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Multirange Vertical Antennas

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ANTENTOP- 03- 2003, # 004

Multirange Vertical Antennas


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

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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