Introduction & Amplitude Modulation

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1 Departent of Eletronis and Couniation Engineering, KUET Introdution & Aplitude Modulation Dr. Monir Hossen ECE, KUET

2 Departent of Eletronis and Couniation Engineering, KUET Introdution (1/) Long distane ouniation is alled Teleouniation Here, Tele Means Long Distane Tehnially Couniation is the suation of: Transission Reeption and roessing of inforation by eletri eans Radio ouniation was greatly iproved during nd world war

3 Departent of Eletronis and Couniation Engineering, KUET 3 Introdution (/) Couniation is widely using after invention of : Transistor Integrated iruit Other seiondutor devies Satellite and Fiber optis

4 Departent of Eletronis and Couniation Engineering, KUET 4 Exaples of Couniation Syste Telephony and Telegraphy Radio Broadasting (Exaple?) oint-to-point & Mobile Couniation Coputer Couniation Radar (Appliations?) Television Broadasting Radio Teleetry Radio aids to Navigation Radio aids to Airraft Landing et.

5 Departent of Eletronis and Couniation Engineering, KUET 5 Blok Diagra of General Couniation Syste Transitter Inforation & Message?? Reeiver

6 Open Syste Interonnetions (OSI) Model Departent of Eletronis and Couniation Engineering, KUET 6

7 Departent of Eletronis and Couniation Engineering, KUET 7 Need For Using High Carrier Frequeny Radiation effiieny ( Inrease/ derease?) Size of antenna ( Large/ sall?) Range of Couniation (Short/ long?) Easy of seletion of radio signal in the reeiver ( Why?)

8 Departent of Eletronis and Couniation Engineering, KUET 8 Classifiation of RF Spetru (1/) λ= v/f = 3*10 8 /f Carrier Frequeny Free spae wave-length () Class ropagation Charateristi Servie KHz 3* VLF Attenuation: always is low KHz KHz LF absorption : Day tie > VLF Night tie = VLF MF Attenuation: Day tie is high Night tie is low 3 30 MHz HF Ionospheri propagation Long distane Co n Long distane Co n & navigation Broadasting: Ship to shore Broadasting and T&T

9 Departent of Eletronis and Couniation Engineering, KUET 9 Classifiation of RF Spetru (/) Carrier Frequeny Free spae wave-length () Class ropagation Charateristi Servie MHz MHz ,000 MHz 10-1 VHF Tropospheri propagation UHF Tropospheri propagation SHF Tropospheri propagation Radar, TV, FM broadast, Short distane Co n Fasiile, TV relay, Air navigation Radar navigation, Radio relay

10 Modulation (1/) KUET Fulbari gate Fulbari gate X Dhaka Only a erson Can go Modulation Inforation Carrier Fulbari gate Only a erson Cannot go Dhaka erson using bus Can go Departent of Eletronis and Couniation Engineering, KUET 10

Voltage in aordane with the Modulating Voltage Inforation Signal (What?

11 Departent of Eletronis and Couniation Engineering, KUET 11 Modulation (/) Aplitude Frequeny hase Definition: It is a proess of vary soe harateristis of the Carrier Voltage in aordane with the Modulating Voltage Inforation Signal (What?) v High Frequeny Signal, V os( t ) hase of the arrier Freq. of the arrier Aplitude of the arrier

12 Appliations & Types of Modulation Appliation Exaples Broadasting of both audio and video signals. Mobile radio ouniations, suh as ell phone. Types of Modulation: Aplitude Modulation Aplitude of arrier is varied with respet to odulating signal Frequeny Modulation Frequeny of arrier is varied with respet to odulating signal hase Modulation hase angle of arrier is varied with respet to odulating signal Departent of Eletronis and Couniation Engineering, KUET 1

13 Departent of Eletronis and Couniation Engineering, KUET 13 Need for Modulation 1) The odulating signal produed by irophone or aera is very weak and very low frequeny (Why?) We know energy in a signal is proportional to its frequeny So this signal an not travel long distane. That is why, weak signal requires high frequeny arrier. ) Height of antenna needed For best result antenna height = the wavelength we know v f V= veloity of light (3*10 8 ) f = frequeny Exaple: if signal is 0KHz wavelength Then antenna height = v/f = ( ratial?) 3) Modulation perits the transission without wire.

14 Departent of Eletronis and Couniation Engineering, KUET 14 Need for Modulation 4. Modulation akes the essage signal ore robust against the noise. 5. Modulation is required to ath the signal frequeny with the bandwidth of the hannel. For exaple: Mirowave ouniation required frequeny of irowave range, Satellite ouniation requires frequeny of satellite ouniation range, FM radio requires FM frequeny range, Optial fiber ouniation required frequeny of optial ouniation range.

