Amplitude Modulation and Frequency Modulation

Modulation basics, Need of Modulation, AM Frequency spectrum, AM generation, FM frequency spectrum, FM generation methods, Advantages and Disadvantages of AM and FM

1. Amplitude Modulation and FREQUENCY modulation 16 Hours 18 Marks Ms. Kavita Giri Lecturer ( ET) Government Residential Womens Polytechnic , Latur

2. Learning Outcomes Interpret necessity of the given type of modulation technique. Compare the working of the given type of AM generation technique Describe with sketches the given parameters of AM signal. Calculate modulation index and power distributions of the given AM signal. Describe with sketches the specified parameters of FM and PM signal. Calculate / Find modulation Index of given FM signal. 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

3. Contents 2.1 Need for modulation Types of Modulation techniques 2.2 Amplitude Modulation : Mathematical representation of AM wave Modulation Index, Bandwidth requirement Representation of AM in time domain. Frequency spectrum in AM wave Total power relation in AM-derivation and simple numerical   Power in side bands- derivation and numerical . Types of AM- DSB, SSB and VSB 2.3 Frequency Modulation Representation of FM in time domain Representation of FM in frequency domain Frequency deviation ratio Modulation index Mathematical representation of FM wave Bandwidth requirements Types of FM – Narrowband and Wideband 2.4 Phase Modulation 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

4. 2.1 Modulation Baseband signal (information signal) is a low frequency signal and cannot travel long distances. I need to reach Mary’s place in 10 minutes…also it is far… what to do??? Tim 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

5. ….2.1 Modulation Baseband signal Information signal Low frequency signal (Tim) Baseband signal Information signal Low frequency signal (Tim) High frequency carrier signal (Bicycle) Modulated signal (Tim riding a bicycle) Just like Tim cannot walk at longer distances, information signal cannot travel a longer distance. Just like Tim rides a bicycle to reach Mary’s house; information signal takes the help of a high frequency carrier to be transmitted to longer distances. 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

6. Modulation is the process of superimposing a low frequency signal on a high frequency carrier wave. ….2.1 Modulation Signals involved in modulation 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

7. ….2.1 Modulation Modulation is the process of superimposing a baseband signal on a high frequency carrier wave. Modulation is the process in which some parameter of the high frequency carrier (amplitude, frequency or phase) is varied in accordance with the modulating signal. Why do we need modulation ??? 1 2 3 4 5 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

8. …2.1 Modulation Without Modulation With Modulation Now consider baseband signal is modulated to f=1 MHz, height of antenna required is, = = 75 meters This antenna height can be practically installed.   Need for modulation 1. Reduction in height of antenna To transmit a baseband signal of f=10KHz, height of antenna required is, = = 7.5km This antenna height is practically impossible to install.   For efficient transmission & reception, height of antenna h = But, , Hence,   Thus we can conclude that due to modulation, antenna height requirement is reduced.

9. ….2.1 Modulation Need for modulation 2. Avoid Mixing of signals If the baseband signals are transmitted, then all signals will be in the same frequency range 20Hz to 20KHz. Thus all signals will be mixed and the receiver cannot separate them. But modulation technique uses different carrier frequency and separates each channel from each other. Thus, use of different carrier frequencies in modulation avoids mixing of signals.

10. ….2.1 Modulation Need for modulation 3. Increases range of communication Baseband signals being low frequency signals, cannot travel a longer distance and are suppressed. This suppression or attenuation of signals is reduced by increasing transmitted signal frequency, so they can travel longer distances. So, as transmitter frequency increases, the range of communication also increases. Thus, use of higher carrier frequencies in modulation increases the range of communication.

