[SI-LIST] Re: Square wave harmonics


> Lucien wrote:
> >
> > Can anyone give me the low-down on square waves! 
> Basically, my
> > question is:  In our physical reality, do square
> waves contain
> > harmonics?  Or does the idea of square wave
> harmonics only exist on
> > paper as a mathematical model, used to PREDICT the
> natural behavior
> of
> > the square wave?


Ideally (or rather academically!), a perfect square
wave cannot be constructed from the the sum of the
Fourier series. I remember this from my college days,
when the professor told us that even though it will be
virtually indisguishable, there is what is called the
Gibbs phenomenon which essentially is the nth sinewave
that will give the square wave the final leading edge
and trailing edge shape. This is the only known
difference between a "real" squarewave and one
composed from the Fourier series stemming from the
fact that a square wave is a discontinuous function
and the Fourier series requires a continuous function.
Other than that, and in practice, it doesn't make any
difference as technology cannot yet switch a voltage
in 0 time obviating any academic differences.

Hans Mellberg

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