Learning objectives are stated at the beginning of each chapter. These learning objectives serve as a
preview of the information you are expected to learn in the chapter. The comprehensive check questions
are based on the objectives. By successfully completing the OCC/ECC, you indicate that you have met
the objectives and have learned the information. The learning objectives are listed below.
Upon completion of this chapter, you will be able to:
Discuss the generation of a sine wave by describing its three characteristics: amplitude, phase,
Describe the process of heterodyning.
Discuss the development of continuous-wave (cw) modulation.
Describe the two primary methods of cw communications keying.
Discuss the radio frequency (rf) spectrum usage by cw transmissions.
Discuss the advantages and disadvantages of cw transmissions.
Explain the operation of typical cw transmitter circuitry.
Discuss the method of changing sound waves into electrical impulses.
Describe the rf usage of an AM signal.
Calculate the percent of modulation for an AM signal.
Discuss the difference between high- and low-level modulation.
Describe the circuit description, operation, advantages, and disadvantages of the following
common AM tube/transistor modulating circuits: plate/collector, control grid/base, and
Discuss the advantages and disadvantages of AM communications.
INTRODUCTION TO MODULATION PRINCIPLES
People have always had the desire to communicate their ideas to others. Communications have not
only been desired from a social point of view, but have been an essential element in the building of
civilization. Through communications, people have been able to share ideas of mutual benefit to all
mankind. Early attempts to maintain communications between distant points were limited by several
factors. For example, the relatively short distance sound would carry and the difficulty of hand-carrying
messages over great distances hampered effective communications.