Products > Test Equipment

Anyone (else) using a vector voltmeter?

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rf-messkopf:

--- Quote from: pdenisowski on June 24, 2024, 01:00:09 am ---Mine has been completely reliable

--- End quote ---

I'm surprised that you don't use the R&S version: https://www.holzleitner.com/el/rohde-schwarz-zpv/index-de.html.  :)

The ZPV can directly indicate circuit parameters and group delay, and has a tuned receiver. There is a tuner plug-in which can measure down to 10 Hz and has 1 megohms BNC inputs, which can be very useful.

Should be a great toy. Maybe I'll snap one up if I come across one cheap.

pdenisowski:

--- Quote from: rf-messkopf on June 24, 2024, 09:04:57 am ---I'm surprised that you don't use the R&S version: https://www.holzleitner.com/el/rohde-schwarz-zpv/index-de.html.  :)

The ZPV can directly indicate circuit parameters and group delay, and has a tuned receiver. There is a tuner plug-in which can measure down to 10 Hz and has 1 megohms BNC inputs, which can be very useful.

Should be a great toy. Maybe I'll snap one up if I come across one cheap.

--- End quote ---

I would have used a ZPV, but our North American instrument loaner pool .... strangely ... doesn't stock any instruments manufactured before German reunification :)

But yes, the ZPV is very cool - much more like a "real" VNA than the HP8405

And good luck finding a used ZPV these days - old HP vector voltmeters (both digital and analog) are pretty easy to find, but I have yet to find a deal (d.h. ein "Schnäppchen") on a ZPV.  And I'm looking .... :)


rf-messkopf:

--- Quote from: pdenisowski on June 24, 2024, 03:19:13 pm ---And good luck finding a used ZPV these days

--- End quote ---

There are almost always some on German eBay, but often for crazy prices and in questionable condition. I don't see me spending 1500 Euros just to play with one when there is already a ZVB sitting on the bench. I'm also currently trying to reduce the pile of essentially unnecessary equipment  :)

Here is one listed at 500 Euros + tax from a dealer, but unclear if that includes a tuner plugin. They are listed separately at 400 to 500 Euros each. :o

G0HZU:
There's a couple of ZPVs on UK ebay for about £160 each but both are spares or repair items. The seller is well known and often sells surplus test gear as untested.

The HP 8405A has the appeal that is it very simple and intuitive to operate, and the big dials are nice to look at when looking at phase drift etc. It also offers recorder outputs at the rear to connect to a decent DVM for logging etc.

However, the IF phase meter and the IF voltmeter in the HP 8405A both use mid 1960s technology and one has to keep the frequency range control set correctly to keep it in lock. So it is a bit fiddly to use it at times. It's probably best viewed as an educational tool today.

For many years, the HP 8405A was also used for measuring crystals. If a synthesised (accurate to <1Hz) sig gen is used with it and a suitable test fixture is made, it is possible to measure the resonant frequency of crystals very quickly and easily. This can also be done with a modern VNA, but it isn't as rewarding as tuning the sig gen and watching for zero phase on the big analogue phase meter on the 8405A.

It's possible to measure to within about 1Hz when using this technique. If the crystal is designed for a 20pF load capacitance, then simply fit a precision 20pF cap in series with it and measure it for series resonance. It's very quick and easy to measure a large batch of crystals using this method. I think some crystal manufacturers would have used this setup.

I'm not sure what the modern equivalent will be, but it will probably be a VNA locked to a decent OCXO frequency reference.

G0HZU:

--- Quote from: coppercone2 on June 24, 2024, 01:27:42 am ---
--- Quote from: G0HZU on June 23, 2024, 10:10:46 pm ---Maybe you should have a look at the service manual to see what is inside the probes and the probe cables. It's a lot more complicated than a piece of coax made with resistance wire.

There are ground connections and also four other wires inside each probe cable. The probe is a sampling gate (similar to that used in a sampling oscilloscope) and there are fine sampling pulses fed up the cables to a diode based sampling gate (followed by a JFET) in the probe tip and the sampling pulses are about 300ps wide. There is a 20kHz IF signal fed back down the probe from the sampler at the tip of the probe. So there is a lot going on inside these probes.

--- End quote ---

it don't matter how many wires so long its possible to re-terminate them in a reliable manner. That style of cable gets damaged near the inlet where the strain relief is, and it can end up being mad difficult just to trim it down 2 inches and reconnect it, if you have that steel or nichrome wire crap for any conductor.

--- End quote ---

I suspect that one reason there is no connector there, is that the differential pair that carries the 300ps wide sampling pulses up to the probe tip needs to have minimal discontinuities all along its length. Adding a detachable connector part way along the probe would degrade this to some degree. So the best solution is a continuous and pure cable pair from the source and then through the cable and up to the resistors at the diode sampling gate in the probe tip. Also, don't forget that this is mid 1960s technology.

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