Chapter 3 -Analog Modulation_Part 1 Studentx - DAR...

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CHAPTER 3 ANALOG MODULATION DAR 31703 Communication System © Muhammad Faizal Ismail JKE, PPD, UTHM
Topics Principles of Amplitude Modulation (AM) AM Analysis Single Sideband AM Principles of Frequency Modulation (FM) FM Analysis Radio Receiver Advantages & Disadvantages of Analog Modulation 3.1 3.2 3.3 3.4 3.5 3.6 3.7
Why we Need Modulation?
3.1 Principles of Amplitude Modulation
3.1 Principles of Amplitude Modulation Definition: Amplitude of carrier frequency change proportionately to the value of the modulation signal. Advantages: Simple modulator circuits Cheap :low-quality form of modulation used for commercial broadcasting of audio & video signal. Disadvantages: Poor performance due to noise Inefficient use of transmitter power. Application: 2 way radio communications, broadcasting, aircraft comm. & citizen band (CB) radio.
AM modulators are nonlinear devices 2 input and 1 output: modulating signal and carrier signal. Several types of amplitude modulation Double Side Band Full Carrier (DSB-FC) Double Side Band Suppressed Carrier (DSB- SC) Single Side Band (SSB) AM generation is shown in Figure 2.1 Modulated wave = AM envelope as shown in Figure 2.2 6 Figure 2.1: Block diagram of Amplitude Modulation Information, V m (t) Carrier, V c (t) Modulator V AM (t) 3.1 Principles of Amplitude Modulation
7 Figure 2.2 AM signal with the envelope 3.1 Principles of Amplitude Modulation
8 AM in action 3.1 Principles of Amplitude Modulation
AM begins with carrier v c , a sine wave with frequency c & amplitude V c : Modulating signal: Then AM is: 9 Derivation of AM Equation 3.1 Principles of Amplitude Modulation Remember : Modulating signal uses the peak value of the carrier as a reference point t f mV V V V V m t f V V V v V V m c c env c m m m c env m c env 2 sin ] / [ 2 sin t f V v m m m 2 sin t f V v c c c 2 sin
10 Where m (modulation index) is defined as V m / V c , hence: The voltage resulting AM wave envelope at any instant is: 3.1 Principles of Amplitude Modulation ) 2 sin 1 ( t f m V V m c env t f t f m V t f V v c m c c env 2 sin ) 2 sin 1 ( 2 sin
This yield, the upper and lower sidebands – frequency & amplitude. 11 Carrier LSB USB Using Trigo ID 3.1 Principles of Amplitude Modulation t f f V t f f V t f V v m c m m c m c c AM ) ( 2 cos 2 ) ( 2 cos 2 2 sin t f f V m t f f V m t f V v m c c m c c c c ) ( 2 cos 2 ) ( 2 cos 2 2 sin ) cos( ) cos( 2 / 1 ) )(sin (sin b a b a b a
AM modulators are non-linear device => non-linear mixing occurs.