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Practical Modeling of
Shortened Helical Antennas
So, it was only one way for me to understand how the
shortened helical antenna works. It is practical way. It is possible
(at first) to make series of shortened helical antennas, measure
(at second) their parameters and base on the measurements made
appropriate conclusions. This way seems to me a very simple one
and I decided to do so.
Well, to make the first, to make row of helical antennas
is not a problem. But the second- do adequately measure of the
parameters of the helical antennas, and on the basis do conclusions
that help to make simulation of the antennas... it is not the
simple task. For adequately measurements there are need lots costly
equipment and antenna polygon. I have not these ones but I was
enthusiastic and anyway I decided to try do it.
In my experimenters
I tried more the 30 different shortened helical antennas, home
brew and commercial made ones. I cannot insist that my measurements
were perfect but the measurements allow me do some conclusion
(that was confirmed on my practice) on design to the helical antennas.
It possible to say, that the conclusions are enough for making
helical antennas in ham practice. Try it or not to believe me!
Details
of Design on my Experimental Shortened Helical Antennas
I made experiments with shortened helical antennas
that were designed to HF bands. I did experiments with symmetrical
helical dipole antennas and with asymmetrical - vertical helical
antennas.
The antennas were coiled on forms of different diameters.
I used lengthes of plastic water tubes
(I have tubes with different standard diameter), fiberglass ski
poles in 16 millimeter diameter, nylon rope in 10 millimeters
diameter.
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Several helical antennas were made on form made from
empty plastic water bottles that was connected together. I have been
used
empty water bottles in 0.5, 1.0,
1.5 and 2 liter volume.
For winding of the helical antennas I used various
copper wires with diameter from 0.3 to 3.0- millimeters. Wires
up to 1.5 mm in diameter have enamel insulation. Wires from 1.0
to 3.0 mm in diameter has different- enamel and plastic insulation.
I used to different electrical wires that I could got. Spiral
for helical antenna was wound evenly over the form.
At design of the antenna the pitch (distance between
the turns) was not less the diameter of the used wire. I experimented
with old rubberized hose from very old vacuum cleaner (made in
the USSR) "Chaika." Metal helix was inside of the hose. The metal
helix was tested by me as a HF helical antenna.
Conditions of the Experiments
Symmetrical helical dipole antennas were located horizontally
at a height of not more than 3.5 meters above the concrete roof
of a nine-story building.
Experimental vertical helical antennas were installed
above the metal rail of the balcony of the 6th floor of a 9-storey
building. Metal rail of the balcony was used as the ground of
the vertical helical antenna. Some of vertical helical antennas
were tested on the roof of a 9-story building. The lower end of
the antennas was at 1 to 1.5 meter above the roof. For ground
of the vertical antenna it was used several wires counterpoises.
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