Konichiwa! Very nice catch! The BFSK is STANAG 4481, 75Bd/850Hz shift offline encrypted by our old friend KG84C
https://www.sigidwiki.com/wiki/STANAG_4481https://en.wikipedia.org/wiki/KG-84Here's your secret message;
Detected KG-84C SYNC with 92% confidence
Initialization vectors: 7D58AADC2A825673 C65BFF94B8CBE16B
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
End of message (idle pattern)
Both Sorcerer and K500 have demodulators/detectors/parsers for S4481 and KG84 use. That said, once you hear an init to KG84 via fsk you'll always recognise it. Most USN S4481 traffic is going to be KG84 or newer encryption device, so when you see/hear 850Hz 50/75 Bd fsk think USN or NATO or Japan.
Konchow for the nice recording.