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