[Elecraft] Power Calibration ?

[Ron D'Eau Claire]

My question for the group is:  Wouldn't it be just as accurate to read
the RF Voltage across the load?
... 73, Fran

Since the power is related to the square of the voltage, any error in
the r-f voltage measurement is squared as well.  

For example, say you have 10 vrms across 50 ohms. That equals 2 watts
(10 squared = 100 divided by 50 ohms). If your measurement is off by
10%, then you might measure 9 vrms or 11 vrms, indicating a power of 1.6
to 2.4 watts - a possible error of +/- 20%.

A 10% r-f voltage measurement error is very easy to have, even with a
very good DMM measuring the d-c coming out of the r-f probe. The
behavior of the diode in the r-f at the power level involved, the
accuracy of the scaling resistances used to provide a 0.707 (rms)
multiplication of the peak d-c level, or the loading effects of the DMM
on a capacitor in a peak-reading meter can all add up to 10% or more
measurement error very easily. 

Ron AC7AC
K2 # 1289