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Re: [TowerTalk] How Helically Wound Verticals Really Work (was : Vertica

To: towertalk@contesting.com
Subject: Re: [TowerTalk] How Helically Wound Verticals Really Work (was : Vertical dipoles)
From: David Gilbert <xdavid@cis-broadband.com>
Date: Thu, 19 Nov 2009 09:53:07 -0700
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
I can't think of any advantage to a helically wound antenna.  
Structurally they are more complex, and electrically they have several 
disadvantages, most of which have already been pointed out here.  I'm 
pretty sure that overall they would be heavier as well since the current 
distribution decreases as you move away from the center of the antenna 
(and a coil without current isn't very useful), so you need a lot more 
wire.  It is possible to clearly see this effect with EZNEC by placing 
the same inductance at various positions along a dipole and looking at 
the resonant frequency.

Which raises an interesting question.  Exactly what is the best 
distribution of inductance along a shortened dipole of arbitrary 
length?  It would seem best to avoid the center of the dipole in order 
to spread the current maximum over as large a portion of the antenna as 
possible, but the further away from the center you put the inductance 
the larger it needs to be for the same amount of loading.  But the 
further way from the center the lower the current, so therefore the less 
the resistive loss in that portion of the coil.

Every time I ponder this it seems to me that capacitive end loading is 
the better choice if proximity effects can be avoided.  ;)

73,
Dave  AB7E




Richard (Rick) Karlquist wrote:
> The point about HWV's is not "do they work?" but "are they worth the 
> trouble to build?".  If you can cover the entire antenna with windings,
> you can just a well, with a lot less work, cover the center 1% with 
> windings and have a center loaded vertical.  So we have shown that it
> is easier to make a center loaded vertical than a HWV.  We agree that
> the center loaded vertical is at least as good and probably better.
> Can anyone present a "value proposition" to justify the HWV?
>
> Rick N6RK
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