PANIMALAR ENGINEERING COLLEGE

(A CHRISTIAN MINORITY INSTITUTION)

JAISAKTHI EDUCATIONAL TRUST

ACCREDITED BY NATIONAL BOARD OF ACCREDITATION (NBA)
Bangalore Trunk Road, Varadharajapuram, Nasarathpettai,
Poonamallee, Chennai – 600 123.

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DEPARTMENT OF ELECTRONICS &

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COMMUNICATION ENGINEERING

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DEPARTMENT OF ELECTRONICS AND COMMUNICATION

ENGINEERING
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EC 6512 COMMUNICATION SYSTEM LAB MANUAL

V SEMESTER ECE
(ODD SEM YEAR 2017-2018)
 DEPARTMENT OF ECE

VISION

To emerge as a centre of excellence in providing quality education and produce

technically competent Electronics and Communication Engineers to meet the needs of
industry and Society.

MISSION

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M1: To provide best facilities, infrastructure and environment to its students, researchers and

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faculty members to meet the Challenges of Electronics and Communication Engineering
field.

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M2: To provide quality education through effective teaching – learning process for their

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future career, viz placement and higher education.
M3: To expose strong insight in the core domains with industry interaction.

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M4: Prepare graduates adaptable to the changing requirements of the society through life
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long learning.
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PROGRAMME EDUCATIONAL OBJECTIVES
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1. To prepare graduates to analyze, design and implement electronic circuits and systems
using the knowledge acquired from basic science and mathematics.
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2. To train students with good scientific and engineering breadth so as to comprehend,

analyze, design and create novel products and solutions for real life problems.
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3. To introduce the research world to the graduates so that they feel motivated for higher
studies and innovation not only in their own domain but multidisciplinary domain.
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4. Prepare graduates to exhibit professionalism, ethical attitude, communication skills,

teamwork and leadership qualities in their profession and adapt to current trends by
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engaging in lifelong learning.

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5. To practice professionally in a collaborative, team oriented manner that embraces the

multicultural environment of today’s business world.
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PROGRAMME OUTCOMES
1. Engineering Knowledge: Able to apply the knowledge of Mathematics, Science,
Engineering fundamentals and an Engineering specialization to the solution of complex
Engineering problems.
2. Problem Analysis: Able to identify, formulate, review research literature, and analyze
complex Engineering problems reaching substantiated conclusions using first principles of
Mathematics, Natural sciences, and Engineering sciences.
3. Design / Development of solutions: Able to design solution for complex Engineering
problems and design system components or processes that meet the specified needs with
appropriate considerations for the public health and safety and the cultural, societal, and
environmental considerations.
4. Conduct investigations of complex problems: Able to use Research - based knowledge
and research methods including design of experiments, analysis and interpretation of data,
and synthesis of the information to provide valid conclusions.
5. Modern tool usage: Able to create, select and apply appropriate techniques, resources,
and modern Engineering IT tools including prediction and modeling to complex
Engineering activities with an understanding of the limitations.
6. The Engineer and society: Able to apply reasoning informed by the contextual knowledge
to access societal, health, safety, legal and cultural issues and the consequent
responsibilities relevant to the professional Engineering practice.

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7. Environment and sustainability: Able to understand the impact of the professional
Engineering solutions in societal and environmental context, and demonstrate the

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knowledge of, and need for sustainable development.
8. Ethics: Able to apply ethical principles and commit to professional ethics and

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responsibilities and norms of the Engineering practice.

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9. Individual and Team work: Able to function effectively as an individual, and as a
member or leader in diverse teams, and in multidisciplinary settings.

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10. Communication: Able to communicate effectively on complex Engineering activities
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with the Engineering community and with society at large, such as, being able to
comprehend and write effective reports and design documentation, make effective
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presentations, and give and receive clear instructions.
11. Project Management and Finance: Able to demonstrate knowledge and understanding
of the engineering and management principles and apply these to one’s own work, as a
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member and leader in a team, to manage projects and in multidisciplinary environments.

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12. Life – long learning: Able to recognize the needs for, and have the preparation and
ability to engage in independent and life-long learning in the broadest contest of
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technological change.
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PROGRAMME SPECIFIC OUTCOMES

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1. Graduates should demonstrate an understanding of the basic concepts in the primary area
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of Electronics and Communication Engineering, including: analysis of circuits containing

both active and passive components, electronic systems, control systems, electromagnetic
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systems, digital systems, computer applications and communications.

2. Graduates should demonstrate the ability to utilize the mathematics and the fundamental
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knowledge of Electronics and Communication Engineering to design complex systems

which may contain both software and hardware components to meet the desired needs.
3. The graduates should be capable of excelling in Electronics and Communication
Engineering industry/Academic/Software companies through professional careers.
EC6512 COMMUNICATION SYSTEMS LABORATORY LT PC 0032

OBJECTIVES:

The student should be made to:

 To visualize the effects of sampling and TDM
 To Implement AM & FM modulation and demodulation
 To implement PCM & DM
 To implement FSK, PSK and DPSK schemes
 To implement Equalization algorithms

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 To implement Error control coding schemes

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LIST OF EXPERIMENTS:

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1. Signal Sampling and reconstruction

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2. Time Division Multiplexing
3. AM Modulator and Demodulator

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4. FM Modulator and Demodulator rin
5. Pulse Code Modulation and Demodulation
6. Delta Modulation and Demodulation
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7. Observation (simulation) of signal constellations of BPSK, QPSK and QAM
8. Line coding schemes
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9. FSK, PSK and DPSK schemes (Simulation)

10. Error control coding schemes - Linear Block Codes (Simulation)
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11. Communication link simulation

12. Equalization – Zero Forcing & LMS algorithms(simulation)
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TOTAL: 45 PERIODS
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OUTCOMES:
At the end of the course, the student should be able to:
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CO1:Simulate end-to-end Communication Link

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CO2:Demonstrate their knowledge in base band signaling schemes through implementation

FSK, PSK and DPSK
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CO3:Apply various channel coding schemes & demonstrate their capabilities towards the
improvement of the noise performance of communication system
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CO4:Simulate & validate the various functional modules of a communication system

BRIDGING THE CURRICULUM GAP

Course outcomes CO1-CO4 is satisfied by Anna university syllabus. To bridge the gap
between Anna University and IIT , experiments like ASK, PWM and PAM are implemented
using hardware and Linear delta modulation and OFDM spectrum simulated using Matlab
and Experiments like FM radio receiver, ASK, FSK and BPSK using Software defined Radio
are included from NIT.
- Course Instructors
 INDEX

S.NO LIST OF EXPERIMENTS PAGE

NO.
1. AM Modulation and Demodulation 2

2. FM Modulation and Demodulation 8

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3. Sampling and Reconstruction 14

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4. Time Division Multiplexing 20

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Simulation of Digital Modulation Techniques-
5. 24

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ASK,FSK,PSK,QPSK,DPSK

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6. Signal Constellation of BPSK, QPSK & QAM 34

7.
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Communication Link Simulation using SDR 46
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8. Digital Modulation – PSK 48
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9. Digital Modulation – QPSK 52

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10. Pulse Code Modulation 58

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11. Delta and Adaptive Delta Modulation 62

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12. Line Coding and Decoding 68

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13. Error Control Coding using MATLAB 74

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14. Simulation of Equalization Techniques 76

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15. Content Beyond Syllabus 82

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LIST OF EXPERIMENTS:

CYCLE I
1. AM Modulation and Demodulation

2. FM Modulation and Demodulation

3. Sampling and Reconstruction

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4. Time Division Multiplexing

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Simulation of Digital Modulation Techniques-

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5.
ASK,FSK,PSK,QPSK,DPSK

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6. Signal Constellation of BPSK, QPSK & QAM

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7. Communication Link Simulationrin
CYCLE II
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8. Digital Modulation – PSK

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9. Digital Modulation – QPSK

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10. Pulse Code Modulation,

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11. Delta and Adaptive Delta Modulation

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12. Line Coding and Decoding

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13. Error Control Coding using MATLAB

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14. Simulation of Equalization Techniques

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EC 6512-Communication System Lab Department of ECE

CIRCUIT DIAGRAM

AMPLITUDE MODULATION

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DEMODULATION
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EC 6512-Communication System Lab Department of ECE

EXPT.NO.1 AM MODULATION AND DEMODULATION

AIM:

To construct amplitude modulator and demodulator circuit and plot the waveforms.

COMPONENTS REQUIRED:

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NAME OF THE EQUIPMENT /
S.NO. RANGE QUANTITY
COMPONENT

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1 Transistor BC 107 1
2 Diode 1N4001 1

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3 Capacitors 0.1µF, 0.01µF 2,1

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100K,22K,500Ω,20
4 Resistors 2, 1each
0K,10Ω

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5 Decade Inductance Box rin 10 mH 1
6 Function Generators 1 MHz 2
7 CRO 20MHz 1
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8 Bread board - 1
9 Regulated Power supply 0-30V 1
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THEORY :

Modulation can be defined as the process by which the characteristics of carrier wave
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are varied in accordance with the modulating wave (signal). Modulation is performed in a
transmitter by a circuit called a modulator.
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Need for modulation is as follows:

 Avoid mixing of signals
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 Reduction in antenna height

 long distance communication
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 Multiplexing
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 Improve the quality of reception

 Ease of radiation.
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Amplitude Modulation is the process of changing the amplitude of a relatively high

frequency carrier signal in proportion with the instantaneous value of the modulating signal.
The output waveform contains all the frequencies that make up the AM signal and is used to
transport the information through the system. Therefore the shape of the modulated wave is
called the AM envelope. With no modulating signal the output waveform is simply the carrier
signal. Coefficient of modulation is a term used to describe the amount of amplitude change
present in an AM waveform. There are three degrees of modulation available based on value
of modulation index.
1) Under modulation : m<1, Em < Ec
2) Critical modulation: m-1, Em = Ec
3) Over modulation: m>1, Em > Ec

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EC 6512-Communication System Lab Department of ECE

MODEL GRAPH:

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EC 6512-Communication System Lab Department of ECE

Demodulation is the reverse process of modulation and converts the modulated carrier
back to the original information. Demodulation is performed in a carrier by a circuit called a
demodulator.

ADVANTAGES:

1) Relatively inexpensive
2) Low quality form of modulation

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DISADVANTAGES:

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1) Low efficiency
2) Small operating range

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APPLICATION:

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1) Commercial broadcasting of both audio and video signals

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2) Two way mobile radio communication such as citizen band (CB) radio.
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PROCEDURE:
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1. Rig up the circuit as per the circuit diagram.

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2. Set the carrier signal using function generator and measure the amplitude and time
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period.
3. Set the modulating signal and measure the amplitude and time period.
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4. Vary the amplitude around the carrier voltage.

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5. Note down the maximum (Emax) and minimum (Emin) voltages from the CRO.
6. Calculate the modulation index using the formula.
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7. Apply the AM signal to the detector circuit.

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8. Observe the amplitude demodulated output on the CRO.

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9. Compare the demodulated signal with the original modulating signal (Both must
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be same in all parameters). Plot the observed waveforms.

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EC 6512-Communication System Lab Department of ECE

TABULATION:
INPUT SIGNAL:

Time period
Signals Amplitude (V) Frequency (KHz)
(ms)

Modulating signal

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Carrier signal

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MODULATED SIGNAL:

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Emax Emin rin Type of
m = (Emax – Emin)/ (Emax + Emin) %
(V) (V) modulation
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DETECTED SIGNAL:
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Amplitude (V) Time period (ms) Frequency (KHz)

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EC 6512-Communication System Lab Department of ECE

RESULT:
Thus the characteristics of AM Transmitter and Receiver are studied and the
waveforms are observed and plotted.

Questions
1. Define Amplitude Modulation.

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A. AM is a process in which the amplitude of the carrier wave is varied in accordance with

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some characteristics of the modulating signal.

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2. What is the need for Modulation?
A. a) Difficult in transmitting signals at low frequencies.

