JPH0642601B

PURPOSE:To reduce the leakage quantity of a radio wave without losing the function of DC brake by devising it that the radio wave leaked from an end opening of an outer tube and a radio wave leaked from a gap between a ferrite board and a conductive ring are absorbed by the ferrite board. CONSTITUTION:Part of the leaked radio wave (other part is to be reflected) from an opening 13a is leaked from a ring gap (insulation ring 23) between a flange 16 and a conductive ring 18 and absorbed by a ferrite board 20 and converted into heat. Moreover, the radio wave leaked from the ring gap (insulation ring 23) between the ferrite board 20 and the conductor ring 18 is absorbed in a 2nd stage ferrite board 20. In converting the outer circumference of the ferrite board 20 by a conductive short-circuit board 21 or a conductive member 22, the radio wave absorbing efficiency of the ferrite board 20 is improved remarkably. Thus, the quantity of the radio wave leaked from the opening 18a of the conductive ring 18 is decreased to nearly 1/1000 or below the leakage quantity from the opening 13a.