K3 AGC hold, initial comments on beta v2.98

[Mike Scott-7]

I live in a noisy environment (typical S-7) and have in the past complained
about K3 audio. I was never sure what was going on but it just sounded rough
and unpleasant. The hardware audio modifications I think helped a little and
most certainly cleaned up the line-out IMD.

Mostly I operate CW mode using fast AGC. The narrower the bandwidth the more
unpleasant the audio became. I operated mostly above 1 KHz bandwidth just to
smooth the sound of background noise as anything narrower was just so
tiring. So I volunteered for the AGC hold version of the firmware.

I can say that I can improve the audio on my end. I can find a way to
operate with the rough audio edge reduced, perhaps by 8-10 dB when I look at
spectrum lab headphone audio. I am guessing that with fast AGC and high
noise that I was hearing IMD products caused by noise modulating the
receiver gain and the effect of gain modulation on the noise [or signal] in
the pass band. At S-7 the DSP AGC really has significantly reduced system
gain so the gain modulation at fast AGC might be substantial in high
background noise areas.

I never really tried slow AGC for CW mode prior to this and I was not in the
habit of riding the RF gain. Note: If I operate with fast AGC I have to
reduce RF gain quite a bit for the audio to lose its edge. Fast AGC just
isn't working well in my environment. I hadn't discovered slow AGC or AGC
off with reduced RF gain as a way to operate.

I am right this moment operating with maximum [1.99 second] AGC hold, I will
play with different settings over time. Listening to a weak signal and
varying the hold parameter I can hear that things seem to improve a little
with the AGC hold greater than 1 second, RF gain at maximum. Larger AGC hold
is probably achieving something similar to my riding the RF gain control.

As a plus I am getting to use band independent VFOs as that is in the
prerelease firmware also. So far it works with no hitches.


Mike Scott - AE6WA
Tarzana, CA (DM04 / near LA)
NAQCC 3535
K3-100 #508 / KX1  #1311


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[Gary, W7TEA]

I have lots of noise as well and use a 80m vertically polarized loop. (The best nearly
invisible antenna I could manage and keep the CCnR cops at bay.)  Not being a
contester and compete in the CW pile ups only when I'm one of a few, I've found
Slow AGC at the fastest setting (40) to work the best.  If I need something faster,
I go to Fast AGC at a pretty slow setting. I seem to get the cleanest signal that
way.

73, Gary W7TEA

<quote author="Mike Scott-7">
I live in a noisy environment (typical S-7) and have in the past complained
about K3 audio. I was never sure what was going on but it just sounded rough
and unpleasant. The hardware audio modifications I think helped a little and
most certainly cleaned up the line-out IMD.

....

Mike Scott - AE6WA
Tarzana, CA (DM04 / near LA)
NAQCC 3535
K3-100 #508 / KX1  #1311