The LF Notebook (from The LOWDOWN, February, 1996) 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 The Blizzard of 96? Seems a little presumptuous for TV gurus to call anything that happens one week into a year "the" anything. After our late-January thaw (which came a few days early), another winter storm hit, this time swamping our friends in the Plains and Midwest with wind and snow. So, was this The Other Blizzard of 96? And what happens if we have more before winter finally departs? Do we call them Blizzard - The Sequel? Blizzard III, IV and V? Forgive me. Cold weather makes me somewhat curmudgeonly at times. Let's go straight to the news and goodies. We received a fair amount of correspondence again this time (although I was beginning to worry around the first of the month). I think we've managed to get all the new correspondence in the column, and part of the backlog as well. Keep it coming. * Bookshelf. In case you have an interest in such things, and haven't already run across this volume, I'd like to recommend the Electronic Filter Design Handbook, Third Edition, by Arthur B. Williams and Fred J. Taylor (McGraw-Hill, 1995). Filters are not the easiest circuits to get a thorough grasp of. A treatment that over-simplifies the subject leaves holes in one's knowledge, while an overly detailed treatment makes for slow going at best, and may cause the reader to skip ahead (or nod off) and miss something important. The authors of this text don't spend a lot of time on the theoretical aspects of filters, but it's there and needs to be understood before you proceed. They don't sugar-coat it either, but if you still remember a thing or two about working with polynomial equations, you'll have no trouble if you take it one step at a time. Chapter 1 starts with modern network theory and introduces the pole-zero concept on page 1. On page 2 you're introduced to the complex-frequency plane and begin with synthesis of filters from polynomials. Before the chapter ends, you see how coefficients in the polynomial equations relate to values of circuit components. All this in eight pages! Chapter 2 is longer. It starts off with frequency response normalization, talks about scaling for frequency and impedance, and demonstrates the essential properties of low-pass, high-pass, bandpass, and band-reject filters, and the transformations necessary to produce them from the fundamental filter equations. By the time this chapter ends, you should have a good understanding of phase delay, step response, and impulse response, in general...and the specific amplitude and phase characteristics of Butterworth, Chebyshev, Bessel, elliptic, and several other filter types! There are chapters specifically on low-pass, high-pass, and other configurations, each dealing with LC and active filters and containing abundant charts and tables for your own design efforts; a chapter on advanced topics in LC filter design; one on design of inductors; and a very much enlarged section on digital filtering and discrete-time signal processing. One appendix covers the texas Instruments TMS320 Digital Signal Processor, for those desiring a practical introduction to DSP. (In modern books, a 3.5" floppy disk is a mandatory part of the back cover, and this one is no exception. Its principal feature is a demonstration of the MONARCH Version 2.0 filter design program.) The second edition of this handbook was an indispensible part of my library, and I'm convinced the third edition will continue that tradition. On To The Mailbag -George J. Karayannopoulos (N2OWO, Atlantic Highlands, NJ; karayan@crow.cybercomm.net) sent his first email as a member of the LWCA. "I just thought I'd let you know of a small, but growing, effort going on among longwave enthusiasts on the Internet. The effort is part of the Worldwide Utility News club on the Internet. As you may know, WUN is an Internet-based club that concerns itself with utility signals below 30 MHz. Beacons, of course, are utility stations, and so a number of us are active in this part of the spectrum as well. WUN maintains a mailing listserver and some of the traffic has to do with beacon catches." "In addition, WUN publishes an electronic newsletter every month, with paper copies available for a nominal cost. I happen to be the longwave column editor. The column is called 'Surfing the Longwaves' and I view it as a forum of longwave enthusiasts, where I play the coordinator's role. Participation in the mailing list, subscription to the newsletter and membership are all free. Just send an email message to majordomo@grove.net with just the text: subscribe wun in the body. For more info on the club, you can send the text: info wun to the same address. (We have no affiliation with Grove enterprises. They just provide listserv services to us.)" "I am looking to expand the longwave activity on the Internet, and so any members of the Longwave Club are more than welcome! The club may also allow some to see what's beyond 500 kHz - hi, hi!" -Cliff Buttschardt (C, HDO, W6HDO; Morro Bay, CA) reports that the beacon is running BPSK as well as CCW. It signs HDO(null) in BPSK mode. I hope I've got his news on the recent digital work in chronological order here. Be aware of course, that some references are to ham activity and some to LF: "Bill Lake has already indicated that he is now printing the HDO(null) beacon well. The same old problem apparently, frequency stability. We interested two others that normally do not have a BPSK interest to finally get going. There will two new stations farther away. One in Tucson (Frank Cathell) and the other in the San Fransisco area. I have made arrangements to ship my MAX800 receiver to Hawaii when I get it back from John West. So far, most of us have had sucess using a synthesizer which creates an accurate 800 