Radio operated siren for rescue vehicle - has car radio reception of other vehicles blocked to superimpose siren

摘要

The rescue vehicles are equipped with a low range wide band transmitter which provides a signal corresponding to the audible siren. The radio signal is picked up by car radios and is superimposed on the radio programme. The siren is thus heard by all drivers, even with their windows shut and the radio on loud. The radio and audible signals are in phase to prevent interference. An improvement can have special receivers on all vehicles, tuned to the rescue siren frequency, with the signal reinforced by a repeater lamp on the car dashboard.