// 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,`" while
the suffix "`-X`" indicates that _WSJT-X_ started as an extended (and
experimental) branch of the program _WSJT_.

_WSJT-X_ Version 1.7 offers eight protocols or "`modes`": *JT4*,
*JT9*, *JT65*, *QRA64*, *WSPR*, *Echo*, *ISCAT*, and *MSK144*.  The
first four are designed for making reliable QSOs under extreme
weak-signal conditions. They use nearly identical message structure
and source encoding.  JT65 and QRA64 were designed for EME
("`moonbounce`") on the VHF/UHF bands and have also proven very
effective for worldwide QRP communication on the HF bands.  QRA64 has
a number of advantages over JT65, including better performance on the
very weakest signals.  We imagine that over time it will replace JT65
for EME use.  JT9 is optimized for the LF, MF, and lower HF bands.  It
is 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 of these
"`slow`" 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 (or even milliwatts) 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.

*ISCAT*, *MSK144*, and optionally *JT9E-H* are "`fast`" modes designed
to take advantage of brief signal enhancements from ionized meteor
trails and other types of scatter propagation. These modes use timed
sequences of 5, 10, 15, or 30 s duration.  User messages are
transmitted repeatedly at high rate (up to 250 characters per second,
for MSK144) to make good use of the shortest meteor "`pings`".  ISCAT
uses free-form messages up to 28 characters long, while MSK144 uses
the same structured messages as the slow modes together with an
abbreviated format with hashed callsigns for messages sent after
initial contact has been established.

*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.

*Echo* mode allows you to detect and measure your own lunar echoes,
even if they are far below the audible threshold.

_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 tracking
for EME QSOs and Echo testing.  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.