Abstract: A cable television (CATV) system is modified to provide two-way telephone communications in a subsplit band below the video signal, preferrably in the range of approximately 5-40 MHz. Each line amplifier in the coaxial cable network is equipped with a bypass strap or bypass circuitry to maintain a signal path through the line amplifier for the telephone signal in the event of failure of the line amplifier. Due to the decreased attentuation resulting from its lower frequency, the telephone signal can typically travel the distance of three or four line amplifier spacings without amplification. Line amplifier failure is a common occurrence in CATV networks. Therefore, the present invention greatly increases the reliability of telephone communications over CATV networks.

Abstract: A system for testing 2B1Q private line data telephony circuits having 2B1Q modulation between the network channel termination equipment and the channel unit. 2B1Q modulation is provided over a single pair of wires connected to the E and M leads of the channel unit. The system can deliver testing signals from two different sources. The first source is from a remote testing system connected to a remote access system which in turn is connected to the T, T1, R, and R1 output leads of the channel unit. The remote testing system generates conventional testing signals which are converted into digital signals for directly communicating with the 2B1Q pair of wires. The remote testing system delivers conventional tests for testing the loopback of the channel connected to the single pair of wires and to the network channel termination equipment. Under a second source of tests, the interface of the present invention directly connects to the T1 carrier.

Abstract: The universal channel unit includes a channel interface circuit that uses a pair of fixed ratio transformers to terminate both two wire and four wire analog transmission facilities on a selectable basis. The universal channel unit also includes a plurality of signalling circuits, each of which is switchably connectable via the channel interface unit to provide a DC signalling interface to match the signalling format required by the associated analog transmission facility. The signalling circuits include: DX, FXO, FXS, and other DC signalling circuits. The AC component of the signals carried by the analog transmission facility is output to an adaptive impedance and balance circuit which functions to closely match the impedance of the analog transmission facility and minimize signal reflections under control of a microprocessor. This impedance and balance network is connected to a PCM interface that includes an adaptive echo canceller circuit as well as equalization and gain control circuits.