US 4,357,495 AGranted

Telephone line feed

AssigneeStandard Telephones and Cables, PLC

InventorsAnthony W. Sweet, Michael P. Dyer

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Abstract

The direct current line feed for a telephone subscriber's line is derived from a variable voltage source connected to the line. In one case, the source is series connected in one leg of the line while in the other case it is connected across the line. In the first case there is a constant current source across the line while in the second case the voltage source is a constant current device. In both cases a pair of matching resistors is connected across the line with the center tap grounded to provide a high resistance balanced termination for the line. In both cases a high impedance monitor is connected across the line to monitor the voltage conditions on the line, and this, via a control circuit controls the voltage source and the separate constant current device if provided. This enables line voltage to be adjusted to take account of line length without introducing undesirably large dissipation.

Claims8

Dependent claims

A line feeding arrangement for a two-wire telephone subscriber's line, including a high valued balancing impedance connected between the two wires of the line, said impedance having a center-tap which is grounded for speech signals, a variable voltage source supplied by the exchange power supply and whose output forms the voltage drive for the line, a high-impedance monitor circuit connected across the line so as to monitor the voltage between the two wires thereof, and a control circuit to which the output of said monitor is connected and which generates a reference voltage condition which is applied to the voltage source so as to control the output voltage thereof, whereby variations in line conditions cause compensatory variations in the line voltage supply, in which the voltage source is connected in series in one of the wires of the line, a constant current circuit connected between the wires of the line in parallel with said balancing impedance, and in which the conditions of the constant current circuit are controlled in accordance with line conditions by said control circuit.

Dependencies are inferred from the claim text.