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b) To minimize signal loss.

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c) To reduce antenna length. rin
3. What are the applications of AM?
A. Amplitude modulation is utilized in many services such as television, standard
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broadcasting, aids to navigation, telemeter, radar, facsimile etc.

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4. What are the different types of AM?

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A. Single Side Band, Double Side Band and Vestigial Side Band Modulation are the
different
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types of AM.
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5. What are the disadvantages of AM?

A. Low efficiency, small operating range, noisy reception.
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EC 6512-Communication System Lab Department of ECE

BLOCK DIAGRAM

FM MODULATOR AND DEMODULATOR

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EC 6512-Communication System Lab Department of ECE

EXPT.NO:2 FM MODULATION AND DEMODULATION

AIM:

To plot the modulation characteristics of FM modulator and demodulator and also to

observe and measure frequency deviation and modulation index of FM.

COMPONENTS REQUIRED:

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NAME OF THE EQUIPMENT /
S.NO. RANGE QUANTITY

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COMPONENT

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1 FM Transmitter and receiver kit 1

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2 CRO rin 20 MHz 1

THEORY:
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Frequency modulation is a type of modulation in which the frequency of the high

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frequency (carrier) is varied in accordance with the instantaneous value of the modulating
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signal.
FREQUENCY DEVIATION f and MODULATION INDEX m f :
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The frequency deviation f represents the maximum shift between the modulated
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signal frequency, over and under the frequency of the carrier.

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f max  f min
f 
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We define modulation index m f the ratio between f and the modulating frequency f.
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f
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mf 
f
FREQUENCY MODULATION GENERATION:
The circuits used to generate a frequency modulation must vary the frequency of a
high frequency signal (carrier) as function of the amplitude of a low frequency signal
(modulating signal). In practice there are two main methods used to generate FM.

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EC 6512-Communication System Lab Department of ECE

MODEL GRAPH:

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EC 6512-Communication System Lab Department of ECE

DIRECT METHOD
An oscilloscope is used in which the reactance of one of the elements of the resonant
circuit depends on the modulating voltage. The most common device with variable reactance
is the Varactor or Varicap, which is a particular diode which capacity varies as function of
the reverse bias voltage. The frequency of the carrier is established with AFC circuits
(Automated frequency control) or PLL (Phase locked loop).

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INDIRECT METHOD:

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The FM is obtained in this case by a phase modulation, after the modulating signal

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has been integrated. In this phase modulator the carrier can be generated by a quartz

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oscillator, and so its frequency stabilization is easier. In the circuit used for the exercise, the

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frequency modulation is generated by a Hartley oscillator, which frequency is determined by
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a fixed inductance and by capacity (variable) supplied by varicap diodes.
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ADVANTAGES:
1. Noise reduction
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2. Improved system fidelity

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3. Efficient use of power

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DISADVANTAGE:
1. Requires a wider bandwidth
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2. Utilizing more complex circuit in both transmitters and receivers.

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APPLICATION:
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1. Television sound transmission

2. Two way mobile radio
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3. Cellular Radio
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4. Microwave
5. Satellite Communication System

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EC 6512-Communication System Lab Department of ECE

TABULATION:

Signals Amplitude (V) Time period (ms) Frequency(KHz)

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Modulating signal

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Carrier signal

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Tmin=
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Modulated signal
Tmax= fmin=
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Demodulated signal
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EC 6512-Communication System Lab Department of ECE

PROCEDURE:
i) Connect the power supply with proper polarity to the kit. While connecting this
ensures that the Power supply is OFF.
ii) Switch on the power supply and carry out the following presetting as shown in
circuit Diagram.
iii) In the FM modulator set the level about 2Vpp and frequency knob to the

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minimum and switch on 1500 KHz.
iv) Observe the Fm modulated waveform from the RF/FM output of the FM

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modulator measure frequency deviation and modulation index of FM.

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v) For demodulation switch on the demodulator and carry out the following

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demodulation connection as shown in circuit diagram.

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vi) Observe the demodulated waveform and plot the graph.
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RESULT:
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Thus the modulation characteristics of FM modulator and demodulator are observed

and plotted.
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Questions:
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1. What is Frequency Modulation?

Frequency modulation (FM) is a technique in which the frequency of the carrier wave is
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varied in accordance with the amplitude of the message signal.

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3. What is the frequency band for FM radio?

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The frequency band for FM radio is about 88 to 108 MHz.

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4. What is the bandwidth of FM signal?

Bandwidth of a FM signal may be predicted using:
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BW = 2 ( + 1 ) fm; where  is the modulation index and fm is the maximum modulating

frequency used.
5.What are the disadvantages of FM?
Compared to AM, the FM signal has a larger bandwidth
6. What are the disadvantages of FM?
High efficiency and better immunity to noise.

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EC 6512-Communication System Lab Department of ECE

BLOCK DIAGRAM:

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CIRCUIT DIAGRAM: (USING MOSFET)

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EC 6512-Communication System Lab Department of ECE

EXPT.NO. 3 SAMPLING AND RECONSTRUCTION

AIM:

To sample a signal with different sampling frequencies and to reconstruct the same.

COMPONENTS REQUIRED:

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NAME OF THE EQUIPMENT

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S.NO. RANGE QUANTITY
/ COMPONENT

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1 Sampling trainer kit - 1

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2 CRO 20MHz 1

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THEORY:
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The analog signal can be converted to a discrete time signal by a process called

sampling. The sampling theorem for a band limited signal of finite energy can be stated
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as,
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” A band limited signal of finite energy, which has no frequency component higher than
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W Hz is completely described by specifying the values of the signal at instants of time

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separated by 1/2W seconds.‟‟ It can be recovered from knowledge of samples taken at the
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rate of 2W per second.

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Sampling is the process of splitting the given analog signal into different samples of
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equal amplitudes with respect to time. There are two types of sampling namely natural
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sampling, flat top sampling. Sampling should follow strictly the Nyquist Criterion i.e. the

sampling frequency should be twice higher than that of the highest frequency signal.

fs  2 fm

Where,

f s  Minimum Nyquist Sampling rate (Hz)

f m  Maximum analog input frequency (Hz).

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EC 6512-Communication System Lab Department of ECE

TABULATION:

MODULATING SIGNAL:

Amplitude (V) Time period (ms) Frequency (KHz)

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SAMPLED SIGNAL:

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Time period (ms) Total

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Sampling
Amplitude Duty No. of (for each sample) Time Frequency
frequency

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(V) Cycle (%) Samples period (KHz)
(KHZ) rinTon Toff
(ms)
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RECONSTRUCTED SIGNAL

Amplitude (V) Time period (ms) Frequency (KHz)

Duty cycle calculation:

D = Ton / (Ton + Toff) = ---------- %

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EC 6512-Communication System Lab Department of ECE

ADVANTAGES:
 It can store retrieve and transmit signals without any loss
 With higher sampling rate they can relax low pass filter design requirements for
ADC and DAC

PROCEDURE:

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1. Give the connections as per the block diagram.
2. Apply the modulating signal and measure its amplitude and time period.

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3. Set the sampling frequency to 80 KHz and note down the amplitude and time

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period of the sampled signal.

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4. Give the sampled signal to the reconstruction circuit and observe the reconstructed

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signal.
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5. Note down the amplitude and time period of the reconstructed signal.
6. Repeat the same procedure for different sampling frequencies.
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7. Plot the above waveforms in the graph.

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EC 6512-Communication System Lab Department of ECE

MODEL GRAPH:

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EC 6512-Communication System Lab Department of ECE

RESULT:
Thus the given signal is sampled with different sampling frequencies and the
waveforms are plotted.

Questions:

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1. What is aliasing effect?
A. The original analog waveform can be recovered from the PAM type samples simply by

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low pass filtering them If fs <fnyquist (2fm) then overlapping of adjacent spectrum

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replicates occurs. This is known as aliasing .Due to under- sampling (for f s<2fm) exact

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analog waveform cannot be recovered,
2. What is the function of Op-amps in this circuit and what is the effect of frequency of

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sampling signal? rin
A. Op-amps acts as voltage followers, if the f s<2fm , then distorted waveform is
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Observed, so to recover the exact signal the sampling signal frequency should be
maintained greater than or equal to the 2fm.
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3. What are the different types of sampling?

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A. Instantaneous sampling, Natural sampling and Flat top sampling.

4. State Sampling Theorem.
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A. The sampling theorem for a band limited signal of finite energy can be stated as,” A
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Band limited signal of finite energy, which has no frequency component higher than W
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Hz is completely described by specifying the values of the signal at instants of time

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EC 6512-Communication System Lab Department of ECE

BLOCK DIAGRAM:

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Patch cord

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EC 6512-Communication System Lab Department of ECE

EXPT.NO.4 TIME DIVISION MULTIPLEXING

AIM:

To perform four channel Time Division multiplexing and De multiplexing.

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COMPONENTS REQUIRED:

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NAME OF THE EQUIPMENT
S.NO. RANGE QUANTITY
/ COMPONENT

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1 Time Division Multiplexing kit - 1

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2 CRO 20MHz 1
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THEORY:
In PAM, PPM the pulse is present for a short duration and for most of the time
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between the two pulses no signal is present. This free space between the pulses can be

occupied by pulses from other channels. This is known as Time Division Multiplexing. Thus,
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time division multiplexing makes maximum utilization of the transmission channel. Each
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channel to be transmitted is passed through the low pass filter. The outputs of the low pass
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filters are connected to the rotating sampling switch (or) commutator.

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It takes the sample from each channel per revolution and rotates at the rate of f s. Thus
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the sampling frequency becomes fs the single signal composed due to multiplexing of input

channels. These channels signals are then passed through low pass reconstruction filters. If

the highest signal frequency present in all the channels is fm, then by sampling theorem, the

sampling frequency fs must be such that fs≥2fm. Therefore, the time space between successive

samples from any one input will be Ts=1/fs, and Ts  1/2fm.

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EC 6512-Communication System Lab Department of ECE

TABULATION
1. TRANSMITTED SIGNALS: 3. RECEIVED SIGNALS:

Time Time
Amplitude Frequency Amplitude Frequency
Channel period Channel period
(V) (KHz) (V) (KHz)
(ms) (ms)

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2. SAMPLED SIGNAL

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Amplitude No.of
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Time period (ms)
Total Time Frequency
Channel (for each sample)
(V) Samples period(ms) (KHz)
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Ton Toff
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MODEL GRAPH:
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EC 6512-Communication System Lab Department of ECE

PROCEDURE:
1. Give the connections as per the block diagram.
2. Apply the four input sinusoidal signals of different frequency to four channels and
measure the amplitude and time period of each signal.
3. Observe and measure the amplitude and frequency of the sampled signal for each

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channel individually.
4. Then observe the multiplexed waveform in the CRO.

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5. Apply the multiplexed signal to the demultiplexer circuit and observe the original

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signals transmitted.

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6. Measure the amplitude and time period of demultiplexed signal for each channel

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individually.

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7. Plot all the waveforms in the graph. er
RESULT:
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Thus the Time division multiplexing and demultiplexing waveforms are obtained.
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Questions
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1. What is multiplexing?
A. It is a process in which a single transmission channel is shared by a no. of base band
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signals.
2. What is TDM?
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A. In TDM, different time intervals rather than frequencies are allotted to different
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signals. During these intervals these signals are sampled and transmitted. Thus, this
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system transmits information intermittently rather than continuously.

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3. What are the advantages of TDM?

A. a)Low cost equipment b) Ease of installation and maintenance c) Low and constant
delay d) unsurpassed voice quality and e) standards based.
4. What are the applications of TDM?
A. In telecommunications and signal processing applications.

