// 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 experimental branch of the program
_WSJT_.

_WSJT-X_ Version 1.7 offers eight protocols or modes: *JT4*,
*JT9*, *JT65*, *QRA64*, *WSPR*, *ISCAT*, *MSK144*, and *Echo*.  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, aircraft scatter, 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-trail reflections or "`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.  

*WSPR* (pronounced "`whisper`") stands for **W**eak **S**ignal
**P**ropagation **R**eporter.  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 station's echoes
from the moon, even if they are far below the audible threshold.

_WSJT-X_ provides spectral displays for receiver passbands as wide as
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.
