[Elecraft] Re: AGC adjustment

Wed Apr 30 01:06:01 2003

This is a darn good question, Earl. As the voltage at U2-5 goes down, the
voltage at pin 1 should also go down. This in turn should increase the gain of
the IF amp (MC1350 on the RF board). At some point the IF amp will be at maximum
gain; this should occur when the voltage at U2-1 is around 3.5-3.7 V. Lower
voltages then would have no effect.

All that AGC OFF does is cut the gain of the AGC mixer (U1, NE602) to nearly
zero. Assuming you installed a resistor value at R1 that resulted in a low
voltage at pin 5 of U2, turning AGC OFF should have no effect on background
noise *unless* there was an unexpected signal present at the AGC mixer's output
that is affected by pulling the bias low at U1 pin 2. (I suppose U2B could also
be in saturation at the voltage you have selected, but this should't happen.)

Gary and I will do some measurements tomorrow and see if we can duplicate what
you're seeing.

Wayne

[email protected] wrote:
> 
> Wayne, N6KR wrote:
> 
> "If the background noise level increases dramatically with AGC off, the
> AGC threshold is probably set too aggressively. A lower voltage setting,
> as measured at pin 5 of U2 on the Control board, might be more
> appropriate."
> ==========
> When I decrease the value of R1 (thereby decreasing the voltage at U2 pin
> 5), the change in background noise becomes even greater when switching
> between AGC ON/OFF.  Why is my K2 working vice-versa?
> 
> 73, de Earl, K6SE
> K2 #2622
> _______________________________________________
> Elecraft mailing list: [email protected]
> You must be a list member to post to the list.
> Postings must be plain text (no HTML or attachments).
> See: http://mailman.qth.net/mailman/listinfo/elecraft
> Elecraft Web Page: http://www.elecraft.com

-- 

http://www.elecraft.com