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EC 6512-Communication System Lab Department of ECE

SIMULATED WAVEFORM

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EC 6512-Communication System Lab Department of ECE

EXPT.NO.5 SIMULATION OF DIGITAL MODULATION TECHNIQUES

1. Simulation of ASK
AIM:
To implement ASK using MATLAB.

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SOFTWARE REQUIRED:

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 MATLAB

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PROGRAM:

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clc;
t=0:0.0001:0.15;

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m = square(2*pi*10*t);

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c = sin(2*pi*60*t); er
y1=(m.*c);
for i = 1:1500
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if(m(i)==1)
y1(i) = c(i);
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else
y1(i) = 0;
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end
end
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figure(1)
subplot(311);
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plot(m);
subplot(312);
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plot(c);
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subplot (313);
plot (y1);
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RESULT:
Thus ASK was implemented using MATLAB.

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EC 6512-Communication System Lab Department of ECE

SIMULATED WAVEFORM

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Pa

25
EC 6512-Communication System Lab Department of ECE

2. Simulation of FSK
AIM:
To implement FSK using MATLAB.
SOFTWARE REQUIRED:
 MATLAB

ge
PROGRAM:

le
clc;
t = 0:0.0001: 0.15;

ol
m = square (2*pi*10*t);

C
c1 = sin (2*pi*60*t);
c2 = sin (2*pi*120*t);

g
s1 = (m.*c1);

in
for i = 1 : 1500
if(m(i)==1)
er
s1(i)=c2(i);
ne
else
s1(i)=c1(i);
gi

end
end
En

figure(2);
subplot(411);
plot(m);
ar

subplot(412);
al

plot(c1);
subplot(413);
m

plot(c2);
subplot(414);
ni

plot(s1);
Pa

RESULT:
Thus FSK was implemented using MATLAB.

26
EC 6512-Communication System Lab Department of ECE

SIMULATED WAVEFORM

ge
le
ol
C
g
in
er
ne
gi
En
ar
al
m
ni
Pa

27
EC 6512-Communication System Lab Department of ECE

3. Simulation of PSK

AIM:
To implement PSK using MATLAB.

ge
SOFTWARE REQUIRED:
 MATLAB

le
PROGRAM:

ol
clc;
c11 = sin(2*pi*60*t);

C
t = 0:0.0001:0.15;

g
m = square (2*pi*10*t);
c22 = sin((2*pi*60*t)+ pi);

in
s2 = (m.*c11); er
for i = 1:1500
if(m(i)==1)
ne

s2(i)=c11(i);
else
gi

s2(i)=c22(i);
En

end
end
figure(3);
ar

subplot(411);
plot(m);
al

subplot (412);
m

plot(c11);
subplot (413);
ni

plot (c22);
subplot(414);
Pa

plot(s2);

RESULT:
Thus PSK was implemented using MATLAB.

28
EC 6512-Communication System Lab Department of ECE

SIMULATED WAVEFORM

ge
le
ol
C
g
in
er
ne
gi
En
ar
al
m
ni
Pa

29
EC 6512-Communication System Lab Department of ECE

4. Simulation of QPSK
AIM:
To implement QPSK using MATLAB.
SOFTWARE REQUIRED: MATLAB
PROGRAM:
clc; clear all; close all;

ge
Tb=1; t=0:(Tb/100):Tb; fc=1;
c1=sqrt(2/Tb)*cos(2*pi*fc*t);

le
c2=sqrt(2/Tb)*cos(2*pi*fc*t);
N=8; m=rand(1,N);

ol
t1=0; t2=Tb;
for i=1:2:(N-1)

C
t=[t1:(Tb/100):t2];
if m(i)>0.5

g
m(i)=1;

in
m_s= ones (1,length(t));
else
er
m(i)=0;
m_s= -1*ones (1,length(t));
ne

end
odd_sig(i,:)=c1.*m_s;
gi

if m(i+1)>0.5
m(i+1)=1;
En

m_s=ones(1,length(t));
else
m(i+1)=0;
ar

m_s=-1*ones(1,length(t));
end
al

even_sig(i,:)=c2.*m_s; qpsk=odd_sig+even_sig;
subplot(3,2,4);plot(t,qpsk(i,:));
m

title('qpsk signal');xlabel('t--->');ylabel('s(t)');
grid on; hold on;
ni

t1=t1+(Tb+.01); t2=t2+(Tb+.01);
end
Pa

hold off ;subplot(3,2,1);stem(m);

title('binary data bits'); xlabel('n--->');ylabel('b(n)');
grid on; subplot(3,2,2);plot(t,c1);
title('carrier signal-1'); xlabel('t--->');ylabel('c1');
grid on; subplot(3,2,3);plot(t,c2);
title('carrier signal-2'); xlabel('t--->');ylabel('c2');
grid on;

RESULT:
Thus QPSK was implemented using MATLAB.

30
EC 6512-Communication System Lab Department of ECE

SIMULATED OUTPUT:

ge
le
ol
C
g
in
er
ne
gi
En
ar
al
m
ni
Pa

31
EC 6512-Communication System Lab Department of ECE

5. Simulation of DPSK
AIM:
To implement DPSK using MATLAB.
SOFTWARE REQUIRED:
 MATLAB
PROGRAM:

ge
clc; clear all; close all;

le
N=10^4

ol
rand('state',100); rand('state',200);
ip=rand(1,N)>0.5,ipD=mod(filter(1,[1 -1],ip),2);

C
s=2*ipD-1;

g
n=1/sqrt(2)*[randn(1,N)+j*randn(1,N)]; Eb_N0_db=[-3:10];

in
for ii=1:length(Eb_N0_db) er
y=s+10^(-Eb_N0_db(ii)/20)*n;
ne
ipDHat_coh=real(y)>0;
ipHat_coh=mod(filter([1 -1],1,ipDHat_coh),2);
gi

nErr_dbpsk_coh(ii)=size(find([ip-ipHat_coh]),2);
En

end
simBer_dbpsk_coh=nErr_dbpsk_coh/N;
ar

theoryBer_dbpsk_coh=erfc(sqrt(10.^(Eb_N0_db/10))).*(1-5*erfc(sqrt(10.^(Eb_N0_db/10))));
close all;
al

figure
m

semilogy(Eb_N0_db,theoryBer_dbpsk_coh,'b.-');
ni

hold on;
Pa

semilogy(Eb_N0_db,simBer_dbpsk_coh,'mx-');
aixs([-2 10 10^-6 0.5]);
grid on;
legend('theory','simulation');
xlabel('Eb/N0,db');ylabel('bit error rate');
title('bit error probability curve for coherent demodulation of dbpsk');
RESULT:
Thus DPSK was implemented using MATLAB.
32
EC 6512-Communication System Lab Department of ECE

OUTPUT:
BPSK

constellation diagram BPSK

5
Received signal
4

ge
signal constellation

le
2

ol
1

C
Quadrature

g
in
-1
er
-2
ne

-3
gi

-4
En

-5
-5 0 5
In-Phase
ar
al
m
ni
Pa

33
EC 6512-Communication System Lab Department of ECE

EXPT.NO. 6 SIGNAL CONSTELLATION OF BPSK, QPSK & QAM

AIM:
To plot the constellation diagram of digital modulation system BPSK, QPSK & QAM
using MATLAB.

SOFTWARE USED:
 MATLAB

ge
THEORY:

le
A constellation diagram is a representation of a signal modulated by an arbitrary digital

ol
modulation scheme. It displays the signal as a two dimensional scatter diagram in the complex
plane at symbol sampling instants. It can also be viewed as the possible symbols that may be

C
selected by a given modulation scheme as points in the complex plane.

g
PROGRAM: BPSK

in
clc; er
clear all;
close all;
ne
M=2;
k=log2(M);
gi

n=3*1e5;
nsamp=8;
En

X=randint(n,1);
xsym = bi2de(reshape(X,k,length(X)/k).','left-msb');
Y_psk= modulate(modem.pskmod(M),xsym);
ar

Ytx_psk = Y_psk;
al

EbNo=30;
SNR=EbNo+10*log10(k)-10*log10(nsamp);
m

Ynoisy_psk = awgn(Ytx_psk,SNR,'measured');
ni

Yrx_psk = Ynoisy_psk;
h1=scatterplot(Yrx_psk(1:nsamp*5e3),nsamp,0,'r.');
Pa

hold on;
scatterplot(Yrx_psk(1:5e3),1,0,'k*',h1);
title('constellation diagram BPSK');
legend('Received signal' ,'signal constellation');
axis([-5 5 -5 5]);
hold off;

34
EC 6512-Communication System Lab Department of ECE

QPSK

constellation diagram 16 PSK

5
Received signal
4 signal constellation

ge
2

le
1
Quadrature

ol
0

-1

C
-2

g
in
-3

-4
er
-5
ne
-5 0 5
In-Phase
gi
En

QAM
constellation diagram 16 QAM
5
ar

Received signal
4 signal constellation
al

2
m

1
Quadrature
ni

0
Pa

-1

-2

-3

-4

-5
-5 0 5
In-Phase

35
EC 6512-Communication System Lab Department of ECE

Program for QPSK & QAM:

clc;
clear all;
close all;
M=16;
k=log2(M);

ge
n=3*1e5;
nsamp=8;

le
X=randint(n,1);
xsym = bi2de(reshape(X,k,length(X)/k).','left-msb');

ol
Y_qam= modulate(modem.qammod(M),xsym);

C
Y_qpsk= modulate(modem.pskmod(M),xsym);
Ytx_qam = Y_qam;

g
Ytx_qpsk = Y_qpsk;

in
EbNo=30;
SNR=EbNo+10*log10(k)-10*log10(nsamp);
er
Ynoisy_qam = awgn(Ytx_qam,SNR,'measured');
ne
Ynoisy_qpsk = awgn(Ytx_qpsk,SNR,'measured');
Yrx_qam = Ynoisy_qam;
gi

Yrx_qpsk = Ynoisy_qpsk;
h1=scatterplot(Yrx_qam(1:nsamp*5e3),nsamp,0,'r.');
En

hold on;
scatterplot(Yrx_qam(1:5e3),1,0,'k*',h1);
title('constellation diagram 16 QAM');
ar

legend('Received signal' ,'signal constellation');

al

axis([-5 5 -5 5]);
hold off;
m

h2=scatterplot(Yrx_qpsk(1:nsamp*5e3),nsamp,0,'r.');
hold on;
ni

scatterplot(Yrx_qpsk(1:5e3),1,0,'k*',h2);
Pa

title('constellation diagram 16 PSK');

legend('Received signal' ,'signal constellation');
axis([-5 5 -5 5]);
hold off;

RESULT:
Thus the constellation diagrams of digital modulation system BPSK, QPSK & QAM are
simulated & plotted in MATLAB.

36
EC 6512-Communication System Lab Department of ECE

INTRODUCTION TO SDR KIT

What is Software defined radio (SDR)?

Software defined radio is defined as an environment where Hardware and Software are
different parts allows user to implement the operating functions of hardware through a
modifiable software. Complete design produces a radio which can receive and transmit widely

ge
different radio protocols (sometimes referred to as waveforms) based solely on the software
used.

le
Where SDR can be used?

ol
Due to its wide RF range it covers a wide range of applications including high frequency
communications, FM and TV broadcast, cellular, Wi-Fi, ISM, and lot more.

C
Starting from simple experiments, it makes you grow in experience and complexity up to being

g
able to deal with competence and master the fundamental elements which makes the Software

in
Based Radio.
er
FEATURES
• RFCoverage from70MHz – 6 GHz RF
ne

• GNU Radio and open BTS support through the open source USRP Hardware Driver
• USB 3.0 High speed interface (Compatible with USB 2.0)
gi

• Flexible rate 12 bit ADC/DAC

• 1TX, 1 RX, Half or Full Duplex
En

• Xilinx Spartan 6 XC6SLX75 FPGA

• Up to 56 MHz of real-time bandwidth
ar

Power
al

• DC Input: 6V
m

SOFTWARE DESCRIPTION
ni

What is GNU Radio?

GNU Radio is a software library, which can be used to develop complete applications for radio
Pa

engineering and signal processing.

