Fourier Transform with both Time Delay and Frequency Shift
$begingroup$
I know that the Fourier transform of a function with time delay can be written as: $$F(x(t-t_0))=X(f)e^{-j2pi f t_0}$$.
The Fourier transform of a function with frequency shift can also be written as: $$F(x(t)e^{j2pi f_0 t})=X(f-f_0)$$.
So what if we have both of them at the time domain, what will be the result in the frequency domain;
$$F(x(t-t_0)e^{j2pi f_0 (t-t_0)})$$.
Will the result be: $$X(f-f_0)e^{-jpi 2 f (t-t_0)}$$.
Also what will be the result of:
$$F(x(t-t_0)e^{j2pi f_0 t)})$$.
Is there an order to apply these properties?
fourier-transform time-frequency
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add a comment |
$begingroup$
I know that the Fourier transform of a function with time delay can be written as: $$F(x(t-t_0))=X(f)e^{-j2pi f t_0}$$.
The Fourier transform of a function with frequency shift can also be written as: $$F(x(t)e^{j2pi f_0 t})=X(f-f_0)$$.
So what if we have both of them at the time domain, what will be the result in the frequency domain;
$$F(x(t-t_0)e^{j2pi f_0 (t-t_0)})$$.
Will the result be: $$X(f-f_0)e^{-jpi 2 f (t-t_0)}$$.
Also what will be the result of:
$$F(x(t-t_0)e^{j2pi f_0 t)})$$.
Is there an order to apply these properties?
fourier-transform time-frequency
New contributor
tamuno is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
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add a comment |
$begingroup$
I know that the Fourier transform of a function with time delay can be written as: $$F(x(t-t_0))=X(f)e^{-j2pi f t_0}$$.
The Fourier transform of a function with frequency shift can also be written as: $$F(x(t)e^{j2pi f_0 t})=X(f-f_0)$$.
So what if we have both of them at the time domain, what will be the result in the frequency domain;
$$F(x(t-t_0)e^{j2pi f_0 (t-t_0)})$$.
Will the result be: $$X(f-f_0)e^{-jpi 2 f (t-t_0)}$$.
Also what will be the result of:
$$F(x(t-t_0)e^{j2pi f_0 t)})$$.
Is there an order to apply these properties?
fourier-transform time-frequency
New contributor
tamuno is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
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I know that the Fourier transform of a function with time delay can be written as: $$F(x(t-t_0))=X(f)e^{-j2pi f t_0}$$.
The Fourier transform of a function with frequency shift can also be written as: $$F(x(t)e^{j2pi f_0 t})=X(f-f_0)$$.
So what if we have both of them at the time domain, what will be the result in the frequency domain;
$$F(x(t-t_0)e^{j2pi f_0 (t-t_0)})$$.
Will the result be: $$X(f-f_0)e^{-jpi 2 f (t-t_0)}$$.
Also what will be the result of:
$$F(x(t-t_0)e^{j2pi f_0 t)})$$.
Is there an order to apply these properties?
