4 July 2019

110A 2400bps modem carrying 1536-bit protocol

Signal recorded on 14600.0 KHz/USB tranks to the KiwiSDR http://collie2.ddns.net:8073/ located in Western Australia. 
The used HF waveform is 188-110A Serial in 2400 bps mode, note the 48 symbols length frames (32+16 UK). ACF value is 200ms that makes 1440-bits/480-symbols: the length of the ACF is due to the short interleaver matrix dimensions for 2400 bps speed (40 rows x 70 columns) as discussed here.
Fig. 1
Once demodulated, we get a stream that has the well-known period of 1536 bits length that can be attributable to the GA-205 multiplexer: don't know if they were using 4 of 12 channels only. Also found the sync characters 9C16 and 9D16 ... but it might be a mere coincidence.  Most likely it's a naval broadcast by the Australian Navy RAN.

Fig. 2
Fig. 3

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