[TowerTalk] Dielectrically lenghtening the boom

[David J. Sourdis - HK1A]

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.

David
HK1A
EC5KXA







> Date: Fri, 18 Dec 2009 21:15:45 -0800
> From: jimlux at earthlink.net
> To: ai.egrps at gmail.com
> CC: towertalk at contesting.com
> 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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