Question

Which of the following demodulator (s) can be used for demodulating the signal x(t) = 5(1 + 2 cos200 πt)s20000πt 

(a) Envelope demodulator 

(b) Square-law demodulator 

(c) Synchronous demodulator

(d) None of the above

Answer 1

(c) Synchronous demodulator

If the given equation is compared with the standard equation

X_AM(t) = A_c(1 + \(\mu\) cos \(\omega\)_mt) cos\(\omega\)_ct the value µ = 2

The modulation index is more than 1 here, so it is the case of over modulation. When modulation index is more than 1 (over modulation) then detection is possible only with, Synchronous modulation, such signal can not be detected with envelope detector.