THE CB ANTENNAS
The antenna is one of the most important elements of a radio station. A judicious choice as well as a careful installation will be the keys of the perfect functioning of your CB set. As a general rule, before selecting an antenna, it’s necessary to know that the highest antennas have the best performance.
SOME TECHNICAL WORDS
The antenna ensures a transformation between two forms of energy. In transmission, it converts an electrical energy supplied by the radio into a radiated electromagnetic energy and, reciprocally, in reception. The ideal antenna for 27 MHz should have a theoretical wave length of 11 meters. In these circumstances, an elementary ¼ wave dipole should measure 2,75 meters. In order to improve the performance, we lengthen the antenna: 1/2, 5/8 or 7/8 wave. The use of a self (coil of copper wire at the base) allows realizing models of different size, still more performing.
THE DIFFERENT TYPES OF ANTENNAS
There are two main categories: the mobile ones and the fixed ones. The first are provided for installations on vehicles, the metallic coachwork serving as ground plane.
They can be magnetic (instantaneous installation and removal, failure at theft etc.) or hole drilling mounted. The magnetic antennas need a control or eventually an adjustment of the SWR after each replacing which is not the case for the hole mounted antennas. The installation must be done on a place of the vehicle with a maximum of metallic surface (ground plane), far away from the jambs of the windscreen and the rear window. If a radiotelephone antenna has already been installed, the CB antenna must be above it.
There are two types of antennas: the pre-adjusted ones and the adjustable ones. The preadjusted antennas are preferably used with a good ground plane (roof or boot). The adjustable antennas offer a larger use range and take advantage of less important ground planes. A hole mounted antenna needs an excellent contact between the antenna and the ground plane; therefore, don’t hesitate to scratch slightly the metal sheet at the level of the screw and the tightening circle. While passing the coaxial cable, don’t pinch nor crush it (risk of break or shortcircuit).
The fixed antennas are essentially for installation on the roof of a building. They are sometimes provided with radiants serving as ground plane. See that they are free at most. If they are fixed on a mast, it will eventually be necessary to install shrouds according to the standards in effect (please consult a professional).