Chapter 5

Getting It from Here to There

Modulators and Demodulators

In many ways, this is the most important chapter of the book, because there’d be no telecommunicating without the devices described in this chapter.

5.1 An Introduction

This chapter is really about two simple things: the modulator, and its opposite, the demodulator. The best way to explain them is to imagine yourself stuck with a particular communication problem. Let’s say after you read Chapter 4, you got excited and built a source coder–a PCM–which turns your voice signal into a digital bit stream (Figure 5.1). You then called up the FCC (Federal Communication Commission) and told them you want to use your source coder to send a digital voice message to a friend. They respond, ...

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