| 摘要 |
To provide a communications system to accurately detect when a mobile transceiver 20 has entered an area where communication with a fixed transceiver is possible, and to start-up the internal circuitry of the mobile transceiver 20, a communications system transmits a start-up pilot signal of a prescribed period from a transponder 4 mounted in a fixed station to a transponder 16 mounted in a vehicle. In the transponder 16, the received signal upon being received by an antenna 10 is detected in a detector 22 and amplified in an amplifier 24. When this signal is greater than a reference voltage VTH1, a pulse is output from a level discriminator 26. This pulse signal is converted into a pulse of constant pulse width in a discriminator pulse generator 28 and integrated in an integrator 30. When the integrated value exceeds a reference voltage VTH2, a start-up discriminator 32 sends a drive signal to actuate the internal circuitry of the mobile transceiver 20. As a consequence, mistaken start-up of the internal circuitry due to noise input is prevented and the internal circuitry is started only when necessary. <MATH> |
