[Elecraft] R1 and the AGC

[Earl W Cunningham]

Earl, K6SE wrote:

"I do a lot of weak signal work on CW and had the same problem until I
played around with the AGC by decreasing the value of R1 on the control
board from 51k to about 22K."

Fred, KT5X asked:

"In the newer K2's where this is adjustable, what voltage is sought and
at what point is it measured?  I would like to look at mine and see if my
R1 should be reduced."
==========
On K2s with S/Ns 3000 and above, R1 is a pot.  The procedure for
adjustment is to set it for 3.8 to 3.9 VDC on pin 5 of U2 on the control
board (this is from memory -- if I'm wrong, others please correct me).

Since this adjustment also affects the S-meter sensitivity, you might
adjust R1 for an S-9 indication (with the preamp off) with 50 uV signal
input to the receiver (actually, this is the way my S-meter turned out
after reducing the value of R1 so that The gain of U2B was correct).

At any rate, S-meter hi-lo calibration will have to be re-done after
adjusting R1.

Another item in the same area that might affect things could be diode
D1's forward resistance.  I hand selected a diode with the least forward
resistance from many in my junk box for D1.  This helped a bit, but not
as much as changing R1.

If your 8-volt regulator outputs a bit more than 8.00 VDC, R1 will have
to be set to a value considerably lower than the nominal 50k.  My
regulator outputs 8.32 VDC, so my final value for R1 was about 22k.

73, de Earl, K6SE