1. 1 ANGLE MODULATION EKT 231 : COMMUNICATION SYSTEM ANGLE MODULATION CHAPTER 3 Part II EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

2. 2 Review on ANGLE MODULATION Part I EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

3. 3 Introduction Angle modulation is the process by which the angle (frequency or Phase) of the carrier signal is changed in accordance with the instantaneous amplitude of modulating or message signal. also known as “Exponential modulation" EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

4. 4 Cont’d… Classified into two types ; –Frequency modulation (FM) – Phase modulation (PM) Used for : –Commercial radio broadcasting –Television sound transmission –Two way mobile radio –Cellular radio –Microwave and satellite communication system EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

5. 5 Cont’d… Advantages over AM:  Freedom from interference: all natural and external noise consist of amplitude variations, thus receiver usually cannot distinguish between amplitude of noise or desired signal. AM is noisy than FM.  Operate in very high frequency band(VHF):88M-108MHz  Can transmit musical programs with higher degree of fidelity. EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

6. 6 FREQUENCY MODULATION PRINCIPLES In FM the carrier amplitude remains constant, the carrier frequency varies with the amplitude of modulating signal. The amount of change (the relative displacement of carrier frequency in hertz in respect to it un-modulated value) in carrier frequency produced by the modulating signal is known as frequency deviation. EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

7. 7 Resting f c Increasing f c Decreasing f c Resting f c Modulating signal Carrier FM EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

8. 8 PHASE MODULATION (PM) PRINCIPLES The process by which changing the phase of carrier signal in accordance with the instantaneous of message signal. The amplitude and frequency remains constant after the modulation process. Mathematical analysis: Let message signal: And carrier signal: EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

9. 9 PM (cont’d) After phase modulation, with the instantaneous voltage will be where = Modulation index of phase modulation K = a constant and called deviation sensitivities of the phase = phase angle of carrier signal.It is changed in accordance with the amplitude of the message signal EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

10. 10 FREQUENCY MODULATION(FM) A process where the frequency of the carrier wave varies with the magnitude variations of the modulating or audio signal. The amplitude of the carrier wave is kept constant. EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

11. 11 FM(cont’d) Mathematical analysis: Let message signal: And carrier signal: EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

12. 12 FM (cont’d) During the process of frequency modulations the frequency of carrier signal is changed in accordance with the instantaneous amplitude of the message signal.Therefore the frequency of carrier after modulation is written as To find the instantaneous phase angle of modulated signal, integrate equation above w.r.t. t EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

13. 13 FM(cont’d) Thus, we get the FM wave as: Where Known as the modulation index for the FM EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

14. 14 Angle-modulated wave in the frequency domain. EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

15. 15 FM(cont’d) Frequency deviation: ∆f is the relative displacement of carrier frequency (Hz) w.r.t its unmodulated value. Given as: Where K is the deviation sensitivity EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

16. 16 FM(cont’d) The peak to peak frequency deviation (2Δf) is called the carrier swing. Therefore: The modulation index is EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

17. 17 Example Given the modulated signal has a frequency deviation of 100kHz and its modulating frequency is 15kHz. (i)Calculate the modulation index. (ii) What happens to the modulation index if the deviation is triple? Solution The modulation index: EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

18. 18 Phase and frequency modulation of a sine-wave carrier by a sine-wave signal: (a) unmodulated carrier; (b) modulating signal; (c) frequency-modulated wave; (d) phase-modulated wave EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

19. 19 Equations for Phase- and Frequency-Modulated Carriers Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

20. 20 FM&PM (Bessel function) Thus, for general equation: EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

21. 21 Bessel function EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

22. 22 B.F. (cont’d) It is seen that each pair of side band is preceded by J coefficients. The order of the coefficient is denoted by subscript m. The Bessel function can be written as n=number of the side frequency m=modulation index EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

23. 23 Bessel Functions of the First Kind, J n (m) for some value of modulation index EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

24. 24 B.F. (cont’d) EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

25. 25 Representation of frequency spectrum EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

26. 26 Example Based on Table of Bessel Functions, what is the relative amplitude of each sideband when the modulation index is 1.0? Solution Refer to Table of Bessel Function J 0 =0.77, 1 st sideband pairs J 1 =0.44, 2 nd sideband pairs J 2 =0.11,3 rd side band pairs J 3 =0.02 EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

