[Elecraft] S-Meter Calibration

[Ron D' Eau Claire]

Jonathan, K1RFD, wrote:

> Incidentally, there is the widespread belief that one S-unit
> equals 6 db.  I
> understand that this is now the exception rather than the rule, and most
> S-meters now run 4 db or less per S-unit.
>
> After all, the higher the S-meter reads, the better the receiver,
> right?  :>


I believe the 6 dB/S-unit came from some of the receiver manufacturers of
the 50's or thereabouts. A manufacturer needs something to have the assembly
line set things to and that seems to have been what many or most of them
settled upon. Even then, many (most?) receivers had widely varying
sensitivity over the HF range so the 'calibration' was only good on the
frequency the factory used.

Ever since before I went to school, 3 dB was used as the "minimum
discernable change in a signal level by ear in a typical radio
communications environment with some background noise and fading due to
propagation". So it seemed to make some sense to define an S-unit as twice
that level or something that would be obviously noticed under most
conditions.

Given that the RST system defines "S" as the signal strength on a 1-9 scale
as measured by the operator's ear, I calibrated my K2 S-Meter with absolute
accuracy. I tuned in a signal that I judged to be "S-9" and adjusted the
meter to indicate S-9. A few other checks and adjustments on signals at S-5
and S-3 completed the calibration. If I ever want to check the calibration
on the K2 to see if the S-Meter is still accurate, all I have to do is tune
in a signal and see if the meter agrees with my ears. If not, the S-meter
needs re-calibrating <G>.

Ron AC7AC
K2 # 1289