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Hint write the coherent demodulator output in terms

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Unformatted text preview: the frequency response shown below. That is, H(f)= f − fc + 1000, fc − 1000 < f < fc + 1000 0, otherwise. Let the filter output be y (t ) . If y (t ) is input to a coherent demodulator (that is, to a system that forms y (t ) cos ( 2π fc t ) ) followed by a LPF with bandwidth = 1 kHz), what is the output? (Hint: Write the coherent demodulator output in terms of M ( f ) and H ( f ) .) 3. Let m1 (t ) and m2 (t ) be two lowpass message signals, each having bandwidth = B Hz. The quadrature carrier multiplexed (QCM) transmitted signal for these messages is defined to be x (t ) = Am1 (t ) cos ( 2π fc t + θ ) + Am2 (t ) sin ( 2π fc t + θ ) where fc >> B and θ is some fixed phase angle. a) What is the bandwidth of the transmitted signal? From your answer, explain why QCM is called a “bandwidth efficient” communication system. b) Suppose that we have a phase- synchronized local oscillator that is capable of generating both cos ( 2...
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