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Entry  Fri Sep 8 00:32:20 2017, awade, Summary, FSS, Schematic block diagram FSS loops CTN_FSS_south_blockdiagram.pdf
    Reply  Thu Sep 14 21:54:26 2017, awade, Summary, FSS, FSS modifications: series resistance (R1 and R2) to monitor points on servo board D040105 
       Reply  Mon Sep 18 00:46:08 2017, rana, Summary, FSS, FSS modifications: series resistance (R1 and R2) to monitor points on servo board D040105 
          Reply  Mon Sep 18 13:34:13 2017, awade, Summary, FSS, FSS modifications: series resistance (R1 and R2) to monitor points on servo board D040105 
             Reply  Tue Oct 10 00:49:34 2017, awade, Craig, Summary, FSS, Replacing U3 on north path (2010:005) FSS servo board. 20171009_220549_Ser6_ComPathTP1toTP5_09-10-2017_175407.pdffmoenfipkniealnd.png20171009_DebuggingNorthPathServoBoard.tar.gz
    Reply  Mon Oct 2 12:30:15 2017, rana, Summary, FSS, LISO & mfil 
       Reply  Wed Oct 18 11:19:15 2017, awade, Summary, FSS, Comparing south TF to LISO model TTFSS_schematics_awades_hand_notes.pdf001.pdf20171017_South_FSSTFs.tar.gz
          Reply  Wed Oct 18 15:42:59 2017, awade, Summary, FSS, Comparing south TF to LISO model 
             Reply  Mon Oct 23 15:05:44 2017, awade, Summary, FSS, Comparing south TF to LISO model Ser7_South_MainBoard_compiledTF.pdfSer5_North_MainBoard_compiledTF.pdf2017-10-20_18.04.18.jpg
                Reply  Wed Oct 25 23:15:51 2017, awade, Craig, Summary, FSS, Comparing south and north TF to LISO model South_MainBoard_EXC-30dBm_compiledTF.pdfNorth_MainBoard_EXC-30dBm_compiledTF.pdfFSS_all.tar.gz
Message ID: 1952     Entry time: Wed Oct 18 11:19:15 2017     In reply to: 1939     Reply to this: 1953
Author: awade 
Type: Summary 
Category: FSS 
Subject: Comparing south TF to LISO model 

[awade, Craig]

Yesterday Craig measured the transfer function of the south path servo board (LIGO-D040105 2010:007) at all the available test points from the input to the board. This was done with an injected signal of 0 dBm (=2*sqrt(50 Ω * 0.0001 W) = 0.45V, there is no 50 Ω loading here on input) over the range 1 kHz to 100 MHz.  The test points were probed with the hp 41800a probe. 

I've overlaid these results with expected LISO simulation; a scanned schematic with labels of stages and nodes is attached below. There is an adjustment of 3 dB made for the two port RF splitter used to spit the output from the HP4395A.  Also the knobs for common and fast gain stages were dialed to 500 out of 1000 in both cases. It appears that this gives pretty much unity gain for both AD602 variable gain chips.

There seems to be fairly good agreement in the common path.  In the PZT path model and measurement disagree below 60 kHz, getting to factors of 100 off at later stages of the loop at low frequencies. This is an open loop measurement, not sure if poor signal to noise is the issue at low frequencies here. Not clear what the discrepancy is here. At high frequencies we expect the PZT path to drop off, first stage op27 has GBW of 8 MHz and is configured as gain 8.7 so should only work up to UGF ~1MHz: the HF drop off in signal to noise makes sense, I guess. 

One big discrepancy is the the fact that the PZT path 239 kHz notch matches well at the test points, but the full test2 to PZT out BNC sees the notch shifted downwards.  This is suspicious. 

The EOM path agrees pretty well along the main path except for poll at 40 kHz. We should check again on the choice of rc components incase we missed a design change. There are no test points on the passive loop over path, we should maybe make a measurement at node 10 or 14 to see what the passive filter elements are doing.

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I had a look at mfil, looks like it achieves the same as our python scripting but requires customizations of the fil files. Now with Craig's parsing methods in pyliso we can arbitrarily modify any component  from python wilst leaving the base FSS_all.fil liso file alone. I'll eventually get around to testing/intergrating mfil against pyliso, but for now they are about the same amount of work to use: at least pyliso can imediatly be used for pretty plots.

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Data attached as zip. You can also clone current repos from https://git.ligo.org/andrew-wade/CTN_noisebudget and https://git.ligo.org/andrew-wade/ctn_labdata

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Attachment 3: 20171017_South_FSSTFs.tar.gz  1.094 MB  Uploaded Wed Oct 18 12:29:06 2017
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