12 April 2018

188-110A 2400S (prob. Egypt-Ny)

slightly modified 188-110A bursts with some voice comms in Arabic, prob. from Egyptian Ny, spotted on 15950.0 KHz/USB 1320z.
It's interesting to note the well visible three 200ms synchronization pattern segmentes (MIL 188-110 § Sync preamble sequence), confirmed by the 200ms spikes in the preamble ACF. Data blocks ACF exhibits 20ms spikes that makes 48 tribit symbols at the speed of 2400Bd: each data block consisting of 32 symbols of unknown data (user data) and 16 symbols of known data (probes).

Fig. 1
Fig. 2 - ACF values for preamble and data blocks
Fig. 3 - frame structure
The short synch preamble (3x200ms) and the used framing (48 symbols, 32+16) point out the 2400bps/S mode, as confirmed by the 5710A modem. 

Fig. 4

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