Since the weak signal, a tip from KarapuZ was decisive to indentify the name of the signal: he sent me his recording of the Chinese-64 modem and it's easy to verify that both the records show the same start sequence of symbols (pic. 1), unless the white-circled descending ramp which is visible in my recording. About that ramp, it's difficult to say if is a new-add to the original signal, maybe for delimiting message segments, or if it's unrelated to the signal: my opinion is that the latter is less probable since the ramp happens in between consecutive sessions without overlapping.
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| pic.1 |
The signal was heard on 16990.2 KHz (cf) around 0910 UTC, it consists of 64 tones, 37.5 Hz spaced, modulated at 37.5 Baud speed (pic. 2): these values sligthly differ form the ones reported in the analysis by radioscanner.ru friends.
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| pic.2 |
It's worth nothing an odd behavior of the signal, seen in both the two recordings: in some segments the tones seem to have a longer duration (~50ms) that in some way could affect the speed computation.
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| pic.3 |