Cable maintenance system

摘要

A cable system includes a cable head end and a plurality of distribution sites having equipment for supplying subscriber station receivers with digital video cable signals from the cable head end. The digital video signal includes a robust data component that is receivable by distribution site receivers and cable subscriber station receivers under very poor carrier-to-noise conditions, that is, where the video signal itself is not usable. The cable head end has capabilities for interrogating distribution site receivers and subscriber station receivers which respond by transmitting designated information concerning differences between the received robust data component and the transmitted robust data component. At the subscriber station receivers, the robust data component is in the form of a training sequence of known characteristics that is compared with a received training sequence. The subscriber station receiver has an equalizer with equalization taps that are changed in accordance with the training sequence comparison. The tap settings are recorded in a register which is interrogated by the cable head end. The distribution site receivers include fixed gain RF amplifiers and develop an IF AGC signal through the use of a counter and a digital-to-analog converter. The counter records in a register the developed IF AGC control voltage which is supplied to the cable head end upon interrogation. The distribution site amplifier receivers also provide information concerning carrier-to-noise ratio and data segment errors.