An Airborne Windshear Detection System measures wind during the Take off and Landing phase by determining the Doppler Shift of backscattered radiation that is transmitted by an on-board laser system. A control system is configured to mechanically control a rotational speed of the generator so that, during a low voltage event, the wind energy converter can continue to operate and supply power to the grid. A plurality of concavo-convex portions is provided on another surface of the fixed contact that faces an anti movable-contact side. In this instance when a plurality of marking devices are penetrated into the ground at spaced positions in a row, a common cable, for example an electrical extension cord or a string of lights can be threaded through empty frames in the row to be supported spaced above the ground.