RF demodulation phases for 2f, 3f, 4f, 10f and 15f might change with this swap.

Replace Attenuator on:

Freq  Value with 
18MHz +3    +2
27MHz +6    +2
36MHz +5    +4
45MHz +2    +1

91MHz 137MH No change.
To keep the input value at 10dbm.

Values based on Epics readbacks.

Tagging DetChar.

We've recovered nominal low noise after this swap -- how ever we're seeing a lot of different behavior within this first few minutes:
 - Some line features below 100 Hz are reduced
 - There is elevated 500 Hz rising as f (like shot noise) noise floor
 - Occasional comb in a similar region
 - 4-5 kHz ratty hump that comes and goes
 - incredible amount of omega glitch above 500 Hz

Just letting you know to keep your eyes peeled that this swap may mean several significant changes to the IFO that we may have to continue to rectify and/or deal with.

  Mike L. called to inquire about the RF45 issue. Per his suggestion, I've informed Keita of the situation. As there is nothing ops can do at this time, will continue to monitor.

In the morning, let's replace the harmonic generator with a spare. If it still glitches it's probably not a glitchy harmonic generator.

In the past the harmonic generator was checked in the lab, but the "check" was for stationary noise and not the glitches (how can we "check" sporadic glitch that might or might not happen for a year?), and the same unit was put back in place.

https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=21094

[Jenne, Sheila]

Hmmm. Reverting the cutoff frequency filters did not fix the problem.  We're leaving them with the old 10Hz filters for now.

We also tried lowering the oplev gains by a factor of 8 on all test masses at the same time (in factor of 2 steps), but that caused CSOFT to start being unhappy, so we put them back to nominal before we lost lock.

We're going to go back to Observe since we don't have another idea right now of how to fix this.

As a note, it looks like this is upconverting with the 36Hz Cal lines to broaden them significantly, which is probably part of the reason we're at a reduced range right now.

Still no clever ideas, but it certainly seems like ITMY's oplev or something in the suspension is suspicious, and perhaps imposing noise through the ASC on the other optics.  All 4 test masses see the 0.43 Hz oscillation in pitch, but ITMY seems to have many harmonics and other "hair" in the oplev spectrum.  Not plotted, but ITMY yaw also sees the 0.43 Hz motion, but the other optics don't seem to see yaw problems.

EDIT to add spot position plot - spots on the test masses aren't moving very much over the last month, so it doesn't seem to be related to that. (Except ETMX yaw - still no idea why that's so scattered)

Beverly, Andy

On 22 Mar, a line of glitches at about 3.3 kHz appeared in apparent coincidence with these ASC problems. A known, always present line at the same frequency shows glitching at about 0.43 Hz (see attached spectrogram). A previous alog (27488) referred to this line as an SRM mode at 3335 Hz. In fact, the SRM spectrum (see attached spectrum) developed a feature at 0.43 Hz on 22 Mar that was not present on 21 Mar. 

We haven't checked out anything related to Beverly's suggestion yet since the 0.43 Hz hasn't seemed to be a problem in the last ~day, and we've had other things to worry about.  But, Sheila's 8Hz oplev cutoffs were in the guardian, so other than the lock that I had changed them back to 10Hz, they've been on the 8Hz cutoffs. 

The DARM spectrum is noticeably better below about 25Hz, so it's good that Sheila's new oplev cutoffs aren't causing any problems, and are just helping.

Agreed, everything looks normal.

Everything looks normal with these trends.

The old plan of waiting around for a while seems to have worked yet again.  Mystery remains.

It would be interesting to see if there are any glitches in the observed LO drive monitors for this chassis coincident in time.  There have been the occasional RF problem with the LO on these devices which would be specific to the demodulator card if it was an LO amplifier problem.

Tagging DetChar for further investigation.