My thoughts on this are that those who are concerned about the slope and threshold settings are barking up the wrong tree. The mush would result if you have your hold time or hang time or decay set too short. With a brief hold time the weaker signal pops up to the level of the stronger on as soon as the stronger one disappears. A longer hold time keeps the relative level of the two signals at the correct relationship. The answer is hold time, not threshold or slope.
Those of us in the southeastern US may have a problem with all the lighting we get. The lightning spikes tend to drive the desired signal too low. So we kinda have to keep hold time short if we are to hear anything. But there should be some level of decent compromise in there somewhere. IIRC the K3 has an AGC setting that helps with this but does not eliminate it.
72 de dave ab9ca/4 On 2/28/17 2:53 PM, Wes Stewart wrote:
I must confess to some bewilderment about the seemingly endless discussion about the adjustment, or mis-adjustment, of AGC slope, threshold or "RF" gain. Claims are made that one's favorite settings cause signals within the passband to retain their relative amplitudes thus allowing the discrimination between them, while less favorable settings compress them into "mush." I will confess that my experience with the design of AGC systems is limited to analog receivers and perhaps there is some digital magic that makes DSP radios act differently from analog ones in this case. But in my experience, AGC control is derived from the stronger signal received. After the SNR is adequate (delayed AGC in 1960s terms, above threshold today), the overall gain is reduced by some amount to maintain a desired output or to prevent overload, and any other signals present suffer the same gain reduction. Hence a signal 30 dB stronger than another is still 30 dB stronger even after the application of AGC. If it isn't then we have a very nonlinear receiver, which is desirable if we're receiving FM but highly undesirable otherwise. My reading between the lines suggests that the "mush" proponents think that after achieving threshold, changing the slope somehow changes the ratio between signals, i.e. there is less gain for strong signals than there is for weaker ones. Frankly, after 60 years of listening to shortwave noise and in my youth working in a machine shop and hanging around too many alcohol and nitro burning race cars, my tinnitus practically drives me nuts at times; I welcome a flat AGC slope. If I'm all wet with this, I'd like to be enlightened. Wes N7WS ______________________________________________________________ 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 ho13d...@gmail.com .
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