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- 1. V. Chandra Sekar © Oxford University Press 2013
- 2. Introduction © Oxford University Press 2013
- 3. Communication Basics Communication deals with the principle of transferring information from one place to another. It involves transmission and reception, and processing of information between these two locations. The source could be in continuous form as in the case of analog communication and as discrete signals as in the case of digital communication. Short distance transmission of information is called baseband transmission. © Oxford University Press 2013
- 4. Communication Basics For long distance transmission, information has to be impressed upon an high frequency component to be able to reach the reception end of communication. The high frequency component is termed as a carrier and the entire process is called modulation. © Oxford University Press 2013
- 5. Need For Modulation To translate the frequency of a low-pass signal to a higher band so that the spectrum of the transmitted bandpass signal matches the bandpass characteristics of the channel. For efficient transmission, it has been found that the antenna dimension has to be of the same order of magnitude as the wavelength of the signal being transmitted. Since C= f for a typical low-frequency signal of 2 kHz, the wavelength works out to be 150 km. Even assuming the height of the Antenna half the wavelength, the height works out to be 75 km, which is impracticable. © Oxford University Press 2013
- 6. Need For Modulation To enable transmission of a signal from several message sources simultaneously through a single channel employing frequency division multiplexing. To improve noise and interference immunity in transmission over a noise channel by expanding the bandwidth of the transmitted signal. © Oxford University Press 2013
- 7. Frequency Translation The modulation process shifts the modulating frequency to a higher frequency, which in turn depends on the carrier frequency, thus producing upper and lower sidebands. Hence, signals are upconverted from low frequencies to high frequencies and downconverted from high frequencies to low frequencies in the receiver. The process of converting a frequency or a band of frequencies to another location in the frequency spectrum is called frequency translation. © Oxford University Press 2013
- 8. Types Of Modulation Depending on whether the amplitude, frequency, or phase of the carrier is varied in accordance with the modulation signal, we classify the modulation as Amplitude modulation Frequency modulation Phase modulation. The method of converting information into pulse form and then transmitting it over a long distance is called pulse modulation. © Oxford University Press 2013
- 9. Transmitter The message as it arrives may not be suitable for direct transmission. It may be voice signal, music, picture, or data. The signals, which are not of electrical nature, have to be converted into electrical signals. This is the role of transmitter. Typical block diagram is illustrated below. © Oxford University Press 2013
- 10. Receiver A receiver is meant to receive the electromagnetic signal which carries the information. It is tuned to receive the required information at a predetermined frequency. The output of the receiver is usually fed into a transducer which converts the information into understandable signal. © Oxford University Press 2013
- 11. Multiplexing When it is required to transmit more signals on the same channel, baseband transmission fails, as in the case of audio signals being broadcast from different stations on the same channel. To encounter this problem either frequency division multiplexing or time division multiplexing is employed. This method of transmitting several channels simultaneously is known as frequency division multiplexing (FDM). In Time Division Multiplexing (TDM) several signals are transmitted over a time interval. Each signal is allotted a time slot and it gets repeated cyclically. The only difference compared to FDM is that the signals are to be sampled before sending. © Oxford University Press 2013
- 12. V. Chandra Sekar © Oxford University Press 2013
- 13. Signals – An Introduction © Oxford University Press 2013
- 14. Signals: Any function that carries information. Shows how a parameter varies with another parameter. Will be dealing with signals with time or frequency as an independent variable Signals © Oxford University Press 2013
