Chapter Oscillators

Teach Yourself Electricity and Electronics Third Edition Book
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Summary of Contents

Teach Yourself Electricity and Electronics Third Edition Book

  • 25CHAPTEROscillatorsSOMETIMES AMPLIFIERS WORK TOO WELL. YOU’VE PROBABLY HEARD THIS WHENsomeone was getting ready to speak over a public-address system. The gain was set toohigh. The person began to speak; sound from the speakers got into the microphone,was amplified, went to the speakers again, and back to the microphone. A vicious cycleof feedback ensued. The result might have been a rumble, a howl, or a shriek. The sys-tem broke into oscillation. The amplifiers became temporarily useless until the gainwas reduced.Oscillation can be controlled, so that it takes place at a specific, stable, predictablefrequency. An oscillator is a circuit that is deliberately designed to oscillate.Uses of oscillatorsSome oscillators work at audio frequencies, and others are intended to produce radiosignals. Most generate sine waves, although some are built to emit square waves, saw-tooth waves, or other waveshapes.The subject of oscillators, once you understand amplifiers, is elementary. All oscil-lators are amplifiers with positive feedback. In this chapter, radio-frequency (RF) os-cillators are discussed in some detail, and then audio oscillators are examined.In radio communications, oscillators generate the “waves” or signals, that are ulti-mately sent over the air. For data to be sent, the signal from an oscillator must be mod-ulated. Modulation is covered in chapter 26.Oscillators are used in radio and TV receivers for frequency control and for detec-tion and mixing. Detectors and mixers are discussed in chapter 27.Audio-frequency oscillators find applications in such devices as music synthesiz-ers, FAX modems, doorbells, beepers, sirens and alarms, and electronic toys.457Copyright © 2002, 1997, 1993 by The McGraw-Hill Companies. Click here for terms of use.