[Elecraft] RX Mush, why the fuss?

[dave]

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
>
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