ID 
Date 
Author 
Type 
Category 
Subject 
2112

Sun Oct 18 22:06:15 2009 
rana  Configuration  Electronics  IP POS is back: ND filter gone, new resistors in 
I tried to compare the IP_POS time series with the IPANG and MC_TRANS but was foiled at first:
1) The IPANG scan rate was set to 0.5 second, so it doesn't resolve the pendulum motions well. Fixed in the .db file.
2) Someone had used a Windows/DOS editor to edit the .db file and it was filled with "^M" characters. I have removed them all using this command: tr d "\r" <ETMXaux.db > new.db
3) The MC_TRANS P/Y channels were on the MC Lock screen but had never been added to the DAQ. Remember, if there's a useful readback on an EPICS screen. its not necessarily in the frames unless you add it to the C0EDCU file. I have done that now and restarted the fb daqd. Channels now exist.
4) Changed the PREC of the IPPOS channels to 3 from 2.
5) changed the sign for the IBQPD (aka IPANG) so that bigger signal is positive on the EPICS screen. 
Attachment 1: Untitled.png


2118

Mon Oct 19 14:48:15 2009 
rana, rob  Summary  Electronics  piezo jena measuring box 
Attached is the schematic of the Piezo Jena driver measuring box made in a Pomona box:
2.2 uF
In o   o Out
 
_ 
_ 1uF R 7.5 kOhms
 
 
GND GND
The 1 uF cap is there to simulate the piezo and the 2.2 uF and 7.5k resistor ac couple the signal for the spectrum analyzer. They give a ~10 Hz corner frequency. 
Attachment 1: PA160153.JPG


Attachment 2: PA160151.JPG


2244

Wed Nov 11 20:57:06 2009 
kiwamu  Update  Electronics  Multiresonant EOM  LC tank circuit  
I have been working about multiresonant EOM since last week.
In order to characterize the behavior of the each components, I have made a simple LC tank circuit.
You can see the picture of the circuit below.
Before constructing the circuit, I made an "ideal" calculation of the transfer function without any assumptions by my hand and pen.
Most difficult part in the calculation is the dealing with a transformer analytically. Eventually I found how to deal with it in the analytical calculation.
The comparison of the calculated and measured transfer function is attached.
It shows the resonant frequency of ~50MHz as I expected. Those are nicely matched below 50MHz !!
For the next step, I will make the model of the circuit with stray capacitors, lead inductors, ... by changing the inductance or something.

Attachment 2: LCtank_complete.png


2262

Fri Nov 13 03:38:47 2009 
kiwamu  Update  Electronics  multiresonant EOM  impedance of LC tank circuit  
I have measured the impedance of the LC tank circuit which I referred on my last entry.
The configuration of the circuit is exactly the same as that time.
In order to observe the impedance, by using Koji's technique I injected a RF signal into the output of the resonant circuit.
In addition I left the input opened, therefore the measured impedance does not include the effect of the transformer.
            results
The measured impedance is attached below; "LCtank_impedance.png"
The peak around 50MHz is the main resonance and it has impedance of ~1500 [Ohm], which should go to infinity in the ideal case (no losses).
In fact the impedance looked from the input of the circuit gets reduced by 1/n^2, where "n" is the turn ratio of the transformer.
By putting the n=4, the input impedance of the circuit should be 93 [Ohm]. This is a moderate value we can easily perform impedancematching by some technique.
I also fitted the data with a standard model of equivalent circuit (see attachment 2).
In the figure.2 red component and red letter represents the design. All the other black stuff are parasites.
But right now I have no idea the fitted value is reasonable or not.
For the next I should check the input impedance again by the direct way; putting the signal into the input.

Attachment 1: LCtank_impedance.png


Attachment 2: LCtank_model.png


2263

Fri Nov 13 05:03:09 2009 
kiwamu  Update  Electronics  multiresonant EOM  input impedance of LC tank  
I measured the input impedance of the LC tank circuit with the transformer. The result is attached.
It looks interesting because the input impedance is almost dominated
by the primary coil of the transformer with inductance of 75nH (see attachment 1).
The impedance at the resonance is ~100 [Ohm], I think this number is quite reasonable because I expected that as 93 [Ohm]
Note that the input impedance can be derived as follower;
(input impedance) = L1 + Z/n^2.
Where L1 is the inductance of the primary coil, Z is the load in the secondary loop and n is the turn ratio.
I think now I am getting ready to enter the next phase \(^o^)/ 
Attachment 1: input_impedance.png


