mirror of
https://github.com/saitohirga/WSJT-X.git
synced 2024-11-18 10:01:57 -05:00
118ad4e1b7
git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@5434 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
21 lines
1.1 KiB
Plaintext
21 lines
1.1 KiB
Plaintext
// 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.
|