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  17047   Fri Jul 29 20:21:11 2022 KojiUpdatePSLFSSSlow/MCAutolocker issue (docker)

MCAutolocker/FSSSlow are not properly documented and not properly working.
Tidy up the script and documentation, or bring it back to megatron


I was aware that the FSSSlow was misbehaving since the shutdown upon the July power outage.
- FSS Slow servo did nothing even though the apparent settings in C1:PSL_SLOW screen looked fine and heart beat blinking
- Wanted to restart FSSSlow at megatron. Despite the login message showing how to do it, the system service does not exist anymore, because it was moved somewhere.
- Searched 40m wiki but found no info how to kill and restart it
- Found an elog. It was moved to docker on optimus ELOG 16480 . The restart procedure can only be found here. Please fix all the documentation inconsistency >> Anchal

According to this elog, the following commands need to be run for starting up MCAutolocker and FSSSlow on optimus:

cd /opt/rtcds/caltech/c1/Git/40m/scripts/MC
sudo docker-compose up -d

- Problem continues. Now FSSSlow is running but only when the IMC is locked. It does not stop even when the IMC lock is lost. How can we debug docker thing?
- This is minor but the MCAutolocker log (/opt/rtcds/caltech/c1/scripts/MC/logs/AutoLocker.log) is no longer updated even though MCAutolocker is running. Was it moved somewhere?

 

  17049   Sat Jul 30 10:38:12 2022 AnchalUpdatePSLFSSSlow/MCAutolocker issue (docker)

The FSSSlow script was not properly documented and it was not working, so I had to use one that I knew worked from CTN. This scripts lives in

/opt/rtcds/caltech/c1/Git/40m/scripts/PSL/FSS/PIDLocker.py

and uses a configuration file

/opt/rtcds/caltech/c1/Git/40m/scripts/PSL/FSS/PIDConfigFSS.yml

The script runs all the time inside docker container which keeps it running. The heart-beat blinker shows if the script is active or not, but it only starts working when C1:IOO-MC_LOCK is 1 and C1:PSL-FSS_SLOWLOOP is 1. The second channel is a button on C1PSL_SLOW screen to engage autolocker. It has to be turned on for FSS to work.

 


docker instructions:

The following message is displayed on login in optimus:

-------------------------------------------------------------------------
This computer runs four services as of Feb 18, 2022 for 40m lab. To check
status of these services, type
> sudo docker ps
For restarting a particular service, type:
> sudo docker restart container_name
where container name can be found from ps command above.
Fimilarly, to check status of a service, type:
> sudo docker logs container_name

In case, you have just rebooted the machine, to start these services do
following:
> cd /opt/rtcds/caltech/c1/Git/40m/softchansmodbus
> sudo docker-compose up -d
> cd /opt/rtcds/caltech/c1/Git/40m/scripts
> sudo docker-compose up -d

To stop the docker services completely, for example before a reboot, do
following:
> cd /opt/rtcds/caltech/c1/Git/40m/scripts
> sudo docker-compose down
> cd /opt/rtcds/caltech/c1/Git/40m/softchansmodbus
> sudo docker-compose down

This should remove all active containers from the computer.

To check IP address of running containers, type:
> sudo docker inspect -f '|| {{range.NetworkSettings.Networks}}{{.IPAddress}}{{end}}   ||   {{.Name}} ||' $(sudo docker ps -aq)

The softchansmodbus directory runs modbusEPICS docker image to host some
useful soft EPICS channels. The scripts directory runs pyep docker
image to run MC autolocker, PMC autolocker and FSS PID locker.
-------------------------------------------------------------------------

For checking log files of autolocker script, on optimus do:

sudo docker logs scritps_AL_MC_1

For checking log files of FSS PID loop, on optimus do:

sudo docker logs scripts_PID_

In the above commands, add < | tail -15> to just see the most recent 15 lines in the log file. change 15 to whatever number of lines you want to see from the end.

At any time, if you want to know how docker is running stuff, check out the /opt/rtcds/caltech/c1/Git/40m/scriptsdocker-compose.yml file for self-explanatory script usage.

I'll add some documentation on the wiki soon. That is indeed required and should have been done already.


Debugging scripts:

All scripts could be debugged by running them on rossa by directly using python command. You can stop the docker container on optimus using:

sudo docker stop container_name

and then run the file on rossa to check it's behavior. After debugging and fixing any issues, please commit the file to gitlab repo and go back to optimus and restart the docker container:

sudo docker restart container_name

I'll add this procedure to a wiki page as well.


Reverting back to systemd on megatron

The setup on megatron was not removed at all. All service files exist in same place and old scripts can be started in the old manner by doing following on megatron:

For FSSSlow:

sudo systemctl enable FSSSlow
sudo systemctl restart FSSSlow

For MC autolocker:

sudo systemctl enable MCautolocker
sudo systemctl restart MCautolocker

For diabling these services again, do:

sudo systemctl stop FSSSlow
sudo systemctl disable FSSSlow
sudo systemctl stop MCautolocker
sudo systemctl disable MCautolocker

Note that one should stop docker containers on optimus before starting these systemd services to avoid conflicting scripts running together.

I have added above instructions on megatron motd. So on loging into megatron, these updated instructions would come.

If someone wants to fix the old scripts and use systemd for managing those scripts, please do so but I won't be able to help in debugging those old scripts. The shell scripts are very complicated and beyond my knowledge and python scripts are lacking documentation.

I'm happy to help debug or extend the functionality of the new scripts that live in the git directory.

  17050   Sat Jul 30 12:48:18 2022 KojiUpdatePSLFSSSlow/MCAutolocker issue (docker)

> it only starts working when C1:IOO-MC_LOCK is 1 and C1:PSL-FSS_SLOWLOOP is 1.

- OK. Your new MCAutolocker does not reflect the lock status to C1:IOO-MC_LOCK. This causes FSS Slow to go crazy when the IMC is not locked. Can you fix that?

- So C1PSL_SLOW.adl screen, which spawns by the "SLOW Servo" button on the FSS screen, has no effect on the FSS SLOW servo anymore. It is obsolete. At least the screen (or the link to the screen) should be removed. (Work on it once you are back.)

- Also, please make a wiki page and copy the description on the previous page.

  17057   Thu Aug 4 11:28:22 2022 AnchalUpdatePSLFSSSlow/MCAutolocker issue (docker)

Added C1:IOO-MC_LOCK to ALConfigMC.yml which solved the isse with FSS Slow. We should tune the FSS Slow Servo PID coefficients for a better performance.

the C1PSL_SLOW.adl screen is not obsolete. It can be used to change the PID coefficients, engage/disengage the PID loop, monitor the PID script blinker, and monitor FAST actuator value C1:PSL-FSS_FAST. the functionality of this screen has not changed from before.

