L. Dartez, J. Kissel

Following up on alog 63905.

Jeff and I took voltage ASD measurements of the output signal from the trans-impedance amplifier channels that are going into the OMC whitening chassis. We plugged the BNC cables mentioned in alog 63905 (work permit #10540) into an SR785 for all measurements. These measurements are intended to inform the A+ O4 OMC DCPD whitening chassis redesign/upgrade.

Data was taken from 10Hz-101.2kHz across 3 overlapping spectral windows (10Hz-6410Hz, 1kHz-52.2kHz, and 50kHz-101.2kHz). The overlapping windows help confirm data integrity & measurement consistency. The violin modes show up prominently in the data, as is to be expected. It's worth noting that the mid- and high-band windows were taken at a lower resolution bandwidth (RBW) than the low-band: 8 Hz vs 64 Hz. This is particularly evident near the violin resonances in the full band plot (attached) between 1kHz and 6.41kHz.

There was a high degree of non-stationarity in the data while the measurements were being taken. The input range had to be changed and re-dialed in several times. Included here are close ups for each of the individual bands. The low- and mid- band datasets show comparisons of the same signal taken with different input ranges on the SR785. Of particular interest is the considerable amplitude shift shown in the low band data between input ranges or -6dBVpk and +4dBVpk. This may point to the signal being noise-dominated in the 10Hz-6410Hz frequency range. Another thought is that we could be seeing spectral leakage caused by the Hanning window ont he SR785. 

Data and measurement configuration notes are located at: /ligo/svncommon/CalSVN/aligocalibration/trunk/Common/Electronics/H1/DCPDTransimpedanceAmp/OMCA/S2100832_SN02/20220713/Data/

Edit: fixed y-axis unit labels after Peter Frischel pointed out major issues with what I had there initially. Thanks Peter!