Hi Steve and Joe, Thanks a lot for the compromise solution in r6080, it is really appreciated.
Going to make tests with it shortly. 73, Igor UA3DJY >Среда, 11 ноября 2015, 18:32 -06:00 от Steven Franke <s.j.fra...@icloud.com>: > >Hi Igor, > >Since this may be of interest to others, I’m copying this reply to the list. >First, I’d like to echo what Joe said earlier. If you are running in JT65A >mode and if your search range is the same for all cases, then you should see >identical results on all platforms and operating systems with the only >difference being execution time. > >Having said that, I agree that r6052 and r6058 should perform differently on >different types of files. In fact, your most recent results are as I would >expect. Recall that r6052 uses a standard floating-point correlation function >for identifying candidates for further processing. If there are no impairments >to the data, then the algorithm used in r6052 should be the most sensitive and >the most accurate. As such, it is no surprise that you see better results with >r6052 for your “AGC OFF” files and for the -24dB files generated by JTSim. > >r6058 uses a 1-bit correlation, which was introduced to mitigate the effect of >AGC-induced noise “stepdown” (for lack of a better term) at the beginning of >the record. It will also mitigate the AGC-induced “stepup” at the end of the >record. This approach turns out to be very effective in cases where the AGC >effect is severe, as in the example files that you provided. To give an idea >of what it does, most of your files produce 100-200 (mostly spurious) >candidates with the standard correlation as used in r6052, whereas the 1-bit >correlation reduces the number of candidates to 10-30 in most cases. This >dramatically reduces execution time, by as much as a factor of 5-10 in some >cases. > >The downside of using 1-bit correlation is a slight loss in sensitivity. > >Just now, in r6080, I’ve committed my latest attempt at finding the best >compromise between robustness and sensitivity. This latest version first uses >the full correlation function to identify candidates. If the number of >candidates is greater than 50, it then goes back and tries again using the >1-bit correlation. This restores the full sensitivity of the decoder for >well-behaved data files (or even for AGC-contaminated data with a narrow >search range) while resorting to 1-bit correlation when warranted. If even the >1-bit correlation produces more than 50 candidates (I have not yet seen this >happen), then the fallback is to reduce ntrials to 100 to keep the decoder >from appearing to “freeze”. > >For future reference, I just ran r6080 on the -24dB test files using a setting >of 8 for random erasure patterns (ntrials=10000), with 2-pass decoding turned >off, and obtained 828 decodes. > >Finally, a comment on your observation that many people have rigs that do not >allow the AGC to be turned off. I expect that many such rigs will have an RF >gain control. My recommendation is to reduce the RF gain to the point where >AGC is activated only on the strongest signals. This will minimize the >AGC-induced noise-step effect and will guarantee maximum sensitivity from the >decoder. For example, on my TS-480 I usually run with the RF gain set at 80 >(out of 100) and only 1-2% of my data files activate the 1-bit correlation >option. In any case, this latest version should “just work” whether or not you >are able to optimize your AGC settings. > >73 Steve k9an > >> On Nov 11, 2015, at 4:12 PM, Игорь Ч < c_i...@inbox.ru > wrote: >> >> Hi Steve, >> >> After long discussion about JT65 decoder in Russian JT65 forum I have been >> completely confused by my last test results on comparison of the r6052 and >> r6058 releases: >> __________________________ >> Audio files with TRX AGC OFF : >> >> release/number of decodes >> >> 6052/609 >> 6058/596 >> __________________________ >> -24 dB Audio files: >> >> release/number of decodes >> >> 6052/765 >> 6058/736 >> __________________________ >> Audio files with TRX AGC ON: >> >> release/number of decodes >> >> 6052/863 >> 6058/932 >> __________________________ >> >> There is significant difference in number of decoded signals between 6052 >> and 6058. >> >> We have faced a problem: some people do use cheap/classic transceivers where >> they may not turn AGC off and they must use JT65 decoder from release 6058. >> Other people do use SDRs or more expensive classic transceivers but for some >> reasons prefer to keep AGC turned ON - hence they also must use decoder from >> r6058. >> >> But some people have possibility and like to keep AGC turned off and they >> would like to get most performance from WSJT-X software, so they do prefer >> to use high sensitivity JT65 decoder from r6052. >> >> What do you think if there is any way to let users to choose appropriate >> JT65 decoder, could you discuss this issue with Joe, please? >> >> 73, >> >> Igor UA3DJY >> >
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