I've also added a wiki page for scripts documentation.

  17065   Mon Aug 8 14:47:10 2022 ranaUpdatePSLFSSSlow/MCAutolocker issue (docker)

can't we just go back to the old python script that was working for many years, and tested? I imagine that as soon as someone besides you tries to debug the docker setup, this is what will happen.

Quote:

Added C1:IOO-MC_LOCK to ALConfigMC.yml which solved the isse with FSS Slow. We should tune the FSS Slow Servo PID coefficients for a better performance.

the C1PSL_SLOW.adl screen is not obsolete. It can be used to change the PID coefficients, engage/disengage the PID loop, monitor the PID script blinker, and monitor FAST actuator value C1:PSL-FSS_FAST. the functionality of this screen has not changed from before.

I've also added a wiki page for scripts documentation.

 

  3346   Sun Aug 1 21:40:27 2010 ranaSummaryPSLFSS: SLOWDC response

I bet you thought that the NPRO slow actuator response could be well represented by a pole at ~0.1 Hz? Well, that's just what they want you to believe.

I attach the response measured in FSS-FAST (with no feedback to the SLOW actuator) when the SLOW is given a step. As you may remember from

kindergarten, the response of a single pole low pass should just be an exponential. Clearly, there's more here than 1 pole.

 I also inserted a factor of 0.01 in the FSSSlowServo code so I could make the gain sliders have reasonable values (they used to all be ~1e-3). The SVN and the MEDM snapshot are updated.

Attachment 1: Untitled.png
Untitled.png
  751   Mon Jul 28 23:41:07 2008 robConfigurationPSLFSS/MC gains twiddled

I found the FSS and MC gain settings in a weird state. The FSS was showing excess PC drive and the MC wouldn't lock--even when it did, the boost stage would pull it off resonance. I adjusted the nominal FSS gains and edited the mcup and mcdown scripts. The FSS common gain goes to 30dB, Fast gain to 22dB, and MCL gain goes to 1 (which puts the crossover back around ~85 degrees where phase rises above 40 degrees).
  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.
  8460   Thu Apr 18 02:51:52 2013 DenUpdatePSLFSS slow servo

Today Rana pointed out that our FSS slow servo is malfunctioning. It has been for a while that our laser temperature control voltage drifted from 0 to 10.

I looked at FSSSlowServo script that runs at op340m and controls the servo. Script disables the servo when MC transmission is less then FSS_LOCKEDLEVEL. But his value was set to 0.2 probably till reference cavity time.

This means that slow servo was not disabled when MC was unlocked. I changed this value to 7000.

Also I increased integral gain from 0.0350 to 0.215 such that fast control is always in the range 4.5 - 5.5

  1050   Wed Oct 15 22:07:52 2008 peteConfigurationPSLFSS ref phase measurements
Optimizing the FSS LO/RF phase at 500 kHz, above the servo band, proved to be noisy and those measurements were useless. Today I repeated
the measurement at 35 kHz and got good signal to noise. I've attached a plot of the 35 kHz peak in dBm as measured at IN2 by SR785, with
an injection into TEST2 at 35 kHz with 0.2 Vpp, as a function of delay in ns given by the delay phase shifter normally used by the 166 MHz.
I fit the bottom (quadratic) portion of this curve, and found an optimum delay of 25.8 ns, which can be implemented as 25.81 ns on the phase
shift box (25 + 1/2 + 1/4 + 1/16). This is an uncalibrated number and meaningless.. For all these measurements a very long SMA cable
(did not measure) was inserted on the RF output of the 21.5 MHz reference box. The actual phase difference depends on these cable lengths
which I didn't measure.

To determine the actual phase difference I compared the LO and RF input points with the 25.81 ns delay, using a scope with poor man's
averaging (33 manual triggers and recording the phase measurements). The phase difference was 8.24 degrees with an error on the mean of 3.4%,
with the LO having the longer effective cable (cable plus delay from the phase delay box). As a sanity check I set the phase delay box
to 20 ns and re-measured, and found 49.5 degrees. (1/21.5 MHz) * (49.5-8.24)/360 = 5.3 ns, which is about the difference between 20 ns
and 25.81 ns. I did the same with 0 ns dialed in, and found a difference of 21.5 ns (I expected 25.8 ns). So it is possible that the
phase delay box isn't too precise.

Finally, to determine the length of cable needed to implement 8.24 degrees of phase at 21.5 MHz with RG58 cable, I made some phase measurements
using the FSS reference box and mismatched cables. I used three cable lengths (93 cm, 140.5 cm, and 169.5 cm ) and two mismatched pairs with
dL of 29 and 76.5 cm. For each pair I took average of 20 measurements, finding 22.54 degrees mean for the dL=29 cm pair (0.78 degrees/cm, or
a speed of light of 1.0e10 cm/s, or 10.6 cm of cable length on the LO) and 43.57 degrees mean for dL=76.5 cm pair (0.57 degrees/cm, or a speed
of light of 1.4e10 cm/s, or 14.5 cm of cable length on the LO). I expected more precise agreement.

Maybe the 21.5 MHz reference box is not zero phase between the outputs. This could be easily tested. It might be interesting to repeat this
measurement with a few more dL values.
Attachment 1: phasedelay.png
phasedelay.png
  1052   Thu Oct 16 09:47:49 2008 YoichiConfigurationPSLFSS ref phase measurements

Quote:
I fit the bottom (quadratic) portion of this curve, and found an optimum delay of 25.8 ns, which can be implemented as 25.81 ns on the phase shift box (25 + 1/2 + 1/4 + 1/16).


The gain of the loop is sinusoidally dependent on the phase delay. So the fit will be better with a function like this: 1/(1+G*sin(dphi + const)).
  1046   Tue Oct 14 14:19:36 2008 peteConfigurationPSLFSS ref phase
Today I made several measurements which should yield the optimized phase for the FSS 21.5 MHz reference. I made two sets of measurements, using the 166 MHz phase delay shifter. For each phase value I made 5 measurements of a 500 kHz injection into test2 at 1 Vpp, with the 4195 spectrum analyzer on in1 with the high impedance probe, 51 points, a 10 kHz range. It was surprisingly noisy. I will make plots using matlab to find the maximum, and hope for consistent results between the two sets of measurements. If it is too noisy or inconsistent I will repeat the measurement at ~800 kHz.

