[Elecraft] K3 AGC THR doesn't go low enough

[Richard Ferch]

G3XRJ wrote:

> Finally I must point out that I'm not saying the K3 is a noisy receiver
> but rather, whatever the AGC does in its present incarnation in the
> digital stream, has the effect of increasing the 'rf gain' from 12
> o'clock to nearly 3 o'clock on overall system noise.

Rather than comparing the noise level at identical gain control 
settings, I believe you should be comparing the noise level at gain 
control settings that result in the same loudness for a fixed-strength 
signal (e.g. a 1 uV signal). After all, what matters is not the absolute 
level of noise at some arbitrarily-chosen gain control setting, it is 
the level of noise relative to the signals you want to listen to.

In your original posting, you were comparing AGC off to AGC on. In order 
to reduce the disparity, you were requesting a lower AGC threshold. This 
would be counter-productive; reducing the AGC threshold increases the 
disparity between AGC on and off. To reduce the overall disparity 
between AGC on and AGC off, you must raise the AGC threshold so the AGC 
has as little effect as possible on weak signals. This may also require 
a re-adjustment of the RF gain control in order to make overall system 
gain on weak signals and noise the same between the two AGC settings (on 
and off, or low and high threshold).

To put it another way, if you like the way the receiver operates with no 
AGC but would like to have AGC protecting your ears for very strong 
signals, set the AGC threshold as high as possible, adjust the rf gain 
controls for the desired noise (and weak signal) level at your ears, and 
then adjust the AGC "slope" setting to affect strong signals the way you 
want it to. The least aggressive AGC action overall occurs with the 
threshold set as high as possible and the "slope" setting as low as 
possible.

There is a very good explanation of the effects of the K3's AGC settings at
<http://www.cliftonlaboratories.com/elecraft_k3_agc_and_s-meter.htm>.

73,
Rich VE3KI