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Trunked radio monitoring system

  • US 5,956,648 A
  • Filed: 03/12/1997
  • Issued: 09/21/1999
  • Est. Priority Date: 03/12/1997
  • Status: Expired due to Term
First Claim
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1. A method of monitoring communications in a trunked communication system in which digital messages incorporating a talk group identification code, identifying a talk group, and a channel assignment code, identifying a frequency on which a voice communication within the talk group takes place, are transmitted over a control channel and voice communications are transmitted over working channels that change between communications, the method comprising:

  • with a frequency tunable receiver, monitoring digital messages on a control channel to detect a first bit pattern in the digital messages;

    upon detection of the first bit pattern in a digital message, storing data subsequently transmitted on the control channel;

    extracting information from the stored data and analyzing the extracted information to obtain a channel assignment code and a talk group identification code;

    comparing the talk group identification code obtained from the stored data to talk group identification codes of interest and, if the talk group identification code obtained from the stored data is a talk group identification code of interest, tuning the receiver to a working channel corresponding to the channel assignment code obtained from the stored data; and

    monitoring voice transmissions on the working channel.

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