10010 Ohm for POP55 vs 50 Ohm for AS55 (cf. http://nodus.ligo.caltech.edu:8080/40m/4763)

I wonder if you used an LED flash light, which emits no IR.

I didn't use LED flash light. We learned from the past (elog #7355). I checked that POP55 and REFL55/165/33/11 are clearly responding to flash flight, but I didn't expect that much difference in DC gain.
I wonder why we could align AS beam to AS55 in Feb 8 (elog #8030), but not in Feb 15 (elog #8091). I will check during the pump down.

I have found two great FET input chips that rival the storied, discontinued AD743. In some ways, they are even better. These parts are the OPA140 and the OPA827.

Below is a plot of the input-referred voltage noise of the two op amps with R_source = 0, along with several others for comparison. The smooth traces are LISO models. The LT1128 and AD797 are BJT-input parts, so their voltage noise is naturally better. However, the performance you see here for the FET parts is the same you would expect for very large source impedances, due to their extremely low current noise by comparison. I have included the BJTs so that you can see what their performance is like in an absolute sense. I have also included a "measured" trace of the LT1128, since in practice their low-frequency noise can be quite higher than the spec (see, for example, Rana's evaluation of the Busby Box). The ADA4627 is another part I was looking into before, the LT1012 is a less-than-great FET chip, and the AD797 a less-than-great BJT.

As you can see, the OPA140 actually outperforms the AD743 at low frequencies, though it is ~2x worse at high frequencies. The OPA827 comes close to the AD743 at high frequencies, but is a bit worse at low ones. Both the OPA140 and OPA827 have the same low-frequency RMS spec, so I was hoping it would be a better all-around part, but, unfortunately, it seems not to be.

The TI chips also have a few more things on the AD743:

• Input current noise @ 1kHz
  • AD743: 6.9 fA/rtHz
  • OPA827: 2.2 fA/rtHz
  • OPA140: 0.8 fA/rtHz (!)
• Input bias (offset) current, typ
  • AD743: 30 pA (40 pA) --- only for V_supply = ±5 V
  • OPA827: ±3 pA (±3 pA) --- up to ±18V
  • OPA140: ±0.5 pA (±0.5 pA) (!) --- up to ±18V
• Supply
  • Both OPA140 and OPA827 can be fed single supplies up to 36V absolute maximum
  • The OPA140 is a rail-to-rail op amp

These characteristics make both parts exceptionally well suited for very-high source impedance applications, such as very-low-frequency AC-coupling preamplifiers or ultra-low-noise current sources.

(Apologies---the SR785 I was using had some annoying non-stationary peaks coming in. I verified that they did not affect the broadband floor).

R.I.P., AD743

 [Yuta, Manasa]

We replaced the dead photodiode on MC REFL PD with a new one (GAP 2000). We measured the frequency response of the PD and tuned the resonant frequency using inductor L5 (in the circuit diagram) to be 29.575MHz - over an average of 10 measurements.

Riju is measuring the characteristics of the PD and will be posting an elog in detail.

Rana suggested that I measure the OPA827 and OPA140 noise with high source impedance so as to see if we could find the low-frequency current noise corner. Below is a plot of both parts with R_s = 0, 10k, and 100k.

As you can see, both parts are thermal noise limited down to 0.1 Hz for up to R_s = 100k or greater. Given that the broadband current noise level for each part is ~0.5-1 fA/rtHz, this puts an upper limit to the 1/f corner of <100 Hz. This is where the AD743 corner is, so that sounds reasonable. Perhaps I will check with even higher impedance to see if I can find it. I am not sure yet what to make of the ~10-20 kHz instability with high source impedance.

EDIT: The datasheets claim that they are Johnson noise limited up to 1 Mohm, but this is only for the broadband floor, I'd guess, so it doesn't really say anything about the low frequency corner.

  This looks pretty good already. Not sure if we can even measure anything reasonable below 0.1 Hz without a lot of thermal shielding.

The 10-20 kHz oscillation may just be the loop shape of the opamp. I think you saw similar effects when using the AD743 with high impedance for the OSEM testing.

After my investigations this afternoon (with help from Sendhil and Shivaraj), I do not find any problems with the POX whitening switching.

