Unid PSK2/FSK2 połączone serie

This is simply a very interesting transmission heard on 14736.5 KHz/USB which consists of repetitive bursts lasting about 12.6 s and separated by an interval of 1300 ms. The most interesting aspect is that a "combined" waveform is used, that is, a first section with PSK2 modulation followed by a second section with FSK2 modulation: both the segments are modulated at the same rate of 31 bps (Figure 1).

Fig. 1 - PSK2/FSK2 "combined" waveform

An interesting feature that my friend cryptomaster pointed out is the PSK2 mode, where the bitstream is transmitted in single bits: this feature can be seen in Figure 2 utilizing both the "oscilloscope" function and the AM demodulator of SA. The demodulation of this bit-keying mode is complicated, seemingly due to the division of the carrier into separate bits.

Fig. 2 - PSK2 segment

The FSK2 section modulation uses a shift of about 370 Hz (measured 373) and the resulting bitstream after demodulation has an 8N1 framing which appears to be transmitted in reverse polarity (Figure 3).

Fig. 3 - FSK2 segment

The interesting things about this curious transmission don't end here: going back to the erstwhile posts I discovered that the FSK2 section carries precisely the same content as the 50Bd/612 FSK2 bursts analyzed any months ago [1] and compared in Figure 4.

Fig. 4

So, it's likely the same (unid) user, possibly experimenting with different waveforms... who knows.

The PSK2 section besides most likely carries the same content of the FSK2 segment, unfortunately demodulation with SA was not successful due to the peculiar mode which is here used.

https://disk.yandex.com/d/HV3j9zdSSRqLww

[1] http://i56578-swl.blogspot.com/2024/11/unid-fsk-50bd612-bursts.html