Citizens band radios, also known as CB radios, were invented to allow personal correspondence over specific AM radio frequencies. Originally there were 23 channels of CB available to users; today there are 40 channels. CB tends to be used to communicate between vehicles with installed CB receivers and antennas. Attaching a CB antenna to your vehicle is easy, but setting it up correctly involves calibrating its length using readings taken from a standing wave ratio meter, also known as an SWR meter.
Plug the coaxial cable coming from the antenna into the "Antenna" coaxial jack on the SWR meter.
Plug the coaxial cable coming from the SWR meter into the "Antenna" coaxial jack on the back of the CB radio.
Shut the hood and all doors on the vehicle.
Turn the CB radio on, and tune it to Channel 1.
Press "Fwd" on the SWR meter.
Hold down the "Transmit" button on the CB radio while turning the dial on the SWR meter until the meter indicates "Cal" or "Set." Release the "Transmit" button.
Press "Swr" on the SWR meter.
Press the "Transmit" button again, and check the reading on the meter. If the reading is in the red, do not operate the radio anymore until the problem is fixed.
Repeat the previous 4 steps on Channel 40.
Shorten the antenna if the reading for Channel 40 is higher than the reading on Channel 1, or lengthen it if it is shorter. If the readings are equal, you're all set.