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40m Log |
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Thu Jan 4 12:46:27 2018, gautam, Update, ALS, Fiber ALS assay 
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Thu Jan 11 14:22:40 2018, gautam, Update, ALS, Fiber ALS assay
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Thu Jan 11 20:51:20 2018, gautam, Update, ALS, Fiber ALS assay
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Tue Jan 16 21:50:53 2018, gautam, Update, ALS, Fiber ALS assay
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Thu Jan 18 00:35:00 2018, gautam, Update, ALS, Fiber ALS assay 
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Fri Jan 19 11:34:21 2018, gautam, Update, ALS, Fiber ALS assay
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Fri Jan 19 23:04:11 2018, gautam, Update, ALS, Fiber ALS assay
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Wed Jan 24 00:33:31 2018, gautam, Update, ALS, Fiber ALS assay
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Wed Jan 24 10:45:14 2018, gautam, Update, ALS, Fiber ALS assay
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Thu Jan 25 23:59:14 2018, gautam, Update, ALS, Fiber ALS assay
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Fri Jan 26 20:03:09 2018, gautam, Update, ALS, Fiber ALS assay
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Wed Jan 31 15:45:22 2018, gautam, Update, ALS, Fiber ALS assay
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Wed Jan 31 16:29:42 2018, gautam, Update, ALS, Modulation depths 
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Wed Jan 31 16:33:53 2018, gautam, Update, ALS, ALS electronics at LSC rack
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Wed Jan 31 22:32:11 2018, gautam, Update, ALS, ALS signal chain + power budget 
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Thu Feb 1 01:24:56 2018, gautam, Update, ALS, D0902745 revamp underway
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Fri Feb 2 00:26:34 2018, gautam, Update, ALS, D0902745 revamp underway
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Fri Feb 2 13:16:55 2018, gautam, Update, ALS, ALS signals whitening switching 
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Mon Feb 5 14:11:01 2018, gautam, Update, ALS, Huge harmonics in ALS channels 
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Mon Feb 5 22:57:28 2018, gautam, Update, ALS, Huge harmonics in ALS channels
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Tue Feb 6 11:13:26 2018, gautam, Update, ALS, Possible source of ground loop identified
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Tue Feb 6 22:55:51 2018, gautam, Update, ALS, Possible source of ground loop identified
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Thu Feb 8 00:33:20 2018, gautam, Update, ALS, D990694 characterization / THD measurement plan
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Thu Feb 8 01:27:16 2018, Koji, Update, ALS, D990694 characterization / THD measurement plan
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Fri Feb 9 13:37:44 2018, gautam, Update, ALS, THD measurement trial
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Thu Feb 8 12:00:09 2018, gautam, Update, ALS, D990694 is NOT differential receiving
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Thu Feb 8 13:13:14 2018, gautam, Update, ALS, D990694 pulled out  
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Thu Feb 8 18:10:36 2018, gautam, Update, ALS, D990694 pulled out
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Wed Feb 7 15:51:15 2018, gautam, Update, ALS, D0902745 revamp complete
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Fri Feb 16 01:34:40 2018, gautam, Update, ALS, D0902745 in-situ testing 
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Tue Feb 20 23:08:27 2018, gautam, Update, ALS, D0902745 in-situ testing
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Thu Feb 22 00:09:11 2018, gautam, Update, ALS, D0902745 in-situ testing  
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Sun Feb 25 00:03:12 2018, gautam, Update, ALS, Daughter board prototyping    
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Mon Feb 26 20:55:56 2018, rana, Update, ALS, Daughter board prototyping
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Tue Feb 27 21:10:45 2018, gautam, Update, ALS, Daughter board testing  
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Wed Feb 28 19:13:25 2018, gautam, Update, ALS, ADC test for differential receiving in c1lsc
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Fri Mar 2 01:45:06 2018, gautam, Update, ALS, new look ALS electronics
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Mon Mar 5 17:27:34 2018, gautam, Update, ALS, new look ALS electronics - characterization
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Thu Mar 8 00:40:25 2018, gautam, Update, ALS, new look ALS electronics - characterization
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Thu Mar 8 19:38:37 2018, gautam, Update, ALS, digital unwhitening of daughter board
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Thu Mar 8 23:50:27 2018, gautam, Update, ALS, First look at new ALS electronics
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Fri Mar 9 01:07:01 2018, gautam, Update, ALS, First look at new ALS electronics
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Mon Mar 12 22:08:31 2018, gautam, Update, ALS, Noisy POX
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Mon Mar 12 23:57:31 2018, gautam, Update, ALS, Noisy POX 
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Mon Mar 19 15:02:29 2018, gautam, Update, ALS, Noisy MC sensing
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Thu Feb 1 15:31:12 2018, gautam, Update, ALS, ALS signal chain + power budget
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Wed Feb 7 10:16:26 2018, gautam, Update, ALS, ALS signal chain + power budget
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Thu Jan 25 13:18:41 2018, gautam, Update, ALS, Fiber ALS assay
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Message ID: 13688
Entry time: Mon Mar 19 15:02:29 2018
In reply to: 13680
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Author: |
gautam |
Type: |
Update |
Category: |
ALS |
Subject: |
Noisy MC sensing |
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The working hypothesis, since the excess noise in single arm locks is coherent between both arms, the excess sensing noise is frequency noise in the IMC locking loop (sensing because it doesn't show up in MC_F). I've started investigating the IMC sensing chain, starting with the power levels of the RF modulation source. Recall that we had changed the way the 29.5MHz signal was sent to the EOM and demod electronics in 2017. With the handheld RF power meter, I measured 13.2dBm coming out of the RF distribution box (this is routed straight from the Wenzel oscillator). This is amplified to 26dBm by an RF amplifier (ZHL-2-S) and sent to the EOM, with a coupled 16dBm part sent to a splitter that supplies the LO signal to the demod board and also the WFS boards. Lydia made a summary of expected RF power levels here, and I too seem to have labelled the "nominal" LO level to the MC_REFL demod board as +5dBm. But I measured 2.7dBm with the RF power meter. But looking closely at the schematic of the splitting circuitry, I think for a (measured) 16.7dBm input to it, we should in fact expect around 3dBm of output signal. So I don't know why I labelled the "nominal" signal level as 5dBm.
Bottom line: we are driving a level 17 mixer with more like +14dBm (a number inferred from this marked up schematic) of LO, which while isn't great, is unlikely to explain the excess noise I think (the conversion loss just degrades by ~1dB). So I will proceed to check further downstream in the signal chain. |