The measured power levels of the RF source harmonics are given below:

We are considering inclusion of bandpass filters centered on 11 and 55 MHz  to suppress the harmonics and meet the requirements specified in Alberto's thesis (page 88).

I started to modify another green PD set.

It so far has the transimpedance of 240 Ohm on CLC409 for the RF output.

It shows the BB output upto ~100MHz.
The measurement shows the transimpedenca of ~90Ohm which is ~25% smaller than the expected gain of 120Ohm.
It is calibrated based on the transimpedances of Newfocus 1611 (10kOhm and 700Ohm for AF and RF).

The next step is to change the transimpedance resister to 2k and replace the PD to S3399 Si PD, which has the diameter of 3mm.
Then, the noise level will be measured. (and replace the RF opamp if necessary)

 Ooh. Can you explain the purpose of the resistors which are connected to the (+) inputs? It looks like some real electronics ninjitsu.

51 Ohm for CLC409

The datasheet of CLC409 uses 25Ohm there. This is to cancel the input bias current of the two inputs of the opamp.

The source impedance (series) of SGD444 is 50Ohm. So I used 50Ohm for the + input shunting.

However, I could probably use anything between 0-50Ohm as the datasheet itself tells that the bias currents are
not related between the two inputs. In addition, I am not sure how much the real series resistance of the PD is.

1kOhm for OP27

This resister is to ensure the (+) input to have a high impedance at high frequencies.

As far as OP27 is behaving as an ideal opamp, the (+) input has a high impedance.
Also if the inductor behaves as the ideal inductor, no photocurrent comes to the AF path.

However, if both of the op27 and the inductor show similar impedances to the RF transimpedance of 240Ohm,
the AF path absorbs some photocurrent and affects the RF transimpedance of the RF output.

We know that the inductor has a self resonance where the shunt capacitance take over the impedance of the coil.
Above that frequency, the inductor is no longer the inductor. The self resonant freq of this inductor is ~300MHz. It is OK, but not
too far from the freq of interest if we like to see clear cut off at around f>100MHz.
Also OP27 is an AF amplifier and I had no confidence about the input impedance of the OP27 at 100~300MHz.

If I put 1k in the (+) input of the OP27, I can ensure the entire AF path has the impedance of ~1k (at least 500Ohm even when L and OP27 are shorted).
I think the chip resister easily works as a resister up to 1GHz.

Problem:

The daqd process was dying every minute or so when it couldn't write frame.  This was slowing down the network by writing a 2.9G core dump over NFS every minute or so. (In /opt/rtcds/caltech/c1/target/fb/).

The problem was /frames/ was 100% full.

Apparently, when we switched the fb over to Gentoo, we forgot to install crontab and a wiper script.

Solution:

We will install crontab and get the wiper script installed.

[Joe, Jamie, Alex]

Fixes:

I asked Alex which cron to use (dcron? frcron?).  He promptly did the following:

emerge dcron

rc-update add dcron default

Copied the wiper.pl script from LLO to /opt/rtcds/caltech/c1/target/fb/

At that point, I modified wiper.pl script to reduce to 95% instead of 99.7%.

I added controls to the cron group on fb:

sudo gpasswd -a controls cron

I then added the wiper.pl to the crontab as the following line using crontab -e.

0 6 * * *       /opt/rtcds/caltech/c1/target/fb/wiper.pl --delete &> /opt/rtcds/caltech/c1/target/fb/wiper.log

Notes:

Note, placing backups on the /frames raid array will break this script, because it compares the amount in the /frames/full/, /frames/trends/minutes, and /frames/trends/seconds to the total capacity. 

Apparently, we had backups from September 27th, 2010 and March 22nd, 2011.  These would have broken the script in any case. 

We are currently removing these backups, as they are redundant data, and we have rsync'd backups of the frames and trends.  We should now have approximately twice the lookback of full frames.

As part of the RF system upgrade some of the demod boards in the lab were modfied.  The filter U5 (see the circuit schematic) was replaced. These changes are tabulated below.

Next, I and Q phase has to be checked for orthogonality. And noise levels of the cards have to measured.

