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How to Tune a CB Antenna
Once a CB antenna has been installed, the next step is to check and, if necessary, adjust the standing wave ratio (SWR). What is SWR? Click here for a brief explanation. This procedure requires nothing more than your installed radio, antenna, and an SWR meter. The ultimate goal of this process is to end up with a SWR of less than 2:1 on all channels. We suggest setting the SWR on both channels 1 and 40.
Cobra 29 Classic with a built in SWR meter
You will want to have your vehicle in an open area while tuning your CB antenna. Tuning the antenna while your vehicle is close to other vehicles, buildings, or even people can give you an incorrect reading. Also, each time you take a reading make sure your doors and hood are closed. If your antenna has a plastic cap on the tip, make sure that is in place each time you take a reading.
Connecting the SWR meter
Some CB Radios come with a built in meter. You will not need an external SWR meter for these radios. The owner's manual will outline operation of the built in meter. For radios without a meter, you will need to connect an external SWR meter. A typical CB radio installation will look similar to the second picture to the right. The third picture shows the same installation with an SWR meter added in. The instructions below outline connecting an external SWR meter and tuning a CB antenna.
Tuning the CB Antenna
- Turn your CB off and disconnect the antenna coax cable from the back of it.
- Connect the end of your antenna coax to the SWR meter where it indicates "antenna"
- Connect the short coax cable coming from the transmitter position on the SWR meter to the back of the CB.
- Close the hood and doors on your vehicle.
- Turn on the CB.
- Set the CB to Channel 1.
- Set the SWR meter to the FWD position.
- Key microphone and turn knob until the SWR meter indicates the "set" position. Un-key microphone.
- Flip SWR meter to the Reflect position.
- Key microphone and look at the reading on the SWR meter. The lower the reading, the better. If the meter shows in red DO NOT operate CB. Re-check your connections.
- Turn CB to channel 40. Follow instructions 7-10 again.
- Adjusting your antenna (matching the 40 channel bandwidth).
- If the reading on channel 1 is higher than the reading on channel 40, you need to lengthen your antenna. Alternately, if the reading on 40 is higher, your antenna is too long.
- For example, if your reading is 1.3 on channel 1 and 2.1 on channel 40 you need to trim down the tip, turn adjusting ring, or pull out wire a small amount, cut it, and tuck it back against the coil.
- If your reading is 2.7 on channel 1 and 1.5 on channel 40 your antenna is too short. the only solution is to add a spring, raise the antenna, or reposition it.
- If any adjustments are needed, they should be made in small increments. Re-check after each adjustment. Be sure to have all components on the antenna when testing, including the tip if there is one.
Once these steps are completed, you can remove the SWR meter from the line or leave it installed.