Mobile communication antennas come in different sizes and shapes. They are also designed to operate on several frequencies, usually divided into several communication services. Some of the communications services include the commercial band, maritime mobile, citizens band (CB radio), etc. Regardless of the frequency or band of the antenna, there are several common considerations to take into account when considering both the type and the location of the mounts of the mobile radio antenna. . This article will review the main issues and discuss the options to consider.
Each type of antenna and support must have a good ground and a good ground plane. While the need for this will vary by frequency, you want to have a good ground and ground plane for each frequency in practical terms. Many base station antennas use earth ground, enhanced through the use of radial ground or non-ground wires, to help form a lift-off point for the radio waves being transmitted. In a car, the flat part of the top of a car forms a ground plane for a mobile antenna. The location of the antenna on that ground plane becomes important. A central location produces the roundest pattern. A location in one direction produces an elongated pattern in the opposite direction with less effectiveness in the direction toward the antenna. While the center of a car roof can be an excellent location for a mobile antenna mount, it can be difficult to connect the coaxial cable to the radio. A simpler solution from a coaxial cable perspective may be the trunk. Many people opt for a trunk lip mount. A bracket in the center of the roof requires drilling a hole in the vehicle, while a boot lip bracket uses set screws to secure the bracket to the lip of the boot.
Radiating 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 ceiling, the ceiling acts as a shield and prevents your body from being irradiated by the antenna as much as possible. If the antenna is mounted on the edge of the trunk, then it is spraying radio frequency energy directly at the car passengers through the rear window of the car. The amount of radio frequency energy and the potential risk vary with the frequency and amount of energy used, as well as the amount of time used.
There are other options and a review of catalogs and blogs on the Internet can provide good quality images and a review of the advantages and disadvantages of many of them. Expect to find antennas mounted on the roof gutters, various sides and the center of the trunk, side panels of a vehicle, front bumpers, rear 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 capacity, time, patience, etc.
Regardless of the location and shape of the ground plane, you need a good radio frequency (RF) ground. Consider this example: if negative RF energy cannot flow to ground, positive RF cannot flow out of the radiating antenna element. I often tell new amateur radio operators that there are three things to know about mobile antenna mounts: Terrain, Terrain, and Terrain.
Once you determine the location of the antenna mount and how to achieve a good radio frequency ground (usually with a strap or wide mesh; radio frequency flows through the OUTSIDE of the metal as opposed to electricity), consider the TYPE mobile antenna support. Remember that search engines and blogs are wonderful things for researching antenna mount types and locations. Any catalog or website may not have every conceivable type of antenna mount. Also remember that each antenna mount will have advantages and disadvantages. I will go through an example of two or three montages and you will probably get an idea.
Consider the classic ball and large spring bracket. For a large whip type of antenna, this may be a good option, but perhaps not perfect, depending on your preferences. Also consider a less strong but less “springy” fixed boot lip support. Now if you hit the branch of a large tree with that whip-style antenna while driving, you will likely have different results with these two mounts. The large spring on the ball and spring bracket will have a lot of “give in” and will allow the whip to remain attached to the bracket with the bracket attached to the vehicle while the whip slides under the tree branch. A fixed bracket attached to the trim of the trunk with a few set screws is likely to come off the trunk and perhaps the trim of the trunk will bend.
There are downsides to the sturdy ball and spring mount that requires four good-sized holes in the vehicle body to mount. A downside in addition to the potential rust and lowering of the trade-in value is the movement of the whip while driving. A springless mount will result in a more stable whip than a spring-loaded one. Remember: the heavier the antenna, the heavier the mount. Radio amateurs bring larger ham radio antennas to metal fabrication shops for customization. Also ask your local car dealer for ideas, as well as anyone who works on trailer manufacturing, etc.