For your reference: Voltage noise of LM7815/LM7915 (with no load)
Recorded transfer functions for the 1cm Si-PD as described on p. 2708
for different biases. I put the plots in there, to keep the info in one place,
where the label on the PD case (which Steve made without asking him) points
I talked to some people recently about the fact that the responsivity (A/W) of the PD
changes even at DC for different biases. I tested this again and should be more precise about this:
The first time I observed this was in the transfer functions as shown on p. 2708.
With 'DC' I meant 'low frequency' there, as you can still see an effect of the bias as low as 100kHz.
Then at one point I saw the responsivity changing with bias also at true DC.
However, it turned out that this is only the case if the photocurrent is too high.
If the photocurrent is 4mA, you need 400mV bias to get the max. responsivity.
For 2mA photocurrent, the responsivity is already maximal for 0V bias.
An effect for relative low frequencies remains however.
The DC check of responsivity was done with white light from a bulb.
We tested out the functionality of the EG&G 113 preamp that I found in one of the cabinets. This is one of the ancestors of the SR560 preamp that we are all used to.
It turns out that it works just fine (in fact, its better than the SR560). The noise is below 3nV/rHz everywhere above 30 Hz. The filter settings from the front panel all seem to work well. And the red knob on the front panel allows for continuous (i.e. not steps) gain adjustment. In the high-bandwidth mode (low pass filter at 300 kHz), there is ~35 deg of phase lag at 100 kHz. So the box is pretty fast.
I would easily recommend this above the SR560 for use in all applications where you don't need to drive a 50 Ohm load. Also the battery is still working after 17 years!
There's several more of the this vintage in one of the last cabinets down the new Y-arm.
This morning the pencil soldering iron of our Weller WD2000M Soldering Station suddenly stopped working and got cold after I turned the station on. The unit's display is showing a message that says "TIP". i checked out the manual, but it doesn't say anything about that. I don't know what it means. Perhaps burned tip?
Before asking Steve to buy a new one, I emailed Weller about the problem.
There should be a supply of extra tips in the Blue Spinny Cabiney (I can never remember it's French name....) The drawer is something like the top row of one of the bottom sets of drawers. You can pick the shape of tip you want, and stick it in.
Albeto and Koji
We took the tip replacement from the blue tower.
I am looking at http://www.cooperhandtools.com/brands/weller/ for ordering the tips.
The burnt one seems to be "0054460699: RT6 Round Sloped Tip Cartridge for WMRP Pencil" We will buy one.
The replaced one is "0054460299: RT2 Fine Point Cartridge for WMRP Pencil" We will buy two.
I like to try this: "0054460999: RT9 Chisel Tip Cartridge for WMRP Pencil" We will buy one.
# gnd n22
# | |
# Rip Rw2
# | | |\
# nt- Rsi-n2- - - C2 - n3 - - - - | \
# | | | | |4106>-- n5 - Rs -- no
# iinput Rd L1 L2 R24 n6- | / | |
# |- nin- | | | | | |/ | Rload
# Cd n7 R22 gnd | | |
# | | | | - - - R8 - - gnd
# gnd R1 gnd R7
# | |
# gnd gnd
What??? I don't see any gray trace of Rs in the plot. What are you talking about?
Anyway, if you are true, the circuit is bad as the noise should only be dominated by the thermal noise of the resonant circuit.
The 1979 vintage RF spectrum analyzer HP4195A sn2904J01587 shipped out for repair today to http://www.avalontest.com
It has a 25 MHZ oscillation when you go below 150 MHZ in your sweep....atm1 with the larger amplitude shows this 25 MHZ
Atm2 is displaying full sweep-sign scans from 1 to 500 MHZ.....here one can clearly see the three segment of the scan:
1, large amplitude 25 MHZ oscillation dominating the spectrum up to 150 MHZ
2, the mid section from 150 MHZ to 300 MHZ with medium size amplitude is normal
3, from 300 MHZ to 500 MHZ the amplitude is decreasing.......showing the disadvantage of using a 300 MHZ oscilloscope
Frank noticed that this particular SR560 had an offset on the output which was unzeroable by the usual method of tuning the trim pot accessible through the front panel.
I tried to zero the offset using the trimpots inside, but it became clear that the offset was due to a damaged FET, so Steve ordered ~20 of the (now obsolete*) NPD5564.
