13 July 2017

a burst ARQ mixed system (MS110 & S4539)


transmission was spotted only once on 7906.0 KHz from 0603 UTC (tune time) until 0639 (signal off). It's a burst ARQ system in which one station uses STANAG-4539 and the other one uses MIL 188-110A, both running at fixed data rates (respectively4800 and 2400 bps) and carrying STANAG-5066 frames. 
Difficult to say who sends data and who send ACKs. Only the Stanag-4539 bursts have a relative good quality for their analysis (Figs. 1,2): these bursts in large part carry STANAG-5066 DTS control frames (D_PDU type 6) so the station that uses 188-110A could be the data sender, although their duration is very short. Most likely it's a test transmission.

Fig. 1 - frame structure of STANAG-4539 bursts
Fig. 2 - 287 symbols period of STANAG-4539 bursts
Since the different framings of MS110A and S4539, the two stations could use a "special" adhoc configuration or a sort of two-demodulation requirement so to discriminate the incoming signals.

It's worth noting that in many D_PDUs (S4539 bursts) the address of the destination node belongs to the block assigned to France (006.014.yyy.zzz) while the source address belongs to a reserved block (015.xxx.yyy.zzz).

Fig. 3



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