To secure a sufficient communication quality by avoiding the occurrence of fading and suppressing fluctuation of the field intensity of radio wave by a space diversity method.
The apparatus is so formed that three antennas 21, 22 and 23 of nurse call transmitters/receivers 2a, 2b, etc. are disposed in the positions of the vertices of an equilateral triangle having sides with equal length in such a manner that the antennas face downward and vertically relative to the surface of a ceiling of a hospital room and/or a corridor where the nurse call transmitters/receivers are attached. The apparatus has a substantial distance between the antennas of nλ/4 (where λ is a wavelength of the radio wave and n is an odd number), so that the position of a node of a standing wave generated due to interference between a direct wave and a reflected wave of a call signal (call radio signal) S1 which is emitted from the nurse call transmitter/receiver, whose call button is operated, as the radio wave is located in a position of nλ/4 from the ceiling, a floor, a wall or the like, or the reflected surface, while the three antennas can be prevented from simultaneously positioned in the node based on the space diversity method.
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TOUYA NORIHITO
NISHIMURA TOMOHIRO
Hiromichi Watanabe