[TowerTalk] Radial Ends Buried???

[Lux, Jim]

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.