DEPARTMENT OF
ELECTRONICS COMMUNICATION ENGINEERING
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V SEMESTER - R 2013
EC6512 – COMMUNICATION SYSTEMS LABORATORY
LABORATORY MANUAL
Name : __________________________
Register No. : __________________________
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Section : __________________________
DHANALAKSHMI
VISION
College of Engineering is committed to provide highly disciplined, conscientious
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enterprising professionals conforming to global standards through value based quality education training.
MISSION
- To provide competent technical manpower capable of meeting requirements of the industry
- To contribute to the promotion of Academic Excellence in pursuit of Technical Education at different levels
- To train the students to sell his brawn brain to the highest bidder but to never put a price tag on heart soul
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DEPARTMENT OF ELECTRONICS AND COMMUNICATION
ENGINEERING
VISION
To impart professional education integrated with human values to the younger generation, so as to
shape them as proficient dedicated engineers, capable of providing comprehensive solutions to the challenges
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in deploying technology for the service of humanity
MISSION
- To educate the students with the state-of-art technologies to meet the growing challenges of the electronics industry
- To carry out research through continuous interaction with research institutes industry, on advances in communication systems
- To provide the students with strong ground rules to facilitate them for systematic learning, innovation ethical practices
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PROGRAMME EDUCATIONAL OBJECTIVES (PEOS)
1. Fundamentals
To provide students with a solid foundation in Mathematics, Science fundamentals of engineering,
enabling them to apply, to find solutions for engineering problems use this knowledge to acquire higher
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education
2. Core Competence
To train the students in Electronics Communication technologies so that they apply their knowledge
training to compare, to analyze various engineering industrial problems to find solutions
3. Breadth
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To provide relevant training experience to bridge the gap between theory practice this enables them to
find solutions for the real time problems in industry, to design products
4. Professionalism
To inculcate professional effective communication skills, leadership qualities team spirit in the students
to make them multi-faceted personalities develop their ability to relate engineering issues to broader social
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context
5. Lifelong Learning/Ethics
To demonstrate practice ethical professional responsibilities in the industry society in the large,
through commitment lifelong learning needed for successful professional career
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PROGRAMME OUTCOMES (POS)
a) To demonstrate apply knowledge of Mathematics, Science engineering fundamentals in Electronics
Communication Engineering field
b) To design a component, a system or a process to meet the specific needs within the realistic constraints
such as economics, environment, ethics, health, safety manufacturability
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c) To demonstrate the competency to use software tools for computation, simulation testing of electronics
communication engineering circuits
d) To identify, formulate solve electronic communication engineering problems
e) To demonstrate an ability to visualize work on laboratory multidisciplinary tasks
f) To function as a member or a leader in multidisciplinary activities
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g) To communicate in verbal written form with fellow engineers society at large
h) To understand the impact of Electronics Communication Engineering in the society demonstrate awareness
of contemporary issues commitment to give solutions exhibiting social responsibility
i) To demonstrate professional and ethical responsibilities
j) To exhibit confidence in self-education ability for lifelong learning
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k) To participate succeed in competitive exams
EC6512 - COMMUNICATION SYSTEMS LABORATORY
COURSE OBJECTIVES
To visualize the effects of sampling and TDM
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- To Implement AM and FM modulation and demodulation
- To implement PCM and DM
- To implement FSK, PSK and DPSK schemes
- To implement Equalization algorithms
- To implement Error control coding schemes
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LIST OF EXPERIMENTS
1. Signal Sampling and reconstruction
2. Time Division Multiplexing
3. AM Modulator and Demodulator
4. FM Modulator and Demodulator
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5. Pulse Code Modulation and Demodulation
6. Delta Modulation and Demodulation
7. Observation (simulation) of signal constellations of BPSK, QPSK and QAM
8. Line coding schemes
9. FSK, PSK and DPSK schemes (Simulation)
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10. Error control coding schemes – Linear Block Codes (Simulation)
11. Communication link simulation
12. Equalization – Zero Forcing and LMS algorithms (simulation)
COURSE OUTCOMES
Simulate end-to-end Communication Link
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Demonstrate their knowledge in base b signaling schemes through implementation of FSK, PSK DPSK.
Apply various channel coding schemes and demonstrate their capabilities towards the improvement of the noise
performance of communication system.
