Fourier Transform with both Time Delay and Frequency Shift












2












$begingroup$


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?









share









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    2












    $begingroup$


    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?









    share









    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.







    $endgroup$















      2












      2








      2


      1



      $begingroup$


      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?









      share









      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.







      $endgroup$




      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





      share









      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.










      share









      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.








      share



      share








      edited 4 hours ago







      tamuno













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      asked 4 hours ago









      tamunotamuno

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      New contributor




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      New contributor





      tamuno is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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      Check out our Code of Conduct.






















          2 Answers
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          3












          $begingroup$

          If you are ever unsure, just go back to the definition and work out the Fourier Transform property for the specific situation:



          $$begin{align*}mathscr{F}left{xleft(t-t_0right)e^{j2pi f_0left(t-t_0right)}right} &= int_{-infty}^infty xleft(t-t_0right)e^{j2pi f_0left(t-t_0right)} e^{-j2pi f t}dt\
          \
          &= int_{-infty}^infty xleft(tauright)e^{j2pi f_0tau} e^{-j2pi f left(tau+t_0right)}dtau \
          \
          &= e^{-j2pi ft_0}int_{-infty}^infty xleft(tauright)e^{j2pi f_0tau} e^{-j2pi f tau}dtau \
          \
          &= e^{-j2pi ft_0}int_{-infty}^infty xleft(tauright) e^{-j2pi (f-f_0) tau}dtau \
          \
          &= e^{-j2pi ft_0} X(f-f_0)\
          \
          end{align*}$$



          $$begin{align*}mathscr{F}left{xleft(t-t_0right)e^{j2pi f_0 t}right} &= int_{-infty}^infty xleft(t-t_0right)e^{j2pi f_0t} e^{-j2pi f t}dt\
          \
          &= int_{-infty}^infty xleft(tauright)e^{j2pi f_0(tau+t_0)} e^{-j2pi f left(tau+t_0right)}dtau \
          \
          &= e^{-j2pi (f-f_0)t_0}int_{-infty}^infty xleft(tauright)e^{j2pi f_0tau} e^{-j2pi f tau}dtau \
          \
          &= e^{-j2pi (f-f_0)t_0}int_{-infty}^infty xleft(tauright) e^{-j2pi (f-f_0) tau}dtau \
          \
          &= e^{-j2pi (f-f_0)t_0} X(f-f_0)\
          \
          end{align*}$$






          share|improve this answer









          $endgroup$





















            1












            $begingroup$

            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.






            share|improve this answer









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              2 Answers
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              2 Answers
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              3












              $begingroup$

              If you are ever unsure, just go back to the definition and work out the Fourier Transform property for the specific situation:



              $$begin{align*}mathscr{F}left{xleft(t-t_0right)e^{j2pi f_0left(t-t_0right)}right} &= int_{-infty}^infty xleft(t-t_0right)e^{j2pi f_0left(t-t_0right)} e^{-j2pi f t}dt\
              \
              &= int_{-infty}^infty xleft(tauright)e^{j2pi f_0tau} e^{-j2pi f left(tau+t_0right)}dtau \
              \
              &= e^{-j2pi ft_0}int_{-infty}^infty xleft(tauright)e^{j2pi f_0tau} e^{-j2pi f tau}dtau \
              \
              &= e^{-j2pi ft_0}int_{-infty}^infty xleft(tauright) e^{-j2pi (f-f_0) tau}dtau \
              \
              &= e^{-j2pi ft_0} X(f-f_0)\
              \
              end{align*}$$



              $$begin{align*}mathscr{F}left{xleft(t-t_0right)e^{j2pi f_0 t}right} &= int_{-infty}^infty xleft(t-t_0right)e^{j2pi f_0t} e^{-j2pi f t}dt\
              \
              &= int_{-infty}^infty xleft(tauright)e^{j2pi f_0(tau+t_0)} e^{-j2pi f left(tau+t_0right)}dtau \
              \
              &= e^{-j2pi (f-f_0)t_0}int_{-infty}^infty xleft(tauright)e^{j2pi f_0tau} e^{-j2pi f tau}dtau \
              \
              &= e^{-j2pi (f-f_0)t_0}int_{-infty}^infty xleft(tauright) e^{-j2pi (f-f_0) tau}dtau \
              \
              &= e^{-j2pi (f-f_0)t_0} X(f-f_0)\
              \
              end{align*}$$






              share|improve this answer









              $endgroup$


















                3












                $begingroup$

                If you are ever unsure, just go back to the definition and work out the Fourier Transform property for the specific situation:



                $$begin{align*}mathscr{F}left{xleft(t-t_0right)e^{j2pi f_0left(t-t_0right)}right} &= int_{-infty}^infty xleft(t-t_0right)e^{j2pi f_0left(t-t_0right)} e^{-j2pi f t}dt\
                \
                &= int_{-infty}^infty xleft(tauright)e^{j2pi f_0tau} e^{-j2pi f left(tau+t_0right)}dtau \
                \
                &= e^{-j2pi ft_0}int_{-infty}^infty xleft(tauright)e^{j2pi f_0tau} e^{-j2pi f tau}dtau \
                \
                &= e^{-j2pi ft_0}int_{-infty}^infty xleft(tauright) e^{-j2pi (f-f_0) tau}dtau \
                \
                &= e^{-j2pi ft_0} X(f-f_0)\
                \
                end{align*}$$



