7 March 2016

Chinese-64: MFSK-64, 37.5/18.7 Bd 37.5Hz

Since the weak signal I asked my friend KarapuZ to send me one of his recordings of the Chinese MFSK-64 modem: it's easy to verify that both the records show the same start sequence of symbols (pic. 1).

The signal, copied on 16990.2 KHz (cf) around 0910 UTC, consists of 64 tones, 37.5 Hz spaced, modulated alternatively at 37.5 and 18.7 symbols/sec speed (pic. 2 for 37.5 Bd speed).

It's worth nothing the characteristic "dual-speed" modulation, seen in both the two recordings: in some segments the speed switches from 37.5 to 18.7 Baud  and conversely (pics 3,4)
pic. 3
pic. 4
The initial part is always modulated at 18.7 Baud and - as said - seems to transport the same data (pic. 5):

pic. 5


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