# Sampling frequency of modulated signal

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.

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Depending on what is meant by modulation, a baseband signal of bandwidth $20$ MHz might give a passband signal of bandwidth $40$ MHz, and depending on what is meant by sampling might need sampling at a rate greater than $80$ MHz. – Dilip Sarwate May 2 '14 at 13:59