Of course you can. Whether you really want to or not is a different matter. This is a tall antenna that catches substantial wind which creates a serious bending moment at the antenna's base. If the R7 is the "only" antenna on your 40' tower, and the tower is strong and secure, there shouldn't be a problem. But if the R7 is on a 1-1/4" diameter mast, with other antennas mounted to that same mast, and the mast projects several feet above the tower top, this is precarious -- or an accident waiting to happen. Ironically, global (widespread) experience indicates this type of vertical works about as well at much lower installed heights as it does at 40 feet...so unless there's some strong, compelling reason to install it on a tower -- don't bother. On a roof top, chimney, eave mount, porch, or even a 6' mast stuck in the ground, it will probably work just as well as on the tower. Good luck!