J. Kissel
EDIT :: False Alarm -- see comment below!

Since I'm at the "what does it all mean?" stage of madness with the OMC DCPD Transimpedance Amplifier (TIA), I decided to make it worse -- I remeasured the original transfer function that triggered me worrying about the TIA response in after the OMC swap (see LHO:75986). I did this to try to corroborate whether there is a change in the DCPDA response above 1 kHz as mentioned in LHO:78090. 

This transfer function is the remote, DAC-driven measurement of the whole DCPD sensing chain -- the transimpedance amplifier, the whitening chassis, and the front-end compensation for the frequency response of those -- this has been described most recently in LHO:71225. 

I *don't* see a difference above 1 kHz, but I *do* see more difference in response below 25 Hz than I had in 2024-Feb-26.

See the attached transfer functions of the DCPDA chain and the DCPDB chain.

Black is pre-OMC swap, 2023-Jul-11.
Brown is post-OMC swap, 2024-Feb-26.
Red is today, also-post OMC swap, 2024-May-28.
All measurements use the S2300003 whitening chassis, and the compensation from the 2023-Mar era compensation we've been using throughout O4.

The only "oh, well it could just be" that I can think of immediately is that the DCPDs had been powered down from 10:10a to 11:30a PDT today to characterize the measurement setup in analog (see LHO:78090), and these were measured "only" 20 minutes after being powered back on at 11:50a. So -- we'll have to take the measurement again at the next opportunity -- such that the TIA electronics have what we think it the appropriate amount of time to thermalize -- a few hours.

           Just maddening.

Data lives in 
    /ligo/svncommon/CalSVN/aligocalibration/trunk/Common/Electronics/H1/SensingFunction/OMCA/Data/
        20240528_H1_TIAxWC_OMCA_S2100832_S2300003_DCPDA_RemoteTestChainEXC.xml
        20240528_H1_TIAxWC_OMCA_S2100832_S2300003_DCPDB_RemoteTestChainEXC.xml