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ID Date Author Type Category Subject
17455   Tue Feb 7 20:10:05 2023 yutaSummaryBHD60 Hz noise investigations around IMC, part 3

[Anchal, Yuta]

We have measured OLTF of IMC loop, and revisited IMC error point calibration again.
Also, we have tried to break the ground loop between MC servo board and TTFSS, but didn't help.

IMC OLTF measurement:
- IMC OLTF was measured using SR785 at TP1A and TP1B. MC servo board settings are the following.
- +4 dB in IN1
- 40 Hz pole, 4000 Hz zero filter was on
- 0 boost
- Eye-ball fit of OLTF gives zeros at [30e3,30e3] Hz, poles at [40,3e3,3e3] Hz (Attachment #1). 40 Hz pole is from 40:4000 Hz fiter in MC servo board and 4kHz zero is compensated by IMC cavity pole (~ 3.79 kHz). We are not sure where two 3k:30k are from.
- Anyway, eye-ball fit gives OLTF gain of 1.7e5 at 60 Hz, which is accidentally roughly the same as previous estimate (40m/17446).

Revisiting IMC error point calibrations:
- We realized that error signal calibration of 13kHz/V a while ago in 2018 (from 40m/14691, which is from 40m/13696) is a calibration for IN1.
- So, 70 uV/rtHz at 60 Hz at TP1A corresponds to 70 uV/rtHz / 4dB / (4e3/60) * 13kHz/V = 0.009 Hz/rtHz, which corresponds to 1.2e-15 m/rtHz.
- The estimated frequency noise at the output of IMC in terms of arm length is 1.2e-15 m/Hz * (1+G) = 2.0e-10 m/rtHz (or 1.4e-10 m RMS considering 0.5 Hz bandwith).
- Noise measured with the same condition but PSL shutter closed was 7 uV/rtHz at 60 Hz (40m/17431). This correspond to 1.2e-16 m/rtHz (or 8.5e-17 m RMS), which is an estimated dark noise.

Summary of frequency noise measurements at 60 Hz:
- 1.4e-10 m RMS (or 1.0e3 Hz RMS) as measured at TP1A (estimate of unsuppressed noise difference between IMC and PSL)
- This being smaller than MC_F measurement is strange, as this should be an estimate of total unsuppressed noise (if 60 Hz noise is coherently cancelling each other, this can be explained).
- 3.1e-9 m RMS (or 2.2e4 Hz RMS) as measured at MC_F
- 4.3e-11 m RMS (or 3.1e2 Hz RMS)  as measured using XARM and YARM
- 1.8e-10 m RMS as measured using FPMI DARM

Buffering MC servo board output to TTFSS:
- We have inserted a battery-powered SR560 in between MC servo board output to TTFSS, trying to break the possible ground loop between 1X2 rack and PSL.
- To do this, we had to lower IN1 gain to -6dB, to avoid saturation of SR560.
- This didn't make any difference in MC_F or POY during YARM lock.

Attachment 1: IMC_OLTF.png
17458   Thu Feb 9 10:19:22 2023 yutaSummaryBHD60 Hz noise investigations around IMC, part 4, using ALS BEAT

[Anchal, Yuta]

Yesterday, we have measured the frequency noise of PSL with IMC locked/unlocked using ALS BEATX/Y to narrow down where the 60 Hz is coming from.
All the measurements so far is consistent with a hypothesis that 60 Hz noise injected after MC_F is picked-off (it could be from MC_F DAQ readout or something in the IMC loop).

Method:
- Measured YARM noise spectra when YARM is locked with POY11 to measure the frequency noise with respect to YARM, and compared with MC_F
- Measured ALS BEATX and BEATY spectra when PSL is free running and when IMC is locked. Here, when "PSL is free running" is done with PSL shutter closed, but all the cables remained the same and FSS loop was in "down" state. Shutters at both ends were closed, and PZT inputs to AUX lasers were terminated to avoid noise injection from PDH locking with dark noise (this was necessary to reduce noise in BEATY).

Result:
- Attachment #1 is YARM noise calibrated into Hz, and Attachment #2 is BEATX and BEATY spectra with PSL free running (solid lines) and IMC locked (dotted lines). Below are summary of noise level at 60 Hz (RMS is calculated using a bandwidth of 0.187493 Hz)

YARM (PSL locked vs Yarm): 6.5e2 Hz/rtHz (2.8e2 Hz RMS)
MC_F (sum of noises in IMC loop): 4.9e4 Hz/rtHz (2.2e4 Hz RMS)
BEATX free (PSL free vs Xend free): 3.3e3 Hz/rtHz (1.4e3 Hz RMS)
BEATX locked (PSL locked vs Xend free): 8.8e2 Hz/rtHz (3.8e2 Hz RMS)
BEATY free (PSL free vs Yend free): 1.6e4 Hz/rtHz (6.9e3 Hz RMS)
BEATY locked (PSL locked vs Yend free): 1.5e4 Hz/rtHz (6.5e3 Hz RMS)

Discussion:
- "BEATX locked" measurement suggests that PSL locked to IMC (and Xend free) has noise less than 3.8e2 Hz RMS. This is roughly consistent with YARM measurement of frequency noise, and suggests that Yarm is stable enough to measure the PSL locked frequency noise.
- "BEATX free" measurement suggests that PSL free run (with cables connected) has noise of 1.4e3 Hz RMS (note that Xend free is less than 3.8e2 Hz RMS).
- MC_F measurement is the sum of noises in IMC loop, including IMC length noise + noise injected at error point (3.8e2 Hz RMS), PSL free run noise (1.4e3 Hz RMS), noise injected at feedback. Therefore, this suggests that 2.2e4 Hz RMS we see in MC_F is from noise injected after MC_F pickoff point (or in the MC_F DAQ readout).
- BEATY having large 60 Hz noise probably comes from noise in the beat measurement.

Next:
- Use BEATX to monitor 60 Hz noise.
- Try terminating PZT input to see if 60 Hz noise reduces. Try different gains at different point of MC servo board and TTFSS when IMC is unlocked to see where exactly 60 Hz noise is coming from.

Attachment 1: YARM_calibrated_noise_20230208_Hz.pdf
Attachment 2: BEATX_BEATY_MCF.pdf
17460   Thu Feb 9 17:33:34 2023 yutaSummaryBHD60 Hz noise investigations around IMC, part 6, TTFSS

[Anchal, Yuta]

Measurements yesterday (40m/17458) suggested that 60 Hz noise is injected after MC_F is picked-off.
So, we terminated PSL PZT input at several points to see where 60 Hz noise is injected.
It seems like the 60 Hz frequncy noise we see in MC_F is from TTFSS box, but the 60 Hz noise we see in YARM is not limited by this.

The 60 Hz noise we see in YARM is probably limited by IMC length noise.

Method:
- We terminated PZT input to the PSL laser at various points one by one and monitored 60 Hz frequency noise using BEATX. PSL shutter was closed and IMC was not locked.

Result:
- Below is the result at 60 Hz (RMS is calculated using a bandwidth of 0.187493 Hz)

Reference from 40m/17458, YARM (PSL locked vs Yarm): 6.5e2 Hz/rtHz (2.8e2 Hz RMS)
Reference from 40m/17458, MC_F (sum of noises in IMC loop): 4.9e4 Hz/rtHz (2.2e4 Hz RMS)
MC_F when PSL shutter is closed but MC servo board configuration at IMC locked state: 2.7e2 Hz/rtHz (1.2e2 Hz RMS) -- this gives IMC loop gain enhanced sensing noise

BEATX free (PSL free vs Xend free): 3.5e3 Hz/rtHz (1.5e3 Hz RMS) -- consistent with previous measurements
With PZT input to NPRO terminated (Attachment #1): 8.1e2 Hz/rtHz (3.5e2 Hz RMS)
Connected a terminated small box (we see in Attachment #1) before NPRO PZT: 6.3e2 Hz/rtHz (2.7e2 Hz RMS)
Connected input terminated Thorlabs PZT driver (MDT694): 5.9e2 Hz/rtHz (2.6e2 Hz RMS)
Connected input terminated summing amp (Attachment#2): 4.4e2 Hz/rtHz (1.9e2 Hz RMS)
Connected input terminated TTFSS (C1:PSL-FSS_MGAIN=-10dB, C1:PSL-FSS_FASTGAIN=-10dB): 3.9e3 Hz/rtHz (1.7e3 Hz RMS) -- consistent with "BEATX free (PSL free vs Xend free)" measurement
Connected input terminated TTFSS (C1:PSL-FSS_MGAIN=-10dB, C1:PSL-FSS_FASTGAIN=+10dB): 7.6e3 Hz/rtHz (3.3e3 Hz RMS)
Connected input terminated TTFSS (C1:PSL-FSS_MGAIN=+4dB, C1:PSL-FSS_FASTGAIN=+19dB): 2.9e4 Hz/rtHz (1.3e4 Hz RMS) -- Nominal gains when IMC is locked; consistent with "MC_F" measurement 40m/17458
Connected input terminated TTFSS (C1:PSL-FSS_MGAIN=+19dB, C1:PSL-FSS_FASTGAIN=+4dB): 1.1e4 Hz/rtHz (4.8e3 Hz RMS)

Discussion:
- Connecting TTFSS increased 60 Hz frequency noise, which suggests that TTFSS is creating this 60 Hz frequency noise.
- Setting TTFSS gains to nominal gains to IMC locked, 60 Hz frequency noise matched with frequency noise measurement using MC_F. This quantitatively supports that TTFSS is creating this 60 Hz frequency noise.
- Increasing C1:PSL-FSS_MGAIN and reducing C1:PSL-FSS_FASTGAIN reduced 60 Hz frequency nosie. This means that some portion of 60 Hz noise is from between these two gains.
- Note that having 60 Hz noise in TTFSS does not necessarily mean that our YARM noise is limited by this, because IMC loop suppresses the TTFSS noise. Assuming all 1.3e4 Hz RMS is all from TTFSS noise, it is suppressed to less than 1.3e4 Hz RMS/2e5 = 6.5e-2 Hz RMS (where 2e5 is IMC loop gain without super boosts, but it is actually higher with them) as frequency noise we see in YARM. YARM noise is measured to be 6.5e2 Hz/rtHz (2.8e2 Hz RMS), so it is not limited by TTFSS noise.
- Also dark noise measured at MC_F (1.2e2 Hz RMS) tells you that the dark noise is not limiting the frequency noise we see in YARM.

