Practical_Antenna_Handbook_0071639586

438 P a r t V I : A n t e n n a s f o r O t h e r F r e q u e n c i e s
of several materials, including heavy solid wire (#8 to #12), tubing, or metal rods. The
overall lengths of the elements are given by:
Driven element:
Reflector:
Director:
L(inches)
= 11,826 (19.5)
F(MHz)
L(inches)
= 12,562 (19.6)
F(MHz)
L(inches)
= 11,248 (19.7)
F(MHz)
Thanks to this antenna’s lightweight construction, there are several alternatives for
making the supports for the elements. In Fig. 19.10, detail A, the spreaders are made
from either 1-in furring strips, trim strips, or (above 2 m) even wooden paint-stirring
sticks. The sticks are cut to length and then half-notched in the center (Fig. 19.10, detail
B). The two spreaders for each element are joined together at right angles and glued
(Fig. 19.10, detail C). The spreaders can be fastened to the wooden boom at points S in
detail C. Follow the usual rules regarding element spacing (0.15 to 0.31 wavelength).
See the information on quad antennas in Chap. 13 for further details. Quads have been
successfully employed on all amateur bands up to 1296 MHz.
One commercial variant of the VHF quad is the Quagi—a Yagi that employs a quad
driven element.
VHF/UHF Scanner Band Antennas
The hobby of shortwave listening has always had a subset of adherents who listen exclusively
to the VHF/UHF bands. Today, scanners are increasingly found in homes but
the objective is not shortwave listening (SWLing)—it’s a desire to learn what’s going on
in the community by monitoring the police and fire department frequencies.
A few people apply an unusually practical element to their VHF/UHF listening. At
least one person known to the author routinely tunes in the local taxicab company’s
frequency as soon as she orders a cab. She then listens for her own address and knows
from that approximately when to expect her cab!
“Scanner-Vision” Antennas
The antennas used by scanner listeners are widely varied and (in some cases) overpriced.
Although it is arguable whether a total-coverage VHF/UHF antenna is worth
the money, there are other possibilities that should be considered.
First, don’t overlook the use of television antennas for scanner monitoring! The
television bands (about 80 channels from 54 MHz to around 800 MHz) encompass most