Cell phone antenna boosters
I've worked in Army commo shops for several years now, and just wanted to let you know, the balls on Humvee antennas have nothing to do with signal reception. They are just plain old plastic, their purpose being to keep you from poking out an eye when you have the antenna tied down to the truck for going through woods or whatever, and release it to put it back up. The antenna is on a strong spring which can fly up quickly if you accidently let go. If we lose the plastic ball, we just put a bunch of tape on it until we get a replacement, since its only there for safety.