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ID Date Author Type Category Subjectup
  6628   Wed May 9 01:14:44 2012 JenneUpdateCDSNo signals for DTT from SUS


UPDATE UPDATE:  Genius me just checked the FE status screen again.  It was fine ~an hour ago when I sat down to start interferometer-izing for the night, but now the SUS model and both of the ETMY computer models are having problems connecting to the fb.  *sigh* 

 Restarted SUS model - it's now happy. 

c1iscey is much less happy - neither the IOP nor the scy model are willing to talk to fb.  I might give up on them after another few minutes, and wait for some daytime support, since I wanted to do DRMI stuff tonight.

Yeah, giving up now on c1iscey (Jamie....ideas are welcome).  I can lock just fine, including the Yarm, I just can't save data or see data about ETMY specifically.  But I can see LSC data, so I can lock, and I can now take spectra of corner optics.

  6630   Wed May 9 08:21:42 2012 JamieUpdateCDSNo signals for DTT from SUS


 c1iscey is much less happy - neither the IOP nor the scy model are willing to talk to fb.  I might give up on them after another few minutes, and wait for some daytime support, since I wanted to do DRMI stuff tonight.

Yeah, giving up now on c1iscey (Jamie....ideas are welcome).  I can lock just fine, including the Yarm, I just can't save data or see data about ETMY specifically.  But I can see LSC data, so I can lock, and I can now take spectra of corner optics.

 This is the mx_stream issue reported previously.  The symptom is that all models on a single front end loose contact with the frame builder, as opposed to *all* models on all front end loosing contact with the frame builder.  That indicates that the problem is a common fb communication issue on the single front end, and that's all handled with mx_stream.

ssh'ing into c1iscey and running "sudo /etc/init.d/mx_stream restart" fixed the problem.

  3535   Tue Sep 7 15:57:07 2010 AlbertoConfigurationComputersNodus connection not working. Fixed

[Joe, Alberto]

The Nodus connection to the Martian network stopped working after someone switched cables on the Netgear router. Apparently that router doesn't like to have the 23 and 24 ports connected at the same time.

Joe fixed the connection just freeing either the 23 or the 24 port.

  463   Thu May 1 12:46:02 2008 josephbConfigurationComputersNodus gateway is up
The computer Nodus is now acting as a gateway machine between the GC network and the martian network in the 40m. It has the same passwords as the rana gateway machine.

Its name on the GC side is nodus (ip: and on the martian side is nodus113 (ip: Will need to update the hosts file on the control room machines so you can just use the name nodus113 rather than the full ip.

Software is still being added to the computer, and it will remain in parallel with the rana gateway machine until everything has been working properly for a week or so.
  13775   Fri Apr 20 16:22:32 2018 gautamUpdateGeneralNodus hard-rebooted

Aidan called saying nodus was down at ~345pm. I was able to access it at ~330pm. I couldn't ssh in from my machine or the control room ones. So I went to 1X7 and plugged in a monitor to nodus. It was totally unresponsive. Since the machine wasn't responding to ping either, I decided to hard-reboot it. Machine seemed to come back up smoothly. I had trouble getting the elog started - it wasn't clear to me that the web ports were closed by default, so even though the startELOGD.sh script was running fine, the 8080 port wasn't open to the outside world. Anyways, once I figured this out, I was able to start the elog. DokuWiki also seems to be up and running now... 

  473   Fri May 9 10:15:36 2008 josephbUpdateComputersNodus has moved
Steve and myself moved Nodus from under the table in the control room, to just above the Rana computer in the control room rack.
  10759   Fri Dec 5 15:41:45 2014 JenneUpdateComputer Scripts / ProgramsNodus on fast GC network

Apparently, some time ago Larry Wallace installed a new, fast ethernet switch in the old nodus rack. Q and I have just now moved nodus' GC ethernet cable over to the new switch.  Dan Kozak is going to use this faster connection to make the data flow over to the cluster not so lag-y.

  1887   Tue Aug 11 23:17:21 2009 ranaSummaryComputersNodus rebooted / SVN down

Looks like someone rebooted nodus at ~3 PM today but did not elog it. Also the SVN is not running. Why?

  1890   Wed Aug 12 10:35:17 2009 jenneSummaryComputersNodus rebooted / SVN down


Looks like someone rebooted nodus at ~3 PM today but did not elog it. Also the SVN is not running. Why?

 The Nodus business was me....my bad.  Nodus and the elog were both having a bad day (we couldn't ssh into nodus from op440m (which doesn't depend on the names server)), so I called Alex, and he fixed things, although I think that all he did was reboot.  I then restarted the elog per the instructions on the wiki.


  11862   Tue Dec 8 15:18:29 2015 ericqUpdateComputer Scripts / ProgramsNodus security

I've done a couple things to try and make nodus a little more secure. Some have worried that nodus may be susceptible to being drafted into a botnet, slowing down our operations. 

1. I configured the ssh server settings to disallow logins as root. Ubuntu doesn't enable the root account by default anyways, but it doesn't hurt.

2. I installed fail2ban. Function: If some IP address fails to authenticate an ssh connection 3 times, it is banned from trying to connect for 10 minutes. This is mostly for thwarting mass brute force attacks. Looking at /var/log/auth.log doesn't indicate any of this kind of thing going on in the past week, at least.

3. I set up and enabled ufw (uncomplicated firewall) to only allow incoming traffic for:

  • ssh
  • ELOG
  • Nodus apache stuff (svn, wikis, etc.)

I don't think there are any other ports we need open, but I could be wrong. Let me know if I broke something you need!

  11869   Wed Dec 9 23:16:13 2015 ranaUpdateComputer Scripts / ProgramsNodus security

NDS2 and the usual ports so that we can use optimus as a comsol server.