Earlier this afternoon / evening I was misleading myself into thinking that either the switching component (ADG333ABR) was broken, or that the whitening op amps (LT1124CS8) were broken on the POX I&Q and POY I&Q channels.  I had not realized until Jamie mentioned the possibility, that some of the DC gain stages were on for POX and POY.  POX and POY (I&Q for both) all had +36dB of gain, so when I was injecting my 60Hz sine wave into those channels, the whitening opamps were already saturated, which is why it didn't look like I was getting any gain.  When I set them all to 0dB (which is what AS11 and REFL11, the other 2 PDs using that whitening board, were set to), all 8 channels behaved the same.

The shaped whitening (which is either bypassed or not, depending on the condition of the software "unwhite" switch) is 2 filters in series, each with a zero at 15Hz, and a pole at 150Hz, with DC gain of 0dB.  For a 60Hz sine wave, this gives a factor of ~4 from each stage.  After setting all of the whitening gains to 0dB, I was able to see on all 8 channels of the board an input sine wave, a larger (by 4-ish) sine wave, and then a larger (by 4ish again) sine.  When I looked at the output of the switch of all 8 channels, the signal was either the same as the input amplitude, or the same as after the 2nd whitening stage, depending on the "unwhite" filters.

Before looking at actual signals, Sendhil and I also had checked to see that indeed, the board was receiving the digital signal input to the switch chip, requesting switching based on the state of the "unwhite" filters.

I looked through the elogs, and the only "symptoms" I find are from an IFO check-up session that Koji, Den and I had back in May, where we declared in the elog that POX whitening may or may not be switching.  See elog 6595.  We didn't mention what the actual symptoms we saw were, so unless Koji or Den remember something that I don't, I cannot confirm that we are no longer seeing those symptoms.  However, based on the number of "?" after "POX whitening not toggling the analog whitening", I don't think that we were totally sure that something was wrong in the first place.

Anyhow, the whitening board in the LSC rack labeled "WF1", serving AS11, REFL11, POX11 and POY11 has had a thorough checkup, and I give it a clean bill of health.

At the time you, den and I worked together, we could not lock the X-arm on TEM00 with the FM1s of the POX11 on.
We could lock the arm only on the higher order mode but he gain was low. Once we turned off the FM1s, we immediately
locked the cavity on TEM00.

Don't you have the direct measurement of the TF with FM1 on and off?

Manasa and Jan were having trouble locking the Yarm, and asked me to take a look at it.  After a good long time of trying to figure out what was going on, it finally occurred to me that I did not turn the DC gain on POX and POY back to the nominal 36dB.  As soon as I did that, both arms acquired lock.  Ooops.

Here are the transfer functions that we took back in 2011 (see elog 4915 and replies) for POX:

The table of all whitening filter zpk values is on the wiki: https://wiki-40m.ligo.caltech.edu/Electronics/WhiteningFilters

I investigated the situation of the two Sorensen supplies in the LSC rack (1Y2).  They are there solely to supply power to the LSC LO RF distribution box.  One is +18 V and the other is +28 V.  All we need to do is make a new longer cable with the appropriate plug on one end (see below), long enough to go from the bottom of the 1Y3 rack to the top of 1Y2, and we could move them over quickly.  Some sort of non-standard circular socket connector is used on the distribution box:

It could probably use thicker conduction wire as well.

If someone else makes the cable I'll move everything over.

I started to look into putting together a 110 MHz demod board to be used as POP110 (see #8399).

We have five spare old-skool EuroCard demod boards (LIGO-D990511).  From what I gather (see #4538, #4708) there are two modifications we do to these boards to make them ready for prime time:

• appropriate LP filter at PD RF input (U5 -> MC SCLF-*)
• swap out T1 transformer network with a commercial phase shifting power splitter (MC PQW/PSCQ)

#4538 also describes some other modifications but I'm not sure if those were actually implemented or not:

• removal of the attenuator/DC block/ERA-5 amp sections at the I/Q outputs
• swap ERA-5 amp with "Cougar"(?) amp at LO input.

What we'll need for a 110 demod:

• U5 -> SCLF-135
• T1 network -> PSCQ-2-120

I'll scrounge or order.

I have re-implemented POP110.  The cable coming from the AS110 diode is disconnected, labeled, and sitting in the cable tray next to the LSC rack. 

