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Fix FT8 encoding description

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git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@8021 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
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Bill Somerville 2017-08-10 18:07:53 +00:00
parent f260531bac
commit b40da9da92
1 changed files with 8 additions and 8 deletions
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doc/user_guide/en/protocols.adoc
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@ -61,15 +61,15 @@ _WSJT-X_ modes have continuous phase and constant envelope.
[[FT8PRO]] [[FT8PRO]]
==== FT8 ==== FT8
Forward error correction (FEC) in FT8 uses a low-density Forward error correction (FEC) in FT8 uses a low-density parity check
parity check (LDPC) code with 75 information bits, a 12-bit cyclic (LDPC) code with 75 information bits, a 12-bit cyclic redundancy check
redundancy check (CRC), and 174 channel symbols. It is thus called an (CRC), and 87 parity bits making a 174-bit codeword. It is thus
LDPC (174,87) code. Synchronization uses 7×7 Costas arrays at the called an LDPC (174,87) code. Synchronization uses 7×7 Costas arrays
beginning, middle, and end of each transmission. Modulation is 8-tone at the beginning, middle, and end of each transmission. Modulation is
frequency-shift keying (8-FSK) at 12000/1920 = 6.25 baud. Each 8-tone frequency-shift keying (8-FSK) at 12000/1920 = 6.25 baud. Each
transmitted symbol carries three bits, so the total number of channel transmitted symbol carries three bits, so the total number of channel
symbols is 174/3 + 21 = 79. The total occupied bandwidth is symbols is 174/3 + 21 = 79. The total occupied bandwidth is 8 × 6.25
8 × 6.25 = 50 Hz. = 50 Hz.
[[JT4PRO]] [[JT4PRO]]
==== JT4 ==== JT4