I measured the TF from the CARM_SERVO_FAST_OUT (the feedback signal to IMC AO path) to CARM error point (K1:LSC-REFL_PDA1_RF45_Q_IN1).
The servo configuration is shown in the attached figure. The REFL power was 1.2 mW.
BTW, how is the generic filter stage for the FAST_DAQ configured in the CARM CMB ?
If it is the same as the standard schematic, there is a whitening filter ([poles;zeros] = [100,100;10,10]).
There is an anti-whitening filter in the K1:LSC-CARM_SERVO_FAST_DAQ filter bank. However, it is not engaged now.
Was it engaged during the measurement ?