Kiwamu, Lisa, Stefan
We increased the 9MHz modulation depth by 3dB. This was done by increasing the IFR drive from 10dBm to +13dBm, and putting 3dB attenuators in all path except the one for the 9MHz EOM. This should raise the 9MHz modulation index from 0.1 (alog 9395) to 0.14. We expect a 9dB stronger signal for the 27MHz.
Indeed with this setting we were able to get a pretty stable lock on the 3f signal (its locked as I type this.)
Some of the settings changes were:
- PRCL gain -0.4
- MICH gain 40
- BS M2 LOCK L: added the comb60 (FM4) and ELP90 (FM9) in addition to the f^2 (FM6) and z30:p100 (FM7)
- We didn't need any additional filters for PRM M2 LOCK L (We only have FM3 FM4 FM8 and FM10).
- We notices the occasional saturation in the REFL27 input, so we lowered the whitening gain to 21dB (val=7), and increased the digital gains from 3 to 4.243. Whitening stages 1 and 2 are also on.
- We also noticed that it prefers slightly hight MICH and PRCL gain for acquisition (we used -0.6 and 60)
- Also, we noticed that the REFLAIR45 (which currently has 0dB whitening gain and only whitening stage 2) tends to saturate during lock acquisition. It seemed to lock quicker without any whitening filters on.
- Even though CDS doesn't report any saturations, we occasionally see the BS optical levers get kicked and ring down. (The BS has optical lever damping.)
The attached plot shows the raw signals of REFLAIR 45 and REFLAIR 27, as well as the drive to the BS M2. (The signals are scaled to gain-match.)
PS: it is still locked on 3f - 16min and counting.