LF NOTEBOOK #19 (THE LOWDOWN October, 1994) News and Comments About LF Radio & Experimental Topics John Davis, PO Box 367, Warm Springs, GA 31830 Fax/Voice: (706) 672-0964 E-mail: johnhdavis@aol.com Longwave/Part 15 BBS: (706) 672-0360 October’s here already? Must be. At this writing, the frost isn’t yet on the pumpkin, but the breezes aren’t nearly as balmy as they were a month ago. After we dried out from the floods and endured a few more severe thunderstorms, late summer turned out to be pretty nearly normal here in Georgia, and September has been delightful so far. If the normal pattern holds, by the time you read this, we’ll have had an abrupt drop in average daily temperatures of about 10 degrees, and there won’t be any more trotting out to the lake for a quick swim just any old time. By October 10, the average wind direction will switch to northwest, and remain there until some time next April. Fortunately, as you’ve probably read in the On The Air section, receiving conditions are a little better than average for this time of year. If nature doesn’t surprise us with some nasty tricks, October may prove to be a real treat. E-mail extravaganza. If you haven’t already, please note the new e-mail address for your columnist, above. Yup. I’ve signed up with America On Line, which results in several advantages for us: (1. This address is a whole heck of a lot easier to remember, not to mention being shorter. (2. It should be a lot more dependable. (I wasn’t been able to sign on to the Learning Link for almost two weeks, due to problems with the host.) And, (3. It makes a lot more files available for the Longwave BBS, sooner than we would otherwise have them. Alas, still no packet radio yet! Maybe next month. Speaking of the BBS, use is increasing with our members, plus readers of Monitoring Times, logging in. The board was mentioned in their September issue, according to Kevin Carey, so hopefully we’ll have a wider user base for messages and new files. Now that the DX season is at hand, the bulletin-board aspect of the system should be increasingly useful, as people post and read messages more often. We already have an increasing number of files each week. I’ve been adding both public domain and shareware files on general electronics and ham topics, but most have direct application to LF in one form or another. The pride and joy of the files right now is the Part 15 FCC Rules, available in long form (covering everything but commercial devices), or short form (main home-experimenter bands only). And the board goes to full-time operation early this month! *Cosmic Connection — Lightning, Part 2. As usual, plans get changed. In this case, it’s for the better. I had hoped to wrap up our ruminations on lightning as a link between earth and space, but at the last minute, I was made aware of more intriguing information that needs some research. We’ll follow up on that next month, but meantime, here are two items for which you may not want to wait. The first is word from Daniel Levit in Illinois that the November, 1994, issue of Earth magazine contains a short article about upward lightning. Walter Lyons of Mission Research Corporation, using low-light cameras on the ground, found these upward discharges to be quite common above Colorado storms. A picture recording three of the eerie forms in one frame heads the article (page 10). The resemblance to jellyfish—or some Star Trek aliens—is truly uncanny. Also noted is the discovery by the Compton Gamma Ray Observatory satellite that gamma bursts in the upper atmosphere may be linked with active storms in some way. In connection with that same thought, Duane Schulke sent this via Internet: “The Compton Gamma Ray Observatory Satellite detected emissions of gamma rays from these things that are a form of auroral discharge, based on my recent readings of references available on the Internet. These documents and references describe a ‘top-down’ generation of increased ionospheric potential and air-earth potential gradients above an altitude of 20km, as a result of solar flares on the sun. If you have access to ftp, do an anonymous login to: xi.uleth.ca -- and get a copy of the documents in the directory: /pub/solar/Docs” Your columnist will attempt to do exactly that before next month, and if you have the capability, you needn’t wait for me. More next time. Miscellaneous-- A really digital receiver is on the market now, in the form of the SoftWave by ComFocus. By the time this reaches print, you’ve probably seen their ad in Popular Communications or elsewhere. But in case you haven’t, it’s not just a computer control program for a regular receiver. This one is a true digital signal processing receiver, and the DSP takes place at IF, not at audio. Half the receiver is in a box to which the antenna and a cable from a PC-compatible computer connect. It houses the front-end and first IF circuitry, which tune under control of the software. Then the analog-digital conversion takes place, and the rest of the receiver is completely digital, residing on a card in the PC! As a result, the IF can be switched for bandwidths anywhere from 11 kHz down to 56 Hz. A real-time spectrum analyzer is built in, and it includes such goodies as automatic Morse decoding, digital noise blanking, and synchronous AM. Coverage is 500 kHz - 30 MHz and 108 - 174 MHz. Price is $1,495 until December 31, and they have a money-back trial offer. For details, call them at 1-800-763-8983. Frequency standard and coordinates, anyone? The August and September issues of 73 have some interesting