Sheila, Elenna

I adjusted the POP9 phase to see if it would improve the coherence of LSC REFL RIN with DARM. In the past, this has been an indication of poor POP9 phasing causing some offset in PRCL.

I tried checking the phase in two ways. First, I engaged the 88 Hz notches in LSC and injected an 88 Hz PRCL line. This result indicated that the POP9 phasing was actually pretty good, in that the signal appeared in I and not Q. The dotted lines in this attachment show this measurement.

Next, I tried a different method, injecting a frequency noise line at 700 Hz. That method showed that there was some signal in Q. I was able to reduce the signal in Q by adjusting the demod phase. The attachment shows the start in dotted blue and red lines, and the end result in solid lines. Overall, this was 2.9 degree change, so not significant.

After that adjustment, I remeasured with the 88 Hz PRCL line and saw a very small difference, shown in the solid lines.

After all that, I am not sure I see a difference in the REFL RIN coherence. Nonetheless, this does seem slightly better, so I SDFed in safe and observe.

I realized after we went to observing that I forgot to unplug the frequency excitation cable. Sorry!