I brought TTFSS set #7 to 40m and kept it in the electronic cabinet.

note that Q4 transistor has not been replaced back to PZT2907A yet. It's still GE82.

Q3 is now pzt3904, not PZT2222A.

Correction:

The (-) input has been decoupled by the capacitor. So the series resistance of the PD is not the matter.
In this sense, we should use 0Ohm for the (+) input shunting.

I am a little concerned about using these low pass filters so close to the band edge. Recall that there is no on-board preamp for the RF input to the mixer.

So, if the input impedance of the filters is not 50 Ohms, we will get some unwanted reflections and sensitivity to cable length.

I think its worth while to check the impedance or S-parameters of these things with the LO activated to find out if we need to remove them or not.

The ITMX/ITMY control swap is complete.

The steps from this elog were followed.

In addition, I did a burt restore of c1sus, c1mcs.

I then swapped all the gain settings from ITMX to ITMY, and reenabled the watchdogs.

I did some basic kick tests (1000 counts into UL coil) and confirmed channels like C1:SUS-ITMX_ULPD_VAR (watchdogs mV readback) corresponded to the correct optic.  I also checked that the POS, PIT, YAW, SIDE produced reasonable damping when engaged.

Problem:

Currently the c1scy, c1mcs, and c1rfm models are reporting an error with receiving some data sent over the GE Fanuc Reflected memory cards.

To be more exact, the C1:SUS-ETMY_ALS signal from the c1gcv FE code on the c1ioo computer going too the Y end is not being received.  However, the C1:SUS-ETMY_LSC signal is.  So the physical RFM card seems to be working.

Similarly, the TRY signal is being sent correctly from the Y end computer.  The X end is working fine and receiving both LSC and ALS signals.

The c1mcs and c1rfm models also receive data from the c1ioo computer and reporting receiving errors.

Theory:

Because the RFM cards are transmitting and receiving at least some channels, I'm guessing there was changes made to the C1.ipc file, which defines the memory locations of these various channels on the RFM network, and that when a model was rebuilt, a different one using the previous IPC file was not, and thus one of the computer is going to the wrong place to either read or write data.

Tomorrow, I'm planning on the  following:

1) Clean out the C1.ipc file (/opt/rtcds/caltech/c1/chans/ipc/)

2) Rebuild all models

3) Run activate_daq.py script

4) Restart models via script

If this doesn't clear up the problem, I'll continue  to bug hunt.

Problem:

I switched the ITMX and ITMY control channels yesterday, but forgot to update the IFO_ALIGN.adl file (/opt/rtcds/caltech/c1/medm/c1ifo/) which had the control labels swapped to make life easier.

Solution:

I swapped ITMX and ITMY control locations on the screen.

Question:

Are there any other screens involving ITMX and ITMY that had controls reversed to make life easier?

 [Kiwamu, Larisa]

The following Video MUX inputs(cameras) and outputs(monitors) have been checked:

MC2F, FI, AS Spare, ITMYF, ITMXF, ETMYF, ETMXF, PSL Spare, ETMXT, MC2T, POP, MC1F/MC3F, SRMF, ETMYT, PRM/BS, CRT1(MON1), ETMY Monitor, CRT2(MON2), CRT4(MON4), MC1 Monitor, CRT3(MON3), PSL1 Monitor, PSL2 Monitor, CRT6(MON6), CRT5(MON5), ETMX Monitor, MC2 Monitor, CRT9, CRT7(MON7), CRT10, and Projector.

Their respective statuses have been updated on the wiki:   (wiki is down at the moment, I will come back and add the link when it's back up)

[Jamie, Jenne, Koji]

We installed the new c1lsc and started the process.

We still need to configure bunch of the EPICS variables, matrices, and some of the filters.
This should be done in order to transmit the signals to the suspensions.
Jenne is going to work on this task tomorrow (Friday) morning,
and Koji will take over the task afternoon/evening.

