There are few antennas that can rival the performance of a beam. The beam concentrates radiation in a specific direction. It also reduces interferrence by favoring the same direction on recieved signals. A four element tri-band beam like the KT-34 pictured will improve both transmitted and recieved signals by nearly 10 decibles. That is about the increase obtained with a 1kw linear amp, but with one very important difference. The improvement will be noticed on recived signals as well. An amplifier cannot do that. The cost of a beam, tower, and rotator is about the same as a good 1kw amplifier.
The tower should raise the beam to at least one quarter wavelength above ground in the case of cubical quad, or a minimum of one half wavelength above ground for the more conventional array. For a tri-band beam covering 20, 15, and 10 meters this will be about 66 feet. Beams that weigh less than 50 pounds can be adequately supported with a well guyed mast made of drill stem pipe. A heavier beam will require a conventional triangular tower.
The rotator must be of quality, heavy duty construction. The less expensive TV antenna roatators will work for lightweight single band quads, but they will not work well (or for long) under the weight of full sized conventional beam.
The tranmission line can be either coax or open wire line. The advantage of open wire line is that the beam can be used over a wider range of frequencies as it is tuned with an antenna tuner. An open wire feeder is more difficult to install with a rotatable antenna but the line loses will be lower and the frequency excursions will be possible. The beam will not work as well on frequencies removed from the design frequencies even with an antenna tuner but it will work as well or better than a dipole at the same elevation. The most common method of feeding a beam is with coaxial cable. Use new, high quality RG-8 or equivalent.
PROVISION FOR OTHER ANTENNAS
Don't miss out on the opportunity to get the maximum use out of the new tower. As a minimum make provision for a two-meter whip at the top of the beam and attach a pulley and halyard below the beam to support the apex of a lower band inverted-vee.
MORE BLOGS ABOUT HAM RADIO.
Last updated Sep-2006
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1996-2006, by Frank Kamp, all rights reserved.