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Chapter 2Overview of current CATV network pSplitters are used at every junction to distribute the signal between branches. Theinterface between truck cables and feeders is done by bridge amplifiers. Moresophisticated amplifiers are used in the distribution loop because noise levels are higherin the feeder cables than in the truck portion. These amplifiers are called line extendersand operate at higher power levels in this part of the system. Line extenders are requiredapproximately every 0.25 miles and are restricted to a maximum of three [99].Taps to connect subscribers are placed approximately every 150 feet. The drop cableconnects the subscriber to the tap and its maximum length is approximately 400 feet.Terminal equipment is the last component of the system. They are the receivers that usethe signal.As the service delivered to subscribers was originally designed exclusively toaccommodate television programming, the service was unidirectional. The signalsdelivered were analogue and replicas of the one a broadcaster sends through theairwaves. Because of this there was no need to modify the television set.2.3.1 CATV spectrum allocationThe spectrum for CATV networks is divided into the downstream and upstreamfrequencies. Figure 2.2 shows the basic downstream and upstream spectrum allocationsand the slight variations in the frequency ranges for Europe (EU), United States (US)and Japan (JP) [109].Upstream digitalchannelsDownstream analoguechannelsDownstream digitalchannels1 2 ...ncrossover region1 2 3 ... m542 (US)55 (JP)65 (EU)88 (US)90 (JP)110 (EU)1 – 6 MHz (plus 200 kHz in EU)1.6 – 6 Mbps (plus 10 Mbps in US)Figure 2.2 – Spectrum allocation on a CATV network.450869 (US)770 (JP)862 (EU)MHz1 – 6 MHz (US, JP)1 – 8 MHz (EU)28 – 40 Mbps (plus 50 Mbps in EU)2-4