Abstract: A rotary dial signal processing circuit and an automatic selecting circuit for combining the rotary dial signal processing circuit with a Touch-Tone digital decoding system. The rotary dial signal processing circuit includes means to interpret line signals as to on/off hook condition, dial pulsing, and completion of a dial pulse sequence. This includes estimation of the time durations of specific signal levels. Thus, for a dial pulse the off-hook signal input goes low for 33-90 ms, causing an appropriate system response; there is no system change for a low input signal of less than 25 ms; a low input signal of over 95 ms is interpreted as on-hook, and causes reset; a high input signal of over 150 ms is interpreted as completion of the dial sequence (timeout). The rotary dial signalling processing circuit counts the sensed dial pulses and provides a 4-bit output code which is compatible with the Touch-Tone code.

Abstract: An automatic incoming telephone call sequencing system is disclosed for use with multiple incoming line key telephone instruments.

Abstract: In a two-wire bidirectional telephone transmission line, a power converter and a directional threshold detector form in combination an impedance transparent bilateral voice-signal controller which can supply stable voice-switched gain to a dominant signal originating from either direction and a simultaneous, equal loss to any signals propagating from the other direction without separating the respective signals.

Abstract: A logarithmic echo canceller is disclosed which simplifies the hardware of the canceller by (a) using a logarithmic format for both the sampled voice signal x.sub.i and the coefficient h.sub.i, (b) using sophisticated algorithms for performing the different computational tasks, and (c) using analog techniques for echo subtraction and error signal generation. The incoming signal is sampled in a sample and hold circuit. The sign of the sampled input signal is sensed and its absolute value is converted directly in a special analog-to-digital converter into an A-law companding code. The whole digitized sample x.sub.i is multiplexed and stored in a plurality of shift registers. An average or pseudo rms value of the samples is computed, and the samples are compared in a comparator with the stored average or pseudo rms value, and if the sample is greater than the average or pseudo rms value, a signal enables updating of the existing value of h.sub.i stored in the H-register.

Abstract: An electronic hybrid for coupling signals between two wire and four wire transmission circuits, and capable of meeting the operating requirements of practical telephone systems. The hybrid includes a pair of terminating impedances serially connected between the two wire port and the circuitry driving that port, the impedances being precisely matched and coupled to a.c. ground, thereby providing a hybrid with excellent longitudinal balance. Amplifiers driving the two wire port through the terminating impedance may be biased to couple a d.c. potential to the two wire line whereby the terminating impedances serve as battery feed resistors. Reverse signal recovery is provided by an amplifier differentially connected to the two wire port, achieving excellent longitudinal rejection and further allowing the amplifier to serve a supervisory function. Two of such hybrids, connected back to back, with amplification interposed therebetween, form an improved transformerless repeater.

Abstract: An echo cancelling system for multiplex circuits, in which an impulse response of an echo-path is obtained from signals at respective ends of the transmission path and the receiving path connected to the echo-path to produce an echo-path model, and in which a pseudo echo signal is then provided to subtract it from an echo signal of the echo-path thereby to cancel the echo signal.

Abstract: A control unit mounting and interconnecting apparatus for telephone desk sets is disclosed which includes a base member including a first plate portion for receiving a printed circuit board and configured to lie within and be supported by a metallic base of the telephone desk set. The base member also includes a second plate portion for supporting a control unit, such as one having a plurality of control keys, and a plurality of walls interconnecting the first plate portion and the second plate portion and defining a recess which slips over an upturned flange of the metallic base of the telephone desk set to maintain the base member in position when installed. Structure is provided in the base member for receiving a printed circuit interconnecting element, of flexible insulating material, which provides electrical interconnections between the control unit and the printed circuit board.

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 telecommunication system includes a plurality of information transmission lines of various length, through which information signals are transmitted, active filters coupled to the information transmission lines, and a switching network coupled with the lines through the active filters, for establishing various connections between the lines in response to subscriber connection requirements. The active filters are of the type whose gain can be controlled and the gain is controlled in response to the length of the line over which the signals are transmitted, whereby the transmission loss of the line is compensated.

Abstract: The circuit complexity of a closed-loop echo cancellation system for use in a two-way communication circuit is reduced by employing a second adjustable signal processing network of the transversal type positioned in the control loop to emulate the characteristic of a recursive adjustable signal processing network. The two signal processing networks in the control loop are adjusted simultaneously to effect echo cancellation. The second signal processing network compensates for the effect of transmission poles in the echo return path and reduces the duration of the impulse response of the echo return path significantly so that the first signal processing network in the control loop is greatly simplified. A third signal processing network of the recursive type is adjusted in accordance with the internal settings of the second network to perform signal processing inverse to that of the second network.

Abstract: An electronic key telephone line circuit is disclosed for controlling the hold and disconnect conditions with respect to associated telephone stations in response to transient signals generated upon on-hook to off-hook and off-hook to on-hook transitions of those stations. Due to the nature of the switchhook contacts, the tip and ring leads open before the A-lead opens. Since the disconnect condition is determined from a transient signal caused by the tip and ring lead opening together with an A-lead open, and since by its very nature the transient response of the tip and ring lead transition can be finished before the A-lead opens, timing is used to delay the transient signal to insure that the line circuit goes into the proper mode.

