I have a 2005 Freightliner Coronado and just purchased 2 Predator 10K antennas. I was told by the store to use just a single antenna on the driverside. I ran new coax to the driverside antenna since the old set-up was for 2 or co-phased. Hooked the antenna to a mirror mount with a Fire-stick stud . Thinking I'm on my way, I checked my SWR's and it was over 3. So I started looking for connection problems. When I couldn't find any thing, I just happened to open the door and saw the SWR drop to 1 with it open about 2". I was confused about this and started to research and found that the problem might be a no ground plane issue since the cab is all fiberglass. But why am I getting great SWR's with the door open? is this a no ground plane problem? Would it help to go back to a co-phased with both antennas? Any help would be GREATLY appreciated. Thanks