The Notebook The Mailbag, News and Comments About LF Radio & Other Experimental Topics John H. 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 "Oh, the weather outside is frightful..." The chorus of the song, I believe, is "let it snow, let it snow, let it snow." It certainly did that last month in some parts of the country...while elsewhere, it was floods, tornados, and the ever-popular lightning. As an example, on January 19, Atlanta had hail and high winds; while central Missouri, around where I went to college, was having 12 - 20 inch snowfalls. Early in the month, we usually have our first serious winter here, but the temperatures warmed up to the 60s. About Christmas time, Brice Anderson sent tongue in cheek greetings: "don't fall down in the snow and ice!" It was 42 deg. F there on the morning of Christmas Eve. But about when we in the South normally expect our late January thaw, lows started heading back to the 20s...I hope only briefly. The early warmth has its down side with all the moisture that's available for storms. Severe lightning caused problems in my neighborhood on January 6, possibly including a house fire. It got both my LF and MF transmitters and the keyer they share. The LowFER is self-contained at the base of its antenna in the present configuration, and sustained minimal damage, although the press of time kept it off about two weeks. The MedFER took a little over three weeks, and involved both the final and exciter. I don't think a single P-N junction or MOS gate in the whole thing survived. I console myself with the thought that few people could have heard it through the QRN had it been on most of that time anyway. Maybe we'll be blessed with a semblance of authentic winter this month. Then again, we don't want to overdo it. Hope springs eternal. Bye, Bye, SoftWave One of the most intriguing first-of-its-kind products appears, sadly, to no longer be with us. Back in early autumn, this column mentioned the Soft- Wave receiver, a hardware and software combination that functioned as a short- wave radio. It was more than just an interface for controlling a radio from a personal computer, though. The front end of the receiver was outside the computer, while a card containing digital signal processing and demodulation (at the second IF frequency) fit inside the PC. It was priced about $1,500. Within weeks, alarming messages started appearing on BBSes and online services. Interested potential customers were having trouble reaching the toll-free number. Some actual customers were wondering how to get upgrades to use a number of the advertised demodulation and decoding features; apparently not all the software had been written at that point. There was briefly hope for reorganization of the company. By the end of the year, though, a certain finality settled over the matter. I talked with the folks at Universal Radio, whose new catalog lists the SoftWave, and they confirmed the company had closed its doors, leaving them with one in stock and little or no prospect for technical support. It's always sad to see promising ideas expire before they have a chance to prove themselves. The time will come, though. I believe I read that Watkins-Johnson has a DSP receiver on the market for about $4,000 now, though I understand the dynamic range is still not quite up to analog standards for that price range.* Improvement will occur rapidly, in terms of both perform- ance and price. We can bet on that. (*Afterword: Reader John Reed pointed out to me some rather good RF performance specs for the Watkins-Johnson HF-1000. I now believe the article I read may have been referring to the number of bits in the A/D conversion, which would affect precision of digital signal processing functions, NOT translate to RF dynamic range performance.) Periodical Shelf Plus This section once again has "plus" appended, because some of the material is catalogs and marginally-periodical periodicals. The "plus" is also appropriate because we've incorporated our "Cosmic Connection" thread into it for this month. * Some of the upward-lightning material cited last month seemed to indicate these discharges do not produce spherics, but might have something to do with coupling the energy of lightning strikes into the magnetospheric duct where whistlers are formed. One of the articles we reference this month suggests a more direct causality. David Jones found the citation and sent me a copy of the article, which I will forward to Dan Levit for further digestion and comment. In case you have a scientific or engineering library accessible, it