Fourier Transform with both Time Delay and Frequency Shift
Clash Royale CLAN TAG#URR8PPP
$begingroup$
I know that the Fourier transform of a function with time delay can be written as: $$mathscrFbigx(t-t_0)big=X(f)e^-j2pi f t_0$$
The Fourier transform of a function with frequency shift can also be written as: $$mathscrFBigx(t)e^j2pi f_0 tBig=X(f-f_0)$$
So what if we have both shift and delay at the time domain, what will be the result in the frequency domain? E.g.:
$$mathscrFBigx(t-t_0)e^j2pi f_0 (t-t_0)Big$$
Will the result be: $$X(f-f_0)e^-j 2 pi f (t-t_0)$$
Also what will be the result of:
$$mathscrFBigx(t-t_0)e^j2pi f_0 t)Big$$
Is there an order to apply these properties?
fourier-transform time-frequency
$endgroup$
add a comment |
$begingroup$
I know that the Fourier transform of a function with time delay can be written as: $$mathscrFbigx(t-t_0)big=X(f)e^-j2pi f t_0$$
The Fourier transform of a function with frequency shift can also be written as: $$mathscrFBigx(t)e^j2pi f_0 tBig=X(f-f_0)$$
So what if we have both shift and delay at the time domain, what will be the result in the frequency domain? E.g.:
$$mathscrFBigx(t-t_0)e^j2pi f_0 (t-t_0)Big$$
Will the result be: $$X(f-f_0)e^-j 2 pi f (t-t_0)$$
Also what will be the result of:
$$mathscrFBigx(t-t_0)e^j2pi f_0 t)Big$$
Is there an order to apply these properties?
fourier-transform time-frequency
$endgroup$
1
$begingroup$
it's really nice to see new contributors use $LaTeX$. thanks.
$endgroup$
– robert bristow-johnson
Feb 5 at 20:37
add a comment |
$begingroup$
I know that the Fourier transform of a function with time delay can be written as: $$mathscrFbigx(t-t_0)big=X(f)e^-j2pi f t_0$$
The Fourier transform of a function with frequency shift can also be written as: $$mathscrFBigx(t)e^j2pi f_0 tBig=X(f-f_0)$$
So what if we have both shift and delay at the time domain, what will be the result in the frequency domain? E.g.:
$$mathscrFBigx(t-t_0)e^j2pi f_0 (t-t_0)Big$$
Will the result be: $$X(f-f_0)e^-j 2 pi f (t-t_0)$$
Also what will be the result of:
$$mathscrFBigx(t-t_0)e^j2pi f_0 t)Big$$
Is there an order to apply these properties?
fourier-transform time-frequency
$endgroup$
I know that the Fourier transform of a function with time delay can be written as: $$mathscrFbigx(t-t_0)big=X(f)e^-j2pi f t_0$$
The Fourier transform of a function with frequency shift can also be written as: $$mathscrFBigx(t)e^j2pi f_0 tBig=X(f-f_0)$$
So what if we have both shift and delay at the time domain, what will be the result in the frequency domain? E.g.:
$$mathscrFBigx(t-t_0)e^j2pi f_0 (t-t_0)Big$$
Will the result be: $$X(f-f_0)e^-j 2 pi f (t-t_0)$$
Also what will be the result of:
$$mathscrFBigx(t-t_0)e^j2pi f_0 t)Big$$
Is there an order to apply these properties?
fourier-transform time-frequency
fourier-transform time-frequency
edited Feb 5 at 20:36
robert bristow-johnson
10.9k31548
10.9k31548
asked Feb 5 at 13:08
tamunotamuno
235
235
1
$begingroup$
it's really nice to see new contributors use $LaTeX$. thanks.
$endgroup$
– robert bristow-johnson
Feb 5 at 20:37
add a comment |
1
$begingroup$
it's really nice to see new contributors use $LaTeX$. thanks.
$endgroup$
– robert bristow-johnson
Feb 5 at 20:37
1
1
$begingroup$
it's really nice to see new contributors use $LaTeX$. thanks.
$endgroup$
– robert bristow-johnson
Feb 5 at 20:37
$begingroup$
it's really nice to see new contributors use $LaTeX$. thanks.
