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Re: [TowerTalk] Dielectrically lenghtening the boom

To: "" <>
Subject: Re: [TowerTalk] Dielectrically lenghtening the boom
From: "David J. Sourdis - HK1A" <>
Date: Sat, 19 Dec 2009 07:15:39 -0500
List-post: <">>

My bad, I was maybe thinking about VF < 1.0. 
I meant dielectric constant > 1.0 instead of <1.0.

Back to the shortened boom Yagi discussion, Dan said something that  I will put 
in my words: That the wave propagating inside a coax "sees" the space contained 
between the inner conductor and the shield filled with the dielectric material.

What if a tube with a few wavelenghts section, like a big waveguide (circular, 
rectangular or elliptical section), is filled with dielectric material and the 
antenna is placed exactly centered along the axis of the tube. I guess that 
mathematically there is a mínimum lenght from where the modeling can 
approximate the behavior of the antena as if it were in a infinite lenght 
medium. Would then the antenna "see" that is contained in an "infinite" block 
of material? 

Of course this would not be practical on HF or even VHF. It's just for the sake 
of learning.


> Date: Fri, 18 Dec 2009 21:15:45 -0800
> From:
> To:
> CC:
> Subject: Re: [TowerTalk] Dielectrically lenghtening the boom
> Andy wrote:
> >> Take a Yagi, and fill the space between elements with a material which its
> >> dielectric constant is less than 1.0 (air's).
> > 
> > You probably meant to write "greater than 1.0".  I'm not aware of materials
> > with dielectric constants less than 1.0.
> > 
> There are composite materials which have apparent permittivity <1 for 
> limited frequency ranges.
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