How to draw spectrum of signal?

Hello. I have problem with understanding how to draw spectrum of this shape in matlab because amplitude is constant when frequency is lower than 1500 and then it change from 1500 to 3000Hz. Thank you.

Answer 1

[Image Analyst]

Did you try plot()?

fm = 1000; % whatever
f = [0, 0, fm/2, fm];
X2 = [0, 1, 1, 0];
plot(f, X2, 'r-', 'LineWidth', 4);
xlabel('f [Hz]');
ylabel('X2(f)');
grid on;