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ID Date Authorup Type Category Subject
  15306   Sat Apr 18 13:32:31 2020 ranaUpdateCamerasGigE w better NIR sensitivvity

There's this elog from Stephen about better 1064 sensitivity from Basler. We should consider getting one if he finds that its actual SNR is as good as we would expect from the QE improvement.

Might allow for better scatter measurements - not that we need more signal, but it could allow us to use shorter exposure times and reduce blurring due to the wobbly beams.

  15312   Thu Apr 23 10:42:02 2020 ranaUpdatePSLFSS debugging attempts

I had set up the 4395 to do this automatically a few years ago, but it looked at the FSS/IMC instead. When the PCDRIVE goes high there is this excess around ~500 kHz in a broad hump.

But the IMC loop gain changes sometimes with alignment, so I don't know if its a loop instability or if its laser noise. However, I think we have observed PCDRIVE to go up without IMC power dropping so my guess is that it was true laser noise.

This works since the IMC is much more sensitive than PMC. Perhaps one way to diagnose would be to lock IMC at a low UGF without any boosts. Then the UGF would be far away from that noise making frequency. However, the PCDRIVE also wouldn't have much activity.

  15313   Fri Apr 24 00:26:59 2020 ranaSummaryPEML.A. EQ from Tuesday night
Attachment 1: April22-EQ.pdf
  15320   Thu May 7 09:43:21 2020 ranaUpdateASCIMC WFS

This is the doc from Keita Kawabe on why the WFS heads should be rotated.

  15325   Tue May 12 17:51:25 2020 ranaSummaryComputer Scripts / Programsupdated LESS syntax highlight on nodus

apt install source-highlight

then modified bashrc to point to /usr/share instead of /usr/bin

  15337   Tue May 19 15:24:06 2020 ranaUpdateBHDBHD mode-matching study

It would be good to have a corner plot with all the distances/ RoCs. Also perhaps a Jacobian like done in this breathtaking and seminal work.

  15345   Fri May 22 10:37:41 2020 ranaUpdateComputer Scripts / ProgramsNDS2 service restarted

was dead again this morning - JZ notified

current restart instructions (after ssh to megatron):

cd /home/nds2mgr/nds2-megatron

sudo su nds2mgr

make -f test_restart

  15346   Mon May 25 10:54:41 2020 ranaUpdateComputer Scripts / ProgramsNDS2 service restarted

so far it has run through the weekend with no problems (except that there are huge log files as usual).

I have started to set up monit to run on megatron to watch this process. In principle this would send us alerts when things break and also give a web interface to watch monit. I'm not sure how to do web port forwarding between megatron and nodus, so for now its just on the terminal. e.g.:

monit>sudo monit status
Monit 5.25.1 uptime: 4m

System 'megatron'
  status                       OK
  monitoring status            Monitored
  monitoring mode              active
  on reboot                    start
  load average                 [0.15] [0.22] [0.25]
  cpu                          0.6%us 1.0%sy 0.2%wa
  memory usage                 1001.4 MB [25.0%]
  swap usage                   107.2 MB [1.9%]
  uptime                       40d 17h 55m
  boot time                    Tue, 14 Apr 2020 17:47:49
  data collected               Mon, 25 May 2020 11:43:03

Process 'nds2'
  status                       OK
  monitoring status            Monitored
  monitoring mode              active
  on reboot                    start
  pid                          25007
  parent pid                   1
  uid                          4666
  effective uid                4666
  gid                          4666
  uptime                       3d 1h 22m
  threads                      53
  children                     0
  cpu                          0.0%
  cpu total                    0.0%
  memory                       19.4% [776.1 MB]
  memory total                 19.4% [776.1 MB]
  security attribute           unconfined
  disk read                    0 B/s [2.3 GB total]
  disk write                   0 B/s [17.9 MB total]
  data collected               Mon, 25 May 2020 11:43:03


  15362   Fri May 29 00:34:57 2020 ranaUpdateLSCArm transmission RIN

how bout corner plot with power signals and oplevs? I think that would show not just linear couplings (like your coherence), but also quadratic couplings (chesire cat grin)devil

  15425   Tue Jun 23 17:54:56 2020 ranaConfigurationVACVac maintenance complete

I propose we go for all CAPS for all channel names. The lower case names is just a holdover from Steve/Alan from the 90's. All other systems are all CAPS.

