Optimum AGC threshold setting

[Bob Evans-4]

W3FPR's answer (below) to S-meter settings triggered a question:  The manual
says to set the AGC to 3.80 V, which I have done, but if I wanted to set it
for "optimum receiver performance", as Don suggests, which way and how far
do I go?  

 

"I usually use the XG1 and check the S-meter with the preamp off on 40
meters - if the AGC Threshold is set for optimum receiver performance, and
CAL S Hi and Lo are set the S-meter usually comes right in at S-9 with the
preamp off."

Thanks,

Bob K5WA

K2/100s #4687 & #5119

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[Don Wilhelm-3]

Bob,

This query comes up often, so
I have started a bit of 'research study' to hopefully obtain a 'number' that
will yield close to optimum performance, and so far I have determined that
the proper voltage setting for the AGC Threshold depends on the actual
voltage output of the 8 volt regulator.  I have started a chart and have
only a few entries.  Based on my current sample size of 5, you can determine
a voltage for the AGC Threshold by subtracting 0.50 volts from the actual
regulator voltage and then divide by 2.  Example, regulator voltage is 7.80
volts; (7.80 - 0.50) = 7.30; 7.30/2 = 3.65 -- if the regulator voltage is
8.10 volts, the AGC Threshold voltage will be 3.80 volts.

Since this is yet a small sample, please do not rely on this being the
proper setting, this is only preliminary, and my current sample variation is
+/- 0.03 volts  - I will refine it as I obtain more data.  In the meantime,
you can help add to my data base by finding the optimum setting for your K2
by doing just as I am on K2 that I align and calibrate - here is the
procedure

Setup conditions:
1. Remove the antenna
2. RF Gain at full clockwise rotation
3. Band = 40 meters
4. DSP (if installed) = Bypass
5. Preamp = off
6. Mode = CW
7. CW filter at 500 to 800 Hz bandwidth
8. AF Gain advanced far enough to hear the receiver noise

Test:
1. Press the PRE/ATT and AGC buttons together to toggle AGC alternately on
and off
2. Listen for a change in the level of receiver noise between AGC on and AGC
off

Monitor and Adjust:
1. Monitor the voltage at Control Board U2 pin 5
2. Adjust Ctrl Bd R1 to the highest voltage where no change in noise is
detected between AGC on and AGC off.

If you wish to add to my database in hopes of obtaining a 'formula', send me
an email with the voltage at U2 pin 5 that you obtained and the voltage at
the output of your 8 volt regulator (Control Board U4, upper pin).  If you
do this, your voltage readings should be to 2 decimal places.

73,
Don W3FPR

> -----Original Message-----
>
> W3FPR's answer (below) to S-meter settings triggered a question:
> The manual
> says to set the AGC to 3.80 V, which I have done, but if I wanted
> to set it
> for "optimum receiver performance", as Don suggests, which way and how far
> do I go?
>
>
>
> "I usually use the XG1 and check the S-meter with the preamp off on 40
> meters - if the AGC Threshold is set for optimum receiver performance, and
> CAL S Hi and Lo are set the S-meter usually comes right in at S-9 with the
> preamp off."
>
> Thanks,
>
> Bob K5WA
>
> K2/100s #4687 & #5119
>
>

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