Introduction
GNU Radio is a free and open-source software development toolkit that provides signal
processing blocks to implement software radios. It can be used with readily-available low-cost
external RF hardware to create software-defined radios, or without hardware in a simulation-like
environment.
GNU Radio is licensed under the GNU General Public License (GPL) version 3. All of the code
is copyright of the Free Software Foundation. While all the applications are implemented using
python language while critical signal processing path is done using C++ language.
37
EC 6512-Communication System Lab Department of ECE

PROCEDURE TO WORK ON GNU Radio Companion:

GNU Radio Companion (GRC) is a graphical user interface that allows you to build GNU Radio
flow graphs. It is an excellent way to learn the basics of GNU Radio. This is the first in a series
of tutorials that will introduce you to the use of GRC.
Procedure for Amplitude modulation:

STEP 1:Click on GRC.

ge
le
ol
C
g
in
er
ne
gi
En

STEP 2: Click on options and name the title and change generate options as WX GUI.
ar
al
m
ni
Pa

38
EC 6512-Communication System Lab Department of ECE

STEP3: Click variable and change ID and value.

ge
le
ol
C
g
in
er
ne
gi

STEP 4: Press control+F and search for signal source.

En
ar
al
m
ni
Pa

39
EC 6512-Communication System Lab Department of ECE

STEP 5: Place the signal source for message signal as amplitude modulation.

ge
le
ol
C
g
in
er
STEP 6: Change the properties in signal source as (i) Output Type: Float
ne

(ii)Waveform: Cosine
(iii)Frequency: 100
gi

(iv)Amplitude: 2 and
En
ar
al
m
ni
Pa

40
EC 6512-Communication System Lab Department of ECE

STEP 7: Place another signal source for carrier signal in amplitude modulation.

ge
le
ol
C
g
in
er
ne

STEP 8: Change properties in signal source as (i) Output type: float

gi

(ii) Waveform: Sine

(iii) Frequency: 100K
En

(iv) Amplitude: 2
ar
al
m
ni
Pa

41
EC 6512-Communication System Lab Department of ECE

STEP 9: Press control + F and search Multiply block.

ge
le
ol
C
g
in
er
ne

STEP 10: Place Multiply for multiply the message signal and carrier signal.
gi
En
ar
al
m
ni
Pa

42
EC 6512-Communication System Lab Department of ECE

STEP 11: Change properties in multiply as (i) ID Type: Float

(ii)Num Inputs: 2

ge
le
ol
C
g
in
er
ne
gi
En

STEP 12: Press Control + F and search for scope sink and Place WX GUI Scope sink.
ar
al
m
ni
Pa

43
EC 6512-Communication System Lab Department of ECE

STEP 13: Change the properties in Wx GUI scope sink as (i) Type: Float
(ii)Num input: 2

ge
le
ol
C
g
in
er
ne
gi

STEP 14: Connect wires of signal source to multiply and connect to WX GUI scope sink.
En
ar
al
m
ni
Pa

44
EC 6512-Communication System Lab Department of ECE

STEP 15: Click Run and stop.

ge
le
ol
C
g
in
er
ne

OUTPUT WAVEFORM:
gi
En
ar
al
m
ni
Pa

45
EC 6512-Communication System Lab Department of ECE

EXPT.NO.7 COMMUNICATION LINK SIMULATION USING SDR

AIM:
To construct an Amplitude modulator and demodulator and using SDR
TRAINER KIT.

ge
EQUIPMENTS REQUIRED:

le
SDR Trainer Kit -1

ol
SMA Connector-1
USB device -1

C
THEORY:

g
AMPLITUDE MODULATION

in
Amplitude modulation is the process of changing the amplitude of a relatively high
frequency carrier signal in proportion with the instantaneous value of the modulating signal.
er
ne
BLOCK DIAGRAM:
gi
En
ar
al
m
ni
Pa

RESULT:
Thus the Amplitude modulation was studied using SDR kit.

46
EC 6512-Communication System Lab Department of ECE

BLOCK DIAGRAM:

ge
le
ol
C
g
in
er
ne
gi
En
ar
al
m
ni
Pa

47
EC 6512-Communication System Lab Department of ECE

EXPT.NO.8 DIGITAL MODULATION – PSK

AIM:

To generate Phase Shift Keying signal and plot the graph.

EQUIPMENTS/COMPONENTS REQUIRED:

ge
S.NO COMPONENTS / EQUIPMENTS QUANTITY

le
ol
1
1. Phase shift keying transmitter kit

C
1
2. CRO

g
1
3. Function generator

in
Few
4. Patch chords
er
ne

THEORY:
gi

To facilitate the transmission of a signal over a communication bandwidth, a simple

En

modulation of digital technique called phase shift keying is adopted, in which the binary signals
symbol „0‟ and symbol „1‟ are transmitted with a phase shift with respect to each other.
At the transmitter side, the message signal which is in analog form is converted to digital
ar

type and is modulated through a sinusoidal carrier frequency. The transmitter output will be a
al

signal in which logic „1‟ and logic „0‟ are represented by an 1800 phase.
m

There are different form of PSK such as BPSK, QPSK etc., At the receiver side using
ni

threshold device, the received signal is converted into either logic „1‟ or logic „0‟.
Pa

APPLICATION:
 Wireless LAN
 RFID
 Bluetooth communication

48
EC 6512-Communication System Lab Department of ECE

MODEL GRAPH

ge
le
ol
C
g
in
er
ne
gi
En
ar
al

TABULATION
m

AMPLITUDE TIMEPERIOD FREQUENCY

SIGNAL
ni

(V) (µs) (KHz)

Pa

Clock
Sin 2
Sin 3
Control Input
PSK Modulated output
PSK Demodulated output

49
EC 6512-Communication System Lab Department of ECE

PROCEDURE:

1. The connections are made as per the block diagram.

2.
The message signal is applied to the input and also the carrier from function generator.
3.
The PSK waveform is obtained.

ge
4.
Tabulate the Amplitude and time period.
5.
Plot the Graph.

le
ol
RESULT:

C
Thus the Phase Shift Keying waveform is obtained and plotted.

g
in
QUESTIONS: er
1.What are the advantages of BPSK?
BPSK has a bandwidth which is lower than of BFSK is the best of all
ne

systems in the presence of noise. It gives the minimum possibility of error

gi

and it has very good noise immunity.

En

2.What are the advantages of differential phase shift keying?

i.No need to generate the carrier at the receiver end. This means that
complicated circuitry for generation of local carrier is avoided.
ar

ii.The bandwidth required for DPSK is less compared to binary PSK.

al

3. What are the disadvantages of differential phase shift keying?

m

The probability of error is high compared to binary PSK.

ni

4.Why is PSK always preferable over ASK in coherent detection?

Pa

ASK has amplitude variations, hence noise interference is more,PSK method

has less noise interference. It is always preferable.
5. What is signal constellation diagram?
Signal constellation refers to a set of possible message points.

50
EC 6512-Communication System Lab Department of ECE

BLOCK DIAGRAM

ge
le
ol
C
g
in
er
ne
gi
En
ar
al
m
ni
Pa

51
EC 6512-Communication System Lab Department of ECE

EXPT.NO.9 DIGITAL MODULATION – QPSK

AIM:

To generate Quadrature Phase Shift Keying signal and plot the graph.

EQUIPMENTS/COMPONENTS REQUIRED:

ge
S.NO COMPONENTS / EQUIPMENTS QUANTITY

le
1

ol
1. QPSK transmitter kit

C
1
2. CRO

g
1
3. Function generator

in
Few
4. Patch chords
er
ne
THEORY:
In pass band digital communication techniques, there are three basic techniques of
gi

modulation. They are PSK, ASK, FSK. The basic form of phase shift keying is binary phase shift
En

keying abbreviated as BPSK. The major disadvantages of BPSK are that, it occupies a much
large bandwidth and each and every bit is modulated by phase shifts.
ar

In order to obtain an efficient usage of channel bandwidth Quadrature phase shift keying
techniques is introduced in which there is a phase shift which occurs for a set of bits which is
al

also called as Dibits. Thus, the phase shift occurs for two bits in sequence and the phase shift
m

generally follows the Gray code sequence.

ni

The QPSK of two bits is obtained by adding the odd position bits and BPSK of even
Pa

position bits and producing QPSK. The Dibits are 00,10,11,01. They have a phase shift of π/4 ,
3π/4, 5π/4, 7π/4 respectively. Thus, the QPSK signal is obtained. The main advantage is that it
utilizes efficiently the bandwidth of transmission channel.
APPLICATION:
 It is widely used in satellite broadcasting
 It is used in streaming SD channels and some HD CHANNELS

52
EC 6512-Communication System Lab Department of ECE

MODEL GRAPH
QPSK-MODULATION

ge
le
ol
C
g
in
er
ne
gi
En

QPSK-DEMODULATION
ar
al
m
ni
Pa

53
EC 6512-Communication System Lab Department of ECE

PROCEDURE:

1. The connections are made as per the block diagram.

2. The modulating inputs and the in phase and Quadrature component carriers are given as
input.
3. QPSK wave is obtained.

ge
4. Tabulate the amplitude and time period of QPSK.

le
5. Plot the graph.

ol
C
g
in
er
ne
gi
En
ar
al
m
ni
Pa

54
EC 6512-Communication System Lab Department of ECE

TABULATION:

SIGNAL AMPLITUDE TIMEPERIOD FREQUENCY

(V) (ms) (KHz)

ge
TON TOFF
ms ms

le
Data in

ol
Q bit

C
I bit

g
Sin 1

in
Sin 2 er
Sin 3
ne
Sin 4
Modulated
gi

output
En

Clock
Demodulated
ar

output
al

PHASOR DIAGRAM
m
ni
Pa

55
EC 6512-Communication System Lab Department of ECE

RESULT:
Thus the QPSK wave is obtained and the waveform is plotted.
QUESTIONS:
1.What are the advantages of QPSK as compared to BPSK?
For the same bit error, the bandwidth required by QPSK is reduced to half
as compared to BPSK.

ge
2.List the advantages of Passband transmission.
a. Long distance.

le
b. Analog channels can be used for transmission.

ol
c. Multiplexing techniques can be used for bandwidth conservation.

C
d. Transmission can be done by using wireless channel also.

g
3.List the requirements of Passband transmission.

in
i.Maximum data transmission rate. er
ii.Minimum probability of symbol error.
iii.Minimum transmitted power.
ne

4. Highlight the major difference between a QPSK signal and a MSK signal.
gi

i. QPSK is a phase modulation

En

ii. MSK is frequency modulation

iii. Band width of QPSK is Fb where as MSK is 1.5 Fb
5.Define QPSK
ar

In QPSK (Quadriphase – Shift Keying), the phase of the carrier takes on one
al

 3 5 7
of the four equally spaced values such as , , and as given by
m

4 4 4 4


ni

2E
Si (t )  cos(2f c t  (2i  1) 0  t  T.
T 4
Pa

0 elsewhere.
1

56
 EC 6512-Communication System Lab Department of ECE

BLOCK DIAGRAM:

PCM
ANALOG TO DIGITAL CONVERTER OUTPUT

Analog Input
SAMPLER QUANTIZER ENCODER
DE -QUANTIZER

ge
le
DECODER

ol
QUANTIZED PAM DIGITALLY ENCODED

C
SIGNAL
FILTER

g
in
er
Demodulated
output
ne
gi

MODEL GRAPH:
En
ar
al
m
ni
Pa

57
EC 6512-Communication System Lab Department of ECE

EXPT.NO.10 PULSE CODE MODULATION

AIM:

To obtain Pulse Code Modulated and demodulated signals using PCM trainer kit.

ge
COMPONENTS REQUIRED:

le
NAME OF THE EQUIPMENT /
S.NO. RANGE QUANTITY

ol
COMPONENT
1 PCM trainer kit - 1

C
2 CRO 10 MHz 1

g
THEORY:
in
er
Pulse code modulation is known as digital pulse modulation technique. It is the process
ne

in which the message signal is sampled and the amplitude of each sample is rounded off to the
nearest one of the finite set of allowable values. It consists of three main parts transmitter,
gi

transmitter path and receiver. The essential operation in the transmitter of a PCM system are
En

sampling, Quantizing and encoding. The band pass filter limits the frequency of the analog input
signal. The sample and hold circuit periodically samples the analog input signal and converts
ar

those to a multi level PAM signal. The ADC converts PAM samples to parallel PCM codes
al

which are converted to serial binary data in parallel to serial converter and then outputted on the
m

transmission line as serial digital pulse. The transmission line repeaters are placed at prescribed
distance to regenerate the digital pulse.
ni

In the receiver serial to parallel converter converts serial pulse received from the
Pa

transmission line to parallel PCM codes. The DAC converts the parallel PCM codes to multi
level PAM signals. The hold circuit is basically a Low Pass Filter that converts the PAM signal
back to its original analog form.

