The LF Notebook (From the June, 1996, 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 - (706) 672-0964 -WWW - http://users.aol.com/lwcanews/ April...cold, wet. May...hot, dry. Not gonna predict about June. Wouldn't be prudent. Nope, not gonna do the forecast thing. (Sorry. The heat got to me.) This column started out looking pretty meager a few days ago, but a lot has happened since. I'm postponing an equipment review I had prepared, some photos, the rest of the introduction, and still we're long. No telling what the finished product will look like, but here goes... *UK Says 73 to LF Ham Band...Or Vice-Versa The British government announced on April 29 that a one-SSB-channel wide slice of spectrum, centered, interestingly, on 73 kHz, is being granted to Class A amateurs there on a Notice of Variation basis. (DOWNLOAD FILE 73khz.txt FOR DETAILS.) Special thanks to Rob J. Gill of Twickenham, England, Jacques d'Avignon (Radio Propagation Forecasting & HF Monitoring Services, Kingston, ON; E-mail: monitor@limestone.kosone.com) and Dr. Jon Iza (EA2SN; e-mail: iapizloj@bicc00.bi.ehu.es; University of the Basque Country) for their help in keeping track of European LF ham issues. A Web page is already available at http://www.users.dircon.co.uk/~stonix/73kHz/ *The Periodical & Catalog Shelf If you're interested in correlating ELF anomalies with possible earth tremors...or to just explore some ways of getting data from transducers into your PC or Mac compatible computer...you might want to look up the April, 1996, Scientific American. I had missed it, but Robert Laney brought that issue's "The Amateur Scientist" column by Shawn Carlson (pp. 100-102) to my attention. The article outlines ways to use Analog Devices' ADXL05 accelerometer chip in an elementary, but useful, seismograph. The device's output reportedly changes by 0.4 volt DC for a 1 g acceleration, and can resolve down to .005 g. Three ADXL05's are used, aligned along x, y, and z axes. The data can be recorded individually, or summed for sending to a single-pen chart recorder. (One would, hopefully, use a better op amp than the plain 741.) The column discusses both hardware and software that can help in data acquisition, and tells how to contact the Society for Amateur Scientists to obtain more information on amateur seismology. (Send $5 to 4951 D Clairemont Square, Suite 179, San Diego, CA 92117. Or, download at http://www.thesphere.com/SAS/.) Benny and the (Blue) Jets. David Jones cites a couple of articles on our new friends in high places: "Geophysical Research Letters, vol.22, no.10, pages 1205- 1208, Red Sprites; also pages 1209 - 1212, Blue Jets; I had my library get these two reports on the aircraft experiment in July 1994. I found them interesting." *DVM follow-up. A few months ago, Will Payne mentioned the Radio Shack digital multimeter that has an RS-232 connection for PC interfacing. You may want to check the June issue of QST for a product review of the model 22-168A digital multimeter. Reviewer Mike Gruber found it to be "an accurate, economical and handy test-bench instrument," though he certainly made note of the minimal documentation for the accompanying software. A small user manual comes with it, while a service manual is sold separately. The user manual describes the meter as auto-ranging, when, in fact, it is not. The catalog description is correct, however. Test results showed it to be remarkably accurate at all but the highest range of each function, and well within reason there. *Frequency counters and other goodies. The new Ramsey catalog is out (800- 446-2295), and the entire line of frequency counters is specially priced at $60 or more off the usual cost. If you have been considering one, now is an excellent time. Their selection of RF test equipment and ham gear continues to grow as well. *The topic that wouldn't die...still more about signal relaying. Another source of goodies that might help in signal relaying is Supercircuits (One Supercircuits Plaza, Leander, TX 78641; 512-260-0333). Their specialty is small CCD video cameras, but they also have both Part 15 and amateur RF gear for various bands, including the license-free 915 MHz and 2.45 GHz bands. *Webbed wonders. Our own Web pages continue to grow... you can get there with http://users.aol.com/lwcanews/ Check it out. There have been some big improvements! The Mailbag, Take One... -Bob Hoffswell (BOB, AA9DH; PO Box 530, Mahomet, IL, 61853; e-mail: harvey@prairienet.org) keeps BOB on whenever spring and summer storms or antenna work aren't underway. He hadn't heard BA since March, but on MF he did hear IE in April, and STLMO was still pretty regular when he wrote. "I've also removed the on-ground radials so I can mow the yard. The signal is about the same 5 miles away without them, with a few ground rods remaining, but I'm not sure about the signal at DX. A check at a recent hamfest 40 miles away seem to show a weaker signal than I'd had at 65 miles previously with the radials, but QRN was heavy," he notes. "I've tried a loop for 1750--pretty small and worked poorly, so I now am back