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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: 12824
Entry time: Mon Feb 13 13:34:44 2017
In reply to: 12822
Reply to this: 12827
12833
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Author: |
gautam |
Type: |
Update |
Category: |
IMC |
Subject: |
IMC length loop - bad SMA cable replaced |
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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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