It avoids us having to force them all to UPPER in the scripts and channel lists.

  15435   Sun Jun 28 16:29:58 2020 ranaUpdateSUSMC1 sat-box de-lidded

does the FLIR have an option to export image with a colorbar?

How about just leave the lid open? or more open? I don't know what else can be done in the near term. Maybe swap with the SRM sat box to see if that helps?

  15449   Sun Jul 5 16:14:41 2020 ranaUpdateComputersrossa re-re-revival

maybe we should make a "dd" copy of pianosa in case rossa has issues and someone destroys pianosa by accidentally spilling coffee on it.

So, in summary, rossa is now all set up for use during lock acquisition. However, until this machine has undergone a few months of testing, we should freeze the pianosa config and not mess with it.

  15450   Sun Jul 5 18:25:42 2020 ranaUpdateElectronicsWFS characterization

in the lab, checkin on the WFS

Sun Jul 5 18:25:50 2020

I redid Gautam's measurements to get a baseline before changing the head, and my results are very different: To me it looks like the WFS2 quadrants are all OK.


Measurement Details:

  1. The whole AG4395 + breadboard Jenne laser is wheeled over next to the SW side of the AP table.
  2. The output of the 1611 goes into channel R of the 4395
  3. I disconnected all the LEMO cables from the head and then plugged a LEMO-BNC cable into the plugs one at a time. The existing LEMO connectors, which take the signals back to the demode board, were all a little loose, so I adjusted them with some pliers (see video).
  4. The Atten = 0 dB for all AG4395 channels
  5. Source drive = 0 dBm. Checked with a -10 dBm drive that there was no change in the observed TFs, so I guess a 0 dBm drive doesn't make things nonlinear.
  6. When I first turned the setup on, the Yellow 'limit' light was ON on the ILX laser current driver, so maybe the modulation wasn't getting to the laser diode as we wish.
  7. did not change any WFS MEDM settings for these measurements. Not sure if any of those buttons work anyway.

I've left the setup as is in case either me or Gautam want to double check. If we're agreed on this response, I'll remove the notches and disable the RF attenuators.

Sun Jul 5 21:42:45 2020

Attachment 1: WFS_attenOff.pdf
  15451   Sun Jul 5 18:39:57 2020 ranaUpdateComputersrossa: printer

I did

sudo usermod -a -G lpadmin controlscheeky

and then was able to add Grazia to the list of printers for Rossa by following the instructions on the 40m Wiki. yes

I installed color syntax highlighting on Rossa using the internet (https://superuser.com/questions/71588/how-to-syntax-highlight-via-less). Now if you do 'less genius_code.py', it will be highlighting the python syntax.

when I try 'sitemap' on rossa I get:

medm: error while loading shared libraries: libreadline.so.6: cannot open shared object file: No such file or directory

  15454   Mon Jul 6 12:43:02 2020 ranaUpdateComputersrossa: lib symlink

yes, I rebooted yesterday to fix the 'steaking white lines' problem in the video/display

maybe we're supposed to edit something besides resolv.conf since that gets over-written on boot for some linux OS

  15473   Mon Jul 13 11:33:18 2020 ranaUpdateComputersrossa: more developmental work

I too, would prefer py3 for everything, but aren't all the cdsutils / gaurdian things still python2?

Is it possible to just make a python2 conda environment on rossa? I would guess that its simple and won't interfere with the regular operation of that machine.

