Fourier Application to Signal Modulation and Demodulation

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Fourier Application to Signal Modulation and
Demodulation

• 3.8
• Kamen and Heck

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3.8.1 Amplitude Modulation

• s(t) Ax(t) cos(?ct)
• Acos(?ct)carrier signal
• x(t) is the information signal
• Figure 3.31
• Example 3.19Figure 3.32
• The Modulation Property can be used to determine
  the Fourier Transform of the signalFigure 3.33.
• S(?) A/2 X(? ?c) X(? - ?c)

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3.8.2 Alternative Form of AM

• s(t) A1 k x(t) cos(?ct) (3.77)
• k is a positive constant called the amplitude
  sensitivity.
• 1 k x(t) gt 0 for all t
• Example 3.20Fig. 3.34.
• S(?) ?A ?(? ?c) ?(? - ?c) Ak/2 X(?
  ?c) X(? - ?c)
• DSB-SC vs. DSB