How to Wire a CB Antenna

by Fred Decker
    Mirror brackets are a possible mounting point when the roof isn't practical.

    Mirror brackets are a possible mounting point when the roof isn't practical.

    Brand X Pictures/Brand X Pictures/Getty Images

    Citizens band radios aren't as widely used as they were at their peak of popularity in the 1970s, but they remain an efficient and inexpensive way to communicate between vehicles. On or off the road, a CB provides reliable communication even in areas where cellular coverage is unavailable. They're limited to 4 watts of transmission power by law, so the primary factor in determining a radio's signal quality is your antenna. A properly installed antenna gives significantly better range.

    Antenna Basics

    Radio signals, and the antennas designed to receive them, are measured by their wavelengths. In the case of CB radios, their waves are 34 feet long. Antennas that size aren't practical for use on a vehicle, but an antenna cut to half or one-quarter of the wavelength also works well. A quarter-wave antenna for CB use would measure 102 inches in length, manageable but still long. Manufacturers make their quarter-wave antennas more compact by incorporating a coil of wire into the design. For example, a 4-foot antenna might incorporate a 54-inch coil, resulting in an effective antenna size of 102 inches.

    Placement

    Unless you have a sunroof or your vehicle's body is made of fiberglass, the very best place for your CB antenna is squarely in the middle of your roof. Your roof serves as the antenna's ground and reflector -- its "ground plane" -- and provides equally good signal in each direction. You can also mount your antenna to your trunk, fender, bumper or the mirror mounts of an RV or truck. Some antenna require a hole to be drilled into your roof, trunk or fender. These require rustproofing and weatherproofing, so many users prefer magnetic mounts. Ensure your magnet is strong enough for the antenna you install.

    Cable

    Depending where you place the antenna, you might need to run cabling through your trunk, door frame, window pillar, or firewall and dash. Car CB antennas typically use RG-58 coaxial cable and a PL-259 or Motorola-type connector. The large PL-259 connector is more common, but feeding it through tight spaces can be problematic. If the cable is permanently attached to the antenna, you might be better off removing the connector, then replacing it when the antenna's in place. Some cables are finished at the radio end but use spade connectors at the antenna end, making them easier to thread through your vehicle. Replacement connectors, and the tools to install them, can be found at RadioShack and other retailers.

    SWR

    Before you begin transmitting with your newly-installed antenna, you should check and adjust its standing wave ratio, or SWR. Some radios have a built-in SWR meter, or you can purchase one inexpensively and connect it between the radio and antenna. Follow the calibration instructions that came with your meter, then test your radio's SWR on Channel 1, and again on Channel 40. Lower numbers are better, ideally in the 1 to 1 1/2 range. If your reading on Channel 1 is higher than on Channel 40, you need to lengthen your antenna slightly. If it's lower, you need to shorten it. Tweak length in small increments, and test after each adjustment.

    About the Author

    Fred Decker is a trained chef and certified food-safety trainer who has written and blogged on food-related topics since 2007. Previously he sold computers, insurance and mutual funds. Decker was educated at Memorial University of Newfoundland and the Northern Alberta Institute of Technology.

    Photo Credits

    • Brand X Pictures/Brand X Pictures/Getty Images