A system is provided for mounting directional antennas on vehicles. The mounting system employs a conventional roof rack as a support base for the antenna mount. In one embodiment, a straight tubular frame member is attachable to the roof rack. An upwardly-extending rotatable shaft extends from adjacent one end of the frame, for supporting the antenna mast, and a downwardly-extending rotatable shaft, supporting a control handle, extends from adjacent the other end of the frame. The rotational movements of the shafts are tied together by a toothed belt which engages sprockets coupled to the shafts. In its preferred form, the control handle includes tactile positioning indicators on its surface which allow the user to sense the direction of the antenna without having to view it. A second embodiment is disclosed which uses a portion of a tubular horizontal bar on a conventional roof rack as part of the support frame of the device. The antenna mounting system allows an operator to fully control the rotation of the antenna through 360-degrees without the need to drill a hole through the roof of the vehicle.