THE LF NOTEBOOK (#28) From the July, 1995, LOWDOWN The Mailbag, News and Comments About LF Radio & Other Experimental Topics John H. Davis, PO Box 367, Warm Springs, GA 31830 -E-mail: johnhdavis@aol.com -Fax: (706) 672-0964 or 655-2627 IT'S AMERICA'S BIRTHDAY once again, and I hope you'll be having a safe and joyous holiday when this issue arrives. It almost goes without saying that LowFERing is not high on everyone's priority at this time of year. But in between lawn mowing, weeding, and dodging the scorching rays of the sun, maybe there'll be a little time for antenna building, or whistler hunting, or equipment construction, or article writing. (The latter two sound particular- ly appealing to me, provided they can be conducted in front of the business end of an effective air conditioner.) As you probably know, the hurricane season got off to a prompt start this year. I haven't heard from our Florida panhandle members since Allison came through, but I hope everyone was far enough inland, or far enough from land- fall, not to have encountered too many problems. Unlike last year, the remains of the storm were the answer to our prayers in west Georgia. A full 24 hours of gentle, soaking rain restored the countryside from late summer brown to its normal shade of early summer green. In the weeks since then, we've had more lightning than rain, but even that is better than the drought of May. If we could just share some of what the central states have had to put up with.... Another good thing about this past month--we've avoided most of the usual summer drought of correspondence! Thanks, everyone. Keep up the good work. Temporary BBS and answering machine suspension. I hate to complicate the process of communicating with this column, even temporarily, but it will be necessary to make some changes to the phone lines serving the BBS and fax/ answering machine. Right now, the answering machine functions are not working, and haven't been reliable for some time. It is being taken out of service for repair. Only facsimile will be available during July and August. If you are unable to get the fax to answer on (706) 672-0964, please use (706) 655-2627. (Fax is usually the most reliable way of getting a message to my attention in reasonable time, but computer fax programs don't always want to transmit to a physical fax machine. Or, sometimes they'll seem to send a page, but what arrives is either blank or just a single black bar along the side. That happened to a fax of unknown origin in early June, so if I haven't answered you yet, that's why...you were the Unknown Faxer.) The Longwave BBS will be kept in service through July 15, then will shut down for an indeterminate length of time. Please be sure to check in before then, especially if you have been using the e-mail services. When the BBS and voice/fax lines return to service, we may have new telephone numbers. Be sure to watch this space in August or September for word. One featured file this month is CCW.ZIP, containing a shareware program based on the VE2IQ COHERENT software and using the same A/D interface. It was written by Ernst Schroder, DJ7HS, with an introduction by Peter Lumb. The chief difference is this program accommodates a number of audio center frequencies and data rates, which may be a blessing or a complication, depending on your situation. A slight change in software distribution. Last time I mentioned anyone wanting software from the BBS copied directly onto disk should not send a donation larger than $3. I'll amend that to $5 for overseas service, since it's probably not feasible to send a full-fledged return mailer with your request, and postage is (lots) higher. If the particular software is shareware with a distribution charge limit, I'll refund the excess in some suitable manner. Periodical shelf. I don't often buy Popular Electronics these days, but I found the August, 1995, issue to contain an interesting article by Karl T. Thurber, Jr., entitled "Long-Delayed Echoes: Fact or Fancy." It's a longer feature than PE customarily indulges in. I'm not sure how many of the theories for the phenomenon are still considered plausible. Still, it may be of interest to our readers, in part because of a mention of magnetospheric ducting and natural radio phenomena, and because of a good list of recommended reading to be found in the piece. The EMF exposure controversy was reactivated somewhat in recent months. (I cringe at the term "electromagnetic fields." I know how to detect an electric field, a magnetic field, and an electromagnetic wave...but I'm not quite sure, from a physics point of view, what an "electromagnetic field" is. Maybe the summer heat is making me too fussy and particular.) The Council of the American Physical Society (APS) this spring issued the results of a study entitled ''Power Line Fields and Public Health,'' mainly pertaining to the hypothesized dangers of cancer from fields associated with power lines and electrical appliances. Then, on June 13, the Frontline documentary