[Elecraft] Receiver Gain

[George, W5YR]

Mike, I have gotten my feet a little wet in this area by replacing R5 with
a 50K pot. R5 determines the gain of the AGC mixer amp and thus the
magnitude of AGC voltage developed as a function of signal level. 

R1, on the other hand, sets the operating bias for the amp and thus
determines at what signal level the AGC compression (determined by R5) sets
in.

I plan install to micro-pots for both R1 and R5 and conduct tests to see
the effects of various threshold and compression levels.

More later . . .

73/72, George    
Amateur Radio W5YR -  the Yellow Rose of Texas
In the 57th year and it just keeps getting better!
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe
K2 #489      Icom IC-765 #2349     Icom IC-756 PRO  #2121


Mike Harris wrote:
> 
> Hi,
> 
> Digging around in the noise floor on ten metres this morning, not long after
> local sunrise and listening CW (ESP Mode) to Europeans in QSO I tried
> switching the agc off.  There was a slight increase in noise level.  I was
> listening with the pre-amp OFF, indeed switching it on just increased the
> noise level and made LED's flicker without doing anything to improve
> intelligibility.  Removing the antenna (Dipole) resulted in a drop in noise
> level which indicates that without the pre-amp the receiver wasn't noise
> limited.  The pre-amp is a noisy beast anyway, or at least mine is and is at
> the wrong end of the feeder.
> 
> With the antenna disconnected and the pre-amp off the same effect could be
> heard when switching the agc on and off.
> 
> My conclusion is that a visit to R1 on the control board as others have done
> would be interesting, maybe change the 51k to 47k to delay the onset of agc
> action a little.  Maybe this is a simple test to see if any particular K2
> receiver is a bit too sensitive in the agc threshold department.
> 
> #1400 has never been deaf and doesn't suffer from any significant change in
> level whilst switching filters down from 700, 400 to 150Hz.
> 
> Regards,
> 
> Mike VP8NO (IOTA SA-002)
> GQRP 10148
> K2 #1400 + KPA100