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40m Log |
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Wed Jan 25 15:41:29 2017, Lydia, Update, IMC, 29.5 MHz modulation depth measurement plan
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Wed Jan 25 17:30:03 2017, Koji, Update, IMC, 29.5 MHz modulation depth measurement plan
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Wed Jan 25 19:39:07 2017, gautam , Update, IMC, 29.5 MHz modulation depth measurement plan
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Fri Jan 27 21:25:11 2017, Lydia, Update, IMC, 29.5 MHz modulation depth
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Sat Jan 28 01:25:51 2017, gautam, Update, IMC, 29.5 MHz modulation depth 
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Mon Jan 30 19:07:48 2017, gautam, Update, IMC, RF AM stabilization box pulled out
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Tue Jan 31 01:07:20 2017, Lydia, Update, IMC, RF AM stabilization box pulled out
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Tue Jan 31 13:46:34 2017, rana, Update, IMC, RF AM stabilization box pulled out
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Tue Jan 31 14:17:48 2017, gautam, Update, IMC, RF AM stabilization box pulled out
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Tue Jan 31 22:07:13 2017, gautam, Update, IMC, RF AM stabilization box revamp
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Tue Jan 31 22:28:39 2017, Lydia, Update, IMC, RF AM stabilization box pulled out
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Wed Feb 1 11:51:19 2017, Koji, Update, IMC, RF AM stabilization box pulled out
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Wed Feb 1 16:45:56 2017, Lydia, Update, IMC, RF AM stabilizer box Modification Plan
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Wed Feb 1 20:49:34 2017, rana, Update, IMC, RF AM stabilizer box Modification Plan
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Wed Feb 1 23:13:30 2017, Lydia, Update, IMC, RF AM stabilizer box Modification Plan
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Sun Feb 5 21:56:50 2017, Lydia, Update, IMC, 29.5 MHz stabilizer box replacement
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Tue Feb 7 12:01:10 2017, Lydia, Update, IMC, 29.5 MHz stabilizer box replacement
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Tue Feb 7 17:00:55 2017, Lydia, Update, IMC, 29.5 MHz stabilizer box replacement
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Fri Feb 10 02:14:10 2017, gautam, Update, IMC, 29.5 MHz stabilizer box replacement
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Fri Feb 10 11:41:43 2017, Lydia, Update, IMC, 29.5 MHz stabilizer box replacement
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Fri Feb 10 13:24:28 2017, rana, Update, IMC, 29.5 MHz stabilizer box replacement
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Fri Feb 10 18:21:21 2017, gautam, Update, IMC, IMC Demod board
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Fri Feb 10 19:32:15 2017, Koji, Update, IMC, IMC Demod board
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Sun Feb 12 01:16:57 2017, gautam, Update, IMC, IMC length loop - summary of changes    
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Mon Feb 13 11:55:14 2017, rana, Update, IMC, IMC length loop - summary of changes
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Mon Feb 13 13:34:44 2017, gautam, Update, IMC, IMC length loop - bad SMA cable replaced
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Mon Feb 13 19:44:55 2017, Lydia, Update, IMC, Front panel for 29.5 MHz amplifier box
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Wed Mar 1 21:15:40 2017, Lydia, Update, IMC, Front panel for 29.5 MHz amplifier box
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Wed Mar 1 23:56:09 2017, gautam, Update, IMC, Front panel for 29.5 MHz amplifier box
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Thu Mar 2 20:32:18 2017, Lydia, Update, IMC, Front panel for 29.5 MHz amplifier box
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Wed Feb 15 23:54:13 2017, gautam, Update, IMC, IMC saga continues... 
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Fri Feb 17 20:10:18 2017, gautam, Update, IMC, WFS servos turned back on
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Sat Feb 18 14:09:06 2017, rana, Update, IMC, WFS servos turned back on
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Sat Feb 18 21:50:48 2017, gautam, Update, IMC, WFS servos turned back on
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Sun Mar 5 12:41:23 2017, gautam, Update, IMC, WFS servo-steppin  
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Message ID: 12767
Entry time: Fri Jan 27 21:25:11 2017
In reply to: 12758
Reply to this: 12768
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Author: |
Lydia |
Type: |
Update |
Category: |
IMC |
Subject: |
29.5 MHz modulation depth |
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[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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