15 June 2018

STANAG-4539: unexpected data rate of 12800 bps

Long transmission (hours) of STANAG-4539 8PSK 2400 Bd bursts spotted on 14 June morning on 7807.2/usb:  each burst lasting 1680 ms and composed of 13 x 287 tribit symbols frames. It's interesting to note the uncoded 12800 bps speed detected by the 5710-A modem: using 8PSK at a modulation rate of 2400Bd, the the maximum data rate obtainable is 4800 bps (7200 bps on-air) therefore there is something wrong somewhere (a data rate of 12800 bps is obtainable using QAM64 modulation at 2400 Bd). STANAG-4539 is an "auto-baud" waveform, so perhaps they use a modified preamble that misleads the modem.
A run of TDoA multilateration says Cornwall (UK) as Tx location, possibly UK MoD tests from St.Eval? 

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https://yadi.sk/d/bpzDxsBX3Xzkn3
 

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