GB998440A - Telephone circuit - Google Patents

Abstract

998,440. Telephone answering circuits. ROBOSONICS Inc. Dec. 30, 1963, No. 51173/63. Heading H4K. A telephone ringing signal detector and answering circuit comprises, Fig. 2, at the subscriber's station 10 a gas-filled tube 42 which is normally non-conducting except on the receipt of ringing pulses from the central station 30 when the gas-filled tube conducts and completes the primary circuit of transformer 72, the signal appearing at the secondary of the transformer being amplified and applied to an answering circuit 60 which operates to close switch 74 and thus put a low impedance, i.e. the primary of transformer 71, across the line so simulating the off-hook condition at the subscriber's station. Capacitor 44 is provided in series with the gasfilled tube 42 and in parallel with resistor 43, the combination forming a relaxation oscillator which oscillates during the peaks of the ringing current and so converts the low-frequency ring- ing signal to a higher frequency signal which may be more easily amplified in amplifier 50. The breakdown potential of tube 42 is arranged to be between the D.C. bias signal on the line and the D.C. bias plus A.C. ringing signal peak.