Importance

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Abstract

A toll telephone coupled to tip and ring conductors of a toll trunk and through which various toll signals flow between a central office and the telephone (such as a coin ground signal to indicate the presence of the coin) has a hook switch with an off-hook condition for instituting the flow of loop current. To allow local, coin-free calls, the telephone has electronic circuitry for applying a simulated coin ground signal to the tip conductor continuously during the off-hook condition to permit coin-free calls to be made from the toll telephone. Additionally, the telephone includes a single relay system for providing an open-loop coin check responsive to a corresponding signal from the central office. The telephone provides a notch filter for discriminating against one of the multiple frequencies of a bong tone, thus allowing the remaining frequency to be detected.

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First Claim