How Does Fourier Transform Analyze Beats in Signals?

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Discussion Overview

The discussion centers around the Fourier transform of a beat signal, specifically the function defined as ##f(t)=\cos((\omega_p+\omega_v) t)+\cos((\omega_p-\omega_v)t)##. Participants explore the implications of the parameters involved, particularly the relationship between ##\Omega## and ##\omega##, and the appropriate notation for the Fourier transform.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant proposes that the Fourier transform of the beat function is equal to ##\frac{1}{2}(\delta(\omega_p+\omega_v-\omega)+\delta(\omega_p-\omega_v-\omega)+\delta(\omega_v-\omega_p-\omega)+\delta(-\omega_p-\omega_v-\omega)##.
  • Another participant questions the correctness of the proposed Fourier transform and seeks confirmation.
  • A participant clarifies that ##\Omega\simeq\omega## indicates that ##\Omega## is approximately equal to ##\omega##, providing an example with specific values.
  • Concerns are raised about the notation used, specifically the choice of symbols for the constants and the variable in the Fourier transform.
  • A later reply suggests using different symbols for clarity, proposing ##\Omega=\Omega_1## and ##\omega=\omega_p-\omega_v=\Omega_2## to avoid confusion.

Areas of Agreement / Disagreement

Participants express differing views on the notation and the implications of the symbols used, indicating that there is no consensus on the best approach to represent the Fourier transform in this context.

Contextual Notes

The discussion highlights potential limitations in notation and clarity, particularly regarding the choice of symbols for constants and variables in the Fourier transform.

Salmone
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What is the Fourier transform of a beat? For example, I want to calculate the Fourier transform of the function ##f(t)=\cos((\omega_p+\omega_v) t)+\cos((\omega_p-\omega_v)t),## where ##$\omega_p+\omega_v=\Omega,\space\omega_p-\omega_v=\omega## and ##\Omega\simeq\omega.##

I think it is equal to ##\frac{1}{2}(\delta(\omega_p+\omega_v-\omega)+\delta(\omega_p-\omega_v-\omega)+\delta(\omega_v-\omega_p-\omega)+\delta(-\omega_p-\omega_v-\omega))##, is it right?
 
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Salmone said:
What is the Fourier transform of a beat? For example, I want to calculate the Fourier transform of the function ##f(t)=\cos((\omega_p+\omega_v) t)+\cos((\omega_p-\omega_v)t),## where ##$\omega_p+\omega_v=\Omega,\space\omega_p-\omega_v=\omega## and ##\Omega\simeq\omega.##

I think it is equal to ##\frac{1}{2}(\delta(\omega_p+\omega_v-\omega)+\delta(\omega_p-\omega_v-\omega)+\delta(\omega_v-\omega_p-\omega)+\delta(-\omega_p-\omega_v-\omega))##, is it right?
Do you have some reason to think your answer is not correct?
 
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vela said:
Do you have some reason to think your answer is not correct?
No, I just want to be sure.
 
What does ##\Omega\simeq\omega## mean?
 
Means that ##\Omega## has a similar value of ##\omega##, for example: ##\Omega=30Hz## and ##\omega=28Hz##
 
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Only slight problem I see is with the chosen symbols, since you chose ##\omega## for the constant ##\omega_p-\omega_v=\omega## you must use another symbol for the variable of the Fourier transform (that is the omega inside the dirac functions). I know we usually say the Fourier transform of ##f(t)## is $$\hat f(\omega)=...$$ but now you have already chosen ##\omega## to denote something else.
 
Delta2 said:
Only slight problem I see is with the chosen symbols, since you chose ##\omega## for the constant ##\omega_p-\omega_v=\omega## you must use another symbol for the variable of the Fourier transform (that is the omega inside the dirac functions). I know we usually say the Fourier transform of ##f(t)## is $$\hat f(\omega)=...$$ but now you have already chosen ##\omega## to denote something else.
I can't edit the post no longer, but let's say ##\Omega=\Omega_1## and ##\omega=\omega_p-\omega_v=\Omega_2##.
 
Salmone said:
I can't edit the post no longer, but let's say ##\Omega=\Omega_1## and ##\omega=\omega_p-\omega_v=\Omega_2##.
ok fine if you put ##\Omega_2## instead of ##\omega## then I guess you are free to use ##\omega## as the variable of the Fourier transform
 

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