Introduction & Amplitude Modulation 18년 1월 3일 10시 50분 49초 Introduction & Amplitude Modulation Dr. Monir Hossen ECE, KUET Department of Electronics and Communication Engineering, KUET © 2007 Microsoft Corporation. All rights reserved. Microsoft, Windows, Windows Vista and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries. The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.

Here, ‘Tele’ Means Long Distance Introduction (1/2) Long distance communication is called Telecommunication Technically Communication is the summation of: Transmission Reception and Processing of information by electric means Radio communication was greatly improved during 2nd world war Here, ‘Tele’ Means Long Distance Department of Electronics and Communication Engineering, KUET 2

Department of Electronics and Communication Engineering, KUET 3 Introduction (2/2) Communication is widely using after invention of : Transistor Integrated circuit Other semiconductor devices Satellite and Fiber optics Department of Electronics and Communication Engineering, KUET 3

Examples of Communication System Telephony and Telegraphy Radio Broadcasting (Example?) Point-to-point & Mobile Communication Computer Communication Radar (Applications?) Television Broadcasting Radio Telemetry Radio aids to Navigation Radio aids to Aircraft Landing etc. Department of Electronics and Communication Engineering, KUET 4

Block Diagram of General Communication System Transmitter Information & Message ?? Receiver Department of Electronics and Communication Engineering, KUET 5

Open System Interconnections (OSI) Model Department of Electronics and Communication Engineering, KUET 6

Need For Using High Carrier Frequency Radiation efficiency ( Increase/ decrease?) Size of antenna ( Large/ small?) Range of Communication (Short/ long?) Easy of selection of radio signal in the receiver ( Why?) Department of Electronics and Communication Engineering, KUET 7

Classification of RF Spectrum (1/2) λ= v/f = 3*108/f Carrier Frequency Free space wave-length (m) Class Propagation Characteristic Service 10 – 30 KHz 3*104 - 104 VLF Attenuation: always is low Long distance P2P Commn 30 – 300 KHz 104 - 103 LF absorption : Day time > VLF Night time = VLF & navigation 300 – 3000 KHz 103 - 102 MF Attenuation: Day time is high Night time is low Broadcasting: Ship to shore 3 – 30 MHz 102 - 10 HF Ionospheric propagation Broadcasting and P2P T&T Department of Electronics and Communication Engineering, KUET 8

Classification of RF Spectrum (2/2) Carrier Frequency Free space wave-length (m) Class Propagation Characteristic Service 30 – 300 MHz 10 - 1 VHF Tropospheric propagation Radar, TV, FM broadcast, Short distance Commn 300 – 3000 MHz 1 - 0.1 UHF Facsimile, TV relay, Air navigation 3000 – 30,000 MHz 0.1 - 0.01 SHF Radar navigation, Radio relay Department of Electronics and Communication Engineering, KUET 9

Department of Electronics and Communication Engineering, KUET 10 Modulation (1/2) Fulbarigate Dhaka X KUET Fulbarigate Only a Person Cannot go Only a Person Can go Fulbarigate Dhaka Person using bus Can go Modulation Information Carrier Department of Electronics and Communication Engineering, KUET 10

Information Signal (What?) Modulation (2/2) Amplitude Frequency Phase Definition: It is a process of vary some characteristics of the Carrier Voltage in accordance with the Modulating Voltage High Frequency Signal, Information Signal (What?) Amplitude of the carrier Freq. of the carrier Phase of the carrier Department of Electronics and Communication Engineering, KUET 11

Applications & Types of Modulation Application Examples Broadcasting of both audio and video signals. Mobile radio communications, such as cell phone. Types of Modulation: Amplitude Modulation Amplitude of carrier is varied with respect to modulating signal Frequency Modulation Frequency of carrier is varied with respect to modulating signal Phase Modulation Phase angle of carrier is varied with respect to modulating signal Department of Electronics and Communication Engineering, KUET 12

We know energy in a signal is proportional to its frequency Need for Modulation 1) The modulating signal produced by microphone or camera is very weak and very low frequency (Why?) So this signal can not travel long distance. That is why, weak signal requires high frequency carrier. 2) Height of antenna needed 3) Modulation permits the transmission without wire. We know energy in a signal is proportional to its frequency For best result antenna height = the wavelength we know Example: if signal is 20KHz Then antenna height = v/f = 15000 m ( Practical?) V= velocity of light (3*108) f = frequency Department of Electronics and Communication Engineering, KUET 13

Need for Modulation 4. Modulation makes the message signal more robust against the noise. 5. Modulation is required to match the signal frequency with the bandwidth of the channel. For example: Microwave communication required frequency of microwave range, Satellite communication requires frequency of satellite communication range, FM radio requires FM frequency range, Optical fiber communication required frequency of optical communication range. Department of Electronics and Communication Engineering, KUET 14