Once I find the phase which yields peak amplitude in in1, I will measure the relative phase between LO and RF going in to the FSS, measure the speed of light in RG58 cable, and construct a new cable which will implement the desired relative phase.
  1054   Thu Oct 16 16:26:26 2008 peteConfigurationPSLFSS phase matching cable installed
RG 405 cable has a solid teflon dielectric, and a velocity factor of 0.69. To get the 8.2 degrees of additional phase on the LO output at 21.5 MHz then requires 22 cm of cable. I made a cable that ended up being 21 cm long after I'd gained some experience putting on the connector. It gives a phase difference between LO and RF of about 10 degrees. It is currently installed.
  2343   Sat Nov 28 20:27:12 2009 KojiUpdatePSLFSS oscillation: Total gain reduced

I stopped by the 40m for some reason and found that the MC trans was 7.5.
This was caused by an oscillation of FSS, which seemed to be started by itself.

The oscillation stopped by reducing the FSS total gain to +9dB (from +11dB).
This is not a permanent fix (i.e. autolocker will restore the gain).
If it seems necessary to reduce the FSS gain always, we change the MC autolocker script.

Attachment 1: 091128_PSL.png
091128_PSL.png
  711   Tue Jul 22 03:03:22 2008 John, RobUpdatePSLFSS open loop transfer function
With the common gain slider maxed out the unity gain frequency is 58kHz.

The reference cavity refl diode appears to be okay. RF OUT/ TEST IN transfer function was normal.
There is a ~220mV offset in the RF out. We removed this using a coupler - no change. We also checked the
diode->FSS cable.

Tomorrow I'll take a closer look at the board.
  715   Tue Jul 22 13:16:09 2008 John, RobUpdatePSLFSS open loop transfer function

Quote:
With the common gain slider maxed out the unity gain frequency is 58kHz.

The reference cavity refl diode appears to be okay. RF OUT/ TEST IN transfer function was normal.
There is a ~220mV offset in the RF out. We removed this using a coupler - no change. We also checked the
diode->FSS cable.

Tomorrow I'll take a closer look at the board.


Should note that the UGF of 58kHz was measured with the test cable (from RFPD to board), so the demod phase was presumably sub-optimal.
  927   Thu Sep 4 17:12:57 2008 YoichiUpdatePSLFSS open loop TF
I changed the gain settings of the FSS servo.
Now the Common Gain is 5dB (the last night it was 2dB) and the Fast Gain is 12dB (formerly 16dB).
I measured the open loop TF with this setting (the attachment).
I also plotted the OPLTF when CG=2dB, FG=20.5dB. With this setting, the MC looses lock every 30min.

You can see that the OPLTF is smoother with FG=12dB.
When the FG is high, you can see some structure around 250kHz. This structure is reproducible.
This may be some interruption from the fast path to the PC path through a spurious coupling.
Attachment 1: FSS-OPLTFs.png
FSS-OPLTFs.png
  908   Mon Sep 1 19:23:17 2008 YoichiConfigurationPSLFSS on an auxiliary loop
Summary: The FSS is now temporarily disabled. Naturally, the MC won't lock. I will fix it tomorrow morning.

Today, I did the 4th item of my TO DO list.
Using a mini-circuit mixer and two SR560s, I constructed an auxiliary servo loop for the reference cavity.
With this loop, I was able to lock the reference cavity without using the FSS box.
By locking the reference cavity with this auxiliary servo, I was able to measure the PC path transfer function.
I will post the analyzed results later.

I borrowed the PD RF and the LO signals from the main FSS loop by power splitters. Therefore, the gain of the main FSS loop
is now about 3dB low. I tried to compensate it by increasing the EOM modulation depth, but the PC path is still a bit noisy.
Probably the already too low LO power is now seriously low (the LO power cannot be changed from EPICS).
Because I did not want to leave the PC path with large output overnight (it will heat up the PA85, and might cause damage, though unlikely),
I disabled the FSS for now.
  910   Tue Sep 2 09:58:42 2008 YoichiConfigurationPSLFSS on an auxiliary loop

Quote:
Summary: The FSS is now temporarily disabled. Naturally, the MC won't lock. I will fix it tomorrow morning.


Now I removed the power splitters for the aux. reference cavity servo. The FSS is back and the MC locks.
I'm now returning one of the active high-impedance probes to the Wilson house. They need it today.
We are left with only one active probe. If anyone finds another active probe in the 40m lab.,
please let me know (according to Rana we should have one more).
  10340   Wed Aug 6 17:29:36 2014 JenneUpdateIOOFSS offset changed

The MC has been unstable and unhappy for the last several hours.  When I looked, I saw that the FSS_FAST monitor has been hovering around 1 V, when it is supposed to be closer to 5ish. 

I changed the C1:PSL-FSS_INOFFSET from -0.08 to -0.8537, and will see if the MC sticks around for longer this time around.

  10341   Wed Aug 6 21:22:09 2014 KojiUpdateIOOFSS offset changed

The fast feedback should be around zero now!

  10344   Thu Aug 7 12:25:14 2014 JenneUpdateIOOFSS offset changed

Quote:

The fast feedback should be around zero now!

 Dang it, I completely forgot.  Well, anyhow, it pulled itself back down to less than 1V, and the MC stayed happy for several hours.  I'm not totally sure what changing the offset did, but the MC seems happy for right now.  I should take a quick look at the error point to make sure that I didn't mess up your tuning.

  1899   Thu Aug 13 22:53:48 2009 YoichiConfigurationPSLFSS nominal common gain changed, MC WFS centered

Koji, Yoichi

We found that the FSS PC feedback easily goes crazy (saturated).
It was because the common gain was too low. Probably the recent decrease of the
laser power is responsible for this.
We increased the nominal value of the common gain from 12 to 16.5.
The value was chosen just to make the PC path quiet. We should check
the FSS UGF later.
 
The MC WFS QPDs seemed off centered. So we unlocked the MC and lowered
the input power by the usual MZ half fringe technique.
Actually, the direct reflection beam was not much off the center. In anyway, we adjusted
the beam to the exact center of the QPDs.
The MC now locks fine.

 

  923   Thu Sep 4 13:48:50 2008 YoichiUpdatePSLFSS modulation depth
I scanned the reference cavity with the NPRO temperature (see the attached plot).
The power ratio between the carrier and the sideband resonances is about 26.8.
It corresponds to gamma=0.38.
The RF power fed into the EOM is now 14.75dBm (i.e. 1.7V amplitude). The NewFocus catalog says 0.1-0.3rad/V. So
gamma=0.38 is a reasonable number.




