Vector Voltmeters vs Oscilloscopes?

Question

I have come across some electronic engineering papers from the mid 1970's where they were testing tunable phase shifters. To measure the phase shift they used a vector voltmeter. As this is not a bit a kit I have come across or is as readily available as an oscilloscope around the university, I am curious as to what advantages or drawback a vector voltmeter might have compared with an oscilloscope, if we are considering phase measurements?

Is there any particular reason you might choose one over the other or might this just have been equipment that was available at the time and suitable for purpose?

A vector voltmeter gives you much higher accuracy both on the voltage and the phase angle values. — Janka, May 27 '19 at 13:21
@Janka, especially considering the capabilities of scopes in the 1970s. — The Photon, May 27 '19 at 14:10

score 4 · Accepted Answer · answered May 27 '19 at 14:07

The 1970's is long before I started engineering work, but at that time an oscilloscope that measured beyond 100 MHz (maybe even 10 MHz) would have been quite an expensive instrument if it was available at all. So oscilloscopes were rarely used for RF work.

Furthermore, 1970's oscilloscopes were entirely analog instruments, and would provide you no assistance in estimating the phase of a signal. Your ability to do this measurement with a 'scope would be limited to your ability to 'eyeball' the phase based on the position of the traces on the screen (probably using an XY trace and estimating the aspect ratio of the ellipse formed on the screen). Maybe you could achieve 10 degrees precision with this method (and the precision and accuracy would depend on the experience of the operator doing the measurement).

Nowadays, oscilloscopes for RF frequencies remain relatively expensive, so you'd still likely use a network analyzer (one component of which is essentially an automated vector voltmeter) to do that measurement, if you were dedicating an instrument to doing it every day (for example, on a production line).

Tony Stewart EE75 · Answer 2 · 2019-05-27T14:36:50.493

A DSO is linear amplitude vs time usually high impedance.
A VVM is linear or logarithmic with amplitude and linear phase vs f and usually 50 Ohms and measures over a far greater dynamic range and better accuracy in phase vs freq. and much wider dynamic range of amplitudes.

Selection depends on the impedance, amplitude and accuracy of your measurements.

Your specs, your choice.

A vector voltmeter function is often included in higher end new products, so these may be obsolete, but a description from an obsolete HP product as follows;

" A vector voltmeter is a fully automatic tuned receiver that makes RF voltage and phase measurements easy. Its narrowband measuring technique gives a dynamic range of over 90 dB and a sensitivity of 10 micro V to trace even the smallest signal. This vector voltmeter also measures the phase difference between its two input channels with at least 0.1 degree resolution over a full +180 to -180 degree range, so they can be used for another complete set of measurements - such as electrical length, phase distortion, or impedance"

Note: this is a 19" rack mount precision radio, not something you can build on a breadboard.

This is how the VVM function can be done with a Network Analyzer, NA

Vector Voltmeters vs Oscilloscopes?

2 Answers2

Your specs, your choice.