Matlab problem about AM and FM

[kidd]

The question is like this:
a.The amplitude modulation(AM)waveform in time and frequency domain.
fm=20HZ,fc=500HZ,Vm=1V,Vc=1V,t=0:0.00001:0.09999

a.The frequency modulation(FM)waveform in time and frequency domain.
fm=250HZ,fc=5KHZ,Vm=1V,Vc=1V,m=10,t=0:0.00001:0.09999

Then my program is like this:
% setting
fm=20;
fc=500;
vm=1;
vc=1;
interval=0.001;
% x-axis:Time(second)
t=0:0.00001:0.09999;
f=0:1:9999;

% y-axis:Voltage(volt)
wc=2*pi*fc;
wm=2*pi*fm;
V1=vc+vm*sin(wm*t);
V2=-(vc+vm*sin(wm*t));
Vm=vm*sin(wm*t);
Vc=vc*sin(wc*t);
Vam=(1+sin(wm*t)).*(sin(wc*t));
Vf=abs(fft(Vam,10000))/10000;

% Plot figure in time domain
figure;
plot(t,Vam);
hold on;
plot(t,V1,'r'),plot(t,V2,'r');
title('AM waveform time-domain');
xlabel('time'), ylabel('amplitude');
grid on;

% Plot figure in frequency domain
figure;
plot(f*10,Vf);
axis([(fc-2*fm) (fc+2*fm) 0 0.6]);
title('AM waveform frequency-domain');
xlabel('frequency'), ylabel('amplitude');
grid on;

%Plot modulating signal
figure;
plot(t,Vm);
title('AM modulating signal');
xlabel('time'), ylabel('amplitude');
grid on;

%Plot carrier signal
figure;
plot(t, Vc);
title('AM carrier signal');
xlabel('time'), ylabel('amplitude');
grid on;
clear;

Is it correct?It is AM program.If it is wrong can u help me correct it?

% setting
vc=1;
vm=1;
fm=250;
fc=5000;
m=10;
% x-axis:Time(second)
t=0:0.00001:0.09999;
f=0:10:99990;

% y-axis:Voltage(volt)
wc=2*pi*fc;
wm=2*pi*fm;
sc_t=vc*cos(wc*t);
sm_t=vm*cos(wm*t);
kf=1000;
s_fm=vc*cos((wc*t)+10*sin(wm*t));
vf=abs(fft(s_fm,10^4))/5000;

% Plot figure in time domain
figure;
plot(t,s_fm);
hold on;
plot(t,sm_t,'r');
axis([0 0.01 -1.5 1.5]);
xlabel('time(second)'),ylabel('amplitude');
title('FM time-domain');
grid on;

% Plot figure in frequency domain
figure;
plot(f,vf);
axis([ 0 10^4 0 0.4]);
xlabel('frequency'), ylabel('amplitude');
title('FM frequency-domain');
grid on;

%Plot modulating signal
figure;
plot(t,sm_t);
axis([0 0.1 -1.5 1.5]);
title('FM modulating signal');

This is FM.

And can let me know what can i get discussion and conclution from this two program?I not very sure i understand what is it doing...

 

[Ouabache]

I wrote a similar program when I had communication theory. My recommendation is to write your code in conjuction with your class notes. As you work through each small set of code, make the lines you are still unsure about; output to the screen or to a file (though I am not sure how you wrote program lines before understanding their meaning). Then as you gain confidence with each set of code, string them together to construct the complete simulation.

You discuss what your program does and how it simulates a real world application. You conclude how well does your program do what you set out to accomplish. You want to elaborate on this, so that you cover all the important points.

 

[tacman]

The first program is correct for AM, but the second program is not entirely correct for FM. Here are some corrections and explanations for the second program:

1. In the setting section, the values for fm and fc should be switched. fm should be 250 and fc should be 5000, as stated in the question.

2. The variable "m" is not used in the program, so it can be removed.

3. In the x-axis for the time domain plot, the values should be from 0 to 0.01 instead of 0.09999, since the time interval is 0.00001 and there are 1000 points plotted.

4. In the y-axis for the time domain plot, the values should be from -1.5 to 1.5 to show the full range of the waveform.

5. In the x-axis for the frequency domain plot, the values should be from 0 to 10000 instead of 10^4, since the number of points in the FFT is 10000.

6. In the y-axis for the frequency domain plot, the values should be from 0 to 0.4 to show the full range of the spectrum.

7. The variable "kf" is not used in the program, so it can be removed.

8. The variable "s_fm" should be calculated using the formula for frequency modulation, which is s_fm = vc*cos(wc*t + kf*vm*cos(wm*t)). In the program, the value of kf is set to 1000, which is the deviation constant for a 1kHz signal. If the question did not specify a value for kf, it is usually assumed to be 1.

9. The FFT should be calculated using 10000 points, not 5000, since the sampling frequency is 10000 Hz.

10. The title for the time domain plot should be "FM waveform time-domain" instead of "AM waveform time-domain".

11. The title for the frequency domain plot should be "FM waveform frequency-domain" instead of "AM waveform frequency-domain".

12. The title for the modulating signal plot should be "FM modulating signal" instead of "AM modulating signal".

13. The amplitude of the modulating signal should be multiplied by 10 to match the m value in the question.

14. The carrier signal plot is not necessary for FM, so it can be removed.

As