Warning signal for emergency vehicle - has directional radio beam to overide radios in other vehicles

摘要

The emergency vehicle is fitted with a narrow beam radio transmitter to operate with the optic and acoustic warning signal. The beam is directed at the traffic ahead and has a number of carrier frequencies to cover every possible radio station. The frequencies are modulated with the warning tone so that any driver with a car radio switched on can easily hear the warning tone, no matter how loud the radio is switched on. The transmitter can be ultrasonic, infrared or radio, with suitable decoding equipment in every car. The warning signal is then fed into the output stage of the car radio. Whether it is switched on or not. the system can be extended to switch the traffic signal ahead of the vehicle.