As deformations of the main reflector of a radio telescope directly affect the observations, the evaluation of the deformation is extremely important. Dynamic characteristics of the main reflector of the Nobeyama 45 m radio telescope, Japan, are measured under two conditions: The first is when the pointing observation is in operation, and the second is when the reflector is stationary and is subjected to wind loads when the observation is out of operation. Dynamic characteristics of the main reflector are measured using piezoelectric accelerometers. When the telescope is in operation, a vibration mode with one nodal line horizontally or vertically on the reflector is induced, depending on whether the reflector is moving in the azimuthal or elevational planes, whereas under windy conditions, vibration modes that have two to four nodal lines are simultaneously induced. The predominant mode is dependent on the direction of wind loads.
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