Touching various parts around TTFSS:
- We moved on to touch various parts around TTFSS to see if 60 Hz noise reduces in MC_F. We removed unused cables around TTFSS interface, touched power cables into TTFSS (both at TTFSS interface in the rack and TTFSS box on PSL table), BNC cables into TTFSS, disconnected slow controls, tried to avoid grounding of cables going into EOM (there is a small box that sums FSS feedback signal and 33.5 MHz; Attachment #3), but 60 Hz noise we see in MC_F didn't change significantly.

Next:
- Check grounding situation around TTFSS box.
- Check IMC length noise and error point noise by monitoring BEATX.
- Check coil drivers for MC1, MC2, MC3 by disconnecting drivers while IMC is locked.
- Try feeding back IMC servo also to MC2 with 60 Hz resonant gain to cancel 60 Hz noise

Note added at 23:50 to clarify:
nIMC : IMC length noise in frequency
nPSL: PSL free run noise in frequency
ne: sensing noise in frequency
nf: feedback noise in frequency
G: IMC loop gain (estimated to be 2e5 at 60 Hz without boosts)

MC_F = G/(1+G) * (nIMC + nPSL + ne + nf) + [noises in MC_F DAQ]
= 2.2e4 Hz RMS
MC_F when dark, MC servo nominal gain = G * ne
= 1.2e2 Hz RMS
PSL frequency noise after IMC lock = G/(1+G) * (nIMC + ne) + 1/(1+G) * (nPSL + nf)
YARM = [PSL frequency noise after IMC lock] + [noises from YARM loop]
= 2.8e2 Hz RMS
BEATX when PSL is free run, TTFSS low gain connected = nPSL + [noises from Xend AUX and BEATX sensing]
= 1.7e3 Hz RMS
BEATX when PSL is free run, TTFSS nominal gain connected = nPSL + nf + [noises from Xend AUX and BEATX sensing]
= 2.9e4 Hz RMS
BEATX when IMC is locked = [PSL frequency noise after IMC lock] + [noises from Xend AUX and BEATX sensing]
= 3.8e2 Hz RMS

So, our estimate is
ne ~ 1.2e2/G Hz RMS (small)
nPSL ~ 1.7e3 Hz RMS
nf ~ 2e4 Hz RMS (this dominates MC_F, but already suppressed enough in [PSL frequency noise after IMC lock])
[PSL frequency after IMC lock] ~ 3e2 Hz RMS (this dominates YARM and BEATX when IMC is locked)
nIMC ~ 3e2 Hz RMS (this dominates [PSL frequency noise after IMC lock])

Attachment 1: NPROandSmallBox.JPG
Attachment 2: TerminatingSummingBox.JPG
Attachment 3: EOMSmallBox.JPG
17461   Mon Feb 13 11:54:54 2023 yutaSummaryBHD60 Hz frequency noise is coming from MC1 coils

[JC, Yuta]

We have found that MC1 coils are causing 60 Hz noise.
Tripping watchdogs for MC1 coils reduced 60 Hz noise seen in YARM by a factor of 100.

Method:
- Locked YARM with POY11 and measured YARM sensitivity to use it for 60 Hz frequency noise monitor0.187493**0.5
- Tripped MC1, MC2, MC3 coil output watchdogs to see if they are causing this 60 Hz frequency noise. IMC WFS were turned off.

Result:
- Attachment #1 is YARM sensitivity and MC_F in Hz with MC1,2,3 untripped (dotted) and MC1 tripped (solid).

YARM (PSL locked vs Yarm), MC1,2,3 untripped: 6.0e2 Hz/rtHz (2.6e2 Hz RMS)
MC_F (sum of noises in IMC loop), MC1,2,3 untripped: 4.8e4 Hz/rtHz (2.1e4 Hz RMS)
YARM (PSL locked vs Yarm), MC1 tripped: 6.6e0 Hz/rtHz (2.9e0 Hz RMS) -- reduced by a factor of 100
MC_F (sum of noises in IMC loop), MC1 tripped: 4.7e4 Hz/rtHz (2.0e4 Hz RMS)

- We have also tried tripping MC2 and MC3 coils, but they didn't make much difference.
- Untripping only one of MC1 face coils created 60 Hz frequency noise, so all the face coils seem to have the same level of 60 Hz noise.

Next:
- Inspect around MC1 coil driver

Attachment 1: YARM_calibrated_noise_20230213_Hz.pdf
Attachment 2: Screenshot_2023-02-13_12-23-23_TrippingMC1.png
17462   Mon Feb 13 17:35:20 2023 AnchalSummaryBHD60 Hz frequency noise is coming from MC1 coils

[Anchal, Yuta]

We think we have narrowed down the source of 60 Hz noise to one fo the following possibilities:

• Ground loop present along the MC1 suspension damping loop
• 60 Hz DAC noise on inputs of MC1 coil driver
• 60 Hz noise injected at dewhitening board before the dewhitening filter

The second and third cases are unlikely because we see 60 Hz noise present only in MC1 coils, not MC3 coils while they both share the same connection from DAC to SOS dewhitening filter boards as they share the SOS dewhitening board D000316-A. So it is unlikely that only the MC1 channels have this noise while the MC3 channels do not.

This inference was made from following observations:

Change Reduction in noise at C1:LSC-YARM_IN1_DQ (dB)
Turn off damping loops, keep coil output enabled 0
Turn off coil outputs (only fast actuation) 43
Turn ON Analog Coil Dewhitening Filter on one face coil only 30
Turn ON Analog Coil Dewhitening Filter on all face coils (attachment 1) 43

Note: Turning ON analog dewhitenign on MC1 coil is done by turning off FM9 switch which is the simulated digital dewhitening filter. Also note that theanalog dewhitening filter has an attenuation of 30 dB at 60 Hz.

MC1 has an unconvetional setup where the satellite amplifier is from the new generation while the coil driver and dewhitening boards are from the old generation. The new generation satellite amplifiers sen PD signal through differential ended signals but the old generation PD whitening interface expects single ended inputs, so we ahve been using PD monitor outputs from the satellite amplifier which connects the ground of the two boards to each other. Maybe this is the reason for the ground loop.

Attachment 1: YARM_calibrated_noise_20230213_Hz_MC1SimDWOnOff.pdf
17463   Tue Feb 14 10:49:04 2023 yutaSummaryBHDMC1 electronics diagram and cable diconnection tests

Below are summary of electronics around MC1 and cable disconnection tests.
These suggest that the 60 Hz noise is probably from somewhere between DAC and the coil driver.
For now, we can work on IFO with SimDW off.

MC1 local damping electronics diagram:
Vacuum Flange
|| DB25 cable x2
Satellite Amp Chassis (LIGO-S2100029, LIGO-D1002818)
|| DB9 split cable
Suspension PD Whitening and Interface Board (LIGO-D000210)
||| 4pin LEMO x3
Anti-aliasing filter
|
ADC
|
CDS
(SimDW is zpk([35.3553+i*35.3553;35.3553-i*35.3553;250],[4.94975+i*4.94975;4.94975-i*4.94975;2500],1,"n") gain(1.020); InvDW is the inverse)
|
DAC
|
SOS Dewhitening and Anti-Image Filter (LIGO-D000316) Shared with MC3
(has 2ea. 800 Hz LPF & 5th order, 1 dB ripple, 50 dB atten, 28Hz elliptic LPF that can be turned on or bypassed)
||||| SMA-LEMO cable x5
("test in" are used; inputs can be disconnected with watchdogs)
SOS Coil Driver Module (LIGO-D010001, LIGO-D1700218)
(HV offsets from Acromag are added at the output (independent from watchdogs))
|| DB9 split cable
Satellite Amp Chassis

Disconnecting cables:
- Disconnecting cables between Satellite Amp Chassis and Suspension PD Whitening and Interface Board didn't help reducing 60 Hz noise.
- Disconnecting LEMO cables between Suspension PD Whitening and Interface Board and Anti-aliasing filter didn't help reducing 60 Hz noise.
- Turning off C1:SUS-MC1_SUSPOS/PIT/YAW/SIDE outputs didn't help reducing 60 Hz noise.
- Turning off SimDW reduced 60 Hz noise.
- Turning off watchdogs reduced 60 Hz noise.

Dewhitening filters:
- When 60 Hz frequency noise was high, SimDW was on, but InvDW was off, which is in a weired state.
- Now, all the MC suspensions have SimDW turned off and InvDW turned on (which supposed to turn on analog dewhitening filter, which is probably 28 Hz ELP which has a notch at 60 Hz)
- Probably, when realtime model modifications for BH44 was made on Jan 17, coil dewhitening filter situation was not burt restored correctly, and we started to notice 60 Hz noise (which was already there but didn't notice because of dewhitening).
- See 40m/17431 for the timeline, possibly related elogs 40m/17359, 40m/17361 about MC1 dewhitening switching on Dec 14-16.