Attachment 1: RCScan.png
RCScan.png
  3561   Sun Sep 12 23:16:52 2010 valeraUpdate FSS mode matching

The attached plot shows the beam scans of the beam leaking from the back mirror of the PMC to the BS cube that first turns the S-pol beam 90 deg to the AOM and then transmits the AOM double passed and polarization rotated P-pol beam to the reference cavity. The beam from the PMC is mode matched to the AOM using a single lens f=229 mm. The ABCD file is attached. The data were taken with VCO control voltage at 5 V. We then reduced the voltage to 4 V to reduce the astigmatism. Tara has the data for the beam scan in this configuration in his notebook.

The beam from AOM is mode matched to the reference cavity using a single lens f=286.5 mm. The ABCD file is attached.

Attachment 1: fss.pdf
fss.pdf
Attachment 2: fssaom-abcd.tiff
Attachment 3: fssrc-abcd.tiff
  758   Tue Jul 29 19:41:38 2008 YoichiUpdatePSLFSS loop transfer functions
Last night I measured a bunch of transfer functions on the FSS loop.
All the loop gains were measured with the common gain = 30db and the fast gain = 18dB.

(1) The first attachment is the overall open loop transfer function of the FSS loop. I put a signal from the Test IN2 and observed signals from IN1 and IN2.
The UGF is about 180kHz.
By increasing the RF amplitude going to the EOM (i.e. increasing the sideband power), I can further increase the gain of the servo.
However, it made the PC drive immediately crazy. Probably it was some oscillation.

(2) Then I locked the ref. cav. with only the PZT actuator. I did so by simply unplugging the cable going to the PC.
Surprisingly, the cavity locked with the *same* gain setting as before. The second attachment shows the open loop transfer function measured in this configuration. It seems wrong, I mean, it should be unstable. But the cavity locked. A mystery.

(3) The third plot is the measured TF from the Test IN1 of the FSS board to the fast out (output to the PZT).

(4) By dividing the TF measured in (2) with the TF of (3), I got the response of the PZT times the cavity response. This is shown in the attachment 4.

(5) We can guess the open loop TF of the PC path by subtracting the TF in (2) from (1). It is shown in the attachment 5.

(6) The filter shape of the PC path is measured by injecting signal from the Test IN1 of the FSS board and observing it at the PC output. Since it is a high voltage output, I reduced the common gain to -8.5dB during the measurement. The attachment 6 is the measured filter shape. The gain is corrected to show what it should look like when the common gain = 30dB.

(7) By dividing (5) with (6), I plotted the response of the PC times the cavity response in the attachment 7. Since the 1/f cavity pole and the response of the PC, which is proportional to f, should cancel out, we expect a flat response above the cavity pole frequency (38kHz). You could say it is a sort of flat, if you have obscured eyes.

The measurement of the PZT open loop TF is very suspicious. According to this, the PC path has a very large gain even at very low frequencies (there is no cross over above 1kHz). This cannot be true. Maybe the cavity's optical gain was low when it was locked with only the PZT. I will re-measure it.
The plot (4) is also strange becaues it does not show the low pass feature expected from the cavity pole.
Attachment 1: OverallOPLTF.eps
OverallOPLTF.eps
Attachment 2: OpltfPZTOnly.eps
OpltfPZTOnly.eps
Attachment 3: PZTFilter.eps
PZTFilter.eps
Attachment 4: PZTxCavityPole.eps
PZTxCavityPole.eps
Attachment 5: OpltfPCOnly.eps
OpltfPCOnly.eps
Attachment 6: PCFilter.eps
PCFilter.eps
Attachment 7: PCxCavityPole.eps
PCxCavityPole.eps
  761   Tue Jul 29 23:04:34 2008 YoichiUpdatePSLFSS loop transfer functions

Quote:

The measurement of the PZT open loop TF is very suspicious. According to this, the PC path has a very large gain even at very low frequencies (there is no cross over above 1kHz). This cannot be true. Maybe the cavity's optical gain was low when it was locked with only the PZT. I will re-measure it.


I measured it again and found that the loop was oscillating at 13.5kHz. I think this oscillation prevented the ref. cavity from building up the power and consequently lowered the optical gain making it marginally stable. So the PZT path open loop TF posted in the previous entry is wrong.

I was able to stop the oscillation by lowering the gain down to CG=-7.6dB and FG=-8.78dB.
The first attachment shows the measured open loop transfer function.
Since the gain setting is different from when the over all open loop TF was measured, I scaled the gain (attachment 2).
However, this plot seems to have too much gain. Scaling it down by 20dB makes it overlap with the over all open loop TF.
Maybe the gain reading on the EPICS screen is wrong. I will measure the actual gain tomorrow.
Attachment 1: OpltfPZTOnlyRaw.eps
OpltfPZTOnlyRaw.eps
Attachment 2: OpltfPZTOnly.eps
OpltfPZTOnly.eps
  905   Fri Aug 29 22:57:48 2008 YoichiUpdatePSLFSS loop transfer functions
I've been measuring a bunch of transfer functions of the FSS related stuffs.
There are a lot to be analyzed yet, but here I put one mystery I'm having now.
Maybe I'm missing something stupid, so your suggestions are welcome.

Here is a conceptual diagram of the FSS control board

                                                          TP3             TP4
                                                           ^               ^
                                                           |               |
RF PD -->--[Mixer]-----[Sum Amp]------>--[Common Gain]--->----[Fast Gain]----[Filter]--> NPRO PZT
              ^     |      ^        |                  |     
              |     V      |        V                  |
LO ---->-------    TP1     IN      TP2                 -->---[Filter]--[High Volt. Amp.] --> Phase Corrector

What I did was first to measure a "normal" openloop transfer function of the FSS servo.
The FSS was operated in the normal gain settings, and a signal was injected from "IN" port.
The open loop gain was measured by TP1/TP2.
Now, I disconnected the BNC cable going to the phase corrector to disable the PC path and locked the ref. cav. 
only using the PZT. This was done by reducing the "Common Gain" and "Fast Gain" by some 80dB.
Then I measured the open loop gain of this configuration. The UGF in this case was about 10kHz.
I also measured the gain difference between the "normal" and "PZT only" configurations by injecting 
a signal from "IN" and measuring TP3/TP2 and TP4/TP3 with both configurations (The signal from the Mixer was
disconnected in this measurement). 

