Bell Telephone Laboratories

Peter Otto Schuh

Timothy Noonan Comerford

Ronald D Biggs

An off-hook/on-hook status check circuit is adapted to be connected in series with either the tip (2) or the ring lead (3) of a telephone subscriber loop (1) at a location remote or apart from the telephone station set (13). The circuit comprises an opto-emitter subcircuit (7) in series with a capacitor (4). These are connected in parallel with a pulsing contact (K.sub.1) which alternately permits the charging of the capacitor by the telephone central office voltage or its discharge through the opto-emitter subcircuit. As the capacitor may only be charged when the telephone station set is off-hook drawing loop current, the opto-emitter subcircuit provides a predetermined output when the capacitor discharges, identifying the off-hook condition of the telephone station set. No output from the opto-emitter subcircuit during the capacitor discharge interval identifies the on-hook condition of the set. If the present circuit comprises an element of a dial signaling system (10), the dial pulse signaling system is able to abort dial pulsing when the telephone set is on-hook and continued dial pulsing is not desirable.

Off-hook/on-hook status check circuit

In order to prevent excessive voltages originating in customer owned terminal equipment from creating a hazardous condition in an associated telephone line, a protective circuit is connected between the equipment and the line. This circuit responds to an unbalanced current flow by disconnecting the equipment from the line and providing a local path to ground for the current. The circuit remains activated as long as the unbalanced current flow continues and reconnects the equipment to the line only when the current flow ceases.

Hazardous voltage protector for telephone line

In a two-wire bidirectional telephone transmission line, a power converter and a directional threshold detector form in combination an impedance transparent bilateral voice-signal controller which can supply stable voice-switched gain to a dominant signal originating from either direction and a simultaneous, equal loss to any signals propagating from the other direction without separating the respective signals.

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Indianapolis, IN, United States of America

Peter Otto Schuh