The basic function of a citizen's band (CB) radio meter is to identify the functionality of a user's CB setup, which includes the CB radio, a CB radio meter and an antenna system consisting of coax and antenna when in operation. Specific CB radio meters are used in target areas to identify problems or to ensure adequate functionality. Included in the types of CB radio meters are power or watt meters, modulation meters and standing wave ratio (SWR) meters.
CB radios typically are required to operate at a maximum power of four watts. Therefore, one can expect his or her CB radio power or watt meter to measure very close to four watts of output. A CB radio meter that measures power contains an input connector for the radio and an output connector for the antenna or dummy load. For the most accurate power reading, a CB radio should be tested with a watt meter while the antenna system has been replaced by a 50-ohm dummy load. The reason for this is because an antenna system does not typically provide a true 50 ohm load, which is what the meter requires to be accurate.
SWR is another measurement that a CB radio meter might provide. SWR is a measure of impedance mismatch between the coax and the antenna. In other words, measuring SWR is another way to test for functionality of the transmission between a CB radio and its antenna.
The ideal SWR would measure at a 1:1 ratio, but such a perfect measurement is unlikely for a CB antenna system. The higher the ratio measured, the greater the impact of the problem. Various diagnostic techniques can be used to determine the true source of a poor SWR measurement.
A modulation meter measuring amplitude modulation, which is what standard CB uses, bases its readings from the audio added to the CB carrier. If modulation is too low, transmissions can be very difficult to hear, even with the volume turned up. If modulation is too high, distortion will occur that might make transmissions difficult to understand and could potentially interfere with adjacent channels. Ideally, modulation would be close to, but not exceed, 100 percent.
Of course, there are meters that combine all three of these readings. The purchase of a CB radio meter would be based on either preference or necessity, if there is a suspected problematic area with the CB setup. CB radio meters might also include other features that tailor to preferences, such as the ability to connect earphones to listen to the output quality. No matter how they are manufactured, measuring wattage, modulation or SWR remains the primary purpose of CB radio meters.