Hey guys I'm trying to build a script to modulate and demodulate an am frequency.

I have my information frequency, and carrier frequency. I modulate the signal and add noise. After I do that I run it through a halfwave rectifier and low pass and high filter. I then use a convolution to remove the noise. I then write the file to a wave file and I should be able to replay file. At the end of all this I should get something similar to the original frequency, but all I'm getting is static.

Here's my code.


close all;
clear all;
fs = 50000;
t = [0:1/fs:5];

f_cut_off1 = 10000;
f_cut_off2 = 10;
f = 2000; %input frequency
fc = 940e3; %carrier frequency

k = length(t)


input_sig = (0.2)*cos(2 * pi * f * t); %input signal

wavwrite(input_sig,fs,32,'input_sig');

carrier_sig = (0.5)*cos( 2 * pi * fc * t); %carrier signal

wavwrite(carrier_sig,fs,32,'carrier_sig')

mod_sig = input_sig .* carrier_sig + carrier_sig; %modulated signal

wavwrite(mod_sig,fs,32,'mod_sig')
%interval to randonize noise
noise = rand(1, k); %random nosie
scale = 2;
new_mod = mod_sig + noise; % mod signal + noise

wavwrite(new_mod,fs,32,'new_mod')

subplot(321), plot(t, mod_sig)
subplot(322), plot(t, new_mod)

%Apply HW Rectifier
for i = 1:k
if new_mod(i) <= 0
x(i) = 0;
else
x(i) = new_mod(i);
end
end

wavwrite(x,fs,32,'hw_rect')

subplot(323), plot(t, x)
rc1 = 1 / (2 * pi * f_cut_off1);
rc2 = 1 / (2 * pi * f_cut_off2);
%Apply Low Pass Filter
num2 = [0 1];
den2 = [rc1 1];
subplot(324), bode(num2, den2)

sys2 = tf(num2, den2);

lpf = lsim(sys2, x, t);




%Apply High Pass Filter

num1 = [rc2 0];
den1 = [rc2 1];

subplot(325), bode(num1, den1)
sys1 = tf(num1, den1);

hpf = lsim(sys1, lpf, t);

vout = hpf;

g = 20;
h = (1 / g) * ones(1, g);

y = conv(h ,vout);



wavwrite(y,fs,32,'vout')



Any ideas? I'm completely stuck.

Thanks!

 

One thread is enough.

 

Sorry I just didn't know which section this should go in.

 

Hello,

Lets continue in the programmers corner thread:
am modulation and demodulation matlab

Bertus