I don't think there are any other ports we need open, but I could be wrong. Let me know if I broke something you need!


  2595   Fri Feb 12 11:56:02 2010 josephbUpdateComputersNodus slow ssh fixed

Koji pointed out that logging into Nodus was being abnormally slow.  I tracked it down to the fact we had forgotten to update the address for the DNS server running on linux1 in the resolv.conf file on nodus.  Basically it was looking for a DNS server which didn't exit, and thus was timing out before going to the next one.  SSHing into nodus should be more responsive.

  2427   Thu Dec 17 09:30:08 2009 AlbertoHowToComputersNodus sluggish

The elog has been quite slow for the last two days. The cause is nodus, that has been slowing down the access to it.

I looked at the list of the running processes on nodus by typing the command prstat, which is the equivalent for Solaris of the Linux "top". I didn't see any particular process that might be absorbing too many resources.

I remember Rana fixing the same problem in the past but couldn't find his elog entry about that. Maybe we should just restart nodus, unless someone has some other suggestion.

  2429   Thu Dec 17 19:03:14 2009 AlbertoHowToComputersNodus sluggish


The elog has been quite slow for the last two days. The cause is nodus, that has been slowing down the access to it.

I looked at the list of the running processes on nodus by typing the command prstat, which is the equivalent for Solaris of the Linux "top". I didn't see any particular process that might be absorbing too many resources.

I remember Rana fixing the same problem in the past but couldn't find his elog entry about that. Maybe we should just restart nodus, unless someone has some other suggestion.

 Problem solved. Nodus and the elog are running fine. It's just that the elog takes some time to make a preview of complex pdf attachments, like those in Kiwamu's entry 2405.

  11162   Mon Mar 23 22:56:54 2015 ericqUpdateComputer Scripts / ProgramsNodus web things

Back when Diego and I were getting all of the web services running up on the new nodus, we inexplicably were not able to get the hosting of the public_html directory and wikis to share the same port of 30889. In ELOG 10793, we stated that public_html was hosted on a new port, 30888, though we didn't really bring much attention to that new fact. 

Unbeknowst to us at the time, this broke other links/bookmarks/sites that people had been using. Koji pointed this out to me the other day, but I have not made any sort of resolution. For now, the public_html directory, and the sites therein, have been taken offline. 

In other nodus news, Jamie has set Nodus' apache service with a certificate for SSL goodness. We want to extend this to the ELOG, which uses a built in webserver, rather than apache. 

He set up a proxy at the https address which will later host the secured elog: https://nodus.ligo.caltech.edu:8081/

When we make the switch to running the ELOG with HTTPS on by default, living on port 8081, we will set up apache to point 8080 at 8081, to preserve all of the old links. 

I.e. this change should effectively be invisible to ELOG users if we implement it right. 

  535   Mon Jun 16 18:26:01 2008 Max JonesUpdateComputer Scripts / ProgramsNoise Budget Changes
In the directory cvs/cds/caltech/NB the following changes were made:

I created temporary files in ReferenceData for the C1 by copying and renaming the corresponding H1 files.
- C1_SRD_Disp.txt
- C1IFOparams.m
- C1_NoiseParams.m

In getmultichan.m I added a C1 case.

In NoiseBudget.m I added a C1 case with modified sources array to include only DARM and Seismic

I appreciate and suggestions. Max.

  364   Fri Mar 7 17:10:01 2008 Max JonesUpdateComputersNoise Budget work
Noise budget has been moved to the svn system. A checked out copy is in the directory caltech. From now on, I will try to use the work cycle as outlined in the svn manual. Changes made today include the following:

Details of the modifications made may be found on the svn system. Please let me know if anyone has a suggestion or concern. Thank you - Max.
  16897   Tue Jun 7 18:32:46 2022 DeekshaUpdateElectronicsNoise Budgeting ADC (of redpitaya)

Made plots on i/p noise of redpitaya . Need to reconsider sampling frequency (to improve plot at lower freq)

  11880   Mon Dec 14 16:46:42 2015 ericqUpdateWienerFilteringNoise Subtraction Puzzler

Here's something to ponder.

Our online MCL feedforward uses perpendicular vertex T240 seismometer signals as input. When designing a feedforward filter, whether FIR Wiener or otherwise, we posit that the PSD of the best linear subtraction one can theoretically achieve is given by the coherence, via Psub = P(1-C). 

If we have more than one witness input, but they are completely uncorrelated, then this extends to Psub = P(1-C1)(1-C2). However, in reality, there are correlations between the witnesses, which would make this an overestimate of how much noise power can be subtracted. 

Now, I present the actual MCL situation. [According to Ignacio's ELOG (11584), the online performance is not far from this offline prediction]

Somehow, we are able to subtract much more noise at ~1Hz than the coherence would lead you to believe. One suspicion of mine is that the noise at 1Hz is quite nonstationary. Using median [C/P]SDs should help with this in principle, but the above was all done with medians, and using the mean is not much different.

Thinking back to one of the metrics that Eve and Koji were talking about this summer, (std(S)/mean(S), where S is the spectrogram of the signal) gives an answer of ~2.3 at that peak at 1.4Hz, which is definitely in the nonstationary regieme, but I don't have much intution into just how severe that value is.

So, what's the point of all this? We generally use coherence as a heuristic to judge whether we should bother attempting any noise subtraction in the first place, so I'm troubled by a circumstance in which there is much more subtraction to be had than coherence leads us to believe. I would like to come up with a way of predicting MISO subtraction results of nonstationary couplings more reliably.

  11918   Thu Jan 7 15:29:54 2016 ericqUpdateWienerFilteringNoise Subtraction Puzzler

The puzzle continues...

