Surveillance systems

Details Surveillance systems Surveillance systems

1980-05-16

1982-09-28

Caldwell, Sr., John W.

Communications: electrical

Condition responsive indicating system

Specific condition

340568, 343 65SS, 455 9, G08B 1314, G08B 1324

Patent

active

043520987

ABSTRACT:
A 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.

REFERENCES:
patent: 3518546 (1970-06-01), Augenblick et al.
patent: 3938125 (1976-02-01), Benassi
patent: 3990065 (1976-11-01), Purinton et al.
patent: 4139844 (1979-02-01), Reeder

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