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ANTENNAS FOR 100 POUND DXPEDITIONS

11 THE EFFECTS OF GROUND The far field plots for the antennas discussed have been made over two specified types of ground: •

Good ground (0.005 S/m, dielectric constant 13)

Poor ground (0.001 S/m, dielectric constant 5)

These are but two of the infinite combinations of ground shapes and conductivity that may appear under our antenna systems. There is a large range of ground types to consider from “free space” (no ground) to a “perfect ground” that has infinite conductivity. The effects of ground are best shown with far field plots. The two plots “good ground” and “poor ground” tell only part of the story. What if we were to put the antenna on the beach (over sand) but right on the ocean’s edge? What if we place the antenna over the end of a dock on the ocean or a fresh water lake? How about mounting the antenna on the roof of a high building? The following sections will investigate the effects of ground on various antenna systems. 11.1 Long ground radials for the Force-12 Sigma-5 All of these situations will produce significantly different results than have been shown with our “standard” two plots of “good” and “poor” ground. We will use the Force-12 Sigma-5 vertical dipole antenna on 20m for our examination of the effects of ground. After seeing plots like the following, it is difficult not to change the way you look at the ground beneath antennas.

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Antennas for 100 Pound DXpeditions - volume 1  

Computer-based antenna modeling and direct experience with lightweight portable antenna systems. Volume 1: Selected high band antennas [20-6...

Antennas for 100 Pound DXpeditions - volume 1  

Computer-based antenna modeling and direct experience with lightweight portable antenna systems. Volume 1: Selected high band antennas [20-6...

Profile for ne1rd
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