[Elecraft] S-Meter Calibration

[Ron D' Eau Claire]

KC4KGU wrote:

> At higher powers, it becomes insanely inaccurate.
> 622w indicated on the VFD (and I trust this meter) shows as just under
> 500w on the MFJ 989C.

That's about 20% error, depending upon how much "under" 500 watts the
reading is on the 989C. My experience is that an RF power meter does very
well to be any more accurate than that unless it is specifically quoted
otherwise.

MFJ gives NO specification for the accuracy of the power meter on the 989C
as far as I have seen, while MFJ does warn that whatever accuracy it offers
is degraded if the reading is on the lower half of the meter scale of if the
tuner isn't showing a perfect match. So I wouldn't expect anything better
than 20% at best.

Elecraft does say that its power output metering is accurate within 10%, but
ONLY at 5 watts output. It could be anything at 0.5 or 10 watts.

If it's important, it's good to be sure the accuracy of a meter is
specified,  the calibration is traceable to some reference "standard", and
the calibration is checked on some regular basis.

Ron AC7AC
K2 # 1289