Joe, You may recall that the subject of K3 "Mush" was discussed on the K3 Contesters Forum earlier this year, and that I suggested that the Group Delay Variations introduced by the narrower bandwidth roofing filters might well be the cause of the "Mush" problem. The recordings of K3's audio sent to me by two owners of the K3 supported this thought, as did the plots made by another K3 owner of the Delay vs. frequency introduced by roofers of differing bandwidths.
A second thought, which I could not post before leaving Scotland, was that the termination of the roofing filter would seem to vary when the HAGC becomes activeThis raises two further points: 1) "What effect does an active HAGC have on a roofer's Group Delay Variations?" 2) "What effect does an active HAGC have on a roofer's Output Odd Order Intercepts (in and outside of the filter's passband), and does this increase the level of filter generated IMD products enough to create audible "mush"? Unfortunately adding a simple resistive pad to isolate the roofer's output from the HAGC's IF circuitry could increase the overall Noise Figure of the receiver too much. It is my understanding that not all K3s exhibit this "mush problem". This does not surprise me because the Delay characteristics of the roofers are probably not specified to keep their cost within affordable limits - i.e. some K3 roofers of x bandwith might exhibit fairly constant delay vs. frequency, others might be quite "wild". 73, Geoff LX2AO On Monday, December 05, 2011 3:36 AM, Joe Subich W4TV wrote: > Remember, IMD is driven by total *peak* signal level. The peak signal > level is not simply the scalar sum of the levels ... it is a vector > sum as the individual signals add in phase. W8FN explained some of the > constraints in terms of peak to average power of multiple CDMA transmit > signals and IMD ... the same applies to receive signals and the peak > voltage handling capability in the IF amplifier/ADC. Six to 10 S4-S5 > signals can create a greater peak voltage (if just for the shortest > time) than a single S9+40 signal. ______________________________________________________________ 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
