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Real-Time Digital Signal Processing from MATLAB to C with the TMS320C6x DSPs, Third Edition, 3rd Edition by Michael G. Morrow, Cameron H.G. Wright, Thad B. Welch

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Chapter 16

Project 7: AM Receivers

 

16.1    Theory

AMPLITUDE modulation (AM) is a very popular modulation scheme. As we discussed in Chapter 15, AM signals are carried in the envelope of the carrier signal. An AM signal with carrier frequency fc = 550 kHz, message frequency fmsg = 5 kHz, and modulation index μ = 0.8, is shown in Figure 16.1. In this figure, the signal’s envelope is clearly sinusoidal. Counting the envelope variations shows that the signal envelope experiences five periods in the displayed time duration of 1 millisecond. The message frequency can now be verified to be fmsg = 5/0.001 = 5 kHz. Since the carrier is displayed as solid shading in this figure, it is impossible to precisely determine its exact frequency without ...

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