I found some reference for computing "multicoherence," which should properly estimate the potential MISO subtraction potential in situations where the witness channels themselves have nontrivial coherence. Specifically, I followed the derivations in LIGO-P990002. The underlying math is related to principal component analysis (PCA) or gram-schmidt orthogonalization. 

This produced the following results, wherein the Wiener subtraction is still below what the coherences predict. 

I've attached the data and code that produced this plot. 

  11933   Thu Jan 14 15:08:37 2016 ericqUpdateWienerFilteringNoise Subtraction Puzzler

The anticlimatic resolution to my subtraction confusion: Spectral leakage around 1Hz. Increasing the FFT length to 256 sec now shows that the FIR WF pretty much achieves the ideal subtraction. 

If nothing else, it's good to have worked out how MISO coherence works.

  11934   Thu Jan 14 18:41:36 2016 ranaUpdateWienerFilteringNoise Subtraction Puzzler

Just not just pedagogical !  Freq domain MISO coherence based subtraction estimation is much faster than calculating MISO WF. And since each bin is independent of each other, this gives us an estimate of how low the noise can go, whereas the Wiener filter is limited by Kramers-Kronig. We should be able to use this on the L1 DARM channel to do the noise hunting as well as estimating the subtraction efficacy of the pseudo channels that you and Rory come up with.

If you can code up a noise hunter example using DARM + a bunch of aux channels, we could implement it in the summary pages code.

  318   Thu Feb 14 17:21:53 2008 Max JonesUpdateComputersNoise budget code changes
In cvs/cds/caltech/NB/matlab/utilities/LSCmodel.m at line 146
I have hardwired in changes to struct lsc. Please see code.
  319   Fri Feb 15 10:28:44 2008 ranaUpdateComputersNoise budget code changes

In cvs/cds/caltech/NB/matlab/utilities/LSCmodel.m at line 146
I have hardwired in changes to struct lsc. Please see code.

The IFOin variable (which I admit is not documented) should refer to a file called
C1IFOparams.m in the ReferenceData directory. This does not yet exist but can be
created by merging L1IFOparams.m with our knowledge of the 40m IFO.
  15482   Wed Jul 15 17:46:05 2020 anchalSummaryALSNoise budget for ALS

I started my attempt on noise budgeting of ALS by going back to how Kiwamu did it and adding as many sources as I could find up till now. This calculation is present in ALS_Noise_Budget notebook. I intend to collect data for noise sources and all future work on ALS in the ALS repo.

The noise budget runs simulink through matlab.engine inside python and remaining calculations including the pygwinc ones are done in python. Please point out any errors that I might have done here. I still need to add noise due to DFD and the ADC after it. For the residual frequency noise of AUX laser, I have currently used an upper limit of 1kHz/rt Hz at 10 Hz free-running frequency noise of an NPRO laser.

  7904   Wed Jan 16 10:57:37 2013 taraSummaryIOONoise budget for MC

I calculated thermal noise in mode cleaner (MC) mirrors and compared it with the measured MC noise. Thermal noise won't be a significant noise source for MC.

== Motivation==

 There is an idea of using MC and a refcav to measure coating thermal noise. One laser is frequency locked to MC, another laser is locked to an 8" refcav. Then the two transmitted beams are recombined so that we can readout the frequency noise. In this case, the transmitted beam from MC is a better reference (less frequency noise) than the beam from refcav. However, we need to make sure that we understand the noise sources, for example brownian noise, thermoelastic noise in both substrates and coatings, in MC more thoroughly.


I used Rana's code for MC's technical noise sources from, svn. The same plot can be found in appendix C of his thesis. Then I added my calculation to the plot.  Jenne pointed me to 40m:2984 for the spot size and the cavity length. The spot radius on MC1 and MC3 is ~ 1.5mm, and ~3.4 mm@MC2, The round trip length is ~27m, thus the frequency fluctuation due to thermal noise is lower than that of refcav by 2-3 orders of magnitude. I calculated Brownian noise in coatings, Brownian noise in substrate, Thermoelastic noise in substrate. I assumed that the coatings are SiO2/Ta2O5, quarter stacks, coatings thickness for MC1/3 = 5um, for MC2 = 8um. The code can be found in the attachment.



Total thermal noise on MC (Brownian + Thermoelastic on substrate and coatings of MC1-MC3) is plotted in dashed red. It is already below 10^-5 Hz/rtHz at ~20 Hz. This is sufficiently low compared to other noise sources. Beat signal from CTN measurement with 8" cavities is plotted in pink, the estimated coating brownian noise is plotted in a yellow strip. They are well above the measured MC noise between 100 Hz to a few kHz. Measuring coating thermal noise on 8" refcav seems plausible with this method. We can beat the two transmitted beams from IMC and refcav and readout the beat signal to extract the displacement noise of refcav. I'll discuss this with Koji if this is a good surf project.


[the internal thermal noise in the original plotted is removed and replaced with the total thermal noise plot instead]

 note:I'm not sure about the current 40m MC configuration. The parameters used in this calculation are summarized in mcnoiseS2L1.m (in the svn page).


  7908   Wed Jan 16 19:08:51 2013 KojiSummaryIOONoise budget for MC

I missed the point.
Do you mean that we can measure the coating thermal noise of the ref cav at the 40m as the IMC is quiet enough?

  7911   Thu Jan 17 01:27:54 2013 Tara(?)SummaryIOONoise budget for MC


I missed the point.
Do you mean that we can measure the coating thermal noise of the ref cav at the 40m as the IMC is quiet enough?

 Yes, it should be. However, what I did was calculating thermal noise of MC. I'm not sure about the 40m IMC's actual noise level. The plot in the entry was taken from LLO's MC in 2003.

  6407   Tue Mar 13 19:14:40 2012 kiwamuUpdateLSCNoise estimatino in the REFL33Q as a MICH sensor

A feasibility study of the REFL33Q as a MICH sensor was coarsely performed from the point view of the noise performance.

