How to Cut Down on Radio Interference on a CB

The CB radio craze peaked in the 1970s, and the equipment is now refined and affordable compared to those glory days. Still a mainstay of truckers and road travelers, CBs are not high fidelity radios. One of the drawbacks of the CB system and its broadcast frequencies is that radio interference is a common occurrence. This interference has a variety of causes, and there are ways to reduce its effects.


Squelch and RF Gain

There is always some level of noise present on CB channels. Most CB radios have two controls to remove interference: the squelch control sets a noise floor level, and the RF, or radio frequency, gain control adjusts RF signal amplification. Use these controls together to remove most interference. Turn both controls fully counterclockwise, and then tune to a channel with no broadcasts. Leave your vehicle off if you're using a mobile radio. Turn the squelch control clockwise until the interference stops, turn the RF gain control clockwise until the interference returns, and then turn it counterclockwise slowly until the interference stops again.

Advanced Equipment Features

Squelch and RF gain set your CB for local, current conditions, but many CB radios also have more advanced noise reduction features that vary widely between manufacturers and models. The feature names are descriptive, such as "automatic noise limiter" or "noise blanker." These features use digital technology to remove common interference sounds from the voice content. Unlike squelch and RF gain, these circuits are not adjustable, and have no external controls beyond an on-off switch.

Antenna Upgrades

The ideal length of a CB antenna is about 36 feet, or equal to a full wavelength of signal in the CB frequency range. Fractions of that wavelength work, but the efficiency decreases with length. Most mobile antenna makers use 1/4 wavelength, or 8 feet, as standard for vehicles. Most antennas are physically shorter than this, using coils to tune the antenna for CB use. Home, or base station, antennas have greater design flexibility, as long as they're tuned to a wavelength or a major fraction.

EM Interference

CB radios also pick up electromagnetic, or EM, interference, and a vehicle has several systems that generate EM waves. The most common culprits are the fuel system, the ignition system and the alternator. Cutting down interference from these sources depends on the quality of installation of your CB radio, as well as the quality of noise suppression in the radio itself. If the radio is not grounded properly to the vehicle's chassis, expect interference levels to be high.

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