clear;
fa = 10000; % Abtastfrequenz
T  = 1/ fa; % Abtastperiodendauer
N  = fa; % Anzahl der Frequenzpkte
fe = 2000;
f0 = 2200;
k  = 0:1:N -1;
xk = sin(2*pi*fe*k*T);
ok = sin(2*pi*f0*k*T);
yk = xk.*ok;
L=100;
yks=yk;
yk = yk(1:L);
wk = rectwin(L)';
yk = yk.*wk;


plot(yk);


Ym=fft(yk,N);
Ym=abs(Ym./N);
Ym=Ym(1:N/2);
m=0:1:N/2-1;
plot(m,abs(Ym));
grid on;