Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1980-10-31
1983-05-17
Caldwell, Sr., John W.
Communications: electrical
Condition responsive indicating system
Specific condition
340505, 343 65SS, 343748, 343788, 343867, 343894, 343898, 343908, G08B 1324
Patent
active
043842810
ABSTRACT:
An electronic theft detection apparatus for detection of saturable magnetic targets has transmitter and receiver antennas formed of single turn loops of rigid metal pipe. The antennas are rectangular and have a width, in the direction of passage, through the interrogation zone, less than the length of a shopping cart. The transmitter antenna is in the form of a rectangular loop and the receiver antenna is of the same overall size and configuration but is bisected with a conductor to form two balanced loops. The antennas are purely inductive and a series resonant circuit is inductively coupled into the transmitter antenna and a parallel resonant circuit is inductively coupled out of the receiver antenna. Special circuits are also provided for temporarily disabling the apparatus when a related lower harmonic frequency signal decreases in amplitude.
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Caldwell Sr. John W.
Knogo Corporation
Nowicki Joseph E.
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