EC0224 – COMMUNICATION LAB - I · PDF fileec0224 – communication lab - i ....

EC0224 – COMMUNICATION LAB - I

Laboratory Manual

DEPARTMENT OF ELECTRONICS AND COMMUNICATIONENGINEERING

SRM UNIVERSITY

S.R.M. NAGAR, KATTANKULATHUR – 603 203.

DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

EC0224 – COMMUNICATION LAB - I (2008-2009)

Revision No: I Prepared By, Date:

Authorized By,

HOD/ECE

SRM University Department of Electronics and Communication Engineering

COMMUNICATION LAB - I Laboratory Report Cover Sheet

EC0224 EVEN SEM – 2009

Name: ______________________________________ Section: Circle One M ( ) TU () W ( ) Th ( ) Fr ( )

Venue: ________________________________________

Title of Lab: ________________________________________ __________________________________________________

Preparation Verification

Staff Signature ______________________

Score _________________________

Completion Verification Staff Signature _______________________ Date, Time __________________________ Score ______________________________

Comments:

________________________________________________________________

________________________________________________________________

________________________________________________________________

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Report

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SRM University

Department of Electronics and Communication Engineering

COMMUNICATION LAB – I

INDEX


EXPT.

No. NAME OF THE EXPERIMENT SCORE SIGNATURE

\

SRM University Department of Electronics and Communication Engineering

COMMUNICATION LAB - I Laboratory Report Cover Sheet


Name: _________________________________________

Section: Tick One M ( ) TU () W ( ) Th ( ) Fr ( )

Venue: ________________________________________ Title of Lab: ________________________________________

Preparation Verification

Staff Signature ______________________

Score _________________________

Completion Verification Staff Signature _______________________ Date, Time __________________________ Score ______________________________

Comments:

________________________________________________________________

________________________________________________________________

________________________________________________________________

________________________________________________________________

Report

Report Score ____________________________

SRM University

Electronics and Communication Engineering

COMMUNICATION LAB – I

INDEX EC0224 EVEN SEM – 2009

EXPERIMENT

NUMBER

NAME OF THE EXPERIMENT SCORE SIGNATURE

LAB 1 : AMPLITUDE MODULATION AND DEMODULATION

In this lab, you will learn how to perform the amplitude modulation and

demodulation and to calculate the modulation index for various modulating voltages.

HARDWARE REQUIRED:

Transistor BC108, Resistors, Capacitors, AFO, CRO, Diode OA79,

Millimeter, Regulated power supply, Breadboard and connecting wires

PREPARATION (PRE-LAB):

Do the complete revision of Amplitude modulation and Demodulation and

find the modulation index for the modulating voltage of 6v and given Vc=6omv,

fc=50 KHz, fm=1KHz.

PART-I:

MODULATION THEORY:

Modulation is defined as the process by which some characteristics of a carrier

signal is varied in accordance with a modulating signal. The base band signal is

referred to as the modulating signal and the output of the modulation process is called

as the modulation signal.

Amplitude modulation is defined as the process in which is the amplitude of

the carrier wave is varied about a means values linearly with the base band signal. The

envelope of the modulating wave has the same shape as the base band signal provided

the following two requirements are satisfied

1. The carrier frequency fc must be much greater then the highest frequency

components fm of the message signal m (t)

i.e. fc >> fm

2. The modulation index must be less than unity. if the modulation index is

greater than unity, the carrier wave becomes over modulated.

DESIGN PROCEDURE:

Given Vc = 50mV, fc = 500 KHz, fm = 100KHz.

Set modulating voltage Vm = 10 V.

Emax = 1.6 V, Emin = 0.7 V

Emax – Emin Modulation index (m) = ------------------ X 100

Emax + Emin = 39.13

TEST PROCEDURE:

1. The circuit connection is made as shown in the circuit.

2. The power supply is connected to the collector of the transistor

3. Modulated Output is taken from the collector of the Transistor

4. Calculate Vmax and Vmin from the Output

PART-II:

DEMODULATION THEORY:

The process of detection provides a means of recovering the modulating

Signal from modulating signal. Demodulation is the reverse process of modulation.

