Hi All
A number of stations have reported excessive false decodes with WSJT-X when
using JT65, such as shown below:
2238 -11 -0.6 1004 #* VK7MO VK7JG QE38 f
2238 -30 4.1 879 ##
2238 -26 1.2 1146 ## GS5BBR 3P4HRY EK73 OOO f
2238 -30 3.9 1305 # 6I9KRF C13XPY DJ90 f
2238 -28 3.3 1425 ## F91INL SP5FIE BG85 OOO f
2238 -26 2.0 1479 ## VK7MO WA3LBI FN20 OOO d16
2240 -11 0.2 1004 #* VK7MO VK7JG QE38 f
2240 -29 4.7 1049 ##
2240 -26 3.2 1219 ## 577TNC XX4XUE GC78 OOO f
2240 -24 -1.3 1241 ## AY0XAJ KN1YKC GM97 OOO f
2240 -23 -1.3 1359 #* -R?CGKCYNKHQX f
2240 -23 3.6 1370 #* 3L2R-8VII0WU f
2242 -12 0.2 1004 #* VK7MO VK7JG QE38 f
2242 -30 3.5 563 #
2242 -23 2.4 1241 ## KF2HOG 242OIQ BP98 OOO f
2242 -24 -0.2 1327 ## B61ERP TY/R45CUB OOO f
2242 -28 -0.1 1370 ## 0V4WH WC6WBQ NM49 OOO f
2242 -27 -1.0 1435 #* VK7MO VK7JG -01 d14
2244 -11 -0.2 1004 #* VK7MO VK7JG QE38 f
2244 -30 4.2 1047 # TM4IYO NY6XSH MQ06 f
2244 -28 3.9 1056 #*
2244 -30 -0.3 1089 # VK7MO OK1KIR JN79 d19
2244 -30 1.9 1157 #* P1GKYU?X?PBE2 f
2244 -30 -0.9 1156 ## 9W9GCA BF4STA HA36 OOO f
2244 -30 2.1 1169 # 5S3YMQ ...... BF28 f
I have seen the problem on Windows 8 and 10 with the publicly released
version r7405. It also occurs on later releases.
In addition to the false decodes some report that the Decode Button stays
highlighted for extended periods of up to 30 seconds into the following TX
period. I suspect this is a secondary effect of the program attempting
excessive decoding on perhaps a slow computer, but I don't see this on my
computers.
In order to help track this down I have produced 4 files on JT65c which
produce the above false decodes and G3WDG has made available at:
https://drive.google.com/drive/folders/0B116IwQIUFNTWnpHU3ZvbTNVeFU?usp=shar
ing
VK7MO VK7JG QE38 is the correct message as transmitted over the air on 1296
MHz terrestrial with JT65c. All the other messages above are false.
The critical conditions required to produce such false decodes are as
follows:
*Sync set to -1
*Aggressive Decoding under the advanced settings tab set to 0
*A signal in within the passband
This behaviour is accentuated by setting Ftol wide to say 500 Hz and
enabling Deep Search. However, many of the false decodes (as indicated by
an "f" ) are not included in the call3.txt file.
For this test set-up, My call is VK7MO, DX call VK7JG and DX grid QE38.
If you set sync to zero rather than -1 the program decodes these four files
correctly under all conditions as follows:
2238 -11 -0.6 1004 #* VK7MO VK7JG QE38 f
2240 -11 0.2 1004 #* VK7MO VK7JG QE38 f
2242 -12 0.2 1004 #* VK7MO VK7JG QE38 f
2244 -11 -0.2 1004 #* VK7MO VK7JG QE38 f
The problem with setting sync to zero is that WSJT-X uses the -1 setting to
display unsuccessful decodes and while it is probably sensible on HF not to
display unsuccessful attempts, on EME most of us like to see decode attempts
even if unsuccessful.
An alternative fix is to set Aggressive Decoding (under the advanced
settings) to greater than 0 but this still produces a second decode attempt
with the following output from these 4 files
2238 -11 -0.6 1004 #* VK7MO VK7JG QE38 f
2238 -26 0.9 1004 ##
2240 -11 0.2 1004 #* VK7MO VK7JG QE38 f
2240 -26 1.4 1004 ##
2242 -12 0.2 1004 #* VK7MO VK7JG QE38 f
2242 -26 3.5 1004 ##
2244 -11 -0.2 1004 #* VK7MO VK7JG QE38 f
2244 -26 4.6 1004 ##
In the interim I suggest that if you are suffering from false decodes (or
getting second decode attempts) on WSJT-X with JT65 the solution is to avoid
setting sync to -1. Hopefully longer term the development group will produce
a fix that will allow sync to be set to -1 so as to see unsuccessful decodes
without the false decodes or second false attempts.
This problem does not occur on JT4 or QRA64 and seems to me to be limited to
the JT65.
73 Rex VK7MO
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