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Old July 18th 06, 10:09 PM posted to rec.radio.amateur.homebrew
AndyS AndyS is offline
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First recorded activity by RadioBanter: Jul 2006
Posts: 119
Default What is a wire antenna's impedance? -followup


John - KD5YI wrote:
Additional response to OP jo9s8as at yahoo.com:

Using an MFJ259B with a #14 AWG (.064 dia) copper wire 19.4 inchs long stuck
into the antenna connector, I measured the following...


Andy comments,
John, your results would be more consistent, and more meaningful,
if you had some sort of ground plane in your experiments.

A wire, by itself, with nothing else, is like trying to light a lamp
with
only one prong plugged into the socket......

The radiating element, which you are measuring, has to have a
counterpoise (ground) to establish the Efield against and an Hfield
around.
In your setup, the housing of the MFJ, and your hand, and probly
other stuff, is the counterpoise, and the results are inconsistent.
I suspect that if you took a measurement, and started to pee on the
ground, the reading would change (grin).......Try it. But keep the
power low :))))

So, while your experiments may give you an idea of what the
resonant frequency and impedance of a piece of wire is, unless you
are able to take consistent, repeatable measurements, you can be
sure that something is not being accounted for..... My suggestion
is that you need a good counterpoise...... Maybe buy a sheet of
corrugated tin from Home Depot, mount the connector in the middle,
with the MFJ on one side and the antenna wire on the other.... You'll
find, I am certain, that your readings will be more consistent.....

This is not a bad ground plane for 2 meters --- I have used one
with good results......

It ain't magic, but there isn't any such thing as a unipole
radiator....

Good luck,

Andy W4OAH