Folks,
I have received several requests from folks wanting to know how to optimize
their AGC Threshold. It is only inferred in the manual. If you want the
best weak signal detection that your K2 can deliver, I recommend doing the
optimization. A bit of discussion first, then how to do it (no meters other
than your ears are required) --
Real optimization depends on what you want to accomplish. Certainly you
don't want the AGC to be activated by internal receiver noise because that
would mean your K2 would never achieve its full gain (and sensitivity)
potential. OTOH, you may choose to have no AGC action with no input signal
(but above your local ambient noise) - the only problem doing it that way is
that you have to be able to inject that amount of noise during the
adjustment, but if you have a constant S-3 power line noise level at your
QTH, you don't want the AGC to respond to that noise because it will
de-sensitize your receiver. If the S-meter is responding to the noise, you
can be certain the AGC is active and reducing the gain!
So choose a condition from the above paragraph as your AGC/no AGC Threshold
point (I set up others K2s for the internal noise condition - I don't know
what the local noise level might be) - for internal noise only, just
disconnect the antenna, for local noise level, choose a time and a band with
no signals when your ambient noise level is correct for making the
adjustment.
The procedure is easy - turn the RF GAIN all the way up, PREAMP on, and the
AUDIO GAIN up enough so you can clearly hear the noise then switch AGC
on/off by pressing both the AGC and PRE/ATT buttons. Adjust the AGC
Threshold pot just to the point where you find no difference in the noise
levels. Once you have found that point, the adjustment is done - measure
the voltage at U2 pin 5 for future reference. Then re-adjust CAL S LO and
CAL S HI (and in that order - they interact) so your S-meter will read
correctly.
Enjoy all the sensitivity (and apparent audio) that your K2 can deliver.
73,
Don W3FPR
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