                $$begin{align*}mathscr{F}left{xleft(t-t_0right)e^{j2pi f_0 t}right} &= int_{-infty}^infty xleft(t-t_0right)e^{j2pi f_0t} e^{-j2pi f t}dt\
                \
                &= int_{-infty}^infty xleft(tauright)e^{j2pi f_0(tau+t_0)} e^{-j2pi f left(tau+t_0right)}dtau \
                \
                &= e^{-j2pi (f-f_0)t_0}int_{-infty}^infty xleft(tauright)e^{j2pi f_0tau} e^{-j2pi f tau}dtau \
                \
                &= e^{-j2pi (f-f_0)t_0}int_{-infty}^infty xleft(tauright) e^{-j2pi (f-f_0) tau}dtau \
                \
                &= e^{-j2pi (f-f_0)t_0} X(f-f_0)\
                \
                end{align*}$$






                share|improve this answer









                $endgroup$
















                  3












                  3








                  3





                  $begingroup$

                  If you are ever unsure, just go back to the definition and work out the Fourier Transform property for the specific situation:



                  $$begin{align*}mathscr{F}left{xleft(t-t_0right)e^{j2pi f_0left(t-t_0right)}right} &= int_{-infty}^infty xleft(t-t_0right)e^{j2pi f_0left(t-t_0right)} e^{-j2pi f t}dt\
                  \
                  &= int_{-infty}^infty xleft(tauright)e^{j2pi f_0tau} e^{-j2pi f left(tau+t_0right)}dtau \
                  \
                  &= e^{-j2pi ft_0}int_{-infty}^infty xleft(tauright)e^{j2pi f_0tau} e^{-j2pi f tau}dtau \
                  \
                  &= e^{-j2pi ft_0}int_{-infty}^infty xleft(tauright) e^{-j2pi (f-f_0) tau}dtau \
                  \
                  &= e^{-j2pi ft_0} X(f-f_0)\
                  \
                  end{align*}$$



                  $$begin{align*}mathscr{F}left{xleft(t-t_0right)e^{j2pi f_0 t}right} &= int_{-infty}^infty xleft(t-t_0right)e^{j2pi f_0t} e^{-j2pi f t}dt\
                  \
                  &= int_{-infty}^infty xleft(tauright)e^{j2pi f_0(tau+t_0)} e^{-j2pi f left(tau+t_0right)}dtau \
                  \
                  &= e^{-j2pi (f-f_0)t_0}int_{-infty}^infty xleft(tauright)e^{j2pi f_0tau} e^{-j2pi f tau}dtau \
                  \
                  &= e^{-j2pi (f-f_0)t_0}int_{-infty}^infty xleft(tauright) e^{-j2pi (f-f_0) tau}dtau \
                  \
                  &= e^{-j2pi (f-f_0)t_0} X(f-f_0)\
                  \
                  end{align*}$$






                  share|improve this answer









                  $endgroup$



                  If you are ever unsure, just go back to the definition and work out the Fourier Transform property for the specific situation:



                  $$begin{align*}mathscr{F}left{xleft(t-t_0right)e^{j2pi f_0left(t-t_0right)}right} &= int_{-infty}^infty xleft(t-t_0right)e^{j2pi f_0left(t-t_0right)} e^{-j2pi f t}dt\
                  \
                  &= int_{-infty}^infty xleft(tauright)e^{j2pi f_0tau} e^{-j2pi f left(tau+t_0right)}dtau \
                  \
                  &= e^{-j2pi ft_0}int_{-infty}^infty xleft(tauright)e^{j2pi f_0tau} e^{-j2pi f tau}dtau \
                  \
                  &= e^{-j2pi ft_0}int_{-infty}^infty xleft(tauright) e^{-j2pi (f-f_0) tau}dtau \
                  \
                  &= e^{-j2pi ft_0} X(f-f_0)\
                  \
                  end{align*}$$



                  $$begin{align*}mathscr{F}left{xleft(t-t_0right)e^{j2pi f_0 t}right} &= int_{-infty}^infty xleft(t-t_0right)e^{j2pi f_0t} e^{-j2pi f t}dt\
                  \
                  &= int_{-infty}^infty xleft(tauright)e^{j2pi f_0(tau+t_0)} e^{-j2pi f left(tau+t_0right)}dtau \
                  \
                  &= e^{-j2pi (f-f_0)t_0}int_{-infty}^infty xleft(tauright)e^{j2pi f_0tau} e^{-j2pi f tau}dtau \
                  \
                  &= e^{-j2pi (f-f_0)t_0}int_{-infty}^infty xleft(tauright) e^{-j2pi (f-f_0) tau}dtau \
                  \
                  &= e^{-j2pi (f-f_0)t_0} X(f-f_0)\
                  \
                  end{align*}$$







                  share|improve this answer












                  share|improve this answer



                  share|improve this answer










                  answered 3 hours ago









                  Andy WallsAndy Walls

                  1,439127




                  1,439127























                      1












                      $begingroup$

                      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.






                      share|improve this answer









                      $endgroup$


















                        1












                        $begingroup$

                        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.






                        share|improve this answer









                        $endgroup$
















                          1












                          1








                          1





                          $begingroup$

                          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.






                          share|improve this answer









                          $endgroup$



                          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.







                          share|improve this answer












                          share|improve this answer



                          share|improve this answer










                          answered 25 mins ago









                          Matt L.Matt L.

                          50.3k23888




                          50.3k23888






















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