Abstract: An adaptive control type echo suppressor which compares the levels of voice signals of sending and receiving paths by a first comparator with each other and cuts off the sending path to suppress an echo when the level of the voice signal of the receiving path is higher than the level of the voice signal of the sending path. A control loop is provided for applying the voice signal from the receiving path to a second comparator via a variable loss circuit for comparing the peak of the integrated value of the same with the peak level of the integrated value of the voice signal of the sending path to effect adaptive control of the variable loss circuit by the output of the second comparator in a manner to reduce the output of the second comparator to zero.

Abstract: Echo canceler for use in a data transmission system, comprising two and four-wire connections and arranged to suppress echo signals occurring in the four-wire connection. This echo canceler is provided with an adjustable signal processing device to which the data signal to be transmitted is applied and which produces a synthetic echo signal. A signal formed by a received data signal and an echo signal is present in the receive path of the four-wire connection. From the signals in the receive path there is now subtracted the synthetic echo signal, in order to generate a residual signal.To adjust the signal processing device an adjusting device is connected thereto to which a digital control signal is applied, which is constituted by a digital version of the residual signal.

Abstract: A combination automobile sun visor and radio and speaker assembly for use in automobiles and other motor vehicles, to be mounted above the windshield in place of a conventional sun visor. The assembly comprises a thin, flat, bidirectional speaker assembly enclosed within a layer of acoustically transparent material, a radio module having a tuner and amplifier mounted in the speaker assembly, and means for mounting the speaker assembly above the windshield. The radio and speaker assembly provides speaker placement which is superior to prior art automobile speakers and provides speakers which may be adjusted and which do not waste interior space.

Abstract: Three double talk detectors (DTD) are used in combination with an echo canceller having an adaptive filter and a center clipper. First and second double talk detectors are used in the presence of double talk to selectively freeze the adaptive filter correction loop and to disable the center clipper. The third double talk detector is used to detect the initial adaptive period of the echo canceller. Control of the adaptive filter and clipper is effectively transferred from the first to the second double talk detector upon termination of the initial adaptive period as determined by the third double talk detector. The third double talk detector also detects a false double talk condition (where the distant talker pauses in speech) and overrides the second double talk detector in order to maintain the clipper in an active state.

Abstract: An echo detector which is able to distinguish a speech signal echo on the outgoing channel without reference to the signal received at the incoming channel.

Abstract: A bilateral current source operates as a two-wire to four-wire converter circuit for an intercom system. The circuit provides a high impedance current driver for putting a local voice signal on the common line connecting the intercom stations. The same circuit acts as a buffer amplifier for connecting voice signals received on the same line to a listening device such as a speaker. The circuit suppresses any sidetones by preventing the local voice signal from being coupled to the listening device.

Abstract: A loop sensing circuit is coupled between a solid state hybrid circuit that provides signal conversion between a pair of unidirectional transmission paths and a bidirectional subscriber loop. The loop sensing circuit includes placing respective protection resistors coupled in parallel with first and second sensing resistors between the hybrid and the subscriber loop terminals to provide a dc current path between the bidirectional subscriber loop and the hybrid circuit.

Abstract: There is disclosed a two- to four-wire hybrid circuit of a telecommunication system. A line coupling circuit, preferably a transformer is connected to a terminal line. Between the coupling circuit and first and second amplifying means each assigned to a receiving branch and a transmitting branch of a transmission line, respectively there is arranged a balancing network composed of an attenuator, a first and a second hybrid impedance. The first impedance connected to the coupling circuit has a value matching the value of a coupled terminal line impedance which is effective at the four-wire side of the coupling circuit. The second impedance and the attenuator interconnect the outputs of the first amplifying means.

Abstract: An improved impedance canceller circuit, for use with two-wire transmission systems of the type encountered in telephony, is adapted to be interfaced with the wires and operates in a manner to effectively eliminate or cancel an unwanted impedance across the wires. The impedance canceller includes a current source, and essentially supplies on the wires all of the current that would otherwise be required by the unwanted impedance in response to a metallic voltage applied across the wires by a signal source, so that the signal source does not supply such current and the unwanted impedance appears as an open circuit to the metallic voltage. At the same time, the impedance canceller provides common mode rejection to longitudinal voltages on the wires.

Abstract: A wall telephone cradle assembly comprised of a housing having a cup shaped pocket on a front face thereof, arranged to hold a hand-held telephone instrument therein. Mounting structures located within the housing are disposed to mount the assembly to a two pin wall telephone receptacle plate.

Abstract: A telephone handset having a magnifying reading glass lens built into the housing along with an electric light bulb positioned to illuminate the field of view of the lens. The end of the handset housing opposite the cord is elongated to accommodate the lens and light bulb, and a pressure operated switch for controlling the light is also mounted in the handset housing. The light bulb is supplied with current via the switch by wires contained within the telephone cord or cable.