11. ….2.1 Modulation Need for modulation 4. Multiplexing is possible Multiplexing is the process in which more than one signals can be transmitted over the same channel simultaneously. This is possible only with modulation. In multiplexing, same channel is used by many signals without mixing. Thus, use of different carrier frequencies in modulation makes multiplexing possible. 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

12. ….2.1 Modulation Need for modulation 5. Improves quality of reception In modulation, modulating signal is mixed with carrier at transmitter side. In demodulation at the receiver, modulating signal is recovered from the carrier. The quality of this demodulated signal is noise free if proper technique is utilised. No external unwanted signals are added in the signal. Thus reduction of noise in modulation improves the quality of reception. 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

13. Types of modulation 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

14. Introduction Amplitude modulation or AM as it is often called, is a form of modulation used for radio transmissions for broadcasting and two way radio communication applications . Although one of the earliest used forms of modulation it is still used today, mainly for long, medium and short wave broadcasting and for some aeronautical point to point communications. 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

15. 2.2 Amplitude Modulation The first amplitude modulated signal was transmitted in 1901 by a Canadian engineer named Reginald Fessenden . He took a continuous spark transmission and placed a carbon microphone in the antenna lead. The sound waves impacting on the microphone varied its resistance and in turn this varied the intensity of the transmission. Although very crude, signals were audible over a distance of a few hundred metres, although there was a rasping sound caused by the spark. History 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

16. 2.2.1 Amplitude Modulation THEORY Amplitude Modulation (AM) is the process of changing the amplitude of a high frequency carrier signal in proportion with the instantaneous value of the modulating signal (information). Principle

17. …..2.2.1 Amplitude Modulation Observations: The frequency of the sinusoidal carrier is much higher than the modulating signal Instantaneous amplitude of the carrier is changed in accordance with the modulating signal Information in the AM signal is contained in the amplitude variations of the carrier of the envelope The frequency and the phase of the carrier remain constant 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

18. …..2.2.1 Amplitude Modulation https:// academo.org/demos/amplitude-modulation/ 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

19. ……2.2.2 Amplitude Modulation Mathematical Representation of AM wave 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

20. ……2.2.2 Amplitude Modulation Mathematical Representation of AM wave Consider a sinusoidal modulating signal or message signal  ( e m ) of frequency ( ω m ) and amplitude ( E m ) given by:                       e m  = E m   sin  ω m t    . . . . . . . . . . . . . . . . . . . . . . . . . .  (1 ) and carrier wave ( e c ) of frequency ( ω c ) and amplitude ( E c ) given by:                       e c  = E c   sin  ω c t  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (2 ) Where, e m  is the modulating signal or message signal e c  is the carrier signal E m  is the maximum amplitude of the message signal E c  is the maximum amplitude of the carrier signal ω m   is the frequency of the message signal ω c  is the frequency of the carrier signal 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur https://electronicscoach.com/amplitude-modulation.html

21. ……2.1.1 Amplitude Modulation Mathematical Representation of AM wave The AM wave is expressed by the following expression, e AM = A sin (2 π f c t ) …………………………………………. (3) Where, A represents the instantaneous value of the envelope. The modulating signal either adds or gets subtracted from the peak carrier amplitude E c. Hence we can represent the instantaneous value of envelope as, A = E c + e m = E c + E m   sin   ω m t ………………………………………….(4) Hence the AM wave is given by, e AM = A sin (2 π f c t ) e AM = [ E c + E m   sin  ( 2 π f m t) ] sin (2 π f c t ) e AM = E c [1 + ( E m / E c ) sin  ( 2 π f m t) ] sin (2 π f c t ) Let m= E m / E c be the modulation index. e AM = E c [1 + m sin  (2 π f m t)] sin (2 π f c t )……………(5) 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

22. ……2.1.1 Amplitude Modulation Modulation Index or Modulation Factor In AM wave, the modulation index (m) is defined as, It is the ratio of amplitude of modulating signal to the carrier signal m = It is also called as modulation factor , modulation co-efficient or degree of modulation . If the modulation index is expressed as percentage, it is called as ‘ percentage modulation ’ %m = x 100 Note that ‘m’ is a dimensionless quantity.   22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

23. Effect of modulation index 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

24. ….Effect of modulation index EC403E – Basics of Communication Ms. Kavita Giri, Lecturer (EC), Govt. Polytechnic, Nagpur I. Perfect Modulation The modulation index is the ratio of the maximum amplitude of the message signal to the maximum amplitude of carrier signal. For example, if the message signal maximum amplitude is 4 volts and carrier signal maximum amplitude is also 4 volts, then the ratio of modulating signal amplitude (4 volts) to the carrier signal amplitude (4 volts) is equal to 1. Therefore , the modulation index in perfect-modulation is equal to one (m   = 1) . Perfect-modulation occurs when the maximum amplitude of the message signal or modulating signal is exactly equal to the maximum amplitude of the carrier signal ( E m   =  E c ). m = 100% Perfect modulation causes no distortion

