If you're wondering if S-meters are calibrated to some standard, the
answer is that they're not. S-meters simply read the AGC voltage, which
is only approximately logarithmic. Therefore, the number of dB per S
unit typically varies from one part of the scale to another. For
example, the S-meter in my Icom 730, on 40 meters, preamp off, varies
from 1.3 to 4.0 dB per S-unit depending on where on the scale you are.
The "10 dB" increments over S-9 vary from 5.6 to 13.5 dB. Receiver
manufacturers are free to make the sensitivity whatever they want, and
seldom exceed about 5 dB per S-unit, because users complain that the
meter is too "Scotch" (insensitive) if they do.

There is a tendency for receivers to be calibrated to about 50
microvolts at one point on the meter, S-9, and there's often a
calibration adjustment for this.

Any "standard" is useless at best and misleading at worst, because it
bears no relation to what S-meters really read.

Roy Lewallen, W7EL

Avery Fineman wrote:
Is there a standard RF input level per "S" Unit?

If so, please post the location. Thanks.