After Steve pointed out the 'deep hoop' issue, we decided to examine putting an RF Amp on the PSL table, between the RF combiner and the triple resonant box.
This will reduce the chances of standing waves in the cables and reduce the radiation induced pick-up in the RF PD and Demod electronics.
We would like to send ~10 dBm from the distribution box to the combiner. We also want to able to get as much as ~33 dBm of drive at 11 and 55 MHz. So the amp should have a gain of ~20-30 dB and an operating range of 10-100 MHz.
Also desirable are low distortion (high IP3) and good reverse isolation ( > 40 dB).
Some possibilities so far (please add your RF Google Results here):
1) Mini-Circuits ZHL-1-2W-S: G = +32 dB, Max Out = +33 dBm, NF = 6 dB, Directivity = 25 dB
2) Mini-Circuits TIA-1000-1R8: G=+40 dB, Max Out = +36 dBm, NF = 15 dB (AC Powered, Inst. Amp), Directivity = 58 dB.
3) Mini-Circuits ZHL-2-8: G = +27dB, Max out = +29 dBm, NF = 6dB, Directivity = 32 dB
4) RFbay MPA-10-40: G = +40dB, Max Out = + 30 dBm, NF = 3.3 dB, Rev Iso = 23 dB
5) No proper stuff from Teledyne Couger
By looking at what Daniel used in the low noise EOM Driver for aLIGO, we found the A2CP2596 from Cougar.
G = +24 dB, NF = 5 dB, Max Out = +37 dBm. It comes in a 2-stage SMA connector package. I've asked Steve to order 2 of them with the appropriate heatsinks.
I have installed a ZFL-500LN on the RF output of POY11. This should reduce the effect of the CM board voltage offsets by increasing the size of the error signal coming into the board. Checking with an oscilloscope at the LSC rack, the single arm PDH peak to peak voltage was something like 4mV, now it is something like 80mV.
The setup is similar to the REFL165 situation, but with the amplifier in proximity with the PD, instead of at the end of a long cable at the LSC rack.
The PD RF output is T'd between an 11MHz minicircuits bandpass filter and a 50 Ohm terminator (which makes sure that signals outside of the filter's passband don't get reflected back into the PD). The output of the filter is connected directly to the input of the ZFL-500LN, which is powered (temporarily) by picking off the +15V from the PD interface cable via Dsub15 breakout. (I say temporarily, as Koji is going to pick out some fancy pi-filter feedthrough which we can use to make a permanent power terminal on the PD housing.)
The max current draw of this amplifier is 60mA. Gazing at the LSC interface (D990543), I think the +15V on the DSUB cable is being passed from the eurocard crate; I don't see any 15V regulator, so maybe this is ok...
The free swinging PDH signal looked clean enough on a scope. Jamie is doing stuff with the framebuilder, so I can't look at spectra right now. However, turning the POY whitening gain down to +18dB from +45dB lets the Y arm lock on POY with all other settings nominal, which is about what we expect from the nominal +23dB gain of the amplifier.
I would see CM board offsets of ~5mV before, which was more a little more than a linewidth before this change. Now it will be 5% of that, and hopefully more manageable.
We started to clean up the RF cables (heliax and PD interface cables) at the LSC rack.
We have pulled out all the RF cables from the small hole on the side-board close to floor. Passing the cables through this hole makes some of the cables much too short for good strain relief. So we removed the side panel on the vacuum tube side and are going to pass the cables into the rack from there at about waist height. We now have plenty of cable lengths to tie them off to the rack at several points.
We have traced all the available Heliax cables and have attached blank tags to them. We have allocated some cables to REFL11, REFL55 and AS55. These are therefore back in working order. We have also taken stock of the available PD interface cables. They do not have consistent names on both ends of the cable and we will identify and label the ends tomorrow.
MC is locked. The auto-locker works fine.
Handing over the system for night time interferometer work now. Will continue with the cabling tomorrow.
The Distribution box is several steps nearer to completion.
1) Soldered capacitors and DC power lines for four units of the distribution box.
2) mounted all the components in their respective places.
3) Tomorrow we prepare the RF cables and that is the last step of the mechanical assembly.
4) we plan to test both the generator and distributon parts together.
Kevin took a transfer function of the newly assembled PD and noticed that the frequency has shifted to 14.99 freom 11. MHz.
