Surveillance systems
Patent 4352098 Issued on September 28, 1982. Estimated Expiration Date: 
May 16, 2000. Estimated Expiration Date is calculated based on simple USPTO term provisions. It does not account for terminal disclaimers, term adjustments, failure to pay maintenance fees, or other factors which might affect the term of a patent.
May 16, 2000. Estimated Expiration Date is calculated based on simple USPTO term provisions. It does not account for terminal disclaimers, term adjustments, failure to pay maintenance fees, or other factors which might affect the term of a patent.Patent References 3518546 Antipilferage system and marker therefor Theft detection system Surveillance method and system with electromagnetic carrier and plural range limiting signals Patent #: 4139844 InventorsAssigneeApplicationNo. 06/150461 filed on 05/16/1980US Classes:340/572.2, Specified relationship between field and detection frequencies (e.g., nth order harmonics)455/9MonitoringExaminersPrimary: Caldwell, Sr., John W.Assistant: Crosland, Donnie L. Attorney, Agent or FirmInternational ClassG08B 13/24 (20060101)Foreign Application Priority Data1979-05-18 GBAbstractA surveillance system transmits a microwave carrier signal through a surveillance zone (14). Two low frequency energy fields are also established in the zone being produced by respective pairs of closely spaced apart low frequency signals radiated from opposite sides of the zone. A receptor reradiator in the zones receives these signals and reradiates a reply signal to a receiver the reply signal consisting of the microwave carrier signal amplitude modulated in accordance with the instantaneous value of the low frequency fields at the location of the receptor reradiator. The receiver separates out preselected intermodulation products and activates an alarm only when the preselected intermodulation products are present. | |
