[HBR] AGC vs. limiting

[hbr@mailman.qth.net]

Stan Mcintosh wrote:
> ... AGC or limiting. Limiting sounds preferable, to me ...

Another issue is the effect on the overall receiver performance.   AGC 
reduces the gain of early stages when you're listening to strong 
signals; this means that strong signals on nearby frequencies don't 
overload later stages causing distortion.   On CW that would show up 
as 'pumping,' changes in the sound, and possibly crossmodulation 
from strong SSB or AM signals.

If you provide and use an RF gain control (like a rheostat in the 
cathode of the RF stage) so signal levels are kept as low as 
possible, no problem.   But to be sure, you have to follow the 'how to 
receive SSB on an old receiver' instructions of turning the RF gain 
way down, the AF full up, then increasing the RF gain just to the 
level where you can copy the desired signal. 

Simpler receivers -- with not much gain ahead of the detector --are 
less likely to have problems.  But AGC's not that hard to do, and it 
makes things simple when you want them that way.  Put in an AGC 
disable switch (or just back the RF gain way down) for times when 
you want to do things manually.  And then enjoy the sound of CW 
through a limiter!

Walt 
KJ4KV