Importance

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Abstract

A communication system is connected to a pair of telephone conductors which supply telephone service to a telephone subscriber. An optically coupled switch connects a first winding of a transformer across the telephone conductors. A second winding of the transformer is connected to a modem for communicating over the telephone conductors via the transformer. A voltage sensor circuit senses the voltage across the telephone conductors and detects a reduction in the voltage level across the conductors which indicates an off-hook condition of a telephone unit of the subscriber connected to the conductors. The voltage sensor circuit also detects the presence of a ring signal on the conductors. The switch is periodically opened so as to disconnect the transformer from the telephone conductors, and permit the voltage sensor circuit to check for an off-hook condition.

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First Claim