is: Hoffman, W. C., "The current-jet hypothesis of whistler generation," J. Geophys. Res., 65,2047-2054,1960. * That article dates back a bit, and I don't know how much credence is currently given to the theory. However, present day research indicates at least the "red sprite" discharges do produce radio emission. That's one of the observations of the University of Alaska team during their summer flights over the Midwest. They describe the sound over a loudspeaker as a "pop" that's distinctly different from regular lightning discharges. The November, 1994, issue of Striking News, just out, has a front-page feature with photos and background information. Contact PolyPhaser Corporation at (702) 782-2511 for a free copy. * Popular Communications for February mentions The LOWDOWN and the drift- net buoy issue in Don Schimmel's "Communications Confidential" column. * The 1995 Universal Radio catalog ($1, 6830 Americana Parkway, Reynoldsburg, OH 43068), as always, contains quite a few items of interest to SWLs and utility DXers, but it seems to me there's more for hams this year too. One product category that caught my attention is antenna distribution amplifiers for driving different receivers from the same broadband antenna. They might not be that useful for longwave work, but would be handy in many receiving applications. However, they are over $200. Active builders might want to consider the item below. * The current Comlinear op amp Data Book contains specs and application notes for a wide range of fascinating devices, including their series of current-feedback op amps. We will try to have a tutorial on these fascinating devices sometime this spring. They bring the advantages of op amps (ease of use, low distortion, precisely defined gain) to RF work. One of the latest types is the CLC449, which has a 1.2 GHz small signal bandwidth, and can be used to drive 50 or 75 ohm transmission lines! ("Small signal" in this case means 0.2 Vp-p. For 2 Vp-p, the bandwidth is still 500 MHz, and the device can slew 2,000 V/us.) This is one chip I'd like to try in an all-purpose distribution amplifier. It could handle everything from audio to video to UHF. Unlike conventional op amps, current-feedback amplifiers do not have a rigid gain-bandwidth trade off. If a conventional chip has a -3 dB point of 200 kHz at unity gain, it will have -3 dB response at 20 kHz in a x10 gain circuit. The properties of a current-feedback op amp, however, are determined mainly by the size of the feedback resistor, and the gain-vs-response effect is about an order of magnitude less. Some other salient specs for the CLC449 (Vcc=+/-5 V, A=2, Load=100 ohms): 3rd order intercept at 70 MHz, 30 dBm; 1 dB compression, 16 dBm; distortion for 2 Vp-p output at 5 MHz, -63 dB 2nd harmonic, -84 dB 3rd harmonic (some deterioration at higher frequencies); non-inverting equivalent input noise, 2 nV/(Sq-rt Hz) (voltage) or 3 pA/(Sq-rt Hz) (current). It can also operate from a single-ended 10 volt supply. I don't have the list of Comlinear distributors handy at the moment, but it will be available through most industrial suppliers; that is, it may not be easy to get in one or two piece quantities. I mainly cite the CLC449 as an example of technology now on the market that we might find useful. A balanced-input preamp for a receiving loop antenna springs to mind. (As you saw in Dan Levit's Natural Radio column last time, instrumentation amplifier ICs make good candidates for such applications, too.) Other products in the Comlinear book also blur the old lines between op amps and specifically designed RF amplifiers. The CLC111 is an 800 MHz closed- loop buffer for video switch buffers, HF active filters, high speed peak detection, etc. The CLC431 and CLC432 dual wideband op amps (62 MHz) are suited for differential applications. The CLC425 is an ultra-low-noise voltage-feedback type with a 1.9 GHz GBW and 1.05 nV/ÖHz input noise voltage, suited for professional audio and low-noise RF amplifiers, with voltage gains of X10 or higher. For information, contact Comlinear Corporation at 4800 Wheaton Drive, Fort Collins, CO, 80525, or (800) 776-0500. The Mailbag * Brice Anderson (BA, IE, Lancaster, IL) sends his usual fine report. He received a visit late last month from Bill Thomas (AL, KC9AL, St. Louis). "We had more to talk over than there was time for. I showed Bill my latest LF antenna and the MF antenna. We are anxious to have a QSO, but Bill's QTH is too noisy, even with a loop. XJ is also anxious to have a QSO with AL." Brice has been trying for my SEA, but says