to upgrading my vertical system. The RadioShack IDer I built here for BOB works great, and is cheap to build using their digital voice recorder chip. Message can only be 20 sec long, but that's fine for me. I'll write it up in the slow season." Bob has possibly persuaded another local ham, N9RVL, to try either an LF or MF beacon this coming fall. He reports other hams in the area are interested, but "they universally have receiving problems....I try to show them using my portable receiving system that they can hear something." -Cecil Wadford (RED; Rt 4, 2589 Oid Dr., Chipley, FL 32428) has a new street address, courtesy of 911 implementation in his area. The physical QTH remains the same, near Wausau, in the Florida panhandle. Receiving conditions have been very bad, "40 db over S-9 most of the time. We have had the electronic plague here this year...high line voltage, lightning, and rain storms." All of his equipment has been down at some point, but "somehow we keep the CCW going most of the time." He has been hearing YD day and night, at 67 miles distance. -Frank Carson (e-mail: FRCARSON@gnn.com) recently put up a small BBS at his home, and would be glad to have LWCA members use it. "It's free, and there is a conference called 'Under 500Khz' specifically for people like us. Again, it's small, and is not networked, but it's free and online 24 hours a day, seven days a week (except maintenance times). I'm working on collecting and placing related files on the board. The name of the BBS is 'Open Channel' and the number is (301) 203-8478." While our established Longwave BBS has a hefty file library and e-mail among its users, its software does not support conferences. Frank's conference area may be a handy way to let folks "talk" among themselves without having to mess with addressing e-mail and looking for it all the time. Sounds worthwhile. -An absent-mindedness "oops" on my part! Wayne Rankin (PO Box 41, Tujunga, CA 91043; packet: WA6MPG @ WB6WFH.#SOCA.CA.USA.NOAM) wrote in March about a possible unique band opening, and he wonders if anyone else experienced it. On Sunday, March 10, reports of New Zealanders on 160 meters prompted him to check the MedFER band ("nothing too exciting"), then down to LF. From 500 kHz down to 270 kHz, "the band was full of new stuff." Below there, nothing, including no LowFERs. Anyone else experience enhancement in that octave on March 10? -David Jones (NR; Columbus, GA) managed to copy RED again on April 30. -Robert L. Laney (RL; 3153 Southfield Dr., Herndon, VA 22071) plans loading coil and tophat experiments this summer, and may be off for storms at times. -Bill Bowers (OK; PO Box 399, Davenport, OK 74026) may have caught a springtime disk-jockey bug: "Lincoln County Oklahoma's only radio station, OK at 189.9 kHz on your dial will be on the air all summer. OK will be pumping out a full one watt of electromagnetic energy into the atmosphere of mid-America without interruption...except for tornadoes and lightning hits." -Bill Cantrell (TEXAS; e-mail: Cantrell_Bill@macmail1.fwrdc.rtsg.mot.com) reports the TEXAS Beacon is back on the air with a much improved signal. "It turns out that the binding posts that allow wires to exit from the ammo-box transmitter case were severely de-Qing performance. I rebuilt the base insulator and replaced the old loading coil with a new one courtesy of Bill Bowers. It has a Q of greater than 500. "That tripled the antenna current. Then I brought all of the wires out through a single hole rather than using binding posts. (I did this to ensure that there would be no losses due to the magnetic field around a wire creating a magnetic flux in the metal box itself via Ampere's Law. If all wires exit the same hole, including the GND return wire, there is no net curent flowing out of the hole, so {curl H} = J = 0, therefore H = 0, neglecting the asymmetry of the wires in the hole.) Flux losses are probably not a big deal compared to the resistive losses (dirt, grime) of the binding posts themselves. "When I got rid of the binding posts, the antenna current more than doubled, so now I am at 6 times what it used to be. I can't wait to get the new Rohn 25G tower up. Then all I need to do is get the top-hat completed. I will get some B&W film and document the upgrades. Should make for a nice article for the LOWDOWN." -Jerry Green (GG, K4UBR; e-mail: k4ubr@ix.netcom.com; packet: K4UBR@N1NFC.