- 12 -
YOU AND YOUR ANTENNA
Three main components comprise a typical Cltizens band installation. They are: the
transceiver, an antenna, and the coaxial cable which connects the antenna to the
transceiver. It is important that all three pieces are installed correctly to give he best
possible range and reliable performance. We hope this information will be helpful for
you to realize the maximum performance of your installation.
ANTENNA
For several reasons, it is impossible to exactly PRE-TUNE an antenna at the factory.
A general range of tuning is done which may suffice, but for best performance, an
antenna should be tuned after it is installed.
Most antennas have some form of tuning capability. Usually, this involves the whip section
sliding into a coil, spring, or metal section. This allows the antenna to be adjusted to the
exact frequency desired. Most antennas are the "broad band" type. When adjusted for
Channel 20, they will perform well from Channels 1-40. An untuned antenna robs you of
range and could cause, after a period of time, substantial deterioration of the performance
of an RF output transistor. We cannot stress enough the importance of tuning your antenna.
The measure of an antenna's Performance is its "SWR" (standing wave ratio).
COAXIAL CABLE
Coaxial cable is used in all Citizens band installations. This cable transfers the power
from your transceiver to the antenna. The output of your transceiver is 50 - 52 ohms.
Your antenna is designed to be 50 - 52 ohms. For this reason, RG58/U or RG8/U cable
is used because it also is 52 ohms and matches the antenna to the unit. The frequency
of the antenna is very important in this area because a mis-tuned antenna can disrupt
the system balance. If this balance is disrupted, standing waves are generated on the
coaxial cable, which results in a loss of power in your transceiver.
UNDERSTANDING SWR (Standing Wave Ratio)
In theory, your transceiver has a 50 ohm output and your antenna Is 50 ohms. If a
50 ohm cable (such as RG58/U or RQ8/U) is used, all the power from your transceiver
will be transmitted via the coaxial cable and radiated by the antenna. Under these
conditions, the SWR (standing wave ratio) of your antenna system would be 1:1. In
practice, the antenna must be 50 ohms and tuned to the exact channel. This condition
seldom exists and standing waves are set up on the cable. This SWR robs you of power
and likewise range. While 1:1 is not always possible to attain, you should tune your
antenna system so the SWR does not exceed 1.5:1 or at maximum 2:1. Here are some
examples of the power losses for various SWR ratios:
