does a mobile mag mount scanner antenna need a foil bottom to use the vehicles roof as ground plane and do i have to some how have the foil contact the metal base of the antenna. thank you
Most of the mag mounts I've used have materials covering the magnet which are insulators (rubber and/or plastic). But if you have one with a metal bottom there's no harm in trying some protective cover (for your vehicle over it), just check the signal levels and make sure it still sufficiently sticks to the car.