Abstract: A rectifier unit for supplying power to a D.C. load including a transformer having a primary, a secondary and a saturable core, the secondary defining an output section and a control section. A ferroresonance control circuit simulates saturation of the transformer core and includes an electronic switch for controlling the degree of simulated core saturation and thereby regulating the rectifier unit output. Rectifier failure alarm circuitry produces a failure alarm in response to a number of rectifier unit malfunctions. The rectifier failure alarm circuitry is coupled to the ferroresonance control circuitry and comprises a rectifier alarm element operable between the first condition wherein a rectifier failure alarm is produced and a second condition. The failure alarm element is operated from its first condition when the electronic switch minimizes the rectifier system output.

Abstract: A circuit for holding the voltage across a rapidly switched semiconductor element such as a transistor used in an inductive circuit to substantially twice the voltage of an input source when the element is switched to its nonconducting state. Also included is circuitry for recovering and returning to the input source the energy stored in the inductance and wiring of the inductive circuit.

Abstract: An inverter drive circuit is disclosed wherein the inverter is a pulse width modulated inverter. The inverter includes a regulator circuit to regulate the width of the pulses which control the conduction of first and second controllable semiconductors in the inverter. The regulator is controlled by the output of the inverter in a feedback arrangement with a current limit circuit as well as an instant current limit to limit the output. A turn-on circuit is utilized to act through a drive transformer to turn on the controllable semiconductors as required. A turn-off circuit acts on the drive transformer and turns off the turn-on signal. A set and reset circuit is provided using first and second drive transformers for first and second controllable semiconductors in the inverter. One transformer is set in order to provide the turn-on and then this transformer is energized in the opposite direction to saturation to obtain a reset.

Abstract: An apparatus for providing simultaneously a multiplicity of independent non-interactive effects on the transmission characteristics of a voice-frequency telephone transmission line. Output voltage and current signal processing circuitry is provided which generates voltages for insertion in series with the line and currents for insertion in shunt with the line. Input voltage and current signal processing circuitry is also provided to sense the signal voltage across and the signal current through the transmission line and to generate a multiplicity of voltages and currents which are functions of the signal voltage and the signal current as well as of the voltages and currents fed back from the output signal processing circuitry to the input signal processing circuitry. A multiplicity of line conditioning control units couple the input signal processing circuitry to the output signal processing circuitry.

Abstract: An apparatus for generating a selected one of a plurality of ringing frequencies utilizing a single frequency source. A first counting means is utilized to divide the source frequency by a first predetermined integer to generate a series of address signals at a rate proportional to the selected ringing frequency. A read only memory is responsive to the address signals for generating a series of values representing points along a sine wave form such that, as the first counting means continuously cycles to a maximum count total equal to the number of values stored in the read only memory, the sine wave form is repetitively generated. If the source frequency is not an integer multiple of the selected frequency, the first integer is selected to generate the closest higher frequency and a second counting means is utilized to increase the time required for the first counting means to generate all of the address signals for one cycle of the sine wave form.

Abstract: A loop extender for adding a series-aiding boost voltage to a subscriber loop of a telephone system and having a d.c. boost voltage supply, an amplifier circiit having an active device connecting the voltage supply in series with a conductor of said loop for applying to the loop a magnitude of boost voltage that is dependent upon the gain of the amplifier circuit, and a further circuit, including a feedback for the amplifier circuit, for controlling the gain of said amplifier circuit in such a way that said gain is increased to cause an increase in the applied boost voltage in response to a rise in the magnitude of the loop current to a first predetermined threshold and/or in such a way that said gain is decreased to cause a decrease in the applied boost voltage in response to a decrease in the magnitude of the loop current to a second predetermined threshold.

Abstract: A circuit for varying the amplification afforded to a-c signals transmitted through a transmission line in accordance with the a-c losses of that transmission line. Gain control circuitry is provided which varies the magnitude of amplifying voltages and currents inserted into the transmission line in accordance with the a-c losses of that transmission line. The gain control circuitry is comprised of a line resistance sensor which establishes a control signal which is a function of the a-c losses of the transmission line. This control signal is applied to the remainder of the gain control circuitry to vary the magnitude of voltages and currents inserted into the transmission line in accordance with that control signal. As a result, the gain control circuit automatically adjusts the gain of a repeater in accordance with each transmission line connected thereto.

