The author labled this mode as a 65-FSK modulation so this is why it is under FSK
A detailed description of the JT65 protocol was published in QEX for September-October, 2005. A Reed Solomon (63,12) error-control code converts 72-bit user messages into sequences of 63 six-bit information-carrying symbols. These are interleaved with another 63 symbols of synchronizing information according to the following pseudo-random sequence:
The synchronizing tone is normally sent in each interval having a “1” in the sequence. Modulation is 65-FSK at 11025/4096 = 2.692 baud.
Frequency spacing between tones is equal to the keying rate for JT65A, and 2 and 4 times larger for JT65B and JT65C.
For EME QSOs the signal report OOO is sometimes used instead of numerical signal reports. It is conveyed by reversing sync and data positions in the transmitted sequence.
Shorthand messages for RO, RRR, and 73 dispense with the sync vector entirely and use time intervals of 16384/11025 = 1.486 s for pairs of alternating tones.
The lower frequency is the same as that of the sync tone used in long messages, and the frequency separation is 110250/4096 = 26.92 Hz multiplied by n for JT65A, with n = 2, 3, 4 used to convey the messages RO, RRR, and 73.
Bandwidth: 177.6 hz
TX duration: 46.8 secs.
FEC code rate: 12/63 = 0.19
Decoding: Berlekamp-Massey algorithm, with erasures
Source encoding of callsigns and grid locators: basic idea from
Clark and Karn's EME-2000 paper
Min SNR:-25db based on 2500hz bandwidth noise