High SWR’s with other antennas besides stock

I had the same problem with my 2018 Cascadia. I ran the stock for first couple years because After a lot of effort I finally got it right, but I don't know how or why. Then it unfixed itself, again, I don't know why.

I haven't made plans to try anything but the stock antenna on my new 2025 because I don't want to spend the time and money spelunking around for a solution. I think the problem is the mirror mount itself, but that's outside my wheelhouse.

 

I see threads on this forum about the need for bonding on the Cascadia. I don't have a Cascadia but apparently bonding is supposed to help. If I got bad results on several different reputable antennas, I'd begin to suspect another problem
BTW get good quality coax

 

When the SWR is 3.0 or higher, that indicates your antenna ground plane is at fault. This is not an antenna tuning or coax problem.
.
. What you want to do is interconnect the large metal components of the truck to form one large antenna ground plane for radio frequency purposes. How you do that is, for example, to connect a short flat strap [similar to a battery ground strap] from bare metal of the door to bare metal of the cab frame. Your goal is to connect the door, cab frame and chassis frame in sequence to form one large metal mass for RF (radio frequency) purposes. You need short flat straps not regular wires.
.
. Do NOT go from the door directly to the chassis frame because the long length will act as an additional antenna.
This has nothing to do with electrical grounding.

 

Don't use the SWR function in the cobra 29's, they are useless. Since you're getting two different SWR readings from both radios on the same antenna, that proves my point. Buy a good external SWR meter with a jumper coax cable, and do the bonding that has been mentioned. Then see what the real SWR is on your antenna system. Hopefully you haven't cut too much off the antennas, otherwise they won't work for the CB band if they are too short.

 

Not trying to put you on the spot, but did you put the nylon washer back on the right spot on the mount ?

 

Yup, even ruined a pair of pants chasing after the suckered when I tried a new antenna.

 

What kind of mount?

Most likely the grounds - RF - don't exist with the new system.