The detector circuit is employed to separate the carrier wave and eliminate the side

bands. Since the envelope of an AM wave has the same shape as the message,

independent of the carrier frequency and phase, demodulation can be accomplished by

extracting envelope.

An increased time constant RC results in a marginal output follows the

modulation envelope. A further increase in time constant the discharge curve become

horizontal if the rate of modulation envelope during negative half cycle of the

modulation voltage is faster than the rate of voltage RC combination ,the output fails

to follow the modulation resulting distorted output is called as diagonal clipping : this

will occur even high modulation index.

The depth of modulation at the detector output greater than unity and circuit

impedance is less than circuit load (Rl > Zm) results in clipping of negative peaks of

modulating signal. It is called “negative clipping “

CIRCUIT DIAGRAM:

TEST PROCEDURE:

1. The circuit connections are made as shown in the circuit diagram.

2. The amplitude modulated signal from AM generator is give as input to the

circuit.

3. The demodulated output is observed on the CRO

4. The various values of modulating voltage signal frequency corresponding

demodulated voltage and frequency are noted and the readings are tabulated.

LAB RESULT:

Thus the amplitude modulation and demodulation were performed and the

modulation index for various modulating voltage were calculated.

QUESTIONS:

1. Based upon your general knowledge of AM and FM broadcasting by listening to

the radio name the frequency occupied by AM and FM broadcast stations?

2. What will happen, if modulation index is greater than 100%? 3. Audio signals are not transmitted by electromagnetic waves. Justify. the

statement.

4. An amplitude modulated amplifier has a radio frequency output of 50w at 100%

modulation. The internal loss in the modulator is low. What output power is

required from the modulator?

5. In what stage modulation is done in high – power A.M transmissions?

ASSESSMENT:

PRELAB : 30 Pts

(Design (10), Circuit (10), Tabulation (10))

LAB PERFORMANCE : 30 Pts

VIVA : 15 Pts

LAB 2: FREQUENCY MODULATION:

In this lab, you will learn how to perform the Frequency modulation using IC

566 and to calculate the modulation index for various modulating voltages.

COMPONENTS REQUIRED:

AFO, IC NE566, Resistors, Capacitor, CRO, Bread board and connection ,

RPS


Do the complete revision of Frequency modulation and its modulation index

and also about IC 566 working principles.

THEORY:

Frequency modulation is a process of changing the frequency of a carrier wave

in accordance with the slowly varying base band signal. The main advantage of this

modulation is that it can provide better discrimination against noise.

FREQUENCY MODULATION USING IC 566

A VCO is a circuit that provides an oscillating signal whose frequency can be

adjusted over a control by Dc voltage. VCO can generate both square and triangular

Wave signal whose frequency is set by an external capacitor and resistor and then

varied by an applied DC voltage. IC 566 contains a current source to charge and

discharge an external capacitor C1 at a rate set by an external resistor. R1 and a

modulating DC output voltage.

The Schmitt trigger circuit present in the IC is used to switch the current

source between charge and discharge capacitor and triangular voltage developed

across the capacitor and the square wave from the Schmitt trigger are provide as the

output of the buffer amplifier.

The R2 and R3 combination is a voltage divider, the voltage VC must be in

the range ¾ VCC < VC < VCC. The modulating voltage must be less than ¾ VCC the

frequency Fc can be calculated using the formula

Fo = 2 (Vcc-Vc) R1 C1 Vcc

For a fixed value of Vc and a constant C1 the frequency can be varied at 10:1

similarly for a constant R! C1 product value the frequency modulation can be done at

10:1 ratio.

CIRCUIT DIAGRAM

TEST PROCEDURE:

1. The circuit connection is made as shown in the circuit diagram.

2. The modulating signal FM is given from an AFO (1KHZ)

3. For various values of modulating voltage Vm the values of Fmax and Fmin

are noted

4. The values of the modulation index are calculated.

LAB RESULT:

Thus the FM circuit using IC566 was performed and the modulation index was

found .

QUESTIONS:

1.What will be the changes in the wave under FM when the amplitude or frequency

of the modulating signal is increased ?

