Преобразование временной области в частотную при модуляции ASK

clc;
clear all;
close all;
%dec2bin(7*20-mod(7,8))
x=[1 0 0 0 0 1 0 1];                                    % Binary Information
bp=2e-3;% bit period
N=length(x);
fs=30000;
disp(' Binary information at Trans mitter :');
disp(x);
%XX representation of transmitting binary information as digital signal XXX
bit=[]; 
for n=1:1:N
    if x(n)==1;
       se=ones(1,fs);
    else x(n)==0;
        se=zeros(1,fs);
    end
     bit=[bit se];
end
t1=bp/fs:bp/fs:fs*N*(bp/fs);
subplot(3,1,1);
plot(t1,bit,'lineWidth',2.5);grid on;
axis([ 0 bp*N -0.5 1.5]);
ylabel('amplitude(volt)');
xlabel(' time(sec)');
title('transmitting information as digital signal');
%XXXXXXXXXXXXXXXXXXXXXXX Binary-ASK modulation XXXXXXXXXXXXXXXXXXXXXXXXXXX%
A1=1;                      % Amplitude of carrier signal for information 1
A2=0.25;                       % Amplitude of carrier signal for information 0                                                         % bit rate
f0=5000;                                                 % carrier frequency 
t2=bp/fs:bp/fs:bp;                 
m=[];
for (i=1:1:N)
    if (x(i)==1);
        y=A1*sin(2*pi*f0*t2);
    else (x(i)==0);
        y=A2*sin(2*pi*f0*t2);
    end
    m=[m y];
end
t3=bp/fs:bp/fs:bp*N;
subplot(3,1,2);
plot(t3,m);
xlabel('time(sec)');
ylabel('amplitude(volt)');
title('waveform for binary ASK modulation coresponding binary information');
figure
 
bp/fs:bp/fs:fs*N;
f=f*fs/N;
mody = abs(fft(m)); 
plot(f, mody)