On 04/07/17 22:56, Jim Brown wrote: > Richard, > > Not nonsense at all. WSJT-X is VERY robust in the ability to reject > this sort of QRM. The screen grab below is a great example. I continue > to be amazed by the decoding in WSJT-X. About 10 days ago, W0OGH > accidentally got out of sync with JA7QVI, calling on his TX cycle, and > on the same frequency. As this screen grab clearly shows, W0OGH was 9 dB > stronger on the 0053Z cycle and 12 dB stronger on the 0055Z cycle, yet > both signals were decoded without error! > > During a wonderful 6M opening this past Friday evening west coast time, > I had a LOT of JT65/JT9 passes with more than 20 clean decodes on each > pass. I regularly see decodes in the -20 to -28 range, even with very > strong signals capturing the AGC. It's only necessary to keep peak > signal levels to the A/D below digital clip.
That's receive levels. I was talking about Tx distortion. While it's certainly the case that WSJT-X's two-pass decoder can *sometimes* decode weak signals underneath overlapping strong ones, this isn't always the case and it can never be a magic cure all. That would have Claude and Harry spinning in their graves. Any kind of spurious crud will raise the noise floor, which is always a bad thing. Also, harmonics really clutter the waterfall. A JT65 signal on, say 700 Hz, will appear between 700-878 Hz. The second and third harmonics will appear between 1400-1756 and 2100-2634 Hz. Just one distorted JT65 signal easily mess up over a kHz of bandwidth in total. With a busy band this can turn the display into an incomprehensible mush. Also, audio harmonics of JT65 signals can spread into the part of the band used by JT9, which does not have a two-pass decoder. The WSJT-X developers are a *very* clever team of 25 people, led by a Nobel-prize winning professor of physics at Princeton, who have considered all this stuff over many years with a forensic, mathematical rigour of the kind that most of us can only guess at. If they say that it's a good idea to keep TX audio above 1500 Hz, I think I'll trust their word over yours. 73, Richard G4DYA 73, Richard G4DYA ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
