Abstract: A security system is provided wherein a portable locator (10) is disposed on a protected person and, with the use of an alarm switch (88), an individual can set the locator (10) to continuously transmit an alarm signal. This alarm signal is comprised of a pseudonoise (PN) code ORed with data and transmitted over a carrier frequency. This carrier frequency is then transmitted to a plurality of fixed receivers (14). The fixed receivers (14) note the time of arrival and then determine via this time of arrival the approximate location of the locator (10). During this time, the locator (10) operates in a high power mode that is sufficient to reach each of the receivers (14). This occurs for a short time and then the locator (10) goes into a low power mode to conserve the battery. During this low power mode, a portable monitor (62) is provided that has two receivers (66) and (68). Two antennas (70) and (72) are associated therewith. The system operates on an angle of arrival method.

Abstract: A positioning system uses a multiplicity of commercial broadcast stereo FM radio signal transmitters, at known fixed locations, each of which transmits a beacon signal having a phase that is un-synchronized with the phases of the beacon signals of the other transmitters. All the beacon signals have a frequency approximately equal to a 19 KHz. A fixed position observer unit, positioned at a known location, receives the beacon signals from all the transmitters in the vicinity, determines their relative phases, and broadcasts data representing these relative phases. Mobile units, at unknown locations, receive these broadcast values, as well as beacon signals from at least three radio transmitters. Each mobile unit includes phase detection circuitry that detects the phases of the beacon signals at the mobile receiver's current position. This is accomplished using a single radio signal receiver.

Abstract: A positioning system uses a multiplicity of commercial broadcast stereo FM radio signal transmitters, at known fixed locations, each of which transmits a beacon signal having a phase that is un-synchronized with the phases of the beacon signals of the other transmitters. All the beacon signals have a frequency approximately equal to a 19 KHz. A fixed position observer unit, positioned at a known location, receives the beacon signals from all the transmitters in the vicinity, determines their relative phases, and broadcasts data representing these relative phases. Mobile units, at unknown locations, receive these broadcast values, as well as beacon signals from at least three radio transmitters. Each mobile unit includes phase detection circuitry that detects the phases of the beacon signals at the mobile receiver's current position. This is accomplished using a single radio signal receiver.