Complete Classification of Modulation Processes (1/2) Amplitude Modulation (AM) i) Single sideband AM (SSBAM) ii) Double sideband AM (DSBAM) iii) Frequency division multiplexing (FDM) Frequency Modulation (FM) Phase Modulation Pulse Modulation Pulse amplitude modulation (PAM) Time Division multiplexing (TDM) Pulse time modulation (PTM) Pulse division multiplexing Pulse code modulation (PCM) Department of Electronics and Communication Engineering, KUET 15

Complete Classification of Modulation Processes (2/2) Digital modulation (DM) Differential PCM (DPCM) Adaptive PCM (ADPCM) Delta modulation (DM) Adaptive delta modulation (ADM) Multiplexing Department of Electronics and Communication Engineering, KUET 16

Amplitude Modulation (AM) Amplitude of the carrier is varied according to amplitude of the modulating signal Modulator Baseband Signal with frequency fm (Modulating Signal) Bandpass Signal fc (Modulated Signal) Channel fc >> fm Voice: 300-3400Hz Source Demodulator Original Signal with frequency fm Sink Department of Electronics and Communication Engineering, KUET 17

Modulation Index or Factor (m) (1/3) it is the ratio of maximum value of the modulating signal to the maximum amplitude of the carrier m = Em / Ec (2) It is the ratio of change of amplitude of the carrier to its original amplitude m = ∆Ec / Ec (3) m = 100* (∆Ec / Ec ) Em Amp. t Ec Amp. t Upper envelope Amp. t Ec Ec + Em Ec - Em Lower envelope Modulated wave Department of Electronics and Communication Engineering, KUET 18

Modulation Index or Factor (m) (2/3) (4) It is the ratio of minimum amplitude to the maximum amplitude of the modulated wave Proof: Emax = Ec + mEc (1) Emin = Ec – mEc (2) Amp. t Ec Emax = Ec + Em = Ec +mEm Emin = Ec – Em =Ec - mEc Em = mEc Department of Electronics and Communication Engineering, KUET 19

Modulation Index or Factor (m) (3/3) Adding Equations (1) and (2) we have: Subtracting Equations (1) and (2) we have: Now: Note: 1) The value of m lies between 0 & 1 2) It is also depends on Amplitude of modulating signal and carrier Department of Electronics and Communication Engineering, KUET 20

Mathematical Analysis of Amplitude Modulated Wave (1/3) Let, the carrier signal, the modulating signal, the amplitude of modulated wave, Let, the voltage equation of modulated wave be [ here, Em = mEc ] Department of Electronics and Communication Engineering, KUET 21

Mathematical Analysis of Amplitude Modulated Wave (2/3) Department of Electronics and Communication Engineering, KUET 22

Mathematical Analysis of Amplitude Modulated Wave (3/3) Frequency spectrum of the above modulated wave: Carrier, A=1. Amplitude mEc/ 2 mEc/ 2 frequency fc fc+fm fc-fm Lower sideband Upper sideband Bandwidth = USB – LSB = (fc + fm ) - (fc - fm ) = 2fm Department of Electronics and Communication Engineering, KUET 23

Practical Amplitude Modulator (1/4 ) Simple Transistor modulator Department of Electronics and Communication Engineering, KUET 24

Practical Amplitude Modulator (2/4) Simple Transistor Modulator: Transistor modulation consists of a resistive mixing network, a transistor, and an LC tuned circuit. The emitter-base junction of the transistor serves as a diode and nonlinear device. Modulation and amplification occur as base current controls a larger collector current. The LC tuned circuit oscillates (rings) to generate the missing half cycle. Department of Electronics and Communication Engineering, KUET 25

Practical Amplitude Modulator (3/4) Series modulator Department of Electronics and Communication Engineering, KUET 26

Practical Amplitude Modulator (4/4) Series Modulator: A series modulator produces high-level modulation without a large and expensive modulation transformer used in collector modulators It improves frequency response It is, however, very inefficient A series modulator replaces the modulation transformer with an emitter follower The modulating signal is applied to the emitter follower The emitter follower is in series with the collector supply voltage The collector voltage changes with variations in the amplified audio modulating signal Department of Electronics and Communication Engineering, KUET 27

