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The SGC Building, 13737 S.E. 26th St. Bellevue, Washington 98005 USA
P.O. Box 3526, 98009 Tel: (425) 746-6310 Fax: (425) 746-6384
© 1997 SGC Inc.
Sometimes people become confused about skin effect or hear some tall tales of antenna design. Skin effect is
the subject of many tales. One of the best stories involves the tarnish on non-insulated copper wire. A radio hobbyist
insisted on non-insulated wire (because the insulation would prevent the signal from leaving wire as easily) and he
would even pull down his wire and sand the tarnish off every spring (for the same reason)! Tarnish and insulation
on an antenna conductor will not hinder its performance. In fact, most people prefer insulated wire better because
they frequently move and replace antennas. The insulated wire slides through trees better and you're not as likely to
cut your hand on a broken strand. Also, insulation protects anything from being burned by the signal that is being
transmitted through the antenna. There's nothing like bumping into a "hot" antenna and getting a nice RF burn
across an arm or leg.
Over the century since radio has been discovered, hundreds (if not thousands) of antennas have been used with
varying degrees of success. The antennas included in this section are some of the most popular. Some of these
antennas are merely variations on another type. Others are variations, but are used in such peculiar circumstances
that they are always considered to be separate types of antennas. Regardless of the style, the shape, or the
construction of the antennas, the wavelength for radio frequencies is always determined with the same equation:
l (length in feet) = -----------------------
However, you will notice that most antennas are half-wave or quarter-wavelength. For these antennas, the
length is exactly 1/2 of the length that you would determine from the equation above. Even if you are not planning
to build your own antenna system, the equations and specifications included here will help you to determine the
length and determine whether you have the space available to install one or more.
The longwire was used as an example for the beginning of the antenna section. The
standard longwire is an unbalanced antenna that is several wavelengths long for the
frequency that it is to be used at. Longwires are typically used because of their excellent
directional properties. Dedicated amateur radio operators and professional monitoring posts often install an array of
these antennas in a half circle, with the ends all pointing in different directions. However, few people have the land
to install antennas that cover several thousand feet in all directions.
ANTENNA TYPES
LONGWIRES AND RANDOM-LENGTH WIRES
936
f (frequency in MHz)
Longwire antennas
have excellent
directional properties.
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