| 摘要 |
PROBLEM TO BE SOLVED: To minimize that an alarm can not be given when the presence of a worker is to be alarmed or that the alarm is given when alarming is not necessary by mounting a specified dipole antenna on the end surface of a vehicle rear part so that an antenna conductor bar is horizontal to the ground. SOLUTION: A dipole antenna is used as a receiving antenna 7A, and it is mounted on a rear gate 10 which is a metallic end surface vertical to the ground in the rear part of a vehicle so as to be horizontal to the ground. The mounting is performed by use of a proper support member. The length of the receiving antenna 7A is set to the length of 1/2: (λ/2) of the wavelength λ of the radio wave used. The rear gate 10 formed of a metal plate acts also as the reflector of the receiving antenna 7A. The reason of mounting on the metallic end surface vertical to the ground is that the end surface is made to act as the reflector, and the reflecting effect of the reflector is made to appear strongly in the backward horizontal direction. |