fourier-transform time-frequency
fourier-transform time-frequency
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tamuno is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
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edited 4 hours ago
tamuno
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asked 4 hours ago
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2 Answers
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$begingroup$
If you are ever unsure, just go back to the definition and work out the Fourier Transform property for the specific situation:
$$begin{align*}mathscr{F}left{xleft(t-t_0right)e^{j2pi f_0left(t-t_0right)}right} &= int_{-infty}^infty xleft(t-t_0right)e^{j2pi f_0left(t-t_0right)} e^{-j2pi f t}dt\
\
&= int_{-infty}^infty xleft(tauright)e^{j2pi f_0tau} e^{-j2pi f left(tau+t_0right)}dtau \
\
&= e^{-j2pi ft_0}int_{-infty}^infty xleft(tauright)e^{j2pi f_0tau} e^{-j2pi f tau}dtau \
\
&= e^{-j2pi ft_0}int_{-infty}^infty xleft(tauright) e^{-j2pi (f-f_0) tau}dtau \
\
&= e^{-j2pi ft_0} X(f-f_0)\
\
end{align*}$$
$$begin{align*}mathscr{F}left{xleft(t-t_0right)e^{j2pi f_0 t}right} &= int_{-infty}^infty xleft(t-t_0right)e^{j2pi f_0t} e^{-j2pi f t}dt\
\
&= int_{-infty}^infty xleft(tauright)e^{j2pi f_0(tau+t_0)} e^{-j2pi f left(tau+t_0right)}dtau \
\
&= e^{-j2pi (f-f_0)t_0}int_{-infty}^infty xleft(tauright)e^{j2pi f_0tau} e^{-j2pi f tau}dtau \
\
&= e^{-j2pi (f-f_0)t_0}int_{-infty}^infty xleft(tauright) e^{-j2pi (f-f_0) tau}dtau \
\
&= e^{-j2pi (f-f_0)t_0} X(f-f_0)\
\
end{align*}$$
$endgroup$
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:
$$mathcal{F}left{x(t-t_0)e^{j2pi f_0(t-t_0)}right}=mathcal{F}left{x(t)e^{j2pi f_0t}right}e^{-j2pi ft_0}=X(f-f_0)e^{-j2pi ft_0}$$
where $X(f)$ is the Fourier transform of $x(t)$.
And, for your second example, with $tilde{X}(f)=mathcal{F}{x(t-t_0)}=X(f)e^{-j2pi ft_0}$ you get
$$mathcal{F}left{x(t-t_0)e^{j2pi f_0t}right}=tilde{X}(f-f_0)=X(f-f_0)e^{-j2pi (f-f_0)t_0}$$
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.
$endgroup$
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2 Answers
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2 Answers
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$begingroup$
If you are ever unsure, just go back to the definition and work out the Fourier Transform property for the specific situation:
$$begin{align*}mathscr{F}left{xleft(t-t_0right)e^{j2pi f_0left(t-t_0right)}right} &= int_{-infty}^infty xleft(t-t_0right)e^{j2pi f_0left(t-t_0right)} e^{-j2pi f t}dt\
\
&= int_{-infty}^infty xleft(tauright)e^{j2pi f_0tau} e^{-j2pi f left(tau+t_0right)}dtau \
\
&= e^{-j2pi ft_0}int_{-infty}^infty xleft(tauright)e^{j2pi f_0tau} e^{-j2pi f tau}dtau \
\
&= e^{-j2pi ft_0}int_{-infty}^infty xleft(tauright) e^{-j2pi (f-f_0) tau}dtau \
\
&= e^{-j2pi ft_0} X(f-f_0)\
