"The LF Notebook" (Sept. 1995 LOWDOWN) The Mailbag, News and Comments About LF Radio Etc. John H. Davis, Box 367, Warm Springs, GA 31830 -E-mail: johnhdavis@aol.com -Fax/Answering Machine: (706) 672-0964 -Longwave/Part 15 BBS: 706/672-0360 Wow! That was some August issue for the Lowdown, wasn't it? Thirty pages of solid information and interesting letters in a late summer edition may or may not be a record, but it certainly was a welcome sight. Thanks and congratulations to all the writers (and artists, in some cases) who put forth the effort to make it a great issue. Your work was appreciated by many of our correspondents this month. There may be a little less material in this particular column this month, but we do have the beacon lists back, and I'm confident the rest of the issue will also be packed with good reading. So, here we go. *Periodical Shelf -"Lend me your comb." A note from Daniel Gates (1226 S. Longfellow #110, Wichita, KS 67207) brings a copy of a short piece from the July 10 issue of Electronic Design. It's a design idea by W. Stephen Woodward of UNC-Chapel Hill titled "Eliminate Periodic Noise." While Daniel hasn't yet built the circuit himself, he says it looks to be an interesting and possibly effective way of getting rid of the harmonics arising from 60 Hz noise pulses. It uses three op amp sections, a CD4013 dual flip-flop, and a CD4016 analog switch controlling two integrating capacitors. The result- ing transfer function gives a comb filter with very deep notches at all harmonics of 60 Hz. We'll see if we can't get rights to reproduce the circuit, or persuade someone to build and report on a variation of it in the near future; meantime, you may be able to find it in your own magazine stack or an engineering library. -Not a periodical, as such, but at least periodically updated: the Longwave BBS. More natural radio recordings are on the board this month, along with the first of my commercially-released shareware (so you'll have to endure a very brief advertisement at log-on; this month it's a simple editor that is like having two sessions of Windows Notepad on screen at the same time), and files relating to Windows 95. Three notes about using the BBS: 1. Some users have difficulty reading the text screens and downloading text files. The only way I've been able to reproduce that particular problem myself is by calling the BBS with a 2400 baud modem. For reasons as yet unknown, perhaps some setup incompatibility, text screens do get scrambled at 2400 baud. If your terminal software lets you do so, download files with the .txt extension not as text, but as regular binary files instead. That usually works well. 2. Some users apparently try to browse the file library as you would with a fancier BBS. The software for this system is very simple (it has to be, or else I couldn't work it) and therefore doesn't give you anything but a cryptic file name anyway...no details of the program, and in no particular order. That's why I disabled the (F)ile list. The best thing to do is log on, download ALLFILES.TXT or its .ZIP counterpart, log off, browse through that file, then reconnect to get the files you want. It saves you a lot of connect time, and furnishes you much more information. 3. During the third week of the month, when this column is usually being finished up, the BBS doesn't get updated as often as during the rest of the month. It may also be off daytimes for maintenance during that period, so just check back. -Something related to the BBS, but a little off the LF track for a moment: We have an increasing number of support files relating to Windows 95, which will have been in release just over a week when you read this. If you haven't heard something about it already, you've been visiting another planet for several months, or really have NO interest in computing whatsoever. (And sometimes I can't blame you.) Even so, I've just heard that Microsoft paid several million for rights to use the Rolling Stones' "Start Me Up" in the ad campaign, so it should be very hard to ignore. Why that particular song? It's a cute play on the Start button that is the key to the new desktop. I've been using the "final beta release" of 95--which was promptly followed by several more; never say "final" in software development--since late March, and a version very close to the commercial product since June. Despite negative comments by a few reviewers who were wishing for something more, and despite a very insidious misinformation campaign by a certain rival software vendor/computer maker, I think 95 is a worthwhile product. I don't much care if it's "too Macintosh-like," as you may hear. There's nothing wrong with us Intel platform users having the same benefits our Mac brethren have had for years, plus a few more. The big difference over Windows 3.1 will be the ease of use for first-time users. The learning curve doesn't start off so steep. If you've already been using Windows, it will take you 5 - 8 minutes to be comfortable working in the new environment, and only a little longer if you're a newcomer. (It's later, when you have to change some hardware or software configurations that you'll have to start learning all over again. Even so, it's not complex, just different.) Whether Windows 95 is something you should get depends on whether you have the hardware to run it (386DX or better, minimum 4 meg of RAM, a few score megabytes free on your hard drive) and whether you anticipate needing 32-bit software in the next year or two. On-line forums are a good place to browse for comments that could help you decide, and to get help after installation if you need it. You'll find me haunting the Windows forums on AOL almost daily, so feel free to stop by and ask questions there, or by mail, or however. We now return to our regularly