As a step toward trying larger DARM offsets, I have flipped the rocker switch on the OMC DCPD whitening chassis to its LowZ state. To match this, I have turned off the HiZ filter in the H1:OMC-DCPD_A and H1:OMC-DCPD_B filter banks.
Attached are some spectra showing the dark noise measured this morning in both the old HiZ and new LowZ states, as compared to last night's 30W lock at NomLowNoise. All of these spectra are taken with both stages of whitening on, as well as the lowpass. Green and brown are with the old HiZ settings, pink and cyan are with the current LowZ settings, and the red and dark blue (also refs 12-15 underneath the red and blue) are from last night's lock with the usual 20mA of light.
In prep_dc_readout, with OMC locked, I changed the height of the dither line from 750 counts to 630 counts, to match the OMC length UGF of 6 Hz measured 2 days ago.
We reverted these changes (dither amplitude, HiZ switch and compensation for HiZ) so that people can get to low noise tonight without redoing the feedforward.