Next:
- Check if analong dewhitening filter actually has 28 Hz ELP by measuring transfer functions
- Design SimDW and InvDW to correctly take into account of real dewhitening filters

17466   Wed Feb 15 16:16:59 2023 AnchalSummaryBHDIMC optics Coil Output Filter corrections

Overtime the coil output filters on IMC optics have drifted into a bad configuration. Today at the meeting, Rana told us the correct configuration for these filters. I'll summarize this here and we have changes the filters on all IMC optics, MC1, MC2, and MC3 to match this configurations:

### MC1 and MC3

Analog side:

Both MC1 and MC3 have a 28 Hz 5th order elliptical low pass filter as teh dewhitening filter in LIGO-D000316

Digital side:

At the coil output filters named as C1:SUS-MC1_ULCOIL, the filter module FM9 is connectd in RTCDS to the analog dewhitening filter such that only one of the two can remain ON. So For MC1 and MC3, we put a ellip("LowPass", 5, 1, 50, 28) filter on FM9 for all 5 coil output filters.

Note: We do not add a inverse dewhitening filter at FM10 like most other optics as inverting this filter will create resonant peaks at the dips of the elliptical filter which we want to avoid and we anyways do not use MC1 and MC3 optics for any kind of actuation above 20 Hz.

### MC2

Analog side:

For MC2, the dewhitening filter is a 10 Hz pole, 30Hz zero like most other suspended optic.

Digital side:

At the coil output filters named as C1:SUS-MC2_ULCOIL, the filter module FM9 is connectd in RTCDS to the analog dewhitening filter such that only one of the two can remain ON. So For MC2 we put a SimDW filter which is matched to the anlog filter. We also put a InvDW filter on FM10, which is the analytical inverse of the SimDW filter. This filter does the anti-dewhitening required on the digital side and should be always ON.

To MC2 equivalent to other IMC optics in terms of overall transfer function for the local damping loops and ASC loops, we need additional 28 Hz elliptical low pass filter in these loops. But such a filter should not be in the path of LSC feedback when MC2 is used for locking CARM with a bandwidth of ~100 Hz. Thus, we put a ellip("LowPass", 5, 1, 50, 28) filter on FM6 of the following filters, which should be always ON as well:

• C1:SUS-MC2_ASCPIT
• C1:SUS-MC2_ASCYAW
• C1:SUS-MC2_SUSPOS
• C1:SUS-MC2_SUSPIT
• C1:SUS-MC2_SUSYAW
• C1:SUS-MC2_SUSSIDE

### Effect on 60 Hz Noise

With the above changes, we see that the 60 Hz noise is same as the previous levels when we use the analog dewhitening filter (28 Hz elliptical filter) for MC1. We can move forward with our science experiments with that configuration but there is still something fishy about MC1 in comparison to MC3 which does not have this behavior. So this still needs to be looked at in future.

### Wiki page for filter details and configurations

Information of this kind should be stored in a wiki page in my opinion. We should have a page where we list all common filter configurations for our suspensions and other loops, that can be generally classified and is useful for understanding legacy configuration for future folks who work here. I'm starting such a wiki page here, where I'll dump more information as I collect it and get time. Everyone is encouraged to update this in there free/procrastination times.

17481   Fri Feb 24 13:29:16 2023 AlexSummaryIMCUpdated angular actuation calibration for IMC mirrors

Also reply to: 40m/17352

Tomohiro, Anchal, and I did the following to make updates to the calibration constants for pitch and yaw on MC1, MC2 and MC3.

To acquire the data used for fitting a curve respective to the change in counts per change in mirror pitch and yaw, we utilized some code that Anchal has already developed.

