J. Kissel, A. Pele

Given that we were suspicious of the one data point that appeared to show model inaccuracies at the most troublesome 0.43 [Hz] mode of H1 SUS ETMY (see LHO aLOG 6933), we took the time to gather a really high (0.001 [Hz]) resolution, open loop gain transfer function. Comparing this against the model reveals the model matches with measurement very very well. No such double peak is visible. 

The only remaining discrepancies are the "known" differences -- a little bit off in frequency for the 0.56 [Hz] first pitch mode, and the ~30 [Hz] zero that's from cross coupling of drive to sensor signal in the readout chain (i.e. not representative of the suspended dynamics).

For posterity, this was measured with the 2013-05-01 filters, with the extra 0.43 and 1 [Hz] boosts installed by Arnaud, and the overall EPICs gain was set to 1.0. We again see that the phase margin is only 19 [deg]. More to come on installation of a better loop design (i.e. installing the one we already have one in our pocket; see LHO aLOG 6760).