$endgroup$
– robert bristow-johnson
Feb 5 at 20:37
add a comment |
2 Answers
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oldest
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$begingroup$
As an alternative to going back to the definitions, as explained in Andy Walls' answer, you can also just apply the rules as you stated them:
$$mathcalFleftx(t-t_0)e^j2pi f_0(t-t_0)right=mathcalFleftx(t)e^j2pi f_0trighte^-j2pi ft_0=X(f-f_0)e^-j2pi ft_0$$
where $X(f)$ is the Fourier transform of $x(t)$.
And, for your second example, with $tildeX(f)=mathcalFx(t-t_0)=X(f)e^-j2pi ft_0$ you get
$$mathcalFleftx(t-t_0)e^j2pi f_0tright=tildeX(f-f_0)=X(f-f_0)e^-j2pi (f-f_0)t_0$$
Of course, recognizing that the function in the second example just equals the first function scaled by $e^j2pi f_0t_0$, we could have written down its Fourier transform directly by scaling the Fourier transform of the first function by the same factor.
$endgroup$
add a comment |
$begingroup$
If you are ever unsure, just go back to the definition and work out the Fourier Transform property for the specific situation:
$$beginalign*mathscrFleftxleft(t-t_0right)e^j2pi f_0left(t-t_0right)right &= int_-infty^infty xleft(t-t_0right)e^j2pi f_0left(t-t_0right) e^-j2pi f tdt\
\
&= int_-infty^infty xleft(tauright)e^j2pi f_0tau e^-j2pi f left(tau+t_0right)dtau \
\
&= e^-j2pi ft_0int_-infty^infty xleft(tauright)e^j2pi f_0tau e^-j2pi f taudtau \
\
&= e^-j2pi ft_0int_-infty^infty xleft(tauright) e^-j2pi (f-f_0) taudtau \
\
&= e^-j2pi ft_0 X(f-f_0)\
\
endalign*$$
$$beginalign*mathscrFleftxleft(t-t_0right)e^j2pi f_0 tright &= int_-infty^infty xleft(t-t_0right)e^j2pi f_0t e^-j2pi f tdt\
\
&= int_-infty^infty xleft(tauright)e^j2pi f_0(tau+t_0) e^-j2pi f left(tau+t_0right)dtau \
\
&= e^-j2pi (f-f_0)t_0int_-infty^infty xleft(tauright)e^j2pi f_0tau e^-j2pi f taudtau \
\
&= e^-j2pi (f-f_0)t_0int_-infty^infty xleft(tauright) e^-j2pi (f-f_0) taudtau \
\
&= e^-j2pi (f-f_0)t_0 X(f-f_0)\
\
endalign*$$
$endgroup$
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
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active
oldest
votes
$begingroup$
As an alternative to going back to the definitions, as explained in Andy Walls' answer, you can also just apply the rules as you stated them:
$$mathcalFleftx(t-t_0)e^j2pi f_0(t-t_0)right=mathcalFleftx(t)e^j2pi f_0trighte^-j2pi ft_0=X(f-f_0)e^-j2pi ft_0$$
where $X(f)$ is the Fourier transform of $x(t)$.
And, for your second example, with $tildeX(f)=mathcalFx(t-t_0)=X(f)e^-j2pi ft_0$ you get
$$mathcalFleftx(t-t_0)e^j2pi f_0tright=tildeX(f-f_0)=X(f-f_0)e^-j2pi (f-f_0)t_0$$
Of course, recognizing that the function in the second example just equals the first function scaled by $e^j2pi f_0t_0$, we could have written down its Fourier transform directly by scaling the Fourier transform of the first function by the same factor.
$endgroup$
add a comment |
$begingroup$
As an alternative to going back to the definitions, as explained in Andy Walls' answer, you can also just apply the rules as you stated them:
$$mathcalFleftx(t-t_0)e^j2pi f_0(t-t_0)right=mathcalFleftx(t)e^j2pi f_0trighte^-j2pi ft_0=X(f-f_0)e^-j2pi ft_0$$
where $X(f)$ is the Fourier transform of $x(t)$.
And, for your second example, with $tildeX(f)=mathcalFx(t-t_0)=X(f)e^-j2pi ft_0$ you get
$$mathcalFleftx(t-t_0)e^j2pi f_0tright=tildeX(f-f_0)=X(f-f_0)e^-j2pi (f-f_0)t_0$$
Of course, recognizing that the function in the second example just equals the first function scaled by $e^j2pi f_0t_0$, we could have written down its Fourier transform directly by scaling the Fourier transform of the first function by the same factor.