Hz signal into an ordinary 1750 meter recevier set to AM, the synthesizer acting as a BFO signal." "I've completed one of Dave Curry's direct conversion transceivers, the 495 model which will allow total battery operation using the Sigma-Delta board and the Compaq laptop. With this arrangement I will start tests in remote locations. Both Bill Lake and I will be getting used to (COHERENT) version 4.4 and the addtional features and enhanced ability to copy below noise." (January 7): "We are doing very well with the BPSK experiments. Bill Lake and soon Dave Curry will be printing. Bill already has proven copy below noise. There will be two more receivers on in a week and two additional in two weeks." -Robert Laney checked in to report "beacon RL is happily chirping (poor choice of words!) away under 30 inches of snow from 'Blizzard 96.' The snow interferred with my plans to lay out some additional radials and in general see if I could improve the output. Would be interested to take the receiver out in the truck and see if the snow cover made any difference in the signal. That will come. Hope all those who were hit by the snow have dug out by now." -Bruce Koehler (BK, YB, AA0YB) reports "trying to make improvements to YB. The latest was a new final amplifier using the complementary pair design described in Lyle Koehler's article "A Versatile Beacon Amplifier." After building this amplifier, YB puts out a respectable signal now." Bruce put up a new, stronger antenna for BK in October, with the help of his wife Jeanne and a neighbor, Gene Geissler. It has an extra set of guy ropes, and an improved top hat. It was made by bowing 5/16" aluminum tubing into what look like bows and bowstrings attached to the mast, with an aluminum skirt wire. (See the drawing on this page.) The skirt wire forms forms a square roughly 10' X 10'. "I really appreciate Jeanne's help with this stuff, I know she thinks I'm nuts to spend so much time listening to noise, but still she helps me put up new antennas when the old ones blow down, and that has happened frequently. I hope the new BK antenna stays up for a long time, I'm happy with its performance." His antenna for YB is also unique. He says it is "hanging from a rope over a high limb in a huge cottonwood tree. The tophat is a triangle frame 7 feet on a side with 3 short downleads coming from the corners. Jeanne helped me haul that one up too. The neighbors must have had a good chuckle when I was shooting weights attatched to my fishing line with a slingshot while standing on my roof. After each miss, I reeled the line in with the fishing rod to try again. After several tries, I finally hit the branch I wanted. From YB where the night time noise level is high, I can only hear 0KVL, LEK, BK, ART, and SAM. But Jan. 11 at about noon, I was able to hear RM using the YB antenna as a receiving antenna. Maybe there's hope for DX at YB yet!" "BK, LEK, and YB are now being keyed by BASIC Stamps, and BK and LEK report wind speed and temperature too. The BK message reads like this: DE BK BK BK WIND 7 TEMP N12 42 . The first number after temp is the outdoor temp which is negative if preceeded by an N. The second number is the crawl space temperature of the Shell Lake, WI cabin. There are a lot of neat things you can do with the BASIC Stamps, and Lyle and I now have the BASIC Stamp 2, which has much more program space, so who knows what we might do with them." -Will Payne (YWK; Crossroads/Dallas, GA) says "Thanks to the folks who sent tips on artificial signals in the VLF/ULF world. I may soon try to move the frequency of YWK just a bit to give Robert Fear some room, since he was on 184.320 first. One can permanently warp a TTL crystal oscillator module by heating the !#$%@&%$ out of it with a torch or big soldering gun. Just try to walk the fine line between warping it and killing it. What YWK really needs is a decent antenna. There is a ham repeater site near here with a free standing (grounded) tower. Has anyone ever tried to shunt feed such at LF?" "I still use the BFO receiving technique to receive whistlers and tweeks which I can't otherwise hear. Nothing so spectacular as the "sferic storm" I stumbled onto the first night, but occasionally enough to be interesting. It seems to me that an LF converter with really pure LO and excellent mixer balance, such as in Lowdown JAN 1996, coupled with an HF rig with a really good crystal SSB filter in the IF would give the same results as the Rycom 6040 in that mode. I don't use a converter, but would be interested in hearing from those that do. Try using an active antenna or buffer amp to match into your converter at audio freqs (hi-z to 50 ohm), then tune as close as you can to the converter LO and let us know what you hear." "Loop antenna status report: The big loop is 12 turns, 200 ft diameter lying on the ground. It works ok, but is oriented for maximum hum, and I have no way of standing a 200 ft dia loop on edge. I get lots of signal, but lots of noise." "The (smaller) "octoloop" is a length of 25 pair telephone wire inside an octagonal loop shield of 3/4 hard copper pipe. Mine is about 7 ft dia. and wired for 50 turns, and gimballed for noise rejection. The pipe shield is a very effective electrostatic shield at MF, and also reduces VLF/ULF micro- phonics, which for obvious reasons plague most loops. The self resonant freq has not yet been measured, but is probably near 12 kHz." "I took the octoloop to the backyard and leaned it against a tree, oriented to null the noise. For the first time ever, I was able to tune my Rycom 6040 to 0 Hz and hear something besides BUZZZ! The loop has good sensitivity with an almost perfect noise null, a real pleasure to operate! I clearly heard FIVE of the eight OMEGA stations, a NiCd battery charger 450 ft away, and some tweeks and