25. ….Effect of modulation index EC403E – Basics of Communication Ms. Kavita Giri, Lecturer (EC), Govt. Polytechnic, Nagpur II. Under Modulation The modulation index is the ratio of the maximum amplitude of the message signal to the maximum amplitude of carrier signal. For example, if the message signal maximum amplitude is 2 volts and carrier signal maximum amplitude is 4 volts, then the ratio of modulating signal amplitude (2 volts) to the carrier signal amplitude (4 volts) is equal to 0.5. Therefore, the modulation index in under-modulation is less than one (m < 1).  Under-modulation occurs when the maximum amplitude of the message signal or modulating signal is less than the maximum amplitude of the carrier signal ( E m   <  E c ). m < 100% Under modulation causes no distortion

26. ….Effect of modulation index EC403E – Basics of Communication Ms. Kavita Giri, Lecturer (EC), Govt. Polytechnic, Nagpur III. Over Modulation The modulation index is the ratio of the maximum amplitude of the message signal to the maximum amplitude of carrier signal. For example, if the message signal maximum amplitude is 6 volts and carrier signal maximum amplitude is 4 volts, then the ratio of modulating signal amplitude (6 volts) to the carrier signal amplitude (4 volts) is equal to 1.5. Therefore, the modulation index in over-modulation is greater than one (m   > 1). Over-modulation occurs when the maximum amplitude of the message signal or modulating signal is greater than the maximum amplitude of the carrier signal ( E m   > E c ). m > 100% Over-modulation causes severe distortion of the waveform of the message signal which results in data loss. Carrier wave experiences 180° phase reversals

27. ……2.1.1 Amplitude Modulation Frequency Spectrum of AM wave Consider the equation for AM wave, e AM = [ E c + E m   cos ( ω m t) ] cos ( ω c t ) e AM = E c [1 + ( E m / E c ) cos ( ω m t) ] cos ( ω c t ) As per the definition of modulation index, m= E m / E c e AM = E c [1 + mcos  ( ω m t)] cos ( ω c t )……………(5) Simplifying we get , e AM = E c cos ( ω c t ) + m E c cos ( ω m t). cos ( ω c t ) ………………(6) For the second term we can use the following identity: 2 cos A cos B = cos (A+B) + cos (A-B) Therefore, equation (6) gets simplified as follows: e AM = E c cos ( ω c t ) + m cos( ω c + ω m )t + m cos( ω c - ω m )t   Carrier Upper Sideband Lower Sideband 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

28. ……2.1.1 Amplitude Modulation Frequency Spectrum of AM wave Carrier Upper Sideband Lower Sideband Observations:

29. ……2.1.1 Amplitude Modulation Frequency Spectrum of AM wave Carrier Upper Sideband Lower Sideband Bandwidth of AM wave The bandwidth of an AM signal is the difference between highest and lowest frequency component. Therefore, BW = f USB – f LSB BW = ( f c +f m ) – (f c - f m ) BW = 2f m 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur The minimum bandwidth requirement of the DSBFC AM system is equal to twice the modulating frequency.

30. ……2.2.2 Amplitude Modulation Total Power relation in AM wave 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

31. ……2.2.2 Amplitude Modulation Total Power relation in AM wave 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

32. ……2.1.1 Amplitude Modulation Total Power relation in AM wave 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

33. Amplitude modulation Advantages of AM AM transmitters are less complex. AM receivers are simple, detection is easy. AM receivers are cost efficient. AM waves can travel a longer distance. Low bandwidth. Applications of AM Radio broadcasting. Picture transmission in a TV system. 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

34. Amplitude modulation Disadvantages of AM The AM wave is also called as ‘Double Sideband Full Carrier (DSBFC)’ signal. The main disadvantages of this technique are: 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

