[Elecraft] K3 AGC Settings Tutorial

[Lyle Johnson]

BACKGROUND

There has been a lot of confusion about AGC in the K3.  Some of it is 
AGC related, some of it is AGC interaction with noise reduction (NR).

A later email will address the noise reduction issue. For now, let';s 
look at the AGC apart from NR.

---

WHY DID THE AGC CHANGE?

WHen we interoduced the HAGC mod a few months ago, it increased the 
dynamic range of the radio before "Hardware AGC" (HAGC) kicked in. HAGC 
is there to protect the analog to digital converter (ADC) from 
over-range.  The mod required that the DSP AGC cover a wider range.

It turned out that the DSP AGC was not doing the job it was intended to 
do on these stronger signals.  We were receiving a steady stream of 
complaints about loud signals being almost painful to K3 operators using 
headphones.  IF flat (SLOE=15) was selected it worked fine, but other 
settings resulted in excessive signal strength.

The AGC control algorithm was recently changed to compensate for this 
problem.  At the same time, the AGC threshold range was adjusted to more 
closely mimic earlier K3 AGC threshold behavior.

---

HOW SHOULD I ADJUST THE AGC?

For most of us, the K3 AGC is simply a matter of OFF|FAST|SLOW. 
HOwever, many peopl prefer an AGC that starts on band noise; others want 
it to start with a weak to moderate signal.

Some people like the audio level to be constant once AGC has been 
activated' others want some sense of increasing loudness as the signal 
strength increases.

Here is how I suggest you set the AGC for your needs.

1) CONFIG:TECH MD ON

This exposes the AGC parameters you can adjust.

2) CONFIG:AGC SLP 015

This makes the audio response flat once the AGC threshold has been reached.

3) CONFIG:AGC THR

Tune around and and adjust this to the desired threshold.  A low number 
means a weaker signal (or noise) will activate the AGC.

Note: THE AGC does NOT drive the S METER, so don't make the mistake of 
conditioning yourself to look at S METER action and think you are seeing 
the affects of AGC adjustments.

Note: Different bands and different days have different amounts of 
noise.  A noise QRN-filled summer noise level is very different than a 
quiet winter evening's noise level.  The AGC doesn't know the 
difference, so it is up to you to change things if you desire different 
thresholds on a seasonal basis.

4) CONFIG:AGC SLP

Now that you have the threshold chosen, tune across loud and weak 
signals.  Adjust the SLP parameter so that stronger signals sound louder 
  by reducing this value from 15.  If you want everything to be "flat" 
above the threshold, leave it at 15.

---

WHAT IS NEXT?

The changes to the AGC have not pleased everyone.  We are embarking on a 
modification and test program to further improve it.  Watch this space!

---

AGC - OTHER

You can also adjust the decay rates for FAST (CONFIG:AGC F) and SLOW 
(CONFIG:AGC S).  Larger values indicate faster decay.  The amount of 
HOLD time that AGC SLOW uses before it commences decay is also settable 
(CONGIF:AGC HLD).

Most people seem to be happy with the defaults.

Thank you for your patience and we continue to work to make the K3 YOUR 
radio.

73,

Lyle KK7P