[TowerTalk] Vertical dipole other choices?

[jimlux]

On 10/20/20 2:02 PM, David Gilbert wrote:
> 
> Dielectric loading works as well in theory, but is obviously more 
> difficult in practice. 

I was thinking more about loading with a permeable magnetic material.


  For grins one day I modeled an 80m vertical (fed
> against a couple of radials) with the vertical portion being 3 inch 
> diameter PVC with a wire running down the center of it.  By pumping DI 
> water (relative dielectric constant about 3.0 if I remember correctly) 
> in from the base of the tube I could shift the resonant point over 100 
> KHz, thereby making it somewhat tunable.  I shudder to think what it 
> would take mechanically to support it, of course, unless I strapped it 
> to the side of my tower with all the attendant coupling effects of doing 
> so.

DI water is epsilon 80, so if you were to submerge the antenna in Lake 
Tahoe, a 8 meter antenna is almost half a wavelength.

Of course, what you improve in terms of match, now you have to radiate 
through the water/air interface.




> 
> I think people have tried similar things using salt water, except 
> without the wire.  I think I even tried modeling that once but found the 
> conductive loss was too high ... don't remember for sure.
> 

There's someone at a Navy lab in SD who build a transformer that coupled 
RF to a stream of salt water. It "worked" but not very efficient.

And people have built antenna with mercury or gallium as a liquid metal.
Or, with plasma (essentially neon tubes)