molten lithium-an un- situation. lem can be called the idealistic and the desirable situation, to say the least. Mod- By making the potential of the cathode pragmatic. Up to now we've looked at the ern cell design has overcome those less than that of the lithium anode, there idealistic approach-designing batteries problems by building a pressure -release will always be some free lithium left when that can store greater and greater amounts valve into the seal of the cells and, in case the total potential of the cell is zero. When of energy. There are problems with that: the of high temperatures, providing a means current flows through the battery in a re- The more energy a battery contains, for the free lithium at the anode to com- verse -voltage situation, it will be carried more engineering it requires to guard bine into more stable lithium compounds. by lithium ions from the anode instead of against the uncontrolled release of the en- The last two major areas of concern ions created by a dangerous chemical re- ergy. In the rest of this article we'll con- with the lithium cell are really problems action in the electrolyte. Altus Corpora- centrate on the more pragmatic ap- with all throw -away batteries-reverse tion has gone one step further to handle proach-designing batteries that can be voltage and charging. The difference be- that problem by designing an elec- reused. tween the two is that the former problem trochemical switch into all of their bat- The most popular rechargeable bat- occurs normally in any series battery set- teries. When the battery voltage goés teries use either a nickel -cadmium or the very up and the latter problem is the result of negative, from either reversal or charging, lead-acid chemistry. Yes, that's circuit conditions. the switch closes, the current through the same lead -acid chemistry that came into and horseless No two batteries have exactly the same cell is shunted, and the actual cell voltage being with running boards characteristics. Since the action of the cell is never allowed to exceed -0.1 volt. And carriages. impossible to predict ex- that voltage is too low to cause any of the is chemical, it's Lead -acid batteries actly when the end of battery life will possibly dangerous chemical reactions The modern lead -acid cell is a far cry come. If a few cells are connected in se- mentioned above. its predecessors. Its open -circuit ries, they will discharge naturally and a Now that we've covered throw-away from voltage is about 2 volts, which means that time is going to come when one cell will batteries from Alkaline to Zinc, the ob- 16 Train for the Fastest Growing Job Skill in America Only NRI teaches you to service and repair all computers as you build your own 16-bit IBM-compatible micro As computers move into offices and homes by the millions, the demand for trained computer service technicians surges forward. The Department of Labor estimates that computer service jobs will actually double in the next ten years-a faster growth than any other occupation. 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SEPARATOR the acid is extremely corrosive and any- charging rates and thing that helps maintain the integrity of A lot of batteries were blown up to com- the battery is a good idea. pile those figures. FIG. 6-CUTAWAY VIEW OF A MODERN LEAD - Rechargeable lead -acid batteries are ACID CELL. Some batteries use a gelled elec- Nickel -cadmium batteries trolyte. available in voltages ranging from 2 to 24 volts and they can be used in any config- Nickel -cadmium (NiCd) batteries are it has the second -highest energy capacity uration you want. Unlike some other bat- the most popular rechargeable batteries of the commercially available batteries, teries, you can either parallel them to on the market today. They are packaged in both disposable and rechargeable. Only a increase the current or put them in series all the standard sizes and the cell's open - lithium-thionyl chloride cell, with an to increase the voltage. Since the energy circuit voltage is 1.25 volts (which makes open -circuit voltage of 3.7 volts, has a density in lead -acid cells is very high, you them a close match for most of the ap- higher energy-density-and it's not re- can get really impressive amounts of plications where throw-away batteries are chargeable! The drawbacks to lead -acid power by packing together a number of used.) Prices depend on where you buy batteries-leakage, highly corrosive acid cells. And how much power the battery them but, in general, it's safe to say that electrolyte, evaporation, and a host of can deliver has nothing to do with how the they're more expensive than alkaline and other problems-have been eliminated in battery was used previously. lead -acid batteries, but cheaper than the designs of more modern cells. Lead - A battery that is normally charged after lithium and silver -oxide batteries. The acid batteries come in a variety of sizes, only a small part of its stored energy has voltage -discharge curve is nice and flat, voltages, and energy capacities and have been used can still deliver its total power meaning that the battery will have a con- characteristics that make them the ideal whenever the situation calls for it. That is stant voltage for most of its discharge cy- energy source for applications requiring a common scenario in applications where cle. Unlike lead -acid cells, nickel - the use of rechargeable batteries. rechargeable batteries are used as emer- cadmium cells are not designed to be used So, you may well ask, if they're so gency backups in case the primary power in a parallel configuration. The normal wonderful why aren't they more avail- fails. Batteries that are constantly charged method of use is to decide what your cur- able? The answer to that is...Well, I can similarly always be counted on to de- rent requirements are and then get cells of haven't the vaguest idea and would appre- liver their full power if the circumstances the needed ampere -hour capacity and ciate finding out why. Possibly the answer require it. In other words, lead -acid bat- connect a number of them in series to has something to do with the ready avail- teries have no "memory" of their pre- build up the voltage you need for your ability of nickel -cadmium batteries, the vious use. system. other major type of rechargeable battery. The charging circuits for these batteries Before we start comparing the two tech- can be as simple or sophisticated as you POSITIVE nologies, let's take the time to find out like. They are capable of being charged at ELECTRODE how each is used. Once that's done, we'll extremely high rates if the proper safe- CAP VENT CAP How you charge them list the advantages and disadvantages of guards are taken. WELDED NYLON SEAL both types and you'll be able to make your depends on how you plan to use them. TAB 1*) INSULATOR own decisions. Table 4 gives you the recommended NICKEL -PLATED Lead -acid batteries are easy to use. charging rates and other information STEEL CASE Anyone who owns a car knows that those you'll need to be able to safely recharge AND NEGATIVE '4 ELECTRODE batteries can operate successfully under the batteries. It's important to stay within the most adverse conditions and are ex- the guidelines shown-overcharging can NEGATIVE tremely forgiving when it comes to things have catastrophic results. PLATE like accidental deep discharge and con- Even though the chemistry of the cells POSITIVE PLATE stantly repeated partial discharge. is designed to be reversible (which is what Figure 6 is a cutaway view of a typical makes the cells rechargeable), overcharg- ABSORBENT SEPARATO R lead -acid cell. Although there are varia- ing them carries the same sort of dangers AND tions from manufacturer to manufacturer, as trying to charge the throw away bat- ELECTROLYTE we discussed last month. During the most of the batteries use the basic con- teries INSULATOR struction shown. The electrolyte is an acid charging cycle of any battery, gas is pro- WELDED TAB 1-1 that.is permanently sealed in the body of duced. A major functions of the elec- cell. worth nothing at this point trolyte is to act as a "depolarizer"-a FIG. 7-A NICKEL -CADMIUM CELL consists of the It's wound together and rather fancy way of saying that it's de- nickel and cadmium strips that that technique (permanently sealing separated by absorbent nylon. in the electrolyte) is starting to be found in signed to absorb the gas produced during car batteries as well. Some companies a charge. However, and this is a really big that make lead -acid batteries "immo- however, the electrolyte can only absorb Figure 7 is a cutaway view of a typical bilize" the electrolyte by gelling it. This gas at a certain rate. If the gas is produced cylindrical NiCd cell. The nickel anode means that the cell can be used in any faster that it can be absorbed, then and cadmium cathode are made in strips position without any risk of the electrolyte BOOM!. Good-bye battery and anything that are wound together into a coil with an leaking out. Even though the construction else that happens to be around and that absorbent nylon separator between them. of the cell usually involves several heavy- can include you, too! Make sure you don't The separator is used to absorb the al- duty seals and double -walled insulation, exceed the recommendations for the kaline electrolyte. It is also permeable to oxygen (the gas produced during the charge cycle). The assembled battery is packed into the outer case, usually made TABLE 5-NICKEL-CADMIUM BATTERY CHARGING PARAMETERS of nickel -plated steel, the external positive and negative contacts are welded Type of charge Charging voltage Charging current Charging time to the electrodes, and the cell is finally (volts per cell) (percent of cell capacity) sealed. The seals keep the electrolyte RAPID Depends on Cell Depends on Cell 1 - 3 hours from drying out and are designed to act as QUICK 2.50 - 3.00 20% 3 - 5 hours pressure -relief valves. If the internal STANDARD 2.50 - 3.00 10% 14 hours TRICKLE 2.50 - buildup of gas gets excessive, the seal will 3.00 5% Continuous open and vent the extra pressure. How well the battery functions afterward de- tery's voltage, you'll see the voltage start that not all cells can be charged at the pends on how much electrolyte is lost. In to increase as all the internal shorts are higher rates. Nickel -cadmium cells are any event, you can bet that the battery will cleared out. If the separator has deterio- too expensive to risk destroying by impa- be but a shadow of its former self. rated in the cell, the battery is beyond tience. All the cells, however can with- The internal resistance of the average salvage and should be replaced. stand the standard 0.1C rate. But let's get NiCd cell is very low-usually less than back to our example. 100 milliohms-which means they can be Recharging batteries If we're going to charge a 4.8 volt se- used in circuits where high discharge - So now that we know everything about ries of batteries that have a 1.2 amp -hour rates are required. Some NiCd cells, lead -acid and nickel -cadmium cells, let's capacity at the standard 0.1C rate and are however, are specifically designed with a find out about how to charge them. The using a transformer with a 9 volt second- higher internal resistance that, although circuits needed can be as sophisticated- ary: lowering the maximum discharge rate, in- or as simple-as you like. Which circuit creases the cells ability to retain a charge. you want to use depends on which cells Button cells and 9 -volt Vsystem = Vtransformer - Vbattery "transistor bat- you use, now fast you want to charge = 9 -4.8 = 4.2 Volts tery" substitutes are usually manufac- them, and how you want to use them. tured like that. The internal resistance of The simplest charging circuit you can Icharge = 0.1C = (0.1)(1.2) = 120mA the cell is a good .guide to the charging have is illustrated in Fig. 8. Calculating rate: The higher the value, the lower the the resistor value and which diode to use Rcharge = Vsystem/Icharge charging rate. The most common cause of is simple. First, let's lay down some gen- = 4.2/.12 = 3511 NiCd cell failure is an improper charging eral guidelines. The transformer you use WATTAGER = rate. should have a voltage at its secondary at (Vtransformer)(Ichar e) _ -9 x .12 = 1.08 WATTS A dead NiCd will be either an open or least twice the open circuit voltage of the short-circuited cell. Open circuits are usu- battery you want to charge and the diode ally the result of electrolyte loss and this is should have a PIV (Peak Inverse Voltage) Finding a resistor with a rating of 1.08 directly caused by constant rapid dis- rating at least twice that. The resistor has watts is going to be difficult, so let's make charging, constantly high charge-rates, or to be able to handle the charging current at a general rule: we'll always bump the val- anything else that will make the cell blow the open -circuit voltage of the battery. To ue up to the next available size. That its seal. Remember that by the time the be on the safe side, let's use the voltage of means a 35 -ohm, 2 -watt resistor. The PIV cell parameters are exceeded enough to the transformer's secondary. Now that we rating of the diode has to be at least twice make the seal open, the high current rate have those things out of the way, let's use the transformer secondary or 18 volts and that caused it in the first place will have Ohm's law to fill in the blanks. it has to be able to handle at least .12 made the battery heat up, and that will amps. Any of the family of 1N4xxx di- make the electrolyte evaporate at a greater odes is a good Vsystem = Vtransformer - (Vbattery + Vdiode) choice for the circuit. In rate. In any event, there's no way to re- this particular case, the 1N4001 is fine. It place the electrolyte, so if you measure Rcharge = Vsystem/Icharge should be noted that we did not take the the internal resistance of the battery with a voltage drop across the diode into account multimeter and find it to be an open cir- WATTAGER = Vtransformer X 'charge when we calculated the parameters of the cuit, the battery is gone forever. circuit. Since the diode drop is going to be Short-circuited cells are another story. The key here is deciding what you want small compared to the other voltages, and Sometimes the separator will get ruptured the charging current (ICHARGE) to be. The our assumptions have built-in safety mar- and metallic salts will form a small bridge rate of current flow through a rechargea- gins, it can reasonably be ignored. If that shunts the current around the rest of ble battery is referred to in terms of the you're building a charger for battery sys- the plate. A high current pulse can burn total capacity of the cell. The rate of tems that have lower voltages and are out the short and the cell can then be charge or discharge for a particular bat- looking for larger charging currents, the charged, since the correct current path has tery is usually given in the C -rate. The C- diode drop should be considered in cal- been restored. Commercial "zap" cir- rate is the current rate in amperes numer- culating the overall system voltage. By cuits use this technique by charging a ically equal to the rated minimum amp - the same token, if the charging current large capacitor and then discharging it hour capacity. If the recommended charg- you need is really small, the diode's for- through the cell. If you monitor the bat - ing rate for a cell is listed as 0.1C, for ward resistance will have to be taken into example, that would tell you that the max- account and subtracted from the calcu- RCHARGt O imum current you can use to charge the lated value of the current limiting resistor. battery is numerically equal to Vio the total If the value of the is I calculated resistor NiCd amp -hour capacity of the cell. If the cell small enough you can do away with it 117V t OR AC was rated at 500 milliamp-hours, 0.1C altogether and let the diode serve as the LEAD -ACID BATTERY would translate into a charging current of current limiter. 50 I T milliamps. A more efficient charger can be built Table 5 shows the various rates of using a full -wave rectifier. The math is FIG. 8-A SIMPLE CHARGING CIRCUIT for nick- charge and how long it will take to fully exactly the same as in our example. Just el -cadmium or leaa-acid batteries. charge a cell. It's important to remember get the values of the circuit parameters 19 ROHARGE RSENSE FULL -WAVE RECTIFIER D 117V TO JO1 TO AC CHARGING 253638 2, BATTERIES TO CIRCUIT , DC TO BATTERY LED1 VOLTMETER TOBE SOURCE BATTERY R1 TO BE ¡ CHARGED 1K FIXED _ o FIG. 9-AS THE BATTERY CHARGES, the cur- FIG. 10-YOU CAN MONITOR THE CHARGING FIG. 11-YOU CAN CLEAR SMALL SHORT-CIR- rent rate will decrease. CURRENT with this simple circuit. CUITS made up of metallic salts in NiCd bat- teries. and plug them into the formulas. More gain enough energy to be at its nominal a predetermined point is reached. elaborate chargers will monitor the state voltage. Rapid charging of cells should not be of charge of the battery and automatically For this reason you shouldn't be tried unless the cell is specifically de- switch over to trickle charging when the alarmed if you measure the current flow in signed to handle very high charging -cur- battery is fully charged. These circuits are your circuit and find it a lot higher at the rents and lots of safeguards are built into used when the initial charge rate is going beginning of the charge cycle. It will soon the charger. This kind of charging takes to be in the "quick" or "rapid" range. drop to a point as close to your calculated place under very controlled conditions. How the circuit is put together will de- value as your component values are close The usual method of operation for this pend on the batteries that are being to their calculated values. If your charger kind of charger is to monitor the tem- charged and what the initial charging rate is designed for the standard rate, you perature of the cell and switch to a trickle is going to be. The actual design of these shouldn't have any problems. charge, (or completely off), when the circuits is involved because it's a good If you use a full -wave rectifier and put temperature of the cell reaches a certain idea to have several levels of protection for the current-limiting resistor between the level. Thermistors and other temperature - the battery. That way if the primary transformer and the rectifier, you will have sensing components monitor the cell and switchover circuit fails, other parts of the a variable -current charger. Current flow control logic that switches the charger to a circuit will save the day. will continue to decrease as the cell takes lower rate. The dangers here shouldn't be mini- on more and more of a charge. That cir- We've already discussed how battery mized. If you overcharge a cell at a high cuit arrangement is shown in Fig. 9. Fig- "zapping" can be used to try and clear out rate of charge, you can, of course, kiss the ure 10 is a handy circuit that you can use to small internal shorts and revive cells that battery good-bye. But we've already seen monitor the current flow. are apparently dead. Figure 11 is the basic that you're running the risk of explosive Basically the small voltage across circuit that's used. When the switch is rupture of the cell from the accumulated RSENSE turns on Ql and the transistor thrown to the left, the capacitor charges, gas and that can destroy a lot more than turns on the LED. (Anything you want and when the switch is thrown to the right, just the battery. I overcharged a 20 -milli - can be substituted for the LED. A relay, the capacitor discharges through the the- amp NiCd button cell-the smallest nick- for example could put another resistor in oretically dead battery and, we hope, el -cadmium battery you can buy. When it series with the current -limit resistor and burns out the small bridges of metallic exploded it blew a hole in the side of the cut the charging current down to a trickle salts that are shunting the current in the charger's plastic case! Be warned and be charge.) The formula for calculating the cell. careful to follow the manufacturer's rec- value of RSENSE is: If the cell can be saved, after you blast it ommendation. RSENSE = 0.65/ICHARGE a few times you should see the voltage There have been charging circuits pub- where 0.65 volt is the voltage needed to starting to rise on the meter. Once that lished repeatedly in any number of maga- turn on the transistor. If you're really a happens, give the cell a few more hits and zines, data books, and so on. Look them whiz at working out circuit parameters, then charge it normally. It won't be as up and decide which one you want to use you could get the value of RCHARGE to good as a good cell, but then again, it in your particular application. I can offer equal RSENSE and do the whole job with won't be as bad as a bad cell. You'll notice you a few general rules and a couple of just one resistor. I can't work things out that I haven't given you any value for the useful tips. for you because the values for the compo- capacitor. Well, the voltage rating should The overall system voltage in your nents depend on the batteries you use, the be at least as much as the largest voltage charging circuit will decrease as the cell charging rate, and many other factors. If in the system, (either the battery or the charges up and the current flowing in the you're careful though, you should be able source), and the capacitance should be as circuit will, naturally enough, start to to build yourself a charger that has several big as you can get. This is one of those drop until it reaches a steady state. This is charging rates and can automatically instances where bigger is better. The more because a discharged cell will rapidly re - switch over to over to trickle charge when capacitance you have, the larger the blast- ing current is going to be and the more chance you're going to have of resuscitat- ing the battery. last helpful hint has to do with one TABLE 6 Our of the most common uses for rechargeable Parameter Lead -acid batteries Nickel -cadmium batteries cells: memory retention and emergency Memory None Requires Reconditioning backup. There are lots of different ways to Current Capacity Generally in Amperes Generally in Milliamps design a circuit that will do the job, but Cost Moderate High the basic idea is shown in Fig. 12. When Weight Generally over 1 pound Generally under 1 pound the DC voltage source is present, the bat- Configurations Parallel or Series Series Only teries charge through R, the current -limit- Available Everywhere Availability Hard to Find ing resistor (because the diode is reverse 50% Loss in 8 Months 50% Loss in 3 Months Shelf Life biased). When the main power supply continued on page 96 20 L JMr TAPE STREAMER FOR YOUR COMPUTER MIKE HUDDLESTON Are incompatible disk formats keeping you from transferring files from one computer to another? This universal cassette interface can solve that problem. And at 4800 baud, it can do it in a hurry! THE COST OF MICROCOMPUTER COMPO- at work on an Intel development system, access drive like a floppy disk-the tape nents seems destined to continue to drop. and brings them home on a cassette so that moves in one direction only, and files Now you can build or buy computers at they can be run on his "homebrew" 8080 - must be accessed sequentially. prices that seemed unbelievable just a few based computer. He has also transferred The Streamer has no provisions for years ago. But when you add floppy -disk BASIC listings from a 6502 -based system motor controls, which greatly simplifies drives, the picture changes. Disk drives to cassette so that the programs could be its construction and interfacing, but re- haven't dropped in price like other com- run on his system. (Of course, while the stricts its operation to the manual mode. If puter hardware has-and it seems likely BASIC implementation may vary from you use short (5 -minute) cassettes, and that disk -drive prices will stay high. Is one system to another, those differences put only one program or one file on each, there a low-cost alternative? are usually easy to work around.) the interface will be easier to use. The Many of you probably have answered, The same thing can be done with other cassettes are cheap and reliable, but their "audio cassettes." Yes, they can be used high-level language programs, like FOR- random accessibility is limited by the time but-when compared to disk drives- TRAN or Pascal: The listings can be it takes to remove one cassette and replace their slow and unreliable performance transferred from one computer to cassette it with another. leaves much to be desired. We'll show tape and then they can be loaded into your In the course of designing the Streamer, you, however, an easy -to -build cassette next computer, without worry of disk several encoding techniques-from Kan- interface that may change all that. compatibility. Obviously, doing the same sas City Standard to FSK and PWM- That interface, which we'll call a thing in these days of endless 51/4 -inch were tried. The method chosen was Man- is a Streamer, very fast, highly reliable disk formats would be virtually impossi- chester encoding, which we'll look at in a universal audio cassette interface de- ble if the systems were not identical. few moments. Methods of data recovery signed to be a low-cost alternative to flop- evolved from the use of filter and phase - py disks. If your computer has an RS -232 Streamer basics locked loops to digital timing. The result port, you can use the Streamer to transfer The name "Streamer" is computer - is a low-cost but high-performance cas- data to any other computer similarly shop talk for "streaming tape interface," sette interface. equipped. You can transfer any program, a term normally used to refer to magnetic - Just what do we mean by "high perfor- written on any computer, to any other tape systems that are used for disk backup. mance?" The data -transfer rate is 4800 computer using a compatible language. If you're looking for something to replace baud or bps (Bits Per Second). What that For example, the author routinely writes floppy -disk drives, you should first under- means is that a 16 -kilobyte program can and debugs assembly-language programs stand that a streamer is not a random- be loaded in as little as 38 seconds. The 21 ,: meteemeemeeezSMAMMfflieMe4M2*:?. Streamer is reliable, too -the cassette some timing variations by accepting stop deck is the limiting factor, so a high- PARTS LIST bits that are either short or long, then re - fidelity type deck is recommended. (The synchronizing on the following start bit. 1/4 10% unless other- author has used a $69 stereo unit for over a All resistors watt, The Streamer extends that idea by send- wise noted year, and has had no permanent errors. ing bits to the cassette tape at a slightly R1-1000 ohms, PC -mount, trimmer po- a occurs, a simple clean- faster rate than its UART receives them. When read error tentiometer (For an RS -232 input with a data -rate of ing of the heads and capstan eliminates R2, R5, R6, R11, R16, R17, R20, R28, to the tape is at the problem.) R29-1000 ohms 4800 bps, the output sent Along with its speed and universality. R3, R4, R7, R8, R13, R14, R18, R19, R22, 5486 bps, allowing a timing mismatch of the cassette streamer has another attrac- R23, R25, R26, R30-10, 000 ohms 12.5%.) If the computers baud -rate clock tive feature: It can be built for about $60. R9-1 Megohm is a little too fast, the Streamer's UART All the electronic parts are standard, and R10-100,000 ohms will be overrun. As we mentioned pre- all are available from the vendors who R12, R21, R27-47,000 ohms viously, RS -232 can accept stops bits that Megohms regularly advertise in Radio -Electronics. R15-10 are either long or short (1' bits for exam- R24-2200 ohms ple). But there is no way to represent a half R31-330 ohms The Streamer circuit bit in Manchester encoding. (That will Capacitors become obvious when we discuss the en- Figure 1 is a schematic of the interface Cl, C4, C13-10 µF, 25 volts, electrolytic circuit-we'll start our look at it with the C2, C21-0.001 µF, ceramic disc coding). So, when the STreamer UART is power supply. The circuit requires a volt- C3, C12, C16-0.1 µF ceramic disc overrun, it fills its idle bit times with age supply between 8 and 16 volts DC at a C5, C7, C17, C18, C20, C22, C23, C24- marks (which is the convention), and in- typical current drain of only about 30 mA. 0.01 or .1 µF bypass capacitors (not serts them as needed to make up an inte- That can be supplied by an external wall shown in schematic) gral number of stop bits. C6, C10-20 pF, ceramic disc plug DC supply or it may be "stolen" That accounts for the difference in C8, C9-250 pF ceramic disc from the computer or the tape deck. If the speed from UART-to-UART, but not for C11-5 pF, ceramic disc the (typically worse) cassette -playback computer supply is to be used, the power C14-100-330 µF, 25 volts, electrolytic Tape is reliably re- can be run through pin 25 of the the DB25 C15-47-220 µF, 25 volts, electrolytic variations. timing connector. If you use a miniature closed- C19 0.01 µF, ceramic disc covered by timing each bit (Manchester circuit phone jack (J3) and wire it as Semiconductors encoding is bit -synchronous), but since shown in the schematic, then you can con- IC1-LM392 or LM2924 op-amp/com- the data may play back faster than it was veniently have your choice of either. parator recorded, it may be returned to the com- Electrolytic capacitor C14 provides fil- IC2-4070 or 74C86 quad XOR gate puter at a still faster rate. To keep things IC3-4040 12 -stage binary ripple counter compatible with RS -232 standards, the tering for the raw DC (which powers the up/down IC4,IC6-4029 presettable bits from the tape are gathered in one at a RS -232 interface and is the input to the counter grouped into 8 -bit words, and re- five -volt regulator, IC15). The negative IC5-4520 dual 4 -bit synchronous coun- time, voltage required for RS -232 is furnished ter turned to the computer at 9600 bps. by a charge pump: Transistor QI is alter- IC7-4011 quad 2 -input NAND gate Synchronous counter IC4 provides the nately turned on and off by a 76.6 -kHz IC8-4027 dual J -K flip-flop Streamer with the tape -data rates. For an clocking signal provided by IC3, and IC9, IC12-74C74 dual D -type flip-flop RS -232 rate of 4800 bps, the tape, as charges developed across C16 are trans- IC10-4015 dual 4 -bit static shift register mentioned earlier, is recorded at 5486 (Intersil) ferred to C15 through D3. A negative volt- IC11-6402 CMOS UART bps; while at 2400 bps, the tape -data rate IC13-4021 8 -stage static shift register age of slightly less magnitude than the is 2560 bps. IC4 and IC2-c form a counter IC14-LM339 quad comparator will developed that divides by either 7 or 15, depending positive supply voltage be IC15-78L05 low power 5 -volt regulator on the bit rate selected by Si. Since its across C15 for use by the RS -232 output D1 -D5 -1N914 or similar be ei- stage. D6, D7 -standard red LED input is 614.4 kHz, its output will The circuit's clock is made up of a 01, Q3 -2N3904 ther 87.77 kHz or 40.96 kHz, sixteen 2.4576 -MHz crystal (XTAL1), and an EX- Q2, Q4 -2N3906 times the tape bit rate. That 16 x bit rate CLUSIVE -OR gate (IC2-d) that's connected XTAL1-2.4576 MHz crystal will be used by both the receiver and the as an inverter. The clock's output is divid- MISCELLANEOUS: PC board, en- transmitter sections. connector, ed by IC3, a 4040 ripple counter, for the closure, DPDT switch, DB25 deck connectors, various frequencies needed by the rest of phono jacks for tape The receiver hardware, solder, etc. at 2, 3, and 5 The CMOS UART, IC 11, has two sepa- the circuit. The outputs pins The following are available from Stone rate functional sections; an NRZ receiver of IC3 are baud -rate clocks for the UART Mountain Engineering Co., PO Box -input (Universal Asynchronous Re- 1573, Stone Mountain, GA, 30086: with parallel output, and a parallel ceiver/Transmitter). Printed circuit board, double -sided NRZ transmitter. (We'll discuss NRZen- The UART uses a clock at 16 times the with plated -through holes, solder coding-and compare it to the Man- data rate, so the signals at pins 5, 3, and 2 masked and silkscreened, for $28; En- chester coding that this interface uses - (which are 153.6 76.8, and 38.4 kHz) closure, with all holes punched and later on in this article.) The receiver sec- correspond to UART baud rates of 9600, legends silkscreened, $16; Both PC tion of the UART, in conjunction with enclosure for $40. All orders 4800, and 2400 bits per second, respec- board and IC 12, IC13, IC14-d, 105-b, IC8-b, and must include $1.50 shipping and han- IC7-d comprise the RS -232 -to -Man- tively. The UART transmitter (which dling, and Georgia residents please converter. Comparator IC14-d, sends data back to the computer) always enclose 3% sales tax. chester runs at 9600 baud, SO its TRANSMITTER along with its associated discrete compo- REGISTER CLOCK, (pin 40) is directly con- nents, converts incoming RS -232 data to nected to pin 5 of IC3. However, since giving of small differences between TTL-level NRZ code. That code is applied data from the computer to the Streamer clocking frequencies. That's important to the serial input (pin 20) of the UART may be either 2400 or 4800 baud, a switch because an RS -232 data stream is contin- receiver section, which is clocked (on pin is provided to select different RECEIVER uous -that is, the stop bit of one word is 17) at the appropriate rate for RS -232 REGISTER CLOCK (pin 17) connections. followed immediately by the start bit of standard compatibility. RS -232 interfaces are usually crystal the next. Although it would seem there is An 8 -bit shift register (1C13) and a flip- controlled. Fortunately, UART's are for- no margin for error, UART's do allow for flop (IC12-b) are connected together to 22 O, IUt-yll O O Q =- O Zp F- O C7 0 F o==Q O --iE O 0 11' Cr,_ U U 4 LL v ó 4 CI o Ñ N Y O nj IE-111 C N N O LO Lt-> O N U II aZ o Op N Vl N U C Ile r(.) y ít.. Y U O O ^ () M ---1E N y - 173. cc N e O U LU iE Y r CO a J 01 CO rn O "' O i O 2M > > U l+fi O) ..4? o J N j2 A a o II 11 :a_ O LL Lo '} ` yH O n . ó U ^ Y 0 m il T0 l0 IJ- O U N I. AAI T Or 1H" U O > CO d O a M ar O O O f0 eT y 90 O ; O 10 N 2 o U 0 e O U a Y II LL ma Z L 19 Uao N d y T Ñ O1 V N M- f0 a O O 7 ]+ h N MCe á N CO U C CO cn > co CO h r ¿ N LL + lO CO O u, d 0 0 O y C O O ¿ a O O = U G taiy O T L W Q CM CC M M CC CL U O LN .0 F 1 el- M CO Ñ o V > O Id co O U ¿ U a QF. N M O U O M 11-, N U U U N W a CO CO a X X ¢ O _ V% > CC U O ' o^ i11 LL U co O CO O á W " O CZ N M e an Q O 1(-111 LL cr N Y W U cc O V Z AAA W N O O ~ L CD H r e.Oj Y O ao v O W 3 ¢ O Q N In C7 J N Q N o > I U + r. be > af O LL U LL U O_ n U Ñ CO O Ill 2 1H" W CC Al°011, v O_ UO U^. V Of LL E - 7 N H Ú a O U CM re - G 11 O .- U Q [--)/2_,z ti- 404.01r - -r CO OCO be X LL U > UtOCL 23 I 1 1 0 IC7, 1 1 here as a synchronous one-shot. It is con- PIN 9 tinually clocked at its COUNT input by the (CLOCK) 16 x a a tape rate from IC2-c, and outputs CARRY (pin 7) IC7, low pulse from its output PIN 8 whenever it reaches a count of 15. Each (NRZ) time a transition is received, however, the output of IC2-a presets the counter to a IC7, value four. So, as long as spaces are PIN 10 of C i I being received, the counter is preset every IC8, eight or so clock pulses, so it never PIN 13 reaches the count of 15 before it is again (2XCLK) I I preset to four. Mark bits, on the other d IC8, hand, have transitions only half as often as PIN 15 space bits, so the counter will reach its (MAN I) terminal count, and output a carry, when a e mark is received. Figure 3-c is the output between the two codes may not be FIG. 2-NRZ-TO-MANCHESTER CONVERSION. The relationship from the one-shot, IC6. apparent, so we should mention that Manchester encoding is based on the presence or absence of synchronous transitions-not on high or low levels. We'll discuss both encoding methods in more detail. Note that the pulses in Fig. 3-c indicate the presence of a mark; no output indi- I I I I I I I I I I I I I I 1 1 0 1 , 1 cates a space. 1 1 1, 1 1. 0 1, 0, 01 ? IC9-a is the clock -recovery flip-flop. ICI, PIN 1 a The clock signal is denved from the re- ceived data; the Streamer's internal clock 1C2, PIN 3 I 1 I I is used only to test the sense of each bit, in b I 111 I IIll1 III 111 with bit -synchronous nature I keeping the I I i I i i J J of this Manchester code. While spaces are IC6, PIN 71 I II I IL being received, IC2-a pulses two times c I I I I I a I , per bit, toggling IC9-a twice. When I I I I I I I mark is received, its single transition tog- IC9, PIN 6 d gles the flip-flop, and then the carry from IC6 presets IC9-a. That corrects the phase a bi IC8, PIN 1 I I of the clock so that, as soon as mark e L is received, the clock runs in the coned' FIG. 3-RECEIVER TIMING DIAGRAM. The Manchester signal received from the tape is shown in a phase. The clock output, IC9-a, pin 6, is transition of (after conditioning by IC1). The output of the transition detector (IC2-a) Is shown in b. Each shown in Fig. 3-d. the Manchester code produces a positive pulse. The carry output from IC6 (used to determine bit sense) is shown in c. The recovered clock is shown in d, while the reconstructed NRZ code at the The sense of each bit is detected by output of IC8-a is shown in e. IC8-a-its output is shown in Fig. 3-e. Wired as a R-S flip-flop, IC8-a is set by the form a 9 -bit parallel -load shift register. is the resulting Manchester code. Re- mark -detector output from IC6, and reset Their serial input, pin 11 on IC13, is held sistors R24 and R25, with capacitor C19, by clocking from the inverted data clock high so that marks are clocked through round off the Manchester bits and reduce from IC9-á, pin 5. The clock and data when nothing is parallel -loaded. Once the their amplitude for application to the tape inputs are applied to IC10, which is wired UART receives a serial word from the deck. as an 8 -bit serial -load shift register. At the computer, IC12-a synchronizes the UART end of an eight -bit word, the contents of to the tape -data rate from IC5-b, loading The transmitter this shift register are transferred to the IC13 with the eight bits from the UART, The transmitter section of IC11, with UART transmitter, which then outputs and IC12-b with a low for a start bit. The the remainder of the circuit components, NRZ code at 9600 bps. 9 -bit register combination now includes a recover the Manchester code from the cas- A bit counter is made up of IC9-b and start bit and eight data bits. sette and convert it to standard RS -232. IC5-a. To understand their operation, as- The shift register is clocked at the tape - The tape signal is applied to Rl, a potenti- sume that IC5-a has its Q4 output (pin 6) bit rate from IC5-b, pin 14. As soon as it is ometer that is normally full on. It is then high. That output is connected to its EN- synchronously loaded by IC12-a, it be- lightly filtered, coupled to an amplifier ABLE input, which means that it will not gins shifting out the loaded data at the stage (ICI -a) and passes to a Schmitt trig- accept any input clocks until Q4 goes low tape rate, and follows it with as many ger (IC1-b), which outputs TTL-level again (i.e., until it is reset). It will remain marks as necessary until the next word is Manchester data at pin 1. If you look at the in that state until a start bit, a space, is loaded. The effect of the circuit is that it signal on IC1 pin 1 with an oscilloscope, detected. simply changes the data rate of the re- you'll see the recovered Manchester code, On the next occurrence of a start bit ceived word; the shift register output from as shown in Fig. 3-a. Since that code is from the bit -sense detector (IC8-a) and a IC12-b is still NRZ-encoded, but now at sensitive only to transitions (and not to the clock from IC9-a, IC9-b's inverted output the faster tape-data rate. level), the signal is applied to R12, C6 and (pin 8) goes high. Since that output is An example of this NRZ code is shown IC2-a, a transition detector, which out- connected back to the RESET input on IC5- in Fig. 2-b, along with the tape rate clock puts a pulse of about one -microsecond at a, the reset operation takes place, which in Fig. 2-a. Those signals are combined in each transition. drops the output from Q4 and re -enables NAND gate IC7 to produce the signal Although we'll be discussing the cod- the counter. As the Q4 output goes low, shown in Fig. 2-c. This is applied to IC8- ing format in detail, for now let us say that IC9-b becomes preset, bringing its inver- b, which is configured as a toggle flip flop. marks will be represented here by transi- ted output back low and removing the The flip-flop will toggle whenever the tions a full bit time apart, while spaces reset command from IC5-a. It is held pre- NAND gate output is high aid the clock have transitions occurring twice each bit set until IC5-a has counted eight clock (Fig. 2-d) makes a positive transition. The time. That is illustrated in Fig. 3-b. pulses, corresponding to eight bits being output of this flip flop, shown in Fig, 2-e, A 4-bit up/down counter (IC6) is used clocked into the shift register. At the ter- 24 MARK cations controllers (UART's, USART's, START MARK etc.). Third, almost every peripheral avail- ¡ B1 82 B3 84 85 86 87 68 TOP NRZ able uses it. I I I a I 1 One characteristic of NRZ code is that I a it must be capable of preserving very long I I 1 I I I PWM periods of idleness or marking. That im- b plies that the link must have a low -end I frequency response reaching down to DC. 1 MAN I I In the typical data -equipment environ- ment, that requirement is met by hard- FIG. 4-THREE WAYS TO REPRESENT the serial data stream 11001010. Shown in a is NRZ or non- wired connections. But when connections return -to-zero encoding. In b is pulse -width modulated encoding, and in c is Manchester IA. without DC continuity are used for data, NRZ code cannot be used. Telephone minal count of eight, Da again goes high, (which are marks). The word size is not lines and audio tape, for example, where and the operation described above re- specified, but is usually five to eight bits, frequency response drops off below about peats. The Da output is also connected and may or may not contain a parity bit for 30 Hz, are two applications for which raw through R13 and C9 to IC2-b, which is eiTor detection. NRZ code is unsuitable. Due to the very connected as an inverter. When the inver- There are several good reasons for the nature of NRZ coding, there is only one ter output switches low, it is differentiated proliferation of NRZ code. First, it's easy place in an entire transmitted word where by C8 and R14, producing a negative to understand. (If you take a look at Fig. bit timing may be recovered during recep- pulse on the UART LOAD input. That 4, you'll probably be able to immediately tion. That is the initial mark -to -space causes the transmitter shift register to load see what's going on with the NRZ code transition at the beginning of the start bit. the data from IC10, and then to com- before we even discuss it.) Second, NRZ Since all other bits in the word are un- mence its transmission to the computer. is supported by numerous LSI communi- defined (and indeed, may be all spaces or The NRZ output from the UART trans- mitter is conditioned by IC14-c and tran- sistor Q4 to invert the data (RS -232 is inverted) and to swing positive and nega- O tive levels, also required by RS -232 con- o000i00 011 a0o 00a10 0 ventions. Emitter followers Q2 and Q3 4,3)O function in a totem -pole configuration to o O o ° give current drive without unduly loading 00000 the supply when operating into a high 0o00 00 O o impedance. o0 0 O The indicator LED's are turned on go o 0 when a bit of either mark or space sense is TAPE N 00 OO received from the tape. That's accom- 0 o plished by AND-ing the pO \ data lines from O IC8-a with the clock line from IC9-a, as- 88888 il t suring that, when an LED is on, a real data stream is being processed. When 11888,88 84 888 data is being decoded, both LED's will flicker at a high rate, giving the ap- O pearance of both being on. During an idle time, when the NRZ data would be mark- 1811--W°III5555F ing, only the MARK LED will be on; if the tape is blank, neither will come on. 88 8888 illlr1mm oses O Manchester encoding O AIE ouT O O o Manchester coding is a method of O'O= O Oo3 phase -encoding serial data. It was intro- p 1i1 111 0 1,9,4.. I = duced during the early days of data re- Oa III cording as a means of efficiently includ- IO n ing clocking information with transmitted o 0 data. ; o The technique was invented at Man- mi chester University in England to be used in Ferranti computers and it is in wide- m ¡ momo spread use today in both the computer and the communications industries. caqui 1: ti /1/111 0 Non -return -to -zero, .6 or NRZ, code is m by far the most common means of serial O data interchange between computers and their peripherals. Whether represented by TTL levels, RS -232 levels, or current oa o jO loops, the conventions are the same: An O idle line stays at a mark level; a data word is represented by a specific number of bits, mark or space, and each data word is 4 4 1/2 INCHES preceded by a start bit (which is a space) FIG. 5-THE COMPONENT SIDE of the double -sided streamer circuit board. Note that the square pads and followed by one or more stop bits represent the positive end of electrolytic capacitors or the banded (cathode) end of diodes. 