Andrew, That elusive 'known accurate wattmeter' may be a challenge to find - especially at the power levels you are attempting to measure. Many (most) wattmeters spec the accuracy as a percentage of full scale - so if you use one good for 10% on a 50 watt scale, the error can be as much as 5 watts - and that is greater than the power that you are trying to measure - not a good situation. So even if you do find a wattmeter that is 'known accurate', it is always prudent to ask "accurate at what power level?". If one is dealing with 100 Watts, 10% may be a tolerable accuracy, but at low power levels, things become more critical on this issue.
May I instead suggest that you use a known 50 ohm resistive dummy load - they are easy to check with an antenna analyzer (ideally X will equal 0), along with either an RF Probe or a 'scope. The RF Probe will read Vrms, while the 'scope (properly calibrated) will read Vp-p. The formulas are (Vp-p^2)/8R or (Vrms^2)/R where R is the resistance of your dummy load. It is easier than the 'telling of it', and will provide better accuracy than most wattmeters. You can call me a 'test equipment skeptic' if you want, but I learned long ago that trusting test equipment without question will lead you into many deep traps. 73, Don W3FPR > -----Original Message----- > > > 0.4W ... > > I was afraid of that -- I recalibrated the tuner with a 50 ohm dummy > load and now it's showing 1.9 W when running on batteries, which sounds > correct. I will further calibrate when I have access to a known > accurate wattmeter. > > Thank you for clarifying. > > --Andrew > _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
