How to see FT in more close picture.

below is my code

--------------------------

lam=1552; %%%nm

lamd=lam*10^(-9); %%m

c=3e8;

freq=c/lamd;  %%Hz
gbps=32e9;  %%Hz
tb=1/gbps;  %%s
lng=10; %%km

beta=0.1;
deltaf=beta/2/tb;

disp=0.088/4*(lam-(1317^4)/(lam^3));   %%ps/(nm*km)

deltat=-disp*lng*c*(10^9)*deltaf/(freq^2); %%ps

%%%%%%%%%%%%%%FFT
L=80e-11;  %%%spatial extent
dt=1e-13; %%1 second - sample spacing
N=L/dt;   %%% number of samples
t=(-N/2:N/2-1)*dt;
f=(-N/2:N/2-1)/(N*dt);

hfunct=sinc(t/pi/tb);
figure();plot(t,hfunct); %%%confirmed

hfft=fftshift(fft(fftshift(hfunct)))*dt;

NN=10;
fv=f(N/4:3*N/4-1);
hv=hfft(N/4:3*N/4-1);
figure();plot(fv,hv);

------------------------

The important part is after FFT.

when I transformed sinc function, it should give signum fuction, and it did. But the problem is, it looks like as if it were taken from very far distance.

How do I see FT graph more closely?

Answer 1

[Walter Roberson]

L = length(fv);
subwindowidx = floor(L*3/8):ceil(L*5/8);   %an area around the centre
plot(fv(subwindowidx), hv(subwindowidx));

[Hoon]

So, all I got is reducing the window.

There is no way I can reduce window, and enhance resolution (i.e., reducing df) simultaneously?