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“Switchable Antenna 80/160 m.” AC 80/160
Low bands of HF spectrum are incontrasted reign of wiring antennas.
Easy to make, cheap and low visible.
This last “ecological” character will be more important in the future. A wiring antenna is low noticeable than a Yagi or a parabolic antenna.
The true problem is to find room where to install this long antennas. I could install a ½wave dipole in the garden. It works well even it’s not very high over the ground (6-10 m.) No news. The trafic on 160m. band was excluded.
The idea to work this interesting band was to use an arm of the dipole and the vertical part of the feeder cable that together forms an L antenna.
To work, an L antenna need a ground reference as better as possible.
A lot of radials, metallic railing, ground leak point, idraulic pipes are useful.
19,5 m. of ½ dipole and about 7 meter of the feeder cable vertical portion, aren’t enough to tune the antenna on 160 m. The reactive capacitance of this aerial was cancelled wrapping a part of the RG58 coaxial cable on a cylindrical dielectric support of 100mm. diameter. This coil is comparable to the bottom coil of a vertical antenna.
In my case were enough 9 links placed side by side. The winding is extended on the cylindrical support for abt. 6cm.
The stocking of the cable must be interrupted at the end of the dummy coil (TX side).
160 m. working mode (mode L)
The stocking of the cable, antenna side, shall be disconnected
The stocking of the cable, TX side, shall be connected to ground.(radials)
80 m. working mode (mode L)
The stocking of the cable, antenna side, and the stocking of the cable, TX side, shall be connected together insulated from ground.
This switch is done by a relay. It can be a “not coaxial” one because the low frequencies.
The matter is the quality of the component (insulation and contact materials). I have used a surplus with 24vcc. Coil. The dipole shall be without balun.
I hope that the drawing would be useful to understand the working principle and the building technique.
We assume that in 80m. the dipole is perfectly tuned. Check only that the relay insertion doesn’t cause R.O.S. The coil don’t has influence on the working apart a current symmetrical function.
The 160m. tuning shall be done reading the R.O.S.
Excite the relay and tune the coil looking for the right number of turns.
To make it easy, wind some more turns on the cylindrical insulator and stick it with tape.
Check the tuning frequency (lower than wanted). Roll down exceeding turns to tune the antenna on 1,840Mhz.
The R.O.S. should be less than 1.5 for the whole assigned band. Like this it’s possible to operate on 80 and 160 m. without antenna tuner with low signal loss on the feeder line.
I would add a note related to the
I used a plastic can. I winded on the coaxial cable coil (see picture) and inside of it I put the relay. It’s locked by a hanger to the cork. Also the coaxial connector, the 24v end the ground screws are locked to the cork.
After to have screwed the cork to the can the device will be waterproof. It will be easily positioned near the ground line.
This antenna allowed me to get the 1° class. Italia single band WPX SSB2000.
This article has been published on Radio Rivista n.5-2002
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