On 26/07/2017 17:01, Black Michael via wsjt-devel wrote:
What is "AP" decoding?
Hi Mike,
let me try a dumbed down explanation, not because I want to dumb it down
but because that is probably as deep as my understanding goes.
When decoding a signal we have some fixed criteria for a good decode, if
we have some prior information about a possible decode then we can mask
out that part of the message and see if it then meets the criteria. This
means that errors in that assumed and masked part do not count towards
the number of errors that have to be corrected.
So for example when looking for CQ calls (DX Call box empty) we might
mask out the CQ word from every candidate signal to see if it then meets
the good decoding criteria. this is only done with signal candidates
that do not not decode with a basic deterministic hard decision
algorithm nor any more advanced soft decision algorithm that is enabled.
Other a priori information might include you own callsign, your QSO
partner's callsign, even the sequence in a current QSO. Some of this a
priori information is only relevant at the QSO frequency or very nearby
and is only used there.
AP decoding places more diligence on the operator as such decodes can be
deceptively valid and you should look at the quality and other decoder
information added after the message before making an assessment on the
accuracy of the decode. For example ' a1' is showing that the "CQ" part
was masked. Furthermore '? a1' is saying that masking the CQ word worked
but the result is close to failing the good decode criteria and has a
higher than normal false decode probability. I am just coding a change
right now that will add a low confidence flag to such UDP decode
messages and also to not spot to pskreporter any such low confidence
decodes.
73
Bill
G4WJS.
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