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Extracting the 5th Harmonic

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March 14th 04, 04:30 AM

Tony

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On Sat, 13 Mar 2004 16:15:53 +0000 (UTC), (Ken Smith)
wrote:

In article ,
John Larkin wrote:
[....]
As the duty cycle deviates from 50%, the even harmonics start to
appear, so you need a better filter to keep them out.

Also as you get nearer the 20-80 duty cycle the amplitude of the 5th
harmonic decreases.

Even worse than that - relying on simple reasoning (no maths), the 5th will be
COMPLETELY suppressed when the input's rising and falling edges are spaced so
they correspond in time with the SAME point in the 5th harmonic waveform,
certainly at 20-80, but also at 40-60, 60-40 or 80-20 - a good reason to make
sure that the 50-50 is stable and accurate.
Tony (remove the "_" to reply by email)

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