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Entry  Mon Dec 2 00:27:20 2019, gautam, Update, ALS, Green ALS resurrection ALSnoiseComparison.pdfALS_TR_RIN.pdfGreemAM.pdf
    Reply  Mon Dec 2 18:20:29 2019, gautam, Update, ALS, EY uPDH post mixer LPF EY_uPDH_LPF.pdfEY_uPDH_OLTF.pdf
       Reply  Mon Dec 2 20:18:18 2019, rana, Update, ALS, EY uPDH post mixer LPF 
          Reply  Tue Dec 3 18:15:42 2019, gautam, Update, ALS, EY uPDH post mixer LPF 
             Reply  Tue Dec 3 21:28:24 2019, gautam, Update, ALS, EY uPDH post mixer LPF uPDH.pdf
       Reply  Tue Dec 3 00:10:15 2019, Koji, Update, ALS, EY uPDH post mixer LPF 
          Reply  Tue Dec 3 00:51:25 2019, gautam, Update, ALS, EY uPDH post mixer LPF 
Message ID: 15059     Entry time: Mon Dec 2 18:20:29 2019     In reply to: 15058     Reply to this: 15060   15063
Author: gautam 
Type: Update 
Category: ALS 
Subject: EY uPDH post mixer LPF 

As part of characterization, I wanted to calibrate the EY uPDH error point monitor into units of Hz. So I thought I'd measure the PDH horn-to-horn voltage with the cable to the laser PZT disconnected. However, I saw no clean PDH fringe while monitoring the signal after the LPF that is immediately downstream of the mixer IF output. I then decided to measure the low pass filter OLTF, and found that it seems to have some complex poles (f0~57kHz, Q~5), that amplify the signal by ~x6 relative to the DC level before beginning to roll-off (see Attachment #1). Is this the desired filter shape? Can't find anything in the elog/wiki about such a filter shape being implemented...

The actual OLTF looks alright to me though, see Attachment #2.

Attachment 1: EY_uPDH_LPF.pdf  90 kB  | Hide | Hide all
EY_uPDH_LPF.pdf
Attachment 2: EY_uPDH_OLTF.pdf  135 kB  | Hide | Hide all
EY_uPDH_OLTF.pdf
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