ENVS 1200 Chapter Notes - Chapter 7: Carrier Wave, Musical Tone, Hertz
13 May 2018
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ENVS 1200 Chapter 7 Notes – Summary
Introduction
• Materials that are not transparent can be used to guide or reflect a wave.
• A satellite dish, for example, works by reflecting radio waves from the dish to a single
point, where they are concentrated and collected by a sensitive receiver.
• Similarly, fiber-optic cables maximize the light at the receiving end of the cable by
guiding the light through the cable.
• In practice, the sine waves that we have discussed are of limited use by themselves.
• A sound made up of a sine wave produces a single, pure tone.
• A 440-Hz sie ae produces the toe called A, for exaple.
• There is not much useful information value (or musical interest) in a pure sine wave
tone.
• Instead, sine waves are used as carriers for the data that we wish to transmit.
• We modulate, or change, one or more of the three characteristics of the sine wave,
amplitude, frequency, or phase, to represent the signal that is to be transmitted.
• Thus, an AM, or amplitude-modulated, radio station at 1100 KHz would use a sine wave
carrier of 1100 KHz.
• The music broadcast on that station would modulate the amplitude of the carrier to
correspond to the sound of the music.
• The AM station uses only one type of modulation.
• You should be able to guess what kind of modulation is used by an FM station!
• To restore the original waveform that was used to modulate the carrier, we use a
demodulator or detector.
• An example of carrier amplitude modulated by another analog signal is shown
• Note that amplitude modulation is symmetric with respect to the center of the carrier
sine wave.
• For digital signals, the carrier signal is modulated with only two possible values, the
alue represetig a ad the alue represetig a .
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