I just installed a Cobra 29 and the SWR meter is reading between high and off the meter. I've been swapping antennas, antenna bases and antenna cords to try to determine the problem.
Best I can figure is the small ground plane. The hood is fiberglass, there is a big fantastic fan hole in my roof, and from the fan back there is the PH.
To try to get better results I moved the magnetic antenna to as near the center of the roof as I could, which means putting it next to the rear corner of the fantastic fan. This is the opposite corner from the power knob to raise the fan cover, and it is on the top not on the fan.
The power sources are isolated- CB goes directly to the starter battery (+) and passenger A pillar (-) with the antenna cord loose. The fantastic fan is powered from the fused distribution block I just put in, and that comes from the house batteries via 10 gauge wire in the overhead.
I set to channel 1 and it was off the meter, so I decided to get the needle back on the meter and turned the SWR calibration all the way down. Then, this happened:
I've reproduced this several times, you have to listen closely the first two times before I zoom in, it's hard to see it move in the video until I zoom.