The answer is that :

  the REFL33Q can be BARELY used as a MICH sensor in the PRMI configuration, but the noise level will be at only sub-nano meter level.

  Tonight I will try to use the REFL33Q to control the MICH DOF to see what happens.



  I neeeeeeeed a 3f signal which is sensitive enough to hold the Michelson in the PRMI configuration so that I can test the single arm + PRMI configuration.
Based on the data I got in the sensing matrix measurement (#6403) I wanted to see how noises in the REFL33Q look like.

(Noise analysis)

  I did a coarse noise analysis for the REFL33Q signal as shown in the attached plot below while making some assumptions as follows.

  •  Optical gain for MICH = 0.8  W/m (#6403)
    • In the plot below, I plotted a unsuppressed MICH motion which had been measured the other day with a different sensor. This is for a comparison.
  •  Shot noise due to DC light on the REFL33 photo diode
    •  With a power of 5.0 mW (#6355)
    • Assume that the responsivity is 0.75 A/W, this DC light creates the shot noise in the photo current at a level of 35 pA/sqrtHz.
    • Then I estimated the contribution of this shot noise in terms of the MICH displacement by calibrating the number with the optical gain and responsivity.
    • It is estimated to be at 60 pm/sqrtHz
  • Dark current
    • I assumed that the dark current is 0.52 mA. (see the wiki)
    • In the same manner as that for the shot noise, the dark current is estimated to be at 20 pm/sqrtHz in terms of the displacement
  • Whitening filter input referred noise
    • I assumed that it is flat with a level of 54 nV/sqrtHz based on a rough measurement by looking at the spectrum of the LSC input signals.
    • The contribution was estimated by applying some gain corrections from the conversion efficiency of the demod board, transimpedance gain, responsivity and the optical gain.
    • This noise is currently the limiting factor over a frequency range from DC to 1 kHz.
  • ADC noise
    • I did the same thing as that for the whitening filter noise.
    • I assumed the noise level is at 6 uV/sqrtHz and it is flat (I know this not true particularly at mHz region the noise becomes bigger by some factors)
    • Then I applied the transfer function of the whitening filter to roll off the noise above 15 Hz.


(Some thoughts)

  •   Obviously the limiting noises are that of ADC and the whitening filter.
    • These noise can be easily mitigated by installing an RF amplifier to amplify the RF signals from the REFL33Q RFPD.
    • Therefore this is not the real issue
  • The real issue is that the shot noise is already at a level of 60 pm/sqrtHz, and we can't suppress the MICH motion less than that.
    • In order to decrease it, one possibility is to increase the modulation depth. But it is already at the maximum.
    • If the REFL165 RFPD is healthy, it is supposed to give us a bigger MICH signal. But it didn't look healthy ... (#6403)
  2223   Mon Nov 9 19:09:09 2009 JenneUpdatePEMNoise floor of the Ranger Seismometer

To estimate the noise floor of the Ranger, Rana and I locked the mass on the seismometer, so there will be no (aka minimal) signal from the motion of the ground in the pickup coil.  We should be seeing primarily the noise of the readout electronics.  We also put the Ranger on top of one of the foam lids from the Seismometer Isolation Boxes to further isolate from ground motion (this didn't change the signal noticeably).  

In this plot, Green is the locked-mass-on-foam noise floor, blue is the regular spectra, with the SR560 AC coupled, and the red is the regular seismic spectra with the SR560 DC coupled.  There doesn't seem to be a noticeable difference between blue and red (the spectra were taken at different times of day, with the red taken at night, when we generally expect things to be quieter).  I'm leaving the SR560 DC coupled.  (Rana had found it earlier this afternoon GND coupled....not sure yet why).

Also, we're not sure that the green curve is true readout noise, vs. how much of it is specifically due to the fact that the mass is locked down.  Especially around a few hundred Hz, the green curve is much higher than the other 2, and at a few tens of Hz there is some weird peak action.  However, this will be okay as a first-run noise estimate for the Ranger's noise floor.

The question at hand is: Do we need to redo any of the Ranger's readout electronics (i.e. replace the SR560 with a Pomona Box circuit) to lower the noise floor, or is it okay as-is?

  2890   Thu May 6 18:43:58 2010 ranaUpdatePEMNoise floor of the Ranger Seismometer

I added a noise model of the SR560 to the LISO opamp.lib. This assumes you're using it in G=100, low-noise mode. The voltage noise is correct, but I had to guess on the current noise because I didn't measure it before. Lame.

This can be compared with the noise that we measure when locking it down...

  1090   Fri Oct 24 22:30:38 2008 Jenne,ranaUpdatePEMNoise from Guralp Seismometer
Attached is a Power Spectrum of the noise on the Vert1 channel of the Guralp seismometer. The noise is in the several hundreds of nV/rtHz up near 50Hz and higher, but is in the several microV/rtHz range at lower frequencies. Our high frequency noise is almost definitely below the noise of the ADC, but the lower frequencies, where we actually care, it's not as clear.

To Do list:
  • Measure the noise of the ADC - is the Guralp Box lower for all frequencies?
  • Use conversion factors to convert this measured noise into the minimum ground motion that we can measure. Is this at least a factor of 100 lower than our regular ground motion?

** UPDATE: This is actually the noise of the Guralp breakout box, not the Guralp itself. It is the noise measured on the output of the box
with the input shorted. The board is configured to have a gain of 20 (10 from the AD620 and 2x for differential drive). We also measured
directly at the AD620 output and all of this noise comes directly from that chip. If Jenne calculates that this noise is too high we would
have to find a replacement with a better low frequency floor (e.g. LT1012 or LT1007 depending on the Guralps source impedance).
  3038   Wed Jun 2 18:36:20 2010 valeraDAQCDSNoise generators in LSP

Alex wrote a new code to implement LSP noise generator. The code is based on 64 bit random number generator from Numerical Recipes 3rd ed ch 7.1 (p 343).

