Abstract: A telephone line interface circuit includes a transformer with tip and ring windings connected between tip and ring feed resistors and tip and ring leads of a telephone line, for feeding energizing current from a telephone facility to the telephone line. A secondary winding in combination with the tip and ring windings couples a.c. signals between the facility and the telephone line. A capacitance device is connected in combination with the secondary winding to simulate a function of a capacitance device as would normally be connected between the tip and ring windings in prior art circuits. The telephone line interface circuit is particularly useful in association with battery reversal responsive telemetry devices as any tendency for false ringer activation, in a connected telephone set, is reduced.

Abstract: A variable gain analog to digital compression encoder apparatus and method is operational for `on the fly` gain adjustments without introducing significant distortion or noise in telephone conversation. An incoming analog signal is fixed gain reproduced as a first stabilized mid-operating point analog signal. A second stabilized mid-operating point analog signal is produced in inverse proportion to the first stabilized mid-operating point analog signal, in response to a signal tapped along a signal division of a difference between the first and second signals. The second signal is compression encoded at a predetermined rate to produce pulse code modulated signal samples. The tap may be varied to change the encoding gain, at any time, in accordance with operating requirements of a telephone apparatus.

Abstract: Communication lines for example telephone loop circuits are typically terminated with line feed circuits such that d.c. and a.c. terminating impedances are dissimilar. The line feed circuit includes tip and ring feed resistors of similar ohmic values for supplying the communication line with energizing current. An a.c. terminating impedance of greater ohmic value than the d.c. terminating resistance is provided by a negative impedance circuit which is a.c. coupled across the communication line, in shunt with the feed resistors.