I replaced this part and adjusted the offsets and balanced the CMRR of the differential inputs mostly according to the manual (p. 17). There are a few notes that should be added to the procedure:
It looks like its working fine now. Steve's ordering some IF3602 (low-noise, balanced FET pair from Interfet) to see if we can drop the SR560's input noise to the sub-nV level.
Noise measured with the input terminated with a BNC short (not 50 Ohms) G=100, DC coupled, low-noise mode:
To try the 3-corner hat method on the Marconis, I started to set up the measurement into the DAQ system.
I have set the bottom 2 in the PSL rack to 11.1 MHz. I use a ZP-3MH level 13 mixer as the phase detector. The top one is the LO, it has an output of +13 dBm.
The bottom one is the test unit, it has an output of +6 dBm (should be close to the right level - the IP3 point is +9 dBm). The top one has external DC FM modulation enabled with a FM dev range of 10 Hz.
Mixer output goes through a 50 Ohm in-line termination and then a BLP-5 low pass filter (Steve, please order ~7 of the BLP-1.5 or BLP-1.9 low pass filter from Mini-Circuits) and then into
the DC coupled of a SR560. After some gain and filtering that feedback goes back to the FM input of the top-Marconi to close the PLL. I adjusted the gain to be as small as possible and still stay locked and not
saturate the ADC.
The input to the SR560 is Tee'd into another SR560 with AC coupled input, G = 1000, low-noise. Its output is going directly to the ADC channel - C1:IOO-MC_DRUM1.
I calibrated the channel by opening the loop and setting the AC coupled gain to 1. This lets the Marconis beat at several Hz. The peak-peak signal is equivalent to pi radians.
As usual, I was befuddled by the FM input. For some reason I always forget that since its a straight FM input, we don't need any filtering to get a plain 1/f loop. The attached plot shows how we get bad gain peaking if you forget this and use a 0.03 Hz pole in the SR560.
The grey trace is the ADC signal with everything hooked up, but the RF input set to zero (via setting Carrier = OFF in the bottom Marconi). It is the measurement noise.
The BLUE trace is very close to the true phase noise beat of the two Marconis with a calibration error of ~5%. I have not corrected for the loop gain: its right now around a 1 Hz UGF and 1/f. Next, I will measure the loop and compensate for it in the DTT calibration.
Then I'll measure the relative phase noise of 3 of the signal generators to get the individual noises.
Bottom line is that the sensitivity of this approach is good and we should do this rather that use spectrum analyzers since its easy to get very long averages and high res spectra. To get 5x better sensitivity, we can just use the Rai-FET box instead of a SR560 for the readout, but just have to contend with its batteries. Also should try using BALUNs on the RF and LO signals to get rid of the ground loops.
To check the UGF, I increased the gain of the PLL by 10 and looked at how much the error point got suppressed. The green trace apparently has a UGF of ~50 Hz and so the BLUE nominal one has ~5 Hz.
The second attachment shows the noise now corrected for the loop gain. IF the two signal generators are equally noisy, then you can divide the purple spectrum by sqrt(2) to get the noise of a single source.
The .xml file is saved as /users/rana/dtt/MarconiPhaseNoise_100504.xml
Where did you get the 55nH based notch from? I don't remember anything like that from the other LSC PD schematics. This is certainly a bad idea. You should remove it and put the notch back over by the other notch.
Why is it a bad idea?
You mean putting both the 2-omega and the 55MHz notches next to each other right after the photodiode?
Just a little while ago, at 2330 UTC on 5/11, I swapped the phase noise setup to use another Marconi - this time its the 3rd one from the top beating with the 4th one from the top (2nd from the bottom).
After a little while, I swapped over to beat the 33 w/ the 199. I now have all the measurements. For the measurement of the last pair, I inserted BALUN 1:1 transformers on the outputs of both signal generators'.
This last pair appears to be the quietest of the 3 and also has less lines. The lines are mainly at high frequency and are harmonics of 120 Hz. Probably from the Sorensen switching supplies in the adjacent rack.
I double checked that the 10 MHz sync cable was NOT plugged in to any of these during this and that the front panel menu was set to use the internal frequency standard. In the closed loop case, the beat frequency between the 33/199 pair changes by less than ~0.01 Hz over minutes (as measured by calibrating the control signal).
