TITLE: AMPLITUDE MODULATION AND DEMODULATION

NAME: N.SHIVAPRASAD DATE: ROLL NO: 14H65A0445 Pg No : ______

AIM:To plot the amplitude modulation and demodulation using matlab software.

TOOLS REQUIRED: PC, MATLAB software.

THEORY: In the amplitude modulation, amplitude of carrier signal wave is varied in

accordance with the modulating or message signal by keeping the phase and frequency of

the signals constant. The carrier signal frequency would be greater than the modulating

signal frequency. Amplitude modulation is first type of modulation used for transmitting

messages for long distances by the mankind. The AM radio ranges in between 535 to 1705

kHz which is great. But when compared to frequency modulation, the Amplitude modulation

is weak, but still it is used for transmitting messages. Bandwidth of amplitude modulation

should be twice the frequency of modulating signal or message signal. If the modulating

signal frequency is 10 kHz then the Amplitude modulation frequency should be around 20

kHz. In AM radio broadcasting, the modulating signal or message signal is 15 kHz. Hence

the AM modulated signal which is used for broadcasting should be 30 kHz.Because of

amplitude modulation wavelength, AM signals can propagate longer distances.For amplitude

modulation, we use simple and low cost circuit; we don’t need any special equipment and

complex circuits that are used in frequency modulation.The Amplitude modulation receiver

will be wider when compared to the FM receiver. Because, atmospheric propagation is good

for amplitude modulated signals.Bandwidths limit is also big advantage for Amplitude

modulation, which doesn’t have in frequency modulation.Transmitter and receiver are

simple in Amplitude modulation. When we take a demodulation unit of AM receiver, it

consists of RC filter and a diode which will demodulate the message signal or modulating

signal from modulated AM signal, which is unlike in Frequency modulation.zero crossing in

Amplitude modulation is equidistant.

PROGRAM:

clc; % clear command window

clear all; % clear all work space

close all; % close all work space

ANURAG GROUP OF INSTITUTIONS AC-LAB Department of ECE

TITLE: AMPLITUDE MODULATION AND DEMODULATION

NAME: N.SHIVAPRASAD DATE: ROLL NO: 14H65A0445 Pg No : ______

t=0:0.001:1; % time period

fm=5; % frequency of message signal

fc=40; % frequency of carrier signal

m=cos(2*pi*fm*t); % equation of message signal

subplot(4,2,1); % (rows,columns,figure number)

plot(t,m); % plotting message signal with respect to time

xlabel('time'); % plotting time along x-axis

ylabel('amplitude'); % plotting amplitude along y-axis

title('message signal'); % title of the signal

grid on; % displays grid on the screen

c=cos(2*pi*fc*t); % equation of carrier signal

subplot(4,2,2); % ( rows,columns,figure number)

plot(t,c); % plotting carrier signal with respect to time

xlabel('time'); % plotting time along x-axis

ylabel('amplitude'); % plotting amplitude along y-axis

title('carrier signal'); % title of the signal

grid on; % displays grid on the graph

u=0.5; % mathematical value of modulation index u

am1=c.*(1+u.*m); % equation used for plotting of under modulated signal

subplot(4,2,3); % (rows,columns,figure number)

plot(t,am1); % plotting under modulated signal with respect to time

xlabel('time'); % plotting time along x-axis

ylabel('amplitude'); % plotting amplitude along y-axis

grid on; % displays grid on the graph

u=1.5; % mathematical value of modulation index

am2=c.*(1+u.*m); % equation used for plotting of critical modulated signal

ANURAG GROUP OF INSTITUTIONS AC-LAB Department of ECE

TITLE: AMPLITUDE MODULATION AND DEMODULATION

NAME: N.SHIVAPRASAD DATE: ROLL NO: 14H65A0445 Pg No : ______

subplot(4,2,4); % (rows,columns,figure number)

plot(t,am2); % plotting critical modulated signal with respect to time

xlabel('time'); % plotting time along x-axis

ylabel('amplitude'); % plotting amplitude along y-axis

grid on; % displays grid on the graph

u=1; % mathematical value of modulation index

am3=c.*(1+u.*m); % equation used for plotting of over modulated signal

subplot(4,2,5); % (rows,columns,figure number)

plot(t,am3); % plottinng over modulated signal with respect to time

xlabel('time'); % plotting time along x-axis

ylabel('amplitude'); % plotting amplitude along y-axis

grid on; % displays grid on the graph

k=abs(hilbert(am1));% eqn for demodulation of under modulated signal

subplot(4,2,6); % (rows,columns,figure number)

plot(t,k); % plotting under demodulated signal with respect to time

xlabel('time'); % plotting time along x-axis

ylabel('amplitude'); % plotting amplitude along y-axis

title('demodulation of undermodulation'); % title of the demodulated signal

grid on; % displays grid on the graph

k=abs(hilbert(am2)); % eqn for demodulation of critical modulated signal

subplot(4,2,7); % (rows,columns,figure number)

plot(t,k); % plotting demodulated signal with respect to time

xlabel('time'); % plotting time along x-axis

ylabel('amplitude'); % plotting amplitude along y-axis

title('demodulation of crticalmodulation');% title of demodulated signal

grid on; % displays grid on the graph

ANURAG GROUP OF INSTITUTIONS AC-LAB Department of ECE

TITLE: AMPLITUDE MODULATION AND DEMODULATION

NAME: N.SHIVAPRASAD DATE: ROLL NO: 14H65A0445 Pg No : ______

k=abs(hilbert(am3)); % eqn for demodulation of over modulated signal

subplot(4,2,8); % (rows,columns,figure number)

plot(t,k); % plotting demodulated signal with respect to time

xlabel('time'); % plotting time along x-axis

ylabel('amplitude'); % plotting amplitude along y-axis

title('demodulation of overmodulation'); % title of the demodulated signal

grid on; % displays grid on the graph

PROCEDURE:

1. click on start.

2. open matlab software.

3.click on file.

4.next click on new and then on script.

5.write the program on the script.

6.after completion of writing the program,save it and then run it.

OUTPUT WAVEFORMS:

ANURAG GROUP OF INSTITUTIONS AC-LAB Department of ECE

TITLE: AMPLITUDE MODULATION AND DEMODULATION

NAME: N.SHIVAPRASAD DATE: ROLL NO: 14H65A0445 Pg No : ______

RESULT: Hence plotted amplitude modulation and demodulation using matlab software.

ANURAG GROUP OF INSTITUTIONS AC-LAB Department of ECE