25 all marks), it is easy to see that there are device's inherent timing instability. width of the recording medium. In order simply no other places in the word that Historically, the most common method to maximize data rate, the available band- can be predicted. That technique is known of audio data recording has been to repre- width should be made use of and the re- as word synchronization, as all the bits of sent NRZ data with two audio tones, one cording format should be bandwidth -effi- the word are recovered by timing from that for mark, and another for space. (That cient. (In other words, the ratio of the one known point. modulation technique is known as FSK or higher audio -tone frequency to the data Word synchronization implies that tim- Frequency Shift Keying.) Those two fre- rate should be low.) The 300 -baud format ing errors are cumulative: The longer the quencies are then detected during play- discussed above uses a 2400 Hz max- data word, the more likely the chances for back with either high -Q audio filters or imum frequency, indicating a frequency recovery errors. Recognizing that, de- phase -locked loops. With either tech- to data ratio of 8 to 1. The Manchester vices using NRZ coding generally are de- nique, some individual tuning is required, code used by the Streamer sports a ratio of signed with crystal -controlled clocks at and the higher the data rate, the more 1 to 1-an eight -fold increase in efficien- each end of the link, and word length is critical the tuning becomes. cy. By doubling the modulation frequen- kept under ten or so bits in order to avoid However, if you're not interested in cy, a 16 x speed advantage is attained! timing errors. maximum performance, then it's possible From the above, we can see that NRZ to design quite simple interfaces. The Building the Streamer coding is unacceptable for audio magnetic combination of modulating fairly high au- Now that we understand the theory of media: Audio tape devices are not respon- dio tones with low data rates allows great- Manchester encoding and of the Stream- sive to DC levels, and the lack of stability ly simplified (and thus lower-cost) de- er's circuit, we can get on to building it. of their motor -driven capstans precludes coder hardware to be used. The old Because of the large number of discrete precision clocking. An audio data inter- Kansas City Standard -300 baud 1200 - components, it is highly recommended face, then, must convert NRZ marks and and 2400 -Hz audio tones-is a prime ex- that the Streamer be built on a printed spaces to signals that can be successfully ample. circuit board. Full scale artwork for the recorded and recovered. In addition, the The Maximum frequency of the audio component and foil sides of a suitable interface must compensate for the tape tones is limited by the available band- circuit board is shown in Fig. 5 and 6. If you can't make your own board, you can buy a pre -etched, drilled, silk-screened, and solder-masked board from the source listed in the parts list. The parts -placement diagram for the Streamer is shown in Fig. 7. When you install the parts, use a clean, low -power soldering iron. The finer the tip, the better. If you purchase a PC board, you'll note that it has a solder mask, so the chances of the solder inadvertently bridging is great- ly reduced. Even so, it pays to be careful. If you make your own board, take par- ONIOR0o ticular care to avoid solder bridges. They may be hard to find and will definitely keep the unit from operating. There is nothing critical about the com- ponents. Everything is available through vendors that regularly advertise in Radio - Electronics. Normal precautions should be taken in the handling of the CMOS IC's as they can be destroyed by static charges. None of the capacitors are used for tim- ing, so they may have tolerances as low as 20% without ill effects. The power -supply filter capacitors, C14 and C15, can be as large as you want (as long as they fit on the board!). If the DC supply isn't filtered, however, C14 must be at least 220 µF to smooth out thé ripples. The Streamer is overdesigned with power -supply bypass capacitors. While it never hurts to include them, feel free to eliminate three or four if you want-it won't impair the circuit's operation. Note that the bypass capacitors-although O listed in the Parts List-were not shown in .a Fig. 1. They are, however, shown in the parts -placement diagram. The resistor values also are not critical. All resistors may have 10% tolerance, and you may even go to either the next higher 4-1/2 INCHES or next lower standard value, if it's more FIG. 6-THE SOLDER SIDE of the streamer circuit board. Note that square pads are used here for the convenient. The PC -mounted potentiom- same reason as on the component side. continued on page 94 26 STEREO Sound For TV BRIAN C. FENTON, TECHNICAL EDITOR A recent FCC decision has set the stage for multichannel television sound. Heres a look at that decision, its technical aspects, and the new dimension in TV sound that it makes possible. STEREO TV IS FINALLY HERE! IT'S THE gether through the EIA (Electronic Indus- The BTSC system most exciting development in television tries Association) whose Broadcast Before late March, 1984, the TV -audio since the introduction of the videodisc Television Systems Committee (BTSC) baseband-the band of frequencies from player and VCR. Interestingly enough, worked 5 years selecting a system as a 0 to 120 kHz that contains a TV signal's while the idea of stereo telev :ion has standard. The transmission system that audio information-was limited to carry been on the minds of the industry for some was chosen by the BTSC was developed ing only audio in the main channel (the time, it was the consumer's interest- by Zenith, and the noise reduction system portion of the baseband from 50 Hz to 15 stimulated by videodisc players and was developed by dbx Corporation. kHz). Now, thanks to the FCC decision, VCR's-that was the driving force behind (Those were selected over transmission the audio baseband is virtually unregu- making it a reality. But Multichannel systems developed by the Electronic In- lated. For most of us, that means that we Television Sound (MTS) is not just stereo dustries Association of Japan and Tele- can now listen to TV in stereo or in a TV-it's a completely new way of using sonics Systems, Inc. and noise -reduction second language. But for broadcasters, it television's audio signal. systems developed by Dolby and CBS means a number of options. Laboratories.) Figure 1 shows a "fully loaded" MTS The FCC decision Together, the Zenith transmission sys- audio baseband. We' Il call it stereo + SAP The Federal Communications Com- tem and the dbx-TV noise reduction sys- service. The frequency -modulated main - mission authorized multichannel TV tem make up the BTSC multichannel channel audio is contained from 50 to 15 sound in late March 1984 by adopting television sound or MTS system. We'll kHz, just as it is in any TV broadcast. new, very general rules regarding TV au- take a close look at both systems a little What ,is different from conventional TV dio signals. As a result of that action, later on in this article. signals is that the baseband also includes stereo TV sound, as well as second -lan- Even though the FCC was presented an amplitude -modulated stereo -dif- guage programming and many other ser- with a proposal for a single MTS system, ference subcarrier, a pilot signal, a SAP vices, are now possible. the Commission's decision still followed (Second -Audio -Program) channel, and a As has been the the FCC's policy of an "open marketplace" policy. That was professional channel. But that is only one late, the Commission did not adopt a sin- based on the (correct) belief that MTS of the possible configurations. Figure 2 gle system as a stereo TV standard. Re- technology will continue to advance shows three other possible configurations: member the FCC's "let the marketplace beyond the BTSC system. However, be- stereo service without SAP capability, decide" decision on AM stereo, and the cause the FCC was aware both of what mono service with SAP capability, and uncertainty and inaction in the market- happened with AM stereo and the indus- mono service without SAP capability. place that it caused. (AM stereo is yet to try's proven desire for a single standard, Note that each configuration leaves room really get off the ground.) But thanks to they endorsed the BTSC system by pro- for a professional channel. the television industry, that's not about to tecting its pilot tone. That means that the The professional channel can be used happen to stereo TV! pilot frequency may be used only by for a wide variety of non -program -related The main difference between the two broadcasters using the BTSC system. By uses. A TV station can use it to relay cases is that the industry-with the restricting the use of the pilot frequency, broadcast materials to other stations, to knowledge of what happened with AM BTSC-type receivers are protected from communicate with remote crews, etc. But stereo-presented a single proposal to the falsely detecting other MTS formats, but the professional channel could also be FCC for adoption. Both broadcasters and any other MTS system can be used if the used to transmit signals to you-or, to be equipment manufacturers worked to- marketplace calls .for it. more precise-to your TV receiver. For 27 PROFESSIONAL STEREO SUBCHANNEL a could be sent to turn on 50 CHANNEL example, signal FM (VOICE) receiver noise -reduction circuitry. An- FSK (DATA) other-though unlikely-possibility is I3-34 kHz VOICE = transmit control 0-1.5 kHz DATA that a TV station could PILOT 1 signals to your VCR so that it wouldn't MAIN CHANNEL L - R I ó 25 AM DSB-SC record commercials. dbx COMPRESSED SAP SUBCHANNEL The professional channel is not re- 15 BW =.05 -15kHz > L + R W stricted to carrying TV -related signals; it 0 SAP FM 75ps can also be used for subsidiary communi- PR EEMPHASIS dbx BW = kHz COMPRESSED like the broadcast 3 -.05-15 cations services (much BW=.05-10kHz fl FM SCA services). 244 3H 541 6 1 2I H IH It's really here! FREQUENCY -fe = 15.734 kHz BASEBAND Before we go into some of the theory FIG. 1-THE "FULLY LOADED" AUDIO BASEBAND for multichannel television sound contains the behind MTS, let us emphasize that stereo stereo subchannel, an amplitude -modu- frequency -modulated main channel, amplitude -modulated television and multichannel TV sound are lated SAP subchannel, and a professional channel. here for real. The first commercial televi- PI LOT - STEREO SUBCHANNEL sion broadcast with stereo sound took 50 place during coverage of the 1984 Sum- MAIN Television PROFESSIONAL CHANNEL(S) mer Olympics in Los Angeles. r CHANNEL < 25 digest, the industry newsletter, notes that w as of November 1, 1984, 7 stations were i on the air with almost 200 others either testing or planning MTS. Table 1 is a list BASEBAND FREQUENCY of those stations. a The Zenith transmission system FM The MTS system that was chosen by dbx COMPRESSED by the FCC is 50 SAP the industry and endorsed up of a transmission system and a ó MAIN made CHANNEL <--PROFESSIONAL CHANNEL- noise -reduction system. The transmission á 25 SAP CHANNEL PROFESSIONAL system selected was developed by Zentih. CHANNEL Lu An important aspect of the Zenith sys- O o tem is that it is compatibile with the exist- ing That is important BASEBAND FREQUENCY NTSC standard. b because any MTS system not compatible with existing TV's would be useless- neither the broadcasters nor the equip- ment manufacturers would support it. 50 In order for MTS signals to be compati- zo MAIN PROFESSIONAL CHANNEL(S) ble with conventional signals, the main CHANNEL á 25 channel must be compatible. Therefore, the main channel of the Zenith system ó signal contains the monaural signal, o which is the sum of the left- and right - BASEBAND FREQUENCY channel signals. (We'll refer to the mon- c aural signal as the stereo sum or L + R FIG. 2-THE AUDIO BASEBAND can be configured in many ways under the new regulations. Here we signal). That L + R signal frequency -mod- each configura- see stereo -only service (a), mono service with SAP (b), and mono service (c). Note that ulates the TV carrier in the same way that tion leaves room for a professional channel. That professional channel can be used for a variety of non-program related applications. a conventional mono signal does. The the stereo difference signal (L - R) amplitude -modulates a subcarrier cen- VISUAL tered at a 31.468 MHz-twice the hori- EXCITER AND zontal scanning frequency, 2fH. A pilot LEFT o TRANSMITTER STEREO signal, which is used by the receiver to RIGHT O0- NOTCHED GENERATOR DIPLEXER decode the stereo information, is located in the audio baseband at the horizontal scanning frequency, fH (15,734 kHz). As OCOMPOSITE AURAL EXCITER AND we mentioned previously, while the rest of TRANSMITTER the audio baseband is virtually unregu- lated, that pilot frequency is protected un- SAP MONITORING der FCC rules. SAP GENERATOR A standard (mono) TV set will ignore AUDIO everything but the main channel and will recover the L + R audio just as it would HORIZONTAL any mono signal. A stereo -capable set, SYNC however, will use the pilot signal both to transmitter is the sum FIG. 3-BTSC TRANSMISSION SYSTEM. The signal that drives the audio (aural) recognize that a stereo signal is present outputs. A diplexer is used so that the video transmitter and audio of the stereo -and SAP -generator and to generate a carrier for decoding the transmitter can use the same antenna. The notch filter at 4.5 MHz reduces one source of audio buzz: the direct spillover of video sideband components into the audio carrier spectrum. L -R component. 28 TABLE 1-MTS BROADCASTERS All stations stereo, non -SAP, unless other- KNBC-TV Los Angeles, CA (NBC) WEDU Tampa -St. Petersburg, (PBS) wise indicated in footnote. KWHY-TV Los Angeles. CA (ind ) FL WBFS-TV Miami, FL* (ind.)a KCEN-TV Temple -Waco, TX (NBC)a Now broadcasting regularly in stereo: WMVS WGlwaukee, WI (PBS)a WNJT Trenton, NJ (PBS)d WTTW Chicago, IL (PBS) WMVT Ivhlwaukee, WI (PBS)a KUAT-TV Tucson, AZ (PBS) WTIC-TV Hartford, CT (ind.) WLCT New London,* CT (ind.) WILL -TV Urbana -Champaign, IL(PBS)e KTLA Los Angeles, CA (ind.)a WNOL-TV New Orleans, LA (ind.) KMPH Visalüa-Fresno, CA (ind.) KIRO-TV Seattle, WA (CBS) WNBC-TV New York, NY (NBC)a WPEC West Palm Beach, FL (ABC)a KOMO-TV Seattle, WA (ABC) WCFE-TV Plattsburg, NY (PBS)a WDBB-TV Tuscaloosa, AL (ind.) WXXI Rochester, NY (PBS) Planning 1986 start: WTXX Waterbury, CT (ind ) KCRA-TV Sacramento, CA (NBC) WSBK Boston, MA (ind.) KETC St. Louis, MO (PBS) WUFT Gainesville, FL (PBS) Planning fall 1984 start: WOIO Shaker Heights, OH* (ind.) WJKS-TV Jacksonville, FL (NBC) WZTZ-TV Boston, MA (ind ) KSMW Spokane, WA* (ind.) WFMY-TV Greensboro -High (CBS) WEDH Hartford, CT (PBS) WACO Waco, TX* (ind.) Point -Winston-Salem, WFS3 Hartford, CT (CBS) WRC-TV Washington, DC (NBC) NC WTLV Jacksonville, FL (ABC)) WHYY-TV Wlmington-Phila., PA (PBS) KSHB-TV Kansas City, MO (ind.) KABC-TV Los Angeles, CA (ABC) Planning start in late 1985: 'VHA-TV Madison, WI (PBS) KTLA Los Angeles, CA (ind.)a KNME-TV Albuquerque, NM (PBS)f WFTV Orlando, FL (ABC) KMSO-TV Missoula, MT* (CBS)f KOAT-TV Albuquerque. NM (ABC) KDNL-TV St. Louis, MO (ind.) WNET N.Y.-Newark (PBS) KTUU-TV Anchorage, AK (NBC) WGGB-TV Sptld.-Holyoke, MA (ABC) KATU Portland, MT (ABC) WAIL-TV Atlanta, GA (ind.) KRBK-TV Sacramento, CA (ind.) WCBB Augusta-Lew'ston- (PBS) Planning start after 1986: KPLR-TV St. Louis, MO (ind.) Portland, ME KMTF Fresno, CA (PBS) KSL-TV Salt Lake City, MO (CBS) WSKG Binghamton, NY (PBS)a WLFI-TV Lafayette -Kokomo, IN (CBS) WMHT Schenectady -Albany- (PBS) WGBH-TV Boston, MA (PBS)a WNMU-TV Marquette, MI (PBS) Troy, NY WNEV-TV Boston, MA (CBS) WITI-TV Milwaukee, WI (CBS) WTVG Toledo, OH (NBC) WNJS Camden, NJ (PBS)e WTSP-TV St. Petersburg -Tampa, (ABC) WNJT Trenton, NJ (PBS)b WKYC-TV Cleveland, OH (NBC) FL KPOL Tucson, AZ* (ind.)f KLBY Cclby, KS* (ind.) KVIE Sacramento, CA (PBS)a WCMH-TV Columbus, OH (NBC) KOTS -TV Seattle, WA (PBS) Planning winter 1984-85 start: WOSU-TV Columbus, OH (PBS) KTVA Anchorage, AK (CBS) WTVN-TV Columbus, OH (ABC) Planning MTS, no date: WGNX-TV Atlanta, GA (ind.) WJBK-TV Detroit, MI (CBS)a WNUV-TV Baltimore, MD (ind.) WBZ-TV Boston, MA (NBC) WKBD-TV Detroit, MI (ind.) WRBT Baton Rouge, LA (NBC) WVIZ-TV Cleveland, OH (PBS) WTVS Detroit, MI (PBS)f WBNG-TV Binghamton, NY (CBS)e KERA-TV Dallas, TX (PBS)a WXYZ-TV Detroit, MI (ABC) WBMG Birmingham, AL (CBS) KOOD Hays-Russell-Gt. (PBS) KTSM-TV El Paso, TX (NBC) KFYR-TV Bismarck, ND (NBC) Bend, KS KVIA-TV El Paso, TX (ABC)a KTVB Boise. ID (NBC) KVVU-TV Henderson -Las Vegas,(ind.) KJEO Fresno, CA (ABC)c KMGH-TV Denver, CO (CBS)a NV WLRE Green Bay, WI (ind.) WGPR-TV Detroit, MI (ind.) WIUD Lakeland, FL* (ind.) KHOU-TV Holston, TX (CBS)a WFIQ Florence, AL (PBS) WMFP Lawrence, MA* (ind.) WVSN-TV Humacao, PR* (ind.) WSWP-TV Grandview, WV (PBS) WPBT Miami, FL (PBS) KIFI -TV Idaho Falls, ID (NBC)e KHON-TV Honolulu, HI (NBC) WYES-TV New Orleans, LA (PBS) WJXT Jacksonville, FL (CBS) WISH -TV Indianapolis, IN (CBS) WEDN Norwich, CT (PBS) KATV Little Rock, AR (ABC) WJCT Jacksonville, FL (PBS) KTIE-TV Oxnard, CA* (ind.) KHJ-TV Los Angeles, CA (ind.)a KHGI-TV Kearney -Hastings, NE (ABC) WPSD-TV Paducah, KY ;NBC) WMAZ-TV Macon, GA (CBS) KARK-TV Little Rock, AR (NBC) WEEK -TV Peoria, IL '(NBC) WCIX-TV Miami, FL (ind.) KTHV Little Rock, AR (CBS)e KPHO-TV Phoenix, AZ (ind.) WCCO-TV Minneapolis -St. Paul, (CBS)f KCET Los Angeles, CA (PBS) KSBW-TV Salinas -Monterey, CA (NBC) MN WISN-TV Milwaukee, WI (ABC) KUED Salt Lake City, UT (PBS)a WNJM Montclair, NJ (PBS)e WTVF Nashville, TN (CBS) KSAT-TV San Antonio, TX (ABC)c WNJB New Brunswick, NJ (PBS)e WDSU-TV New Orleans, LA (NBC) KOVR-TV Sacramento, CA (ABC) WEDY New Haven, CT (PBS) WJTC Pensacola, FL* (ind.) WFSU-TV Tallahassee, TN (PBS) WNYC-TV NY, NY (PBS) KAET Phoenix, AZ (PBS) KETV Omaha, NE (ABC) KOLO-TV Reno, NV (ABC) Planning spring 1985 start: WOFL Orlando, FL (ind.)a KXTV Sacramento, CA (CBS) WTBS Atlanta, GA (ind.) WXEX-TV Richm'd-Petersb'g, VA(ABC) KPBS-TV San Diiego, CA (PBS)a WJZ-TV Baltimore, MD (ABC)a KTSP-TV Phoenix, AZ (CBS) KPIX San Francisco, CA (CBS) WTTO Birmingham, AL (ind.) WPBO-TV Portsmouth, CH (PBS) KSAF-TV Santa Fe, NM (ind.) KWHF Boise, ID* (ind.) KBYU-TV Provo, UT (PBS) WAKA Selma, AL (CBS) new, Cedar City, UT* KTSL Sacramento, CA (ind.)a KOLR-TV Springfield, MO (CBS) WMAQ-TV Chicago, IL (NBC) KSDK St. Louis, MO (NBC)e WTOV-TV Steubenville, OH- (NBC, WCET Cincinnati, OH (PBS)a KRON-TV San Francisco, CA (NBC)f Wheeling, WV ABC) KHBS Ft. Smith, AR (ABC)e KTEH Sar Jose, CA (PBS)e KAII-TV Wailuku, HI (NBC) KMSG Fresno (Sanger), CA* (ind.) WSJU San Juan, PR* (ind.)e KAUZ -TV Wichita Falls, TX (CBS) WXII Greensboro -High (NBC) WMHT Schenectady -Albany- (PBS) Point-Winston-Salem, Troy, NY * Construction permi`, not on air. NC WVIA-TV Scranton -Wilkes (PBS) a Stereo & program -related SAP WITF-TV Harrisburg, PA (PBS) Barre -Hazleton, PA b Non -program -related SAP only new, Idaho Falls, ID* (ind.) C KTBS-TV Shreveport, LA (ABC)e Program -related SAP only WFYI Indianapolis, IN (ind.) KREM -TV Spokane, WA (CBS) d Adding stereo to SAP WRLR Las Vegas, NV* (ind.) KSCH -TV Stockton -Sacramento* (ind.) e Stereo and ron -program -related SAP WIYE Leesburg, FL (ind.) CA f Stereo, program and non -program SAP 29 goes a 75p.s preemphasis (as FM radio LOWPASS COMPOSITE TV-audio signals nor- FILTER STEREO signals and mono mally do) while the L -R signal under- goes a variable compression (the amount of compression is determined by the dbx compressor). We'll soon look at pre - emphasis and compression circuitry. To prevent overmodulation and inter- LOWPASS with portions of the base - CLIPPER ference other FILTER band (including the pilot and SAP channel), both signals are fed through 0- LOWPASS L+R FILTER 0 0 clippers and lowpass filters. 75/1s Although not shown in Fig. 4. equal- A PREEMPHASIS ° T izers are normally included in one or both AM- R 21H of the L + R and L -R paths. They are DSBSC LOWPASS, placed there to help ensure proper stereo CLIPPER FILTER separation. R LOWPASS L -R 0- FILTER Because the dbx-compressor output dbx may contain a large amount of noise, it COMPRESSO R may be difficult to measure such things as CONTROL SIGNAL stereo separation. To overcome that, as shown in Fig. 4, switches are provided to take the compressor and/or the clippers HORIZONTAL TH and lowpass filters out of the circuit. SYNC PILOT ° 4fH PLL 2 2 A subcarrier at 2fH, twice the horizon- tal line frequency, is AM-DSBSC (AM double-sideband, suppressed carrier) The composite stereo output contains L R. L R, FIG. 4-STEREO GENERATOR BLOCK DIAGRAM. modulated by the compressed L sig- and pilot signals. -R nal and is summed with the pre - emphasized L + R signal. The 2fH subcarrier signal is also divided by two to MODULATED SAP SUBCARRIER supply the pilot tone. The composite ster- eo signal that is output from the stereo generator contains the stereo sum (mono) signal, the stereo difference signal, and 5r 5tH the pilot tone. HORIZONTAL PHASE LOOP BANOPASS SYNC DETECTOR FILTER VCO FILIER o The SAP generator A block diagram of the other major component of the Zenith transmission system-the SAP generator-is shown in Fig. 5. The SAP audio is processed in SAP much the same way that the stereo -dif- °AUDIO LOWPASS ference signal is. A lowpass filter is used FILTER LOWPASS CLIPPER to remove high -frequency components FILTER that could overload the compressor, and a dbx clipper is used to prevent overmodulation COMPRESSOR of the SAP subcarrier and thus prevent interference with the rest of the audio CONTROL SIGNAL baseband. Equalization, which was used in stereo generator to preserve stereo FIG. 5-SAP GENERATOR BLOCK DIAGRAM. The SAP generator can use the same compressor that is the used in the stereo -signal generator. separation, is not needed here. Note the 5fH phase -locked loop in Fig. By combining the stereo sum and dif- that the Zenith composite signal that 5. The compressed audio is added to the ference signals in -phase and out -of-phase, drives the aural (audio) transmitter is the PLL control voltage and thus frequency - the stereo decoder can reconstruct the in- sum of two signals-the stereo -generator modulates the VCO (voltage controlled dividual left- and right -channel signals. and SAP-generator outputs. oscillator). The frequency modulated sub - That can be seen by the following equa- carrier is then passed through a bandpass tions: The stereo generator filter to protect the other audio signals (L+R)+(L-R) = 2L The input to the stereo -generator, as from SAP spillover interference. (L+R)-(L-R) = 2R shown in Fig. 4, is made up of three sig-. Now, if we look back to the block di- If you're familiar with broadcast FM ster- nals: the left- and right -channel signals agram of the Zenith transmission system eo, you've probably noticed that stereo and the horizontal -sync signal. The L and (Fig. 3), we see that the outputs of the are TV uses a somewhat similar encoding R signals are first fed through lowpass stereo generator and SAP generator method. There are some differences. The filters to remove out -of-band components added together to form the composite sig- most important-which we'll describe in that could cause crosstalk and inter - nal, which frequency-modulates the TV detail-is that the AM stereo -difference modulation. The L and R signals are then audio carrier. subcarrier is compressed. fed to a matrix circuit that forms the ster- dbx noise reduction A block diagram of the Zenith trans- eo -sum (L + R) and -difference (L - R) mission system is shown in Fig. 3. Note signals. Note that the L + R signal under- As we mentioned earlier, the BTSC 30 system is similar to the broadcast -FM stereo system. And, ust like broadcast FM, the high-freque cy components of the BTSC signal cont in more noise than the low -frequency omponents. The L -R subcarrier is, o course, at a higher frequency than the ain channel, and therefore suffers from ore noise. The Zenith trans ision system in - creases the modulatio level or deviation of the L -R signal to elp matters some - what, but the differen is limited to 6 dB because too much m ulation will cause interference to the ain channel. Even with the increased odulation of the L -R channel, the n ise level of stereo reception is about l dB greater than mono reception even ruder ideal recep- tion conditions. In less -than -idea conditions, the noise -level differenc would be worse. For example, in a gra e B reception area (where the received _cure is somewhat snowy but considered cceptable by most THIS COMPONENT -STEREO VIDEO SYSTEM from G -E car be adapted for stereo TV. people), the mono sig al -to -noise ratio is about 65 dB-most I teners won't hear cne way to ensure that the system will be you will hear that signal, and not the noise any noise. Without noise reduction, accepted by the public!) of the transmission medium. You can see however, the stereo s nal-to-noise ratio that principle in action yourself by record- would be about 50 d That's 5-10 dB Companding ing on cassette tape-and at the same worse than a standar compact cassette The dbx-TV system is a companding level-both a low -frequency tone and without noise reducti i! It's obvious that system': The signal is encoded or COM- some music with a much broader spec- for stereo TV to sel its performance pressed before it is transmitted and then trum (some rock -'n -roll music, for exam- would have to be bett - than that. To get decoded or exPANDed by the receiver. ple). You will note that the recording of that better performanc a noise -reduction Two types of compansion (or compandor- the rock music will have much less per- system is needed that ill: ing) are used by dbx: spectral and wide- ceivable noise. If you record the low fre- Provide noise redu ion even in poor - band. We'll get to the details shortly. quency tone at a higher level; it will reception areas. Companding (like other noise -reduc- appear to have less noise than the original Preserve the dynam range of the input tion methods) works to reduce noise using recording of the same tone. signal without losing adroom (the safe- the principle of masking: That is, if the From the above description, we can see ty margin between the aximum level and desired signal is loud enough and has a that for the dbx-TV system to work, it the actual level of sev e overload). broad enough frequency spectrum, then must meet two criteria. First, the level of Prevent the subcarr r from interfering with transmitted powe levels. (The mod- ulation level of the c Tosite-signal de- pends on the sum of t L+R and L -R signals, the modulati level of the sum AUIJIO must be limited-not st the level of the SWITCH separate signals.) Be reliable regar ss of manmade SAP noise. Be reasonably inex nsive and simple to implement. The Broadcast Syst s Test Commit - tee of the EIA felt that e dbx-TV system SUM CHANNEL best met those criteri better than other L+R L+R COMPENSATION systems. AND DEEMPHASIS We mentioned that e most important characteristic of any TS signal is its MATRIX compatibility with xisting signals. L -R TV (COMPRESSED DIFFERENCE dhY- TV L -R I Therefore, we can't anything to the DETECTOR CHANNEL FILTER EXFANDER main channel. That rks out fine-the noise in a 1 system comes multichan SAP from the higher-freq ncy subcarriers. The stereo (L R) sig 1, however, is en- SAP CHANNEL - FILTER coded, as is the SAP hannel. Both the SAP (COMPRESSED! stereo difference sign. and the SAP sig- nal use the same encod g scheme so that, FIG. 6-TIHE STEREO DECODER can use the sarre expander for stereo and SAP decoding, and the same speakers can be for as shown in Fig. 6, a re eiver needs only a used either stereo or SAP programming. it may be desirable, however, to use a separate SAP expander and separate SAP speaker. That's because the SAP channel isn't limited to single decoder that c. be switched be- carrying second -language programming. It could _arry an extra audio signal to enhance what's on the tween the two. (Keep g costs down is main speakers, or it could carry non-programrel.ted material. 40 m INPUT OUTPUT o N-T 30 a 20 dS 10 LOW PASS FIXED VARIABLE VARIABLE CLIPPER FILTER -- PRE -EMPHASIS GAIN ELEMENT PRE -EMPHASIS á 0 -10 20 50 100 200 500 1K 2K 5K 10K 20K FREQUENCY -Hz SPECTRAL COMPRESSOR FIG. 8-FIXED PREEMPHASIS FREQUENCY RMS BANDPASS RESPONSE curve shows that the combined DETECTOR FILTER effect of the of the 75µs and 390-µs networks helps to overcome the large amounts of noise present in poorer -reception areas. 30 WIDEBAND COMPRESSOR 20 RMS BANDPASS DETECTOR FILTER 10 FIG. 7-BLOCK DIAGRAM of the dbx-TV compressor. Note that the compressor contains three main sections: a fixed preemphases network, a spectral compressor network. and a wideband compressor network. -30 the audio signal must be high when com- mostly high or mostly low frequencies, 20 50 100 200 500 1K 2K 5K 10K 20K pared to the background noise. Second, spectral companding is used. The spectral FREQUENCY -Hz the spectrum must be wide enough to compressor examines the frequency con- FIG. 9-SPECTRAL COMPRESSION. Here we see the rangeof variation in frequency -re- noise. Another im- tent of the signal and varies the high - mask the background sponse that the spectral compressor can pro- portant consideration is that the compand- frequency preemphasis accordingly. In duce. The spectral compressor examines the ing process must not add any distortion to other words, the high -frequency pre - input signal to determine the appropriate pre the desired signal. Figure 7 shows a block emphasis is boosted in signals that con- emphasis or deemphasis. diagram of the dbx-TV compressor that tain low frequencies. But if a signal meets those criteria. We'll cover its main contains mostly high frequencies, some image of the compressor. Spectral com- sections separately. deemphasis is provided. panding gives us high masking regardless The range of the frequency response of of the frequency content of the input sig- Fixed preemphasis the spectral compandor is shown in Fig 9. nal and also helps to maintain the neces- Because the level of the background As you can see in the figure, that range is sary headroom by using preemphasis only noise increases with frequency-by 3 -dB broad, which ensures that masking will be when necessary. The range of the frequen- per octave in the stereo channel of the provided. That's because the encoded sig- cy response available from the combina- Zenith system and 9 dB per octave in the nal is dynamically adjusted so that it con- tion of the spectral compandor and fixed SAP channel-masking will occur only if tains a high proportion of-but not too preemphasis is shown in Fig. 10. the spectrum of the transmitted signal much-high frequencies contains quite a bit of high -frequency in- A spectral expander is used in the re- Wideband companding formation. ceiver to restore the program signal to its Even with fixed preemphasis and spec - Unfortunately, the energy of most pro- proper amplitude. It is essentially a mirror continued on page 93 gram material is concentrated at relatively low frequencies, so keeping the program - signal amplitude levels high will not mask the noise sufficiently. We can, however, change the spectrum of the audio signal so that it is more evenly balanced between highs and lows by using preemphasis. FM broadcasting and mono TV -audio uses a 75 -microsecond pre - emphasis. In the dbx-TV system, two pre - emphasis networks are used to reduce noise and hiss in even less -than -ideal re- ception areas. The frequency response of the complete fixed preemphasis is shown in Fig. 8. A deemphasis network must, of course, be included in the receiver. As you might guess, fixed preemphasis is not enough: Signals that already con- tain mostly high frequencies will be over- modulated, and low-level signals that contain only low frequencies will still be noisy, even with the strong preemphasis. Spectral companding To get around the problem of reducing CIRCUIT CARDS FOR THE dbx comparding system were designed to make implementation of noise in program signals that contain multichannel TV sound easy for broadcasters. 32 What can you do with electronics? Ask CIE. Computer technology. Satellite communi- Let us get you started today. Just call toll - cations. Cable television. Cellular radio. Digital free 1-800-321-2155 (in Ohio, 1-800-362-2105) electronics. Robotics. The hottest careers in or mail in the handy reply coupon below electronics. And CIE can get you started. or card to Cleveland Institute of Electronics, By teaching you the basic theory and prin- 1776 East 17th Street, Cleveland, Ohio 44114. ciples of how they work. Why CIE? Because we're the leader in specialized electronics education with over 25,000 students. With over 50 years of proven &RIMEWorld Headquarters experience teaching electronics without Cleveland Institute of Electronics, Inc. 1776 East 17th Street Cleveland, Ohio 44114 classroom sessions. And with plenty of hands on, practical experience using our specialized Please send me your CIE Off -Campus Studies Catalog, including details about the Associate Degree program. training laboratories. I understand there is no cost for the catalog and a CIE Whether it's learning new skills or upgrading representative may call, but there is no obligation. old ones, CIE can start you where you want, Print Name take you as far as you want. From the basics Address Apt. No to CIE's Associate in Applied Science Degree in Electronics. We've done it for thousands of City State Zip students. We can do it for you. Age Area Code Phone No Check box for G.I. Bill bulletin on Educational Benefits -1 Veteran I 1 Active Duty MAIL TODAY! RA -07 L - f D) Here's a unique project that uses sound to detect motion. Use it with a burglar alarm, a door opener, or in a number of other applications. DAVID M. BENZEL IN THIS ARTICLE, WE'LL BE LOOKING AT A the reflected wave is different in frequency several component values in the circuit. low-cost motion -detector sensor suitable from the one sent out, moving objects in Referring to Fig. 1, a block diagram of the for a wide variety of applications. Among the range of the device can be detected. circuit, the high -frequency bandpass am- other things, the project can be used to The above formula provides important plifiers must be able to pass frequencies detect intruders, turn on the lights when information for the choice of bandwidths from about 16.5 kHz to 17.5 kHz while someone enters a room, or open a door and cutoff frequencies. The value for fs attenuating all other frequencies. They when it is approached. Presently, five of for the project was chosen as 17 kHz be- must be able to pass and amplify the the units, controlled by a KIM computer, cause that is about where the inexpensive source and reflected frequencies, while are being used in various rooms of the tweeters used start to roll off and because rejecting other tones such as talking, out- author's home as a burglar alarm system. that frequency is inaudible, or barely au- side noise, etc. The low-frequency ampli- They have been in use successfully for fier must be able to pass over a year. the frequencies of 17.2 kHz - 17.0 kHz and 17 Theory of operation kHz -16.8 kHz, or frequen- The theory behind this project is not cies from 0 to 200 Hz. new. In fact, the original idea for it came The amount of audio about while discussing police -radar fun- power needed to drive the damentals. The basic principle behind the transmitter and amount of operation of both police radar and this amplification needed in the project is the doppler shift. Most people receiver, were determined have observed that effect at one time or experimentally. Incidently, another. Remember that train whistle or be sure to use high -frequen- car horn that sounds high pitched while cy tweeters capable of oper- coming toward you, and drops to a, lower ating at 17 kHz. Do not pitch as it moves away? That phenomenon substitute small radio re- is caused by the doppler shift, and the placement -speakers, as they change of frequency of the sound can be generally do not have the expressed mathematically for reflection proper frequency response. from a moving object as follows: The project was almost aban- VM doned in its early stages, due fR=fs to insufficient sensitivity of VM±VO those small speakers. where fR is the frequency of the return dible, to most people. wave, fs is the frequency of the source Seven miles -per -hour (or ten feet -per- Circuit description wave, VM is the velocity of a sound wave second) is a reasonable maximum speed The circuit operates in a fairly straight- at 70°F at sea level and is equal to 1119 for a walking person. Substituting those forward manner. Turning first to the re- feet/second, and Vo is the velocity of the values in the above equation, we can find ceiver (see Fig. 2), the first stage is a high - moving object. the range of return frequencies. If moving Q, high -gain bandpass amplifier. It That same formula applies to any type toward the source: provides a voltage gain of about 100. The of wave by substituting the correct VM; active-filter components were scaled to 17 1119 i.e. for radar using radio waves, VM is fR = 17,000 x - 17153.9 Hz kHz and bandpass characteristics suitable 1119 -10 186,300 miles per second. The above for- to pass the desired 16.5 kHz to 17.5 kHz, mula simply means that if a wave of If moving away from the source: while maintaining high attenuation at known frequency is sent out, the reflected higher and lower frequencies. Note the 1119 wave will in frequency the fR = 17,000 x - 16849.4 Hz decoupling circuit at R2 and Cl, used to be different if 1119+10 reflecting object is moving. Therefore by ensure stability and to isolate the op -amp having a device that is able to determine if The above values are used to determine from any supply noise. Capacitor C2 is 34 used to set the high -frequency rolloff 25VRMS =2.5V RMS =2V RMS characteristics of the op -amp and helps _700µV P-P =7V P -P P -P AT 10 FT =70mV P -P =5V prevent ICI from oscillating. Integrated circuit IC1 should be a fairly high -fre- quency op -amp; the same holds true for IC2 and IC3. If you are substituting a =4V DC AT 10FT device other than the one specified, check IC4 the manufacturers data sheet to be sure it 1C1 1C2 1C3 j04 TTL SCHMITT OUTPUT 17 in- 17 -kHz /02 I has sufficient gain at kHz. For 17 -kHz LOW - TRIGGER --o BANDPASS BANDPASS FREQUENCY stance, a 741 op -amp would not work here OUTPUT AMPLIFIER AMPLIFIER AMPLIFIER r STAGE since its gain drops to a maximum of SPKR 1 about 40 at 17 kHz. Impedance matching 0=STILL SZ C6 1 = MOTION and voltage step-up between the tweeter RECEIVER 01 03 T TWEETER - 100mV P -P (used here as a sound detector rather than = AT 10 FT. a sound source) and the first stage is done by T1 an audio trans- =-3.5V RMS 8-ohmJl000-ohm -12V P -P =10V P -P former. That transformer is placed in the TRANSMITTER f'L SINGLE UNIT BYPASS circuit so that the 8 -ohm side is connected (V V\/V to the speaker. The second stage is a high -frequency I 555 amplifier with a gain of about 100. Low - 4 -WATT POWER DISTRIBUTION R22 OUTPUT 17 -kHz FREQUENCY frequency attenuation is provided by C3 AMPLIFIER OSCILLATOR CONTROL AMPLIFIER R 24 and R3. High -frequency attenuation and >1\--L4\ stability is provided by C5. Power -supply SPKR2 OUTPUT LEVEL LINE LEVEL decoupling is taken care of here by R5 and 8S2 TRANSMITTER C4. The magnitude of the received 17 - TWEETER kHz signal at this point should be about 4 FIG. 1-BLOCK DIAGRAM of the sonic motion -detector system. Voltages given assume an object to 8 volts P-P. located 10 feet away. If there is a moving object in the range of the device, there will be another fre- quency present at the output of that stage. In addition to the 17 kHz being reflected Cl R2 from the walls, doors and other stationary 150µF/20V 18052 C4 R29 objects, there is also a weaker signal 7.+12V w 150µF/20V 18052 whose frequency is determined by the )1+ . 1M > +12V speed of the moving object. Those two 1C2 C7 R7 T10pF signals (a strong 17 -kHz signal and a 1µF 1K 1 C5 1 C3 weaker ± doppler signal) appear as an R3 7 "«. 5pF Ve 8 .02 1K amplitude -modulated waveform. Ger- 6 1 ,,,, 8 Ri i( manium diodes DI and D2 are used to 10K LM301 1C2 detect that AM signal, much like a crystal 4 R4 10K LM301 radio. The third stage is a variable -gain low - /)) R9 - frequency bandpass amplifier that rolls SPKR 1 R8 off slowly below 15 Hz and above 200 Hz. ' R27 "' R28 3.9K 3.9K 120K Those the average +14.5V - frequencies represent _c8 +17v range of doppler-shifted frequencies as 0022 determined earlier in the article. That - óó22 Z Z C17 stage uses a potentiometer, R6, to control = T.0022 +12V MC7812 unit sensitivity; it varies gain from 1 to H( t 200. C16 R10 C31 C about The output of that stage should .0022 3.9K.9K 3.9KK C30 .1 be about 5 volts P-P, if there is motion in 25µF/I = 25V the range of the device. AC and C12 That signal is rectified by D3 +12V +5V +12V 150µF/ D5 D4. The DC produced by those diodes is 1N4733 20V C11 fed to an integrator. The integrator makes C15 OUTPUT .001 R12 .02 C14 -L = sure that motion is detected for about two - 1/6 74LS14 1502/1/2 WATT 10µF/ C10 tenths of a second before setting off the O2" R17 R16 35µF/ D4 R14 10V 14 1N34A 47052 47052 10V 1N34A Schmitt trigger (the fourth stage). That 47052 2 3 ensures that random system noise and R18 room noise will not trip the unit. In addi- 2.2K + C13 R15 1/6 74LS14 tion, by placing C6 on the input of the 2µF/ 47052 D3 C6 - Z 10V 220µF/ TTL Schmitt trigger, the unit will always 1N34A R13 6V power up in the "not tripped" or still 18052 01 mode. 1N34A The transmitter circuit (see Fig. 3) is +5V quite simple in operation. A 555 timer is R6 ii EL D1 200K used as an oscillator to produce the 17 - FIG. 2-A TWEETER, SPKR 1, is used as a sound-detectio-i element by the receiver as shown in this kHz carrier. It is a good idea to use a schematic. polystyrene capacitor for C26 (the .01µF +12V +12v PARTS LIST C24 R23 22µF/ 20V 47012 All resistors'/a-watt, 10% unless other- wise noted 1 C19 R1, R4, R5-10,000 ohms, trimmer poten- = 100µF/ LM380 20V tiometer OUTPUTS LINE R20 R2, R13, R29-180 ohms (TO SPKR1 LEVEL 68K FREQUENCY R3, R7-1000 ohms IN STAND- 8 ALONE UNIT C18 R20K22 R6-200,000 ohms, potentiometer 10µF/ R19 OR OUTPUT 4,5,7, R8, R9-120,000 ohms 10V 1K AMPLIFIERS o 10,11, R10, R11, R27, R28-3900 ohms IN MULTI -UNIT , 12 R12-150 ohms, 1/2 watt SYSTEM- ;r J SEE C20 R14 -R17, R23-470 ohms TEXT) C21 C25 C26 1.OµF/ 680pF ^ . O1 R18-2200 ohms 120V R19, R24-1000 ohms, multi-turn trimmer T.01 potentiometer R20, R21, R25-6800 ohms FIG. 3 -THE OUTPUT OF the LM380, IC1, is used to either drive a speaker in a stand-alone system, or R22-20,000 ohms, multi -turn trimmer an output amplifier in a multi -unit system. potentiometer R26-1200 ohms Capacitors in the 555 -oscillator timing circuit) to re- µF, C28 +12V C1, C4, C12-150 20 volts, electrolytic duce frequency drift with temperature. 100µF/20V C2-10 pF, ceramic disc The signal can take one of two paths after C3, C15-.02 µF, ceramic disc that depending on whether a single- or ) C5-5 pF, ceramic disc R25 µF, 6 volts, electrolytic multiple -unit setup is involved. _ C27 4- L.M380 C6-220 6.8K C7-0.1 µF, ceramic disc In single -unit systems, a 555 timer and 10µF/10V C8, C9, C16, C17-.0022 µF, polystyrene a other audio 8 2 single LM380, or suitable C10-35 µF, 10 volts, electrolytic power -amplifier, are used to drive the C11, C22-.001 µF, ceramic disc tweeter (see Fig. 3). An LM380 is directly 4,5,7, - 1K4 C13-2 µF, 10 volts, electrolytic SPKR a high -gain audio -power amplifier capa- -- 10.11, OUTPUT C14, C18, C27-10 µF, 10 volts, elec- 2 12 ble of producing about 3 watts of audio C29 LEVEL trolytic power. Other desirable characteristics of 1.0µF/ C19-100 µF, 20 volts, electrolytic 20V v..- INPUT C20, C29-1 µF, 20 volts, electrolytic that amplifier are that it requires only one (FROM C21-680 pF, ceramic disc power supply, and its inputs are ground DISTRIBUTION referenced. AMPLIFIER - C23, C25-.01 µF, ceramic disc SEE TEXT) C24-22 µF, 20 volts, electrolytic In which the author's set-up, uses units C26-.01 µF, polystyrene in five different rooms, the LM380 shown FIG. 4-IN MULTI -UNIT SYSTEMS, only a single oscillator/distribution-amplifier is used. The C28-100 µF, 20 volts, electrolytic in Fig. 3 serves as a distribution amplifier. output from that circuit (shown in Fig. 5) is fed to C30-30 µF, 25 volts, electrolytic Its output is fed to a second LM380, an output amplifier, such as the one shown here, Semiconductors which serves as an output amplifier, in located in each unit. IC1-1C3-LM301 operational amplifier each unit (see Fig. 4). IC4-74LS14 hex Schmitt trigger The project requires 12 volts. Here, that IC5-555 timer +12v voltage was derived by feeding 14.5-17 IC6, IC7-LM380 operational amplifier IC8-MC7812 12 -volt regulator volts from a wall -plug supply to a 12 -volt D1 -D4, D6 -D8 -1N270 or 1N34A regulator housed in the receiver case. 05-1N4733 Zener One problem with that set-up is that the LED1-green LED with holder (Radio - system becomes disabled if power in the Shack 276-019 or equivalent) house is interrupted. A solution to that 1.2K 81 T1 -transformer, 1000 -ohm primary, 8 - problem is to supply a battery back-up as 12V NiCd ohm secondary (Radio -Shack shown in Fig. 5. The circuit shown in that 273-1380 or equivalent) figure will enable BI, a battery pack made I SPKR1, SPKR2-tweeter (Radio -Shack up of 10 NiCd cells in series, to cut in any 40-1270 or equivalent) Miscellaneous: Perforated construction time that power is interrupted. It will also FIG. 5-A BATTERY BACK-UP will keep the sys- tem active in case of a power interruption. board, metal project boxes (2), cabinet trickle charge the cells so that the batteries materials (see text), wire, solder, etc. will not become depleted during the long (hopefully!) periods between uses. by, we suggest using 1/4 -watt units instead. be compromised, the least expensive suit- Here are some tips: The ground leads able components were used. With careful Construction should be of heavier wire to reduce induc- shopping, the cost of building a unit Although there is little that is critical tance. Make an attempt to separate inputs should run about $35.00, or less if you about the circuit, good construction prac- from outputs on the gain stages. Keep have a well stocked junkbox. tices should be followed. The author's leads short. Make absolutely sure to use a The cabinet shown here and on the prototypes were built on perforated con- regulated, filtered power supply as shown; cover was made out of acrylic plastic for struction board and point-to-point wiring remember, the three stages have a com- appearance reasons. The author's pro- was used with good results. Figure 6 bined gain of around 1,000,000. It is a totypes, however, were made from shows the receiver and output -amp board good idea to house the receiver in a plywood, which is cheaper and easier to layout used by the author. Note that R6 shielded box separate from the transmit- work with. When you make your cabinet, and LEDI are brought outside of the box ter. And be sure to use shielded cable from be sure that it is large enough to accom- housing the receiver circuit and are ce- the tweeter to the receiver. modate the two tweeters and the two mented to the cover of that box. Also Y8 - Common parts are used in this design, boards. The tweeters can be mounted on watt resistors were used in the prototype. and they are easy to obtain from a number the front panel of the cabinet with either As those resistors can be difficult to come of sources. Where performance would not continued on page 90 36 Flat Panel Color TV A practical flat -panel color display has long been a dream. Now, thanks to a recent breakthrough, that dream has come true. Here's a look at that breakthrough, and the revolutionary TV that makes use of it. CARL LARON, ASSOCIATE EDITOR MOST READERS OF RADIO -ELECTRONICS display developed by Epson, on the other shown in Fig. l -b, the molecules stand on are familiar with the first generation of hand, the picture is generated by rows of end, parallel to the electric field. Since flat -panel LCD -TV's that began appear- pixels (picture elements). Each pixel is then the light is no longer twisted, light ing during the past year. While they repre- switched on and off by a microscopic that passes through the rear polarizer is sented a significant step forward in tech- thin-film transistor. The pixels in the Ep- absorbed by the front polarizer. nology, they left a bit to be desired in son display are not phosphors, however, Before a successful liquid -crystal dis- terms of performance. Among other but are liquid crystals. play could be created, some relatively dif- things, those displays suffered from blur- Liquid crystals are long organic mole- ficult technical problems needed to be ring; images seemed to flow across the cules with the optical properties of both solved. For one thing, conventional liquid screen, leaving comet -like trails behind. liquids and solids. In the display, the liq- crystals, the kind used in watch and cal- Also, up to now, the displays were avail- uid -crystal material is sandwiched be- culator displays, switch relatively slowly. able in black -and -white versions only. tween two polarizers whose transmission (By switch, we mean change from their Those drawbacks have been elimi- axes are orthoganal (separated by 90 de- twisted to their untwisted orientation nated, however, in a new development re- grees) to each other. When no electric when an electric field is applied, and back cently announced by Epson (23530 field is present, the condition shown in again when it is removed.) That problem Hawthorne Blvd., Suite 100, Torrance, Fig. 1-a, the liquid crystal molecules are was solved through the development of a CA 90505). That development is a flat - arranged so that the one nearest the front liquid -crystal that reacted faster to the panel, color, liquid -crystal display with a polarizer is parallel to that polarizer's presence or absence of an electric field. very fast response time. In fact, despite its transmission axis, and the one nearest the Incidently, the blurring that is a com- lower resolution, the quality of the picture rear polarizer is parallel to that polarizer's mon problem of earlier LCD -TV displays that can be produced by the Epson display transmission axis. The successive layers is caused by slow switching times; Ep- is comparable to that of a CRT. of molecules twist gradually through the son's display switches fast enough to to- 90 degrees between the front and rear po- tally eliminate such blurring. A flat -panel display larizers. Light that enters through the rear Other significant problems were the In the CRT that we are all familiar with, polarizer is twisted 90 degrees by the liq- low contrast of liquid -crystal displays and the picture is created by sweeping an elec- uid crystal molecules and passes out the the fact that most were capable of only tron beam across a phosphor -coated front polarizer. producing dark images on a light back- screen in response to a video signal. In the But when an electric field is present, as ground or light images on a dark back - 37 color image is created by selectively ex- citing red, blue, and/or green phosphors arranged in a tight matrix. In the Epson system, color is created through the use of color filters. Tiny red, ¿'s . blue, and green filters are placed in a tight matrix pattern, and the entire arrange- `.