It's not at all my intent to make up more work for you to do. What I was
mostly interested in was just how much the spiral construction of the
resistor adds to its inductance -- is it or isn't it significant, or is
the inductance mostly due to the component size and the leads? And it
still seems to me that you could just measure a wrapped or painted
resistor in the same fixture as you did the intact resistor. The
difference in measured inductances should be the contribution of the
spiral element.

Although it would be interesting to see how small the inductance of a
leaded resistor could possibly be, it's probably of more practical use
to know the inductance of a leaded resistor with some realistic length
of leads attached, which is I believe what you've already done. Anyone
needing less inductance than that would be wise to abandon leaded
resistors and go to SMD.

Roy Lewallen, W7EL

Ian White, G3SEK wrote:

Paul Burridge wrote:

On Thu, 2 Dec 2004 23:20:40 +0000, "Ian White, G3SEK"
wrote:


What does a typical "test jig" consist of Ian? That's one thing that's
always puzzled me about these kind of measurements; particularly at
UHF++.


One that minimizes unwanted or uncontrolled lead lengths. In general,
one that is based on solid lumps of metal and large, broad,
low-inductance conducting surfaces.

I had simply bent the resistor wires so that one end pushed into the
centre of the VNA's N socket, and the other wire was literally tied onto
the body of the socket. However, the measurement showed that most of the
small inductance could be accounted for by those two wires - which you'd
never leave as long as that in a practical layout.

To home in on the inductance of the resistor body itself, I'd have to
build a jig that allows the wire lengths to be reduced almost to zero.
Harold W4ZCB sent a picture of something he uses, which is just a brass
plate soldered to the back of an SMA connector. The Device Under Test is
then soldered directly between the centre pin and somewhere on the plate.

But I'm afraid my only visit to the workshop last weekend was to dump
yet another cardboard box on the floor.