// 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 "`**W**eak **S**ignal communication by
K1**JT**,`" while the suffix "`-X`" indicates that _WSJT-X_ started as
an extended (and originally 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 may replace JT65
for EME use.  JT9 was originally designed for the LF, MF, and lower HF
bands.  Its submode JT9A 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 submodes *JT9E-H* are "`fast'"
protocols 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 between two stations.

*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.