On Mon,3/6/2017 11:29 AM, Don Wilhelm wrote:
This is often referred to as "AGC Pumping".
Yes, BUT -- there is distortion associated with AGC action, and that distortion is what is perceived as "mush."
[Remember that the fundamental definition of distortion is "anything in the output that's not the input multiplied by a constant. Distortion can include time-variable gain, non-constant amplitude and phase response as a function of time or frequency, and amplitude non-linearity, variable time response. ALL of these distortions have the potential for confusing the ear-brain when trying to get intelligence from a signal, or providing aural satisfaction when listening to music. The K2 provides a great example. It sounds great and audio is easy to copy when listening to a SSB signal through the TX filter, but sounds awful and makes copy very difficult when the crystal filters are stagger tuned to provide narrower bandwidth. That's because the frequency response is pretty flat for the TX filter, but looks like a side view of the Rocky Mountains with the stagger tuned filters, and because every change in amplitude response is accompanied by non-constant phase response.]
More important -- this "mush" problem is NOT a theoretical concept -- the problem has been experienced by hundreds of great CW operators in contests and DX pileups. Those operators have, by careful experimenting based on their understanding of how AGC works, and by listening to the results of tweaking AGC parameters, developed settings that SOLVE THE PROBLEM. Caps added for emphasis. In general, their solutions are quite similar, differing only in degree.
This is NOT a problem for casual contesters or DXers, who either don't call CQ in contests or don't have a big enough station or a callsign that's rare enough in a given contest to generate a pileup. Most of the time I'm operating I fall into the first category, but occasionally the second. I've tried the recommendations of several top CW contesters, and I do agree that the result is making multiple callers easier for my brain to separate.
73, Jim K9YC ______________________________________________________________ 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 Message delivered to arch...@mail-archive.com
