This is a Formula spline with default settings.  The formula plugged into the Y parameter actually gives us something pretty close to what we are looking for, although its range is only one wave.  The formula is:

100.0Sin(tpi)

I do wish I'd payed attention in my math classes.  At any rate it isn't that necessary to have a fundamental understanding of the formula, only what it does.  In this case it very conveniently produces a curve that is perfect for this purpose.

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