the entire band below 182 kHz is filled with S9-level broadband trash at night there. He has also been listening for JDH (John Hoopes, back on the air from Georgia), but without success so far. I've been hoping for some time to describe Brice's LF antenna system, and this may be our chance. The problem he faced was being able to erect some- thing taller than the 28-foot pole of the past two seasons, while being prohibited from lifting any significant weight. The solution turned out to be 35 feet of 2-inch Schedule 40 PVC pipe. A compound pulley and rope system allowed him to pull up the PVC pipe mast. Four sets of guys keep it in place, broken up with insulators every 25 feet. A pulley at the top suspends a continuous loop of nylon rope, which in turn supports the vertical run of #14 stranded wire. This allows for con- veniently raising the vertical run and top hat wires from the ground, and lowering them in the event of an ice storm or if additional work is needed. Eleven top hat radials have been installed, though they were not present when the photo on the next page was taken. They are #18 wire, and extend at an angle of about 60 deg. from the vertical. Brice performed the final tuneup on October 29, having been able to reduce the antenna coil inductance significantly compared to the previous antenna. It loads with 140 ma of rf antenna current at 900 milliwatts to the final. The basic ground system is 16 buried radials, 16 on the surface, and two ground rods. The surface system is quite extensive ("several thousand feet"), but by early December, Brice's experiments convinced him that was unnecessary at his QTH. He is able to disconnect the surface radial system at will, and finds the antenna current doesn't change at all and the field strength meter in the shack remains constant, too. He notes that Bill Diggins (8LXJ) had similar results on an expedition to Kentucky and Tennessee a few years ago. Apparently, Ohio is also blessed with conductive soil at LF, for Brice says YHO has no room for radials and uses ground rods. Both BA and YHO are known for their excellent coverage, so there must be something to the notion. He is quick to point out that option may not hold true for all soil and all instal- lations. (In the South, "ground wave" is synonymous with "line of sight." Here at SEA, I made major improvements to the top hat of my antenna over the holidays, requiring extensive retuning...but the antenna current didn't budge. In this case, the antenna impedance has obviously changed, so I suspect my ground system was woefully lossy, absorbing the difference. The roll of chicken wire fence I formerly used to supplement the radials is about rusted away! Time to spend a few bucks more.) Moral: Start with a modest ground system, but one you can add to until you enter the region of dimishing returns. * Lyle Koehler (LEK, MIN, K0LR; Aitkin, MN) notes: "XJ and I had QSOs on December 15, 16, 30 and 31, and on January 1, 2, 3, 4, 5, and 9. The flurry of QSOs with XJ starting December 30 was made possible when he began a regular schedule of running his beacon for 5 minutes before the hour and then calling CQ on the hour. On some evenings we had two or three QSOs at 1-hour intervals. The total XJ-LEK QSO count for this season now stands somewhere around 24." On MF, he describes conditions during the past month ranging from very good to very poor. Lyle says he appreciated the article by Bill Bowers on varactor diodes. "It answered some questions I had about their Q and the effect of using two diodes back-to-back. There is probably another advantage to using a back-to- back pair in remote tuning applications. The change in capacitance across the circuit during large signal swings is mostly cancelled because the signal voltage changes the bias on the two diodes in opposite directions. This should minimize intermodulation products from strong signals. I use three MVAM109s in parallel in my remote-tuned LF preamp. Out here in the boondocks you can get by with that because there's only one AM broadcast station within about 35 miles. In the city I'd probably hear a wash of broadcast station intermod." * Doug Williams (OER, Watauga, TN) is one who wishes for more seasonal conditions. "I stayed up late to listen for Lowfers tonight (Jan. 13) but the static level here is 10db over S9 so no luck there. The temp outside is a balmy 55 F. When is winter going to arrive? On 1-9-95 I heard WI and KRY. KRY was really booming in. I was able to copy his entire transmission, including his full QSL address, after only a couple of repeats. The