Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1993-02-03
1994-09-20
Swann, Glen
Communications: electrical
Condition responsive indicating system
Specific condition
340551, 340552, G08B 13187
Patent
active
053493397
ABSTRACT:
An apparatus for the detection of labels used for preventing theft of goods and provided with an electric resonant circuit [(21) and] having a resonant frequency [(fr)] in the MHz range [comprises] has a transmitter [(1)] and a receiver [(2)]. The transmitter [(1)] generates a transmitting signal sequence, whose frequency is wobbled in wobble cycles over and beyond the given resonant frequency of the labels and [radiates] which is radiated by means of a transmitting antenna [(11)]. Signal generation in the transmitter [(1)] takes place digitally and with coinciding phase position with respect to each wobble cycle. In the receiver [(2)] the signals received by means of a receiving antenna [(12)] are scanned and digitized synchronously with signal generation in the transmitter [(1)]. From the digitized signal values of n wobble cycles a background is formed and subtracted from the digitized signal values of the in each case last wobble cycle. A long-term and a short-term background can be formed and the latter is subtracted from the former. By background subtraction it is in particular possible to [discriminate time] eliminate relatively [stationary] time stationary interference, such as is particularly caused by transmitting signal diffractions and reflections on objects present in the vicinity of the transmitting and/or receiving antenna.
REFERENCES:
patent: 4531117 (1985-07-01), Nourse et al.
patent: 4663612 (1987-05-01), Mejia et al.
patent: 4686517 (1987-08-01), Fockens
patent: 5023598 (1991-06-01), Zemlock et al.
Actron Entwicklungs AG
Swann Glen
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