EC6512 - COMMUNICATION SYSTEMS LABORATORY
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CONTENTS
| Sl. No. | Name of the Experiment | Page No. |
|---|---|---|
| CYCLE 1 - EXPERIMENTS | ||
| 1 | Signal sampling reconstruction | 7 |
| 2 | Time division multiplexing | 13 |
| 3 | AM modulation demodulation | 18 |
| 4 | Frequency modulation demodulation | 26 |
| 5 | PCM modulation demodulation | 33 |
| 6 | Delta modulation demodulation | 38 |
| 7 | Line coding decoding techniques | 45 |
| CYCLE 2 – EXPERIMENTS | ||
| 8 | Error control coding using MATLAB | 51 |
| 9 | Design of BPSK, QPSK, QAM using MATLAB | 53 |
| 10 | Design of FSK, PSK DPSK using MATLAB | 55 |
| 11 | Communication link simulation using MATLAB | 57 |
| 12 | Zero forcing LMS equalization algorithms using MATLAB | 59 |
| ADDITIONAL EXPERIMENTS BEYOND THE SYLLABUS | ||
| 13 | Pulse amplitude modulation | 61 |
| 14 | Amplitude modulation demodulation using LabVIEW | 64 |
Expt. No. 1
CYCLE 1 - EXPERIMENTS
SIGNAL SAMPLING AND RECONSTRUCTION
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Aim:
To study the process of sampling and reconstruction of signals using analog sampling trainer kit
Apparatus required:
1. Analog signal sampling and reconstruction trainer kit – 1 No.
2. Dual Power Supply – 1 No.
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3. Patch cords – 6 Nos.
4. CRO (30 MHz) – 1 No.
Theory:
Sampling is defined as measuring the value of an information signal at predetermined time interval. The rate at
which the signal is sampled is known as the sampling rate or sampling frequency. The types of sampling are
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natural sampling and flat top sampling.
A continuous time signal can be processed by processing its samples through a discrete time system. For
reconstructing the continuous time signal from its discrete time samples without any error, the signal should be
sampled at a sufficient rate that is determined by the sampling theorem.
Sampling theorem
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If a signal is band limited and its samples are taken at sufficient rate than those samples uniquely specify the
signal and the signal can be reconstructed from those samples. The condition in which this is possible is known
as Nyquist sampling theorem.
A signal whose spectrum is band limited to D Hz [X(f) = 0 for f >D can be reconstructed from its samples
taken uniformly at a rate fs > 2D samples/sec. The minimum sampling frequency is fs = 2D Hz.
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Reconstruction of Signals
The process of reconstructing a continuous time signal x(t) from its samples is known as interpolation. In the
sampling theorem a signal x(t) band limited to D Hz can be reconstructed from its samples. This reconstruction is
accomplished by passing the sampled signal through an ideal low pass filter of bandwidth D Hz.To
recover x(t) or X(f), the sampled signal must be passed through an ideal low pass filter having bandwidth D Hz
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and gain T.
Sample and hold circuit is used to operate on analog information in a time frame which is expedient. This circuit
works by sampling a segment of the information holding it and then converts it into some readout or a form of
control signal.
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Procedure:
1. Assemble the sample and hold circuit with the desired components.
2. Give the input signal from the function generator.
3. Do not exceed the input signal above 10 volt.
4. Set the frequency of the input signal to 600 Hz.
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5. Set the frequency of the sample signal to 5600 Hz.
6. Integrate the sampling inputs.
Circuit Diagram
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Tabulation
| Signal | Amplitude (V) | Time period (s) |
|---|---|---|
| Message signal | ||
| Carrier signal | ||
| Sampled output |
Analog signal sampling and reconstruction trainer kit
Result:
Thus the sampling and reconstruction of signal was studied and verified using sampling reconstruction trainer
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kit.
Outcome:
After completion of this experiment, the students will be able to understand the discretization process of
continuous time signal.
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Applications:
1. Analog-to-digital conversion (ADC)
2. Digital-to-analog conversion (DAC)
3. Storage, and transmission
4. Telephone and encrypted walkie-talkie (8000 Hz sample rate)
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5. Wireless intercom and wireless microphone transmission (Audio Sampling)
Viva - voce
1. Define - Sampling Theorem
2. What is the necessary sufficient condition for sampling reconstruction of a signal?
3. Define - Nyquist rate
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4. Define - Nyquist interval
5. What are the different types of sampling techniques?
6. What is the effect on sampled signal if fs< 2 fm?
7. Draw the amplitude spectrum of sampled signal if fs< 2 fm, fs =2 fm, fs > 2 fm.
8. What is aliasing effect in sampling? How to avoid it?
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9. Why do we use pre-filtering in sampling?
