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Entry  Thu Jan 4 12:46:27 2018, gautam, Update, ALS, Fiber ALS assay FiberALS.pdfFiberALS.svg.zip
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          Reply  Tue Jan 16 21:50:53 2018, gautam, Update, ALS, Fiber ALS assay 
             Reply  Thu Jan 18 00:35:00 2018, gautam, Update, ALS, Fiber ALS assay IR_ALS_20180118.pdfC2B4C1DD-6528-4067-9C13-6BD248629AD6.MOV
                Reply  Fri Jan 19 11:34:21 2018, gautam, Update, ALS, Fiber ALS assay IR_ALS_20180119.pdf
                   Reply  Fri Jan 19 23:04:11 2018, gautam, Update, ALS, Fiber ALS assay 
                      Reply  Wed Jan 24 00:33:31 2018, gautam, Update, ALS, Fiber ALS assay IMG_6866.JPG
                         Reply  Wed Jan 24 10:45:14 2018, gautam, Update, ALS, Fiber ALS assay 
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                               Reply  Wed Jan 31 15:45:22 2018, gautam, Update, ALS, Fiber ALS assay IMG_6875.JPG
                                  Reply  Wed Jan 31 16:29:42 2018, gautam, Update, ALS, Modulation depths PMCmodDepth.pdfXPDH.pdf
                                  Reply  Wed Jan 31 16:33:53 2018, gautam, Update, ALS, ALS electronics at LSC rack 
                                     Reply  Wed Jan 31 22:32:11 2018, gautam, Update, ALS, ALS signal chain + power budget FiberALS_PowerBudget.pdfpreampProposed.pdf
                                        Reply  Thu Feb 1 01:24:56 2018, gautam, Update, ALS, D0902745 revamp underway PSLinterlock.png
                                           Reply  Fri Feb 2 00:26:34 2018, gautam, Update, ALS, D0902745 revamp underway 
                                              Reply  Fri Feb 2 13:16:55 2018, gautam, Update, ALS, ALS signals whitening switching ALS_whitening_switching.pdfALS_whitening_switching_works.pdf
                                                 Reply  Mon Feb 5 14:11:01 2018, gautam, Update, ALS, Huge harmonics in ALS channels ALSpowerlineHarmonics.pdf2A1B3AC4-4059-416A-AD88-8AB0431D7A55.jpeg
                                                    Reply  Mon Feb 5 22:57:28 2018, gautam, Update, ALS, Huge harmonics in ALS channels 
                                                       Reply  Tue Feb 6 11:13:26 2018, gautam, Update, ALS, Possible source of ground loop identified A68AF89C-E8A9-416D-BBD2-A1AD0A51E0B5.jpeg
                                                          Reply  Tue Feb 6 22:55:51 2018, gautam, Update, ALS, Possible source of ground loop identified 
                                                       Reply  Thu Feb 8 00:33:20 2018, gautam, Update, ALS, D990694 characterization / THD measurement plan D990694THD_trial.pdf
                                                          Reply  Thu Feb 8 01:27:16 2018, Koji, Update, ALS, D990694 characterization / THD measurement plan 
                                                          Reply  Fri Feb 9 13:37:44 2018, gautam, Update, ALS, THD measurement trial THD_trial.pdf
                                                       Reply  Thu Feb 8 12:00:09 2018, gautam, Update, ALS, D990694 is NOT differential receiving 
                                                          Reply  Thu Feb 8 13:13:14 2018, gautam, Update, ALS, D990694 pulled out IMG_5131.JPGIMG_5133.JPGD990694-B_cuttingPlan.pdf
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                                              Reply  Wed Feb 7 15:51:15 2018, gautam, Update, ALS, D0902745 revamp complete 6613CD37-5014-44AE-B1FE-6F6A8137DF62.jpeg
                                                 Reply  Fri Feb 16 01:34:40 2018, gautam, Update, ALS, D0902745 in-situ testing BeatMouthX_20180216.pdfIMG_5134.JPG
                                                    Reply  Tue Feb 20 23:08:27 2018, gautam, Update, ALS, D0902745 in-situ testing BeatMouthX_20180220_diffOut.pdf
                                                       Reply  Thu Feb 22 00:09:11 2018, gautam, Update, ALS, D0902745 in-situ testing daughterBoard_TF.pdfdaughterBoard_noise.pdfIMG_6906.JPG
