At 05:32 PM 5/17/01 -0400, Sean H. Breheny wrote:
>Hi Dave,
>
>I think this has come up before but I can't shut up :-) Why do you say that
>a sine wave contains harmonics? My guess is that you are saying that in
>practicality, when you try to create a sine wave, you can't totally avoid
>harmonics and you usually end up with mostly even ones, which may be true.
>Nonetheless, a pure sine wave has no harmonics because that is what Fourier
>series are based upon, sine waves. I think it is especially misleading in
>this case to state that a sine wave is an infinite series of harmonics,
>too, because this will lead people who are trying to create sine waves to
>think that they must ensure the presence of such harmonics, when in reality
>it is best to reduce them as much as possible because as long as they are
>present, you don't have a perfect sine wave (the total harmonic distortion
>is greater than 0).


Sorry, brain short.  :)
Correct. Sine is F only.
Square is F plus 3F, 5F.... in decreasing infinitum



>I agree, though, that what Freddie was trying to do is not practical and he
>needs to make some kind of rough ADC (R2R ladder or PWM much faster than
>than the sine wave freq followed by a simple low pass filter, as Scott just
>suggested).

Scott suggested PWM, which works too. You keep the PWM frequencies way up
out of the desired frequency, and you can filter it reasonably easy.



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