J. Kissel, T. Shaffer

I've remeasured transfer functions on H1 SUS ZM1 after TJ has improved the UL flag situation (see LHO aLOG 41001). I'm sad to say this has changed the problem, but not fixed it:
    - The primary P and L mode frequencies are still low with respect to the model and other suspensions in L2L and P2P
    - There is now Y cross coupling seen in L2L where there was not before (and is never expected to be there)
    - What was one extra mode below the primary Y resonance in Y2Y, is now two, and the lower of the two doesn't correspond to an L, P, or Y mode. (Maybe it's a T R or V mode?)

For this measurement, the ISI is now floating and damped.

Suggestions (in order from NONINVASIVE to DRASTIC): 
    - Investigate LL OSEM. 
        - Comparing EUL L and P drive to OSEM UL LL UR LR basis response plots -- pages 7 and 8 of 2018-03-16_1643_H1SUSZM1_M1_ALL_TFs.pdf against 2017-08-08_1520_H1SUSRM2_M1_ALL_TFs.pdf and 
2018-01-24_1909_H1SUSZM2_M1_ALL_TFs.pdf  -- one can see that ZM1's LL OSEM has less response than is typical (i.e. typically LL and LR show roughly the same response).
        - Also, In the L to UL LL UR LR plot, (pg 7) one can see some coupling to modes at 6.1 and 8.8 Hz in LL that's not in the other OSEMs. ZM2 shows some minor 8.8 Hz coupling, but it appears in all OSEMs.

    - Measure some of the fundamental parameters of the suspension
        - Do we have the right wire length? The right wire thickness?
        - The Y2Y TF worries me, and so does the reduced frequency of the L and P TFs. It makes me worried that there's some mechanical parameter of the suspension is wrong. 
        - The tip tilts, to-date, have had remarkably reproducible transfer functions, and H1 ZM1 is definitely an outlier -- see allhttss_2018-03-16_Phase3a_AllHTTS_ALL_ZOOMED_TFs.pdf. OK, OK, H1 OM1's pitch frequency is a little bit low, but all DOFs of H1 ZM1 look obviously different.

    - Back off all eddy current damping magnets, EQ stops and any other adjustable thing that might possible by rubbing. See what anything changes.

    - (Measure H1 OM2 before you do this, but) swap in-vacuum cables between OM2 and ZM1. In otherwords, use an entirely different, known-to-be-healthy (to be confirmed with the prior measurement) suspension's electronics chain, so as to completely rule out all electronics questions.

    - Completely replace the tip-tilt for a spare, and swapping the optic into another suspension.

It really is depressing how difficult these new single stage suspensions are to debug! HAM Single State Suspensions (HSSS) are supposed to be the easy ones...