[Test-Equipment] Complex impedance measurement

[Dave Brown]

The vector voltmeter ( probably an HP 8405?) can be used to measure the
amplitude and phase of one channel reference to the other.
If you want to do Z measuring above say, 100 MHz, in a nominal 50 ohm
system, then the best (read easiest!)  way is to get a suitable dual
directional coupler covering the frequency range of interest and hook both
channels of the vector volt meter up to that. The method is fairly straight
forward and requires minimal number crunching to get answers. There used to
be HP App notes dealing to all this but they may not be around now. Someone
is bound to have copies of it/them. I may even have some here but the filing
system is still chaotic!

If you want to get direct complex Z indications below 100 MHz (down to 1 MHz
with the 8405) then there are other methods, along the lines of what you
have suggested, that can be used. Both the old HP vector Z meters (4800
[500kHz] and 4805 [100MHz] ) basically do what you have proposed but in
different ways-constant current sources and constant voltage sources are
used with current and voltage metering to generate the basic signals needed
to get complex Z output.

I have a few articles and references in a file I have somewhere here on this
topic that I could rustle up if they might be useful.

73
Dave
ZL3FJ

----- Original Message -----
From: "Sandy and Kees Talen" <windy10605@juno.com>
To: <test-equipment@mailman.qth.net>
Sent: Sunday, January 12, 2003 6:34 AM
Subject: [Test-Equipment] Complex impedance measurement


> I'd like to bounce this off some experts......
>
> I'm looking for a Vector Impedance Meter. I have a Vector
> Voltmeter (no manual on it). I take it the Vector Voltmeter
> basically indicates phase shift between two AC voltages.
>
> Using a signal generator as a source, can I connect a small
> series "non inductive" resistor with the unknown impedance,
> measure that as current, compare the input voltage phase to
> the output current phase to get the Z phase (reactance). Then
> calculate the Resistance part of Z by using the input voltage
> and output current ?
>
> 73  Kees K5BCQ
> _______________________________________________
> Test-Equipment mailing list
> Test-Equipment@mailman.qth.net
> http://mailman.qth.net/mailman/listinfo/test-equipment
>