  15474   Mon Jul 13 11:36:08 2020 ranaUpdateLSCMC2 coils need DC balancing?
  1. if IMC REFL is not increasing, I don't think its a mis-alignment. Usually, REFL is a more sensitive indicator of alignment than TRANS since its usually near zero. Maybe the MC2 TRANS PD is not centered or doesn't have enough lens action.
  2. to reduce the DC load on MC2, you could have a slow releif drive the ETMs and DC and minimize LSC-MCL
  15505   Wed Jul 29 11:57:59 2020 ranaUpdateBHDIn-air BHD - CDS and wiring summary

3. I agree - this whitening will be handy to have for diagnostics.

4. I think in principle, we can ask a company to make the custom cables for us to save us some hand labor. Rich/Chub probably know the right companies to do small numbers of dirty cables.

5. Can't we just a single Noliac PZT in the same way that the OMC does? Or is the lead time too long?

6. Do we need active steering for this in-air test? I'm not even sure how we would get the alignment signal, so maybe that's a good reason to figure this out.

  15509   Fri Aug 7 11:23:47 2020 ranaUpdateBHDMonte Carlo Simulations

that's great. I think we would like to figure out how to present this so that its clear what the distribution of TFs is. Maybe we can plot the most likely curve as well as a shaded region indicating the 5% and 95% values?


I've pushed an MCMC simulation to the A+ BHD repo (filename MCMC_TFs.ipynb). The idea is to show how random offsets around ideal IFO change the noise couplings of different DOFs to readout.

and then we add the loops

  15533   Tue Aug 18 13:55:23 2020 ranaUpdateALSWhitening and ALS noise

No, there should be no unscheduled visits from any inspector, marshal, tech, or vendor. They all have to be escorted or they don't get in. If they have a problem with that, please give them my cell #.


For the ALS, in addition to the beat note spectrum, I think we need to know the loop gain use to feedback to the ETM to determine the true cavity length fluctuation. w/o ALS, the noise would be only due to the seismic noise, OSEM damping noise, and the IR-PDH residual. Those are all suppressed by the ALS loop, but then the ALS loop puts its sensing noise onto the cavity. So, if I'm thinking about this right, the ALS beat noise > 200 Hz doesn't matter so much to the CARM RMS. So the whitening seems to be doing good in the right spot, but we would like to have another boost in the green PDH to up the gain below ~300 Hz?

  15546   Sat Aug 29 18:52:42 2020 ranaUpdateIOOIMC gain change

I lowered the (FAST) PZT gain on the IMC/FSS servo today.

I noticed that the MC locks looked unstable a lot of the day, and during lock the PCDRIVE channel is above 1 Vrms (which means the loop is oscillating, ttypically at the PZT/EOM crossover frequency).

I changed the default setting from 22 to 20 19 dB in the PSL Settings screen so the mcup script will use this for now. Feel free to revert if this turns out to be a Fluke (which you would think is a terrible name for a company, but...)

  15547   Sat Aug 29 20:07:48 2020 ranaUpdateElectronicsWFS characterization

I set up to do the WFS head modifications today, but I was shot down in flames due to a missing AC/DC adapter.

The Prologix GPIB-ethernet dongle needs +8-13 V to run. Some riff raff has removed the adapter and I was thunderstruck to see that it had not been returned.

I did the usual hunt around the lab looking for something with the right specs and connector. I found one that could do +9V and had the right connector, but it didn't light up the adapter so I put it back in black SP table.

I'll order a couple of these (5 ordered for delivery on Wednesday) in case there's a hot demand for the jack / plug combo that this one has. The setup is in the walkway, but I returned the AS table to the usual state and made sure the IMC is locking well.

  15550   Sun Aug 30 11:29:33 2020 ranaUpdateGeneralpower blink?

My power at home winked out for a second this morning, but it looks like either nothing happened in the 40m lab or else it rode it out.