The scripts used to take time averaged data points of the IMC mirrors can be found by entering the command s into a terminal window to enter the scripts folder. Then enter the path "SUS/angActCal" The following scripts will be found there to be used for this experiment: angActCal.py & parabolaFit.py To take data we used the angActCal.py function with set values for the time averaging = 5 s, settle time = 5 s, and adjusted the offset such that we would acquire approximately 20 data points given our ASC Bias limits. We defined the limits for each plot based on where the transmission fall off from the maximum value reached an average range of 10,000 counts. The "readChannel" for each was the "C1:IOO-MC_TRANS_SUMFILT_OUTPUT" and can be found from the site map at IOO>Lock MC> see MC2_TRANS The adjustment channels for Pitch and yaw on each IMC mirror were entered as the offset value found in the IMC screen at ALIGNMENT OFFSETS > BIASPIT/BIASYAW > OFFSET For the code to work, the offset switch must be turned on. parabolaFit.py The data from MC1, MC2, and MC3 for pitch and yaw was saved to individual text files which were then entered into the parabolaFit.py function to get the results seen in attachment 1 and 2. The above images show the printout from the plot fitting function and one of the graphs produced.  Optic ACT Fit curve factor for DC (1/cts^2) MC1 PIT 2.41 +/- 0.01 e-3 MC1 YAW 4.12 +/- 0.02 e-3 MC2 PIT 5.75 +/- 0.03 e-3 MC2 YAW 8.48 +/- 0.13 e-3 MC3 PIT 1.83 +/- 0.03 e-3 MC3 YAW 4.52 +/- 0.05 e-3 From the fitted curve values we then derived the equations that will soon be described further by Tomohiro (see entry _____) to arrive at the final callibration constants.  Optic ACT Callibration constant at DC (urad/cts) MC1 PIT 12.66 +/- 0.03 MC1 YAW 6.64 +/- 0.02 MC2 PIT lock6.83 +/- 0.02 MC2 YAW 4.69 +/- 0.04 MC3 PIT 11.03 +/- 0.09 MC3 YAW 6.96 +/- 0.04 Final Calibration Constants for MC1, MC2, & MC3 We then utilized our calculated calibration constants (as seen bellow) to adjust the following filter parameters in the IMC control panel. To make the updates such that the IMC screens show the correct urad values at the output of the filter banks, we must do the following steps to MC1, MC2, and MC3: First, to make changes to our calibration filters, we must first shut off the pitch and yaw feedback loop controls. TO do so for the Lock Filters, we will set the pitch and yaw SUS ASC inputs to 0 but entering the sitemap > IOO > C1IOO_WFS_MASTER Nex head to action at the top right, and we can select "MC WFS relief 60s", this will relieve the values from the pitch and yaw inputs to the 40m Mode Cleaner Alignment settings to save the overall alignment and allow us to turn off the WFS servos to make the necessary adjustments on the lock filters. Once we have waited a sufficient amount of time for the values on the ASC inputs to hover around 0, select Turn WFS ON/OFF button and choose "Turn OFF MCWFS Servo" Next, we will press on the "on/off" button (see attachment 3 - circled in orange) for pitch and yaw found in just the LOCK FILTERS windows. Once these are off we will stay in the same screen and adjust the gain values (boxed in yellow) for pitch and yaw. Next, we will take the current value and divide it by the newly found corresponding calibration constant. This is to adjust for the changes we will be making on the output end of the filter banks such that all values in the feedback controls are normalized to the same scale. The changes made here can be seen bellow:  Damp Filter Orig Damp Filter NEW Lock Filter Orig Lock Filter New MC1 PIT 40.0 3.160 1.0 0.079 MC1 YAW 40.0 6.024 1.0 0.151 MC2 PIT 5.0 0.732 1.0 0.146 MC2 YAW 5.0 1.066 1.0 0.213 MC3 PIT 3.0 0.272 1.0 0.091 MC3 YAW 5.0 0.718 1.0 0.144 Now that these changes have been made in the damp and lock filter banks, with the pitch and yaw feedback loops STILL OFF, we may adjust the newly made calibration filters for pitch and yaw (as seen in attachment 4). The "P" and "Y" filters may be opened (boxed in red) and we may adjust the gain (circled in yellow). Because each of these filters have just been created, the value is set to 1. This value can be completely replaced with the calibration constant found in our table above. Thus we will now change MC1 Pitch to have a "gain" of 12.66 and so forth. Once each of the calibration filters have been updated, you may go back into the damp filters and reinitiate the feedback loops. Once all values have been entered, This concludes the updating of the IMC filter calibration constants at DC. Attachment 1: angActCal_C1-SUS-MC1_BIASPIT_OFFSET_to_C1-IOO-MC_TRANS_SUMFILT_OUT_1361152703.png Attachment 2: Screenshot_2023-02-23_16-47-58.png Attachment 3: InkedScreenshot_2023-02-23_17-02-13.jpg Attachment 4: InkedScreenshot_2023-02-23_17-02-49.jpg 17482 Fri Feb 24 13:33:22 2023 TomohiroSummaryIMCUpdated angular actuation calibration for IMC mirrors Alex, Anchal, and I did the following to make updated angular actuation calibration for IMC mirrors. This is the revised version of Anchal's: 40m/16125. In order to make the calibration formulas, we consider a matrix $A$: connecting displacements and rotations of the IMC's beam waist to PIT and YAW rotations of every mirror $\begin{pmatrix} x_\mathrm{c} \\ y_\mathrm{c} \\ \theta_\mathrm{c} \\ \phi_\mathrm{c} \end{pmatrix} = A \begin{pmatrix} \theta_1 \\ \theta_2 \\ \theta_3 \\ \phi_1 \\ \phi_2 \\ \phi_3 \end{pmatrix}.$ The parameters used in the above equation are listed in the next table.  $x$ horizontal displacement of beam waist position $y$ vertical displacement of beam waist position $\theta$ PIT of the beam axis and/or each mirror $\phi$ YAW of the beam axis and/or each mirror $c$ (subscript) parameters for the beam $i = 1, 2, 3$ (subscript) parameters for $\mathrm{MC}_i$ $\mathrm{MC}_{1, 3}$ are the flat mirrors and $\mathrm{MC}_2$ is the curved mirror in IMC. Components in $A$ are refered from F. Kawazoe+ 2011 (doi: 10.1088/2040-8978/13/5/055504). In the paper, displacement and/or rotation of the beam parameters obtained from the PIT and YAW of each mirror are obtained not by $\theta_{1, 3}, \phi_{1, 3}$ but by common or differential rotation of both two flat mirrors $\theta_\pm \equiv \theta_1 \pm \theta_3, \phi_\pm \equiv \phi_1 \pm \phi_3$. Therefore, we divide $A$ into two parts $A_1, A_2$ (relation $A = A_1 A_2$): • $A_1$: relation between the beam parameters and the PIT and YAW rotation with $\theta_\pm, \phi_\pm$ $\begin{pmatrix} x_\mathrm{c} \\ y_\mathrm{c} \\ \theta_\mathrm{c} \\ \phi_\mathrm{c} \end{pmatrix} = A_1 \begin{pmatrix} \theta_+ \\ \theta_- \\ \theta_2 \\ \phi_+ \\ \phi_- \\ \phi_2 \end{pmatrix}.$ • $A_2$: relation between $\theta_\pm, \phi_\pm$ and $\theta_{1, 3}, \phi_{1, 3}$ $\begin{pmatrix} \theta_+ \\ \theta_- \\ \theta_2 \\ \phi_+ \\ \phi_- \\ \phi_2 \end{pmatrix} = A_2 \begin{pmatrix} \theta_1 \\ \theta_2 \\ \theta_3 \\ \phi_1 \\ \phi_2 \\ \phi_3 \end{pmatrix} = \begin{pmatrix} 1 & 0 & 1 & 0 & 0 & 0 \\ 1 & 0 & -1 & 0 & 0 & 0 \\ 0 & 1 & 0 & 0 & 0 & 0 \\ 0 & 0 & 0 & 1 & 0 & 1 \\ 0 & 0 & 0 & 1 & 0 & -1 \\ 0 & 0 & 0 & 0 & 1 & 0 \\ \end{pmatrix} \begin{pmatrix} \theta_1 \\ \theta_2 \\ \theta_3 \\ \phi_1 \\ \phi_2 \\ \phi_3 \end{pmatrix}.$ $A_1$ is represented by revewing F. Kawazoe+ (2011): $A_1 = \begin{pmatrix} 0 & 0 & 0 & 0 & - \sqrt{L^2 + d^2} & 0 \\ \dfrac{R - L}{\sqrt{2}} & 0 & -R & 0 & 0 & 0 \\ 0 & \dfrac{1}{\sqrt{2}} & 0 & 0 & 0 & 0 \\ 0 & 0 & 0 & \dfrac{R - L}{R - (L + d)} & 0 & - \dfrac{R}{R - (L + d)} \end{pmatrix}.$ Here we use $R$ as RoC of $\mathrm{MC}_2$$L$ as height from the shorter side of the isoscele triangle, and $d$ as half-long length of the shorter side. Intuitive discussion about the components are written in the last of the log. Transmitted power is reduced by the small displacement and/or the small rotation of the beam axis, and can be represented by the Gaussian factor. It is described in /users/OLD/kakeru/oplev_calibration/oplev.pdf by Takahashi-san: • parallel displacement $\left( \mathrm{e}^{- \frac{\beta^2}{{2w_0}^2}} \right)^2 \approx 1 - \frac{\beta^2}{{w_0}^2}$ where $\beta$ is the small displacement of the beam waist. It corresponds to $x_\mathrm{c},~y_\mathrm{c}$$w_0$ is beam waist diameter inside IMC. • beam axis rotation $\left( \mathrm{e}^{- \frac{\alpha^2}{{2\alpha_0}^2}} \right)^2 \approx 1 - \frac{\alpha^2}{{\alpha_0}^2}$ where $\alpha$ is the small rotation of the beam axis. It corresponds to $\theta_\mathrm{c}, \phi_\mathrm{c}$$\alpha_0$ is divergence angle of the beam and is written by $w_0$ and wavelength of laser $\lambda$ $\alpha_0 = \frac{\lambda}{\pi w_0}.$ Total power reduction is measured by multiplied gaussian factor of the displacement and the rotation. We can obtain the calibration formulas $\eta$ with summed reduction Gaussian factor \begin{align} &\frac{\beta (x_c (\vec{\Theta}), y_c (\vec{\Theta}))^2}{{w_0}^2} + \frac{\alpha (\theta_c (\vec{\Theta}), \phi_c (\vec{\Theta}))^2}{{\alpha_0}^2} \notag \\ &\qquad\quad= \eta_{\cdot 1\mathrm{P}}~{\theta_1}^2 + \eta_{\cdot 2\mathrm{P}}~{\theta_2}^2 + \eta_{\cdot 3\mathrm{P}}~{\theta_3}^2 + \eta_{\cdot 1\mathrm{Y}}~{\phi_1}^2 + \eta_{\cdot 2\mathrm{Y}}~{\phi_2}^2 + \eta_{\cdot 3\mathrm{Y}}~{\phi_3}^2 \notag \end{align} where $\vec{\Theta}$ is the vector of the PIT and YAW rotation $\vec{\Theta} \equiv \left( \theta_1, \theta_2, \theta_3, \phi_1, \phi_2, \phi_3 \right)^\mathrm{T}$. $\eta_{\cdot i \mathrm{P}}, \eta_{\cdot i \mathrm{Y}}$ are the calibration fomulas of PIT and YAW in 40m/16125 defined by Anchal, respectively, and have a unit of $\mathrm{1/rad^2}$. Every calibration fomula is expressed as follows: $\eta_{\cdot 1,3 \mathrm{P}} = \frac{(R - L)^2}{2 {w_0}^2} + \frac{1}{2 {\alpha_0}^2}~,~~\eta_{\cdot 2\mathrm{P}} = \frac{R^2}{{w_0}^2},$ $\eta_{\cdot 1,3 \mathrm{Y}} = \frac{L^2 + d^2}{{w_0}^2} + \frac{(R - L)^2}{{\alpha_0}^2 \left\{ R - (L + d) \right\}^2}~,~~\eta_{\cdot 2\mathrm{Y}} = \frac{R^2}{{\alpha_0}^2 \left\{ R - (L + d) \right\}^2}.$ We intuitively describe how to obtain the components in $A_1$. The detail is discussed in F. Kawazoe+ (2011). • $A_1 (1, 5)$: 2-flat mirrors rotate with differential YAW $\phi_-$ When the 2-flat mirrors rotate, the shape of the isoscele triangle is thick, that is, the beam waist does not rotate but slightly displaces from its original one. Considering that the longer side of the triangle are almost perpendicular to the shorter side and $\phi_- \ll 1$$x_\mathrm{c}$ can be obtained by focusing on the right triangle shown in the following picture $x_\mathrm{c} = - \sqrt{L^2 + d^2} \tan \phi_- \approx - \sqrt{L^2 + d^2} \phi_-.$ • $A_1 (4, 4)$: 2-flat mirrors rotate with common YAW $\phi_+$ From $\phi_+ \ll 1$, new triangle beam line is very similar to the isoscele triangle by rotating $\phi_+$ from original one. So $\phi_c$ is approximated to $\phi_+$, but actually the new one is breaked its symmetry. The result becomes as follows $\phi_\mathrm{c} = \frac{R - L}{R - (L + d)} \phi_+.$ • $A_1 (4, 6)$: curved mirror rotates by $\phi_2$ It is similar to the case of $\phi_+$. But the pivot to rotate the triangle is near than the case $\phi_+$, so $\phi_\mathrm{c}$ has bigger factor than that of $\phi_-$ $\phi_\mathrm{c} = - \frac{R}{R - (L + d)} \phi_2.