Dave,
> So, I stand corrected on being too loose with the method. I
> should have pointed out the limitation of the "decreasing input
> impedance method." And that limitation is that the radials must
> be symmetrical and all of the same length.
The "problem" with simulation is the assumption that ground (earth)
is homogeneous and uniform. With "real" ground this is certainly
not the case - probably even with (relatively) large open areas
that were formerly tilled fields. In the typical urban/suburban
site there are many things in the earth that will effect the
soil characteristics - particularly on 160 meters where the skin
depth extends many feet into the earth.
> Now it sounds like even this is not the case with actual
> measurements. Have you measured increasing input impedance
> for additional radials in a symmetrical arrangement? If so, I
> would like to understand this. Understanding and getting sims
> to match measurements (and vise versa) is what I do.
I do not think that even NEC-4 can be trusted (Christman
notwithstanding) to be more than a rough estimate with real
earth. My own yard goes from extremely poor soil (Florida
sand dunes) to reasonably good areas of extensive treatment
for my wife's flower gardens to worse than poor (places in
which original construction debris was buried). All of that
area would be encompassed by a radial field of 60 x 100'
radials.
73,
... Joe, W4TV
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