14 June 2020

50Bd/500 FSK (likely CIS Gov/Mil)


My friend cryptomaster (thanks) confirmed the user (CIS networks) and he also pointed out that the 128-bit sequence is actually a 64-bit sequence that is transmitted in opposite polarity:

As well as the central part of the message which is the same 64-bit sequence (here 13-bit shifted) but with one bit in error:

11 June 2020

Unid (likely CIS) 50Bd/500 FSK message recorded on 12221 KHz (cf) at 1035z using the KiwiSDR "nsk" located near Novosibirsk, Russia. Notice the LFSR sequences generated by the polynomials x^7 + x^5 +x + 1 (128 bytes length) and x^5 + x^4 + x + 1 (Fig. 1).

Fig. 1 - the two LFSR sequences
Although the shift is an integer multiple of the speed, the two FSK tones do not preserve their phases (Fig. 2).

Fig. 2 - phases of the two FSK tones

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