series on PBS examined the matter, too. I was a bit concerned at first, when it appeared the program was taking an alarmist tone, but it turned out to be a well balanced presenta- tion. Interviewed were families who believe their children may have con- tracted cancer from exposure to power lines, and Paul Brodeur, whose New Yorker articles played a major role in bringing the question to public scrutiny. (Alas, it appears to me Brodeur has abandoned the journalist's role for that of advocate. Of the APS's study, he agitatedly asserted that physicists have no place in the debate, and accused studies that don't support a cancer link of being part of an industry-government cover-up.) The program also showed how certain fallacies of statistical analysis can suggest connections that aren't supported by broader data, and looked at the contradictory studies. It appears, for instance, at least some of the experimental results suggesting cellular chemistry changes cannot be duplica- ted by other labs. And, upon review, it appears some of the occupational hazard studies have been seriously flawed, even to the extent of misidentifying telephone employees as linemen, when they were actually office workers. (I did not tape the program, unfortunately, so I do not know at this writing whether a transcript is available. I'll try to find out by next issue.) The American Physical Society Panel on Public Affairs did not conduct a new study, as such, but reviewed previous reviews of the literature, examined epidemiological data, looked at several selected and suggested papers, and interviewed a number of experts. Their background paper draws a general conclusion, reproduced in part: " The scientific literature and the reports of review panels show no consistent, significant link between cancer and the 60-Hz ELF fields. This literature includes epidemiological studies, research on biological systems, and the analyses of theoretical mechanisms....The preponderance of the... findings have failed to substantiate those studies that have reported specific adverse health effects from exposure to 60 Hz ELFs. It is always possible that some minor carcinogenic connection might be found, but the present data do not establish that connection. For expenditures for mitigation to be justified, there should be some consistent, meaningful combination of the following factors: (a) A plausible coupling mechanism at the cellular level exists, (b) the coupling must produce consistent biochemical changes, (c) the biochemical changes must be detrimental, (d) meaningful epidemiological data should determine the degree of danger, and finally, (e) upper-bound EMF mitigation costs should be comparable to those for other dangers mitigated in society. The current level of spending for ELF mitigation is more than a billion dollars a year, an amount which clearly cannot be justified on the basis of applying the above criteria to the data. This spending has been driven by the combination of unlimited 'prudent avoidance' in a fearful society." A summary, and a background report by David Hafemeister of CalPoly, are available on the World Wide Web through the APS home page at: http://aps.org, under Recent Additions. I wasn't able to get the entire document in one connection. (Commentary:) Personally, I find the emphasis on money in the APS conclusion a bit disconcerting. Still, there's apparently reason to be skeptical of of an ELF-cancer connection at this time. A seeming correlation at one site isn't matched by a correlation at many similar sites; an experiment that produces corroborating evidence at one lab isn't confirmed by similar experiments elsewhere; and it's almost impossible for occupational epidemiological studies to distinguish between potential exposure hazards. (How many power company linemen have no exposure to creosote, or PCB transformer oil, or hydraulic fluid? How many repair technicians have no exposure to lead fumes, contact cleaner solvents, or smoke from burnt plastic insulation? Effects of these factors may be much stronger than magnetic fields.) The APS review also only considered 60 Hz fields. Many of us work with RF, ranging from VLF to microwaves, for which credible authorities have established exposure guidelines. So what are most people to believe? After all, we live in a society that simultaneously accepts such fuzzy notions as "crystal power" and "channeling" on the one hand, and on the other expects science to be precise, definite and accurate in all things at all times. I call this latter the Star Trek Syndrome. Typical scene: (SOUND EFFECT: "Red Alert" klaxon.) COMPUTER: Warning! Radiation will reach fatal levels in two minutes! SCOTT: Sir-rr, I canna fabricate a proper shield to enclose the whole ship in less than three minutes, maybe four. SPOCK: Mr. Scott, if you can cease being emotional for a moment, may I suggest you modify the Framistat Probe to reverse the flow in the Doubletalk Generator. SCOTT: Aye, the Roddenberry-Berman Technique. But that's only a theory, Mr. Spock. KIRK: I suggest you try to make it a reality, Scotty. (EFFECT: Sudden attack by Romulans causes camera to shake. Bridge crew falls down to the left, then to the right, for 90 seconds.) COMPUTER: Radiation levels rising. Your goose will be cooked in --mark--20 seconds from now. SCOTT: Bridge, if I turn this thing on, it could blow us all to bits. SPOCK: Mr. Scott, in 11-point-3579545 seconds, it won't matter. COMPUTER: If I were you, I'd be saying my prayers. 