10. What is reconstruction of sampling theorem?
11. What are the types of filters used in reconstruction?
12. Define - Sample Hold Circuits
13. Differentiate second order; fourth order and sixth order low pass filters in reconstruction process.
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14. Explain the sampling reconstruction process.
15. What is the difference between discrete and digital signals?
16. Define - Digital Signal
17. What is the need for converting a continuous signal into a discrete signal?
18. Explain zero-order hold circuit.
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19. How to convert an analog signal into a digital signal?
20. Differentiate flat top sampling from natural sampling.
21. Define - Natural Sampling
Expt. No. 2
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TIME DIVISION MULTIPLEXING
Aim:
To study the process of time division multiplexing of four signals using sampling trainer kit
Apparatus required:
1. TDM trainer kit – 1 No.
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2. Dual Power Supply – 1 No.
3. Patch cords – 6 No.
4. CRO (30 MHz) – 1 No.
Theory:
Time Division Multiplexing (TDM) is a method of transmitting and receiving independent signals over a common
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signal path by means of synchronized switches at each end of the transmission line so that each signal appears
on the line only a fraction of time in an alternating pattern.
Procedure:
1. Switch ON the power supply.
2. Make initial settings on TDM Trainer kit as follows.
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(a) Set all sine wave voltages to 2V,
(b) Make the wiring connections as in wiring diagram.
3. Display the multiplexed signal at test point T14 on channel 1 and 250Hz sine wave at test point T2 on
channel 2 of oscilloscope.
4. Display the 500Hz sine wave at test point T3 on channel 2 in place of 250Hz, identify sampled version of this
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sine wave in TDM signal note down.
5. Observe 1 KHz 2 KHz waveforms at test point T4 T5 respectively on oscilloscope
6. Display the TDM waveform (test point T14) on channel 1 channel synchronization signal (test point T13)
on channel 2 of oscilloscope .
7. Display 250Hz sine wave at test point T2 on channel 1 and output sine wave at test point T16 on channel 2 of
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Oscilloscope.
8. Similarly, observe input output 500Hz, 1 KHz and 2 KHz sine waves on oscilloscope .
Circuit Diagram
Time division multiplexing
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Tabulation
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| Sl. No. | Signal | Amplitude | Time period (s) |
|---|---|---|---|
| 1. | Message signal 1 | ||
| 2. | Message Signal 2 | ||
| 3. | TDM signal |
Result:
Thus the TDM was studied the different types of signals are multiplexed using TDM Technique.
Outcomes:
After completion of this experiment the students will be able to understand the concept of multiplexing the
signals.
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Applications:
1. The plesiochronous digital hierarchy (PDH) system, also known as the PCM system, for digital
transmission of several telephone calls over the same four-wire copper cable (T-carrier or E-carrier)
or fiber cable in the circuit switched digital telephone network
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2. The synchronous digital hierarchy (SDH)/synchronous optical networking (SONET) network
transmission standards that have replaced PDH.
3. The Basic Rate Interface and Primary Rate Interface for the Integrated Services Digital
Network (ISDN).
4. The RIFF (WAV) audio standard interleaves left and right stereo signals on a per-sample basis
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5. The GSM telephone system
Viva - voce
1.What is meant by multiplexing technique ?
2.What are the different types of multiplexers?
3. What is the transmission band width of a PAM/TDM signal?
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4. What is the crosstalk effect in PAM/TDM system?
5. What are the advantages of TDM system?
6. Distinguish between TDM and FDM.
7. What is the value of Ts in TDM system?
8. What are the applications of TDM system? Give some example.
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9. What is meant by signal overlapping?
10. Which type of modulation technique will be used in TDM?
Expt. No. 3
AM MODULATION & DEMODULATION
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Aim:
To transmit a modulating signal after amplitude modulation using AM transmitter receives the signal back after
demodulating using AM receiver
Apparatus required:
1 Resistor - 4 No.
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2 Capacitor - 1 No.
3 Diode 2 No.
4 AM transmitter receiver
trainer kit - 1 No.
5 CRO-1 No.
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6 Patch cards – 6 No.
Theory:
AMPLITUDE MODULATION
Amplitude Modulation is a process by which amplitude of the carrier signal is varied in accordance with the
instantaneous value of the modulating signal, but frequency and phase of carrier wave remains constant.
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The modulating carrier signal are given by
Vm(t) = Vm sin?mt
Vc (t) = Vc sin?ct
The modulation index is given by, ma = Vm/ Vc.