We needed to find the current RLC combination. So we removed the ferrite core from L5 rendiring it to its aircore value of 0.96/muH. We then used this to find the Capacitance of the PD (117pF)
We used this value to compute the inductance required to achieve 11.065MHz which turned out to be 1.75microH.
This was not reachable with the current L5 which is of the type 143-20J12L (nominal H=1.4 micro Henry).
We therefore changed the inductor to SLOT 10 -3-03. It is a ferrite core, shielded inductor with a plasitc sleeve. Its nomial valie is 1.75 microH
We then tested the DC output to see if here is a response to light. There was nonel. l
The problem was traced to the new inductor. Surprisingly the inductor coil had lost contact with the pins.
I then replacd the inductor and checked again. The elecronics seems to work okay.. but there is a very small signal 0.8mV for 500microW.
There seems to be still something wrong with the PD or its electronics.
RF Distribution box has been mounted in the 1Y2 rack and is ready for use.
The box receives 11 and 55 MHz Demod Signals from the RF source located in the 1X2 rack.
We wish to have roughly 2 dBm of output power on each line coming out of the RF distribution box. So I adjusted the attenuators inside the box to get this.
I also looked at why the 2x output looked so distorted and found that the input power was around 17 dBm whereas the maximum allowed (as per the datasheet of Minicircuits MK-2) is 15dBm. So I increased the attentuation on its input line to 5dBm (up by 2dBm) The input power levels are around 14.6dBm now and the distortion has come down considerably. However the net output on the 2x lines is now down to 0.7dBm. We will have to amplify this if we need more power.
The schematic and the power output are now like this:
The mechanical assembly of RF distribution box is 99% complete. Some of the components may be bolted to the teflon base plate if needed.
All RF cables and DC voltage supply lines have been installed and tested. I removed the terminal block which was acting as a distribution box for the common zero voltage line. Instead I have used the threaded holes in the body of each voltage regulator. This allows us to keep the supply lines twisted right up to the regulator and keeps the wiring neater. The three regulator bodies have been wired together to provide a common zero potential point.
I did a preliminary test to see if everything is functioning. All units are functioning well. The output power levels may need to be adjusted by changing the attenuators.
The 2x frequency multiplier outputs are not neat sine waves. They seem to produce some harmonics, unlike the rest of the components.
I will post the measured power output at each point tomorrow. The RF power meter could not be found in the 40m lab. We suspect that it has found its way back to the PSL lab.
Frank is recommending these PhaseTrack-210 as phase stable low loss rf coax cables.
Last week I noticed that the high power amplifiers in the Frequency Generation Box became hot after 2 hours of continuous operation with the lid of the box closed. When I measured their temperature it was 57C, and it was still slowly increasing (~< 1K/hr).
According to the data sheet, their maximum recommended temperature is 65C. Above that their performances are not guaranteed anymore.
These amplifiers aren't properly dissipating the heat they produce since they sit on a plastic surface (Teflon), and also because their wing heat dissipator can't do much when the box is closed. I had to come up with some way to take out their heat.
The solution that I used for the voltage regulators (installing them on the back panel, guaranteeing thermal conduction but electrical isolation at the same time) wouldn't be applicable to the amplifiers.
I discussed the problem with Steve and Koji and we thought of building a heat sink that would put the amplifier in direct contact with the metal walls of the box.
After that, on Friday I've got Mike of the machine shop next door to make me this kind of L-shaped copper heat sink:
On Saturday, I completely removed the wing heat dissipator, and I only installed the copper heat sink on top of the amplifier. I used thermal paste at the interface.
I turned on the power, left the lid open and monitored the temperature again. After 2 hours the temperature of the amplifier had stabilized at 47C.
Today I added the wing dissipator too, and monitored again the temperature with the lid open. then, after a few hours, I closed the the box.
I tracked the temperature of the amplifier using the temperature sensors that I installed in the box and which I have attached to the heat sink.
I connected the box temperature output to C1:IOO-MC_DRUM1. With the calibration of the channel (32250 Counts/Volt), and Caryn's calibration of the temperature sensor (~110F/Volt - see LIGO DOC # T0900287-00-R), the trend that I measured was this:
The heat sink is avoiding the amplifier to overheat. The temperature is now compatible with that of the other component in the box (i.e., crystal oscilaltors, frequency multiplier).