Attachment 2: input_impedance2.png


2286

Tue Nov 17 21:10:35 2009 
rana  Summary  Electronics  Busby Low Noise Box: Photos and Upgrades 
It looked like the Busby Low Noise Box had too much low frequency noise and so I upgraded it. Here is a photo of the inside  I have changed out the 0.8 uF AC coupling cap with a big, white, 20 uF one I found on Rob's desk.
The Busby Box is still working well. The 9V batteries have only run down to 7.8V. The original designer also put a spare AD743 (ultra low current FET amp) and a OP27 (best for ~kOhm source impedances) in there.
Here's the noise after the fix. There's no change in the DC noise, but the AC noise is much lower than before:
I think that the AC coupled noise is higher because we are seeing the current noise of the opamp. In the DC coupled case, the impedance to ground from the input pins of the opamp is very low and so the current noise is irrelevant.
The change I implemented, puts in a corner frequency of fc = 1/2/pi/R/C = 1/2/pi/10e3/20e6 = 0.8 Hz.
Overall, the box is pretty good. Not great in terms of current noise and so it misses getting an A+. But its easily a solid A. 
2288

Wed Nov 18 00:38:33 2009 
rana  Summary  Electronics  Voltage Noise of the SR560's OUTPUTs (the back panel) 
I've measured the voltage noise of the SR560's lead acid battery outputs; they're not so bad.
Steve ordered us some replacement leadacid batteries for our battery powered preamps (SR560). In the unit he replaced, I measured the noise using the following setup:
SR560 Busby Box
(+12V/GND) AC Input Out  SR785
The SR785 was DC coupled and autoranged. The input noise of the SR785 was measured via 50 Ohm term to be at least 10x less than the SR560's noise at all frequencies.
Its clear that this measurement was spoiled by the low frequency noise of the Busby box below 10 Hz. Needs a better preamp. 
2292

Wed Nov 18 14:55:59 2009 
kiwamu  Update  Electronics  multiresonant EOM  circuit design  
The circuit design of multiresonant EOM have proceeded.
By using numerical method, I found the some best choice of the parameters (capacitors and inductors).
In fact there are 6 parameters (Lp, L1, L2, Cp, C1, C2) in the circuit to be determined.
In general the less parameter gives the less calculation time with performing the numerical analysis. Of course it looks 6 parameters are little bit large number.
In order to reduce the arbitrary parameters, I put 4 boundary conditions.
Each boundary conditions fixed resonant peaks and valleys; first peak=11MHz, third peak=55MHz, first valley=19MHz, second valley=44MHz.
So now the remaining arbitrary parameters successfully get reduced to 2. Only we have to do is optimize the second peak as it to be 29.5MHz.
Then I take C1 and C2 as free parameters seeing how the second peak agree with 29.5MHz by changing the value of the C1 and C2.
the red color represents the good agreement with 29.5MHz, in contrast blue contour represents the bad.
You can see some best choice along the yellow belt. Now what we should do is to examine some of that and to select one of those. 
2294

Wed Nov 18 16:58:36 2009 
kiwamu  Update  Electronics  multiresonant EOM  EOM characterization  
In designing the whole circuit it is better to know the characteristic of the EOM.
I made impedance measurement with the EOM (New Focus model 4064) and I found it has capacitance of 10pF.
This is good agreement with the data sheet which says "510pF".
The measured plot is attached below. For comparison there also plotted "open" and "10pF mica".
In the interested band( from 1MHz to 100MHz), EOM looks just a capacitor.
But indeed it has lead inductance of 12nH, resistance of 0.74[Ohm], and parasitic capacitance of 5.5pF.
In some case we have to take account of those parasites in designing.

2295

Wed Nov 18 22:38:17 2009 
Koji  Update  Electronics  multiresonant EOM  EOM characterization  
How can I get those values from the figure?
Quote: 
But indeed it has lead inductance of 12nH, resistance of 0.74[Ohm], and parasitic capacitance of 5.5pF.


2340

Wed Nov 25 20:44:48 2009 
kiwamu  Update  Electronics  Multiresonant EOM  Qfactor  
Now I am studying about the behavior of the Qfactor in the resonant circuit because the Qfactor of the circuit directly determine the performance as the EOM driver.
Here I summarize the fundamental which explains why Qfactor is important.

The EOM driver circuit can be approximately described as shown in figure below
Z represents the impedance of a resonant circuit.
In an ideal case, the transformer just raise the voltage level ntimes larger. Rin is the output impedance of the signal source and usually has 50[Ohm].
The transformer also makes the impedance Z 1/n^2 smaller. Therefore this configuration gives a following relation between Vin and Vout.
Where G is the gain for the voltage. And G goes to a maximum value when Rin=Z/n^{2}. This relation is shown clearly in the following plot.
Note that I put Rin=50 [Ohm] for calculating the plot.
Under the condition Rin=Z/n^{2}( generally referred as impedance matching ), the maximum gain can be expressed as;
It means that larger Z makes more efficient gain. In our case, interested Z is considered as the impedance at a resonance.
So what we should do is making a resonant circuit which has a higher impedance at the resonance (e.g. high Qresonant circuit).

