Abstract: Apparatus for reducing the susceptibility of line signal repeaters to induced currents includes a zener diode/diode stack which provides the line repeater with a constant voltage drop when the DC line current is above the minimum required bias current. When the DC input current plus an induced component from the line exceed the load requirements of the repeater, the excess current is conducted through a blocking diode to charge an energy storage device. But, when the DC input current and the induced component oppose each other, the energy stored in the energy storage device is used to supplement the input current to just maintain the required repeater voltage.

Abstract: Analyzer for monitoring the traffic of a group of trunks conveying decimal code signalling and dialling impulses and multifrequency code signalling and dialling signals. It comprises multifrequency signalling receivers in a number smaller than the trunks of the group which are connected to the trunks only during the time when the same convey multifrequency signals. As this time is variable according to the phase succession of the telephone call, means are provided for defining the last decimal code impulse before the beginning of multifrequency signalling which serves for connecting a multifrequency signalling receiver to the trunk and the last multifrequency code signal according to the call phase succession which serves for disconnecting the multifrequency signalling receiver from the trunk.

Abstract: A switching arrangement for telephone subsets having key-controlled selection units is described. The selection unit has three connection points and is replaceable. It includes a pulsing relay responsive to a pulse generator actuated by the selection keys. A bistable relay disables a speech circuit, and maintains a connection of a transmitting and feeding circuit extending through the selection unit.

Abstract: An electronic hybrid circuit for coupling a two-wire communication path with a four-wire communication path is disclosed wherein the use of transformer coupling is eliminated. The hybrid features a novel arrangement whereby the unbalanced four-wire path incoming voice signal is amplified, then converted to a pair of balanced signal components by complementary signal injection devices coupled to opposite sides of the two-wire path. Each resultant balanced component is injected in series with a DC battery feed potential via current amplifiers in each signal injection means. Balanced two-wire path output signals are converted for transmission to the outgoing portion of the four-wire path by coupling the two-wire path to the series combination of a differential amplifier and an output buffer amplifier.

Abstract: An off-premises line circuit is disclosed which allows two telephone stations separated by a distance greater than lamp range to share a common central office or PBX line. Lamp signals as well as hold release commands are exchanged between stations by a signaling pair of leads. The off-premises line circuit is arranged so that either station may release the hold condition without regard as to which station established that condition.

Abstract: An electronic replacement for a telephone transformer for connecting a two-wire circuit to a four-wire circuit comprises a first differential amplifier having a constant gain feedback loop. The feedback loop comprises an opto-electronic coupler and a second differential amplifier. A DC source connected to the first differential amplifier by a switch produces biasing current for a photo transistor in the opto-electronic coupler. A DC supply to the line on the two-wire side is provided by a source connected to the wires by transistor circuits connected as active reactances.

Abstract: There is disclosed an electronic key telephone line circuit having a communication path interface capable of being connected across the communication pair during both the busy and idle conditions of the line circuit. The circuit is arranged such that both the pre-ring test and the impedance test from the central switching machine are satisfied while at the same time presenting a linear impedance for communication signals. Opto isolators are used and coupled with lightning surge protection and a capacitance and resistance bridge to allow permanent connection across the communication pairs. The circuit includes a hold bridge impedance, separate from the signal detection circuitry, switchable across the communication path.

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 ouput 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 20 Hz threshold detector senses signals from the two-wire input/output 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 controlling multiple signalling sources within a key telephone system for the establishment of priorities. The circuit inhibits connection to, or permits disconnection of a secondary signal source from a selected amplifier whenever a primary signal source is connected to the same amplifier. Circuitry is also provided to indicate the disconnect condition.

Abstract: A test jack assembly for use on printed circuit cards in which two interlocking pieces of plastic material are employed to rigidly support and insulate a number of jack springs from each other and provide contact terminals whereby the entire assembly may be easily connected to a printed circuit board.

Abstract: Intended to give cost, size and possibly performance advantage over a conventional hybrid transformer arrangement, by using operational amplifiers with semiconductors. Typically the input and output at the 4-wire side are each unbalanced, and the 4-wire side input path involves a line driver comprising driver amplifiers for each conductor of the balanced 2-wire line. The driver amplifiers are operative over a resistor bridge network extending to the 2-wire line. Another pair of series-connected operational amplifiers constitute a common mode rejection receiver between the 2-wire line and the 4-wire output and are controlled from diagonals of said bridge. It is necessary to provide for cancellation of the coupling between the 4-wire incoming and outgoing paths, and this is effected by using a signal from the output of the inverting amplifier for disablement of the receiver.

