Thread: Fourier transform of heaviside functions.

Well i found this question in my tutorial:
f(t) = 5[H(t-3) - H(t-11)], find the fourier transform.
Ans: (-10/w)(sin w)exp(-2iw)

i am totally blur on how to even start. I tried the general method of fourier transform but got no closer to the answer.

integrate from 3 to 5 for 5.exp(-iwt)

Couldn't find any table with Fourier transform for H(t-a).

All help are appreciated.

what we get is a pretty classic result: a square signal in the time domain transforms into sinc in the frequency domain.
The Fourier transform of a step function includes something called Dirac's delta function you can read more about this in the following article:

Fourier Transform--Heaviside Step Function -- from Wolfram MathWorld

ok i understand until line 3 but how did you get from the last term in line 3 to line 4? i wasn't taught sinc functions before.Also can you try getting the answer given for this question. i want to learn how to solve such questions since it has a probability of coming out in exam. thank you

If you haven't learned about the sinc function then forget about the fourth line.

Anyway that's the answer I get, maybe it can be transformed into the answer you were given although I'm pretty sure that my answer is correct:



and if indeed the two answers are equivalent then you won't get points taken off for this answer.

aight thanks i will try getting the answer required from then answer you give ^-^