2 October 2014


Serdolik MFSK-34, aka CROWD-36,  is a MFSK-34 system with 40Hz spaced tones modulated at speed of 40Bd speed. The needed bandwidth is ~ 1500 Hz. This waveform is also known as CROWD-36 just because the grid of the tones clearly exhibits 2 empty places, so that the possible tones sums to 36 (34+2).

In the past CROWD.36 transmitted encrypted information in the form of 5 digit numbers then later moved to online encryption. These days the mode seems to be being used for link setup information with the actual traffic being sent in another mode such as OFDM if the conditions are suitable. So we'll have frequently a long MFSK-34 sequence repeating the same chars (cit. from Rivet decoder).

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