[Elecraft] K3 receiver desensing on CW during contest

[Steve Ellington]

Is this correct?
If a cw signal falls within the DSP passband it should and will pump the 
AGC. If a CW signal falls outside the DSP passband it should not pump the 
DSP's AGC. The problem here is defining what the DSP's passband it. If a 
signal is just outside the audio range of the DSP (can't be heard) then I 
would consider it "outside the DSP passband" and it should not pump the AGC 
however this is never the case. I see moderate signals just slightly outside 
the audio passband that pump the AGC. This is partly what is confusing us. 
Signals that we can't hear pumping the AGC worry us. What we hear coming 
from the speaker doesn't match how the AGC is responding. If my WIDTH is set 
for 100hz and a signal is at 110hz, I won't hear him but my S-meter responds 
to him as well as my AGC "desenses" (reduces gain).
All of this has nothing to do with the roofing filter.
Steve Ellington
N4LQ at carolina.rr.com
----- Original Message ----- 
From: "Jim Brown" <jim at audiosystemsgroup.com>
To: "Elecraft List" <elecraft at mailman.qth.net>
Sent: Monday, February 23, 2009 1:46 PM
Subject: Re: [Elecraft] K3 receiver desensing on CW during contest


> It seems that this thread is VERY confused about how AGC works to
> control the RF gain. I also suspect that some are using the radio
> with too much RF gain. The settings that W4ZV posted are pretty
> much what I use, except that I regularly also run the RF gains
> (both main and sub) at about 2 o'clock when I hear signals getting
> buried in the background noise.
>
> I also think many do not understand the definition of desense.
> Desense occurs when a gain stage is driven into clip so badly that
> the bias point shifts and reduces the gain (worst case, to
> cutoff). So far, I've never heard my K3s desense. I have heard a
> strong station pump the AGC when I'm copying a weak station. I've
> also heard massive phase noise and clicks from a dirty transmitter
> (most recently, a JA who was only about 5dB over S9 when I was
> trying to run JAs 1 kHz away from him on 40M).  And there's a JA
> who made it into my logbook on 80M with a power exchange of 1
> watt!  He wouldn't have with any other radio.
>
> One expansion of W4ZV's comments regarding perception of pitch.
> Human sight and hearing are logarithmic. Human hearing works on
> the basis of what acousticians call "critical bands," which are
> logarithmic, and which are tied to the physical construction of
> the human hearing system itself. The filter between our ears is
> better able to separate a 50 Hz pitch difference at 300 Hz than at
> 900 Hz! That's one reason why some CW operators like to work at
> lower pitches when the going gets tough.
>
> 73,
>
> Jim Brown K9YC
> (Member Acoustical Society of America)
>
>
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