Having worked for Delta Electronics, Inc. in Virginia, a long time
ago, I remember that we had an in-house RF calibration system
approved by the FCC. We built RF ammeters for MW broadcasting, and
the TCA series is probably the industry standard now, since Weston RF
ammeters are ancient. The TCA used a current transformer and a
specially linearized RF diode rectifier circuit. However, to
calibrate these was the question. We had a homemade thermal transfer
standard. The RMS power of a clean sinewave at 1 MHz would heat one
side of a Ballentine dual thermocouple the same as DC. We would dial
up the DC current from a Fluke current standard, which went out to
NIST regularly for recalibration. This would then be balanced against
an RF level control from a generator, to get a null reading of the
output. (I assume that they still make these). I'm missing a few
details now, its from memory over 20 years ago that I worked there.
Then we had the RF level traceable to NIST. The TCA was fed the same
RF (coming from a small lab power amplifier made by ENI). We set them
to within 1% I believe (no modulation). The point is that it is
possible to get FCC approved RF power measurements with things
besides an Agilent Signal Generator or Bird Wattmeter. I also
remember that Eaton/AIL used to make a huge broadband RF wattmeter
calibration system that had some sort of transfer standard.
73
John
K5PRO
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