Thanks - I actually do already adjust AF to about 65dB. Scott AD6YT
On Mon, Jan 13, 2020 at 10:20 AM Jim Brown <j...@audiosystemsgroup.com> wrote: > > On 1/13/2020 7:10 AM, Tox wrote: > > I've been using a kx3 to play with ft8. Finding intermittent severe > > QRM is rendering it deaf to due desense. (Signals that are coming in > > at -5 disappear from the waterfall when the source fires.) > > There is some bad advice in the setup instructions for WSJT-X to set the > RX audio drive to the computer at 30 dB indicated on the green level bar > at the bottom right of the display. This WILL cause weak signals to be > lost to the decoder in the presence of a very strong one. I've learned > to set that audio drive level so that, with RX signals present, that > green bar is around 70 dB but never turns red (a bit over 80 dB). > > For those reading the mail -- the logic is simple. The A/D converter has > a dynamic range of about 90 dB. The green bar shows where the top of > that 90 dB is set. Let's say a very strong signal, 50 dB over S9, takes > over the AGC and hits the computer at 40 dB. Another signal in the > waterfall would have to be S9 +10 dB to be decoded -- any weaker signal > falls below the range of the A/D! But if I set the green bar to 75 dB, > an S9 signal would be 25 dB above the bottom of the decoder. Each S-unit > is 5 or 6 dB (depending on each mfr's definition of an S-unit); if 5 dB, > S8 would be 20 dB above the bottom, S7 15 dB, S6 10 dB, S5 5 dB. Now, a > signal between S4 and S5 can be decoded. > > Another point. The appearance of the spectrum display can be deceiving, > making signals appear wider than they are. WSJT-X can decode signals > that appear to be covered by strong adjacent signals. The apparent > covering is an artifact of how the waterfall is able to display > amplitude of the received signal. The decoder sees "beneath" what the > display shows. > > 73, Jim K9YC > ______________________________________________________________ > 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 scott.sm...@gmail.com -- Scott Small ______________________________________________________________ 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
