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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: 12767     Entry time: Fri Jan 27 21:25:11 2017     In reply to: 12758     Reply to this: 12768
Author: Lydia 
Type: Update 
Category: IMC 
Subject: 29.5 MHz modulation depth  

[gautam, Lydia]

We set out to measure the 29.5 MHz power going to the EOM today but decided to start by looking at the output of the RF AM stabilizer box first. We wanted to measure the AM noise with a mixer, so we needed to know the power it was giving. We looked at the ouput that goes to the power combiner on the PSL table and found it was putting out only -2.0 dBm (~0.5 Vpp)! This was measured by taking a spectrum with the AG4395 and confirmed by looking on a scope.

To find out if this could be adjusted, we found an old MEDM screen (/opt/rtcds/caltech/c1/medm/c1lsc/master/C1LSC_RFADJUST.adl) and moved the 29.5 MHz EOM Mod Index Adjust slider while measuring the voltage coming in to the MOD CONTOL connection on the front of the AM stabilizer box. Moving the slider from 0 to 10 changes the input voltage linearly from -10 V to 10 V measured with a DMM at the cross-connects as we couldn't find an appropriate adapter for the LEMO cable. The 29.5 MHz modulation only appeared for slider values between 0 and 5, after which it abruptly shuts off. However, changing the slider value between 0 and 5 (Voltage from -10 to 0) does not change the amplitude of the output.

This seems like a problem; further investigation into the AM stabilizer box is neccessary. This DCC document outlines how to test the box, but we can't find a schematic. Since we don't have any mixers that can handle signals as small as -2 dBm, we gave up trying to measure the AM noise and will attempt to measure that and the reflection power from the EOM + resonant circuit once this problem has been diagnosed and fixed.

GV: After some digging, I found the schematic for the RF AM stabilization box (updated wiki and added it to the 40m document tree). According to it, there should be up to +22dBm of RF AM stabilized output to the EOM available, though we measured -2dBm yesterday, and could not vary this level by adjusting the EPICS voltage value. Neglecting losses in the cabling and the power combiner on the PSL, this translates to a paltry 0.178Vrms*0.6*8mard/Vrms ~ 0.85 mrad of modulation depth (gain at 29.5 MHz of the triple resonant circuit taken from this elog)... I think we need to pull this 1U chassis out and debug more thoroughly...

 

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