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Minor tweaks to User Guide.

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git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@7384 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
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Joe Taylor 2016-12-15 20:09:06 +00:00
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doc/user_guide/en/vhf-features.adoc
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@ -154,32 +154,38 @@ image::JT65B.png[align="center",alt="JT65B"]
=== QRA64
QRA64 is an experimental mode in the Version 1.7 alpha release of
_WSJT-X_. The mode is designed especially for EME on VHF and higher
bands; operation is generally similar to JT65. The following screen
shot shows an example of a QRA64C transmission from DL7YC recorded at
G3WDG over the EME path at 24 GHz. Doppler spread on the path was 78
Hz, so although the signal is reasonably strong its tones are
broadened enough to make them hard to see on the waterfall. The red
curve shows that the decoder has achieved synchronization with a
signal at approximately 967 Hz.
QRA64 is an experimental mode in Version 1.7 of _WSJT-X_. The mode is
designed especially for EME on VHF and higher bands; its operation is
generally similar to JT65. The following screen shot shows an example
of a QRA64C transmission from DL7YC recorded at G3WDG over the EME
path at 24 GHz. Doppler spread on the path was 78 Hz, so although the
signal is reasonably strong its tones are broadened enough to make
them hard to see on the waterfall. The red curve shows that the
decoder has achieved synchronization with a signal at approximately
967 Hz.
image::QRA64.png[align="center",alt="QRA64"]
The QRA64 decoder makes no use of a callsign database. Instead, it
takes advantage of _a priori_ (already known) information such as the
one's own callsign and the encoded form of message word `CQ`. In
normal usage, as a QSO progresses the available _a priori_ (AP)
information increases to include the callsign of the station being
worked and perhaps also his/her 4-digit grid locator. The decoder
always begins by attempting to decode the full message using no AP
information. If this attempt fails, additional attempts are made
using available AP information to provide initial hypotheses about the
message content. At the end of each iteration the decoder computes
the extrinsic probability of the most likely value for each of the
message's 12 six-bit information symbols. A decode is declared only
when the total probability for all 12 symbols has converged to an
unambiguous value very close to 1.
takes advantage of _a priori_ (AP) information such as the one's own
callsign and the encoded form of message word `CQ`. In normal usage,
as a QSO progresses the available AP information increases to include
the callsign of the station being worked and perhaps also his/her
4-digit grid locator. The decoder always begins by attempting to
decode the full message using no AP information. If this attempt
fails, additional attempts are made using available AP information to
provide initial hypotheses about the message content. At the end of
each iteration the decoder computes the extrinsic probability of the
most likely value for each of the message's 12 six-bit information
symbols. A decode is declared only when the total probability for all
12 symbols has converged to an unambiguous value very close to 1.
TIP: In _WSJT-X_ Version 1.7 QRA64 is different from JT65 in that the
decoder attempts to find and decode only a single signal in the
receiver passband. If many signals are present you may be able to
decode them by double-clicking on the lowest tone of each one in the
waterfall. A multi-decoder like those for JT65 and JT9 has not
yet been written.
=== ISCAT