(New page: CT signal: <math>x(t) = 2\sin(2 \pi t) - (1 + 3j)\cos(5 \pi t)\,</math> <math>x(t) = 2 * \frac{e^{j2\pi t} - e^{-j2\pi t}}{2j} - (1 + 3j)*\frac{e^{j5\pi t} + e^{-j5\pi t}}{2}\,</math> ...)
 
 
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CT signal:
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[[Category:problem solving]]
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[[Category:ECE301]]
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[[Category:ECE]]
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[[Category:Fourier series]]
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[[Category:signals and systems]]
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== Example of Computation of Fourier series of a CT SIGNAL ==
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A [[Signals_and_systems_practice_problems_list|practice problem on "Signals and Systems"]]
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----
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For the CT signal:
  
 
<math>x(t) = 2\sin(2 \pi t) - (1 + 3j)\cos(5 \pi t)\,</math>
 
<math>x(t) = 2\sin(2 \pi t) - (1 + 3j)\cos(5 \pi t)\,</math>
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<math>x(t) = \frac{1}{j}e^{j2\pi t} - \frac{1}{j}e^{-j2\pi t} - \frac{1+3j}{2}e^{j3\pi t} - \frac{1+3j}{2}e^{j3\pi t}\,</math>
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<math>x(t) = \frac{1}{j}e^{j2\pi t} - \frac{1}{j}e^{-j2\pi t} - \frac{1+3j}{2}e^{j5\pi t} - \frac{1+3j}{2}e^{j5\pi t}\,</math>
 
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<math>x(t) = \frac{2}{j}e^{5*j\pi t} - \frac{2}{j}e^{-5*j\pi t} - \frac{2+j}{2}e^{3*j\pi t} - \frac{2+j}{2}e^{-3*j\pi t}\,</math>
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<math>\omega_0\,</math> ends up being <math>\pi\,</math> for this signal
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So because of that, in my last step, i was able to determine what value of K's i had.  (k = 3,-3,5,-5)
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So then you just take the coefficients of those terms to get the <math>a_k\,</math>
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Therefore:
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<math>a_3 = \frac{-2-j}{2}\,</math>  
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<math>x(t) = \frac{1}{j}e^{2*j\pi t} - \frac{1}{j}e^{-2*j\pi t} - \frac{1+3j}{2}e^{5*j\pi t} - \frac{1+3j}{2}e^{-5*j\pi t}\,</math>
  
  
  
<math>a_{-3} = \frac{-2-j}{2}\,</math>
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<math>\omega_0\,</math> = <math>\pi\,</math> therefore k = 2,-2,5,-5
  
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Applying the coefficients to get the <math>a_k\,</math>
  
  
<math>a_5 = \frac{2}{j}\,</math>
 
  
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<math>a_5 = \frac{-1-3j}{2}\,</math>    <math>a_{-5} = \frac{-1-3j}{2}\,</math>
  
  
<math>a_{-5} = \frac{-2}{j}\,</math>
 
  
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<math>a_2 = \frac{1}{j}\,</math>          <math>a_{-2} = \frac{-1}{j}\,</math>
  
  
For every other k:
 
  
<math>a_k\, = 0</math>
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For K \neq [2,-2,-5,5], <math>a_k\, = 0</math>
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----
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[[Signals_and_systems_practice_problems_list|Back to Practice Problems on Signals and Systems]]

Latest revision as of 11:04, 16 September 2013


Example of Computation of Fourier series of a CT SIGNAL

A practice problem on "Signals and Systems"


For the CT signal:

$ x(t) = 2\sin(2 \pi t) - (1 + 3j)\cos(5 \pi t)\, $


$ x(t) = 2 * \frac{e^{j2\pi t} - e^{-j2\pi t}}{2j} - (1 + 3j)*\frac{e^{j5\pi t} + e^{-j5\pi t}}{2}\, $


$ x(t) = \frac{1}{j}e^{j2\pi t} - \frac{1}{j}e^{-j2\pi t} - \frac{1+3j}{2}e^{j5\pi t} - \frac{1+3j}{2}e^{j5\pi t}\, $


$ x(t) = \frac{1}{j}e^{2*j\pi t} - \frac{1}{j}e^{-2*j\pi t} - \frac{1+3j}{2}e^{5*j\pi t} - \frac{1+3j}{2}e^{-5*j\pi t}\, $


$ \omega_0\, $ = $ \pi\, $ therefore k = 2,-2,5,-5

Applying the coefficients to get the $ a_k\, $


$ a_5 = \frac{-1-3j}{2}\, $ $ a_{-5} = \frac{-1-3j}{2}\, $


$ a_2 = \frac{1}{j}\, $ $ a_{-2} = \frac{-1}{j}\, $


For K \neq [2,-2,-5,5], $ a_k\, = 0 $


Back to Practice Problems on Signals and Systems

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Correspondence Chess Grandmaster and Purdue Alumni

Prof. Dan Fleetwood