UNID 12371 USB signal: Mystery solved.

The peculiar signal seems to be the result of audio feedback:

http://signals.taunus.de/PUB/Feedback.HTML

The above article resolves most of the similar "mystery" signals like "the whales". However, I can't forget that...

Any sufficiently advanced technology is indistinguishable from noise.

UNID (encrypted voice?) on 12371 kHz using University of Twente web SDR

I had the chance to use the free web SDR service provided by the University of Twente in Netherlands. It covers the entire HF and is an excellent way to monitor the bands from office :-)

As I was scanning the bands, I found a peculiar transmission on 12371 USB at approx. 1237z (14/09). I am not sure if the tuning and mode selected is correct, but here is what I heard (recorded from the soundcard output), and this is a spectrogram image:

 12371USB 14/09/2012 1237z (click for larger)

Any ideas?

73
Manolis