WSJT-X/doc/user_guide/introduction.adoc

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_WSJT-X_ is a computer program designed to facilitate basic amateur
radio communication using very weak signals. The first four letters in
the program name stand for “Weak Signal communication by K1JT,” while
the suffix “-X” indicates that _WSJT-X_ started as an extended (and
experimental) branch of the program _WSJT_.

_WSJT-X_ Version 1.6 offers four protocols or “modes”: JT4, JT9, JT65
and WSPR.  The first three are designed for making reliable 
QSOs under extreme weak-signal conditions. They use nearly identical
message structure and source encoding.  JT65 was designed for EME
(“moonbounce”) on the VHF/UHF bands and has also proven very effective
for worldwide QRP communication on the HF bands.  JT9 is optimized for
the LF, MF, and lower HF bands.  It is about 2 dB more sensitive than
JT65 while using less than 10% of the bandwidth.  JT4 offers a wide
variety of tone spacings and has proved very effective for EME on
microwave bands up to 24 GHz.  All three of these modes use one-minute
timed sequences of alternating transmission and reception, so a
minimal QSO takes four to six minutes — two or three transmissions by
each station, one sending in odd UTC minutes and the other even. On
the HF bands, world-wide QSOs are possible using power levels of a few
watts and compromise antennas.  On VHF bands and higher, QSOs are
possible (by EME and other propagation types) at signal levels 10 to
15 dB below those required for CW.

WSPR (pronounced “whisper”) stands for Weak Signal Propagation
Reporter.  The WSPR protocol was designed for probing potential
propagation paths using low-power transmissions. WSPR messages
normally carry the transmitting station’s callsign, grid locator, and
transmitter power in dBm, and they can be decoded at signal-to-noise
ratios as low as -28 dB in a 2500 Hz bandwidth.  WSPR users with
internet access can automatically upload their reception reports to a
central database called {wsprnet} that provides a mapping facility,
archival storage, and many other features.

_WSJT-X_ provides spectral displays for passbands up to 5 kHz,
flexible rig control for nearly all modern radios used by amateurs,
and a wide variety of special aids such as automatic Doppler control
for EME QSOs.  The program runs equally well on Windows, Macintosh,
and Linux systems, and installation packages are available for all
three platforms.

_WSJT-X_ is an open-source project released under the {gnu_gpl}
(GPL). If you have programming or documentation skills or would like
to contribute to the project in other ways, please make your interests
known to the development team.  The project’s source-code repository
can be found at {devsvn}, and most communication among the developers
takes place on the email reflector {devmail}.  User-level questions
and answers, and general communication among users is found on the
{wsjt_yahoo_group} email reflector.