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)
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