4 GHz carrier is DSB Sc modulated by a low pass message signal with maximum frequency of 2 MHz. The resultant signal is to be ideally sampled. The minimum frequency of the sampling in train should be (a) 4 MHz (b) 8 MHz (c) 8 GHz (d) 8.004 GHz?

According to Nyquist sampling theorem, a bandlimited signal should be sampled equal to greater than the twice of the maximum frequency component of the signal. In this example, the spectrum after up-conversion has a maximum frequency ofMHz +2MHz =MHz. So the sampling frequency required to prevent aliasingMHz =8.GHz. Right answer (d)