1. ANALOG COMMUNICATION SYSTEMS
Name : J.RAJANIKANTH
Designation: Associate Professor
Department: Electronics & Communication Engineering
College: Siddarth Institute of Engg & Technology

2. ANALOG COMMUNICATION SYSTEMS
Tuesday, November 27, 2018

3. ANALOG COMMUNICATION SYSTEMS
11/27/2018
ANALOG COMMUNICATION SYSTEMS
ANALOG COMMUNICATION SYSTEMS
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4. ANALOG COMMUNICATION SYSTEMS
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7. OLDEN COMMUNICATION ANALOG COMMUNICATION SYSTEMS
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8. ANALOG COMMUNICATION SYSTEMS
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9. ANALOG COMMUNICATION SYSTEMS
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10. ANALOG COMMUNICATION SYSTEMS
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11. ANALOG COMMUNICATION SYSTEMS
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12. ANALOG COMMUNICATION SYSTEMS
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13. • To analyze various analog modulation and demodulation techniques.
Course Objective:
• To study the fundamental concept of the analog communication systems.
• To analyze various analog modulation and demodulation techniques.
• To know the working of various transmitters and receivers.
• To understand the influence of noise on the performance of analog communication systems, and to acquire the knowledge about information and capacity.
Learning Outcome:
• Acquire knowledge on the basic concepts of Analog Communication Systems.
• Analyze the analog modulated and demodulated systems.
• Verify the effect of noise on the performance of communication systems.
• Know the fundamental concepts of information and capacity.
ANALOG COMMUNICATION SYSTEMS
Tuesday, November 27, 2018

14. Acquired knowledge about pulse modulation systems.
Course Name: Analog Communication Systems (C226) Year of Study: 2016 – 17
C226.1
Able to generate amplitude modulation systems in both the time and frequency domains.
C226.2
Able to generate angle modulation systems in both the time and frequency domains
C226.3
Analyze the effect of noise on the performance of communication systems.
C226.4
Acquired knowledge about pulse modulation systems.
C226.5
Know the fundamental concepts of information and channel capacity.
C226.6
Able to distinguish different modulation techniques and their applications
ANALOG COMMUNICATION SYSTEMS
Tuesday, November 27, 2018

15. ALL THE POWERS IS WITHIN U, YOU CAN DO ANYTHING AND EVERY THING
ALL THE POWERS IS WITHIN U, YOU CAN DO ANYTHING AND EVERY THING SWAMI VIVEKANANDA
ARISE AWAKE AND STOP NOT TILL THE GOAL IS REACHED SWAMI VIVEKANANDA

17. Synonims Illicit= illegal obstinate=Refuse to change the opinion antonyms affluentpoor obsecure distinct

18. Communication systems
Digital
Analog
The block diagram on the top shows the blocks common to all communication systems
ANALOG COMMUNICATION SYSTEMS
Tuesday, November 27, 2018

19. Remember the components of a communications system:
Input transducer: The device that converts a physical signal from source to an electrical, mechanical or electromagnetic signal more suitable for communicating
Transmitter: The device that sends the transduced signal
Transmission channel: The physical medium on which the signal is carried
Receiver: The device that recovers the transmitted signal from the channel
Output transducer: The device that converts the received signal back into a useful quantity
ANALOG COMMUNICATION SYSTEMS
Tuesday, November 27, 2018

20. Analog Modulation
The purpose of a communication system is to transmit information signals (baseband signals) through a communication channel
The term baseband is used to designate the band of frequencies representing the original signal as delivered by the input transducer
For example, the voice signal from a microphone is a baseband signal, and contains frequencies in the range of Hz
The “hello” wave is a baseband signal:
ANALOG COMMUNICATION SYSTEMS
Tuesday, November 27, 2018

21. Remember the radio spectrum:
Since this baseband signal must be transmitted through a communication channel such as air using electromagnetic waves, an appropriate procedure is needed to shift the range of baseband frequencies to other frequency ranges suitable for transmission, and a corresponding shift back to the original frequency range after reception. This is called the process of modulation and demodulation
Remember the radio spectrum:
For example, an AM radio system transmits electromagnetic waves with frequencies of around a few hundred kHz (MF band)
The FM radio system must operate with frequencies in the range of MHz (VHF band)
AM radio
FM radio/TV
ANALOG COMMUNICATION SYSTEMS
Tuesday, November 27, 2018

22. This process is accomplished by a device called a modulator
Since the baseband signal contains frequencies in the audio frequency range (3 kHz), some form of frequency-band shifting must be employed for the radio system to operate satisfactorily
This process is accomplished by a device called a modulator
The transmitter block in any communications system contains the modulator device
The receiver block in any communications system contains the demodulator device
The modulator modulates a carrier wave (the electromagnetic wave) which has a frequency that is selected from an appropriate band in the radio spectrum
For example, the frequency of a carrier wave for FM can be chosen from the VHF band of the radio spectrum
For AM, the frequency of the carrier wave may be chosen to be around a few hundred kHz (from the MF band of the radio spectrum)
The demodulator extracts the original baseband signal from the received modulated signal
To Summarize:
Modulation is the process of impressing a low-frequency information signal (baseband signal )onto a higher frequency carrier signal
Modulation is done to bring information signals up to the Radio Frequency (or higher) signal
ANALOG COMMUNICATION SYSTEMS
Tuesday, November 27, 2018