The first attachment shows the normal open loop gain (purple) and the PZT only open loop gain scaled by the 
gain difference (about 80dB). The scaled PZT open loop gain should represent the open loop gain of the PZT
path in the normal configuration. So I expected that, at low frequencies, the scaled PZT loop TF overlaps the normal
open loop TF.
However, it is actually much larger than the normal open loop gain.
When I scale the PZT only TF by -30dB, it looks like the attachment #2.
The PZT loop gain and the total open loop gain match nicely between 20kHz and 70kHz.
Closer look will show you that small structures (e.g. around 30kHz and 200kHz) of the two
TFs also overlap very well. I repeated measurements many times and those small structures are always there (the phase is
also consistently the same). So these are not random noise.

I don't know where this 30dB discrepancy comes from. Is it the PC path eating the PZT gain ?

I have measured many other TFs. I'm analyzing these.
Here is the TO DO list:

* Cavity response plot from AOM excitation measurements.
* Cavity optical gain plot.
* Reconstruct the open loop gain from the electric gain measurements and the optical gain above.
* Using a mixer and SR560(s), make a separate feedback circuit for the PZT lock. Then use the PC path
  to measure the PC path response.
* See the response of the FSS board to large impulse/step inputs to find the cause of the PC path craziness.
etc ...
Attachment 1: OPLTFs.pdf
OPLTFs.pdf
Attachment 2: OPLTFsScaled.pdf
OPLTFsScaled.pdf
  907   Mon Sep 1 04:34:00 2008 ranaUpdatePSLFSS loop transfer functions
I started from 6th item in Yoichi's todo list.

1) Increased the setpoint of the thermostat next to the framebuilder from 73F to 79F. Its freezing over there
in the room with the drill press. Steve's illegal mercury thermometer is reading 19 C.


2) Looked the RFPD's output spectrum using the 20 dB coupled output from the coupler that's in-line.
The first attached PDF file (n.pdf) has several plots:
page 1: 0-500 MHz anomolous peaks at 138 & 181 MHz but nothing too crazy
page 2: 0-100 MHz 80 MHz peak is RF pickup from the VCO Driver - not on the light
page 3: 10-30 MHz totally nuts
page 4: 18-25 MHz that's just wrong

The RF spectrum should only have some action around 21.5 MHz and a little peak at 2x 21.5 MHz. All that extra
junk means that something is broken!


3) To see if I could rid of any of the 80 MHz signal or any of that other trash from 18-25 MHz, I wound the RF cable
around a large toroidal ferrite core. This should have given us many uH of inductance for any signals common to
both the center and shield of the cable with no effect on the differential RF signals. There was no effect.


4) Next went to look at the 21.5 MHz Crystal Oscillator Reference card (D980353...I bet you can't figure out how
this one works). These have the Mini-Circuits SMA 30 MHz low pass (SLP-30) filters on both the LO and EOM outputs.

FSSLO.PNG shows the waveform after 20 dB attenuation going into a scope terminated with 50 Ohms.
FSSLO-Spec.png shows the spectrum of this signal - its pretty distorted. Here's the levels
   f (MHz) |  before filter (dBm) | after filter (dBm)
   ---------------------------------------------------
     21.5  |       -12.8               -13.1       
     43            -24                 -46
     64.5          -50               < -80
     86            -64               < -80

This would be OK after the filter, but the level is very low. Only 7dBm (accounting for my 20 dB att) !!
The FSS uses a JMS-1H mixer which needs, as everyone knows, a +17 dBm LO signal. Que lastima.

There seems to be something wrong already, but wait...


5) PC25.PNG shows the output signal going to the EOM from 0 - 25 MHz. The step that's visible there at
around 10 MHz is just something inherent to the analyzer (??). But see all that crap there down below
5 MHz ? That is NOT supposed to be there.

pc.pdf shows on the first page the comparison in EOM drive with 2 different slider values on the
RF AM adjust screen for the FSS. But page 2 is the punchline of this long entry: There is a bunch of
excess junk on the drive signal going to the FSS's phase modulator.
The FSS is then trying to handle
this extra frequency noise and getting into trouble.

We have to fix this board. I have also ordered a few SBP-21.4 from mini-circuits (SMA bandpass around 21.4 MHz)
just in case. Another option is to just replace this thing with a Marconi and an RF amp.






Attachment 1: n.pdf
n.pdf n.pdf n.pdf n.pdf
Attachment 2: FSSLO.PNG
FSSLO.PNG
Attachment 3: FSSLO-Spec.png
FSSLO-Spec.png
Attachment 4: PC25.png
PC25.png
Attachment 5: pc.pdf
pc.pdf pc.pdf
  791   Mon Aug 4 13:43:02 2008 YoichiSummaryPSLFSS loop calibration
As a part of the effort to repair the FSS loop bandwidth, I tried to calibrate the FSS loop.

First, I scanned the MOPA frequency by injecting a triangular wave into the ramp-in of the FSS box, which goes to the PZT of the NPRO.
The first attachment shows the transmitted light curve (pink one) along with the PDH signal (light blue).
The sweep was very slow (0.1Hz for 2Vp-p). From this measurement, the FWHM was 6.8e-3V. Then fpol = FWHM/2=3.4e-3V, where fpol is the cavity pole frequency.
So the PZT's DC response is 294*fpol/V. If we use the canonical fpol=38kHz, it is 11.172MHz/V.

Then I tried to measure the cavity pole. First I tried the cavity ring down measurement, by blocking the beam abruptly. Unfortunately, my hand was not fast enough.
The ring down shape was not an exponential decay.
I then locked the reference cavity only using the PZT with very narrow bandwidth (UGF=2kHz). I injected signal into the external modulation input of the 80MHz VCO
for the AOM. The second attachment shows the transfer function from this input to the IN2 (mixer output monitor port) of the FSS servo box.
To plot this, I corrected the measurement for the open loop TF (i.e. multiplying the measured TF with (1+G)), and other filters in the path (8MHz LPF after the ext. mod.
input of the 80MHz VCO, and an RCL network after the mixter). The gain looks like a cavity pole, but the phase decreases very rapidly.
If you look at the third attachment showing a wider band transfer function, there are notches at 1.8MHz and above. I couldn't find this kind of filter in the schematic.
Maybe this is the RFPD's bandpass filter. I will check this later. From these plots, it is difficult to tell the cavity pole frequency. From the -3dB point, fpol is around 83kHz,
but from the phase=-45deg point, fpol is around 40kHz.

