These developments are really due to the talent of Steve, K9AN, and not Joe- don't lose sight of that. Steve has made incredible progress- let's hope he finds some more tricks up his sleeve!
-Chase On Sat, Oct 31, 2015 at 6:05 PM, Michael Black <mdblac...@gmail.com> wrote: > Color me impressed and shiver-me-timbers. > Only been running this a short while but it's decoding stuff I can't even > see now buried in QRM! > > Great job guys!! > > 73 > Mike W9MDB. > > > On Sat, Oct 31, 2015 at 3:43 PM, Steven Franke <s.j.fra...@icloud.com> > wrote: > >> Hi Joe and all, >> >> I’ve just committed a batch of modified routines associated with my >> attempts to improve the low-SNR performance of wsjt-x. >> >> I did a number of experiments aimed at identifying why wsjt-x was not >> performing as well as wsjt on our low-snr test files. I used the jt65 test >> program and the usual set of 1000 .wav files, each of which contains a >> single simulated signal with -24dB snr. The original batch of test files >> was generated using JTSim, and contain 8-bit data at 11.025kS/s. I used the >> *nix program “sox” to convert the files to 16-bits at 12kS/s. >> >> I started by doing some tests that convinced me that the solution would >> involve decreasing the estimation errors for both f0 and dt. In order to >> get to the bottom of this with my sanity intact, I ended up making the >> changes necessary to remove all empirical dt offsets and also all >> zero-padding at the beginning of data arrays. Negative dt’s are handled by >> testing indices to ensure that they remain within the bounds of the >> relevant arrays. >> >> At present, the convention is that dt is referenced to the beginning of >> the wav file. So a transmission that starts at 1.0 second into the file >> will have a time stamp of 1.0. It will be a simple matter to subtract 1 >> from the displayed value to make the numbers equivalent to what the current >> wsjt-x prints out. >> >> I gave up tracking the effect of each and every change - but I believe >> that the most significant ones are: >> (i) Using full-symbol coherent integration when calculating ccf between >> data and sync sequence instead of the prior scheme which did half-symbol >> integration and then summed the powers from the two half-symbols >> (ii) Added a “peakup” step to the final dt calculated using >> 1/16-of-a-symbol steps. This gets us to sub-1/16-symbol accuracy which >> makes a noticeable improvement at low SNR’s. >> (iii) For reasons that I don’t understand - on my data, it seems to be >> slightly better to fit for a(1),a(2),a(3), but then ignore a(3) when >> tweaking the frequency. >> >> Since I had to make a significant number of changes, I’ve confined them >> to renamed routines that have the _exp appended to the normal filename. >> These modified routines are invoked in the Makefile.jt65, but they are not >> yet used in 1.6.1. I’d like to know that you can reproduce my improved >> results and that you are comfortable with the changes before we consider >> moving them into wsjt-x. >> >> Here’s a summary of the improvement on my data: >> >> -24 dB files, ntrials=10000 >> before changes: 639/1000 (this is what the current 1.6.1 gives) >> after changes: 827/1000 >> >> 333 hf .wav files recorded on 20m, 2 passes, ntrials=1000 >> before: 4044 >> after: 4150 >> >> Steve k9an >> >> >> >> >> ------------------------------------------------------------------------------ >> _______________________________________________ >> wsjt-devel mailing list >> wsjt-devel@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/wsjt-devel >> > > > > ------------------------------------------------------------------------------ > > _______________________________________________ > wsjt-devel mailing list > wsjt-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/wsjt-devel > > -- Chase Turner W4TI http://w4ti.com
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