Deployment of a modern broadband network provides both opportunities and challenges. Because the network is used to deliver a range of services beyond CATV, it must be both versatile and highly reliable. A flexible design allows reconfiguration both to accommodate technological change and to meet changing business requirements. Return plant and the management of return plant signals used to deliver advanced services are particularly important, as is signal level management in the headend. This application note addresses these issues | APPLICATION NOTE Overview Deployment of a modern broadband network provides both opportunities and challenges. Because the network is used to deliver a range of services beyond CATV it must be both versatile and highly reliable. A flexible design allows reconfiguration both to accommodate technological change and to meet changing business requirements. Return plant and the management of return plant signals used to deliver advanced services are particularly important as is signal level management in the headend. This application note addresses these issues. Aligning the Return Plant and Establishing Unity Gain One of the first issues to consider is alignment of the return plant. To align the return plant of a broadband HFC system we must establish unity gain of that return plant. This means that the loss between each amplifier section equals the gain in that section . a gain of 0 dB. This applies to all amplifiers - line extenders trunk and distribution amplifiers - as well as fiber optic nodes. If return path unity gain is not established return path signals from some legs of the network could arrive at the fiber node return laser transmitter too hot thereby causing distortion. Decreasing some return path signals in order to compensate for or equalize the levels may cause the carrier-to-noise level to be unacceptable. Aligning the return path for unity gain begins at the return path transmitter amplifier closest to the headend - typically a fiber optic node -and then proceeds out to the ends of the system. See Figure 1. At each return path amplifier a signal of known power is inserted into the input port. The unit is then padded so that the power received at the headend is at the desired level. Figure 1 1-952-938-8080 1-800-366-3891 RF Worx RF Signal Management Opportunities in Broadband Networks RF Signal Management Opportunities Figure 2 depicts a commonly used automated alignment system. This system uses a sweep signal to set up the return path .
