Fourier Transformation and Harmonics

[Siyu D]

If a complex wave is composed of three components at 100Hz,120Hz and 200Hz and its fundamental frequency is the GCD of this three numbers, 20Hz. The harmonic frequencies are whole-number multiples of the fundamental frequency, but in this case, there are only 5th, 6th and 10th harmonics. Where are other harmonics like 2th, 3th or someting like that?

[Simon]

The signal you describe is quite extreme. Those other harmonics exist but have zero amplitude. Even the fundamental (we could call this the first harmonic) has zero amplitude.

A more reasonable example would be a square wave, in which only the odd harmonics have energy and all the even ones (2nd, 4th, 6th, …) have zero amplitude.

[Author]

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