2. The FM station have less noise while receiving the signal. Justify your answer.

3. What happens when a stronger signal and a weaker signal both overlap at the same

frequency in FM?

4. Name two applications of two way mobile radio?

5. Which mathematical expression is used to decide the side band amplitudes in a FM

signal ?

ASSESSMENT:

PRELAB : 30 Pts



VIVA : 15 Pts

LAB 2: PULSE AMPLITUDE MODULATION AND DEMODULATION

In this lab, you will learn how to perform the pulse amplitude modulation and

demodulation and to calculate the modulation index for various modulating voltages.


. Transistor, AFO, IC NE566, Resistors, Capacitor, CRO, RPS.


Do the complete revision of Pulse Amplitude Modulation and Demodulation

theory.

THEORY:

Pulse amplitude modulation is a scheme, which alters the amplitude of

regularly spaced rectangular pulses in accordance with the instantaneous values of a

continuous message signal. Then amplitude of the modulated pulses represents the

amplitude of the intelligence.

A train of very short pulses of constant amplitude and fast repetition rate is

chosen the amplitude of these pulse is made to vary in accordance with that of a

slower modulating signal the result is that of multiplying the train by the modulating

signal the envelope of the pulse height corresponds to the modulating wave .the Pam

wave contain upper and lower side band frequencies .besides the modulating and

pulse signals.

The demodulated PAM waves, the signal is passed through a low pass filter

having a cut –off frequencies equal to the highest frequency in the modulating signal.

At the output of the filter is available the modulating signal along with the DC

component

PAM has the same signal to noise ratio as AM and so it is not employed in

practical circuits

CIRCUIT DIAGRAM:

TEST PROCEDURE:

MODULATION

1. Make the circuit as shown in circuit diagram

2. Set the pulse generator output to be 41Vpp at 100HZ

3. Set AFO output at 2 Vpp 100HZ

4. Observe the output wave form on a CRO

5. Tabulate the reading.

DEMODULATION:

1. Connect the circuit as shown in figure

2. Given the modulated output with AFO used to the input of the circuit.

3. Vary the potentiometer so that modulating signal is obtained.

4. Measure the amplitude of the signal and verify with that of the input.

LAB RESULT: Thus the pulse amplitude modulation was performed and its corresponding

demodulation was also performed.

QUESTIONS:

1. What is the process of sampling an analog signal at a high rate ? 2. Which multiplexing technique is used to transmit both digital and analog signals? 3. Why PAM is not preferable in digital transmission? 4. Which device is used to track PAM frequency variations in the clock recovery circuit ? 4. What kind of switches are commonly used in PAM multiplexers? ASSESSMENT:

PRELAB : 30 Pts



VIVA : 15 Pts

Lab3: PRE –EMPHASIS AND DE-EMPHASIS CIRCUITS

In this lab, you will learn how the characteristics of Pre-emphasis and De-emphasis

differ from each other.


Transistor, AFO, IC NE566, Resistors, Capacitor, CRO, RPS.


Do the complete revision of Pre-emphasis and De-emphasis theory.

THEORY: PRE-EMPHASIS: The circuits are the transmitting side of the frequency modulator. It is used to

increase the gain of the higher frequency component as the input signal frequency

increased, the impendence of the collector voltage increase. If the signal frequency is

lesser then the impendence decrease which increase the collector current and hence

decrease the voltage.

DE-EMPHASIS: The circuit is placed at the receiving side. It acts as allow pass filter. The

boosting gain for higher frequency signal in the transmitting side is done by the pre-

emphasis circuit is filtered to the same value by the low pass filter. The cut off

frequency is given by the formula

Fc = 1/2π RC Where R = 2 π fc L

DESIGN FORMULA: Fc = 1/2 π R C (assume =R = 10 KΩ, C = 0.01μf) R = 2 π fc L; L=1/ 2 π fc TEST PROCEDURE:

1. The circuit connection are made as shown in the circuit diagram for the pre-

emphasis and de-emphasis circuits

2. A power supply of 10V is given to the circuit

3. For a constant value of input voltage the values of the frequency is varied and

the output is noted on the CRO

4. A graph is plotted between gain and frequency

5. The cut frequencies are practical values of the values of cut off frequency \are

found, compared and verified.

