Hi regarding the HP power meters

HP 430?? was the first of the microwave power meters ?its coaxial thermistor mount HP 477 ?10 mhz to 10 Ghz?

The HP 430 sold for $300? in 1967?? and? the ?HP 477 sold for $75? in 1967??

I did all my early microwave experiments with the? 430 ?and then progressed onto a 431

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The improved system using a second thermistor in the coaxial thermistor mount for temperature compensation HP 431 ?& HP 478 and a wider dynamic range

The HP 431 sold for $475? in 1967?? and? the ?HP 478 sold for $155? in 1967??

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Currently looking for wave guide power sensors above 50 ghz

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Regards Paul B?

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The GM / Marconi TfT deivces are thermocouple arrays. Bismuth /nichrome couples bad as a electrical generation device but can be made to match 50R.
The resistor thermocouple types were common in RF ammeters and some power meters. The early?Marconi TF144 signal generator models used them for the output meter.
The classic thermistor detector is the HP 478A that was first used?with the 431A power meter around 1961 and still made today at $5000 a pop. The analogue ?432B power meter was discontinued a few years ago with a final price of over $10,000 but the pair can be picked up for a few hundred dollars used. They built a new digital meter for the 478A the N432A at $10,000. but none if these appear in the Keysight power meter guide tables.

So why is this "old tech" still made? the answer is in the guide:
"Not discussed is the Keysight family of thermistor sensors and the associated Keysight 432A power meter. This venerable technology now is used almost exclusively for the
standardization and traceability of power measurements from the U.S. National Institute of Standards and Technology and other international standards agencies. Because the Keysight 432A power meter and thermistor sensor technology is based on the highly precise DC-substitution method, the sensors are used as transfer standards, traveling between the user’s primary lab and the NIST measurement services laboratory.
Users interested in such metrology power-transfer processes may request Keysight’s AN 64-1, 5965-6630E and AN 64-4, 5965-8167E application notes."
Basically you can use a head with any 431/432/N432 meter and a accurate DC?DVM to get transfer accuracy to?a national standard. The "meter" is just a servo to balance the bridge and the accuracy is at the DC voltage. They do special variants of the head?with larger blocking capacitors for low frequency work.
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Robert G8RPI.

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