$endgroup$
add a comment |
$begingroup$
As an alternative to going back to the definitions, as explained in Andy Walls' answer, you can also just apply the rules as you stated them:
$$mathcalFleftx(t-t_0)e^j2pi f_0(t-t_0)right=mathcalFleftx(t)e^j2pi f_0trighte^-j2pi ft_0=X(f-f_0)e^-j2pi ft_0$$
where $X(f)$ is the Fourier transform of $x(t)$.
And, for your second example, with $tildeX(f)=mathcalFx(t-t_0)=X(f)e^-j2pi ft_0$ you get
$$mathcalFleftx(t-t_0)e^j2pi f_0tright=tildeX(f-f_0)=X(f-f_0)e^-j2pi (f-f_0)t_0$$
Of course, recognizing that the function in the second example just equals the first function scaled by $e^j2pi f_0t_0$, we could have written down its Fourier transform directly by scaling the Fourier transform of the first function by the same factor.
$endgroup$
As an alternative to going back to the definitions, as explained in Andy Walls' answer, you can also just apply the rules as you stated them:
$$mathcalFleftx(t-t_0)e^j2pi f_0(t-t_0)right=mathcalFleftx(t)e^j2pi f_0trighte^-j2pi ft_0=X(f-f_0)e^-j2pi ft_0$$
where $X(f)$ is the Fourier transform of $x(t)$.
And, for your second example, with $tildeX(f)=mathcalFx(t-t_0)=X(f)e^-j2pi ft_0$ you get
$$mathcalFleftx(t-t_0)e^j2pi f_0tright=tildeX(f-f_0)=X(f-f_0)e^-j2pi (f-f_0)t_0$$
Of course, recognizing that the function in the second example just equals the first function scaled by $e^j2pi f_0t_0$, we could have written down its Fourier transform directly by scaling the Fourier transform of the first function by the same factor.
answered Feb 5 at 17:15
Matt L.Matt L.
50.6k23889
50.6k23889
add a comment |
add a comment |
$begingroup$
If you are ever unsure, just go back to the definition and work out the Fourier Transform property for the specific situation:
$$beginalign*mathscrFleftxleft(t-t_0right)e^j2pi f_0left(t-t_0right)right &= int_-infty^infty xleft(t-t_0right)e^j2pi f_0left(t-t_0right) e^-j2pi f tdt\
\
&= int_-infty^infty xleft(tauright)e^j2pi f_0tau e^-j2pi f left(tau+t_0right)dtau \
\
&= e^-j2pi ft_0int_-infty^infty xleft(tauright)e^j2pi f_0tau e^-j2pi f taudtau \
\
&= e^-j2pi ft_0int_-infty^infty xleft(tauright) e^-j2pi (f-f_0) taudtau \
\
&= e^-j2pi ft_0 X(f-f_0)\
\
endalign*$$
$$beginalign*mathscrFleftxleft(t-t_0right)e^j2pi f_0 tright &= int_-infty^infty xleft(t-t_0right)e^j2pi f_0t e^-j2pi f tdt\
\
&= int_-infty^infty xleft(tauright)e^j2pi f_0(tau+t_0) e^-j2pi f left(tau+t_0right)dtau \
\
&= e^-j2pi (f-f_0)t_0int_-infty^infty xleft(tauright)e^j2pi f_0tau e^-j2pi f taudtau \
\
&= e^-j2pi (f-f_0)t_0int_-infty^infty xleft(tauright) e^-j2pi (f-f_0) taudtau \
\
&= e^-j2pi (f-f_0)t_0 X(f-f_0)\
\
endalign*$$
$endgroup$
add a comment |
$begingroup$
If you are ever unsure, just go back to the definition and work out the Fourier Transform property for the specific situation:
$$beginalign*mathscrFleftxleft(t-t_0right)e^j2pi f_0left(t-t_0right)right &= int_-infty^infty xleft(t-t_0right)e^j2pi f_0left(t-t_0right) e^-j2pi f tdt\
\
&= int_-infty^infty xleft(tauright)e^j2pi f_0tau e^-j2pi f left(tau+t_0right)dtau \
