By Marc Ryba, Motorola Broadband Communications Sector
Present day cable systems run a mix of both analog and digital signals. As digital services evolve, HDTV becomes reality, and competition from fully digitized direct satellite services increases, migration toward a full digital spectrum is inevitable. Moving to a full digital multiplex raises some concerns with regard to distribution and signal quality. Digital signals produce noise-like distortions that extend throughout the spectrum. Full digital channel loading will decrease the measured C/N (Es/No) in the QAM channels. This paper will present the results of lab tests to determine optimum levels for digital signal distribution and the effect of a full digital multiplex on a modern cable plant. Digital signal quality issues are also investigated.