Now the POP diode path is:

Thorlabs 10CF ----many meters of heliax cable-----> Bias Tee ------> RF amplifier ------> Splitter ------> Bandpass 21.7MHz --------> POP22 demod board

                                                                                                                   |                                                                                    |

                                                                                                                   |                                                                                    |

                                                                                                                   V                                                                                  V

                                                                                                            POP DC                                                                        High pass 100MHz

                                                                                                                                                                                                        |

                                                                                                                                                                                                        |

                                                                                                                                                                                                       V

                                                                                                                                                                                              Lowpass 150MHz

                                                                                                                                                                                                       |

                                                                                                                                                                                                       |

                                                                                                                                                                                                      V

                                                                                                                                                                                        POP110 demod board

This SCPQ-150+, which is surface mount, might also work in place of the PSCQ-2-120, which is through-mount.  Would need to be reconciled with the board layout.

 For the 110 MHz demod boards, we would ideally have a plugin bandpass filter. If you have some specs in mind, you can email mini-circuits or pulsar microwave about making a custom part; its not too expensive usually.

For the meantime, you should remove the onboard one and replace with a combination of low/high pass filters from Mini-Circuits. If you put a SLP-150 and a SHP-100 in series, the insertion loss should be less than 1 dB.

I think the ERA amps are OK for now, but they die with time, so they just need to be tested and replaced if necessary.

I'm having Steve order the following:

2x  SXBP-100+
2x  SCLF-135+
2x  PSCQ-2-120+

If you want him to add anything to the order let him know ASAP.

While helping Riju out this afternoon, I noticed that the timing fiber that goes to the OMC rack (near the AP table) was bent, and is now possibly kinked, after the installation of the fiber splitter box. 

The fiber was hanging from the back of the rack, and had been strain relieved.  However, the path that the fiber was taking is now occupied by the fiber splitter for the RF PD diagnostic stuff.  So, the installation of the fiber splitter box put the old timing fiber under tension, causing the fiber to be bent at a little over 90 degrees, since it was pulled tightly against the corner of the splitter's front panel. 

I adjusted the strain relief so that the fiber is loose again, although there is still a bit of a kink that you can feel.  Things (for now) seem to be working, since the 1pps light on the front of the box at the top of the OMC rack is still blinking happily, indicating that the 1pps is still getting there. 

We are not using most of the stuff in that rack right now, but if we have problems in the future, we should check out the fiber to make sure it is still good.

Yesterday, I pulled out the AI board for the PRM/BS SUSs. (After the investigation it was restored)

Contrary to our expectation, the board D000186 was not Rev. A but Rev. B.

According to Jay's note in D000186 (for Rev.D), the differences of the Revs are as follows

Rev.A: Initial Release (Analog Biquad version, 4dB 4th order elliptic with notches)
Rev.B: Filter implemented by Freq Devices chip
Rev.C: Differential input version with better RF filtering
Rev.D: 3rd order 0.5dB ripple Cheby with notches at 16K&32K, DB25 input version

I went to the WB EE shop and found bunch of AI filter modules. At least I found one Rev.A and six Rev.D.
I found at least one Rev. C.

I took Rev.A and Rev. D to see the difference of the transfer functions.
Rev.A has more ripple but steeper roll-off. Rev. D is flater at the pass band with slower roll-off.
Rev.D has more phase lag, but it will be fine once the entire frequency response is shifted to x4 high frequency.
The notch frequency of the Rev. D looked right.

I made the empirical pole/zero modeling of the transfer functions.
The LISO models are attached as the ZIP file.
I faced an unexplainable phase behavior at around one the notches for Rev.A.
This may suggest there could have been internal saturation is the stage during the sweep.

More importantly, Rev. D has differential inputs although the connector formfactor is different from the current 40pin IDC.
In fact we should not use Rev.A or Rev.B as they have single end inputs.
Currently the inputs of the AI's for the SUSs are single ended while the DACs are differential.
This means that
1) We waste a half of the DAC range.
2) The negative outputs of the DACs are short-circuited. OMG
3) The ground level fluctuation between the DAC and the SUS rack fluctuates the actual actuation voltage.

Now I am looking at the noise performance of the filters as well as the DAC output noise and range.
I hope we can use Rev.D by replacing the connector heads as this will remove many of the problems we currently have.

 [Eric, Alex]

We added our reference photodetector (Newport 1611, REF DET) to the southern edge of the AS table, as pictured. The detector's power supply is located under the southwest corner of the table, as pictured. We have connected the detector to its power supply, and will connect the detector's fiber input and RF output tomorrow.

EDIT: this is about the RFPD frequency response setup...

[Eric, Alex]

For the RFPD frequency response project, we routed the fiber that will connect our REF DET (on the AS table) to our 1x16 optical splitter (in the OMC_North rack), as pictured. (The new fiber is the main one in the picture, which ends at the right edge near REF DET) Note that we secured the fiber to the table in two places to ensure the fiber would remain immobile and out of other optical paths already in place.