35. Amplitude modulation 1. AM needs larger bandwidth The carrier signal in the DSBFC system does not convey any information. The information is contained in the sidebands only. But the sidebands are images of each other and hence both of them contain the same information. All the information can be conveyed by only one sideband. The bandwidth of DSBFC system is 2fm. This is due to simultaneous transmission of both the sidebands, out of which only one is sufficient to convey all the information. Thus the bandwidth of DSBFC is ‘double’ than actually required. Therefore DSBFC is a ‘bandwidth inefficient’ system. 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

36. Amplitude modulation 2. Power wastage due to DSBFC transmission As we know, the total power transmitted by an AM wave is given by, P t = P c + P USB + P LSB P t = P c + P c + P c ……………………………………(1) Out of the three terms in eq.(1), carrier component does not contain any information and one sideband is redundant. So, out of the total power, P t = P c + P c + P c P t = P c (1 + + ) P t = P c (1 + ) P t = P c (1 + ), the power wasted is given by, Power Wastage = P c + P c = (1+ ) P c   Thus the power in one sideband and carrier is wasted when using ‘DSBFC system’

37. Amplitude modulation 3 . AM wave gets affected by noise When a AM wave travels from the transmitter to the receiver over a communication channel, noise gets added to it. The noise will change the amplitude of the envelope of AM in a random manner. As the information is contained in the amplitude variations of the AM wave, the noise will contaminate the information contents in the AM. Hence the performance of AM is very poor in presence of noise. Thus the noise immunity of AM is very low. Envelope is distorted due to noise 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

38. double sideband supressed carrier ( dsbsc ) Drawback of DSBFC In the process of Amplitude Modulation, the modulated wave consists of the carrier wave and two sidebands. The modulated wave has the information only in the sidebands.  Sideband  is nothing but a band of frequencies, containing power, which are the lower and higher frequencies of the carrier frequency. The transmission of a signal, which contains a carrier along with two sidebands can be termed as  Double Sideband Full Carrier  system or simply  DSBFC . It is plotted as shown in the following figure . Such transmission is inefficient. Because , two-thirds of the power is being wasted in the carrier, which carries no information. 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

39. double sideband supressed carrier ( dsbsc ) Principle of DSBSC If this carrier is suppressed and the saved power is distributed to the two sidebands, then such a process is called as  Double Sideband Suppressed Carrier  system or simply  DSBSC . It is plotted as shown in the following figure . 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

40. Double sideband suppressed carrier (DSBSC) modulation 2.9.1 Principle of DSBSC DSB-SC is an amplitude modulated wave transmission scheme in which only sidebands are transmitted and the carrier is not transmitted as it gets suppressed .  The carrier does not contain any information and its transmission results in loss of power. Thus only sidebands are transmitted that contains information. This results in saving of power used in transmission. This saved power can be inserted into the 2 sidebands. Hence, ensuring a stronger signal that transmits over long distances. As during suppression, the baseband signal does not get affected in any way. As we know that transmission power and bandwidth are the two important parameters in a communication system. Thus, in order to save power and bandwidth, DSB-SC modulation technique is adopted. Why DSBSC 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

41. Double sideband suppressed carrier (DSBSC) modulation 2.9.2 Generation of DSBSC A product modulator generates a DSB-SC signal. The signal is obtained by the multiplication of baseband signal x(t) with carrier signal cos ω c t By frequency shifting property of Fourier transform- From the above equation, it is clear that only 2 components are present in the spectrum. These two are the two sidebands that are placed at + ω c and - ω c . 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

42. Double sideband suppressed carrier (DSBSC) modulation 2.9.2 Generation of DSBSC 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

43. Double sideband suppressed carrier (DSBSC) modulation 2.9.3 Mathematical Expression of DSBSC In order to get an exact an idea about the suppression of carrier in DSB-SC system. Consider the baseband or modulating signal, x(t ) = A x cos (2π f x t ) and the carrier signal, c(t ) = A c cos (2π f c t ) The mathematical representation of the signal at the output of the product modulator is given as- s(t ) = x(t).c(t) Further , 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

