Finding a Fourier representation of a signal

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Discussion Overview

The discussion revolves around finding the Fourier representation of a given piecewise signal, specifically whether to use a Fourier series or a Fourier transform. Participants explore the implications of the signal's periodicity and its representation in the frequency domain.

Discussion Character

  • Homework-related
  • Exploratory
  • Debate/contested

Main Points Raised

  • One participant is unsure whether to use a Fourier series or Fourier transform for the given signal, which consists of constant values over specified intervals.
  • Another participant questions the periodicity of the function, noting that it appears to have a period T but is zero for values greater than T, creating ambiguity.
  • A later reply emphasizes that the function cannot be both periodic and zero for t > T, suggesting the need for clarity in defining the signal's characteristics.
  • There is a suggestion that the Fourier transform should be calculated as an integral, but uncertainty remains about how to graph the resulting function, which may have both real and imaginary components.
  • One participant mentions an advanced expression for energy spectral density that could be graphed, indicating a potential direction for further exploration.

Areas of Agreement / Disagreement

Participants express differing views on the periodicity of the signal and whether to use a Fourier series or transform. The discussion remains unresolved as no consensus is reached on the appropriate approach or representation.

Contextual Notes

Participants highlight limitations regarding the definition of periodicity and the implications for the Fourier representation. There is also mention of potential complexities in graphing the Fourier transform due to the presence of real and imaginary parts.

Adir_Sh
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Given the following signal, find the Fourier representation, ##V(jf)= \mathfrak{F}\left \{ v(t) \right \}##:

##
v(t)=\left\{\begin{matrix}
A, & 0\leqslant t\leqslant \frac{T}{3}\\
2A, & \frac{T}{3}\leqslant t\leqslant T\\
0, & Else
\end{matrix}\right.
##

Then sketch ##V(jf)##.

Homework Equations

:[/B]
I don't know whether in such a given form of a signal (apparently looks quite simple, involving constants only) I should use a Fourier SERIES representation or a Fourier TRANSFORM representation. If it's a Fourier Transform representation, then I don't know how would the signal look like in the frequency domain. I tried to Calculate the Transform according to its definition, yet couldn't quite get to anything "sketchable", at least not something I can see it.

The Attempt at a Solution

:[/B]
Given below:
https://lh3.googleusercontent.com/RyZyGteipLYWd0P_Wp-lIOTGLqc2ZhrSdu22MgjI_S65ul7lYjivK5Tt5dOd-P-DdAdEztuVWdfy-2BK3FOEufhfdNqACycPa3pLYl1NGUjqFphMDJfK0MxlqSJKlM3Nhx1FlHIYCypqTekUrmj0y4sGwWpHWwuuIQMKlcck8aY8jJkEzv71Rg9AxcYheJ-Nr2lVLTnZ1jXf2FPQhbsTBR5aX1xDc3RyFYbmPHddMUAn0YA0xVL7hkejWtD6SEK_0ZP_qd2mUiW0STSbKE5bfHaypjezUVle-t8WBNz-WpVmCs8n12_bkKHpN2VPI3PQSAHE3VF9oJwa4iuTBiX0SQZc1FFcjzMrqy86xtEt_8r8v1qVKz2a8UpF_2g_86Tszy-ANPbwb25SuS41kk85QGpKJjjm0CKKoEyLaBFVisFIWQwIhNb9bDsEBfvl_nTTz8OISX88diDUyhbrN7rV7gcVxHvugexaZ2IVHkpbmXm2hYRI1lxOX21OEuxP4VoTbZAWcFXhl5b3Q4yo565BuF1ea3yQSH77PT0-mhQdWj2V=w1144-h643-no


Thanks in advance for your help,

Adir.
 
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Hint: Is the function periodic in the time domain? What implications does that have for the answer?
 
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Dr. Courtney said:
Hint: Is the function periodic in the time domain? What implications does that have for the answer?
It is periodic in the sense that it has a period ##T##. However, It has a 0 value for time values larger than T, so that's a bit tricky to determine the signal's periodicity. But that's the first "mine" in finding my way here.
 
Adir_Sh said:
It is periodic in the sense that it has a period ##T##. However, It has a 0 value for time values larger than T, so that's a bit tricky to determine the signal's periodicity. But that's the first "mine" in finding my way here.
Either it's periodic or it's zero for t > T. Can't have it both ways.
It sure looks like you're supposed to find the Fourier transform (integral).
Don't know about "graphing" V(jf). It may have real and imaginary parts; I don't have the time to look at your math in detail but if you did it right there are indeed real and imaginary parts to the transform. Which means I don't know about graphing the function. But maybe you messed up somewhere & there are only real or imaginary parts so then you could graph that.
Ther is an expression for the energy spectral density between two frequencies f1 and f2, given the Fourier integral of a pulse, but it's kind of advanced. But that can be graphed since it's a real number.
 
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