KHULNA UNIVERSITY
Electronics &
Communication Engineering Discipline
Course No: ECE 3106
Course Title :Analog Communication Sessional.
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Experiment No :01
Name
of the experiment: Study and observation of Amplitude Modulation in MATLAB.
|
Submitted To:
Md. Mahbub Hossain Submitted
By:
Associate Professor Kangkan Bhakta
ECE Discipline ID:130910
Khulna University. 3rd Year,1st
Term
ECE Discipline
Abdullah Al- Mamun
Bulbul Khulna University.
Lecturer
ECE Discipline
Khulna University.
Objective:
1.
To study the theory of amplitude
modulation.
2.
To observe and analysis the
amplitude modulated wave.
3.
To get introduce in MATLAB
Theory:
Amplitude
modulation (AM) is a technique used in electronic communication, most commonly
for transmitting information via a radio carrier wave. AM works by varying the
strength of the transmitted signal in relation to the information being sent.
For example, changes in the signal strength can be used to specify the sounds
to be reproduced by a loudspeaker, or the light intensity of television pixels.
A
sinusoidal carrier wave
A
sinusoidal message wave
An
amplitude modulated wave
Amplitude
modulation is a type of modulation where the amplitude of the carrier signal is
varied in accordance with the information bearing signal. The envelope, or
boundary, of the amplitude modulated signal embeds the information bearing
signal. The total power of the transmitted signal varies with the modulating
signal, whereas the carrier power remains constant.
Required
components:
1. MATLAB
software
Procedure:
clc;
clear;
a=10;
b=5;
k=.05;
f=20000;
w=500000;
t=[0:0.001:100];
m=a*sin(2*3.1416*f*t);
c=b*cos(2*3.1416*w*t);
s=b*(1+(k*m)).*cos(2*3.1416*w*t);
subplot(3,1,1);
xlabel('Time');
ylabel('Amplitude');
title('Sine Wave');
plot(t,m,'r');
grid on;
hold on;
subplot(3,1,2);
xlabel('Time');
ylabel('Amplitude');
title('Cosine Wave');
plot(t,c,'g');
grid on;
hold on;
subplot(3,1,3);
xlabel('Time');
ylabel('Amplitude');
title('Modulated
Wave');
plot(t,s,'g');
grid on;
hold on;
hold off;
Simulation Results:
Discussion:
a.
The amplitude of 
is always less than unity.
is always less than unity.
b. The
carrier frequency 
is much greater than the message frequency 
that is
is much greater than the message frequency that is
c. Amplitude
modulation is very easy, cheap and little consumption of bandwidth.
d.
Amplitude modulation is wasteful of
power.
Conclusion:
Here
we have to choose suitable frequency for carrier which is greater than
frequency of baseband signal for desired output and time duration and interval also
chosen properly otherwise plotted output becomes clumsy or over magnified.
Objective:
1.
To observe and analysis the DSB-SC
modulation.
2.
To able to analysis the upper and
lower sideband of DSB-SC modulation.
3.
Get a idea of modulation index
range of DSB-SC modulation.
4.
To get introduce in MATLAB
Theory:
The modulation envelope is the waveform observed
when the carrier, upper sideband and lower sideband are combined in a single
impedance and observed as time versus amplitude.
If
a sinusoidal carrier wave
A
sinusoidal message wave
An
DSB-SC modulated wave
Required
components:
1. MATLAB
software
Procedure:
clc;
clear;
a=10;
b=5;
k=.05;
f=20000;
w=90000;
t=[0:0.001:100];
m=a*sin(2*3.1416*f*t);
c=b*cos(2*3.1416*w*t);
s=m.*c;
subplot(3,1,1);
xlabel('Time');
ylabel('Amplitude');
title('Sine Wave');
plot(t,m,'r');
grid on;
hold on;
subplot(3,1,2);
xlabel('Time');
ylabel('Amplitude');
title('Cosine Wave');
plot(t,c,'g');
grid on;
hold on;
subplot(3,1,3);
xlabel('Time');
ylabel('Amplitude');
title('Modulated
Wave');
plot(t,s,'g');
grid on;
hold on;
hold off;
Simulation Results:
Discussion:
1.
The value of amplitude sensitivity of modulator (ka) is always zero to one.
2. The
carrier frequency is much greater than the message frequency that is
is much greater than the message frequency that is
3 Here upper and lower side band is not very clear for small variation
of frequency. For this the s(t) signal is not accurate.
Conclusion:
After study this experiment , I have understood the
DSB-SC Modulation and I successfully finished the experiment.
Objectives:
1. To
understand the principle of Amplitude Modulation.
2. Measuring
and adjusting an amplitude modulator circuit.
3.
Calculating the percent of modulation.
Theory:
Let consider
a sinusoidal carrier wave c(t) defined by
C(t) = Ac
cos(2*3.1416*f*t)
Where Ac
is the carrier amplitude
and f is the carrier frequency. To simplify the exposition without affecting
results obtained and conculation reached, we have assumed that the phase of the
carrier wave is zero. Let m(t) denote the baseband signal that carries the
specification of the message. Amplitude modulation(AM) is defined as a process
in which the amplitude of the carrier wave c(t) is varied about a mean value ,
linearly with the baseband signal m(t).
As a
function of time as follows:
S(t) = Ac [1+k*m(t)]cos(2*3.1416*f*t)
Necessary
Components:
1.
Module
KL 92001
2.
Module
KL 93002
3.
Oscilloscope
4.
Modulator
unit
5.
Demodulator
Procedures:
1.
The
connections of the module were connected as the circuit diagram.
2.
Then
the readings were taken from the oscilloscope CRT.
Calculations:
Calculation
of modulation index;
M=[E(max)-E(min)]
/ [E(max)+E(min)]
Here,
E(max)= 24 minimum squares of oscilloscope
E(min)= 17 minimum squares of oscilloscope
M= [(24 –
17) / (24+17)]*100%
=17.073%
Discussion:
1.
The
readings were taken by CRT monitor of the oscilloscope as it could not be hold
, the backlash fault could be happened.
2.
The
Lab was so small and only one kit available on the lab.
3.
The
less M is the fewer error .
Conculation:
The modulation index(M) was viewed in oscilloscope.
[ Please don't copy it , take idea from it @kangkan].
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