Voice of Korea - transmitters

[kk6pr]

North Korea's SWL station can always be identified by the ~2Hz pulsing of their transmitter, especially noticeable during quiet segments with no audio.  I was wondering what might cause this - unregulated power from the generators they use to power the transmitters?

Audio:  https://drive.google.com/open?id=1Bz9WS4qt5w_IOLnFWOha22cHbxCUDX9t

[redhat]

Do you actually see carrier frequency shift on the waterfall or spectral display?  It sounds to me like slow speed data, or background noise in their audio chain.

+-RH

[kk6pr]

I don't see any carrier shift and the spectrograph on my kiwi isn't detailed enough to see what part of the audio spectrum is actually being affected.  I'm using a raspberry pi - but next time I fire up my desktop, I'll try to look at it with a better audio editor.

I assume it's caused by a variation of transmitted power.  I haven't heard any other stations with this consistently identifiable characteristic - and it's too regular to be caused by propagation.

[Josh]

Could be intentional msk or something like that, my money's on the/a multiplicity of devices in the audio chain all with low level noise adding up to the sumptuous soundfeast as recorded. Some hfbcasters, however, are reputed to have sent messages via their carrier to espions or to especialised forces for their respective govs.

[redhat]

an I/Q recording would be helpful in determining the nature of said beast.  AMSS might sound similar to this as well.

+-RH

[kris]

Could be intentional msk or someth Some hfbcasters, however, are reputed to have sent messages via their carrier to espions or to especialised forces for their respective govs.

This is an interesting observation. Although I also noticed this phenomenon in disbelief, for example "pirate station?" R. Europe from Russia. In the intervals between the music I hear a clear keying of the carrier with a fast CW signal. In Poland, in 1972-1991, a 2MW transmitter operated at 227kHz with the highest antenna mast in the world at that time, 642m high. Apparently, his collapse was not an accidental mistake when repairing the suction. It is said that it also served the Russians to send secret messages to their submarines, using very slow carrier modulation.
After this incident, the Russians more easily agreed to withdraw their troops from Poland.
https://tech.wp.pl/maszt-radiowy-w-konstantynowie-najwyzszy-obiekt-na-swiecie-stal-w-polsce-6123962871343233a

[Josh]

The view from atop that tower must have been grand.

[thecolonel]

It's also interesting to listen to the Voice of Korea on one of the SDR receivers in Japan or East Asia/Siberia during those transmissions. It's quite often that you will hear either what appears to be feedback in the audio or what appears to be an echo as if there are two transmitters operating on the same frequency but slightly off in their timing. I don't know if anyone else has noticed such but I've done a few SDR recordings from the East Asia SDR receivers and it seems there's some sort of echo or audio issue on the same frequencies. Try 13760 khz, 15180 khz, 15245 khz and others around the East Asia daylight time of 2200 UTC to about 0900 UTC.

I found it to happen here and there but not real bad unlike the garbage audio that came out of Radio Cairo on 9900 or the new 31 meter frequencies I heard while back. For a while they did improve the overmodulated audio then it was like it was back to the old days. I wish my local nearby 5000 watt AM station would figure out that overmodulated audio sounds like garbage in general.