\y ment is placed in front of the LCD. The matrix is arranged so that one of the color- ed filters is placed in front of each TFT (pixel). ill1111111 Let's see how the system works. If, for a instance, a red area is to be created, the the light 90 FIG. 1-WHEN NO ELECTRIC FIELD is present, the liquid -crystal molecules twist degrees, TFT's at the blue and green filters are thus allowing it to pass through the front polarizer as shown in a. When an electric field is applied, the molecules no longer twist the light so that the light is absorbed by the front polarizer as shown in b. turned on, preventing light from passing through them. In the meantime, light con- tinues to pass freely through the red filter. GLASS Conversely, if blue is desired, the TFT's at OUTPUT LIQUID ELECTRODE CRYSTAL the red and green filters are turned on; if green is desired, the TFT's at the blue and COMMON red filters are turned on. ELECTRODE Colors can, of course, be combined to THIN FILM produce others. White is created by turn- TRANSISTOR II ing off all of the pixels in an area, thus 1 1ri,, e allowing all of the colors through. Black is created by turning on all of the pixels, POLARIZER thus blocking all light. A full gamut of other colors and shades (see Fig. 3) can be created by selectively turning on or off the various pixels in a region. `fa% POLARIZER COLORED FILTERS FIG. 2-THE EPSON DISPLAY consists of a rear horizontal polarizer, liquid -crystal cell, and front vertical polarizer. The electric field is applied using a unique system consisting of thin-film transistors and a common electrode. ground. (See Fig. 1.) the difference between the black and white levels is not very great. The solutions Epson's solution to that problem is a Prior to the development of Epson's technique called "active -matrix address- display, multiplexing was used in liquid - ing." In it, the 240 row and 220 column FIG. 3-A WIDE VARIETY OF COLORS and crystal display devices to control the thou- electrodes are all placed on a single glass shades can be created using various combina- sands of pixels needed to generate an im- substrate. On the opposite side of the dis- tions of red, green, and blue. age. In multiplexing, rows of electrodes play is a common electrode. are placed on one side of the liquid crys- At each row and column junction, a The Elf tal, while columns of electrodes are Thin Film Transistor (TFT) is located. Epson's first application of its new placed on the other; the junctions where Those transistors, made from poly- technology is its Elf flat -screen TV (see the rows and columns crossed would cor- crystalline silicon, turn on whenever a Fig. 4). According to the manufacturer, respond to a pixel. pixel is to be activated. Which pixels are that tiny color TV should be on store To turn on a pixel, control pulses would to be turned on is controlled by the driver shelves by the time you read this. be fed in rapid succession to each row. circuitry of the device. Through the use of The Epson Elf is almost transistor -radio Those pulses would turn on selected elec- TFT's, each pixel receives the full voltage sized, measuring 3.15 x 6.3 x 1.22 trodes in that row. Meanwhile, all of the required for turn -on. As that voltage is no inches, and weighs just 1.1 pounds. The column electrodes would be pulsed simul- longer a time -weighted average, the on- set features a 2 -inch, diagonal -measured taneously. While the voltage generated by off ratio is much higher than in multiplex- screen. The heart of the device is the new the column electrodes would be insuffi- ed devices, resulting in good contrast lev- flat -panel LCD unit, which is shown in cient to affect the liquid crystal mole- els. A diagram of Epson's LCD system is Fig 5 and described above. cules, when the column and selected -row shown in Fig. 2. The tiny TV can be powered from any electrodes are both pulsed, the voltage one of three power sources. Those are level is sufficient to effect the liquid crys- Adding color either standard or rechargable "AAA" - tal molecules and they respond. Once the problem of devising a suitable sized cells, an AC power adaptor, or a car - That technique has a serious draw- monochrome display was solved, the next battery adaptor. back-poor contrast. The reason for it is step was the addition of color. The ap- Among the user controls are TINT, that the time -weighted average on -off proach taken was not unlike that used in COLOR, and BRIGHTNESS. All VHF and voltage ratio is very low, which means that conventional color CRT's. In those, the UHF TV channels can be received, and 38 pixels are used to create the image in the LCD. Even so, the image was extremely watchable. The color reproduction was true and the contrast level was acceptable for viewing even in a brightly lit office. Other aspects of the set are pretty much what you would expect in a set of this FIG. 4-THE EPSON ELF is as small as s paperoack book, weighs just ow- one pound, and car type. Sound quality is definitely not "hi- operate indoors or out. It makes use of Epson's flat -screen color liquid -crystal display. fi," but it is adequate. The level of the audio is quite sufficient for personal lis- tening in all but the noisiest environ- ments. For those, you would want to use an earphone or a headset anyway. Al- though we tried the unit out in the "con- crete canyons" of Manhattan, with all of the reception problems that that entails, the overall quality of the picture and sound was good on all receiveable VHF and UHF channels. There were a few "bird- ies" (spurious signals) generated by the unit when tuning between the high and low VHF bands, but those were inconse- quential. Whenever a product makes use of a technological breakthrough, you would expect the initial price to be high. The Epson Elf is no exception. The suggested list price of the unit at the time of this writing was $500. As with any other new technology, however, expect prices to fall as more units are sold and the costs of production go down. FIG 5-THIS FLAT-SCREEN color liquid -crystal display is the heart of Epson's new Elfpocket-sized TV. The size of the display used in the Elf was not selected primarily because of the channel selection is done via a slide-rule adaptor, mini -earphone, handstrap, soft current popularity of small -screen person- type tuner. There is also an earphone jack carrying case, and a 27 -inch telescopic al TV's. The cost of the display is directly that allows the use of a standard earphone antenna. Optional accessories include related to its size. Thus, although a set or mono headset for private viewing. car-battery adaptor and a rechargable bat- with a somewhat larger display (up to When used outdoors, conventional tery pack. There is also a fold -out tilt stand about 5 -inches) is within the current tech- TV's are faced with the problem of poor in the rear. nology, the cost of such a display would contrast due to the high ambient light lev- After spending some time with the make the set too expensive to market els. But because the Elf uses a backlighted unit, our overall impressions of it are very practically at the present time. display, a unique feature turns the tables favorable. This set has advanced the state- Eventually, of course, those costs, too, on that troublesome problem. The rear of of-the-art of LCD imaging manyfold. The will come down. Once they do, the ap- the unit can be opened, allowing the sun's picture produced is far better than those plications for the Epson display are almost rays to be used as the light source for the produced by previous LCD devices. The limitless. Indeed, company reasearchers backlighted LCD. That greatly improves addition of color is also a major step for- are looking at a number of future prod- viewing in outdoor settings. When the ward. ucts, including a flat -panel liquid -crystal back is opened, a switch allows you to In fairness, however, we must point out TV that could be hung on a wall like a turn off the set's internal light source (it's that the image is nowhere near as sharp as picture. While such a set is still many no longer needed) to conserve batteries. that produced by a comparable -sized CRT years away, the development of products The Elf comes with a number of stan- display. That reduced resolution is, of like the Elf have brought it a little closer to dard accessories. Those include an AC course, caused by the fact that far fewer realization. R -E 39 I- c-31) \"1S CMOS C1 CLOCK SOUAREWAVE OUTPUT 1/6 4049 CIRCUITS FIG. 1-THIS 2 -GATE CMOS ASTABLE operates at 1 kHz with the component values shown. The next time you need a clock generator, pick out one of these CMOS-based designs. RAY MARSTON CMOS LOGIC IC'S CAN EASILY BE USED TO The output of the astable circuit in Fig. Cl make squarewave-generator or "clock" 1 switches (when lightly loaded) almost circuits that are both inexpensive and fully between the zero and positive supply highly versatile. The outputs can be sym- rail values. But the RI -Cl junction is pre- metrical or non -symmetrical, and the os- vented from swinging below zero or above cillators can be either free -running or the positive rail levels by on -chip clamp- gated. The gated oscillators can be de- ing diodes at the input of ICI -a. That 4 signed to turn on with either logic -0 or characteristic causes the operating fre- SQUAR EWAVE logic -I signals, and to give either a logic -0 quency of the circuit to be somewhat de- OUTPUT or a logic -1 output when in the "off" pendent on the supply: Typically, the 1/6 4049 mode. You can even use those "cheapo" frequency falls by about 0.8% for a 10% is circuits as simple VCO's (Volt- rise in supply voltage. If the frequency FIG. 2-THE "COMPENSATED" VERSION of the age -Controlled Oscillators) or as frequen- normalized with a 10 -volt supply, the fre- 2 -gate astable oscillator has excellent frequen- cy-modulated oscillators. quency falls by 4% at 15 volts or rises by cy stability with variations In supply voltage. If you want VCO operation with excel- 8% at 5 volts. lent linearity and versatility, then you have The operating frequency of the circuit voltages during circuit operation and thus to be slightly more particular about the IC shown in Fig. 1 is also influenced by the improve the frequency stability of the cir- you use. We'll get to that in just a little individual gates that are used. You can cuit. Typically, when R2 is ten times the while. But first, the basics: 2 -gate CMOS expect the frequency to vary by as much as value of Rl, the frequency varies by only squarewave-generator or astable circuits. 10% between individual IC's. The output 0.5% when the supply voltage is varied symmetry of the waveform also depends between 5 and 15 volts. An incidental Two -gate astable oscillators on the particular IC used and, in most benefit óf R2 is that it gives a slight im- The simplest way to make an astable cases, the circuit will give a non -sym- provement in the symmetry of the output circuit is to wire two CMOS inverter metrical output. In most "hobby" or of the astable. stages in series and use the R -C feedback other non -precision applications, those The basic and compensated astable cir- network shown in Fig. 1. That circuit gen- defects of the basic astable circuit are of cuits of Figs. 1 and 2 can be built with a erates a decent squarewave output and op- little practical importance. good number of detail variations, as erates at about 1 kHz with the component We should note here that for the circuit shown in Figs. 3 to 5. In the basic astable values shown. The frequency is inversely in Fig. I-and all of the others that we'll circuit, for example, Cl alternately proportional to the R C time constant, so present this month-the supply voltage charges and discharges via R1 and thus it can be raised by lowering the values of indicated by " + V" can be anywhere has a fixed symmetry. Figures 3 to 5 show either Cl or Rl. Capacitor Cl must be a from 3 to 18 volts DC. Also, the CMOS how the basic circuit can be modified to non -polarized type; it can have any value IC's used are all of the "B -series" type give alternate charge and discharge paths from a few tens of pF to several µF. Re- (with improved gate -oxide protection.) for Cl and thus to allow the symmetry to sistor Rl can have any value from about 47 Figure 2 shows an improved, "compen- be varied at will. kilohms to 22 megohms. With those sated" astable circuit in which R2 is wired The circuit in Fig. 3 is useful if you ranges of values, the operating frequency in series with the input of IC1-a. That need a highly non -symmetrical waveform can vary from below 1 Hz to about 1 MHz. resistor must have a value that is large (such as a pulse). Capacitor Cl charges in For variable -frequency operation, R1 relative to R1; its main purpose is to allow one direction via R2 in parallel with Rl, to should be replaced by a series combina- the RI -Cl junction to swing freely below generate the mark (or pulse) part of the tion of a fixed and a variable resistor. the zero and above the positive supply rail waveform. It charges in the reverse direc- 40 SQUAREWAVE R3 and R2, and in the other direction via signal. That is shown by the two basic OUTPUT Dl and the upper half of R3 and R1.*The versions of the gated astable multivibrator cl duty cycle can be varied over a range of in Figs. 8 and 9. 01 1.11 to 11:1 via R3. Figure 6 shows a couple of ways of using the basic astable circuit as a very IN simple VCO. The circuit in Fig. 6-a can be OUT used to vary the operating frequency over a limited range via an external voltage. +V For satisfactory operation, R2 must be at least twice as large as Rl. Its actual value depends on the required frequency -shift range: A low R2 value gives a large fre- IN c- quency -shift range, and a larger R2 value b FIG. 3-YOU CAN MODIFY THE 2 -gate astable to gives a small frequency -shift range. The give a non -symmetrical output.. The "mark" time is controlled by the parallel combination of R1 circuit in Fig. 6-b acts as a special -effects VCO and R2. The "space" time is controlled by only in which the oscillator frequency OUT OUT R2. rises with input voltage, but switches off c IN cI o a completely when the input voltage falls d P Cl below a value preset by R3. WO -INPUT NAND OR NOR gates can .01 be usad as inverters. As we'll see, they permit CONTROL -VOLTAGE gated operation. As with any other CMOS IC. be 01 INPUT sure 1N4148 to tie all unused inputs to one of the supply SQUAREWAVE rails. R3 OUTPUT R2 R2 100K 100K 180K 'SPACE MARK R1 Cl C1 R1 68K .01 .001 R1 680K 10K 3 2 5 4 1/64049 GATE IN 4 8 6 ®1 /6 4049 SQUAREWAVE 1 /4 4011 8 1/4 4011 OUTPUT R2 16 4049 1/6 4049 100K CONTROL -VOLTAGE OUTPUT FIG. 4-THE "MARK" AND "SPACE" times can INPUT be independently varied by R2 and R3 respec- SQUAREWAVE FIG. 8-THIS GATED ASTABLE has a normally - OUTPUT tively. R3 low output. It is gated on by a high input. 100K CUT-OFF ADJ Cl Cl R2 +V 05 100K .01 OUTPUT R1 +V +V R1 10K 02 54148 R2 M/S 100K 14 RATIO 5 GATE 100K 1/6 4049 IN 1 /6 4049 +V O 154148 1/4 4001 02 b R1 e101( nr_ C w C1.*01 o Uni rwGE-CONTRO' ' cm ne = 680K Cl CILLATOR or VCO is shown in a. Shown in b is a .001 VCO that cuts off when VIN falls below a value is 8 that preset by R3. 1/6 4049 1/6 4049 FIIG. 9-THIS GATED ASTABLE has a normally- hiigh output. It is gated or by a bw Input. Gated astable circuits SQUAREWAVE OUTPUT All of the astable circuits of Figs. 1 to 6 FIG. 5-THE DUTY CYCLE OF THIS ASTABLE is can be made using NAND or NOR gates Note specifically from those two cir- fully variable from 1:11 to 11:1. instead of inverters. Simply replace the cuits that the NAND version is gated on by inverters with one of the gates as shown in a logic -1 input and has a normally -low tion via R2 only, to give the space be- Fig. 7. output, while the NOR version is gated on tween the pulses. Using NAND and NOR gates instead of by a logic -0 input and has a normally high Figure 4 shows the modifications for inverters has a practical advantage-it lets output. Pull-up (or pull -down) resistor R2 generating a waveform with indepen- you modify all of the circuits in Figs. 1-6 can be eliminated from the circuits if 1C1 - dently variable mark and space times; the for gated operation. In other words, the a is direct -coupled from the output of a mark time is controlled by Rl, R2, and astables can be turned on and off by exter- preceding CMOS logic stage. Dl, and the space time is controlled by nal signals. All you have to do is to use a In the basic gated astable circuits of Rl, R3, and D2. 2 -input NAND (4011B) or NOR (4001B) Figs. 8 and 9, the output signal terminates Figure 5 shows the modifications to gate in place of the inverter in the ICI -a as soon as the gate drive signal is re- give a variable duty-cycle (or mark/space position, and apply a control signal to one moved. Consequently, any noise present ratio) output while maintaining a near- of the gate input terminals. By choosing at the gate terminal also appears at the constant frequency. Here, Cl charges it the appropriate gate, you can control your outputs of those circuits. Figures 10 and 11 one direction via D2 and the lower half of astable by either a high or a low gate show how to modify the circuits to over - 41 ultra -high -gain non -inverting amplifier OUTPUT and its main timing components (RI -C1) cl are transposed (relative to the 2 -gate asta- GATE OUTPUT 1pF IN ble). Because of the very high overall gain R2 of the circuit, it produces an excellent and 100K glitch -free squarewave output, ideal for 14 i 8 0 clock -generator use. . 91W. be © 1/4 4011 The basic ring -of-three astable can r, 7 1/4 4011 subjected to all the design modifications Cl that we've already looked at for the basic lpF R1 680K 2 -gate astable-it can be used in either Mh-- basic or compensated form and can give FIG. 15-THIS ASTABLE IS GATED on by a logic - a GATE either symmetrical or non -symmetrical 0 signal and has a normally low output. IN 01 output, etc. The most interesting varia- 1N4148 22K tions of the circuit occur, however, when it is used in the gated mode, since it can be gated via either the ICI -b or IC1-c stages. GATE 13 a.. FIG. 10-SEMI-LATCHING OR "NOISELESS" Figures to 16 show four variations on IN OUTPUT gated astable has a normally -low output and is that gating theme. +V R2 gated on by a high input. The circuits in Figs. 13 and 14 are both 100K gated on by a logic -1 input signal, but the 4 10 +V 61:11). 1/4 4001 1/4 400.1 OUTPUT 31/4 4001 Cl R2 GATE 22K 01 1pF 1N4148 R1 IN 680K 02 FIG. 16-THIS ASTABLE IS GATED on by a logic - 1N4148 and has a normally high output. 1/6 4049 1/6 4049 0 signal circuit in Fig. 13 has a normally -low out- OUTPUT put, while that of Fig. 14 is normally-high. FIG. 12-THE "RING -OF -THREE" astable makes Similarly, the circuits in Fig. 15 and 16 are an excellent clock generator. both gated on by a logic -0 signal, but the output of the circuit in Fig. 15 is normally- Cl low, while that of Fig. 16 is normally- 1pF high. 61 FIG. 11-ALTERNATIVE SEMI -LATCHING asta- 680K ble has a normally-high output and is gated on Cl .10 4046 VCO circuits 1µF by a low input. To close this look at CMOS square - wave generator circuits, let's consider come that problem. There, the gate signal some practical VCO applications of the of IC1-a is derived from both the "outside 4046 phase -locked loop (PLL) IC. Figure world" and from the output of IC1-b via 4011 1/4 4011 1/4 4011 17 shows the internal block diagram and the diode OR gate (D1, D2, and R2). As pinout of the 4046, which contains a cou- o soon as the circuit is gated from an exter- ple of phase comparators, a VCO, a Zener nal signal applied via D2, the output of diode, and a few other bits and pieces. ICI -b reinforces or self-latches the gating For our present purpose, the most im- via D1 for the duration of one-half astable portant part of the chip is the VCO sec- cycle. That eliminates any effects of a tion. That VCO is a highly versatile noisy external gate signal. The outputs of FIG. 13-THIS GATED "RING -OF -THREE" asta- device: It produces a well -shaped sym- the "semi -latching" gated astable circuits ble has a normally -low output and is gated on by metrical squarewave output, has a top -end a logic -1 signal. are thus always complete numbers of half frequency limit in excess of 1 MHz, has a cycles. voltage -to -frequency linearity of about 1%, and can easily be "scanned" through Ring -of -three circuits a 1,000,000:1 range by an external voltage The 2 -gate astable circuit is not gener- applied to the VCO input terminal. The ally suitable for direct use as a "clock" frequency of the oscillator is governed by generator with fast -acting counting and the value of a capacitor (minimum value dividing circuits. That's because it tends 50 pF) connected between pins 6 and 7, to pick up and amplify any supply -line 8 by the value of a resistor (minimum value noise during the "transitioning" parts of ®D3 rap. 4 0 10K) wired between pin 11 and ground, its operating cycle and to thus produce 1/4 7 1/4 4011 ®: and by the voltage (any value from zero to the supply voltage) applied to VCO-input squarewaves with "glitchy" leading and = GATE IN trailing edges. A far better type of clock R2 pin 9. generator circuit is the ring -of-three asta- 100K Figure 18 shows the simplest possible ble that is shown in Fig. 12. way of using the 4046 VCO as a voltage - The Fig. 12 ring -of -three circuit is sim- controlled squarewave generator. In that FIG. 14-THIS GATED "RING -OF-THREE" asta- ilar to the basic 2 -gate astable, except that ble has a normally -high output and is gated on circuit, the C1 -RI combination deter - its "input" stage (ICI-a-IC1-b) acts as an by a logic -1 signal. (continued on page 89) 42 VICTOR MEELDIJK DID YOU KNOW THAT: SELECTING Polystyrene foil capacitors may be better for timing circuits than polycarbo- nate types? Tantalum capacitors are not recom- THE BEST mended for any application where current spikes are present? A hybrid potentiometer consisting of RESISTOR/CAPACITOR a wirewound element and a conductive plastic track will have a life span that is 10 times greater than that of a wirewound potentiometer? There's to Power wirewound resistors can be op- much more selecting components for your designs erated with a body temperature of 275°C, and projects than meets the eye. In this article, we'll look at the and that some can operated at body tem- various types of resistors and capacitors, and what factors you peratures of as high as 500°C? From the above, it should be clear that should consider when selecting which type to use. there's a lot to know about the many dif- ferent types of resistors and capacitors available. That's because each type has its composition resistor is used in applica- classified according to the techniques own unique characteristics, and those tions where initial tolerance need not be used in their manufacture. characteristics make some types of re- closer than ± 5% with long term stability One such technique is vacuum deposi- sistors and capacitors far better for certain no better than ± 20%. tion, which is also known as evaporated applications than others. Selecting the For variable resistors, one problem is metal film. In it, a nickel -chromium alloy proper component for a particular ap- that the carbon element requires a high is superheated in a vacuum. The alloy plication is vital in order to ensure the contact force to ensure that any variation vaporizes and is deposited reliability of your design. In this article, in the contact resistance remains within on a ceramic sub- we'll look at the various factors that you acceptable limits. That results in high strate. Small quan- should consider when selecting resistors shaft -torque and poor adjustability. tities of con- and capacitors for your projects. Carbon elements are sus- tami - ceptible to moisture ab- Resistors sorption and such When selecting a resistor, consider sta- moisture absorption bility, noise, power dissipation, environ- can cause the resis- ment, AC requirements, and resistance. tance to change Actual resistance value is a function of by as much as tolerance, voltage coefficient, tem- 20%. That re- perature coefficient, and drift with time. sistance shift The power rating is based. upon ambient can be .re- temperature and derating. Derating, versed if the which is the operation of a component at device is something less than 100% of its specified baked at high rating, may be necessary because of en- temperatures vironmental conditions. (100°C). Resistor compositions include carbon, film, and wirewound for fixed resistance Film resistors units, and cermet and conductive plastic Metal -film de- for variable resistors. Figure 1 shows vices are used in ap- many of the types of resistors available. plications requiring higher stability and preci- Carbon resistors sion than available from car- Carbon -composition units have a re- bon devices. In addition, metal - sistive element that is molded from car- film resistors should be used in bon powder that has been mixed with a applications where AC is present. Op- phenolic binder to from a uniform re- eration is satisfactory from DC to the sistive body. That device, molded with MHz range. Metal -film units have low end leads, is a general purpose resistor temperature coefficients and suffer little capable of withstanding temperature and degradation to ambient temperatures of electrical transient shocks. The carbon- 125°C and higher. Film resistors can be er than .0001 inches thick) and is used in applications requiring high power density or the capability of surviving power spikes or overloads. Those units are suitable for some precision applications, but not those requiring an extremely high degree of pre- cision. Bulk metal resistors, made in a process that is properietary to the Vishay Corpora- tion, metal foil is laminated to a substrate and then chemically etched to produce a conductive path. The flat element is used exclusively for high -precision applica- tions and has tight tolerances and an ex- FIG. 1-THERE ARE MANY DIFFERENT resistor compcsitions and types Among them are carbon. film, wirewound. cermet. and conductive plastic. cellent temperature coefficient. TABLE 1-RESISTOR SELECTION GUIDELINES nants, called dopants, are used to control resistor characteristics such as resistance TYPE SPECIFICATIONS AND NOTES range. Those resistors are used in applica- Carbon composition Resistance range: 2.7 ohms to 100 megohms Power rating: to 2 watts require an extreme degree of tions that Tolerance: 5°o to 20% precision. Temperature coefficient: --200 to 8000 PPM C In sputtering, a nichrome target is heat- Noise: less than 6 µVIV ed and bombarded by argon atoms. That Derating factors: 50% power. 80% voltage results in metal atoms being knocked off Notes: General purpose. Excellent transient and surge handling and deposited on a substrate. Resistors capabilities. RF produces capacitive effects end to end, and manufactured using that sputtering tech- operation at VHF or higher frequencies reduces effective nique are also suitable for applications resistance due to dielectric losses. Resistance increases by 20 humid conditions. that require a high degree of precision. during storage under Carbon compos tion Resistance range: 50 ohms to 10 megohms In metal -oxide deposition; a chemical potentiometer Power rating: to 5 watts vapor is used to deposit a tin -oxide film Temperature coefficient: 1000 PPM `0 onto a glass substrate. That technique, let Derating factors: 50% power. 80% voltage which is primarily used by Corning is Life expectancy: 5.000.000 rotations used to produce resistors for general-pur- Failure mode: noise pose, semi -precision, and precision ap- Notes: High shaft torque causes poor adjustability plications. Carbon Film Resistance range: 10 ohms to 25 megohms Thin-film resistors are highly stable. Power rating: 0.1 to 10 watts have low -noise characteristics, and have a Tolerance: 2% to 10% Temperature coefficient: -- 200 to - 1000 PPM -C very low -coefficient. They temperature Noise: less than 10 µV.V are used in digital multimeters, precision Derating factors: 50% power. 80% voltage voltage -dividers, attenuators, A/D and Notes: General purpose, cost less than carbon-corrpcsition D/A circuits, and in current -summing ap- units plications. Metal film Resistance range: 10 ohms to 3 megohms (high voltage types: Typical thin-film resistors are sputtered 1 kilohm to 30 gigohms) tantalum nitride, deposited chromium co- Power rating: to 10 watts (high voltage types: to 6 watts) balt, or nichrome, on a substrate. Sub- Tolerance: 0.1% to 2% strates of alumina, sapphire, glass, Temperature coefficient: = 25 to _ 175 PPM - C less than 0.1 µV.'V or silicon are used. Noise: quartz, beryllia Life expectancy (potentiometers): 100.000 rotations Thin-film resistor networks are also Failure mode: resistance change or catastrophic failure available; those are housed in DIP's and Derating factors: 50%ó power. 80% voltage SIP's (Single !mine Package). Notes: Fair degree of precision in lower value units. Hign In individual resistors, the terminals stability, long life, and excellent high -frequency performance. used may be either surface or wrap- Resistance values stable to about 100 MHz: begin to decrease around types. Wrap -around terminals beyond that frequency. Used in high -frequency tuning circuits, wrap around the side of the substrate al- measuring circuits, filters, etc. 10 megohms lowing to the underside. Ter- Film networks Resistance range: ohms to 33 connections to 1.6 watts per network silver over nickel, Power rating: to 0.2 watts per element, minals of solder, Tolerance: 0.1% to 5% platinum, or platinum gold are available. Operating temperature range: - 55 to + 125'C Trimming of the resistor is done either Temperature coefficient: _ 25 to 300 PPM/°C mechanically or by using a laser. Notes: Tracking between resistors 5 PPM °C In thick -film resistors, a ceramic sub- mChip resistors Resistance range: 1 ohm to 100 megohms strate is coated (silk screened-a mecha- Power rating: to 2 watts nized stenciling process) with a glass - Tolerance: 1% to 20% 125`C metal material and then fired (to cure it) at Operating temperature range: - 55 to ma- Power wirewound Resistance range: 0.1 ohm to 180 kilohms a high temperature. The glass -metal watts pal- Power rating: to greater than 225 terials include nichrome, silver Tolerance: 5% to 10% ladium, platinum, ruthenium, rhodium, Temperature coefficient: less than - 260 PPM'' C gold and a tantalum -modified tin oxide. Noise: low static, high dynamic noise levels That film is up to 100 times thicker than Derating factors: 50°° power. 80°o voltage evaporated or sputtered metal film (great - 44 Carbon -film resistors were introduced sprayed on, applied with a transfer wheel, portant. Those devices are generally satis- to perform the same basic functions as or dipped on. factory for use at frequencies up to carbon -composition resistors, but at a The rod is then cut to size, leaded end 20kHz. They are available with various lower price. Just like composition types, caps are attached, and the unit is trimmed insulating/moisture preventative coatings they lack the ability to withstand transient to a precise value. The resistor is then such as vitreous enamel, cement, molded voltage spikes and have a poor tem- coated with an insulating material. Car- phenolic, glass sleeves, or silicone. perature coefficient. bon -film resistors are available in the Vitreous enamel units have excellent An axial -lead, carbon -film resistor is same resistance values as carbon -com- moisture -resistance properties and will made by screening carbon based resistive position units and have a typical tolerance not burn (although they may melt) under inks on a ceramic rod and then firing the of ± 5%. high overload conditions since they are assembly. Alternate techniques include made from a glass type material. depositing pure carbon by cracking a hy- Wirewound resistors Silicone, which also has excellent drocarbon gas or by depositing a nickel Wirewound resistors are used where moisture -resistance characteristics, is an film for resistor values of less than 10 large power dissipation is required and organic material and is more flammable at ohms. The resistive element may also be where AC performance is relatively unim- lower overload conditions than vitreous enamel. It will also emit gases under over- load conditions leaving deposits on elec- TABLE 1 CONTINUED trical contacts. TYPE SPECIFICATIONS AND NOTES Cement coatings are composed of in- Precision wirewound Resistance range: 0.1 ohm to 800 kilohms organic materials. Those coatings are es- Power rating: to 15 watts sentially flameproof but can be made to Tolerance: .01% to 1% burn if subjected to high overloads for Temperature coefficient: varies with resistance long periods. Resistors coated with that Noise: low static, high dynamic noise levels material are also subject to changes in Life expectancy (potentiometers): 200,000 to 1,000,000 value with exposure to moisture. rotations Aluminum and water-cooled housings Failure mode: failure Catastrophic are also available. Those housings facili- Derating factors: 50% power, 80% voltage tate the transfer of heat away from the Notes: Wirewound resistors are used in low-tolerance, high - power dissipation applications where AC performance is not resistive element. critical. Power dissipation depends on heat sink or air flow In wirewound resistors, three alloys are around the device. When mounting on a PC board, standoffs commonly used for the resistive element. should be used to prevent charring the board. Not suitable for They are nickel -chromium, Copper-nick- use at frequencies above 50 kHz. Wirewound potentiometers do el, and gold -platinum. Nickel -chromium not suffer from contact resistance variations. The units can be is the most common due to its excellent manufactured with low temperature coefficients and tight temperature coefficient (less than ± 5 tolerances. Applications include motor speed controls, lamp PPM/°C) and its availability in many dif- dimmers, heater controls, etc. Precision types are used in servo mechanisms. ferent diameters. Copper-nickel is the Cermet Resistance range: 50 ohms to 5 megohms next most popular, with a temperature co- Power rating: to 2 watts efficient of ± 20 PPM/°C. The gold -plati- Life expectancy (potentiometers): 50 to 500,000 rotations num alloy, that is actually a complex alloy Failure mode: noise of gold, platinum with small amounts of Derating factors: 50% power, 80% voltage copper and silver has a high temperature Notes: Very stable under humid conditions. Low temperature coefficient of ± 650 PPM/°C, but has low coefficients. Low end resistance (2 ohms). Short life expectancy. resistance. That resistance is 85 ohms/ High resolution of the resistive element allows for more precise cmf (cmf is a circular mil foot, a hypo- trimmer settings. Less reactance in high -frequency applications than wirewound units, and are lower in price. Cermet is also the thetical quantity equivalent to one foot of thick film used in resistor networks and chip resistors. wire that is .001 inches in diameter) while Conductive plastic Resistance range: 150 ohms to 5 megohms nickel -chromium has a resistivity of 800 potentiometers Power rating: to 1 watt ohms/cmf. The gold -platinum alloy can Temperature coefficient: -600 to -300 PPM/°C also' withstand harsh environments. Life expectancy: 100,000 to 4,000,000 rotations The ceramic core of a wirewound re- Failure mode: Noise sistor is either beryllium oxide, which bas Derating factors: 50% power, 80% voltage a high cooling capability, alumina (alumi- General purpose Resistance range: 1 ohm to 15 kilohms, depending on power conductive plastic rating num oxide) or steatite, which has the potentiometers Power rating: to 1000 watts lowest thermal conductivity of the three Precision conductive Resistance range: 100 ohms to 500 kilohms materials but is low cost. Figure 2 shows plastic potentiometer Power rating: to 7 watts some steatite cores. Tolerance: 3% Wirewound resistors are most often Temperature coefficients: less than 70 PPM/°C used in voltage divider circuits, as power- Life expectancy: Greater than 2,000,000 rotations supply bleeder resistors, or as series drop- Conductive plastic Resistance range: 10 ohms to 100,000 ohms ping resistors. Variable devices are used trimmers Power rating: to 1 watt where voltage and current variations are Notes: long life Conductive plastic potentiometers have a expected, such as motor-speed and heater expectancy and low -noise characteristics. Resistance will shift if exposed to humidity. controls. Precision variable types are used Hybrid Resistance range: 200 ohms to 250,000 ohms in servo systems requiring precise elec- potentiometers Power rating: to 7 watts trical and mechanical performance. Tolerance: 5% Temperature coefficient: less than ± 100 PPM/°C Other resistor types Life expectancy: 10,000,000 rotations For low resistance/high current ap- plications, edgewound ribbon type power r -T--r-ll Cermet is also the thick film used in resistor networks and in chip resistors. Conductive plastic potentiometers have a resistive element consisting of a blend of resin (epoxy, polyester, phenolics, or polyamides) and a carbon powder applied to a plastic or ceramic substrate. The plas- tic substrate results in a better temperature coefficient due to greater compatability between the ink and the substrate. Those devices have a long rotational life and excellent contact resistance variation, or low noise. End resistance is low, two ohms maximum. Conductive plastic units are suitable for use in applications that require a con- sistent temperature coefficient over a lim- ited temperature 'range, such as - 25°C to 75°C. Temperature coefficient values of - 200 PPM/°C may be attained by special processing of the carbon material or by incorporating metal powders, or flakes, into the element. Nickel, silver, and cop- FIG. 2-MANY WIREWOUND RESISTORS use steatite cores, such as the one; Ehowr here. per are frequently used in low-resistance devices. Conductive -plastic elements, like carbon units, vary in resistance when exposed to humid conditions. Figure 3 shows cermet, carbon, and conductive plastic units. Hybrid potentiometers are wirewound units with a conductive -plastic track de- posited along the contact path of the re- sistive element. That results in a device that has a better resolution and a longer life, by a factor of 10, over wirewound types. Compared to conductive -plastic units ,'hybrid devices have a higher power handling capability, due to the wirewound element. Like wirewound units however, they have stray capacitance at higher fre- quencies and have high contact resistance and marginal output smoothness when drawing current through the wiper con- tact. Table 1 summarizes the resistor types available, their characteristics, recom- mended applications, and suggested de - rating factor. Use of a derating factor is an effective means to decrease the failure rate of most devices since device life is stress and temperature dependent. Derating is FIG. 3-POTENTIOMETERS can use resistive elements made of many differen. rr aterials. Three such accomplished by either decreasing part from left to right, are cermet, carbon, and conductive plastic, materials, shown above stresses such as power/voltage or current or by selecting a higher ráted part. Op- timum derating occurs at or below the resistors are available. Designed for Cermet devices are very stable under point where an increase in stress or oper- power handling up to 1000 watts (at cur- humid conditions and have low tem- ating temperature results in a large in- rents up to 100 amps) these devices are perature coefficients of ± 100 PPM/°C. crease in the device failure rate. made up of steel ribbons wound into a coil Conductive -plastic or hot-molded carbon One note about Table 1: The values and and supported by ceramic insulators. potentiometers, for example, have an rating shown are provided as guidelines. They are generally rated for normal opera- average temperature coefficient of ± 1000 While they apply to the most commonly tion with a temperature rise of 375°C. PPM/°C. In variable resistors, however, found units, it is not impossible to find Those units are used in power -supply test- the cermet element is abrasive and long units with slightly, or greatly, different ing and in motor -braking systems. (You periods of rotational cycling.will wear out specifications. may have seen them underneath subway the wiper long before similar use would While that concludes our look at re- cars, especially the older trains in New wear out the wiper in resistive -film or sistors, our look at component selection is York City.) conductive -plastic units. Cermet potenti- far from over. In the folowing part of this Cermet devices have a resistive element ometers are available in low resistance article, we'll turn our attention to the fac- made by combining very fine particles of values, which makes them useful in many tors that should be considered when se- ceramic, or glass, with precious metals. audio applications. lecting capacitors. 46 TABLE 2-CAPACITOR SELECTION GUIDELINES CERAMIC Notes: DC blocking, filter, bypass, coupling, and transient supres- sion applications. Close tolerance, high frequency Values: 1 pF to 2.2 µF capability (40-400 kHz) Tolerance: 10% or 20% and high insulation resistance. Not suitable for sam- ple/hold circuits, fast Voltage rating: 3.3 volts to 6 kilovolts DC settling amplifiers, or filters due to dielectric absorption Dissipation factor: to 5% characteristics. Small size, medium stability, and long life expectancy Temperature coefficient: to 200,000 PPM/°C under load. For NPOs- Metalized polyester/polyester foil- Tolerance:.25% to 10% Values: .001 to 100 µF Temperature coefficient: 0±30 and 0±60 PPM/°C Voltage rating: up to 1500 WVDC Notes: General purpose high insulation -resistance devices used Dissipation factor: 1% (at 25°C and 120 Hz) for transient decoupling of IC's and compensation of reactive Temperature range: -55 to + 125°C (with 50% derating above changes caused by temperature variations. Applications include 85°C) filtering, bypass, and non -critical coupling in high frequency cir- Notes: See polycarbonate for typical applications. Moisture resis- cuits. Frequency sensitive (capacitance will vary with frequency) tant and high insulation resistance. Small size, medium stability so characteristics should be measured at intended operating fre- and very good load life. Capacitance will however vary widely with quency. Should be mounted next to components being compen- temperature. Foil units are generally lower cost than metalized sated, and shielded from sources of heat. Due to low voltage failure types. Polyester film is commonly known as Mylar, which is a problems, should not be operated significantly under rated voltage DuPont trademark. under humid conditions. In circuit design, considerations should be given to changes in the dielectric constant caused by tem- Polystyrene foil- perature, electric field intensity, and shelf aging. Values: to 10 µF Voltage rating: up to 1000 WVDC CERAMIC CHIPS Dissipation factor: .03% (at 25°C and 120 Hz) Values: 10 pF to .18 µF Temperature range: -40 to + 85°C without derating Tolerance: 5 to 20% Notes: Used in timing, integrating, and tuned circuits. High insula- Temperature range: -55 to +125°C tion resistance, and small capacitance change with temperature. Insulation resistance: greater than 100,000 megohms Has excellent dielectric absorption characteristics. Large size with excellent stability and very good load life. MICA Paper/metalized Values: 1 pF to .1 µF paper/paper foil- Voltage ratings: 100 to 2500 volts DC Values: to 100 µF Voltage Temperature range: - 55 to + 150°C rating: to 5000 WVDC Temperature range: to + Temperature coefficient: - 20 to + 100 and 0 to + 70 PPM/°C - 30°C 100°C (derated by 30% over 75°C) Derating factor: 60% voltage (dipped case) and 40% voltage (molded case) Temperature coefficient: greater than 4,500 PPM/°C Mica chips- Notes: General purpose. Medium stability and very good load life. Large size; low cost. Metalized paper has Values: 1 to 10,000 pF paper coated with thin Voltage rating: to 500 volts layer of zinc or aluminum and are smaller than metal foil units. They are, however, prone Notes: Used in timing, oscillator, tuned circuits, and where precise to dielectric breakdown of insulation resis- tance and have high frequency filtering is required. Capacitance and impedence poor surge handling capability. Paper foil units used in high limits are very stable and capacitors perform very well at frequen- voltage/high current applications. Their dissipation factor varies with cies of 10 kHz to 500 MHz. Devices using silver in their construction temperature. Maximum temperature is + 125°C. are very susceptable to silver ion migration resulting in short cir- Polypropylene foil/metalized polypropylene- cuits. Failures can occur in a few hours if capacitors are exposed to Values: to 10 µF DC voltage stresses, humidity, and high temperature. Voltage rating: to 400 volts DC and 270 volts AC (foil units: 200 to 1600 volts DC and 300 to 440 volts AC) GLASS Temperature range: - 55°C to + 105°C Values: .5 to 10,000 pF Tolerance: to 5% Notes: Foil units are used in tuned circuits, integrating circuits, Voltage rating: 100 to 500 volts DC timing circuits, and CRT deflection circuits. Metalized units are Temperature range: - 55°C to + 125°C used in DC blocking circuits. Good high frequency capability, high Temperature coefficient: 0 to 140 PPM/°C insulation resistance, close tolerance, high stability, and excellent Notes: High insulation resistance, low dielectric absorption and dielectric absorption characteristics. fixed temperature coefficient. Has much higher Q than mica de- Less common types- vices. Performs very well at high frequencies up to 500 MHz and Polysulfone: Similar to polycarbonate and polyproplyene capaci- can operate in range of 100 kHz to 1 GHz. Capable of withstanding tors. Small size, high temperature range (to 150°C), suitable for severe environmental conditions but are susceptable to mild me- high -frequency applications, and high insulation resistance. Excel- chanical shocks and should be mounted accordingly. lent in high current and military applications. Not for sample/hold, fast settling amplifiers, or filters due to dielectric PAPER/PLASTIC DIELECTRICS absoption charac- teristics. Poor history of availability. Many dielectric and case configurations are available. Each type Polyvinylidene fluoride: Considered experimental; Has high di- has its own characteristics. For example, metalized paper units electric constant (about four to twelve times that of polyester de- have low insulation resistance and are prone to dielectric break- vices), which results in a very small sized capacitor. Those units down failures. Plastic types have superior moisture characteristics suffer from significant capacitance change with temperature, par- than paper units. Polycarbonate and Mylar types are used in ticulary at low temperatures. applications that require minimum capacitance change with tem- Polyethylene terphthalate: For applications that require high re- perature, such as tuned or timing circuits. liability; high insulation resistance Metalized polycarbonate and polycarbonate film- at high temperatures. Metalized paper polyester/paper polyester foil: The foil unit Values: up to 50 µF has a slightly better dissipation factor than the metalized type. Voltage rating: to 1000 WVDC Operat- ing temperature of - 55°C to +125°C with voltage ratings of 240 to Dissipation factor: .5% (at 25°C 120 and Hz) 300 (DC) available. Temperature range: - 55 to + 125°C Paper polyproplyene: Available in voltage ratings of 400 to 800 Derating factors: 50% voltage; 80% of rated temperature (continued on page 87) 47 Capacitors mance in a specific applica- There are a lot of factors you should tion or environment. consider in selecting resistors for your Each type of capacitor is projects and designs. As you might ex- discussed below, and pect, the same holds true for capacitors. the important spec- In capacitor selection, you should consid- ifications and er such things as operating temperature, considerations humidity, AC ripple, and operating fre- that pertain to quency. In addition, capacitance, as well the type of ca- as other capacitor specifications such as pacitor are current rating, leakage current, voltage summarized rating, and life expectancy, should be con- in Table 2. Ta- sidered so that the device chosen will be ble 3 is a glos- appropriate for the application at hand. sary of capaci- Materials used in manufacturing a ca- tor terms and pacitor, as well as how those materials specifications. have been assembled, will effect capacitor One note about specifications. As an example, capaci- Table 2-the speci- tance is based upon electrode area and the fications shown there type and thickness of the dielectric used. are only provided as - Varying any or all of those things will, of guidelines. It is certainly course, change the capacitance of the de- possible to find units with vice. But that is not the only parameter slightly, or even greatly different that will change. specifications. For instance, if the electrode surface area of an aluminum electrolyic capacitor Ceramic capacitors is increased (to increase the unit's capaci- Ceramic capacitors are used in many tance) through the use of finely etched applications. For instance, they are used electrode foils, the device will have a as bypass capacitors. They are also used to larger ESR (Equivalent Series Resistance) compensate for temperature -caused than similar smooth-metal foil units. That changes in resonant frequency in tuned is becáuse the ESR depends upon the vol- circuifs. When used in that second ap- ume of the foil used. plication, the ceramic capacitors should You can also increase capacitance by be mounted close the the tuned circuit, Mica capacitors using dielectrics with high dielectric but be shielded from any heat generating There are two types of mica capacitors. (high -K) constants. But capacitors that components. One type is a stacked foil unit consisting use high -K dielectrics are not as stable The EIA has broken ceramic capacitors of alternate layers of metal foil (or deposit- (they are more sensitive to temperature into categories. Class 1 capacitors are ed metal film) and sheet mica insulators. and voltage variations) and generally have those that have very predictable tem- The metal foil layers are connected to- a higher dissipation factor than capacitors perature vs. capacitance characteristics. gether with tin -lead foil strips with termi- that use dielectrics with lower dielectric One type of Class 1 ceramic capacitor is nals attached by using solder coated constants. the NPO (Negative -Positive -Zero) capac- pressure clips. Capacitor package styles also should be itor. That designation means that the The second type of mica capacitor is the considered. High lead inductances, com- negative and positive temperature coeffi- silver -mica capacitor. Those have a silver mon to tubular units, restrict high -fre- cients of the device are zero and that they electrode material screened on the mica quency performance. Tubular ceramic suffer almost (nothing is ever absolute) no stampings, which are then assembled as capacitors however, are the most stable change in capacitance vs. temperature. described above. The silver -mica capaci- form of capacitor and, since there is no Other Class 1 capacitors have very predic- tors are very susceptible to silver-ion mi- opposing electrode to provide stray capac- table changes in capacitance with tem- gration, which can occur within a few itance pickup, almost the total capaci- perature. hours, when exposed to high DC -voltage tance is provided by the ceramic. For instance, a ceramic capacitor that is stress, high humidity, and high tem- Dipped or molded radial -lead packages specified as N750 has a negative tem- perature. The ion migration results in the reduce interconnection impedances by al- perature coefficient of 750 parts -per -mil- capacitor short circuiting. lowing the capacitor to be mounted close lion, per-degree-centrigrade. That is, for To keep internal inductance small for to a PC board surface. each degree centigrade the temperature high -frequency use, button -style silver - Chip capacitors have contacts, rather rises, the capacitance of the capacitor will mica capacitors have the anode connected than leads, to even further reduce inter- drop 750 parts -per -million. through the center of the stack of mica connection impedances. In addition, Class 2 capacitors are those that are sheets. The other terminal is formed by those devices are thin enough to mount non-linear. Their temperature coefficients the case, which is connected to all points beneath unsocketed IC's, thus reducing are specified by a three letter code that around the outer edge of the electrode. the length of a trace for a bypass capacitor. specifies the low and high temperature That design permits the current to fan out That is important in high -frequency cir- ranges and the maximum change in ca- in a 360° pattern from the center terminal cuitry since a printed -circuit board trace pacitance from that at 25°C. Table 4 thus providing the shortest RF current can have an inducance of IO nanohenries/ shows the EIA Class 2 code, and what the path from the center terminal to the chas- inch. various designations mean. As an exam- sis. Capacitors come in a variety of styles ple, an X7R capacitor will vary in capaci- One of the more common micas used including ceramic, mica, paper, plastic, tance by no more than a factor of ± 15% for capacitors is Muscovite mica, which aluminum, and tantalum types. over the temperature range of - 55°C to comes from India. That substance has a Each type was designed for best perfor- + I25°C. (continued on page 87) 48 SatejjiteflYl HFYISId Know Before you Buy Here are some things to think about before you buy that TVRO system. BOB COOPER, JR.'