[BC] Ground system

[Cowboy]

On Friday 10 February 2012 10:39:43 pm Steve Lewis wrote:
> SO... If the point is to avoid coupling to the earth, then what explains the
> effect of ground conductivity?

 OK, we want to avoid direct coupling to the dirt so as to avoid
 antenna currents in the dirt, because such currents will be
 dissipated as heat, merely making worms cozy warm, contributing
 nothing to coverage, at transmitter power expense.
 The near field return currents on the ground reduce quickly with
 distance from the feed point, becoming small enough in practical
 terms as to become almost completely irrelevant beyond about 1/2
 wavelength from the radiator.

 Ground conductivity deals more with conduction of the
 so called "ground wave."
 The ground wave does not traverse the ground itself, but is merely an
 induced image of the direct wave passing overhead. Energy is taken from
 the direct wave in order to induce a current on the ground, the "ground wave."
 So, if conductivity is poor, a greater percentage of that energy is dissipated
 as heat on the surface of the dirt, making less available as receivable signal.


-- 
Cowboy