Owen Duffy wrote:
On Thu, 29 Dec 2005 12:13:17 -0700, Wes Stewart
wrote:



I've provided a spreadsheet that facilitates the calculations over a
range of frequencies.

www.qsl.net/n7ws/8405.zip

So a couple of trips to the end of the cable are all that are required
to calibrate the setup.

(I must confess, I haven't tried this program with a line much over a
few inches in length to determine whether my calibration functions can
handle it, but I think so.)


That's a good idea!

Wes, does it collect enough information to be able to correctly
calculate a phase constant on longer feedline. Some work for the next
version perhaps?

A potential problem is cable loss. When the line Z0 is close to the
impedance being measured, loss doesn't have much effect. But if the two
impedances are very different, a surprisingly small amount of loss can
have a significant effect on the observed input impedance.

Of course, the short circuit measurement will give you the cable loss,
which can then be used in the calibration process. It's just that you
wouldn't be able to do the correction by the simple equivalent of a
Smith chart rotation.

Roy Lewallen, W7EL