10...9...8... KIRK: (Dramatic lighting effect on eyes, overacting) Sometime today, if you please, Mr. Scott. COMPUTER: Bye, y'all...3...2... (EFFECT: Flicker of lights, accompanied by "zap" sound, then klaxon stops. Crew cheers.) COMPUTER: Radiation within normal limits. All decks report no injuries or or side effects, except strained credulity. Now safe to initiate sponsor's commercial message. The public likes issues that are clearly yes/no, black/white, go/no go, definitely fatal or absolutely harmless. It's the maybes and percentages that turn them off. Just speaking for myself, I'm not going to be overly concerned about ELF...although I am sitting in front of a computer monitor that complies with the Swedish magnetic field standard. Nothing wrong with a moderate amount of prudence, I always say. What's your view? On To The Mailbag - Lyle Koehler (LEK, K0LR; Aitkin, MN) reports "LowFER activity is well into the summer doldrums. I still hear BK on weekends (when the QRN isn't 20 dB over S9). One pleasant surprise came last week when I was testing a home brew 10-watt transmitter on 40 meter CW and ran into Brice, W9PNE. We had a pleasant chat and compared notes on lousy LF conditions. Well, as we say in Minnesota, 'If Summer comes, can Winter be far behind?'" Lyle had some comments on the McCallie "compatible double sideband modulator" in the May, 1995, Lowdown. "The way the author described the operation of the circuit, I couldn't see how it would provide true DSB modulation. So I breadboarded the circuit and used a scope to try to see what's really happening. When I first hooked it up, I didn't have much RF drive on the transistor base, and RF was present at the output only on negative swings of the audio signal. As I cranked up the drive, the scope pattern started looking like a DSB modulated signal, although one half of the cycle was pretty distorted and there was some carrier present even with no audio." "Here's what seems to be going on in the circuit: On negative swings of the audio signal, the base-collector junction becomes forward biased and acts like a diode switch that connects the RF input to the output. When the collector swings positive, Q1 is an inverting amplifier, and the RF that appears on the output is 180 degrees out of phase with the input. So in fact you do get DSB modulation from the circuit. There is a reasonable amount of carrier suppression*, (with proper adjustment of the RF and audio levels) and the audio sounds fairly good on a SSB receiver despite what it looks like on the scope." *Your columnist does not propose to get embroiled in controversy, but there does seem to be quite a bit of interest in this circuit, so I'll at least venture out to ankle depth in the waters. Lyle analyzes the circuit much as I first did. I said, "Ah, a shunt chopper modulator," when I first saw it. I used a variation on that idea at one time to impress a telemetry signal onto a high audio frequency subcarrier, then demodulated it in a product detector, on the assumption that lack of a steady DC component in the modulating signal was equivalent to carrier suppression. In reality, though, there is a DC component, resulting from the rectified (halfwave) audio in the CDSB circuit. There is also a carrier component. It varies with the modula- ting envelope, and can be seen quite clearly on a spectrum analyzer. Ironically, just about everyone who has had something to say on the subject appears to be right to a substantial extent. Mr. McCallie calls it compatible DSB, and Lyle confirms that it can be received that way. It even looks like DSB on a scope. However, Max Carter also appears to be correct in saying it is supermodulated AM, because that's evident from spectrum analysis. I thought "unidirectional chopper modulator," while Max thought "amplitude modulator." On later reflection, I realized it can also be described as a single-quadrant multiplier. All are the same mathematically, and are fundamentally the same in practice. Anyway, Lyle kindly went on to say, "Of the various schemes for DSB modulation, the one I like best is your high-level, high-efficiency circuit from the November, 1992, and January, 1993, issues of the LOWDOWN. My LowFER transmitter already has an XOR-gate BPSK modulator and would need only a few external components for DSB operation. Maybe when band conditions improve I'll try some DSB transmissions." - Perry F. Crabill, Jr. (W3HQX, 225 Milam Drive, Winchester, VA 22602) took particular interest in the May Lowdown article about data being phase modulated