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This mode is indented for very slow and extremely weak signals at 4.375 baud

The author labled this mode as a 4-toned FSK that is why it is under FSK type of modes

FEC in JT4 uses a strong convolutional code with constraint length K=32, rate r=1/2, and a zero tail.
This choice leads to an encoded message length of (72+31) x 2 = 206 information-carrying bits.
Modulation is 4-tone frequency-shift keying (4-FSK) at 11025 / 2520 = 4.375 baud.
Each symbol carries one information bit (the most significant bit) and one synchronizing bit.
The two 32-bit polynomials used for convolutional encoding have hexadecimal values 0xf2d05351 and 0xe4613c47, and the ordering of encoded bits is scrambled by an interleaver. The pseudo-random sync vector is the following sequence (60 bits per line):


Min. SNR is -23 db referenced to 2500hz bandwidth noise levels
TX duration is 47.1 seconds
Bandwidth is 17.5 hz
Modulation: 4-FSK

If you ran across this mode on the air and was not familair to this mode , you might think this is a birdie in your radio , due to the small bandwidth.
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Club Log
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Sound of JT4
Image of JT4