LAB RESULTS: The characteristics of pre –emphasis and de emphasis circuits were studied and a

graph was drawn between gain (in db) and frequency.

QUESTIONS:

1. Which range of frequencies are more prone to noise interference?

2. How to reduce the noise during transmission in FM ?

3. Which technique is used at the receiver side to reconstruct the original signal?

4. What should be the time constant for the de emphasis circuit?

5. Why pre-emphasis is done after modulation?

ASSESSMENT:

PRELAB : 30 Pts



VIVA : 15 Pts

LAB 5: AMPLITUDE MODULATION USING MATLAB®

In this lab, you will learn how to perform the Amplitude Modulation simulation using

MATLAB®

SOFTWARE REQUIRED:

MATLAB, Computer installed with Windows XP or higher Version.


Do the complete revision of Amplitude Modulation theory and know few functions in

MATLAB.

PART-I:

MATLAB® INTRODUCTION

MATLAB® is a programming language and numerical computing

environment. The name MATLAB® is an acronym for “Matrix Laboratory”. As it

name suggests it allows easy manipulation of matrix and vectors. Plotting functions

and data is made easy with MATLAB®. It has a good Graphic User Interface and

conversion of matlab files to C/C++ is possible. It has several toolboxes that possess

specific functions for specific applications. For example Image Processing, Neural

Networks, CDMA toolboxes are name a few. An additional package, Simulink, adds

graphical multidomain simulation and Model-Based Design for dynamic and

embedded systems. Simulink contains Blocksets that is analogous to Toolboxes. It

was created by Mathworks Incorporation, USA. MATLAB® has become a defacto

programming language for Engineers. Writing MATLAB programs for modulation

applications require knowledge on very few functions and operators. The operators

mostly used are arithmetic operators and matrix operators. To know more type in the

command prompt ‘help ops’. MATLAB will give a list in that to know on specific

operator say addition type in the command prompt ‘help plus’. MATLAB will give

how to use and other relevant information.

Commonly used graphical functions are plot, figure, subplot, title, and

mathematical functions are sin and cos only. The mathematical functions sin and cos

are self explanatory. The graphical function figure will create a new window and then

subsequent graphical commands can be applied. The plot function usually takes two

vectors and plot data points according to given vector data. In this case it will time Vs

signal. Subplot function is used when two or more plots are drawn on the same figure.

As title function suggests it helps to write title of the graph in the figure. For further

details type ‘help plot’ or ‘help subplot’ in the command prompt and learn the syntax.

ALGORITHM: 1. Create a vector ‘t’ (time) that varies from zero to two or three cycles with an

interval 1/1000 or 1/5000.

2. Create a message signal with single sine frequency or combination of few sine

frequencies. All the frequency used in message signal should be less than the

carrier frequency likewise amplitude of message signals should be less than

carrier amplitude. [AmSin(2πfmt)]

3. Create a carrier signal. [AcSin(2πfct)]

4. Create the modulated signal using the AM equation [Am

(1+maSin(2πfmt))Sin(2πfct) ]

5. Plot the AM signal. Verify the practical modulation index with theoretical one.

TEST PROCEDURE:

1. Open the MATLAB® software by double clicking its icon.

2. MATLAB® logo will appear and after few moments Command Prompt will

appear.

3. Go to the File Menu and select a New M-file. (File NewM-file) or in the left

hand corner a blank white paper icon will be there. Click it once.

4. A blank M-file will appear with a title ‘untitled’

5. Now start typing your program. After completing, save the M-file with

appropriate name. To execute the program Press F5 or go to Debug Menu and

select Run.

6. After execution output will appear in the Command window .If there is an error

then with an alarm, type of error will appear in red color.

7. Rectify the error if any and go to Debug Menu and select Run.

LAB RESULT:

Thus the amplitude modulation was simulated and the modulation index for

various modulating voltage were calculated.

