- #1
roam
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Homework Statement
Match each discrete-time signal with its DFT:
Homework Equations
The Attempt at a Solution
I am mainly confused about Signal 7 and Signal 8.
Signal 1 is the discrete equivalent to a constant function, therefore its DFT is an impulse (Dirac ##\delta##), so it corresponds to DFT 3.
DFT of an impulse is a constant. Therefore Signal 6 corresponds to DFT 5.
Signal 2 is a sampled version of a full period of a cosine. So we expect ##X(1)## and ##X(-1)## to be nonzero (##X(-1)## really is ##X(N-1)=X(25)##). Therefore Signal 2 corresponds to DFT8.
By similar arguments, Signal 4 has exactly 2 cycles of a cosine and corresponds to DFT2. And Signal 3 has one and a half periods of a cosine, as we do not have complete periods we should expect spectral leakage, so signal 3 corresponds to DFT4 (the main peaks are around 1 & 2 plus negative frequencies). Likewise, Signal 5 corresponds to DFT7.
Here is a summary of the results so far:
Only Signals 7 & 8 and DFT 6 & 1 are left:
Any explanation would be greatly appreciated.