Products > Test Equipment
Anyone (else) using a vector voltmeter?
G0HZU:
I had a go at logging my newer HP 8405A VVM (made in 1986) to see how stable the phase is over time. This is done using a DVM connected to the phase recorder at the back of the meter.
The result is quite good and it appears to have drifted about 0.005 degrees in 200 seconds. This is much better than my older HP 8405A but I have recently improved the stability of the 20kHz reference oscillator on the older meter. So it might now be similar to the plot below.
G0HZU:
I'm not sure if this counts but I also use an Analog Discovery 2 using its network analyser mode. This measures and displays voltage and phase. It can also measure impedance using a series sense resistor. The main disadvantages with the AD2 are that it only works well up to a few MHz and it isn't very sensitive.
I also have a similar test fixture for the HP 8405A that uses a series sense resistor in a test fixture.
This was the first fixture I made for it as I wanted to measure negative resistances up at VHF using the IV method.
I also made a cheap clone of the HP 'tee' used with the HP 8405A. These can be difficult to buy cheaply now so I designed my own. The aim of the tee is to preserve a low VSWR up into UHF when the probes are used in a 50R system. The aim is to absorb the 2.5pF loading capacitance of the probe into the tee so it maintains a low VSWR when connected.
I also designed some simpler (compensated) terminations for my 8405A and these work well up at a few hundred MHz.
shabaz:
You're right, I'm not happy with that either. I put in the sizing hack because when I asked a small group for feedback, the response was it was too tiny for comfortable reading on mobile. I'm not very knowledgeable in this area, and tried finding a way to scale the text, but the settings currently only work for the paragraph text, and the headings (and images) explode in size on desktop as you've experienced. Mobile view looks great I feel, at least, it appears very comfortable on my mobile, and on the phones of a few people I asked to check. I'd like the desktop view to be comfortable and not crazy-huge as it is now. I'll ask a web developer friend to help out and create a pull request with a proper method that works for all. The workaround for now on desktop is to resize the browser window narrower, otherwise there are huge headings/images : (
shabaz:
(Hopefully) resolved pretty much! I phoned a friend, and a suggested method was to use 'media queries'. Now it's fairly readable on mobile and desktop. I'll tweak the settings further to make it more graceful in the sizings, but for now hopefully it's a lot more readable than before (you might have to do Shift-F5 etc to clear cache if it currently still looks massive).
shabaz:
--- Quote from: shabaz on June 23, 2024, 04:01:55 pm ---I have a few analog meters if I ever get around to experimenting a little. It would be interesting to recreate a simple experiment using a sig-gen.
--- End quote ---
Just for a bit of fun I gave it a quick attempt. I have not investigated what circuit topology was actually used in the past, my really ugly circuit just uses what I had, in terms of existing scraps of experiments all joined up. All passive, no power supply!
I manually slowly adjusted the phase on one sig-gen output, from -180 degrees to +180 degrees, and observed the output on a 'scope with a very slow timebase setting. I guess the output could be low-pass-filtered and drive a meter needle, although as-is, there's no indication of positive or negative phase.
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