After finding that the new lines and a broad peak at around 1020Hz are correlated with the RF AM monitor channels and RF45 out of loop sensors but not in-loop (https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=23552), I went to the floor and started to move the Tenma power supply from the wall AC outlet to the power strip in the PSL rack, and move the +-17V from the ISC rack to the PSL rack.

We powered off the RF AM monitor by first disabling the +-30V output of Tenma, then disconnecting the +-17V connector from the ISC rack, then disconnecting the AC power cable of Tenma from the AC outlet. One of these actions kicked the IFO out of lock.

When the IFO locked again, the lines and the peak were still there. At this point, RF AM monitor was still connected to the EOM, but the +-17V cable was disconnected from the supply, and the +-30V supply AC power cable was disconnected. In the first attachment, the red trace ("RFAM monitor power disconnected outside of the PSL room") corresponds to this state. The second attachemnt shows the connection cartoon.

The blue trace is from this morning when RFAM monitor was connected and working (third attachment for the cartoon). Black is from a week ago, i.e. no RFAM monitor unit.

Then we totally isolated RF AM monitor from everything else by terminating the coupled output of the couplers, and disconnecting the DAQ cable from the AA chassis. Green trace ("RF AM monitor totally disconnected") corresponds to this state as well as the fourth attachment. The lines and the 1020Hz peak definitely got smaller but they're still there.

At this point, we could remove the couplers and pull everything out to completely revert back to the old configuration to see if the noise goes away.

However, doing so means breaking the lock again, and considering the relocking difficulty we experienced today, I talked with Michael Landry and we agreed to run the IFO as is till tomorrow.

As of now, LSC-MOD_RF9 channels are not measuring anything.