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Re: [TenTec] New and Improved Terminology

To: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Subject: Re: [TenTec] New and Improved Terminology
From: Steve Hunt <steve@karinya.net>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Fri, 07 Jan 2011 14:22:05 +0000
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>
Folk who have been following the discussion may be interested in this chart:


It shows how the optimum take-off angle of an 80m quarter-wave vertical 
mounted over Sandy Soil varies as the radius of an excellent ground 
screen (Salt water) is gradually extended outwards. It was produced by 
using the capability of EZNEC to have two different radial ground media, 
as I described earlier.

Please note that this is simply an exercise in determining how far from 
the antenna, ground conditions affect the take-off angle; we're letting 
EZNEC do the trig that we could otherwise easily do ourselves with some 
simple maths.

Notice that as the ground screen grows from zero to about 100ft - the 
range in which we might typically install a ground radial system - the 
take-off angle barely changes. At the other extreme, above 500ft we are 
beyond the Fresnel Zone in which reflections are taking place, and there 
are no more improvements to be had. All the "action" takes place between 
100ft and 500ft.

Unfortunately, for many of us that's an area that might well be outside 
our property boundary. Even if it is not, at that radius the areas are 
so great that we would need to put down massive amounts of copper to 
have any significant effect on the ground conductivity. Hence Rudy 
Severn's comment: "Any practical ground system will not affect the 
radiation angle or far-field pattern!"

Steve G3TXQ
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