scheduled LF topics.... *On To The Mailbag - Steve McGreevy has uploaded more neat WAV files from his LF monitoring to the Longwave BBS, and also some to the Internet. There was a mishap with the e-mail address last time, though. The correct address is: spmcgrvy@ix.netcom.com. Steve reports, "There is a WWW (World Wide Web) page based at the U of Iowa that now has my natural radio files available for downloads (not as much as is now on this bbs). The address is: http://www-pw.physics.uiowa.edu/mcgreevy/ Larry Granroth has been gracious to do this for me. There are also links to other related topics including Project INSPIRE." "Also, check out the rec.radio.shortwave usenet group for a story I wrote for Donald Cyr, entitled 'A whistler listener's story' (not original title). There are 3 parts to it, #59300-59302." The article may be on the BBS by now, too. "On July 31-August 2 had nice whistlers each evening around sunset! They sounded like 2-hop type. I only listened to them from the backyard." Steve adds that both the WR-3 and WR-3E whistler receivers are still available. - Lyle Koehler (K0LR, LEK, MIN) has received favorable comments on his universal preamp article last month, and I imagine there will be plenty more as folks build and use the circuit. It's also available in Windows Write form on the BBS now. "Nothing to report this month except more QRN. I'm trying to put together my comments on an LF ham band but don't know from day to day whether I'm really for it or against it - hi. One of the reasons for supporting a ham band is that we might be able to coexist better with them than with some other service that might grab 'our' band." - Bruce Koehler (AA0YB, BK, YB) expresses similar sentiments: "I agree with most of what John West has to say about a possible LF ham band. I like things the way they are now and fear that hams may crowd the band with high power signals. I talked to my dad recently about it and he used an analogy that relates to what they're doing to the woods behind my Maplewood home. They have started a new residential development there and I'm afraid I'll lose my low noise location for my receiving loop. I liked things the way they were there, too, but if they had decided to make a golf course, I probably would have preferred that over the residential development. LF could become inhabited by something worse than hams, like GWEN." Speaking of noise, Bruce has been trying to cope with S9 +10 db power line noise at the Shell Lake, WI, cabin. No help from the power company yet. He can still hear LEK with some difficulty. His own BK is on weekends when there are no storms. The original BK antenna, made from a windsurfer mast, blew down. It's back up with a different top hat, a wire triangle with one corner connected to the top of the mast, and the others tied off with rope to a telephone pole and a TV antenna mast. The loading coil inductance is reduced, but "the tuning seems broader and the signal may be slightly weaker at my dad's location. I have certainly increased the antenna capacitance, but also somehow managed to increase losses. The antenna I had late last summer and fall seemed to work the best, but it blew down twice in about a month." A new beacon, YB, may be on the air soon from the Maplewood QTH. - Doug Williams (OER, KB4OER; 135 Hughes Rd, Watauga, TN 37694) shares John West's concerns about preserving what's good about 1750 meters, but says he has mixed feelings. "I think that making 1750 meters a ham band will be a good thing in the long run. I think the band would benefit from more activity. I don't forsee 1750 turning into a 'plug-n-play' band. I doubt the FCC would allow us to use 100 watts. Probably 5 - 10 watts would be more like it. And oh, wouldn't it be nice to be rid of that silly 50 foot antenna restriction? Wouldn't it be great to have your transmitter inside the shack and feed the antenna with a length of coax instead of being forced to locate the transmitter (or at least the final) at the base of the antenna? I say make it a ham band. Let us have 5 or 10 watts out to whatever size antenna we care to put up, and let us use whatever narrowband mode we care to use." Despite the summer weather, Doug has been building the VLF transmitter circuit from the July, 1990, Popular Electronics. It's for the 7 - 10 kHz range. A TV horizontal width control ("found at a TV repair shop....the owner said it had been on his shelf for 20 years!") serves as the oscillator inductor, and the tank is 10" wide, 12" long, and has enough 18-gauge magnet wire to weigh in about 9.3 mH. So much capacitance is needed to resonate the tank that connecting a normal size antenna has little effect on tuning. Doug will first be using the OER 40' vertical, and will let us know how that does. He anticipates moving the OER antenna away from trees to a clearer spot in the yard before his October 1 target date for resuming operation. A new ground system will be needed, maybe including some chicken wire this time. - Cliff Buttschardt (W6HDO, C; Morro Bay, CA 93442) disagrees with some of John West's remarks last month about hams in the LF band. On the other hand, he sees another option..."what we really need is to leave the 1750 meter band alone and simply ask for a power increase to ten watts. By the way, have you seen the voltages generated by power greater than 10 watts??? One hundred watts is simply lethal and not to be recommended to the novice, or anyone else in a home envioronment without adaquate protection. Indeed, an extension to below 160 KHz is a viable alternate too, but one the GWEN people will object to strongly. So the long term goal is the elimination of the useless GWEN system and the power increase to ten watts WITHOUT the necessity of making it a ham band." Given the practical limits on antenna