Terence L Sullivan

US Patent:

59566485, Sep 21, 1999

Filed:

Mar 12, 1997

Appl. No.:

8/820338

Inventors:

Terence Brennan - Melbourne FL
Terence Sean Sullivan - Berkeley CA

Assignee:

G/Tracker Technologies LLC - Henderson NV

International Classification:

H04Q 700

US Classification:

455518

Abstract:

A method and apparatus for passively monitoring communications in a trunked communication system. Digital messages transmitted over a control channel at a particular frequency are monitored with a receiver. When a first bit pattern is detected in a digital message, subsequently transmitted data is stored. Information is extracted from the stored data to obtain a channel assignment code indicating a frequency over which communications take place and a talk group identification code identifying a talk group in the trunked communication system participating in a communication. If the talk group is a talk group of interest, the receiver is tuned to the frequency corresponding to the channel assignment code so that voice communications are successfully monitored. The receiver is tuned to the control channel after each voice communication so that a communication including multiple transmissions on different frequencies is coherently monitored by retuning the receiver in accordance with the received channel assignment codes. In an alternative embodiment, separate receivers are provided for the control channel and for voice communications.