Do ION7550 and ION7650 meters use cosine (cos) or sine (sin) based Fast Fourier Transform (FFT)?

The FFT decomposition in the ION7550 and ION7650 meters use a cosine based function. The latest firmware for the 7550/7650 (v350 and above) also notes in its code comments that sine inputs are rotated 90 degrees to compensate for the cosine based FFT function. In other words, they are translated into cosine functions to keep unity.

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  Date Created: October 13, 2008
  Last Revised: February 23, 2009
  Public
  Original Author: KG
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