- 15. Signals are classified as: Continuous and discrete. Causal and Non causal. Even and Odd. Deterministic and Random Real and complex Energy and power type Signals © Oxford University Press 2013
- 16. Discrete Signals © Oxford University Press 2013
- 17. Continuous Signals © Oxford University Press 2013
- 18. Causal Signals © Oxford University Press 2013
- 19. Even & Odd Signals © Oxford University Press 2013
- 20. ( )sin sin ( ) , t c t t π π = © Oxford University Press 2013 Special Signals
- 21. Sgn(t) = 1, t > 0 = -1, t < 0 © Oxford University Press 2013 Signum Signals
- 22. Impulse or Delta signal ( ) 1 ( ) ( ) ( ) t and v t t dt v t δ δ ∞ −∞ ∞ −∞ = = ∫ ∫ © Oxford University Press 2013
- 23. Classification Of Systems Discrete time and Continuous Time systems. Time Invariant and Time varying systems Causal and Non Causal system Instantaneous and Dynamic systems Stable and Unstable systems © Oxford University Press 2013
- 24. Fourier Series & Transform 1. Fourier series: - Any periodic of function of time x(t) having a fundamental period ‘T’ and frequency 1/T can be represented as an infinite series of sinusoidal waveforms of fundamental and its harmonic frequencies. 2. If a function is x(t), its Fourier series is given by: 0 1 1 ( 0 cos(2 ) sin(2 )n n n n x t a a fnt b fntπ π ∞ ∞ = = =+ +∑ ∑ © Oxford University Press 2013
- 25. Where: 2 0 2 2 2 1 ( ) 2 2 ( ) cos 2 ( ) sin(2 ) T T T n T n a x t dt T nt a x t dt T T b x t nt dt T π π − − = = = = ∫ ∫ © Oxford University Press 2013
- 26. Fourier Transform To represent aperiodic function Fourier transform is used Unlike Fourier series, this representation will be continuous in frequency domain It is given by: Also x(t) can be obtained from X(f) as: x(t) = 2 ( ) ( ) j ft X f x t e dtπ ∞ − −∞ = ∫ ∫ ∞ ∞− dfefX ftj π2 )( © Oxford University Press 2013
- 27. Laplace Transform 1. It converts time domain signal into frequency domain a plane called ‘s’ plane having as the real part and ω as the imaginary part. 2. Laplace transform is given by the expression: 3. The inverse Laplace transform is given by: σ ( ) ( ) ( ) . . ( ) ( ) st jw t x x t e dt i e X x t e dtσ ω ω ∞ − −∞ ∞ − + −∞ = = ∫ ∫ 1 ( ) ( ) 2 st x t X s e ds jπ ∞ ∞ = ∫ © Oxford University Press 2013
- 28. Z Transform Z transform is a polar representation compared to rectangular representation in Laplace transform It is for discrete time function Z transform of a function x(t) is given by: Inverse Z transform is given by: In Z transforms a term ROC is defined as “region of convergence” where the Z transform of a function has finite value. [ ] [ ] n X z x n z− = ∑ 1 [ ] [ ]x n x z Z = © Oxford University Press 2013
- 29. V. Chandra Sekar © Oxford University Press 2013
- 30. Amplitude Modulation © Oxford University Press 2013
- 31. Amplitude of the carrier is changed in proportion to the instantaneous amplitude of a message signal Carrier frequency must be relatively higher than the message frequency Modulation index ‘m’ is the ratio of Em/Ec Percentage of modulation = m x 100% Amplitude Modulation © Oxford University Press 2013
- 32. AM Envelope © Oxford University Press 2013
- 33. Frequency Spectrum Of AM Wave © Oxford University Press 2013
- 34. Power Spectrum Of AM © Oxford University Press 2013
- 35. Suppressed Carrier Systems Double side band (DSB) system Single side band system(SSB) SSB with pilot carrier Independent side band (ISB) system Vestigial side band (VSB) system Other AM Systems © Oxford University Press 2013
- 36. AM Waveforms For AM, DSB & SSB © Oxford University Press 2013
- 37. Single Sideband Advantages: Lesser power consumption. Conservation of bandwidth. Noise reduction. Less fading. Disadvantages: Requires complex receiver. At the receiver, coherent carrier has to be generated. In case of pilot carrier, at the receiver end it has to be boosted properly. © Oxford University Press 2013
- 38. Square law Modulators Switching Modulators Transistor Modulators Low level Medium level High level AM Modulators © Oxford University Press 2013
- 39. Balanced Modulators 1. Balanced ring Modulator 2. Balanced bridge Modulator 3. Transistor balanced Modulator 4. FET balanced Modulator SSB Generation 1. The filter method 2. The phase shift method 3. The Third method Types Of Modulators © Oxford University Press 2013
- 40. AM Demodulators 1. Rectifier detector 2. Envelope detector Detector Distortions 1. Diagonal peak clipping 2. Negative peak clipping SSB Reception 1. Coherent detection 2. Reception with pilot carrier Demodulators, Distortions & Reception © Oxford University Press 2013
- 41. AM Transmitters Low Level AM DSBFC Transmitter © Oxford University Press 2013
