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4.4-6 An LSB signal is demodulated coherently, as shown in Fig. P4.4-6. Unfortunately, because of the transmission delay, the received signal carrier is not 2 cos wet as sent, but rather, is 2 cos((a + Aw)t + 8). The local oscillator is still cos wc. Show the following. (a) When 8 = 0, the output y(t) is the signal m(t) with all its spectral components shifted (offset) by A. Hint: Observe that the output y(t) is identical to the right-hand side of Eq. (4.20a) with we replaced with Aw. (b) When Aw = 0, the output is the signal m(o) with phases of all its spectral components shifted by 8. Hint: Show that the output spectrum Y(A) =M()eld for f20, and equal to M (S)e=;8 when f <0. (c) In each of these cases, explain the nature of distortion Hint: For part (a), demodulation consists of shifting an LSB spectrum to the left and right by Wc + Aw and low-pass-filtering the result. For part (b), use the expression (4.20b) for VLSBC), multiply it by the local carrier 2 cos (ac++ 8), and low-pass-filter the result.
Figure P.4.4-6 L5B (1) y (1) Low-pass filter 2 cos (we + A) +0]
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