Message payloads contain either 77 bits, as in FT4, FT8, and MSK144, or 50 bits for the WSPR-like messages of FST4W. Submodes are given names like FST4-60, FST4W-300, etc., the appended numbers indicating sequence length in seconds. FST4 offers T/R sequence lengths of 15, 30, 60, 120, 300, 900, and 1800 seconds, while FST4W omits the lengths shorter than 120 s. The new modes use 4-GFSK modulation and share common software for encoding and decoding messages. FST4 and FST4W do not require the strict, independent phase locking and time synchronization of modes like EbNaut. The FST4 protocol is optimized for two-way QSOs, while FST4W is for quasi-beacon transmissions of WSPR-style messages. As a consequence, fundamental sensitivities of FST4 and FST4W are better than other WSJT-X modes with the same sequence lengths, approaching the theoretical limits for their rates of information throughput. Decoders for these modes can take advantage of the very small Doppler spreads present at these frequencies, even over intercontinental distances. WSJT-X 2.3.0 introduces FST4 and FST4W, new digital protocols designed particularly for the LF and MF bands. Repair a defect that could cause the jt9 slow mode decoder process to exit incorrectly with a failure status. Repair a defect that caused crashes at start up for some macOS Big Sur users. Add time stamp to error message boxes to aid diagnosis. FST4/W: Disable envelope shaping at start and end of transmission when environment variable FST4_NOSHAPING=1. See summaries below and for the prior release candidates (2.3.0-rc1 through -rc4) of this version for details. WSJT-X 2.3.0 General Availability release adds the new modes FST4 and FST4W along with many defect repairs. WSJT-X: New in Version 2.3.0 The WSJT Development Group has announced the general availability release of WSJT-X Version 2.3.0.
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