How to Tune an Antenna
Go to an open area free from buildings, trees, radio towers, or other structures.
Put your radio and antenna in the positions in which you will use them.
For a CB radio, put the radio in the car and the antenna on the body of the vehicle. For a portable radio, move away from any vehicle and stand alone with the radio
Remove any connections between the antenna and the radio.
Attach the radio to the transmitter socket on the SWR meter using a coaxial cable.
Attach the antenna to the antenna socket on the SWR meter using a coaxial cable.
Set the radio to minimum power and to FM or CW mode.
Tune to the lowest band available. On a CB radio, tune to Channel 1.
Transmit from the radio or, on a CB radio, press the talk button.
Observe and record the SWR reading. It should be in the form of a ratio, e.g. 2.2:1.
Repeat Steps 6-8 for the highest band available, or, on a CB radio, Channel 40
Determine from the difference between the SWR readings whether your antenna is too short or too long.
If the SWR reading on the lowest band, or Channel 1, is greater, your antenna is too short. If the SWR reading on the highest band, or Channel 40, is greater, your antenna is too long.
Adjust your antenna accordingly, and very slightly.
For most antennas, this means manually lengthening or shortening the antenna. For a wire antenna, clip off a bit of the end to shorten it (if you have a wire antenna that is already too short, you will need to get a new antenna).