- 42. High Level DSBFC Transmitter © Oxford University Press 2013
- 43. SSB Transmitter SSB suppressed carrier Transmitter: BPF is used to remove the other sideband © Oxford University Press 2013
- 44. Phase Shift Method © Oxford University Press 2013
- 45. SSB Transmitter With Pilot Carrier © Oxford University Press 2013
- 46. AM Receiver © Oxford University Press 2013 Super Heterodyne Receiver
- 47. SSB Pilot Receiver © Oxford University Press 2013
- 48. Communication Receiver © Oxford University Press 2013
- 49. Selectivity Sensitivity Dynamic range Fidelity Bandwidth Noise temperature and equivalent noise temperature © Oxford University Press 2013 Receiver Parameters
- 50. Costas Loop © Oxford University Press 2013
- 51. V. Chandra Sekar © Oxford University Press 2013
- 52. Angle Modulation © Oxford University Press 2013
- 53. Angle modulation includes both frequency and phase modulations. In Frequency Modulation(FM), the frequency of the carrier is changed with respect to amplitude of the message signal In phase modulation(PM), the phase of the carrier is changed with respect to amplitude of the message signal Unlike AM, both FM and PM are nonlinear, hence much more difficult to implement and analyze. Introduction © Oxford University Press 2013
- 54. 1. Modulation index for FM wave is given by: Where ∆f is the frequency deviation and fm is the modulating frequency 2. The expression for an FM wave is: 3. Modulation index for PM wave is given by: where, is the phase deviation given by: 4. The expression for an PM wave is: m f f β ∆ = ( ) cos[2 sin{2 ( )}]FM c mf t A f t f tπ β π= + p mm k E= pK p m k E θ∆ = ( ) cos[2 cos{2 ( )}]PM c mf t A f t f tπ θ π= + ∆ Modulation Index & Deviation © Oxford University Press 2013
- 55. Frequency & Phase Modulator Phase modulator can be used to generate FM wave and FM modulator can be used to generate PM wave as shown: © Oxford University Press 2013
- 56. FM & PM Waves © Oxford University Press 2013
- 57. FM with β <<1 is called narrowband FM Expression for narrow band FM: f(t) = Vc {cos ωct - cos (ωc – ωm) t + cos (ωc + ωm) t} Phasor diagram of narrowband FM: Narrowband FM © Oxford University Press 2013
- 58. FM with β > 10 is called wideband FM Expression for wideband FM: f(t) = Jo(β) cos ωc t – J1(β){ cos(ωc – ωm) t – cos(ωc – ωm) t}+ J2 (β) { cos (ωc - 2ωm) t + cos (ωc + 2ωm) t} – J3 (β) { cos (ωc - 3ωm) t – cos (ωc - 3ωm t) } + ------- The function Jn(β) is called the Bessel function. The spectrum is composed of a carrier with an amplitude Jo (β) and a set of side bands spaced symmetrically on either side of the carrier at frequency separation of ωm, 2ωm, 3ωm --- and so on. Unlike AM, FM has an infinite number of side bands along with carrier. These side bands are separated from the carrier by fm, 2fm, 3fm ---------. Wideband FM © Oxford University Press 2013
- 59. Bessel Function As A Function Of β © Oxford University Press 2013
- 60. Bessel Function Values © Oxford University Press 2013
- 61. Carson’s formula for bandwidth of FM system Band width = 2(∆f + fm) HZ For low modulation index, in case of narrow band FM since 2∆f << fm, equation reduces to Band width = 2fm and for wide band FM where ∆f >> fm, equation reduces to Band width = 2∆f. Average power in sinusoidal wideband FM: PT = Vc 2 Jo 2 (β) /R + 2Vc 2 /R { J1 2 (β) + J2 2 (β) + J3 2 (β) + ---------- } = Vc 2 /R [ J0 2 (β) + 2 { J1 2 (β) + J2 2 (β) + J3 2 (β) + -------------- }] = Pc [ Jo 2 (β) + 2 { J1 2 (β) + J2 2 (β) + J3 2 (β) + ------------------- }] where Pc is the unmodulated power Vc 2 /R. Bandwidth Requirements For Angle Modulated Waves © Oxford University Press 2013
- 62. The expression for sinusoidal FM is: Kp em(t) = Kp Em sin ωm t = ∆ Φ sin ωm t where ∆ Φ = Kp Em, ∆ Φ is defined as “Peak phase deviation” and is directly proportional to the peak modulating signal. Sinusoidal Phase Modulation © Oxford University Press 2013
- 63. Phasor Representation © Oxford University Press 2013
- 64. FM generation Varactor diode modulators Reactance modulators Modulators using linear integrated circuits Indirect methods for narrow band and wideband PM generation: Varactor diode in direct PM modulators Direct method with transistor FM & PM Generation © Oxford University Press 2013
- 65. Slope detector Balance slope detector Foster Seeley discriminator Ratio detector Demodulator using PLL Quadrature detector Zero crossing detector FM Detectors © Oxford University Press 2013
- 66. Crosby Direct FM Transmitter: FM Transmitter © Oxford University Press 2013
- 67. Indirect FM Transmitter © Oxford University Press 2013