on LW broadcast transmitters, because of an experience some years ago: "My friend Bob Hiltner, W3GHX, lived in Silver Spring, MD, about half a mile from WTOP-AM in Wheaton, which ran 50 kw on 1500 kHz. Bob's amateur band receiver was a Collins 75A4, which featured a tunable first IF which ended at 1500." Tuning the low end of the amateur bands caused the variable IF to tune down to 1500, resulting in interference, so they were experimenting with a tuned trap. "When we used the BFO while making measurements, we observed that WTOP's carrier apparently was being keyed with some sort of frequency shift teletype signal." "After making sure this wasn't some sort of artifact in the receiver, we called our friend Granville "Granny" Klink, W3AFV, WTOP-AM's chief engineer. He verified our findings about the FSK modulation, and said that it was a U.S. government test using standard broadcast teletype communication for some unspecified and probably classified purpose. The agency involved furnished WTOP a special exciter; this was connected to a private phone line that provided the keying information and caused the 1500 kHz carrier to shift plus and minus 19 Hz (within the 20 Hz tolerance allowed AM stations by the FCC). This may have been 25 or 30 years ago, and I don't remember how long the test continued." Perry's letter jogged your columnist's memory a bit. I remember reading about the FSK tests at WTOP, but not what they were being used for at that time. There was speculation that the technique could be used commercially for delivering data services to the home or office, such as stock market quotations and detailed weather forecasts. A predecessor, as it were, of the digital services now being implemented by some AM and FM broadcasters, I suppose. For some years, there were footnotes in the FCC Rules enabling this kind of modulation on AM stations, but apart from some transmitter telemetry, I'm not sure if it was ever used much. Now, AM stereo pilot frequencies are protected, and this may make FSK difficult or impossible on AM. Can anyone shed further light on this? - Tom (Doc) Gruis (D, K0HTF; Des Moines, IA) passed along his e-mail addresses for our reference: docgruis@aol.com, or 76775.424@compuserve.com. He continues to operate LowFER D and amateur radio beacons with his ARS call on various bands. The grid reference there is EN31dx. Doc also would like to be in the sorta-contest I mentioned last time. He writes, tongue in cheek: "I did think of a way for you to postpone things, but don't feel like sending it along yet. Maybe later..." - John Gillespie (55 West 4th St., Hamilton, ON, L9C 3M5) renewed recently, with a note that says, "This club is truly amazing. Each month I'm impressed with news, articles, loggings, and mostly the participation." John recently obtained three portable frequency selective voltmeters, Sierra models 127C and 127A-Y, in good shape. He reports, "They tune down to 0 kHz (or at least 2 kHz), and up to 350 kHz. One is very sensitive, and I am not sure, but I think I am hearing spherics and maybe even super strong whistlers using a 100 foot longwire. The other two need a little TLC, plus adjustments, so I ordered a service manual from Tuckers in Texas." His letter was sent just before the Victoria Day holiday weekend, when he hoped to take the instruments out of town, "and hopefully find a quiet spot to really check things out." - Cecil A. Wadford (RED; RR 4 Box 756E, Chipley, FL 32428) filled us in on his new address this month, though he said RED was still not quite ready to go back on the air. The 50 foot telephone pole for the antenna had been ordered but not yet set when he wrote. "A 20-foot square loop is on the board, made from 4-inch PVC pipe....My BPSK receiver (Max Carter type) is half finished to date." "Receiving on a 3-foot loop at ground level, have been able at times to copy YD in Port St. Joe at 50 air miles, when I get a break in the noise level." Noise has been 30 db over S9 much of the time, but does not seem to be power line or man made. "Even GWEN signals are covered up most of the time." The new QTH is in the outer edge of Wausau, FL, despite the Chipley mailing address, at 30 deg. 38' 30.9" N, 85 deg. 34' 44.2" W. Cecil says "at seventy-three I don't get things done as quick as when I was younger," but hopes to be back on in July. - Don Burns (Plantation, Florida. E-mail:donburns@shadow.net or epur01@ email.mot.com) was glad to hear about the Internet LF activity in the rec.radio.shortwave Usenet area. "I will start monitoring r.r.s. FYI, there is also occasional discussion on the QRP-L mail list." - Harry Waugh (4657 Livingston Avenue, Dallas, TX 75209-6024; tele- phone: (214) 350-8336, FAX (214) 350-0307. E-mail: 73624.63@compuserve.com) describes himself as "one who 'reads the mail' on the LOWDOWN and I really take an interest in it cover to cover." "For many years I have followed developments in spherics and earth phenomena and in particularly in the detection of lightning strikes. There was an old