At 2:00 we plan to run fiber from our laser module (in rack 1Y1) to our 1x16 optical splitter (in the OMC_North rack) and measure the power output at one of the splitter's output ports. We plan to keep the output power limited to less than 0.5 mW per optical splitter output.

[Eric, Alex]

We decided that the POY Table would be a better home for our REF DET (Newport 1611 FC-AC) than the AS Table. We moved the PD to the POY Table (1st attachment) and routed a fiber from our 1x16 Optical Splitter in the OMC_North rack to the POY Table. REF DET's power supply is now located under the POY table (2nd attachment). We left the fiber described in the previous post on the AS Table.

Afterwards, we hooked a fiber up to our laser module to test it (3rd attachment). The laser was not being distributed, just going to one fiber with a power meter at its end. Everything turns out, but we realized we need to read the power supply's manual before continuing. 

 [Eric, Alex]

Our RF Switch arrived today, and we mounted it in rack 1Y1 (1st attachment). 

We connect our input fiber and all of our output fibers to our 1x16 optical splitter (2nd attachment). Note that the 75 meter fiber we are using for the splitter's input is in a very temporary position (3rd attachment - it's the spool).

We successfully turned our laser on and tested the optical splitter by measuring output power at each fiber using our Thorlabs PM20 power meter. Data was taken with the laser running at 67.5 mA and 24 degrees Celsius:

Detector name                  Power

 [Eric, Alex]

We successfully used our system to modulate the input to a single photodetector. The RF Out of the network analyzer went to the Mod In of our laser, which was operating at 98 mA. The laser's output was sent to our 1x16 optical splitter. This provided input signals for both our reference detector and AS55. Our reference detector's output was sent to the network analyzer's R input, while the AS55's output was sent to the network analyzer's A input. 

We still need to work out the specifics of how the modulation works. Specifically, we want to look at the amplitude of the network analyzer's output. Additionally, we may have been saturating our reference detector, causing noise problems.

[Eric, Alex]

We used our setup from yesterday (elog #8940) to measure transimpedance measurements for AS55, REFL11, REFL33, and REFL55, using our Newport 1611 FC-AC as reference. We connected the fibers to their respective telescopes such that the beams focused on their photodetectors, using a multimeter to maximize photodetector DC output. Plots are attached. At first glance, the poles seem to be where they're supposed to be.

Note that the procedure used today is similar to what the eventual automated procedure will be. The main differences are (1) The RF Switch will be used rather than manual switching (2) NWAG4395A will be used to collect data rather than netgpibdata (3) Data will be fit using vectfit4.m and compared to some canonical set.

 [Alex, Eric]

Today I spent some time mounting the launcher and performing the same data collection for POX11. I think I still need to focus the launcher so the photodetector gets a good signal, but the data from today wasn't too bad.  Additionally, I worked on matlab scripts to improve PDFR data analysis.

This time I collected data from the network analyzer using NWAG4395A in the netgpibdata directory. The advantage of this is that the computer tells the network analyzer to perform the sweep as well as retrieving the data.

For analysis, I improved my implementation of vectfit4.m so that it focuses in on the particular photodetector's predicted peaks and thus ignores much of the noise, giving a better fit. The raw data is the red circles in the 2nd attachment, while the fit is the blue line. I also had the program return the frequency value of the peak. For POX11, this was 1.106e+07 Hz.

I also finagled copies of existing programs to enable one to plot multiple transfer functions on the same axes. This function is /users/alex.cole/plottwo.m. I will eventually use this to compare new data to some canonical data so that we may monitor photodetector performance over time.

The eventual plan is to generate two plots per photodetector, one of which will compare new data to the canonical set, the other of which will show the fit of the data. Both will have subplots that zoom in around regions of interest (known peaks and notches), and the plot which displays the canonical set will also have Q's of peaks and their locations.

For the photodetector frequency response project, I finished the construction of our baluns chassis and mounted it in rack 1Y1 (1st picture).

After consulting with Jenne, I mounted the fiber launcher for REFL165 on the AS table such that it would not cause an obstruction. I aligned the launcher using a multimeter to monitor the DC output of REFL165, but looking at the data I got, it seems I need to do a better alignment/focusing job to get rid of a bunch of noise.

