Help with DC in fourier transform please

[lucasLima]

Hello everyone,

So, i have a big test tomorrow and my professor said i should study the DC level in Fourier transform , in the frequency domain.

So, i did a little research and found out that the dc level is the percentage of the time a signal is active, and that's all.

Can't see how that's relevant in the Fourier transform. Something to do with it going to zero?
Any help is aprecciated, any subject you think i should look into.

 

[ElijahRockers]

dc level is the percentage of the time a signal is active

If I am interpreting DC correctly, this means constant signal, as opposed to AC, or alternating current.

The Fourier transform of an infinite (in time) constant signal is a dirac delta function. The Fourier transform of a finite (in time) constant signal is a sinc function.

Perhaps that is what is meant by DC in this case