Posted by
Dave Hachadorian on
Dec 05, 2010; 4:36pm
URL: http://elecraft.85.s1.nabble.com/Recommended-AGC-settings-for-separation-of-signals-in-CW-pile-ups-tp5804756p5805442.html
>CQ WW CW is now over. We used K3s at P3F this year. While
>performance was
>generally considered good, some questions were raised over the
>effectiveness
>of the K3 in separating signals in large piles.
--------------------------------------------------------------------------------------
This is a subject that keeps coming up, over and over again. The
most recent discussion was on the K3 Reflector, and below is my
November 23 posting on the subject "Mushy Audio on CW." The only
solution I have found that works well is to turn AGC OFF, and use
an external audio amplifier, so that you can keep the K3's AF
gain at a low level in order to defeat the K3's ridiculously
distorting AF Limiter.
-----------------------------
23 November 2010
The K3 does indeed have major problems if you are on the
receiving end of a pileup.
There is really no setting of AGC that will keep multiple callers
from mushing together.
The only good way to use the K3 in a pileup is to turn AGC OFF,
but there is a major problem with that too - extreme distortion
when loud signals hit the AF Limiter threshold.
The only immediate answer, short of adding external equipment,
is to turn AGC OFF, and ride the RF gain so that weak signals are
readable, but loud signals stay below the AF Limiter threshold.
K3NA has published an article on setting receiver RF and AF gain
with AGC turned off:
http://wiki.contesting.com/index.php/Setting_receiver_gain_controlsUnfortunately, K3NA's procedure doesn't work well with the K3.
There is no single setting of RF and AF gain that will keep weak
signals readable and loud signals out of the harsh AF Limiter.
If you have an extremely sensitive set of headphones (lots of
audio for low driving power), the K3NA procedure helps quite a
bit, but you will still be reaching for the RF gain control quite
frequently. I tried plugging my headphones into the SPEAKER AF
output, so that I could turn down AF gain and keep loud signals
out of the limiter, but managed to blow up the fragile speaker
amplifier chip, but that's another story. I don't recommend
using the speaker amplifier for anything other than the internal
speaker, or an efficient external non-amplified speaker. Sooner
or later you will be looking at a $100+ repair bill for the
speaker amplifier chip.
I complained about mushy pileup audio a long time ago, and the
Elecraft folks did make some changes to the AGC parameters, but
the problem was not solved. Here are the best AGC settings for
pileup use that I can find:
AGC DCY = SOFT (supposedly reduces IMD)
AGC HLD = 0.20 (supposed to be like riding the RF gain if agc is
set SLOW)
AGC PLS = NOR
AGC SLP = 000 (makes loud signals louder than weak ones)
AGC THR = 008 (the highest threshold before AGC action begins)
AGC-F = 120 (the default, but the best agc setting is SLOW
anyway)
AGC-S = 020
AGC FRONT PANEL SELECTION = SLOW
Although the above settings are the best with AGC that the K3 can
do, I still find them inadequate for dealing with a pileup. After
a lot of experimentation, here is what I have come up with as a
workaround solution:
AGC OFF
AF LIM = NOR 030
Use an external audio amplifier (sound card). Then you can keep
the K3's AF gain turned way down, keeping loud signals out of the
AF Limiter. I have back to back 1N5818 Schottky Diodes across
the sound card output as a soft limiter for ear protection. I
connect the K3's LIN OUT to the sound card, and set LINE OUT =
PHONES so that I can still use the K3's AF Gain control.
This has all been discussed previously on the main Elecraft
Reflector. You can search the MARC archives for "K6LL pileup."
The message with "workaround solution" in the subject discusses
the external audio amplifier.
Dave Hachadorian, K6LL
Yuma, AZ
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