Network path test circuit

A test circuit for use in testing telephone call connections established through a switch network of a telephone switching office, said test circuit comprising

• means for generating a test tone signal,
• means for momentarily coupling said tone signal generating means simultaneously to both a transmit and receive path comprising one of the telephone call connections,
• means responsive to said tone signal generating means for measuring impedance reflected by the call connection transmit and receive paths into said coupling means, and
• means for enabling the telephone switching office to initiate establishment of another telephone call connection through the switch network when a predetermined value of the measured reflected impedance indicates a wire transposition in the call connection transmit and receive paths.

A test circuit for use in testing a telephone call connection established through a switch network of a telephone switching office from a four-wire incoming trunk to a two-wire outgoing hybrid trunk, said test circuit comprising

• generator means for generating a test tone signal,
• hybrid means having an input circuit and a pair of output circuits for coupling a tone signal appearing on the input circuit simultaneously to both output circuits,
• relay means responsive to the telephone switching office and having contacts for momentarily connecting said generator means to the hybrid means input circuit and each of the hybrid means output circuits individually to a transmit path and a receive path of the four-wire incoming trunk,
• first path means connected across said generator means for generating a first tone signal having a predetermined voltage level,
• second path means including the hybrid means input circuit and connected across said generator means by operation of said contacts for generating second tone signals of voltage levels corresponding to values of impedance reflected back over the telephone call connection from the two-wire hybrid trunk through the switch network to the hybrid means input circuits,
• amplifying and rectifying means coupled to said first and said second path means for generating a first output voltage from said first tone signal and various values of a second output voltage in response to said second tone signals,
• detector means coupled to said amplifying and rectifying means for generating a bias voltage output signal when said second output voltage is greater in magnitude than a predetermined value of said first output voltage and for inhibiting the generation of the bias voltage output signal when said second output voltage is less in magnitude than the predetermined value of said first output voltage, and
• means coupled to said detector means and responsive to the bias voltage output signal thereof for signaling absence and presence of wire transpositions in the call connection transmit and receive paths to the telephone switching office and for enabling the telephone switching office to establish another call connection when the reflected impedance appearing at the hybrid means input circuit indicates a wire transposition in the call connection transmit and receive paths.

A switch network path reversal test circuit for use in testing transmit and receive paths of a telephone connection established through a telephone switching office, said test circuit comprising

• a tone signal generator
• a hybrid having an input circuit and a pair of output circuits for coupling a tone signal appearing on the input circuit simultaneously to both output circuits,
• a relay responsive to the telephone switching office having make contacts for connecting said tone signal generator to the hybrid input circuit and each of the hybrid output circuits individually to the transmit and receive paths, and
• means coupled to said tone signal generator and said hybrid by operation of said relay for detecting presence of path reversals occurring in the transmit and receive paths of the telephone connection in accordance with the transmit and receive path inpedances reflected into the hybrid input circuit.