Guy Thank you for putting me straight on the terminology. Perhaps I can rephrase my question.........
The hardware AGC appears to be set at a level which precludes effective utilisation of the 100dB+ DR of the DSP system. This seems to suggest the existence of something between roofing filter and ADC which needs protecting due to it having rather less than 100dB+ DR? 73 Bob, 5B4AGN On 19 November 2010 15:44, Guy Olinger K2AV <[email protected]> wrote: > 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 <[email protected]> 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 > > ______________________________________________________________ > > Elecraft mailing list > > Home: http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/mmfaq.htm > > Post: mailto:[email protected] > > > > This list hosted by: http://www.qsl.net > > Please help support this email list: http://www.qsl.net/donate.html > > > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
