[Elecraft] k3 NR Audio level increase

[Bob Cunnings]

Apparently NR *is* upstream of AGC, since a while back NR was
disallowed unless AGC was enabled [1] in order, according to K2VCO, to
prevent instability [2].

By the way, I can observe this instability (a "wup-wup" oscillation)
in LSB/USB modes with an S9 carrier, and AGC settings on the "light"
side (high threshold, low slope, with THR=8 and SLP=0 being the
extreme). I ran into this tuning through shortwave BC stations with NR
enabled with THR and SLP set to 5. I'm using firmware version 3.11.

What seems odd to me is that although I can reproduce the audio level
increase cases observed by others when NR is enabled, the S-meter
indication doesn't change - I suppose that the S-meter pickoff point
is upstream of NR?

On the flip side you mention, if notch filtering was before AGC as you
wish, would you expect the S-meter indication to change when the notch
filter is active?

Bob NW8L

[1] http://www.mail-archive.com/elecraft@mailman.qth.net/msg58245.html
[2] http://www.mail-archive.com/elecraft@mailman.qth.net/msg60930.html

On Sat, Apr 25, 2009 at 12:55 PM, Joe Subich, W4TV <lists at subich.com> wrote:
>
> It's not working as it should ... there should be no volume
> change when engaging NR.  Noise reduction should work on the
> audio AFTER AGC.  If anything, the test results below should
> show a very slight drop with NR due to the removal of the
> unwanted (broadband) components but the peak level should
> not change.
>
> This NR problem is the flip side of the issue with the notch
> filter ... Notch is working AFTER the AGC where it should
> work before AGC while NR is working before the AGC where it
> should work AFTER the AGC.
>
> 73,
>
>   ... Joe, W4TV
>