° SATELLITE TV EDITOR INSTALLING A HOME TVRO SYSTEM GAN BE A CONFUSING AND bewildering experience. That is especially true for a newcomer to the field of satellite TV. (Though such a newcomer brings with him none of the long held "old wives' tales" concerning the field; a person can know "too much" and consequently be leary of the often simplistic technical explanations and instructions that are so common in the TVRO field.) Even so. installing the system is less of a challenge than the task of selecting the equipment. There is an entire family of "buzz words" in TVRO (even TVRO itself is something of a buzzword, standing for Tele Vision Receive Only), and they defy understanding to those who are "outside looking in." If you do not understand the buzz words, then the industry's literature is *PUBLISHER, CSD MAGAZINE virtually useless because most of it has LNA + FEED been written with the belief that the reader MASTER is at least "versed" in the terminology. So RECEIVER where do you start? We hope here! WITH ALL CONTROLS SINGLE One or more? CHANNEL We have developed a "chain of deci- AT 70 MHz DOWN CON VERTER sions" for you to follow in both under- 2 WAY 70 MHz OUTPUT SPLITTER standing how a TVRO system works, and in formulating your own concept of how you might wish to select and perhaps in- stall such a system for your home. We'll SLAVE ask you some questions and from your RECEIVER answers we'll follow different routes to arrive at the equipment selection that most suits your needs. That will make it sim- pler for you to create your own system "on paper" since you will only concentrate on those system elements that pertain to the particular system design you have chosen. MASTER RECEIVER Our first question is: Do you need to 12 CHANNELS have control of your satellite program se- (500 MHz WIDE) IN BDC IF lection located at more than one spot in RANGE your home? That seems like an innocent DOWN CONVERTER 2 WAY (500 MHz WIDE enough question. but the answer has SPLITTER IF OUTPUT) many ramifications, as we are about to learn. The important thing to remember about is it can be done SLAVE program selection that RECEIVER only at the satellite receiver. Satellite sig- nals are in the microwave range, from 3700 to 4200 MHz. At those frequencies, b cable losses are tremendous. To prevent FIG.1-IN THE SYSTEM shown in a, only the transponder selected at the downconverter is passed to the receivers in the system; all receivers can be used only to view the same signal. In a block- that, the downconverter-essentially the downconversion system (shown in 6), each receiver is free to select the channel that is to be viewed. first IF stage of a satellite receiver-is located outdoors at the dish. Since the IF quent stage in the receiver itself. Since Virtually none of the programs or services is much lower than the frequency of the each receiver connected to the output of repeat their transmissions on two different satellite signals, doing that allows ordi- the first IF stage now has access to all of satellites, so you in effect have a potential nary coax to be used between the dish and the satellite frequencies, each receiver can of 24 x 12, on more than 280 TV chan- the rest of the satellite receiver. be used to independently select the signal nels in space right now. (As a practical The drawback to that is that the selec- that will be viewed. matter, seldom do we find more than 90 of tion of the frequency to be received is In a block downconversion system, we those potential video channels in use at performed in that first IF, under control of still have a master receiver and one or any single moment.) the receiver. Therefore only a single fre- more slave receivers, although each re- STo change channels, you first select the quency is carried over the coax line. That ceiver has the ability to independently satellite you wish to view, and then select signal is fed to the receiver for further tune in any transponder/channel they wish the channel you wish on that satellite. processing, and then fed to your TV. usu- (see Fig. l -b). We'll see why, shortly. For Changing channels is all electronic; ally via either Channel 3 or 4. While it is now, just remember that you do have a changing satellites involves repointing the possible (and economical) to share the choice; the same program in all rooms on dish from one area of the sky to another. satellite receiver output between two or all TV sets as selected by the master, or Which brings us to the dish positioner, more television sets located in the same individualized reception selected at any a device that uses either a motor-driven or home, it follows that the individual select- receiver location by either the master or manually operated mechanical arm to ing the program from the TVRO receiver attendant slave units. point the dish. will in turn select the satellite -fed pro- gram for all the TV's fed from that re- Selecting the control location Moving the dish ceiver. A setup of that type is shown in Having selected a desirable approach to It is now time to turn to our second Fig. l -a. In that diagram, all satellite pro- planning a home system, we now move question: Do you wish to be able to move gram selections are done at one site, into some of the subordinate questions your dish from one satellite to another by called the master location; all other loca- you must face. For instance, let's consider remote control? tions are called slave locations. It follows dish control. That question presupposes that you will that having all the slave locations depen- Whatever downconversion scheme you wish to move your dish somehow. If not dent upon the program selected at the select, you must still decide how and from by remote control, you can always trot out master location may not be the most desir- where you will move the dish. Here are into the side or backyard and move it by able system for your home, but how do we some basic facts to consider: hand when you wish to change satellites. get around it? The answer is with block SA modern satellite can carry as many as Without a motorized dish, positioner sys- downconversion. 24 separate TV channels or programs, tem, your dish will most likely still have a In block downconversion, the first IF simultaneously. mechanical arm that will allow you to do stage passes the entire band of satellite 'There are more than a dozen satellites the same thing manually (overlooking the signals. Selection of the satellite frequen- within view of a typical backyard dish futility of trying to move the dish pre- cy you wish to view is done in a subse- located in most parts of North America. cisely, at 2 AM in the morning, during a , thunderstorm or blinding snowstorm, units can be extended with remote pick- dressed in your bathrobe!). ups all over the house; anyplace you can Turning to the motorized units, the run a wire back to the master receiver can basic dish positioner is a pretty simple be a secondary pickup point for an in- device. It consists of a jackscrew con- frared unit. And, if your remote is of the nected to a motor with reversible wind- RF variety, its signals will not be impeded ings, so the jackscrew can turn clockwise by such things as walls and floors, so you or counterclockwise upon command from can simply wander with the remote and a control unit located inside the house. change both channels and satellites from Perhaps we should note here that even if anyplace in the house. you've opted for a block-downconversion system, you will still be able to control the Picture quality the dish positioner from only one location Our next question is: "What level of in the house. That's the reason one of the A DISH POSITIONER is nothing more than a picture quality is acceptable?" Before you receivers in Fig. 1-b is still denoted as a motorized jackscrew that extends and retracts answer that, however, perhaps we should upon master receiver. All other locations will command. Simplistic drive/controller rephrase that to read: "What level of pic- still be able to select which transponder packages provide east and west movement un- der pushbutton control, while more elaborate ture quality are you willing to pay for?" they wish to view, but not which satellite. systems Include location sensors and location The following may help make that deci- Getting back to the dish positioner, if memory. sion a little easier. the dish is properly installed, as the jack- You have doubtless heard that having a screw rotates the dish will move in such a satellite system in your home is the next way as to track or follow something best thing to being inside a network con- known as the Clarke Orbit belt. That's the trol room. And it in fact can be. But it can arc in the sky, directly above the equator at also be a test of your eyesight since there a height of some 22,300 miles, where the are many low-cost, marginally perform- geostationary satellites used for satellite ing, home systems. Perhaps a good analo- TV are located. gy would be to compare those low-cost The most basic dish positioners are systems to a shirt pocket AM radio, that much like the early home TV -antenna ro- for $3.95 does indeed "receive" AM sig- tors that required that the user hold down nals. But, as you might imagine, how well on the button until the new TV station was it receives them for that price is an entirely peaked -in. They, too, require that the user different matter. hold down a button while the dish tracks THIS DISH CONTROLLER is just about the ulti- mate in luxury; its handheld infrared You will have to decide what level of across the sky. control can be extended to distant points in house for total picture quality you want for your system But that task can get to be tedious. control over the dish and system. and, as you might suspect, the better the Consider, for instance, the following. quality, the higher the cost. According to Let's say you have been watching WTBS onds. That's a long time to be standing recently conducted national surveys, the on transponder 18 on Galaxy I (GI). That's there with your finger on a button. average home TVRO system, installed by down low to the ground at the far western If holding a button down and waiting a, dealer (often referred to as a turnkey end of the satellite belt. It is a Thursday for the dish to move to the right satellite is system), costs just under $3000 ($2993, if evening, and you decide you want to not your idea of modern technology, pre- you like exact figures). Yet you have most watch Boresight, a special program, in- pare to spend extra money for extra con- likely seen advertisements for complete tended for TVRO owners, that reports on venience. For instance, dish positioners systems that you can install yourself for new products and developments in the can be programmed, as we noted earlier, under $500. On the other hand, there are TVRO industry. That program is transmit- so that you simply push one (or two) but- systems on the market that even today can ted via transponder 20 on RCA F4, a tons to tell the dish to move from wherever run $8000. Logic should suggest that the satellite that is much higher in the belt. To it is now to where (ie. which satellite) you $8000 system must do something the repoint the dish from G1 to F4, requires want it to be. $500 system does not do, or the guy sell- that the dish track quite a distance through A preprogrammed dish positioner nat- ing the $8000 systems would shortly be in the arc, passing 8 to 10 other operating urally costs more than a non -programmed another line of work. satellites along the way. one, and one with a remote control costs What are those differences? There's To repoint the dish, the first thing you even more. But a remote -controlled unit convenience, for instance. You will cer- do is set your receiver to receive transpon- offers a significant advantage. With it, tainly not find such things as motorized der 20 (remember that transponder fre- there are techniques available to allow you dish positioners or remote control on a quencies are the same on each satellite, to extend the range of the remote control $500 system you install yourself; those making the job of tuning a lot easier). out of the room where the master receiver are items found only on upper -price Then push, and hold down, the button that is located. And that is true whether your bracket systems. But what about recep- causes the dish to track to the east. Con- remote is of the infrared or RF variety. tion quality? tinue to hold down the button while the Let's take a look at an example. There are three factors that directly dish tracks across the sky. As you are In our example, the master unit is lo- effect the quality of the reception you can tracking and passing satellites in the belt, cated in the family room where much of expect. We'll try to deal with each in such the programming on transponder 20 on the TV viewing is done. But, there is also a way that you will understand the trade- those satellites will appear on your TV. a slave unit in the bedroom. The question offs involved. When you finally have the dish pointed at here is whether you should I9,cate the mas- One of those factors is dish size. With RCA F4, the Boresight program that you ter in the bedroom and the slave in the present technology, it is not yet possible to were looking for will appear. That tells living room (weighing whether it is more produce as clear pictures from as many you that the dish is correctly aimed and inconvenient to get out of bed to change channels with a 6 -foot dish as it is with a that you can release the button. satellites than it is to get out of a chair.) 12-foot dish. Dish size relates directly to One problem with all of that is that the Remote control to the rescue. dish gain, or the sensitivity of the system. operation will typically take about 60 sec - The range of infrared remote -control It would be nice to be able to tell you that with a 6 -foot dish you will receive 47 in New Jersey, Connecticut, or Florida. If effective. There is not a great deal of price channels, with an 8 -foot dish 52 channels. he took the same small dish to Kansas. difference between an 85 -degree unit and with a 10 -foot dish 68 channels and with a Oklahoma. etc.. he'd find 50 or 60 clean a 120 -degree unit anymore (not at the 12 -foot dish 92 channels. Unfortunately, channels to watch. dealer level, anyhow). But the 55 -degree we cannot do that because how many Now, how do you find out what kind of units can still cost from two to four times channels you can receive, and at what dish you are going to need or want to be' as much as a 100 -degree unit. quality level, also depends on where you satisfied? Check around your own area. Gain is important too, but here you install the dish. Inspect dishes that have been installed and almost have to take the word of somebody Between the Hughes (Galaxy). RCA see what the reception looks like. who has selected the component units for (Satcom), Western Union (Westar), Ask to see transponders 2.4, 10. 14, and you. Some receivers work no better with a AT&T (Comstar and Telstar). Canadian 22 on RCA Satcom F3R. Those are uni- 50 -dB gain LNA than they do with a 40 - (Anik) and other satellite families now versally weak. If they look clean, you are dB gain LNA. In some systems, the trend littering the Clarke Orbit belt, we have probably watching a good performing is to take some of the gain away from the many different philosophies of how a sat- system for its size, in the 48 states. LNA (such as dropping it from 50 dB to ellite should beam its signal toward earth. 40 dB) and then to make up for it by RCA, for example. believes that all satel- adding additional gain stages in the re- lites should favor the mid -western part of ceiver proper. the U.S. with gradually weaker signals in Then again, some receivers don't use all directions (towards both coasts). LNA's; they use LNB's or LNC's. An Hughes believes that all satellites should LNA is a stand-alone amplifier that does cover significant parts of a hemisphere nothing but amplify. It is followed by a (which is substantially larger than the stand-alone downconverter that does U.S. alone). AT&T sees no reason to nothing but convert frequencies. An LNB cover anything but the 48 continental is a Low -Noise Block downconverter, states. which means that the amplifier and a That means that the signal strength re- block downconverter are packaged in a ceived on the ground (the pattern of signal single housing or container. The LNB strength is often referred to as the satel- now has a noise temperature rating but it lite's footprint) varies from location to lo- will no longer have a gain rating since the is cation, and from satellite to satellite. A 6 - INCREASING THE DISH SIZE to 12 -feet provides gain part of the converter package and foot dish in Florida works poorly on Sat- a rock -steady, noise -free signal. the meaning of that rating is lost in the com, but better on Galaxy. A 10 -foot dish marriage of the two units. produces perfect AT&T (CBS and ABC) If you are west of the Rockies, ask to see An LNC. or a Low -Noise Converter, is network signals in Kansas. but produces transponder 21 on F3R (The Weather the combination of the LNA and a stan- virtually no pictures at all in the Bahamas. Channel). If it is not perfect, the dish is dard -type downconverter. Again, they are We could fill pages with that kind of infor- probably not large enough. rated with a noise temperature but not a mation, but all it would do is confuse you. If you are along the east coast, ask to see gain specification. Instead, we offer the following: transponder 8 on F3R (CBN) and tran- Which is best is not an easy question to *People who live in the central part of the sponder 5 on Galaxy 1 (Showtime). answer since no one is really best. That's U.S. (such as Kansas and the surrounding Again, they are weaker than the others because those units are part of a system states) are best off because most satellites and as such will help you judge a system's and are worthless unless connected to a at least maintain maximized signal performance. receiver. A really great LNB, for exam- strengths into the center of the U.S. If you are outside the U.S., in the Carib- ple, will not produce good quality recep- People who live in New England and bean, ask to see all of the above plus tion when connected to a system with a Florida are worst off with the exception of Telstar 301 (96 degrees west), transpon- not -so -good receiver. those who live in Hawaii, because both of ders 2 and 10 for the CBS and ABC net- Fortunately, most of the people who these portions of the continental land work feeds respectively. make receivers also make or offer an mass are least favored by most of the satel- Another factor influencing the quality LNB, LNC, or stand-alone downcon- lites that carry video programming. of the reception is the sensitivity of the verter to which the installer adds an LNA (Hawaii. because of its distance from the Low -Noise Amplifier, or LNA. This is the as part of a complete receiver package. So continental U.S.. is covered only by low- signal booster/amplifier that is installed at you are not likely to run into the option of power spot beams. Only about 50% of the the dish proper. They are rated in two - selecting which amplifier will go with available channels are carried by those ways: by something called noise tem- which receiver. beams, and because of their low power. perature, and by their gain. Some people-including many satel- dishes less than 12 -feet in diameter are Noise temperature is a measurement lite -TV dealers-believe that you can generally not useable.) performed on LNA's to determine how trade off low noise temperatures for Which brings us to a completely unre- much noise they add to the satellite sig- smaller dish size. For example, you may liable rule of thumb: Use bigger antennas nals while they amplify them. Noise is be told that you have the choice between around the edges of the 48 continental bad, clean signal is good, therefore an an 8 -foot dish with a 75 -degree LNA or a states and use smaller antennas as you get LNA that adds less noise is better than one 10 -foot dish with a 100 -degree LNA. They closer to the central states. that adds more noise. may even tell you that the performance Now, here's why that rule of thumb Noise shows up on the screen as snow will be the same with either choice. completely unreliable. A 6 -foot dish in (called sparklies in the TVRO trade). That's simply not true. A lower noise New Jersey will work quite well; but only Noise degrades the picture and sound. LNA can help make up for the shortcom- on certain of the Galaxy and Satcom tran- LNA noise temperatures fall between 55 ings of a smaller dish, but you can't en- sponders. If a person will be happy (as in degrees and 120 degrees Kelvin at the tirely get back the gain lost by cutting satisfied) with say 15-18 clean channels present time. A 55 -degree unit is more back the dish's diameter two feet by using and a multitude of others that are not clean expensive than a 120 -degree unit. Most a better LNA. In other words, you can't (as in snow and interference), he's a candi- systems sold today routinely use 85- or recover a signal that you never had in the date for a small dish at a cheap price. even 100 -degree units because they are cost first place. 52 H 16, though it is expected to grow to as many as 26 within a year). And the audio that is relayed is not limited to just the w video signal's audio channel (or channels J in the case of stereo). Each transponder 2 has numerous audio subcarriers that carry a a wealth of subsidiary services. Which leads us to our next question: Are you interested in the program audio -18 MHz 0 +18MHz -18 MHz 0 +18 MHz -18 MHz 0 +18 MHz for television only, or do you also want the FREQUENCY FREQUENCY FREQUENCY non -television audio services? a b c FIG. 2-WIDE VERSUS NARROW BANDWIDTH. While most video information is concentrated in the Program audio (the audio that acco center portion of the signal (see a), luminance and color detail information is found at the signal edges, panies the video signal) is normally tra s- as is the majority of the noise. Using a narrow bandwidth IF (see b) allows most of that noise to be cut- mitted on a specific subcarrier freque y t off, but at the expense of the color detail and luminance. Using a wide bandwidth IF (see c) allows all of between 5 and 8 MHz; for example, .8 the picture information to be processed, but will also provide a noisier picture. MHz. A TVRO receiver has a tuning k ob that allows continuous tuning of the sub - IF bandwidth dish, because of your location, or both), carrier frequencies. As a point of informa- Finally, the third factor is receiver IF you may need to sacrifice color and detail tion, around 80% of the program audio bandwidth, a parameter that has a direct to get a useable picture. subcarriers are on 6.8 MHz, another 10% bearing on the quality of the pictures you Receiver data sheets specify IF band- are on 6.2 MHz and the balance are scat- receive. Take a look at Fig. 2-a. It shows width. Some go for the narrow end, a few tered between 5 and 8 MHz. how the energy of a typical satellite TV go for the wide end. Most hang out in the You might expect that the program au- signal is concentrated. Note that the ma- middle, with bandwidths between 24 and dio on the various satellites and transpon- jority (about 90%) of the energy is con- 26 MHz. ders would follow a more -or -less uniform centrated in the center portion of the One last point before we move on. If format. Unfortunately, that is not the case. signal. As a result, the signal strength in your installation includes a projection TV, For instance, consider audio bandwidth. that region is high enough to override the you may not have a real choice as far as Because there are no FCC or even industry natural noise level. (Noise is caused by a bandwidth is concerned. That's because standards to follow, the programmers have variety of sources including atmospheric those sets "blow up" the image signifi- been free to choose almost any bandwidth conditions, local and space interference, cantly. What was a small blemish on a 12 - that suits their needs. sunspots, etc. As a result, for a signal to inch screen (and perhaps not visible to the That has put the satellite receiver de- be useable, it must override that noise naked eye) becomes a glitch or glob on a signer in a bind. That's because while "level.") But at the outer edges of the four- or six-foot screen. Worse than that, most program audio is transmitted with an signal. the concentration of energy is when you take a picture designed to be FM (deviation) bandwidth of around 250 much lower and the noise is no longer viewed on a 19 -inch tube and blow it up to kHz, some are far greater. The Nashville completely overridden. Because of that, projection -TV size, the scanning lines Network and The Disney Channel, for about 90% of the noise in a signal is found themselves become visible. And when example, have bandwidths that are closer at the edges of that signal. your satellite receiver has lost the depth - to 500 kHz. To get around that, most It is of course possible to design a re- of-color and the luminance detail because receivers give you two selectable audio ceiver with either a narrow or a wide IF of a narrow receiver bandwidth, the pic- bandwidths, labeled narrow and wide. bandwidth. With a narrow bandwidth, as ture becomes fuzzy and indistinct; it sim- If the receiver you use does not have an shown in Fig. 2-b, the band edges are ply loses its ability to be a pleasing, well appropriate bandwidth for the audio sig- cutoff, allowing only the stronger central defined video image. nal you wish to receive, it is obvious that portion of the signal to pass. Witha wide So when the installation includes such the reception will not be satisfactory. bandwidth, as shown in Fig. 2-c, all of the a set, the best advice is to stick with a dish When you tune in an audio subcarrier that signal. as well as all of the noise pass. that's large enough to allow you to use a is wider than the receiver's bandwidth, Now, with 90% of the picture informa- receiver with a wide bandwidth. the audio sounds muddy and indistinct. tion contained in the central portion of the When you tune in subcarrier that is nar- signal, it would seem logical to go the Audio considerations rower, on the other hand, the audio sounds narrow bandwidth route to obtain as Satellite television "broadcasting" is scratchy or noisy. Therefore, you want to noise -free a signal as possible. There is not broadcasting at all. It was never in- select a receiver that has an appropriate one major flaw to that, however. tended to be a system to transmit individ- range of bandwidths for the services that That flaw is that two important parts of ual programs to individual homes; it sort you are interested in receiving. We'll re- the picture information are contained in of wound up that way because people got turn to some tests you can conduct to that ten percent of the signal that is thrown together and starting building equipment determine that shortly. away. Those are the depth -of -field of the that would receive the satellite signals. So far we have been concerned with color and the high resolution detail in the Satellite television is simply a relay sys- program audio. It is possible for a tran- black and white. To retain all of the color tem, using a single repeater station in -the - sponder to transmit not only its own pro- depth and all of the luminance (black and sky to relay uplinked microwave signals to gram audio, but also a considerable white) detail, you need a to go the wide stations around the country. Con- number of non -TV -program related audio bandwidth route. sequently, unlike regular TV, AM, or FM (see Fig. 3-a). The WGN transponder If the satellite signal is good and strong, broadcasting, no regulatory agency has (F3R, TR3), for example, has more than a you can afford to select a wider bandwidth ever prescribed technical standards to dozen subcarriers that carry material that since the sheer strength of the signal will which every satellite program relayer must has nothing to do with the television. allow the receiver to display a high adhere (aside from rules governing inter- Some of those are data signals, while quality, noise -free picture even with that ference to other users). others are music broadcast services in- wider bandwidth. On the other hand, if As you might expect in such an en- tended for use by AM and FM radio sta- the signal is weak (because of your having vironment, there are a number of different tions. chosen a smaller -than -recommended audio formats currently in use (currently Satellite Music Network, as an exam- 53 GUARD BAND Those allow you to treat the audio inde- pendent of the video. Again they, like the TVRO receivers with built-in audio tun- ing controls, should be compared as we previously suggested, since the mere fact TV VIDEO SUBCARRIERS that it is a stand-alone audio subcarrier tuner is no guarantee that the designer has F allowed for the proper blend of audio 42 5 8 bandwidths in use. FREQUENCY -MHz Avoiding hype a When home TVRO systems first came into the marketplace, all dishes were large, all dishes moved by hand (if at all), and everything cost a great deal of money. Today, fully 70% of the LNA's, 60% of the receiver's, 20% of the motor drives, and 10% of the dishes are created outside CO V CO < N O CO CO CO CO N CO o, M M CO O of North America. And the percentage of CO CO CO CO CO products being manufactured off shore FREQUENCY -MHz has been getting larger by the month. b Panasonic and Uniden have been recent FIG. 3-A TYPICAL TRANSPONDER SIGNAL consists of the video signal, a guard band, and a number non-U.S. entrants into the marketplace. of audio subcarriers (see a). The audio subcarriers for F3R, transponder 3 (WGN) is shown in b. Numerous U.S. firms, although still ple, uses several subcarriers on the WGN Your first concern is that the receiver branding their products as "U.S.-made, transponder to carry an adult contempo- that interests you will be compatible with now are having assembly done in Korea, rary music service, a country and western the level of audio services you desire. Re- Taiwan, Hong Kong, or even Mexico. music service, and an MOR (Middle Of gardless of whether you want stereo or Even Europe is in the North American the Road) music service. Each of those is not, you do want clean program audio. It TVRO act (Luxor from Sweden). With transmitted in stereo (see Fig. 3-b). may be difficult to ascertain what is clean nearly 500,000 home systems sold during And stereo brings in a some further and crisp if you are trying to listen to a 1984 and up to 750,000 home systems complications. two-inch speaker crammed into the side forecast for 1985, the market has become We've already mentioned that there are of a TV set. So ask to have the audio fed large enough to attract many of the better many different systems used to transmit through a good sound system. known volume producers. monoaural audio. There are, as you might Now, how good is the audio system? It is, however, a marketplace that exists by now have guessed, also different tech- Here are some benchmarks. almost exclusively within North America niques used to transmit stereo sound. Tune in transponder 6 on F3R (SPN/ and the surrounding areas (where US and When the left audio is transmitted on Satellite Program Network). Place the re- Canadian satellites can be received). That one channel and the right audio is trans- ceiver in the narrow position and look for is not likely to change in the foreseeable mitted on another channel, we have what the next -to -highest subcarrier (7.695 future since North America utilizes cer- we call discrete stereo. To receive discrete MHz); it will be a "comedy channel" tain satellite frequencies and those satel- stereo, the receiver designer has to build (famous comedians doing comedy rou- lites provide certain services that exist no into the TVRO system two separate audio tines). See if the audio is noisy. That ser- place else in the world in the same format. subcarrier tuners; one of which the user vice uses a very narrow bandwidth, and if If you are reading this overseas, the first tunes to a designated subcarrier frequency the narrow position provides clean, crisp bit of hype to avoid is that you can buy a (such as 5.58 MHz) and the other of sound here, then the receiver should do a satellite dish and watch HBO in Ghana, which is tuned to another separate subcar- good job with all narrow-bandwidth sig- Singapore, etc. The world of international rier frequency (such as 5.76 MHz.). One nals. satellite reception is an entirely different audio channel is found on one of the sub - Tune in transponder 4 or 24 on Galaxy 1 subject from that addressed here, and the carriers, the other channel is found on the (The Disney Channel). If the receiver is $500 to $8000 systems we have discussed second subcarrier. The system connects to stereo capable, set it for mono, and select won't even dent the requirements you will the in -home stereo system simply by con- a wide bandwidth. Now tune in the audio face outside of North America or the Car- necting the right output of the TVRO re- at 6.8 MHz. Check to see if the audio is ribean. ceiver audio to the right input on the "muddy" sounding. That audio channel The next bit of hype to avoid deals with stereo, and so on. uses a very wide bandwidth and if the signal scrambling. The present industry Not all stereo is transmitted in that for- audio is crisp and not muted, that receiver exists to some extent because with a home mat. Some are transmitted in a matrix should have no problem with most wide format. There are still two separate sig- bandwidth audio signals. nals, but each involves mixing the left and Perhaps more so than the video sec- right channels in a L+ R, L -R format. It tions, the audio sections vary widely in still requires a pair of subcarriers. One performance between different receiver might be on 5.80 MHz and the other on models and brands. There is a possible 6.80 MHz, for example. With that sys- alternate solution if you fall in love with a tem, the user tunes one of his subcarrier receiver that has great video but not all of tuners to 5.80 MHz, and the other to 6.80 the audio features you would like (not all MHz, and inside the TVRO receiver, ma- receiver designers have hopped on the trix decoder circuits separate the right and "tune -every -audio service" bandwagon left signals so they can once again be fed yet). to a home stereo system. Stand-alone audio subcarrier tuners are STAND ALONE audio subcarrier tuners allow Now some buying tips. available from a number of sources. you to treat the audio separately from the video. 54 cram as many satellites into that portion of the sky set aside (by international agree- ment) for U.S. (and Canada/Mexico) use as possible. They want to move the satel- 99 lites closer together, without causing in- terference between satellites to the users (1/2 POWER BEAMWIDTH on the ground. At the present time, U.S. 3.02 DEGREES) INTERFERENCE satellites are spaced 2.5 to 4 degrees apart BEAMWIDTH .., HALF -POWER in the Clark Orbit belt. The majority of the 6 -FOOT 101 BEAMWIDTH least 3 degrees DISH present satellites are at from their neighbors, but the FCC warns us that within the next five years or so, they want to make all satellites uniformly 2 degrees apart. is that 103° The catch for small dish owners those dishes under 8 to 10 feet in diameter have no proven ability to still function properly when satellites get down to 2 105° degree spacing. And smaller dishes, 6 feet in size and down, will almost surely have very real problems. With those dish- es, when you are pointed at the desired satellite, signals from other satellites on 107° both sides, two degrees away, will cer- 12 -FOOT tainly cause some amount of interference. DISH Your satellite receiver, seeing both the de- (1/2 POWER BEAMWIDTH sired signal and the non -desired signals 1.47 DEGREES) HALF -POWER INTERFERENCE will simply treat the non -desired signals BEAMWIDTH BEAMWIDTH as interference or noise. The bottom line will be less -than -perfect reception. - I I To be sure that your dish will still be 1114 useable when 2 -degree spacing becomes the norm, our advice is to get a guarantee. the FIG. 4-THE DISH'S SIZE directly affects it beamwidth. As is shown here, the smaller diameter Most responsible dish manufacturers will dish, the larger the beamwidth. That can prove to be a problem fo small diameter dishes if two -degree spacing is used. In that case, signals from adjacent satellites can be a source of interference. certify to you, in writing through the deal- er, that their dish will function with two - TVRO you can tune in satellite program super-small systems using dishes in the degree satellite spacing. feeds from services such as HBO and four foot to less -than -seven foot category. Showtime. For many years those services We already know that small dishes have Warranties and guarantees have been open, or available to anyone less gain,, and even in Kansas (where sig- Finally, we leave you with this observa- with a TVRO. And for many years, there nals are generally strongest) people still tion. Early TVRO products were only as have been rumors and there has been spec- prefer 10 -foot dishes. They also will have good as the local dealer's ability to cope ulation that some (or all) of those services problems dealing with two -degree spac- with failures and to respond to the cus- will scramble. ing. Let's see more about that. tomer/user's plea for assistance. But, Naturally if a substantial quantity of Satellites. as we have seen, stretch times are changing. those 90 or so real TV channels did across the sky in a belt over the equator. Well over 50% of all electronic units scramble, the desirability of owning a Each satellite is assigned an orbital slot by and perhaps an even greater percentage of TVRO might change. some agency (such as the FCC in the dishes now carry manufacturer warran- As you read this, at least HBO and U.S.). The satellite stays within 35 miles ties. A 12 -month original equipment man- Cinemax are virtually ready to turn on of that slot at all times; if it wanders, its ufacturer promise of performance or scrambling equipment. Showtime and orbit is corrected via telemetry. That is replacement statement is pretty standard The Movie Channel have announced they important because if a satellite were to these days. and some extend to two years will also scramble. So. does that spell the wander considerably, it would be difficult and more. end of TVRO? to track with a satellite dish, and its sig- Your bill of sale should make direct Not at all. The programmers, if and nals could interfere with those from an reference to the warranty/guarantee when they scramble, are doing so because adjacent satellite. coverage and if the original equipment the home TVRO market is now reaching a In fact, it is because they are suffi- manufacturer provides his own printed point where the programmers can antici- ciently apart in the sky that the whole statement, that document should become pate some new, additional revenues from system works at all, since they do use the a part of your records just in case. TVRO's. They want to do business with same channels and we depend upon the The TVRO product area has become far TVRO system owners and after they directivity of our dish to look only at a more sophisticated, in both technology scramble, there is every reason to expect single satellite at a time. That directivity is and business experience at the dealer that they will make their services available called the dish's beamwidth, and that level, in just the last 12 months. The in- to you for a reasonable monthly fee; not beamwidth depends greatly on the diame- dustry is a rising star that many expect to unlike cable TV charges for the same ser- ter of the dish-the larger the dish's phys- continue to grow rapidly for the next five vices. So the hype that all signals will ical size, the narrower or smaller that years or more. These may no longer be the scramble (four out of 90 is hardly all) and beamwidth (see Fig. 4), So, small dishes pioneering days of yesteryear, but there is TVRO's will be useless is just propaganda have broad beamwidths and big dishes still plenty of excitement and challenge in from ill-informed reporters. have narrow beamwidths. finding the right equipment package for The final bit of hype to avoid deals with Now to our problem. The FCC wants to your own home. R -E Installing your TVRO > BOB COOPER, JR.