wideband Akula

A dear friend of mine sent me a very very interesting recording of a short Akula transmission consisting of the usual Akula 500Bd/1000 FSK preceeded by 15 DBPSK modulated tones, symbol rate of 500Bd (as Akula II).

Fig. 1

As already discussed in a previous post [1] the 15 DBPSK channels and the FSK segment transport the same data (Figure 2), probably using such a width signal - about 30 kHz - should provide good noise immunity. 

Figure 2

Most interestingly, the signal was recorded using an SDR receiver near Kiev, so given that:
1) Akula waveforms are used for subcomms
2) signal strength is impressive (Figure 3)
the presence of Russian subs in the Black Sea could be assumed...

Figure 3 - waterfall image, thanks to my friend who recorded the signal

https://disk.yandex.com/d/HrJYX195Q9kRDw

[1] https://i56578-swl.blogspot.com/2021/02/15-channel-30khz-cis-akula-shark.html