Mystery Multiplex Signal

[mmcc]

I see this signal, sometimes for several hundred KHz, sometime for over 1MHz, spanning anywhere from 2MHz-70MHz.



1.  2MHz-70MHz (bandwidth of several hundred KHz to 1MHz)
2.  Visible 24/7
3.  Continous (Can sometimes switch on/off on certain frequencies)
4.  Receiver Mode - N/A
5.  UK
6.  Looks like a multiplex signal.  Has an unstable modulation of around 25Hz.

For reference, here is the audio:
https://www.sigidwiki.com/wiki/Unidentified_Signal_5

Any ideas?

[BoomboxDX]

Dumb question time: You're certain this isn't some sort of RFI?

Does the signal propagate? I didn't hear any obvious fading in the sound clip.

Personally, I haven't heard anything exactly like that signal. The closest noise to it is OTHR (over the horizon radar).  The famous Russian Woodpecker of the 1970's and 80's had a similar sound and pulse rate, but it also moved around a lot, and most times you could hear fading of some sort.

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[mmcc1]

Sorry for the late reply.  Lost my login details and emails are not being received for a password reset.  I have been looking at this signal for a number of weeks.  I'm fairly confident that it is not RFI at this stage.  As far as I can tell, its an undisclosed OTH radar located somewhere along a line that passes through Alaska, Canada, Greenland and Ireland.

The below image shows that each channel is independently modulated:

https://imgur.com/urRTaYE

I caught the signal changing modes, from an unstable 40ms pulse, on each channel to a more stochastic pulsed output.  Then I caught each of the channels sweeping the frequencies.

https://imgur.com/iUOgV6e

The only two known OTH radars are Nostradamus in France and the Polar OTH in Canada.  But this seems to be something new.

[rwrv]

This is caused by powerline ethernet. I've had the same happen and it went when the powerline system was replaced for another one.