[Elecraft] [K3] AGC White Paper

[Jim Brown]

On Mon,3/6/2017 11:29 AM, Don Wilhelm wrote:
> This is often referred to as "AGC Pumping". 

Yes, BUT -- there is distortion associated with AGC action, and that 
distortion is what is perceived as "mush."

[Remember that the fundamental definition of distortion is "anything in 
the output that's not the input multiplied by a constant. Distortion can 
include time-variable gain, non-constant amplitude and phase response as 
a function of time or frequency, and amplitude non-linearity, variable 
time response. ALL of these distortions have the potential for confusing 
the ear-brain when trying to get intelligence from a signal, or 
providing aural satisfaction when listening to music. The K2 provides a 
great example. It sounds great and audio is easy to copy when listening 
to a SSB signal through the TX filter, but sounds awful and makes copy 
very difficult when the crystal filters are stagger tuned to provide 
narrower bandwidth. That's because the frequency response is pretty flat 
for the TX filter, but looks like a side view of the Rocky Mountains 
with the stagger tuned filters, and because every change in amplitude 
response is accompanied by non-constant phase response.]

More important -- this "mush" problem is NOT a theoretical concept -- 
the problem has been experienced by hundreds of great CW operators in 
contests and DX pileups. Those operators have, by careful experimenting 
based on their understanding of how AGC works, and by listening to the 
results of tweaking AGC parameters, developed settings that SOLVE THE 
PROBLEM. Caps added for emphasis. In general, their solutions are quite 
similar, differing only in degree.

This is NOT a problem for casual contesters or DXers, who either don't 
call CQ in contests or don't have a big enough station or a callsign 
that's rare enough in a given contest to generate a pileup. Most of the 
time I'm operating I fall into the first category, but occasionally the 
second. I've tried the recommendations of several top CW contesters, and 
I do agree that the result is making multiple callers easier for my 
brain to separate.

73, Jim K9YC