Harmonics question

[Marjan Urekar]

> 
> I understand that a square wave is made up of sine waves, but what are the
> exact frequencies that the harmonics oscillate at?  For example, if you
> have a square wave at 130Hz are all the harmonics octaves up and down from it?

uh,if memory serves me they are 
 at  fn = n x 130 hz , n=0,1,2,.... oo
(well, at  +/- n ,if you're familiar with Fourier)
for perfect square you need infinite number of
harmonics,for approx. just first few...
It is square wave which is infinite sum of
sin and cos functions... 
some harmonics are not there depending on if you
have pure square (50% duty cycle) or some pulse.
Amplitudes of harmonics depend of DC offset,
signal amplituse,unipolar/bipolar pulses etc.
So,when you run your unsuspecting little 130hz
signal trough VCF and you get nice sine wave
at 130hz ,you've filtered out fundamental harmonic
(n=1),shape of sine depends on how good your filter is.
(as some other harmonics get trough at lower amplitudes).


marjan