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Thu Sep 4 17:44:27 2008
FSS error signal spectrum
Attached is a spectrum of the FSS error signal.
There are a lot of sharp peaks above 100kHz (the UGF of the servo is about 200kHz).
These are mostly harmonics of 77kHz. They are the current suspects of the FSS slew rate saturation.
I remember when I blocked the light to the PD, these peak went away. So these noises must be
in the light. But I checked it a few weeks ago. So I will re-check it later.
One possible source of the lines is a DC-DC converter in the NPRO near the crystal.
We will try to move the converter outside of the box.
Uploaded Wed Oct 8 17:28:27 2008