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Entry  Wed Feb 18 21:10:21 2009, rana, Update, IOO, MC Drumhead mode lost again 
    Reply  Thu Jul 30 21:26:16 2009, rana, Update, IOO, MC Drumhead mode mc2drum.png
Message ID: 1322     Entry time: Wed Feb 18 21:10:21 2009     Reply to this: 1814
Author: rana 
Type: Update 
Category: IOO 
Subject: MC Drumhead mode lost again 
In early December, Caryn and I noticed that the MC Drumhead mode was visible at the Qmon point of
the MC demod board using a spectrum analyzer and no external excitation of the MC mirrors. We then
started tracking the MC Drumhead modes.

Today I found that it is gone again. It also wasn't there when I looked for it in 2007. Mad

I looked at the MC error point spectrum and it seemed reasonable. Changing the gains in the MZ, ISS, PMC, & FSS
had no good effect on the noise spectrum.

The voltage noise above 10 kHz in the MC error point is increasing like ~f. I think that this means that
the leftover is the noise from the FSS. Below 10 kHz it is the noise of the VCO (10 mHz/rHz).

One possibility is that the high frequency noise changes with the mood of the NPRO. There should be no
frequency noise induced by the decay of the PA diode power. We can do an NPRO SLOW scan to see if there
is some kind of mode hop noise happening.
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