Necessary condition for sampling without distortion

A distorted signal of frequency fm is recovered from a sampled signal if the sampling frequency fs is


a) fs> 2fm
b) fs< 2fm
c) fs= 2fm
d) fs>= 2fm

Correct Answer: b) fs< 2fm


If the signal of frequency fm is sampled at the rate fs >= 2fm only then the spectrum of the sampled signal is obtained without overlapping. For fs <2fm the sampled signal spectrum overlap each other, and therefore the signal cannot be recovered easily. For reconstruction of signal to be free from distortion, the important condition is

fs >= 2fm
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