[TowerTalk] Fwd: Dielectrically lenghtening the boom

[hanslg at aol.com]

 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 <hk1kxa at hotmail.com>
To: towertalk at contesting.com <towertalk at contesting.com>
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 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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