Target: To lock the Michelson with the new RF/LSC

Status

RF generation box: READY - already ready to go to the IOO rack. (Suresh)

RF distribution box: In Progress - the internal components are to be connected. (13th evening - Suresh)

Placing PD and CCD: Done - PD and CCD on the AP table (13th Afternoon - Aidan, Larisa with supervision of Kiwamu)

Cabling1: Done - PD signal AP table to the demodulator (13th Afternoon - Jamie with supervision of Suresh)

Cabling2: Done - RF generation box (IOO Rack) to the demodulator

Demodulator: In Progress - Test and install (13th night - Kiwamu with supervision of Suresh)

LSC model: Done - Run the new LSC model. (It is named as "C1LST" so far) (13th evening - Jamie)

LSC medm: Done on 14th - Modify the current LSC medm screens Update the EPICS database Adjust the matrices (- Jenne with supervision of Koji)

[Joe, Alex]

Problem Symptoms:

There were red lights on the status screen indicating RFM errors for the c1scy, c1mcs and c1rfm processes.

The c1iscey, c1sus machines were receiving data sent over the RFM network from the c1ioo computer with a bad time stamp, a few cycles too late.  The c1iscex computer was receiving data from c1ioo fine.

Problem:

The c1iscex RFM card had gotten into a bad state and was somehow slowing things down/corrupting data.  It didn't affect itself, but due to the loop topology was messing everyone else up.  Basically the only one who wasn't throwing an error was the culprit.

Solution:

Hard power cycling the c1iscex computer reset the RFM card and fixed the problem.

[Jenne Koji]

The PD signals are transmitted to the suspension now.

The trigger thresholds were set to -1. This means the triggers are always on.

[Koji / Kiwamu]

The Michelson was locked with the new LSC realtime code.

(what we did)

 --  Fine alignment of the Michelson, including PZTs, BS and ITMY.

  Since the X arm has been nicely aligned we intentionally avoided touching ITMX. The IR beam now is hitting the center of both end mirrors.

  At the end we lost X arm's resonance for IR. This probably means the PZTs need more careful alignments.

-- Signal acquisition

 We replaced the RFPD (AS55) that Aidan and Jamie nicely installed by POY11 because we haven't yet  installed a 55MHz RF source.

The maximum DC voltage from the PD went to about 50 mV after aligning steering mirrors on the AP table.

The RF signal from the PD is transferred by a heliax cable which has been labeled 'REFL33'.

Then the RF signal is demodulated at a demodulation board 'AS11', which is one of the demodulation boards that Suresh recently modified.

Although we haven't fully characterized the demod board the I and Q signal looked healthy.

Finally the demod signals go to ADC_0_3 and ADC_0_4 which are the third and fourth channel.

They finally show up in REFL33 path in the digital world.

-- Control

 With the new LSC code we fedback the signal to BS. We put anti-whitening filters in the I and Q input filter banks.

We found that dataviewer didn't show correct channels, for example C1LSC_NREFL33I showed just ADC noise and C1LSC_NREFL33Q showed NREFL_33I.

Due to this fact we gave up adjusting the digital phase rotation and decided to use only the I-phase signal.

Applying a 1000:10 filter gave us a moderate lock of the Michelson. The gain was -100 in C1LSC_MICH_GAIN and this gave us the UGF of about 300 Hz.

 Note that during the locking both ETMs were intentionally misaligned in order not to have Fabry-Perot fringes.

While Kiwamu was working on the RF cabling at the LSC rack, I removed 80% of SMA cables which were not connected anywhere.
The rack is cleaner now, but not perfect yet. We need patch panels/strain relieving for heliaxes, cleaning up of the RF/LO cables, etc.

During checking the 11MHz demod boards I found that the I-Q relative phase showed funny LO power dependence.

It is now under investigation.

 In the plot above the green curve represents the I-Q phase of a 11MHz demod board (see here).

It showed a strong dependence on the LO power and it changes from -60 deg to -130 deg as the LO power changes.

This is not a good situation because any power modulation on the LO will cause a phase jitter.

For a comparison I also took I-Q relative phase of a 33MHz demod board, which hasn't been modified recently.

 It shows a nice flat curve up to 5 dBm although it looks like my rough measurement adds a systematic error of about -5 deg.

