Abstract: Apparatus for providing auditory and tactile recognition of a light signal associated with a line-selector pushbutton of a multi-line telephone instrument. A photocell is provided for sensing the light signal. An oscillator generates a sine wave voltage which is amplified and applied to excite a piezoelectric crystal into vibration in response to activation of the photocell. An auxiliary pushbutton is disposed in alignment with the line selector pushbutton so that manual depression of the auxiliary pushbutton actuates the line selector pushbutton. Vibration of the crystal in response to the light signal acts upon the auxiliary pushbutton to impart the vibration thereto so that the presence of a light signal is sensed by vibration of the auxiliary pushbutton.

Abstract: A telephone set scanning type key telephone system, in which a plurality of key telephone sets are connected in parallel, to a key service unit through control lines composed of a display information line, key information line, a terminal selecting line and a clock line. Each key telephone set comprises a display memory, a key memory, a terminal coincidence circuit and a gate. The terminal coincidence circuit collates a selecting code transmitted thereto from the key service unit through the terminal selecting line and applies clock pulses transmitted thereto from the key service unit through the clock line to the gate to drive the display memory and the key memory only when the selecting code is coincident with the terminal number.

Abstract: Echo propagation is prevented on four-wire signaling path to two-wire signaling path connections. A first transmission path portion is extended from the receive leg of the four-wire signaling path to the transmit leg and a second transmission path portion is extended from this point to the two-wire signaling path, the first and second transmission path portions thereby forming a bidirectional path carrying signals from the two-wire signaling path and from the receive leg. Detection circuitry is located in the first transmission path portion and develops a voltage signal which determines the direction of signal transmission between the four-wire and two-wire signaling paths. Echo propagation is prevented during signal transmission from the four-wire signaling path to the two-wire signaling path by opening the transmit leg of the four-wire signaling path.

Abstract: A network has a transformer coupled open-circuit stable negative impedance. A positive impedance is included in the network as a shunt impedance, so as to thereby render the network both open-circuit stable as well as short-circuit stable.

Abstract: Signal transmission circuit characteristics are supplemented by a negative conductance circuit in which current sources of complementary polarity are connected in shunt between the conductors of the signal circuit. Changes in the voltage level of one side of the signal circuit are sensed at a point common to the two sources and applied through a positive impedance to control the current output magnitude of one of the sources for effecting a supplementing of the signal circuit current as though the changed voltage level had been applied in the presence of a negative form of that impedance connected at that common point.In additional embodiments, different, or variable, positive impedance are connected in the sensing circuit output coupling to cause the negative of such impedance to appear at such signal circuit terminal.

Abstract: Transmission system for transmitting signals modulating a carrier between two main stations via parallel coaxial lines the inner conductors and the non-earthed outer conductors of which are connected to the earthed main stations via capacitors. The main stations contain low-frequency signal sources which in parallel with direct-current supply sources are connected to the supply current loop for the repeaters included in the coaxial lines. The low-frequency cross-talk due to the low-frequency signals is suppressed by means of compensating circuits.

Abstract: A power amplifier for use in uni-directional telephone line signal amplification requirements on voice and data grade circuits includes a balanced input transformer and associated differential line transient protection circuit and line matching network, a balanced differential voltage feedback amplifier circuit with externally interchangeable, balanced, passive, terminated attenuators in the voltage feedback path for varying the amplification factor of the signal amplifying circuit, a balanced-to-unbalanced common mode rejection circuit, low and high cut frequency filters, and a balanced output transformer with associated output line matching and circuit protection components. The interchangeable attenuators are calibrated and marked in terms of overall power amplification resulting from their individual and specific use in the circuit.

Abstract: Transmission and signaling range of a telephone transmission line is extended by controllably inserting boost potentials into the line to series aid an applied central office battery. Insertion of the potentials is realized by sensing the direction of current flow in the line and switching a corresponding potential into the line. Optical isolators, each including a light emitting diode and phototransistor, are advantageously employed as line current sensors and switching elements. Insertion of boost potential into the line is controllably delayed in response to changes in the direction of current flow caused by apparent reversals in the polarity of the applied central office battery.

Abstract: Centering device for an adjustable transverse filter of a digital echo canceller in a telephone network, in which said transverse filter produces samples of a synthetic echo signal y (t) deduced from N servo-controlled weights C representing the samples of the pulse-response of the echo path and deduced from the same number of samples X (T) of a signal x (t) in the reception line, and in which the N samples X (T) are delayed in a delay circuit ahead of said transverse filter, the delay time being given by the minor rank of said coefficients C lying above a threshold value, this minor rank being detected at the end of given convergence time of said transverse filter.

Abstract: A large scale key-telephone system or telephone exchange system having approximately eighty extension channels and a push-button dial system has been disclosed. A common unit in the system is a DTMF oscillator, which is installed in each telephone set, according to a prior art. The present system is completely compatible with thus prior key-telephone system or exchange system.

Abstract: A nonlocking key telephone station is arranged to display full line status information when the station is on-hook and for normally illuminating only the key lamp associated with the line in use at the station when the set is off-hook. To permit a user to discern the full status of the lines terminating at the set when the set is off-hook, circuitry responsive to the depression of one of the keys at the station is provided for displaying full line status information.

