Hirose, Tanaka
### Abstract
I observed the 24 kHz beacon signals in OMC REFL WFS RF demodulated signals with Moku:lab and DGS, probably. But They are too small, maybe because the excitation signal from DGS is too small by the lowpass filter of DAC. So I wanna replace the bypassed DAC and check the excitation signal and the beacon signal become large.
### What I did
- This morning, Hirose-san and I brought the two Moku:lab, Miyoki-san's, and DGS's to OMC rack. Miyoki-san's one is connected to the monitor port of RF demodulated OMC REFL WFS1 I and WFS 2 I. DGS's one is connected to the monitor port of DARM.
- The alignment to AS seems to be not good according to OMMT2 TRANS QPD. I centered the beam about both OMMT2 TRANS QPDs with OMMT1.
- After the alignment, I locked X-arm. I closed the QPDV centering loop and locked OMC.
- Then, I excited the drumhead mode of ETMX with the beacon oscillator. At first, I searched the frequency of the drumhead mode monitoring CARM signal. I found the frequency is 23.691 kHz. (fig. 1)
- I also found the beacon signals in RF-demodulated OMC REFL WFSs (Fig. 2), but they are too small, especially the one in OMC REFL WFS1 (the red one in Fig.2), which is almost the same level of noise.
- Moreover, I measured the spectra of RF-demodulated OMC REFL WFS1 and WFS2 signals with diaggui. Fig.3 and Fig. 4 show the results. The small peak of 23.691 kHz can be seen in OMC REFL WFS2, but it cannot be seen in OMC REFL WFS1.
- I know the excitation signal from DGS is lower to -20 dB due to the 10 kHz lowpass filter in the AI filter. This may be the reason why the beacon signals are such small. So I wanna replace the AI filter, which bypassed the lowpass filter.