First Design of the Helical Antenna
Helical vertical antenna at its relatively small height
may provide a good operation in the Air. It is possible to find
the statement at lots ham publications in the internet and in
paper magazines. So I decided to make my own helical antenna originally
for 160 meter band and prove if the helical antenna works so well.
Design of my helical antenna was based on source from internet
and magazines that I had at my hand. What I have made in reality
is shown in Figure 1.
Some words why the antenna looks so. Mast of the antenna
was made from Fiberglass tubes in 103 cm length and 5 cm in outer
diameter. It was surplus tubes from a military mask net. In Canada
those tubes very often are sold in some auto (for example, Princess
Auto) and hobby shop. EBAY as well has wide range of selection
of the tubes- just type “Fiberglass Round Tube.” The design of the tubes
allows connect one tube to another one and that results easy create
antenna mast in any length. At first I planned to use 12 such
tubes to create my helical antenna. On the top of the mast I planned
to install a fishing rod in 6 meter length. I planned wound 77
meters of the 14- AWG wire around of the mast. The Helical Antenna
intended to be installed at my backyard.
So step-by-step I wound
the wire along the fishing rod then along the first section from
the Fiberglass tube then erect the design that was lean
on to wall and then later on to roof of my house, then install
the next section of the Fiberglass tube, wound the wire around
the section, made next step, next, next and..
Alas! The gigantic mast fall dawn because the base of Fiberglass
tubes could not stand such mechanical force that caused upper
tubes from the mast. My plan was corrected and the complete design
of my Helical Antenna is shown in the Figure 1. The mast contained just 8 Fiberglass sections
with broken fishing rod in 4 meter length. Overall length of the
antenna was near 12 meters with near 60 meter wire wound around
of the mast.
It was good looking high Helical Antenna but… it was
a little problem. With help of my transceiver internal Antenna
Tuner I may match the antenna on all amateurs HF bands but not
on the 160 meter. I decided to add to the antenna a loading coil.
The coil was wound on a water pipe that has diameter 5- cm and
in 120 cm length. Coil contained 54 turns (it was near 15 meter)
With this coil my Helical Antenna could match on all
HF amateur bands and of course on the 160 meter. The coil was
sitting on a plastic garbage can near base of the antenna. Figure 2
shows the coil near antenna base.
Loading Coil near
Feeding circuit of the antenna looks like a little
complicated but it is logically clear. At first to the antenna
was connected a 100 feet of 450- Ohm two wire line. The line was
going from the antenna to my basement. Then the line was connected
to Balun 9/1. It was allowed to me use
a 15 feet of coaxial cable that was going from basement to my
shack. RF- Choke was created near the Balun.
It was the coaxial cable wound on a ferrite core- yoke from old TV. The choke may contain
10- 15 turns that is not a critical.