Figure 3 12 shows the AM wave resulting when a square wave modulates a sine

Figure 3 12 shows the am wave resulting when a square

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Figure 3-12 shows the AM wave resulting when a square wave modulates a sine wave carrier. In Fig. 3-12( a ), the percentage of modulation is 50; in Fig. 3-12( b ), it is 100. In this case, when the square wave goes negative, it drives the carrier amplitude to zero. Amplitude modulation by square waves or rectangular binary pulses is referred to as amplitude-shift keying (ASK). ASK is used in some types of data communication when binary information is to be transmitted. Another crude type of amplitude modulation can be achieved by simply turning the carrier off and on. An example is the transmitting of Morse code by using dots and dashes. Amplitude Modulation Fundamentals 103 Figure 3-10 Frequency spectrum of AM broadcast band. 540 kHz 10 kHz channel 535 kHz 1 550 kHz 2 560 kHz 3 1590 kHz 106 1600 kHz 1605 kHz 107 Pulse modulation Seventh harmonic Fifth harmonic Third harmonic Sidebands produced by the fundamental and its harmonics Fundamental f c Carrier Figure 3-11 Frequency spectrum of an AM signal modulated by a square wave. Amplitude-shift keying (ASK)
104 Chapter 3 Figure 3-12Amplitude modulation of a sine wave carrier by a pulse or rectangular waveis called amplitude-shift keying. (a) Fifty percent modulation. (b