Bell Telephone Laboratories

Tadikonda N Rao

Jeffrey H Derby

Rouben Toumani

Barry Sheldon Bosik

Thomas G Wilson, Jr

A bilateral repeater for communication transmission lines is described in which the opposite directions of transmission are separated by frequency bands for amplification. The repeater is powered from a power conversion unit energized from the line potential. The repeater includes three-electrode gas tube breakdown devices connected across the repeater for each conductor of the transmission line. The third electrodes in the gas tubes are cross-connected together with no ground connection.

Repeater overload circuit

A bilateral transmission line repeater is disclosed in which opposite directions of transmission are separated into different frequency bands. The amplifiers for each direction of transmission include an automatic gain control circuit for controlling the gain of the amplifier. Gain control for the inward bound amplifier (toward a central location such as a telephone central office) is under the control of an automatic gain control signal derived from the outward bound signal as well as from the inward bound signal. Feedback around the gain control amplifier is accomplished using a current mirror circuit to avoid loading the amplifier output.

Repeater level control circuit

A power converter circuit is disclosed utilizing pulse width modulation for power regulation. A rapid acting surge protection circuit for the power driving switch is operated from a string of zener diodes to disable the power switch. A base charge removal circuit is included for dissipating accumulated base charges on the driving transistor without the need for a bipolar driving signal for the power transistor.

Converter drive circuit

A single channel carrier system is disclosed in which carrier techniques are used to add a second private talking path on a normal telephone subscriber loop. A central office unit modulates the second subscriber's signal to an inaudible range while the remote subscriber's unit demodulates this signal to recover the voice signal. The same process is used in the opposite direction utilizing a different carrier frequency. Each unit includes a carrier receiver having automatic gain control circuits and a variable attenuation circuit. The automatic gain control circuit includes a direct current clamp to minimize excursions of the AGC signal in the absence of a received carrier. The variable attenuation circuit uses a diode bridge shunting the signal path and controlled by the AGC signal. A linear carrier oscillator is implemented by providing a constant current source of oscillation energy.

Transceivers for single channel carrier telephone systems

A single channel carrier system for telephone service is disclosed including a remote terminal having a battery charger for charging a battery during idle periods to power the remote carrier electronics. The remote electronics include a ringing generator and supervisory circuits to implement normal telephone supervision over the carrier channel. The ringing generator is a DC-to-DC converter for stepping the battery voltage up to ringing voltage level. This high unipolar ringing voltage is then interrupted at a 20 Hz rate during the ringing portion of the ringing cycle. Simple diodes serve to isolate the unipolar ringing signals from other portions of the circuit.

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Morris Township, NJ, United States of America

Tadikonda N Rao