RE: [VHFcontesting] 6m Array Switching

["David A. Pruett" <k8cc@comcast.net>]

At 04:52 PM 7/3/04 -0400, Mike Clarson wrote:
> David: Is the "ground gain" a real number? When doing non-ionizing 
> radiation calculations, (same thing, but usually in the transition zone 
> between near field and far field) one is supposed to figure in ground 
> reflection, but one never sees it when doing actual measurements.--Mike, WV2ZOW

Mike,

It is real for horizontal antennas over ground.  The vertical radiation 
pattern of the antenna is formed by the direct radiation leaving the 
antenna combined with radiation which is reflected off of the ground.  If 
the reflecting surface is perfect, 6 dB of gain occurs for vertical angles 
where the direct radiation and reflection align.

If there is no reflecting surface, ground reflection does not occur.  For 
example, when the antenna is located on a high mountaintop with steep 
slopes, the only ground reflection occurs at EXTREMELY low radiation angles 
(essentially grazing the horizon).

This is a simplistic explanation, but it's in line what they taught us in 
electromagnetics in college.

Dave/K8CC


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