Telephone line selection and isolation method and apparatus

Apparatus for indentifying and isolating a selected telephone line from among a plurality of telephone lines at a location remote from the central office, upon the application of a test signal to the selected line, comprising:

• input/output means coupling each line of the plurality of lines to a respective subscriber line;
• line selection means coupled to said input/output means, for selecting an evaluation line in a preselected sequence from among the plurality of lines in response to an input sequencing signal, and providing signals from said evaluation line as an evaluation output;
• filter means coupled to said line selection means for filtering said evaluation output within a preselected wide frequency band and providing a filtered signal output;
• control and detection means coupled to said filter means, operational in an initial detection mode for detecting the presence of an initial detection signal in an initial detection band within said wide frequency band during a first time interval and, upon detection of said initial detection signal, operational in a validation mode for detecting the presence of as validated test signal by detecting the presence of a validation signal lying in a validation band within said initial detection band during a second time interval, said second time interval being longer than said first time interval, for providing as an output a "commence test" signal upon detection of said validated test signal or a said input sequencing signal upon failure to detect a said initial detection signal during said initial detection mode or said validation signal during said validataion mode, said control and detection means is operational in said initial detection mode to detect a leading edge of saisd initial detection signal, to activate a time base pulse generator upon detection of said leading edge, to deactivate said time base pulse generator upon a first preselected number of periods of the frequency of said initial detection signal, to accumulate the pulses generated by said time base pulse generator during said first preselected number of periods and to detect the presence of said initial detection signal within said intial detection band from the number of pulses accumulated during said first preselected number of periods of the frequency of said initial detection signal;
• and
• isolation means coupled to said control and detection means and to said input/output means, for disconnecting said evaluation line from said respective subscriber line in response to said "commence test" signal.