Joe made two instances in the LSP model.

The attached plot shows the spectra and coherence of two generators. The incoherence is ~1/Navg - statistically consistent with no coherence.

  5624   Thu Oct 6 05:18:20 2011 kiwamuUpdateLSCNoise in AS55 was from clipping : fixed

It turned out the noise in AS55 was due to a clipping.  After fixing the clipping the noise successfully went down.

I was going to briefly check the clipping and go ahead locking DRMI, but for some reason I couldn't stop myself from working on this issue.

Here is a plot of the noise spectra taken before and after fixing the clipping.

The configuration of this measurement is exactly the same as that I did before (#5595)


(what I did)

 + Locked power-recycled ITMY so that the AS beam is bright enough to work with.

 + Shook BS at 1 Hz in the YAW direction

 + Looked around the AP table with an IR viewer and searched for a clipping moving at 1Hz.

 + Found the first lens in the AS beam path has clipped the beam at the upper side. A tiny portion of the beam was clipped.

 + Corrected the beam height to 4 inch by steering the very first mirror.

 + Raised the height of the lens because it was about 3.5 inch or so.

 + Found the lens had a scratch (~1 mm size ) at 1 cm blow the center on the surface.

   => I tried finding a spare 2 inch lens with a long focul length, but I couldn't find it,

        So I left the lens as it is, but we should buy some 2 inch lenses just in case like this.

 + Replaced the 1 inch beam splitter by 2-inch 99% BS so that most of the light goes into the RFPD and a little bit goes into the camera.

Quote from #5595

The AS55 signal contains more noise than the REFL signals.

  710   Mon Jul 21 19:55:16 2008 rana,jenneConfigurationIOONoise in MC_F
Jenne put the MC board on extender today - its still that way but everything is probably connected (check AO).

We measured the TFs of the DAQ section for MC_F because of how everything looked wrong in the plots Jenne
put in the log earlier. Everything we measured today seemed to jive with the schematic. We also looked up
the original traveler for this board which Betsy filled in years ago: it also is in spec for the DAQ filtering.

So then I looked at the power spectrum of the output signal to the VCO. It had lots of HFC (high frequency crap).
I adjusted the parameters of the FSS (common gain, fast gain, RF phase Astonished) and lowered the MC common gain. This
produced a global minimum in that 4D parameter space.

I think that basically, the FSS gain is too low even with the common gain slider maxed. Having the fast gain up
at 19 dB like I had left it was bad - even though it minimizes the PC control signal, it produces a lot of HFC
up around 100 kHz in MC_F. After John (finally) gets around to measuring the FSS loop we can figure out how to
better tune this. The MC gain then has to be tuned so as to best minimize the HFC given the new FSS gain; there's
basically no coupling from the MC gain to the FSS loop shape so its always best to tune the FSS first. Pleased

The RF phase of the FSS was a mystery - I have no idea why it should do anything and I have never heard of this
and I don't know why I tried it today. But...changing it by ~0.6-0.7 slider units reduced the HFC by another factor
of ~3. Somebody should put this slider into units of degrees.8-)

Here's a table of the changes. Please make these the new nominals:
you asked for:   diff 2008/07/21,13:00 2008/07/22,2:44:16 utc '.*FSS.*|.*MC.*'
LIGO controls: differences, 2008 07/21 13:00:00 utc vs. 2008 07/22 02:44:16 utc
__Epics_Channel_Name______   __Description__________   __value1____     __value2____
C1:IOO-MC_REFL_GAIN                                    22.000000        19.000000
C1:IOO-MC_REFL_OFFSET                                  0.818380         0.818100
C1:PSL-FSS_MGAIN                                       10.000000        30.000000
C1:PSL-FSS_PHCON                                       2.073170         1.413170

The attached plot shows the "SERVO" TNC output of the board; this is supposed to be the same as the voltage going to the
VCO box. So its V/Hz transfer function is flat above 40 Hz. Tomorrow Jenne will post more data and remove the extender

Since I only used an SR785, I only saw noise up to 100 kHz. Its key to use an RF spectrum analyzer when checking out
the FSS and the MC systems.
  5842   Tue Nov 8 18:06:43 2011 MirkoUpdateAdaptive FilteringNoise injections to MC1-3 PIT & YAW

With fancy analysis tools approaching usability I looked some more into noise projections from PIT,YAW motion of the MC mirrors to MC length.

Injection channels are: C1:IOO-MC1-PIT_EXC. Actual injection signal is recorded in C1:IOO-MC1-PIT_OUT and similar.
Source channels for the projection are C1:IOO-WFS1_I_PIT_OUT_DQ and similar.
Response channel is C1:OAF-MCL_IN_IN1 or C1:IOO-MC_F_DQ.
MC auto-alignment was off.

1. Fixed sine injection @ 0.5Hz

Every injection lasted 4mins.

Start time DOF Amplitude [counts_pk] rough SNR in ASD BW 0.04Hz
16:09 MC1PIT 25 -
16:14 MC1YAW 40 12
16:21 MC2PIT 35 5
16:26 MC2YAW 35 5
16:34 MC3PIT 45 5
16:39 MC3YAW 45 -

2. Filtered white noise injection

Generated white noise from 0.5Hz-20Hz, then filtered that in the C1:IOO-MC1-PIT and similar filters by the following TF, (Notch 1Hz, Q=3, 40dB &  2 zeros @ 1.1Hz)


All injections lasted 4mins. I left the filters in the first filter bank but disabled them. 

