Practical_Antenna_Handbook_0071639586

398 P a r t V : H i g h - F r e q u e n c y A n t e n n a s f o r S p e c i a l i z e d U s e s
characteristics in the area. Although they are clearly not appropriate for long-term installations,
they should work fine for the short run.
Summary
The ideas presented in this chapter are meant to help the reader maximize his/her signal
under adverse conditions in the field. While methods of getting antennas up in the
air under difficult circumstances are substantially different from those techniques we
would normally employ at our home or business, the electromagnetic principles that
maximize signal transmission and reception do not change. In particular, remember
these key points:
• Try to make horizontal (or inverted-vee) antennas as close to an electrical halfwavelength
as possible; don’t rule out the use of traps to allow easier multiband
operation in a limited space.
• Try to make any vertical monopoles as close to an electrical quarter-wavelength
as you can; if you can get the base of the vertical off the ground, create a groundplane
antenna with two or three l/4 radials on each band to be used. If the
vertical must remain ground-mounted, try to put down eight or more radials
total, with lengths as long as you can make them, up to a maximum of l/4 on
the lowest frequency of intended use.
• If you have only a single elevated support available, consider either a sloping
dipole or an inverted-vee on the lower HF frequencies. Spread the legs of the
inverted-vee as far apart as possible.
• Select your antenna to match the type of communications you need. If you are
primarily interested in contacting others in your own general area (i.e., within
a few hundred miles) on HF, use a horizontal wire. If you’re on a DXpedition to
a remote South Sea island, you’ll probably want to use a vertical on the beach.
• Make sure you have a meter for reading both forward and reflected power or,
alternatively, VSWR. Most of today’s small HF transceivers have that capability
built in. At VHF and UHF, however, it may be necessary to bring along a standalone
wattmeter or SWR bridge.
• Similarly, make sure you have an antenna tuner for the HF bands—either built
into the rig or as a separate accessory. For VHF and UHF ground planes, as well
as mobile whips, however, all you may need is an Allen wrench to adjust the
top section of the vertical whip.
• Be sure to bring rope, twine, insulators, and short lengths of coax and other
cables, with the proper connectors on each end.