$ • $A_1 (2, 3)$: curved mirror rotates by $\theta_2$ It is completely the same as the discussion of linear cavity which has flat end mirror and curved input mirror. $y_\mathrm{c} = - R \tan \theta_2 \approx - R \theta_2.$ • $A_1 (2, 1)$: 2-flat mirrors rotate with common PIT $\theta_+$ It is also the same as the linear one except that 2-flat mirrors are angled by 45 degrees. Angled 45 degrees reduce the effective rotation by factor of $1/\sqrt{2}$. The detail is discussed in A. Freise (2010). $y_\mathrm{c} = (R - L) \tan \left( \frac{\theta_+}{\sqrt{2}} \right) \approx (R - L) \frac{\theta_+}{\sqrt{2}}.$ • $A_1 (3,2)$: 2-flat mirrors rotate with differential PIT $\theta_-$ The differential rotation with the effect of $1/\sqrt{2}$ directly reflects to the PIT rotation of the beam $\theta_\mathrm{c} = \frac{\theta_-}{\sqrt{2}}.$ 17491 Fri Mar 3 18:47:13 2023 PacoSummaryBHDLO phase POS noise coupling - I I tried some LO PHASE noise coupling measurements today. With MICH locked using AS55_Q, I control the LO phase using the single RF (BH55_Q) or double RF (BH44_Q) demodulation error signals. The calibrated error and control points for single RF sideband sensing are shown in Attachment #1. In either case feedback loop is closed using FM5, FM8 first with a gain of 1.5 and then a "boost" using FM4. The actuation point is LO1 POS and the UGF was measured to be ~ 35 Hz for both. ** While doing this measurement, I noticed our LO_PHASE dark noise is significantly contributing 180 Hz, 300 Hz and other high line harmonics into the control signal rms so that may be something to look into soon. I first thought I could use the remaining sensor to measure the noise coupling (e.g. BH44 locks LO phase and BH55 senses injected noise or viceversa), but these two sensing schemes give two different LO phase sensitivities so I decided to just use the calibrated control signals. ### -- Noise coupling for BH55_Q -- After locking the LO_PHASE I inject 2 Hz wide uniform noise into three different frequency bands *within the control bandwidth* through C1:SUS-LO2_LSC_EXC, C1:SUS-AS1_LSC_EXC, and C1:SUS-AS4_LSC_EXC. The injected noise settings are captured by Attachment #2 (the screenshot of the excitation settings in diaggui). I read back the calibrated C1:HPC-LO_PHASE_OUT_DQ representing the true LO_PHASE noise within the control bandwidth and also calibrate the injected noise spectra with the help of the actuation coefficients in [elog40m:17274]. The result is summarized in Attachment #3. The diaggui template and data for this measurement are saved under /opt/rtcds/caltech/c1/Git/40m/measurements/BHD/BH55Q_NoiseCoupling.xml ### -- Noise coupling for BH44_Q -- I repeat the same procedure as above and the injected noise settings, and the result is summarized in Attachment #4. The diaggui template and data for this measurement are saved under /opt/rtcds/caltech/c1/Git/40m/measurements/BHD/BH44Q_NoiseCoupling.xml ### - Discussion - It seems that noise injected along the AS beam path (AS1-AS4 dither) couples more into the control point of the LO phase. I also seem to be off in terms of calibrating the noise excitation (even though I scaled using the suspension actuation from [elog40m:17274]. General feedback on the methods used for this measurement are welcome of course. ### - Next steps - - Extend this to single RF + audio dither scheme and double audio dither schemes (although it's hard because the control bandwidth is pretty low already) - Investigate line noise in RFPD + demod chain (present on the dark noise). - Investigate other more interesting noise couplings, e.g. angular degrees of freedom, RIN, laser freq noise, etc... - Repeat under more relevant IFO configurations (e.g. FPMI) Attachment 1: lophasenoise_bh55Qcontrol.png Attachment 2: bhnoisecoupling_excscreenshot.png Attachment 3: bh55q_noisecoupling.png Attachment 4: bh44q_noisecoupling.png 17517 Wed Mar 22 18:38:54 2023 PacoSummaryBHD"On why BH55 senses the LO phase, a finesse adventure of loss and residual DARM offsets" [Paco, Yehonathan] I took over the finesse calculations Yehonathan had set up for BHD. The notebook is here and for this post I focused on simulating what we might expect from our single RF vs dual RF sensors (55 MHz and 44 MHz respectively) in terms of LO phase control. The configuration is simple, only MICH is included (no ETMs, no PRC, no SRC). The LO phase is changed by scanning LO1, the differential loss is changed by scanning the ITMXHR loss parameter (nominally at 25 ppm), and the microscopic DARM offset is changed by scanning the BS position by +- 6 nm. Finesse estimates the sensor response by taking the demodulated sideband magnitude (BH55, BH44) with respect to a 1 Hz LO1 signal modulation. This can be done for a set of LO phase angles so as to get the nominal LO phase angle where the response is maximized. I first replicated the plots from [elog17170] for the two sensors in question. This is just done as a sanity check and is shown in Attachment #1. This plot summarizes our expectation that the single RF sideband sensor should have a peak response to the LO phase around 90 deg away from the nominal BHD readout phase angle (0 deg in this plot). In contrast, the double RF demodulation scheme has a peak response around the nominal LO phase angle. Attachment #2 looks at a family of similar plots representing differential loss changes between the two MICH arms. We tune this by changing the ITMX loss in finesse, and then repeat the calculation as described above. It seems that for the simple MICH, differential loss of ~ 10000 ppm does not impact the nominal LO phase angle where the responses are maximized for either sensor (note however that the response magnitude maybe changes for single RF sideband sensing at extremely high differential loss). Finally, and most interestingly Attachment #3 looks at a family of similar plots representing a set of microscopic DARM offsets (+- 6 nm). This is tuned by changing the BS position ever so slightly, and the same calculation is repeated. In this case, the nominal LO phase angle does change, and it changes quite a lot for the single RF demod. It looks like this might be enough to explain how we can sense the LO phase angle with a single RF sideband, but I think the next interesting point would be to simulate the effect of contrast defect by changing the ITM RoCs (to scatter into HOMs) or the non-thermal ITM lenses (to probe the TEM00 contrast defect effect). Any comments / feedback at this point are welcome, as we move forward into other configurations where more serious thermal effects might be introduced (PRMI). Attachment 1: LOphase_sensors.pdf Attachment 2: LOphase_sensors_loss.pdf Attachment 3: LOphase_sensors_darmoffset.pdf 17518 Thu Mar 23 14:20:29 2023 KojiSummaryBHD"On why BH55 senses the LO phase, a finesse adventure of loss and residual DARM offsets" This is interesting. With the FPMI, the DARM phase shift is enhanced by the cavity. Therefore, I suppose the effect on the BH55 is also going to be enhanced (i.e. a much smaller displacement offset causes a similar LO phase rotation). 17521 Thu Mar 23 19:15:39 2023 yutaSummaryLSCPRMI locked using REFL55 [Paco, Yuta] We locked PRMI in sideband using REFL55_I and REFL55_Q. Lock is not quite stable probably due to alignment fluctuations, and power recylicing gain is breathing. PRMI preparations: - We aligned PRM using PRY (PRM-ITMY) cavity. Aligning PRM to oplev QPD center or last PRM alignment values in May 2022 (! see 40m/16875) didn't work, but we were in the middle of these two, both in pitch and yaw. - After this, we centered PRM oplev, aligned REFL camera, POP RFPD (which provides POP22, POP110, and POPDC), and REFL11. PRY/PRX locking: - PRY/X was locked using REFL55_I or REFL11_I. Locking configuration which gives UGF of ~100 Hz was as follows REFL55_I (24 dB whitening gain, 76.02 deg demod angle) C1:LSC-PRCL_GAIN=-0.03 REFL11_I (18 dB whitening gain, 32.55 deg demod angle) C1:LSC-PRCL_GAIN=-0.8 FM4,5 used for acquisition, FM1,2,6,9 turned on triggered. - Attachment #1 is the measured OLTF when PRY was locked. - When PRY is flashing, ASDC_OUT, POPDC_OUT, POP22_I, POP11_Q flashes upto 0.33, 1000, 30, 80, respectively. PRMI locking: - PRMI was locked using REFL55_I for PRCL and REFL55_Q for MICH using the following configurations to give UGF of ~100 Hz for both DoF. PRCL REFL55_I (24 dB whitening gain, 76.02 deg demod angle) C1:LSC-PRCL_GAIN=-0.03 FM4,5 for acquisition, FM1,2 turned on triggered using POPDC. Actuating on 1 * PRM MICH REFL55_Q (24 dB whitening gain, 76.02 deg demod angle) C1:LSC-MICH_GAIN=+0.9 FM4,5 for acquisition, FM1,2 turned on triggered using POPDC. Actuating on 0.5 * BS - 0.275 * PRM - REFL55 demodulation phase was the same as FPMI and PRY. We checked this is roughly enough by measuring the sensing matrix to minimize PRCL component in Q. - MICH actuation of PRM/BS ratio was roughly tuned by minimizing the sensing of MICH component in REFL55_I. - PRCL and MICH gain was estimated by measuring the amplitude of error signals in PRY or PRM-misalgined MICH, and comparing that in PRMI. - Attachment #2 shows the screenshot of the configuration. - Attachment #3 and #4 are measured OLTF for PRCL and MICH. - Attachment #5 shows the time series data when PRMI is locked. Next: - Tune PRM local damping - Tune REFL55 demodulation phase better by measuring the sensing matrix - Measure PRM actuation efficiency to check what is the right BS/PRM balancing - Estimate power recycling gain and compare with expectations - Lock PRMI using REFL11, AS55 - PRMI BHD Attachment 1: Screenshot_2023-03-23_15-58-25_PRY_OLTF.png Attachment 2: Screenshot_2023-03-23_18-48-25_PRMIlocking.png Attachment 3: Screenshot_2023-03-23_18-41-25_PRCL_PRMI.png Attachment 4: Screenshot_2023-03-23_18-40-55_MICH_PRMI.png Attachment 5: Screenshot_2023-03-23_18-44-12_PRMISB.png 17522 Fri Mar 24 12:54:51 2023 yutaSummaryLSCActuator calibration of PRM using PRY PRM actuator was calibrated using PRY by comparing the actuation ratio between ITMY. It was measured to be PRM : -20.10e-9 /f^2 m/counts This is consistent with what we have measured in 2013! (40m/8255) Method: - Locked PRY using REFL55_I using the configuration described in 40m/17521 (UGF of ~100 Hz) - Measured transfer function from C1:LSC-(ITMY|PRM)_EXC to C1:LSC-PRCL_IN1 - Took the ratio between ITMY actuation and PRM actuation to calculate PRM actuation, as ITMY actuation is known to be 4.90e-9 /f^2 m/counts (40m/17285). Result: - Attachment #1 is the measured TF, and Attachment #2 is the actuator ratio PRM/ITMY. - The ratio was -4.10 on average in 70-150 Hz region, and PRM actuation was estimated to be 4.90e-9 * -4.10 /f^2 m/counts. MICH actuator for PRMI lock: - When BS moves in POS by 1, BS-ITMX length stays the same, but BS-ITMY length changes by sqrt(2), so MICH changes by sqrt(2) and PRCL changes by -sqrt(2)/2. - So PRM needs to be used to compensate for this, and the ratio will be BS + k * PRM, where k = 26.54e-9/sqrt(2) / -20.10e-9 * sqrt(2)/2 = -0.66 - So, good MICH actuator will be 0.5 * BS - 0.33 * PRM, which is not quite consistent with the rough number we had yesterday (-0.275; 40m/17521), but agrees with the Gautam number (-0.34; 40m/15996). - PRMI sensing matrix for REFL55 needs to be checked again. Summary of actuation calibration so far: They are all actuator efficiency from C1:LSC-{OPTIC}_EXC

