Optimal Control of Intermodulation Distortion in Hybrid Fiber-Coaxial CATV Systems

A general quadratic phase relationship for the NTSC video carriers has been used as the basis for minimizing the Peak/RMS ratio of the broadband HFC signal as well as the second- and third-order intermodulation distortion products. Emphasis is placed on distortion products which fall outside the band occupied by the NTSC signals and thus degrade digital performance. An experimental phase-controlled coherent HRC CATV system consisting of 81 live video channels and four 64 QAM digital channels has been used to demonstrate the advantages of an optimal phase-controlled headend over traditional systems.