[Elecraft] S-Meter Sensitivity

[k6se@juno.com]

Regarding the AGC circuit on the control board, it seems to me that the
value of R1 on the control board would ideally be adjusted precisely to
the point where switching the AGC on/off would result in the same amount
of background hiss (with no antenna connected), thereby setting the AGC
threshhold level for max IF gain with the AGC turned on.  If, to achieve
this, it means reducing the value of R1 would reduce the normal ~7.3 VDC
to a somewhat lower voltage on pin 5 of U2.

My op amp theory  knowledge isn't that great, but it would seem that this
would in turn decrease the level out of pin 1 of U2, thereby decreasing
the amount of AGC (V AGC) fed back to the IF amplifier and to the S-meter
(V SMTR via the MCU at pin 3 of U6).

Does anyone know which pin this AGC signal comes out of the MCU at (and
goes to the A/D circuit which drives the LED array on the front panel
board)?  SR DOUT, SR CK, or SR WRT?

73, de Earl, K6SE
68 countries with K2 #2622 and counting.....