On 1/14/11 11:18 AM, Sam Andrews wrote:
> A very interesting thread with much input from knowledgeable folks.
> I believe much of the commentary in the ARRL Antenna Book comes from
> research done by Jerry Sevick, W2FMI in the late 60s and early 70s and
> originally appearing in a series of articles in QST magazine. Sevick
> undertook a massive project that gathered data from many different radial
> layouts and lengths, including radial, rectangular, and with the wires in
> those configurations connected together laterally in different grid fashions
> or left independent of each other. Much of his research was centered on
> short verticals (less than 1/4 wave) where the low input impedance makes
> ground losses very important to overall system efficiency, as pointed out by
> Steve, G3TXQ in this thread. His conclusion that a 120-radial system is
> optimum, to my knowledge, has not been factually disputed.
"optimum" in what sense.
N6LF did a very extensive set of measurements and models over the past
couple years which goes a long way towards saying that 120 radials is
way past the point of diminishing returns.
That 120 radial thing is from Brown, Lewis and Epstein, and was
originally formulated as a FCC shortcut to avoid having to do a proof of
performance on a non-directional AM transmitter (i.e. rather than spend
the money to measure field strength on all the cardinal radials and so
forth, you could say, we've installed the FCC standard ground field).
Granted, the more copper you put down, the better your performance will
be, until you've paved the surface with solid copper to several
wavelengths away. But Rudy's data seems to show that long before that,
you'll get to where the difference isn't measurable.
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