Subj : Todays New Gear Tip
To   : All
From : Daryl Stout
Date : Tue Aug 15 2017 08:01 am

Antennas 

Antenna choice is the single biggest factor in determining whether
you'll be able to communicate effectively with any type of radio.
Handheld radios come with a stubby, flexible antenna ("rubber duck")
that attaches directly to the radio for convenience. These are
fairly sturdy, but are not very efficient. Consider purchasing a more
efficient mobile whip antenna with the necessary connector or adaptor
for your radio. At home you can attach a mobile antenna to a metal
surface or structure. Longer, more efficient antennas to replace
the rubber duck are also available. For repeater and FM voice
communication, the antenna should be oriented vertically ("vertically
polarized") to match the signals from repeaters and other hams. 

Mobile antennas are mounted on the outside of a car. Temporary mounts
using magnets (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 frequency.)

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 learn how to install your own connectors; both to
have the skill and to save money! The ARRL's online Technical Information
Service www.arrl.org/tis/ and the ARRL Antenna Book and ARRL Handbook
contain methods of installing connectors on coaxial cable.


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