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( RTTY LOOP J Marc I. Leave y, M.D. WA3AJR 4006 Win lee Road Randallstown MD 21133 Okay, now, how many of you out there have heard of iRL? Come on, raise your hand s. Tha t's o ne , t wo, three . . . hmmm, not too many. I guess this goes along wi th what one of the guys from the company told me. You see, they have a new RTTY demodulator, the FSK 1000, and, in his words, "Whi le we haven't expected the FSK 1000 to stu n the free wo rld and enrich us overnight, we stil l can't quite see wh y people would want to spend almost two hundred bucks more for something else." We ll, after looking at the FSK 10Cl0, I don 't know what the problem is either. Over the past few months, we have covered many dem odul a tor design s and considered what makes a good dem odul a to r. A common desi gn point of many of these was the inc lusion of a limiter stage in the front end. What the limiter does is boost the sig nal inp ut to a c lipped or limited level so that in theory - all sig nals present are processed to the same arnpli tude . In practice, however, this only works for signals tha t are in the clear or reasonab ly noi se-tree . The ability to work without a limiter, in true limiterless (often called AM) mode , is a distinct advan tag e on our ofte n crowded ham band s. Unfortunately, most of the demodulator s marketed to th e Any amat eur have not featured true limiterless operati on. While a fro nt-panel switc h may be marked " LIMITER ON/OFF" or "AMIFM", there is usua lly no way to vary the input level to best take advantage of what sig nal the re is. Further, selective fading without adequate logi c to allo w insta ntaneous reception on mark or space can be equally disastrous . The FSK 1000 changes all that. A front-panel inp ut level contro l and an LED which lights upon clipping, th us exc eeding the li near range, make limit erless operation of the FSK 1000 easy. By adjusting the imput so tha t th e LED is just extf n- guished, maximum capability is ensu red. By increasing the input level, any degree of clipping fro m co ntrolled to hard limiting may be achieved. Clearly, all sig nals are not alike. Now there is no reason that the demodulator needs to sta y the same, eit her. Another bugaboo of demod u lator design has been the filters. Through the years, filters have ranged, as we have seen, from TV-width coils to toroids to coilless acti ve filte rs. The problem has alw ays been to maintain adequate selectivity, gain , and bandwidth at reasonable cos t vs. perf ormance trade- off. Well , iRL has come through , again, by using modern, six th-order active filters in the FSK 1000. This permits selectable bandwidth and tunable peaks to cov er any shift fro m 50 to 1000 Hz, wi th switch selection of 850 Hz, 425 Hz, and 170 Hz. The shift change is accomplis hed by tuning a multipole bandpass filter of consta nt bandwidth, rather tha n using audio frequency mixe rs in a heterodyning process. Thus, audio image probl ems, bird ies, and spurio us frequen cies are min i mized. Now, as if the guts were not impressive enough, the boys at iRL have also wor ked hard to provide a heck of a box. The circuit board is a hefty 3132·inch glass epo xy number, and the pots and other components are name brands. Full -sized, sta n dard connect ors are used on the rear skirt; no scrounging for mole x plug s here. The who le thing is encl osed in an anodized aluminum bo x that unscrews for service but looks like it will support a TO on top of it. (I said "looks li ke it will " - 1 have not do ne it !) There are even a bunch of options, as if the bas ic unit weren't enough . You can get a video board mount ed in side and make a full term inal. ASCII-to-Baudot conversions go wi th that One. Some of the standard feature s are even more imp ressive , how ever. A RS·232 keyboard can be hooked into the back to key the loop, and RS-232 outputs are available also . That means the thing will work with our computer terminal, without a 50·mA loop at all. There is a keyboardacti vat ed sw itch (hitting any key turns on your transmitter) and a CW 10 key jack. Tuni ng meters , scope outputs . . . 1even think it makes a pretty good cup of cottee. There are a few gripes, however. First off , look at the picture . I seriously co nsidered having a contest to see how many of you could tell which push-but ton on the front pane l was pushed . You see, even in real life, it is hard as the devil to tell what shi ft you are on, whet her autost art is on or off, or whatever. Som e form of indicator, LED, or whatever, or changing to tog gle swi tches is needed to clear up that front panel. Speaking of clarity, abou t mid way between th e delta-tune and input knobs is a small knob labeled "THRESHOLD." This knob was added to late produ cti on runs, and allows you to adjust the autosta rt threshold (tha t is, the level at which the autost art will start) from the front panel. Fine, but the re is no calibration , sca le, or logging on the knob. No way to know where it is set nor return it to a previous setting. Bad news, fell as. And one last note: tne autostart. When I fir st sta rted playing with this thing, about a minute or two into the session, the front lights died and the printer went off . Now, if ju st the prin ter and loop had gone off, I would have known the autostart disengaged. But killing the front-panel li ghts made me think I'd blown a fuse. Only a fortuitous signal brought fife to the machine and saved the day. Really, now, why not leave the light s alon e? Other- The FSK 1000 from iRL. wi se, when ki lling equipment at the end of the day, there is no qui ck way to know the thing is on. All in all, howe ver, I have to commend the fol ks at iRL. They have turned out a solid demodulator that well sho uld stun the free world. The FSK 1000 currentl y sells for $449.00, and you can see their ads here in 73 or write to iRL, 700 Tayl or Road, Columbus, Ohio 43230. I received a lett er recently from Tom Waarvik of Indiana polis, Indiana, who related that he was a begi nner, with a Teletype Model KSR-35 and a modem, and that he wan ted to be able to receive Morse, Baud ot, and ASCII on tha t setup. He notes tha t much of the commercial gear is over his budg et, and he is looking for cheap way s of code co nversion. Well, Tom, this is where the co mput er in the shack co mes in handy. There are reams of publ ished programs fo r receiving any or all of these modes with just about any of the popular computer chips. You might c heck back issues of 73 and Microcomputing magazines. In September and December, 1979, t listed many of these articles in this columm. See if you can scrounge a copy in your area, or chec k with 73's back issue department. Which computer? Well, I am partia l to the 6800 and have written some fa irly sophisti cated progr ams to work RTTY on one. But whic h ever you can get within your budget , 6800 , 8080, Z·80, Apple, Pet, or TRS·BO, they can be made to work on RTTY and Morse. That is probably the best way to go. 18 73 Magazine. October, 1980
