N = 1000;
fs = 400;

t = 0:1/fs:(N-1)/fs;

f1 = 20;
f2 = 70;
f3 = 150;

A1 = 2;
A2 = 1;
A3 = 4;

phi1 = 0;
phi2 = pi/4;
phi3 = pi/6;

n = randn(1,1000);

x1 = A1*sin(2*pi*f1*t + phi1);
x2 = A2*sin(2*pi*f2*t + phi2);
x3 = A3*sin(2*pi*f3*t + phi3);

x = x1+x2+x3;

SNR = max(x)/5;

noise = mod(n,SNR);

subplot(3,1,1), plot(t,x+noise);
xlabel('czas [t]');
ylabel('x(t)')

y = fft(x);
m = 20*log10(abs(y));
p = unwrap(angle(y));

f = 0:fs/N:fs - fs/N;

%index = (1:fs);

subplot(3,1,2), plot(f,m); %wykres amplitudy
ylabel('modul amplitudy'), grid on
subplot(3,1,3), plot(f,p*180*pi); %faza
ylabel('faza [stopnie]'), grid on
xlabel('Czestotliwosc [Hz]')

clear all;
clc;

%********************************************************************

N = 300;
fs = 1500;

t = 0:1/fs:(N-1)/fs;

f1 = 120;
f2 = 127;
f3 = 250;

A1 = 2;
A2 = 1;
A3 = 4;

phi1 = 0;
phi2 = pi/4;
phi3 = pi/6;

n = randn(1,N);

x1 = A1*sin(2*pi*f1*t + phi1);
x2 = A2*sin(2*pi*f2*t + phi2);
x3 = A3*sin(2*pi*f3*t + phi3);

x = x1+x2+x3;

SNR = x.^2/(35*20*log10(abs(n)));

noise = mod(n,SNR);

subplot(3,1,1), plot(t,x+noise);
xlabel('czas [t]');
ylabel('x(t)')

y = fft(x);
m = 20*log10(abs(y));
p = unwrap(angle(y));

f = 0:fs/N:fs - fs/N;

%index = (1:fs);

subplot(3,1,2), plot(f,m); %wykres amplitudy
ylabel('modul amplitudy'), grid on
subplot(3,1,3), plot(f,p*180*pi); %faza
ylabel('faza [stopnie]'), grid on
xlabel('Czestotliwosc [Hz]');