Using the latest BRUCO results, I've annotated a hi-res spectrum from last night's lock. Peaks, bumps, and so on are labeled with the largest coherent channels.
There are a few peaks, at 46, 166, 420, and 689Hz, that are coherent with PRCL/SRCL, and they have changed since the blue reference (Mar 19th at 18:00). This might be due to the POP --> POPAIR switch.
The source of the 300Hz lines has been identified, it's the BS violin modes. The frequency is given in Mark Barton's table of predicted violin resonances (thanks Jeff!).
We turned off all the ring heater power supplies yesterday; this got rid of a line at ~74Hz but didn't change the 55Hz line and its harmonics. These lines are certainly due to some electronics in the EX racks.
Features coherent with the IMC WFS and the PSL persicope are probably the same thing (input beam jitter), hopefully from the same source (PSL PZT mount).
As I think is known, there is a filter solution for the ring heater driver to eliminate the fan noise. It is the same basic design as was used in the Seismic Coil Driver fans. We just need to make these available for installation soon. Added this to my to-do list.
The 160 and 420 Hz peaks are moving in frequency with a timescale of some minutes. The moves in a coherent way, in the sense that the frequencies seem pretty much to maintain a ratio of 2.5
See my previous log entry for an analysis of the line wandering.
It turns out the 55Hz line is actually a 57Hz line, and it's the Hartmann camera. This was explored in detail at LLO a long time ago, I should have remembered.
I have turned off the HWS box in the EX electronics rack. This eliminated the 57Hz line and harmonics from the rack magnetometer, but for some reason the overall noise floor has increased, see attached. Probably turning off the camera is a better solution, as Aidan recommends in the LLO log. We'll see if this affects the noise.
