[Elecraft] Setting Up For WSJT-X Receive Levels

[Tox]

Thanks - I actually do already adjust AF to about 65dB.

Scott
AD6YT

On Mon, Jan 13, 2020 at 10:20 AM Jim Brown <jim at 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
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-- 
Scott Small