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40m Log |
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Tue Oct 8 18:35:09 2019, gautam, Update, LSC, Locking prep
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Wed Oct 9 18:15:26 2019, gautam, Update, LSC, PRMI 3f locking
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Wed Oct 9 22:02:58 2019, gautam, Update, LSC, REFL55 whitening issue
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Thu Oct 10 01:12:56 2019, gautam, Update, LSC, Locking studies
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Wed Oct 16 11:42:17 2019, gautam, Update, LSC, Poor separation of PRCL/MICH in 3f signals
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Thu Oct 17 11:19:28 2019, gautam, Update, LSC, Locking activity last night 
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Tue Oct 22 00:52:27 2019, gautam, Update, LSC, Locking updates
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Tue Oct 29 01:24:45 2019, gautam, Update, LSC, More locking updates 
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Tue Oct 29 15:13:19 2019, gautam, Update, LSC, More locking updates
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Wed Oct 30 01:27:00 2019, gautam, Update, LSC, More locking updates
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Wed Oct 30 11:53:41 2019, gautam, Update, LSC, MICH loop shape tuning 
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Wed Oct 30 17:08:40 2019, gautam, Update, LSC, POP22 investigation
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Mon Nov 4 15:29:47 2019, gautam, Update, LSC, POP signal path
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Mon Nov 4 16:06:58 2019, gautam, Update, LSC, POP optical path    
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Tue Nov 5 11:52:27 2019, gautam, Update, LSC, Locking notes
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Wed Nov 6 02:08:48 2019, gautam, Update, LSC, Locking updates
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Wed Nov 6 17:05:45 2019, gautam, Update, LSC, CARM calibration  
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Wed Nov 6 17:45:34 2019, gautam, Update, LSC, ~
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Mon Nov 18 21:04:38 2019, gautam, Update, LSC, Locking - some ideas
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Wed Nov 20 01:07:18 2019, gautam, Update, LSC, Locking - progress
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Wed Nov 20 12:14:17 2019, gautam, Update, LSC, Locking - progress
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Wed Nov 20 17:20:24 2019, Yehonathan, Update, LSC, QPD Investigation
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Wed Nov 20 17:52:00 2019, gautam, Update, LSC, QPD MEDM screen update  
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Wed Nov 20 21:29:28 2019, gautam, Update, LSC, PRG ~13
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Fri Nov 22 00:54:14 2019, gautam, Update, LSC, locking notes
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Mon Nov 25 19:11:22 2019, gautam, Update, LSC, ALS noise re-look
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Wed Nov 27 23:24:01 2019, gautam, Update, LSC, No shaking but no inspiration either
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Sun Dec 1 13:38:48 2019, rana, Update, LSC, No shaking but no inspiration either
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Tue Dec 3 00:03:57 2019, gautam, Update, LSC, Green ALS also shows elevated noise with high arm buildup
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Wed Dec 4 19:54:27 2019, gautam, Update, LSC, A look to the past
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Thu Dec 5 01:54:39 2019, gautam, Update, LSC, Partial CM board path engaged
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Fri Dec 6 00:02:48 2019, gautam, Update, LSC, What is the correct way to set the 3f offsets?
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Fri Nov 15 12:08:04 2019, gautam, Update, LSC, POPDC whitening board
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Tue Oct 29 17:40:48 2019, gautam, Update, LSC, More locking updates 
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Message ID: 15009
Entry time: Mon Nov 4 15:29:47 2019
In reply to: 15001
Reply to this: 15010
15029
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Author: |
gautam |
Type: |
Update |
Category: |
LSC |
Subject: |
POP signal path |
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There are many versions of the POP22 signal path I found on the elog, e.g. this thread. But what I saw at the LSC rack was not quite in agreement with any of those. So here is the latest greatest version.
Since the 2f signals are mainly indicators of power buildups and are used for triggering various PDH loops, I don't know how critical some of these things are, but here are some remarks:
- There is no Tee + 50 ohm terminator after the minicircuits filters, whose impedance in the stopband are High-Z (I have been told but never personally verified).
- The RF amplifier used is a Minicircuits ZFL-1000-LN+. This has a gain of 20dB and 1dB compression output power spec of 3dBm. So to be safe, we want to have not more than -20dBm of signal at the input. On a 50-ohm scope (AC coupled), I saw a signal that has ~100mVpp amplitude (there is a mixture of many frequencies so this is not the Vpp of a pure sinusoid). This corresponds to -16dBm. Might be cutting it a bit close even after accounting for cable loss and insertion loss of the bias tee.
- We use a resistive power splitter to divide the power between the POP22 and POP110 paths, which automatically throws away 50% of the RF power. A better option is the ZAPD-2-252-S+.
- The Thorlabs PDA10CF photodiode (not this particular one) has been modelled to have a response that can be approximated by a complex pole pair with Q=1 at ~130 MHz. But we are also using this PD for measuring the 110 MHz PD which is a bit close to the band edge?
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