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21 lines
1.1 KiB
Plaintext
21 lines
1.1 KiB
Plaintext
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// Status=review
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//Needs work!
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JT9 is designed for making minimally valid QSOs at LF, MF, and HF. It
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uses 72-bit structured messages nearly identical (at the user level)
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to those in JT65. Error control coding (ECC) uses a strong
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convolutional code with constraint length K=32, rate r=1/2, and a zero
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tail, leading to an encoded message length of (72+31) × 2 = 206
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information-carrying bits. Modulation is nine-tone frequency-shift
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keying, 9-FSK. Eight tones are used for data, one for
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synchronization. Eight data tones means that three data bits are
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conveyed by each transmitted information symbol. Sixteen symbol
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intervals are devoted to synchronization, so a transmission requires a
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total of 206 / 3 + 16 = 85 (rounded up) channel symbols. The sync
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symbols are those numbered 1, 2, 5, 10, 16, 23, 33, 35, 51, 52, 55,
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60, 66, 73, 83, and 85 in the transmitted sequence. Each symbol lasts
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for 6912 sample intervals at 12000 samples per second, or about 0.576
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seconds. Tone spacing of the 9-FSK modulation is 12000/6912 = 1.736
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Hz, the inverse of the symbol duration. The total occupied bandwidth
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is 9 × 1.736 = 15.6 Hz.
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