 - to do -

* check RF power in every point of LO path on the circuit

* check if there is saturation by looking at wave forms.

Plotting the data points yielded by the spec analyzer of my first LPF yielded a result that was not expected: the desired cutoff frequency wasn't achieved because of some extra 100k resistance that wasn't taken into consideration. (see  here ). I have redrawn the Bode graphs for this configuration so that it is easier to see that it is wrong (first attachment)

After some calculation adjustments, it was found that the capacitor value could remain at 10uF, but the resistance needed to be changed to 100k to maintain a gain of 0.5 and critical frequency at 0.1Hz. Second attachment is the Bode graph that results from this configuration.

Note: Bode graphs are both in Log-Linear scales (Wikipedia said so)

[Rana, Koji, Kiwamu]

 Moreover the amplitude of the I and Q signals are highly unbalanced, depending on the LO power again.

This implies the coil for a 90 degree splitting won't work at 11 MHz since the coil is home made and used to be designed for a specific frequency (i.g. 24.5 MHz).

We decided to use a Mini circuit 90 deg splitter instead. Steve will order few of them soon and we will test it out.

I was investigating the beat note amplitude on the vertex PD again yesterday. The incident power on the PD was 150uW in the PSL green beam and 700uW in the X-ARM green beam. With perfect overlap and a transimpedance of 240, I expected to get a beat note signal of around 25mV or -19dBm. Instead, the size was -57dBm. Bryan and I adjusted the alignment of the green PSL beam to try and improve the mode overlap but we couldn't do much better than about -50dBm. (The noise floor of the PD is around -65dBm).

When we projected the beams to the wall of the enclosure, the xarm beam was 2 to 3x as large as the PSL green beam, indicating that the beam size and/or curvatures on the PD were less than ideal. There is a telescope that the XARM beam goes through just before it gets to the PD. I mounted the second lens in this telescope on a longitudinal translation stage. With some finagling of the position of that lens we were able to improve the beatnote signal strength to -41dBm.

Obviously the ideal solution would be to measure the beam size and RoC of the PSL beam and XARM beams and then design a telescope that would match them as precisely as possible because there's still another 20dB signal strength to be gained.

One way to avoid some of the bad stuff in there is to take the 1 dBm input and amplify it to ~21 dBm before splitting and sending in to the Level 17 mixers.

One way to do this is by using the A3CP6025 from Teledyne-Cougar. Its an SMA connectorized amp which can put out 25 dBm and has a gain of 24 dB. We can just glue it onto the demod boards. Then we can remove the ERA-5 amplifiers and just use the broadband splitter as Kiwamu mentioned.

 We will make them all green !!

Again, all the files are available in the svn.

https://nodus.ligo.caltech.edu:30889/svn/trunk/suresh/40m_RF_upgrade/

Problem:

The original matrix naming conventions for the front ends was broken.  It used _11, _12,...,_1e, _1f, _110, _111 and so forth.  The code was changes to use _1_1, _1_2,...,_1_16,_1_17, and so on.

In addition the matrix of filter banks was modified to use the same naming convetion (instead of starting at zero, it now start with one).

Work Done:

I rebuilt all the models, and restarted them all.

I wrote a simple script to modify the burt restore files to have the correct names for all the stored matrix values.

I also modified all the suspension screens, by modifying the default screens in /opt/rtcds/caltech/c1/medm/master/

The C1SUS, C1SCX, C1SPX, C1SCY, C1SPY, and C1MCS models had their foton filter files modified to put filters into the newly changed named filters

Just a curiosity:

I just wonder how you have distingushed the difference between _111 and _111.

They are equivalent alone themselves. Have you looked at the contexts of the lines?
Or you just did not have the larger matrix than 16x16, did you?

[Steve / Suresh / Kiwamu]

90 % of unused video cables have been removed.

Still a couple of video cables are floating around the video MUX. They will be removed in the next week's session.

The suggested layout of the 1Y2 Rack is shown below.

To simplify the wiring, I have largely kept demod boards with the same same LO frequency close to each other. 

