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Old November 24th 08, 12:41 AM posted to rec.radio.amateur.antenna
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Default Low-angle Elevation Gain of a 1/4-wave Vertical Monopole

"christofire" wrote:
I think there's some confusion there about polarisation. VP requires
lowest height to achieve a peak at zero degrees elevation; HP requires a
frequency-specific height and low height usually results in an elevated
beam.

____________

But a v-pol monopole up to 5/8-wavelength in electrical height, and mounted
with its base near the earth _always_ launches its maximum relative field at
zero degrees elevation (the horizontal plane) -- regardless of the quality
of the r-f ground it uses, its operating frequency, or earth conductivity at
the antenna site.

Radiation launched at low elevation angles by such a monopole is
progressively less than in the horizontal plane. But its h-plane radiation
(especially), and its low-angle radiation as launched are nowhere nearly as
poor as shown in a NEC-2 analysis for these values over real earth -- which
is what leads to the erroneous conclusions of many people.

The reason for this is that a NEC-2 analysis over a "real" earth is based on
the field surviving at an infinite distance from the monopole, and over over
a flat earth, at that !

But if that was the true radiation envelope of the elevation pattern
actually launched by that monopole, then daytime AM broadcasting would be
impossible (reality check).

The real-world, h-plane field intensity measurements made in 1937 from such
v-pol monopoles at 3/10 of a mile over real earth of poor conductivity by
Brown, Lewis & Epstein of RCA showed peak fields that were within a few
percent of the theoretical maximum possible for monopole heights of about 45
through 90 degrees.

RF http://rfry.org


 
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