MC is locked - lost lock around 11:25 AM and then relocked.

  15566   Wed Sep 9 20:52:45 2020 ranaSummaryIOOwandering line in IMC

since the summary pages are working again, I was clicking through and noticed that there's a wandering peak in the whitened IMC spectrogram that goes from 10-30 Hz over the course of a day.


anyone know what this is ?

  15574   Tue Sep 15 19:17:30 2020 ranaUpdateIOOMC F spectrum

that's a very curious disconnection

the "Pentek" whitening board that carries the MC channels has jumpers to enable either 1 or 2 stages of 15:150 whitening. Looks lik MC_F has 2 and MC_L has 1.

I guess the MC_F signal is so low because of the high gain on the FSS board.  We could lower the FSS common gain and increase the IMC board's VCO gain to make up for this. Maybe 6 dB would be enough. IF that is risky, we could also up the analog gain on the whitening board.

  15581   Sat Sep 19 11:27:04 2020 ranaUpdateGeneralM4.5 EQ in LA

the seismometers obviously saturated during the EQ, but the accelerometers captured some of it. It looks like there's different saturation levels on different sensors.

Also, it seems the mounting of the MC2 accelerometers is not so good. There's some ~10-20 Hz resonance its mount that's showing up. Either its the MC2 chamber legs or the accelerometers are clamped poorly to the MC2 baseplate.

Sun Sep 20 00:02:36 2020 edit: fixed indexing error in plots

* also assuming that the sensors are correctly calibrated in the front end to 1 count = 1 um/s^2 (this is what's used in the summ pages)

Attachment 1: Sep18-EQ.pdf
  15583   Sat Sep 19 18:08:34 2020 ranaUpdateGeneralM4.5 EQ in LA

the EQ was ~14 km south of Caltech and 17 km deep


the seismometers obviously saturated during the EQ, but the accelerometers captured some of it. It looks like there's different saturation levels on different sensors.

Also, it seems the mounting of the MC2 accelerometers is not so good. There's some ~10-20 Hz resonance its mount that's showing up. Either its the MC2 chamber legs or the accelerometers are clamped poorly to the MC2 baseplate.

I'm amazed at how much higher the noise is on the MC2 accelerometer. Is that really how much amplification of the ground motion we're getting? If so, its as if the MC has no vibration isolation from the ground in that band. We should put one set on the ground and make the more direct comparison of the spectra. Also, perhaps do some seismic FF using this sensor - I'm not sure how successful we've been in this band.

Attaching the coherence plot from ldvw.ligo.caltech.edu (apparently it has access to the 40m data, so we can use that as an alternative to dtt or python for remote analysis):

Coherence (GWpy) result, image #: 288304

It would be interesting to see if we can use the ML based FF technology from this summer's SURF project by Nadia to increase the coherence by including some slow IMC alignment channels.

  15589   Sun Sep 20 23:12:13 2020 ranaSummaryALSALS noise budget update

I think the digital loop in the ALS budget is too optimistic. You have to include all the digital delays and anti-aliasing filters to get the real response.

aslo, I recommend grabbing some of the actual spectra from the in-lock times with nds and using the calibrated spectra as inputs to this mode. Although we don't have good models of the stack, you can sort of infer it by using the calibrated seismometer data and the calibrated MC_F or MC_L channels (for IMC) or XARM/YARM signals for those.

  15594   Tue Sep 22 12:14:42 2020 ranaSummaryALSALS noise budget update

This ALS loop is not stable. Its one of those traps that comes from using only the Bode plot to estimate the loop stability. You have to also look at the time domain response - you can look at my feedback lecture for the SURF students for some functions.

  15605   Wed Sep 30 19:45:56 2020 ranaUpdateGeneralHEPA blower startup capacitor replacement

it would be a good idea for us to have an auto-reminder to have us check the flow of all the HEPAs in the lab and elog it once a year so that we can replace filters and pre-filters appropriately.

