[Elecraft] AGC OFF --> S-meter gone?

[Ferguson, Kevin]

The logarithmic response of most S-meters (the K2's included)is achieved via
the non-linear (multiplication) negative feedback inherant of any AGC loop.

If the loop is opened so that AGC is disabled, yet the detected signal
strength (which would be the AGC voltage were it still active) is still used
to drive an S-meter, then the logarithmic response of the meter is becomes
nearly linear instead.  This will make the meter nearly useless except on
very weak signals. To achieve logarithmic response, the AGC must be active
so that the detected signal strength is allowed to "fight" the incoming
signal. 

Best to learn to judge signal strength "by ear" in any case...that always
works, and the calibration doesn't even shift between various rig
manufacturers, etc.