WHEN OUR CUSTOMERSTALK•.• WE LISTEN. Tom Gentry, K5VOU Dallas, TX And we respond with unexcelled RTTY equipment. One reason RTIY equipment designed by HAL is always state-of-the-art quality is our open channel of communicatio ns with customers. We want to hear the "What if's . . ." and "How about's . . ." that come from active and dedicated RTIY operators. Our engineers have combined customer ideas with their own to create the most advanced equipment features and capabilities in the industry. It adds up to greater enjoyment of RTIY operatio n and a dependability factor backed with a full one-year warranty. Write or give us a call. We'll be glad to send you our new RITY catalog. I11IJ HAL COMMUNICATIONS CORP. ,.- 345 Box 365 Fo r our Euro pean Custome rs Contact: Urban a, Illinois 61801 Richter & Co., 0 3000 Hannover 1 2 17·36 7·7373 Transradio SA, 6816 Bissone/Lugan o
Page 1 and 2: Ii Gift to , enty Years of 73 o 174
Page 3 and 4: Rack Attack from DenTron Components
Page 5 and 6: Escape from Mt. St. Hel e ns! .....
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Page 25 and 26: 73's ICOM IC·720 DEAR OM: There ar
Page 27 and 28: MEMORY KEYER BREAK THROUGHI New l
Page 29 and 30: INTIMIDATED BY MORSECODE? THE NEWAE
Page 31 and 32: Solid-State H.F. Kilowatt Amplifier
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Page 38 and 39: Edward t. M ulvin WBQI FF 34()()54t
Page 40 and 41: Phot o E. The AB C " That's Incredi
Page 42 and 43: W erner M . Ma urer W1QMS Kefl y Dr
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Page 50 and 51: Joseph D. Novak K40VK 2420 Luckett
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Robert B. Grove WA 4 PYQ Grove Ente
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proveme nt over the origina l To uc
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channe l l ; ente r 139.1 MHz into
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Joseph H. Cowen WA 5TUM P.O. Box 76
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an advance piece and aft erthe-fac
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School and ret ired surgeon Dr. N i
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73 Magazine Staff Field Strength fo
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Photo B. Front of th e con verted Y
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TE1: ANTENNA SYSTEMS l-BoO-654 -}2}
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Fig. 9. This view sho ws how the ra
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"' 0." -t ee' I CONNECTOR~ TO IlR M
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1'::1" ~~4 ""ATTENTION MOBILE HAMS
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Patrick M cGuire W BSHGR 102 Dunca
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SECURE THIS END TO BOT TO M PL ATE
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Then buy a small can of red spray e
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Description a) Print frame (same as
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MEMORY KEYER BREAKTHROUGHI The rema
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INTIMIDATED BY MORSE CODE? THE NEW
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RTTY Demodulators ~~;~~ e $449. 00
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BUU Directlromthe Tri·EK@ Factoru
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• CALL 1 N8AD 2 KB8/>J'1 l WAlDCS
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• •• Computerize your log boo
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is sim p lif ied and refined t o al
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.... Reader SelVice- see page 274 7
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IIEW IIIFFEIEIiT FROM BARKER & WILL
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Have you ever wondered why the best
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P ~ESCA l£ I NPUT C2 C1 I~ ;;-----
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A 40-pin socket must be used for th
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un til it changed tone and wo und d
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MF.J 941C Versa Tuner II , i i 11f!
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Two fuses are incl uded fo r safe t
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pu shed for th e switch to SSB and
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A M ATEUR RADIO 73 6' YIO carRad¥
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162 73 Magazine . Oct ober, 1980 19
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Jean Shepherd K20 RS Some Guys Make
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1975 August 1: ~ '3~fr EOi TORJI'\.
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Mike Mods for the KDK-2016A - impro
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Clock Blocks a compendium of TTL an
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73 Magazine Staff Build a Better Ba
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TUfTS Electronic Department Store,.
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TUfTS Electronic Department Stor~.T
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and 5. The purpose of the divide-by
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3500. To do this division by 3500,
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l i mi t er o utput on p i n twe lv
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Radio Amateurs! Tempo Handh
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QRP ARCI ANNUAL OCTOB ER QSO PARTY
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("----~) FUNl from page 28 5) The "
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you need a friend w ho works fo r M
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FREE! RADIO AMATEURS WORLD ATLAS wi
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SatelliteT~ FORTHE HOME Sick of Net
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schematics, formulas, construction
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Th e Comm issio n s tated , " Lo ok
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MFJ RECEIVER ANTENNA TUNER/PREAMPLI
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c lasses are proving that it is pos
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• linear Converters for SS B, CW,
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