On 1/30/2014 1:17 PM, Fred Abse wrote:
On Wed, 29 Jan 2014 20:26:16 -0800, Jeff Liebermann wrote:

You really want a vector impedance meter:

He's actually doing what a vector impedance meter does - the hard way.

Attempting to do, and not the hard way the cheap way.

I built a tight unit this morning, 3.9% or 7.4% error measuring a 3090
ohm resistor, depending on which way I swap the scope probes*.
The measurement didn't change from 100kHz to 10MHz, so now I think
I've tamed the strays. When I get new probes and if they act identical,
I'll work on accuracy.


A vector voltmeter might be of more use in Mike's case. More versatile.

I have one one the back burner. I want to try to work the kinks out of
this, see if I can make an easy to build device for someone that has a
scope and frequency counter, so they could check C, L or Z, at
frequencies up to 10 MHz.
Simple, at this point I have panel mount BNC, a 50* ohm resistor, small
piece of perf board and wire.

Here's a couple of pictures to show the simplicity.
The top picture shows the resistor under test.
The bottom shows the sense resistor.

http://s395.photobucket.com/user/Qma...10be8.jpg.html

http://s395.photobucket.com/user/Qma...cde6b.jpg.html


The sense resistor must be mathematically subtracted. A 50 ohm sense
resistor
with 15pf scope probe in parallel is changed by less than 0.1 ohm, at 10MHz.

* new probes on the way.
**I had a 47.5 ohm 1% resistor.