ANORDNING FOR ASTADKOMMANDE AV EN STYRSIGNAL NER EN RADIOFREKVENSSIGNALMOTTAGARE ER AVSTEMD TILL EN VALD RADIOFREKVENSSIGNALS MITTFREKVENS

摘要

A system is provided for developing a gating signal when a radio-frequency signal receiver is tuned to the center-frequency of a selected radio-frequency signal. The system comprises circuit means for tuning the receiver to a plurality of frequencies within a range of frequencies which includes the selected signal and for producing an intermediate frequency signal corresponding to the frequency to which the receiver is tuned. A frequency discriminator is coupled to the circuit means and is tuned to a predetermined frequency, with the frequency discriminator being responsive to the intermediate frequency signal for developing an output signal having a DC component which varies systematically in accordance with the deviation of the intermediate frequency signal from said predetermined frequency. A detector is coupled to the frequency discriminator and is responsive to the DC signal component for developing a gating signal, with the gating signal having a first value when the DC component has a value between preselected upper and lower threshold values and with the gating signal having a second value when the DC component has a value which is not between the upper and lower threshold values. A gating circuit is coupled between the circuit means and an electromechanical transducer and is responsive to the gating signal for enabling reproduction of audio signals by the transducer only when the gating signal has the first value.