Vm = Vmax - Vmin Vc = Vmax + Vmin
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The amplitude of the modulated signal is given by,
VAM(t) = Vc (1+ma sin@mt) sin?ct
Where
Vm = maximum amplitude of modulating signal
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Vc = maximum amplitude of carrier signal
Vmax = maximum variation of AM signal
Vmin = minimum variation of AM signal
Formula Used:
M= (Vmax - Vmin / Vmax + Vmin ) * 100
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Where, M = Modulation index
Vmax = Maximum peak amplitude
Vmin = Minimum peak amplitude
if
M < 1 Under modulation
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M = 1 Critical modulation
M > 1 over modulation
Procedure:
1. Give the modulating signal input to the Amplitude modulator.
2. Increase the amplitude of the modulating signal to the required level.
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3. Observe the amplitude and the time duration of the modulating signal using CRO.
4. Observe the amplitude modulated output from the output of amplitude modulator stage .
5. Calculate the modulation index
Circuit Diagram
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AM Modulation
AM Demodulation
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Tabulation
| Signal | Amplitude (V) | Time Period (s) | Frequency (Hz) |
|---|---|---|---|
| Message | |||
| Carrier | |||
| Modulated | |||
| Demodulated |
Result:
Thus the AM signal was transmitted using AM trainer kit the AM signal detected using AM detector kit.
Outcome:
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After the completion of this experiment the students will be able to design construct the amplitude modulated
demodulated wave.
Applications:
1. Commercial broadcasting of both audio and video signals
2. Two way mobile radio communication such as citizen band (CB) radio.
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3. Facsimile transmission
Viva - voce
1. What is modulation and demodulation?
2. Draw the phasor diagram of AM signal.
3. What is the degree of modulation?
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4. Explain the need of modulation and demodulation?
5. What is analog modulation? State the various techniques.
6. Why frequency modulation is better than amplitude modulation?
7. Which type of modulation is used in TV transmission?
8. What is depth of modulation?
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9. What are the different types of AM generation?
10. Define Modulation Index
11. What are different types of analog modulation techniques?
12. What are the other names of message signal? What are the other names of carrier signal?
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13. Write the equation of AM signal .Explain each parameter of the equation.
14. Define - Amplitude modulation
15. What is the range of Audio frequency signals? What is the range of Radio frequency signal?
16. What are the applications of Amplitude modulators?
17. How many generation methods are there to generate an AM wave? What are the methods of
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demodulation of an AM wave?
18. Explain the operation of diode detector circuit.
19. Write the formula for modulation index. Differentiate under, over perfect modulation in AM.
20. As the amplitude of message signal increases, modulation index increases or decreases?
21. Define - Single tone modulation
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22. Draw the frequency spectrum of AM wave.
23. If modulation index is 100%, calculate the ratio of total power to carrier power of an AM wave.
Expt. No. 4
FREQUENCY MODULATION & DEMODULATION
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Aim:
To transmit a modulating signal after frequency modulation using FM transmitter receive the signal back after
demodulating using FM receiver
Apparatus required:
1. Resistor 4 No.
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2. Capacitor - 1 No.
3. Diode 2 No.
4. AM transmitter Receiver
trainer kit - 1 No.
5. CRO 1 No.
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6. Patch cards - 6 No.
Theory:
Frequency modulation (FM) is a form of modulation that represents information as variations in the
instantaneous frequency of a carrier wave. In analog applications, the carrier frequency is varied in direct
proportion to changes in the amplitude of an input signal. Shifting the carrier frequency among a set of discrete
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values can represent digital data, a technique known as frequency-shift keying. FM is commonly used at VHF
radio frequencies for high-fidelity broadcasts of music speech Normal TV sound is also broadcast using FM. A
narrowband form is used for voice communications in commercial amateur radio settings. The type of FM used
in broadcast is generally called wide-FM, or W-FM.
In two-way radio, narrow-fm (N-FM) is used to conserve bandwidth. In addition, it is used to send signals into
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space.
FM is also used at intermediate frequencies by most analog VCR systems, including VHS, to record the
luminance (black,white) portion of the video signal. FM is the only feasible method of recording video and
retrieving video from magnetic tape without extreme distortion, as video signals have a very large range of
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frequency components — from a few hertz to several megahertz, it is too wide for equalizers to work with due to
present of electronic noise below -60 dB. FM also keeps the tape at saturation level, therefore acts as a form of
noise reduction, a simple limiter can mask variations in the playback output.The FM capture effect removes
print-through pre-echo.
Procedure:
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FM Modulator:
1. Switch ON the Power supply.
2. Connect the sine wave generator output to frequency modulator input.
3. Select the low frequency carrier (or) high frequency carrier.
4. Connect the CRO input to the frequency modulator output.
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