[Elecraft] k3 NR Audio level increase

[Bob Cunnings]

I've only just now noticed that the "oscillation" when NR is enabled
that I hear when tuning through an S9 carrier in USB/LSB happens only
when VOX is enabled. In fact, I just now noticed that the red TX
indicator is illuminated when this happens - although there is no
indication of power out on either the K3 or the outboard power meter.

So with AGC SLP=5, THR=5, NR enabled, VOX enabled, tuning through S9
carrier triggers this on USB/LSB, but not CW.

Very strange.

Bob NW8L

On Sat, Apr 25, 2009 at 3:20 PM, Bob Cunnings <bob.cunnings at gmail.com> wrote:
> 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
>>
>