Chap2 - Chapter 2 Continuous-Wave Modulation Analog Modulation is the subject concerned in this chapter 2.1 Introduction Analog communication

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Chapter 2 Continuous-Wave Modulation Analog Modulation ” is the subject concerned in this chapter. © Po-Ning [email protected] Chapter 2-2 2.1 Introduction ± Analog communication system ² The most common carrier is the sinusoidal wave. Carrier wave (Analog)
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© Po-Ning [email protected] Chapter 2-3 2.1 Introduction ± Modulation ² A process by which some characteristic of a carrier is varied in accordance with a modulating wave (baseband signal). ± Sinusoidal Continuous-Wave (CW) modulation ² Amplitude modulation ² Angle modulation © Po-Ning [email protected] Chapter 2-4 2.1 Introduction Amplitude Modulation Frequency Modulation Baseband signal Sinusoidal carrier
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© Po-Ning [email protected] Chapter 2-5 2.2 Double-Sideband with Carrier or simply Amplitude Modulation ± Two required conditions on amplitude sensitivity ² 1 + k a m ( t ) 0, which is ensured by | k a m ( t )| 1. ± The case of | k a m ( t )| > 1 is called overmodulation . ± The value of | k a m ( t )| is sometimes represented by “percentage” (because it is limited by 1), and is named (| k a m ( t )| × 100)% modulation. ² f c >> W , where W is the message bandwidth. ± Violation of this condition will cause nonvisualized envelope . index modulation or y sensitivit amplitude is where ), 2 cos( )] ( 1 [ ) ( Signal Modulated ) ( Baseband ) 2 cos( ) ( Carrier a c a c c c k t f t m k A t s t m f A t c π + = = © Po-Ning [email protected] Chapter 2-6 2.2 Overmodulation overmodulaion 1 | ) ( | t m k a
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© Po-Ning [email protected] Chapter 2-7 2.2 Example of Non-Visualized Envelope © Po-Ning [email protected] Chapter 2-8 2.2 Example of Visualized Envelope
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© Po-Ning [email protected] Chapter 2-9 2.2 Transmission Bandwidth [] ) ( ) ( 2 ) ( ) ( 2 ) ( ) 2 cos( )] ( 1 [ ) ( c c c a c c c c a c f f M f f M A k f f f f A f S t f t m k A t s + + + + + = + = δ π 2 W Transmission bandwidth B T = 2 W . © Po-Ning [email protected] Chapter 2-10 2.2 Transmission Bandwidth ± Transmission bandwidth of an AM wave ² For positive frequencies, the highest frequency component of the AM wave equals f c + W , and the lowest frequency component equals f c W . ² The difference between these two frequencies defines the transmission bandwidth B T for an AM wave.
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© Po-Ning [email protected] Chapter 2-11 2.2 Transmission Bandwidth ± The condition of f c > W ensures that the sidebands do not overlap. © Po-Ning [email protected] Chapter 2-12 2.2 Negative Frequency ² Operational meaning of “negative frequency” in spectrum ± If time-domain signal is real-valued , the negative frequency spectrum is simply a mirror of the positive frequency spectrum . ± We may then define a one-sided spectrum as ± Hence, if only real-valued signal is considered, it is unnecessary to introduce “negative frequency”. . 0 for ) ( 2 ) ( sided - one = f f S f S
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© Po-Ning [email protected] Chapter 2-13 2.2 Negative Frequency ± So the introduction of negative frequency part is due to the need of imaginary signal part .
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This note was uploaded on 02/15/2011 for the course SYSC 3501 taught by Professor Fewrf during the Spring '11 term at Carleton.

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Chap2 - Chapter 2 Continuous-Wave Modulation Analog Modulation is the subject concerned in this chapter 2.1 Introduction Analog communication

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