* SATELLITE TV EDITOR Take the guesswork out of TVRO installation with this step-by-step guide. THE FIRST STEP IN SETTING UP A HOME band (also called the C -band). That is a north (with true north being 0 degrees). TVRO system, before spending even one microwave -frequency band and like all Thus, a satellite due south of you would dollar on equipment, is to sit down and do other microwave signals, there can be no have an azimuth of 180 degrees, while due some thinking. For instance, have you physical obstructions between the signal southwest would have an azimuth of 270 given any thought to where the dish is source (the satellite) and the dish. Thus degrees. going to be located? Unfortunately, for your dish should be located so that no Note that our reference point is true reasons we will get into in a moment, not buildings, trees, hills, or other "obstruc- north. Because the north pole and the every yard can accommodate a dish. If tions" block its view to the south or south- magnetic pole are not in the same loca- yours turns out to be one of those, you west. tion, the compass that points north may could try to place the dish on your roof; The satellites that are located due south actually be pointing ten degrees or more but that requires some special mounting of your location will be the ones that are away from true north. When we lay out or considerations, as a dish elevated in that the highest in the sky. Those located to the plan a system, and we try to determine if manner is subjected to quite a bit of wind southeast or southwest of your location we have any blockage from our intended and ice loading. An improper installation will be located close to the horizon (i.e. dish location toward the satellite, it is im- can lead to a damaged dish, or worse, a close to the ground). We specify a satel- portant that we correct our magnetic north damaged house. lite's position in the sky, from your loca- to true north if there appear to be any close When you are planning out where you tion, using something called look angles. blockages in the area. are going to locate your dish, there are There are two look angles that count: how The local airport control tower, the lo- certain rules that should be observed: far up or above your horizon the satellite is cal survey office, a stationary or engineer- The satellites are located in a belt over located, and the angular bearing from ing supply store that sells USGS Geodetic the equator, at a height of 22,300 miles your location to the satellite's location. Survey Maps will have available to you the (see Fig. 1). If you are in North America, The "up" direction or angle is called proper magnetic correction to be applied that generally means that the satellites the elevation. It is the angle formed by a to a compass reading for your locale. If will be south to southwest of you. line drawn from your dish to the horizon your location is Colorado, for example, The majority of satellites transmit back and a line drawn from your dish to the the compass will point 14 degrees west of to earth using frequencies in the 4 -GHz satellite of interest. The angular bearing is true north. Once you have the proper cor- *PUBLISHER, CSD MAGAZINE called azimuth and it is referenced to true rection factor, it is a simple matter to de - 56 and azimuth settings for virtually any sat- ellite from any location. It can be a bit SBS(') SBS(') SBSI) ANIK difficult to use, but it does get the job 3 2 1 8 WESTAR WESTAR 95°YB 97°W 99°W 109°w WESTAR 5 GALAXY done. 2 TELSTAR SBS 3 ANIK 123°W 79°W 301 C2 If someone in your area already has a 91'W 1314°W SPA CEN ET SATCOM COMSTAR TELSTAR 96° w 101°W 105° W SATCOM AURORA TVRO, you could also use a compass and 20 3 302 30 1 72°W 76°W 88°W GALAXY WESTAR ANIK 120°W an "inclinometer" (a device used to mea- 4 p ANIK 131°W 143°W GALAXY SATCOM 3 99°W C3 CONSTAR 2 4 93.5° W 104.5°W sure elevation angles) to measure the vari- 117.5°W 4 SATCOM SPACENET 74'W 83°W 127 W 1R ous look angles. (One commonly used 2 139° 69°W EARTH W inclinometer is the Craftsman Universal Protractor, Plumb & Level, available from your local Sears.) To do so, use the compass to measure .the azimuth heading 12 GHz BAND SATELLITE (that is easy to do with wire mesh dishes, FIG.1-CHARTING THE SATELLITES. The positions of all North American satelli:es in the Clarke Belt as you can simply stand behind the dish are shown here. and use the feedhorn support as a pointing guide). Next, use the inclinometer to mea- TRUE NORTH WITH DECLINATION sure the elevation heading at the dish's DEVIATION ALLOWANCE back plate. Repeat the procedure for every ? satellite that the TVRO owner can view. MAGNETIC INDICATED When you are done, you should have a set TRUE NORTH of readings that looks somewhat like the WEST one shown in Table 1. SATELLITE HEADING Once we have the headings to 270°AZIMUTH the satel- lites from our location, we can use that // information to determine if our selected dish site is appropriate. To do that: Stand in the selected spot. Use a compass to determine true north, COMPASS as previously described. True south will be 180 degrees To SATELLITE HEADINGS from true north. make FROM 270° TO 180° things easier, use stakes to mark out a line from true north to true south. Using the information for our hypo- thetical location, our chart tells us that TRUE SOUTH TRUE Westar 4 is located on a true bearing of EAST 214.4 degrees. Use a simple plastic pro- r / tractor (the type found at a drugstore SATELLITE school -supplies counter), laid on the SATELLITE HEADING\ HEADING ground, or a compass, to determine where 180° AZIMUTH 90° AZIMUTH 214.4 degrees is from our spot (remember, SATELLITE HEADINGS true north is 0 degrees, true south, 180 FROM 180° TO90° degrees). Face in that direction, and with the inclinometer FIG. 2-WHEN DETERMINING WHERE a satellite is, relative to your location, be sure to allow for the temporarily mounted on difference between magnetic north and true north. a short piece of lumber such as a 1 x 2 (make sure that the piece is straight) tip [ermine the direction of true north and to has that information for your area (as we the 1 x 2 plus inclinometer upward until use that information to locate the azimuth said, the settings do change with each it reads approximately 34 degrees. headings of the various satellites (see Fig. locale or region, since your latitude and If you can sight along the line indicated 2). longitude to the nearest degree determines by the inclinometer and not see anything We now know that the satellites are how you need to point your dish). but sky (assuming, of course, that you are located more or less to our south, and at Invest $15.00 or so in a satellite aiming facing in the proper direction), then your some elevation above the horizon. But we guide. For instance, World Satellite Aim- site will be fine for your dish (see Fig. 3). still don't know exactly where they are. ing Guide (PO Box 2347, Shelby, NC Now, what kind of changes can you Unfortunately, we can't provide a simple 28150) provides an aiming guide for $15 expect if you don't live in or near our answer to that, as the answer varies from that allows the user to find the elevation selected location (Albany, New York)? location to location. Obviously the satellite belt stays in the So it is still somewhat difficult to calcu- same position; so as you move north, late which location on our property might south, east, or west from our example have a clear access or view to the satellite location, the apparent position of that belt belt. To do that properly we need a refer- in the sky is going to change. ence source, some type of "pointing There are several rules of thumb that guide" that will allow us to take our own apply and a look at Table 2 will help show location (by geographic latitude and long- how those rules of thumb are applied. itude coordinates) and then determine that The farther south you live, the higher our view of the desired satellites is clear. and higher the satellites appear in the sky A full description of that subject is beyond (the converse of that being that the farther the scope of this article so we will give you north you go, the lower they appear in the AN "INCLINOMETER" is a .aluable tool in TVRO some other choices: installation. Here we see how one commonly sky). Find somebody locally who already available unit is used. Satellites due south of you will always 57 to. Additional height accomplishes TABLE 1 -ELEVATION AND AZIMUTH HEADINGS nothing here, since the satellite signal ar- rives just as strong to a clear-vision site Azimuth Satellite Orbit Location Elevation located on the ground as it does to a sim- 252.4° RCA F1 R 139° W 9.4° ilar site on a roof. W 12.3° 249.0° Galaxy G1 134° Sometimes, however, you simply can RCA F3R 131° W 15.1° 246.0° not satellite the you Comstar D3 128° W 17.1° 243.6° "see" the belt (or part ANIK D1 105° W 31.4° 221.4° want) from a ground -located site. Up, on Westar 4 99° W 34.3° 214.4° the roof, is the only choice left. Westar 3 91° W 37.5° 204.1° Satellite antennas are available in a RCA F4 83° W 39.5° 193.1° number of design configurations. Here Galaxy G2 74° W 40.4° 178.5° are the choices open to you: Solid metal, made of either aluminum TABLE 2 -LOOK ANGLES or steel; there are also solid dishes made of fiberglass. All those tend to be strong, Concord, NH Port Au Prince, Haiti Pratt, KS Mexico City, DF but heavy. They also present a solid sur- 72W) (37.7N, 98.7W) (19.4N, 99.1W) (43.2N, 71.5W) (19N, face to the wind, and wind is an important Satellite Elev. Azimuth Elev. Azimuth Elev. Azimuth Elev. Azimuth consideration when you are mounting the F1 R/139 W 8° 254° 13.2° 262° 29.6° 234° 39.7° 249° G1/134 W 11.6° 250° 18.1° 260° 33° 229° 44.6° 245° dish on a roof or tall pole. F3R/131 W 13.7° 248° 21° 259° 35° 225° 47.4° 243° Screen -mesh dishes are lightweight D3/128 W 15.8° 245° 24° 258° 37° 222° 50° 240° and present less wind loading since some AD1/104 W 30.9° 223° 47.4° 243° 45.6° 188° 67° 195° of the wind will blow through the mesh W4/99 W 33.4° 217° 53° 236° 46° 180° 67.7° 180° surface. As such, mesh dishes are pre- W3/91 W 37° 207° 59° 227° 45° 167° 66° 157° ferred for roof mounting. F4/83 W 39° 196° 64.4° 211° 43° 155° 61.2° 139° If it is not possible to mount your dish 123° G2/72 W 40° 181° 67.6° 180° 38° 140° 52.1° on the ground, there are two options that evgieeneen are available to you. The antenna can be mounted on a metal pole (typically 3 to 5 be highest in the sky (ie. be of the max- Mexico City (19.4 north and 99.1 west) inch OD, schedule 40, steel), which is in imum elevation). Satellites significantly and Pratt, Kansas (37.7 north and 98.7 turn supported along the side of a house or southeast or southwest of you will have west). Again from Table 2, from Mexico building, so that just a short stub pro- the lowest elevation City, the look angles for FIR are 39.7 trudes above the roof line. Otherwise, The most difficult satellites to receive degrees elevation, and 249 degrees special roof-mounts, which use three or are those that are located very close to azimuth. From Pratt, those angles are four metal legs to attach to the roof, your own horizon (ie. at elevations of less 29.6 degrees and 234 degrees, respec- provide a platform for the antenna itself. than 15 degrees). We'll see why, shortly. tively. As you can see from the preceding, The top of such mounts usually end up Table 2 shows the subtle changes that satellites appear higher in the sky at long- being a 3 to 5 inch OD pipe, since most take place when two locations at the same itudes that are closer to their own. On the antennas have a collar that requires a pipe longitude but at differing latitudes wish to other hand, at greatly different long- of that size to slide down over as the point receive the same satellites. For example, itudes, the satellite appears closer to the of attachment. both Port Au Prince (Haiti) and Concord horizon. When you reach a point around 5 An unsupported steel pipe, no matter (New Hampshire) happen to be near 72 degrees elevation (ie. your antenna would how strong, or a tower can' t be counted on degrees west longitude. But the look an- only be pointed up by 5 degrees), you to hold the dish steady and stable in the gles, particularly the elevation, vary sig- begin to have special problems with satel- air. That is important since the dish must nificantly between the two -to RCA FIR, lite microwave reception. In particular, stay pointed at the satellite with a stability- for example. From Concord, the elevation noise problems created by the earth itself accuracy in the region of V8 inch in all is 8 degrees (barely above the horizon), can become severe, since the antenna is kinds of weather. The dish cannot sit up and the azimuth is 254 degrees. From Port now pointing so low to the earth that it is there and move about in the breeze (be- Au Prince, the same satellite has an eleva- barely skimming over the distant horizon. cause the pipe is moving slightly under tion of 13.2 degrees, and an azimuth of So special and unpleasant circum- the force of the wind). If it does that, the 262 degrees. stances prevail for low look angles. Even pictures will fade in and out (mostly out) What about locations that are farther if you live on a mountain top and have no as the wind moves the dish about ever so west? Let's consider the look angles from obstructions, you may find ultra -low look - slightly (1/2 inch play might seem slight, angle reception a special challenge. but in this case it is far too much). To review, select a location for your And, a three or four legged rooftop dish where the dish center (not merely the mount has to be installed so that the anten- top edge) has a clear, unobstructed view of na does not rip loose (taking part of the CLEARANCE / the satellite belt. If you do not have such a roof with it!) in a strong wind. Remember ANGLE / location available (and many do not), you that even a mesh antenna is not too dif- will have to settle for reception of just ferent, for windloading purposes, from a IMAGINARY those satellites that you can "see" from sail; and the same wind forces that drive a CENTER OF DISH your location. sailboat will rip and tug at the dish and its mount. People who have attempted to at- / r Up or down tach rooftop mounts with long lag screws You have two choices for where you through the roofing material usually come will install the dish-on the ground back in a short time to pick up a tangled (which is the best choice, if possible) or mess from the yard below (or worse yet, a on a roof. You gain nothing (but potential neighboring yard). About the only accept- FIG. 3-WHEN SELECTING A SITE for your dish, be sure that there are no obstacles between the grief) if you mount your dish anywhere able method of installing a three or four dish and any satellites that you wish to view. but on the ground when you do not have legged mount on a roof is to place a steel plate (1/4th inch thick or more) under the for that matter; it is best to check before A model system roof and use lag bolts, rather than lag you start to make sure you comply. Of course, no two systems are exactly screws, to ensure that the legs of the alike, although each will have the same mount are attached to and through the Equipment protection basic parts and approach to system de- steel plate below, rather than merely to the Our look at protecting TVRO equip- sign. To wrap things up, we'll walk wooden roofing structure-which is cer- ment will cover two major topics: protect- through the elements of a "model" sys- tain to give under pressure. ing the equipment that is outside from tem, including how it is selected and how being damaged by weather or moisture, it is installed. Our model will use a block Routing the cables and protecting any of the electronic equip- downconversion scheme, since that Your dish will interconnect with the ment from electrical spikes and tran- seems to be the most popular receiver electronics inside your home via some sients. Let's first see how we can protect format for 1985. quantity and type of cables. Here is a outside equipment from the elements. Let's start out with the dish, as that is rundown on some of the cabling that In any type of system we have at least an where most people perceive the system to you're liable to find in a TVRO installa- LNA/LNB/LNC unit out of doors. It has a begin. We have already looked at why and tion. signal input end, which is connected to where you want to locate the dish, and A length of coaxial cable (RG -59/U or the feedhorn, and a signal output end that why certain types of installation pro- RG -6/U) that's used to carry the signal is connected directly to the indoor equip- cedures may be more attractive than indoors from the outdoor mounting LNB/ ment. (If we are dealing with an LNA, we others. So, what else do we need to know LNC or downconverter. will also have a separate downconverter about the dish? A three to five (or more) conductor between the LNA and the indoor equip- Well, for one thing, the dish surface cable that's used to carry the motor drive ment.) The connections between the must be highly accurate. As you may voltage to the dish positioner jackscrew, LNB/LNC, or the LNA/downconverter, know, the surface of most dishes are para- and carry sensor "feedback" signals back are made with coaxial cable, as previously bolic shaped so that the weak signals that inside to the dish positioner control box. discussed. Those cables must be able to bounce off them are focused at a single A piece of RG -59/U or RG -6/U (or in withstand weather/environmental condi- point. That concentrating of signal pro- some systems simply a pair of wires) tions such as moisture, heat, cold, dirt, duces a signal that is strong enough for the that's used to carry a tuning voltage from and dust. Moisture, in particular, can be a following electronics to process. As the indoor receiver out to the downcon- serious problem. would follow, then, the more accurate the verter/LNC (in systems in which only a Moisture of any type must be kept out surface the stronger the signal produced; single frequency is passed from the down - of the system. That means out of the in other words, the higher the gain. But, converter to the receiver). LNA/LNB/LNC, separate downconverter how do you select a dish that has an accu- A two or three conductor cable used to (if used), and any connectors. Special rate surface? Here are some rules of select the polarization of the LNA. moisture-barrier compounds have been thumb. Those are the basics, but some systems developed; one such is Coax -Seal (avail- Dishes that are "parabolic both ways" use even more cable between the dish site able at Radio Shack). Those compounds are generally better than dishes that use and the inside electronics. Now, how does seal any equipment housing or connector/ "flat panels". Parabolic both -ways simply one route all of that cable safely and at- fitting so that it resists moisture penetra- means that the panel sections follow the tractively-or at least reasonably so? The tion. parabolic curve lengthwise (from center logical way is to bury the cable under- Moisture and ice present special prob- to outer edge) and crosswise (across the ground. There are two ways to accomplish lems to TVRO dish positioners. The jack- panel). Some dishes use flat panel sec- that: use so-called direct burial cable, or screw drives are apt to freeze when they tions that follow the parabolic curve only route the cable through a length of PVC get coated with ice and snow. (Another, from center outward to the rim edger pipe. Direct burial cables are now avail- related problem is that snow may fill the Dishes that use flat panel construction able in a single weatherproof sheath or dish, and the combined weight of the have less gain than those that are parabolic wrapping that contains all of the individu- snow and dish may be more than the drive both ways, assuming that all other factors al wires or cables needed. With it, you can move. The solution to that problem, (size, shape -accuracy, etc.) are the same. bring indoors only one large cable, rather of course, is to make sure that any snow The difference in gain is on the order of 1 than several individual cables. But even if has been cleared from the dish before at- dB, and possibly greater. you do chose to use that type of cabling, tempting to move it.) Dishes that use ribs with structural sup- the use of a PVC pipe is recommended. If you live in an area where ice and port should have greater surface accuracy Direct burial cable is, for instance, not snow are common, anticipate winter then those that have ribs that are simply immune to damage from a burrowing ani- problems with motor drives. A cage or pressed into a parabolic shape. Metal has mal, such as a rodent (those nasty little shield, probably best custom-made by "memory"-when you stamp, stretch, or creatures can really do quite a bit of you for your installation, to keep the ice force a piece of metal to follow the para- damage to cables), and such cable is fair from coating the motor drive and freezing bolic curve, the metal wants to regain its game for anyone armed with a shovel or a up the system would be a good Saturday original shape (i.e., a straight piece of spade. afternoon project after the system is in- aluminum or steel). It is possible that with Make sure when you select your cable stalled. And it sure beats missing the time, plus heat and cold, the metal may that you take the following points into Super Bowl in late January because of a lose some of its surface accuracy. consideration: heavy ice storm! The rear support structure of the dish is The length of your cable is important; As to transient or surge suppression, very important. It provides rigidity for the some of the control wires and the signal for safety's sake: All TVRO hardware entire dish and ensures that it does not (coaxial) cable have specified maximum should be protected with an external sur- warp or bend out of the desired shape. lengths. If your runs of cable exceed those ge/transient supressor. Those plug-in de- Unfortunately, most of us are probably lengths, line losses may cause your sys- vices (available from many sources and incapable of evaluating a back -plate sys- tem to fail to work altogether. often for under $10) will save you count- tem for its ability to maintain dish shape. Some areas have special electrical in- less moments of frustration. Remember, Still, a dish minus any form of back -plate stallation codes affecting TVRO's (Los anything in the TVRO system should be system should at best be suspect. Angeles, for example). You may need an so protected, even if the equipment sup- Assembly details vary from dish to outdoor wiring permit before you install plier makes his own claim for internal dish. We are going to give you some your cables, or the entire TVRO system surge and transient protection. guidelines; but out of necessity, they will 59 sides appears to be out of alignment, there is a potential warp in the framework hold- ing the dish. Find out why and fix it, because a warped dish will not work prop- erly. If your dish is of the screen -mesh vari- ety, don't hesitate to use lots and lots of clips (attaching the mesh to the under sup- port pieces). The clips do more than as- sure that the screen mesh won't blow away; they force the mesh down to the undercarriage and therein ensure that the surface will follow as closely as possible the desired parabolic curve. USE PLENTY of clips! In many designs, the Clips are seldom "fun" to install, and mesh surface adheres to supportive under the tendency is to shortcut the job and structure only when lashed down with clips. If install just enough to get by. That is a bad you use too few clips, the system will not per- form to specifications. mistake, as performance of a screen -mesh dish depends upon forcing the surface into be generic rather than specific. When as- a near-parabolic curve; and that only hap- sembling your own dish, follow the in- pens when the mesh actually adapts to the structions supplied with the unit. parabolic curved undercarriage -support Most dishes assemble upside down, pieces. Take an extra hour to put in lots and work should be done on a flat surface. and lots of clips and you will be properly' All pieces should fit and all bolts should rewarded with first-class pictures. slide through without your having to tug at Get plenty of help to lift the dish onto parts, pry with heavy wedges, or (heaven the mount. If the dish gets away from you forbid!) drill new holes for bolts. If you and falls, it will hit on a edge and bend or FEED -SUPPORT ARM places the feed and LNA (or LNB LNC) at the focal point of the dish. The find something does not fit (i.e. holes do warp; probably permanently. If that hap- feed arm adjusts in and out to ensure precise not line up), stop and stand back. Before pens, you'll be best off starting all over setting for maximum signal. you attack the stuck part with a pry bar or again. drill, see if perhaps you have misaligned The dish mount should include instruc- of the dish at several points. The dish some previously installed part that, in tions for setting something called declina- should be equal distance from the rim to turn, results in the new part not aligning tion offset for your locale. That is a special the feed edge all the way around. Other- properly. adjustment, usually built into the rear of wise, the dish is warped and/or is some- All name -brand dishes are now "gang the arm protruding back from or away how off center. drilled," which means that all of the holes from the rear of the dish. It is very impor- are drilled at one time and in one opera- tant if you want your dish to track the Tracking the dish tion. Workman error (misdrilling one Clarke Orbit belt properly. You will need There are numerous techniques for lo- hole) is virtually a thing of the past. Be- an inclinometer to set that offset adjust- cating your first satellite with your dish; fore you curse the manufacturer's quality ment. Most dish manuals have a chart that once that's done, assuming everything is control, check your own! lists the declination offset amount for vari- working properly, the dish should auto- When assembling the dish superstruc- ous states or areas. matically track through the remaining sat- ture, or in the case of fiberglass or solid The feed is that device that mounts on a ellites in the Clarke Orbit belt. The metal surface dishes, don't wrench tight- pole out in front of the antenna. Its job is technique we would like to share with you en any bolts until all pieces in the "pie" to gather the reflected signal and pass it on is among the oldest, but it works very are in place. There is always a small to the rest of the TVRO system. It needs to well. amount of adjustment room in connecting be adjusted properly if your system is to Start by making sure your declination segments together and if you start taking work. Some feeds allow only one adjust- (offset) is properly adjusted. Now, using up that adjustment room by wrench tight- ment by the installer; others allow several. the chart you prepared that shows the ele- ening before you have all of the pieces in The most basic adjustment is setting the vation and azimuth headings for your lo- place, you may adjust yourself right out of distance away from the dish. The dish cation to the various satellites, select a the tolerances required to slide the last manual will tell you the focal length, and satellite that is fairly low to your west, piece into place. that is the distance measured from the such as Gl, F3R, or D4. When you do tighten up the bolts with center plate of the dish, at the hub, to the Take the elevation heading (15.1 de- wrenches, follow a pattern. Do the inside edge of the feed that is nearest to the grees for F3R from Albany, New York for (closest to the center or hub) bolts first, for center of the dish. Use a rigid tape mea- example) and hand -adjust the antenna's example, and do the bolts opposite one sure and slide the adjustable feed pole or elevation (using the motor drive control if another (across the hub or center) working pipe to reach that distance. you have one) so that an inclinometer laid around the dish (i.e. 12 o'clock and then 6 Another adjustment is the side -to -side against the flat back on the dish reads 15 o'clock, 3 o'clock and then 9 o'clock, and centering. That, if available or required degrees. Now you have the dish set for one soon). When all inner bolts are tight, then with your dish, ensures that the feed is satellite's elevation. start over with the same pattern on the looking squarely at the center of the dish, Next, turn on the monitor or TV set outer rings of bolts. and therefore all around the dish surface (this assumes, of course, all of the elec- When the dish is completed, carefully equally. tronics is now hooked up-we'll talk turn it over so that it faces up. That lets you If you want to make sure that the feed is more about that later) and set the receiver sight across the dish from the near side to properly centered (left and right, up and to either scan (if a scanning feature is the far side to see if the two align pre- down), take a roll of string or long metal available) or a strong signal (such as tran- cisely. Now move 90 degrees around the tape measure and measure the distance sponder 7 on F3R, which is ESPN). Slow- dish and sight across it again. If any of the from the edge of the feed front to the rim ly rotate the dish on its pipe -stand mount toward the expected azimuth heading for ment. Modern satellites (all but Westar 3 F3R (246 degrees in Albany). With the are modern by today's standards) transmit dish already set at the proper elevation, 24 channels of possible service. Twelve of you will "run across" F3R as you come up those channels are transmitted using ver- on the 246 degree heading. Stop there and tical polarization, and 12 using horizontal temporarily lock down the bolts that tight- polarization. Polarization, of course, is en the dish -mount collar to the pipe -stand the technique that makes it possible to mount. cram 24 channels of programming into Now operate only the motor control or the frequency space allocated to 12. But hand crank, and move the dish east. Place that's not our concern here. (For more the receiver in scan so that the receiver is information on that topic see "All About changing channels automatically as the Satellite TV," in the June 1984 issue of dish moves. As the dish's azimuth head- Radio -Electronics.) Instead, we'll con- ing changes, the polar -mount mechanism centrate simply on how you install and will also cause the dish elevation to properly adjust the feed. change, raising the dish higher and higher The feed installs on a plate of some sort as it tracks to the east. That allows it to at the end of the feed arm or bracket. As track the arc of the Clarke Satellite belt. we mentioned earlier, the length of that (We have been assuming all along that you feed arm can be adjusted so that the feed is are using a polar mount; other types are properly located. In addition, however, available, but they are very difficult to the arm (or in some cases, only the plate adjust when moving from satellite to sat- that the feed is mounted op) rotates. Let's ellite.) Along the way, you will note flash- see how that rotation is used to make the es of signal as the dish tracks first past one skew adjustment. satellite, then another. Stop when the dish First of all, install the feed on the plate is aimed at F4; transponder 7 (National using the hardware provided. Adjust its Christian Network) on that satellite is also distance to the center of the dish as de- strong in most areas. scribed earlier. Once the system is operat- Now, adjust only the dish's mechanical ing on at least one satellite, tune in a ELEVATION is set on this antenna with turn- elevation setting for best picture; do not signal. Note, using one of the many satel- buckles. touch the azimuth adjustment (i.e. don't lite TV guides (sometimes, one of those is spin the dish on the pipe mount by loosen- even included with your dish) whether the necessary, to make all signs of the ver- ing the collar to pipe bolts). When you transponder you are viewing is horizon- tically polarized transponder 7 signal dis- have peaked for best signal, operate the tally or vertically polarized. Going back appear. Once that's done, tighten the bolts motor drive or hand crank and return to to our old friend, F3R, transponder 7, we that lock the feed -support arm in place. F3R. find that it is vertically polarized (on that Once you are back to that satellite, if satellite, odd -numbered transponders are The electronics the picture is no longer as good as it was vertically polarized; even -numbered ones Everything we have discussed up to this when you first found it, adjust only the horizontally polarized). Set the polariza- point applies to any type of TVRO system azimuth by carefully loosening the collar tion control in your system for vertical. you might install. The rules are the same to pipe set bolts and nudging the antenna Examine the signal displayed on the for LNA/downconverter, LNB, or LNC first one way and then the other. When you monitor. Then switch to transponder 8, systems. The type of system you select have the picture peaked, re -tighten the and re-examine the signal. If automatic will, however, affect what follows. bolts in the following manner. polarization switching is built into re- As we feel that block downconversion Make each bolt finger tight. ceiver, the act of changing transponders (BDC) offers some significant advan- While watching the receiver signal - should also have changed the polarization tages, such as the ability to have multiple level meter (or if none is available, the TV of the feed and you should have a good receivers without restricting the choice of screen, although that's a poor second picture. If your receiver does not have viewing to a single transponder. we will choice), take a wrench and make one automatic switching, you will have to set outline a system that uses that technology. quarter turn on each of the collar tighten- the polarity, via the appropriate control, A BDC system consists of the following: ing bolts in succession. Do not tighten one for horizontal. Some form of signal amplification at all the way and then move on to the next, Unless you are extremely lucky, there is the feed (LNA, LNB). since by doing so, you will slip or slide the bound to be some evidence of the tran- Some form of frequency downconver- collar on the pipe. sponder 7 signal present. That may in- sion. If you use an LNA, you will need a Repeat the sequence, a quarter turn at a clude drifting vertical lines, or even two separate block downconverter. If you use time, until all bolts are tight. Do not over- video signals (the one from transponder 8 an LNB, the downconverter and LNA are tighten; those bolts typically will break off and a weaker one from transponder 7). If in a single package. if you use more than moderate wrench present, we obviously need to remove any Cabling from the LNA/downconverter pressure. sign of the vertically polarized transpon- or LNB to the receiver Return to F4R and double check that it der 7 signal. (If you have a receiver with Signal splitters that will allow you to is still peaked. If necessary, re -touch its automatic polarity switching, the first step route the satellite signals to multiple re- signal level by carefully adjusting the ele- is to temporarily disconnect the polarity ceivers (if your system calls for that). vation adjustment. (If adjustment is control lines between the receiver and the The job of the block downconverter is needed, it is usually caused by an ill - LNB-simply unplug them from the back to convert the satellite's 3.7- to 4.2 GHz threaded rod or turnbuckle.) of the receiver.) To do that, mechanically signals to sóme lower band of frequen- rotate the feed support arm a touch until cies. Among other things, that allows the The feed system any signs of the adjacent transponder dis- connection between the dish and the re- The information on centering the feed appear. Now, switch back to transponder ceiver to be made using common coax, aside, there is one adjustment required on 7, but leave the polarity control set for rather than special high -frequency (and the feed proper. That is the skew adjust- horizontal. Once again, rotate the feed, if very high cost) cable. The output frequen- 61 LNA + tion and polarization selection. FEED Power for the LNB (or LNA and block downconverter) comes from the master receiver and is usually supplied via the MASTER RECEIVER! same coaxial cable that carries the output CONTROLS from the downconverter indoors In satellite TV "lingo" the downcon- 20 dB verter is labeled the headend. or more OOWNCONVERTER GAIN 2 WAY 2 WAY IF LINE SPLITTER SPLITTER simply, the point where the signals ori- ;-s AMP SLAVE ginate. The downconverter has some out- 950 TO 1450 RECEIVER MHz BLOCK put level, specified in dBmV, where 0 OUTPUT dBmV is 1 millivolt (measured across a 3.7TO 75 -ohm coaxial cable). A typical 4.2 GHz signal level from a block downconverter is +10 dBmV. 2 WAY SLAVE That + lOdBmV has to be SPLITTER RECEIVER signal shared between each of the receiver locations. (The typical satellite receiver requires a minimum input signal level of 0 dBmV.) There are two approaches to that. For POWER TO OOWNCONVERTER/LNA PATH larger systems, a tapped trunk approach, SLAVE similar to that used by cable companies is RECEIVER the best route to go. For a relatively small system (4 or fewer receiver locations), as FIG. 4-A FOUR -RECEIVER SYSTEM. Use of the line amplifier ensures that signal levels will be shown in Fig. 4, the splitter approach is sufficient to overcome any line loss or the loss caused by the splitters. recommended, since it makes slightly better use of the available signal levels. In cies of a block downconverter varies by faced and solved by CATV and MATV Fig. 4, we show a system with two re- manufacturer, and range from 270 - operators. ceiver locations on the ground floor, and to -770 -MHz to 1140 -to -1640 -MHz, but There is, however, an important dif- two receiver locations on the second floor. all have one thing in common: They all ference. In setting up a home distribution The connection from the downconverter use a 500 -MHz band of frequencies, such system for satellite TV, we cannot simply to the house is made using a single length as 450 to 950 MHz. That is because, in the march into our local parts supplier (such of RG -6/U. At the entry to the house, we block downconversion systems, all sig- as Radio Shack) or a local CATV supply have a two-way splitter; between the nals in the 500 -MHz input band (4.2 GHz house, and purchase the components we downconverter and the splitter we also - 3.7 GHz = .5 GHz = 500 MHz) are need. That's because the frequencies used have a line amplifier, but let's ignore that output to the receiver. Thus, the output in satellite TV are generally higher than for now. The splitter splits the signal into band is a faithful reproduction of the input those used for cable or broadcast TV. two "legs". One of those legs, as we said band, only lower in frequency. Thus, since the signal splitters, taps, and before, feeds the two downstairs re- Even though the output of the down - so on, generally available from the above ceivers. To do that, the signal is fed to a converter is much lower in frequency than mentioned sources, are designed for use second two-way splitter. One output from the input, it is still high enough for line at lower frequencies, they will work that splitter feeds the master receiver, loss to become a significant problem, es- poorly, or not at all, for our application. while the other goes to the first -floor pecially at the high end of the range of Fortunately, appropriate equipment, in- slave. (Note that the control signals and output -frequency bands used. The trick, tended specifically for satellite -TV ap- power are fed from the master receiver to then, is to ensure that each receiver in the plications, is made by several manufac- the LNA/downconverter.) Meanwhile. home system receives adequate signal turers. and should be available from your the second leg is once again fed to a two- strength from the block downconverter. installer or dealer. way splitter whose outputs are used to That factor must be considered when feed two upstairs slave receivers. planning your system. Also, in a multi- Loss and gain While we've just outlined what looks to ple -receiver setup, the individual receiver Receivers in a satellite system are cate- be a very efficient small distribution sys- locations should be isolated from one an- gorized as masters and slaves. The dit: tem, can we be sure that it will work as other to ensure that there is no unwanted ference is that the master receiver, which intended? To answer that, we have to keep interaction between those units. should be located where there is the most some points in mind. Neither problem is really anything TV traffic, controls certain functions for The downcoverter output is approx- unique to satellite TV. They've all been the entire system, such as satellite selec- imately + 10dBmV (though that can vary, so check the manufacturer's specifications for your unit). TABLE 3-CABLE LOSS The minimum acceptable input level at each receiver is OdBmV. Top end frequency Cable type Loss per 100-feet From the above, it appears we can sus- 770 MHz RG -6/U 6.0 dB tain about 10dB of loss before we run into 770 MHz RG -59/U 7.5 dB problems. That loss will come from two 950 MHz RG -6/U 7.0 dB sources: the splitters and the cable. Turn- MHz RG -59/U 8.8 dB 950 ing first to the splitters, there are two be- MHz RG 9.5 dB 1450 -6/U tween each receiver 1450 MHz RG-59/U 11.0 dB and the downcon- 1640 MHz RG -6/U 10.1 dB verter. The typical two-way splitter has 1640 MHz RG -59/U 12.0 dB 4.0dB of "loss." (Actually, only about I dB is really lost, the balance of the 4 dB is (continued on page 93) All About OPTOCOUPLERS Interfacing digital signais to real -world devices has always been a difficult task. But optocouplers can help make it easy! DANIEL M. FLYNN HOW OFTEN HAVE YOU WANTED TO INTER - face a logic circuit to real -world devices that operate from an AC source or a high DC voltage? That interfacing problem can be overcome in many ways. But perhaps the best way is to use an optocoupler. Optocouplers have a lot to offer: electrical isolation, logic -circuit compatibility., small size, and high reliability. Optocouplers can be used in applica- tions that require electrical isolation- when the low DC output of a logic circuit is used to control an AC motor. Since a logic circuit is incapable of delivering an AC voltage, and AC induced in the logic circuit can cause all kind of trouble, the motor and the logic circuit must be elec- trically isolated. And that's where the op- tocoupler really comes in handy. switch, or light-activated SCR. Figure 1 electrical parameters of the IRED. They An optocoupler might be used in ap- shows the schematic symbols for those are: IF, diode forward current; VF, diode plications where the high-level output of a types. Although other types are available, forward voltage, and VR, maximum re- metering device is fed to a micro- those shown are the most common. verse voltage. (See Fig. 2.) processor-controlled circuit to automat- Signals are transmitted between the two Because the DC output and transfer pa- ically start or stop operation at a electrically isolated elements by means of rameters differ depending on the type of predetermined point. (Consider a robotic a light path, or light source. The two ele- detector element used by the optocoupler, assembly line, for example.) ments cannot reverse their roles. And we'll list and define them separately ac- In this article, we'll look at several op- since there are no electrical connections cording to the detector. tocoupler circuits that may be used to in- between them, a signal passes through the Phototransistor- and photodarlington- terface logic circuits to the "real world," unit in one direction only. type optocouplers work on the same prin- or to interface any low -voltage circuit to ciple. The collector -to -base junction is one that operates on higher voltage. But Optocoupler parameters enlarged and works as a reverse -biased before we do that, we should first take a To successfully design with op- photodiode controlling the transistor. closer look at what optocouplers are and tocouplers, a clear understanding of their That is, radiation striking the junction discuss their parameters. parameters is required. Because we'll be generates electron -hole pairs, which are dealing only with low -frequency circuits, swept across the junction by the field de- Optocoupler basics we'll define only the DC parameters of veloped across the depletion region. The The optocoupler (also called op- those devices. The DC parameters are di- parameters for the photodarlington and toisolator or photocoupler) is a single vided into input, output, and current - phototransistor types are: component consisting of a light source transfer ratio. Ic, maximum continuous collector and photodetector. The two elements are The Current Transfer -Ratio or CTR is (output) current isolated from each other by a transparent the ratio of the input current to output V(BR)CBO, maximum collector to base insulator, and the assembly is completely current of an optocoupler (at a specified breakdown voltage enclosed in an opaque package. bias). It is often represented by r. That V(BR)CEO, maximum collector to emit- The light source for most optocouplers value depends on the efficiency of the ter breakdown voltage is a gallium arsenide (GaAs) IRED (/n- IRED and the spacing between input and V(BR ECo, maximum emitter to collec- fraRed Emitting Diode). The detector, or output elements. The area, sensitivity, tor breakdown voltage output element, may be a phototransistor, and gain of the detector also play a role. Optocouplers that use light -activated photodarlington, light -activated bilateral The DC input parameters define the bilateral switches in the output are de - 63 GLOSSARY OF OPTOELECTRONIC TERMS Bandgap (electronic)-the potential dif- ference between the valence and con' duction bands, which determines the forward voltage drop and frequency of light out of a diode. a b Current transfer ratio (electronic)-the ratio of input current to output current at a specified bias of the optocoupler. Dark current (electronic)-the leakage current of a photodetector with no inci- dent light, usually ICE& Detector (radiometric)-a device that changes light energy (radiation) to elec- trical energy. Effective irradiance (electronic)-IR perceived by a detector. Emittance (radiometric)-power radi- FIG. 1-MOST COMMON OPTOCOUPLERS: a has a phototransistor output; b, a photodarlington; c, a light -activated bilateral switch, and c has an SCR output. ated per unit area from a surface. Emitter (radiometric)-a source of radi- ation. The specifications for three optocoup- Infrared (photoelectric)-radiation of ling devices -4N33, 4N26, and longer wavelength than normally per- MOC3010-are given in Table 1, Table 2, ceived by the eye; i.e., .78 to 100 micron iv/ and Table 3 respectively. wavelengths. Irradiance (radiometric)-radiated Voltage level shifters power per unit area incident on a sur- When a logic circuit is required to ac- face, broadband analogy to illumina- cept inputs from the real world, it is often tion. FIG. 2-THE INPUT ELEMENT of most op- Isolation voltage di- necessary to shift the voltage level of an (electronic)-the tocouplers is a gallium arsenide (GaAs) IRED. electric withstanding voltage capability input signal to 5 -volt logic levels. If the of an optocoupler under defined con- signed for applications that require iso- input is a DC signal, it can be interfaced to dition and time. lated triac triggering, low -current isolated the logic circuit using an optocoupler Light current (electronic)-current AC switching, and high electrical isola- without electrically tying the two together through a photodetector when illumi- tion. For that type of device the param- (i.e., the two circuits do not share a com- nated under specified bias conditions. eters are: mon ground.) Optocoupler (electronic) --a single component that transmits electrical in- IT(RMs>, maximum on -state RMS cur- The advantage to that is that any noise rent or voltage spikes on the signal -circuit formation between a light source and a light VDRM, maximum repetitive off-state ground are not directly impressed on the detector, which are not electrically connected; also called optoisolator or output terminal voltage logic -circuit ground. An optocoupler can photocoupler. VTM, peak on -state voltage. also be used to convert AC signals to 5 - Photoconductor (electronic)-a mate- Light -activated SCR optocouplers are volt logic levels, while isolating the logic rial whose resistivity is a function of the designed for applications that require high circuit from the high AC voltage. radiation level falling on it. electrical isolation between low -voltage Source (radiometric)-a device that provides radiant energy. circuitry (like those using IC's) and the +5V AC line. The parameters for the SCR de- vices are: IT(RMs), maximum on -state RMS cur- tocoupler's diode input. rent When a 12 -volt signal is presented to VDRM, maximum repetitive off-state the input, current flows through R1 and output terminal voltage the IRED. That current lights the IRED, VRM, maximum reverse voltage and the light striking the pho- The transfer parameters of an op- todarlington's collector -to -base junction tocoupling device (as above) is mentioned OUTPUT causes it to turn on. The photodarlington the measure of the ratio of current trans- output is used here because its large CTR mitted between the input and output ele- R2 value allows enough current to pass ments. For phototransistor and pho- 47Oí through resistor R2 to develop the re- todarlington type units, the parameters quired voltage at the output for a logic 1. are: The output signal can now be used to drive CTR (II), ratio (in percent) of the mini- FIG. 3-THIS CIRCUIT MAY be used to trigger a TTL gate Input. a logic -gate input. mum high collector output -current to di- Removing the 12 -volt DC signal turns ode current at a given VCE and IF. Figure 3 shows one optocoupler ap- the photodarlington off, and R2 pulls the VCElsat), the collector-to -emitter sat- plication where a 12 -volt DC (VIN) input output low. (In low -speed switching cir- uration voltage is converted to 5 -volt logic levels. Here we cuits, the base input of photodarlingtons For light -activated bilateral switch and see a circuit using a 4N33 optocoupler. and phototransistors typically remain un- SCR types: (Specifications for that device are given in connected. However, high-speed circuits IFT, maximum IRED trigger current Table 1.) The 12 -volt input causes the out- use the base input to increase the switch- required to latch (trigger) the output put of the optocoupler to go to a high logic ing speed of the device.) IH, holding current required for the out- level. In addition, any common -mode When designing similar circuits for put to remained latched noise is rejected because of the op - various DC -input levels, remember that 64 the value of R2 is determined by the input parameters of the logic gate being fed. TABLE 1 4N33 The value of R2 given by: SPECIFICATIONS R2 < VIL/11L Minimum Typical Maximum Units where VIL is the low-level input, gate volt- IF 80 mA age and IIL is the low-level input, gate Input VF (IF =10mA) 1.2 1.5 V current. VR 3 V The value of R1 is found by first solving Ic 30 100 mA for Ic (collector current): V(BR)CBO 30 V Ic = VIH/R2 Output V(BR)CEO 30 V where VIH is the high-level input to the V(BR)ECO 5 V driven gate and R2 is resistance in ohms. Coupled Ic (IF =10mA, VcE=10V) 50 mA Next, solve for IF (diode forward current): Parameters VcE(sat) (IF= 8mA, Ic = 2mA) 1.0 V IF = Ic/1I where is of the optocoupler. To 'q the CTR TABLE 2 find the CTR, go to the specification sheet 4N26 SPECIFICATIONS in Table 1 and look under the heading Ic for the coupled parameters. From that we Minimum Typical Maximum Units get: IF 80 mA 1.1 1.5 V -11 = le/IF = 50/10 = 5 Input VF (IF =10mA) Now the nominal value for R1 is given by: VR 3 V R1 = (VIN - VF)/IF Ic 100 mA As an example, let's calculate the val- 70 V Output V(BR)CBO ues of R1 and R2 for Fig. 3, assuming that V(BR)CEO 30 V the driven logic gate is a standard 7400 V(BR)ECO 7 V series. For that type of device, the input Coupled CTR (IF= 10mA, VcE =10V) 20 ° ó .8 VIH = 2 parameters are: VIL = volt, Parameters VCE(sat) (IF = 50mA, Ic = 2mA) 1 5 V volts, and IIL'= -1.6mA. Therefore, the value is given by: of R2 TABLE 3 R2 < VIL/IIL = .8/(1.6 x 10-3) < 500 MOC3010 SPECIFICATIONS Now it can be seen that R2 is chosen to be the largest common resistor value that Minimum Typical Maximum Units is less than 500, which is 470 ohms. IF 50 mA Using the value of R2, solve for the col- Input VF (IF =10mA) 1.2 1.5 V lector current: VR 3 V lc = VIH/R2 = 2/470 = 4.3mA IT (RMS) 100 mA where 2 is the high-level gate input volt- Output VORM 250 V age and 470 is the value of R2 in ohms. VTM (IT.