Example of Amplitude Modulation The information signal is usually not a single frequency but a range of frequencies (i.e., band). For example, frequencies from 20Hz to 15KHz. If we use a carrier of 1.4MHz, what will be the AM spectrum? Soln: In frequency domain the AM waveform are the lower-side band frequency (fc - fm), the carrier frequency fc, the upper-side frequency/band (fc + fm). Bandwidth: 2×(15K-20)Hz. 1.4 MHz frequency fc fc-fm =1,385,000Hz to 1,399,980Hz fc+fm =1,400,020Hz to 1,415,000Hz Department of Electronics and Communication Engineering, KUET 28

Modulation Index of AM (1/3) Department of Electronics and Communication Engineering, KUET 29

Modulation Index of AM (2/3) Department of Electronics and Communication Engineering, KUET 30

Modulation Index of AM (3/3) Department of Electronics and Communication Engineering, KUET 31

Power Distribution in the AM Wave (1/4) We know power in a voltage wave Total power in an AM wave, PT = P(LSB) + PC + P(USB) Power contained in carrier is: [ Ec = Maxm value ] Power contained in LSB is: Power contained in USB is: Department of Electronics and Communication Engineering, KUET 32

Power Distribution in the AM Wave (2/4) Total power in AM wave is: Department of Electronics and Communication Engineering, KUET 33

Power Distribution in the AM Wave (3/4) Power in both side bands is: Ratio of sideband power to total power is: Department of Electronics and Communication Engineering, KUET 34

Power Distribution in the AM Wave (4/4) For 100% modulation m = 1 So the side bands contain 1/3rd (33%) of the total power of the AM wave Department of Electronics and Communication Engineering, KUET 35

Example 1) A transmitter supplies 10Kw power to an aerial when unmodulated. Determines the power radiated when modulated to 30%. Sol: Here, Pc = 10Kw m = 0.3 PT = ? We know, PT = Pc(1+m2/2) = 10[1+(0.3)2/2] =10.45 Kw Department of Electronics and Communication Engineering, KUET 36

Example 2) A 100v, 10KHz carrier is modulated with the help of a 5v, 50Hz signal. Calculate- modulation factor(m) Amplitude of each sideband Frequency of each sideband Bandwidth of modulated wave Sol: (a) (b) Amplitude of each sideband (c) Frequency of sidebands, USB = fc+fm = 10000+50 =10050Hz LSB = fc- fm = 10000-50 =9950Hz (d) Bandwidth BW=USB-LSB = 10050-9950 =100Hz Department of Electronics and Communication Engineering, KUET 37

Example 3) A 100v, 100KHz carrier is modulated with the help of a 10v, 1KHz signal to the extent of 50%. Write down the equation for the AM wave. Sol: Here, m=0.5, Ec = 100v, Em = 10v, fc= 100KHz, fm= 1KHz We know AM wave is: Department of Electronics and Communication Engineering, KUET 38

Example Department of Electronics and Communication Engineering, KUET 39

Self Study: All related examples & Problems of GK Mithal 4) An AM wave is represented by the equation. Determine (1) m, (2) Ec, (3) fm, (4) fc, (5) Emax, (6) Emin, (7) BW Sol: We know standard AM wave equation Comparing this equation with the above equation. We get (1) m = 0.7 (2) Ec = 20 (3) fm = 1KHz (How?) (4) fc = 100KHz (How?) (5) Emax = Ec + m Ec =34v (6) Emin = Ec - m Ec =6v (7) BW = 2fm =2KHz Self Study: All related examples & Problems of GK Mithal 40 Department of Electronics and Communication Engineering, KUET

Example 5) Determine the percentage of the ratio of the sidebands power to the total output power of the AM wave for m = 0.5 and m = 0.3. Soln: for m=0.5 m = 0.3 Department of Electronics and Communication Engineering, KUET 41

Limitations of The AM The useful power is contained in the sidebands & even at 100% modulation the sidebands contain only 33% of the total power & hence the modulation efficiency is poor. Due to poor efficiency transmitter has very poor range. The reception in this modulation is noisy. The audio reception is poor quality due to noisy reception. Department of Electronics and Communication Engineering, KUET 42

Modulation Used in Various Communications Radio Broadcasting: Frequency range: 20Hz to 30MHz Modulation type: Amplitude modulation TV Broadcasting: Frequency range: VHF and UHF Modulation type: For picture => AM For Sound => FM Satellite Broadcasting: Frequency range: Up to 30GHz Department of Electronics and Communication Engineering, KUET 43

Modulation Used in Various Communications Telephony, Telex, Telegraphy: Frequency range: Up to 30GHz Modulation type: FM Mobile System : Frequency range: Below 30MHz => AM Above 30MHz => FM Department of Electronics and Communication Engineering, KUET 44

Department of Electronics and Communication Engineering, KUET Thanks for Your Kind Attention Department of Electronics and Communication Engineering, KUET