AM

1. Analog Communication Systems-
ECE3001
Prof. Dr. G.Aarthi,
Associate Professor, SENSE
Cabin: TT-132
Email: aarthi.g@vit.ac.in

2. General Course Information
• Prerequisite: Analog Electronic circuits, Signals and systems.
• Theory - 3 credits- 3 Hours per week –Totally 45 Hours
• Lab – 1 credit- 2 Hours per week

3. Course Objectives:
• To impart students the need, design, analysis and applications of Linear AM
modulators and demodulators.
• To introduce and describe the Angle Modulation, demodulation and the concept
of pre-emphasis and de-emphasis.
• To elaborate the super-heterodyne receiver and the Figure of Merit in DSB-SC,
SSB, AM and FM receivers.
• To describe the sampling, pulse modulation schemes-PAM, PWM and PPM and
the multiplexing techniques FDM and TDM.

4. Expected Course Outcome:
• Able to comprehend the elements of electronic communication system.
• Able to design AM, DSB-SC and SSB-SC modulation and demodulation, and to
calculate the power of AM, DSB-SC and SSB-SC schemes.
• Able to design DSB-SC and SSB-SC modulator and demodulator.
• Comprehend and compare the FM and PM generation and design, distinguish
Wideband and Narrowband FM signals.
• Comprehend and compare different angle demodulators.
• Able to design radio receivers, identify role of AGC, and compute noise voltage,
signal-to-noise ratio, noise figure, noise temperature and figure of merit.
• Determine the Nyquist sampling rate of a given signal, explain aliasing effect,
Comprehend and compare the different pulse modulation techniques.

5. Module:1 Introduction to Communication Systems:
• Need and Importance of Communication
• Elements of a Communication System
• Types of communication systems
• Electromagnetic Spectrum used in communication.
• Concept of bandwidth and power
• Receiver characteristics
• Need for modulation

6. Module:2 Linear Modulation :
• Amplitude modulation
• Frequency spectrum of AM
• Power in AM wave
• Generation of AM signal
• Square law modulator
• Switching modulator
• AM demodulation
• Envelope and square law demodulation.

7. Module:3 Bandwidth and Power Efficient AM
Systems :
• DSB-SC modulation
• Power saving in DSB-SC
• Synchronous detection
• Quadrature null effect.
• SSB-SC
• VSB generation and demodulation
• Comparison of linear modulation systems with respect to power,
bandwidth and receiver complexity
• Low level and high level AM transmitters

8. Module:4 Angle Modulation:
• Principle of frequency and phase modulation
• Relation between FM and PM waves
• Frequency deviation
• Bandwidth of FM
• Narrow band and wide band FM
• FM transmitter
• Bessel functions and Carson’s rule
• Generation of FM and PM wave
• Comparison of AM and FM.

9. Module:5 Demodulation of Angle Modulated
Signals:
• FM detectors
• Slope detectors
• Phase discriminators
• Ratio detectors.
• Feedback Demodulators
• The Phase Locked Loop
• Frequency Compressive Feedback Demodulator.
• Pre-emphasis and de-emphasis.

10. Module:6 Receivers and Noise in Communication
Systems:
• Tuned Radio Frequency (TRF)
• Super-heterodyne receiver(AM and FM)
• Choice of IF and Oscillator frequencies
• Tracking – alignment – AGC
• AFC Noise and its types
• Noise voltage - Signal-to-noise ratio
• Noise figure - Noise temperature
• Figure of Merit in DSB-SC, SSB, AM and FM receivers

11. Module:7 Pulse Modulation Systems:
• Sampling theorem
• Types of Sampling
• Pulse modulation schemes
• PAM, PPM and PWM generation and detection
• Pulse code modulation
• Conversion of PWM to PPM
• Multiplexing Techniques - FDM and TDM
• Problems related to FDM and TDM

