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Home  Telephone Exchange Service and Systems Variable and Invariable Substation Circuits |
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Variable and Invariable Substation CircuitsSatisfactory telephone communication could be carried on over a system in which the receiver was removed from the circuit at the sending end when speaking was in progress and in which the transmitter was removed from the receiving end when listening was going on. Such an arrangement would be efficient because it would eliminate the losses in the other units not being used. Such a circuit is known as a variable telephone circuit. A circuit in which such changes cannot be made is an invariable telephone circuit.ref.2 To eliminate troublesome switching operations, the invariable telephone circuit is commonly employed. There is consequently a loss of power in the receiver of a set during talking, and also a loss of power in the transmitter of a set during listening.
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Last Update: 2011-05-30