Even with the lid closed the temperature is not too high.
Two things remain untested yet:
1) effect of adding a MICA interface sheet between the heat sink and the wall of the chassis. (necessary for gorund isolation)
2) effect of having all 3 amplifiers on at the same time
I am considering opening air circulation "gills" on the side and bottom of the chassis.
Also we might leave the box open and who ever wants can re- engineer the heat sink.
- Ideally we would like that the heat sink had the largest section area. A brick of metal on top the amplifier would be more effective. Although it would have added several pounds to the weight of the box.
- We need these amplifiers in order to have the capability to change the modulation depth up to 0.2, at least. The Mini-Circuit ZHL-2X-S are the only one available off-the-shelf, with a sufficiently low noise figure, and sufficiently high output power.
There were several parts in this box which did not have shunting capacitors across their input power lines. Only the four RF amps (ZHL-2) had them.
I soldered two capacitors (100 microF electrolytic and 150pF dipped mica) across the power supply lines of each of the following units: 11MHz oscillator, 29.5 MHz oscillator, Wenzel 5x frequency multiplier and the 12x RF amplifier (ZHL-1HAD).
It was quite difficult to reach the power inputs of these units as some of them were very close to the inner walls of the box. To access them I undid the front panel and found that there were several very taut RF cables which prevented me from moving the front panel even a little.
I had to undo some of the RF cables and swap them around till I found a solution in which all of them had some slack. At the end I checked to make sure that the wiring is in accordance with the schematic present here.
This is how the RF generation box might soon look like:
A dedicated wiki page shows the state of the work:
The RF multiplexer is configured as shown in the figure. It is now effectively a 15x1 RF mux.
To select a required channel:
Run the script as shown below
>python rfMux.py ch11
For channel 10 to 16, you can just enter the required channel number and it is routed to the output.
For channel 1 to 8, you only need to input the required channel number as above. No need to run the code again to select ch9 after selecting ch1-8
How the NI-8100 controller works:
Whenever any channel of one switch is selected, the output of the other switch is set to its ch0 (ch1 and ch9 in the figure).
So selecting ch1-8 will automatically select ch9 as output for the other switch. IF you send a command to select ch9 afterwards, the first switch will be automatically set to ch1 and not stay on what you had selected before.
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.
All of the LSC RF PDs have been aligned. I didn't really change much of anything, since for all of them, the beam was already pretty close to center. But they all got the treatment of attaching a Voltmeter to the DC out, and adjusting the steering mirror in both pitch and yaw, finding where you fall off the PD in each direction, and then leave the optic in the middle of the two 'edges'.
Before aligning each set (PO, Refl, AS), I followed the procedure in Rob's new RF photodiode Wiki Page.
Also, for superstitious reasons, and in case I actually bumped them, I squished all of the ribbon cable connectors into the PDs, just in case.
REFL33, AS55, REFL55,REFL165,REFL11,POX11,POP22
There were quite a few more demodulator units labelled with PD names. Do any of them need to be included in the automated frequency response measurement system? Please let me know so that I can include them to the RF switch and check them for proper illumination, which i will do for all the above PDs next week.
In the order that makes more sense to me, it looks like you have:
REFL11, REFL33, REFL55, REFL165,
We don't really need POP22 right now, although we do want the facility to do both POP22 and POP110 for when we (eventually) put in a better PD there. Also, we want cabling for POP55, so that we can illuminate it after we re-install it. If we're working on 2f PDs, we might as well consider AS110 also, although I don't know that there was a fiber layed for it. The big one that you're missing is POY11.
A new RF cable has been included for POY11. Cabling for POP55 and POP110 might or might not exist. I will check and report it.
[Koji, Jenne, Kevin]
Jenne worked on fixing REFL11 last week (see elog 4034) and was able to measure an electrical transfer function. Today, I tried to measure an optical transfer function but REFL11 is still not responding to any optical input. I tried shining both the laser and a flashlight on the PD but could not get any DC voltage.
I also completed the characterizations of POX. I redid the optical transfer function and shot noise measurements. I also took a time series of the RF output from the PD when it was powered on with no light. This measurement shows oscillations at about 225 MHz. I also measured the spectrum with no light which also shows the oscillations at 225 MHz and smaller oscillations at ~455 MHz.
