Frequency modulation and demodulation (MATLAB + Simulink):

Objective:

Frequency modulation

Definition:

In FM (Frequency Modulation), the frequency of the carrier signal or wave should a high frequency is modified following the instantaneous amplitude of the modulating signal or wave should low frequency. Frequency modulated signals or waves are commonly utilized in television as well as radio transmission systems etc.

Explanation:

FM (Frequency Modulation) signals can be directly plotted utilizing simple MATLAB functions. The MATLAB code is shown below, the use of relevant code is also provided as described form (%Comment field ). The given Matlab program is capable of taking two input frequencies as well as modulation index from the user.

Mathematical representation:

Let the modulating signal be given as

while the carrier signal be

then the modulating signal e(t) is given as

Here ‘m’ is the modulation index.

• Maximum sampling frequency required
• Modulating index will denote depth

MATLAB Code

t=0:0.0001:1;
a=5;
fm=input('Enter Message Freq = ');
fc=input('Enter Carrier Freq = ');
fs=input('Enter Sampling Freq (fs>=2*fc) = ');
m=5;
sm=a*sin(2*pi*fm*t);
subplot(4,1,1);
plot(t,sm);
xlabel('time');
ylabel('amplitude');
title('Message signal');
grid on
sc=a*sin(2*pi*fc*t);
subplot(4,1,2);
plot(t,sc);
xlabel('time');
ylabel('amplitude');
title('carrier signal');
grid on
sfm=a*sin((2*pi*fc*t)+(m.*sin(2*pi*fm*t)));
subplot(4,1,3);
plot(t,sfm);
xlabel('time');
ylabel('amplitude');
title('Modulated signal');
grid on
fdev=fc+10;
fdem=fmdemod(sfm,fc,fs,fdev);
subplot(4,1,4);
plot(t,fdem);
xlabel('time');
ylabel('amplitude');
title('Demodulated signal');
grid on

Output:

Enter Message Freq = 10

Enter Carrier Freq = 100

Enter Sampling Freq (fs>=2*fc) = 4000

Frequency Modulation and Demodulation in Simulink:

Assessment Questionnaire

1. Why we use frequency modulation?
2. Why frequency modulation is better than amplitude modulation?
3. What is the basic difference between AM and FM?
4. Which type of modulation is used in TV transmission?
5. What are analog modulation and state various techniques?
6. What is the FM spectrum?
7. What is the depth of modulation?

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