18 March 2016

CIS 5 x MFSK-16 + BPSK 250Bd

this interesting signal (supposed to be used by "Russian Intelligence") has been heard on 13497.0 KHz and 15812.0 KHz USB on 30 October (from 1300z to 1330z) and on 15845.0 KHz USB on 18 March (from 1300z to 1320z).
The most interesting feature are the BPSK inserts, each 10 seconds, that modulate in turn 6 different 250 Hz spaced carriers at 250 symbols/sec. Apparently there isn't a certain order of choice of the six carriers or a sort of cycle so it's difficult to say something about the scope of these inserts. Since they do not carry informations, they could be sent for tuning filters and equalizing MFSK demodulator purposes, but it's only my guess.

About the MFSK part, it's possible to individuate five distinct MFSK-16 channels with tone separation of 20Hz and 10Bd speed

Most likely the signal is a sort of FTD waveform. All the heard transmissions end with the same ~860 ms sequence  2 frequencies, modulated in some frequency time shifted method.

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