The plots can be found at http://lhocds.ligo-wa.caltech.edu:8000/40m/Electronics/POX?action=show.
This is looking better, but the fit data for the TF should be plotted along with the data. The data should be made up of points and the fit a line.
For the fit, we should have the Q of the main resonance as well as the peak height of the main resonance and the values of the gain at the notch frequencies.
Also the peak as well as the notches should have the frequencies fit for and labeled. In principle, you can make the plot on the wiki have all of the data. Then in the end we can print the plot in a small size and glue it to the PD's backside.
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).
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.
The SLP-50 filters which were on the 55 MHz lines have been replaced with the SBP-60. Their respective characteristics are given below:
SBP-60 has lower insertion loss and higher return loss.
This may however change the phase of I and Q in the demod boards and they will therefore need to be readjusted. Currently the output power level of 55 MHz demod is at 2dBm, whereas it ought to be at 6dBm. I have not yet corrected that. Once that is completed Kiwamu will adjust the phases.
I shifted the temperature sensor to a new location. See the photograph below. I noticed that the higher temperature is reached on the side where there are two RF Amps. So it would be better to check the temperature of that area and make sure that it remains well below 65 deg. The operating maxium is 65deg C
Here is a picture of the new RF source layout.
And here is a photograph of it
RF Source box has been mounted in the 1X2 rack.
Heliax cables have been directly attached to the box and anchored on the side of the 1X2 rack. Here is a list of Helix cables which have been connected so far.
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.
I have posted the attached RF status update and 1Y2 rack layout to the svn.
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.
We need a distribution unit in the LSC rack to: 1) collect the demod signals coming from the Frequency Generation Box 2) adjust the power level 3) generate 2nd harmonics (for POP) 4) distribute the demod signals to the single demodulation boards.
The base line plan is the following:
The box can be build up gradually, but the priority goes to these parts:
I need help for this work. I know exactly how to do it, I just don't have the time to do it all by myself.
Besides the Distribution Box, the demodulation part of the upgrade would still require two steps:
1) upgrade the Band Pass Filters of the demodulation boards (I have all the parts)
2) cabling from the distribution box to the demod board (one-afternoon kind of job)
I have prepared several diagrams outlining the current state of the RF System.
These are uploaded into the svn40m here and will be kept uptodate as we complete various parts of the task. These plans have taken into account
the new priorities of the LSC (set out by Koji here )
We (Koji, Kiwamu and I) took stock of the RF cables which we have inherited from the earlier RF system and have made new plans for them.
I took stock of the filters purchased for the modifying the demod boards. We have pretty much everything we need so I will start modifying the boards right away. The following table summarises the modifications
LP Filter (U5)
We seem to have a spare SHP-175. I was wondering where that is supposed to go.
This is the status and tentative schedule for completing the various tasks. I have put the dates based on priority and state of the hardware.
The RF Cable layout plans are drawn on top of a Lab Layout. The various subsystems are drawn (not to scale) on separate layers. The graffle files are located here . I thought they might come in handy for others as well.
I have made several changes to Craig's script for better pythonism. Its more robust with different libraries and syntaxes and makes a tarball by default (w/o a command line flag). These kinds of general util scripts will be going into a general use folder in the git.ligo.org/40m/ team area so that it can be used throughout the LSC.
I don't think we need/want a coherence calculation, so I have not included it. Usually, we use coherence to estimate the uncertainty, and here we are just plotting it directly from the dist of the sweeps so coherence seems superfluous.
I very badly forgot to log about this in the crush of surfs.
I removed Koji's proto-beatbox RF comparator amp from the X arm ALS setup. I was investigating hacking it onto one of the discriminator channels in the new beatbox, now that Yuta/Koji's Yuta/Koji's phase tracker is making the coarse beatbox path obsolete. Upon further reflection we decided to just go ahead and stuff the beatbox board for the X arm, and use the proto-beatbox to test some faster ECL comparators. This will be done first thing in the morning.
In the meantime the old amp is in my cymac mess on the far left of the electronics bench.
I pulled out the RF amplifier box from the IOO rack and swapped the amplifiers for FOL beat frequency amplification. The earlier gain of 62dB (ZFL500LN + ZFL500LN) was reduced to 40dB gain (ZFL500LN+ZFL2AD).
