| 摘要 |
PURPOSE:To omit many invasion sensors by adjusting respective arrangement positions of transmitting and receiving antennas so that the receiving antenna is positioned on a fading generating position of radio waves radiated from the transmitting antenna into a warning area and deciding the existence of an invader in accordance with the change of a propagating state of the radio wave between the transmitting part and receiving part. CONSTITUTION:In case of setting up the transmitting and receiving antennas 2, 3, the fading generating position of radio waves radiated from the transmitting antenna 2 into the warning area A is checked while observing the lighting state of light emitting diodes L1-L4 in a receiving level display part 27 of the receiving part 3. The receiving antenna 3 is arranged on the fading generating position and the level of a transmission signal is set up so that the receiving output level of the receiving part 4 is dropped lower than a prescribed level. When an invader X enters into the warning area A, the propagating state of radio waves is changed and the fading generating position is changed. The change is detected by a level deciding part 26 in the receiving part 4 and an informing means 5 is driven.
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