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+// Status=review
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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 "`**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*, *ISCAT*, *MSK144*, *WSPR*, 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 proven
+highly 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 and optionally 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 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.
+