Abstract: Within a key telephone system, there is provided a circuit for completing a direct signalling path from a first station to another station in the system. By depressing a button at the first station designated with identifying indicia of the other station, a direct speaking connection is made from the first station to the other station. The first station may be an attendant's position with direct key appearance for each station to which the attendant is to have direct access. In a preferred form, the called station has a loudspeaker associated with the station instrument. In this instance, a direct call results in a signalling tone directed to the loudspeaker, following which the attendant can converse with the speaker-equipped station. With an attendant's position, depression of a direct station key automatically places a line to which the attendant had been connected on hold.

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: Telephone dial mounting assemblies are disclosed wherein a uniquely constructed pair of resilient mounting elements, such as in the form of spring clips with bifurcated U-shaped leg sections, are secured to and interposed between the dial and associated support structure, permanently secured within a telephone housing, and having suitably dimensioned and positioned spring clip-receiving openings formed therein. Such a modular mounting assembly is not only of simplified, inexpensive and reliable construction, but advantageously allows dials of the same or different types to be rapidly and simply mounted within or removed from a telephone housing regardless of any differences either in the overall structural dimensions, or in the spacing or location of the attachment brackets or tabs, that may exist between alternative dials.

Abstract: An echo suppressor for use in the send path of the four-wire part of a long distance telephone circuit employs frequency-selective center clipping. The bandwidth of the channel in which echo occurs is subdivided in contiguous bands or subchannels by appropriate filtering, and each resulting signal is center clipped by a center clipper. Threshold control voltages are predicted from knowledge of the average speech amplitude distribution characteristic as a function of frequency. This characteristic is subdivided into the same frequency bands as that used by the center clippers, and the ratios of energies in the bands are used to equalize the ratios of the control voltages that determine the center clipper thresholds. This technique is implemented through the use of a peak rectifier, the input of which is coupled to the receive path of the echo suppressor and the output of which is connected to each of the filtered subchannels by a resistive dividing network.

Abstract: An asynchronous, regenerative, digital repeater for use in bipolar digital signalling systems includes an amplifier for receiving and amplifying incoming signals, a first monostable multivibrator for producing regenerated pulses responsively to the output of the amplifier, an output circuit for producing a bipolar pulse train responsively to the output of the multivibrator, and a second multivibrator for inhibiting the first multivibrator for a predetermined interval following the trailing edge of each output pulse to prevent the first multivibrator from responding to the electrical overshoot at the trailing edges of the incoming pulses.

Abstract: A common control digital echo suppressor is disclosed which is configurable as full or split selectively on a channel-by-channel basis. Improved break-in and reduced hangover are provided by an arrangement for approximating the anticipated echo signals more accurately and by a wait-window technique to better distinguish between impulse noise and speech for break-in. The echo signal arrangement accurately approximates anticipated echo during both the rising and falling portions of speech signals. The wait-window technique provides for substantially instantaneous break-in, then a short wait period for impulse noise to subside, followed by a speech sampling window. If outgoing signals are detected during the window, suppression removal goes into a full break-in state. Otherwise, suppression is reinserted at the end of the window.

Abstract: A maximum value tracing circuit employed in echo suppressors and the like for selecting the peak values of digitized voice signals. The digitized value of a signal previously stored in a register is continuously compared with the present digitized value. The larger value of the compared signals is stored in the register after application of each clear signal to the register.First and second maximum value tracing circuits of the type described may be employed in combination with a comparator-selector circuit for comparing the outputs of the first and second maximum value extraction circuits to produce a comparison output signal representative of the larger of the two compared outputs derived from the first and second maximum value extraction circuits, which output signal is utiized for providing reliable, high speed echo suppression.

Abstract: A negative impedance repeater for amplification in telephone lines operating at voice frequency comprises two converters, one of them stable with open terminals and the other stable with short-circuited terminals; each converter is loaded by a fixed network of passive impedances chosen according to the characteristic impedance of the line to be amplified, and provided with means, external to the network of passive impedances, for adjusting the feedback, and consequently the conversion ratio. The conversion ratios of the two converters may be varied independently from each other so that in the case of loaded lines their product may be kept always constant and this allows to adjust the repeater gain without modifying its impedance, while for unloaded lines it is possible to obtain that such product increases with a certain law by increasing gain, and this fact causes an equalization at the highest frequencies of the band, which is necessary for this type of lines.