For the most part, and as Wayne has said several times, ANY non-linear
gain characteristic is going to create some distortion of a signal, and
it will create additional passband mixer products if multiple signals
exist. Those distortion and mixer products will blur whatever you're
trying to copy. Keep in mind that narrow filters help reduce the
candidates for mixing, and that noise spikes count as "signals".
AGC is by definition non-linear gain, but so is the AF LIM audio
limiter, and in my opinion the trick for working pileups is to use just
enough AGC (or use none at all and ride the RF GAIN control) to keep the
audio from reaching the AF LIM threshold. K6LL and others have pointed
out that the max limit of 30 for that setting should probably be raised,
but I've been able to find acceptable AGC settings that seem to keep my
head from banging up against that ceiling. A very good reference for me
was the set of curves generated by K8ZOA, and by looking at them you can
see the extreme non-linearity that exists for aggressive AGC settings
... especially around the threshold breakpoint. Using low values of AGC
THR appear to me to be a very bad idea for any kind of weak signal
contest work.
http://www.cliftonlaboratories.com/Documents/Elecraft%20K3%20Transceiver%20AGC%20Parameters%20and%20S-meter.pdfThe only thing more non-linear than a non-linear gain characteristic is
a time varying non-linear gain characteristic that changes rapidly
enough to occur during the signal(s) you're trying to copy. In a
contest you generally want to have quick AGC recovery for snappy QSOs,
but fast AGC with aggressive threshold and slope settings is probably
the worst of all possibilities, especially in the presence of noise
spikes. It just whipsaws the gain curve around all over the place.
The K3 has a wide enough range of available AGC settings to do the job
you need to do ... or ... to make a mess out of your receiver, depending
upon the conditions. I really like the addition of the AGC DCY = SOFT
feature, but I do not like the default settings for AGC THR and AGC SLP.
There certainly is no ideal AGC setting anyway. The best settings for
single signal copy in a low noise situation (like prowling for weak DX)
are certainly not going to be very good for working DX in a contest, and
the ideal settings for working a strong signal pileup on 20m when the
band is quiet probably won't work very well for distinguishing between
multiple weaker signals in the midst of 80m noise spikes. Personally, I
think a neat feature for a piece of software like K3_EZ would be to
allow multiple combinations of AGC settings that could be stored and
recalled as needed for changing conditions instead of having to change
each parameter singly and separately. Just click on a box (say one of
five or six?) and send the appropriate full set of AGC settings to the
K3 on the fly.
All that being said, my AGC settings are almost identical to yours
except that I have AGC PLS = OFF. My K3 is only about 6 weeks old,
though, and I haven't had a chance to use it in very many contests, so
I'm still experimenting a LOT with the settings myself.
73,
Dave AB7E
W1UE wrote:
> I'm planning on a major effort in the RDXC this weekend, so I just
> downloaded the beta firmware
> 3.03 and installed it in my K3. After installing, my AGC parameters are
> as follows:
> AGC Dcy Soft
> AGC Hold .30
> AGC PLS Norm
> AGC SLP 000
> AGC THR 008
> AGC -F 120
> AGC -S 020
>
> Since I haven't used this before (and am a confirmed AGC OFF user on
> CW), what kind
> of parameters will give me the best performance in a pileup with 10
> stations calling?
>
> I've gotten used to AGC OFF, but there is a LOT of RF gain tweaking and
> occasional
> BLASTING out of the headphones when a strong signal follows a weak one.
> Using the
> AF LIM of even 030 creates too much distortion on even fairly weak signals.
>
> I should have time in this contest to play with the AGC settings, so I'm
> open to any suggested
> settings that anyone has.
>
> Dennis W1UE
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Mar 18, 2009; 11:53am
