Automatically adjustable bidirectional-to-unidirectional transmission network

A transmission network adapted to couple a unidirectional receive path and a unidirectional transmit path to a bidirectional path including a 2-wire nonloaded type cable comprising:

• a canceler including means for generating a correction signal which is substantially a replica of an error signal developed in the network and included as a component of a transmit signal supplied to the transmit path, said correction signal generating means including a plurality of controllably adjustable impedance elements;
• controllable signal generating means for supplying predetermined test signals to the receive path;
• signal detection means for detecting signal amplitudes on the transmit path;
• means for algebraically combining said correction signal with the transmit signal;
• control means for generating control signals to controllably adjust said plurality of impedance elements in said correction signal generating means in at least a first procedure including a first prescribed adjustment sequence, each of said impedance elements being adjusted in said first adjustment sequence while supplying a corresponding one of said test signals to the receive path to obtain an amplitude null in the transmission path as detected by said detection means, said first adjustment sequence including multiple iterative adjustment of predetermined ones of said impedance elements for automatically converging said correction signal generation means to have an optimum transfer function which substantially matches the impedance developed in the network when the bidirectional path is connected thereto so that said correction signal is substantially a replica of the error signal,
• said first adjustment sequence including iterative adjustment of predetermined ones of said impedance elements in predetermined groups and multiple iterative adjustment of said groups of impedance elements until no change in the impedance adjustments occur, and
• said first procedure including a determination of whether a first frequency associated with a predetermined first one of said adjustable impedance elements at which a corresponding first pole or first zero occur is equal to or greater than a second frequency associated with a predetermined second one of said adjustable impedance elements at which a corresponding second pole or second zero occur, and said control means generating control signals to constrain impedance settings of said first and second impedance elements so that the first frequency does not substantially exceed said second frequency.