ADVANTAGES:
1. Secrecy
2. Noise resistant and hence free from channel interference

58
 EC 6512-Communication System Lab Department of ECE

TABULATION:
TRANSMITTED SIGNAL:
Amplitude (V) Time period (ms) Frequency (KHz)

SAMPLED SIGNAL:

ge
No. of Time period (ms) Total Time Frequency

le
Channel Amplitude(V) samples (for each sample) Period (KHz)

ol
Ton Toff (ms)

C
g
in
RECEIVED SIGNAL: er
Amplitude (V) Time period (ms) Frequency (KHz)
ne
gi

PCM OUTPUT:
En

DC Voltage Encoded values

(V) D6 D5 D4 D3 D2 D1 D0
ar

-5
al

-4
m

-3
ni

-2
Pa

-1
0
1
2
3
4
5

59
EC 6512-Communication System Lab Department of ECE

DISADVANTAGES:
1. Requires more bandwidth

APPLICATION:
1. Compact DISC for storage
2. Military Applications.

ge
PROCEDURE:
1. Give the connections as per the block diagram.

le
2. Measure the amplitude and time period of the input signal.

ol
3. Measure the amplitude and time period of the sampled signal.

C
4. Apply the input signal to the PCM kit and observe and measure the PCM output.
5. Plot the waveforms in the graph.

g
RESULT:
in
er
Thus the Pulse Code Modulated signals are obtained and the waveforms are plotted.
ne
gi

Questions:
En

1. What is the need of parallel to serial converter?

A. To transmit all the bits in one channel.
ar

2. What is the use of Companding?

A. Companding is used to overcome quantizing noise in PCM.
al

3. What are the applications of PCM?

m

A. Because of high immune to noise it can be used for storage systems in CD recording.
ni

4. What should be the minimum B.W. required to transmit a PCM channel?

Pa

A. BT = vW where v = no. of bits used to represent one pulse, W = Maximum signal

frequency.

60
EC 6512-Communication System Lab Department of ECE

BLOCK DIAGRAM
BLOCK DIAGRAM FOR DELTA MODULATION AND DEMODULATION

ge
le
ol
C
g
in
er
ne
gi
En
ar
al
m
ni
Pa

61
EC 6512-Communication System Lab Department of ECE

EXPT. NO. 11 DELTA AND ADAPTIVE DELTA MODULATION

AIM:

To obtain Delta Modulated and Adaptive Delta modulated waveforms.

COMPONENTS REQUIRED:

ge
NAME OF THE EQUIPMENT /
S.NO. RANGE QUANTITY
COMPONENT

le
Delta Modulation & Adaptive
1 - 1
Delta modulationTrainer kit

ol
2 CRO 10 MHz 1

C
3 Patch cords - 10

g
4 Power Supply (0-30) V 1

in
THEORY:
er
Delta modulation uses a single bit PCM code to achieve digital transmission of analog
ne

signal. With conventional PCM, each code is a binary representative of both the sign and
gi

magnitude of a particular sample. The algorithm of delta modulation is simple if the current
sample is smaller than the previous sample a logic0 is transmitted. If the current sample is larger
En

than the previous sample a logic 1 is transmitted.

ADVANTAGES:
ar

 Simple system/circuitry
al

 Cheap
m

 Single bit encoding allows us to increase the sampling rate or to transmit more
ni

information at some sampling rate for the given system BW.

Pa

DISADVANTAGE :
 Noise and distortion.
 Major drawback is that it is unable to pass DC information.

APPLICATION:
 Digital voice storage
 Voice transmission
 Radio communication devices such TV remotes.
62
EC 6512-Communication System Lab Department of ECE

MODEL GRAPH:

ge
le
ol
C
g
in
er
ne
gi
En

TABULATION:
ar

DELTA MODULATION
al

AMPLITUDE (V) TIME PERIOD (ms) FREQUENCY

(HZ)
m
ni

Input Signal
Pa

Integrator 1 output

Sampler output

Integrator 3 output

Filter output

Demodulated output

63
EC 6512-Communication System Lab Department of ECE

THEORY:
Adaptive delta modulation is delta modulation system where the step size of DAC is
automatically varied , depending on the amplitude characteristics of the analog input signal. A
common algorithm for an adaptive delta modulator is when three consecutive 1s or 0s occur, the
step size of the DAC is increased or decreased by a factor of 1.5

ge
APPLICATION:
 Audio communication system

le
ol
C
g
in
er
ne
gi
En
ar
al
m
ni
Pa

64
EC 6512-Communication System Lab Department of ECE

MODEL GRAPH:

ge
le
ol
C
g
in
er
ne
gi
En

TABULATION:
ADAPTIVE DELTA MODULATION
ar
al

TYPE OF SIGNAL AMPLITUDE (V) TIME PERIOD (ms) FREQUENCY

m

(HZ)
ni

Input Signal
Pa

Integrator 2 output

Sampler output

Integrator 3 output

Filter output

Demodulated output
65
EC 6512-Communication System Lab Department of ECE

PROCEDURE:
1. Connections are to be given as per the block diagram.
2. Observe the modulated waveforms.
3. Measure the amplitude and time period of both the waveforms.
4. Plot the graph.

ge
5. Repeat the above procedure for adaptive delta modulation also.
RESULT:

le
Thus Delta Modulated and Adaptive Delta Modulated waveforms are obtained.

ol
Questions

C
1. What is Delta Modulation?

g
A. Delta modulation is a system of digital modulation developed after pulse

in
modulation. In this system, at each sampling time, say the Kth sampling time, the
er
difference between the sample value at sampling time K and the sample value at the
ne
previous sampling time (K-1) is encoded into just a single bit.
2. What are the drawbacks of Delta Modulation?
gi

A. Slope overload distortion and Granular noise effect are the drawbacks of Delta
En

Modulation.
3. What are the advantages of Delta Modulation?
ar

A. The advantages of Delta Modulation are simple system/circuitry; cheap, single bit
encoding allows us to increase the sampling rate or to transmit more information at
al

some sampling rate for the given system BW.

m

4. Can DC information be passed using Delta Modulation?

ni

A. No, DC information cannot be passed using Delta Modulation.

Pa

66
EC 6512-Communication System Lab Department of ECE

BLOCK DIAGRAM

ge
le
ol
C
g
in
er
ne
gi
En
ar
al
m
ni
Pa

67
EC 6512-Communication System Lab Department of ECE

EXPT. NO. 12 LINE CODING AND DECODING

AIM:
To analyze line coding and decoding techniques.

COMPONENTS REQUIRED:

ge
NAME OF THE EQUIPMENT

le
S.NO. RANGE QUANTITY
/ COMPONENT

ol
1 Line coding & decoding kit - 1
2 Connecting plugs - 1

C
3 CRO 10 MHz 1

g
in
THEORY: er
NON-RETURN TO ZERO signal are the easiest formats that can be generated. These
ne
signals do not return to zero with the clock. The frequency component associated with these
signals are half that of the clock frequency. The following data formats come under this
gi

category. Non-return to zero encoding is commonly used in slow speed communications

En

interfaces for both synchronous and asynchronous transmission. Using NRZ, logic 1 bit is sent as
a high value and a logic 0 bit is sent as a low value.
ar
al

a) NON-RETURN TO ZERO-LEVEL (NRZ-L)

This is the most extensively used waveform in digital logics. All „ones‟ are represented by
m

„high‟ and all „zeros‟ by „low‟. The data format is directly available at the output of all digital
ni

data generation logics and hence very easy to generate. Here all the transitions take place at the
Pa

rising edge of the clock.

b) NON-RETURN TO ZERO-MARK (NRZ-M)
These waveforms are extensively used in tape recording. All „ones‟ are marked by change in
levels and all‟zeros‟ by no transitions, and the transitions take place at the rising edge of the
clock.

68
EC 6512-Communication System Lab Department of ECE

LINE CODING WAVE FORM:

ge
le
ol
C
g
in
er
ne
gi
En
ar
al
m
ni
Pa

69
EC 6512-Communication System Lab Department of ECE

c) NON-RETURN TO ZERO-SPACE (NRZ-S)

This type of waveform is marked by change in levels for „zeros‟ and no transition for „ones‟
and the transitions take place at the rising edge of the clock. This format is also used in magnetic
tape recording.
d) UNIPOLAR AND BIPOLAR
Unipolar signals are those signals, which have transition between 0 to +VCC. Bipolar

ge
signals are those signals, which have transition between +VCC to –VCC.
e) BIPHASE – LINE CODING(BIPHASE -L):

le
With the Biphase – L one is represented by a half bit wide pulse positioned during the

ol
first half of the bit interval and a zero is represented by a half bit wide pulse positioned

C
during the second half of the bit interval.

g
f) BIPHASE MARK CODING(BIPHASE-M):

in
With the Biphase-M, a transition occurs at the beginning of every bit interval. A „one‟ is
er
represented by a second transition, half bit later, whereas a zero has no second transition.
g) BIPHASE SPACE CODING(BIPHASE-S):
ne

With a Biphase-S, a transition occurs at the beginning of every bit interval. A „zero‟ is
gi

marked by a second transition, one half bit later; „one‟ has no second transition.
En

h) RETURN TO ZERO SIGNALS:

These signals are called “Return to Zero signals” since they return to „zero‟ with the
clock. In this category, only one data format, i.e, the unipolar return to zero(URZ); With the
ar

URZ a „one‟ is represented by a half bit wide pulse and a „zero‟ is represented by the absence
al

of pulse.
m

i) MULTILEVEL SIGNALS:
ni

Multilevel signals use three or more levels of voltages to represent the binary digits, „one‟
and „zero‟ – instead of normal „highs‟ and „lows‟ Return to zero – alternative mark inversion
Pa

(RZ - AMI) is the most commonly used multilevel signal. This coding scheme is most often
used in telemetry systems. In this scheme, „one‟ are represented by equal amplitude of
alternative pulses, which alternate between a +5 and -5. These alternating pulses return to 0
volt, after every half bit interval. The „Zeros‟ are marked by absence of pulses.

70
EC 6512-Communication System Lab Department of ECE

TABULATION:

ONE ZERO

TON(ms) TOFF(ms) TON(ms) TOFF(ms)

ge
Clock

le
Data Input

ol
NRZ-L

C
NRZ-M

g
in
NRZ-S
er
BIO-L
ne

BIO-M
gi

BIO-S
En

URZ
ar
al
m
ni
Pa

71
EC 6512-Communication System Lab Department of ECE

PROCEDURE:
1. Connect power supply in proper polarity to the kits DCL-05 and DCL-06 and switch it on.
2. Connect CLOCK and DATA generated on DCL-05 to CODING CLOCK IN and DATA
INPUT respectively by means of the patch-chords provided.
3. Connect the coded data NRZ-L on DCL-05 to the corresponding DATA INPUT NRZ-L, of
the decoding logic on DCL-06.
4. Keep the switch SW2 for NRZ-L to ON position for decoding logic as shown in the block
diagram.

ge
5. Observe the coded and decoded signal on the oscilloscope.
6. Connect the coded data NRZ-M on DCL-05 to the corresponding DATA INPUT NRZ-M,
of the decoding logic on DCL-06.

le
7. Keep the switch SW2 for NRZ –M to ON position for decoding logic as shown in the block

ol
diagram.
8. Observe the coded and decoded signal on the oscilloscope.

