I believe the hardware AGC would be activated if the *combined* strength of all signals within the crystal filter passband gets above the threshold of S9+25 dB or so. This means that multiple unwanted signals don't have to reach the threshold strength *individually* for AGC pumping to occur, but there would have to be *a lot* of closely spaced unwanted signals at S8 to cause a problem if a narrow roofing filter is used. Also under those conditions, the operator would be unlikely to report that individual unwanted signals are no more than S8. I suppose one could also have a case where the wanted signal is almost strong enough to set off the hardware AGC, and a single, weaker signal gets through the roofing filter (but not the DSP) and adds just enough to the combined signal to cause hardware AGC action, resulting in an audible effect on the stronger wanted signal.
73, Erik K7TV ----- Original Message ----- From: "Barry N1EU" <barry.n...@gmail.com> To: <elecraft@mailman.qth.net> Sent: Monday, February 23, 2009 9:59 AM Subject: Re: [Elecraft] K3 receiver desensing on CW during contest > > > Peter Wollan-2 wrote: >> >> Aha. It sounds like the "desense" problem arises when the DSP filter >> is narrower than the roofing filter. A strong station within the >> roofing passband but outside the DSP passband will shut down the >> receiver through AGC. >> >> I think we all misled ourselves by the impression that desense was >> impossible in the K3. It's working just as it ought -- but operators >> need to widen out the DSP to the full width of the roofing filter, >> when there are strong stations every few Hz. A bit counter-intuitive, >> perhaps. >> > > Correct me if I'm wrong, but a strong station within the > roofing passband but outside the DSP passband will NOT shut down the > receiver through AGC unless the strength exceeds s9+25dB (when hardware > AGC > kicks in due to ADC dynamic range limits). > > 73, > Barry N1EU > -- > View this message in context: > http://n2.nabble.com/K3-receiver-desensing-on-CW-during-contest-tp2369819p2373077.html > Sent from the Elecraft mailing list archive at Nabble.com. > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > 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:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
