I received this signal around 7 MHz. I've checked all over the "Signal Identification Wiki", but cannot find anything similar to this. I'm pretty sure this is some simple FSK, but that is the exact type?

The signal is at around 2200Hz (in audio file). Partial spectrogram:

partial signal spectrogram

The WAV can be downloaded here: https://nofile.io/f/CjEk6A513W8/radiodata.wav

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    It's just too fast for any FSK that I've seen before. – Risahas Dec 28 '17 at 19:51
  • What frequency was this on (approximately)? – Mike Waters Dec 28 '17 at 20:19
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    It was about 7 MHz. – Risahas Dec 28 '17 at 20:27
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    your plot is pretty meaningless when you don't give us dimensions on the y and x axes. Is one pixel x direction a microsecond? a millisecond? a second? is one pixel of y direction 1 Hz? 1 kHz? 1 MHz? Is this a frequency/time plot at all? Why is this "fast" for an FSK signal? If it really is FSK (which is likely, but there's corner cases that look like FSK but are generated differently), then I'd argue it's even a pretty slow one, given that you can seemingly clearly, without much Gibb's phenomenon showing up, "read" it from a periodogram. – Marcus Müller Jan 2 at 12:51
  • @MarcusMüller I'm sorry, but I can't remember the exact zoom which I've used in 'Sonic Visualiser', and hence the exact resolution of the provided spectrogram. There is a WAV file provided too. Thank you a lot for your advice, I'll take it for sure! :) Anyway the question is not actual now, and the question can be closed with Rich Morgan's answer being the closest. Unfortunately I haven't found the actual nature of this signal. Thank you! – Risahas Jan 8 at 13:38

I copied a test transmission from H.A.A.R.P. on this frequency in the 1990s. It was on 6.99 MHz @ 0430 - 0435 UTC. I have a card from them 3/8/97 confirming my reception. Perhaps that's what it is.

  • Turned out that this is just an ASCII modem trasmission with FSK, like this one: youtube.com/watch?v=y3ZT-1y4eeY – Risahas Jan 9 at 12:53

First Guess is PSK-31 loaded as a CW signal, offset to 2200.

  • Definitely not PSK-31. – Phil Frost - W8II Jan 3 at 17:21
  • Definitely not PSK-31. – Phil Frost - W8II yesterday Thank you Phil. I have no measured observation to back-up my answer. Peter Martinez (G3PLX) introduced PSK-31 into amateur radio in December 1998, so the time-frame is possible. – user3690746 Jan 4 at 17:51

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