Richard - K9OM writes:
"can EZNEC or similar modeling programs
accurately determine which quad array: 1/4 waves, 1/2 waves, or 5/8 waves...
will outperform the other in real life? "
Real life is a strange thing. When you look at the patterns from models,
EZNEC, MININEC, Etc., and ponder the far field plots, you have to wonder
whether anyone could actually discern a difference (using an S meter as a
guide) between a signal slightly off beam and one on beam but arriving at an
obtuse angle. The pattern may show a -3 or -6 db gain plot. However, an S
meter is far from accurate as a means of comparing signals. Add QSB, QRN,
etc. and you have an almost meaningless measurement.
Real life includes things that are not in the model. What about that 80
meter dipole only 66' away? How about a metal building or internal house
wiring at the QTH? To expect a model to contain these features is an
impossibility. Add the variability in QTH layout and the real world gets
even more interesting. An antenna that plays like a bandit one place may
actually be a dog at another. Why? You often never know -- a rain gutter
coupling to an element, variations in ground, etc.
What the model can show you is the approximate pattern and load under ideal
circumstances. That's it! Given the chance to build one without a model
and build it with a model, I know which way I would choose to work.
Antennas are way to much work to build to not have them play as expected.
>From my experience, you get them to play on the computer screen and you will
have much better success getting them to play well in the back yard. Real
life differences in feed point, resonance, etc., which deviate from model
results, often illustrate issues that were not anticipated and can be
corrected with good engineering (e.g. radiating guys, end coupling, etc.)
Besides that, I bet I've modeled 9 antennas for every one that actually gets
built. The 9 were never built because the model convinced me that it would
be a waste of time, energy, and money.
My $0.02
Ford-N0FP
ford@cmgate.com
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