9 June 2015

Chinese mixed mode QPSK 2400Bd + MFSK-8 125Bd

As reported in the log of 5 June
05/06/15 16148.5 --- Chinese Mil 2105 USB mix mode: MFSK-8 (125/250) + QPSK 2400Bd
05/06/15 16148.5 D54 Chinese Mil 2103 USB MIL 188-141A clg N50
on 16148.5 USB I heard the callsign D54 calling N50 using the MIL 188-141A protocol, both the callsigns belong to a Chinese Mil network. After a few seconds the M188-141A was followed by an odd bursty waveform sounding like the previous ALE but un-decodable (signal 1 in pic.1).

Pic. 1
Talking with KarapuZ about this signal he told me that is a mixed mode QPSK 2400Bd + MFSK-8 125Bd used by Chinese Military (signal 2 in pic.1) and he provided me a recording of this waveform.
As said above, the MFSK segments are manipulated at 125 Baud and consist of eight tones, 250 Hz spaced, just like the standard MIL 188-141A (pic. 2); trying to decode it you do not get anything although the tones are in the expected position: k500 recognizes it as [AQC mode], but it's clearly wrong, while other deciders prints non-sense ASCII strings.

Pic.2 MFSK-8
Perhaps they do not use this MFSK waveform as an ALE resource since they just use the standard MIL 188-141A, as reported by many listeners and in my logs too.
About the PSK segments it was pretty easy to get its boudrate and carrier (2400Bd and 1800 Hz), unfortunatelly not the same thing for the phase-plane (pic. 3): a better signal could help.

Pic.3
Both the two recordings are downloadable from here:
https://www.dropbox.com/s/bvhodhs85wfekpy/mix%20mode%20chinese.wav?dl=0
https://www.dropbox.com/s/gg5mlbob31i00y9/05-Jun-2015-211122%2016.148500%20MHz.wav?dl=0 

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