Start time DOF Amp. @ 0.5Hz [counts_pk (?)]
17:01 MC1PIT 250
17:10 MC1YAW 400
17:16 MC2PIT 400
17:21 MC2YAW 400
17:26 MC3PIT 500
17:31 MC3YAW 500


  2436   Mon Dec 21 01:14:08 2009 ranaSummaryElectronicsNoise measurement of the Rai Weiss FET preamp box

 I shorted the input to the box and then put its output into the SR560 (low noise, G = 100, AC). I put the output of the SR560 into the SR785.

*** BTW, the 2nd channel of the SR785 is kind of broken. Its too noisy by a factor of 100. Needs to go back for repair once we get started in the vac.

The attached PNG shows its input-referred noise with the short.

The picture shows the inside of the box before I did anything. The TO-5 package metal can is the meaty super dual-FET that gives this thing all of its low noise power.


In the spectra on the right are two traces. The BLUE one is the noise of the box as I found it. The BLACK one is the noise after I replaced R1, R6, R7, & R10 with metal film resistors.

The offset at the output of the box with either an open or shorted input is +265 mV.

I think we probably should also replace R2, R3, & R1, but we don't have any metal film resistors lower than 100 Ohms in the kit...but hopefully Steve will read this elog and do the right thing.

  2417   Tue Dec 15 00:02:10 2009 ranaUpdatePEMNoise of the Ranger SS-1 Seismometer

I wanted to see what the noise of the Ranger seismometer should be. I used LISO and file ranger.fil (in our LISO SVN) to calculate the voltage noise referred to the input. In this model, we represent the EMF from the moving magnet in the coil as a voltage source at 'nin' which drives the coil impedance. This is the same approach that Brian Lantz uses in his noise modeling of the GS-13 (PDF is on our Ranger wiki page).

In the simulation, I used the OP27 as a placeholder for the SR560 that we use (I don't know the current noise of the SR560). To do this, I use the new 'inputnoise' feature in LISO (its in the README, but not in the manual).

You can see that we would be limited by the input current noise of the OP27. So we would do a lot better if we used an FET based readout amp like the AD743 (or equivalent) or even better using the new multi-FET readout circuit that Rich Abbott has developed. Clearly, its also silly to have a load resistance in there - I put it in because the manual says to do it, but all it does is damp the mass and reduce the size of the signal.

#  Noise sim for the Ranger SS-1 seismometer
#                            \
#                           | \            
#           n2- - - ----  - |  \          
#            |    |         | op1>-- n4 - r4 -- no
#           Rg   RL     n3- |  /     |           
#       n1 - |    |     |   | /      |                
#           Lg    |     |    /       |                        
#            |    |     | - - - R2 - -                    
#           nin  gnd   R1 
#                       |
#                      gnd

We previously measured the Ranger's self noise by locking it down.

The 1/f^3 noise that we see below 1 Hz is roughly consistent with the noise model: to get from my plot into meters you have to multiply by:

(1 + f)^2


340 * f^2

P.S. Secret PDF handshake: You can make your non-compliant applications like LISO or DTT produce a thumbnailing PDF by using Acrobat to open the file and export it as PDF/A.

In the second attachment, I have used an OPA827 (new low-noise FET input amp from TI) as the readout amplifier. This seems like a good choice - main drawback is that Digikey backordered my OPA827s by 19 weeks!

  7040   Thu Jul 26 16:08:59 2012 YaakovUpdateSTACISNoise plot update

I have a tentative noise plot for the STACIS that includes accelerometer noise, geophone noise, and platform motion with the STACIS off. (Accelerometer noise was measured for the VEL and NONE setting, which are settings on the accelerometer box which make the accelerometer signal correspond to velocity and acceleration, respectively. ) I'm focusing on sensor noise because this is the variable I am looking at changing, and knowing how the sensor noise translates into STACIS platform motion is therefore important.



The accelerometer and geophone noise I determined as described in my last eLog (http://nodus.ligo.caltech.edu:8080/40m/7027) Along the way I found out several things of importance:

1) Horizontal geophones are ONLY horizontal geophones. This is obvious in retrospect, because the springs supporting the magnet inside must be oriented based on vertical/horizontal operation.

2) The geophones in the STACIS are GS-11D (geospace), with a sensitivity of 32 V/m/s (compared to about 3.9 V/m/s for the accelerometers in VEL setting).

3) The accelerometers have different V/m/s sensitivities. I noticed the voltage output of one was consistently higher than the other, leading to very high noise estimates, but then Jenne showed me the actual calibration factors of the individual accelerometers which differed by as much as 0.4 V/m/s (a few percent difference). Taking this into account made the noise plots much more reasonable, but variations in calibration could still create some error.

The accelerometer noise agrees fairly well with the specs on the Wilcoxon page (http://www.wilcoxon.com/prodpdf/731A-P31%2098079a1.pdf). The geophone noise seems surprisingly low; it is even better than the geophone below about 4 Hz. 

To see how this noise translates into actual platform motion, I took PSDs of the STACIS while it was off, on with accelerometer feedback, and on with geophone feedback (the "off" PSD is in the above noise plot). Using this data I'm working on estimating a transfer function that shows how the sensor noise translates to motion so I can come up with a sensor noise budget.



This shows that the geophones are actually doing a better job of isolating than the accelerometers, which is not surprising if the noise plot is accurate and the geophones are actually lower noise. It must be noted, though, that the noise plot was for the horizontal geophones whereas the plot above is for the vertical axis which may have a different noise level. Also, the vertical have some extra isolation by being enclosed in a metal stack with rubber padding at its base.

