Question

In this assignment, you will be working with two sinusoidal
signals. The higher-frequency signal

   c(t) = cos(2*pi*F*t) (where F is in Hertz)

will be referred to as "carrier"; while the lower-frequency
signal

   v(t) = 1.5 + cos(2*pi*f*t + q) (f in Hz, again)

will be referred to as "envelope". Note that the envelope has
a positive offset of 1.5 units.

In amplitude modulation (AM), the envelope multiplies the carrier
and the resulting product signal

  

is the AM signal.

_________________________________________________________________

Your code should generate three signal vectors. Plot them in a
SINGLE figure consisting of THREE subplots (3 rows, 1 column).
The SUBPLOT function should be used. EACH subplot should have
labels on the horizontal and vertical axes, and also the
appropriate title:

   CARRIER, AM SIGNAL 1 and AM SIGNAL 2

  
(i)    Suppose that F = 200 Hz (above). Create a time vector td
   that contains 800 samples of c(t), spanning 50 periods.
   td should have the form

       td = 0 : d : 50*T-d

   where T is the period of c(t) and d is to be determined.

Answer 1

clc;

close all;

clear all;

%XXXXXXXXXXXXXXXXXXXXXXXXXXX Define AM modulation Index XXXXXXXXXXXXXXXXXXX

disp(' example: m=1 means 100% modulation');

%m=input(' Enter the value of modulation index (m) = ');

m=1; % for 100% modulation

if (0>m||m>1)

error('m may be less than or equal to one and geter than to zero');

end

%XXXXXXXXXXXXXXXXX modulating signal generation XXXXXXXXXXXXXXXXXXXXXXXXXX

Am=1; % Amplitude of modulating signal

fa=20; % Frequency of modulating signal

Ta=1/fa; % Time period of modulating signal

d=Ta/999

t=0:d:50*Ta-d; % Total time for simulation

ym=Am*cos(2*pi*fa*t); % Eqation of modulating signal

figure(1)

subplot(4,1,1);

plot(t,ym), grid on;% Graphical representation of Modulating signal

title ( ' Modulating Signal ');

xlabel ( ' time(sec) ');

ylabel (' Amplitud(volt) ');

%XXXXXXXXXXXXXXXXXXXXX carrier signal generation XXXXXXXXXXXXXXXXXXXXXXXXXX

Ac=Am/m;% Amplitude of carrier signal [ where, modulation Index (m)=Am/Ac ]

fc=fa*10;% Frequency of carrier signal=200Hz

Tc=1/fc;% Time period of carrier signal

yc=Ac*cos(2*pi*fc*t);% Eqation of carrier signal

subplot(4,1,2);

plot(t,yc), grid on;% Graphical representation of carrier signal

title ( ' Carrier Signal ');

xlabel ( ' time(sec) ');

ylabel (' Amplitud(volt) ');

%XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX AM Modulation XXXXXXXXXXXXXXXXXXXXXXXXXXXXX

y=Ac*(1+m*cos(2*pi*fa*t)).*cos(2*pi*fc*t); % Equation of Amplitude

%modulated signal

subplot(4,1,3);

plot(t,y);% Graphical representation of AM signal

title ( ' AM signal1 ');

xlabel ( ' time(sec) ');

ylabel (' Amplitud(volt) ');

grid on;

%xxxxxxxxxxxxxxxxx Envolope of AM signal xxxxxxxxxxxxxxxx

yam=1.5+Am*sin(2*pi*fa*t); % Eqation of Envolope of modulated signal

subplot(4,1,4);

plot(t,yam), grid on;% Graphical representation of Envolope of AM signal

title ( ' AM Signal2 ');

xlabel ( ' time(sec) ');

ylabel (' Amplitud(volt) ');

Sorry here i plotted modulating signal even so I have to use 4 subplots.

If you want only three please use 3 instead 4 at all occurences of subplot keyword. And remove the first part. I had assumed modulation index=1 and modulating signal frequency=20Hz.

Hope this is clear to you. For any queries please comment below.

Thank you:)

Hope