For the photodetector frequency response project, our new RF Switch Chassis (NI pxie-1071) arrived today. I took the switches out of the old chassis (Note for future generations: you have to yank pretty darn hard) and put them in the new chassis, which I mounted in rack 1Y1 as pictured. 

The point of this new chassis is that its controller is compatible with our control room computer setup. We will be able to switch the chassis using TCP/IP or telnet, aiding in our automation of the measurement of photodetector frequency response.

Notes to the fiber team:

I am aligning beam onto the RFPDs (I have finished all 4 REFL diodes, and AS55), in preparation for locking. 

In doing so, I have noticed that the fiber lasers for the RFPD testing are always illuminating the photodiodes!  This seems bad!  Ack!  

For now, I blocked the laser light coming from the fiber, did my alignment, then removed my blocks.  The exception is REFL55, which I have left an aluminum beam dump, so that we can use REFL55 for PRM-ITMY locking, so I can align the POP diodes.

EDIT:  I have also aligned POP QPD, and POP110/22.  The fiber launcher for POP110 was not tight in its mount, so when I went to put a beam block in front of it and touched the mount, the whole thing spun a little bit.  Now the fiber to POP110 is totally misaligned, and should be realigned.

What was done for the alignment:

1. Aligned the arms (ran ASS).

2. Aligned the beam to all the REFL and AS PDs. 

3. Misaligned the ETMs and ITMX. 

4. Locked PRM+ITMY using REFL11.
The following were modified to enable locking
(1) PRCL gain changed from +2.0 to -12.
(2) Power normalization matrix for PRCL changed from +10.0 to 0.
(3) FM3 in PRCL servo filter module was turned OFF.

5. POP PDs were aligned.

 For the RF PD Frequency Response Measurement project, we get each PD signal from the "PD RF Mon" output of each demodulator board corresponding to our PD under test. Therefore we can't neglect the frequency response of various filters inside the demodulator board. I used our Agilent 4395 Network Analyzer to gather frequency response data for each demodulator board being considered for the RFPD frequency response project (AS55, REFL11, REFL33, REFL55, REFL165, POX11, POP22, POP110).

The NA swept over a frequency range of 1-500 MHz. Data was collected using NWAG4395A (from the netgpibdata directory). It should be noted that the command line options -a 16 -x 15 (averaging=16 and excitation amplitude=15 dBm[the max]), in addition to the usual command line options described in the help file, were used to minimize noise. 

The data is located in /users/alex.cole. The file names are in the format [PDNAME]DemodFilt_1000000.dat (e.g. REFL11DemodFilt_1000000.dat). Results for POP110 are shown below.

This post pertains to the fiber-coupled diode laser mounted in rack 1Y1.

To turn the laser on, first turn the power supply's key (red) to the clockwise. Then make sure that the laser is in "current" mode by checking that the LED next to "I" in the "Laser Mode" box in lit up. If the light is not on, press the button to the right of the "I" light until it is. Now press the output button (green). This is like removing the safety for the laser. Then turn the dial (blue) until you have your desired current. Presently, the current limit is set to around 92 mA.

To turn the laser off, dial the current back down to 0mA and turn the key (red) counterclockwise.

 I routed cables (RG405 SMA-SMA) from several demodulator boards in rack 1Y2 to the RF Switch in rack 1Y1 using the overhead track. Our switch chassis contains two 8x1 switches. The COM of the "right" switch goes to channel 7 of the "left" switch to effectively form a 16x1 switch. The following is a table of correspondences between PD and RF Switch input.

ThePOP110 demod board has not yet had a cable routed from it to the switch because I ran out of RG405.

We should also consider how important it is to include MCREFL in our setup. Doing so would require fabrication of a ~70 ft RG405 cable. 

 This post describes how to use the Automated Photodetector Frequency Response System.

On the mechanical side, turn on:

-the diode laser (in rack 1Y1)

-the RF Switch (in rack 1Y1)

-the reference PD (under the POY table)

-the AG4395A Network Analyzer

The NA’s RF output should go to the laser’s modulation input, the reference PD’s output should go to the NA’s R input, and the RF Switch Chassis’s output (which is the combination of the two switches’ COM channels using a splitter) should go to the NA’s A input.

Once this is done, navigate into /users/alex.cole and run PDFR.sh. This script collects data for each photodetector under consideration by switching using a python script and communicating with the NA via GPIB. It then sends all the data to RF.m, which fits the functions, plots the latest data against canonical data, and saves the plots to file.