QUESTIONS:

1. What is the difference between stem and plot functions?

2. What is the use of clean and close statements?

3. Find the answer the following program code

a=[1 2 3] ; b=[4 5 6]; c=[a;b] ; d=[ a b];

4. Explain the following file formats .m, .asv, .mat used in MATLAB

5. What is use of “;” command?

ASSESSMENT:

PRELAB : 30 Pts

(program)


VIVA : 15 Pts

LAB 6: FREQUENCY MODULATION USING MATLAB®

In this lab, you will learn how to perform the Frequency Modulation simulation using

MATLAB®

SOFTWARE REQUIRED:

MATLAB ,Computer installed with Windows XP or higher Version.


Do the complete revision of Frequency Modulation theory and know few functions in

MATLAB.

PART-I:

MATLAB® INTRODUCTION

MATLAB® is a programming language and numerical computing

environment. The name MATLAB® is an acronym for “Matrix Laboratory”. As it

name suggests it allows easy manipulation of matrix and vectors. Plotting functions

and data is made easy with MATLAB®. It has a good Graphic User Interface and

conversion of matlab files to C/C++ is possible. It has several toolboxes that possess

specific functions for specific applications. For example Image Processing, Neural

Networks, CDMA toolboxes are name a few. An additional package, Simulink, adds

graphical multidomain simulation and Model-Based Design for dynamic and

embedded systems. Simulink contains Blocksets that is analogous to Toolboxes.It was

created by Mathworks Incorporation, USA. MATLAB® has become a defacto

programming language for Engineers.

Writing MATLAB programs for modulation applications require knowledge

on very few functions and operators. The operators mostly used are arithmetic

operators and matrix operators. To know more type in the command prompt ‘help

ops’. MATLAB will give a list in that to know on specific operator say addition type

in the command prompt ‘help plus’. MATLAB will give how to use and other

relevant information.

Commonly used graphical functions are plot, figure, subplot, title, and

mathematical functions are sin and cos only. The mathematical functions sin and cos

are self explanatory. The graphical function figure will create a new window and then

subsequent graphical commands can be applied. The plot function usually takes two

vectors and plot data points according to given vector data. In this case it will time Vs

signal. Subplot function is used when two or more plots are drawn on the same figure.

As title function suggests it helps to write title of the graph in the figure. For further

details type ‘help plot’ or ‘help subplot’ in the command prompt and learn the syntax.

ALGORITHM: 1. Create a vector ‘t’ (time) that varies from zero to two or three cycles with an

interval 1/1000 or 1/5000.

2. Create a message signal with single sine frequency. All the frequency used in

message signal should be less than the carrier frequency likewise amplitude of

message signals should be less than carrier amplitude. [AmSin(2πfmt)]

3. Create a carrier signal. [AcCos(2πfct)]

4. Create the modulated signal using the FM equation [Ac Cos(2πfct+βSin(2πfmt) ]. β

stands for modulation index. Choose value more than 1.

5. Plot the FM signal.

TEST PROCEDURE:

1. Open the MATLAB® software by double clicking its icon.

2. MATLAB® logo will appear and after few moments Command Prompt will

appear.

3. Go to the File Menu and select a New M-file. (File NewM-file) or in the left

hand corner a blank white paper icon will be there. Click it once.

4. A blank M-file will appear with a title ‘untitled’

5. Now start typing your program. After completing, save the M-file with

appropriate name. To execute the program Press F5 or go to Debug Menu and

select Run.

6. After execution output will appear in the Command window .If there is an error

then with an alarm, type of error will appear in red color.

7. Rectify the error if any and go to Debug Menu and select Run.

LAB RESULT:

Thus the Frequency modulation was simulated and the modulation index for

various modulating voltage were calculated.

QUESTIONS:

1. Write MATLAB statement to display 9 (3 by 3) within a same window.

2. Find the answer Lowzero after executing following code.

LowZero=10; Lowzero=15;

lowzero=Lowzero+2*LowZero;

3. Write a code to plot 10Hz cos signal.

4. What is meant by script m-file and function m-file?

5. Find the answer for following statement 10 / 2 \ 5 - 3 + 2 * 4

ASSESSMENT:

PRELAB : 30 Pts

(program)


VIVA : 15 Pts

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