- 100mA) 2.5 3.0 V The value of IF is found from: Coupled IF 8.0 15 mA IF = Ic/r) = 4.3/5.00 = 1.0mA Parameters IH 100 Now look up IF under the input heading and le under output. Since neither of the calculated values exceed the maximum ratio is only 46%. 117 VAC ratings of the 4N33, we can now solve for The circuit in Fig. 4 converts a 24 -volt +5V R1: input, VIN, to an inverted 5 -volt output. VIN -VF 12-1.2 That is, a high input causes the output to R1 = 10.8K - - go low. When a 24 -volt signal is present, R1 IF I x 10-3 56K current flows through the IRED, and the The value the 4N33 closest common resistor to phototransistor conducts. Because the one calculated for R1 is 10K. ONC output of the device is taken at its collec- Decreasing the value of R1 increases tor, the input to the logic gate is low. the loading effect on the signal source and I When the input signal is removed, the decreases the transfer efficiency. For in- phototransistor turns off and R2 pulls the stance, in a similar circuit with RI chosen output high. The 4N26 is used here in- OUTPUT to yield a IF of 20mA, the current -transfer 4 stead of the 4N33 because of its lower O value. Table 2 shows the specifi- #R2 24VDC +5V VcE(,at) cations for the 4N26. 47052 is The resistance of for R2 not critical. D1 Cl R2 R1 A nominal value for R1 for any input volt- 1N4383 35µF T 2.2K 4N26 10K NC age (VIN) level is given by: R1 = (VIN - VF)IF where FIG. 5-NON-INVERTING circuit that converts 5 OUTPUT 117 volts AC to to 5 -volt logic levels. IF = [(VCC-VCE(sat))/R2-IIL]/T). The IF value guarantees that the pho- totransistor will saturate. The value of R1 1 5 - .4 + .0016 _ iomA when VIN is 24 volts is easily found. Let's F 10,000 .20 say that the driven gate is once again a Using that value, you can now find the 7400 series TTL. Since R2 is 10K and the resistance of R1: FIG. 4-THE BASE CONNECTION OF the 4N26 gate requires an input current, IIL, of R1 = 24 - 1.1/10 x 10-3 = 2.3K is used to increase switching speed. - l .6mA, then: The closest standard value is 2.2K. A non -inverting circuit that converts a +v 117 volts AC to a 5 -volt logic level is shown in Fig. 5. With a 117 -volt input applied, current flows in the IRED for R5 33052 R6 one-half the AC cycle and in diode Dl R1 R2 1800 10K 1MEG during the other half. 14 During each positive half-cycle, the zl 7 photodarlington conducts. That causes a 6 pulsating DC voltage to develop across C2 R2, which is then filtered by capacitor Cl. Z 35µF The voltage across Cl forces the gate input high. When the AC input is removed, the +v IC1 photodarlington turns off. The voltage R4 555 t14 100K across Cl drops as the capacitor dis- 5 charges R2. Now, R2 pulls the D Q Qi through 2N2222 gate input low. 1C2 1/24013 TO 117 VAC 3 2 Load control CLK When interfacing logic circuits to the 4 6 yC1 Tal +V 01 TO FROM LOGIC T1 ROOM LIGHT 1N4001 GATE 6.3 V V C3 ...L' +V 35µF E , 117 VAC L C4 35µF I I ^ R1 -0 O R3 I 10K L_ __J SI MAT SWITCH FIG. is a 0.1 9-THE OPTOCOUPLER triggered by one-shot to turn on room lights when some one steps on the mat switch. Si. TO 117VAC real world, a logic gate output is often gin of safety. The largest load that the FIG. RELAY logic 6-A can be used to interface required to control a 117 -volt AC load. MOC3010 can handle is 12 watts. gates to real world devices, but circuit require- ments may exclude its use. The relay circuit of Fig. 6 can be used in The circuit in Fig. 8 overcomes the such applications. However, many circuit power switching limitation of the design requirements may exclude the use MOC3010. Now we see that the output of of a relay. the MOC3010 is used to gate a power The optocoupler designs shown in Fig. triac. The value for R1 is calculated in the 7 and Fig. 8 provide electrical isolation same way as done for R1 in Fig. 5. and control without the disadvantages of The minimum current required to trig- the relay-circuit design. The control cir- ger the triac determines the maximum val- cuit of Fig. 7 may be used to drive loads ue for R2, while the power dissipation of with small AC power requirements. Here the triac gate determines the minimum a MOC3010 optocoupler is used; its pa- value for R2. The maximum value of R2 is rameters are shown in Table 3. given by: When the logic -gate output is low, cur- R2 = L(2Vs - VTM)/ISM J - RL rent flows through the IRED of the op- where VTM is the output parameter of the FROM tocoupler. if IF is equal to IFT, the optocoupler, IGM is the maximum gate LOGIC bilateral switch output is triggered into trigger current of the triac, and Vs is the GATE conduction. Since the bilateral switch AC supply voltage. FIG. 7-THIS CIRCUIT MAY be used in applica- conducts in both directions, power is de- tions that have small AC power requirements. Load control application livered to the load during the positive and negative halves of the AC cycle. As the Figure 9 shows a circuit that can turn TO +5v output of the logic gate that's feeding the room lights on and off as the pressure -mat 117 switch, is VAC optocoupler goes high, IF is reduced be- Si, activated. The 555 timer, low IH of the MOC3010 and the bilateral ICI, is configured as a monostable (one- MOC3010 switch turns off. shot) to de -bounce Si and allow time for The maximum value for RI is given by: the person to step off the mat. The output of IC1 at pin 3 is fed to half MT2 VCC(MIN) VF(MAX) VOL R1 - - of a 4013 dual, D -type flip-flop, IC2-a, so 1Fr that it is triggered on each clock pulse. where VF and IFT are parameters of the When the Q output of IC2-a is high, tran- optocoupler used and VOL is the low-level sistor Ql conducts. That provides a path to 2 output voltage of the logic gate. ground for the diode current, and that, in FROM LOGIC Choose the largest resistor value avail- turn, causes the IRED to conduct. The GATE able that's less than the calculated value. light from the IRED striking the pho- FIG. 8-HERE THE MOC3010 is used to trigger a Remember, the logic gate must be capable todetector causes it to turn on triggering triac to accommodate larger load requirements. of sinking a current of IFT with some mar- TRI, delivering power to the load. R -E 66 LI L_I Ananog IN THE "OLD" DAYS-WHEN TTL. rent of the transistors.) When we (Transistor-Transistor Logic) was move the control switch to + V, a much more interesting thing hap- the only game in town-all sorts of 14 hassles used to crop up when you -1 pens. The P-channel gate is now designed circuitry that had both grounded and the N channel gate is Not at + V. Both transistors are turned digital and analog elements. L 13 only were there different voltage re- on and points "A" and "B" are quirements for each section, but connected to each other through the transients generated by one section 12 transistors. Since we're using two of the circuit were a problem for the complementary transistors, the cir- other section. All sorts of design cuit of Fig. I can handle current tricks had to be dreamed up if you 11 flow in either direction. The P - expected the circuit to be reliable channel transistor will conduct in and glitch -free. the one direction and the N -channel Designing the interface portion 10 transistor will conduct in the other. of the circuit also presented its own In other words, we can use the cir- special problems. Schemes of in- cuit to pass either digital or analog credibly complex circuitry had to signals. be dumped in the middle of an oth- The OFF resistance of the circuit erwise sane and orderly design. will be pretty high since we're es- The benefits you could enjoy by GND sentially looking at a reverse -bi- using digital logic to control analog ased silicon diode. The ON signals were often outweighed by resistance will be low; it's deter- the problems inherent in the de- mined by the voltage across and the sign. transistors and their physical Fortunately those days are gone characteristics. Although that forever. With the introduction of looks wonderful, let's see what's CMOS (Complementary Metal wrong with it-and what can be Oxide Semiconductor) technology done to make it better. Switches For starters, the ON resistance is a few years ago, most of the design problems we've been talking about went ROBERT GROSSBLATT going to be on the high side (about 500 out the window. The construction tech- ohms) for low-level analog signals. Run- niques used in the design of the chips in ning audio through that amount of resis- that family opened up whole new worlds tance, especially low -voltage audio, can of possibilities. Because CMOS uses both With CMOS switches, you can lead to possible termination problems and floating A further problem with P- and N -channel MOS transistors, (re- use digital techniques to con- signals. member that the "C" in CMOS means the circuit of Fig. 1 is that the resistance is Complementary), we aren't limited to trol analog signals. going to change as the voltage changes having the current flow in only one direc- across points A and B. That's because tion. Everything depends on how we con- there's always a voltage drop across a tran- nect up the transistors on the chip. We can sistor and the conductivity of even the see some of the possibilities that appear if world's most perfect transistor will vary we connect the P- and N -channel tran- somewhat with changes in voltage and sistors back to back as shown in Fig. I. +v A frequency. There's one more problem with the cir- The simple CMOS switch cuit of Fig. I. Even though the transistors Q1 1 1 Q2 When SI, the control switch, is con- --NI are a matched pair built on the same sub- st N strate, they are not exact complements of nected to ground, the gate of the -chan- P -TYPE 1 1 N -TYPE nel transistor is grounded and the gate of each other. That means that the signal path the P-channel (because of the inverter) is B from point "A" to point "B" won't be at volts. Since both transistors are exactly the same as the path from "B" to +V 1-SIMPLE CMOS ANALOG SWITCH. When are FIG. "A." In practical terms, that means that turned off, points "A" and "B" iso- S1 is switched to V, a signal path is created lated from each other. (Well, that's not between points "A" and "B." When S1 is switch- the resistances are going to be slightly entirely true-because of the leakage cur- ed to ground, the path is opened. different in each direction, and the switch will run the risk of distortion and latch -up if the current flow gets up around the max- imum limits of the transistors. The improved CMOS switch +v Its for those and other reasons that the type of switch circuit shown in Fig. 1 was soon referred to as a "simple" switch and s the semiconductor manufacturers intro- duced an "improved" version. Figure 2 is the schematic of the im- proved version. At first glance at seems as if there has been quite a bit of change, but a second look will show you that we've simply made a few common-sense addi- tions to the circuit of Fig. I. Two inverters have been added to the control input of the FIG. 2-IMPROVED SWITCH. The ON resistance has been decreased at the expense of a greater signal switch to isolate the control voltage from leakage when the switch is turned off. the voltages being switched. That pre- vents the possibility of the control voltage subject to the same sort of damage from start oscillating. Since the inverters will being modulated by the voltages across static electricity that you can expect with have no clear path to either end of the the switch terminals. The high ON any other CMOS IC. The oxide layer be- supply rail, they'll draw a lot of power and resistance of the simple switch has been tween the gate and channel of a CMOS you'll be running the risk of blowing up reduced by adding two new transistors, transistor is extremely thin and can be the IC and doing severe damage to the Q4 and Q5, in parallel with Q1 and Q2. punctured by even a moderate amount of other parts of your circuit. Since they're in parallel, the voltage drop static discharge. Follow the same han- All those usage rules may make things across the two pairs will be less than it was dling procedures you would with any seem a lot worse than they really are. But in the simple switch-and a smaller volt- MOS device and never insert or remove in practical terms, CMOS switch IC's are age drop means a smaller resistance. one of those IC's from a circuit that's extremely easy to use and provide solu- Because the controlling inverter is iso- powered up. It will ruin the chip-and tions to design problems by using meth- lated from the control switch, we can add your whole day. ods that simply didn't exist before the Q3 to make sure that the switching pairs 2. The amount of current you can route introduction of CMOS technology. of transistors stay off when the control through the switch changes somewhat Table 1 is a listing of some of the switch switch is connected to ground. Since Q3 with the supply voltage, but it should nev- packages that are available. As you can is an N -channel transistor, a logic -low at er be more than 25 mA for improved see, some of the IC's are multiplexer/de- it's gate will turn it on and help make sure switches and 15 mA for simple ones. Try- multiplexers-switch configurations that that the other transistors are held in cutoff ing to force more current through the are controlled by onboard binary de- when the switch is opened. Remember switch will do things like degrading the coders. They're a little bit slower than the that we added the extra switching pair, Q4 internal transistors (if you're lucky) or plain switch packages, but they come in and Q5, to lower the voltage drop across blowing them up (if you're not). really handy when you're looking for an the switch. Well, nothing is without a 3. There are voltage limits to your input easy way to distribute analog data. price. The cost of the lower resistance we signals. Never allow the voltage swing of Before we examine some of the infinite achieved was the increased possibility of the input to go above the supply rail or amount of uses for these IC's, let's exam- signal leakage through the switch when below ground. That isn't as much of a ine one consequence of usage rule 3-the it's turned off. Even though Q3 goes a restriction as it would seem because input voltage can't exceed the IC's power long way in helping to lock the other tran- CMOS IC's can operate over an as- supply. Although the voltages running sistors in cutoff, the simple switch of Fig. tonishingly wide power-supply range. If around in a digital system are usually I is still a better choice if your application you're sure that the voltage swing of the within those limits, analog signals are demands the absolute lowest leakage cur- signals going through the switch in your something else. It's perfectly normal for rent when the switch is turned off. circuit is going to exceed the range of the an analog signal to swing below system By using the basic principles we've just power supply, you're going to have to do ground. That is especially possible if the analyzed, chip designers have come up some designing to meet that restriction. analog signals are being generated by cir- with an incredible variety of CMOS Since CMOS can operate safely at up to 15 cuitry whose power supply is separate switches. By combining the switches volts however, you shouldn't have too from the digital supply. Figure 3 is a graph with other digital circuits, MSI (Medium much of a problem: It's a fairly simple that illustrates that problem perfectly. The Scale Integration) IC's have been de- matter to cut an input signal down to size digital voltage is between 0 and V + and signed that can solve almost any circuit ahead of the switch and boost it back up the analog swing is between + (V/2) and switching problem. On -chip binary coun- afterwards. - (V/2). Although the voltage ranges are ters and decoders allow the use of stan- 4. Never let the control pins float. That's the same (V volts), it's evident that the dard binary addressing to control the especially true if you have signal voltages difference in the values is going to present switching in a circuit. It doesn't take a always present at the switch inputs. Don't a special design problem-or at least one great deal of imagination to realize the forget that a general rule for all CMOS that has to be solved before the switches enormous advantage of being able to easi- design is that all inputs have to go some- can be used to process analog data. ly switch analog signals using digital con- where. Remember that the control pins The solution is the same as it is with op - trol lines. Before you rush out and pick up are connected to inverters inside the IC. If amps: The IC has to be powered by a some of those IC's, let's take a look at the control inputs are floating, the state of bipolar supply. You're going to have to do some of the rules you have to follow when the switches will be indeterminate at best something about generating a negative you use them. and haywire at worst. More than likely, voltage for the IC. That means using cen- 1. CMOS technology is used to make the inverters will bias themselves into lin- ter-tapped transformers or some other ar- analog switches. That means that they are ear operation and the whole circuit will rangement to produce the negative 68 TABLE 1-ANALOG SWITCH IC TYPES Pin 3 is the center pole of the switch and it will be connected to whatever pole is des- IC type Switch type Quantity ON resistance Frequency Operating speed ignated by the three -bit word presented to response the weighted select pins (9, 10, and 11). 4016 SPST 4 500 ohms 40 MHz 25 MHz @12 volts Pin 6 is an enable or inhibit control for the 4051 1 of 8 1 80 ohms 40 MHz 2 MHz @12 volts IC-if it's made high the inputs will be 4052 1 of 4 2 80 ohms 40 MHz 2 MHz @12 volts disconnected from the output. That's a 1 MHz 2 MHz @12 volts 4053 of 2 3 80 ohms 40 useful feature because there might very 4066 SPST 4 80 ohms 40 MHz 30 MHz @12 volts well be times when you want no channel 4067 of 16 1 200 ohms 40 MHz 5 MHz @12 volts Pin 7 gives us an easy 4097 1 of 8 2 200 ohms 40 MHz 5 MHz @12 volts to be connected. 4529 1 of 4 2 300 ohms 35 MHz 5 MHz @12 volts way to make the IC usable for both digital or and analog applications. 10 of 8 1 300 ohms 35 MHz 5 MHz @12 volts If you're going to use the 4051 to han - v DIGITAL HIGH .- VOLTAGE LEVEL - -4170- -( 13 )-- -- 12 }- d 11)- -(F0)--( V ANALOG SIGNAL 2 ¡ + VOLTAGE SWING DIGITAL LOW V VOLTAGE LEVEL 2 j V Ì I FIG. 3-SITUATIONS WHERE THE ANALOG sig- i I nal swings below the system ground require L____ _J that a bipolar supply be used to power the IC. voltage level. The exact amount of power you'll need from a negative supply will depend on how you're using the switch, -- J I the frequency the input voltage, the I I r- - - of output load, and so on, but the current 1 I ( 5 10 V demand will never exceed about to milliamps. Since so little is needed, a I I I center-tapped transformer is really over- i kill. A more realistic approach is to get below system ground by using some I GND "Mickey -Moused" circuits or even one of the IC's specifically designed for the job, 2 1-' -( 3 1- -( 4 --( 5 - -( 6 a - 74 such as Intersil's ICL-7660 voltage con- verter. FIG 4-QUAD ANALOG SWITCH. Functional diagram of the 4016 and 4066 switches. Some real devices Figures 4 and 5 show you two of the 1---(1-(1-5-(1-4)-(1-3\-(1-2)-(5)-4iä)--(9j IC's in the family of analog switches. basic types of Since they're typical of the 1+V 2 B Ci switches available, understanding them i will make you familiar with the other IC's in the series. ti-o03A SELECT I The 4016 (in Hg. 4) is a package con- taining four simple switches exactly like I-V 1 the ones we analyzed. The 4066 is a pin - l for-pin replacement containing four im- proved switches. The switches can be I ganged together any way you want to sat- I, isfy whatever switching needs you have. I I A high signal on any control pin will close 1 its associated switch and a low signal will II 1 open it. i Aside from the rules and limitations i we've already discussed, there's nothing I 7 5 special you have to watch out for when 4 6 INHI A/D GND I you use this IC. The switches are all inde- 1 )--( 5 6 )--( i--(ä- pendent of each other and the crosstalk `- )--( 2)-1 3-( 4 1--( 7 between them is very low-isolation is on the order of about 50 dB. FIG. 5-ROTARY ANALOG SWITCH, the 4051, is essentially the same as its mechanical counterpart. The 4051 (in Fig. 5) is one of the MSI rotary type switches we discussed before. and can be used, like its mechanical coun- dle only digital signals, you should tie pin It's a single -pole, eight -position switch terpart, to either select or distribute data. 7 to ground. That pin is connected to cir- 69 cuitry inside the IC that takes care of the +v tially an open circuit, crosstalk is less than voltage translation needed to handle ana- 50 dB, and because CMOS is an inher- log signals. When analog signals are ently noise immune logic -family, that sort going to be routed through the chip, you of circuit is a real possibility. should connect it to the lowest voltage The question of video switching is in- level in your system. That would be the teresting. The analog switches have more lower limit of the analog voltage swing CONTROL than enough speed and bandwidth to han- presented to the chip. In practice, that INPUTS dle it. Even the slowest devices can pass would probably be whatever negative frequencies up to 40 MHz and premium voltage level you're generating in your IC's can go way past that. I've built video system. switchers using analog switches and, Remember that you can't ever let the beyond the normal precautions you take input signals exceed the voltage range when working with high frequencies, no spanned by the supply levels on pin 8 and particular problems showed up. Re- pin 16. If you connect pins 16 and 7 to + 6 member: I'm talking about NTSC vid- and -6 volts respectively, and connect eo-not un -demodulated broadcast tele- pin 7 to ground, you can handle analog vision signals. TV signals would be a bit voltages of up to 12 volts and still use 6 - of a problem because you'd be looking at VOUT volt digital -control signals to select the VHF and UHF signals. You might be able channel you want selected in the IC. to handle the extreme lower end of the Even the slowest. of the analog switches VHF band, but that's about it. Since will operate at 2 MHz with a 12 -volt sup- Channel 2 centers around 58 MHz, you're ply. The frequency response of the switch- starting out at the upper limit of most es is typically 40 MHz. That means that FIG. 6-SIMPLIFIED SCHEMATIC of a digitally analog switches. And since UHF begins controlled variable -gain control. you can easily switch audio signals and somewhere around 440 MHz, it's out of even standard NTSC video signals. Since the propagation times are on the order of about 200 nanoseconds, you're probably thinking that these devices can be used for popless audio switching, remote control INN OFF of analog signals, and so on. ON Digitally controlled gain Well you're absolutely right. Let's look at two basic examples. Figure 6 shows 13 how you could use a 4066 to digitally o 14 Ló control the gain of an amplifier. The am- 15 plifier is an op -amp in a non -inverting o configuration, and the gain is determined 12 -0 A 11 INPUTS by the amount of resistance in the feed- 1 B 10 1 0 -o SELECT o back path. o C 9 By putting a binary word on the control 0 5 -o vouT pins, we can have any one of 16 possible o- gain settings that are both precise and 4 repeatable. Obviously that circuit is not the last word in this sort of thing, and we're not limited to using a 4066. We can gang as many switches as we want, use one of the "rotary" switches, or any com- FIG. 7-INPUTS TO AN AMPLIFIER can be switched in any order using the select lines. bination at all. Microprocessor control of things is a real possibility and the range of that you don't have to switch channels in the question. The best approach is to de- control you have will be limited only by any particular order as you do with me- modulate those signals before the analog - the width of your data bus. chanical switching. You might refer to switch circuitry, and cut the frequencies The advantages of digital gain -control that sort of circuit as a random-access down to a level more easily handled by the are obvious. Anyone who has fooled selector. Since those are analog switches, switches around with audio knows the insidious you can turn the circuit upside down and CMOS switches are the digital win- nature of 60 -Hz hum from the power use it to send a signal to a selected out- dows to the analog world. No logic family lines. As you run more and more lengths put-in other words, a distribution ampli- has ever been able to directly process the of shielded cable, your chances of main- fier. signals those IC's were designed to han- taining a clean signal get less and less. That isn't as trivial an observation as it dle. Although they can be used to deal That's in sharp contrast to digital signals: may seem. Remember that the 4051 will with digital data, their real advantage You can grind the digital control lines into scan outputs at greater than 2 MHz. That comes in being able to deal internally with the dirt and not upset anything. (Well, immediately brings to mind a unique sort analog voltages. The next time you design almost anything.) of distribution amplifier. A little bit of circuitry for audio or video signals, using Figure 7 shows you how you can use a design ingenuity will allow you to use one these specialized IC's can save you time at 4051 to select the inputs to an amplifier. If amplifier to feed eight outputs by scan- the bench. They'll also help reduce the you use that sort of arrangement with au- ning the outputs so quickly that there's no number of problems with power supplies dio signals, the transition from one chan- noticeable signal loss at any one of them. and provide you with an elegant solution nel to another will be smooth, popless, (That's similar to multiplexing LED dis- to what used to be an impossibly compli- and absolutely undetectable. Notice also plays.) Since the OFF resistance is essen - cated problem. R -E 70 =7_1- Are you still using your scanner's built-in antenna? Build one of these custom antennas and pull in those weak signals you've been missing! LOREN FREBURG need. Not the general-purpose (do -every- to that particular length then, generally thing -half-way) type, but one designed to speaking, the longer the antenna, the bet- IF YOU'VE RECENTLY BOUGHT A SCANNER/ be optimum for the frequency you are ter. Built-in antennas obviously don't monitor, you've probably become hooked most interested in, and yet provide good meet that criterion. A third problem with on evesdropping. You have also probably reception on the other frequencies! built-in antennas is that reflections from come to the realization that the skimpy There are three limitations to the built- nearby objects upset performance. Any- little antenna that screws into the top of in antenna. First, the height is too low. thing that is electrically conductive can the unit has serious limitations. Reception High -frequency radio waves tend to travel absorb radio -frequency (RF) energy and from highway-patrol mobile units may in straight lines, so low positioning limits then re -radiate it, causing interference or come and go. Fire department transmis- the antenna's performance. Rooftop signal drop out. Such re -radiators include sions from portable units may be inaudi- mounting allows the antenna to "see" far- any thing metallic from hoùse-wiring to ble from just a few miles away. And ther because the horizon is more distant. pipes, and even metal pictuìe frames. sometimes you may hear only the base The higher you can get your antenna, the A well designed outdoor antenna can station side of a conversation in a neigh- better. Second, the length of the filaments overcome all those problems. The three boring town. are arbitrarily chosen and possibly too antennas that we'll be describe, ground If you've had similar experiences, an short. A correctly designed antenna is of a plane, extended double -Zeppelin and external antenna may be just what you particular length. If an antenna isn't made coaxial collinear, offer the best perfor- 71 mance, and ease of construction at a low state in which the natural response fre- antenna, and visa versa. cost. They all share two characteristics: quency of a circuit coincides with the fre- The radiation pattern of a transmitting they are vertically polarized (mobile units quency of the applied signal. In other antenna is a three-dimensional represen- require vertical antennas) and they're om- words, it's a condition in which a mini- tation of its relative efficiency in radiating nidirectional. mum amount of energy is needed to main- power in different directions, as shown in There are several public service bands tain current flow. That condition exists in. Fig. 1. (Don't be concerned with the ter- that you're probably interested in. Those an antenna when its length is exactly one- minology, which appears to be describing bands are shown in Table 1. The bands are half wavelength (X/2) long. Only a small a transmitting, rather than a receiving, divided that way because radio frequen- amount of additional energy is needed to antenna: The functions and terminology cies are widely separated between bands. overcome losses in the conductor. are interchangeable.) The frequency determines the physical Let's take the analogy of a playground An antenna that radiates equally well in size a of particular type of antenna. Table swing (a rather crude example of reso- all directions can be represented by a 2 shows the typical antenna height of each nance, but it will illustrate our point). If a sphere, with the antenna being a point at antenna for a given band. swing is pushed gently once every pass, the very center. Such an antenna, which its motion is sustained indefinitely with exists only in theory, is called an isotropic Antenna theory little additional energy. But, if the swing radiator. Electromagnetic radiation travels at a is pushed at a rate that doesn't exactly The fundamental resonant antenna velocity of 186,000 miles per second (C) coincide with its movement, the smooth - (one-half wavelength long) is called a di- in free space or a vacuum, and more slow- flowing motion is interrupted. (You might pole when the feedline is connected to its ly through other substances-for exam- say that it has met some resistance.) Thus, center. Such antennas radiate energy in a ple, about 2/3 the free -space velocity maximum performance is obtained when figure -8 pattern, with a tiny hole in the through solid polyethylene. (The velocity the antenna is at, or at least near, reso- center as shown in Fig. 1-a. The dipole in a particular medium divided by the nance. runs through that hole. velocity in free space is termed the ve- Before we leave our swing, let's consid- locity factor.) er polarization from the simplest point of MINIMUM That radiation travels in a wave -like view. Although not a strict mathematical motion; the distance between successive explanation, the similarity gives some waves is defined as a wavelength. (The idea of its importance. A properly timed symbol for wavelength is X). Frequency is push, whether from the back or the side, defined as the number of waves passing a will maintain motion. However, our MAXIMUM MAXIMUM given point in one second. So a wave- swing is designed for front -to -back mo- length (in miles) is equal to 186,000 miles tion (you might say it's polarized). Like- per second divided by the frequency or wise, an antenna is polarized. Current number of waves per second. should flow along a conductor, not across One wavelength, in miles, is expressed it. MINIMUM as X = 186,300/f, where X is the wave- Antenna impedance is a difficult con- a length in miles and f is the frequency in cept to grasp because it doesn't really hertz. Likewise, wavelength can be ex- exist. It is only the mathematical quantity DIPOLE pressed in meters: X = 3 x 105/f, where X obtained by dividing the instantaneous is the wavelength in meters and is the voltage by the instantaneous f current, DOUBLE ZEPP frequency in hertz. which varies all along the antenna con- Because we're working with distance ductor. In a theoretical antenna in free measured in feet and frequency in mega- space, the current at the end is zero and hertz (MHz), the formula can be rewritten the voltage is at maximum. Thus, the im- as: X = 984/f, where X is expressed in feet pedance is seen to be infinite. and f in MHz. For example, a frequency At a point on the conductor where the 8 -ELEMENT of 984 MHz has a wavelength of one foot. voltage is zero and the current at max- COLLINEAR (As the frequency increases the wave- imum, the impedance is zero. The impor- ANTENNA length decreases. The opposite is true as tance of antenna impedance becomes ORIENTATION frequency decreases.) apparent when we attempt to transfer en- b Resonance is another point that we ergy in an antenna to a feedline and then to FIG. 1-ANTENNA RADIATION PATTERNS: a shows that the radiation pattern of a dipole is should consider. Resonance is defined as a a receiver or scanner. Maximum energy most intense at a point perpendicular to its cen- transfer occurs when the impedances are ter; b compares directional patterns for the TABLE 1 matched-ideally, a 50 -ohm monitor three antenna types. PUBLIC SERVICE BANDS connected via 50 -ohm feedline to the point on the antenna where the impedance Figure 1-a also Frequency shows that maximum is also 50 ohms. radiation Band Range Wavelength (maximum sensitivity in receiv- That allows all energy picked up by the ing VHF -low 30-50 MHz 33 ft. - 20 ft. antennas) is in a direction perpen- antenna to be transferred VHF-high 118-136 MHz 8 ft. - 7 ft. to the scanner, dicular to the orientation of the dipole. 148-174 MHz 6.6 ft. - 5.7 ft. assuming there are no other losses. The Moving toward the ends of the dipole, UHF -low 410-470 MHz same applies for transmitting antennas, signal pickup is at minimum. The dipole 2 ft UHF -high 470-512 MHz except for power differences. A proper is usually wired at its center because the transmitting antenna is a proper receiving theoretical impedance is 73.14 ohms, and that is a convenient TABLE value to match to a 2 feedline. TYPICAL ANTENNA LENGTHS The gain of a particular antenna is an Band Ground Plane Extended Double-Zepp Coaxial -Collinear expression of the amount of energy radi- VHF -low 6 ft. + radials 32 ft. 80 ft. ated (or picked up) in the direction of the VHF -high 11/2 ft. + radials 8 ft. 20 ft. highest gain, and compared to a reference UHF 6 inches + radials 2'/2 ft. 6Y ft. antenna. Let's use, for example, the hypo - 72 thetical isotropic antenna (which radiates TABLE 3 equally well in all directions) as our refer- CORRECTION FOR DIAMETER OF ROD ence standard. If both the isotropic anten- OR TUBING na and a dipole each radiate all of their will have some gain Wavelength Correction energy, the dipole Ratio ( because its energy is concentrated in Antenna Diameter Factor 0.945 fewer directions. Thus, the gain of an an- 50 70 0.950 tenna is a function of its radiation pattern. 100 0.955 A high -gain antenna has a radiation 200 0.960 GROUND PLANE pattern that's highly directional. Antenna 400 0.965 REPLACES gain is expressed in decibels (dB): dB = 1000 0.970 BASIC DIPOLE LOWER ELEMENT 10 log PA/PR, where PA is the power den- 4000 0.970 a b sity or field strength of the antenna being compared and PR is the field strength of complex and often unpredictable nature of the reference antenna. But how do we get reflections, they are best avoided. a gain with our antenna if we need recep- One way to minimize ground reflection tion from all directions? We don't really problems is to make an artificial ground need reception from all directions, just all an integral and therefore predictable part compass directions. Signals from above of the antenna system. That's an impor- or below us are not needed, and that's the tant feature of the ground plane antenna. key to unlocking better performance. Design theory must be combined with If the dipole antenna is positioned ver- the available materials to make an anten- GROUND PLANE RADIALS tically as shown in Fig. 1-a, its radiation na. The antennas described here use com- AT 45° INCLINE pattern wraps around it (like a coil monly available materials, and building c wrapped around a stick) and there is 2.14 them requires a minimum amount of FIG. 3-THE EVOLUTION of the ground plane dB gain relative to the theoretical iso- tools. The antenna elements themselves antenna: a shows the basic dipole; in b, the lower half of the dipole is replaced by a ground tropic radiator. To obtain more gain the are made from brass brazing rods, alumi- plane, and c shows the ground plane bent down- pattern must be compressed, making it num tubing, or coaxial cable. ward at a 45 angle. flatter and wider. One way to flatten out Brazing rods are available from weld- the pattern is to stack half-wave dipoles ing supply houses or someone who does (ground -plane) replaces the lower half of and connect them so that the currents are brazing (such as auto repair or machine the dipole in Fig. 3-b and functions much additive (in phase). shops). Aluminum tubing can be bought like a reflector. It has about 1.8 dB less Both the extended double Zeppelin and in most hardware stores and home im- gain than a dipole, but often outperforms the coaxial -collinear antennas are varia- provement centers. Coaxial cable and a dipole in spite of that. That's because it tions of the stacked -dipole technique. connectors can be obtained from elec- is less affected by reflections from the Their radiation patterns are shown in Fig. tronics supply houses and the mis- ground, which can cancel out antenna cur- 1-b, along with that of the dipole type. cellaneous materials may be picked up at rent. (Note that the ground plane antenna, your local hardware store. The ground plane itself is usually made which is our third antenna type, is simply It should be emphasized that when de- of wire extending from the base of the a dipole that has been modified). signing an antenna, the dimensions are vertical element. The ideal antenna would only a starting point. Use your imagina- have a continuous ground, perhaps made Antenna design tion to combine the measurements with from a sheet of copper. A series of wires, Until now, we've been talking only the- materials that you feel comfortable with or radials, approximates that condition. ory; but, in the real world, there are addi- or have on hand. Remember, materials The more radials used, the closer we ap- tional considerations. The antenna diame- can be modified. For instance, two braz- proach the ideal. ter itself must be taken into account at the ing rods are easily soldered together to The wires can be self-supporting if higher frequencies. That's because a make longer elements so long as the joint made from a stiff rod or tubing. The im- "fat" antenna acts electrically as though it is first wrapped with copper wire (see Fig. pedance of a ground plane antenna is were physically longer. Thus, the antenna 2). Likewise, two pieces of tubing may be about 30 ohms when the plane is flat. By must be made shorter than theory indi- telescoped if necessary. lowering the radials by 45° (as shown in cates. Table 3 shows the correction factor Fig. 3-c) its impedance is made close to that the calculated wavelength must be 50 ohms, which matches available coaxial multiplied by to obtain more accurate re- cable and typical scanner/monitors. Also, sults. lowering the radials lowers the radiation Another factor affecting antenna per- pattern, which effectively increases its formance is the presence of the ground gain. beneath an antenna, which acts like an A ground plane may be made from a "electrical mirror." The reflected RF coaxial chassis connector and wire. Fig- reaches the antenna later than the signal ure 4 shows how to find the correct length strike the antenna directly. Those late -ar- for the radials and antenna element to be riving signals are added to the first, and mounted on the connector. The antenna RODS may be soldered FIG. 2-TWO BRAZING are made from brass either increase or decrease antenna cur- together if longer elements are needed. element and radials rent, depending upon the length of the brazing rods, which are available in 3 -foot delay. lengths and in diameters from %e to % That delay depends on the proximity of Ground plane inch. The rods are fairly rigid, yet may be the antenna to reflective materials like One of the most common communica- bent as needed. They're easy to solder, nearby buildings, metal objects, bodies of tions antennas is the ground plane. (Fig- certainly an advantage when elements water, and ground. All have similar reflec- ure 3 shows how dipole evolves into a longer than 3 feet are needed. Use thinner tive properties, and their effect is a func- ground plane antenna). In Fig. 3-a, we rods for extensions and thicker rods next tion of their conductivity. Because of the have the basic dipole. An artificial ground to the coaxial connector. 