Abstract: A common control circuit is disclosed for controlling bypassing relays to disconnect telephone line auxiliary circuits from their respective lines preparatory to line testing or for other desired purposes. The control circuit responds to a bypass request signal applied to a line by operating an associated bypassing relay and by activating a timing circuit. The timing circuit and other circuitry cooperate to hold the bypassing relay operated for a time interval sufficient for fulfilling the purpose of the bypass. For serving a bypass request received while another request is being served, the appropriate bypassing relay is operated when the subsequent request is received and the timing circuit is reactivated to insure a sufficient test time for the subsequent request. All operated bypassing relays are held operated until the expiration of a time interval during which no new bypass requests are received.

Abstract: A telephone Range Extender with Gain (REG) is disclosed for extending the range of loop lengths over which telephone service can be provided. This is accomplished by providing voice frequency gain, a higher voltage talking battery, and supervisory and signaling circuitry for increasing the level of supervisory and signaling currents at the central office end.The range extender requires no adjustment for loops of different lengths. A .pi. configuration negative impedance amplifier includes an adjustable gain circuit responsive to the resistance of the connected loop to automatically adjust the gain of the amplifier to the length of the loop. At the same time, an impedance matching circuit is transformer-coupled to the loop. The frequency shaping of the negative resistance amplifier and the impedance matching network, when reflected through the transformer, provides acceptable impedance matching for a wide range of loop lengths and wire gauges.

Abstract: There is disclosed a circuit for generating tone signals from clocking signals present on each key telephone line circuit. The tone signals are transformer coupled onto the communication leads by an optional plug-in-board arrangement. In present installations music-on-hold is provided by connecting an external music source to each line card. There is also disclosed an arrangement for utilizing the optional plug-in-board to provide either tone-on-hold or music-on-hold by simply reversing a plug-in connector.

Abstract: Subscriber-interface elements of a telephone station set are combined in and on a swivel panel. In one embodiment which is useful in automobile radiotelephone applications, the panel is a sun visor and includes arrangements to hold the handset in place even when the panel is upside down and to draw the handset up against the panel if the handset should be dropped during or after a call. Control buttons are arranged on the panel close to the user and, in the automobile embodiment, on a portion of the panel which is closest to the driver's line of vision. A cable connecting various station set elements to a control processor and radio extends through a swivel axle for the panel for convenient access to automobile body passageways from the visor to other locations of the automobile.

Abstract: There is disclosed a circuit for providing various lamp signals to a line lamp of a key telephone station. The circuit is arranged with a single ac switch or triac for each line circuit. The triac is driven at the desired rate by a circuit which generates a series of phase-shifted digital zero crossing signals having the desired duty cycle rate. Advantage is taken of the fact that the triac only requires energization at the zero crossing of the ac signal.

Abstract: An improved Range Extender with Gain (REG) comprises a floating loop current detector, a new dial pulse reshaper and a new control logic circuit. The loop current detector is powered by means of a floating power supply which renders the detector insensitive to spurious common-mode subscriber loop currents. The dial pulse reshaper comprises logic gates with two feedback paths for regenerating minimum make and break periods. The control logic circuit for controlling the relays in the REG is an asynchronous logic circuit particularly designed to avoid conventional differentiation circuits and timing problems associated with Automatic Number Identification.

Abstract: A hybrid system utilizing a plurality of operational amplifiers provides for appropriate isolation of input and output signalling. A signal initially appearing at the incoming path of the four-wire line appears as a balanced signal at the two-wire input/output end of the system but is effectively canceled from appearing at the output path of the four-wire input/output end. A signal initially placed on the two wire input/output end of the system appears at the output of the four-wire input/output end but is effectively canceled from the input line of the four-wire input/output end. A direct current path for common battery supply of loop current, while maintaining line impedance match over the audio frequency bandwidth is maintained.

Abstract: The invention discloses a multiplex digital echo suppression system in which on each of the transmitting and receiving sides the PCM signal for each channel is converted into the parallel signal and also into the absolute value signal representing the absolute value of the PCM signal by eliminating the sign bit; thus converted signals are accumulated for a predetermined time in a transmitting-side and receiving side accumulators and then compared in a comparator so that the output is derived from the comparator when the accumulated signal in the transmitting-side accumulator is higher in level than the signal accumulated in the receiving-side accumulator; in response to the output signal from the comparator, a first timer is set to a first predetermined time during which the signal is derived from the first timer; when the signal level in the receiving-side accumulator is higher than a predetermined level of a threshold level comparator, the output is derived therefrom and applied to a second timer which in t

Abstract: A self-adjusting voice frequency repeater for subscriber loops of varying ohmic resistances utilizing a multiplier-divider arrangement is disclosed.