I also swapped one of the broken sma cables that was connecting the two amplifiers with a good one. Front ports of the module were relabeled and the box was put back on the rack.
During the course of this work, I had to turn OFF the green BBPDs on the PSL table to protect them and they have been powered up after putting the module back.
As Koji found one of the spare channels of the ALS/FOL RF amplifier box nonfunctional yesterday, I pulled it out to fix it. I found that one of the sma cables did not conduct.
It was replaced with a new cable from Koji. Also, I rearranged the ports to be consistent across the box, and re-labeled with the gains I observed.
It has been reinstalled, and the Y frequency counter that is using one of the channels shows a steady beat freq.
I cannot test the amplitude of the green X beat at this time, as Koji is on the PSL table with the PSL shutter closed, and is using the control room spectrum analyzer. However, the dataviewer trace for the fine_phase_out_Hz looks like free swinging cavity motion, so its probably ok.
Today I was around the IOO rack.
I shutdown the power to the beat PDs on the PSL table and disconnected the D sub 3w3 connector that was powering the RF amplifier panel on the IOO rack.
I moved the RF amplifier from the panel to a box that can go on the rack. The box will also hold the RF amplifiers that will be used for FOL. I have not completed putting in all the amplifiers. But the RF amplifier for ALS is in place and the box has been installed on the IOO rack for locking tonight. The power supply to the green beat PDs has been switched ON.
I took the out of loop noise measurements for ALS X and Y and the attachment is the screenshot of it (X and Y have rms of ~300Hz and ~400Hz).
I had to touch the Y end steering mirrors for green to get maximum GTRY before making thes measurments.
I pulled out the RF amplifier box from the IOO rack again and added the new RF amplifiers for FOL.
I replaced one of the decoupling capacitors of the ALS beat note RF amplifier ; the poloproylene capacitor with a ceramic capacitor (0.1uF) .
After putting back the box, I confirmed that we had a beat note. I did not get a chance to measure the ALS noise after putting back the box because the IFO was already occupied.
I will post a detailed elog of the components in the RF amplifier box once I am done with it (hopefully tomorrow)!
The components of the RF amplifier box are in place. The RF amplifier box has been mounted on the IOO rack and the front panel connections have been labeled. Attached is the photo of how things look in the inside for future reference.
Sometime in the next few days the box will be pulled out to replace the panel mount SMA barrels in the front with insulated ones.
The RF analyzer was returned to the control room. There are two beat notes from X/Y confirmed.
I locked the arms and aligned them with ASS.
When the end greens are locked at TEM00, X/Y beat amplitudes were ~33dBm and ~17dBm. respectively.
I don't judge if they are OK or not, as I don't recall the nominal values.
I gutted one of the $2 red laser pointers to build a laser source whose amplitude we could modulate at RF frequencies. Basically, I cut off the bulk of the housing from the pointer and soldered a BNC connection into the two terminals that the 2x 1.5V batteries were connected to. When I applied 3V across this BNC connector the diode still worked. So far so good.
Next I added a bias tee to the input. I put 3V across the DC input of the bias tee and added a -3dBm signal into the RF port of the tee. The laser beam was incident on a PDA100A (bandwidth of 1.7MHz) and, sure enough, Kiwamu and I could see a flat response in the amplitude at a given drive frequency out to around 1.7MHz.
We should check the response on a faster PD to see how fast the laser diode is, but we should be able to use this now to check the RF response of the green beat note PD.
1. Add some capacitors across the DC input of the bias tee.
2. Do something about the switch on the laser diode.
3. Attach some labels to the laser that specify what is the required DC voltage and the maximum acceptable RF modulation amplitude.
I spent part of the afternoon cleaning up the area next to the Mode Cleaner where we keep all of our RF stuff: Attenuators, BNC/SMA/LEMO adapters, Mini-Circuits items, and all sorts of other things which are useful while looking at our electronics/RF stuff.
We got another set of "Lyon" drawers, which aided in the organization process....Bob ordered 2, so we now have a 'spare' drawer set if anyone can think of something else to organize (unless this was premeditated for optics or something else?).
As you can see in the picture, (1) it's no longer a total disaster over there, and (2) some of the drawers have sub-divisions to make it faster and easier to find what you're looking for. Please help out by putting things away in their proper place, and adding more labels or dividers to the drawers if there's something else which needs a 'spot'.