  15638   Thu Oct 22 13:04:42 2020 ranaUpdateElectronicsHV coil driver packaged into 2U chassis

what is the noise level before the HV stage? i.e. how well is the acromag noise being filtered?

  15671   Tue Nov 10 15:13:41 2020 ranaUpdateGeneralETMY suspension eigenmodes

For the input matrix diagonalization, it seemed to me that when we had a significant seismic event or a re-alignment of the optic with the bias sliders, the input matrix also changes.

Meaning that our half-light voltage may not correspond to the half point inside the LED beam, but that rather we may be putting the magnet into a partially occluding state. It would be good to check this out by moving the bias to another setting and doing the ringdown there.

  15677   Mon Nov 16 00:02:34 2020 ranaUpdateElectronicsMore systematic noise characterization

true. also try to choose a cap with a goow high frequency response. In the Electronics Noise book by Ott there's some graph about this. I bet you good do a Bing search and also find something more modern. Basically we want to make sure that the self resonance is not happening at low frequencies. Might be tought to find one with a good HF response, a high voltage rating, and > 1uF.


Yes. The datasheet has a recommendation circuit with 10uF caps. Companies are careful to show reproducible, reliably functional circuit examples on datasheets. So, if the caps are there you should try to replicate the design.


Additional bypass capacitors? I use 0.1 uF, 700V DC ceramic capacitors as bypass capacitors close to the leads of the PA95, as is recommended in the datasheet. Can adding a 10uF capacitor in parallel provide better filtering? I'm not sure if one with compatible footprint and voltage rating is readily available, I'll look around.

  15679   Tue Nov 17 00:26:32 2020 ranaUpdateElectronicsSR560s in need of repair/battery replacement

yes, both problems can be fixed. Usually we just order some spare lead-acid batteries from SRS (Steve may have some spare ones somewhere). The DC offset often comes from a busted FET input. I bought 50 of those at one point - they're obsolete. Its also possible to replace the input stage with any old FET pair.

I'll handle the one with the offset if you leave it on my desk.

  15691   Sat Nov 28 21:44:53 2020 ranaUpdateASCPlanned mods for WFS head

I don't think your simulation looked inaccurate (at least not to me). In my opinion, we just want to minimize any excess noise from intermodulation. Of course, its possible that stuffing too many notches will make it difficult to have the same low noise as a simple circuit, so that's worth considering.

Also, the intermodulation is mainly a problem when the other peaks are not suppressed by some feedback: e.g. POP55_I can have excess noise if POP55_Q or POP11_I are not controlled by some MICH/PRCL/SRCL loops.

For the WFS, perhaps this is not a significant issue, but I'm not sure. My suggestion is to stuff 11 & 55 for sure, and then the others depending on the amplitude of the peaks and the consequent intermodulation. IF it works with all stuffed, that seems good. If its tricky to get it to work with all stuffed, I'd back off on a couple of them...but it probably takes more careful thought to figure out which ones are least important.

  15700   Thu Dec 3 11:02:35 2020 ranaUpdateElectronicsElectrical LO signal for AS WFS

looks good to me.

The thing I usually look for is how much the downstream system (mixers, etc) can perturb the main oscillator. i.e. we don't want mixer in one chain to reflect back and disturb the EOM chain. But since our demods have amplifiers on the LO side we're pretty immune to that.

  15732   Fri Dec 11 09:28:52 2020 ranaUpdateBHDMonte Carlo loop coupling Simulations

Cool. Can you give us Bode plots of the open loop gain for each of the 5 length control loops?


I have rebuilt the MCMC simulation in an OOP fashion and incorporated Lance/Pytickle functionality into it. The usage of the MCMC now is much less messy, hopefully.


