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git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@3666 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
25 lines
1.2 KiB
Plaintext
25 lines
1.2 KiB
Plaintext
// Status=review
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//Needs work!
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JT9 is designed for making minimal QSOs at LF, MF, and HF. It uses
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72-bit structured messages nearly identical (at the user level) to
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those in JT65. Error control coding (ECC) uses a strong convolutional
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code with constraint length K=32, rate r=1/2, and a zero tail, leading
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to an encoded message length of (72+31) × 2 = 206 information-carrying
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bits. Modulation is nine-tone frequency-shift keying, 9-FSK.
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Eight tones are used for data, one for synchronization. Eight data
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tones means that three data bits are conveyed by each transmitted
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information symbol. Sixteen symbol intervals are devoted to
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synchronization, so a transmission requires a total of 206 / 3
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+ 16 = 85 (rounded up) channel symbols. The sync symbols are those
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numbered 1, 2, 5, 10, 16, 23, 33, 35, 51, 52, 55, 60, 66, 73, 83, and
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85 in the transmitted sequence.
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Each symbol lasts for 6912 sample intervals at 12000 samples per
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second, or about 0.576 s. Tone spacing of the 9-FSK modulation is
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12000/6912 = 1.736 Hz, the inverse of the symbol duration. The total
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occupied bandwidth is 9 × 1.736 = 15.6 Hz. A generated JT9 signal has
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continuous phase and constant amplitude, and there are no key clicks.
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The transmitter's power amplifier need not be highly linear.
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