Tuning a Comet CA-2x4sr nmo for GMRS 467

[WRVU954]

I have the Comet CA-2x4sr nmo antenna on a magnet mount on the center of the roof of my 2014 F-150. Its great swr on Ham Bands. When I have my Wouxun KG1000g hooked to it for GMRS its fine up to freq 462.675, The local repeater tx is 467.675 and on low power the SWR is acceptable at 1.99. But on Medium Power its 2.39 and on High Power its over 3.00! I live on the edge of the closest repeater and want to tune it to a lower SWR for 467.675 and I cannot find any info on which section to trim and how much? With Ham bands being 1.01 I have room to work to bring the 467 lower. Can anyone explain how to tune it lower swr on 467? Thanks!

[Lscott]

There are some set screws where the bottom element slides into the base. Just loosen those and slide the entire antenna down a bit to raise the frequency. DON'T mess with any of the other elements.

I've ran some SWR sweeps on the one I have and a buddy with one on a lip mount for the hood on his pickup truck. The match can vary significantly with the mount type and location. 

I would be VERY suspicious of the SWR reading changing with power level, it shouldn't. That could be due to the output of the radio generating a lot of harmonics at the higher power, or the SWR meter itself isn't functioning right. I would recommend you try another SWR meter, another manufacture if possible, and see if you get the same behavior. As a side note this issue,with changing SWR reading with power level, is something I've read about online from other people who have this model.