aLIGO LHO Logbook

H1 SPI

jeffrey.kissel@LIGO.ORG - posted 12:37, Tuesday 21 July 2026 - last comment - 09:10, Thursday 23 July 2026(91157)

H1SPIH23 QPD Whitening Compensation Turned ON

J. Kissel

The QPD channels in the H1SPIH23 PD array have a z:p = 0.39:39.6 Hz whitening filter in their analog transimpedance amplifier (D1001974-v8). As such, I've installed and turned on an "antiWh" compensation filter = zpk([39.8],[0.39],1,"n") in FM2 of all the H1:SPI-H23_OL_QPD_{A,B}_SEG{1,2,3,4} banks, and accepted the turn on in the SDF system and committed the filter filter to the userapps repo rev 35564.

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jeffrey.kissel@LIGO.ORG - 09:10, Thursday 23 July 2026 (91207)

Link

Here's a screenshot of the SEG filters after the whitening is turned ON. 
The output of the SEG filters are therefore calibrated into units of ADC volts, proportional to the photocurrent and thus the power from each segment.
Eventually, we may install a [mW/V] calibration based on LHO:90105 to turn this (and mostly the SUM) into [mW], but for now, we stick with ADC [V].

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