C
9. Connect the code data NRZ-S on DCL-05 to the corresponding DATA INPUT NRZ-S, of
the decoding logic on DCL-06.

g
10. Keep the switch SW2 for NRZ-S to ON position for decoding logic as shown in the block

in
diagram.
11. Observe the coded and decoded signal on the oscilloscope.
er
12. Use RESET switch for clear data observation if necessary.
13. Unipolar to Bipolar/Bipolar to Unipolar:
ne
a. connect NRZ-L signal from DCL-05 to the input post IN Unipolar to Bipolar and
Observe the Bipolar output at the post OUT.
b. Then connect bipolar output signal to the input post IN of Bipolar to Unipolar and
gi

observe Unipolar out at post OUT.

En

RESULT:
Thus the line coding and decoding techniques were analyzed and observed and the graph
is plotted.
ar

Questions
1. What is a digital signal?
al

A. A digital signal is a discontinuous signal that changes from one state to another in
discrete steps. A popular form of digital modulation is binary, or two levels, digital
m

modulation.
ni

2. What is Line Coding?

A. Line coding is the process of arranging symbols that represent binary data in a
Pa

particular pattern for transmission.

3. What are the common types of line coding used in communication?
A. The most common types of line coding used in fiber optic communications include non-
return-to-zero (NRZ), return-to-zero (RZ), and biphase, or Manchester.
4. In NRZ code, does the presence of a high-light level in the bit duration represent a binary
1 or a binary 0?
A. The presence of a high-light level in the bit duration represents a binary 1, while a low-
light level represents a binary 0.
5. How can the loss of timing occur in NRZ line coding?
A. loss of timing may result if long strings of 1s and 0s are present causing a lack of level
Transitions.
72
EC 6512-Communication System Lab Department of ECE

OUTPUT:
COMPUTATION OF CODE VECTORS FOR A CYCLIC CODE
Msg=
1 0 0 1
1 0 1 0

ge
1 0 1 1

le
Code =

ol
1 1 0 1 0 0 1

C
0 1 1 1 0 1 0

g
in
0 0 0 1 0 1 1
SYNDROME DECODING
er
Recd=
ne

1 0 1 1 1 1 0
gi

Syndrome=7(decimal), 1 1 1(binary)
En

Parmat=
1 0 0 1 0 1 1
ar

0 1 0 1 1 1 0
al

0 0 1 0 1 1 1
m

Corrvect=
ni

0 0 0 0 0 1 0
Pa

Correctedcode=
1 0 1 1 1 0 0

73
EC 6512-Communication System Lab Department of ECE

EXPT.NO. 13 ERROR CONTROL CODING USING MATLAB

AIM:
a. To generate parity check matrix & generator matrix for a (7,4) Hamming code.
b. To generate parity check matrix given generator polynomial g(x) = 1+x+x3.
c. To determine the code vectors.
d. To perform syndrome decoding

PROGRAM:

ge
Generation of parity check matrix and generator matrix for a (7,4) Hamming code.

le
[h,g,n,k] = hammgen(3);

ol
Generation of parity check matrix for the generator polynomial g(x) = 1+x+x3.
h1 = hammgen(3,[1011]);

C
Computation of code vectors for a cyclic code

g
clc;

in
close all;
n=7;
er
k=4;
msg=[1 0 0 1; 1 0 1 0; 1 0 1 1];
ne

code = encode(msg,n,k,'cyclic');
msg
gi

code
En

Syndrome decoding
clc;
close all;
ar

q=3;
n=2^q-1;
al

k=n-q;
parmat = hammgen(q); % produce parity-check matrix
m

trt = syndtable(parmat); % produce decoding table

recd = [1 0 1 1 1 1 0 ] %received vector
ni

syndrome = rem(recd * parmat',2);

syndrome_de = bi2de(syndrome, 'left-msb'); %convert to decimal
Pa

disp(['Syndrome = ',num2str(syndrome_de),.....
' (decimal), ',num2str(syndrome),' (binary) ']);
corrvect = trt(1+syndrome_de, :);%correction vector
correctedcode= rem(corrvect+recd,2);
parmat
corrvect
correctedcode

RESULT:
Thus encoding and decoding of block codes are performed using MATLAB.

74
EC 6512-Communication System Lab Department of ECE

SIMULATED OUTPUT:

Symbol error rate with equalizer: 0

Symbol error rate without equalizer: 0.3310

Scatter plot

ge
2.5
fitered signal
2

le
equalized signal
ideal signal constellation
1.5

ol
1

C
0.5
Quadrature

g
0

in
-0.5 er
-1
ne
-1.5

-2
gi

-2.5
En

-2 -1 0 1 2
In-Phase
ar
al
m
ni
Pa

75
EC 6512-Communication System Lab Department of ECE

EXPT.NO. 14 SIMULATION OF EQUALIZATION TECHNIQUES

1. Simulation of Zero Forcing Equalizer.

AIM:
To simulate the Zero Forcing Equalizer using MATLAB.
SOFTWARE USED: MATLAB
THEORY:
Equalizer can be employed to mitigate the ISI for a smooth recovery of transmitted
symbols and to improve the receiver performance

ge
Zero forcing (or) linear equalizer which processes the incoming signal with a linear filter. It is
classified into two

le
(a) Symbol spaced equalizer
(b) Fractionally spaced equalizer

ol
Symbol spaced equalizer:
A symbol spaced linear equalizer consist of a tapped delay line that stores samples from the input

C
signal. Here the sample rates of both input & output signals are equal to 1/T.
Fractionally spaced equalizer:

g
A Fractionally spaced linear equalizer is similar to a symbol spaced equalizer,but the former

in
receives K input samples before it produces one output sample & updates the weights, where K
is an integer. Here the output sample rates is 1/T,while that of input sample is K/T.
er
PROGRAM
ne

clc;clear all;close all;

M=4;
gi

msg=randint(1500,1,M);
modmsg=pskmod(msg,M);
En

sigconst=pskmod([0:M-1],M);
trainlen=500;
chan=[.986;.845;.237;.123+.31i];
ar

filtmsg=filter(chan,1,modmsg);
eqobj =lineareq(8,lms(0.01),sigconst,1);
al

[symbolest,yd]=equalize(eqobj,filtmsg,modmsg(1:trainlen));
h=scatterplot(filtmsg,1,trainlen,'bx');hold on;
m

scatterplot(symbolest,1,trainlen,'r.',h);
scatterplot(sigconst,1,0,'k*',h);
ni

legend('fitered signal','equalized signal','ideal signal constellation');

Pa

hold off;
demodmsg_noeq=pskdemod(filtmsg,M);
demodmsg =pskdemod(yd,M);
[nnoeq,rnoeq]=symerr(demodmsg_noeq(trainlen+1:end),msg(trainlen+1:end));
[neq,req] = symerr(demodmsg(trainlen+1:end),msg(trainlen+1:end));
disp('symbol error rate with equalizer:');
disp(req);
disp('symbol error rate without equalizer:');
disp(rnoeq)
RESULT:
Thus the Zero Forcing Equalizer is simulated in MATLAB.

76
EC 6512-Communication System Lab Department of ECE

SIMULATED OUTPUT:

Enter the system order,N=5

Enter the number of iterations,M=200

system output
1.2
desired

ge
output
1
error

le
0.8
true and estimated output

ol
C
0.6

g
0.4

in
er
0.2
ne

0
gi
En

-0.2
0 20 40 60 80 100 120 140 160 180 200
number of iterations
ar
al
m
ni
Pa

77
EC 6512-Communication System Lab Department of ECE

2. Equalization using LMS Algorithm

AIM:
To simulate Least Mean Square (LMS) algorithm to adaptively adjust the coefficients of
an FIR filter.

SOFTWARE USED:
MATLAB

ge
THEORY:
The LMS recursive algorithm used for adjusting the filter coefficients adaptively so as to

le
minimize the sum of squared error is described below.

ol
Let x[n] be the input sequence and y[n] be the output sequence of an FIR filter. Then,the

C
output is given by the expression

g
Y[n]=∑ h[k]x[n-k], n=0,1,……M
Where h[n] is the adjustable coefficients of FIR filter.
in
er
Let the desired sequence be d[n].Then, the error sequence e[n] is given by
ne

e[n] = d[n] – y[n] , n=0,1,……M

The LMS algorithm starts with any arbitrary choice of h[k],say h0[k].For example, we
gi

may begin with h0[k]=0,0 ≤ k ≤ N-1.After that each new sample x[n] enters the adaptive filter
En

,we compute the corresponding output, say y[n], form the error signal e[n]=d[n]-y[n],and update
the filter coefficients according to the equation
ar

hn[k] = hn-1[k] +µ.e[n].x[n-k], 0 ≤ k ≤ N-1,n=0,1…..where µ is called step size parameter, x[n-k]

al

is the sample of input signal located at the kth tap of the filter at time n and e[n]x[n-k] is an
m

approximation(estimate) of the negative of the gradient for the kth filter coefficients.
The step size parameter µ controls the rate of convergence. Large value of µ leads to
ni

rapid convergence and smaller value leads to slower convergence. If µ is made too large,the
Pa

algorithm becomes unstable.

In order to ensure convergence and good tracking capabilities in slowly varying channels,
the step size parameters is given by µ=1/5NPx where N is the length of the adaptive FIR filter
and Px is the average power in the input signal which is approximated by
M
1
Px 
1 M
x
n 0
2
( n) .

78
EC 6512-Communication System Lab Department of ECE

SIMULATED OUTPUT:

comparison of actual weights and estimated weights

0.7
actual weights
estimated weights
0.6

0.5

ge
0.4

le
ol
0.3

C
0.2

g
in
0.1
er
0
1 1.5 2 2.5 3 3.5 4 4.5 5
ne
gi
En
ar
al
m
ni
Pa

79
EC 6512-Communication System Lab Department of ECE

PROGRAM:
clc;clear all;close all;
N=input('enter the system order,N=');
M=input('enter the number of iterations,M=');
if((N>=2)&&(M>=2))
x=rand(M,1);
b=fir1(N-1,0.5);
n=0.1*randn(M,1);

ge
d=filter(b,1,x)+n;
h=zeros(N,1);

le
Px=(1/length(x))*sum(x.^2);

ol
mu=1/(5*N*Px);
for n=N:M

C
u=x(n:-1:n-N+1);
y(n)=h'*u;

g
e(n)=d(n)-y(n);

in
h=h+mu*u*e(n); er
end
hold on;plot(d,'g');
ne

plot(y(),'r');
semilogy((abs(e())),'m');
gi

title('system output');
xlabel('number of iterations');
En

ylabel('true and estimated output');

legend('desired','output','error');
ar

hold off;
figure,plot(b','k+');
al

hold on,plot(h,'r*');
legend('actual weights','estimated weights');
m

hold off;
ni

title('comparison of actual weights and estimated weights');

else('system order and number of iterations should be greater than 1');
Pa

end

RESULT:
Thus the Least Mean Square (LMS) algorithm is simulated in MATLAB.

80
EC 6512-Communication System Lab Department of ECE

CIRCUIT DIAGRAM:

ge
le
ol
C
g
in
er
ne
gi

DEMODULATOR
En
ar
al
m
ni
Pa

81
EC 6512-Communication System Lab Department of ECE

CONTENT BEYOND SYLLABUS

EXPT.NO.1 AM MODULATION AND DEMODULATION USING IC2206
AIM:

ge
To construct amplitude modulator and demodulator circuit and plot the waveforms.

le
COMPONENTS REQUIRED:

ol
NAME OF THE EQUIPMENT /

C
S.NO. RANGE QUANTITY
COMPONENT

g
1
IC2206 1

in 47K,1K,10K,
2 Resistors
er 3,1,1,1
220Ω
ne
3. Capacitors 0.01µF,0.1µF 1,2
gi

THEORY:
En

MODULATOR:
An amplitude modulated signal is composed of both low frequency and high frequency
ar

components. The amplitude of the high frequency (Carrier) of the signal is controlled by the low
al

frequency (modulating) signal. The envelope of the signal is created by the low frequency signal.
m

If the modulating signal is sinusoidal, then the envelope of the modulated radio frequency (RF)
ni

signal will also be sinusoidal. The circuit for generating an AM modulated waveform must
Pa

produce the product the of the carrier and the modulating signal.