pops. Even inside the house, I hear OMEGA, WWVB and the stronger sferics." Will says the octoloop is easy to make and costs about $20. He has pre- pared an article for future inclusion in the LOWDOWN. Additional details are on the BBS. Will recently contacted Bob Confrey, who has been experimenting with a 1200 turn coil, and offered some suggestions for improving DC stability in the preamp. "There are several solutions for this, including the monolithic chopper amps from Maxim. I propose simple AC coupling with a corner freq in the neighborhood of 0.01 Hz to eliminate DC drift. An RC network consisting of a 10 uF polypropylene or polystyrene capacitor and a 10 meg resistor should do the trick. A 0.01 Hz to 40 Hz response would allow the use of 25 Hz power grids from Africa as a test beacon....Life at 1200 turns sounds fascinating, and I wonder how low I could go." On another experimental topic, "A very sensitive and accurate magnetometer may be easily built using a magnetic needle compass inside a Helmholtz coil. Plot the frequency of oscillation of the compass needle as a function of coil current. Use a cheap compass which swings around a lot, not the good damped type. At zero frequency, the DC ambient magnetic field is equal and opposite the known field in the Helmholtz coil. The Helmholtz coil can be oriented along the three dimensional magnetic field vector, or else three orthogonal measurements may be taken separately. After the first time, you know the slope of the line for your compass, so two data points would be enough. A good college physics lab experiment, but could a PC and mechanism log continuous data unattended?" -Tom (Doc) Gruis (D) sent "a note to let you know that this lowly LOWFER in Des Moines, Iowa, at Grid EN31dx, is also on AOL, as well as on 175KHz. I have put together a new ID'er that is still "D" but with a longer and much more pronounced steady carrier period." "It is really cold here just now, and I have offered to replace my good neighbor's dimmer unit with a switch or an RFI resistant one. Reception is usually pretty difficult from mid-BC band on down. I would probably do better trying to send DC through the water pipes!" "Would an e-mail address list be a good idea?" Sounds good to your columnist. How about letting us know this month what you think? -Bill Cantrell (TEXAS) announces, "The TEXAS Beacon is back on the air as promised. It is still on the old tower (no top-hat yet), but I did get the concrete for the new tower base and guy points poured. I am working on finding a good high-strength, high-resistance insulator to support the tower base. I plan to replace the old tower this summer and will try experimenting with partially inductive top-loading with Bill Bower's data and assistance. I have a new 40 foot Rohn 25G tower ready to go up and will raise it "inverted" in order to use the base plate as a platform to weld radials for the top-hat, similar to Joe Saloka's KRY beacon (Dec'92 LOWDOWN) article. (Engineering work at Motorola and pursuit of a Ph.D. sure does slow things down!)" -Cecil Wadford (RED, Wausau/Chipley, FL) wrote with additional information on his beacon this month. This is the first winter for his 30-foot vertical antenna with 20-foot top hat, and it survived Hurrican Opal's 75-plus m.p.h. winds without flinching. Four 40-foot elevated ground wires, with individual loading coils, are used because of poor soil in the area. Each ground "catches" about 60 ma of RF. It is intended as a temporary antenna, until he is ready to raise his 40- foot helical version. A photo accompanied Cecil's letter, and I hope to be able to enlarge it a bit and prepare it for black-and-white reproduction in time for next month. -Bill Bowers (OK; Box 399, Davenport, OK 74026) saw December's discussion of the Kiwa loop for LF. "I have been using the Kiwa loop circuit on my 16 foot ferrite loop and it works great. All that is necessary to use it for LF is just to add turns to the loop, as the electronics work just fine. I am using about 2 mH in my tuning coil, and i tunes from 150 to 400 kHz." Recent coil tests resulted in an accumulation of Litz wire, including various lengths of 60x42, 100x44 and 200x44 sizes. Bill says, "I would be happy to send it to anyone who wound be interested. He reports OK is now transmitting from its new antenna and ground system, resulting in a 5 db improvement at John Reed's QTH in Ponca City, Oklahoma! -Phillip Gentile (SVZ, W2SVZ; PO Box 233, Bridgeport, NY 13030) sent some information on his beacon when he announced its commissioning, and it may be of interest to prospective beacon operators. "The beacon consists of a CMOS oscillator/divider chip (MC14060) dividing a 5.68 MHz crystal by 32. The keyer is a BASIC Stamp programmed to produce the ID, which gates the divider network. The /32 output directly drives an N-channel ECG2382 FET. Silver mica capacitors totalling 18,000 pf resonate a torroid matching transformer....Antenna current has been measured at 200 mA using a clamp-on RF milliammeter as described in the April, 1994, LOWDOWN." Phillip has generously offered to make the schematic and parts list available upon request. He received three local reception reports before even writing to us, so this is a beacon that should do pretty well. -Brice Anderson (BA, IE) got the new crystal he had ordered for MedFER IE and has moved it to 1,704.18. He added some wire to the tophat for his LowFER antenna and raised its ends some, which seems to have added a bit to his signal strength. Brice and his wife made their New Year's resolution "Get your kicks in 96." That followed the successful keeping of the 1995 resolution, "Stay alive in 95." Footnote. I hope we'll all be able to keep those same resolutions ourselves this year. Enjoy yourself, send in your news, and have a great month! - - -