[TVARC] Alphanumeric Characters in FT8 Responses

[K2PS Pete Stafford]

I think you've got it.  I've wondered about the Enable AP choice in the WSJT
Decode menu.  Now I know!

 

Thanks, George.

 

73, Pete, K2PS

 

From: k2dm at comcast.net <k2dm at comcast.net> 
Sent: Saturday, June 8, 2024 10:55 AM
To: K2PS Pete Stafford <psk2ps at gmail.com>; 'Ed Deichler'
<k2te.1nh at gmail.com>; 'villages reflector' <TVARC at mailman.qth.net>
Subject: Re: [TVARC] Alphanumeric Characters in FT8 Responses

 

Could this be it?  From the WSJT-x manual:  (the formatting didn't copy)

 

12. Decoder Notes 12.1. AP Decoding The WSJT-X decoders for FST4, FT4, FT8,
JT65, and Q65 include procedures that use naturally accumulating information
during a minimal QSO. This a priori (AP) information increases sensitivity
of the decoder by up to 4 dB, at the cost of a slightly higher rate of false
decodes. AP is optional in FT8 and JT65, but is always enabled for Q65 and
for FT4 and FST4 when decode depth is Normal or Deep. For example: when you
decide to answer a CQ, you already know your own callsign and that of your
potential QSO partner. The software therefore "knows" what might be expected
for at least 57 message bits (28 for each of two callsigns, one or more for
message type) in the next received message. The decoder's task is thus
reduced to determining the remaining 15 bits of the message and ensuring
that the resulting solution is reliable. AP decoding starts by setting AP
bits to the hypothesized values, as if they had been received correctly. We
then determine whether the remaining message and parity bits are consistent
with the hypothesized AP bits, with a specified level of confidence.
Successful AP decodes are labeled with an end-of-line indicator of the form
aP , where P is one of the single-digit AP decoding types listed in Table 1.
For example, a2 indicates that the successful decode used MyCall as
hypothetically known information. Type a7 , used only in FT8 mode, uses
information from the previous Rx sequence. Table 1. FST4, FT4, and FT8 AP
information types aP Message components a1 CQ ? ? a2 MyCall ? ? a3 MyCall
DxCall ? a4 MyCall DxCall RRR a5 MyCall DxCall 73 a6 MyCall DxCall RR73 a7
(Call_1 or CQ) Call_2 ? If a codeword is found that is judged to have high
(but not overwhelmingly high) probability of being correct, a ? character is
appended when the decoded message is displayed. To avoid misleading spots of
occasional false decodes, messages so marked are not forwarded to PSK
Reporter (https://pskreporter.info/pskmap.html). Table 2 lists the six
possible QSO states that are tracked by the WSJT-X auto-sequencer, along
with the type of AP decoding that would be attempted in each state in FT4 or
FT8. The FST4 table (not shown) is the same except that it omits the
decoding attempts for AP types 4 and 5 to save time. Table 2. FT4 and FT8 AP
decoding types for each QSO state State AP type CALLING STN 2, 3 REPORT 2, 3
ROGER_REPORT 3, 4, 5, 6 ROGERS 3, 4, 5, 6 SIGNOFF 3, 1, 2 CALLING CQ 1, 2
Decoding with a priori information behaves slightly differently in JT65.
Some details are provided in Tables 3 and 4. Table 3. JT65 AP information
type

 

George K2DM

 

  _____  

From: tvarc-bounces at mailman.qth.net <mailto:tvarc-bounces at mailman.qth.net>
<tvarc-bounces at mailman.qth.net <mailto:tvarc-bounces at mailman.qth.net> > on
behalf of K2PS Pete Stafford <psk2ps at gmail.com <mailto:psk2ps at gmail.com> >
Sent: Saturday, June 8, 2024 10:41 AM
To: 'Ed Deichler' <k2te.1nh at gmail.com <mailto:k2te.1nh at gmail.com> >;
'villages reflector' <TVARC at mailman.qth.net <mailto:TVARC at mailman.qth.net> >
Subject: Re: [TVARC] Alphanumeric Characters in FT8 Responses 

 

Yes, and no clue.  

 

Pete

 

From: tvarc-bounces at mailman.qth.net <mailto:tvarc-bounces at mailman.qth.net>
<tvarc-bounces at mailman.qth.net <mailto:tvarc-bounces at mailman.qth.net> > On
Behalf Of Ed Deichler
Sent: Saturday, June 8, 2024 10:07 AM
To: villages reflector <TVARC at mailman.qth.net <mailto:TVARC at mailman.qth.net>
>
Subject: [TVARC] Alphanumeric Characters in FT8 Responses

 

I'm sure many have noticed the "a#" (a2, a3, a7, etc.) characters that occur
in the response line when working stations in FT8.  I haven't been able to
find an explanation as to what they mean.

 

Anybody have a clue?

 

73 de Ed

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/tvarc/attachments/20240608/29b1f428/attachment.html>