Reactively decoupled dual channel keying circuit for wide-band frequency

Abstract

A keyable control circuit, has sensing coils located in the vicinity of a plurality of locations where lock control is desired. At least one swept high-frequency oscillator, which is connected to each sensing coil, generates an rf signal, rapidly swept over a wide frequency band. When an external keying circuit, containing more than one resonant circuit, each correctly tuned to a predetermined keying frequency, is inductively coupled to a sensing coil, each resonant circuit absorbs rf energy as the oscillator frequency is swept past its resonant frequency. Electrical interaction between the resonant circuits is accomplished by reactive cancellation. Energy absorption in the external keying circuit induces corresponding reductions in rf energy in the sensing coil as the oscillator frequency is swept past the keying frequencies. Tuned detectors within the keyable control circuit produce a control signal when energy reduction is sensed at each of the predetermined keying frequencies. If correct absorption fails to occur at any one or more of the predetermined frequencies, the control signal is withheld. A time-gating system enables selective direction of the control signal to one or more using locations while excluding others. This function finds convenient application in automotive use where it is frequently desired to enable simultaneous unlocking of one or more doors while excluding unlocking of the deck lid. A dead-oscillator detector averts attempted actuation of the unlocking function by the coupling of untuned energy-absorbing material, such as iron, to a sensing coil.