Dear Sally, You ask for a reference in relation to my assertion that there is an absence of even harmonics in a square wave as derived during one mode of the open and closed functions of the cords. I'm sure you are conversant with Fourier Analysis. When this is applied to any wave shape its sinusoidal components and their relative amplitudes can be fairly simply derived.
Unfortunately I find it difficult to copy in the appropriate formulae for you but I'm sure you are in a position to source these for yourself. Let me try..
Fundamental (F1) = A [1/pi/2]= 2A/pi (F2) = A [sinpi/pi] = 0 (F3) = A [-1/3pi/2] = 2A/3pi ... and so on. In a practical square wave the 11th harmonic is seen as the limit.
A is Peak to Peak amplitude. The KEY is that whenever "n" is an EVEN number, we are taking the sine of a multiple of "pi" or (180 degrees). The sine of any multiple of "pi" is ZERO.
The Fundamental is about 63%, the second harmonic is ZERO and the third harmonic is 21% and so on down to the 11th.
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