Topband: Multiple Ground Systems

[Tom Rauch]

I would think that a defining
> characteristic of a "ground screen" would be that the 
> voltage is everywhere
> the same, which is certainly not the case for radials -

Any screen that reflects or serves as a ground, even a solid 
sheet, has voltage differences along its length otherwise it 
couldn't have current flow.
The real issue is current density and path impedance, 
especially in the lossy media below the or around the 
radial.

 >their voltage and
> current vary in the same way as one half of an ordinary 
> doublet.

I doubt that. The velocity factor is nowhere similar to a 
wire some distance from earth.

> I would therefore expect that connecting together the 
> "radial fields" of
> vertical radiators driven with currents of different 
> amplitudes and/or
> phases would have numerous and relatively serious 
> consequences because the
> boundary conditions at the ends of the "radials" are 
> changed.

Then why do broadcast stations using that method have no 
problems at all, and have patterns and efficiencies very 
close to those predicted from perfect grounds?

The only real problem is when the ground has an inadequate 
number of radials, especially when the radials are some 
distance above earth.

73 Tom