Abstract: A tone responsive disabling circuit for disabling prior to the transmission of data on a telephone transmission line a device which is connected to the line for improving voice transmission on the line. The disabling circuit operates in response to the transmission on the line of a tone signal whose frequency falls within a predetermined band width and which also has a predetermined amplitude and minimum duration. The disabling circuit processes the signal transmitted on the line to generate two control signals. One of the control signals is a function of the transmission line signal. The other is a function of the energy contained in the transmission line signal which lies in a predetermined frequency band which is not the tone frequency band. When the control signal which is a function of the transmission line signal is greater in amplitude than both a reference signal and the energy related control signal, a phase locked loop is enabled to capture the tone signal and disable the voice improving device.

Abstract: An artificial reverberation apparatus for audio frequency signals, comprises a first delay device preceded by an adder. A feedback circuit couples the output of the delay device to an input of the adder to give a loop signal gain of less than unity. The adder is preceded by a second delay device with the same delay time as said first-mentioned delay device. The signal to be delayed is applied to the input of said second delay device and also to the adder via a transmission path. The ratio of the signal gain of the transmission path to the signal gain of said second delay device is equal to but of opposite sign to said loop signal gain. Preferably the signal gain of the transmission path is equal to but of opposite sign to the signal gain of said feedback circuit. Furthermore, a plurality of apparatuses can be connected in cascade with the delay devices of the different apparatuses all having different delays.

Abstract: A wall mounting adaptor for a telephone set is arranged for attachment to a wall outlet, releasably latched thereto, and the telephone set releasably attached to the adaptor. The telephone set can be a set normally for use as a desk set and can be attached to and detached from the adaptor at will, leaving the adaptor in place. Provision is made for both a line cord and a power cord, and storage means can be provided for excess line cord.

Abstract: A hybrid circuit for coupling a two wire transmission path to a receive path and a transmit path of a four-wire transmission path comprises a receive port, a transmit port, and a two-wire port. The receive port is connected to a non-inverting input of a differential amplifier whose output is connected via a winding of a transformer to an impedance. The inverting input of amplifier is connected via a winding to the junction of winding and impedance. The transmit port is connected via a winding W3 to the junction of winding and impedance. The two wire port is connected to a winding on the transformer.Signals applied to the receive port are coupled to the two-wire port but produce voltages across the impedance and winding which cancel to the transmit port whereas signals applied to the two-wire port are transferred to the transmit port. The use of the amplifier enables a smaller transformer to be used.

Abstract: A hybrid circuit comprising a current amplifier connected between the receive path and the transmission path of a four-wire transmission path, the common output of the current amplifier being connected to a two-way transmission path and the balancing impedance and an impedance transformer being provided between the other end of either the balancing impedance or the two-way transmission path, which results in a simple hybrid circuit.

Abstract: Echo canceller for use in a homochronous data transmission system, comprising two-wire and four-wire connections and arranged for suppressing echo signals occurring in the four-wire connection. This echo canceller comprises an adjustable signal processing arrangement to which the data signal to be transmitted is applied and which produces a synthetic echo signal. A signal formed by a received data signal and an echo signal is present in the receive path of the four-wire connection. To generate a residual signal, the synthetic echo signal is subtracted from the signals in the receive path.For the adjustment of the signal processing arrangement there is added to this residual signal, outside the receive path of the four-wire connection, an auxiliary signal which is not correlated to this residual signal. The sum signal thus obtained is sampled with a suitably chosen sampling rate which is harmonically related to the symbol rate.

Abstract: An electronic hybrid voice frequency repeater having a pair of term sets interconnected by a four-wire circuit for separating the two directions of signal transmission and amplifying each direction separately. Each term set couples the repeater's four-wire circuit to a two-wire line and has a differential current driver for driving the two-wire line and a differential amplifier connected in a feedback loop for sensing the differential signal voltage across the two-wire line, to drive the current driver and to feed an incoming differential signal on the two-wire line to the repeater's four-wire circuit while nulling signals arriving at the term set from the four-wire circuit to prevent them from returning to the four-wire circuit. Other features disclosed include a low frequency clamping circuit, an adjustable-gain amplifier, and an equalizer for non-loaded cable.

Abstract: This invention relates to a loudspeaker protection device which disconnects the drive unit, or units, of the loudspeaker from an amplifier when the voltage across, or the current through, the drive unit, or one of the drive units, exceeds a predetermined level. The protection device includes a bistable device comprising a complementary pair of transistors arranged to be changed from the reset state to the set state when the voltage on an input terminal exceeds a predetermined level. The transistors are arranged to be both non-conductive when the device is in the reset state and both conductive when the device is in the set state. When the transistors are conductive, the collector current of one of them flows through the coil of an electromagnetic relay having normally closed contacts in the output circuit of the amplifier.

Abstract: A multi-station telephone communication system in which there is designated a master station and several other stations. Each of the stations is capable of communicating with any of a large number of standard telephone lines and non-locking pushbuttons are utilized to select the lines connected to each station. Each station is capable of monitoring the active line on which any of the other stations is communicating. Additionally, the master station is capable of supervising the conversation in any of the other stations by an ASSIST LOOP connection, in which the master station can overhear the conversation, but communicate one way with only one of the parties in the two-way communication. Each station is provided with a turret having panels in which are mounted their respective displays for indicating the active lines which are in communication with the respective turret as well as the lines in active communication with the other stations.