_WSJT-X_ offers eleven
different protocols or modes: *FST4*, *FT4*, *FT8*, *JT4*, *JT9*,
*JT65*, *Q65*, *MSK144*, *WSPR*, *FST4W*, and *Echo*.  The first eight
are designed for making reliable QSOs under weak-signal
conditions. They use nearly identical message structure and source
encoding.  JT65 was designed for EME ("`moonbounce`") on VHF and
higher bands and is mostly used for that purpose today.  Q65 is
particularly effective for tropospheric scatter, rain scatter,
ionospheric scatter, TEP, and EME on VHF and higher bands, as well as
other types of fast-fading signals.  JT9 was designed for the HF and
lower bands.  Its submode JT9A is 1 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.  The "`slow`" modes use timed sequences of
alternating transmission and reception.  JT4, JT9, and JT65 use
one-minute sequences, 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.  FT8 is four times faster (15-second T/R
sequences) and less sensitive by a few dB.  FT4 is faster still (7.5 s
T/R sequences) and especially well-suited for radio contesting.  FST4
is designed especially for the LF and MF bands.  Both FST4 and Q65
offer a wide variety of timed sequence lengths, and Q65 a range of
tone spacings for different propagation conditions.  On the HF bands,
world-wide QSOs are possible with any of these modes using power
levels of a few watts (or even milliwatts) and compromise antennas.
On VHF bands and higher, QSOs are possible (by EME, scatter, and other
propagation types) at signal levels 10 to 15 dB below those required
for CW.

*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`".  MSK144 uses the same
structured messages as the slow modes and optionally an abbreviated
format with hashed callsigns.  

Note that some of the modes classified as slow can have T/R sequence
lengths as short the fast modes.  "`Slow`" in this sense implies
message frames being sent only once per transmission.  The fast modes
in _WSJT-X_ send their message frames repeatedly, as many times as
will fit into the Tx sequence length.

*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 with two-minute
sequences they can be decoded at signal-to-noise ratios as low
as -31 dB in a 2500 Hz bandwidth. *FST4W* is designed for
similar purposes, but especially for use on LF and MF bands.
It includes optional sequence lengths as long as 30 minutes and
reaches sensitivity thresholds as low as -45 dB.  Users
with internet access can automatically upload WSPR and FST4W
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 and to make other measurements useful for optimizing
your EME station's performance.