[Elecraft] RF-Gain & S-Meter (again)

[Mike Morrow]

Ron wrote:

> It sounds like you have an unusual receiver in that SX-101...the
> S-meter response to the RF gain control was one specific to that
> receiver, not the general rule.

Phil wrote:

> I had an SX-101 from 1961 through 1974.  IIRC it was a separate
> "chain" that was not affected by the AGC/RF gain setting that
> produced the voltage that drove the S-meter.

In some sense, there *are* two gain control systems in the SX-101
for the RF and IF stages.  Stage gain is reduced by:
(1)  AGC, which as it gets larger for stronger signals increases bias
     voltage to the RF and IF stages.  This is the input to the S-meter.
            PLUS
(2)  Manual RF gain, which manually increases the resistance in the
     cathode circuits of the RF and IF stages to reduce stage gain,
     independent of AGC bias voltage.

The more common method for the past 65 years or so has been to use the AGC
circuit to reduce stage gain for both automatic AND manual gain control:
(1A) AGC, which as it gets larger for stronger signals increases bias
     voltage to the RF and IF stages.  This is the input to the S-meter.
            PLUS
(1B) Manual RF gain, which manually increases the bias voltage in the
     AGC circuit to the RF and IF stages, and thus directly affects
     the S-meter just as any AGC bias voltage increase would.

Mike / KK5F