  15759   Mon Jan 11 19:10:10 2021 ranaUpdateBHDMonte Carlo loop coupling Simulations
  • looking better, but the CARM plot still looks weird.
  • you should plot from 0.01 - 10,000 Hz
  • All of the loops should have true integrators below 1 Hz.
  • I don't think these loops are stable; the Bode plot is not a good way to check stability for LTI systems since you can be fooled by phase wrapping.
  15804   Thu Feb 11 16:58:52 2021 ranaSummaryBHDSatellite Amplifier Very Low frequency noise After modifications

I expect that a single OSEM channel can't be better than 1e-10 m/rHz above 5 Hz, so probably something wrong in the calibration. 1.6 V/mm seems right to me, so could be some place else.

  15827   Fri Feb 19 18:22:42 2021 ranaUpdateLSCPRFPMI sensiing matrix woes

I would:

  1. look at the free swingin michelson. Should be able tu null that siggnal in all ports to define the Q phase.
  2. If things are weird, put an RF signal nto the demod board mhich is offset from the LO by ~100 Hz and verify the demod/whitening chain is kosher.
  3. Lock PRMI and drive lines > 200 Hz. If PRC/MICH are not orthogonal, then there may be a mis tuning of RF SB wavelength and cavity lengths.
  4. IF PRMI is sort of healthy, we could be having a weird SB resonance in the arms.
  15831   Sun Feb 21 20:51:21 2021 ranaUpdateGeneralHousekeeping + PRMI char

I'm curious to see if the demod phase for MICH in REFL & AS chamges between thi simple Mcihelson and PRMI. IF there's a change, it could point to a PRCL/f2 mismatch.

But I would still bet on demod chain funniness.

  15854   Tue Mar 2 13:39:31 2021 ranaUpdateLSCPRM violin filter excessive?

agreed, seems excessive. I always prefer bandstop over notch in case the eigenfrequency wanders, but the bandstop could be made to be just a few Hz wide.


  15881   Mon Mar 8 19:22:56 2021 ranaSummarySUSIMC suspension characterization

Herewith, I describe an adventure

  1. Balance the OSEM input matrix using the free swinging data (see prev elogs).
  2. Balance the coil actuation by changing the digital coil gains. This should be done above 10 Hz using optical levers, or some IMC readout (like the WFS). At the end of this process, you should put a pringle vector into the column of the SUS output matrix that corresponds to one of the SUS OSC/LOCKIN screens. Verily, the pringle excitation should produce no signal in MC_F or da WFS.
  3. use the Malik doc on the single suspension to design feed-forward filters for the SUS COIL filter banks. You can get the physical parameters using the design documents on DCC / 40m wiki and then modify them a bit based on the eigenfrequencies in the free swinging data.
  4. Model the 2x2 system which includes longitudinal and pitch motion. Consider how accurate the filters must be to maintain a cross-coupling of < 3% in the 0.5-2 Hz band.
  5. Is this decoupling forsooth still maintained when you close the SUS damping loops in the model? If not, why so?
  6. Make step response measurements of the damping loops and record/plot data. Use physical units of um/urad for the y-axes. How much is the step response cross-coupling?
  7. Consider the IMC noise budget: are the low pass filters in the damping loops low-passing enough? How much damping is demasiado (considering the CMRR of the concrete slab for seismic waves)?
  8. Can we use Radhika's AAA representation to auto-tune the FF and damping filters? It would be very slick to be able to do this with one button click.

gautam: For those like me who don't know what the AAA representation is: the original algorithm is here, and Lee claims his implementation of it in IIRrational is better, see his slides.

  15882   Mon Mar 8 20:11:51 2021 ranaFrogsComputer Scripts / Programsactivate_matlab out of control on Megatron

there were a zillion processes trying to activate (this is the initial activation after the initial installation) matlab 2015b on megatron, so I killed them all. Was someone logged in to megatron and trying to run matlab sometime in 2020? If so, speak now, or I will send the out-of-control process brute squad after you!

