Gte Automatic Electric Laboratories Incorporated

Gte Communication Systems Corporation

Gte Automatic Electric Incorporated

Gte Communications Products Corporation

Gte Communication Products Corporation

Tom L Blackburn

Otto G Wisotzky

David J Farrell

Method and apparatus is disclosed for identifying faults in a subscriber carrier telephone system utilizing out-of-band pilot signals and comprising pluralities of cables and repeaters that are alternately connected in series between carrier equipment at a central office location and a subscriber station. Equipment at the office location transmits selected numbers of test pulses, having a test frequency that is between the transmitted and received channel and pilot frequencies, to the first cable. The pulses are detected at the first repeater and counted. A microprocessor is responsive to the test pulse count in the repeater for initiating associated tests on the cable and/or repeater, or for retransmitting test pulses on the next cable to the next repeater for causing it it perform designated tests. The results of the tests are sent to the office equipment in the form of reply pulses having a frequency that is below the lowest channel frequency.

Method for locating faults in a carrier subscriber communication system

Method and apparatus is disclosed for identifying faults in a subscriber carrier telephone system utilizing out-of-band pilot signals and comprising pluralities of cables and repeaters that are alternately connected in series between carrier equipment at a central office location and a subscriber station. Equipment at the office location transmits selected numbers of test pulses, having a test frequency that is between the transmitted and received channel and pilot frequencies, to the first cable. The pulses are detected at the first repeater and counted. A microprocessor is responsive to the test pulse count in the repeater for initiating associated tests on the cable and/or repeater, or for retransmitting test pulses onto the next cable to the next repeater for causing it to perform designated tests. The results of the tests are sent to the office equipment in the form of reply pulses having a frequency that is below the lowest channel frequency.

Apparatus for locating faults in a carrier subscriber communication

Method and apparatus is disclosed for identifying faults in a subscriber carrier telephone system utilizing out-of-band pilot signals and comprising pluralities of cables and repeaters that are alternately connected in series between carrier equipment at a central office location and a subscriber station. Equipment at the office location transmits selected numbers of test pulses, having a test frequency that is between the transmitted and received channel and pilot frequencies, to the first cable. The pulses are detected at the first repeater and counted. A microprocessor is responsive to the test pulse count in the repeater for initiating associated tests on the cable and/or the repeater, or for retransmitting test pulses on the next cable to the next repeater for causing it it perform designated tests. The results of the tests are sent to the office equipment in the form of reply pulses having a frequency that is below the lowest channel frequency.

Repeater for carrier subscriber communication system

A microprocessor controller converts one or more sensor signals to a time multiplexed digital signal which is converted to an analog voltage signal by a digital-to-analog converter. A switching circuit, under the control of the microprocessor, selectively applies the analog signal to a plurality of current sources thereby setting the output current from each current source.

Apparatus for controlling a plurality of current sources

An FDM subscriber carrier system with two pilots located adjacent the upper and lower ends of the high frequency band uses the detected pilot levels at a repeater to adjust the gain and slope amplifiers in both directions of transmission. A microprocessor, programmed to identify the cable transmission characteristics, uses status signals derived from the two detected pilots to produce control signals to adjust and optimize the gain and slope settings of line amplifiers.

Analog subscriber carrier system repeater with automatic gain and slope

An FDM subscriber carrier system with two pilots located adjacent the upper and lower ends of the high frequency band uses the detected pilot levels at a remote terminal to adjust the gain and slope amplifiers in both directions of transmission. A microprocessor, programmed to identify the cable transmission characteristics, uses status signals derived from the two detected pilots to produce control signals to adjust and optimize the gain and slope settings of line amplifiers.

Analog subscriber carrier system terminal with automatic gain and slope

A signal detection circuit having a balanced modem is described. A switching circuit responsive to a selected linear input signal provides a square wave having the same frequency as the linear input signal. The modem, using a DC bias provided from the square-wave signal, is responsive to the square wave and linear input signals for providing a DC output having a magnitude proportional to the magnitude of the selected linear input signal.

Signal detector apparatus

A resistor and diode means are electrically connected in series between nodes A and B on the base electrodes of first and second transistors of a differential amplifier. These nodes A & B are also connected to a source of temperature-compensated load-sensitive reference voltage and to a tap point, respectively, that senses current in the loop of a carrier-serviced subscriber's telephone set. The base and emitter of a control transistor are also connected to associated nodes A and B. Conduction of the diode means and control transistor prebiases the latter and reduces the reference voltage during an on-hook condition. When the handset goes off-hook, the node B voltage rises faster than that on node A for decreasing the conduction rate of the control transistor to indicate an off-hook condition, and eventually cutting off the control transistor prior to the diode means. This operation of the diode means extends the loop length over which the circuit will detect an off-hook condition. With the diode means cut off, the second transistors collector voltage biases an FET in the loop for varying the resistance thereof and making the loop current a prescribed value for loop lengths that are less than a limiting value.

Carrier subscriber telephone off-hook detector

A DC control current is developed in a first transistor circuit and the control current is responsive to a control voltage which is proportional to the output voltage of a fixed gain amplifier. A reference voltage is applied to a second transistor which provides the normal operating bias for said fixed gain amplifier, and, also, provides a variable impedance via the diode circuit of the base-emitter junction. This diode circuit is a part of a variolossor that also includes a resistor which is connected in the series path between the signal source and the fixed gain amplifier. The bias voltage of the second transistor does not change but the diode impedance varies as the control voltage varies so as to maintain the amplifier output constant.

