21 October 2017

strong 4+4 π/4 DQPSK 75Bd Chinese modem

Strong copy of the 4+4 DQPSK 75Bd Chinese modem on 17149.7 KHz/USB at 0915, 1128 and 1129 UTC.

Fig. 1
Fig. 2
Fig. 3
Note the different periods in preamble, 36-bit length, and data segments, 12-bit length: most likely a 6-bit structure signal with 1 stop bit (Fig. 6)

Fig. 4 - 36-bit period in the preamble segments
Fig. 5 - 12-bit period in the data segments
Fig. 6 - 6-bit signal

The same signal was also heard few hours later (around 1130z) at -91dB and no QSB: too good conditions for a signal coming from China:

By the way, the Algerian Navy recently acquired three C28A Corvettes built in China [1] by Hudong-Zhonghua Shipbuilding Group, a subsidiary of China State Shipbuilding Corporation, this could explain the strength of the signal.