Abstract: A protective handset cord cover is secured around a handset cord to prevent the handset cord from becoming tangled with itself. The cover is of sufficient length to accommodate a normal and customary stretched length of the handset cord so that the handset cord is prevented from twisting upon itself and becoming entangled. The cover is of a flexible, planar material and is easily placed around a handset cord. The cover is particularly suited for use with handset cords having modular ends which are removable from a phone base at one end and from a handset at the other end or, in an alternate embodiment, for use with older model telephones or car phones in which the handset cord is permanently secured to the phone base at one end and to the handset at the other end.

Abstract: An adaptive compensator circuit is provided which includes a first echo compensator, responsive to data signals from the transmitter, for providing a first compensation signal for compensating an echo signal component which is linearly related to the digital signals to be transmitted. A second echo compensator, responsive to both the first compensation signal and the corrected received signal provides a second compensation signal for compensating the nonlinear echo signal component. An adder, responsive to the first and second echo compensation signals, provides a summed compensation signal. The data signals from the receiver are corrected by means of the summed compensation signal. In another embodiment, the second echo compensator is responsive to both the corrected received signal and the current symbol being transmitted by the transmitter and the (N-1) preceding symbols.

Abstract: A security device for a telephone instrument including a separate handset to prevent full access to the telephone dial or push-buttons but allow unobstructed access to the handset. The instrument is placed between base and cover portions of the device to partially enclose the instrument and block access to the dial or push buttons to prevent outgoing calls, which portions may be releasably locked together with a locking device.

Abstract: An echo canceller in a modem cancels echoes from hybrid transformers on both the near end and the far end. The echo canceller has a variable delay which may be adjusted to conform to a round trip of an echo. An adaptive filter has a number of delay circuits, each adding an increment of delay. A number of these delay circuits are selected in order to provide a selected delay time.

Abstract: A handset for use with a key pad wherein the body of the handset is provided with one or more apertures which are adapted to permit access to one or more keys of the key pad when the handset is brought to a position proximate to the key pad.

Abstract: A voice signal compression system wherein the compression threshold may be adjusted to a calibrated level. The system includes a variable gain amplifier for amplifying a voice input signal based on the application of a variable control voltage. A driver increases the power gain of the amplified input signal to provide a power-boosted output signal. In addition to applying the power-boosted output signal to an acoustic output transducer, the power-boosted output is also applied both to a peak detecting comparator and to a threshold reset timer. The comparator produces a digital output that triggers an attack/decay timing generator which produces the control voltage for the variable gain amplifier. The comparator initially is set to a high threshold state by the threshold reset timer. As the levels and peaks of the input signal increase, the comparator begins to trigger digital pulses to the attack/decay timer.

Abstract: An echo canceller circuit contains a network of capacitors binary-stepped in their capacitance, whose one set of plates, representing a center of the network, each are switchably connectable to a reference potential or, in the case of less significant bits of digital information to be converted, to ground potential, or to a fraction (U3, U4) of the reference potential. To avoid difficulties which might result from the offset voltage of an integrated operational amplifier (V) connected to the capacitor network, the network is composed of two symmetrical halves (COo' to C32o; COn' to 32n).

Abstract: The present invention provides a technique for data detection signal processing for removing echo interference and/or distortion from a received 2B1Q coded signal. According to the preferred technique, the received 2B1Q signal Q, where q=(-3, -1, +1, +3), is shifted one bit to the left to generate a corresponding shifted symbol alphabet S, where S=(-2, 0, +2, +4). The shifted received signals are then processed through a transversal filter. That is, the signal is provided to a delay line which is tapped at intervals corresponding to the symbol width of the received signal. Each tap along the delay line is connected through an amplifier to a summing device that provides an output y(n), where ##EQU1## The tap gains, or coefficients a.sub.j, are set to subtract the effects of interference from symbols that are adjacent in time to the desired symbol. In an adaptive embodiment of the invention, the output y(n) resulting from the convolution between the transmitted symbols s(n) and the gain coefficients a.sub.j.

Abstract: A circuit is described for recognition of two-tone compound signals of two frequency ranges (F1 to F4, F5 to F8) in telephone installations with a limited transmission band width. Band pass filters (11, 12) whose output signals are added up and weighted individually are provided in a number corresponding to the number of possible single tones. The weighted output signals are each compared with the output signal sum of one of two frequency ranges (F1 to F4, F5 to F8 ) in order to signal a valid single tone. To increase the certainty of speech, another summand (Su, So) that is derived from a summation of the output signals of at least two other band pass filters (13) whose mid-band frequencies (F9 to F11) are outside the two frequency ranges (F1 to F4, F5 to F8) is also sent to the summation circuit.

Abstract: An adaptive transversal filter is characterized by a first adaptive filter for generating a plurality of estimated impulse response coefficients representing an impulse response of a transmission path. An averaging circuit is coupled with the first adaptive filter, and generates a plurality of average estimated impulse response coefficients having values in accordance with the average values over a most recent time interval of associated ones of the estimated impulse response coefficients, and a second adaptive filter receives the average estimated coefficients. The average estimated impulse response coefficients more closely represent and have less variance with respect to the actual impulse response of the transmission path than do the estimated coefficients, and the second filter generates an estimate of an echo signal through a process including convolution of the average estimated coefficients and an input signal.