The fitting function, fit.m, also outputs peak frequency to the command line. This function uses PD name data (e.g. ‘REFL33’) to choose an interval with minimal noise to fit.

The main script prompts the user to press enter after each NA sweep to make sure that measurements don’t get interrupted/put out of order by RF switching.

Once you're done, you should turn off the laser, NA, RF Switch, and reference PD.

Troubleshooting

Sometimes, the NA throws up and doesn’t feel like running a particular sweep. If this happens, it’s a good idea to keep the matlab script from trying to analyze this PD’s data. Do this by opening up RF.m and commenting out the calls to ‘fit’ and ‘canonical’ for that PD.

If fit.m complains about a particular set of data, it is often the case that the N/P ratio (where N is order of approximation and P is number of points in the interval) is too high. You can fix this by reducing N or making the PD’s frequency range (chosen in the fnew_idx line) larger.

Choosing a single PD

If you only want to grab the transfer function for one PD, first look up which switch input it belongs to. This information is contained in /users/alex.cole/switchList. To turn the switch to a particular input, type something like:

python rf.py “ch7”

This command uses TCP/IP to tell the switch to look at channel 7. Switch input numbers range from 1 to 16, though not all of them are in use.

Once the switch is looking at the correct input, you can run a sweep and download the data by typing /opt/rtcds/caltech/c1/scripts/general/netgpibdata/NWAG4395A -s 1000000 -e 500000000 -c 499000000 -f [filestem for output] -d [path of directory for output] -i 192.168.113.108 -g 10 -x 15. 

I have modified one of the spare demod boards that was sitting above the electronics bench (the one which was unlabeled - the others say 33MHz, 55MHz and 165MHz) to be the new AS110 demod board.  In place of the T1 coil, and the C3 and C6 resistors, I have put the commercial splitter PSCQ-2-120+.  In place of U5 (the low pass for the PD input) I have put an SCLF-135+. 

In order to figure out how to make the pinout of the PSCQ match up with the available pads from T1, I first pulled the "AS11" board (it's not something that we use, so it would be less of a tragedy if something happened while I had the board pulled).  However, while the PCB layout is the same, the splitter for the low frequencies (PSCQ-2-51W) has a different pinout than the one I need for the 110MHz.  So, I put AS11 back, and pulled the POP110 board. (After I noted the pinout on POP110, I reinstalled that board.  To get it out, I had to unplug the I and Q outs of POP22, but I have also replugged those in).

For my new AS110 demod board, I copied the pin connections on POP110.  I have made a little diagram, so you can see what pins went where.  The top 2 rectangles are the "before" installation cartoon, and the bottom is the "as installed" cartoon.

The one thing that must be noted is that, because of the pinout of the splitter and the constraints of the board layout, the +0 degrees (I-phase) output of the splitter is connected to the Q channel for the rest of the demod board.  This means that the +90 degrees (Q-phase) output of the splitter is connected to the I channel for the rest of the demod board.  This is not noted for POP110, but is true for both:  The I and Q channels of the 110 MHz demod boards are switched.  In practice, we can handle this with our digital phase rotation.

Daytime tomorrow, I will test my new board as Suresh did in elog 4736.  Before we get to use AS110, we need (a) some LO juice from the RF distribution box, and (b) a spot to plug the board in, in the LSC rack.  Meditating on how those are going to happen are also tasks for daytime tomorrow.

OK, but what kind of filter should we be actually using? i.e. what purpose the 135 MHz low pass serve in contrast to a PHP-100+ ?

 Hmmm. Indeed. This is just cutting off higher frequency stuff, but anything from other lower sidebands still gets through.  I should actually stick in the SXBP-100's, which will band pass from 87-117 MHz.  These have an insertion loss at 100 MHz of 1.64 dB. 

Jamie ordered 2 of these, so I can put one in each of AS110 and POP110. 

I measured the phase split between the I and Q signals of my AS110 board.  To do so, I plugged the board into an empty slot next to the PD DC readout / whitening board in the LSC rack.  I borrowed the POP110 local oscillator, and used a Marconi to generate a "PD input".  (I'm roughly following what Suresh did in elog 4736).  Our 11MHz is currently 11.066134MHz, so I had the Marconi going at 110.662340 MHz (1kHz from 10*11MHz), and I had the Marconi source at -13dBm.  

