On 1/3/20 9:26 AM, Jim Brown wrote:
On 1/3/2020 9:15 AM, David Gilbert wrote:
I modeled a simple 80m vertical with one elevated radial 10 feet above
ground
Not the best model for evaluating the effect of wire resistance --
ground losses dominate. Better to model with a GOOD radial system.
or model with a perfect ground - then the ground losses aren't an issue
and you can measure the loss in the radiator.
Or, if you think that the current distribution will change depending on
"real ground" vs perfect conductor ground, model 4 cases:
lossless antenna and lossless ground
lossy antenna and lossless ground
lossless antenna and lossy ground
lossy antenna and lossy ground
and then you can evaluate the various effects.
typically, what I do for these things is model with a range of loss
parameters for the antenna - ohms/meter or metal conductivity.
4nec2 has a capability to model while varying a parameter in a
systematic way. And, of late, I've been doing parametric studies by
generating NEC input files with a python script. It's pretty easy to
set up the geometry once, and just have a sequence of LD, FR, RP, XQ
cards to iterate.
here's an example stepping through frequencies, and printing only the
feedpoint and 2 principal plane cuts.
GW 1 50 0 -.1 0 0 -450.000000 0.000000 0.000500
GW 2 50 0 .1 0 0 450.000000 0.000000 0.000500
GM 0 0 0 0 0 0 0 0.010000
GW 901 1 0 -.1 0.010000 0 .1 0.010000 0.000500
GE 0 1
GN 3 0 0 0 3.000000 -0.005030
LD 5 0 0 0 58001000.000000
FR 0 1 0 0 0.011
PT 0 901 1 1
RP 0 91 2 1000 0.0 0.0 1.0 90.
XQ
GN 3 0 0 0 3.000000 -0.005030
LD 5 0 0 0 58001000.000000
FR 0 1 0 0 0.012
PT 0 901 1 1
RP 0 91 2 1000 0.0 0.0 1.0 90.
XQ
GN 3 0 0 0 3.000000 -0.005030
LD 5 0 0 0 58001000.000000
FR 0 1 0 0 0.013
PT 0 901 1 1
RP 0 91 2 1000 0.0 0.0 1.0 90.
XQ
{FWIW, this is calculating the input impedance of a 900 m dipole 1mm in
diameter near the surface of the moon, 3+0.00503j is the complex
permittivity of Lunar regolith -
https://www.colorado.edu/project/lunar-farside/}
NEC does calculate the AC impedance (skin effect) using the resistivity
and permeability of the wire - see routine ZINT(). page 361 of NEC2
theory part 2 pdf file, or page 93 of the NEC4TheoryMan.pdf
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