44. Double sideband suppressed carrier (DSBSC) modulation 2.9.3 Mathematical Expression of DSBSC The maximum frequency is f c + f x The minimum frequency is f c – f x As we know, Bandwidth is given as BW = f max – f min BW = f c + f x – (f c – f x ) BW = 2f x Thus, at the output, the DSB-SC wave contains a signal whose frequency is twice the frequency of the baseband signal. 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

45. Double sideband suppressed carrier (DSBSC) modulation 2.9.4 Carrier suppression in DSB-SC (Balanced Modulator) The carrier without any information content is suppressed by a balanced modulator. Its principle of operation is such that, It can be a diode, JFET or BJT that possess non-linear resistance characteristic . A non-linear device has the capability to produce 2 sidebands with a carrier. But, a balanced mode connection of 2 non-linear devices produces a DSB-SC signal. When two signals of the different frequency are passed through a non-linear resistance then an amplitude modulated signal with the suppressed carrier is achieved at the output . Carrier suppression… How????? 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

46. Double sideband suppressed carrier (DSBSC) modulation 2.9.5 Balanced Modulator using Diodes 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

47. DOuble sideband suppressed carrier (DSBSC) modulation 2.9.5 Balanced Modulator using Diodes As we can see that the baseband input signal is applied at the input of 2 diodes that are 180⁰ phase reversed with each other through a centre tapped transformer. Hence the input at D 1 , v 1 = cos ω c t + x(t) and input at D 2 , v 2 = cos ω c t – x(t) At the output side tuned bandpass filter is obtained by parallel connection of RLC circuit. So, the current through D 1 is given as 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

48. Double sideband suppressed carrier (DSBSC) modulation 2.9.5 Balanced Modulator using Diodes Similarly , the output voltage is given by v o = i 1 R – i 2 R On substituting the above-given value of i 1 and i 2 in the output equation , we will have, v o = R [2 a x(t)] (+ 4b x (t) cos ω c t )] Therefore , the output is, v o = 2aR x(t) + 4bRx (t) cos ω c t modulating signal DSB-SC signal 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

49. Double sideband suppressed carrier (DSBSC) modulation 2.9.5 Balanced Modulator using Diodes Thus, from the above expression, it is clear that output voltage is a combination of modulating signal along with the DSB-SC signal. After the elimination of the modulating signal, the DSB-SC signal is then passed to the LC bandpass and is received at the output. Thus we will have , 4bR x(t) cos ω c t = K x(t) cos ω c t at the output. 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

50. Double sideband suppressed carrier (DSBSC) modulation Advantages Disadvantages Applications It provides 100% modulation efficiency. Due to suppression of carrier, it consumes less power. It provides a larger bandwidth. It involves a complex detection process. Using this technique it is sometimes difficult to recover the signal at the receiver. It is an expensive technique when it comes to demodulation of the signal . During the transmission of binary data, DSB-SC system is used in phase shift keying methods. In order to transmit 2 channel stereo signals, DSB signals are used in Television and FM broadcasting. 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

51. single sideband suppressed carrier ( sSBSC ) modulation 2.10.1 Definition It is also known as SSB-SC which is an acronym for Single Sideband Suppressed Carrier as it allows suppression of one sideband and carrier completely . As we know, DSB-SC modulation technique generates an output wave having twice the bandwidth as that of the original modulating signal . So , in order to avoid doubling factor of bandwidth in such modulation system, the SSB-SC modulation technique was introduced. Single sideband modulation (SSB) is an amplitude modulation scheme in which only a single sideband is transmitted through the channel. 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

52. single sideband suppressed carrier ( sSBSC ) modulation 2.10.2 Why is the suppression of a sideband allowed in SSB modulation? The two sidebands of the modulated signal are particularly related to each other. In other words, we can say the two sidebands carry similar information. Thus , for the transmission of information, we need only one sideband. So , by suppressing one sideband along with the carrier, no any information is lost. Hence, the bandwidth requirement also gets reduced to half and there are chances for an accommodation of twice number of channels using the SSB modulation technique. 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