last time I heard KRY was in 1992 (a good year). I heard KRY again on 1-11-95 (but not as strong), also WI, and, for the first time ever, XJ. XJ started out weak, and after about five minutes really started booming in, only to fade out again about ten minutes later." Doug reports building a new beacon keyer for OER using the design by Scott Edwards (73 magazine, June '94) and "it works great." His most recent project is a regenerative preamp from the latest Ken Cornell Low & Medium Frequency Scrapbook. "Far Circuits sells PC boards for this one for those of us (like me) who don't like to breadboard....I completed the renerative preamp and am still testing it. I can tell you that it is very selective and requires a fine touch on the controls." * Cliff Buttschardt (C, W6HDO, Morro Bay, CA) sent a nice letter with his beacon update. Cliff has been a merchant marine radio operator since retiring as a teacher, and has been at sea for prolonged periods over the past several years. He says "that is to come to a halt, however, as it appears Chevron is terminating the American ships with the American operators." The C beacon is normally on 187.65, but has operated on the alternate 166.666... frequency with BPSK quite a bit this season. (It's off sometimes for 160 meter contests.) "At this point there seems little reason to continue with the older means of communications as there are few that care to dig using old fashioned CW. Not that I bemoan the passing of an era, but rather the advent of DSP has far exceeded the results gotten from the 'HDO audio filter' that seemed so good just five years ago. Max Carter has aided in digital communications, and the Los Angeles group continues with faster speeds using AMTOR and similar FSK techniques. Also, with three experimenters moving out of the central California area, and Mike Mideke and Jim Ericson already in new locations, there are no CW beacons left." Cliff acknowledges the work of Dave Curry and Bill de Carle in making modern equipment and techniques available to the rest of us, noting "Coherent CW...far exceeds expectations. Dave and Bill deserve much support." He also sent along details of the C transmitter site. Watch for these next time. (AFTERWORD: Probably in the April edition.) * Dexter McIntyre (WA4ZIA, 16164 Pless Mill Road, Stanfield, N.C. 28163) writes: "I have had an interest in LW for many years. Built beacon xmtter around 1970 but never did much with it. Having recently seen the article in CQ, I joined the Longwave Club and recently got first newsletter. Was surprised and pleased to see well organized activity. I built a tuned loop and am receiving WI from Pickens, SC, very well. Have even heard it during daylight a time or two. It is very Q5 about 95% of the time. Heard the operator at the key Monday evening (12/26) and tried to get my xmitter on line but missed him. My original was xtal controlled, and found the xtal to be broken. I can transmit with a HP signal generator which I modified for keying. Will try to get an amp going for it. I have a 50 ft. vertical above a metal building for transmit. My QTH is 27 miles East of downtown Charlotte, 136 miles from WI." * I hear that David Jones (Columbus, GA) paid a visit to John Hoopes's JDH at his new QTH in December. Bonaire is a small spot in the road south of Warner Robins, Georgia, where John used to be stationed. (Actually, sub- divisions and school construction are causing the area to grow pretty rapidly.) David got to see the transmitter in operation, and stopped along the road several times on his way back home to listen with his bamboo pole antenna and regen receiver. He picked up the signal to about 70 miles out with that setup. * Robert L. Laney (RL, WB7PZU 3153 Southfield Drive, Herndon, VA 22071- 1910) is "happy to report that I have my Lowfer antenna up and have made some trial transmissions. Have made trials on 186.59 kHz, but there seems to be some peroidic warbling signals near this frequency. I have another crystal to work 188.59 so may be trying this frequency part of the time as well. I guess that my operation for the moment will be intermittent because I have yet to get a weather-proof container to locate the amplifier at the base of the antenna. In addition, I think that I have a lot of experimenting to do to get the most out of the system." "The antenna is a 35-foot Radio Shack telescoping TV mast with a 5 foot extension of 3/4-inch copper pipe, upon which is a top hat consisting of 4, 10-foot copper radials. The mast is insulated from the ground with a Moose- head beer bottle (Widely reputed to have excellent dielectric properties after proper preparation; namely, draining of the somewhat conductive liquid content.