Chapter 3: Transmission Media

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OVERVIEW

To exchange information between people separated by a distance has been a necessity throughout the history of mankind. Long ago, people used fire for communicating over a limited distance; they used birds and messengers for long distance communication. The postal system still provides an excellent means of sending written communication across the globe.

Communication over long distances, not just through written text but using other media such as voice and video, has been achieved through electrical communication. This discipline deals with conversion of information into electrical signals and transmitting them over a distance through a transmission medium. In this chapter, we will study the various transmission media used for electrical communication, such as twisted pair, coaxial cable, optical fiber, and the radio. We will study the characteristics and the advantages and disadvantages of each for practical communication systems. Free space (or radio) communication particularly provides the unique advantage of support for mobility—the user can communicate while on the move (in a car or an airplane). However, the radio spectrum is a precious natural resource and has to be used efficiently. We will also discuss the issue of radio spectrum management briefly in this chapter.

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