GATE 2015 EC – Question 33
Consider the signal $s(t) = m(t)\cos(2\pi f_c t) + \hat{m}(t)\sin(2\pi f_c t)$ where $\hat{m}(t)$ denotes the Hilbert transform of $m(t)$ and the bandwidth of $m(t)$ is very small compared to $f_c$. The signal $s(t)$ is a
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Correct answer: (C) band-pass signal
Explanation
A message and its Hilbert transform combined with a cosine and sine carrier like this gives a single sideband signal. The spectrum sits in a narrow band around $f_c$ with no energy near zero frequency, so it is a band-pass signal.