[SI-LIST] Re: Square wave harmonics
- From: "Doug McKean" <dmckean@xxxxxxxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Mon, 26 Nov 2001 18:21:41 -0800
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?
You're asking a loaded question.
For our purposes they do contain harmonics. There is enough
modeling of signals to suppose that indeed there are harmonics
within by using things such as phase delays, group delays, group
velocity, etc ... to predict behavior and performance.
On the other hand, I've talked with folks who actually believe
that simply constructing a circuit which responds to a particular
frequency after being hit with the leading edge of a square wave,
(be it a spectrum analyzer or whatever) essentially nothing more
than a step function, is no "proof" that harmonics exist in a signal.
You're simply creating something to respond a certain way and
respond it does under the right circumstances.
And also on the other hand, I would assume that the Fourier
sum is actually limit process, the true square wave being the
limit of the asymptote. As such, the Fourier can't be looked
upon as a "real" thing. I can't remember to well, but I did read
Fourier's work about this when he was studying heat with it,
and I seem to remember he treated it more as a curiosity with
a high correlation.
Regards, Doug McKean
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