  15914   Fri Mar 12 13:01:43 2021 ranaSummarySUSCoil Rs & Ls for PRM/BS/SRM

ugh. sounds bad - maybe a short. I suggest measuring the inductance; thats usually a clearer measurement of coil health

  15921   Mon Mar 15 20:40:01 2021 ranaConfigurationComputersinstalled QTgrace on donatella for dataviewer

I installed QTgrace using yum on donatella.angel Both Grace and XMgrace are broken due to some boring fight between the Fedora package maintainers and the (non existent) Grace support team. So I have symlinked it:

controls@donatella|bin> sudo mv xmgrace xmgrace_bak
controls@donatella|bin> sudo ln -s qtgrace xmgrace
controls@donatella|bin> pwd

I checked that dataviewer works now for realtime and playback.cool Although the middle click paste on the mouse doesn't work yet.angry

Attachment 1: cutiegrace.png
  15938   Thu Mar 18 12:35:29 2021 ranaUpdatesafetyDoor to outside from control room was unlocked

I think this is probably due to the safety tour yesterday. I beleive Jordan showed them around the office area and C&B. Not sure why they left through the control room.


I came into the lab a few mins ago and found the back door open. I closed it. Nothing obvious seems amiss.

Caltech security periodically checks if this door is locked but it's better if we do it too if we use this door for entry/exit.


  15939   Thu Mar 18 12:46:53 2021 ranaUpdateSUSTesting of new input matrices with new data

Good Enough! Let's move on with output matrix tuning. I will talk to you guys about it privately so that the whole doesn't learn our secret, and highly sought after, actuation balancing.

I suspect that changing the DC alignment of the SUS changes the required input/output matrix (since changes in the magnet position w.r.t. the OSEM head change the sensing cross-coupling and the actuation gain), so we want to make sure wo do all this with the mirror at the correct alignment.


  15942   Thu Mar 18 21:37:59 2021 ranaUpdateLSCPRMI investigations: what IS the matrix??
  • Locked PRMI several tmes after Gautam setup. Easy w IFO CONFIG screenheart
  • tuned up alignment
  • Still POP22_I doesn't go above ~111, so not triggering the loops. Lowered triggers to 100 (POP22 units) and it locks fine now. smiley
  • Ran update on zita, and now it lost its mounts (and maybe its mind). Zita needs some love to recover the StripTool plots  sad
  • Put the $600 ebay TDS3052 near the LSC rack and tried to look at the RF power, but found lots of confusing information. Is there really a RF monitor in this demod board or was it disconnected by a crazy Koji cheeky ? I couldn't see any signal above a few mV.angry
  • Put a 20 dB coupler in line with the RF input and saw zip. Then I put the RF signal directly into the scope and saw that the 55 MHz signal is ~30 mVpp into 50 Ohms. I waited a few minutes with triggering to make sure I was getting the largest flashes. Why is the optical/RF signal so puny? surprise This is ~100x smaller than I think we want...its OK to saturate the RF stuff a little during lock acquisition as long as the loop can suppress it so that the RMS is < 3 dBm in the steady state.
Attachment 1: PXL_20210319_045925024.jpg
  15950   Sun Mar 21 19:31:29 2021 ranaSummaryElectronicsRTL-SDR for monitoring RF noise / interference

When we're debugging our RF system, either due to weird demod phases, or low SNR, or non-stationary noise in the PDH signals, its good to have some baseline measurements of the RF levels in the lab.

I got this cheap USB dongle (RTL-SDR.COM) that seems to be capable of this and also has a bunch of open source code on GitHub to support it. It also comes mith an SMA coax and rabbit ear antenna with a flexi-tripod.

I used CubicSDR, which has free .dmg downloads for MacOS.It would be cool to have a student write some python code (perhaps starting with RTL_Power) for this to let us hop between the diffierent RF frequencies we care about and monitor the power in a small band around them.

ELOG V3.1.3-