Interference at Odd vs Even Harmonics: Is the Square Wave Really Square?

[cyclone24]

If I look at the Fourier transform of the square wave signal, the peaks are at the odd multiples. In the device that I am working on, I would expect the interference at the odd harmonics of the center frequency.

But I see the interference at even harmonics. When is this possible?

(Only if the square wave is not really square?)

 

[waht]

(Only if the square wave is not really square?)

Nothing is ideal in the real world.

 

[schip666!]

The harmonic structure of a pulse signal depends on the duty-cycle. A real 50% square wave has the odd-harmonic structure you mention. Varying the pulse-width will produce different harmonics.

 

[cyclone24]

It turns out that the difference in rise and fall times lead to different harmonics (odd/even)...