Anderson Roy E, Merigo Miguel A: Mobile locator system for metropolitan areas. General Electric Company, July 25, 1972: US3680121 (82 worldwide citation)

A locator system is disclosed wherein the vehicle whose location is unknown transmits a short, modulated radio frequency pulse. Receiving stations about the periphery of the area being serviced phase compare the received signal with a standard time reference signal. The phase difference is used to d ...