[Amps] Dummy Loads & Wattmeters

[Alex Eban]

...a very old method was to use a thermocouple heated by a resistor equal to
the load (usually 50 ohms). Then the thing was heated with DC until the
thermocouple's output equaled the RF generated signal. The DC power was
easily measured to a 1 of 2 percent precision and both were equal. In
addition the arrangement was able to measure the true RMS value of the
signal; this didn't matter if the  signal was single frequency but the
inherent precision was there. It's true that attenuators were needed but
they could be made quite precise.
The method worked so well that at least one instrument I know of was made by
HP along these lines: the HP 3400. as far as I know it's still being made,
although it's calibrated for 600 ohms.
Alex	4Z5KS

-----Original Message-----
From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
Behalf Of Gary Smith
Sent: Thursday, December 03, 2009 8:30 PM
To: garyschafer at comcast.net; 'Dennis OConnor'; amps at contesting.com
Subject: Re: [Amps] Dummy Loads & Wattmeters

Reading the threads on this issue leads me to ask the question: other than
the calorimeter that Doc Kirkby has suggested, and yes that method is beyond
the scope pof most of us hams, how did the early discoverers and users/
appliers of this phenomemom arrive at the the output figures that they did?
By guess or by golly?  Or by mentods we haave come ot ignore?

Just my curious .02.,

73,
Gary...wa6fgi

 
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