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Entry  Tue Sep 15 15:10:48 2015, gautam, ericq, rana, Summary, LSC, PRFPMI lock & various to-do's powerSpec0915.pdf
    Reply  Tue Sep 15 18:35:21 2015, ericq, Summary, LSC, some further notes 
       Reply  Tue Sep 15 20:44:13 2015, gautam, Summary, LSC, Checking the delay line phase shifter DS050339 IMG_20150915_193100.jpgCalibration.pdf
       Reply  Thu Sep 17 03:48:10 2015, ericq, Summary, LSC, some further notes 
          Reply  Thu Sep 17 13:06:05 2015, ericq, Summary, LSC, Low input impedance on CM board 
Message ID: 11609     Entry time: Thu Sep 17 03:48:10 2015     In reply to: 11601     Reply to this: 11611
Author: ericq 
Type: Summary 
Category: LSC 
Subject: some further notes 

Something odd is happening with the CM board. Measuring from either input to OUT1 (the "slow output") shows a nice flat response up until many 10s of kHz. 

However, when I connect my idependently confirmed 120Hz LPF to either input, the pole frequency gets moved up to ~360Hz and the DC gain falls some 10dB. This happens regardless if the input is used or not, I saw this shape at a tee on the output of the LPF when the other leg of the tee was connected to a CM board input. 

This has sabotaged my high bandwidth ALS efforts. I will investigate the board's input situation tomorrow.

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