The problem with the STACIS in the past was the differential motion it introduced. I think this might be because the horizontal isolation was not uniform for each chamber. This means that even what would be symmetric motion (no differential length change) would be translated to differential motion because one end is more fixed than the other. Having accelerometers or better-padded geophones (maybe like the vertical geophones) in the STACIS ought to help with this by making the horizontal isolation more consistent and thus reducing differential motion. So the key may not be the geophone noise as much as varying geophone sensitivities or variation in how well they're mounted in the STACIS. I can test this by swapping out the horizontal geophones with other spares, changing the tightness of the mount, and seeing if either of these changes the horizontal isolation significantly, since these are factors that may differ from unit to unit.

I will also compare horizontal closed loop response with geophone vs. accelerometer feedback to see if the geophones are only doing a good job in the above plot because of their extra padding (the vertical stack).

  15751   Wed Jan 6 22:47:41 2021 gautamUpdateALSNoisy ALS


I want to get back to locking the interferometer so I can test out the newly installed AS WFS. However, the ALS noise is far too high, at least the transition of arm length control from IR to ALS fails reliably with the same settings that worked so reliably previously. I worked on investigating it a bit today.


In the latter half of last year, I was focused on the air-BHD setup, so I wasn't checking in on the ALS noise as regularly. 

  1. On Aug 17, the noise was fine.
  2. But on Oct 29, the noise is bad (and it continues to remain so, to the point where I cannot lock the interferometer). 
  3. Koji and Anchal confirmed nothing was touched while they were investigating the ALS system, also on Oct 29. The spectra attached in #15650 don't make any sense to me, the noise at 100 Hz cannot be <100mHz/rtHz. So, inconclusive.

Excess noise:

All tests are done with the arm cavity length locked to the PSL frequency using POX. Then, the EX laser is locked to the arm cavity length using the AUX PDH servo. The fluctuations in the beatnote between the two lasers is what is monitored as a diagnostic. See Attachment #1. The reference traces in the top pane are from a known good time. The large excess noise between ~80-200 Hz is what I'm concerned about.

A separate issue that can improve the noise is to track down the noise in the 20-80 Hz band - probably some IMC frequency noise issue.

Noise budget:

See Attachment #2

  • I am pretty confident the electronics after the beat mouth are not to blame - I injected a 50 MHz signal from a Marconi and adjusted the signal amplitude to mimic what we get from the beat mouth. The trace labelled "DFD electronics noise" is the noise in this config.
  • The unsuppressed AUX frequency noise was measured with an SR785 (converted to freqnecy noise units knowing the PDH horn-to-horn voltage and the cavity linewidth). I didn't confirm the sensing noise level (dark noise of the AUX PDH loop), but I figure that at 100 Hz (voltage noise of ~100 uV/rtHz on the SR785), we are above the sensing noise level, and so are truly measuring the in-loop frequency noise of the stabilized AUX laser. I also confirmed that the loop UGF was ~10 kHz and phase margin was ~60 degrees, which are nominal numbers.
  • The fact that the excess noise is only in the X arm channel means the PSL frequency is not to blame.

So what could it be? The only things I can think of are (i) the beat mouth photodiode (NF1611) or (ii) excess noise in the fiber carrying the light from EX to the PSL table (but only on this fiber, and not on the EY fiber). Both seem remote to me - I'll test the former by switching the EX and EY fiber inputs to the beat mouth, but apart from this, I'm out of ideas... 

To avoid this kind of issue, we should really have scripted locks of all the basic IFO configs and record the data to summary pages or something - maybe something to do once Guardian is installed, it'd be pretty hacky to do cleanly with shell scripts.

  15752   Thu Jan 7 19:16:11 2021 gautamUpdateALSNoisy ALS

I'm also wondering why the error monitors for the X and Y loops report such wildly different spectra for the suppressed frequency noise of the AUX laser relative to the cavity length, see Attachment #1. The y-axis should be approximately Hz/rtHz. In both cases, the servo's error point monitor is connected to the DAQ system via a G=10 SR560. With the SR785, I measure for EX a nice bucket-shaped spectrum, bottoming out at ~10 uV/rtHz around 40 Hz, see Attachment #2. The SR560 should have an input-referred noise much less than this at the G=10 setting. The ADC noise level is only ~5 uV/rtHz, and indeed, the EY spectrum shows the expected shape. So what's up with the EX error mon? Tried swapping out the SR560 for a different unit, no change. And both the SR560 noise, and the ADC noise, check out when everything is checked individually. So some kind of interaction once everything is connected together, but it's only present at EX...

Today, I tried switching the EX and EY fibers going into the beat mouth, but I preserved the channel mapping after the beat mouth by switching the electrical outputs as well (the goal was to make sure that the beat photodiodes weren't the issue here, I think the electronics are already exonerated since driving the channel with a Marconi doesn't produce these noisy features). The EX spectrum remains noisy. I've switched everything back to the nominal configuration now to avoid further confusion. So it would appeat that this is real frequency noise that gets added in the EX fiber somehow. What can I do to fix this? The source of coupling isn't at the PSL table, else the EY channel would also show similar features. Visually, nothing seems wrong to me at EX either. So the problem is somehow in the cable tray along which the 40m of fiber is routed? This is already inside some nice foam/tubing setup, what can be done to improve it? Still doesn't explain why it suddenly became noisy...

  15753   Thu Jan 7 20:07:27 2021 KojiUpdateALSNoisy ALS

How about resurrecting the PSL table green beat for the X arm to see if the non-fiber setup shows the same level of the freq noise (e.g. the PDH locking became super noisy due to misalignment etc).

  15754   Thu Jan 7 21:16:22 2021 gautamUpdateALSNoisy ALS

I thought about it, but wouldn't that show up at the AUX PDH error point? Or because the loop gain is so high there we wouldn't see a small excess? I suppose there could be some clipping on the Faraday or something like that. But the GTRX level and the green REFL DC level when locked are nominal.


How about resurrecting the PSL table green beat for the X arm to see if the non-fiber setup shows the same level of the freq noise (e.g. the PDH locking became super noisy due to misalignment etc).