information on interfacing a LORAN receiver to a PC. It’s in the “Above and Beyond” column, part of which has been dealing with 10 GHz...so why not 100 kHz for a little relief? Anyway, the emphasis is on extracting position information, but the board they use apparently also provides information on the offset of its internal 8 MHz oscillator, as measured using the LORAN pulses. Those pulses are derived from an atomic clock, and the internal oscillator sample is available to the outside world. So, there’s a possible means to discipline a local frequency standard. If the pulse train clock itself were available, we could phase lock to it directly. While your columnist has the specs for LORAN signals, I have no practical experience with the receiver circuitry. Can any of our readers enlighten us further? Now To The Mailbag . . . • Bart Prater (VA, N4ZV, Smith Mtn. Lake, VA) has two changes to his LowFER this month. Formerly XA, it will now sign VA in parallel with its MF counterpart. And, he has moved it to 188.700 to dodge a PLC on the old frequency. No LowFERs heard so far this season, but LF generally seems in good shape for this early in the year. Bart is one of several correspondents this month who express interest in transmitting loops. (See also the letters from Tim Brannon and Todd Roberts, below.) Bart suggests possibly using old hard line, or even RG-8 as the conductor. • Rick Wright (KA5YWH, ex-1SUN, now R; Durant, OK) changed his beacons’ calls to R because of needing their keying computer for another project this season. Everything else remains the same. Rick reports: “I've been invited to speak again at the Lake Texoma Hamarama, and I note that audiences of 15-30 attend my LF presentations. This shows at least a passing interest in LF among hams, and they certainly pick up the freebies that I lay out. I usually hold a demo of LF receiving techniques, using my beacon and TEXAS as the targets. It is no accident that the two local beacons are near each other in frequency - I did that to aid Bill Bowers and also for my Hamarama demos. “This has been a good summer. I actually got a chance to build some LF circuits, all while my funded (chemistry) research projects at the university produced interesting and publishable results . We've also had quite a parcel of the public in our driveway observing Jupiter's impact scars with my 10 inch Newtonian telescope during July's big event - kids and grown-ups alike.” • David W. Johnson (XP, WA4NID; Alpine Rd., Durham, NC; email: djohnson@acpub.duke.edu; packet WA4NID@KB4WGA.NC.USA.NA) has this to say: “Last time I reported on the new location (a house!) and my plans. Finally I am announcing a new beacon on the air. This one is MW, on 1675 kHz CW, call is XP (in honor of my wife, Xiao-ping).The beacon is the 4024/4011/BS170 design from Ken Cornell. I hope to improve the ERP in weeks ahead by adjustments in the antennaloading circuit. The frequency may not be the best, but any changes will be reported to THE LOWDOWN. I plan to operate this beacon 24 hours, except for use in QSOs and adjustments.I have been promoting longwave and Part 15 operation to the hamclubs in the area, and have found several people interested. Hopefully we will get several on the air soon in the Triangle area.” The next step, Dave says, is an LF beacon. The circuitry has been built and partially tested, and progress proceeds slowly on the antenna. It may be on the air some time this month. He concludes: “My new inverted L antenna for160 meters seems to work well, and holds promise for winter QRP DX activities on the ham "top band". Best wishes to all the LWCA gang!” • John Kepner (WD6DFG, Charleston, WV) is a new member who asks “what would be the best way for a off the shelf ham to get started in the 1750 and medfer bands... I have available a TS-430s as a receiver but plan on a transmitter and beacon within the next year.” He can be reached via the Longwave BBS, or on e-mail at Compuserve 75266,760. • Tim Brannon (KF5CQ, Dallas, TX) enquires: “With all the enthusiastic reviews in the ham magazines about those small loop antennas from AEA and MFJ, I wonder how successful this approach would be for transmitting at 1750 meters. This might be an interesting project for guys like me who are living in apartments or on small lots.” Any comments, folks? Also, Tim would appreciate your thoughts on receivers. “From reading the loggings column in the Lowdown, I see lots of people using ham rigs as their LF receivers, but I also have seen comments from guys saying that many transceivers are not very sensitive in the LF range. I use a converter now with an old Yaesu receiver, but I plan to buy a new transceiver this fall--something like a TS-450 or same price range. Can anyone tell me their experience with these radios at LF. Are there any real standouts, or any real "dogs" to avoid?” • David Jones (1600 Hilton Ave., Columbus, GA) reports hearing ABC on 1677 so far this season, but hasn’t heard my MedFER yet. At the low end of the spectrum, David was using his whistler receiver at the time of the comet collisions with Jupiter, and encountered “two weak whooshy whistlers” at 0726:56 and 0727:17 UTC on the day fragment G hit, and sent a tape to a ham in Atlanta who has primarily been collecting 20-30 MHz emissions. It’s hard to say if the whistler emission resulted from the crash, but “Tom says the accuracy is now plus or minus six minutes.” David will send a copy of the recording to anyone who might be able to shed more light on sferics. • John Lyman (TAL, Tacoma, WA) expresses