| 摘要 |
An intrusion warning system for indicating the presence of an intruder in a given area comprises a single antenna wire (4) encircling said area and insulated from the ground, a high frequency (e.g.1 kHz to 10 kHz) oscillator (1) for feeding a high frequency signal to the antenna (4), a coupling impedance (2), for example a capacitor, connected between an output terminal of the oscillator (1) and the antenna (4), and a signal processing means (5) which produces an alarm upon detecting a change to beyond a predetermined level of the voltage on the antenna (4), as induced by the proximity of an intruder. <IMAGE> |
