[Elecraft] Re: AGC MOD

[Wayne Burdick]

Isaac,

> The new AGC circuit has a 51k pot in series with a 5.1k res. to GND.
> Why not just replace the 51K R1 with  a bare 50K POT? (is this some sort of protection?)

The revision B K2 has a 50 k pot. The extra 5.1 k resistor in series is there to
adjust the range of resistance in this circuit upward by 10% (so that it's about
5 k to 55 k), which should cover every possible AGC threshold adjustment requirement.

The vast majority of K2 revision A owners will NOT have to make any change to
R1. To see a change is warranted, listen to background noise on a very quiet
band, then turn off the AGC (by holding PRE/ATTN and AGC together). If the
background noise comes up significantly in volume, R1 is probably slightly too large.

If this is the case, you can temporarily install a high-value pot across R1, as
you mentioned. Once you have determined the optimal value, you can replace R1
with a new fixed value resistor. Typically it will be between 39 and 51 k. 

There are two other things to keep in mind regarding a change to R1:

1. You should re-test AGC performance on large signals

2. You'll need to re-calibrate the S-meter (CAL S HI and CAL S LO)

73,
Wayne