82
EC 6512-Communication System Lab Department of ECE

TABULATION:
MODULATING SIGNAL

Time period
Signals Amplitude (V) Frequency (KHz)
(ms)

ge
Modulating signal

le
Carrier signal

ol
C
MODULATED SIGNAL

g
in
Emax (V) Emin (V)
er
m = (Emax – Emin) / (Emax + Emin) %
ne
gi
En

DETECTED SIGNAL
ar
al

Amplitude
Frequency (KHz) Time period (ms)
m

(V)
ni
Pa

83
EC 6512-Communication System Lab Department of ECE

DEMODULATOR:
A single diode can be used to detect the AM signal and is called PN diode detector or

envelope detector. The diode acts as a rectifier in removing half the envelope resulting in the

base band signal with a Dc offset. The offset is removed with a series capacitor, producing the

ge
output.

le
Envelope detectors are not perfect. All diodes are nonlinear, and will distort the envelope

ol
when it is near the zero voltage level. This effect can be minimized by using a diode with a low

C
forward voltage drop and a strong signal(several 100mV) at the detector.

g
in
PROCEDURE: er
1. Rig up the circuit as per the circuit diagram.
ne

2. Set the carrier signal to 8V, 10 KHz using function generator and measure the
gi

amplitude and time period.

En

3. Set the modulating signal 4V,1 KHz and measure the amplitude and time period.

4. Vary the amplitude around the carrier voltage.

ar

5. Note down the maximum (Emax) and minimum (Emin) voltages from the CRO.
al

6. Calculate the modulation index using the formula.

m

7. Apply the AM signal to the detector circuit.

ni
Pa

8. Observe the amplitude demodulated output on the CRO.

9. Compare the demodulated signal with the original modulating signal (Both must be

same in all parameters). Plot the observed waveforms.

84
EC 6512-Communication System Lab Department of ECE

MODEL GRAPH:

ge
le
ol
C
g
in
er
ne
gi
En
ar
al
m
ni
Pa

85
EC 6512-Communication System Lab Department of ECE

ge
le
ol
C
g
in
er
ne
gi
En
ar
al
m
ni
Pa

RESULT:
Thus the characteristics of AM Transmitter and Receiver are studied and the waveforms
are observed and plotted.

86
EC 6512-Communication System Lab Department of ECE

CIRCUIT DIAGRAM:

FREQUENCY MODULATION:

ge
le
ol
C
g
in
er
ne
gi
En

FREQUENCY DEMODULATOR:
ar
al
m
ni
Pa

87
EC 6512-Communication System Lab Department of ECE

EX.NO. 2 FM MODULATOR AND DEMODULATOR USING IC 2206

AIM:

To perform frequency modulation and demodulation .

COMPONENTS REQUIRED:

ge
NAME OF THE
S.NO. EQUIPMENT / RANGE QUANTITY

le
COMPONENT

ol
1 IC2206 1

C
10K,3.3K,150Ω,
1,1,1,1,1,
2 Resistors 47K,10K(POT),
2,2
560Ω, 4.7K

g
in
3 Capacitors 10µF,1µF,0.01µF,470pF 2,1,3,1
4 Function Generators 1 MHz 2
er
5 CRO 20MHz 1
ne

6 Bread board - 1
gi

7 Regulated Power supply 0-30V 2

En

THEORY :
Frequency modulation(FM) conveys information over a carrier wave by varying its
ar

instantaneous frequency (contrast this with amplitude modulation ,in which the amplitude of the
al

carrier is varied while its frequency remains constant).Frequency modulation is defined as the
m

process in which the instantaneous frequency of the carrier varies in accordance with the
ni

instantaneous values of the modulating signal. Frequency modulation can be regarded as phase
Pa

modulation where the carrier phase modulation is the time integral of the FM modulating signal

Frequency demodulation is the process of retrieving the original modulating signal from the

modulating signal. A common method for recovering the information signal is through a Foster-

seeley discriminator. The various application of FM modulator and demodulator are

Broadcasting, magnetic tape storage, sound, radio.

88
EC 6512-Communication System Lab Department of ECE

TABULATION:

Time period Frequency(KHz)

Signals Amplitude (V)
(ms)

ge
Modulating

le
signal
Carrier signal

ol
C
Modulated Tmin= fmax=

signal

g
Tmax= fmin=

in
Demodulated er
signal
ne

MODEL GRAPH
gi
En
ar
al
m
ni
Pa

89
EC 6512-Communication System Lab Department of ECE

PROCEDURE:

1.The circuit connection are made according to the circuit diagram.

2.The power supply and ground connections are made.

3.The modulating input signal and carrier signal is given using function generator.

ge
4.The frequency modulated wave is seen on the CRO

le
5.The modulated signal is sent as input to a demodulator circuit and demodulated
signal is observed on the CRO.

ol
C
g
in
er
ne
gi
En
ar
al
m
ni
Pa

RESULT:
The modulating signal was frequency modulated and demodulated.

90
EC 6512-Communication System Lab Department of ECE

CIRCUIT DIAGRAM:

ge
le
ol
C
g
in
er
ne
gi

MODEL GRAPH
En
ar
al
m
ni
Pa

91
EC 6512-Communication System Lab Department of ECE

EXPT.NO.3 DIGITAL MODULATION – ASK

1. Using hardware
AIM:

To generate Amplitude Shift Keying signal using operation amplifier 741.

ge
COMPONENTS REQUIRED:

le
NAME OF THE EQUIPMENT /
S.NO. RANGE QUANTITY

ol
COMPONENT
1 IC 741 - 1

C
2 Resistors 1K 3

g
3 Capacitors 0.01µF 2

in
4 Decade Resistance Box er 2 to 3K 1
5 Function Generator 1 MHz 1
ne

6 CRO 10 MHz 1
7 Bread board - 1
gi

8 Dual Power supply 0-15V 1

En

THEORY:
ar

In digital modulation technique, binary „1‟ or „0‟ is transmitted by changing the

al

amplitude of the carrier signal and is called Amplitude Shift Keying. A sinusoidal signal
m

is used as the carrier signal. The carrier signal is allowed to pass through to transmit
binary „1‟ and is switched off to transmit binary „0‟. The carrier signal is generated using
ni

OP-amp. A square wave is used as the binary signal to be transmitted.

Pa

DESIGN:
Assume f0 = 16KHz
Let C= 0.01 μF
1 1 1
f0 = ;R= =  1KΩ
2RC 2f0c 2 *16 *10 * 0.01*106
3

Let R1= 1KΩ

 Rf 
A = 1+  ;
 A = 3 ; Rf = 2KΩ
 R1 

92
EC 6512-Communication System Lab Department of ECE

PIN CONFIGURATION:

ge
le
ol
C
TABULATION:

g
MODULATING SIGNAL:

in
er
Vm (V) Ton (ms) Toff(ms) Frequency(KHz)
ne
gi
En

CARRIER SIGNAL:
ar
al

Vc(V) Time period (µs) Frequency(KHz)

m
ni
Pa

ASK OUTPUT:
No. of Time period of Total Time period(ms) Amplitude Frequency
cycles each cycle (µs) Ton(ms) Toff(ms) (V) (KHz)

93
EC 6512-Communication System Lab Department of ECE

PROCEDURE:
1. Connections are given as per the circuit diagram.
2. Measure the amplitude and time period of the square wave input signal.
3. Remove the square wave input and ground that terminal. Now the circuit is a wein
bridge oscillator.

ge
4. Verify whether the sinusoidal carrier signal is generated or not. Note down the
amplitude and time period of the carrier signal.

le
5. Apply the square wave input signal and note down the amplitude and time period of

ol
the ASK output signal.

C
g
in
er
ne
gi
En
ar
al
m
ni
Pa

RESULT:
Thus the Amplitude Shift Keying signal is generated and the waveforms are
observed

94
EC 6512-Communication System Lab Department of ECE

CIRCUIT DIAGRAM:

ge
le
ol
C
g
in
er
MODEL GRAPH:
ne
gi
En
ar
al
m
ni
Pa

95
EC 6512-Communication System Lab Department of ECE

EXPT.NO. 4 PULSE AMPLITUDE MODULATION

AIM:

To construct Pulse Amplitude Modulator and Demodulator circuits and observe

the waveforms.

ge
COMPONENTS REQUIRED:

NAME OF THE EQUIPMENT /

le
S.NO. RANGE QUANTITY
COMPONENT

ol
1 OP-AMP µA 741 1

C
2 Transistor BC 108 1
3 Capacitors 0.1µF 2

g
in
4 Resistors 1K,10K,22K,1.5K 2,1,1,3
5 Function Generators 1 MHz 2
er
6 CRO 10MHz 1
ne

7 Bread board - 1
gi

8 Regulated Power supply 0-15V 1

En

9 Dual Power supply 0-15V 1

DESIGN:
ar

Low pass filter design:

1
Let f  1KHz. ; Let C  0.1F ; R= .
al

2f C
m

Substituting we get,
R = 1.5 K 
ni

THEORY:
Pa

In Pulse Amplitude Modulation the carrier is a periodic train of pulses. It is

discontinuous, discrete process i.e. the pulses are present only at certain distinct intervals
of time hence it is most suited for messages that are discrete in nature. However with the
help of sampling techniques continuously varying signals can be transmitted on pulsed
carriers. Generally pulse modulation and coding go hand in hand as in telegraphy and
teletype. The pulse modulated signal, despite the term modulation is base band signals.
The base band coding schemes are the actual coding schemes for base band transmission.
96
EC 6512-Communication System Lab Department of ECE

PIN DIAGRAM

ge
TABULATION:
MODULATING SIGNAL:

le
Time period Frequency

ol
Vm (V)
(ms) fm (KHz)

C
g
CARRIER SIGNAL:
in
er
Vc (V) Ton Toff Total Time Frequency
ne

(µs) (µs) period (µs) fc (KHz)

gi
En
ar

PAM OUTPUT:
Vmax Vmin No.of Time period Frequency
al

(V) (V) cycles (KHz)

m

Ton (ms) Toff (ms)

ni
Pa

Vout
Time period (ms) Frequency(KHz)
(V)

97
EC 6512-Communication System Lab Department of ECE

PROCEDURE:
1. Rig up the circuit as shown in the figure.
2. Using a function generator generate the carrier signal which is of pulse type with
amplitude Vc and frequency fc.
3. Using another function generator generate the modulating signal which is analog with

ge
amplitude Vm and frequency fm.
4. Select the frequency of the carrier signal in such a way that it satisfies sampling

le
theorem.

ol
5. Set the above arrangement and switch on the power supply.

