Abstract: A testing system for testing a selected telephone carrier channel wherein that channel is selectively interrupted at a selected repeater station along its route and bi-directionally looped back for testing. Selection and the looping back process is controlled by a central control unit located at a central telephone exchange and remote control units located at repeater stations. Significantly, the central unit is operated by a dialed telephone call to it, and responsive to additionally dialed digits, it effects the selection of the particular route for the channel in question and a particular repeater station and channel. Actual looping back is effected by a transformer coupling arrangement which additionally provides for the D.C. integrity of the channel.

Abstract: A telephone-telephone line tester wherein a telephone line serving a user is selectively coupled and uncoupled to either or both an audio amplifier or a user's telephone circuit whereby telephone user difficulties may be readily determined as between the telephone line or user's circuit and equipment.