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
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.
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.
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.
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.
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.
Results from both of these antennas are very good
and many amateur radio operators throughout the world have used these antennas.
The Inverted "V" is exactly that, the antenna looks
like a upside down "V" when erected.
Each wire should be at a 45 to 60 degree angle from the center point.
Illustrated below is an inverted "V" antenna.
The half wave Sloper is also a very simple wire
to construct. The feed point for this antenna is at the center insulator.
The wire slopes to the ground at about a 45 degree angle. Excellent
results can be obtained from this antenna.
Illustrated below is a half wave sloper.
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