\
end{align*}$$
$$begin{align*}mathscr{F}left{xleft(t-t_0right)e^{j2pi f_0 t}right} &= int_{-infty}^infty xleft(t-t_0right)e^{j2pi f_0t} e^{-j2pi f t}dt\
\
&= int_{-infty}^infty xleft(tauright)e^{j2pi f_0(tau+t_0)} e^{-j2pi f left(tau+t_0right)}dtau \
\
&= e^{-j2pi (f-f_0)t_0}int_{-infty}^infty xleft(tauright)e^{j2pi f_0tau} e^{-j2pi f tau}dtau \
\
&= e^{-j2pi (f-f_0)t_0}int_{-infty}^infty xleft(tauright) e^{-j2pi (f-f_0) tau}dtau \
\
&= e^{-j2pi (f-f_0)t_0} X(f-f_0)\
\
end{align*}$$
$endgroup$
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:
$$begin{align*}mathscr{F}left{xleft(t-t_0right)e^{j2pi f_0left(t-t_0right)}right} &= int_{-infty}^infty xleft(t-t_0right)e^{j2pi f_0left(t-t_0right)} e^{-j2pi f t}dt\
\
&= int_{-infty}^infty xleft(tauright)e^{j2pi f_0tau} e^{-j2pi f left(tau+t_0right)}dtau \
\
&= e^{-j2pi ft_0}int_{-infty}^infty xleft(tauright)e^{j2pi f_0tau} e^{-j2pi f tau}dtau \
\
&= e^{-j2pi ft_0}int_{-infty}^infty xleft(tauright) e^{-j2pi (f-f_0) tau}dtau \
\
&= e^{-j2pi ft_0} X(f-f_0)\
\
end{align*}$$
$$begin{align*}mathscr{F}left{xleft(t-t_0right)e^{j2pi f_0 t}right} &= int_{-infty}^infty xleft(t-t_0right)e^{j2pi f_0t} e^{-j2pi f t}dt\
\
&= int_{-infty}^infty xleft(tauright)e^{j2pi f_0(tau+t_0)} e^{-j2pi f left(tau+t_0right)}dtau \
\
&= e^{-j2pi (f-f_0)t_0}int_{-infty}^infty xleft(tauright)e^{j2pi f_0tau} e^{-j2pi f tau}dtau \
\
&= e^{-j2pi (f-f_0)t_0}int_{-infty}^infty xleft(tauright) e^{-j2pi (f-f_0) tau}dtau \
\
&= e^{-j2pi (f-f_0)t_0} X(f-f_0)\
\
end{align*}$$
$endgroup$
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:
$$begin{align*}mathscr{F}left{xleft(t-t_0right)e^{j2pi f_0left(t-t_0right)}right} &= int_{-infty}^infty xleft(t-t_0right)e^{j2pi f_0left(t-t_0right)} e^{-j2pi f t}dt\
\
&= int_{-infty}^infty xleft(tauright)e^{j2pi f_0tau} e^{-j2pi f left(tau+t_0right)}dtau \
\
&= e^{-j2pi ft_0}int_{-infty}^infty xleft(tauright)e^{j2pi f_0tau} e^{-j2pi f tau}dtau \
\
&= e^{-j2pi ft_0}int_{-infty}^infty xleft(tauright) e^{-j2pi (f-f_0) tau}dtau \
\
&= e^{-j2pi ft_0} X(f-f_0)\
\
end{align*}$$
$$begin{align*}mathscr{F}left{xleft(t-t_0right)e^{j2pi f_0 t}right} &= int_{-infty}^infty xleft(t-t_0right)e^{j2pi f_0t} e^{-j2pi f t}dt\
\
&= int_{-infty}^infty xleft(tauright)e^{j2pi f_0(tau+t_0)} e^{-j2pi f left(tau+t_0right)}dtau \
\
&= e^{-j2pi (f-f_0)t_0}int_{-infty}^infty xleft(tauright)e^{j2pi f_0tau} e^{-j2pi f tau}dtau \
\
&= e^{-j2pi (f-f_0)t_0}int_{-infty}^infty xleft(tauright) e^{-j2pi (f-f_0) tau}dtau \
\
&= e^{-j2pi (f-f_0)t_0} X(f-f_0)\
\
end{align*}$$
$endgroup$
If you are ever unsure, just go back to the definition and work out the Fourier Transform property for the specific situation:
$$begin{align*}mathscr{F}left{xleft(t-t_0right)e^{j2pi f_0left(t-t_0right)}right} &= int_{-infty}^infty xleft(t-t_0right)e^{j2pi f_0left(t-t_0right)} e^{-j2pi f t}dt\
