[Antennas] Re: vertical angles...

[Danny Richardson]

At 11:53 AM 9/8/2006, you wrote:

>"Yes, twelve feet, but remember that the base is twenty feet above
>ground."
>
>But RF ground reference is the radial system. The launch angle is from
>that ground, not earth.

The radial system provides a return current path and has almost negligible 
influence on the elevation angle. The number and length of the radials will 
effect the antenna's efficiency (gain) but not the antenna's elevation 
angle pattern. On the other hand a change the earth conductivity will. 
(Check out the elevation angles shown in just about any antenna book 
for  monopole mounted over perfect, sea-water, good, average and poor 
ground conditions will bare this out.) The elevation launch angle is 
developed by combination the antenna's radiation along with the earth's 
reflections/refractions - out to several wavelengths beyond the radials.

Additionally, when you raise the antenna - including its radial system - 
above ground it is now a ground plane and the height above ground will 
determine the number of lobes and their launch angles.

This can be easily confirmed using NEC modeling.

73,
Danny, K6MHE



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