Finally, I calibrated the cavity's optical gain by locking the Ref. Cavity with only PZT, and injecting a signal into the loop.
The signal was injected from Test-In2 of the FSS servo box and the transfer function from the PZT output signal (TP10) to IN1 (mixer output) was measured.
The transfer function was corrected for a 10Hz LPF after TP10.
The attachment4 shows a nice flat response up to 30kHz. Above 30kHz, the measurement is too noisy. The optical gain at DC is about 22dB from the PZT drive to the error signal (IN1).
Using fpol=38kHz, it means 887kHz/V calibration factor for the signal at IN1. There is a mixer output monitor DAQ channel in the FSS but it seems to be not working at the
moment. I will look into this later. There is a gain of 10dB between IN1 and the mixer monitor channel.
By looking at the phase response of the attachement4, there is a cavity pole like behavior around 30kHz. If we assume the PZT response is flat up to this frequency, it is
roughly consistent with fpol=38kHz.

I was not able to take a sensible spectrum of IN1 using the network analyzer. When the FSS servo was engaged, the signal was too small.
I will try to use an AF spectrum analyzer later to get a calibrated spectrum.
Attachment 1: P7310048.JPG
P7310048.JPG
Attachment 2: cavity-response.pdf
cavity-response.pdf
Attachment 3: cavity-response2.pdf
cavity-response2.pdf
Attachment 4: cavity-gain.pdf
cavity-gain.pdf
  124   Tue Nov 27 15:45:08 2007 robConfigurationPSLFSS loop

It's unclear (to me, at least) what was the end result of the FSS path tweaking before Thanksgiving. Today I measured the open loop gain, and it was still around 100kHz, even with the gain sliders maxed out, but it looked really crappy with a sharp cutoff around the UGF. Then, on a lark, I pushed around the "Input Offset Adjust" slider, which sums an offset into the signal coming out of the mixer. By moving this slider to 7V, I got the UGF to 500kHz with 45 deg of phase. That would be fine, and we could go offset hunting, but the same thing happens if one puts in a large negative value! I don't really understand what's going on, but it seems like weirdness in the electronics. Unfortunately the web interface to the conlog is not running (presumably because the `new' linux1 doesn't have its apache server running) and my command line conlog efforts have been stymied. So, I don't know what the historical settings of this offset are, but zero is definitely not a good setting right now. Here's a snapshot:

FSS
UGF: 500kHz
CG : 24dB
FG : 19dB
input offset: 7V
Phase Adjust: 1.09V
Phase Button: 0
RF Amp Adjust: 7.38V

margins:
phase: 45 deg
gain: 8dB
Attachment 1: FSSsmall.jpg
FSSsmall.jpg
  3574   Wed Sep 15 01:58:28 2010 valeraUpdatePSLFSS locking

The RefCav is locked and aligned. I changed the fast gain sign by changing the jumper setting on the TTFSS board. The RefCav visibility is 70%. The FSS loop ugf is about 80 kHz (plot attached. there is 10 dB gain in the test point path. this is why the ugf is at 10 dB when measured using in1 and in2 spigots on the front of the board.)  with FSS common gain max out at 30 dB. There is about 250 mW coming out of the laser and 1 mW going to RefCav out of the back of the PMC. So the ugf can be made higher at full power. I have not made any changes to account for the PMC pole (the FSS is after the PMC now). The FSS fast gain was also maxed out at 30 dB to account for the factor of 5 smaller PZT actuation coefficient - it used to be 16 dB according to the (previous) snap shot. The RefCav TRANS PD and camera are aligned. I tuned up the phase of the error signal by putting cables in the LO and PD paths. The maximum response of the mixer output to the fast actuator sweep of the fringe was with about 2 feet of extra cable in the PD leg.

I am leaving the FSS unlocked for the night in case it will start oscillating as the phase margin is not good at this ugf.

Attachment 1: DSC_2510.JPG
DSC_2510.JPG
  3575   Wed Sep 15 03:08:26 2010 KojiUpdatePSLFSS locking

Brilliant! This is the VERY way how the things are to be conquered!

Quote:

The RefCav is locked and aligned. I changed the fast gain sign by changing the jumper setting on the TTFSS board. The RefCav visibility is 70%. The FSS loop ugf is about 80 kHz (plot attached)  with FSS common gain max out at 30 dB. There is about 50 mW coming out of the laser and a few mW going to RefCav out of the back of the PMC. So the ugf can be made higher at full power. I have not made any changes to account for the PMC pole (the FSS is after the PMC now). The FSS fast gain was also maxed out at 30 dB to account for the factor of 5 smaller PZT actuation coefficient - it used to be 16 dB according to the (previous) snap shot. The RefCav TRANS PD and camera are aligned. I tuned up the phase of the error signal by putting cables in the LO and PD paths. The maximum response of the mixer output to the fast actuator sweep of the fringe was with about 2 feet of extra cable in the PD leg.

I am leaving the FSS unlocked for the night in case it will start oscillating as the phase margin is not good at this ugf.

 

  1048   Tue Oct 14 19:24:34 2008 YoichiConfigurationPSLFSS light power reduced
Rana, Yoichi

To change the gain distribution in the FSS, Rana reduced the VCO power for the AOM to reduce the light incident to the reference cavity.
Now the transmitted power of the RC is 2.3V compared to 6.5V before.
The FSS common gain can be increased to 5dB. I haven't changed the normal gain for this slider, so the mcup script will still set
the common gain to 1.5dB after an MC lock.
With this change, we take some gain from the optical part and give more gain in the electronics.
This might relieve the slew rate limit problem if it is happening in an early stage of the electronics.
  575   Thu Jun 26 18:24:28 2008 YoichiUpdatePSLFSS input ofset slider problem - fixed
I checked the FSS servo interface board and found that a LT1125CSW used to differentialize offset channel was broken (no virtual short).
So I replaced it. Now the slider is working.
The op-amp was hitting the rail. So it seems like we had been applying the maximum offset to the FSS input all the time.
The reason why the FSS loop still worked with the large offset is that the applied offset (~14V) is attenuated by a factor of 500 at the summing point.
  10928   Thu Jan 22 02:56:07 2015 ericqUpdateIOOFSS input offset adjusted

Since Rana's overhaul of the IMC, the FSS input offset had been sitting at zero. 

Over the last day or so, I had noticed the MC refl wall striptool trace looking noisier, and earlier this evening, we were suffering from a fair amount of downtime due to IMC unlocks, and failure to autolock for times on the order of ten minutes. 

While we had used ezcaservo for this in the past, I set the FSS offset manually tonight. Namely, I popped open a dataviewer trace of MC_F, and scanned the FSS offset to make MC_F go to zero. It required a good amount of offset, 4.66 V according to the FSS screen. I did this while the FSS slow servo was on, which held the FSS Fast output at zero. 

That was four hours ago; MC_F is still centered on zero, and we have not had a single IMC unlock since then. The MC refl trace is thinner too, though this may be from nighttime seismic. 

