Broadcast system for distribution automation and remote metering

A narrowband bidirectional radio communication system comprising:

• (A) a plurality of independent paired radio receiver and transmitter means wherein said receivers are adapted to detect broadcasted sync and address & control signals from an existing standard AM broadcast station in its forward link, and said transmitters are adapted to accept RF reference and sync signals from its companion receiver and to accept reply message signals from message sources connected at their respective inputs and to transmit said reply message signals synchronously on a corresponding plurality of closely spaced radio carrier frequencies that are phase-locked to the carrier of said broadcast station in the reverse link to a central station receiver selectively in response to coded address & control signals transmitted from the local radio broadcast station;
• (B) the central station receiver being adapted to receive said radio reply signals simultaneously at said plurality of closely spaced reverse link radio carrier frequencies, and to simultaneously detect said sync signals from said broadcast station and employ them to synchronously demodulate the radio signals from said plurality of remote transmitters,
• (C) central controller means adapted to generate digital address & control signals being synchronized to said sync signals broadcasted by said AM radio station.
• (D) a local AM radio broadcast station adapted to generate and broadcast special sync signals derived from its master oscillator and adapted to receive and broadcast digital address & control signals received from said central controller by modulating the phase of its normally broadcasted radio frequency carrier at small angle subaudible rates that do not suppress and spread its normally unused residual carrier power by more than a predetermined amount nor interfere with normal transmissions of said radio station that are simultaneously broadcast.