I took a transfer function using the SR785 between the I and Q outs of the AS110 demod board, and got a magnitude misbalance of 0.809 dB, and a phase split of 110.5 degrees.  This isn't so close to 90 degrees, but this may be a problem with the splitter that we're using, as Suresh detailed in elog 4755.  In that elog, he measured a phase split of POP110 of 105 degrees, unless the power going into the splitter was pretty high.  As with POP110, since I expect that we'll usually only look at one channel (I, for instance), this isn't such a big deal for AS110. 

I have left, for now, the board in the empty slot.  It looks like (I'm going to go check) there are 3 open channels on the whitening board that has the PD DC signals.  So, the only thing left to figure out is how we want to get some local oscillator action for this new board.

EDIT: Yes, those channels are available.  Right now (as a remnant from testing the whitening filters waaaay back in the day) they are called C1:LSC-PDXXX I, Q, DC.  I'll use 2 of those for the AS110 I and Q. 

As I see it, we have a few options for getting the 110 MHz LO to both the POP110 and AS110 demod boards.  

The current situation is described by Kiwamu in elog 5746.  The 55 MHz signal comes into the box, and is split 4 ways, with each path having 19.7 dBm.  One of these 4 is for 110.  It has a 2dB attenuator (giving us ~17.7 dBm), and then it goes to an MK-2 frequency multiplier.  I'm a little lost on why we're giving the MK-2 17 dBm, since it says that it can handle an input power between 1 - 15 dBm.  It has ~16 dB conversion loss, so the 110 output of the distribution board has (according to the drawing) 1.9 dBm.  The demod boards have a 10 dB attenuator as the first element on the LO path, so we're giving the ERA-5 -8 dBm. 

We can either amplify the 110 leaving the distribution box, split it, and then attenuate it to the appropriate level for the demod boards, or we can change the attenuators on the POP110 and AS110 demod boards. 

Since we seem to be over driving the 2x frequency multiplier, I think I should change the 2dB attenuator to a 5dB attenuator, so we're giving the 2x multiplier ~15 dBm.  The conversion loss of ~16 dB means we'll have -1 dBm of 110 MHz.  I want to amplify that by ~10 dB, to give 9 dBm.  Attenuate by 5 dB to get to 4 dBm, then split into 2, giving me 2 110 MHz spigots, each of ~1 dBm.  Since the demod boards expect between 0-2 dBm for the LO's, this should be just fine.

Thoughts, before I start scrounging parts, and pulling the RF distribution box?

- Do we have an appropriate amplifier?

- True challenge could be to find a feedthrough for the new port. (or to find a space for the amplifier in the box)

- PDXXX channels is on the DC whitening filter module. There could be some modification on this module (like diabling the whitening gain selector).

- We don't have AS11 and AS165, and so far it is unlikely to use AS11. i.e. The feedthrough, the slot on the crate, the whitening, and the channels can be trasnsition from 11 to 110.

I have pulled the RF distribution box out of the rack, so I can look at it, and modify it to have 2 110 MHz spigots. I'm going to make the mods as in elog 9072.

Before I pulled the distribution box, I turned off the RF Generation Box, so don't be surprised that the MC will not lock.  I have terminated the cables that bring the 11 and 55 MHz signals from the generation box to the distribution box, so if someone does turn on the generation box, there won't be bad reflections.

To get the box out, in addition to unplugging all of the cables that go to the distribution box, I had to disconnect 2 of the ADC ribbon cables from the top row of RFPD demod / whitening / ADC boards, since they were in the way.  Everything is labeled, so it should be easy to put back together.

Note to Future Jenne:  Past Jenne put the screws needed for those ADC cables and to hold the box in the rack, in the plastic box that is on the floor in front of the LSC rack. 

Also, I measured the 110 MHz port before I pulled the board, so I would know what my "before" looked like.  I was using the 300MHz 'scope's measurement functions, so these are in volts, not dBm.  Amplitude = 1.33V, RMS = 456 mV, freq = 109.4-111.9 MHz

After scrounging for parts, and opening up the box, I have modified my proposal to the following:

Note that the freq multiplier is supposed to take, at maximum, 15 dBm.  The reason I put the 5 dB attenuator, then an amplifier, then another attenuator is that I don't know of / can't find easily a 10 dB amplifier with the usual case type on the MiniCircuits site.  (If anyone knows of one off the top of their head, that would be handy.  Then I'd remove the attenuator between the multiplier and the amplifier, and make the 10 dB attenuator a 5 dB.)

Anyhow, the ZFL-500HLN can only output 16 dBm of power, and I don't think I have space for another ZHL-2 (which can output up to 26 dBm) inside the box, so I put an attenuator before, as well as after, the amplifier. 

