There exists many variations to the half wavelength
dipole, I will describe a couple of them on this page. They are the Inverted "V"
and the Half Wave Sloper. I am not going to discuss how these antennas function,
I will however describe what they look like and how they are built.
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Although the antenna lengths can be determined by using the same
equation as a dipole (468 / Frequency in MHz), you will find that the lengths are
actually a bit too long. This works fine though since you can just trim each
side back to reduce your match.
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Here is an example of how to use the formula. For the 30 meter band, the
frequency that you might select is 10.125 MHz. Using the equation above, you
will find that the total length of wire required is 46.22 feet (468 / 10.125),
this is about one half of a wavelength. This length is then divided by two
(23.11 feet), giving you two quarter wavelength sections. Each section will make
up one half of the antenna and they are connected at the center by an insulator
to the two antenna wires. Soldering and weather proofing the connections will
provide for a solid connection and long life for the antenna.
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As with most antennas, these antennas can be supported at
the center with anything that may be handy: a mast, a tree, a tower, or any
other structure. Some sort of insulator must be used to isolate the antenna wire
from the structure itself.
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Each antenna may be fed either with coax or ladder line.
If you use the formula for the half wave antenna, you will be able to use 50 ohm
coax without any matching device.
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The ends of the wire are not placed directly on the ground,
they should be suspended several feet above the ground (10 feet or more to
prevent anyone or anything coming in contact with the wire.) A peg and a length
of rope can be used to anchor it to the ground, as illustrated
below.
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Results from both of these antennas are very good and many
amateur radio operators throughout the world have used these
antennas.
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