Jim Brown wrote:
>>> 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.
That sounds like a neat experiment and AutoEZ's "Resonate" button
makes it easy to automatically adjust the length of the radial pair
(modeled as a dipole) for resonance as the height above ground is
changed.
Using bare copper #12 wire, here is how the velocity factor changes as
the height is raised from 0.2" to 100" (~8.3 ft) at four different
frequencies. This is with EZNEC's "Average" ground, conductivity =
0.005 S/m and dielectric constant (relative permittivity) = 13.
https://i.postimg.cc/76r7FHng/image.png
And this is with three different ground characteristics all at the
same frequency.
https://i.postimg.cc/BQ7FqcCZ/image.png
If you have AutoEZ and you'd like to play with the model file you can
download it from here:
https://ac6la.com/adhoc/VF_vs_Radial_Pair_Height.weq
Instructions for use are shown on the Variables sheet. And if you
don't have AutoEZ but you *do* have Microsoft Excel (sorry, not Libre
Office or Open Office) you can use the free Demo version of AutoEZ
(https://ac6la.com/aepurchase.html) just by changing the number of
segments on the Wires sheet to 29. You'll also need the free EZNEC v.
7.0 (https://eznec.com/).
Dan, AC6LA
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