Mobile antennas for vehicular communications

Of great importance in the application of mobile radio equipment is the type of antenna mounting used. Only when properly mounted can the antenna operate at the highest possible efficiency. Furthermore, the antenna can not be expected to stand up under the physical abuse encountered unless correctly mounted. In the past, a tripod mount was used when an antenna of the order of five to seven feet in length was to be mounted on a vehicle. Support at three points minimized the danger of bending the body or fender of the vehicle and provided an extremely sturdy mount. However, it did not allow rod flexure, and resulted in very high breakage. In addition, the tripod arms had the disadvantage of catching debris and thus lowering the antenna efficiency by adding a secondary path to ground. The objections to the tripod mount were overcome with the swivel mount, which consists of a split ball mounted on a flat insulating plate. An outstanding feature of the swivel is its ability to mount the antenna vertically on any surface regardless of the angle of the surface with the vertical. A low inertia rod with a maximum stress taper is usually used in conjunction with the mount. If further shock protection is desired, a specially designed spring may be added between the mount and the antenna rod. The constant of the spring should be low enough so that an appreciable part of the bending moment is bypassed from the antenna rod.