[Elecraft] K3 DSP AGC Question

[Dave - AB7E]

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" <w3fpr at embarqmail.com>
To: "Joe Subich, W4TV" <lists at subich.com>,
    <elecraft at mailman.qth.net>
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 
>     
>