4 January 2018

MFSK-4 session using 250Bd/500Hz & 160Bd/320Hz

Interesting MFSK-4 transmission recorded by my friend Mike (Mike Cache-Ortiz, mco) on 17423.0 KHz/USB: during the session  the mode (speed and separation) changes from 250Bd/500Hz to 160Bd/320Hz (Figs. 1,2).

Fig. 1
Fig. 2
I asked my friend Karapuz if he knew this transmission and he directed me to a radioscanner post where he describes a similar signal: in that case the variations were (Bd/Hz) 500/1000, 400/800, 250/500 and 125/250:
It's worth nothing that Karapuz measured a 336-bit period in all those modes, as reported in the mentioned link, and I found just the same value in both the 250/500 and 160/320 modes (Figs 3,4). Probably it's the same (Russian?) system.

Fig. 3
Fig. 4

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