Abstract: An automatic H-register clear system for the prevention of erroneous convolution in adaptive digital echo cancellers is disclosed. Incoming signals from the H-register are accumulated and compared to a predetermined threshold value and when the value is exceeded, the H-register is cleared with the occurrence of the internal housekeeping cycle of the echo canceller. The clearing of the H-register allows a new impulse response model to be generated from new sampled data. In one embodiment using analog implementation, the accumulation takes place using a sequence of signal processing of digital-to-analog conversion, full wave rectification followed by integration of the signal. In another preferred embodiment using a counter detection system, each word is compared to a threshold and if this value is exceeded, a counter is indexed. If the value of the count in the counter exceeds a predetermined number during the sampling interval, the H-register is cleared.

Abstract: A converter, for converting a dual-tone multi-frequency (DTMF) signal produced by a TOUCH-TONE telephone to a 2-out-of-7 coded representation of the "dialed" number, includes an oscillator having a frequency much higher than the frequencies of the tones, a high band circuit for high band tone frequencies, and a low band circuit for low band tone frequencies. Each circuit includes a filter for passing the respective band of tone frequencies from an input terminal, a limiter for translating a received tone sine wave passed by the filter to a corresponding square wave, a counter, a switch enabled by the square wave output of the limiter for coupling the output of the oscillator to the input of the counter during a cycle of the square wave from the limiter, and a decoder for translating the resulting count in the counter to a signal on an output line representing one of the tone frequencies.

Abstract: An attachment to key telephone system apparatus is disclosed which permits an intercom substation to access a trunk telephone line. This includes an intercom-to-trunk line access unit for coupling telephonic communications between its input and a selected one of a plurality of trunk lines connected to its output. The unit contains a selector, an advancing means and means responsive to at least one dial digit selection type signal at an input for advancing the selector to a trunk line directly or by means of a nonbusy trunk hunting mode of operation. Relay means are provided at a key service unit, responsive to operation of push button switch means at the selected intercom substation, for interrupting the communications circuits between the intercom substation and the intercom circuit in the key service unit and establishing the communication circuits between the intercom substation and the input of the intercom-to-trunk access unit.

Abstract: A double coil relay has one coil coupled between the ring conductor and ground and the other coil coupled between the tip conductor and a negative direct current voltage. The tip and ring conductors are coupled to telephone subsets external to the line circuit. The double coil relay lights subset busy lamps external of the line circuit when a subset is off-hook. A branched telephone circuit is also provided for voice signals in a normal conversation mode with another telephone subset external of the line circuit coupled to another line circuit identical to the present line circuit and a selecting paging mode. A second single coil relay is coupled to the double coil relay to provide the normal conversation mode and to select the paging mode with the single coil relay disabling the conversation mode when the paging mode is selected. The two relays are operated by power supply voltages and polarities present in a conventional key telephone system service unit external of the line circuit.

Abstract: An intercommunication link for a multiple link key telephone system with a combination lamp-button on each handset for each available link. In each link, a line seeking intercom service is sensed to operate a relay in the link selected. A lamp flash signal on the lamp of the selected link is initiated. In this condition, all other links are disabled and none can be accessed when one link is in the lamp flashing condition. The called local number of the desired intercom station is dialed and when the called station line is answered, a second relay in the selected link operates to release the first relay. On operation of the second relay, a steady lamp indication is sent to both stations in the conversation. Other free links may be accessed at this time. Thus, only during this intercom signaling phase are the remaining free links affected.

Abstract: A telephone intercommunication system where a plurality of stations have access to a plurality of lines. Each station has a pushbutton type keyset which is connectible to integrated circuits associated with each line and are utilized and generate signals for controlling central office switching equipment.

Abstract: The present invention relates to a device which is to be used in conjunction with key telephone systems, as for example, intercom systems. More particularly, the invention consists of a device for decoding the pulse output from rotary dial telephones, indicating which digit has been dialed and selectively signalling the called party. Special features include acceptance of a wide range of pulse speeds and ratios with decoding immunity to the initial hookswitch closure and the last opening. The latter permits the digit "1" to be used, providing for an additional signal function. A decoding matrix operates a relay tree with provisions for either single or two-digit codes. The device is intended for use in key telephone systems which include rotary dial telephones.

Abstract: In areas utilizing telephone switching equipment that will only accept dial pulses, a conversion unit, that fits into the space formerly occupied by the dialing mechanism in a standard telephone subscriber's unit, provides touch-pad dialing. The conversion unit accepts input signals, representing digits, from a standard 3 .times. 4 matrix touch-pad at an asynchronous rate and starts out-pulsing at the required pulse repetition rate as soon as the first digit signal is received. During each touch-pad button depression, an audio tone is supplied to the subscriber unit earpiece. The conversion unit provides for programmable toll restriction that permits selective prohibition of out-pulsing at each subscriber unit. At the instant a restricted input signal is received, the conversion unit provides a steady audio tone to the earpiece and stops out-pulsing. To prevent hookswitch dialing, the conversion unit extends the break period of the electronic pulsing switch.

Abstract: A self-balancing telephone-type hybrid having two sets of conjugate ports, wherein conjugacy is maintained between receiving and transmitting ports despite wide variations in impedance conditions at the line and/or balance ports. Included are means of differentiating between bridge unbalance due to impedance unbalance and that due to a signal being injected into the line port.