article in Scientific American regarding this. It is so old that the electronics used vacuum tubes. Anyway, the article (Amateur Scientist) described a piece of equipment that would not only detect strikes but would display the event on a cathode ray tube. It would give approximate bearings of the strike in relation to the loop antennas. I always wanted to build one of these things but never got around to it. "Recently a friend demonstrated to me a piece of avionics in his plane that had a CRT and displayed strikes. It presented the information in the form of a dot representing the strike and gave the bearing and distance rela- tive to the nose of the aircraft. I was impressed with the instrument. It was made by 3M and is called 'Stormscope'. "My curiosity has almost consumed me about the workings of this instru- ment. I can see how the bearing of the strike is derived, much like the one in the Scientific American article, I suppose, but as to the distance measuring aspect, I have a hard time with that. Could it be that the processor for the instrument takes the signal and analyses it with respect to high and low frequency content with respect to time and assigns a range figure accordingly? I have noted in monitoring natural radio signals with my 'Inspire' receiver that some of the strikes are pops and some are pings and some are chirps." Your columnist admits to being clueless on the operation of this fascina- ting instrument. Are any of our readers familiar with it, or have any good ideas? - Rob Gill (G8DSU; Twickenham England; email: rob.gill@ps.com) recently braved the hazards of trans-Atlantic phone lines to try to download the spectrogram program from the BBS, but will probably send a disk. He notes, "Obviously transatlantic downloads are not for the faint hearted!" He also sends some good news: "An UK amateur LF allocation seems a little nearer! Last week we heard that the UK Radiocommunications Agency is consider- ing an allocation around 73kHz. Initially it will be available on the basis of individual authorisation. Later it will probably become a general amateur allocation. No timescales are being quoted so it's at least a year away. I doubt that the band will be wide enough for speech but it will be good to get some beacons on air and do some CW or BPSK work." "In the meantime there is growing interest in LF communications for cave communications. Although this is essentially inductive radio many of the challenges are common to "proper" radio. There are also a number of other, more physical, challenges as I discovered when I joined the UK Cave Radio and Electronics Group and found myself in a cave up to my neck in ice cold water on my first field meeting! Not quite where I'd thought my interest in the low end of the spectrum would have lead me. The group has a worldwide member- ship and publishes a quarterly journal with a good mix of theoretical and practical articles. Recent issues have covered ground system effectiveness, speech processing, the use of CB rigs with transverters, the use of high spec audio devices rather than RF techniques for LF receivers and a host of other topics. I'd be happy to arrange a sample copy for anyone who is interested." Rob also had compliments for all the folks who work on this publication. "I really do look forward to receiving The Lowdown each month. How you guys put together such a polished publication on a monthly basis amazes me." - Allen Mattis (Houston, TX. E-mail: afmattis@i-link.net) thought about those of us in Georgia when Allison was headed our way. Folks in his area also have plenty of experience with tropical storms that wander inland. The storm was a major static producer over a wide area, too. "I can't do any decent monitoring of the NDB band with Allison in the Gulf. The noise level is S9+, even in the daytime, with Allison out there." - Dugald S. McDougall sent a letter about the signing off of beacon VLF, as shown in the listing last month, but when it came time to prepare the Note- book, it sprouted legs and ran up under some other papers. Mac wanted to pass along word to Ken Cornell that he used the two-crystal heterodyne exciter from Ken's Scrapbook, with an FET final. The transmitter produced plenty of power and "a clean-keying, harmonic-free signal," but the problem lies in constructing "an antenna that will get out more than 10 miles." Mac is a supporter of an LF ham band, along the lines of New Zealand's, and says without the antenna restrictions, the band "would be teem- ing with signals from one end of the country to the other!" Maybe we'll get him back on the air eventually. He continues to monitor NDBs, though, recently logging six or seven new countries in the Caribbean and South America, and a lot of 25 watt domestic beacons as far as Texas. Footnotes. There were no reported beacon changes or loggings for the "Top End" this month, so it is not in this issue. It will return next time, though, hopefully in an improved format. Keep all your LF and MF news coming in. 73. - - -