To look into the detail when the IMMT1 trans bumps would start, I compared a time series of some channels during lock aquitision today. Fig. 1 is the time series of relevant channels, while Fig. 2 is the IMMT1 trans QPD's spectrogram (1 sec resolution). The time 0 is the same instance for usability. It seems the timing around 7-8 sec would be the starting time of the bumpy at 20-30Hz; in this spectrogram, the 117 Hz bump would not be clearly seen, but in spectra at the corresponding time, it can be seen (need 1 Hz resolution with 3 avg, for example). Anyway, looking at the corresponding time in Fig. 1, the shook timing would be seen in IMMT1 trans signal (the first blue curve), and maybe the following two would be the relevant clues:
- PRM pitch suddenly responded to something at 8 sec.
- REFL RF PD' DC suddenly responded to something at 7.5 sec.
Maybe there might be another hidden state changes... For wider time window, see Fig. 3. At around 30 sec, ADS dithering of PRM started (not shown here, but dithering BS and IMMT2 also started simultaneously).
Anyway, totally no idea I have. Need more accumulation of facts.
