Abstract: An Automatic Gain Control (AGC) circuit which compensates receiving sensitivity on the part of subscribers depending on the line status of a central office line (C.O.L.) in a private branch exchange (PBX), by means of using an analog system, utterly.

Abstract: Particularly though not exclusively for use in voice communication equipment concerned with voice storage and playback along telephone lines and having the extended networking facility for host computer-controlled direct connection between callers on a pair of lines, a method of and apparatus for improving voice quality in such a connection involving sensing the origination of voice on one of the lines and thereupon reducing signal attenuation between the lines to enable amplified gain transmission from that line to the other line of the pair, while increasing signal attenuation between the lines in the opposite direction to suppress signal communication in such opposite direction; and vice versa, when the voice signal originates on the other line.

Abstract: An enhanced amplifier for interconnecting a two-wire, bidirectional cable side transmission path and a two-wire bidirectional equipment side transmission path in a communication system includes a first hybrid splitter and a second hybrid splitter. The first hybrid splitter is formed of a cable-to-equipment voltage sense amplifier, a shunt current driver, and a series current compensator for generating a first simulated terminating impedance. The second splitter is formed of an equipment-to-cable voltage sense amplifier, the shunt current driver and the series current compensator for generating a second simulated terminating impedance. Other features disclosed include automatic gain adjustment circuitry for automatically setting the gain in gain/equalizer circuits to a fixed level. Further, auto-balancing circuitry is provided for adjusting automatically and continuously both equipment and cable side balance networks.

Abstract: A key telephone system comprised of a key service unit connected to a plurality of local sets via four-wire conductors for providing full duplex signal communication between the key service unit and sets. Signals are carried by a first pair of each of the conductors for unidirectional transmission of signals from each set to the key service unit, and the remaining pair of conductors carries signals transmitted by the key service unit for reception by one or more of the sets. Four-to-two wire signal conversion and line impedance balancing is effected by one or more trunk circuits of the key service unit in the event one or more of the local sets are connected via the key service unit for communication between the sets and the outside telephone lines.

Abstract: Circuits embodying the invention include apparatus for sensing the amplitude and the frequency of the signals received from one section of a telephone cable and for propagating onto the succeeding section of telephone cable only those received signals having an amplitude greater than a predetermined level and whose frequency is within the predetermined range.

Abstract: The present invention is a method and apparatus for implementing a two stage AGC circuit. In the preferred embodiment, the present invention is used as part of a receive channel in a modem. The first stage of the AGC is a "coarse" AGC and is used to track large signal transients of an input signal. The coarse AGC locks on to transient signals without excessive settling time. In operation, the coarse AGC acquires a new signal by using a nonlinear clipped feedback loop technique supported by a linearized feedback loop. The coarse AGC stage uses an error signal derived from the noncoherent power fluctuations of the incoming signal. The second stage of the AGC circuit is a "fine" AGC using a decision-directed coherent amplitude error signal and a quick linear feedback loop to correct for finer signal level fluctuations. The fine AGC has a high pass characteristic which decouples its response from that of the equalizer for stability reasons.

Abstract: The invention relates to a method for the gain control of an intermediate amplifier used in two-wire connections of a dial telephone network. The invention is also concerned with an intermediate amplifier used in such connections, the direction of the gain of the amplifier being controlled in accordance with the signal strength. The method comprises measuring the amplitudes of signals coming from different transmission directions, comparing the measured amplitudes of signals coming from different directions with each other, and controlling the gain of controllable amplifiers (12, 22) on the basis of the difference value of the amplitudes by applying a control voltage to the controllable amplifiers (12, 22) through reversephase control adapters (13, 23).

Abstract: Direct relay equipment includes a first antenna, a second antenna, an up direction circuit connected from the first antenna via a first circulator to the second antenna via a second circulator, and a down direction circuit connected from the second antenna via the second circulator to the first antenna via the first circulator. In the up direction circuit and the down direction circuit, the received signal having a frequency f.sub.1 from the first (or second) antenna is amplified by a microwave amplifier, the output of the microwave amplifier is converted to a signal having a frequency f.sub.2 (sending frequency), the signal having the frequency f.sub.2 is amplified by the same amplifier, and the amplified signal having a frequency f.sub.2 is sent from the second (or first) antenna.

Abstract: A typical active impedance line feed circuit includes tip and ring amplifiers being controlled in response to signals at tip and ring voltage taps by control circuit to exhibit a.c. impedance and d.c. resistance characteristics for the purpose of supplying energizing current via tip and ring terminals for tip and ring leads of a two wire communication line. In one example of the active impedance line feed circuit, improved operational tolerance of longitudinal interference and of a ground fault condition is provided by a d.c. amplifier being responsive to voltages at the tip and ring terminals. The circuit is characterized in that an inverting input of the d.c. amplifier is connected via resistors to the tip and ring voltage taps. In operation, the d.c.

Abstract: A DC control loop is disclosed which is used in conjunction with a control circuit to precisely set the maximum control voltage produced by the control circuit for maximizing the gain of an attenuator controlled thereby. The attenuator includes a current mirror having an output for sourcing a DC current the magnitude of which is proportional to the gain of the attenuator and the control circuit includes a capacitor that is charged or discharged accordingly to vary the magnitude of the control voltage. The DC control loop includes a circuit for sinking the current supplied from the current mirror and a current of a predetermined magnitude, the circuit being coupled to the output of the current mirror and a transistor which is turned on when the magnitude of the current from the current mirror equals the magnitude of the current sank by the circuit to inhibit further charge or discharge of the capacitor whereby the gain of the attenuator is held at a predetermined maximum value.

Abstract: A transformerless hybrid circuit arrangement for a subscriber line interface circuit of a telecommunications exchange is disclosed. A preferred embodiment of the hybrid arrangement comprises a first and a second operational amplifier plus a differential amplifier connected together in the following manner: The non-inverting input of the first operational amplifier is connected to a first reference voltage and the output of this amplifier is connected (1) via a first resistor to one wire of the two-wire subscriber line, and (2) via a third resistor to the inverting input of the amplifier. The non-inverting input of the second operational amplifier is connected to a second reference voltage and to the receiving branch of the four-wire line of the telecommunications exchange.