- 68. Super heterodyne Receiver FM Receivers © Oxford University Press 2013
- 69. Double Superheterodyne Receiver © Oxford University Press 2013
- 70. Phased Lock Loop It is a feedback system that generates a signal that has a fixed relation to the phase of a reference signal . A phase locked loop circuit responds to both the frequency and phase of the input signals, by changing the frequency of the voltage controlled oscillator until it matches to the reference input in both frequency and phase. Hence it is a negative feedback system except that the feedback error signal is a phase rather than a current or voltage signal as usually the case in conventional feedback system. © Oxford University Press 2013
- 71. PLL Block Diagram (Analog) © Oxford University Press 2013
- 72. PLL Block Diagram (Digital) © Oxford University Press 2013
- 73. Data and Tape Synchronization Modems FSK Modulation FM Demodulation Frequency Synthesizer Tone Decoding Frequency Multiplication and Division PLL Applications © Oxford University Press 2013
- 74. Is a powerful technique to generate RF signals. A direct digital synthesizer operates by storing the points of a waveform in digital format, and then recalling them to generate the waveform. The rate at which the synthesizer completes one waveform then determines the frequency. Direct Digital Synthesis © Oxford University Press 2013
- 75. Direct Digital Synthesis © Oxford University Press 2013 Block Diagram :
- 76. V. Chandra Sekar © Oxford University Press 2013
- 77. Pulse Modulation © Oxford University Press 2013
- 78. Pulse Modulation In analog pulse modulation, the carrier is a periodic pulse train The amplitude, position and width of the carrier pulse train are varied in a continuous manner in accordance with the corresponding sample value of message signal. Thus in Pulse modulation, information is transmitted basically in analog form, but the transmission takes place at discrete times. © Oxford University Press 2013
- 79. In the case of digital pulse modulation the message signal is represented in a form that is discrete in both time and amplitude The data is transmitted as a sequence of coded pulse. This type of modulation is also called pulse code modulation (PCM). PCM is the most widely used form in the field of Telecommunication. Digital Data transmission provides a higher level of noise immunity, more flexibility in the band width Power tradeoff possibility of providing more security to data and ease of implementation using large scale integrated circuits. © Oxford University Press 2013
- 80. Pulse width modulation (PWM) Pulse position modulation (PPM) Pulse amplitude modulation (PAM) Pulse code modulation (PCM) Predominant Methods Of Pulse Modulation © Oxford University Press 2013
- 81. Pulse Width Modulation © Oxford University Press 2013
- 82. Pulse Amplitude Modulation © Oxford University Press 2013
- 83. Pulse Amplitude Modulation © Oxford University Press 2013
- 84. Pulse Modulation Technique © Oxford University Press 2013
- 85. PCM offers a method of over coming some of the disadvantages of other type of pulse modulation. In PCM the instantaneous amplitude of the sample is represented by a binary code resulting in a series of ones and zeros or mark and space. All pulses have the same height and same shape Since only ones and zeros are sent. The receiver has only to detect the presence or absence of a pulse. A distorted pulse does not degrade the signal as long as the pulse can still be recognized. Hence PCM is less sensitive to noise than wither PAM or PWM Pulse Code Modulation (PCM) © Oxford University Press 2013
- 86. PCM Transmitter & Receiver © Oxford University Press 2013
- 87. When more than one application or connection share the capacity of one link it is called multiplexing. This results in better utilization of resources. A typical example is, many conversations over telephone line, trunk line, wireless channel, etc. A few examples of multiplexing are: TDM- Time division multiplexing FDM- Frequency division multiplexing WDM- Wavelength division multiplexing CDMA- Code division multiple access Multiplexing © Oxford University Press 2013
- 88. FDM Transmitter © Oxford University Press 2013
- 89. FDM Receiver © Oxford University Press 2013
- 90. Synchronous TDM Transmitter © Oxford University Press 2013
- 91. Synchronous TDM Receiver © Oxford University Press 2013
- 92. Analog Carrier System Using FDM © Oxford University Press 2013
- 93. Digital Carrier System Using TDM © Oxford University Press 2013

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