Finally got the 3-cornered-hat measurement of the IFRs done. The result is attached.
s12, s23, & s31, are the beat signals between the 3 signal generators.
s1, s2, & s3 are the phase noise of the individual generators made by the following matlab calculation:
%% Do the hat
s1 = sqrt((s12.^2 + s31.^2 - s23.^2) / 2);
s2 = sqrt((s12.^2 + s23.^2 - s31.^2) / 2);
s3 = sqrt((s31.^2 + s23.^2 - s12.^2) / 2);
%% Do the hat
s1 = sqrt((s12.^2 + s31.^2 - s23.^2) / 2);
s2 = sqrt((s12.^2 + s23.^2 - s31.^2) / 2);
s3 = sqrt((s31.^2 + s23.^2 - s12.^2) / 2);
As you can see, there is now an estimate of the individual noises. We can do better by doing some fitting of the residuals.
The real test will be to replace the noise one here with the good Wenzel oscillator and see how well we can estimate its noise. If the 11 MHz crystals don't show up, I can just try this with the 21.5 MHz one for the PSL.
In this morning I found daqawg didn't work.
After looking for the cause, I found one of the vme racks mounted on 1Y6 doesn't work correctly.
It looks like the vme rack mounting c0daqawg could not supply any power to the frontends.
Now Steve and I are trying to look for a spare for it.
Notes on May 25th
Don't do the following things !! This causes bad cross-talking of CPUs mounted on the crate.
I moved c0daqawg and c1pem1 from 1Y6 vme crate to 1Y7 crate due to the bad power supply.
Another problem: c0dcu1 doesn't come back to the network.
After moving them, I tried to get back them into the RFM network. However c0dcu1 never came back, it still indicates red in C0DAQ_DETAIL.adl screen.
Alberto and I did even "nuclear option" (as instructed), but no luck.
I got a VME crate from Peter's lab. It is already installed in 1Y6 instead of the old broken one.
I checked its power supply, and it looked fine. It successfully supplies +5, +12 and -12 V. And then I put c0daqawg and c1pem1 back from 1Y7.
Now I am trying to reboot all the front end computers with Peter's VME crate. A picture of the VME crate will be updated later.
[Alex, Joe, Kiwamu]
Eventually all the front end computers came back !!
There were two problems.
(1): C0DCU1 didn't want to come back to the network. After we did several things it turned the ADC board for C0DCU1 didn't work correctly.
(2): C1PEM1 and C0DAQAWG were cross-talking via the back panel of the crate.
(what we did)
* installed a VME crate with single back panel to 1Y6 and mounted C1PEM1 and C0DAQAWG on it. However it turned out this configuration was bad because the two CPUs could cross-talk via the back panel.
* removed the VME crate and then installed another VME crate which has two back panels so that we can electrically separate C1PEM1 and C0DAQAWG. After this work, C0DAQAWG started working successfully.
* rebooted all the front ends, fb40m and c1dcuepics.
* reset the RFM bypath. But these things didn't bring C0DCU1 back.
* telnet to C0DCU1 and ran "./startup.cmd" manually. In fact "./startup.cmd" should automatically be called when it boots.
* saw the error messages from "./startup.cmd" and found it failed when initialization of the ADC board. It saids "Init Failure !! could not find ICS"
* went to 1Y7 rack and checked the ADC. We found C0DCU1 had two ADC boards, one of two was not in used.
* disconnected all two ADCs and put back one which had not been in used. At the same time we changed the switching address of this ADC to have the same address as the other ADC.
* powered off/on 1Y7 rack. Finally C0DCU1 got back.
* burtrestored the epics to the last Friday, May 21st 6:07am
To get a feel for the Capacitive Bridge problems, we setup a simple bridge using fixed (1 nF) caps on a breadboard. We used an SR830 Lock-In amplifier to drive it and readout the noise.
We measured the cap values with an LCR meter. They were all within a few % of 0.99 nF.
With a 0.5 V drive to the top of the bridge, the A-B voltage was ~2 mV as expected from the matching of the capacitors.
(** Note about the gain in the SR830: In order to find the magnitude of the input referred signal, one has to divide by G. G = (10 V)/ Sensitivity. 'Sensitivity' is the setting on the front panel.)
