Getting to NLN tonight hasn't been a problem so far, but there seem to be a forest of features at 18khz that are upset, and I don't see any filters to handle them. Attached spectra are from the current lock stretch (blue) and the 2 hour lock from 23 hours ago. The features around 18040 hz have been the most problematic, maybe the current bandpasses are good for some of the peaks in that region, but not others? The peak at 18038.5 has been the worst, none of the filters seem to do any good. So far I've had the best luck using a gain of 1000 on Mode 27, but .....
And before I could hit post 18038.5 rang up and broke the lock.
Just got done talking to Terra and Keita. With Keita's approval (because it seems to be required to get the IFO running stably), Terra walked me through making a new bandpass filter for this mode:
cheby2("BandPass",4,40,237,240)butter("BandPass",2,237,240)notch(238.5,20,30)gain(31.6228)
This is installed as 18038p5Hz in FM5 on Mode 27 (Terra suspects this mode is also on ETMY). Turning it on created SDF diffs that I've accepted, and I hit the intent bit 20 seconds before 6:00 local.
Jim is awesome and mode seems to be holding stable.
This one was a bit confusing because we have two ETMY modes close to one another, one at 18038ish Hz and one at 18042ish, Hz as seen in Jim's spectum. This is probably the source of TJs problems last night (sorry TJ), though when I checked earlier today the peak I trended from his shift was within the BP so I didn't suspect that to be the problem. Jim scooted over the BP and PLL set frequency to be over the 18038 Hz mode. Next day I'm in, I will create a new mode so that the two can be differentiated. Note though that the 18042 Hz mode did not go unstable just now even though we weren't damping it. I'll look into the last several locks and see which seems to be the regularly problematic one. We also weren't driving quite hard enough; Jim increased the damping gain which worked much better.
For now: If Mode27 seems unresponsive, open PI DTT and check if the growing peak is at 18038 or 18042 Hz. Then check the following:
- Open Mode27 in the PI medm screen.
- Open the BandPass filter bank
- Change the mode27 Bandpass filter if necessary (filters for both options now exist) to cover the correct peak frequency
- Open the PLL screen for that mode
- Set the PLL 'set frequency' to 238 (if the peak is at 18038) or 242 (if the peak is at 18042)