This is a report about a small task that has been in Daniel's commissioning calendar for a long time (see for example alog 10451).

I checked the signals of REFL_A and compared them with the in-air ones to check if they are functional.

The signal levels seem reasonable and therefore I conclude that REFL_A is functional without a problem. See below for more details.

Comparison of the signal level:

Before doing anything, I adjusted the demod phase of REFL_A_RF45 which had not been set to a useful number. It is now set to be 5 deg. This maximized the PRY signal in the in-phase output. On the other hand, REFL_A_RF9 seemed already good and therefore I didn't change the demod phase. Then I locked the PRY and injected a 10 Hz excitation in order to compare the responses between the in-vac and in-air ones using dtt. Note that I only used the in-phase signals as the q-phases don't really give a good signal in this situation. At the same time, the DC power on the PDs were measured to be 14200 cnts and 8020 cnts at REFL and REFLAIR respectively. This means that the in-vac one should show a higher response by a factor of 1.77 due to the difference in the power falling on the diodes.

Unfortunately, I wasn't able to figure our whether S1300533 or S1300534 is in HAM1. So for now I use transimpedance gain of 600 and 730 Ohms for 9 MHz and 45 MHz respectively which should give us a coarse estimation of the signal levels.

Expected and measured ratios of the 9 MHz detectors:

• REFL_RF9_I / REFLAIR_RF9_I = 600 Ohm / 245 Ohm x 1.77 = 4.33
• Measured ratio = 3.8
• Discrepancy is about 14% or 1.14 dB. This is acceptable.

Expected and measured ratios of the 45 MHz detectors:

• REFL_RF45_I / REFLAIR_RF45_I = 730 Ohm / 341 Ohm x 1.77 = 3.79
• Measured ratio = 3.15
• Discrepancy is about 20% or 1.6 dB. This is acceptable.