INTRUSION WARNING SYSTEM

摘要

An intrusion warning system for indicating the presence of an intruder to a given area includes an antenna provided around the area and which is insulated from the ground; an oscillator is provided for feeding an alternating current signal to the antenna, and a coupling impedance is connected between an output of the oscillator and the antenna; the coupling impedance includes an arrangement to vary the impedance to an appropriate value such that the voltage fed to the antenna is approximately 50% of the voltage fed from the oscillator to the coupling impedance; by this arrangement the detection sensitivity is always kept at an optimum; the system also includes a signal processing apparatus for producing an output signal responsive to a change in the voltage of the alternating current on the antenna exceeding a predetermined level.