[Elecraft] K3 DSP AGC Question

[Joe Subich, W4TV]

> It may be a dance, but hopefully careful intelligent musing 
> over the matter is convincing people that they should get the 
> ambient well down in the analog-to-digital converter (ADC) 
> operating range. If they do, a -99 threshold is a -109 
> threshold, and further backing off RF gain can make it a -119 
> or -129 threshold as far as the ADC is concerned, and 
> headroom is being used for what headroom should be used for.

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 
    


> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net 
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Guy 
> Olinger K2AV
> Sent: Monday, February 08, 2010 1:49 PM
> To: nospam.lists at subich.com
> Cc: elecraft at mailman.qth.net
> Subject: Re: [Elecraft] K3 DSP AGC Question
> 
> 
> It may be a dance, but hopefully careful intelligent musing 
> over the matter is convincing people that they should get the 
> ambient well down in the analog-to-digital converter (ADC) 
> operating range. If they do, a -99 threshold is a -109 
> threshold, and further backing off RF gain can make it a -119 
> or -129 threshold as far as the ADC is concerned, and 
> headroom is being used for what headroom should be used for.
> 
> One thing for sure, there has not been a good-enough 
> presentation of what is going on, and people really don't 
> seem to get it.  For something that is plain indisputable 
> physics, people are still running PRE and max RFgain on 80 
> with fast AGC, and are honestly dismayed and confused about 
> the inevitable outcome, incorrectly blaming the rig for being 
> natively noisy, no-work NR and NB, filter "ringing", unable 
> to pull signals out of noise, and more.
> 
> Maybe the variable gain by band in the MP (with a menu 
> override) was really a better strategy for a default. This 
> same issue dogged Orion owners, and by the chatter a lot of 
> them never understood either.
> 
> There IS something entirely separate with the headphone audio 
> and HI-Z headsets, high volume levels, maybe a sharp 
> saturation point, and mush, just haven't nailed it yet.
> 
> 73, Guy.
> 
> On Mon, Feb 8, 2010 at 12:01 PM, Joe Subich, W4TV 
> <lists at subich.com> wrote:
> >
> >
> >> Likely?  I don't know.
> >
> > Likely is a better choice since raising the AGC threshold 
> seems to be 
> > the primary goal of much of the "PRE/ATT/RF Gain dance" we've seen 
> > recently.
> >
> > The hardware AGC (HAGC) would seem to provide an ultimate limit on 
> > level to the ADC - unless the ADC can't handle the 
> transient peaks - 
> > so a higher threshold for the DSP derived AGC would be 
> helpful in many 
> > ways.
> >
> > 73,
> >
> >   ... Joe, W4TV
> >
> >
> >
> >
> >> -----Original Message-----
> >> From: elecraft-bounces at mailman.qth.net 
> >> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Lyle Johnson
> >> Sent: Monday, February 08, 2010 11:24 AM
> >> To: elecraft at mailman.qth.net
> >> Subject: Re: [Elecraft] K3 DSP AGC Question
> >>
> >>
> >> Hello Joe!
> >> > Assuming that the threshold values have not changed in a 
> major way 
> >> > since Jack's measurements, would it be possible to 
> extend the range 
> >> > of threshold values - say to AGC THR=016 at about -80dBm 
> (assuming 
> >> > 2 dB per step)?
> >> >
> >>
> >> Possible?  Yes.
> >>
> >> Likely?  I don't know.  There are a lot of side effects 
> that happen 
> >> when the threshold is raised...
> >>
> >> 73,
> >>
> >> Lyle KK7P
> >>
> >
> >
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