HP Power Meters

A collection of documentation and information related to HP Microwave Power Meters and sensor heads.

Head Testing
Notes by Brian, W6BY, on testing sensor heads similar to the 478A thermistor head. This was originally on Brian's web pages, but copied here because that site is down now.
478A Sensor internals
PNG image of a hand drawing I made showing the internals of a 478A power meter head.
431/432 Head Pinout
A gif image showing the function of the pins on a sensor head like the 478A or K486A.
Head circuits
A gif image scanned from a 431 meter manual, showing the circuits in the various 431/432-style power meter sensors.
A text-version diagram of the head circuits, similar to the gif image above.
431C Theory
A simple theory of operations for the HP 431C power meter. I wrote this many years ago when I was trying to understand how the meter worked. I found this a bit easier to follow than the description in the HP manual. It also generally applies to the 432 meter.
478A Manual
A ZIP file containing a series of jpg files that are scans of an old HP manual (1967) describing the operation and maintenance for the 478A sensor. The scans are not very good quality, but the information is great.
New 478A Manual
A current (2020) PDF file of the 478A Manual from Keysight. Pretty much the same info as the one from 1967 but nice and clean. I almost forgot that the 478A is still a current product.
8481A Manual
A pdf document with scans from selected portions of the Operating and Service manual for the thermocouple sensors used on HP 435 or 436 power meters.
435 Meter App Note
A zip file with portions of HP App Note AN64-1 relating to thermocouple-based power meters like the 435 or 436.
Fundamentals of RF and Microwave Power Measurements
A PDF file containing the complete Agilent app note AN64-1C.
478A Tester from 1978 Electronics mag
An image capture of an article from 1978 in Electronics magazine. It describes a tester circuit for measuring Rd and Rc balance in an HP 478A power sensor head.
WA1MBA 478A webpage
A webpage by Tom WA1MBA on the 478A.



Tech Info
Head Testing 478A Sensor internals 431/432 Head Pinout Head circuits Sensors.txt 431C Theory 478A Manual New 478A Manual 8481A Manual 435 Meter App Note Fundamentals of RF and Microwave Power Measurements 478A Tester 1978 WA1MBA 478A webpage