#SEGA; Middleburg,FL) reports "a BlackJack scrub oak about 40 feet tall decided it was tired and fell smartly across my guys of the GG antenna." It also took out HF ham antennas, so some more trees are due for removal before the beacon returns in the fall. "I will testify to any who care to know that when a tree falls in the forest it SURELY DOES MAKE NOISE....I have been downloading McGreevy's Natural sounds and also the neat Gram 22 and I really am looking forward to getting the CD-ROM that he is going to have on the market soon." Jerry hopes for more stable weather this summer than we had during the winter, but he's hoping it won't be lightning free. His house is 3 miles from Camp Blanding, where Dr Uman of the University of Florida conducts rocket-triggered lightning tests, to study its effects on utilities. "I hope to have a WR3E receiver,recorders and loop antenna ready for the summer session of tests....If I can somehow arrange a visit to the site and meet some of the staff from U. of Fl. I hope to find their schedules and coordinate my recordings with their activities." -Lyle Koehler (LEK; Aitkin, MN; e-mail: lek@juno.com) says "I haven't done much LF listening except during the daytime. Last Saturday RM, SAM, ART, BK and 0KVL were all on at the same time. I'm hoping YB gets back on the air one of these days so I can have the rare treat of six LowFERs during the summer season." From The Mailbag, Take Two... (Having more or less committed myself to a followup on this topic from last time, I will print another letter in full on the BPSK DX record claim, with my own editorial remarks and other letters afterward. I do not propose to print further complete letters about whether we should or shouldn't have published the report. I do not intend to stifle discussion, though. Write whatever you feel. Such letters will receive the same treatment as any others, including condensation and sometimes minor comment.) Dave Rickett (15600 Del Prado Drive, Hacienda Heights, CA 91745; e-mail DaveR73769@aol.com) writes again. Parenthesized numerals are mine, and denote material upon which I comment later: "The LOWDOWN May issue pointed out the importance of verifying a major Part 15 1750m band dx contact. The theme of this letter moves to the issue of failure to disclose." "Your editorial referred to Clifford Buttschardt's report in the May issue for aspects of the California source of the dx contacts in Colorado and Minnesota. Cliff's report explicitly states that the input power was recently reduced to just under 1 Watt.(1) The remaining data of 9 V and 'pins' a 300 ma RF ammeter suggests the feed power still exceeds 1 W. This information alone demonstrates the reported dx was not Part 15 compliant at the time of the contact.(2)" "Cliff also reports some antenna particulars such as over 100 radials but conspicuously fails to describe the radials length, the vertical metallic electrically conductive structural height, the length of any guy wires if any, or the length of any shorter radiating wires in close proximity to the vertical antenna structure.(3) I have experimentally tested various center feed dipoles and verticals to a good earth ground which are just at the 15 m limit in Part 15. The Cu conductor sizes included #20, #12, and one fourth inch tubing. The 1/4" tubing was marginally the most effective but the lowest voltage to draw 1 W from a precision signal generator was 70 V.(4) The maximum current into the various configurations was therefore 14 mA. Cliff was describing a major antenna but it is not in conformance with Part 15.(5)" "The dx report in the March issue (if the detection is valid)(6) is obviously not from a Part 15 source. LOWDOWN should openly state that the March issue dx report was not confirmed to be in conformance with Part 15.(7) LOWDOWN's open and trusting acceptance of reported material needs to be balanced if its integrity is to be retained." "As for the reception end, the BPSK bit rate and a functional description of the DSP 'null' method have still not been reported in LOWDOWN.(8) The bit rate is a major limit on narrow band pass and DSP frequency resolution. Bit rate, therefore, limits the best signal to noise ratio that is obtainable from a Part 15 signal that would be expected to be no more then 10-19 W/m2 in Colorado. Based on Cliff's report I no longer believe that the reported dx signal was actually that small, but the bit rate and detection method need to be reviewed openly in LOWDOWN for reasonableness and lack of bias if this approach is the future basis for an actual Part 15 long dx contact reported in LOWDOWN." Comment: It is certainly reasonable for anyone making an extraordinary technical claim to support and defend their data. But the issue upon which Dave appears most insistent is not only the possibility of doing the deed, but whether it was done in a way that should have been reported in The LOWDOWN. I will therefor restate the reasons why I had no qualms about publishing the announcements. Understand, first, that the LOWDOWN department editors don't just print anything we're handed. Robert Montgomery, of "DX Downstairs," recently shared with me some experiences with implausible reception loggings. This is a balancing act we all perform. Almost two years ago, I received an anonymous fax about a method of coupling LF signals into the power line neutral wire. Much later, its author contacted me and wanted to know why I didn't print it. The main reason, of course, was that we didn't know the source before. Also, I cannot find anything in present Part 15 rules that permits off-premises power line conduction by anyone except the power utilities. (Quite the contrary, there are stringent limits on conducted signals above 9 kHz.) It is up to an author to support the legitimacy