—Ed.) that rests on a block of pressure-treated wood. To assure good electrical properties, the top 5 feet of copper pipe are soldered to 3 no. 10 copper wires that are distributed down the steel mast and joined together at the bottom. The wires are held to the steel mast with stainless steel hose clamps. In addition, the overlapping sections of steel mast and the steel mast and copper extension are joined with stainless steel screws." "All the components--the power supply, exciter, keyer, and amplifier-- were constructed from Ken Cornell's scrapbook, with virtually no problems getting the equipment to work. I think that his books have been a major influence on my 'getting serious' about this rather dubious activity." * George M. Jacob (GIR, KA3GIR, New Eagle, PA) reports this season that he kept GIR on the air last summer, and plans to do so until further notice. As of December, the season was off to a slow start in western Pennsylvania. "I guess the mild weather doesn't promote LowFER work, since it is not the same when you don't have to crunch through the snow to get to the antenna and freeze your hands while you get little RF burns peppering your thumb and forefinger as you tune for maximum smoke. I have been trying to get my antenna system tuned down to 50 ohms for months now, 10 minutes at a time.... Still have open coils with clip leads on them connecting the system together!" The plan is to achieve a better match to the receiver and accomodate 50 ohm test equipment. The present 300 ohms is an improvement from the earlier 1,300 ohms. George would like "to say hello to all those who keep on listening and trying to modify their systems to promote use of the band. I have a few left I will try to hear. Hope to try some new techniques this year to dig those signals out of the mud. I heard lots of good signals last year, but the band was open. No fun! I want to hear them when the band isn't open, but our local power company is determined to prevent that." * Sam Eastey Sr. (SAM, W0IMG, Crystal, MN) included a note with his beacon update that I meant to use last time. He reports Lyle Crivits (K0FTI) regularly monitors 1750 meters, and "on December 8 or 9, at about 2:00 pm on 186.66 (just below LEK) heard a beacon FK with a series of dots between identification. He usually hears LK, BK, and ART. * Bill de Carle (2IQ, VE2IQ, St-Adolphe d'Howard, QC) reports no QSLs yet, and offers the thought, "We need more people out there with good receivers and copies of the COHERENT program. MAX has done a miracle with a new design for an excellent lowfer receiver that works with my ADC/software. It should be a terrific performer and also quite inexpensive." * Bill Thomas (AL, KC9AL, St. Louis) was still waiting for the arrival of winter when I received his letter last month, "to get rid of moisture on the transmit antenna and also to rid us of the thunderstorms." Like many folks, he finds conditions not quite up to last year. As we reported earlier, he has gone to VFO operation. This was done to avoid a carrier near the old frequency (186.25). The VFO seems pretty stable and has only a slight chirp. "It's worth the ability to move to any frequency," he adds. * Fred Larrick (FL, N3FL, Silver Spring, MD) sent word of his new LoMedFER beacon on 512.5 kHz last time. It was operating with a VFO when it went on the air, but a crystal was in the plans. Fred describes the antenna as a "center fed (vertical) dipole with top and bottom hats, located in the attic of my house. The loading coil is a ferrite core which allows quick adjustment after changes are made to the top/bottom hats. When the final configuration is reached, the ferrite coil will be replaced with a high-Q air- core coil. Thus far I have copied the beacon in my car at a distance of 15 airline miles (outside the office building where I work). I expect a major improvement when the ferrite core inductor is replaced with an air core coil." * Bart Prater (VA, N4ZV, Moneta, VA) is another LowFER operator taking the VFO route this year because of QRM on his previous frequency. "Actually, it's been kind of interesting wandering around the band." The VFO oscillates in the 6 MHz range, and its output is fed to a divide-by-32 chip in the roof- top final. The divider provides a clean drive waveform for the IRF-510 final. Bart reports the system holds within 10 Hz..."good enough for aural work and cheaper than all those crystals." Til next month, 73. . . .