The antenna design is based on the known “Bazooka”
antenna. Vertical part of the antenna is a half from the “Bazooka”
antenna. Counterpoises are usual for any vertical antenna. I used
two counterpoises because it is hard to place more at my 45- degree-
slope roof. Vertical part of the antenna made of fiberglass tube
with diameter 14/10x2, 18/14x2, 23/19x2 (O/D/T). All tubes were
in 2- meter length. The tubes were sandpapered degreased and coated
with primer and enamel paint.
Figure 1 shows antenna’s design. Figure 2 shows design of part 1 from Figure 1. Figure 3
shows design of part 2 from Figure
3. Figure 4 shows design of part 3 from Figure 1. Figure 5
shows way to insert coaxial cable into the tube.
Antenna is tuned to resonance with help of the length
of the counterpoises. It needs to use counterpoises with length
more the show at Figure 4.
Then the counterpoises are shortened to the antenna resonance.
The ends of counterpoises that connected to feeding coaxial cable
are placed at one meter above the metal roof. Another ends of
the counterpoises fastened through ceramic nut insulators at the
hip of the roof.
My antenna was installed on the roof of the 5- level
house that has height at 22 meters. The antenna has almost omnidirectional
pattern. Figure 6 shows
data for the antenna . The data were taken off with help Antenna
Analyzer AA- 330.
Antenna made from different types of coaxial cables
(Russian coaxial cables: RK-50- 7- 13, RK- 75- 9- 16, RK75-4-113)
was tried and tested in field conditions.
R9WI ex RA9WFD, Boris Krivosheev
almost no differences in the antenna operation for all of the
antenna design. However for the real antenna coaxial cable (part
2 of the Figure 1) should be chosen on the antenna power.
Antenna was fed through 50- Ohm coaxial cable with the length
(it is noncritical) of 28- meter.
The antenna was tuned to resonance at the 20-meter
band. However my ICOM-746PRO with help of the internal ATU could
match the antenna on the upper HF- Bands (off course, with some
losses!) from the 20 to 10 meter. With the the antenna I had QSOs
with Japan (6500- km) at 17 and 15 – meter.
Antenna may be used in field operation when instead
rigid tubes a plastic fishing rod would be used.