J. Kissel

I was looking to do some coil balancing on ETMY this morning, and found that my signal to noise ratio at 4 Hz was very poor. So, I compared the performance of ETMY's optical lever against the three other test masses' lever performance, which confirmed that ETMY's lever is 1-2 orders of magnitude worse than any other optical lever, from 0.5 Hz to 10 Hz. I also found the digital compensation for the electronics in correct (and have subsequently fixed it).

This performance level makes the optical lever pretty unusable for any mid-to-high-frequency characterization. We should consider swapping the previous optical lever back into place. If not, at least consider turning on the third and final stage of whitening.

%%%%% Details %%%%%
Recall that ETMY's optical lever is of a new "glitch free" variety, as installed by Jason and Suresh back in May (see LHO aLOG 42104, and subsequent characterization in LHO aLOG 42249. One can see in the 5th attachment that the performance was comparably bad then as well.

Comparing the newly changed whitening / gain settings on the daughter board against the bit map from when the gains were tune for the original optical lever (see LHO aLOG 14782) 
Rack          Board      Optical Lever    Config Board  |------------------ Switch Status ----------------|
              Number                       Installed?    Board    Switch             
SUS H1-R2       1          ETMY               Yes          B0       1       +24 [dB]     X            OFF          
  (pg 4)                 (pgs 5-6)                         B1       2       +12 [dB]     X            OFF                  
                                                           B2       3       +6  [dB]     X            OFF               
                                                           B3       4       +3  [dB]     X            OFF
                                                           B4       5       (1:10)            X       ON
                                                           B5       6       (1:10)            X       ON
                                                           B6       7       (1:10)       X            OFF
                                                           B7       8       Latch        X            OFF
                                                              Total ETMY TF = (1,1:10,10), G = 0 [dB]
which confirms what the daughter board was before the settings were changed (i.e. 4th attachment to LHO aLOG 42104),
and after it was changed (i.e. 5th attachment to the same aLOG) -- though the (z:p) = (1:10) whitening filters were not mentioned  
Rack          Board      Optical Lever    Config Board  |------------------ Switch Status ----------------|
              Number                       Installed?    Board    Switch             
SUS H1-R2       1          ETMY               Yes          B0       1       +24 [dB]          X       ON          
  (pg 4)                 (pgs 5-6)                         B1       2       +12 [dB]          X       ON
                                                           B2       3       +6  [dB]     X            OFF               
                                                           B3       4       +3  [dB]          X       ON
                                                           B4       5       (1:10)            X       ON
                                                           B5       6       (1:10)            X       ON
                                                           B6       7       (1:10)       X            OFF
                                                           B7       8       Latch        X            OFF
                                                              Total ETMY TF = (1,1:10,10), G = (24+12+3=) 39 [dB]

However, after revisiting the digital compensation for the whitening, I found that all three compensating filter modules are on, which is incorrect for the above filter settings.
I've subsequently turned *OFF* the third compensation filter in the H1:SUS-ETMY_L3_OPLEV_SEGn banks.

The attached performance ASDs show the comparison of performance (and shows ETMY in both the incorrectly compensated and correctly compensated filters). The correctly compensated optical lever indeed shows that the correctly calibrated performance is *even worse* than when mis-calibrated, showing an equivalent displacement noise 1.5 to 2 orders of magnitude worse than other test mass optical levers. 

Note that all SUS in each chamber were DAMPED in this measurement, and the optical levers were centered on their QPDs. The chamber's seismic isolation configuration was FULLY_ISOLATED.