12. Module:8
• Contemporary Issues

13. Text/Reference Books:

14. Course Rubrics(Theory)
• Continuous Assessment Test –I (CAT-I) -15 Marks
• Continuous Assessment Test –II (CAT-II) - 15 Marks
• Digital Assignment-1 - 10 Marks
• Quiz-1- 10 Marks
• Quiz-2- 10 Marks
• Final Assessment Test (FAT) - 40 Marks

15. Module 1
Introduction to
Communication
systems

16. Communication System
A B
Engineering System
Genetic System
Social System
History and fact of communication

17. What is a communications system?
• Communications Systems: Systems designed to
transmit and receive information
Info
Source
Info
Sink
Comm
System

18. Basic Communication system

19. History of Communications

21. Communication system Block Diagram

22. Input Transducer

23. Transmitter

24. Channel

25. Communication Channels

28. Receiver

29. Output Transducer

30. Transceivers
• A transceiver is an electronic unit that incorporates
circuits that both send and receive signals.
• Examples are:
• Telephones
• Fax machines
• Handheld CB radios
• Cell phones
• Computer modems

31. Attenuation & Noise
• Signal attenuation, or degradation, exists in all media of
wireless transmission. It is proportional to the square of the
distance between the transmitter and receiver.
• Noise is random, undesirable electronic energy that
enters the communication system via the communicating
medium and interferes with the transmitted message.

32. Types of Communication systems

33. Types of Electronic Communication
• Electronic communications are classified according
to whether they are
1. One-way (simplex) or two-way (full duplex or half
duplex) transmissions
2. Analog or digital signals.

34. Simplex
• The simplest method of electronic communication is
referred to as simplex.
• This type of communication is one-way. Examples are:
• Radio
• TV broadcasting
• Beeper (personal receiver)

35. Full Duplex
• Most electronic communication is two-way and is
referred to as duplex.
• When people can talk and listen simultaneously, it is
called full duplex. The telephone is an example of this type of
communication.

36. Half Duplex
• The form of two-way communication in which only one
party transmits at a time is known as half duplex. Examples are:
• Police, military, etc. radio transmissions
• Citizen band (CB)
• Family radio
• Amateur radio

38. Types of Electronic Communication
Analog Signals
• An analog signal is a smoothly and continuously varying
voltage or current. Examples are:
• Sine wave
• Voice
• Video (TV)

39. Analog Signals
Analog signals (a) Sine wave “tone.” (b) Voice.
(c) Video (TV) signal.

40. Types of Electronic Communication
Digital Signals
• Digital signals change in steps or in discrete increments.
• Most digital signals use binary or two-state codes.
Examples are:
• Telegraph (Morse code)
• Continuous wave (CW) code
• Serial binary code (used in computers)

41. Digital Signals
Figure 1-6: Digital signals (a) Telegraph (Morse code). (b)
Continuous-wave (CW) code. (c) Serial binary code.

45. Electromagnetic spectrum

48. Electromagnetic spectrum

49. Concept of Bandwidth and Power in Communications

50. Power(dBW and dBm)

51. Receiver Characteristics

52. Modulation

53. Modulation

54. Modulation

56. Need for Modulation
• Reduction in the height of antenna
• Multiplexing is possible
• Avoids mixing of signals
• Increases the range of communication
• Improves quality of reception

57. Reduction in the height of antenna

58. Reduction in the height of antenna

59. Multiplexing-Sharing a Medium

60. Multiplexing-Sharing a Medium

61. Multiplexing-Sharing a Medium

62. Avoids mixing of signals
If the baseband sound signals are transmitted without using the modulation by
more than one transmitter, then all the signals will be in the same frequency
range i.e. 0 to 20 kHz .
Therefore, all the signals get mixed together and a receiver can not separate
them from each other .
Hence, if each baseband sound signal is used to modulate a different carrier then
they will occupy different slots in the frequency domain (different
channels). Thus, modulation avoids mixing of signals .

63. Improves Quality of Reception
With frequency modulation (FM) and the digital communication techniques such
as PCM, the effect of noise is reduced to a great extent .
This improves quality of reception