Phase Angle Voltmeter

[aw_rw1]

Does anyone know how a phase angle voltmeter works?

I am suppose to read a voltage from one, but I am not sure what the voltage means. Is it the VRMS of signal or a combination of the signal and reference?

Attached is a picture of a North Atlantic 321A.

[0culus]

If it works like my HP vector voltmeter (probably very similar) you make phase measurements by establishing a known phase reference using the left hand input (marked "ref"...the accessories for mine include a coaxial short for this purpose) and making phase measurements of the signal of interest relative to that using the phasemeter scale. The magnitude is read off the voltmeter scale. In the case of the 8405A [1], it works on a 50 ohm system, so with some simple transformations, you can then plot points at different frequencies on a Smith chart. It was a poor man's VNA from a time when VNAs were basically nonexistent, and when they did show up (HP 8410 system being one of the earliest, iirc), they were beyond the budget of many labs. The 8405A, incidentally, also has an interesting feature with two 20 kHz outputs on the rear panel. These are essentially sampled versions of the RF signals on the inputs, with phase relationship preserved, so even a very narrowband oscilloscope could be used to look at signals up to 1GHz.

[1]: https://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1966-05.pdf