Method and apparatus for electronic surveillance

Details Method and apparatus for electronic surveillance Method and apparatus for electronic surveillance

1978-03-03

1980-06-03

Swann, III, Glen R.

Communications: electrical

Condition responsive indicating system

Specific condition

340505, G08B 1322

Patent

active

042064538

ABSTRACT:
A high frequency generator projects an electronic wave into a surveillance area to establish a first field. At least one control zone is set up within the surveillance area by two low frequency (LF) generators. The first LF generator establishes a second field in the control zone. The second LF generator establishes a third field only at a control zone margin, thereby defining the limits of the control zone. Presence within the control zone of a transponder causes reradiation of a signal comprised of the high frequency and LF signal, which provides an output signal. Additional control zones may be set up within the surveillance area by the addition of further LF generators.

REFERENCES:
patent: 3707711 (1972-12-01), Cole et al.
patent: 3895368 (1975-07-01), Gordon et al.
patent: 3990065 (1976-11-01), Purinton et al.
patent: 3996555 (1976-12-01), Dow
patent: 4016553 (1977-04-01), Novikoff et al.
patent: 4087802 (1978-05-01), Williamson
patent: 4139844 (1979-02-01), Reeder

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