// Status=review
//Needs work!

JT9 is designed for making minimally valid QSOs at LF, MF, and HF. It
uses 72-bit structured messages nearly identical (at the user level)
to those in JT65. Error control coding (ECC) uses a strong
convolutional code with 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.  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.  Each symbol lasts
for 6912 sample intervals at 12000 samples per second, or about 0.576
seconds. Tone spacing of the 9-FSK modulation is 12000/6912 = 1.736
Hz, the inverse of the symbol duration. The total occupied bandwidth
is 9 × 1.736 = 15.6 Hz.
