By Rezin Pidgeon, Jr., Scientific-Atlanta, Inc.
Results of a study to determine the measure and perceptibility of cross-modulation distortion in a CATV system are presented. Subjective tests evaluate the interference to a television picture or test pattern caused by one to 24 independent video-modulated carriers. Design of the test system enabled cross modulation to be measured and observed without being obscured by triple-beat distortions. Although cross modulation is not a predominant factor, it is of more concern ~n a phase-locked system because of suppression of triple-beat distortion.
Cross modulation can result in both AM and PM components. In distribution amplifiers, the PM component may be the larger of the two, particularly at the higher channel frequencies, although generally only the AM component is measured. In these tests, the AM and PM distortion components are measured separately and the relative importance of each is shown.