Hooking up now to A-B: the signal is ~10x larger than the 'dark' noise everywhere. 2 uV/rHz @ 100 Hz, 10 uV/rHz @ 10 Hz, 50 uV/rHz @ 1 Hz. The spectrum is very non-stationary; changing by factors of several up and down between averages. Probably a problem with the cheapo contacts in the breadboard + wind. The gain in this state was still 1000. So at 1 Hz, its 50 nV/rHz referred to the input.
To convert into units of capacitance fluctuation, we multiply by the capacitance of the capacitors (1 nF) and divide out by the peak-peak voltage (1 V). So the bridge sensitivity is 50e-9 * 1e-9 = 5 x 10^-17 F/rHz.
If we assume that we will have a capacitive displacement transducer giving 1 nF capacitance change for a 0.1 mm displacement, this bridge would have a sensitivity of 5 x 10^-12 m/rHz @ 1 Hz. We would like to do ~50-100x better than this. The next steps should be:
The measurement setup for the Capacitor Bridge Test is still sitting on one of the work benches.
Unless the experiment is supposed to continue today, the equipment shouldn't have been left on the bench. It should have been taken back to the lab.
Also the cart with HP network analyzer used for the test was left in the desk area. That shouldn't have left floating around in the desk area anyway.
The people responsible for that, are kindly invited to clean up after themselves.
Using the three Marconis in 40m at 11.1 MHz, the Three Cornered Hat technique was used to find the individual noise of each Marconi with different offset ranges and the direct/indirect frequency source of the rubidium clock.
Rana explained the TCH technique earlier - by measuring the phase noise of each pair of Marconis, the individual phase noise can be calculated by:
S1 = sqrt( (S12^2 + S13^2 - S23^2) / 2)
S2 = sqrt( (S12^2 + S23^2 - S13^2) / 2)
S3 = sqrt( (S13^2 + S23^2 - S12^2) / 2)
I measured the phase noise for offset ranges of 1Hz, 10Hz, 1kHz, and 100kHz (the maximum allowed for a frequency of 11.1Mhz) and calculated the individual phase noise for each source (using 7 averages, which gives all the spikes in the individual noise curves). The noise from each source is very similar, although not quite identical, while the noise is greater at higher frequencies for higher offset ranges, so the lowest possible offset range should be used. It appears the noise below a range of 10Hz is fairly constant, with a smoother curve at 10Hz.
The phase noise for direct vs indirect frequency source was measured with an offset range of 10Hz. While very similar at high and low frequencies for all 3 Marconis, the indirect source was consistently noisier in the middle frequencies, indicating that any Marconis connected to the rubidium clock should use the rubidium clock as a direct frequency reference.
Since I can't adjust settings of the Marconis at the moment, I have yet to finish measurements of the phase noise at 160 MHz and 80 MHz (those used in the PSL lab), but using the data I have for only the first 2 Marconis (so I can't finish the TCH technique), the phase noise appears to be lowest using the 100kHz offset except at the higher frequencies. The 160 MHz signal so far is noisier than the 11.1 MHz signal with offset ranges of 1 kHz and 10 Hz, but less noisy with a 100 kHz offset.
I still haven't measured anything at 80 MHz and have to finish taking more data to be able to use the TCH technique at 160 MHz, then the individual phase noise data will be used to measure the noise of the function generators used in the PSL lab.
I also removed two of the AM stabilizers from the 1Y2 rack. The other one, which is currently running th MC modulations, is still in the rack, and there it is going to remain together with its distribution box.
I stored both AM stabilizers and the Stochmon box inside the RF cabinet down the East arm.
Today we measured the phase noise of the oscillator used for the FSS.
The source is a Wenzel crystal at about 21.5MHz that Peter Kalmus built some time ago.
We basically used the same technique that Frank and Megan have been using lately to measure the Marconi's phase noise.
Today we just did a quick measurement but today next week we are going to repeat it more carefully.
Attached is a plot that shows the measurement calibrated for a UGF at about 60 Hz. The noise is compared to that specified by Wenzel for their crystal.
The noise is bigger than that of the MArconi alone locked to the Rubidium standard (see elog entry). We don't know the reason for sure yet.
We'll get back to this problem next week.
I reconnected the RF signal to the FSS and to the FSS' EOM so that we could lock the refcav again.