15 Departent of Eletronis and Couniation Engineering, KUET 15 Coplete Classifiation of Modulation roesses (1/) Aplitude Modulation (AM) i) Single sideband AM (SSBAM) ii) Double sideband AM (DSBAM) iii) Frequeny division ultiplexing (FDM) Frequeny Modulation (FM) hase Modulation ulse Modulation o ulse aplitude odulation (AM) o Tie Division ultiplexing (TDM) o ulse tie odulation (TM) o ulse division ultiplexing o ulse ode odulation (CM)

16 Departent of Eletronis and Couniation Engineering, KUET 16 Coplete Classifiation of Modulation roesses (/) Digital odulation (DM) o Differential CM (DCM) o Adaptive CM (ADCM) o Delta odulation (DM) o Adaptive delta odulation (ADM) Multiplexing

17 Aplitude Modulation (AM) Aplitude of the arrier is varied aording to aplitude of the odulating signal Sink Soure Channel Modulator Deodulator Baseband Signal Bandpass Signal with frequeny with frequeny f f (Modulating Signal) (Modulated Signal) f >> f Voie: Hz Original Signal with frequeny f Departent of Eletronis and Couniation Engineering, KUET 17

18 Modulation Index or Fator () (1/3) (1) it is the ratio of axiu value of the odulating signal to the axiu aplitude of the arrier Ap. = E / E E Ap. E t t () It is the ratio of hange of aplitude of the arrier Upper envelope to its original aplitude = E / E (3) E + E Ap. E - E = 100* ( E / E ) E t Lower envelope Modulated wave Departent of Eletronis and Couniation Engineering, KUET 18

19 Departent of Eletronis and Couniation Engineering, KUET 19 Modulation Index or Fator () (/3) (4) It is the ratio of iniu aplitude to the axiu aplitude of the odulated wave Ap. E = E E in = E E =E - E E E ax = E + E = E +E t E E ax ax E E in in roof: E ax = E + E (1) E in = E E ()

20 Departent of Eletronis and Couniation Engineering, KUET 0 Modulation Index or Fator () (3/3) Adding Equations (1) and () we have: E ax E E in Subtrating Equations (1) and () we have: E ax E E in Now: E Eax Ein E E E ax Note: 1) The value of lies between 0 & 1 ) It is also depends on Aplitude of odulating signal and arrier in

21 Matheatial Analysis of Aplitude Modulated Wave (1/3) Let, the arrier signal, the odulating signal, the aplitude of odulated wave, e ESint e E Sin t Let, the voltage equation of odulated wave be Departent of Eletronis and Couniation Engineering, KUET 1 A E e A E ESint A E ESint A E ESint A E ( 1 Sin t) e e [ here, E = E ] ASint E ( 1 Sin t) Sin t

22 Departent of Eletronis and Couniation Engineering, KUET Matheatial Analysis of Aplitude Modulated Wave (/3) t Sin t Sin E t Sin E e ) ( t Sin t Sin E t Sin E e } ) ( ) ( { t Cos t Cos E t Sin E e t Cos E t Cos E t Sin E e ) ( ) (

23 Departent of Eletronis and Couniation Engineering, KUET 3 Matheatial Analysis of Aplitude Modulated Wave (3/3) Frequeny spetru of the above odulated wave: Aplitude Lower sideband E / f -f Carrier, A=1. f f +f Bandwidth = USB LSB = (f + f ) - (f - f ) = f E / Upper sideband frequeny

24 Departent of Eletronis and Couniation Engineering, KUET 4 ratial Aplitude Modulator (1/4 ) Siple Transistor odulator

25 Departent of Eletronis and Couniation Engineering, KUET 5 ratial Aplitude Modulator (/4) Siple Transistor Modulator: Transistor odulation onsists of a resistive ixing network, a transistor, and an LC tuned iruit. The eitter-base juntion of the transistor serves as a diode and nonlinear devie. Modulation and aplifiation our as base urrent ontrols a larger olletor urrent. The LC tuned iruit osillates (rings) to generate the issing half yle.

26 ratial Aplitude Modulator (3/4) Series odulator Departent of Eletronis and Couniation Engineering, KUET 6

27 Departent of Eletronis and Couniation Engineering, KUET 7 ratial Aplitude Modulator (4/4) Series Modulator: A series odulator produes high-level odulation without a large and expensive odulation transforer used in olletor odulators It iproves frequeny response It is, however, very ineffiient A series odulator replaes the odulation transforer with an eitter follower The odulating signal is applied to the eitter follower The eitter follower is in series with the olletor supply voltage The olletor voltage hanges with variations in the aplified audio odulating signal

28 Departent of Eletronis and Couniation Engineering, KUET 8 Exaple of Aplitude Modulation The inforation signal is usually not a single frequeny but a range of frequenies (i.e., band). For exaple, frequenies fro 0Hz to 15KHz. If we use a arrier of 1.4MHz, what will be the AM spetru? Sol n : In frequeny doain the AM wavefor are the lowerside band frequeny (f - f ), the arrier frequeny f, the upper-side frequeny/band (f + f ). Bandwidth: (15K- 0)Hz. 1.4 MHz frequeny f -f =1,385,000Hz to 1,399,980Hz f f +f =1,400,00Hz to 1,415,000Hz