\
&= e^-j2pi ft_0int_-infty^infty xleft(tauright)e^j2pi f_0tau e^-j2pi f taudtau \
\
&= e^-j2pi ft_0int_-infty^infty xleft(tauright) e^-j2pi (f-f_0) taudtau \
\
&= e^-j2pi ft_0 X(f-f_0)\
\
endalign*$$
$$beginalign*mathscrFleftxleft(t-t_0right)e^j2pi f_0 tright &= int_-infty^infty xleft(t-t_0right)e^j2pi f_0t e^-j2pi f tdt\
\
&= int_-infty^infty xleft(tauright)e^j2pi f_0(tau+t_0) e^-j2pi f left(tau+t_0right)dtau \
\
&= e^-j2pi (f-f_0)t_0int_-infty^infty xleft(tauright)e^j2pi f_0tau e^-j2pi f taudtau \
\
&= e^-j2pi (f-f_0)t_0int_-infty^infty xleft(tauright) e^-j2pi (f-f_0) taudtau \
\
&= e^-j2pi (f-f_0)t_0 X(f-f_0)\
\
endalign*$$
$endgroup$
add a comment |
$begingroup$
If you are ever unsure, just go back to the definition and work out the Fourier Transform property for the specific situation:
$$beginalign*mathscrFleftxleft(t-t_0right)e^j2pi f_0left(t-t_0right)right &= int_-infty^infty xleft(t-t_0right)e^j2pi f_0left(t-t_0right) e^-j2pi f tdt\
\
&= int_-infty^infty xleft(tauright)e^j2pi f_0tau e^-j2pi f left(tau+t_0right)dtau \
\
&= e^-j2pi ft_0int_-infty^infty xleft(tauright)e^j2pi f_0tau e^-j2pi f taudtau \
\
&= e^-j2pi ft_0int_-infty^infty xleft(tauright) e^-j2pi (f-f_0) taudtau \
\
&= e^-j2pi ft_0 X(f-f_0)\
\
endalign*$$
$$beginalign*mathscrFleftxleft(t-t_0right)e^j2pi f_0 tright &= int_-infty^infty xleft(t-t_0right)e^j2pi f_0t e^-j2pi f tdt\
\
&= int_-infty^infty xleft(tauright)e^j2pi f_0(tau+t_0) e^-j2pi f left(tau+t_0right)dtau \
\
&= e^-j2pi (f-f_0)t_0int_-infty^infty xleft(tauright)e^j2pi f_0tau e^-j2pi f taudtau \
\
&= e^-j2pi (f-f_0)t_0int_-infty^infty xleft(tauright) e^-j2pi (f-f_0) taudtau \
\
&= e^-j2pi (f-f_0)t_0 X(f-f_0)\
\
endalign*$$
$endgroup$
If you are ever unsure, just go back to the definition and work out the Fourier Transform property for the specific situation:
$$beginalign*mathscrFleftxleft(t-t_0right)e^j2pi f_0left(t-t_0right)right &= int_-infty^infty xleft(t-t_0right)e^j2pi f_0left(t-t_0right) e^-j2pi f tdt\
\
&= int_-infty^infty xleft(tauright)e^j2pi f_0tau e^-j2pi f left(tau+t_0right)dtau \
\
&= e^-j2pi ft_0int_-infty^infty xleft(tauright)e^j2pi f_0tau e^-j2pi f taudtau \
\
&= e^-j2pi ft_0int_-infty^infty xleft(tauright) e^-j2pi (f-f_0) taudtau \
\
&= e^-j2pi ft_0 X(f-f_0)\
\
endalign*$$
$$beginalign*mathscrFleftxleft(t-t_0right)e^j2pi f_0 tright &= int_-infty^infty xleft(t-t_0right)e^j2pi f_0t e^-j2pi f tdt\
\
&= int_-infty^infty xleft(tauright)e^j2pi f_0(tau+t_0) e^-j2pi f left(tau+t_0right)dtau \
\
&= e^-j2pi (f-f_0)t_0int_-infty^infty xleft(tauright)e^j2pi f_0tau e^-j2pi f taudtau \
\
&= e^-j2pi (f-f_0)t_0int_-infty^infty xleft(tauright) e^-j2pi (f-f_0) taudtau \
\
&= e^-j2pi (f-f_0)t_0 X(f-f_0)\
\
endalign*$$
answered Feb 5 at 14:20
Andy WallsAndy Walls
1,459127
1,459127
add a comment |
add a comment |
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$begingroup$
it's really nice to see new contributors use $LaTeX$. thanks.
$endgroup$
– robert bristow-johnson
Feb 5 at 20:37