http://elecraft.85.s1.nabble.com/K3-Wide-AGC-threshold-tp5755595p5756115.html
Thank you for putting me straight on the terminology. Perhaps I can
utilisation of the 100dB+ DR of the DSP system. This seems to suggest the
> That's not the "wide" AGC. It's the defensive hardware AGC that is in
> the actual IF string after the roofing filter before the analog to
> digital converter (ADC). It's function is to limit the level
> presented to the ADC as you surmise. It is also primitive, easily
> seen in the schematics. Handling strong signals without any AGC
> pumping, using an SSB roofer ahead of a CW DSP bandwidth, I doubt was
> a design goal of the RX. What you experience is common for those
> without a CW roofer.
>
> There was some variation in how the K3 handled this which was up in
> beta firmware very early on, and various settings were evaluated by
> the community. I'm sure you can find the blow-by-blow back in the
> archives.
>
> 73, Guy.
>
> On Fri, Nov 19, 2010 at 10:17 AM, Bob Henderson <
[hidden email]> wrote:
> > As a new K3 owner, it is entirely possible I am treading ground already
> well
> > trodden. My apologies should this be so.
> >
> > While waiting for delivery of an Inrad 500Hz roofing filter, I have been
> > accumulating experience with S/N 4904. I am enjoying my new rig greatly,
> > although I confess to finding an odd thing or two puzzling. One of these
> > relates to the level at which wide AGC has been set.
> >
> > My primary shack transceiver is a home built, G3XJP designed Picastar,
> which
> > has a similar architecture to the K3 but is based upon the much older
> Analog
> > Devices ADSP2181 and AD1885 AC'97 codec. Unlike the K3 with its multiple
> > choice roofing filter bandwidths, my Picastar uses a single 4kHz wide
> roofer
> > in all modes. The thing puzzling me is that I find de-sensing by strong
> > signals within roofer b/w but outside DSP b/w far more noticeable on the
> K3
> > than on Picastar. I expected the opposite to be true given the Picastar
> > codec has only a 16 bit ADC whereas the K3 has 24 bit.
> >
> > A quick measurement reveals K3 wide AGC threshold around 70dB above MDS
> > whereas on Picastar it is closer to 80dB. With Star's 16 bit ADC this
> > equates to around 10dB headroom whereas the K3's 24 bit ADC implies
> headroom
> > in excess of 30dB. On the face of things it would appear some 20dB of
> extra
> > defence against strong signals in the no man's land between roofer b/w
> and
> > dsp b/w has been sacrificed. I am wondering why? Perhaps I am missing
> > something?
> >
> > Thanks.
> >
> > Bob, 5B4AGN
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