[Elecraft] K3 2.7 k Filter vs. 2.8 k

[Vic K2VCO]

K4IA at aol.com wrote:

> Well, sorta kinda.  If the unwanted signal gets in  and pumps the AGC, then 
> the DSP might knock down the signal but won't be able to  do anything about the 
> AGC pumping.  Then, you won't hear the signal if it  is weak.  That is the 
> whole issue of the DSP being in or out of the AGC  loop and it generated a 
> mountain of controversy with the Orion when TT moved the  DSP to within the loop.

The K3 has two AGC loops. One is part of the DSP, so as long as the DSP 
does not overload, a signal outside the DSP passband but within the 
crystal filter passband will not cause the AGC to pump.

But, if the signal is greater than, I think, S9+30 (30 dB above 50 uv), 
then it might overload the DSP. So in that case, the analog AGC which is 
outside of the DSP kicks in to prevent that, and you would notice a gain 
reduction on the desired signal.

This is where you could use a narrower roofing filter. I ordered 2.8, 
1.0, and 0.4 KHz filters. I noticed this effect with huge signals by 
listening with the bandwidth set to 450 Hz, which uses the 1 KHz crystal 
filter. Moving it to 400 Hz causes the narrower filter to be activated, 
which eliminates the pumping.
-- 
73,
Vic, K2VCO
Fresno CA
K3 no. 00007 ('James')
http://www.qsl.net/k2vco