Steve,
please don't equate AP assisted decodes with low levels (I prefer the
term weak signals). AP decoding techniques, like the other FEC
mechanisms, allow missing information to be recovered. Weak signals are
not the only cause of missing information, truncated or otherwise
interrupted signals are just as likely to require FEC, and AP if
enabled, to successfully decode them. As I said, it is virtually
impossible to eliminate this sort of false decode without compromising
the purpose of AP decoding, unless information not received on air is
used to make the decisions. That's the operator's job and not something
that we feel WSJT-X should be attempting.
Yes, examples of false decodes, along with supporting .WAV files, and
settings necessary to reproduce them, are welcome but unless there is
common cause that can be detected by the application, like
unrealistically low SNR values combined with marginal sync detection and
maximum FEC required, there's little that can be done.
73
Bill
G4WJS.
On 25/05/2020 12:54, Stephen VK3SIR wrote:
Bill,
Fully aware of that:-) Yet you have asked for reports when these occur. I am in a
far-away land to many where low-level, low confidence signals are the norm and not
the exception. Around 40% of the 40 contacts made today with the new version have
been > -18dB. Without the reduced confidence in-use I'd be in constant RR/73
loops !
In in the last few minutes I have another .... again with a /R ! You want this
one was well?
114715 -18 0.3 825 ~ VK3VM PA6UES/R R BM44 ? a2
I'll send that one as well as its now 2 in 60-odd minutes of operation.
73
Steve I
VK3VM / VK3SIR
-----Original Message-----
From: Bill Somerville<[email protected]>
Sent: Monday, 25 May 2020 9:43 PM
To:[email protected]
Subject: Re: [wsjt-devel] WSJT-X 2.2.0-rc2 False Decode
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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