27. 27 Example What are the relative amplitudes of frequency components for a 1 MHz carrier, modulated by a 10 kHz signal, with m=2.0? Solution Refer to Table of Bessel Function J 0 =0.22, 1 st sideband pairs J 1 =0.58, 2 nd sideband pairs J 2 =0.35,3 rd side band pairs J 3 =0.13 and 4 th side band pairs J 4 =0.03 EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

28. 28 Example An FM modulator has the following information; Determine; (i)Number of sets of significant frequency (ii)Their amplitude (iii)Draw the frequency spectrum. EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

29. 29 Solution (i) Number of sets of significant frequency Based on B.F table, for m=1, 3 sets of significant side frequencies. (ii) Their amplitude J 0 (V c )=0.77(10); Carrier J 1 (V c )=0.44(10), ; 1 st sideband pairs J 2 (V c )=0.11(10); 2 nd sideband pairs J 3 (V c )=0.02(10); 3 rd side band pairs EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

30. 30 (iii) Draw the frequency spectrum. Solution (cont’d) EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

31. 31 Angle Modulation Part 2 FM Bandwidth Power distribution of FM Generation & Detection of FM Application of FM EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

32. 32 FM Bandwidth Theoretically, the generation and transmission of FM requires infinite bandwidth. Practically, FM system have finite bandwidth and they perform well. The value of modulation index determine the number of sidebands that have the significant relative amplitudes If n is the number of sideband pairs, and line of frequency spectrum are spaced by fm, thus the actual minimum bandwidth using Bessel table: With n = number of significant sidebands = modulating signal frequency EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

33. 33 FM Bandwidth (cont’d) Carson’s rule also can be used to estimate the bandwidth regardless of modulation index EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

34. 34 Example An FM modulator has the following information; Determine (a)Actual minimum bandwidth from the B.F table. (b)Approximate minimum bandwidth using Carson’s rule. (c)Plot the output frequency spectrum for the Bessel approximation EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

35. 35 Solution Given; (a)Actual minimum bandwidth from the B.F table. m=10kHz/10kHz=1, from B.F table, B=2(3x10kHz)=60kHz. (b) Approximate minimum bandwidth using Carson’s rule. EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

36. 36 (c) Plot the output frequency spectrum for the Bessel approximation EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

37. 37 Deviation Ratio (DR) The worse case modulation index which produces the widest output frequency spectrum. Where ∆f (max) = max. peak frequency deviation f m(max) = max. modulating signal frequency EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

38. 38 Example An FM broadcast-band transmitter has a maximum frequency deviation of 75kHz and a maximum modulating signal frequency of 15kHz. Determine the deviation ratio. Solution The deviation ratio (i.e the worst case modulation index). From the B.F table, a modulation index of 5 gives 8 significant sidebands. Then B=2(8x15kHz)=240kHz. EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

39. 39 FM Power Distribution As seen in Bessel function table, it shows that as the sideband relative frequency increases, the carrier amplitude,J 0 decreases. This is because, in FM, the total transmitted power is always constant and the total average power is equal to the unmodulated carrier power, that is the amplitude of the FM remains constant whether it is modulated or not. The total power in angle-modulated wave is equal to the power of the un-modulated wave. EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

40. 40 FM Power Distribution (cont’d) In effect, in FM, the total power that is originally in the carrier is redistributed between all components of the spectrum, in an amount determined by the modulation index, m f, and the corresponding Bessel functions. At certain value of modulation index, the carrier component goes to zero, where in this condition, the power is carried by the sidebands only. EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

41. 41 Average Power The average power in unmodulated carrier The total power in the angle modulated carrier. The modulated carrier power is the sum of the powers of the carrier and the side frequency components as follow; EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

42. 42 Example An FM modulator has the following information; Determine; (i) The unmodulated carrier power for the FM modulator (Assume R L =50 Ω ) (i) The total power in the angle modulated wave. EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

43. 43 Generation of FM Two methods of FM generation: A. Direct method (carrier freq varied (deviated) directly by the modulating signal) i)straight forward, requires a VCO whose oscillation frequency has linear dependence on applied voltage. ii)Advantage: large frequency deviation iii)Disadvantage: the carrier frequency tends to drift and must be stabilized. iv)Example circuits: 1) Reactance modulator 2)Varactor diode 3)Linear Integrated circuit FM modulators EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

44. 44 1) Reactance modulator Generation of FM (cont’d) The modulating signal varies the reactance of the transistor causes a corresponding change in the resonant frequency of the oscillator tank circuit (carrier frequency) EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