of his own methods. In the case at hand, however, I still feel the ground work was laid as solidly as it can be with such an informal organization as we have. I can understand people seeing articles titled "BPSK This" or "BPSK That," and their eyes glazing over, on the assumption such high tech stuff is a pipe dream that'll never affect them. The only problem is, it's here. Point by point through Dave's objections: (1) Anyone who operates a real-world beacon for any length of time, and is conscientious enough to measure his operating parameters regularly, finds periodic readjustment necessary. That doesn't imply that it was ever significantly over 1 watt. (2) From my own beacon experience, I see nothing about 9 VDC input that indicates non-compliance. It's a perfectly reasonable final stage input voltage. While an antenna RF current of 300+ mA is unusual, it doesn't demonstrate anything either. Over the past 10 years, beacon operators have reported antenna currents as low as 65 mA to nearly 400 mA for beacons, depending on the efficiency of the ground system (number and types of radials, soil conductivity, etc.), the size of the top hat, construction of loading coils, and so on. (3) It would be nice to have antenna details, but for months, everyone involved with the project has been a little preoccupied to write articles. Again, this is not a formal scientific journal, where publication is withheld until everything has been reviewed by peers and all the lab equipment serial numbers have been duly logged. But neither are these people who showed up once, made an outlandish claim, then disappeared. They're still here, continuing their work, and I wouldn't have printed the report if they weren't. I expect we'll see a full write-up in due course. (4) Unfortunately, these antenna trials suffer from equal or greater lack of detail. How was 1 watt of power from the precision signal generator determined? Seventy volts RMS would suggest an impedance of 4900 ohms at the measurement point, for one watt, if the load was a pure resistance. Few generators are designed to accurately measure power into such a load. A real-world LowFER vertical antenna is invariably part of a resonant circuit, where voltages and circulating currents are much higher. This is sometimes referred to as "reactive power," and is not the same as I^2*R, since it involves reactance. This current can be quite high if the loss resistances (ground loss and coil loss, mostly) are kept low, because the loaded Q of the resonant circuit will then be higher. The value of R in a short vertical antenna is normally much smaller than the reactive impedances. Hence, legal "real" power across R is entirely consistent with a high circulating current. (5) The stated 14 mA value appears to be an assumption that does not take matching into account, as described above. It does not demonstrate non-compliance. (6) I, personally, have no doubt of the validity of Lyle's detection in Minnesota. He has long been a reliable member. The screen dump that he sent from the COHERENT program, published in April was not his first DX reception, but one of several. Functionally, that image is the same as a tape recording of the reception. (Better, because you literally can't hear a BPSK signal that's below noise, although it can be demodulated.) (7) The LWCA is not equipped to verify Part 15 compliance in anyone's experimental activity, and has never made a representation of doing so. I personally believe it would be an insult to run a disclaimer with a report such as this; though, as I said before, we would not have run it at all, were there reasonable doubt. (8) These last points, I have to say, are simply incorrect. If one has read Max Carter's "BPSK Bits" series over the last nine years, or Bill de Carle's articles on his COHERENT software, it should be clear that the default standard ASCII BPSK bit rate is 10 bits, or one character, per second. (Max has experimented with slower rates in hardware, but that's an exception.) Frame grabbing, however, is another matter, and slows down the apparent decision making, effectively narrowing detection bandwidth further. This has also been discussed in print. What follows is not a complete bibliography, just a few issues I could find with articles directly mentioning BPSK parameters, coverage tests, or both: Mar. '87 (*), Sept. '87, July '88, Nov. '88, May '89 (p. 17), Aug. '89, Feb. '90, Mar. '90, Apr. '90, May '90, June '90, Feb. '91, Mar. '91, Apr. '91 (p. 14**), May '92 (p. 15#), May '94, July '94, Sept. '94 (##), Dec. '94, Apr '95, May '95. My library is temporarily missing some back issues, where there are additional articles to be found. All articles above have BPSK in their titles, except those for which I put page numbers. Of special note: *Max Carter's initial definition of BPSK in The LOWDOWN, as near as I can determine. **Cliff Buttschardt's description of modes used at San Luis Obispo, when the beacon was still MPM. # First mention of frame grabbing. ## Description of COHERENT software and Max's measurements of below-noise reception. Concluding