\
&= int_{-infty}^infty xleft(tauright)e^{j2pi f_0tau} e^{-j2pi f left(tau+t_0right)}dtau \
\
&= e^{-j2pi ft_0}int_{-infty}^infty xleft(tauright)e^{j2pi f_0tau} e^{-j2pi f tau}dtau \
\
&= e^{-j2pi ft_0}int_{-infty}^infty xleft(tauright) e^{-j2pi (f-f_0) tau}dtau \
\
&= e^{-j2pi ft_0} X(f-f_0)\
\
end{align*}$$
$$begin{align*}mathscr{F}left{xleft(t-t_0right)e^{j2pi f_0 t}right} &= int_{-infty}^infty xleft(t-t_0right)e^{j2pi f_0t} e^{-j2pi f t}dt\
\
&= int_{-infty}^infty xleft(tauright)e^{j2pi f_0(tau+t_0)} e^{-j2pi f left(tau+t_0right)}dtau \
\
&= e^{-j2pi (f-f_0)t_0}int_{-infty}^infty xleft(tauright)e^{j2pi f_0tau} e^{-j2pi f tau}dtau \
\
&= e^{-j2pi (f-f_0)t_0}int_{-infty}^infty xleft(tauright) e^{-j2pi (f-f_0) tau}dtau \
\
&= e^{-j2pi (f-f_0)t_0} X(f-f_0)\
\
end{align*}$$
answered 3 hours ago
Andy WallsAndy Walls
1,439127
1,439127
add a comment |
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:
$$mathcal{F}left{x(t-t_0)e^{j2pi f_0(t-t_0)}right}=mathcal{F}left{x(t)e^{j2pi f_0t}right}e^{-j2pi ft_0}=X(f-f_0)e^{-j2pi ft_0}$$
where $X(f)$ is the Fourier transform of $x(t)$.
And, for your second example, with $tilde{X}(f)=mathcal{F}{x(t-t_0)}=X(f)e^{-j2pi ft_0}$ you get
$$mathcal{F}left{x(t-t_0)e^{j2pi f_0t}right}=tilde{X}(f-f_0)=X(f-f_0)e^{-j2pi (f-f_0)t_0}$$
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:
$$mathcal{F}left{x(t-t_0)e^{j2pi f_0(t-t_0)}right}=mathcal{F}left{x(t)e^{j2pi f_0t}right}e^{-j2pi ft_0}=X(f-f_0)e^{-j2pi ft_0}$$
where $X(f)$ is the Fourier transform of $x(t)$.
And, for your second example, with $tilde{X}(f)=mathcal{F}{x(t-t_0)}=X(f)e^{-j2pi ft_0}$ you get
$$mathcal{F}left{x(t-t_0)e^{j2pi f_0t}right}=tilde{X}(f-f_0)=X(f-f_0)e^{-j2pi (f-f_0)t_0}$$
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:
$$mathcal{F}left{x(t-t_0)e^{j2pi f_0(t-t_0)}right}=mathcal{F}left{x(t)e^{j2pi f_0t}right}e^{-j2pi ft_0}=X(f-f_0)e^{-j2pi ft_0}$$
where $X(f)$ is the Fourier transform of $x(t)$.
And, for your second example, with $tilde{X}(f)=mathcal{F}{x(t-t_0)}=X(f)e^{-j2pi ft_0}$ you get
$$mathcal{F}left{x(t-t_0)e^{j2pi f_0t}right}=tilde{X}(f-f_0)=X(f-f_0)e^{-j2pi (f-f_0)t_0}$$
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:
$$mathcal{F}left{x(t-t_0)e^{j2pi f_0(t-t_0)}right}=mathcal{F}left{x(t)e^{j2pi f_0t}right}e^{-j2pi ft_0}=X(f-f_0)e^{-j2pi ft_0}$$
where $X(f)$ is the Fourier transform of $x(t)$.
And, for your second example, with $tilde{X}(f)=mathcal{F}{x(t-t_0)}=X(f)e^{-j2pi ft_0}$ you get
$$mathcal{F}left{x(t-t_0)e^{j2pi f_0t}right}=tilde{X}(f-f_0)=X(f-f_0)e^{-j2pi (f-f_0)t_0}$$
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 25 mins ago
Matt L.Matt L.
50.3k23888
50.3k23888
add a comment |
add a comment |
tamuno is a new contributor. Be nice, and check out our Code of Conduct.
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