Method and apparatus for electronic surveillance of precisely de

Details Method and apparatus for electronic surveillance of precisely de Method and apparatus for electronic surveillance of precisely de

1976-05-24

1978-05-02

Swann, III, Glen R.

Communications: electrical

Systems

Call station

340258C, G08B 1322

Patent

active

040878023

ABSTRACT:
A high frequency generator projects an electronic wave into a control zone under surveillance to establish a first field. A frequency modulated (FM) generator is used for establishing a second field throughout the zone. A third field of the same FM carrier frequency, but with a different modulation, is established only at extreme ends of the control zone to define the limits of the control zone. Presence only within the control zone of a transponder causes the reradiation of a signal comprised of the FM signal and the high frequency signal, which in turn activates an alarm circuit.

REFERENCES:
patent: 3707711 (1972-12-01), Cole et al.
patent: 3895368 (1975-07-01), Gordon et al.
patent: 3996555 (1976-12-01), Dow

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