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Trunked radio monitoring system

  • US 6,519,472 B1
  • Filed: 09/20/1999
  • Issued: 02/11/2003
  • 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 working channel 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 may change between communications, the method comprising:

  • with a frequency tunable receiver, monitoring and storing digital information transmitted on a control channel;

    testing portions of the stored information for a pattern of bits identifying a message including a channel assignment code and a talk group identification code, to identify a message;

    upon finding a message, extracting from the message the channel assignment code and the talk group identification code;

    comparing the talk group identification code extracted from the message to a plurality of talk group identification codes of interest and, if the talk group identification code extracted from the message is one of the talk group identification codes of interest, tuning the receiver to the working channel corresponding to the channel assignment code extracted from the message; and

    monitoring voice transmissions on the working channel without participating in the voice communications.

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