[Elecraft] APF and audio limiting

[Ron D'Eau Claire]

Um, Joe, he did not say "bring up" as you quoted. Are you certain that by
saying "bring to the level" he did not mean bring louder signals *down* to
the level of the AF gain? That's how I read it.

Your observation about the best AGC operation is excellent for
communications work. Often people have AGC working "backwards", raising the
background noise level to room-filling volume when no signal is present.
That's how AGC for AM worked, originally, both for auto and home radios. As
a station faded, the AGC raised the volume to compensate, keeping the
speaker output the same. So, as one was crusin' down the highway listening
to The Wolf Man spin tunes on the AM band one might hear the background
noise come up in a weak-signal area, then drop down again as the signal
regained strength.

73,

Ron AC7AC

-----Original Message-----

>> Remember, the AGC is only supposed to bring things to the level of
 >> your AF output setting.

No. AGC should never "bring up" the level.  AGC *REDUCES* the level of
signals above the AGC threshold.  One normally sets the audio level for
signals *at the AGC threshold* or below and AGC keeps stronger signals
from exceeding that level (by the amount of the "slope" if one is not
using a "hard" threshold).

The difference with an *AUDIO PEAK FILTER* is that the APF is in the
AUDIO circuit *AFTER* the detector and *OUTSIDE* the AGC loop.  Since
the PEAK gain of the K3 APF is roughly 10 dB - see the response here:
http://n1eu.com/K3/K3_apf.htm - this can cause an issue with strong
signal but is a big advantage with signals at or near the noise level
(and below the AGC threshold).  Of course, the gain is exactly why APF
can be turned on and off ... you don't want it on with strong signals -
only with those at the noise signals where it makes a difference!

73,

    ... Joe, W4TV