In-service cable television measurements

摘要

A cable television measurement system uses a modified spectrum analyzer for determining both carrier-to-noise and triple beat ratios for a cable television (CATV) system. The modified spectrum analyzer is triggered for single sweep during the vertical interval of a selected channel, and the noise amplitude, peak sync tip amplitude and frequency of the channel are determined. The carrier-to-noise ratio is determined from the noise amplitude and the peak sync tip amplitude and the ratio and frequency are displayed. For triple beat ratio measurements a headerd unit coupled between a television signal source and a combiner in the CATV headend prior to distribution offsets a selected channel by a predetermined frequency for a specified number of lines in the vertical interval. The modified spectrum analyzer measures the peak sync tip amplitude and a triple beat amplitude at the end of the specified number of lines. The triple beat ratio is determined from the triple beat amplitude and the peak sync tip amplitude and displayed.