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Entry  Thu Jul 16 03:01:57 2015, ericq, Update, LSC, Old beatbox hooked back up beat_comparison.pngaLIGO_vs_beatbox.xml.zip
    Reply  Thu Jul 23 03:09:05 2015, ericq, Update, LSC, aLIGO demod board lives! beatbox_vs_aLIGO.png
       Reply  Thu Jul 30 14:42:03 2015, ericq, Update, LSC, aLIGO demod board lives! partialALSbudget.pngdemodDriveLevels.pngALScoherences.pngpartialALSbudget.zip
          Reply  Thu Jul 30 15:58:00 2015, ericq, Update, LSC, Beat note Alignment fluctuation effects measured RF_RIN.pngRF_RINspec.pngRFampCoh.xml.zip
             Reply  Tue Aug 4 03:02:30 2015, ericq, Update, LSC, Beat note Alignment fluctuation effects measured coherences.pnglinX.png
                Reply  Tue Aug 11 02:40:29 2015, ericq, Update, LSC, 50m delay lines - Rough calibrations 
Message ID: 11438     Entry time: Thu Jul 23 03:09:05 2015     In reply to: 11419     Reply to this: 11468
Author: ericq 
Type: Update 
Category: LSC 
Subject: aLIGO demod board lives! 

I'm a little mystified. Peeking inside the aLIGO demod board, I saw that the reason that two of the channels weren't working was that their power connectors weren't plugged in, so no real mystery there. 

I hooked up the board at the electronics bench, and found the noise to be completely well behaved, in contrast to the measurements I made when it was in the LSC rack. I've taken it back out to the LSC rack, and given it the X beatnote, and it seems to be performing pretty well. 


I switched between the aLIGO demod board and beatbox during the same lock / beat. The LSC board performs margnially better from 3-100 Hz. The high frequency noise comes from the green PDH loop (coherence is near one above a few hundred Hz), so we don't expect any difference there. 

To me, the beatbox noise looks like there is a broad feature that is roughly the same level as the real cavity motion in the 10-100 Hz range. So, I think we should use the aLIGO board afterall, presuming the noise doesn't shoot back up when I remount it in the rack...


The ALS noise is getting low enough where our normal approach of measuring ALS sensing noise by simply taking the PSD of the signal when the arm is PDH locked is not quite valid anymore, as it is sensing the real cavity fluctuations. Doing a frequency domain coherent subtration of the PSDs suggests a sensing noise RMS of ~150Hz for ALSX. 

When the X arm is locked on ALS, POX sees about 250Hz RMS out of loop noise, which isn't the greatest; however, I used to be happy with 500Hz. By eye, sweeping through IR resonance is smoother. The real test is to get the Y arm ALS running, and swing it through PRFPMI resonance...


Fair warning, the LSC rack area is not so tidy right now, the demod board is resting on a stool (but not in the way of walking down the arm). I'll clean this up tomorrow. 

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