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SEQUENTIAL TONE SELECTIVE CALLING COMMUNICATION SYSTEM AND COMPONENTS THEREOF

  • US 3,613,004 A
  • Filed: 03/09/1964
  • Issued: 10/12/1971
  • Est. Priority Date: 03/09/1964
  • Status: Expired due to Term
First Claim
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1. In a communication system for selectively transmitting carrier signals carrying a control tone and a call-indicator tone and intelligence from a transmitter to at least one selected receiver, the combination comprising a transmitter including a tone-generating circuit for generating a preselected control tone, means for generating a call-indicator tone, a modulating circuit for modulating the carrier signals in accordance with the control tone and the control-indicator tone and the intelligence to be transmitted, a transmitter output circuit coupled to said modulating circuit for transmitting the carrier signals including the control tone and the call-indicator tone and the intelligence to be transmitted, a receiver including an input circuit for receiving the signals from said transmitter, a detecting circuit coupled to said input circuit for detecting the control tone and the call-indicator tone and the intelligence in the signals, an audio circuit for converting the intelligence into sound waves, a coupling circuit coupling said detecting circuit to said audio circuit for coupling the intelligence and the control tone thereto, a squelch circuit coupled to said coupling circuit and operative in a first condition thereof to render said coupling circuit inoperative and operative in a second condition thereof to render said coupling circuit operative, a first control circuit coupled to said squelch circuit an responsiVe to the application of the carrier signals to said receiver for generating a first control signal, a second tone control circuit coupled to said squelch circuit and responsive to the application of the control tone to said receiver for generating a second control signal, and squelch circuit being responsive to the application thereto of said first and second control signals for actuating said squelch circuit from the first condition thereof into the second condition thereof to render said coupling circuit operative to pass the call-indicator tone therethrough, means for maintaining said squelch circuit in the second condition thereof until the removal of said first control signal therefrom, a third tone control circuit coupled to said coupling circuit and responsive to the application thereto of the call-indicator tone from said coupling circuit for producing an output from said third tone control circuit, and a call-indicator annunciator coupled to said third control circuit and actuated by the output therefrom, whereby said receiver is operative to operate said call-indicator annunciator upon the application thereto of both the control tone and the call-indicator tone from said transmitter, the removal of said first control signal from said squelch circuit changing said squelch circuit from the second condition thereof to the first condition thereof to render said coupling circuit inoperative.

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