45. 45 2) Varactor diode modulator Generation of FM (cont’d) Varactor diode – deviate the frequency of the frequency produced by oscillator tank circuit. EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

46. 46 Generation of FM (cont’d) B) Indirect method: Armstrong modulator by using frequency-up conversion that involves 2 methods : a.Heterodyne method b.Multiplication method Heterodyne-mix two frequencies together in a nonlinear device or to translate one frequency to another using nonlinear mixing. EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

47. 47 Wideband Armstrong Modulator EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

48. 48 FM Detection/Demodulation FM demodulation –is a process of getting back or regenerate the original modulating signal from the modulated FM signal. –It can be achieved by converting the frequency deviation of FM signal to the variation of equivalent voltage. –The demodulator will produce an output where its instantaneous amplitude is proportional to the instantaneous frequency of the input FM signal. EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

49. 49 FM detection (cont’d) To detect an FM signal, it is necessary to have a circuit whose output voltage varies linearly with the frequency of the input signal. The most commonly used demodulator is the PLL demodulator. Can be use to detect either NBFM or WBFM. EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

50. 50 PLL Demodulator Phase detector VCO Low pass filter Amplifier FM input Vc(t) fV c0 V 0 (t) V0(t) is the modulating signal EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

51. 51 PLL Demodulator The phase detector produces an average output voltage that is linear function of the phase difference between the two input signals. This low frequency component is selected by LPF. After amplification, part of the signal is fed back through VCO where it results in frequency modulation of the VCO frequency. When the loop is in lock, the VCO frequency follows or tracks the incoming frequency. EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

52. 52 PLL Demodulator Let instantaneous freq of FM Input, f i (t)=f c +k 1 v m (t), and the VCO output frequency, f VCO (t)=f 0 + k 2 V c (t); f 0 is the free running frequency. For the VCO frequency to track the instantaneous incoming frequency, f vco = f i ; or EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

53. 53 PLL Demodulator f 0 + k 2 V c (t)= f c +k 1 v m (t), so, If VCO can be tuned so that f c =f 0, then Where Vc(t) is also taken as the output voltage, which therefore is the demodulated output EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

54. 54 Comparison AM and FM Its the SNR can be increased without increasing transmitted power about 25dB higher than in AM Certain forms of interference at the receiver are more easily to suppressed, as FM receiver has a limiter which eliminates the amplitude variations and fluctuations. The modulation process can take place at a low level power stage in the transmitter, thus a low modulating power is needed. Power content is constant and fixed, and there is no waste of power transmitted There are guard bands in FM systems allocated by the standardization body, which can reduce interference between the adjacent channels. EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

55. 55 Application of FM used by most of the field VHF portable, mobile and base radios in exploration use today. It is preferred because of its immunity to noise or interference and at the frequencies used the antennas are of a reasonable size. EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

56. 56 Summary of Angle Modulation EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

57. 57 Summary (cont’d) EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

58. 58 Summary (cont’d) Bandwidth: a)Actual minimum bandwidth from Bessel table: b) Approximate minimum bandwidth using Carson’s rule: EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

59. 59 Summary (cont’d) Multitone modulation (equation in general): EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

60. 60 Summary (cont’d) EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

61. 61 Summary (cont’d)- Comparison NBFM&WBFM EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

62. 62 ANGLE MODULATION Part 3 Advantages Disadvantages EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

63. 63 Advantages Wideband FM gives significant improvement in the SNR at the output of the RX which proportional to the square of modulation index. Angle modulation is resistant to propagation-induced selective fading since amplitude variations are unimportant and are removed at the receiver using a limiting circuit. Angle modulation is very effective in rejecting interference. (minimizes the effect of noise). Angle modulation allows the use of more efficient transmitter power in information. Angle modulation is capable of handing a greater dynamic range of modulating signal without distortion than AM. EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

64. 64 Disadvantages Angle modulation requires a transmission bandwidth much larger than the message signal bandwidth. The capture effect where the wanted signal may be captured by an unwanted signal or noise voltage. Angle modulation requires more complex and inexpensive circuits than AM. EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II

65. 65 END OF ANGLE MODULATION EKT 231 : COMMUNICATION SYSTEM EKT 231 : COMMUNICATION SYSTEM -2007/08(II)- ANGLE MODULATION-PART II