A DSB-LC AM signal has the following form s(t) = A(1 + m (t))cos(2 ft). a) b) c) d) e) f) Assume that s(t) = 5cos(6nt) +20cos(10zt) + 5cos(14zt) Find the modulating signal m(t) and the power efficiency of this DSB-LC AM modulation. [5 marks] Let A = 20, f=5 and 0.5. Suppose that the message signal m(t) in s(t) is replaced by sin (71) Write down the (time domain) expression for the corresponding modulated nt signal. [3 marks] Plot the time domain waveform of the modulated signal in b). Sketch the demodulation output using an envelope detector. [4 marks] Sketch the spectrum for the modulated signal in b). sin (nt) is t Hint: The Fourier transform of x(t) = X (f) = = {1 fi