BS   : 26.54e-9 /f^2 m/counts in MICH (40m/17285)
ITMX :  4.93e-9 /f^2 m/counts (
40m/17285)
ITMY :  4.90e-9 /f^2 m/counts (
40m/17285)
LO1  : 26.34e-9 /f^2 m/counts (
40m/17285)
LO2  :  9.81e-9 /f^2 m/counts (
40m/17285)
AS1  : 23.35e-9 /f^2 m/counts (
40m/17285)
AS4  : 24.07e-9 /f^2 m/counts (
40m/17285)
ETMX : 10.91e-9 /f^2 m/counts (
40m/16977, 40m/17014)
ETMY : 10.91e-9 /f^2 m/counts (
40m/16977)
MC2 : -14.17e-9 /f^2 m/counts in arm length (
40m/16978)
MC2 :   5.06e-9 /f^2 m/counts in IMC length (
40m/16978)
MC2 :  1.06e+05 /f^2 Hz/counts in IR laser frequency (
40m/16978)
PRM : -20.10e-9 /f^2 m/counts (
40m/17522)

Attachment 1: PRMActuatorTF.png
Attachment 2: PRMActuatorRatio.png
17523   Fri Mar 24 15:05:41 2023 yutaSummaryLSCPRMI sensing matrix and RF demodulation phase tuning

PRMI sensing matrix was measured under PRMI locked with REFL55_I and Q.
MICH actuator is 0.5*ITMX-0.5*ITMY (to have more pure MICH, according to 40m/15996) and PRCL actuator is PRM.
RF demod phases seem to be good within a degree or so to minimize PRCL component in Q.

Sensing matrix with the following demodulation phases (counts/m)
{'AS55': 2.1, 'REFL55': 76.02, 'REFL11': 32.63833493469488}
Sensors       MICH @311.1 Hz           PRCL @313.31 Hz
AS55_I       (+0.31+/-1.48)e+09 [90]    (+6.56+/-2.23)e+10 [0]
AS55_Q       (-3.49+/-0.87)e+08 [90]    (+4.62+/-1.80)e+09 [0]
REFL55_I       (-1.52+/-5.61)e+09 [90]    (+3.21+/-1.36)e+11 [0]
REFL55_Q       (+8.77+/-0.46)e+09 [90]    (+5.01+/-3.63)e+09 [0]
REFL11_I       (-0.23+/-1.92)e+08 [90]    (+1.13+/-0.47)e+10 [0]
REFL11_Q       (+0.39+/-2.14)e+07 [90]    (-4.00+/-9.79)e+07 [0]

Phase for AS55 to minimize PRCL in Q is 6.14+/-2.08 deg (4.04+/-2.08 deg from current value)
Phase for REFL55 to minimize PRCL in Q is 76.91+/-0.75 deg (0.89+/-0.75 deg from current value)
Phase for REFL11 to minimize PRCL in Q is 32.44+/-0.50 deg (-0.20+/-0.50 deg from current value)

Next:
- Lock PRMI in carrier
- PRG is not so stable; Measure g-factor of PRC using Kakeru-Gupta method (40m/8235)

17524   Sun Mar 26 19:13:48 2023 yutaSummaryLSCPRMI sensing matrix and RF demodulation phase tuning

that is really a lot of high precision for the REFL_11 demod phase...

for this kind of measurement, I wish we had a python code that would plot this measurment relative to our Finesse/PyKat model so we know if this table is like "Oh, nothing to see here." or "Wow! that's a Nobel prize worthy measurement !!"

17525   Mon Mar 27 20:28:57 2023 PacoSummaryBHD"On why BH55 senses the LO phase, a finesse adventure of loss and residual DARM offsets"

Yuta pointed out that the BH55 signal was weirdly never going to zero, so I actually tuned the demod angle and made sure I was reading the right (Q) quadrature. This doesn't affect our previous qualitative conclusion about DARM offsets, but here's an updated gif which also makes visualization easier (?).

Attachment 1: MICH_BHD_darmoffset.gif
17526   Tue Mar 28 10:58:03 2023 ranaSummaryBHD"On why BH55 senses the LO phase, a finesse adventure of loss and residual DARM offsets"

but what about including the DC reflectivity imbalance of the arms? there would be another BH55 term from that field maybe.

17528   Wed Mar 29 16:36:04 2023 PacoSummaryBHD"On why BH55 senses the LO phase, a finesse adventure of loss and residual DARM offsets"

I repeated the calculations but with FPMI (last case was all MICH). The qualitative behavior is the same, the BH55 sensing is mostly affected by residual darm offset. If the darm offset is of a couple of nm, the single RF sideband may sense the LO phase at as much as > 20 deg away from the nominal phase angle. This is not too different from the MICH case; so maybe I overlooked something about how I define FPMI in the calculation.

Attachments #1-3 show the plots of the BH55 (single RF sideband) and BH44 (double RF sideband) sensitivity to LO phase fluctuations around various nominal LO phase angles. Attachment #1 looks at the effect of differential loss, Attachment #2 looks at the effect of differential dc reflectivity (of the ITMs), and Attachment #3 looks at the effect of residual darm offsets. Dashed lines show the orthogonal quadrature (I) of the demodulated RF signals (always minimized).

Attachment 1: FPMI_LOphase_sensors_loss.pdf
Attachment 2: FPMI_LOphase_sensors_dcrefl.pdf
Attachment 3: FPMI_LOphase_sensors_darmoffset.pdf
60   Sun Nov 4 23:22:50 2007 waldmanUpdateOMCOMC PZT and driver response functions
I wrote a big long elog and then my browser hung up, so you get a less detailed entry. I used Pinkesh's calibration of the PZT (0.9 V/nm) to calibrate the PDH error signal, then took the following data on the PZT and PZT driver response functions.:

• FIgure 1: PZT dither path. Most of the features in this plot are understood: There is a 2kHz high pass filter in the PZT drive which is otherwise flat. The resonance features above 5 kHz are believed to be the tombstones. I don't understand the extra motion from 1-2 kHz.
• Figure 2: PZT dither path zoom in. Since I want to dither the PZT to get an error signal, it helps to know where to dither. The ADC Anti-aliasing filter is a 3rd order butterworth at 10 kHz, so I looked for nice flat places below 10 KHz and settled on 8 kHz as relatively harmless.
• Figure 3: PZT LSC path. This path has got a 1^2:10^2 de-whitening stage in the hardware which hasn't been digitally compensated for. You can see its effect between 10 and 40 Hz. The LSC path also has a 160 Hz low path which is visible causing a 1/f between 200 and 500 Hz. I have no idea what the 1 kHz resonant feature is, though I am inclined to point to the PDH loop since that is pretty close to the UGF and there is much gain peaking at that frequency.
Attachment 1: 071103DitherShape.png
Attachment 2: 071103DitherZoom.png
Attachment 3: 071103LSCShape.png
Attachment 4: 071103DitherShape.pdf
Attachment 5: 071103DitherZoom.pdf
Attachment 6: 071103LSCShape.pdf
Attachment 7: 071103LoopShape.pdf
61   Sun Nov 4 23:55:24 2007 ranaUpdateIOOFriday's In-Vac work
On Friday morning when closing up we noticed that we could not get the MC to flash any modes.
We tracked this down to a misalignment of MC3. Rob went in and noticed that the stops were
still touching. Even after backing those off the beam from MC3 was hitting the east edge of
the MC tube within 12" of MC3.

This implied a misalignment of MC of ~5 mrad which is quite
large. At the end our best guess is that either I didn't put the indicator blocks in the
right place or that the MC3 tower was not slid all the way back into place. Since there
is such a strong stickiness between the table and the base of the tower its easy to
imagine the tower was misplaced.

So we looked at the beam on MC2 and twisted the MC3 tower. This got the beam back onto the
MC2 cage and required ~1/3 if the MC3 bias range to get the beam onto the center. We used
a good technique of finding that accurately: put an IR card in front of MC2 and then look
in from the south viewport of the MC2 chamber to eyeball the spot relative to the OSEMs.

Hitting MC2 in the middle instantly got us multiple round trips of the beam so we decided
to close up. First thing Monday we will put on the MC1/MC3 access connector and then
pump down.

Its possible that the MC length has changed by ~1-2 mm. So we should remeasure the length
and see if we need to reset frequencies and rephase stuff.
62   Mon Nov 5 07:29:35 2007 ranaUpdateIOOFriday's In-Vac work
Liyuan recently did some of his pencil beam scatterometer measurements measuring not the
BRDF but instead the total integrated power radiated from each surface point
of some of the spare small optics (e.g. MMT, MC1, etc.).

The results are here on the iLIGO Wiki.

So some of our loss might just be part of the coating.
63   Mon Nov 5 14:44:39 2007 waldmanUpdateOMCPZT response functions and De-whitening
The PZT has two control paths: a DC coupled path with gain of 20, range of 0 to 300 V, and a pair of 1:10 whitening filters, and an AC path capacitively coupled to the PZT via a 0.1 uF cap through a 2nd order, 2 kHz high pass filter. There are two monitors for the PZT, a DC monitor which sniffs the DC directly with a gain of 0.02 and one which sniffs the dither input with a gain of 10.