I then started a 3 sec. period trianglewave on the AOM drive amplitude to see if there is a direct coupling from RIN to Frequency. Ideally we will be able to measure this by looking at the RCTRANS and the FSS-FAST.
Alastair found that the foam hut that he and Jan put on top of the Rb clocks to temperature stabilize them was too good of an insulator. The Rb boxes had gotten very hot and became internally unlocked as seen on the front panel.
After we let them cool down with the box off, I turned them back on. After several minutes the 'Locked' light came back on. Some minutes after that the '1PPS Sync' light also came on, indicating that the two had become somewhat synchronized. It really means that the frequencies are kind of close: I think its roughly that f1-f2 < 2 mHz.
I put the yellow box back on and have left it with a small gap on the bottom so that the hot air can get out. Hopefully, this will protect the clocks from the wind, but not cause them to overheat.
The signal going to the DAQ right now is DC-coupled, with a gain of 1. The peak-peak beat signal in this situation is 6300 counts.
My guess is that the clocks will by synchronized by tomorrow afternoon so that we can get the measurement done. Please don't disturb the clocks or the yellow box around them. Try to minimize any activity around that area.
[Jenna & Alastair]
We changed the locking time constant on one of the Rubidium clocks using the RbMon software that came with it. We had to use the ancient Dell laptop latitudeD810 because it has a serial port built in, and we couldn't get the usb->serial adapter to work right with the clock. We tried the usb connector on more than one computer, and we had installed the right adapter and the computer seemed to recognize it fine, it just wouldn't communicate with the clock. We even tried it with the Dell latitute laptop and it still failed to work, so the only way seems to be to use the serial port directly.
The clock has a default time constant of 18.2 hours because it's designed to be locked to a GPS clock which is less stable than the Rb clock itself, so we changed it to a time constant of .57 hours. We also changed the length of the BNC cables to get the DC offset to 10mV, but then as I was typing this, we opened up data viewer to look at the real time data and saw the output suddenly leap up, and found that the offset is now -5mV mysteriously, so we went to investigate and found that the gain of the SR560 was still set to 1 from a calibration. We beat one of the clocks with a marconi for a few minutes with the gain still at this level to do another calibration, and then hooked the clocks back up together and upped the gain to 100. The DC offset is currently about 2.5mV. We're going to leave them alone for a few hours, and then check to see what the signal looks like over that period.
Alastair and I restarted the c1iovme around the time of my last elog entry (~3:20).
I took some measurements of the clock this morning, first without the box, then with the box, then without the box again. All the noise levels look pretty much the same. When I first put the box on, it was only propped up on one side, so I think the clocks got a bit overheated and the data looks ridiculous, which is the first plot. I took it off and let them cool down a bit, and then put the box on, this time with a generous 3 inch gap at the bottom all the way around, and it seemed to be fine after that.
The calibration for the data is pi (rad) /6415 (counts) /100.
Aidan: I edited this post to change the plots from Postscripts to PDFs.
We unsynched the clocks by unhooking the 1pps locking. I've added it to the plot of the other measurements here, and we've divided by a factor of sqrt(2) in the calibration to get the phase noise from just one clock, so the calibration is now
pi (rad) /6415 (counts) /100/sqrt(2).
I've also added the noise of the clock according to SRS to the plot.
The units of this plot are rad/rt(Hz). I've no idea why it just says magnitude.
This is a known thing (at least to me and Rana), so it's not just you. When you put in some points like your PD Spec, the units disappear, and I've never figured out how to get them back while keeping the points. Thanks for putting the units in your entry though. If anyone else does know how to get the units to 'stick' where they're supposed to be, that would be helpful.
I took a look at the data from the middle of the night to see if it was significantly quieter than the data from the day, but it doesn't seem to be. The plot shows data from yesterday around 12:30pm and from this morning around 2am. It's a bit quieter at low frequencies, but not by much.
Here's an overview of the rubidium measurement:
We have two SRS FS275 Rubidium clocks which are locked together using the built-in PLL through the 1pps input/output. The default time constant for this locking is 18.2 hours because it's designed to be locked to a GPS. We changed this time constant to .57 hours (as decribed in this elog entry) to get the clocks to more reliably lock to each other. We then mix the 10MHz outputs together using a 7dbm mixer (see elog here and picture below)
The signal then goes through an AC-coupled SR560 with a gain of 100 and LPF at 10kHz, and is then fed into the DAQ. In the first picture below you can make out what all the lights are labeled, and in the second you can see what lights are on. I couldn't get a picture that did both in one, sadly.
