TopBand: ground losses

Thu, 14 Aug 1997 22:23:03 +0000

> From:          sears@rell.com
> Date:          Thu, 14 Aug 97 16:57:41 +0000

>      A ground mounted 1/4wave vertical with the highly conductive Gumbo 
>      soil of North Texas really helps the far field pattern.
> Author:  Peter Chadwick <Peter.Chadwick@gpsemi.com> at internet
> Date:    8/14/97 5:30 PM
> Following on from Jim's point, how far out from the base of the vertical 
> do you need to go with a method of reducing ground losses? 

Several wavelengths with many hundreds of radials if you are worried 
about low angle radiation. If you don't do that, a 1/4 wave out will 
get you most of the way to perfection at higher angles but you need a 
bunch of radials...at least 60.

> probably a half wavelength or so. However, the USAF study on antennas for 
> airborne SINGCARS suggested that a vertical over an infinite resistance 
> ground gave the best low angle radiation. So maybe a vertical dipole in 
> Arizona?

I believe Antarctica (where the ice is very thick) is the 
closest place to this on earth, but I'm not totally sure.

Lowest zero angle loss occurs at both zero resistance and infinite 
resistance. At zero resistance the media is an infinite conducting 
groundplane with no surface attenuation, and at zero conductivity 
(with no dielectric losses) it's just like freespace. 

Hence the unwritten law. The station you are trying to work always 
lives where the dirt is somewhere near the conductivity where low 
angle loss is near its worse.

Neither rock or salt water is at one of the "perfect" extremes. 
Even the moon isn't resistive enough to be transparent or 
"low loss".

73 Tom

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