  15755   Thu Jan 7 23:25:19 2021 KojiUpdateALSNoisy ALS

If the sensing noise level of the end PDH degraded for some reason, it'd make the out of loop stability worse without making the end pdh error level degraded.
It's just speculation.


  15756   Fri Jan 8 20:01:11 2021 gautamUpdateALSNoisy ALS

I did this test today. The excess noise around 100 Hz doesn't show up in the green beat.

See Attachment #1. The setup was as usual:

  • X-Arm cavity length stabilized to PSL frequency using the POX locking loop.
  • EX laser frequency locked to the X-Arm cavity length using the AUX PDH loop.
  • The "BEATX" channel records frequency fluctuations in the beat sensed on the IR beat photodiode, while the "BEATY" channel records frequency fluctuations in the beat sensed on the Green beat photodiode.
  • Since the green beat frequency fluctuations are twice that of the IR beat frequency fluctuations, I scaled the former ASD by a factor of 0.5 so as to compare apples to apples.
  • At low frequencies, the green beat is noisier, but that channel doesn't show the excess noise at mid frequencies you see in the IR beat. So the AUX PDH sensing noise is not to blame I think.

So, this excess appears to truly be excess phase noise on the fiber (though I have no idea what the actual mechanicsm could be or what changed between Aug and Oct 2020 that could explain it. Maybe the HEPA?

For this work, I had to spend some time aligning the two green beams onto the beat photodiode. During this time, I shuttered the PSL, disabled feedback via the FSS servo, turned the HEPA high, and kept the EX green locked to the arm so as to have a somewhat stable beat signal I could maximize. Everything has been returned to nominal settings now (obviously, since I locked the arms to get the data).

You may ask, why do we care. In terms of RMS frequency noise, it would appear that this excess shouldn't matter. But in all my trials so far, I've been unable to transition control of the arm cavity lengths from POX/POY to ALS. I suppose we could try using the green beat, but that has excess low frequency noise (which was the whole point of the fiber coupled setup). 


How about resurrecting the PSL table green beat for the X arm to see if the non-fiber setup shows the same level of the freq noise (e.g. the PDH locking became super noisy due to misalignment etc).

  13688   Mon Mar 19 15:02:29 2018 gautamUpdateALSNoisy MC sensing

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.

  13679   Mon Mar 12 22:08:31 2018 gautamUpdateALSNoisy POX

[kevin, gautam]

we tested my noisy POX hypothesis tonight. By locking the single arm with POX, the arm length is forced to follow PSL frequency, which is itself slaved to IMC length. From Attachment #1, there is no coherence between the arm control signal and MC_F. This suggests to me that the excess noise I am seeing in the arm control signal above 30 Hz is not originating from the PSL. It also seems unlikely that at >30Hz, anything mechanical is to blame. So I am sticking with the hypothesis that something is wonky with POX. For reference, a known "normal" arm control signal spectrum looks like the red curve in this elog.


  13680   Mon Mar 12 23:57:31 2018 gautamUpdateALSNoisy POX

[kevin, gautam]

Kevin suggested I shouldn't be so lazy and test the POY spectrum as well. So we moved the timing card back to c1iscey, went through the usual dance of vertex machine reboots, and then got both single arm locks going. Attached spectrum shows that both POX and POY are noisy. I'm not sure what has changed that could cause this effect. The fact that both POX and POY appear uniformly bad, but that there is no coherence with MC_F, suggests to me that perhaps this has something to do with the work I did with Koji w.r.t. the power situation at the LSC rack. But we just checked that

  1. All the demod board front panel LED indicators are green.
  2. Marconi and all RF amplifier boxes are on (but we didn't actually measure any RF power levels yet tonight).
  3. We checked the KEPCO power supplies in the little cabinet along the Yarm, and all of them are reporting the correct voltages/currents as per Steve's (recently updated) labels.
  4. Checked the expansion chassis at the LSC rack for any red lights, there were none.

Another observation we made: note the huge bump around 70Hz in both arm control signals. We don't know what the cause of this is. But we occassionally noticed harmonics of this (i.e. 140, 210 Hz etc) appear in the control signal spectra, and they would grow with time - eventually, the X arm would lose lock (though the Y arm stayed locked).

I'm short on ideas for now so we will continue debugging tomorrow.

Unrelated to this work: Kevin reminded me that the high-pitched whine from the CRT TVs in the control room (which is apparently due to the flyback transformer) is DEAFENING. It's curious that the "chirp" to the eventual 15kHz whine is in opposite directions for the QUAD CRTs and the single display ones. Should be a Ph6 experiment maybe.

Update 2:30pm Mar 13: The furthest back I seem to be able to go in time with Frames is ~Jan 20 2018. Looking for a time when the arms were locked from back then, it seems like whatever is responsible for a noisy POX and POY was already a problem back in January. See Attachment #2. So it appears that the recent work at 1Y2 is not to blame...

  15728   Thu Dec 10 16:24:13 2020 gautamUpdateEquipment loanNoliac PZT --> Paco

I gave one Noliac PZT from the two spare in the metal PMC kit to Paco. There is one spare left in the kit.

  11689   Wed Oct 14 16:53:22 2015 KojiUpdateGeneralNon inverting buffer for SR560

Eric needed a buffer to drive low input impedance (~130Ohm) of his pomona box, I quickly made a non-iverting buffer with G=+10. The DC power is obtained from the back of SR560. It uses 1.02K and 9.09K
to have the gain of ~10. The chip is OP27. In fact this limits the output swing to be +/-5V for the load resistance of 130Ohm. Eric thinks this is enough. If we need more, we need to swap the chip.

As SR560s tend to saturate too quickly, it would be very useful to have this kind of kit in all the labs
once it is packed in a box.

ELOG V3.1.3-