Continuing my little adventure into RF power meters, since I didn't have an immediate way to confirm that the 478A thermistor mount that I recently got was good beyond the resistance values being "normal", and neither the 432A meter that came with it, nor a 431B I already had were known to be working properly, I, of course, applied a TEA solution to establishing a basis for comparison: I bought a tested and calibrated 432A with 478A and cable.
So, now with a good starting point, I know the following:
1. My unknown 431B will need work since I cannot zero it with the known-good thermistor.
2. My unknown 432A
does work properly with the good thermistor.
3. My unknown 478A does not zero using the known-good meter.
4. Both cables are good.
With the two 432A meters, although they do zero properly, they are a bit drifty, especially on the -10 and -20 dB ranges. The newer meter drifts faster than the earlier one that I got, even after being on for over half an hour. I assume that it's an issue with drifty components in the meter, but could it be the thermistor?
0culus, or anyone else with one of these HP meters, does your meter + thermistor (no source attached) quickly drift off zero at or near its most sensitive range?