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Candidate releases are intended for beta testers: individuals interested in testing the programme's new features and providing feedback to the WSJT Development Team. The first candidate release for WSJT-X 2.3.0 introduces FST4 and FST4W, two new modes designed for use on the LF and MF bands. FST4 is optimized for two-way QSOs, while FST4W is for quasi-beacon transmissions of WSPR-style messages. Further details and operating hints can be found in the "Quick-Start Guide to FST4 and FST4W":
https://physics.princeton.edu/pulsar/k1jt/FST4_Quick_Start.pdf. Links to installation packages for Windows, Linux, and Macintosh are available on http://physics.princeton.edu/pulsar/k1jt/wsjtx.html.