Figure 6 A three range
antenna tuning with the help of thick wire
Vibrators have length (λ/4)*(0.5-0.9).
Each vibrator is matched with coaxial cable with help of its own
a 'lengthening' coil. You can use this design if you have a lack
of place.
It is not wise to use more than three vibrators for a multi- range vertical
antenna, because overall efficiency of the antenna drops in this
case. Such multi- vibrators antenna will be too complicated at
adjusting.
Remember:
Two and more resonance (a quarter wave)
counterpoises for each operation range of the antenna should be
used. However, if the antenna is placed at a small altitude above
a metal roof and the braid of the coaxial cable has a good electrical
contact with the metal roof, the antenna could be used without
any counterpoises.
RF choke should be used:
An RF- choke on the coaxial cable should be installed at feeding
terminals. . The RF-choke precludes leaking of RF- currents on
to outer braid of the coaxial cable. Without the RF-choke the
outer braid of the coaxial cable serves as a radiating part of
the vertical antenna. It gets to TV and RF- interferences when
the antenna operates on transmission. 10 - 30 ferrite rings (permeability
does
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Figure 7 A simple design
suitable for 40 - to 160-M
Figure 8 A simple design
suitable for 40 - to 160-M with 'lengthening' coil
not matter) hardly dressed on the
coaxial cable end at the antenna terminal make the RF-choke.
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