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I <br /> Notes Chapter 4 <br /> 1A digital radio's tuning system employs a frequency synthesizer. At its heart is an oscillator that <br /> generates a very precise reference frequency from which the synthesizer derives all possible output <br /> frequencies. <br /> 2Unintended acoustic feedback causes squeals or howls in public address systems. Too much sound <br /> from the loudspeakers reaches the microphone and creates a self-sustaining oscillation. <br /> 3Often, a preamplifier, tuner, and power amplifier are packaged as a receiver.A.combination pre- <br /> amplifier and power amplifier is an integrated amplifier. Multichannel"home theater"systems <br /> include special signal processors,additional speakers, and amplifiers. <br /> 4Audio rectification generally does not cause stereo-system interference which arises only when <br /> the FM tuner is selected. Such interference is due to RF signal overload,also called blanketing. We <br /> will cover blanketing later. <br /> 5Almost 20 years ago, Congress authorized the FCC to set RF immunity standards for consumer <br /> electronic devices, but the Commission has never exercised that power. <br /> 6Cellular networks employ frequencies that used to be high-numbered UHF TV channels. <br /> • <br /> • <br />