To get the most out of your CB radio, you need an antenna that is properly tuned. Having a high SWR reading can not only cause interference on your CB radio, it can actually damage it. Here are some steps to test the standing wave ratio of your antenna system and tune it for maximum performance.
- Choose a clear, unobstructed location to adjust the SWR Antennas are very sensitive to objects close to them. Go to an open area to tune your antennae, such as a parking lot or remote field. This can also be done at home, provided you are not close to the house. Do not try to tune inside a building, under trees, near or under power lines, or with someone standing next to the antenna. This distorts the signal and causes a reflection back into the antenna giving false readings. Also, close all doors, the hood, and the trunk lid.
- Setting the SWR Test with the radio only. If you have an amplifier, turn it off or preferably remove it from installation.
- Insert the antenna whip into the chrome antenna adjustment mast at the top of the coil.
- Using either the meter built into the radio or a good external SWR meter, calibrate on channel 20. Switch back to SWR and record the readings on three channels 1, 20, & 40.
- If the lowest SWR reading occurs on channel 1, the antenna length is too long and must be shortened. Loosen the mast set screws and lower the whip 1/4 into the mast. Tighten the mast set screw and again read SWR. Repeat until the lowest SWR is obtained. If the whip is fully lowered into the mast and the SWR is still high, remove the whip from the mast. Using a hacksaw, grinder, or bolt cutters, cut 1/4 from the bottom part of the whip antenna. Re-insert the whip into the mast and test again for SWR. Repeat the above procedure until the SWR is below 1.5 of all channels.
- If the lowest SWR reading occurs on channel 40, the antenna whip is too short and must be raised. Loosen the mast set screws, raise the whip 1/4, re-tighten the set screws, and test SWR again. Repeat the above procedure until the SWR is below 1.5 of all channels
Common Causes of High SWR
- A poor ground plane is often the cause of high SWR. Select a sound ground plane with an entire metal surface
- It would be best to run the ground straps to as many parts of the vehicle’s chassis as possible. Your goal should be to keep them as short as possible
- Improper antenna installation and mounting of the antenna are other factors causing the problem. To avoid any ground loops, we advise you to mount the antenna exactly as instructed in the manual and ground every part of the CB antenna mount correctly
- Use a voltage meter to determine the vehicle’s points that might hinder your system’s grounding, and then try to ground those parts to improve your ground plane
- A damaged coaxial cable or PL-259 is a very common issue behind high antenna SWR readings. When troubleshooting, check for these damages, which are commonly found on fiberglass antennas
- A coax can get twisted, shorted, or pinched while routing through the vehicle. It might come damaged when buying from the market. Hence it is essential to check your coax cable thoroughly before purchasing. Use a 50-ohm coax for single antennas and a 75-ohm coax for dual antennas
These are just some tips. But be sure to check out the complete guide on how to tune your CB antenna.