Abstract: A circuit compensating for the attenuation caused on a line by an LS series type notch filter at frequencies less than the filter cut-off frequency, with such filter connected across said line and a reference voltage, includes a first resistor (R) in series on the line, a series circuit comprising a capacitor (C1) and a second resistor (R1) connected across the line and reference voltage, the capacitor being connected on the side of a first terminal of the first resistor, and an amplifier, the input of which is connected to the connection point of a capacitor and second resistor and the output of which is connected to the second terminal of the first resistor, such amplifier having a transconductance at said lower frequencies capable of ensuring the injection of a current equal to the sum of currents deviated by the series circuit and the filter.

Abstract: Retrofit apparatus for being mounted on a telephone terminal block previously mounted at a subscriber's premises and for providing a demarcation point at the telephone terminal block between an incoming telephone line and a subscriber premises line previously connected through first terminal means provided on the telephone terminal block, including telephone jack means for being connected to the first terminal means; second terminal means for being connected to the subscriber premises line upon the subscriber premises line being disconnected from the incoming telephone line; and telephone plug means connected to the second terminal means and for being plugged into the telephone jack means to interconnect the incoming telephone line and the subscriber premises line and for being unplugged from the telephone jack means to provide the demarcation point and permit the plug of an operating telephone to be plugged into the telephone jack means to facilitate determination of whether a fault exists on the incoming te

Abstract: A double talk detector for echo cancellers monitors the ratio of four wire transmit in energy to transmit out energy (ERLE), along with the change and direction of change of an estimated impulse response, to control updating of the estimated inpulse response. When the ERLE is low and the directional change of the impulse response is high, indicating an end path switch, the double talk detector enables the estimated impulse response to be updated. If the directional change of the impulse response and the ERLE are both low, indicating the occurrence of double talk, the detector inhibits updating of the impulse response until either the ERLE becomes sufficiently high, indicating single talk, or the directional change of the impulse response becomes sufficiently large, indicating an inconverged state of the canceller. The arrangement allows convergence of the echo canceller to be properly controlled both in response to double talk and to changes in the impulse response of the end path.

Abstract: A customer inquiry unit that allows the recognition of human speech in the presence of an initial prerecorded message transmitted by the customer inquiry unit via a telephone network. The customer inquiry system is designed to be utilized to respond to inquiries received via the telephone network. The system functions by responding to a telephone call received via the network to transmit an initial speech message to the customer. Due to a variety of network problems, a portion of the speech energy of the message is reflected back to the inquiry system. This reflected energy is commonly referred to as an echo. If the customer starts to speak before the inquiry system has finished the initial message, the system utilizes an echo canceler to remove the echo received back from the telephone network and only transfers the speech response to a recognition subsystem. The echo canceler adapts to the telephone network during the initial portion of the initial speech message before the customer can respond.

Abstract: A telephone subscriber circuit of a telephone exchange comprising active circuit elements with a capacitively-complex input impednace, wherein the signal which is to be transmitted from the exchange to the subscriber is amplified by two operational amplifiers operating in push-pull and is fed via two coupling arms, formed by a series arrangement of a capacitor and a resistor, into the subscriber loop which is itself supplied with d.c. current via two supply resistors. The subscriber circuit in accordance with the invention serves as a compensation network which directionally isolates the signals of the two speech directions and which includes two arms via which the symmetrical subscriber signal is supplied to a subscriber amplifier. In accordance with the invention the entire complex input impedance is sub-divided into a complex and a real component. The complex component serves as a coupling arm which supplies the LF-signal which is to be transmitted and which blocks the d.c.

Abstract: A network interface device and enclosure adapted to interconnect incoming telephone wiring to subscriber premises wiring. The device, according to one embodiment, comprises first electrical terminals adapted to be connected to the subscriber premises wiring, second electrical terminals adapted to be connected to the incoming telephone wiring, a removable module disposed between the first and second electrical terminals, the module having space for a telephone circuit and the module having electrical connections for connecting the module with the second terminal; a cable coupled to the first terminals, the cable including a plug at an end of the cable distant from the first terminals, and a jack located on the module adapted to receive the plug, the jack being electrically coupled to the electrical connections for connecting the module with the second terminal.

Abstract: The present invention provides a power drive circuit which is transformer isolated from the circuit developing the drive signals, but which does not lose its DC reference voltage. This technique results in the desired isolation without the undesirable possibility of operating the output transistors in an unsafe DC region, which is a particular problem when the output transistors are FET devices. In accordance with the present invention, pulse transformers are used to drive the power FET devices.

Abstract: A so-called switching voltage regulator for an interface circuit in a telephone subscriber line, being of a type adapted to control the on/off states of an electronic switch, connected to the interface circuit and consisting of first and second transistors interconnected into a Darlington arrangement, comprises an ON-state sensor connected as an input to the collector of the first transistor and an OFF-state sensor connected as an input to the base of the first transistor, and a pair of current extractor devices respectively associated with the related bases of the first and second transistors. Also provided are first and second current sources, each connected to a corresponding current amplifier. The first of the amplifiers powers both current extractor devices. The second amplifier and a third current source are connected to the base of the second transistor.

Abstract: The disclosure relates to a headphone-convertible telephone hand set which can be converted into a headphone-like telephone and produce double-form or stereo-like sound in its receiver, thus permitting the present telephone to be worn on a user's head to free the user's hands as well as to improve the normal function with increased clarity.

Abstract: A circuit for implementing a connection of an operational amplifier, and for achieving the switchable sensitivity of the same, as well as the in-and-out switchable filter elements, which results in a low cost, universally applicable line circuit interconnect circuit.