There are two plots included below. The first measures the transfer function of the AC monitor / AC drive. It shows the expected 2 kHz 2d order filter and an AC gain of 100 dB, which seems a bit high but may be because of a filter I am forgetting. The high frequency rolloff is the AA and AI filters kicking in which are 3rd order butters at 10 kHz.

The second plot is the DC path. The two traces show the transfer function of DC monitor / DC drive with and with an Anti-dewhitening filter engaged in the DC drive. I fit the antidewhite using a least squares routine in matlab constrained to match 2 poles, 2 zeros, and a delay to the measured complex filter response. The resulting filter is (1.21, 0.72) : (12.61, 8.67) and the delay was f_pi = 912 Hz. The delay is a bit lower than expected for the f_pi = 3 kHz delay of the AA, AI, decimate combination, but not totally unreasonable. Without the delay, the filter is (1.3, 0.7) : (8.2, 13.2) - basically the same - so I use the results of the fit with delay. As you can see, the response of the combined digital AntiDW, analog DW path is flat to +/- 0.3 dB and +/- 3 degrees of phase.

Note the -44 dB of DC mon / DC drive is because the DC mon is calibrated in PZT Volts so the TF is PZT Volts / DAC cts. To calculate this value: there are (20 DAC V / 65536 DAC cts)* ( 20 PZT V / 1 DAC V) = -44.2 dB. Perfect!

I measured the high frequency response of the loop DC monitor / DC drive to be flat.
Attachment 1: 07110_DithertoVmonAC_sweep2-0.png
Attachment 2: 071105_LSCtoVmonDC_sweep4-0.png
Attachment 3: 07110_DithertoVmonAC_sweep2.pdf
Attachment 4: 071105_LSCtoVmonDC_sweep4.pdf
68   Tue Nov 6 14:51:03 2007 tobin, robUpdateIOOMode cleaner length
Using the Ward-Fricke variant* of the Sigg-Frolov method, we found the length of the mode cleaner to be 27.0934020183 meters, a difference of -2.7mm from Andrey, Keita, and Rana's measurement on August 30th.

The updated RF frequencies are:
3  fsr =  33 195 439 Hz
12 fsr = 132 781 756 Hz
15 fsr = 165 977 195 Hz
18 fsr = 199 172 634 Hz
* We did the usual scheme of connecting a 20mVpp, 2 kHz sinusoid into MC AO. Instead of scanning the RF frequency by turning the dial on the 166 MHz signal generator ("marconi"), we connected a DAC channel into its external modulation port (set to 5000 Hz/volt FM deviation). We then scanned the RF frequency from the control room, minimizing the height of the 2 kHz line in LSC-PD11. In principle one could write a little dither servo to lock onto the 15fsr, but in practice simply cursoring the slider bar around while watching a dtt display worked just fine.
69   Tue Nov 6 15:36:03 2007 robUpdateLSCXARM locked
Easily, after resetting the PSL Uniblitz shutters. There's no entry from David or Andrey about the recovery from last week's power outage, in which they could have indicated where the procedure was lacking/obscure. Tsk, tsk.
76   Wed Nov 7 09:38:01 2007 steveUpdateVACrga scan
pd65-m-d2 at cc1 6e-6 torr
Attachment 1: pd65d2.jpg
81   Wed Nov 7 16:07:03 2007 steveUpdatePSLPSL & IOO trend
1.5 days of happy psl-ioo with litle bumps in C1:PSL-126MOPA_HTEMP
Attachment 1: psl1.5dtrend.jpg
82   Thu Nov 8 00:55:44 2007 pkpUpdateOMCSuspension tests
[Sam , Pinkesh]

We tried to measure the transfer functions of the 6 degrees of freedom in the OMS SUS. To our chagrin, we found that it was very hard to get the OSEMs to center and get a mean value of around 6000 counts. Somehow the left and top OSEMs were coupled and we tried to see if any of the OSEMs/suspension parts were touching each other. But there is still a significant coupling between the various OSEMs. In theory, the only OSEMS that are supposed to couple are [SIDE] , [LEFT, RIGHT] , [TOP1, TOP2 , TOP3] , since the motion along these 3 sets is orthogonal to the other sets. Thus an excitation along any one OSEM in a set should only couple with another OSEM in the same same set and not with the others. The graphs below were obtained by driving all the OSEMS one by one at 7 Hz and at 500 counts ( I still have to figure out how much that is in units of length). These graphs show that there is some sort of contact somewhere. I cant locate any physical contact at this point, although TOP2 is suspicious and we moved it a bit, but it seems to be hanging free now. This can also be caused by the stiff wire with the peek on it. This wire is very stiff and it can transmit motion from one degree of freedom to another quite easily. I also have a graph showing the transfer function of the longitudnal degree of freedom. I decided to do this first because it was simple and I had to only deal with SIDE, which seems to be decoupled from the other DOFs. This graph is similar to one Norna has for the longitudnal DOF transfer function, with the addition of a peak around 1.8 Hz. This I reckon could very be due to the wire, although it is hard to claim for certain. I am going to stop the measurement at this time and start a fresh high resolution spectrum and leave it running over night.

There is an extra peak in the high res spectrum that is disturbing.
Attachment 1: shakeleft.pdf
Attachment 2: shakeright.pdf
Attachment 3: shakeside.pdf
Attachment 4: shaketop1.pdf
Attachment 5: shaketop2.pdf
Attachment 6: shaketop3.pdf
Attachment 7: LongTransfer.pdf
Attachment 8: Shakeleft7Nov2007_2.pdf
Attachment 9: Shakeleft7Nov2007_2.png
83   Thu Nov 8 11:40:21 2007 steveUpdatePEMparticle counts are up
I turned up the psl HEPA filter to 100%
This 4 days plot shows why
Attachment 1: pslhepaon.jpg
87   Fri Nov 9 00:23:12 2007 pkpUpdateOMCX and Z resonances
I got a couple of resonance plots going for now. I am still having trouble getting the Y measurement going for some reason. I will investigate that tommorow. But for tonight and tommorow morning, here is some food for thought. I have attached the X and Z transfer functions below. I compared them to Norna's plots - so just writing out what I was thinking -

Keep in mind that these arent high res scans and have been inconviniently stopped at 0.5 Hz .

Z case --

I see two small resonances and two large ones - the large ones are at 5.5 Hz and 0.55 Hz and the small ones at 9 Hz and 2 Hz respectively. In Norna's resonances, these features arent present. Secondly, the two large peaks in Norna's measurement are at 4.5 Hz and just above 1 Hz. Which was kind of expected, since we shortened the wires a bit, so one of the resonances moved up and I suppose that the other one moved down for the same reason.

X case --

Only one broad peak at about 3 Hz is seen here, whereas in Norna's measurement, there were two large peaks and one dip at 0.75 Hz and 2.5 Hz. I suspect that the lower peak has shifted lower than what I scanned to here and a high res scan going upto 0.2 Hz is taking place overnight. So we will have to wait and watch.

Pitch Roll and Yaw can wait for the morning.
Attachment 1: Xtransferfunc.pdf
Attachment 2: Ztransferfunc.pdf
88   Fri Nov 9 09:37:55 2007 steveUpdatePSLhead temp hiccup
Just an other PSL-126MOPA_HTEMP hiccup.
The water chiller is at 20.00C
Attachment 1: headtempup.jpg
93   Mon Nov 12 10:53:58 2007 pkpUpdateOMCVertical Transfer functions
[Norna Sam Pinkesh]

These plots were created by injected white noise into the OSEMs and reading out the response of the shadow sensors ( taking the power spectrum). We suspect that some of the additional structure is due to the wires.
Attachment 1: VerticalTrans.pdf
96   Mon Nov 12 15:18:34 2007 robUpdatePSLISS

After John soldered a 3.7 MHz notch filter onto the ISS board, I took a quick TF and RIN measurement. The out-of-loop RIN is attached, including a dark noise trace, and with the gain slider at 10dB. The UGF is 35kHz with a phase margin of 30deg. John is currently doing a more thorough inspection, and will detail his findings in a subentry.
Attachment 1: ISS.png
97   Mon Nov 12 23:44:19 2007 JohnUpdatePSLISS

 Quote: After John soldered a 3.7 MHz notch filter onto the ISS board, I took a quick TF and RIN measurement. The out-of-loop RIN is attached, including a dark noise trace, and with the gain slider at 10dB. The UGF is 35kHz with a phase margin of 30deg. John is currently doing a more thorough inspection, and will detail his findings in a subentry.

No progress on the ISS tonight. I tried to implement a new filter (attached)to try and gain some phase before the notch. If anything this made things worse. More work is needed.

The ISS loop is off and the power is off at the chassis.
Attachment 1: ISSfilter.jpg
98   Tue Nov 13 14:33:40 2007 JohnUpdatePSLISS filter
The transfer function from 'In Loop Error Point Monitor' to TP3 the filter out test point on the ISS board.

-33dB at 3.715MHz.
Attachment 1: PB130035.JPG
Attachment 2: DSC_0165.JPG
101   Wed Nov 14 12:47:19 2007 tobinUpdatePSLISS
John, Tobin

With John's notch filter installed and the increased light on the ISS sensing diode, we were able to get a UGF of about 60 kHz with the gain slider set to about 20 dB. This morning we met with Stefan to learn his ISS-fu.

