[Elecraft] OT-Wattmeter Errors

[Paul Christensen]

> Do you believe yours? Article notes +/-5% is typical for lab grade 
> wattmeters.

Even some of the pseudo-lab-grade wattmeters can vary from published 
specifications.   One very popular wattmeter with a perfect review rating on 
eHam, suffers from very poor indicated VSWR accuracy below 5-watts.  Based 
on what I could measure here, it was symptomatic of the low-power accuracy 
problems described by Roy Lewallen, W7EL, in the February 1990 issue of QST. 
Although the manufacturer claims calibration to NIST traceability, it is 
likely calibrated at moderate power levels.  This wattmeter is frequency 
compensated -- but not temperature compensated.

OTOH, I own two competing wattmeters that are truly temperature compensated 
with NIST-traceable calibration, and VSWR agree with each other down to 100 
mW.

Paul, W9AC