Sheila, Pep, TVo

Motivated by the extra DARM noise below 90 Hz (see Jenne's Alog-37590), Sheila thought that maybe it was do to the CARM loop moving around due to optical gain changes after the Montana EQ.

So we went to the LVEA during commissioning time to take a transfer function (Picture 2), and found the UGF to be around 24 kHz and about 15 degrees phase margin

In a previous Alog-36686, it seemed like a good UGF was around 18 kHz so we decided to change the gain on the REFL servo from 7db to 6db.  This shifted the UGF down to 17 kHz and about 65 degrees of phase margin (Picture 1). 

However, this didn't really help DARM solve its mystery noise mentioned above, so the search continues.