Mobile communications antennas come in all different sizes and shapes. They also are designed for operation on various frequencies usually divided into various communications services. Some the communications services include the business band, maritime mobile, citizens band (CB radio), etc.. Regardless of the frequency or band of the antenna there are several common considerations to think through when considering both the type and location of mobile radio antenna mounts. This article will review the major issues and discuss options to consider.
Each type of antenna and mount needs to have a good ground and a good ground plane. While the need for this will vary by frequency, having a good ground and ground plane is desired for every frequency in practical terms. Many base station antennas use the physical ground, enhanced through the use of ground radial wires or not, to help form a take-off point for radio waves being transmitted. On a car the flat portion of the top of a car forms a ground plane for a mobile antenna. Location of the antenna on that ground plane becomes important. A center location produces the most nearly round pattern. A location towards one direction produces an elongated pattern in the opposite direction with less effectiveness in the direction towards the antenna. While the center of the roof of a car can be a great location for a mobile antenna mount it may be difficult to work the coaxial cable back to the radio. An easier solution from the coaxial cable’s perspective may be the trunk. Many people opt for a trunk lip mount. A mount in the center of the roof requires drilling a hole in the vehicle while a trunk lip mount uses set screws to hold the mount to the lip of the trunk radio strap.
Radiation of as much radio frequency energy as possible is both a good thing and a problem. If the antenna is mounted in the center of the roof, the roof acts as a shield and prevents your body from being radiated by the antenna to the extent practical. If the antenna is mounted on the trunk lip then it is spraying radio frequency energy right at the passengers of the car right through the back window of the car. The amount of radio frequency energy and potential risk varies with frequency and amount of power used as well as amount of time used.
Other options exist and a review of catalogs and blogs on the internet can provide good quality pictures and review of the advantages and disadvantages of many of them. Expect to find antennas mounted on the gutters of the roof, various sides and center of the trunk, side panels of a vehicle, front bumpers, back bumpers and even the engine hood. Remember that there is no 100% perfect solution and the best solution for a particular person will depend on the type of antenna, type of vehicle, budget, technical ability, time, patience, etc..