His recommendations for the ISS include:
• Replace the cables from the board to the front panel connectors if this hasn't already been done.
• Replace the input opamps with 4131's. Be sure to test both positive and negative input signals.
• Check that all the compensation capacitors are in place and are 68 pF
• Make sure all the feedback loops have high frequency rolloff
• The ISS board reads the PDs differentially; make sure the PD sends differentially.
• Add a big (ie 10uF tantalum) capacitor to the PD to suppress power supply noise
• Add bigger power supply bypass caps to the ISS
I just took sensing noise spectra (from the PD DC bnc ports) and then took the photodiodes off the table to check that they have the negative end of the differential line connected to ground. (I placed black metal beam blocks on the table in place of the ISS PD's. Also, from the ISS schematic, it looks like it sends a differential output to the PD DC bnc ports, but we have been plugging them directly into the SR785 (grounding the shield). We should make a little BNC-doodle that separates the signal+shield to go into the A and B inputs on the spectrum analyzer.) Opening up one of the photodiodes, it appears that the negative line of the differential output is not connected. Will continue later this afternoon.
102   Wed Nov 14 16:54:54 2007 pkpUpdateOMCMuch better looking vertical transfer functions
[Norna Pinkesh]

So after Chub did his wonderful mini-surgery and removed the peek from the cables and after Norna and I aligned the whole apparatus, the following are the peaks that we see.
It almost exactly matches Norna's simulations and some of the extra peaks are possibly due to us exciting the Roll/longitudnal/yaw and pitch motions. The roll resonance is esp prominent.

We also took another plot with one of the wires removed and will wait on Chub before we remove another wire.
Attachment 1: VerticalTransPreampwireremovedNov142007.pdf
Attachment 2: VerticalTranswiresclampedNov142007.pdf
103   Wed Nov 14 17:50:00 2007 tobinUpdatePSLISS
Here's the current wiring between the ISS and its PDs:

 pin cable PD ISS 1 blue +5 +5 2 red +15 +15 3 white -15 -15 4 brown OUT IN PD + 5,6,7,8 no connection no connection GND 9 black GND IN PD -

The schematics for the ISS and the PDs are linked from our wiki.

We'll connect the ISS GND to the PD GND.
105   Thu Nov 15 17:09:37 2007 pkpUpdateOMCVertical Transfer functions with no cables attached.
[Norna Pinkesh]

The cables connecting all the electronics ( DCPDs, QPDs etc) have been removed to test for the vertical transfer function. Now the cables are sitting on the OMC bench and it was realigned.
Attachment 1: VerticaltransferfuncnocablesattachedNov152007.pdf
106   Thu Nov 15 18:06:06 2007 tobinUpdateComputersalex: linux1 root file system hard disk's dying
I just noticed that Alex made an entry in the old ilog yesterday, saying: "Looks like linux1 root filesystem hard drive is about to die. The system log is full of drive seek errors. We should get a replacement IDE drive as soon as possible or else the unthinkable could happen. 40 Gb IDE hard drive will be sufficient."
109   Thu Nov 15 18:37:06 2007 tobinUpdateComputerspossible replacement for linux1's disk
It looks like the existing disk in linux1 is a Seagate ST380013A (this can be found either via the smartctl utility or by looking at the file /proc/ide/hda/model). It appears that you can still buy this disk from amazon, though I think just about any ATA disk would work. I'll ask Steve to buy one for us.
110   Fri Nov 16 11:27:18 2007 tobinUpdateComputersscript fix
I added a tidbit of code to "LIGOio.pm" that fixes a problem with ezcastep on Linux. Scripts such as "trianglewave" will now work on Linux.
# On Linux, "ezcastep" will interpret negative steps as command line arguments,
# because the GNU library interprets anything starting with a dash as a flag.
# There are two ways around this.  One is to set the environment variable
# POSIXLY_CORRECT and the other is to inject "--" as a command line argument
# before any dashed arguments you don't want interpreted as a flag.  The former
# is easiest to use here:

if (uname =~ m/Linux/) {
# Add an environment variable for child processes
$ENV{'POSIXLY_CORRECT'} = 1; } 111 Fri Nov 16 14:11:26 2007 tobinUpdateComputersop140 Alan called to say that Phil Ehrens will be coming by to take op140 off our hands. 112 Fri Nov 16 14:31:43 2007 tobinUpdateComputersop140 disks Phil Ehrens stopped by and took op140's disks. Attachment 1: DSC_0173.JPG 117 Tue Nov 20 11:10:07 2007 tobinUpdateComputersepics access from matlab I installed "labca", which allows direct access to EPICS channels from within Matlab. It comes with both Linux and Solaris binaries (and source) but I've only tried it on linux. To set it up, run these shell commands: pushd /cvs/cds/caltech/users/tf/build/labca_2_1/bin/linux-x86 setenv PATH${PATH}:pwd
cd /cvs/cds/caltech/users/tf/build/labca_2_1/lib/linux-x86
setenv LD_LIBRARY_PATH \${LD_LIBRARY_PATH}:pwd
popd
Then start matlab, and within matlab type:
addpath /cvs/cds/caltech/users/tf/build/labca_2_1/bin/linux-x86/labca
help labca
foo = lcaGet('C1:PSL-FSS_RCTRANSPD')
It seems like reasonably well-written software, and is being actively maintained right now. If we like it, I can build a more recent version, install it in a more permanent location, etc.
121   Wed Nov 21 14:31:41 2007 robUpdatePSLFSS twiddle

I `tweaked' the FSS path today. Here's what I did:

1) Shut down the FSS autolocker

2) Turn off FSS servo

3) Assume the beam coming back from the AOM is double-first-order, and don't make any changes large enough to lose it.

4) Tweak the alignment of these components to maximize the incident power on the RC reflected diode:

a) PBS before AOM
b) AOM
c) curved mirror after the AOM

5) Translate the AOM such that the beam moves away from the PZT, then when it levels off (no more power gains with movement),
move it back just a little bit so there's a teensy drop in power. This should but the beam as close to the edge as possible,
but whether or not it's the best place is still to be determined.

6) Lock the FSS, and align the mirrors into the frequency reference cavity.

After all this, the RC transmitted power went from .57 to .73 -- probably not a big enough change to account for the missing loop
gain, but we'll know more once the loop gets measured (after Alberto stops hogging the Agilent network analyzer).

Other possible routes include a systematic check of the upstream path (e.g., the Pockels cell) and just increasing the pickoff fraction for the FSS.
127   Tue Nov 27 20:47:00 2007 tobinUpdatePSLFSS
Rana, Tobin

We looked at the RF PD signal to the FSS (siphoning off a signal via a minicircuits directional coupler) and also took an open loop transfer function of the FSS. In the transfer function we saw the step at 100 kHz (mentioned by Rob) as well as some peculiar behavior at high frequency. The high frequency behavior (with a coupling of ~ -20 dB) turns out to be bogus, as it is still present even with the beam blocked. Rearranging the cabling had no effect; the cause is apparently inside the FSS. The step at 100 kHz turns out to be a saturation effect, as it moved as we lowered the signal amplitude, disappearing as we approached -60 dBm. (Above the step, the measurement data is valid; below, bogus.)

Transfer functions will be attached to this entry.

Some things to check tomorrow: the RF signal to the PC, RF AM generation by the PC, LO drive level into the FSS, RF reflection from the PC, efficiency of FSS optical path, quality of RF cabling.
Attachment 1: fss-tf0001.pdf
128   Wed Nov 28 04:21:46 2007 ranaUpdatePSLFSS

 Quote: Rana, Tobin We looked at the RF PD signal to the FSS (siphoning off a signal via a minicircuits directional coupler) and also took an open loop transfer function of the FSS. In the transfer function we saw the step at 100 kHz (mentioned by Rob) as well as some peculiar behavior at high frequency. The high frequency behavior (with a coupling of ~ -20 dB) turns out to be bogus, as it is still present even with the beam blocked. Rearranging the cabling had no effect; the cause is apparently inside the FSS. The step at 100 kHz turns out to be a saturation effect, as it moved as we lowered the signal amplitude, disappearing as we approached -60 dBm. (Above the step, the measurement data is valid; below, bogus.) Transfer functions will be attached to this entry. Some things to check tomorrow: the RF signal to the PC, RF AM generation by the PC, LO drive level into the FSS, RF reflection from the PC, efficiency of FSS optical path, quality of RF cabling.

I would also add to Tobin's entry that we believe what Rob was seeing was saturation.

With the bi-directional coupler in there, the RF signal into the FSS board clearly went UP if moved the offset slider away from zero.
With a scope looking at the IN2 testpoint, we can see that there's less than 2 mV offset at zero slider offset.

One tangential thing we noticed with the coupler is that, in lock, the amount of reflected RF is around the same as that going in to the mixer.
I have always wanted to look at this but have only had uni-directional couplers in the past. I think that the double balanced mixer is inherently
not a 50 Ohm device during the times where the diodes are being switched. IF that's the case we might do better in the future by having an RF
buffer on board just before the mixer to isolate the PD head from these reflections.
134   Wed Nov 28 17:41:34 2007 robUpdatePSLFSS again
I investigated the FSS a bit more today. I looked at the signals coming out of the FSS frequency reference, and saw that both the LO and PC drive were distorted, non-symmetric waveforms. In addition, the LO path had a 3dB attenuator, meaning the mixer was starved. I placed mini-circuits SLP-30 filters in both paths, and now both are nice sine waves. I also took out the 3dB att. With this work, and the CG slider maxed out at 30, the FSS open loop gain (for real this time) goes up to ~250kHz. Still needs more investigation.
136   Wed Nov 28 19:44:18 2007 tobinUpdatePSLHEPA
I found the HEPA turned off completely. I turned it on.
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