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Re: [TowerTalk] Radial Ends Buried???

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Radial Ends Buried???
From: "Lux, Jim" <jim@luxfamily.com>
Date: Sat, 19 Nov 2022 07:10:37 -0800
List-post: <mailto:towertalk@contesting.com>
On 11/18/22 2:10 PM, Jim Brown wrote:
On 11/18/2022 1:28 PM, Wes wrote:
By serendipity, I measured the input impedance of one radial against all of the others and it's resonant at 1.84 MHz.
About ten years ago, I did the experiment of modeling a pair of 
radials cut to a free-space resonance,  starting with them as close as 
NEC2 would allow it, and raising them in small increments to several 
feet. VF with that closest contact was about 0.7. By 3-4 ft, was close 
to free space, taking the #14 THHN jacket into account. I also did 
some measurements of THHN #14 pairs laying on the ground, but don't 
recall the result. 

To a first order, the propagation speed slows as sqrt((1+epsilon)/2) (i.e. it's like being immersed in a dielectric of half air/half epsilon)
The interesting aspect is that for a dipole (or a wire) on the surface, 
a large fraction of the power radiates into the soil, the fraction is 
epsilon ^(3/2), so with soil with epsilon 15, about 58 times as much 
power goes into the soil, as opposed to radiates up in to the air. So 
radials work a LOT better on poor rocky soil than on "good wet" soil.

If you want the theory: Rutledge, D. and M. Muha (1982). "Imaging antenna arrays." IEEE Transactions on Antennas and Propagation 30(4): 535-540.
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