The Heliax cables land on the top and bottom of the of subracks.  These are currently flexible plastic sheets.  Steve has agreed to replace them with something more rigid.  It would be good to have eight N-type connectors on the top and eight  at the bottom.  As  demod boards occur in sets of eight per subrack.  So it would be convenient if the 11 and 55 Mhz Heliax cables land on the top and the rest at the bottom.  In the layout I have shown the current situation. 

The LO signals to the boards come from the RF Distribution box and this is kept in the middle so that cables to both the subracks can be kept short.

The outputs of the AA filter boards from both subracks  have to be connected to the SCSI Interface board with a twisted pair ribbon cable. 

The east side window guides  will be replaced by one long U-channel. There will be drilling into 2x2 steel frame. It should be done by 2pm today

This should remove the jerking motion of windows hitting the individual guides.

New right angle PVC, 2 x 2 x  1/4" installed at the AP table to strain relief the 1/4" spiral corrugated RF coaxes.

The anti aliasing box was opened up at the back to accommodate the junction board and the SCSI cable towards the ADC. Aluminum plate was attached to the bottom to hold the strain relief clamp.

Three more hanging junction cards will be replaced in this manner.

 The installation went smoothly. There will be no more banging the doors into  guides on the east side.

Atm2 showing the west side as is today

A new 90 degree splitter, PSCQ-2-51W, has arrived today and I installed it on a demod board called AS11.

Results of the I-Q phase measurement with the new splitter will be reported soon.

 * Picture 1 = before removal of the handmade coil

 * Picture 2 = after removal of the coil and the associated capacitors

 * Picture 3 = after soldering PSCQ-2-51-W

A less LO power dependence on the relative phase was found. The new 90 deg splitter works better.

From -3 dBm to 10 dBm in LO power, the relative phase is within 90 +/- 5 deg.

As a comparison I plot the phase that I measured when the handmade coil had been there (green curve in the plot).

 I will also measure amplitude unbalances between I and Q.

Restarted the elog with the script.

As seen in the previous measurement the first harmonic of both the 11 MHz and 55 MHz outputs are about 30dB
higher than desired.  In an attempt to attenuate these and higher harmonics I introduced SBP-10.7 filters into
the 11MHz outputs and SLP-50 filters into the 55 MHz outputs.
Then I measured the height of the harmonics again and found that they were suppressed as expected.  Now harmonic
at 22 MHz is 58dB lower than the 11 MHz fundamental.  And the 110 MHz is lower by 55 dB compared to the 55 MHz
fundamental.  None of the higher harmonics are seen => they are below 70dB

SLP-50 has an insertion loss(IL) of 4.65 dB and Return Loss(RL) of 3dB.  It would be better to use SBP-60
(IL=1.4 dB and RL=23dB)

The filter on the 11 MHz lines is okay. The SBP-10.7 has IL=0.6 dB and RL=23 dB.

RF Amp operating temperature

Earlier measurement reported by Alberto in LIGO-T10004-61-v1 based on the LM34 temperature sensor were lower than that shown by placing a calibrated thermocouple sensor directly on the heat sink by about 5deg C. The difference probably arose because the LM34 was located on a separate free-hanging copper sheet attached to the RF Amp by a single screw, resulting in a gradient across the copper strip.   I tried to move the LM34 which was glued down, but broke the leads in the process.  I then replaced it with another one mounted much closer to the heat sink and held it down with a copper-strip clamp.  There is no glue involved and there is heatsink compound between the flat surface of the LM34 and the heatsink.  Picture attached. 

  The picture also shows the new filters which have been put in place to reduce the harmonics.  Note that the SBP-10.7 which was to go on the 11 MHz Demod output is located much farther upsteam due to space constraints.

Amplitude imbalance between I and Q in a demod board, AS11, with the new 90 deg splitter was measured.

It shows roughly 10% amplitude imbalance when the LO power is in a range from 0 to 5 dBm. Not so bad.

  With the handmade coil there used to be a huge imbalance (either I or Q goes to zero volt while the other keeps about 1 V rms) as the LO power decreases.

But with the new 90 deg splitter now there are no more such a huge imbalance.

