| 摘要 |
PCT No. PCT/SE95/01189 Sec. 371 Date Apr. 9, 1997 Sec. 102(e) Date Apr. 9, 1997 PCT Filed Oct. 13, 1995 PCT Pub. No. WO96/12263 PCT Pub. Date Apr. 25, 1996An electronic alarm system of the kind used in commodity surveillance systems includes an alarm element which is adapted to receive a magnetic alternating field transmitted from a transmitter by means of a transmitter coil and also adapted to re-transmit a magnetic alternating field, wherein a receiver which includes a receiver coil is adapted to receive and detect the re-transmitted alternating field. The transmitter coil and the receiver coil are one and the same coil (1). Between the transmitter (TX) and the receiver (RX) on the one side and the transmitter-receiver coil (1) on the other side, there is provided an electronic unit (14) which includes a transformer (5) and a resistance (2) which are so adapted that when transmitting, a first part of the transmitter power will be applied to the transmitter coil (1) and the remaining part, a second part, will be applied to the resistance (2). When receiving a first part of the received signal will be applied to the receiver (RX) and the remaining part, the second part, will be applied to a circuit or to a resistance. Only a small part of the transmitter power will reach the receiver.
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