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Re: [TowerTalk] Coaxial antenna elements

Subject: Re: [TowerTalk] Coaxial antenna elements
From: "Dan Zimmerman N3OX" <>
Date: Mon, 12 May 2008 15:56:21 -0400
List-post: <">>
>  It seems to be one of those ideas that's trying to be too clever while not 
> realizing it's not clever at all...

I think "velocity factor" coaxial antennas are a perfect example of
the dangers of viewing antennas from the feedpoint only!

A field strength measurement, a quick spin of the antenna while
capturing the rig audio into G4HFQ's Polar Plot, or a simple A/B test
with a known-functioning dipole, anything that actually measured the
radiation characteristics of such an array might have told a different
story.  N0KHQ apparently did A/B tests against a Sterba Curtain and
said the antenna had "good" F/B but it's hard to draw any conclusions
from that (and hard for me to believe there's any F/B to speak of)..
who knows how the Sterba  Curtain was working on the band tested?

I think N6RY's comments in the old post referenced in the original
here tell the story... the reactance change with length is so steep
for stubs near resonance that a little stub trimming can resonate ANY
length antenna (albeit with vastly varying loss).

So you're guaranteed to be able to find a solution where you can
resonate the outside of the coax shield on an electrical quarter wave
long piece of coax by making small adjustments to the length.  That
lends itself to very easy empirical discovery with just an SWR
analyzer.... and if the antenna impedance hits 50+j0 or close to it,
we're done ;-)

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