This morning, the possibility of performing the SPRB drift control with the error signals obtained from the B4_QD2 demodulated signals at 12 MHz or 112 MHz has been implemented.

The selection of the error signals has to be done in the process SPRB_Quadrants, by pushing one of the following buttons: "DC", "12MHz", "112MHz".

This still needs to be tested with the interferometer. The 112 MHz signals seem to be a bit more stable than the 12 MHz, thus we advocate to try with the 112 MHz signals first.

We have also reduced the VGA gain of the B4 QD1 and QD2 RF channels. The old gain value was 4.8V/V and the new gain value is 2V/V (corresponding to gain code 0x24 in the dbox_bench configuration). This should solve the issue of saturation for the quadrants mentioned in entry 53998.

The B4 QD1/2 demodulation mezzanines were then reconfigured:

2021-11-30-10h17m59-UTC    info masserot     Reconfigure SPRB_DEMOD_B4_QD2 in SPRB_dbox_bench
2021-11-30-10h19m26-UTC    info masserot     Reconfigure SPRB_DEMOD_B4_QD1 in SPRB_dbox_bench

A side effect of this action is that the demodulation phases of the B4 quadrants need to be retuned.