At 12:23 PM -0600 12/30/02, John von Gonten wrote:
>Has anyone dealt with or know what kind of performance can be had
>from W9INN's shortened dipoles??
>
>I am looking for a way to get something in the air
>To use for 160M shows to have a 71' space-saver and I am
>Trying to figure out if it would perform well, or acceptably
>
The best way to answer your question is by modeling via NEC-4, or at
least NEC-2. The radiation resistance of an antenna that short is
very very low, so you must to work really hard to reduce the losses.
NEC will show you what they are, quantitatively, so you can make
intelligent engineering decisions and stumble around in the dark not
knowing what matters a lot, and what doesn't.
Potentially you need to worry about resistive losses in the loading
coil(s) or whatever resonates the antenna, in the feed/matching
arrangement, in the transmission line (unless you transform impedance
at the feedpoint of the antenna), in the antenna tuner (again, unless
you transform impedance at the antenna or in the feedline), and in
the ground, which will be in the near field of the antenna unless
you can get it up more than about 100 feet. NEC-4 will be able to
calculate the ground losses, but NEC-2 will not.
Modeling is more helpful in a situation like this than simply
erecting the antenna and trying it, because it's much too difficult
to vary the important parameters experimentally.
-Chuck, W1HIS
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