http://elecraft.85.s1.nabble.com/K3-in-a-cw-pileup-needs-work-tp4523884p4550918.html
gain to override the noise of the next stage.
That assumes any IMD is produced only in the first mixer.
(first) mixer. Without specific analysis, the weakest link
is probably the ADC followed by the second mixer. If it was
improve the dynamic range. That's why I would do two stages
in the 8.125 MHz IF, if needed.
but low enough to avoid overload down the line.
... Joe, W4TV
> -----Original Message-----
> From: Don Wilhelm [mailto:
[hidden email]]
> Sent: Wednesday, February 10, 2010 1:06 AM
> To: Joe Subich, W4TV
> Cc:
[hidden email]
> 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
> >
> >
> >
> >
> >> -----Original Message-----
> >> From:
[hidden email]
> >> [mailto:
[hidden email]] On Behalf Of Guy
> >> Olinger K2AV
> >> Sent: Monday, February 08, 2010 1:49 PM
> >> To:
[hidden email]
> >> Cc:
[hidden email]
> >> 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
> >> <
[hidden email]> 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:
[hidden email]
> >>>> [mailto:
[hidden email]] On Behalf Of
> Lyle Johnson
> >>>> Sent: Monday, February 08, 2010 11:24 AM
> >>>> To:
[hidden email]
> >>>> 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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> >>>
> >> ______________________________________________________________
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