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[TowerTalk] Fwd: Dielectrically lenghtening the boom

Subject: [TowerTalk] Fwd: Dielectrically lenghtening the boom
Date: Tue, 22 Dec 2009 23:02:57 -0500
List-post: <">>
 One thing everyone seems to forget is how to get the wave out of the 
dielectrics after it is generated by the very much smaller antenna. You could 
reduce the size major if you surround it with water (e=80). The wave will be 
nearly totally reflected when it reach the surface between water and air (and 
it is air we will have it to end up in).

It seems that do this for high frequency such as cell phones etc is feasible 
but hardly for an 80 or 160 meyer application.

de Hans - N2JFS



-----Original Message-----
From: David J. Sourdis - HK1A <>
To: <>
Sent: Sat, Dec 19, 2009 7:15 am
Subject: Re: [TowerTalk] Dielectrically lenghtening the boom

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 
the behavior of the antena as if it were in a infinite lenght medium. Would 
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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