Are the following frequency domain signals valid DTFT's (Discrete Time Fourier Transforms)? Answer yes or no, and justify your answer.

a) $X(\omega) = \omega + \pi$

b) $X(\omega) = i + \pi$

c) $X(\omega) = \sin(10\omega)$

d) $X(\omega) = \sin(\omega/10)$

I'm just very unsure as to how to go about this question (what methodology to use). Could anyone possibly point me in the right direction? Thanks!

  • 4
    $\begingroup$ Shouldn't a valid DTFT be $2\pi$-periodic? $\endgroup$ – Matt L. Mar 17 '14 at 8:27
  • 1
    $\begingroup$ Maybe consulting a table of DTFTs will give you some ideas as to what typical DTFTs look like. $\endgroup$ – Dilip Sarwate Mar 17 '14 at 12:42

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