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The author labled this mode as a 9-FSK modulation so this is why it is under FSK

FEC in JT9 uses the same strong convolutional code as JT4: constraint length K=32, rate r=1/2, and a zero tail,
leading to an encoded message length of (72+31) × 2 = 206 information-carrying bits. Modulation is nine-tone frequency-shift keying, 9-FSK at 12000.0/6912 = 1.736 baud

. Eight tones are used for data, one for synchronization. Eight data tones means that three data bits are conveyed by each transmitted information symbol.

Sixteen symbol intervals are devoted to synchronization, so a transmission requires a total of 206 / 3 + 16 = 85 (rounded up) channel symbols.

The sync symbols are those numbered 1, 2, 5, 10, 16, 23, 33, 35, 51, 52, 55, 60, 66, 73, 83, and 85 in the transmitted sequence. Tone spacing of the 9-FSK modulation for JT9A is equal to the keying rate, 1.736 Hz. The total occupied bandwidth is 9 × 1.736 = 15.6 Hz.

Modulation: 9-FSK
Bandwidth: 15.6 hz
TX duration: 49 secs.
Baud: 1.736
Min SNR:-27db based on 2500hz bandwidth noise

If you ran across this on the radio and not famialar with the mode you might think it is a birdie in your radio due to the small bandwidth.

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Sound of JT9
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