The remaining 10 % imbalance possibly comes from the fact that we are using ERA-5 in each I and Q path. They may have such gain imbalance of 10%.

We should check the ERA-5 gains so that we can confidently say ERA-5 causes the amplitude imbalance.

Then our plan replacing the ERA-5s (see here) will sound more reasonable.

Problem:

Way back, Jay had D-sub to SCSI adapters made to adapt our existing Sander box AA filters to the new SCSI based IO chassis.  However, these did not fit inside the box.

At the time, we simply left the cards outside hanging, which was a hack and needed to be replaced.

Solution:

Steve modified a black AA filter box so that it could fit the D-sub to SCSI adapter board on it, plus strain relief the SCSI cable, rather than let it hang.  The back of the box was cut, and an extending piece of metal attached to the bottom of the box.  The adapter board was screwed into the box, the SCSI plugged in, then the SCSI cable is clamped to the extending metal as well.

This modification will be propagated to the 3 remaining AA filter boards using the D-sub to SCSI adapter.

To design a new resonant EOM box I started reviewing the prototype that I've built.

As a part of reviewing I checked an important thing that I haven't carefully done so far :

I compared the measured input impedance with that of predicted from a circuit model. I found that they show a good agreement.

So I am now confident that we can predict / design a new circuit performance.

* * * (input impedance) * * *

 Performance of a resonant circuit is close related to its input impedance and hence, in other words, determined by the input impedance.

Therefore an investigation of input impedance is a way to check the performance of a circuit. That's why I always use impedance for checking the circuit.

The plot below is a comparison of input impedance for the measured one and one predicted from a model. They show a good agreement.

(Note that the input impedance is supposed to have 50 Ohm peaks at 11, 29.5 and 55 MHz.)

 
* * * (circuit model) * * *

To make the things simpler I assume the following three conditions in my model:

 1. inductor's loss is dominated by its DC resistance (DCR)

 2. capacitor's loss is characterized only by Q-value

 3. Transformer's loss is dominated by DCR and its leakage inductance

All the parameters are quoted from either datasheet or my measurement. The model I am using is depicted in the schematic below.

Basically the Q-vaules for the capacitors that I used are quite low. I think higher Q capacitors will improve the performance and bring them to more 50 Ohm.

The performance plots for POX_11 in the wiki are horrendous and the schematic is missing.

I opened up the box and found all kinds of horrors. There were multiple tunable parts and a flurry of excess nonsense.

The top 2 worst offenders:

1) The main tunable inductor was busted. I removed it and found that the coil was open. Too much indelicate soldering in its vicinity had melted the wire. Someone had put extra inductors and capacitors around it to make it seem as if the PD was working fine, but the noise performance was off by a factor of ~100.

2) The MAX4107 had a 1.4k series resistor. This make the output go through a 1450/50 voltage division which is not nice for the SNR. I removed it.

I then struggled for awhile to get a sensible response. It turned out that the TEST IN input was not giving me a sensible TF. Jenne and I fired the Jenne laser at it and found that the 11 MHz main resonance is there. In the morning I'll finish this off and post more results. I think its going to end up being fine.

We are going to have to take a careful look at all the RFPDs if this one is any indication...

I used the Jenne AM laser to tune up the PD (used to be POX_11 but now is called REFL_11). In addition to the notch at 22 MHz, I have also put in a LC notch at 5*f = 55.3 MHz. The transfer function below shows the RF OUT of the PD v. the drive to the laser. I didn't divide out by the 1811 because its not on the EE bench.

While checking whitening filters on the LSC rack, I found some epics controls for the whitening looked not working.

So I powered two crates off : the top one and the bottom one on 1Y3 rack.

These crates contain c1iscaux and c1iscaux2. Then powered them on. But it didn't solve the issue.

 with script

A new 90 deg splitter, PSCQ-2-51W, has been installed on another demod board called AS55.

It shows a reasonably close 90 degree separation between the I and Q signals at 55 MHz with various LO and RF power.

So far we have ordered only three PSCQ-2-51Ws for test. Now we will order some more for the other demodulators.

 Some plots will be posted later.