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.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek