I started to follow these burst from ~0800z on USB 16257.0 (16259.0 cf) on 17 October, they appeared pretty regularly in seconds 10, 25 and 40 (mm.10, mm.25, mm.40) for more than one hour then they stopped, or at least I did not hear them anymore.
The signal have 18 tones preamble followed by a sort of mixed PSK-4/PSK-8 modulation at 2400 symbols/sec, carrier is measured at ~1900Hz (but I could be mistuned). The SA phase-plane module vaguely reveals a PSK-8 constellation when its n-ary detector is set to 8, but that same constellation comes out also in case of 4-ary. ACF/CCF is 20ms lenght and is visible in the phase detector after the preamble.
It looks like the Chinese DQPSK, but I am not positive about this identification; the recording is available on simply request: comments are welcome!
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| Pic. 1 - the unid burst |
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| Pic.2 - 4-ary and 8-ary constellations |
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| Pic. 3 - phase detector output, note the 20ms pattern |
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Pic. 4 - CCF and signal frame
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