Operating instructions
Choosing a Ham Radio 13
(mag-mounts) or clamps (lip-, trunk-, mirror-mount, etc) and permanent through-the-body
mounts provide a ground-plane for the antenna. You can purchase the complete antenna
system, including the whip, mount, and cable or you can purchase a separate mount with
cable. Antennas attach to the mount by one of several different methods: a threaded base,
PL-259/SO-239, and NMO are the most common. Your antenna will need to match the
mount. An on-glass antenna does not need the metal ground plane, using an adhesive pad
to attach to the vehicle’s window, but is usually less efficient and may not work with some
types of auto glass.
Antennas are generally rated in terms of gain – how well they concentrate signals in a
preferred direction. Gain is specified in dB and every 3 dB of gain doubles your signal’s
strength. An omnidirectional antenna or “omni” radiates equally well in all horizontal
directions and can be used with base, mobile, and handheld radios. The gain of an omni
antenna concentrates the signal towards the horizon.
At home, you may want to install a permanent antenna such as the common ground-
plane antenna with three or four radials. Mounted in the clear, a ground-plane will give
good performance. The J-pole antenna operates similarly to the ground-plane, but does not
require radials. Collinear antennas with several sections working together look like ground-
planes, but are longer and have higher gain. A Yagi antenna is a type of rotatable beam
antenna that has gain in one direction and is used to communicate with stations that are
out of range of simple omnidirectional antennas. A rotator is needed to point a beam in the
desired direction.
If you purchase an antenna without the connecting feed line, use a high-quality cable that
has low losses at VHF and UHF frequencies. (All cables have increasing loss with frequen-
cy.) For distances shorter than 50 feet, RG-8 or RG-213 are fine. At 2 meters, RG-8X can
be used up to 50 feet, but no longer than 25 feet at 70 cm. You won’t need ultra-low-loss
“hard-line” or specialty cables to get started. For longer “runs” of cable, ask for help from
your Elmer, from a radio store, or from the manufacturer’s specifications to choose the
right cable. While cables are available with connectors pre-installed, you should eventually
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Figure8
Whip
Mountandbase
(NMOstyle)
Magnet
Coaxialcable
Surfaceofvehicle
Figure8–Onepopulartypeoftemporarymobileantennamountusesmagnetsandisoften
referredtoasamag-mount.