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).
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| Fig. 1 |
As already discussed in a erstwhile post [1] the 15 DBPSK channels and the FSK section transport the same data (Figure 2), most likely utilizing specified a width signal - about 30 kHz - should supply good sound immunity.
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| Figure 2 |
Most interestingly, the signal was recorded utilizing an SDR receiver close Kiev, so given that:
1) Akula waveforms are utilized for subcomms
2) signal strength is awesome (Figure 3)
the presence of Russian subs in the Black Sea could be assumed...
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| 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