73 Don't forget to correct the lengths of the various elements for the diameter of mate- H --0.5a 0.5a-- rial you're using. Figure 5 shows how the radials and ele- 0.25X 234 LENGTH ment are connected. It is best to use eight STUBS f radials as shown. Four radials will work. but not as well. Bend them downward 45° THREE HALF -WAVE SECTIONS TOTAL = and space evenly around the fitting. Sol- LENGTH 1.50X der the vertical element to the center pin of the fitting. INCREASED SPACING 45°r Now prepare the mast by making four 0.5x- j*-- 0.57 --1 11/2 inch lengthwise cuts in a piece - of tubing. The inside diameter of the tubing should be close to the diameter of the plug SO -239 (about 3/4 inch). The plug will be held in TOTAL LENGTH = 1.50X CHASSIS CONNECTOR the end of the tubing. Connect the plug to b the cable and insert the assembly in the slit 4 OR 8 RADIALS end of the tubing, as shown in Fig. 6. FIG. 4 -THE GROUND PLANE antenna is built on Then secure the assembly in place with a a coaxial chassis connector. hose clamp. j*-o.64x 0.64x ---.j The antenna may now be screwed onto the plug and moved to its final location. The ground plane is easily self-supporting 0.1 IX when designed for the VHF (high) and STUBS UHF bands. However, when the lengths CENTER SECTION OPENED of the elements are 6 feet, as with the VHF TOTAL LENGTH = 1.50X low band, a little wind can really whip c those rods around. FIG. 7 -THE EVOLUTION of the extended double- That problem is easily solved by adding Zeppelin antenna. In each case, the total length a little bracing. The radials may be sup- is equal to 1.5 x. ported by 1 x 1 inch piece wood or light- weight tubing. Support is not needed all the way to the ends, about half to a third of is out of phase, which reduces the total the length should do. The vertical element current and gain. When the spacing be- FIG. 5-GROUND PLANE antenna -base; brazing must be braced with non-conductive ma- tween the ends of each element is 0.28 of rods form the artificial ground and antenna ele- ment. terial like a wooden dowel, 1 -inch square a wavelength, the increased gain, due to piece of wood, plastic PVC tubing or sim- wider spacing, more than makes up for ilar material. the lower gain caused by the short, out -of- phase sections. So the gain of the antenna Extended double -Zeppelin is at maximum. The extended double -Zeppelin antenna Figure 7-c shows the extended double- is a frequently -used modification of the Zepp with an opening in the center con- design originally used in World War II ductor, which is the low -impedance point. Zeppelins, which is where the antenna got However, its impedance is still several its name. The Zeppelin, or Zepp antenna times greater than the desirable 50 ohms. is a resonant, end -fed antenna with a two - A closer match may be obtained by using wire transmission line. The design pre- a standard television transformer-balun, sented here has an antenna element con- the type used to connect 75 -ohm coaxial nected to each conductor, hence the name cable to either a 300 -ohm antenna or 300 - double-Zepp. ohm television input. In the double-Zepp design, three half- The vertical, center -fed Zepp is made of wavelength sections are connected end to tubing, which allows the feedline to be end, as shown in Fig. 7. The induced run down its center where it cannot affect currents in the two outside elements flow antenna performance. The tubing's diam- toward the center conductor. Any induced eter must be large enough to handle the current in each of the center X/4 sections coaxial cable, and the bolts that will hold (phase -reversing stub) flow in opposite di- it to the mast. rections relative to each other, so their The antenna is made of 3/4 -inch tubing, FIG. 6 -THE GROUNC PLANE antenna's con- sum is zero. as shown in Fig. 8, which allows the necting cable is run through the center of the That means that resultipg current in the feedline to be run down the center where it tubing. center section will be due only to the cur- cannot affect the antenna's performance. rent induced in the antenna itself. When The center (phasing) stub is made from The vertical element should be X/4 the antenna elements are close together, as brass brazing rods; 3/6 -inch diameter for a long. Cut the rod about % inch longer shown in Fig. 7-a, those elements inter- VHF -low, and %I6 inch for the VHF-high initially, and do the final cut after solder- act, reducing the total current flow and the or UHF bands. Calculate the length of ing to the chassis connector. Note that the gain of the antenna. each section using Fig. 9 as a guide. Then ground -plane radials are each 5% longer That problem is overcome by wider correct the length for the diameter of the than X/4. That length includes the dis- spacing (see Fig. 7-b). Of course, the ele- material used in each section according to tance contributed by the base. Again, the ment is now longer than a half-wave- Table 3. The calculation for the stub final cutting is done after installation. length. That means that part of the current length must include the length of the leads 74 transformer leads to the end of the phasing stub, and connect it to the coaxial cable with the appropriate connector. The mast material must be a non-con- ductor. Wood that has been weather- proofed with two coats of varnish or poly- ht urethane is a good choice. Shorter anten- nas for UHF or VHF -high band are easily supported on 2 x 2 -inch lumber, but for VHF low, use a 2 x 4 or even a 4 x 4, depending on the height the mast will be. Before raising the mast, cover all the elec- trical connections with silicone rubber ce- ment to prevent oxidation. The upper element of the extended dou- ble-Zepp does not have to be made of tubing since there's no coaxial cable to TRANSFORMER shield. For UHF and VHF high band, you may prefer to use brazing rods, very small diameter tubing, or even heavy -gauge FIG. 8 -CENTER OF THE extended double-Zepp copper wire for smaller sections. The antenna. Note the orientation of the balun trans- lower element is, of course, all tubing. former and phase reversal stub. The very top of the upper element is an 81/2 -foot fiberglass, CB whip antenna. on the transformer, see Fig. 10, which The whip antenna is bolted to a metal should be cut as short as possible. cap, which is then bolted to a lower 51/2 - FIG. 9 -EXTENDED DOUBLE-ZEPP. Calculate If the antenna is intended for the VHF - foot aluminum tubing. That reduces both the length of the elements as shown. low band. 30-50 MHz, each element will wind resistance and weight for this tall, be from 12- to 20 -feet long. That means effective antenna. The total length of the other side is the outside braiding as that you'll need more than one length of antenna will be about 14 feet. the shown in Fig. 11-a. The feedline is con- tubing. Use two sizes, maybe '/a and 7A - inch diameters, so that one fits inside the Coaxial -collinear antenna nected to the center of a half-wave dipole. on other. Use the larger size for the portions This antenna is a modification of the Figure ll-b shows the dipole folded nearest the feedline connection. Cut two stacked -dipole. It is made of coaxial cable itself and Fig. 11-c is the folded dipole one -inch long slots lengthwise on the out- and all the elements lie on the same line, with the center conductor extended. side end of larger tube, and insert the hence the name, coaxial -collinear. (Refer Additional half -wave sections are of smaller one. Use a hose clamp to hold to Fig. 11.) One side of the dipole is the stacked on with the center conductor them together. center conductor of the coaxial cable and each section connected to the outside Drill two 3/3a -inch holes in each element to mount the antenna on the mast and hold the phasing stub: one 1/4 -inch from the end and the other about 4-6 inches from the end. Bend the brazing rod to form the stub. That's easily done by temporarily inserting the bolts into the tubing and then bending the rods around them. Cut to the final length after forming the bends. Mount the antenna and phasing stub near the top of the mast (see Fig. 8) with No. 10 machine screws and washers. Run the coaxial feedline, preferably RG -8/M, through the lower tubing before inserting the screws. The RG -58/U has higher losses, but will fit easily. (If you've chosen RG -8/U, either solid or foamed dielectric, there's will not be enough space for the machine screws and the larger cable.) Secure the tubing to the mast with U -bolts. Although not necessary, the phasing stub may be bent into a semicircle around the mast. That streamlines the appearance and reduces the stress slightly because the stub does not have to support as much feedline. That's particularly advantageous for the VHF low -band antenna. Solder the FIG.10-EXTENDED DOUBLE-ZEPP with balun transformer connected; the transformer leads should be cut as short as possible. 75 braid of the next as shown in Fig. 11-d. The single most important requirement assembly is in position. Slide the cord The braid acts as a shield, preventing a for a good coaxial -collinear antenna is through the PVC tubing and pull the as- signal from reaching the center conductor. patience. The work is not difficult, but it sembly through using the cord for sup- The result is that every other half-wave can be time consuming, especially if port. With the antenna inside the tubing, section is exposed to the incoming signal you're not comfortable with coaxial ca- there will be about a foot of nylon cord and the induced current is in phase, thus ble. Concentrate on only one joint at.a protruding from the top. Tie a large knot providing gain. The configuration at the time. Be careful when connecting the sec- an inch beyond the end of the top wire top of the antenna array makes each leg of tions; an accidental short circuit can turn section and then cap the end of the tubing, the series of dipoles equal in length. The your carefully engineered antenna into with the knot just outside. feedline is therefore connected at the very just a random length of wire. If the cap fits too tightly, file a notch on center, where the impedance is lowest and Calculate the lengths of the sections the outside of the tubing to accommodate comes closest to matching the feedline. according to Fig. 12. Then correct for the the cord. Glue the cap in place and dab a The basic design can be modified for velocity factor of the coaxial cable you're little glue on the knot so it won't come more or less gain. Eight half-wave sec- using, usually 0.66 for the solid di- loose. Your antenna is now ready to be tions provide about a 6 -dB gain over a electric. For example, a half-wave section taken to its final location. simple dipole, and sixteen sections give designed for 155 MHz: Depending on the antenna's length, about a 9 -dB gain. Because of its length, X = 984/115 = 6.348 feet you may want to brace it with lumber. And the design is most applicable for VHF X/2 = 6.348/2 = 3.174 feet if it is exceptionally long, you may have to high -band and UHF signals. 3.174 x 0.66 = 2.094 feet use guy wires as well. Non -stretching The coaxial cable used should have a After determining the dimensions, be- 50 -ohm impedance with a solid di- X/4 SECTION gin by preparing one end of your coaxial (BRAZING ROD, COPPER electric. (RF travels slower in solid poly- cable as shown in Fig. 13. Do not cut to TUBING OR COPPER WIRE) LENGTH = ethylene, thus the antenna can be made length until after the end is properly pre- 246 X 0.66 shorter.) Use either RG -8/U or RG -58/U. f pared. That way, if you make a mistake BRAID CONNECTED The RG -8/U is heavier and stiffer, but has you TO CENTER lose only an inch or so rather than the LENGTH = lower losses. The RG -58/U is easier to 246 entire section. Do the same for each of the X 0.66 solder with a small soldering iron. eight sections, preparing one end and then N4 SECTION cutting to length. (By the time you return T to complete the other end of each section SECTION X/2 LENGTH = BRAID you'll be an expert!) 492 X 0.66 Prepare the coaxial cable by stripping away some of the insulation according to Fig. 13; a tubing cutter or knife work well, LENGTH = but be careful if you use a knife. It is a )14 2ªs X 0.66 good idea to tin the copper braid before FOLDED DIPOLE f FE ED LINE joining the sections, but be careful not to overheat the polyethylene core. If the core melts, it runs over the braid making fur- FEEDLINE ther soldering almost impossible. If you use high -quality coaxial cable DIPOLE with a closed braid, you will not experi- FOLDED BASIC DIPOLE ence the difficulty of molten plastic ooz- f= FREQUENCY IN MHz a b LENGTH IN FEET ing through the spaces, as you would with the cheaper stuff. n u. IL-I.uMAIAL-I.uLLIIYCAM antenna almen- After preparing the individual sections, sions are shown here. Note that the center con- ductor of each x/4 section is connected to the begin connecting them (see Fig. 14). Note braid of the next. that at the joint, the center conductor of each section is joined with the shielding of the next. Be careful that you leave no 1/4" --r (BRAID) frayed ends of braid that might short the INSULATION joint. The best way to handle that is to lay 1/16" the center conductor of one section on the (DIELECTRIC) braid of the next and wrap the braid end around the joint as shown in Fig. 14. Seal each joint with silicon rubber ce- ment and wrap it securely with 1/4" electrical (CENTER CONDUCTOR) tape to protect it from moisture and make it stronger. Slide the FIG. 13-PREPARE THE COAXIAL cable sections completed antenna by stripping off some Insulation and peeling into a length of heavy-walled (Schedule back the braided sheilding. 40) PVC plastic tubing about 3/4 inch in diameter. The thicker RG -8/U coaxial -polypropylene clothesline is fine. The guy will easily slide through the tubing. But wires EXTENSION don't have to go to the very top CENTER EXTENDED BECOMES BRAID AND the lighter RG -58/U needs some help: For because at least 5 feet will be self-support- PROCESS support, use a small nylon cord about %a ing even in extremely high wind. IS REPEATED inch in diameter cut a foot longer than the d antenna. Tie knots in the cord every foot Which antenna is best? rm.. I I-t.uAAIAL-t.uLLIrvtmrt antenna maae or so and tape to your antenna, starting at The three different antennas described from coaxial cable: a is a basic dipole; b shows the bottom. the dipole folded on itself; in c, the center con- varying in size, complexity, performance, ductor is extended, and d shows two stacked Put the tape on the top side of the knot and appearance. Begin designing your coaxial sections. to prevent it from slipping when the entire antenna by choosing the type that best 76 suits your needs. In making your deci- sion, you must consider all the variables. TABLE 4 You can be assured that any choice made ANTENNA SELECTION GUIDE is an improvement over your monitor's built-in antenna system. Extended Coaxial -Collinear First, pick the band for which the anten- Band Ground Plane Double-Zepp If you are lucky, all fre- na will be used. VHF -low Shortest antenna Fairly tall Excessive length will quencies used by your local services Radials may need support but no radials be in one band, and close together in Good Choice frequency. Use Table 1 to help make that selection. VHF -high Reasonable length Highest gain Short in frequen- Neat installation Neat installation Often you will be interested Easy construction cies in all three bands; therefore you must Good choice decide which is most important to you. UHF Small size is Highest gain That choice should not be too painful. Tiny difficult to build Neat installation Easy Your new antenna will probably outper- construction Good choice form the built-in one on all frequencies solely because it is mounted higher and away from interfering objects. diameter, with a foamed -dielectric is an excellent cable for our purposes. Try to avoid RG -8/U. It is larger in diameter, less flexible, and costs more. If you can find RG -8/M (miniature RG -8/U) it is also a good choice. It's only slightly thicker than RG -58/U and ex- hibits a good balance of flexibility and low loss at a reasonable cost. Remember when choosing your cable that signal loss in- creases with frequency and feedline length. For long runs at high frequencies, it is an excellent idea to use the best cable that you can afford. You'll also need a Motorola -type plug to connect the feedline to your scanner. The simplest place to bring the feedline into the house is usually in the vicinity of a window. Drill a small hole through a non - movable part that can be easily patched later if necessary. The window frame, top or bottom is best for that. Some houses FIG. 14-FINISHED JOINT: Note that the center conductor is placed on the braid and braid ends allow easy access through a basement vent wrapped around to secure conductor in place before soldering. and then up through the floor. When running coaxial cable, avoid After choosing the band, consider how antenna falls or is blown down during a sharp bends and be certain that the exter- the antenna will look, where it will be storm, where will it land?" It might also nal connections are weather sealed. The located, and is there enough room for the be a good idea to ask: "If I fall during foamed -dielectric cable in particular can radials; will the coaxial -collinear be too installation, where will I land?" absorb moisture, which increases feedline tall? Do you really need a lot of gain? Try to pick a location where you'll need losses. And don't feel obligated to keep Table 4 is provided to help with that deci- only the minimum amount of feedline. In the antenna in the original location sion. With that out of the way, go to the other words, don't place the antenna 200 chosen. Sometimes raising or lowering it section that describes the antenna and be- feet away from the receiver's location sim- a few feet, or moving it sideways can make gin building it. Be sure to follow all in- ply to gain 10 feet in height. The height a big difference. structions carefully. advantage will be overshadowed by addi- There are often unpredictable influ- tional losses due to the extra feedline. ences in the area, like power, telephone, Installation Also try to keep as much of the feedline or cable TV lines and maybe even your For optimum performance, an antenna vertical as possible. own rain gutters. Regardless of how good should be positioned high and in the open. Use coaxial cable to connect the anten- your antenna is, there will always be dis- Remember that reception is best when the na to your monitor. It is rugged, flexible, tant, weaker signals barely audible over antenna is within the line of sight of the and the shielding allows you to place it in the noise. The position of the antenna may transmitting antenna. Don't pick a loca- any convenient location. Running the ca- make a big difference. tion that is hazardous to get to, and never ble along metal gutters will have no effect. Consider turning the disadvantage of a place an antenna near any electrical line Coaxial cable is available in a wide variety closely placed metal downspout or TV- before, during, or after installation. And of sizes and efficiencies, with corre- antenna mast to an advantage. If either is do not mount near metal objects. sponding costs. Pick one that has a nomi- spaced X/4 from your antenna and parallel Other than the obvious shock hazards nal 50 -ohm impedance. to it, it can function as a reflector. That presented by power and telephone lines, An important difference between ca- provides less gain in the direction of the nearby metal objects can change the bles is the structure of the dielectric mate- reflector, but more gain in the opposite effective inductance of the antenna and, rial. If it's foamed it will have signifi- direction. If you live on the far side of thereby, reduce its performance. Also, cantly less loss at radio frequencies than town, that may be exactly what you need. before installation, ask yourself: "If the the solid core. RG -58/U, about % inch in R -E 77 CL 'Zen. Cellular Mobile Telephones MARC STERN Thanks to cellular telephone, the capacity of cur mobile telephone systems has increased dramatically. Here's a look at the technology that makes cellular telephone possible. IMAGINE SITTING ON A BEACH, FAR AWAY FROM HOME OR telephone lines, and being able to carry on a phone conversation with a friend across town, or across the country. Well, the technology necessary to let that minor miracle occur is currently being put in place. What we are talking about is, of course, cellular telephone. With cellular telephone, it is possible to place or receive a call via a mobile or porta- ble unit from almost any location. Interestingly, the history of cellular com- munications began in 1968. At that time, the FCC freed the spectrum in the 806 -960 -MHz region and challenged the communications industry to use that spectrum for maximum public benefit. In 1971, AT&T proposed using those frequencies for a cellular telephone system. In the ensuing years, the tech- nical problems were solved, test systems were built, and rules for the 78 systems is a low number of users. In tradi- tional VHF -based radiotelephone sys- tems, due to the low number of CENTRAL--,\ TO conversations that are possible at a time, OFFICE the saturation level for the system is about 1,200 mobile units. That means that there POWERFUL TRANSMITTER are few people who can actually use the mobile phone system, and there is usually a long waiting list in any urban area. With cellular telephone, though, as many as 100,000 can make use of the system. 20-50 MILES A Cell Is Born Central to the cellular radiotelephone system is the concept of a cell. That is the service area of one transmitter/receiver and it is just one part of a larger network. As shown in Fig. 2, at the center of the cell EACH CAR REQUIRES is the cell site, which consists of a low - A SEPARATE CHANNEL power transmitter, a receiver, and an elec- center that links the cell FIG. 1-CONVENTIONAL MOBILE TELEPHONE SERVICE uses one central base station to transmit a tronic switching powerful signal over an area of up to 50 miles in diameter. Only one two-way conversation at a time can to the rest of the cellular system. Each of be held over a given channel In the coverage area and the number of channels is limited. those cell sites, in turn, is linked to a Mobile Telephone Switching Office (MTSO), which is the ultimate arbiter of the entire cellular network. The MTSO, in turn, links the cellular system with the 1 TELEPHONE wire telephone system run by the local OFFICE phone company. The electronics that makes the cellular i system possible is located at the cell site. In addition to the transceiver (transmitter- receiver) needed for the cellular system, at each site is a sophisticated computer system that not only controls the trans- ceiver, but also the mobile units-in con- junction with the mobile unit's internal microprocessor and circuitry-as well as the local switching operation to the MTSO. For the cellular system to work, when a CELL SITE car moves from cell to cell, there must be - 16 ->(LOW -POWER TRANSMITTER, ,04-re, an orderly transition; communications ETC.) must be transferred cleanly from cell to cell, and the mobile unit must only com- municate via one cell site at a time. To each cell site is assigned FIG. 2-CELLULAR MOBILE TELEPHONE SERVICE is provided through a system that is composed of achieve that aim, three major elements: cell sites, a mobile telephone switching office (MTSO), and dedicated intercon- a set-up channel, which only handles data necting circuits. In the cellular system, the coverage area is divided into small areas called cells, hence signals, in addition to a given number of the name. voice channels. The set-up channel, which is used by all of the mobile units in cellular industry were issued. In 1983, the cient only to cover a small area, called a the cell, is used to initiate calls and assign first commercial cellular system started cell (hence the name). If cells are suffi- a user to a voice channel. The receiver in a operation. ciently far apart, they can simultaneously subscriber's mobile unit scans all of the use the same set of frequencies. (To en- set-up channels in a system and selects the The cellular telephone system sure proper separation, adjacent cells are one that is the strongest. Communications To understand how cellular telephone assigned different sets of frequencies.) then commence via that cell site and only works, it is necessary ,to discard some Thus, where only one conversation could that cell site. long -held ideas about mobile telephone. occur at a time over a given frequency in a Transitions between cell sites (see Fig. In conventional mobile telephone sys- service area, now hundreds could take 3) are handled by the cell site electronics. tems, a single central base-station is used place over the same coverage area. The mobile unit monitors the voice chan- to transmit a powerful signal over an area Also, instead of using fairly high- nel for a "hand-off" signal. That signal is of up to 50 miles (see Fig. 1). In that powered mobile units -25 watts or sent by the cell site when the signal system, only a single conversation may be more-to carry on conversations, each strength at the cell site drops below a held over a given frequency or channel in cellular mobile unit is lower powered certain level and it has been determined the service area. ranging from 0.6 to 3 watts. In addition, that another cell site is receiving a stron- In cellular systems, several low -power the cellular system makes handheld porta- ger signal (each cell site has a scanning transmitters, with their associated re- ble phones both practical and possible. receiver for that purpose). The hand-off ceivers, are scattered about an area. Each Finally, the last notion that must be signal instructs the mobile unit to change transmitter operates at a power level suffi- discarded about traditional mobile -phone frequencies. During the change, the audio 79 TO MTSo TRANSMITTING ANTENNA FIG. 3-CELLULAR HAND-OFF occurs as a car moves from cell to cell. During the transfer, which is coordinated by equipment in the MTSO, RECEIVING the user sees no apparent change in transmis- ANTENNA sion quality. (6 ANTENNAS, 60° BEAMWIDTH FACING ADJACENT is muted for 150 to 400 milliseconds; such 60° SECTO RS) a time interval is not perceptible to the user. Once the mobile unit exchanges RECEIVING ANTENNA handshaking (6 EQUALLY SPACED signals with the new cell AROUND TOWER) site, communications resume on the new TRANSMITTING frequencies. ANTENNA A closer look Let's look more closely at the cellular radiotelephone system to see how all the TYPICAL TOWER LAYOUT POLAR VIEW electronics and computers do their tasks. a b And what better way to look at the system FIG. 4-A TYPICAL TOWER LAYOUT is shown in a. Note that the transmitting receiving than walking and antennas through a typical call? are located at different parts of the tower. The arrangement of the receiving antennas, as seen from the To initiate a call, all a mobile user has top of the tower, is shown in b. to do is lift the handset of his radi- otelephone and dial the number he wants. At that time, the microprocessor -con- on different parts of the tower. In a typical call to be switched to the most appropriate trolled unit sends a brief burst of digital installation, such as the ones used in cell. At the same time, the mobile unit information to the transceiver, alerting the Motorola systems, there are six 60 -degree switches frequencies to a pair that is avail: cell site that the user wants to make a call directional receiving antennas spaced able in the new cell site. The frequency and that it is present in the site's coverage around the tower, each with a gain of pair in the old cell site is then freed. area. about 17 dB (see Fig 4-b). Diversity recep- Monitoring the received signal strength Next, the cell site equipment sends a tion techniques are used. In diversity re- is not only important in determining the digital signal back to the mobile unit tell- ception, signal strengths at the antennas location of the mobile unit, but it is also ing it to standby while it is assigned a are monitored, with the one receiving the important in keeping the power levels frequency pair from the frequency allot- strongest signal being used for the com- within the cellular system down. Signal ment assigned to the central site. (Cellular munications. Computers handle the task strength is monitored by the cell site, and phones operate in the full -duplex mode, of analyzing the signal strengths and mak- when it exceeds a certain level, the cell which means that both the caller and per- ing the antenna selection. site orders the mobile unit to cut back on son called can hear and talk at the same The receiving antennas and computer the output power. Thus, the potential for time. To do that, discrete frequencies are equipment also team up to handle another interference is very small. used for transmission and reception. The task-determining the position of each typical frequency separation between communicating mobile unit in the cell. To Cost transmit and receive is 45 MHz. Spacing do that, the computer samples the re- At the moment, cellular service isn't between channels is 30 kHz and there are ceived signal strength at each antenna, inexpensive. Most units are selling in the 666 duplex channels in all.) and uses a special direction -finding al- $2000-$3000 range, though prices for gorithm to determine the exact location of equipment will likely drop as more Continuous contact and the mobile unit. more units come on the market. As you One of the interesting capabilities of Monitoring continuously, that informa- might expect at that price, most cellular the cellular radiotelephone system is its tion is constantly updated and is fed back telephones are loaded with bells and ability to provide continuous coverage to the master computer at the MTSO. The whistles. Multi -phone -number memo- across a large geographic expanse. computer at the MTSO is the arbiter that ries, last number redial, digital readouts, In order to do that as a mobile station takes the information on the location of horn alert (used to alert the user to a call moves from one area to another, the entire the mobile unit and if the signal strength while he is out of the car), and LED status cellular system must know the exact loca- falls below a certain level-about 17 dB lights used to indicate such things as no tion of that mobile system and it must be (c arrier-to-interfe rence-and-noi se )-the service in a particular area are all found on ready to enable a hand-off of that mobile MTSO decides its time for a hand-off typical cellular phones. As to monthly between cell sites-all without the user between cells. charges, including access charges and being aware of it. While all of that is going on, the com- time on the system, those are currently To do that requires some interesting puter in the MTSO is also polling nearby averaging out at about $150. computerized gyrations. Look at a cell cell sites, asking them which one is re- Overall, cellular radio is an exciting site tower, such as the one used in the ceiving the mobile unit the strongest. The concept whose time has come. It prom- Motorola system and shown in Fig. 4, and cell sites, in turn, look for the signal and ises truly portable telecommunications, you will see something interesting-the reply. Using the information received which will keep anyone in touch wherever transmit and receive antennas are located from the cell sites, the MTSO orders the they go. R -E 80 L High-Power REINHARD METZ Ampl'if'ier YOU'VE PROBABLY ALWAYS WANTED TO Get high performance and high fidelity from this own a high-performance, high -power ster- It feels equally eo amplifier. If you don't have one, there FET stereo amplifier. are two likely reasons why: You are not at home in your living room or in a disco! sure you need that much power and you are deterred by the cost. But these days, with the increasing popularity of digital tion, and straightforward simplicity. Also, audio disc players, there is a new motiva- However, for many years only N -channel lack a secondary -breakdown tion for owning a high -power amplifier devices were available-only recently MOSFET's (Secondary breakdown in bi- that can faithfully reproduce a wide dy- have their P -channel counterparts ap- mechanism. localized heating effect namic range without distortion. And peared at reasonable prices, making it polar devices is a in which "hot spots" develop under high - while the cost of commercial high -power possible to design amplifiers with remark- conditions. A hot spot then con- amplifiers is still high, we'll describe a able performance but little complexity. current ducts even more current, creating more very high-performance design that you As we'll see shortly, MOSFET's aren't heat, which, in a positive -feedback man- can build at a reasonable cost. Just what the only transistors used in the amplifier. may lead to a catastrophic destruction do we mean by "high performance?" Ta- Ahead of the output stage, a fully comple- ner, design combines of the device.) ble 1 summarizes the characteristics of our mentary bipolar breakdown, bi- design. simplicity with high performance. Because of secondary be operated within a One of the most important features of polar devices must Why MOSFET's? area that often falls far short of the the design is the use of power MOSFET "safe" and power- in a complementary Although the evolution of power device's stated static current output transistors -opera- configuration. Those transistors, by MOSFET's has primarily been (and still dissipation characteristics. Safe circuits (whose mis - themselves, eliminate a number of the is) fueled by power -supply applications, tion -area limiter notorious) must usually associated with their bi- there are a couple of reasons why operation has often been problems circuits. Because polar counterparts. MOSFET's make ideal devices for audio - be used in bipolar do not exhibit secondary The highly desirable characteristics of amplifier output stages. First, they allow MOSFET's and more reliable de- power MOSFET's for audio amplifiers the design of amplifiers with very wide breakdown, simpler be used. have been recognized for a few years. bandwidths, high slew rates, low distor- signs can 81 would make the stage operate far less effi- ciently.) The relatively high gate -capaci- tance of the power MOSFET's is also somewhat easier to drive in the common - source configuration. Resistors R31 through R38 help to sup- press the parasitic oscillations that might otherwise occur with the extremely fast transistors used. Zener diodes D14 and D15 limit the amount of drive available to the output. Finally, Ll and R42 serve to isolate the amplifier output from capaci- tive loads at very high frequencies. The inverter/driver stage consists of Q15 through Q20. Its purpose is to deliver bias and drive signals to the FET output stage. Their basic requirement is to sit at about 3.5 volts with respect to the source, increasing about .3 volt per ampere of output current. Transistor Q29 forms a conventional voltage multiplier, which, in this case, multiplies the voltage across D3, D4, and D5 and D16 to about 7 volts. The 7 -volt bias is presented to the bases of Q16 and Q17, which form the bottom transistors of a pair of complementary cascode amplifiers. of 10 is set by An output -stage gain A shows the response to a 10 -kHz squarewave the FIG. 3-AM LIFIER RESPCNSE CHARACTERISTICS. R21, R22, R25, and R26. Therefore, inp.it at 150 warts in o an 8 -ohm load while b shows the response into a 1 -ohm, 1µF load. Shown in c voltage generated by Q29 is split in half anc d are the step responses at 5G watts and full output, respectively (both with input filter C2 and reflected up against the two supply removed). Note the excellent slsw-rae and risetime capabilities. rails as a pair of bias voltages across R23 and R26. Those voltages, along with the provided by C10, R30, C6, and C11. shown AC drive -signals from the previous stage, Some optional components are in the power - are passed along to emitter followers Q19 in the schematic, notably and Q20, which have the high -current supply section. First, there is TC1, the drive capacity required by the gate capaci- thermal cutout made by Elmwood sensors RI tance of the output devices. Using cas - (1655 Elmwood Ave., Cranston, code stages here, as well as in the input 02907). It is normally closed, and opens is and voltage -gain sections, serves the dual at 70°C. Another optional component purpose of splitting the emitter-collector SRI, an inrush limiter made by Keystone voltage and power drops among two tran- (Thermistor Div., St Marys, PA 15857). sistors per rail, while increasing the open - For home applications, those shouldn't be loop frequency response of the amplifier. necessary. However, if you plan to run the The voltage -gain stage consists of tran- amplifier continuously at high power (in a FIG. 4-FULL-POWER OUTPUT with a 5 -kHz disco, for example), you should include sistors Q11 through Q14, again configured level is about sinewave input. Note the clipping you can. as complementary cascode amplifiers. ±75 volts. all the protection The collector loads for Q12 and Q13 are .1 Amplifier performance the input impedance of Q16 essentially .5 and Q17. That is in the neighborhood of Some of the response characteristics of .2 250W the amplifier are shown in the os- 50K, leading to a stage gain of about 50 3 5rriW (the quotient of 50K and R17 or R18). W 1' cilloscope photographs in Fig. 3. For ex- Capacitors C3 and C4 increase the fre- w .05 ample, in Fig. 3-a we see the response to a 10 squarewave at 150 watts into 8 quency response of the stage. Zener di- ó .02 -kHz set the base ohms. Figure 3-b shows the response with odes D8, D9, D10 and Dll .01 voltages for the upper transistors in the a 1 -ohm, 1-µF load. Figures 3-c and 3-d cascodes. 10W' show the step response at 50 watts and full Now we'll look at the input stage, output, respectively. (Those two risetime Q8. Those .001 tests were made with input -filter capacitor which consists of Q1 through .5K1K 5K 10K 20K 20 50 100 .2K 2K C2 removed.) Figure 4 shows the full - transistors are connected as complemen- FREQUENCY-Hz power output with a 5 -kHz sinewave in- tary-cascode differential amplifiers, sup- FIG. 5-TOTAL HARMONIC DISTORTION (THD) put. Figure 5 shows the total harmonic plied by current -sources Q9 and Q10. The at 1 kHz. gain is set at about 100 by the ratios of R3 distortion from less than 1 watt to 250 to R5 and R13 to RI1. this amplifier has, even very low output watts at 1 kHz. Resistor R8 is used to zero the output offsets (in the tens of millivolts) can deliv- Building the amplifier voltage by varying the collector currents er many amps into a short. of Ql-Q4, compensating for any VBE off- The overall voltage -gain of the ampli- It is essential that a printed -circuit sets that may exist in Q1,Q2, Q5, and Q6. fier is set at about 30 by the ratio of R40 to board be used for the amplifier. Figures 6 That is important, because with an ex- R39. A 3 -dB rolloff is set at about 3 Hz by and 7 show foil patterns for the component tremely low output -impedance such as C5. High -frequency compensation is and solder side respectively. Note that one 84 board is required for each channel. If you don't want to etch your own boards, etched, pre -drilled, and plated -through boards are available; see the Parts List for information. If you do want to etch your own boards from the patterns shown, keep in mind that the board uses plated -through holes. You can, of course, get around that by soldering some of the components, including the output transistors, on both sides of the board. Note that the wiring to the output transistors is incorporated in the PC -board layout. That keeps the wire lengths to the output devices to a mini- mum. (It also simplifies construction by eliminating 48 wires, reducing the chance of error in that particularly critical area!) Before we begin with the construction details, we should point out that the values shown in the schematic are for 1% -toler- 6 1/4 INCHES ance resistors. For most applications, it is FIG. 6-THE COMPONENT SIDE of the amplifier board is mainly used as a ground plane. not essential that you use such parts. Thus, the parts list also shows acceptable values for 5% -tolerance resistors. (One source for 1% resistors is Digi-Key Corpo- ration, Highway 32 South, P.O. Box 667, Thief River Falls, MN 56701.) Once you have your boards and compo- nents, you can begin construction by re- ferring to the parts -placement diagram in Fig. 8 and by installing the fixed resistors. Check the values with an ohmmeter as you go, and be sure that the leads are sufficiently far from the ground plane! Next, install capacitors, carefully checking values and ensuring that the po- larized electrolytic types are properly ori- ented. Follow by installing the diodes, except for D3-D5. (Those three diodes mount on the output -transistor heat sink, and should not be installed yet.) Again, be careful of the polarity-the diode band indicates the cathode. Next, install the transistors (except for the output tran- 61/0 INCHES sistors Q21-Q28). Transistors Q19 and FIG. 7-THE SOLDER SIDE of the amplifier board. Remember that you need one board for each Q20 should be mounted with insulators channel. and heatsink compound. (If you look closely at Fig. 9, you'll see some heatsink sink is desirable for the TO -220 package, We should make a final note that wiring compound around those transistors.) but is not essential. length should be kept to a minimum, with Transistors Q12, Q13, QI5, and Q18 use The Wakefield type 512 is available in a less than 2 inches from transistor to PC TO -S -type heat sinks. 14 -inch long extrusion, which needs to be board. Even with that length, a ferrite Adjust potentiometers R8 and R19 to cut in half to yield the two 7 -inch pieces bead is necessary on each gate lead, and their middle positions and install. (For called for. After you cut it, drill holes for using coaxial cable is recommended. R19, which is a multiturn potentiometer, the output transistors according to the you will need to use an ohmmeter.) You layout shown in Fig. 11. To keep the tran- Preparing the chassis will have to make Ll: Wind 15 turns of 16 - sistor-mounting hardware to a minimum, The design and construction of a chas- gauge magnet wire on R42. Solder to the you might want to drill and tap the heat sis for the amplifier is not critical. The leads of R42, and install the assembly. sink. However, screws with nuts may also author's prototype was built with rack The PC boards are now complete. be used. The optional over -temperature mounting in mind. It consists of an 8 x 17 sensor and thermal -compensating diodes inch bottom plate with 1 inch turned up at Preparing the heat sink D3-D5 should also be glued to the heat the front and back. The front plate is The Wakefield heat sinks that are used sink as shown in Fig. 11. 19 x 17 inches. As shown in Fig. 10, the for the output transistors (see Fig. 10) If you have a confined -space applica- two heat sinks mount on the back of the were not chosen arbitrarily. Their design tion, you can mount the two heat sinks unit, leaving a 2' x 7 -inch strip for a is almost 100% more efficient for natural back to back; they will then readily accept small plate where the input and output convection applications than con- a muffin fan for forced convection. For jacks and fuses are mounted. Finally, an ventional designs of equivalent volume. home applications, however, we recom- 81/4 x 31 -inch U-shaped piece of perfo- You can use other heat sinks but a mini- mend natural convection-to eliminate rated metal makes up the cover. mum surface area of 800 square inches per the noise, filter, and/or temperature -sens- Begin mounting the components with channel is required. A flat -backed heat ing aspects typically associated with fans. the transformer, bridge rectifier, filter ca- 85 o o Q25 026 Q28 .1"r ` u\\`a`,. -75V R7 C13 Ch -R16 - J1 INPUT R18- 06 t R28 C4 - R7 RI4 R,3 013 o Q20 016 R 016 04, 05* "'I 610 R2 D2 010J -612- -611- FIG. 9 -AMPLIFIER BOARD is shown here I F1 --R25- C7 pill C5 mounted on heat sink. Note that 012, 013, 015, R24 L R30 D9 and 018 use TO -5 type heat sinks. R42 R22- 1J1 R19 1 R39 6 Q1 OUTPUT iJC Q4 Q3 o 019 Qt5 010 j R9 I ! R27 012-1111*- C3 R3 07I .... R4 R23 R17 R32 R34 6i4 R15 C12 633 021 022 Q23 Q24 'SEE TEXT FIG. 10 -COMPLETE STEREO AMPLIFIER with o o o o cover removed. The chassis configuration is not FIG. 8 -PARTS -PLACEMENT DIAGRAM for the amplifier board. Refer to the text for information on at all critical. mounting the output transistors (021-028) on a heat sink. pacitors, and fuse -holders. Then, mount the power switch, pilot lights, and level controls on the front panel. Next you'll have to make up a suitable mounting plate and install output jacks that are insulated from their mountings. Install the input -fuse holder and the power cord with a strain relief Then wire the transformer primary and secondary as shown in the schematic. If you plan to use 3""4" LEADS the optional thermal cutouts, leave a pair of wires to go to the heat-sink area. Use 4 HOLES 4 HOLES #43 DRILL #43 DRILL 18 -gauge (minimum!) wire in the power 4-40 TAP 4-40 TAP supply. We recommend that you use some EPDXY 03-05 EPDXY APPROXIMATELY simple color code for the DC wiring-it THERMAL HERE will help reduce the possibility of errors CUTOUT HERE during subsequent tests. 1.4" Locate a suitable single -point ground, such as a screw through the bottom of the chassis near the power supply, and attach the filter capacitors' common power-sup- ply ground to it. If you use a 3 -wire power cord, do not ground or terminate the cord's ground lead. 2 9" 2.9" Checkout procedures The amplifier checkout is by far the CENTER LINE most important part of building this am- FIG. 11 -HEAT-SINK DRILLING GUIDE. Note that some parts are fastened with epoxy to the heat sink. plifier, so, shift into low gear and proceed with great care. main power fuse and, with the DC fuses greater than 100K. If it is, temporarily First we strongly advise you to make a F2-F5 not installed, apply power. Check connect one board to F2, F3 and ground. final visual check of all parts placements the two supplies for ± 75 volts. Remove Connect a clip -lead from the collector of on the circuit boards and the power -supply power, and discharge the filter capacitors Q4 to the collector of Q3. Connect an- wiring. Then, before applying any power, through a 1K resistor. other clip -lead from the collector of Q7 to measure each supply terminal with an Next, install a pair of 1/4 -amp fuses for the collector of Q8. Temporarily clip -lead ohmmeter to ground. An initial low read- F2 and F3. Measure the resistance from D3, D4, and D5 into the current. Apply ing should slowly move up to high resis- each power -supply input to ground on power, and measure the voltage between tance as the capacitors charge. Install the both driver boards. The reading should be (continued on page 92) 86 tions that require high stability in a hostile peratures, and good capacitance over a RESISTOR/CAPACITOR environment. Those devices can with- wide temperature range. (However, an ex- Continued from page 48 stand vibration, acceleration, extreme ception to that are the metalized-we'll moisture, vacuum, and high operating talk about metalization in a moment- temperatures; they are, however, suscepti- paper units, which have low insulation dielectric constant between 6.5 and 8.5. ble to damage from mild mechanical resistance and are prone to dielectric can be split into thin sheets, is nonpor- shocks. They have a life expectancy of breakdown.) Plastic types are less af- ous, and does not readily absorb 30,000 hours or greater. fected by humid conditions than paper moisture. Glass capacitors perform very well at units since they are non-absorbent. Plastic Mica capacitors are temperature and high frequencies up to 500 MHz, and have capacitors, such as polycarbonate and frequency stable, have a low dissipation a frequency range of 100 kHz to 1 GHz. polyester (Mylar) types, are generally in- factor, and perform well at frequencies up Because of their characteristics, those de- tended for applications where minimum to 500 MHz. Those high precision units vices are commonly used in missile and capacitance change with temperature is are used in a variety of applications, in- spacecraft electronics. required. They are especially suited for cluding tuning circuits, oscillators, fil- tuned and precision -timing circuits. ters, and RF power circuits. Paper/plastic capacitors In metalized capacitors, a thin film of Paper and plastic capacitors are used in metal is deposited directly on the paper or Glass capacitors applications that require high and stable plastic dielectric. Doing that gives the ca- Glass capacitors are used in applica- insulation resistance at high tern- pacitor a "self-healing" characteristic TABLE 2-CAPACITOR SELECTION GUIDELINES (Continued from page 47) (AC). Operating temperature from - 40°C to +80`C. tolerences. Large values available. Etched foil has 10 times the Teflon/Kapton: Has a temperature range of - 55-C tc 250°C capacitance per unit volume as plain foil types. Peak AC and with a temperature coefficient of .009% °C. Teflon's extremely low applied DC voltages should not exceed rated maximums. Usable dielectric absorption makes it good for critical sample and hold to 200 kHz. Non -polarized foil are used in tuned low -frequency circuitry. Those capacitors used in specialized applications such circuits, phasing low -voltage AC motors, and in servo systems. as oil well drilling equipment. Those capacitors are large in size Sintered slug units are used in low -voltage power supply filtering since the dielectric is not available in thin gauges. and in DC applications. Can not withstand any reverse voltage. Parylene: Manufactured by Union Carbide, those capacitors are Leakage current lowest of all tantalum types; no appreciable leak- equivalent to polystyrene types in performance but are rated to age below 85°C. Usable to frequencies of 1 MHz. + 125°C, versus + 85°C for polystyrene. ALUMINUM ELECTROLYTIC TANTALUM ELECTROLYTIC Values: .68 to 220,000 µF Solid type- Tolerance: -10 to + 75% Values: .001 to 1000 µF Voltage rating: up to 350 volts Temperature range: 55°C TO +85°C (if derated, to +125°C) Temperature range: - 55°C to + 85°C (if derated, to +125°C) Voltage rating: 6 to 120 volts DC Dissipation factor: varies with temperature Tolerance: 5% TO 20% Temperature coefficient: varies with temperature Leakage current: varies with temperature Notes: Used in filter, coupling, and bypass applications where Derating factor: 50% voltage large capacitance values are required and capacitances above Notes: Used in low -voltage DC applications such as bypass, coup- nominal can be tolerated. Sum of the applied AC peak and DC ling, and blocking. Not for use in RC timing circuits triggering voltages should never exceed the the rated DC voltage. Aluminum systems, or phase shift networks due to dielectric absorption electrolytics are larger than tantalum electrolytics but less expen- characteristics. Also not recommended for applications subject to sive. Loss of capacitance, to as little as 10% of rated value, will voltage spikes or surges. High capacitance in a small solume with occur as the aluminum oxide electrode electrochemically com- excellent shelf life. Solid types not temperature sensitive and have bines with the electrolyte. Oxide film deterioration also requires lowest capacitance -temperature characteristic of any electrolytic capacitors to be "re-formed" after storage to prevent dielectric unit. Dielectric absorption and high leakage currents make them failure. That involves application of rated voltage for a period of 30 unsuitable for timing circuits. Except for non -polarized units, these minutes, or more, to restore initial leakage current value. Over time, devices should never be exposed to DC or peak AC voltages in dissipation factor can rise by as much as 50%. Four terminal excess of 2% of their rated DC voltage. To prevent fai ures due to devices are available (two leads for each connection) that offer low leakage or shorting when series connecting for highar voltages, ESR and inductance at high frequencies. Those units were de- parallel each unit with a shunt resistor. signed for use in switching power supplies. Chip types- Values: .068 to 100 µF TRIMMER CAPACITORS Tolerance: 5% to 20% Values: range from .25 to 1 pF and 1 to 120 pF. Voltage rating: 3 to 50 volts DC Glass/Quartz: Low loss, high Q, and high stability for high tuning Frequency range up to 300 MHz. Temperature range: - 55°C to - 125-C sensitivity applications. Leakage current: varies with temperature. Sapphire: High level of performance between 1 and 5 GHz. Non -solid types- Plastic: High grade units can be operated up to 2 GHz. Values: .5 to 1200 µF Ceramic: Smallest sized single turn units with maximum capaci- Tolerance: -15 to +30, and 20% tance under 100 pF. Capacitance changes with temperature. Voltage rating: to 350 WVDC Air: High level of performance through UHF Band, from 300 MHz Temperature range: -55°C to + 85°C (if derated, b + 125°C) to 1 GHz. Leakage current: varies with temperature Mica: Has wide capacitance range and relatively high current Notes: Polarized foil units are used for bypassing or filtering out handling capability. low -frequency pulsating DC. Allowance must be made for leakage Vacuum/Gas: Used for high voltage applications. Values from 5 to current. Not suitable for timing or precision circuits due to wide 3000 pF, with voltage ratings from 2 to 30 kilovolts (DC). 