C
6. Observe the corresponding waveforms with the help of CRO and plot them on the

g
graph.

in
7. Apply the Pulse Amplitude Modulated signal to the input of the demodulator circuit
er
and note down the demodulated signal and plot in on the graph.
ne

RESULT:
gi

Thus the Pulse Amplitude Modulator and demodulator circuits are constructed
En

and the waveforms are observed and plotted.

ar
al
m
ni
Pa

98
EC 6512-Communication System Lab Department of ECE

CIRCUIT DIAGRAM:

ge
le
ol
C
g
in
er
ne

TRIGGER CIRCUIT
gi
En
ar
al
m
ni
Pa

99
EC 6512-Communication System Lab Department of ECE

EXPT.NO.5 PULSE WIDTH MODULATION

AIM:

To generate the Pulse Width Modulated signal using 555 timer.

ge
COMPONENTS REQUIRED:

NAME OF THE EQUIPMENT /

le
S.NO. RANGE QUANTITY
COMPONENT

ol
1 IC 555 - 1

C
2 Diode 1N4148 1
3 Capacitors 0.1µF, 0.01µF 3,2

g
in
4 Resistors 6.8K,10K,1.8K 2,1,1
5 Function Generator 1 MHz 1
er
6 CRO 20 MHz 1
ne

7 Bread board - 1
gi

8 Regulated Power supply 0-15V 1

En

DESIGN:
Assume carrier frequency f 0 = 750 Hz.
ar

1.45
The operating frequency of IC 555 timer is given by f 0 
( R A  2 R B )C
al

Let C = 0.1 f ,Let R A  RB ,Substituting we get,R A  6.4k ;R A  6.8k

m

THEORY:
Pulse Time Modulation is also known as Pulse Width Modulation or Pulse Length
ni

Modulation. In PWM, the samples of the message signal are used to vary the duration of
Pa

the individual pulses. Width may be varied by varying the time of occurrence of leading

edge, the trailing edge or both edges of the pulse in accordance with modulating wave. It

is also called Pulse Duration Modulation. Pulse width modulation is a one in which each

pulse has fixed amplitude but width of the pulses is made proportional to amplitude of the

modulating signal at that instant.

100
EC 6512-Communication System Lab Department of ECE

MODEL GRAPH:

ge
le
ol
C
g
in
er
ne

TABULATION:
gi

MODULATING SIGNAL:
En

Vm (V) Time period (ms) Frequency(Hz)

ar
al
m
ni
Pa

PWM OUTPUT:
Amplitude Time period of each pulse (ms)
(V) Ton Toff Ton Toff Ton Toff Ton

101
EC 6512-Communication System Lab Department of ECE

Pulse width increase when signal amplitude increases in positive direction and decreases

when signal amplitude increases in negative direction. Pulses of PWM is of varying pulse width

and hence of varying power component. So transmitter should be powerful enough to handle the

power of maximum pulse width. But average power transmitted is only half is peak powerThe

ge
main advantage of PWM is system will work even if the synchronization between the transmitter

le
and receiver fails. The emitter coupled monostable multivibrator is an excellent voltage to time

ol
converter. Since its capacitor charges if the voltage is varied in accordance with the signal

C
voltage, a series of rectangular pulses will be obtained with varying width as required.

g
in
PROCEDURE: er
1. Rig up the circuit as shown in the circuit diagram.
ne
2. Note down the amplitude (Vm) and time period of the modulating signal.
3. Observe the output at „A‟ (carrier signal) and measure the amplitude (Vc) and
gi

time period.
En

4. Observe the spike output at „B‟ and measure the amplitude and time period.
5. Apply the modulating signal input and trigger input and observe the PWM output.
ar

6. Note down the amplitude and time period of all the signals and plot them on the
graph.
al
m
ni
Pa

RESULT:
Thus the Pulse Width Modulated signal is generated using IC 555 timer and its
Waveforms are plotted.

102
EC 6512-Communication System Lab Department of ECE

SIMULATION OUTPUT:

ge
le
ol
C
g
in
er
ne
gi
En
ar
al
m
ni
Pa

103
EC 6512-Communication System Lab Department of ECE

EXPT.NO.6 SIMULATION OF LINEAR DELTA MODULATION

AIM:
To simulate the linear delta modulation using MATLAB.

SOFTWARE USED:
MATLAB

ge
PROGRAM:

le
clc;
clear all

ol
close all
fs=100;

C
t=0:1/fs:2;
m=sin(2*pi*t);

g
plot(m);

in
hold all;
AM=1;
er
FM=1;
d=2*pi*FM*AM/fs;
ne

for n=1:length(m);
if n==1;
gi

e(n)=m(n);
eq(n)=d*sign(e(n));
En

mq(n)=eq(n);
else
e(n)=m(n)-mq(n-1);
ar

eq(n)=d*sign(e(n));
mq(n)=mq(n-1)+eq(n);
al

end
end
m

stairs(mq)
ni
Pa

RESULT:

Thus the MATLAB code for linear delta modulation was written & output is verified.

104
EC 6512-Communication System Lab Department of ECE

SIMULATED OUTPUT:

ge
le
ol
C
g
in
er
ne
gi
En
ar
al
m
ni
Pa

105
EC 6512-Communication System Lab Department of ECE

EX.NO.7 OFDM SPECTRUM

AIM:

To write and simulate the MATLAB codes for OFDM spectrum (Guard interval insertion).

ge
THEORY:

le
Orthogonal frequency-division multiplexing (OFDM), essentially identical to coded OFDM

ol
(COFDM) and discrete multi-tone modulation (DMT), is a frequency-division multiplexing
(FDM) scheme used as a digital multi-carrier modulation method. A large number of closely-

C
spaced orthogonal sub-carriers are used to carry data. The data is divided into several parallel

g
data streams or channels, one for each sub-carrier. Each sub-carrier is modulated with a

in
conventional modulation scheme (such as quadrature amplitude modulation or phase-shift
er
keying) at a low symbol rate, maintaining total data rates similar to conventional single-carrier
ne
modulation schemes in the same bandwidth.
gi

OFDM has developed into a popular scheme for wideband digital communication, whether
En

wireless or over copper wires, used in applications such as digital television and audio
broadcasting, wireless networking and broadband internet access.
ar

The primary advantage of OFDM over single-carrier schemes is its ability to cope with
al

severe channel conditions, without complex equalization filters. Channel equalization is

m

simplified because OFDM may be viewed as using many slowly-modulated narrowband signals
rather than one rapidly-modulated wideband signal.
ni
Pa

106
EC 6512-Communication System Lab Department of ECE

SIMULATED OUTPUT:

ge
le
ol
C
g
in
er
ne
gi
En
ar
al
m
ni
Pa

107
EC 6512-Communication System Lab Department of ECE

PROGRAM:
clear all;
Fd=1; % symbol rate (1Hz)
Fs=1*Fd; % number of sample per symbol
M=4; % kind(range) of symbol (0,1,2,3)
Ndata=1024; % all transmitted data symbol
Sdata=64; % 64 data symbol per frame to ifft
Slen=128; % 128 length symbol for IFFT
Nsym=Ndata/Sdata; % number of frame -> Nsym frame

ge
GIlen=144; % symbol with GI insertion
GI=16; % guard interval length

le
vector initialization X=zeros(Ndata,1); Y1=zeros(Ndata,1); Y2=zeros(Ndata,1);
Y3=zeros(Slen,1); z0=zeros(Slen,1);z1=zeros(Ndata/Sdata*Slen,1);

ol
g=zeros(GIlen,1);
z2=zeros(GIlen*Nsym,1);z3=zeros(GIlen*Nsym,1);

C
random integer generation by M kinds X = randint(Ndata, 1, M);
digital symbol mapped as analog symbol Y1 = modmap(X, Fd, Fs, 'qask', M);

g
covert to complex number Y2=amodce(Y1,1,'qam');

in
for j=1:Nsym;
for i=1:Sdata;
er
Y3(i+Slen/2-Sdata/2,1)=Y2(i+(j-1)*Sdata,1);
end
ne

z0=ifft(Y3);
for i=1:Slen;
gi

z1(((j-1)*Slen)+i)=z0(i,1);
end
En

for i=1:Slen;
g(i+16)=z0(i,1);
end
ar

for i=1:GI;
g(i)=z0(i+Slen-GI,1);
al

end
for i=1:GIlen;
m

z2(((j-1)*GIlen)+i)=g(i,1);
end
ni

end
Pa

graph on time domain figure(1);

f = linspace(-Sdata,Sdata,length(z1)); plot(f,abs(z1));
Y4 = fft(z1);
if Y4 is under 0.01 Y4=0.001 for j=1:Ndata/Sdata*Slen;
if abs(Y4(j)) < 0.01 Y4(j)=0.01;
end
end
Y4 = 10*log10(abs(Y4));graph on frequency domain figure(2);
f = linspace(-Sdata,Sdata,length(Y4)); plot(f,Y4);axis([-Slen/2 Slen/2 -20 20]);

RESULT:
Thus the MATLAB code for OFDM Spectrum was written & output is verified.
108
EC 6512-Communication System Lab Department of ECE

OUTPUT WAVEFORM:

ge
le
ol
C
g
in
er
ne
gi
En
ar
al
m
ni
Pa

109
EC 6512-Communication System Lab Department of ECE

EX.NO: 8 PULSE POSITION MODULATION

AIM:

To write and simulate in the MATLAB codes for Pulse position modulation.

ge
THEORY:

PROGRAM:

le
clc;

ol
clear all;
close all;

C
fc=1000;
fs=10000;

g
fm=200;

in
t=0:1/fs:(2/fm-1/fs);
mt=0.4*sin(2*pi*fm*t)+0.5; er
st=modulate(mt,fc,fs,'PPM');
dt=demod(st,fc,fs,'PPM');
ne
figure
subplot(3,1,1);
plot(mt);
gi

title('message signal');
En

xlabel('time period');
ylabel('amplitude');
axis([0 50 0 1])
subplot(3,1,2);
ar

plot(st);
title('modulated signal');
al

xlabel('time period');
m

ylabel('amplitude');
axis([0 500 -0.2 1.2])
ni

subplot(3,1,3);
plot(dt);
Pa

title('demodulated signal');
xlabel('time period');
ylabel('amplitude');
axis([0 50 0 1])

RESULT:

Thus the MATLAB code for PPM was written & output is verified.

110
EC 6512-Communication System Lab Department of ECE

EXPT.NO. 9 COMMUNICATION LINK SIMULATION USING SDR

AIM:
To study all digital modulation techniques using SDR TRAINER KIT .

EQUIPMENTS REQUIRED:

ge
SDR Trainer Kit -1
SMA Connector-1

le
USB device -1

ol
THEORY:

C
FREQUENCY MODULATION

g
It is a type of modulation in which the frequency of the high frequency (Carrier) is varied

in
in accordance with the instantaneous value of the modulating signal. The FM modulator is used
er
to combine the carrier wave and the information signal in much the same way as in the AM
transmitter. The only difference in this case is that the generation of the carrier wave and the
ne

modulation process is carried out in the same block.

gi

BLOCK DIAGRAM:
En
ar
al
m
ni
Pa

111
EC 6512-Communication System Lab Department of ECE

OUTPUT WAVEFORM:

ge
le
ol
C
g
AMPLITUDE PHASE SHIFT KEYING

in
ASK is the simplest modulation technique, where a binary information signal directly
er
modulates the amplitude of an analog carrier. ASK is similar to standard amplitude modulation
ne

except there are 2 output amplitudes possible. It is also referred as on-off keying.
gi

BLOCK DIAGRAM:
En
ar
al
m
ni
Pa

112
EC 6512-Communication System Lab Department of ECE

OUTPUT WAVEFORM:

ge
le
ol
C
g
in
er
FREQUENCY SHIFT KEYING
In FSK, modulating signal is a binary signal that varies between two discrete voltage levels
ne

rather than a continuously changing analog waveform.

gi

BLOCK DIAGRAM:
En
ar
al
m
ni
Pa

113
EC 6512-Communication System Lab Department of ECE

OUTPUT WAVEFORM:

ge
le
ol
C
g
BINARY PHASE SHIFT KEYING

in
The simplest form of PSK is binary phase shift keying( N=1 and M=2). 2 phases are
er
possible for the carrier. One phase represents logic 1 & other phase represents logic 0. As the
ne

input signal changes state, the phase of the output carrier shifts between two angles that are
separated by 180° BPSK is a form of square wave modulation of a continuous wave (CW)
gi

signal.
En

BLOCK DIAGRAM
ar
al
m
ni
Pa

114
EC 6512-Communication System Lab Department of ECE

OUTPUT WAVEFORM:

ge
le
ol
C
g
in
er
ne
gi
En
ar
al
m
ni
Pa

Result:
Thus all digital modulation techniques was designed and performed using SDR
TRAINER KIT.

115