  684   Wed Jul 16 17:36:51 2008 JohnDAQPSLFSS input offset
I changed the nominal FSS input offset to 0 from 0.3. Tolerance remains unchanged at +/-0.05.
  8587   Thu May 16 01:41:31 2013 JenneSummaryIOOFSS gain settings set

Quote:

I'm not sure yet what this points to as the best gain settings.  We can of course explore more of the space.  I'm going to leave it at 13/23.5, which leaves the PC RMS at ~1.5 and the FAST Monitor at ~6.0.

 I changed the value of the nominal FSS common gain in the PSL Settings screen (It's called the 'FSS global gain' there).  To get to this screen:  sitemap -> PSL_main -> PSL_settings.  The MC autolocker reads these settings from the screen and uses those values.  Now the FSS returns to this value of 13 that Jamie has chosen.  For the past few days, it's been going back to the old value of 10.1 .  The FAST gain was already set to this 23.5 value.

  929   Thu Sep 4 17:44:27 2008 YoichiUpdatePSLFSS error signal spectrum
Attached is a spectrum of the FSS error signal.
There are a lot of sharp peaks above 100kHz (the UGF of the servo is about 200kHz).
These are mostly harmonics of 77kHz. They are the current suspects of the FSS slew rate saturation.
I remember when I blocked the light to the PD, these peak went away. So these noises must be
in the light. But I checked it a few weeks ago. So I will re-check it later.

One possible source of the lines is a DC-DC converter in the NPRO near the crystal.
We will try to move the converter outside of the box.
Attachment 1: FSS-Error-Spe.png
FSS-Error-Spe.png
  15310   Wed Apr 22 17:29:14 2020 gautamUpdatePSLFSS debugging attempts

Summary:

On Monday, I hooked up an AG4395 to the PMC error point (using the active probe). The idea was to take a spectrum of the PMC error point every time the FSS PC drive RMS channel indicated an excursion from the nominal value. An initial look at the results don't suggest that this technique is particularly informative. I'll have to think more about a workaround, but please share your ideas/thoughts if you have some.

Also, the feature in the spectrum at ~110 kHz makes me suspect some kind of loop instability. I'll measure the IMC loop OLG at the next opportunity.

Details:

  • The PMC servo bandwidth is ~2 kHz, so above this, the PMC error point should be a faithful monitor of the PSL frequency noise, provided the sensing noise is low enough.
  • The PMC error point sensing noise is ~100nV/rtHz (I'm monitoring this straight after the Minicircuits mixer+bandpass filter that we are using as a demodulator). This corresponds to ~2 Hz/rtHz, using the ~10 MHz/V PDH discriminant calibration from January. Seems consistent with this elog.
  • I was hoping to see if there was a particular frequency band in which the noise gets elevated, and if the crossover frequency is a few kHz and the IMC servo BW is ~110 kHz, I would have expected this to be in the 10-100 kHz region. Possibly my frequency resolution isn't good enough? But with the Agilent, doing a finer grid would mean a longer measurement time, in which case the IMC might lose lock before the measurement is done.
  • But, as shown in Attachment #1, there isn't any clear evidence, from the ~20 excursions that were recorded last night. The color of the line is meant to be indicative of the average value of the PC drive RMS channel in the measurement time.
  • A significant bottleneck in this whole process is that it takes ~1 minute to initiate the GPIB measurement, and download the data. The pseudo-code I used is:
    • While the IMC is locked, watch PCdrive RMS EPICS channel's "ALARM" state, which becomes non-zero when the PCdrive RMS exceeds 1 V (this is how it is defined in the EPICS db record right now).
    • Make sure this isn't a transient feature - I do this by waiting 5 seconds and checking that the ALARM flag is still flagged.
    • Initiate a AG4395 measurement over GPIB - I use the measurement span of 1 kHz - 1 MHz with a BW/span ratio of 0.1%, 5 averages.
    • Check that the IMC is still locked (if it got unlocked while the measurement was made, presumably the measurement is garbage).
  • Is there a better monitor of the laser frequency noise? I can imagine using POX/POY which I think have a lower electronics noise floor but I'm not sure if that's true at 100 kHz and having the arms locked in addition to the IMC seems more complicated...
  • Since we are planning a laser upgrade, is this worth spending more time on? I may leave the measurement running on pianosa in a tmux session while I'm not in the lab...
Attachment 1: FSSspec.pdf
FSSspec.pdf
  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.

  991   Thu Sep 25 10:48:29 2008 YoichiUpdatePSLFSS calibration again
I did a calibration of the FSS error signal again with a different method.
This time, I swept the laser frequency with the NPRO PZT around a resonance.
The attached figures show the transmitted light power and the PDH error signal vs the applied voltage to the PZT.
From the width of the transmitted light power peak, we can obtain the PZT voltage to the laser frequency coefficient,
i.e. the HWHM (Half Width Half Maximum) equals to the FSR (38kHz).
Once the PZT is calibrated, the PDH error signal can be calibrated by the fitting the central slope with a line.

I repeated the measurement 8 times and fitted the obtained data to get the HWHM and the slope.
The results are the following:
PZT calibration = 6.3 +/-0.1 MHz/V
PDH calibration = 6.5 +/-0.5 kHz/V

Note:
(1) The calibration coefficient (6.5kHz/V) is almost consistent with the previous value (6.83kHz/V elog:958). However, that calibration
used a considerably different value for the PZT calibration (11.172MHz/V elog:791). The discrepancy in the PZT calibration is understandable
because my previous PZT calibration was very rough. The fact that the two calibrations still agree is a mystery.

(2) In the transmitted power curve, there seems to be a slight distortion, probably due to the thermal effect.
We should reduce the power to the reference cavity to remove this effect.

(3) This measurement was done after Peter installed his RF source. The demodulation phase had not yet been optimized. We should
repeat the calibration after he optimizes the phase.

(4) I used the Tektronix oscilloscope for the measurement.
Using the ethernet-wireless converter, you can connect the scope to the network from anywhere in the lab.
No hard wire required anymore.
Then you can download the data from a web browser. It is cool !
Attachment 1: PDTrans.png
PDTrans.png
Attachment 2: PDHsignal.png
PDHsignal.png
  958   Wed Sep 17 17:31:24 2008 YoichiUpdatePSLFSS calibration
I calibrated the reference cavity error signal with the following procedure.

(1) I disconnected the PC path BNC cable and locked the RC only using the PZT. To do so, I had to insert a 20dB attenuator
in the RF signal path going to the EOM to reduce the gain of the loop sufficiently.
The normal RF level going to the EOM is 17dBm. With the attenuator it is of course -3dBm.

