Richard Harrison wrote:
Paul, VK3DIP wrote:
"Is there a better way (which doesn`t involve large sums of money) to
measure antenna impedance at say 146 MHz?"

Use a line of any number of 1/2-wavelengths to connect the antenna to a
VHF admittance or impedance bridge complete with signal source and
bridge detector (VHF receiver). Measure away and record your results.

I've been out of town and not following this thread. Here's what I do
for HF - knowing the length, VF, and attenuation factor of ladder-line.
Trim the laddder-line until the impedance looking into the ladder-line
is purely resistive. Draw the corresponding SWR circle on a Smith Chart.
Using the line-attenuation factor, draw an SWR circle outside of that
one. The antenna feedpoint impedance lies on that outside SWR circle.
Calculate the exact electrical length of the length of ladder-line
being used and use the Smith Chart to track from the purely resistive
feedpoint impedance back to the antenna feedpoint impedance on the
largest SWR circle.

Of course, the accuracy of the final indirect measurement depends upon
the accuracy of all the parameters used in the calculation. My accuracy
has always been good enough for what I needed.

I've never done it with coax but I assume the same principles apply.
--
73, Cecil http://www.qsl.net/w5dxp



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