By Robert L. Howald and Timothy J. Brophy, Motorola Broadband Communications Sector
Forward path digital loading has become common in HFC signal multiplexes over the past several years. The added bandwidth on HFC systems requires not just improved frequency response from the equipment in the distribution chain, but it also requires hardware with better dynamic range. As the forward path signal load increases with heavy digital loading, the total output power that must be achieved without degrading distortion is increased. Depending on plant layout, the total power could also be shared by backing down the analog load as a tradeoff with the increasing digital load’s effects. However, with slightly lower analog levels, CNR would degrade unless a lower noise floor exists. Thus, ideally, devices with improved dynamic range yield the most flexibility.