hope that your columnist has been able to avoid all the “floods...lightning, fire ants, plagues, famine and everything else hitting the Southeast this year.” (Actually, famine is about the only thing that hasn’t struck, and it’s the one thing on the list that would probably be good for me in small doses. However, with a new car payment to make now, localized famine may be a possibility this winter!) John’s winter schedule for TAL will continue as 0000 Friday to 1200 Monday, with intermittent weekday operation. He says the antenna has been moved farther from power lines, but time hasn’t permitted a top-hat yet. “Word is the ‘monsoon season’ is coming earlier this year, so I’ve got house repairs, etc., to do before then.” For beacon information or to schedule additional hours, you can fax John at (206) 472-0579. • Lyle Koehler (LEK/MIN, KØLR, Aitkin, MN) sent an article updating his complementary-pair final amplifier circuit from last fall. While it has been reliable in LF applications, MF performance “turns out to be marginal at best. Fortunately it doesn't take much modification to make it work right.” The update may appear elsewhere in this issue. Lyle has considerable news from the north. “We've already had one night of temperatures near the freezing mark, and thoughts of LowFER projects are starting to surface again after the summer doldrums. I've downloaded Bill de Carle's latest COHERENT software and am anxious to try copying Max Carter's signal when the QRN lets up. It's going to be tough setting and holding 1-Hz accuracy with my current setup, and a whole new receiving system may be needed to copy coherent BPSK. Looks like a good winter project. “Bad news department: Carl, WØMCN has moved to a townhouse and CRL is permanently off the air. LEK's crystal-controlled exciter still hasn't been repaired after a lightning hit. My beacon is still on almost full time but is VFO somewhere around 186.9 kHz, sometimes identifying as LEK but more often as MIN. “Good news: Just got a note from my son, Bruce, telling about a new LowFER antenna at his lake cabin in Shell Lake, WI. I heard his beacon signal BK (97 miles away) yesterday afternoon and again this morning at RST 489 through the static crashes. He's using a windsurfer mast about 18 feet long with a 3-foot wooden extension and a 4-foot top hat, all mounted on the roof of a 10-foot high storage building. Presently his ground system is just the power-supply ground. He plans to extend the vertical part of the antenna by a few feet and improve his ground system before winter. Right now BK is operating intermittently on about 187.46 kHz, weekends only. Bruce is considering full-time operation after the end of the thunderstorm season. Maybe we'll have a Wisconsin station to add to the list.” (Note: For computer buffs with sound cards, the BBS contains a file called BK.WAV, which Lyle recorded during that session.) He reports a new Timewave DSP-59+ audio filter “provides some improvement over my IC-751A receiver when picking signals out of the QRN, and should really help in separating weak signals from nearby interfering carriers this winter. Another addition is a Soundblaster 16 card, which I hope to use with some spectrum-analysis software for quick scans of LF and MF frequencies.” • Todd Roberts (ABC, WD4NGG, Hilton Head Island, SC) has been experimenting with improved drive for LF and MF final amplifiers. The project began as a way to feed FET finals via a 50-foot run of coax, but evolved into a quest for maximum efficiency as well. The solution wouldn’t be ideal for someone on a critical battery drain budget; but if sufficient current is available, the method provides truly stunning efficiencies by switching the FET rapidly and cleanly for true Class D or E mode. Todd will fill you in on the details soon. He has also been experimenting with a transmitting loop antenna on MF, according to Bart Prater (VA). The regular vertical is on 1643.5 kHz, while the loop is on 1677.5. I’ve heard both frequencies well here in Georgia. Bart says both have been Q5 there, and the different radiation angles cause one signal to fade as the other one builds. Whistler Receiver Update The whistler receiver design presented last month generated some interest among readers and BBS users, for which I am grateful. There is one small correction, and some optional modifications. The correction involves replacing the 82 pf capacitor in the first stage with a 120 or 150 pf capacitor. It’s not absolutely essential to make this change, but it does reduce the Omega tones. Nor are the clamping diodes in the first stage necessary if one is using a whip antenna and avoiding storms, but they’re handy under other circumstances. If you plan to use the receiver with a long antenna, it will be desirable to reduce the terminating impedance. This could be done by decreasing the 3.3 M and 10 M fixed resistors and raising the value of the 150 and 470 pf capacitors, but it’s a lot easier to add a pot at the input, as shown at right. The pot also makes allowance for the likelihood of antennas having different lengths and elevations. Use an insulated shaft, if feasible. Other variations are possible. Your comments and questions will be welcomed, as always. (The file WHISTLER.ZIP contains the full updated text and pictures.) Til next month, 73... • • • - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - WANT TO TRADE: Near-mint RAK-7 with power supply and photo-copied manual, for Collins R-389 or other tube type VLF receiver. Dave Simpson, N2ZWX (315) 446-1258 after 7:30 PM.