I looked at the HAM1 table-top L4C to CHARD pitch feedforward again during a lock today, and it seemed like there was enough coherence to try this again. The design seemed a little easier this time, but the measured transfer function was a little hairier and it doesn't get as much improvement. Locking the RMs vertically seem to have much reduced the HAM1 Z to CHARD coupling, so this time I looked at RY to pitch.

First attached plot is the rather minor improvment I was able to get in CHARD. Red and blue are two on tests, green is an off test. Jenne looked at a couple of DARM channels and didn't really see any improvement there.

Second plot is the theoretical subtraction from MCCS2 in matlab, blue is the unsubtracted CHARD P, red is CHARD P after subtracting all of the TT L4C RY coherence. This plot made me think it was worth trying this, the improvement at 15-20hz is like a factor of 5. Sad I wasn't able to get that here.

Third plot is the filter design. Not a lot to say otherwise, this a lot like the work from before the HAM1 vent, just maybe not as worth it this time around.

I'm leaving this running, but if people want to turn it off, there is a an on/off masterswitch called HAM1 FF MASTERSW on my ISI senscor config screen, in the middle.