53. single sideband suppressed carrier ( sSBSC ) modulation 2.10.3 Mathematical Expression Let the modulating signal be, m(t ) = A m cos (2π f m t ) and carrier signal c(t ) = A c cos (2π f c t ) As we have discussed the similar expression in DSB-SC modulation. So, here we can write , It is a combination of 2 sidebands , However , we know that the DSB-SC amplitude modulated wave requires a bandwidth of 2f m . But, due to the presence of single sideband in SSB modulation, the bandwidth requirement is reduced to half. Hence, bandwidth in case of SSB-SC amplitude modulation wave is f m . 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

54. single sideband suppressed carrier ( sSBSC ) modulation 2.10.4 Methods for generating SSB 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

55. single sideband suppressed carrier ( sSBSC ) modulation 2.10.4 Methods for generating SSB 1. Frequency discrimination method (Filter method ) 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

56. single sideband suppressed carrier ( sSBSC ) modulation 2.10.4 Methods for generating SSB 1. Frequency discrimination method (Filter method ) The balanced modulator employed here generates DSB-SC amplitude modulated wave as its output. As the DSB output contains the two sidebands, and only carrier component is suppressed, so sideband suppression filter is needed further in order to eliminate one of the 2 sidebands . The filter characteristics should be such that, it must have flat passband and should possess high attenuation beyond the passband . So, to have such a response, the tuned circuit must have a very high Q factor . To have such a high Q factor it is needed that the difference between modulating frequency and carrier frequency to be high. There is no any practical way to achieve such a high value . 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

57. single sideband suppressed carrier ( sSBSC ) modulation 2.10.4 Methods for generating SSB 1. Frequency discrimination method (Filter method ) Thus, modulation at the initial stage is carried out at a low frequency of about 100 KHz by the balanced modulator. After this one sideband is suppressed by the filter. But, as the SSB signal frequency is very low in comparison to transmitter frequency. So, a balanced mixer and crystal oscillator are employed in the circuit to boost the frequency of SSB signal up to the level of transmitter frequency . Then the SSB signal is fed to a linear amplifier for further amplification. The process of frequency boosting is sometimes also termed as Up-conversion . Basically to eliminate unwanted sideband- LC, ceramic, crystal or mechanical filter are used. Though ceramic or crystal filters are low in cost but provides better results at operating frequency above 1 MHz. Among all these mechanical filters possess the best characteristics thus is widely used. 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

58. single sideband suppressed carrier ( sSBSC ) modulation 2.10.4 Methods for generating SSB 1. Frequency discrimination method (Filter method ) Advantages of Filter method: It provides sufficiently flat and wide bandwidth. By this method, we can have suitable sideband suppression . Disadvantages of Filter method : Frequency up-conversion at the end is necessary as the system does not generate SSB at high frequencies. Expensive filter increases the overall cost of the system. 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

59. single sideband suppressed carrier ( sSBSC ) modulation 2.10.4 Methods for generating SSB 2. Phase Shift Method 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

60. single sideband suppressed carrier ( sSBSC ) modulation 2.10.4 Methods for generating SSB 2. Phase Shift Method 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

61. single sideband suppressed carrier ( sSBSC ) modulation 2.10.4 Methods for generating SSB 2. Phase Shift Method Advantages of Phase shift method : It does not require a frequency up-conversion stage. The modulating signal can be a low-frequency audio signal. Switching between the sidebands is easier . Disadvantages of Phase shift method : The designing of phase shifting circuitry is complex. It requires phase shifting to be accurate, which is a difficult task. 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

62. single sideband suppressed carrier ( sSBSC ) modulation Advantages Disadvantages Applications It allows multiple signals to transmit. SSB technique requires less bandwidth as compared to DSB technique. Less power is consumed. It allows transmission of the high power signal. It provides less interference to noise due to the reduction in bandwidth. Implementation of SSB holds complex nature. It is expensive. SSB technique requires a transmitter and receiver to be highly frequency stable. As some slight change in frequency will deteriorate the quality of the signal. It is needed in all such applications where power saving and low bandwidth is required. The technique is utilized in point to point communication. It is also used in land and air mobile communication. It also finds its applications in telemetry and radar communication. 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur