Posted by
David Gilbert on
Feb 10, 2010; 6:38am
URL: http://elecraft.85.s1.nabble.com/K3-in-a-cw-pileup-needs-work-tp4523884p4546261.html
I also think that the current max AGC threshold is too low, but I have another question. Why is it necessary for the K3 AGC to have such a sharp elbow at the point where the AGC kicks in? The Clifton Labs plots show such a sharp bend that it seems multi-signal in-band intermod is inevitable, especially with higher SLP settings. Wouldn't it be feasible, and more desirable, to have some more gradual inflection point? I would think that something like a parabolic shape would be better, and the DSP AGC is just the implementation of an algorithm, correct? I suppose that would tend to blur the distinction between different THR settings, but so what?
Maybe somebody can educate me ...
73,
Dave AB7E
------Original Mail------
From: "Don Wilhelm" <
[hidden email]>
To: "Joe Subich, W4TV" <
[hidden email]>,
<
[hidden email]>
Sent: Wed, 10 Feb 2010 01:06:09 -0500
Subject: Re: [Elecraft] K3 DSP AGC Question
Joe,
Can you elaborate your reasons for this suggestion. I had come to
believe that the best situation is to place attenuation before the first
mixer to give the greatest amount of dynamic range (headroom).
Yes, I agree that the AGC Threshold could be raised in the K3 and would
be beneficial. I have felt the default of 005 was too low.
73,
Don W3FPR
Joe Subich, W4TV wrote:
> Perhaps one should get the ambient well down in the ADC operating
> range but killing gain (adding loss) before the first mixer and
> the roofing filter is not the way to do it. If you want to
> better align the dynamic range of the receiver (or specifically
> the ADC) to conditions, the attenuation should come in the
> IF - preferably divided between the first IF and 2nd IF.
>
> However, there would still be no apparent reason that the K3
> should not be capable of sustaining an AGC threshold at least
> 10 db higher than currently set with AGC THR = 008 whether
> that be reached with preamp on, preamp off or attenuator on.
>
> 73,
>
> ... Joe, W4TV
>
>
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