A very naive question... A signal with bandwidth of 20 MHz is modulated using a carrier of 1 GHz. What will be the sampling frequency? I was asked this question during an interview. I answered 2 GHz but the interviewer said it will be 40 MHz. Can anyone explain it? Thanks.
Nyqvist-shannon sampling theorem only says that your sampling frequency should be greater than twice the bandwidth of the signal and not twice the carrier frequency of the signal. Hence you can modulate your 20 MHz signal at any carrier frequency you need and still get back your original signal by sampling at greater than 40 MHz. Hence you need not sample at 2GHZ for recovery of signal, you can do away with a sampling frequency greater than 40 MHz itself For a more clear understanding refer to bandpass sampling.