Abstract: A circuit for identifying which one of two parties has initiated a toll call. Circuitry connected to the subscriber drop of one party, e.g., the tip party of a two-party telephone line, generates a ground mark during the toll ticketing condition when that tip party has initiated a toll call. Loop current sensing circuitry senses the loop current flowing in the subscriber drop to the tip party. Voltage sensing circuitry senses the potential, with respect to ground, on each conductor of the telephone line. Switching circuitry applies a groundmark to the telephone line when loop current flow to the tip party has been interrupted and negative potential is applied to the tip conductor. Circuitry is also provided which prevents the application of a ground mark when a ringing voltage is applied to the line.

Abstract: A circuit for varying the amplification afforded to a-c signals transmitted through a transmission line in accordance with the length of that transmission line. Circuitry is provided which establishes a control signal which is a function of the a-c losses of the transmission line. This control signal is applied to an amplifying network which varies the amplification of signals transmitted through the transmission line in accordance with the magnitude of that control signal, and thereby automatically adjusts the repeater for operation with any transmission line to which it is connected.

Abstract: A circuit for varying the amplification afforded to a-c signals transmitted through a transmission line in accordance with the a-c losses of that transmission line. Gain control circuitry is provided which varies the magnitude of amplifying voltages and currents inserted into the transmission line in accordance with the a-c losses of that transmission line. The gain control circuitry is comprised of a line resistance sensor which establishes a contol signal which is a function of the a-c losses of the transmission line. This control signal is applied to the remainder of the gain control circuitry to vary the magnitude of voltages and currents inserted into the transmission line in accordance with that control signal. As a result, the gain control circuitry automatically adjusts the gain of a repeater in accordance with each transmission line connected thereto.

Abstract: A circuit for providing a regulated a-c or d-c output voltage from an unregulated a-c input voltage. A series inductance is connected between the regulator input and the regulator output to support the difference in voltage between the unregulated a-c input voltage and the regulated a-c or d-c output voltage. A controllable shunt reactance is connected to the source of input voltage, through the series inductance, to vary the current through and the voltage across the series inductance. Control circuitry controls the magnitude and the capacitive/inductive character of the current which the shunt reactance draws through the line inductance, as required, to establish and maintain the regulated output voltage at the desired output current.

Abstract: A circuit for varying the amplification afforded to a-c signals transmitted through a transmission line in accordance with the a-c losses of that transmission line. Gain control circuitry is provided which varies the magnitude of amplifying voltages and currents inserted into the transmission line in accordance with the a-c losses of that transmission line. The gain control circuitry is comprised of a line resistance sensor which establishes a control signal which is a function of the a-c losses of the transmission line. This control signal is applied to the remainder of the gain control circuitry to vary the magnitude of voltages and currents inserted into the transmission line in accordance with that control signal. As a result, the gain control circuitry automatically adjusts the gain of a repeater in accordance with each transmission line connected thereto.

Abstract: A circuit for varying the amplification afforded to a-c signals transmitted through a transmission line in accordance with the length of that transmission line. Circuitry is provided which establishes a control signal which is a function of the a-c losses of the transmission line. This control signal is applied to an amplifying network which varies the amplification of signals transmitted through the transmission line in accordance with the magnitude of that control signal, and thereby automatically adjusts the repeater for operation with any transmission line to which it is connected.

Abstract: A circuit for providing a regulated a-c or d-c output voltage from an unregulated a-c input voltage. A series inductance is connected between the regulator input and the regulator output to support the difference in voltage between the unregulated a-c input voltage and the regulated a-c or d-c output voltage. A controllable shunt reactance is connected to the source of input voltage, through the series inductance, to vary the current through and the voltage across the series inductance. Control circuitry controls the magnitude of the current which the shunt reactance draws through the line inductance, as required, to establish and maintain the regulated output voltage at the desired output current.

Abstract: A circuit for reducing or eliminating the effect of the stray capacitance of the windings of a transformer on signals coupled through that transformer. Circuitry is provided for generating voltages and currents which simulate the presence of a negative capacitance and for coupling those voltages and currents to a transformer in cancelling relationships to the stray capacitance thereof. Circuitry is also provided for imposing an upper frequency limit beyond which capacitance cancellation will not occur. The upper frequency limit stabilizes the circuitry and allows signal transmission to be limited to a predetermined desired band of frequencies.