my remarks, I believe the foundation for the DX claim was well prepared. Having said as much as I know about the subject, maybe more, I will now shut up and let our members do the talking. - Lyle Koehler (lek@juno.com) adds some background. He remarks first that "the LOWDOWN is an experimenter's journal and doesn't have a pre- publication review process. That's the way it should be. Any of us can get ideas or loggings published, allowing readers to shoot them down, use them, or (in the best scenario) improve on them. LowFER DXing has a very short season. If everything in the LOWDOWN had to go through a review process, we could kiss the season goodbye before the news got into print. "The first few receptions of Cliff's beacon here in Minnesota were made using an old version (v 2.5c) of COHERENT, which was probably written before anyone, including Cliff, knew there was going to be a BPSK beacon with the HDO identifier. Regarding verification of "special conditions such as unusual propagation effects" I have no idea how we were supposed to do that. I don't feel that 1600-mile reception of a LowFER BPSK beacon was all that extraordinary." "The only quantitative information I have on LF DX propagation is contained in a series of articles by John Adcock, VK3ACA in the June through September 1991 issues of the Australian journal AMATEUR RADIO, mainly August. From the predicted curves of propagation at 196 kHz, it is evident that surface-wave propagation is not a significant factor at distances beyond 2000 km, even over sea water. With 100 watts effective radiated power, the predicted field strength at 2600 km is about 7 dB above 1 uV per meter for single-hop ionospheric propagation, and 0 dB above 1 uV per meter for two-hop mode. "It's interesting that the predicted two-hop field strength remains almost constant to beyond 4000 km. Ground-wave reflection losses are fairly low at LF. They should not be a factor in single-hop propagation and apparently do not strongly influence two-hop propagation either. If a California beacon can be heard in Hawaii over mostly sea-water, there's at least a statistical possibility that comparable DX can be achieved over land. "Another article by John Adcock (The Day We Crossed the Tasman on Long Wave, AMATEUR RADIO, April 1993) describes two LF experiments lasting a few hours each, with an ERP of about 8 watts. Signals from Gordon, Victoria, were heard by several stations in New Zealand and across the continent in Perth. A table in this 1993 article predicts a field strength of 8.6 dB above 1 microvolt per meter for one-hop propagation at 2600 km, with only 10 watts ERP. This is more than 10 dB higher than the predicted strength in the earlier article. I haven't attempted to contact the author to find the reason for the discrepancy. Because sky-wave propagation is statistical, and variations much greater than 10 dB in path loss are common, maybe both numbers are right! "A really good LowFER setup will have a radiation resistance of around 0.1 ohm, total antenna circuit losses of 10 ohms or less, and 75 per cent or better transmitter efficiency. It's possible to achieve an effective radiated power of 7.5 milliwatts, or about 41 dB below 100 watts. That puts the nominal received signal strength at 34 dB below 1 microvolt per meter if we use Adcock's more pessimistic prediction for one-hop propagation at 2600 km. "Thermal noise in the receiver should not be the limiting factor in LowFER reception. Ambient night-time noise levels will exceed the receiver thermal noise floor if you have a properly designed loop a few feet or greater in diameter and a good preamp, or an active whip a few feet long. Geography is a significant factor in the ambient noise level. "Obviously, a receiving location in a quiet rural area like Aitkin County, MN has a lower man-made noise level than almost anyplace in or near a large population center. Atmospheric noise is usually the limiting factor here after the TV set gets turned off. Because atmospheric noise originates primarily in thunderstorms, it decreases at higher latitudes. On quiet winter nights here in Minnesota at latitude 46.5 degrees north, we probably have an atmospheric noise level around 30 dB below 1 microvolt per meter in a 10-Hertz bandwidth. I arrived at this number by extrapolating noise data from a couple of references. "One source was an ancient copy (4th Edition) of REFERENCE DATA FOR RADIO ENGINEERS. The other source was a reproduction of some curves which I believe appeared in a paper by A. D. Watt and E. L. Maxwell in the June 1957 IRE PROCEEDINGS. Adcock's August 1991 article predicts a similar noise level. His predictions are also obtained by extrapolation of published data, but the references were not identified. Stations to the southwest of me such as MAX and HDO have an advantage over stations to the southeast because most winter QRN originates southeast of here. The noise level is minimized when my receiving loop is oriented to peak the signals from stations in the southwest (or northeast, since the loop is bidirectional). "Even with a 10-Hz