Introduction to AM

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ANALOG COMMUNICATION
(204189)
Ms. S. N. Motade
INDEX
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Analog Communication
Teaching Scheme Lectures 4 Hrs/Week Practical
2 Hrs/Week
Examination Scheme Theory Online 50 Marks Theory
Paper 50 Marks Practical 50 Marks
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Unit - I AMPLITUDE (LINEAR) MODULATION Baseband
Carrier communication, Generation of AM (DSBFC)
its spectrum, Power relations applied to
sinusoidal signals, DSBSC- multiplier modulator,
Non linear generation, Switching modulator, Ring
modulator its spectrum, Modulation Index.
SSBSC, ISB VSB, their generation methods and
comparison, AM Broadcast Technical
Standards. Unit - II ANGLE MODULATION Instantan
eous Frequency, Concept of Angle Modulation,
Frequency Spectrum, Narrow Band Wide Band FM,
Modulation Index, Bandwidth, Phase Modulation,
Bessels Function its Mathematical Analysis,
Generation of FM (Direct Indirect Method),
Comparison of AM FM.
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Unit - III AM FM RECEIVERS Block Diagram of AM
FM Receivers, Super Heterodyne Receiver,
Performance Characteristics Sensitivity,
Selectivity, Fidelity, Image Frequency Rejection
and IFRR. Tracking, De-emphasis, Mixers. AM
Detection Rectifier Detection, Envelope
Detection Demodulation of DSBSC Synchronous
Detection Demodulation of SSBSC Envelope
Detector FM Detection using PLL. Unit - IV
NOISE Sources of Noise, Types of Noise, White
Noise, Thermal Noise, Shot Noise, Partition
Noise, Low Frequency or Flicker Noise, Burst
Noise, Avalanche Noise, Signal To Noise Ratio,
SNR of Tandem Connection, Noise Figure, Noise
Temperature, Friss Formula for Noise Figure,
Noise Bandwidth.
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Unit - V BEHAVIOR OF ANALOG SYSTEMS IN PRESENCE
OF NOISE. Baseband Systems, Amplitude Modulated
Systems- DSBSC, SSBSC AM, Angle modulated
systems Phase Modulation, Frequency Modulation,
Threshold in Angle Modulation, Pre-emphasis
De-emphasis in FM, Comparison of performance of
AM FM systems. Unit - VI PULSE ANALOG
MODULATION Band Limited Time Limited Signals,
Narrow Band Signals Systems, Sampling Theorem
in Time Domain, Nyquist Criteria, Types of
Sampling Ideal, Natural, Flat-Top, Aliasing
Aperture Effect. Pulse Analog Modulation PAM,
PWM PPM. PCM Generation Reconstruction,
Bandwidth Requirement of PCM. Differential PCM,
Delta Modulation Adaptive DM (Only Block
Diagram Treatment).
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• Text Books
• B. P. Lathi Modern Digital Analog
  Communication Systems 3rd Edition, Oxford Press
  Publication.
• 2. Dennis Roddy Coolen Electronic
  Communication, PHI (Fourth Edition)
• Reference Books
• Simon Haykin Communication Systems, John
  Wiley Sons (Fourth Edition)
• Taub Schilling Principles of Communication
  Systems, Tata McGraw Hill.
• 3. George Kennedy Electronic Communication
  Systems, Tata McGraw Hill (Fifth Edition)
• 4. Frenzel Principles of Electronic
  Communication Systems, Tata McGraw Hill( 3rd
  Edition)

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• COMMUNICATION THEORY
• Process of exchanging information.
• Transfer of information from one location to the
  other.
• Barriers
• Language Interpreter, learning other languages
• Distance - Invention of electricity,
• Telegraph invented in 1854,
• Telephone in 1876,
• Radio in 1887.
• Use of computers in communication.

Today we cant imagine our lives without the
knowledge information that arrives from around
the world by electronic communications.
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COMMUNICATION SYSTEM Sends message/(s) from
source to destination.
(1) Transmitter
(2) Receiver
(3) Channel
Transmitter
Receiver
Channel
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COMMUNICATION SYSTEM
Information Source Input Transducer
Transmitter
Noise Source
Channel
Information Signal
Output Transmitter
Receiver
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Communication Channel- The communication
channel provides the link between the transmitter
and the receiver. The various channels
includes, Telephone Channel For voice and
data communication over long distance.
Frequency Range 300 3400 Hz. SNR 17 -30
dB. Linear Phase response for data/image
application (not important for voice).
Transmission rate 16.8 kbps.
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Co-axial Cable Wide Bandwidth (39 GHz).
Free from external interference. Repeater
spacing (1 km disadvantage) Date Rate (274
Mbps)
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Optical Fiber Largest Bandwidth (1000 THz)
Free from electromagnetic interference (EMI)
Repeater spacing (gt100 km)
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Classification of Communication System
Parameter
Transmission
Technique
Bandwidth
Media
Analog
Base band
Digital
Broadband
Wired
Simplex
Duplex
Wireless
Half Duplex
Full Duplex
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Baseband signals-
The original information signals either in
analog or digital form.
Audio 0 to 4KHz Video 0 to 6MHz
Baseband Communication System

• Dedicated Wired Channel
• Low Frequency
• Short Distance

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Baseband Communication System
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• LIMITATIONS/Need of Modulation
• Incompatibility with the media - voice signals
  cant be transmitted directly by radio.
• Covers short distance.
• Very high antennas are required for EM waves at
  audio frequency.
• 1MHz ? 75 Mtr. height
• 15KHz ? 5000 Mtr.
• Antenna of this type is impractical.
• (4) Simultaneous transmission of audio signals
  cause interference.

To overcome above mentioned limitations and
enable multiplexing of communication channels the
modulation is needed.
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MODULATION- Process of putting information onto
a high frequency carrier for transmission .
Carrier Signal
Modulator
Modulating Signal
Modulated Signal

• Reduces the height of antenna.
• Increases the range of communication.
• Avoids mixing of signals.
• Enables the multiplexing of channels.
• Improves the quality of reception.

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TYPES OF MODULATION-
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MCQ

• In a communication system, noise is most likely
  to affect the signal
• 1) At the transmitter v 2) in the channel
• 3) In the information source 4) At the
  destination
• Indicate the FALSE statement. Modulation is used
  to
• Reduce the bandwidth used
• Separate differing transmissions
• Ensure that intelligence may be transmitted over
  long distances
• Allow the use of practicable antennas
• Baseband signals can be ------
• 1) Only digital signals 2) only analog signals
• v 3) Analog or digital signals 4) None of above

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MCQ

• The information signal from information source is
  converted into ------signal by the transmitter
• 1) Mechanical 2) physical
• 3) Optical v 4) electrical
• In wireless communication communication medium
  is----
• 1) Optical fibers v 2) free space
• 3) Coaxial cables 4) none of above
• Baseband signals can also be referred as-----
• v 1) Modulating signal 2) carrier signal
• 3) Modulated signal 4) none of above
• Original information signals are referred as
• 1) Audio signal v 2) baseband signal
• 3) Carrier signal 4) video signal

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MCQ

• ----cannot be transmitted directly over long
  distance faithfully
• 1) AM signal 2) FM signals
• 3) Carrier signals v 4) Baseband signals
• To transmit baseband signal of frequency 15 kHz
  directly-----meters of antenna height is required
• 1) 7500 2) 50
• v 3) 5000 4) 10000