23. Basic analog communications system
Baseband signal (electrical signal)
EM waves (modulated signal)
Transmitter
Input transducer
Transmission Channel
Modulator
EM waves (modulated signal)
Carrier
Baseband signal (electrical signal)
Receiver
Output transducer
Demodulator
ANALOG COMMUNICATION SYSTEMS
Tuesday, November 27, 2018

24. Types of Analog Modulation
Amplitude Modulation (AM)
Amplitude modulation is the process of varying the amplitude of a carrier wave in proportion to the amplitude of a baseband signal. The frequency of the carrier remains constant
Frequency Modulation (FM)
Frequency modulation is the process of varying the frequency of a carrier wave in proportion to the amplitude of a baseband signal. The amplitude of the carrier remains constant
Phase Modulation (PM)
Another form of analog modulation technique which we will not discuss
ANALOG COMMUNICATION SYSTEMS
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25. About Modulation Application Examples
broadcasting of both audio and video signals.
Mobile radio communications, such as cell phone.
Basic Modulation Types
Amplitude Modulation: changes the amplitude.
Frequency Modulation: changes the frequency.
Phase Modulation: changes the phase.
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26. Amplitude Modulation Carrier wave Baseband signal Modulated wave
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Amplitude varying-frequency constant

27. Frequency Modulation Carrier wave Baseband signal Modulated wave
Large amplitude: high frequency
Baseband signal
Small amplitude: low frequency
Modulated wave
Frequency varying-amplitude constant
ANALOG COMMUNICATION SYSTEMS
Tuesday, November 27, 2018

28. AM vs. FM AM requires a simple circuit, and is very easy to generate.
It is simple to tune, and is used in almost all short wave broadcasting.
The area of coverage of AM is greater than FM (longer wavelengths (lower frequencies) are utilized-remember property of HF waves?)
However, it is quite inefficient, and is susceptible to static and other forms of electrical noise.
The main advantage of FM is its audio quality and immunity to noise. Most forms of static and electrical noise are naturally AM, and an FM receiver will not respond to AM signals.
The audio quality of a FM signal increases as the frequency deviation increases (deviation from the center frequency), which is why FM broadcast stations use such large deviation.
The main disadvantage of FM is the larger bandwidth it requires
ANALOG COMMUNICATION SYSTEMS
Tuesday, November 27, 2018

29. AMPLITUDE MODULATION
Several different ways of amplitude modulating the carrier signal by m(t) :
(a) conventional double-sideband AM,
(b) double sideband suppressed-carrier AM,
(c) single-sideband AM,
(d) vestigial-sideband AM.
each way results in different spectral characteristics for
the transmitted signal.
ANALOG COMMUNICATION SYSTEMS
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30. Conventional Amplitude Modulation
AM modulation model
A conventional AM signal
in the time domain
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31. Conventional Amplitude Modulation
AM modulation model
A conventional AM signal
in the time domain
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32. Conventional Amplitude Modulation
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33. Conventional Amplitude Modulation
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34. Modulating signal m(t) is a sinusoid :
Example 5.1.1
Modulating signal m(t) is a sinusoid :
Determine the AM signal, its upper and lower sidebands, and its spectrum.
Solution：the AM signal is expressed as
modulation index:
ANALOG COMMUNICATION SYSTEMS
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35. The lower sideband component is:
so that
The lower sideband component is:
The upper sideband component is :
ANALOG COMMUNICATION SYSTEMS
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36. The spectrum of the AM signal
The power of carrier component is Ac2 / 2
The power of two sideband is Ac2 β/ 4
ANALOG COMMUNICATION SYSTEMS
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37. Conventional Amplitude Modulation
Since the envelope is slowly varying, the positive and the negative halves of each cycle have almost the same amplitude.
integral of
is almost zero .
ANALOG COMMUNICATION SYSTEMS
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38. Conventional Amplitude ModulationSo
Note that the second component is much smaller than the first component ( ). This shows that the conventional AM systems are far less power efficient than the DSB-SC systems described in next subsection.
ANALOG COMMUNICATION SYSTEMS
Tuesday, November 27, 2018

39. Conventional Amplitude Modulation
Demodulation of Conventional AM Signals
rectify the received signal
lowpass filter
DC component
output of the envelope detector
envelope detector
gain factor due to the signal demodulator
ANALOG COMMUNICATION SYSTEMS
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40. SQUARE LAW DETECTOR ANALOG COMMUNICATION SYSTEMS
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41. AM ENVELOPE DETECTOR ANALOG COMMUNICATION SYSTEMS
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42. Synchronous Detector ANALOG COMMUNICATION SYSTEMS
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43. Double-Sideband Suppressed-Carrier AM
DSB-SC AM signal is obtained by
ANALOG COMMUNICATION SYSTEMS
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44. Double-Sideband Suppressed-Carrier AM
Spectrum of the DSB-SC AM Signal.
The bandwidth occupancy of the amplitude-modulated signal is 2W
the channel bandwidth required
Bc=2W.
And it does not contain
a carrier component
For this reason, u(t) is called a suppressed-carrier signal.
ANALOG COMMUNICATION SYSTEMS
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45. Double-Sideband Suppressed-Carrier AM
ANALOG COMMUNICATION SYSTEMS
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