Antenna System - Realistic TRC-490-18 Owner's Manual

ANTENNA SYSTEM
The antenna system includes the transmission line, and it is very important that you use the correct type
of transmission line. The transmission line should be of the coaxial type and should have an impedance
equal to the antenna impedance.
Since your Transceiver is designed to operate most efficiently into a 50 ohm load, it is best to use a type
of coaxial cable with an impedance of 50 ohms. We suggest type RG-58/U for short lengths and RG-8/U
for long lengths.
Generally speaking, you should keep the length of the transmission line to a minimum. Remember that
line losses increase with frequency. Use foam-insulation coax for best results.
The above discussion is as important for reception as it is for transmission. If a mismatch exists between
the antenna and the receiver, the excellent sensitivity and signal-to-noise ratio of the receiver circuitry
will be defeated.
FIXED STATION ANTENNAS
The most popular fixed station antenna is a complex colinear or ground plane.
Beam antennas provide maximum gain and maximum directivity. The directivity can be a disadvantage
unless a rotor is used. Since a beam antenna is directional, it greatly reduces noise and interference from
all other directions. This can be a decided advantage on the CB bands where man-made noise is a
problem.
GROUND PLANE DUAL 6-ELEMENT BEAM VERTICAL BEAM
BASE STATION ANTENNAS
Your Radio Shack store carries a complete line of base station CB antennas and accessories. For
maximum efficiency, we strongly recommend using an SWR meter to aid in the proper matching
between your antenna and Transceiver.
The antenna system should be adequately grounded.
Always use a lightning arrester for your antenna system.
MOBILE STATION ANTENNAS
Mobile CB antennas are one of two types. a full-length or a loaded whip. Your Radio Shack store carries
a complete line of both types of mobile antennas.
The location of the antenna has a great effect on the antenna efficiency and directivity. Antennas
mounted in the center of the roof radiate equally in all directions. A bumper-mounted antenna radiates
in a pattern directly in front of and to the rear of the vehicle, with maximum radiation directly away
from the vehicle, in a horizontal plane.