// Status=review

_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'',
and the “-X” suffix indicates that _WSJT-X_ started as an extended
(and experimental) branch of program _WSJT_.

_WSJT-X_ currently offers two protocols or “modes,” JT65 and JT9.
Both are designed for making reliable, confirmed QSOs under extreme
weak-signal conditions. They use nearly identical message structure
and source encoding.  JT65 was designed for EME (“moon-bounce”) on the
VHF/UHF bands and has proved very effective for worldwide QRP
communication on the HF bands, too.  JT9 is optimized for the LF, MF, and HF bands.
It is about 2 dB more sensitive than JT65 while using less than 10% of
the bandwidth.  Both 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 with power levels of a few watts and compromise
antennas.

_WSJT-X_ can display a bandpass as large as 5 kHz and transparently
provides dual-mode reception of both JT65 and JT9 signals.  If your
receiver can be configured with at least 4 kHz bandwidth in USB mode,
you can set the dial frequency to one of the standard JT65 frequencies
— for example, 14.076 MHz for the 20-meter band — and display the full
JT65 and JT9 sub-bands simultaneously on the waterfall.  You can then
make QSOs in both modes using nothing more than mouse clicks.

Plans for future program development call for _WSJT-X_ and _WSJT_ to
merge together. _WSJT-X_ will gradually acquire the additional modes
JT4, FSK441, and ISCAT that are now supported in _WSJT_.  The entire
WSJT-related effort is an open-source project, released under the GNU
General Public License (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}.