                                                          Reply  Sun Feb 25 00:03:12 2018, gautam, Update, ALS, Daughter board prototyping schematic.pdfdaughterBoard_TF.pdfdaughterBoard_noise.pdfTEK00000.PNGdaughterBoard_noise.pdf
                                                             Reply  Mon Feb 26 20:55:56 2018, rana, Update, ALS, Daughter board prototyping 
                                                                Reply  Tue Feb 27 21:10:45 2018, gautam, Update, ALS, Daughter board testing IMG_6912.JPGIMG_6913.JPGIMG_6914.JPG
                                                                   Reply  Wed Feb 28 19:13:25 2018, gautam, Update, ALS, ADC test for differential receiving in c1lsc c1lsc_ADCtest.png
                                                                   Reply  Fri Mar 2 01:45:06 2018, gautam, Update, ALS, new look ALS electronics IMG_6916.JPG
                                                                      Reply  Mon Mar 5 17:27:34 2018, gautam, Update, ALS, new look ALS electronics - characterization BeatMouthX_20180305_diffOut.pdf
                                                                         Reply  Thu Mar 8 00:40:25 2018, gautam, Update, ALS, new look ALS electronics - characterization BeatMouthX_20180305_diffOut.pdf
                                                                            Reply  Thu Mar 8 19:38:37 2018, gautam, Update, ALS, digital unwhitening of daughter board TFfit.pdf
                                                                               Reply  Thu Mar 8 23:50:27 2018, gautam, Update, ALS, First look at new ALS electronics BeatMouth_OOL.pdf
                                                                                  Reply  Fri Mar 9 01:07:01 2018, gautam, Update, ALS, First look at new ALS electronics ALS_vs_POXnoise.pdf
                                                                                     Reply  Mon Mar 12 22:08:31 2018, gautam, Update, ALS, Noisy POX NoisyPOX_20180312.pdf
                                                                                        Reply  Mon Mar 12 23:57:31 2018, gautam, Update, ALS, Noisy POX NoisyPOXandPOY_20180312.pdfnoisyPOX_Jan2018.pdf
                                                                                           Reply  Mon Mar 19 15:02:29 2018, gautam, Update, ALS, Noisy MC sensing 
                                        Reply  Thu Feb 1 15:31:12 2018, gautam, Update, ALS, ALS signal chain + power budget 
                                        Reply  Wed Feb 7 10:16:26 2018, gautam, Update, ALS, ALS signal chain + power budget 
                      Reply  Thu Jan 25 13:18:41 2018, gautam, Update, ALS, Fiber ALS assay preampProposed.pdf
Message ID: 13608     Entry time: Mon Feb 5 22:57:28 2018     In reply to: 13606     Reply to this: 13609   13621   13623
Author: gautam 
Type: Update 
Category: ALS 
Subject: Huge harmonics in ALS channels 

Did some quick additional checks to figure out what's going on here.

  1. The SOS/dewhite board for which I didn't have a DCC number is D000316. It has a single ended output.
  2. I confirmed that the origin of this noise has to do with the ground of the aforementioned D000316 - as mentioned in my previous elog, having one end of a BNC cable plugged into the whitening board D990694 and the other end terminated in 50ohms yields a clean spectrum. But making the ground of this terminator touch the ground of the SMA connector on the D000316 makes the harmonics show up.
  3. Confirmed that the problem exists when using either the SMA or the LEMO monitor output of these D000316 boards.

So either something is busted on this board (power regulating capacitor perhaps?), or we have some kind of ground loop between electronics in the same chassis (despite the D990694 being differential input receiving). Seems like further investigation is needed. Note that the D000316 just two boards over in the same Eurocrate chassis is responsible for driving our input steering mirror Tip-Tilt suspensions. I wonder if that board too is suffering from a similarly noisy ground?

Quote:
 

Am I missing something obvious here? I think it is impossible to do a THD measurement with the spectrum in this condition...

 

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