[Elecraft] [K3] AGC Settings and DSP 1.87

[Lyle Johnson]

DSP firmware 1.87 corrects two AGC problems occasionally resulting in 
complaints of unexpectedly loud signals in an operator's headphones.

The first lowers the AGC threshold.  It was inadvertently raised 
sometime after release 1.47.  It is now back to its original range.

The second corrects a problem in the AGC slope.  As signals grew 
stronger, the AGC was not properly restricting their range, particularly 
for signals from about S9 to the activation of hardware AGC (about S9+5 
or 10 in the earliest K3s; about S9+20 in later K3s and those with the 
HAGC mod).

The new code sets the slope of the AGC as "linear in dB."  This means 
that if you have it set for, say, 1 dB of output change for 10 dB of 
signal change, then an input signal change of 40 dB will result in about 
a 4 dB change in the audio level.

The slope now ranges from essentially flat output (CONFIG:AGC SLP 15) to 
about 3.75 dB audio rise per 10 dB signal rise (CONFIG:AGC SLP 0).  Each 
step is about 0.25 dB audio change per 10 dB of input signal change.

You probably won't need to alter any AGC settings in your K3, but you 
may want to experiment with different values of CONFIG:AGC THR and 
CONFIG:AGC SLP.  Remember, there is no "correct" setting; the K3 is 
designed to be tailored to your preferences.

Enjoy!

73,

Lyle KK7P