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Entry  Wed Jan 25 15:41:29 2017, Lydia, Update, IMC, 29.5 MHz modulation depth measurement plan 
    Reply  Wed Jan 25 17:30:03 2017, Koji, Update, IMC, 29.5 MHz modulation depth measurement plan 
       Reply  Wed Jan 25 19:39:07 2017, gautam , Update, IMC, 29.5 MHz modulation depth measurement plan 
          Reply  Fri Jan 27 21:25:11 2017, Lydia, Update, IMC, 29.5 MHz modulation depth  
             Reply  Sat Jan 28 01:25:51 2017, gautam, Update, IMC, 29.5 MHz modulation depth  IMC_mod.pdfLockMCNew.png
                Reply  Mon Jan 30 19:07:48 2017, gautam, Update, IMC, RF AM stabilization box pulled out 
                   Reply  Tue Jan 31 01:07:20 2017, Lydia, Update, IMC, RF AM stabilization box pulled out AM_stablilizer_annotation.pdf
                      Reply  Tue Jan 31 13:46:34 2017, rana, Update, IMC, RF AM stabilization box pulled out 
                         Reply  Tue Jan 31 14:17:48 2017, gautam, Update, IMC, RF AM stabilization box pulled out 
                            Reply  Tue Jan 31 22:07:13 2017, gautam, Update, IMC, RF AM stabilization box revamp 
                            Reply  Tue Jan 31 22:28:39 2017, Lydia, Update, IMC, RF AM stabilization box pulled out AM_noise.pdf
                               Reply  Wed Feb 1 11:51:19 2017, Koji, Update, IMC, RF AM stabilization box pulled out 
                                  Reply  Wed Feb 1 16:45:56 2017, Lydia, Update, IMC, RF AM stabilizer box Modification Plan RF_AM_stabilizer_modification.pdf
                                     Reply  Wed Feb 1 20:49:34 2017, rana, Update, IMC, RF AM stabilizer box Modification Plan 
                                        Reply  Wed Feb 1 23:13:30 2017, Lydia, Update, IMC, RF AM stabilizer box Modification Plan 
                                           Reply  Sun Feb 5 21:56:50 2017, Lydia, Update, IMC, 29.5 MHz stabilizer box replacement 
                                              Reply  Tue Feb 7 12:01:10 2017, Lydia, Update, IMC, 29.5 MHz stabilizer box replacement RF_amp.pdf
                                                 Reply  Tue Feb 7 17:00:55 2017, Lydia, Update, IMC, 29.5 MHz stabilizer box replacement 
                                                    Reply  Fri Feb 10 02:14:10 2017, gautam, Update, IMC, 29.5 MHz stabilizer box replacement 
                                                       Reply  Fri Feb 10 11:41:43 2017, Lydia, Update, IMC, 29.5 MHz stabilizer box replacement 
                                                          Reply  Fri Feb 10 13:24:28 2017, rana, Update, IMC, 29.5 MHz stabilizer box replacement 
                                                             Reply  Fri Feb 10 18:21:21 2017, gautam, Update, IMC, IMC Demod board 
                                                                Reply  Fri Feb 10 19:32:15 2017, Koji, Update, IMC, IMC Demod board 
                                                                   Reply  Sun Feb 12 01:16:57 2017, gautam, Update, IMC, IMC length loop - summary of changes DemodBoardOrthogonality.pdfIMC_PDH.pdfTEK00001.PNGIMC_OLTF.pdfFSS_gain_comparison.pdf
                                                                      Reply  Mon Feb 13 11:55:14 2017, rana, Update, IMC, IMC length loop - summary of changes 
                                                                      Reply  Mon Feb 13 13:34:44 2017, gautam, Update, IMC, IMC length loop - bad SMA cable replaced noisy_PMC_REFL.png
                                                                         Reply  Mon Feb 13 19:44:55 2017, Lydia, Update, IMC, Front panel for 29.5 MHz amplifier box rfAmp.pdf
                                                                            Reply  Wed Mar 1 21:15:40 2017, Lydia, Update, IMC, Front panel for 29.5 MHz amplifier box RF_amp_(1).pdf
                                                                               Reply  Wed Mar 1 23:56:09 2017, gautam, Update, IMC, Front panel for 29.5 MHz amplifier box 
                                                                                  Reply  Thu Mar 2 20:32:18 2017, Lydia, Update, IMC, Front panel for 29.5 MHz amplifier box 
                                                                         Reply  Wed Feb 15 23:54:13 2017, gautam, Update, IMC, IMC saga continues... MCstrip.pngIMCweirdness.png
                                                                            Reply  Fri Feb 17 20:10:18 2017, gautam, Update, IMC, WFS servos turned back on 
                                                                               Reply  Sat Feb 18 14:09:06 2017, rana, Update, IMC, WFS servos turned back on 
                                                                                  Reply  Sat Feb 18 21:50:48 2017, gautam, Update, IMC, WFS servos turned back on WFS_error_noise.pdf
                                                                                     Reply  Sun Mar 5 12:41:23 2017, gautam, Update, IMC, WFS servo-steppin WFS_stepping.pngWFS_comparisons.pdfWFSdigitalAA.pdf
Message ID: 12824     Entry time: Mon Feb 13 13:34:44 2017     In reply to: 12822     Reply to this: 12827   12833
Author: gautam 
Type: Update 
Category: IMC 
Subject: IMC length loop - bad SMA cable replaced 

I was a little confused why the In1 Gain had to be as high as +10dB - before the changes to the RF chain, we were using +27dB, and we expect the changes made to have increased the modulation depth by a factor of ~25, so I would have expected the new In1 Gain to be more like 0dB.

While walking by the PSL table, I chanced upon the scope monitoring PMC transmission, and I noticed that the RIN was unusually high (see the scope screenshot below). We don't have the projector on the wall anymore, but it doesn't look like this has shown up in the SLOW monitor channel anyways. Disabling the MC autolocker / closing the PSL shutter had no effect. I walked over to the amplifier setup in 1X2, and noticed that the SMA cable connecting the output of the amplifier to the EOM drive was flaky. By touching the cable a little, I noticed that the trace on the scope appeared normal again. Turning off the 29.5MHz modulation source completely returned the trace to normal.

 

So I just made a new cable of similar length (with the double heat shrink prescription). The PMC transmission looks normal on the scope now. I also re-aligned the PMC for good measure. So presumably, we were not driving the EOM with the full +27dBm of available power. Now, the In1 Gain on the MC servo board is set to +2dB, and I changed the nominal FSS FAST gain to +18dB. The IMC OLTF now has a UGF of ~165kHz, though the phase margin is only ~27 degrees.. 

Quote:

MC Servo Board

  • After some tweaking, I settled on +10dB "In1 Gain". Here, locking was much more reliable, and I was able to smoothly turn on the Super Boosts. The attached OLTF measurement suggests a UGF of ~118kHz and phase margin of a little more than 30 degrees. There is room for optimization here, since we have had UGFs closer to 200kHz in the recent past. 
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