HFU HF Underground
Loggings => HF Mystery Signals => Topic started by: Mixer on April 02, 2020, 0420 UTC
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Noted on the WOR mailing list by several individuals UTC 2 April 2020 since at least 0110 UTC. A data signal of some kind, about 6 KHz wide, causing a lot of interference to WWV on 5.000 MHz.
Lower edge about 4.997 MHz and upper edge about 5.005 MHz.
It was quite strong at my QTH in upstate NY when checking at 0210 UTC, but is weaker now. Being heard on multiple Kiwi SDRs, with midwestern and eastern receivers getting much stronger signals than in the western US. I could even here it weakly on the U Twente Web SDR in the Netherlands.
Preliminary TDOA analysis seems to be pinpointing a “hot zone” on an axis from northern Indiana up towards Chicago, and indeed signal levels on individual Kiwis near Indianapolis and Chicago appear to be quite strong.
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I did not get a chance to look at this signal closely, however, at first glance it was 850 Hz shift FSK. It appeared to have only two tones of actual data, however 5 or 6 tones were seen, making it very wide. Each of the tones appeared to be a duplicate of one or the other of the two tones with unique data.
Total guess here, but it looked like a distorted STANAG 4481 FSK signal. I would guess a spur or broken transmitter.
Unfortunately, I did not make any recordings of the signal, literally every receiver and PC here at the desk was tied up making other recordings at the time.
T!
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Still ongoing at 1425 UTC 02 APR. Weak but noticeable here in NY state, with WWV also being heard. It’s still quite strong on Kiwis in the midwest, but I can’t hear it at the moment on your Kiwi in California.
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Audible here in MD at 1714 UTC.
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1800 UTC - Steady S7 signal in WNY. Five to six tones are present.
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The signal was still present at 1830 UTC, same spread of 4997 to 5005 kHz. I tuned in very strong signals via KiwiSDRs located around the Northeast, with only a very weak signal in other areas of North America.
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Still S9 here in NC
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Bet it's 4985 Davidsonville, MD S4481 fsk with spurs.
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I have it here in Toronto, pretty strong, been going all day. Here's a snippet of waterfall.
(https://cdn.discordapp.com/attachments/505438028911869964/695421515734450196/unknown.png)
Here's a short recording in original PCM, and a 90 minute recording encoded to Vorbis to save space.
https://cdn.discordapp.com/attachments/400099900840214529/695380332324585572/17-06-16_Unknown_4997.62_kHz.wav (https://cdn.discordapp.com/attachments/400099900840214529/695380332324585572/17-06-16_Unknown_4997.62_kHz.wav)
https://cdn.discordapp.com/attachments/675850914732572697/695424474706739200/17-14-23_Unknown_4997.14_kHz.ogg (https://cdn.discordapp.com/attachments/675850914732572697/695424474706739200/17-14-23_Unknown_4997.14_kHz.ogg)
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At 0515 on 3 APR, there now appears to be just a standard 850 Hz FSK transmission, with the lower frequency at about 5001.6 and the upper at 5002.4
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Bet it's 4985 Davidsonville, MD S4481 fsk with spurs.
I just ran the TDOA algorithm twice in a row using Kiwis in Virginia, Pennsylvania, Maryland and Ohio on 4985, and it did pinpoint it pretty close to its actual location (the center of the bullseye was about 75 miles southwest of Davidsonville). I then immediately ran the TDOA twice on the mystery signal using the same 4 Kiwis, and it showed a completely different result - multiple spokes with no clear source - indicating probable 1 or 2 hop propagation from a different location.
I’ll try it again later today during daytime if it’s still on.
Right now, the transmission is back to standard FSK, about 1.5 KHz above WWV.
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Bet it's 4985 Davidsonville, MD S4481 fsk with spurs.
Unfortunately it probably is not, I compared the two signals and the 5000 USB signal was unique data to any S4481 FSK I could find for comparison. I checked them all from 2000 kHz to 14000 kHz (propagation left nothing above that for me to check).
I agree, it looks like S4481 FSK, and my first thought was spurs, but I could not find a matching transmission anyplace.
T!