A cable tensioning system includes a reaction frame which contains a sliding platform arranged to move linearly within the frame, and a clam-type cleat attached to the sliding platform. The cleat features one or more grooves, each of which comprises two arrays of opposing ridges that converge to form a V-shape groove adapted to receive a length of cable. The ridges of each groove are tilted relative to an axis perpendicular to the grooves longitudinal axis, such that the cable is progressively captured between the ridges of the opposing arrays as it settles into the crotch of the groove when moved in a first direction, and can be disengaged from the cleat by relaxing the axial force on the cable and moving it in the opposite direction. A linear actuator mechanism may be coupled to the sliding platform to move the platform with respect to the reaction frame.
