Camilla, Andrei, Naoki, Sheila

There have been many examples of times when the filter cavity length locking error signal peak to peak seems to be correlated with worse range over the last 3 months, I've attached some screenshots of examples. This was true before the May 16th change in the status of the CO2 ISS channel , 78217, and before the output arm damage that happened April 22nd.

Some of these times correspond to times when there is a whistle visible in the FC WFS signals 78263, others do not.  These whistles in the FC WFS channel have been present throughout all of O4, but they do go away sometimes for several days, this last week they do not seem to have been present.  Andrei has identified a candidate wandering line in the IOP channels for these WFS that was last week ~10 kHz away from the 105kHz RLF-CLF signal, today that line seems to be gone.

Last week, the filter cavity error signal peak to peak became much noisier than it was previously (screenshot), until June 15th at around 15 UTC when things returned to the previous state.  Camilla identified that this started a few hours after the time of the ringdown measurement attempt, 78422, and that there haven't been any ZM1/2/3 alignment changes.  During that time period, the FC error signal from around 0.7-9 Hz has higher and variable, in addition, the low frequency noise was changing and varriying the RMS as it has done before.  The attached screenshot shows some of the typical low frequency variation (compare yellow to blue), a whistle in the yellow trace, and in red a time during last week's elevated noise when the low frequency was relatively quiet but there is elevated noise from 0.7-9Hz.