I finished assembling the frequency generation unit for the upgrade. I tested it through to check that the power levels are as expected at the various connection (see attached png, showing in black the design power values, and in red the measured ones).
Because of some modifications made on the design along the construction, I have to recalculate the SNR along the lines.
I can now start to measure phase noise and distortion harmonics.
A document with a description of the design and the results of the characterization measurements will be available in the end.
I've taken the FSS frequency generation box out of the 1Y1 rack. It's sitting on one of the electronics benches. I'm measuring its phase noise.
A few weeks ago, on Jul 24, Rana and I measured the phase noise of the FSS frequency box (aka the 'Kalmus Box'). See elog entry 3286.
That time, for some reason, we measured a phase noise higher than we expected; higher than that of the Marconi.
I repeated the measurement today using the SR785 spectrum analyzer. Here is the result:
(The measurement of July 24 on the plot was not corrected for the loop gain. The UGF was at about 30 Hz)
To make sure that my measurement procedure was correct, I also measured the combined phase noise of two Marconis. I then confirmed the consistency of that with what already measured by other people in the past (i.e. Rana elog entry 823 in the ATF elog).
This time the noise seemed reasonable; closer to the Marconi's phase noise, as we would expect. I don't know why it was so bad on July 24.
The shoulder in the Marconi-to-Marconi measurement between 80Hz and 800Hz is probably due to the phase noise of the other Marconi, the one used as LO.
I'm going to repeat the measurement connecting the setup to the DAQ, and locking the Marconi to the Rubidium standard.
Ultimately, the goal is to measure the phase noise of the new Sideband Frequency Generation Box of the 40m Upgrade.
Today I put the FSS frequency box back into the 1Y1 rack.
To power it on, I turned on the 24V and 15V Sorensen switches in the same rack.
The PMC crystal board in the same rack should not be affected (it runs with 10V), but, to make sure it was not powered, I disconnected it from its crate. Since the board was disconnected from the EOM for the PSL table's upgrade, I wanted to avoid having the RF output floating.
We just have to remember to plug it back in, when we need it again.
I just turned on the other Sorensen's too in 1Y1.
I measured the phase noise of the LO output of the FSS box from the DAQ. I'm attaching the results.
As we expected, the measurement is limited by the internal phase noise of the Marconi.
The measurement was done as shown in this diagram.
The differences between this setup and the one used previously is the lack of the 50 Ohm terminator in the mixer output and
that the SR560 readout with the G=100 should come before the first SR560 via T, so as not to be spoiled by the high noise of the G=1 SR560.
I removed the 50 Ohm in-line terminator when I did the measurement with the SR785. The for some reason I was getting more noise, so I removed it.
Now I put it back in and I did the measurement with the DAQ. I also moved the SR560 that amplifies the signal for the DAQ, Tee'ing it with the input of the in-loop SR560.
Now the setup looks like this:
And the phase noise that I measure is this:
Comparing it with the phase noise measured with the previous setup (see entry 3506), you can see that the noise effectively is reduced by about a factor of 2 above 10 Hz.
With the setup now working, we should now test the power filtering for the crystal and amplifier.
I found this very interesting German maker of cool cable cutting tools. It's called Jokari.
We should keep it as a reference for the future if we want to buy something like that, ie RF coax cable cutting knives.
Yeah, this looks nice.
And I also like to have something I have attached. This is "HOZAN P-90", but we should investigate American ones
so that we can cut the wires classified by AWG.
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.
Here are the results of my phase noise measurements on the 7 outputs of the Frequency Generation Box. (BIN=95L applied by DTT). See attached pdf for a higher definition picture.
The plot shows that the phase noise of the 11 MHz outputs (Source, EOM modulation signal, Demodulation signal) is as low as that of the Marconi. The Marconi is limiting my measurement's resolution.
The mode cleaner signal's oscillator (29.5 MHz output, blue trace) is higher than the 11MHz above 1KHz.
The 55MHz signals have all the same phase noise (traces overlapped), and that is higher than the 11 MHz ones from about 100Hz up. i don't know what's going on.
I need to use the spare 11MHz Wenzel crsytal to have a better reference source for the measurement.
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)