So how do i check the SWR?
OK, well, there's a good place to start.
If you installed these radios and antennas yourself but didn't check SWR/Reflected Power, then we might as well start there.
Did the issue appear as soon as these radios/antennas were installed, or did it show up later?
Checking SWR/Reflected power requires either an SWR meter designed for the frequencies/power you are using or a specific piece of test gear designed to measure return loss.
Basically what it tells you is if your antennas are resonate at the right frequencies and thus radiating the power that the radio is feeding them.
If the antennas are not resonate (or there is a cable fault), the antenna system will not radiate all the power. What's left over is sent back down the cable. That can re-radiate inside the vehicle and cause all kinds of issues. It will also cause the RF amplifier in your radio to be running in an unbalanced state and cause a lot of excess heat. Too much and/or too long of this excess heat will damage the final transistor in your radio - as in poof of magic smoke and the radio don't go no more without a few hundred dollar shop visit.
So, you could go out and buy/borrow the gear to do this, or take it to a shop and have them put it on their antenna analyzer.
Purchasing the equipment isn't a big deal. You can pick up halfway decent hobby grade SWR meters at a ham radio shop for $50-$100. A good investment. You could buy higher end gear if you ever plan on doing this work professionally, plan on doing a lot of installs, or just have money to burn. A used Bird 43 and the right slugs will run you $150 - $300.
You could also get an MFJ antenna analyzer for around $250.
Or, you could get a piece of high end gear like a service monitor or a spectrum analyzer with a tracking generator for somewhere around $20,000.00
Much easier to just go to a shop if you only plan on doing this once. Or, spend the bucks and get the hobby/amateur grade SWR meter and you'll probably be set for life.
Or, find an amateur radio club and see if one of them will help you out.
