| 摘要 |
PURPOSE:To prevent the erroneous operation in which an alarm signal is transmitted in spite of the fact that a passenger does not fall into the sea by installing a switching device which alternately switches a plurality of antennas in the sufficiently shorter time than the continuation time of the electric waves of a transmitter and connects the antenna with a receiver. CONSTITUTION:A subsidiary machine 1 as transmitter transmits electric waves intermittently in a certain cycle. Two antennas 2a and 2b are installed at different positions so that the electric waves can be received at a certain level by either of the antennas 2a and 2b even if the position or the attitude of a passenger having the subsidiary machine changes. Further, a switching device 3 is connected to a receiver 4 by alternately switching the output of the antennas 2a and 2b, and a detection part 13 receives the output signal of the receiver 4 and outputs an alarm signal which shows the cut-off of the electric waves transmitted from the subsidiary machine 1. Since the switching time by the device 3 is sufficiently shorter than the continuation time of the electric waves transmitted by the subsidiary machine 1, the presence of the electric waves can be certainly detected.
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