[Elecraft] K4 Question

[Jim Brown]

On 6/23/2020 4:53 PM, Adrian wrote:
> An excessive strength FT8 signal is easy to remove with notch.

Yes, BUT -- the notch introduces phase shift, which can degrade 
decoding.  K1JT recommends running the IF wide and letting WSJT-X 
separate signals.

I DO strongly differ with the advice in the WSJT-X manual for setting 
levels. Instead, I recommend setting audio gains so that the green bar 
indicating audio level as close as possible to the top without it 
turning red on when strong signals are present. I find Slow AGC works 
well for me, because both the strongest signals AND my local noise vary 
widely.

Why do I recommend this? Simple. The practical dynamic range of a 16-bit 
A/D is about 90 dB (96 dB theoretical, but linearity tends to degrade at 
the low end of the range); if there's a 50 dB over S9 signal in the 
passband and it's set to 78 dB on the green bar, we can decode signals 
28 dB below S9. At 5 dB/S-unit, that's between S3 and S4. If the 
strongest signal is 40 dB over S9, we can almost get down to S1.

This doesn't matter, of course, if your noise level is S8, but it 
matters a LOT if it's a lot lower.

73, Jim K9YC