I took a transfer function measurement yesterday in the early afternoon actuating in P and plotted P2P and P2Y to see the state of our P2Y cross coupling. It looks like swapping out the F3 QOSEM a couple days ago resulted in a bit less P to Y cross coupling? I will be having another go at P to Y measurements (as well as Y to P) once BSC2 is quiet, but results as of now seem to indicate that the P to Y cross coupling has gone down by an order of magnitude since last week.

We will mostly be focusing on the P to Y plots

The last P2Y comparison we did (in green) was from measurements taken on 06/25/2026 (90753). Between that measurement and the second measurement (in blue) taken July 1st at 19:47 UTC, the only change we had made was swapping out the F3 QOSEM since the coil pins were grounding to the chamber (90834). Comparing these two measurements, even if we just look at the frequencies where the coherence is good for the second measurement, it seems that the second measurement is over an order of magnitude lower than it was last week (same excitation and amplitude).

Then we went in and aligned QOSEMs in the afternoon, and afterwards (July 1st at 23:51 UTC) I took another measurement with 10 averages instead of the previous 5 to try and get better coherence, but the coherence ended up worse in most places. I'm not exactly sure why this is the case here. Having trouble with coherence is partially a sign that there is just less cross coupling, but also it would obviously be good to have better coherence. The few places where the coherence is okay though seems to corroborate with the magnitude of the second measurement. The P to P TFs for all three measurements still match and look great.