On 25/05/2020 12:04, Stephen VK3SIR wrote:
Folks,
I just picked up a false decode that can be replicated when played back
through WSJT-X 2.2.0 rc2:
104945 -23 -0.5 1623 ~ VK3VM FH9ZZV/R ND49 ? a2
Research suggests this is not a genuine call and is definitely a false decode
(i.e. ND49 = middle of Southern Ocean). I have noted that many false decodes in
the previous version are reported with /R !
As one cannot send attachments via email I'll reforward this email plus the
.wav file directly to Bill and Joe for further analysis.
73
Steve I
VK3VM / VK3SIR
Steve,
AP decodes flagged as low confidence ('?' marker) should always be
considered dubious, and unless there is other evidence that the decode
is genuine it should be ignored. Without using knowledge not obtained on
air it is virtually impossible for the decoder to eliminate such false
decodes without damaging the capabilities of the AP decoding mechanism.
AP decodes of the 'a2' category are only detected shortly after a CQ
call IIRC.
The FT8, FT4, and MSK144 decoders give virtually every possible message
equal weight. The message types that allow a '/P' or '/R' (grid rover
station) prefix to a standard callsign have a 50% probability per
possible callsign that random data will unpack as one of those prefixes,
so they will be far more common in false decodes than in genuine
messages where the expected likelihood is far lower.
73
Bill
G4WJS.
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