> The March/April 2004 issue of NCJ has a great article by
Al Christman, K3LC, on
> optimizing the number and length of radials given the
amount of wire available
> and the type of soil in which the radial field will be
placed. I have a few
> questions.
Hi Jim,
I don't want to rain on anyone's parade, but absolutely the
least accurate way to use models is to use them to predict
losses with wires near or in the soil. I equate using a
model to predict the number and length of radials or the
performance of a low dipole something about as useful as
using dial calipers to measure rubber bands.
There are a large number of reasons for this:
First, you'd never have any idea what your average ground
characteristics are. There isn't even a practical way to
measure localized characteristics that has any accuracy.
Second, virtually all installations are not over homogeneous
media. Not only does moisture vary, the layers of soil are
stratified. What are you going to do, design each radial for
optimum placement and length??
Third, the amount of change in performance and the possible
savings are so small it isn't even worth talking about.
Fourth, the models have never been verified.
If you throw down 50 radials 1/4 wl long, you'll be at 96%
or more of the maximum feed efficiency you can every obtain.
The only way to do better would be with 120 really long
radials, where you might pick up another percent or two.
I really don't see any reason to get so "A R" about saving
about 15 bucks in copper, when the whole exercise is a guess
anyway and the change (even if the guess is correct) is so
insignificant. But hey, it gives people something to talk
about I guess.
73 Tom
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