Chapter Overview

In the modulation process, the baseband voice, video, or digital signal modifies another, higher-frequency signal called the carrier, which is usually a sine wave. A sine wave carrier can be modified by the intelligence signal through amplitude modulation, frequency modulation, or phase modulation. The focus of this chapter is amplitude modulation (AM).

Chapter Outline

3-1 AM Concepts
3-2 Modulation Index and Percentage of Modulation
3-3 Sidebands and the Frequency Domain
3-4 AM Power
3-5 Single-Sideband Modulation
3-6 Classification of Radio Emissions

Chapter Objectives

• Calculate the modulation index and percentage of modulation of an AM signal, given the amplitudes of the carrier and modulating signals.
• Define overmodulation and explain how to alleviate its effects.
• Explain how the power in an AM signal is distributed between the carrier and the sideband, and then compute the carrier and sideband powers, given the percentage of modulation.
• Compute sideband frequencies, given carrier and modulating signal frequencies.
• Compare time-domain, frequency-domain, and phasor representations of an AM signal.
• Explain what is meant by the terms DSB and SSB and state the main advantages of an SSB signal over a conventional AM signal.
• Calculate peak envelope power (PEP), given signal voltages and load impedances.