the general format of an inverted tree. Thus, the head of the structure, referred to as the headend, resembles the root of a tree and emits signals that flow onto branches either directly to subscribers or which are further split onto additional branches, also known as subbranches, for routing to subscribers. Depending on the dis- tance from the headend to subscribers, amplifiers may be installed on main branches and subbranches. Headend Figure 7.5 illustrates the general inverted tree structure of a cable TV transmission system. Note that the headend of the system is commonly connected to one or more satellite earth stations. The earth stations are Fiber in the Neighborhood antenna Figure 7.5 The basic cable TV network structure. Mixer tower Earth Headend Station The basic cable TV network structure resembles an inverted tree. receive-only (RO) satellite dishes designed to receive television signals transmitted via one or more satellites. Each satellite has a series of transponders that receive and rebroadcast TV signals; thus, you can con- sider the satellite transponder to represent a big audiovideo relay station in the sky. To ensure that the fixed location earth stations receive the TV signals throughout the day, geostationary satellites are used. Such satellites orbit the earth at a distance of approximately 26,000 miles above ground level, enabling the satellite to rotate in tandem with the rotation of the earth. In this manner the satellite stays in a fixed location relative to the ground, beaming such programming as HBO (Home Box Office), Show- time, the nightly news of major television networks, and other programs that many readers watch each day. SATELLITE RECEIVERS At the cable system headend, satellite receivers in the form of antennas mounted on an earth station or a nearby tower receive local programming from the immediate area. Both satellite-received programming and local programming are modu- lated by frequency onto the cable TV operator's network, with specific Chapter Seven programming placed 