29 Departent of Eletronis and Couniation Engineering, KUET 9 Modulation Index of AM (1/3) 100% Modulation

30 Modulation Index of AM (/3) Departent of Eletronis and Couniation Engineering, KUET 30

31 Modulation Index of AM (3/3) Departent of Eletronis and Couniation Engineering, KUET 31

32 Departent of Eletronis and Couniation Engineering, KUET 3 ower Distribution in the AM Wave (1/4) We know power in a voltage wave (aplitude) o Total power in an AM wave, T = (LSB) + C + (USB) o ower ontained in arrier is: C E E [ E = Max value ] value R.M.S. E o ower ontained in LSB is: ) ( E E E C LSB o ower ontained in USB is: ) ( E E E C USB

33 Departent of Eletronis and Couniation Engineering, KUET C C C T Total power in AM wave is: C C T ) (1 C T ) (1 C T ower Distribution in the AM Wave (/4)

34 Departent of Eletronis and Couniation Engineering, KUET 34 USB LSB SB ower in both side bands is: 4 4 C C C SB ) (1 C C T SB Ratio of sideband power to total power is: T SB ower Distribution in the AM Wave (3/4)

35 Departent of Eletronis and Couniation Engineering, KUET 35 ower Distribution in the AM Wave (4/4) For 100% odulation = 1 1 SB T 3 So the side bands ontain 1/3 rd (33%) of the total power of the AM wave

36 Departent of Eletronis and Couniation Engineering, KUET 36 Exaple 1) A transitter supplies 10Kw power to an aerial when unodulated. Deterines the power radiated when odulated to 30%. Sol: Here, = 10Kw = 0.3 T =? We know, T = (1+ /) = 10[1+(0.3) /] =10.45 Kw

37 Departent of Eletronis and Couniation Engineering, KUET 37 Exaple ) A 100v, 10KHz arrier is odulated with the help of a 5v, 50Hz signal. Calulatea. odulation fator() b. Aplitude of eah sideband. Frequeny of eah sideband d. Bandwidth of odulated wave Sol: (a) E E E 0.05*100 5v (b) Aplitude of eah sideband. () Frequeny of sidebands, USB = f +f = =10050Hz LSB = f - f = =9950Hz (d) Bandwidth BW=USB-LSB = =100Hz

38 Departent of Eletronis and Couniation Engineering, KUET 38 Exaple 3) A 100v, 100KHz arrier is odulated with the help of a 10v, 1KHz signal to the extent of 50%. Write down the equation for the AM wave. Sol: Here, =0.5, E = 100v, E = 10v, f = 100KHz, f = 1KHz We know AM wave is: E E e ESint Cos( ) t Cos( ) t e E E E Sin( f ) t Cos(f f ) t Cos(f f ) t

39 Departent of Eletronis and Couniation Engineering, KUET 39 Exaple e 100Sin68000t 0.5* *100 Cos(68000 Cos( ) t 680) t e 100Sin68000t 5Cos6170t 5Cos63480t

40 Exaple 4) An AM wave is represented by the equation. e 0(1 0.7Sin680t) Sin68000t Deterine (1), () E, (3) f, (4) f, (5) E ax, (6) E in, (7) BW Sol: We know standard AM wave equation e E (1 Sin t) Sin t Coparing this equation with the above equation. We get (1) = 0.7 () E = 0 (3) f = 1KHz (How?) (4) f = 100KHz (How?) (5) E ax = E + E =34v (6) E in = E - E =6v (7) BW = f =KHz Self Study: All related exaples & robles of GK Mithal Departent of Eletronis and Couniation Engineering, KUET

41 Departent of Eletronis and Couniation Engineering, KUET 41 Exaple 5) Deterine the perentage of the ratio the sidebands power to the total output power of the AM wave for = 0.5 and = 0.3. Sol n : for =0.5 SB T 100% (0.5) (0.5) 100% 11.11% = 0.3 SB T 100% (0.3) (0.3) 100% 4.3%

42 Departent of Eletronis and Couniation Engineering, KUET 4 Liitations of The AM The useful power is ontained in the sidebands & even at 100% odulation the sidebands ontain only 33% of the total power & hene the odulation effiieny is poor. Due to poor effiieny transitter has very poor range The reeption in this odulation is noisy The audio reeption is poor quality due to noisy reeption

43 Modulation Used in Various Couniations Departent of Eletronis and Couniation Engineering, KUET 43 Radio Broadasting: Frequeny range: 0Hz to 30MHz Modulation type: Aplitude odulation TV Broadasting: Frequeny range: VHF and UHF Modulation type: For piture => AM For Sound => FM Satellite Broadasting: Frequeny range: Up to 30GHz

44 Modulation Used in Various Couniations Departent of Eletronis and Couniation Engineering, KUET 44 Telephony, Telex, Telegraphy: Frequeny range: Up to 30GHz Modulation type: FM Mobile Syste : Frequeny range: Below 30MHz => AM Above 30MHz => FM

45 Departent of Eletronis and Couniation Engineering, KUET Thanks for Your Kind Attention

Modulation Technique:

Modulation Technique: Modulation Tehnique: There are two basi failies of ontinuous-wave odulation tehniques: 1. Aplitude odulation, in whih the aplitude of a sinusoidal arrier is varied in aordane with an inoing essage signal.