| 摘要 |
PURPOSE:To reduce the installation cost of a device by using a loop coil which is buried under a road surface to sense a vehicle even for vehicle communication, and simultaneously performing communication operation between a ground equipment and a vehicle-mounting equipment and vehicle sensing operation at different frequencies. CONSTITUTION:The oscillating circuit 10 of a ground equipment applies a signal of frequency f1 to a tuning circuit 12 and a phase comparator PD13, which makes a phase comparison between outputs of the circuits 10 and 12. Before a vehicle enters into a loop coil 2, the outputs of the circuits 10 and 12 are in phase with each other and the output of the PD13 is 0. Once the vehicle enters into the coil 2, the signal applied to the PD13 shifts in phase and the PD13 outputs a signal to a level detecting circuit 14, which when detecting a level higher than a specified value, outputs a vehicle sense signal (d) through a holding circuit 17. For communication between the ground equipment and a vehicle-mounting equipment, the ground equipment modulates a carrier of frequency f2 by a signal (g) to transmit the resulting signal through BPFs 27 and 18, and receives a signal of frequency f3 from the vehicle-mounting equipment through a BPF20. The vehicle-mounting equipment receives the signals of f1 and f2 through an antenna and the BPF and transmits the signal f3 through the BPF. |
