Why do you have a high SWR?
An inappropriate ground plane is one of the major causes of high SWR readings. You should 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. Keep the straps as short as possible. The system should be grounded well with the plane so that readings can be normalized.
Improper installation and mounting of the antenna is another factor causing the problem. To avoid any loopholes, we advise that you mount the antenna as prescribed in the manual and ground every part of the CB system properly.
You can 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 is a big reason behind high SWR readings.
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.
POOR CB ANTENNA MOUNTING LOCATIONS
If you have achieved an SWR reading somewhere between 2.0 and 3.0, your system is not tuned correctly and needs to be dialed in better.
Another major factor leading to such high SWR readings is the poor location for mounting your CB antenna. Your mounting location is a poor one if it has the following characteristics:
The antenna is below the roofline.
The antenna is blocked or covered most of the time.
The antenna is too close to metal buildings or structures.
If your mounting location has these three characteristics, change it immediately.
Make sure you are using the correct length whip.
If you have an SR-A10MM, the whip length should be 62".
The SR-A10 Trucker uses a 49" whip.