By Steve Dehart and Richard Serafin, Philips Broadband Networks Inc., & Samir Hulyalkar and David Bryan, Philips Laboratories, & Larry Bennett, Hewlett Packard
To transmit digitally compressed video with co-existing analog video over cable television (CATV) systems, the entire CATV bandwidth is frequency-division-multiplexed (FDM) into 6 MHz wide channels. For reliable data transmission, it is necessary to design an adaptive digital equalizer to compensate for the linear distortion effects, for example, the microreflections, introduced in such a 6 MHz CATV channel. This paper describes the characterization of the linear distortion effects as viewed by a digital adaptive equalizer in a 6 MHz CATV channel by developing measurement techniques using existing equipment. In contrast to other proposed techniques, this method has the added advantage of non-intrusive characterization of the channel, i.e., it is not necessary to interrupt existing cable service to characterize the channel. The advent of a new type of spectrum analyzer has greatly facilitated our work. Laboratory tests are performed to validate the measurement techniques. Finally, channel measurements are obtained for an in-house cable system.