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Re: [TowerTalk] Coaxial antenna elements

To: "Steve Hunt" <>,
Subject: Re: [TowerTalk] Coaxial antenna elements
From: "Dan Zimmerman N3OX" <>
Date: Mon, 12 May 2008 14:44:12 -0400
List-post: <">>
>  The conclusions in a nutshell are:
>  1) It's an electrically short dipole which is centre-loaded by two
>  inductive coax stubs
>  2) Made from RG58 the stubs add considerable series resistance, leading
>  to unacceptable losses
>  3) The stubs' series resistance, added to the short dipole's low Rrad,
>  tends to produce acceptable SWR figures which may well fool the unwary
>  into thinking the antenna is behaving well!
>  4) Performance bandwidth is much reduced, although not as much as if the
>  stubs were lossless :)
>  5) In a multi-element array, other factors such as
>  driver/reflector/director spacings will preclude the antenna size
>  shrinking uniformly by the Velocity Factor.
>  Apologies if this is all "old hat". The results were of interest to me
>  and seem to confirm Terry's (N6RY) comments in a very old thread:

I agree 100% on all counts, and even if this is "old hat" it bears
repeating every once and a while.  I did the same kind of modeling
exercise (no measurements) when someone on eHam was asking if this
sort of antenna was any good.  There's even a further trouble with
N0KHQ's Moxon in that the reflector shield isn't even split, so the
reflector doesn't even have stubs in series !

I'm glad you have the site up, it will be a good reference for warning
people away from this construction ;-)

It's probably one of the more damaging antenna myths out there, tnx
for taking the time to write it up!


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