Abstract: A primary antenna reflective structure is supported for pivotal movement in the elevation direction between the zenith and horizontal points. Drive motors via a bull gear rotates the antenna through its permissible travel. Inertia counterbalance is utilized to control the motion of the antenna. That counterbalance comprises a pinion driven by the bull gear. Left and right guides are integral with the pinion and followers are contained within housings and are adapted to be driven by the guides. The followers move in opposite directions and either compress or relax springs which are housed concentric with the guides. The guides comprise either a ball screw or roller screw, and the followers either a ball nut or roller nut.