I think I have space inside the box for all the bits and pieces I'll need, although to do things correctly, I need to drill holes in the teflon mounting plate to mount the amplifier and splitter.

I also think that I have space on the front panel to put another isolated SMA feedthrough.

I have, on my desk, all the parts (except for mounting screws, and cables between things) to make these modifications to the distribution box. 

The RF distribution box is still on the bench, so again, don't be surprised that the MC doesn't lock.

I have completed my modifications as proposed in elog 9096, but I want to do a couple of quickie tests in the morning before I declare it ready for service.

 I have removed the 135 MHz low pass from my new AS110 demod board, but these SXBPs have different feet than the SCLFs, so I want to confirm with Koji or someone that I can solder them in the same way, before I get carried away and destroy anything.  I should be able to finish this up tomorrow, plug in the demod board and the distribution box, and try out AS110 triggering, etc, tomorrow night.

I have reinstalled the RF distribution box, as well put in the AS110 demod board.  I plugged everything back in, and turned it all on.

The switch on the distribution box may be starting to fail.  When I was turning the box on, I could depress the button, and see the blue glow, but it wouldn't catch, so when I removed my finger, the glow went away.  I was afraid that I'd have to pull the box, but after a few more button toggles, I got it to stay on.  I'm leaving it for now, but we should remember that this may be a problem.

I will look at the phases of all the PDs, but none should need changing except POP 110.  Every other PD has the exact same cables as before.

Temporary fix for the switch: give a bit of oil to the button

Permanent fix: buy better switches.

I noticed that the MC3 LL sensor was apparently dead according to its suspension screen. Since it was only the fast ADC channel and not the SLOW PDmon, I could tell that it was just in the ADC cabling. I pushed in a few of the MC3 sensor cables on the front and back of the PD whitening board and it came back OK. According to this trend of the past 40 days and 40 nights, it started slipping on this past Wednesday morning.

Was anyone walking near MC2 or the suspension electronics racks before noon on Wednesday (Oct. 2nd)?

The power supply to the ADC box on the IOO rack (that reads the beat I & Q signals) was pulled out because it did not run through any fuse and was connected directly to the power supply. 

There were already connections running from the +/-5 V power supply. They were powering the mode cleaner demod board rack. In order to remove the ADC power connectors from the power supply, I notified Jenne in the control room because turning off the power supply would affect the MC. I switched off the +/-5V power supplies at the same time. The ADC power connectors were removed. The +/-5V power supplies were then turned ON again at the same time. Jenne relocked the MC after this.

I have still not connected the ADC to the fuse rack power supply because this requires the +/-5V power supplies to be turned OFF again in order to pull out new connections from the fuse rack and I need to make a new ADC power connector with thicker wires.

I switched OFF the +/-5V power supplies on the IOO rack to hook up the ADC power connectors through 250mA fuses to +/-5V. Since these power supplies were powering the MC demod boards, MC remained unlocked during the process. I turned the power supplies back ON and MC relocked itself after this.

The first picture shows that there is indeed a DAC next to the ADC in the LSC IO chassis. The second picture shows how there are two cables, each one carrying 8 channels of DAC. The third one shows how these come out of the coil drivers to handle the Tip/Tilt mirrors which point the beam from the IMC into the PRC. It should be the case that the second Dewhitening filter board can give us access to the next 8 channels for use in driving an audio signal into the control room or an ISS excitation.

Rana, Gabriele and I are trying to measure the FSR of the PRC (elog about that later), and we turned off the power to the RF generation box so that we could switch cables at the EOM combiner.  However, as in elog 9101, the power button won't latch when we try to turn the power back on.  All 3 of us tried, to no avail.  For our measurement, poor Gabriele is standing holding the button pushed in, so that we can have some RF sidebands. 

Tomorrow, we'll have to pull the RF generation box, and put in a better switch.

I replaced the stupid broken fancy button with a simple sturdy switch. I had to file out the hole in the chassis a bit, but the switch is pressed in tightly and securely. I put the box back in the rack, but the power cable was coming directly from the power supplies with no fuses. The box was drawing ~.9 and 1.5 Amps from two supplies, so I put 2A fuses on both. Plugged everything back in, and the mode cleaner locks, so it looks like all is well.

RXA: When its so close, I prefer to size it up by 1 step. Please change to 5A fuses. Otherwise, we may blow them from power glitches.

Q: 5A fuses have been swapped in