If your whip is beside any metal it will cause swr reading, that is why i had to put a rubber hose from the bottom of the whip to just above the cab. You know it will interfere with ground because if i hold a 4' flourescent light bulb beside my antenna it will light it up while I am talking. With that said I know the whip beside metal will interfere with swrs and I put a swr meter on my radio with the whip beside the cap and the swr was high. When i put the rubber hose on the whip to seperate it from the cab my swr came down to 1.5.