Chapter List

6.1 Introduction

This chapter is the first of three devoted to the headend. Chapter 6 covers the ways in which signals get into the headend. Chapter 7 will cover the electronics used in processing the signals once they get into the headend, and Chapter 8 will cover topics related to the signals after they have been processed.

Chapter 6 deals primarily with antennas of various types used to capture signals for the headend, and with propagation of signals from the source to those antennas.

Although cable operators usually use antennas to receive signals, antennas are sometimes described in terms of their operation when transmitting signals. The principle of duality applies, which states that an antenna is capable of operating as either a radiator or receptor of power. This principle is based on Maxwell s equations, which describe the co-existence of radiated fields and those contained within a conductor, without defining which causes the other.

6.2 Off-Air Reception

Cable television got its start as a community antenna service, in which a large antenna was erected in a favorable place and signals from it were supplied to the community. Today, off-air channels still tend to be some of the more watched though other channels are also popular. Some cities remain prime candidates for a community antenna service since propagation conditions don t lend themselves to good off-air reception at all locations. Cities located in mountainous terrain are good examples. As cable and broadcast television have learned to cooperate, it is becoming more common for cable headends to be supplied with a direct feed from the broadcaster. That way, the so-called perils of the radio path don t take their toll on the signals. Even so, it is still common for local and distant broadcasters to be picked up using off-air antennas.