> Then, there are some papers from folks who have tried
looking at the
> impedance of a balanced line laid on the surface.
Apparently, the problem
> here is that while the "line laid between two ideal
layers" is relatively
> tractable both in an analytical and experimental sense,
the "run of the mill
> insulated balanced line laid on the dirt" (and weeds) is
not. (Having tried
> some early experiments with the latter, I can heartily
agree... ). Small
> variations in spacing of the wires from the dirt have a
big effect.
I've made similar measurements here, but with ladder line
inside a PVC pipe that was buried. The line had terrible
loss.
My point is I'd never rely on detailed conclusions of how
many or how long the radials need to be when they are based
on models. Better to just install as many as you can as long
as you can make them. That way you can be sure you did the
best you can.
I've had as few as 20 1/4 wl radials come down to normal
base impedance with a 1/4 wl vertical here, and in other
spots just a few hundred feet away I've had to double that
number before things became stable. I always use 50-60
minimum to be safe, even where it looks like 20 would be OK,
because I don't know what the soil does over time.
73 Tom
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