receiver bandwidth, which is about what the DSP filtering action of the COHERENT software provides, the signal-to-noise ratio of the strongest California LowFERs at this location would normally be less than unity. However, LF sky-wave signal strengths can vary up and down (especially down, unfortunately) by quite a few dB. There appear to be ionospheric "sweet spots" on LF, just as there are on MF and HF. "Short-term improvements in LF signal-to-noise ratios of 10 dB or more are not uncommon. That would give our hypothetical California LowFER a 6 dB signal-to-noise ratio. Not good enough for aural CW copy, but beacon identification should be within the reach of the COHERENT BPSK software with the frame grabber function. I've used frame grabber settings of 127 to receive HDO when conditions were marginal, down to 7 or 15 when conditions were really good. And I've literally watched hours of garbage characters printing on the screen when the signals weren't recoverable at any setting. "It's beyond my ability to estimate the extremes of the statistical variations in LF propagation. However, I believe that if a well-designed LowFER station on one coast is sending BPSK and several people are listening in quiet locations on the opposite coast, a transcontinental LowFER DX record can be set next season. "The real test of BPSK will be its ability to support two-way contacts. Truly "real time" LowFER DX QSOs are likely to be rare, because the frame grabber may have to integrate many repetitions of a message to pull it out of the noise. Message lengths are also limited by the duration of the band opening, which may be half an hour or less. But that's also true of ham radio DXing, where an exchange often consists only of the call letters and a signal report (599, usually, unless the station is really weak!). In weak-signal CW work, it's common practice for the sending station to repeat the signal report over and over so the brain of the receiving operator can perform a function analogous to the frame grabber that Bill de Carle has built into the COHERENT BPSK software. "Over the past several years I've made audio tape recordings of a number of LowFER CW beacons. Most of them are located between 1000 km and 1600 km from here. Although these distances pale in comparison to the California-Hawaii record, the recordings demonstrate that long-distance LowFER reception is possible over land when conditions are right. "People like Max Carter, Bill de Carle and John West are to be applauded for their dedication in making the ideas, hardware and software for BPSK available to the average experimenter." -Bill Cantrell (TEXAS), Lead RF Engineer for the Motorola Cellular Infrastructure group, comments on lower-than-noise digital reception. "The coherent signalling techniques being used by Max Carter and others is nothing new. It was described in detail in past issues. When you repeat the same message over and over coherently, it allows the receiver to use noise averaging to effectively average out (reduce) the noise level, similar to what manufacturers do with RF spectrum analyzers. "We do something similar with our CDMA (Code Division Multiple Access) cellular telephone signalling schemes. This allows us to receive data transmissions at 21 dB below thermal (kTB). I should mention that at the VLF frequencies, the background noise level is much higher than kTB, so it makes the job that much tougher. But even without the high-tech signalling, I have received my own TEXAS (CW) beacon from 300+ miles away using conventional Q-multiplier ahead of the receiver to narrow the bandwidth down to a few Hz. So (the) report of 700 miles is not surprising." -Bill de Carle (e-mail: bill@ietc.ca) writes: "Many thanks for printing the letter from Dave Rickett in the May LOWDOWN, and for taking the time to write such a thoughtful response. A certain healthy skepticism from readers is always welcome. As the author of the original COHERENT BPSK algorithm, I can assure you there is nothing in the code which would make it favor Cliff's HDO beacon! There is a story that if you let a bunch of chimpanzees type away for long enough they would eventually produce the entire works of Shakespeare just by coincidence. If you run the COHERENT software with pure noise as input, the probability of getting HDO on the screen over and over is for all practical purposes: zero. I'd much rather take my chance on winning a big lottery jackpot. In fact, the odds against getting a screenful of solid copy like the one shown in the April LOWDOWN are so astronomical I would have to conclude that the most likely explanation for it would be that Cliff's beacon was actually received in Minnesota just as claimed." -Steve Ratzlaff indicates we LF hobbyists are a bit behind the times, actually. "Defense contractors have been doing systems that do this sort of thing for years, it's nothing new. What is new is having the technology finally show up at the hobbyist/experimenter level." Footnote. Summertime, and the livin' is easy...but don't let that keep you from sending us your news and views. 73. - - -