(2) Using the SR785, I injected signal into the Test-IN2 (a sum-amp after the mixer) of the FSS box and measured the TF from the Ramp-IN to the IN1.
When the Ramp-In switch is off, the Ramp-IN port can be used as a test point connected to the PZT drive signal path just before the output.
There is a RC low-pass filter after the Ramp-IN. IN1 is the direct output from the mixer (before the sum-amp).
The attm1 is the measured transfer function along with the fitting by a first order LPF.
From this measurement, the DC transfer function from the applied voltage on the PZT to the error signal is determined to be 163.6 (V/V).
Since the RF level is lowered by 20dB, the cavity gain in the normal operation mode is 10 times larger (assuming that the modulation depth is
linearly proportional to the applied voltage to the EOM).

(3) According to elog:791, the conversion factor from the voltage on the PZT to the frequency change of the NPRO is 11.172MHz/V. Combining this with the
number obtained above, we get 6.83kHz/V as the calibration factor for converting the error signal (mixer output) to the frequency at DC.
Using 38kHz cavity pole frequency, the calibration factor is plotted as a function of frequency in the attm2.

(4) I took a spectrum of the error signal of the FSS and calibrated it with the obtained calibration factor. See attm3.
The spectrum was measured by SR785. I will measure wide band spectra with an RF analyzer later.

TO DO:
1: Use the actual modulation depth difference to extrapolate the calibration factor obtained by with a low RF signal for the EOM.
The cavity sweep was already done.

2: I assumed 38kHz cavity pole. I will measure the actual cavity pole frequency by cavity ringdown.

3: Measure out-of-the-loop spectrum of the frequency noise using PMC and MC.
Attachment 1: PZTresp.png
PZTresp.png
Attachment 2: Calibration.png
Calibration.png
Attachment 3: FreqNoiseSpectrum.png
FreqNoiseSpectrum.png
  3573   Wed Sep 15 01:27:52 2010 rana, steve, valeraUpdatePSLFSS cables connected

- connected the TTFSS cables (FSS fast goes directly to NPRO PZT for now)

- measured the reference cavity 21.5 MHz EOM drive to be 17.8 dBm

-  turned on the HV for the FSS phase correcting EOM (aka PC) drive

- connected and turned on the reference cavity temperature stabilization

- connected the RefCav TRANS PD

- fine tuned the RefCav REFL PD angle

  15230   Thu Feb 27 15:50:37 2020 gautamUpdateElectronicsFSS box power cable removed

In 1X1, there is a box labelled "FSS REF" below a KEPCO HV supply. This box had a power cable that wasn't actually connected to any power. I removed said cable.

  10370   Tue Aug 12 18:20:13 2014 ericqUpdateIOOFSS box TFs

I made some measurements of the FSS box today, to have TFs for a loop model, but also to see what the difference between the different inputs was. 

As a reminder, the FSS box takes the error signal from the MC servo, does some filtering, and sends out two outputs: one to the laser PZT via KojiBox and Thorlabs HV amplifier, and one to be summed with the PMC modulation signal to the PC. Rana found the schematic at D040105

The MC error signal currently enters via a port called "IN1", but there is also a "Test 1 in," which experiences different filtering. I measured the TFs from each of these inputs to both the FAST and PC outputs. There is also an IN2, that is added after the offset point, but was not able to make a good measurement, for reasons unknown. From these TFs, I inferred the difference between the PC and FAST path, as well as the difference between IN1 and Test 1 in.

Specifically, I plugged the cable that is usually connected to the MC servo output, labelled "TO FSS BOX", into the RF out of the AG4395. I then took a BNC cable from the FAST out, or PC out, and fed it into a mini circuits DC block (BLK-89-S+), and then into input A, after checking on a scope that the signal was roughly zeroed and not too huge. Unbeknownst to me at the time, the PC drive output can be pretty big, and could potentially fry the analyzer's input. Fortunately, I think I avoided this fate. 

FSSbox.pdfFSSfilt.pdf

A ~1.3 MHz bump can be seen here, which would conspire with the bump in the demod board I measured yesterday, to steal even more phase around 1MHz. Maybe we can modify the FSS box to help our gain peaking situation out. 

The data is attached.

RXA: Shazam!

Attachment 3: FSSdata.zip
  10380   Wed Aug 13 23:08:17 2014 ranaUpdateIOOFSS box TFs

As EQ pointed out recently, we're injecting into the FSS error point just after an RF pi filter, but before the VGA. We wondered what the weird filter impedance was doing to our signal if we inject after it. I used LISO to model this FSS common section and attach the plots.

The first plot shows the TF between the Test 1 input and the AD602 VGA input. This is NOT the input that we are actually using.

The second plot shows the TF between the IN1 port (which we are actually using) and the VGA input.

Neither of them shows the 1 MHz bump that we see in the measurements, so I suspect that the board has been modified...the hunt continues. We've got to pop the top of the TTFSS and take photos and measure from IN1 to VGA input.

** FSScomm.fil is now in the LISO SVN. The following command line will run it with two different cases and cat the PDF files into one. If you use an auto-refresh PDF viewer like Okular or Mac Preview, its a nicer display than the usual GNUplot window:

./mfil FSScomm.fil; sleep 1; pdftk FSScomm_run*.pdf cat output FSScomm.pdf

Attachment 1: FSScomm.pdf
FSScomm.pdf FSScomm.pdf
  1061   Mon Oct 20 20:50:09 2008 YoichiConfigurationPSLFSS board chip replacement
A quick update.

I changed two AD797s on the FSS board to AD829s to mitigate the 50MHz oscillation, which I plan to report later.
For some reason, the PA85 was broken after the replacement. So I had to replace it with a spare one too.
Right now the FSS is back and working. The oscillation is gone.
However, the maximum achievable gain is still about the same as before.
  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.
  2722   Sun Mar 28 23:17:46 2010 ranaSummaryPSLFSS Work from Sunday: noise spec

This is the error point spectrum - it is filled with huge multiples of ~75 kHz as Yoichi noticed a couple years ago.

I tried to use the netgpib.py package to read out the Agilent 4395, but the SVN had been corrupted by someone saving over the netgpib.py package. To get it to work on rosalba I reverted to the previous version, but whoever is busy hacking on netgpib.py needs to checkin the original package and work on some test code instead.

I also noticed that the default output format for the AG4395.py file is in units of Watts. This is kind of dumb - we need someone to develop this package a little as Yoichi did for the SRS785.

Attachment 1: in2.png
in2.png
ELOG V3.1.3-