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40 lines
2.1 KiB
Plaintext
40 lines
2.1 KiB
Plaintext
[[NEW_FEATURES]]
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=== New in Version {VERSION}
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_WSJT-X 2.3.0_ introduces *FST4* and *FST4W*, new digital protocols
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designed particularly for the LF and MF bands. Decoders for these
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modes can take advantage of the very small Doppler spreads present at
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these frequencies, even over intercontinental distances. As a
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consequence, fundamental sensitivities of FST4 and FST4W are better
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than other _WSJT-X_ modes with the same sequence lengths, approaching
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the theoretical limits for their rates of information throughput. The
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FST4 protocol is optimized for two-way QSOs, while FST4W is for
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quasi-beacon transmissions of WSPR-style messages. FST4 and FST4W do
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not require the strict, independent phase locking and time
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synchronization of modes like EbNaut.
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The new modes use 4-GFSK modulation and share common software for
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encoding and decoding messages. FST4 offers T/R sequence lengths of
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15, 30, 60, 120, 300, 900, and 1800 seconds, while FST4W omits the
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lengths shorter than 120 s. Submodes are given names like FST4-60,
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FST4W-300, etc., the appended numbers indicating sequence length in
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seconds. Message payloads contain either 77 bits, as in FT4, FT8, and
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MSK144, or 50 bits for the WSPR-like messages of FST4W. Message
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formats displayed to the user are like those in the other 77-bit and
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50-bit modes in _WSJT-X_. Forward error correction uses a low density
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parity check (LDPC) code with 240 information and parity bits.
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Transmissions consist of 160 symbols: 120 information-carrying symbols
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of two bits each, interspersed with five groups of eight predefined
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synchronization symbols.
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*We recommend that on the 2200 and 630 m bands FST4 should replace JT9
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for making 2-way QSOs, and FST4W should replace WSPR for propagation
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tests*. Operating conventions on these LF and MF bands will
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eventually determine the most useful T/R sequence lengths for each
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type of operation. We also expect that the 60 second variant of FST4
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(FST4-60) will outperform JT9 for DX QSOs on HF bands due, in part,
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to the FST4 decoder's ability to use AP decoding for messages received
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from a QSO partner. In addition, FST4 provides the added benefits
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associated with 77-bit messages and auto-sequencing.
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