Variolosser for an automatic gain control circuit

An integrated current source comprising a discrete resistor having one side thereof electrically connected through a PNP transistor to a first DC supply voltage and through series connected base-emitter diodes of a first pair of NPN transistors to a temperature stable DC supply voltage. The other side of the resistor is electrically connected to ground through series connected base-emitter junctions of a second pair of NPN transistors, with the base emitter junctions of the first and second transistor pairs being poled in opposite directions. The NPN transistors are caused to have collector currents that make the base-emitter junction voltages cancel on opposite sides of the resistor. This causes the temperature stable supply voltage to be established across the resistor in order to set a reference current in it, and in an NPN transistor driving the load, that is substantially constant and independent of temperature.

Temperature compensated current source

A regulating amplifier circuit with each transistor of a differentially connected pair thereof having a base electrode connected through an associated varistor to a first control transistor, the series combination of each varistor and the control transistor being driven by a variable DC bias voltage. The first control transistor is responsive to a gain control voltage for varying its conduction rate through the varistors and thus the gain of the circuit. A first resistor, the primary conduction path of a second control transistor, and a second resistor are electrically connected in series between a fixed DC supply voltage and a ground reference potential, with the second transistors collector voltage being coupled through an emitter follower as the bias voltage. Negative feedback of the first control transistors collector voltage to the second control transistors base electrode causes the magnitude of the bias voltage to vary for maintaining the first control transistor operating out of the saturation region over an extended range of input signal levels.

Method and apparatus of controlling bias voltage in regulating amplifiers

A first network can be switched into and out of connection with a lowpass filter disposed at one of the two opposite carrier terminal ends of a loop transmission path employing a double-sideband carrier. When the filter and network are so connected, an oscillator producing a first test signal of selected frequency and amplitude is formed. This signal modulates the carrier wave generated by the existing carrier oscillator at this terminal end. The modulated signal passes along the path to the opposite terminal end where it is demodulated and detected. The detector threshold is set so that the detector responds to the demodulated first test signal, but does not respond to normal voice and other test signals. The detected demodulated signal energizes the station carrier oscillator at the opposite end whereby its carrier wave is modulated. The resultant second modulated test signal passes back along the path to the original terminal where it is demodulated, and the presence of the carrier is detected. The amplitude of the demodulated signal also may be measured and compared to that of the original test signal to establish the loss in the transmission path.

Apparatus and method for remote testing of a loop transmission path

An AC input signal and a DC supply voltage are applied to a tapped coil having end points from which differential input signals are coupled to a differential variolosser that controls the gain of cascaded differential amplifiers. The two output terminals of the cascaded amplifiers are electrically connected together through a pair of equal valued resistors to provide a DC reference voltage at the junction of the two resistors, where the AC signals cancel. The reference voltage is coupled to one side of a high-gain differential control amplifier and to both sides of a differential half-wave rectifier circuit. One side of the rectifier is also connected to one output of the cascaded amplifiers for detecting an amplified signal there. The detected signal is integrated and coupled to the other side of the control amplifier to produce the control signal which regulates the drive current to and loss presented by the variolosser, and thus the level of the input signals to the cascaded amplifiers.

Regulating amplifier

Gain control circuits in the base and emitter circuits of a common-emitter transistor amplifier stage each include pluralities of resistors and electrically conductive screw-type switches which are connected together such that the net changes in decibel values of gain provided by closing individual switches are cumulative. Resistors in the emitter gain control circuit are electrically connected in parallel with the emitter resistor in the AC equivalent of the amplifier in various configurations by closing screw switches to decrease the effective emitter resistance and thereby increase the decibel value of amplifier gain in steps of prescribed magnitudes. The switches are selectively closed in a prescribed manner to provide step changes in the decibel value of the net gain of the stage in discrete consecutive steps of the same magnitude. Transistor amplifiers with emitter gain control circuits may be connected in series to provide additional steps and range of voltage gain.

Transistor amplifier stage with selectively adjustable gain control

Gain control circuits associated with the base and emitter electrodes of a common-emitter transistor amplifier stage include pluralities of electrically conductive screw-type switches and resistors. The net gains provided by the associated gain control circuits are cumulative and determine the net gain of the stage. The gain changes provided by individual switches of the base and emitter gain control circuits are also cumulative, the switches being selectively closed in a prescribed manner to provide step changes in the decibel value of the net gain of the stage in discrete steps of the same magnitude. A plurality of transistor amplifiers with associated emitter gain control circuits may be connected in series, with the decibel values of voltage gains thereof also being additive, to provide additional steps and range of voltage gain. Series resistors in the base gain control circuit are selectively short-circuited by screw switches to decrease the input resistance of the amplifier stage. A bridging resistor is selectively connected across certain of the series resistors by one of these screw switches for causing the associated step change in the input impedance of the stage to be more nearly equal to the desired value. Resistors in the emitter gain control circuit are electrically connected in parallel with the emitter resistor in the AC circuit equivalent of the amplifier in various configurations by screw switches to decrease the effective emitter resistance and thereby increase the decibel value of amplifier gain in steps of prescribed magnitude. The emitter gain control circuit may be AC coupled to the emitter resistor and the emitter electrode of the amplifier. Alternatively, one side of this gain circuit may be directly electrically connected to the emitter electrode. A resistive voltage divider network is then connected to the other end of this gain control circuit and across the positive and negative terminals of a source of bias voltage. The network resistors are selected to provide the same DC bias voltage on both sides of the emitter gain control circuit. This prevents DC current flowing through the emitter gain control circuit as the resistance thereof is changed and thereby maintains the DC bias level on the transistor constant. In this manner, the effective emitter resistance, and thus the amplifier gain, may be changed to any desired value without changing the operating point of the amplifier.

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San Jose, CA, United States of America

Tom L Blackburn