Codan Radio Radio Repeater Systems Training Guide - Manual (Page 29)

RADIO REPEATER SYSTEM | TRAINING GUIDE
Chapter 3: Repeater System Equipment Page 21
The physical size and construction of the antennas becomes important when you consider the type of
housing and antenna mounting that you will require for your repeater, which in turn is determined by
the weather conditions at your chosen site and the amount of antenna gain your calculations show that
you will require.
Note that your system also includes mobiles and portables, for which the most common antennas are
the “whip” and “rubber-ducky” respectively. Remember that these antennas are also manufactured for
use on a specifi c frequency or a narrow band of frequencies. These antennas are a compromise and
provide little or no gain to the signal from the transmitter. Depending on the degree of compromise,
they may even show a loss.
Remember when using high gain antennas that the higher the gain, the smaller the cross-sectional
area of the radiation pattern. This is an advantage in links as it reduces the chance of multiple paths
caused by refl ections and is a disadvantage on drops as it will leave near-fi eld shadows, as shown in
Figure 3-1.
Figure 3-1: Antenna Patterns
Offset Antenna pattern
Shadow caused by
vertical pattern of drop,
gain-type antenna.
Little or no reflection
from Link Antenna beam.