size in the band, even low powers do result in hefty voltages. He says, "I have had some experience with 100 watt stations in the past on these frequencies. The worst shock I've ever gotten was off a 1 kw BC station on 550. Feels more like DC than RF as it does not burn. I simply do not know how the VK's and ZL's protect themselves. One very good point to be made is that one watt is just such low power that decent measurements can not be made!" On the CCW and BPSK front, Cliff reports that since the last Lowdown, "we have changed to '35 up' frequencies. That is, CCW activity is now 35 KHz up from the botton end of all the ham bands except 30 meters: 3535,7035,10115,14035 etc. You can see the change in thirty meters and can appreciate the problems with that narrow band full of digital signals. We now have had many two way contacts on CCW, primarily by my efforts and efforts of W6VKP in Los Altos." - Brice Anderson (BA, W9PNE; Lancaster, IL) is an avid amateur operator and LF enthusiast who has definite opinions on the ham band question. "I have come to the conclusion that 1750 meters should NOT become a Ham band. I have been active on 1750 meters for many years, ever since Vince Pinto published his LowFER newsletter. In fact, it was his newsletter that got me started." "It was my reception of TH and later VP, the first reception of LowFER signals at a distance over 150 miles or so, that awakened the community to the possibilities of LF. It took me years and many antenna improvements before BA was heard on the east coast. I have never used an antenna over 40 feet high and my top hats have generally been modest T or umbrella arrangements." Based on audiences for Brice's talks on LF to ham clubs, he is concerned about the caliber of operators who might show up on the band and the use of "many watts of power....All the hours of careful listening for those brief, elusive openings would be rendered useless. The fascination with LF propagation would be overwhelmed by a barrage of signals." Recurring thunderstorms have been the bane of Brice's LF work this spring and summer. The last beacon reception of the season was YHO on April 1. Since then, it has all been QRN. A falling tree broke his 300' receiving wire, a limb crushed the top hat on the MF antenna, and half of his apple tree fell, breaking one of the elevated radials for the MF antenna. By the end of June, rainfall was over 8" above normal. More recently, "a limb blew into the plastic garbage pail that houses my LowFER final. The plastic was badly deteriorated by years in the sun and weather, so it shattered into countless pieces. The bottom held water well enough to submerge the final in rain water, old leaves, insect bodies, etc. I finally got it all cleaned up and mounted in a new container." It was still not back working into the antenna in early August, but should be soon if it isn't already. - John R. (Rick) Wright (R, KA5YWH; Box 4184 Stn A, SEOSU, Durant, OK 74701) seemed to like the idea of "KA5YWH and R-beacon" as a rock band name. He says, " Actually, I own a good guitar that I haven't played for years, so the rock band is not liable to prosper if it has to depend on my talent!" That's a shame. I thought we might be able to bill ourselves as "the world's most Lowdown band," or something similar. He did have some thoughts on gravity wave detector circuits: "The circuit mentioned by Dan Levit, I think, is one and the same as the "Rainbow" radar detector kit advertised for $12 in the Marlin P. Jones catalog. It is supposed to detect changes in a capacitor. One of our electronics professors let a student build one as a project, but they didn't believe it worked. So out of curiosity, I built one and took it to a nearby airport which has a surveillance radar (TRSA). To my everlasting surprise, the thing worked (and without a gain antenna), responding with a modest but clearly audible "tweet" at the radar's PRF (pulse recurrence frequency) every time the radar antenna scanned through my azimuth. This was from about two miles, and I was listening to the audio signal and watching the radar dish through binoculars. It also worked on a weather radar, which has a much lower PRF. I taped what I was hearing. "Inspection of the circuit reveals that it is nothing more than a regeneratively sensitized audio amplifier, using an op amp with a unity- gain frquency in the low MHz range. With provisions for audio tuning to the correct PRF, it should be reasonably sensitive to pulsed radar signals, but the design is really not of radar warning receiver quality. The circuit itself definitely isn't microwave stuff, and effects in the capaci- tor could be the basis for the circuit's sensitivity to microwaves. In that case, one explanation for the circuit's response is the 'microwave acoustic effect,' where pulsed microwave fluences deposit energy not only as heat but also as transient acoustic waves (which also convert to heat). Continuous microwave irradiation just causes heating and no acoustic effects. In the beam of a pulsed surveillance radar the weak sound waves generated this way could make the capacitor behave as a capacitance microphone. Indeed, if you tap the capacitor with a nonconducting rod, the circuit responds with a 'bong'. As for the gravity wave aspect, I'm not so sure about any of that." Microwave acoustic effects are discussed in an article by C. Chou, A. Guy and R. Galambos, "Auditory Perception of Radiofrequency Electromag- netic Fields", Journal of the Acoustical Society of America, Volume 71, page 1321, 1982. The copy of the circuit Rick sent does look very similar to the one presented last month. The Marlin P. Jones catalog claims the microwave detection works from 50 MHz to 500 GHz. Rick says he'd like to have a source which could test that! Til next month, 73. - - -