A DSB-LC AM signal has the following form s(t) = A(1 + m (t))cos(2 ft). a)...

 

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A DSB-LC AM signal has the following form s(t) = A(1 + μm (t))cos(2π 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 πt Hint: The Fourier transform of x(t) = X (f) = › = {1 fi<0.5 elsewhere [3 marks] Now suppose that we change the modulation method to DSB-SC. The message signal m(t) and carrier frequency are the same as in b). Determine the (time domain) expression for the corresponding modulated signal. [5 marks] Plot the waveform of the modulated signal in question e). Sketch the demodulation output using an envelope detector. [5 marks] A DSB-LC AM signal has the following form s(t) = A(1 + μm (t))cos(2π 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 πt Hint: The Fourier transform of x(t) = X (f) = › = {1 fi<0.5 elsewhere [3 marks] Now suppose that we change the modulation method to DSB-SC. The message signal m(t) and carrier frequency are the same as in b). Determine the (time domain) expression for the corresponding modulated signal. [5 marks] Plot the waveform of the modulated signal in question e). Sketch the demodulation output using an envelope detector. [5 marks]

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