87 called "clearing." If there is a hole or contaminent in the dielectric of the capac- TABLE 4 itor, a short may occur, resulting from the heavy current flow in the fault area. In a Letter Number Maximum Low Temp. High Temp.Letter Capacitance metalized capacitor, that heavy current Symbol Symbol Symbol Change flow will melt away a very small part of the A ±1.0% thin metal film, thus disconnecting the B ± 1.5% fault from the capacitor. These capacitors Z + 10°C +45°C 2 C ±2.2% are best for analog circuits because the D ± 3.3% momentary current flow during the clear- 4 + 65°C ing action may result in a spurious signal E ±4.7% and cause false triggering in digital logic Y - 30°C 5 + 85°C P ± 10.0% circuits. R ± 15.0% 6 +105°C Metalized plastic devices work well in S ±22.0% switching power-supply output filters be- X - 55°C 7 + 125'C T ± 22%-33% cause they have a comparatively low ESR, U ± 22%-56% as well as stable temperature charac- V ± 22%-82% teristics. When using those capacitors in such an application, however, be sure that the unit selected is rated to handle the voltage surges produced by the circuit. electric absorption characteristic has been generally larger than tantalums, and are Tantalum electrolytics discharged to "zero," it may still be hold- less expensive. One problem with alumi- Tantalum capacitors offer high capaci- ing a considerable charge. That, as you nums is that they will change capacitance tance in a small package size and have an might imagine, can cause considerable (drift) over time. That is caused by the excellent shelf life. Various types of tan- problems in timing circuits and the like. aluminum oxide electrodes chemically talum electrolytic capacitors are available Tantalum capacitors also are not rec- combining with the electrolyte. Because including solid, sintered slug, plain foil, ommended for circuits that produce of that, capacitance can drop substan- etched foil, wet slug, and chip. Applica- spikes, surges, or pulses. If their voltage tially, to 10% of rated values. Those units tions include low-frequency filtering, by- rating is exceeded by even a few volts, the also have a limited shelf life due to oxide passing, coupling, and blocking. The device is likely to fail. film deterioration and must be "re- solid types are not temperature sensitive Tantalums may be polarized or non - formed" after long periods of storage. Re- and have a lower capacitance -temperature polarized. Polarized capacitors should forming consists of applying the capaci- characteristic than any other electrolytic never be exposed to a reverse DC or peak tor's rated voltage to the unit for a period capacitor. AC' voltage greater than 2% of its rated of 30 minutes. Re-forming also prevents Applications that tantalums are not DC voltage. Non -polarized units, as their dielectric breakdown or shorting. In addi- suitable for are in RC timing circuits, trig- name would apply, do not suffer from that tion, the dissipation factor of these de- gering systems, or phase -shift networks. limitation. Non -polarized units are made vices can rise as much as 50%. That's because they have high "dielectric up of two polarized units in series with To prevent electrolyte evaporation and absorption" characteristics. That is, their cathodes connected together. component cleaning problems, aluminum when a capacitor is discharged, the di- electrolytics sometimes have an epoxy electric retains a residual charge. Thus, Aluminum electrolytics end seal. However, without a vent, such even if a capacitor that has a high, di - Aluminum electrolytic capacitors are capacitors may explode if exposed to re- verse or overvoltage conditions. Aluminum electrolytics are used in fil- TABLE 3-GLOSSARY tering, coupling, and bypass applications were large capacitances, and capacitance DC leakage-Small current that flows Equivalent series resistance (ESR)- that are higher than the nominal value, through or across the surface of the di- Energy losses in the capacitor due to lead can be tolerated. electric or insulation of the capacitor. resistance, termination losses, and dis- sipation in the dielectric. Trimmer capacitors Dielectric-Insulating material between the plates of a capacitor. Insulation resistance (IR)-Measure of Trimmer capacitors fall into three cate- a capacitor's insulation quality expressed gories: multi -turn, single turn, and com- either in megohms Dielectric absorption-A property of a or as a time constant, pression types. Multi -turn capacitors have RC, in seconds, That value capacitor's dielectric such that even when determines a either glass, quartz, sapphire, plastic, or capacitor's leakage current for a the capacitor is discharged to zero, a re- continu- air dielectrics, while ously applied DC voltage when a capaci- single -turn devices sidual charge remains stored in the di- use ceramic, plastic, or air dielectrics. electric. tor is fully charged. Compression types use a mica dielectric. Temperature coefficient-A capacitor's Glass, quartz, or air dielectric devices Dissipation Factor-Important in AC ap- change in capacitance per °C. May be are selected for applications requiring low plications, it is the ratio of effective series positive, negative, or zero and is usually resistance (ESR) to capacitive reactance expressed in parts per million per °C loss, high Q, stability, and tuning sen- Xc, and is usually expressed as a percen- (PPMI'C). sitivity. Glass and quartz devices are used tage. The dissipation factor factor varies at frequencies up to 300 MHz. Air di- with temperature, humidity, and frequen- Working voltage (WVDC)-The recom- electrics are usable to about 1 GHz. For cy. mended maximum voltage at which a ca- frequencies I pacitor should be operated of GHz, sapphire dielectrics offer the best performance. Electrolyte-Current conducting solution factor figure of merit Quality (0)-A used Ceramic and plastic styles are less ex- (liquid or solid) between two electrodes or mostly in tuned circuit applications. It is pensive, with high grade plastic plates of a capacitor. defined as a 1/DF or Xc/ESR. dielectric devices being usable at frequencies up to 2 GHz. R -E 88 Figure 20 shows how the pin -12 resistor CMOS CLOCKS Voo can be used to determine the minimum (AIInnPC% from page 42 operating frequency of a restricted -range L VCO. In that circuit, is determined 16)-- fMIN r------by C1 -R2 and fMAx is determined by the combination of Cl and the parallel resis- tance of R1 and R2. PHASE COMP 1 IN !14)SIGNAL PHASE COMP 1(2 T. D OUT COMPARATOR PHASE COMP2 OUT( 13 1IN PHASE PULSES( OUTPUT VCO OUT PIASE COMP 2 ) (4 V cc T R2 h 100K FREQUENCY (6) 9 i-- Tc' T 7r-t SOURCE DEMOD 410) FOLLOWER OUT T VCO R2 J -946-4 12 r R1 FIG. 21-ANOTHER RESTRICTED -RANGE VCO. 1111 1M The maximum frequency is determined by the T C1 -R1 time constant; the minumum frequency is determined by the time constant C1(R1 R3). (5L- - Y Vss 1ZEN ER L------181- - - - -(15)- - J -- Cl Y 0047 Av FIG. 17-INTERNAL BLOCK DIAGRAM of the 4046 phase -locked loop IC. mines the maximum frequency that can be R2 +9V 100K obtained pin 9 voltage at max- C1 (with the OUTPUT FREQUENCY imum) and R2 controls the actual frequen- cy by applying a control voltage to pin 9: GATE IN -9V +9)/ f R2 100K FREQUENCY R2 100K FREQUENCY L R3 100K FIG. 20-THIS RESTRICTED -RANGE VCO has a FIG. 22-THIS GATED WIDE -RANGE VCO uses frequency range from about 72 Hz to 5 kHz. an external inverter. The frequency falls to a very low value (a Figure 21 shows an alternative version FIG. 18-A BASIC WIDE -RANGE VCO spanning fraction of a Hz) with pin 9 at zero volts. of the restricted -range VCO, in which from about zero to about 5 kHz (determined by The effective control -voltage range of pin fMAx is controlled by C1 -R1 and fMIN is R2). 9 varies from roughly 1 volt below the determined by Cl and the series combina- supply value to about 1 volt above ground, tion of RI and R2. Note that, by making a Cl and gives a frequency span of about suitable choice of the R1 and R2 values, OUTPUT aoa7 1,000,000:1. Ideally, the supply voltage to the circuit can be made to "span" any the circuit should be regulated. desired frequency range from 1:1 to near - We've said above that the frequency of infinity. the circuit shown in Fig. 18 falls to near - Finally, it should be noted that the VCO R2 zero when the input voltage is reduced to section of the 4046B can be disabled by 100K zero. Figure 19 shows how the circuit can taking pin 5 of the package high (to logic 1 FREQUENCY be modified so that the frequency falls all level) or enabled by taking pin 5 low. That the way to zero-all that's needed is a feature makes it possible to gate the VCO high -value resistor (R3) between pins 12 on and off by external signals. Figure 22 Ri and 16. Note here that, when the frequen- illustrates that feature and shows how the 68K = cy is reduced to zero, the VCO output basic voltage -controlled oscillator circuit FIG. 19-THE FREQUENCY OF THIS VCO can be randomly settles in either a logic 0 or a can be gated via a signal applied to an varied all the way down to zero. logic 1 state. external inverted stage. R -E 89 MOTION DETECTOR your scope or meter to pin 6 of IC2. You should see several volts of 17 -kHz signal continued from page 36 at that pin. Next we'll set the 555 frequen- cy and the transmitter-output level. Point both speakers in the same direction, away from nearby objects. Observing your scope or meter, make sure the signal level DELETED is less than 7 -volts P -P on the scope or less FROM FINAL than 2.5 -volts RMS on the AC meter. Ad- DESIGN just the transmitter-level control to obtain those voltages. Now adjust the transmit- ter-frequency control for maximum in- dication on your scope or meter. That is the final setting for the frequency potenti- ometer. Be sure to have the level potenti- ometer set for about 7- volts P-P at IC2. It is interesting at this point to observe the amplitude modulation of the 17 -kHz sig- nal that is caused by movement. On to the final amplifier stage. Detector diodes Dl and D2 and the following low - frequency bandpass filter feed a signal to IC3 that is proportional to the low -fre- quency amplitude variations of the 17 - C28 C27 C29 (SEE kHz carrier. IC3 amplifies that voltage to a TEXT) useful level. Connect your scope or meter FIG. 6-THE AUTHOR'S PROTOTYPE was built on perforated construction board. Note that the unit to pin 6 of IC3. With the sensitivity con- shown here, the receiveroutput-amplifier combination used in multi -unit systems, is a prototype and trol set to mid -range, you should see differs slightly from the final design. about I -volt P-P or V3 -volt RMS, which represents circuit noise etc. Moving your screws or glue. Be sure to cut holes out of Receiver alignment is almost as hand in front of the speakers should cause the front piece to allow sound to leave or straightforward as the transmitter. You the output of this stage to hit both rails. reach the tweeters unimpeded. probably noticed that Tl is not located on Your scope should see a squarewave down the receiver board. To save room on the to about 1 volt and up to about 11 volts Circuit alignment circuit board, it is mounted on the receiver when a moving object is near the tweeter. The easiest way to align the circuit is tweeter. Connecting the receiver tweeter An AC voltmeter should see greater than 3 with an oscilloscope, although it can also to the receiver board and applying power volts with nearby movement. be done with a VOM or VTVM. to the unit, we are ready to proceed. Note: The last stage of the receiver is a Let's first check out the transmitter, re- to align the receiver, the transmitter must 74LS14 Schmitt trigger, IC4. Its signal ferring back to Fig. 3 as we go. Power up be operating as it is the signal source. It comes from diodes D3 and D4, which the transmitter with the speaker con- will help to have both tweeters pointing in rectify the low -frequency AC of the pre- nected. If the circuit is operating, there is the same direction and away from moving vious stage. The output of the diodes is a good chance a loud high-pitched tone objects. Also, try to point them toward a connected to an integrator, which is con- will be emitted from the tweeter, so you wall or surface that is no less than 10 feet nected to the input of the 74LS14. If all is may want to do this part of the checkout in away. well, when the voltage at that point a secluded part of your house! Connect First of all, the DC -level potentiome- reaches about 1.7 volts, pin 4 of IC4 will your test instrument to pin 3 of the 555 ters, Rl, R4, and R5 on all the op -amps, go high and LEDI will light, indicating timer. If using a scope, you should see a should be adjusted. Disable the transmit- movement in front of the detector. 12 -volt P-P squarewave. If using a VOM, ter for those measurements since they are you should see about 6 volts on the DC DC adjustments. Starting with IC1, a Interfacing scale. Moving on to the output of the scope or meter should be connected to pin Interfacing the unit to the outside world LM380, connect to the speaker side of the 6 of each respective op -amp. Adjust ICI is a matter of preference. Using an intrud- output coupling capacitor. When using a and IC2 to read about 5.25 -volts DC. Ad- er alarm as an example, the easiest way to scope, you should see a fairly distorted just IC3 to get about 6-volts DC. do something useful with the circuit sinewave of about 10-volts P-P. If using a Now turn on the transmitter. Looking at would be to connect the output directly to VOM, there should be about 3.5 volts on signal at pin 6 of IC1 with a scope, you a "noise maker" of some type. You would the AC scale. The level control of the line should see some indication of a 17 -kHz probably want to have an outside hidden driver and/or output amplifier should be sinewave. You should be able to see some or key switch to turn the unit on or off. adjusted to obtain the above values. If you small amount on the AC scale of your A more sophisticated approach would have a frequency counter, adjust the fre- VOM or VTVM. Depending on your be to drive a one-shot (possibly made quency potentiometer to get about 17 meter, you may need to put a 1-µF capaci- from the unused sections of the 74LS14 kHz. If you don't have a counter, a rough tor in series with the meter to block the and some capacitors) to keep the alarm on adjustment can be made by turning the DC level at the measurement points. If for a minute or so to ensure that the intrud- frequency potentiometer so that a loud you see no signal at that point, it is time to er leaves! In the author's home, a KIM high pitched tone is heard. Then adjust the adjust the transmitter frequency to obtain computer and interface provides power potentiometer so that the tone gets higher maximum signal. It will help to point the and monitors the outputs of five units. A in frequency. Continue turning the poten- transmitter tweeter directly toward the re- one -key code on the KIM keypad enables tiometer until you can barely hear the tone ceiver tweeter. the units when the house is empty, and a produced. For the average ear, you should Assuming you have a 17-kHz signal at six -key code turns off the units when the now be adjusted to around 17 or 18 kHz. ICI, we can now check out IC2. Connect house is occupied. R -E 90 EQUIPMENT REPORTS ternating rate of 450 Hz for 5 mally took to center the chart. seconds. Once the chart is framed, the continued from page 10 Part of the initial setup pro- framing procedure does not have cedure requires adjusting the to be repeated as long as the same be "in the ballpark" the recorder framing so the picture is "cen- station is received. works properly. Once the tuning is tered" on the paper, thereby The recording rate is 120 spm set for a particular station, it does avoidüng loss of part of the picture. (Scans Per Minute). It takes ap- not have to be readjusted because That is done by observing the print proximately15 minutes to receive a the recorder can accommodate a as it is made by the stylus and 10- x 12 -inch chart. A station might rather broad receiver drift. (We got pressing the FRAME switch until the broadcast several charts followed excellent results from a low-cost chart is centered on the paper. The by an "end" tone, which stops the receiver.) Prior to broadcasting FRAME switch causes the framing to recorder. The cycle will be repeat- weather charts, the radiofacsimile change in small discrete incre- ed the next time a chart is broad- station transmits an automatic ments, and we found about five to cast. start signal that shifts 1500 Hz and seven increments was all it nor- (continued on page 96) 2300 Hz at a 300 Hz rate for 5 sec- onds. The recorder starts, prints the chart, and is automatically stopped when the station broad- casts the same tones, but at an al- Get every issue! IBM -COMPATIBLE MATRIX PRINTER SUBSCRIBE Canon has showcased its latest advance TODAY! in NLQ Printers. The company's new A-40 impact matrix printer provides max- Use the order imum support for IBM PC application programs. It's printing speed is a fast 140 form below. characters -per -second in draft mode (11 x 9 dot matrix, Pica). 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R -E L J 91 circuit for checking the matching is shown FET POWER AMPLIFIER PARTS in Fig. 12. They should be matched to be LIST-BARGRAPH DISPLAY and CLIPPING INDICATORS continued from page 86 within 100 millivolts of gate voltage at 50 All resistors areY4 watt, 5%, unless oth- mA of drain current and 200 millivolts of erwise specified. gate voltage at 2 amps of drain current. R43-24,000 ohms Make the 2 -amp >measurement quickly. R44, R46, R53-12,000 ohms To mount the transistors, first bend the R45, R52, R70-22,000 ohms leads up at a 90 -degree angle right at the R47, R54-1000 ohms point where their width changes. Spread R48, R55-470,000 ohms the leads a bit and insert in board. Solder R49, R51, R58, R59, R61, R62-10,000 carefully while aligning the transistors as ohms R50, R56-150 ohms much as possible in a common plane. R57, R60-53,000 ohms (They may be temporarily screwed to the R63, R65-1200 ohms heat sink as a holding fixture for this oper- R64, R66-7500 ohms ation.) Solder short leads from D3-D5 to R67-350 ohms, 20 watts the bottom of the driver board, carefully R68-15,000 ohms observing polarity. Apply heat -sink com- R69-2200 ohms, 5 watts pound and insulators to the transistors, Capacitors FIG. 12-TO CHECK THE MATCHING OF TRAN- and screw the driver and output -transistor C18, C19-1 µF, 10 volts, electrolytic SISTORS, you might want to use this simple assembly to the heat sink, using insulat- C20-2.2 µF, 10 volts, electrolytic circuit. Start by setting the potentiometer's Semiconductors ing shoulder washers. Tighten carefully. wiper voltage to zero. Then turn it up to the IC1-LM139 Quad op -amp desired drain current and measure the voltage Measure each transistor's tab (or case, Q30-ECG291 as shown. For N -channel devices (IRF630), V if you are using TO -3's) to the heatsink. D17, D18 -1N4001 should be 5 volts. For P -channel devices The readings should all be infinite, indica- D19, D20-1N4741A 11 volts, 1 -watt, (IRF9630) . V should be -5 volts. ting no insulator shorts. (If you are using Zener the bases of Q16 and Q17. It should be TO -3 output parts, it will be necessary to D21-1N4735A 6.2 volts, 1 watt, Zener near 7 volts. Adjust R19, and observe this run individual leads to each transistor. D22-1N4744A 15 volts, 1 watt Zener voltage changing. Leave it at 6.8 volts. When doing that, be extremely cautious: D23-1N4750A 27 volts, 1 watt, Zener Measure the voltage from the emitter of Double-check all your connections and LEDI, LED2-Standard red LED DISP1, DISP2-NSM39158 logarithmic Q19 to the + 75 -volt supply, and the volt- keep your leads as short as possible. age from bargraph display with driver (National) the emitter of Q20 to the - 75 - Don't forget to install a ferrite bead on Other components volt supply. One should be around 7 volts each gate lead if you are using TO -3's. In S2, S3-SPDT and the other about .6 volt. Remove no case should the wiring to the tran- The following items are available from power, discharge the filter capacitors, re- sistors be more than 2 inches in length.) A&T Labs, Box 552, Warrenville, Illi- move clip leads, and repeat with the other Install the heatsink and driver assemblies. nois, 60555: Etched, drilled, plated - driver board. Wire one channel to F2 and F3 with 18 - through PC boards, $22 each; Power Next, solder the output transistors to gauge (minimum) wire. Connect a wire transformer, $69 each; Set of 8 the driver board. Note that it is important from the circuit board ground, near the matched power FET's, $66; Drilled that the transistors be matched (within output, to the chassis single -point heatsink (type 512), $27. Add 5% ship- each particular ping and handling, 12% for trans- type) so that they will ground. Install a 1/2 -amp fuse for F3, and a former. Illinois residents include share the output current equally. A simple 1 -mA fuse for F2. Apply power, and 5-1/4% sales tax. +75V CHI INPUT +5V .4 017 check for a current through F3 of less than 1N4001 500 mA. Also +27V 25 check that the output volt- R43 848 R49 R45 CLIP age at Ll is between ± I volt. If either of 24K ' 470K ¡ 10K 22K LE01 those tests fail, immediately turn off R47 9 3 R50 power, and look for the source of the prob- 1K 15052 a lem before proceeding. Adjust R19 to set 8 ICI continued from page 32 7, 40 continued from page 62 á 30 tral companding, we still have a problem 2 20 with low-level signals (especially low -fre- w simply the signal being split into two quency, low-level signals). That's why the X10 parts.) So before we even consider cable dbx system also uses wideband compand- 0 losses, we have 8dB of loss. Now, what ing, which adjusts the level of all frequen- about those cable losses? cies to keep the signal level high at 102.1 50 100 200 500 1K 2K 5K 10K 20K The cable losses will be considerable. times. That companding method, .,i.os FREQUENCY-Hz Just how much will depend upon what response is shown in Fig. 11, reduces the FIG. 10-THE COMBINATION OF fixed pre - frequencies are output by the downcon- -input emphasis and spectral compression leads to verter. Remember that various receiver dynamic range of the compressor to a responses that can range from nearly flat manufacturers offer different output -fre- signal by a factor of 2:1 dB-the low-level high -frequency boost of 55 dB at 15 kHz! signals are boosted while high-level sig- quency ranges. And the top end or highest nals are reduced. The result is that the 100% 100% frequency in the range will have the great- signal is always above the noise floor and z 30wo30%- -30% est loss. Table 3 shows the typical losses 17% always below 100% modulation (so as not F 8.99% 8.99% for RG -6/U and RG -59/U coax at various to interfere with other parts of the spec- 3% typical "high -end" frequencies. ? trum). 1%95%- 1% Note that the values given in Table 3 are The wideband expander in the receiver only typical, and will vary (sometimes NOISE is essentially a mirror image of the com- 1a% c .1% greatly) with the grade and manufacturer. pressor. It restores the signal to its proper COMPRESSED It is important to understand that neither amplitudes by reducing the level of low- INPUT SIGNAL OUTPUT RG -6/U nor RG -59/U are really intended level signals and increasing the level of FIG. 11-WIDEBAND COMPANSION. The com- for use much above 900 MHz (try to locate high-level signals. pressor reduces the dynamic range of input sig- manufacturer specifications above 900 nals by increasing the level of low-level signals MHz and you will quickly agree!) so the and reducing the level of high-level signals. The Stereo TV equipment expander restores the signal to its original am- cheaper grades of RG -59/U "TV-hook-up We mentioned earlier that many sta- plitude. cable" sold prepackaged by many of the tions are stereo capable-or wil be short- national chain stores are apt to suffer far ly. TV set manufacturers are getting set, greater losses (ner 100 feet) than what is too. You'll see sets with built-in stereo quoted here. Our best advice is to stick to capabilitity, you'll see set -top decoders, quality cables from manufacturers who and you'll also see Hi-Fi VCR systems will supply you with guaranteed loss - tailored specifically for multichannel tele- per-100 foot characteristics. vision sound. In cities with large bilingual So, if we have lost 8dB of signal in our populations, it's likely that we'll see SAP- two splitters-and we can only lose 10 dB only decoders. before we have a signal -level problem, it Some of those devices are already on would appear we have 2dB left to lose in the market. And as stereo capability be- the cable. If our system uses a downcon- comes a selling point, you're sure to see NOISE REDUCTION CIRCUITRY for the dbx sys- verter with an IF output of 950-1450, that tem is available in Three different IC configura- more. And you can be sure that Radio - tion. The paper clip is shown to provide a sense means that we only can use about 21 feet Electronics will keep you up to date. R -E of scale. of RG -6/U cable (total) for our hookup if we are to have satisfactory results at the high end of the band. It is unlikely that we can reach all four sets in this system with no more than 21 feet of cable between the downconverter and the most distant TV receiver location. The solution is to use an amplifier. As with the splitters we looked at ear- lier, line amplifiers intended for cable ser- vice often do not operate well at the frequencies output by satellite -TV down - converters, especially the higher frequen- cies. Fortunately there are a number of manufacturers that offer equipment spe- cially intended for satellite -TV service. Satellite -TV amplifiers typically have gains of 20dB, with a slope of 2 or 3 dB. For those unfamiliar with it, let's explain what is meant by slope. Remember that cable losses increase with frequency. A length of RG -6/U, for example, may have 9.5dB of loss at 1450 MHz, but it will have only 7.0dB of loss at 950 MHz. That's a 2.5dB differential, and the object of our system is to maintain not only a BUILT IN STEREO AND SAP DECODING are what make this 25 -inch Zenith Smart Set different from most other TV's currently on the market. A stereo amplifier is built In, but audio -output jacks are also minimum of OdBmV to each receiver, but provided for greater flexibility. (continued on page 96) 93 as an extra precaution, the PC board uses tion of your tape deck. TAPE STREAMER square pads to denote the positive end for Installing the Streamer inside a com- continued from page 26 the capacitors, and the cathode (banded) puter is the least attractive option, as this end of the diodes. The parts -placement precludes its use with other computers. pattern shows the transistor orientation for One of the most important uses for the eter may be replaced, if desired, with a TO -92 packages. If you use substitute Streamer is to transfer files from one com- 1000 -ohm resistor, as long as a jumper is transistors, be careful that the right wires puter to another, and that cannot be ac- added between the audio input terminal go into the right holes. The LED's must complished if it is dedicated to one unit. and the negative side of Cl. That potenti- have long enough leads to reach the front If the Streamer is to be mounted in its ometer is used only when extremely poor panel. own enclosure, the procedure should be quality tape information requires an addi- The Streamer PC board may be to:.. Assemble the PC card. 2. Wire the tional "tweak." In normal use, it will mounted in its own enclosure (the one you DPDT switch (S1) to the card. 3. Wire the never be touched. see in the photos is available from the connectors on the rear panel. 4. Install the The use of IC sockets always seems to source mentioned in the Parts List). Alter- card and attach the rear panel wires. Fol- be a controversy. On the one hand, includ- natively, it can be mounted inside your low the schematic for the proper connec- ing them adds a potential long-term re- computer, or even inside the tape deck. tions to the DB -25 and the closed-circuit liability problem; on the other, trouble Mounting it inside the tape deck is a good jack carefully. The power connection to shooting soldered -in IC's is a nightmare. idea if the tape deck supplies the Streamer DB -25 pin 25 is optional, and may be Ultimately, it is the decision of the power (as long as the deck won't be used omitted if an external supply is to be used. builder; but we recommend their use, as for other recording!). Baud -rate switch Si long as high -quality sockets are used. can be eliminated, since only one data Troubleshooting Be careful to observe polarity on the rate will be used, and the DB -25 con- Initial trouble -shooting can be accom- diodes and electrolytic capacitors. The nector can be located on the rear of the plished with an ordinary 20,000 ohms/ proper polarity is shown in Fig. 7. If you deck. Locating the LED's may be a prob- volt (or better) volt-ohm-milliameter. study the foil patterns, you'll notice that lem, though, depending on the configura- Connect the VOM, on its highest current sol SO soi PIN 13 PIN 2 PIN 3 (+V) I S01 (RS -232 OUT) (RS -232 IN) PIN 7 (GND) -C23- Q3 -R28- -R29- Ç,15 -C16- Q4 R26 F1/2 R21 R27 ID5 -R30- R20 IC15a C21 T* 1C14 + C14 Q2 lrr Q1 D4 J +C13 -R19- -R23- LED 2 MARK -C12- -R16- - -'J- -v R31 CI8 v 520 C24 -XTAL1- C0 C'1 ICE IC3 Iss IC 10 -014-- -R 13- L_ ' LED 1 D1 _C8- -C9 - SPACE R18 C7 1C2 v -v IC7 IC11 -R11- -012- IC4 S1 -a i 2400 C16 RE 4800 I C 1 C15 C22 2400 1 S 1-b R7- -RB- 4800 BAUD -RS- -R6- v R25 v RATE -R4- +-C4- IC12 -R3--- -C3 -- IC5 ICE IC13 C17 -R2- -C2- R241 - C19 + 1 r ---R1 I J1 J2 AUDIO INPUT AUDIO (FROM TAPE) OUTPUT (TO TAPE) FIG. 7-PARTS PLACEMENT DIAGRAM for the Streamer shows both the on -board and off -board components. 94 scale, between the Streamer and its power through the keyboard. The same can be which is probably resident in the comput- supply. The streamer should draw in the done with source files, or, for that matter, er you now use. The routine the author range of 10-30 mA, and no LED's should any ASCII file. uses on his system, like many others, be on. A very high current would indicate Machine -language program storage transmits in sequence a delimiter stream, a short or a component in backwards, and retrieval can be handled by any of a a load address, 255 bytes of data, and then while a low current would indicate an great many approaches, at least one of a checksum. That is followed imme- open in either the power supply lines or diately by the next load address, data, the ground return. checksum, and so forth, until all the data If the above test is successful, remove is done. When the tape is played back to PARTS LIST the meter and connect the Streamer di- the computer, each checksum is com- power supply. Measure the pared with a calculated checksum, and rectly to the All resistors 1/4 watt, 10% unless other- + 5 volt supply at any convenient place. If wise noted any error causes the routine to halt. it is above 5.25, or below 4.75, IC15 may R1-1000 ohms, PC -mount, trimmer po- If you ever run across data errors when be defective. Now measure the voltage at tentiometer loading programs back into your comput- the end of R21 closest to Q2. There should R2, R5, R6, R11, R16, R17, R20, R28, er, the cause is probably dirty tape heads. be a negative voltage with a magnitude R29-1000 ohms Simply cleaning the heads should elimi- slightly less that that of the positive sup- R3, R4, R7, R8, R13, R14, R18, R19, R22, nate the problem. R23, R25, R26, R30-10, 000 ohms ply. If there is, that indicates the clock, the When configuring your RS -232 port, Megohm R9-1 remember that the Streamer works with 8 - negative supply, and IC3 are functioning. R10-100,000 ohms 15. bit data words. Those eight bits can be all Measure the the voltage on IC8, pin If R12, R21, R27-47,000 ohms it reads about 2.5 volts, then the Man- R15-10 Megohms data, seven data and one parity bit, or chester encoder is working. R24-2200 ohms seven bits, no parity, and at least two stop Connect the encoder's AUDIO OUTPUT R31-330 ohms bits. The only real requirement is that start to the AUDIO INPUT. Adjust R1 to the nor- Capacitors bits must be at least nine bit -times apart, mal full -on position. (If you are using the Cl, C4, C13-10 µF, 25 volts, electrolytic such as with eight data bits and one stop PC board, this is the full -clockwise posi- C2, C21-0.001 µF, ceramic disc bit. In storing 7 -bit ASCII files, it is nor- C3, C12, C16-0.1 µF ceramic disc tion, viewed from the board's edge.) If the mal to follow with a parity bit. The C5, C7, C17, 018, C20, C22, C23, C24- MARK LED comes on, both the encoder Streamer will treat the eighth bit as part of 0.01 or .1 µF bypass capacitors (not the data, faithfully recording it and play- and decoder are working. That is about all shown in schematic) ing it back. The Streamer itself does no the testing that can be done with a VOM. C6, C10-20 pF, ceramic disc If everything looks good, it should work C8, C9-250 pF ceramic disc parity checking; it simply records the data properly the first time. C11-5 pF, ceramic disc and returns what is presented to it. If an oscilloscope is available for test- C14-100-330 µF. 25 volts, electrolytic The audio output of the Streamer is ing, much more extensive trouble shoot- C15-47-220 µF. 25 volts, electrolytic designed to present a signal compatible ing may be by referring to 010 0.01 µF, ceramic disc with the audio input of a hi-fi type tape accomplished Semiconductors deck. Since modern decks have input - the schematic and the theory of operation. IC1-LM392 or LM2924 op-amp/com- level the control should be ad- A word of caution, however; the bit se- parator controls, quence that appears at the output of IC12- IC2-4070 or 74086 quad xoR gate justed for best performance. Unlike con- b wiii be in a different order than that 103 -404012 -stage binary ripple counter ventional cassette interfaces, that adjust- received. That "bit shuffling" was done to 104,106-4029 presettable up/down ment is not critical at all. To determine simplify the board layout. The received counter your optimum adjustment, use the tape bits, then, will also be in a scrambled IC5-4520 dual 4 -bit synchronous coun- counter to record segments at various set- order until IC10 corrects them. ter tings, then play them back, noting any 107-4011 quad 2 -input NAND gate recovery errors. The errors should occur 108-4027 dual J flip-flop Using the Streamer -K at the extremes of the level control set- IC9, IC12-74074 dual D -type flip-flop set the control approx- The Streamer is one of the simplest IC10-4015 dual 4 -bit static shift register tings. Simply add-ons to any computer system. As long 1011-6402 CMOS UART (Intersil) imately half way between where errors as your computer has an RS -232 port ca- 1013-4021 8 -stage static shift register occurred, and you're under way. pable of a transmission rate of 4800 baud IC14-LM339 quad comparator The Streamer can be used with low-cost and a reception rate of 9600 baud, and as IC15-78L05 low power 5 -volt regulator portable tape recorders, with some loss of long as you have some sort of software to D1 -D5 -1N914 or similar performance: Because of their lower support storing and loading, you should D6, D7 -standard red LED bandwidth capability, the Streamer must 01, 03-2N3904 have no problems. The tape machine can be operated at 2400 baud instead of 4800 Q2, Q4 -2N3906 (which is possible with most be just about anything -even a cheap por- XTAL1-2.4576 MHz crystal usually table (although, as we'll mention shortly, MISCELLANEOUS: PC board, en- modem hi-fi decks). you'll sacrifice some performance). If you closure, DPDT switch, DB25 connector, The audio signal out of the streamer is have a tape deck as part of your stereo phono jacks for tape deck connectors, about 0.9 Volt peak to peak, which suits system, it's probably ideal. hardware, solder, etc. most decks just fine. But you'll probably The supporting software may be the The following are available from Stone have to reduce that level if you want to SAVE and LOAD commands with a Mountain Engineering Co., PO Box apply it to a portable recorder. You can do BASIC interpreter, as long as they can be 1573, Stone Mountain, GA, 30086: that with either a resistive voltage divider board, double -sided routed to an RS -232 port. BASIC pro- Printed circuit at the recorder's input, or by simply re- with plated -through holes, solder by ducing the value of R24: Try values in the grams can also be conveniently saved masked and silkscreened, for $28; En- LISTing them out to the Streamer, and closure, with all holes punched and 100- to 1000 -ohm range. read back in through an RS -232 port as- legends silkscreened, $16; Both PC Whether you use the Streamer for pri- signed as the console. The latter method board and enclosure for $40. All orders mary data and program storage, disk has the advantage of allowing BASIC pro- must include $1.50 shipping and han- backup, or to exchange programs with grams from different machines to be load- dling, and Georgia residents please other computers, it will undoubtedly be a ed, as the ASCII listing is, in effect, the enclose 3% sales tax. welcome addition to your computer sys- same information that would be entered tem. R -E 95 BATTERIES TVRO BUYER'S GUIDE continued from page 20 TABLE 7- continued from page Y. BATTERY MANUFACTURERS to also attempt to keep fails, the diode is forward biased and the the level "bal- anced" (i.e. the same) at NiCd batteries provide power to the load. Lithium batteries the input to each receiver and on each channel. The calculations for finding the value of R A "sloped amplifier" has 2 to and the considerations for choosing the Altus Corporation 3 dB more gain at 1450 1610 Crane Court MHz than it does diode are exactly the same ones we dis- at 950 MHz. That San Jose, Ca. 95112 sloped gain acts to cussed for our simple charger. There are compensate for the expected additional other, more elaborate schemes for using cable losses at the Tadiran higher frequencies. rechargeable batteries like this, but they Variel Avenue 6312 In summary, many of the original prob- all use this approach. Diodes are used to Woodland Hills, Ca. 91367 lems of TVRO reception have been steer the current where you want it and the elimi- Varta Batteries, Inc. nated by newer equipment designs. 150 Clearbrook Road Everything about .TVRO equipment has Elmsford. N.Y. 10523 become more consumer/user "friendly" in the past 18 months, and the industry is Lead -acid batteries rapidly approaching a "mature" design level from which innovation will switch to product efficiencies rather than product Technacell TO MAIN features. Most equipment now arrives on 2117 South Anne DC SOURCE St. your doorstep with Santa Anna, Ca. 92704 reasonably adequate installation instruction manuals, and most Eagle Pitcher Ind., Inc. equipment now carries at least a one-year PO Box 130 OEM warranty. R -E Seneca, Mo. 64865 FIG. 12-ONE OF THE MOST POPULAR applica- Gould Inc. EQUIPMENT REPORT tions for rechargeable batteries is backing up 931 N. Vandalia St. power supplies. St. Paul, Minn. 55114 continued from page 91 Nickel -cadmium batteries biasing of the diodes is switched by the The Alden Weatherchart Re- corder (which is also available in presence or absence of the main power Gould Inc. supply. 931 N. Vandalia St. kit form) is supplied with two pa- We now come to the question of which St. Paul. Minn. 55114 per cassettes, three spare stylus battery type you should use. Well, the belts, the audio matching trans- answer is, as we saw with disposable bat- Varta Batteries, Inc. former, two spare fuses, and a se- teries last month, it depends. As a general 150 Clearbrook Rd. lection of notably Elmsford, N.Y. 10523 good manuals. rule, lead -acid batteries are used where The operator's manual is superb; it the current draw is going to be heavy and General Electric is clear, concise, unwordy, and is NiCd's are used where I it's not. Now Battery Business Dept. well illustrated. Also supplied is a know that these are all relative terms but, PO Box 861 directory of worldwide facsimile like I said, it depends. Gainesville, FI. 32602 a For practical purposes, let's just say stations, guide to understanding that if the current draw is going to be radiofacsimile weather charts, and consistently in the multi -ampere range, a technical manual that includes go for lead -acid. If it's under an amp, look based batteries as well as the zinc -carbon the step-by-step kit assembly. at NiCd cells. The relative merits of each ones so you can make an overall com- The kit version is priced at $995, system are summed up in Table 6 and the parison. the wired version (the model we voltage -discharge curves for some of the By now you should know enough about tried) sells for $1995. R -E various batteries are shown in Hg. 13. I've all the different battery chemistries to put in the curves for some of the lithium- make an intelligent decision as to which battery system (or combination of sys- L.L.1 tems) is best for your application. And if ADVERTISING INDEX 100 you're not exactly sure, you should have Free Information Number Page 90 LITHIUM enough information to know what the 209 AMC 8 80 right questions are. 214 AP Products CV3 NICKEL- 70 Battery manufacturers will be more 207 Beckman CV4 CADMIUM CIE 33 60 than happy to send you data sheets, cata- - LEAD 213 Command 50 Productions 6 ACID logs, and application notes so you can find 203 Datak West 9 40 out whatever you want to know. Table 7 is - Dick Smith 3 30 ZINC -CARBON a good beginning list of companies you - Electronic Technology Today 12 20 210 Fluke CV2 10 can contact for information. Don't hesi- 205 Jameco II o tate to write to them-they know more 208 J&W 9 0 2 3 4 5 6 50 than you do and can save you lots of time 202 Kepro 4 TIME -HOURS and trouble. And a postage stamp is a 211 Micro Mart 7 204 Mouser 4 FIG. pretty cheap insurance policy when it 13-VOLTAGE DISCHARGE CURVt.S for NRI 17 various types of comes to saving twenty worth - batteries discharged at the 0 2C dollars of 212 Oregon Microwave 6 rate. Note the break in the hours scale. batteries. R -E - Pacific Cable 5 206 Pacific One 8 96 A P's newest series ACE Boards is easy to spot. The econorriral A1-Circuil _valuators_ Just ook for tie tvards with the bright blue back - ACE 109 and ACE 113. plates Hobby sts and professionals alike will find The 700 serias is starti-lg off with two . C -E Boards in these new ACE Boards offer more quality for less :he [most pcpuler size configurations. And look for an- money tnan any Diher so derless nauncemens of other A.C.E.100 breadboard on the narket. Stords in tte future What maces the A -CE Board'" 100 Our ACE -09 gives you a series so special? _otal of 840 tie First, they cost BL joints with 8 buses And th :'s always and thr- binding important NEW Li E SERIES aos-s. The ACE 118 Second, the back. Sete is ou even more blue to shove -het capai Ity w th 1824 total made of a heaver meta THAT L.. L SAVE tie pcànts. 16 Duses and alloy :ian our CE Board 200 4billing post:.. series. That e>t-a weight makes lJ w you don have t= settle for it a little more slable on a S O IVi E sec rate beards :o save money. table . 4nd that nearts Now -here's =n A -G -E it's a ita ter and SERIOUS that r ght for any easier fora beg nne- -o a li.atior J_Ist look for war- with. G REE1 the Light blua hack- But most inpararr of all, the ACE 100 ser as alates on our A.3 -E Board 100 series beads. And for boarls are mace w th :he same high standards of all your circJit tub is needs, for any size project, quality that hava been a part of A P PFODUC-S ook for the A P PROOIJOTS name_ since cur beginr'nç in l%7. From our larst A C E Boarc with over 50)C tie points to a single tie pcint Sugçe;ted retail price block, our sprin clie-erminals give you nothing tut ACE 109 $20.95 ,CE 118 $39.95 good solid contact on every connection. The - JO For th> name of the d st-,L -u or v rarest you, cAl TOLL FFEE series has the same couble-sided adhesive foam 18001 321-9668. In Ohio, call cal ect: (2161 354-2101) found in our 200 series. It insulates to prevent shorts ,__ and seals the bottom) of the individual spring c ip cR A P PRODUCTS INCORPCRATED cells. And our A.C.E. Board 100 series comes with cur 9325 Progress Parkway guarantee hat if your ACE Board doesn't work Box 540 Mentor, Ohio 44060 perfectly, return it to your A P PRODUCTS d stribu*-ar. [2131 354-2101, TWX: 810-425-2250 He'll replace it, nc hassles. In Cenada c;311 henbrook Electrones t4- 6(477-7722 Electricity yid water don't mix. At All the Heavy Duty series rotating the function selector knob. least no,t4n our Heavy Duty Digital- meters measure up to 1000 volts You'll find these features in Multimeters. Because these Oops AC and 1500 volts DC, with full a full line of Heavy Duty DMMs Proof' instruments are protected overload protection to those that offer a 4'2 digit readout, by a system of seals to ensure maximum voltages even on the 0.05% VDC accuracy, a 10 -amp contamination -free dependability lowest range settings. Overload current range, a 2000 -hour battery in even the cruddiest conditions. circuitry also provides transient life, diode test, true RMS and tem- Other abuse -proof features protection to 6KV on all voltage perature measurement. All this and include the best mechanical pro- ranges and up to 600 volts on all a no -questions, one-year warranty. tection ever built into a precision resistance ranges. You'll want to try one out, Digital Multimeter. In fact, every We also invented a unique, of course, so drop into one of our Oops Proof multi - long -life rotary switch for our your nearest elec- meters will survive a drop from Digital Multimeters. You can actu- tronics distributor ten feet onto a concrete surface! ally feel the difference just by and drop one. Our ©1985 Beckman Industrial Corporation, A Subsidiary of Emerson Electric Compam. 630 Puente Street, Brea, CA 92621 (714) 671-4801). CIRCLE 207 ON FREE INFORMATION CARD