2341

Thu Nov 26 02:08:34 2009 
Koji  Update  Electronics  Multiresonant EOM  Qfactor  
The key point of the story is:
"The recipe to exploit maximum benefit from a resonant EOM"
 Make a resonant EOM circuit. Measure the impedance Z at the resonance.
 This Z determines the optimum turn ratio n of the stepup transformer.
(n^{2} = Z/Rin where Rin is 50Ohm in our case.)
 This n gives the maximum gain G_{max} (= n/2) that can be obtained with the step up transformer.
And, the impedance matching is also satisfied in this condition.
OK: The larger Z, the better. The higher Q, the Z larger, thus the better.
(Although the relationship between Z and Q were not described in the original post.)
So, how can we make the Q higher? What is the recipe for the resonant circuit?
=> Choose the components with smaller loss (resistance). The details will be provided by Kiwamu soon???
When I was young (3 months ago), I thought...
 Hey! Let's increase the Q of an EOM! It will increase the modulation!
 Hey! Let's use the stepup transformer with n as high as possible! It will increase the modulation!
 Hey! Take the impedance matching! It will increase the modulation!
I was just too thoughtless. In reality, they are closely related each other.
A high Q resonant circuit has a high residual resistance at the resonant frequency. As far as the impedance is higher than the equivalent output impedance of the driving circuit (i.e. Z>Rin n^{2}), we get the benefit of increasing the turn ratio of the transformer. In other words, "the performance of the resonant EOM is limited by the turn ratio of the transformer." (give us more turns!)
OK. So can we increase the turn ratio infinitely? No. Once Rin n^{2} gets larger than Z, you no longer get the benefit of the impedance transforming. The output impedance of the signal source yields too much voltage drop.
There is an optimum point for n. That is the above recipe.
So, a low Q resonant EOM has a destiny to be useless. But high Q EOM still needs to be optimized. As far as we use a transformer with a low turn ratio, it only shows ordinary performance.

2403

Sat Dec 12 07:36:56 2009 
rana  HowTo  Electronics  How to Measure the Length of a Cable: Interferometry 
Need to measure the length of the cable, but too lazy to use a measuring tape?
Then you too can become an expert cable length measurer by just using an RF signal generator and a scope:
 Disconnect or short (not 50 Ohm term) the far side of the cable.
 Put a T on the near side of the cable.
 Drive the input of the T with your signal source.
 Look at the output of the T with the scope while sweeping the signal source's frequency knob.
The T is kind of acting like a beamsplitter in an asymmetric length Michelson in this case. Just as we can use the RF phase shift between the arms to measure the Schnupp asymmetry, we can also use a T to measure the cable length. The speed of light in the cable is documented in the cable catalog, but in most cases its just 66% of the speed of light in the vacuum. 
2436

Mon Dec 21 01:14:08 2009 
rana  Summary  Electronics  Noise measurement of the Rai Weiss FET preamp box 
I shorted the input to the box and then put its output into the SR560 (low noise, G = 100, AC). I put the output of the SR560 into the SR785.
*** BTW, the 2nd channel of the SR785 is kind of broken. Its too noisy by a factor of 100. Needs to go back for repair once we get started in the vac.
The attached PNG shows its inputreferred noise with the short.
The picture shows the inside of the box before I did anything. The TO5 package metal can is the meaty super dualFET that gives this thing all of its low noise power.
In the spectra on the right are two traces. The BLUE one is the noise of the box as I found it. The BLACK one is the noise after I replaced R1, R6, R7, & R10 with metal film resistors.
The offset at the output of the box with either an open or shorted input is +265 mV.
I think we probably should also replace R2, R3, & R1, but we don't have any metal film resistors lower than 100 Ohms in the kit...but hopefully Steve will read this elog and do the right thing. 
Attachment 1: IMG_0242.JPG


2450

Thu Dec 24 01:25:29 2009 
kiwamu  Update  Electronics  impedance analyzing 
The validation for high impedance measurement has been well done.
The impedance measurement is one of the keys for designing the EOM circuit.
So far I was very struggling to measure the high impedance ( above several 1000 Ohm) at RF because the EOM circuit has a high impedance at its resonance.
Finally I realized that the measured impedance was suppressed by a parasitic resistance, which especially reduces the impedance at the resonance.
Also I found that we can extract the TRUE impedance data by subtracting the effect of the parasitic resistance from resultant data.
In order to confirm whether this subtraction works correctly or not, the impedance was directly remeasured with another analyzer for crosscheck.
The followers are details about the remeasurement.
(measurement )
The measurement has been performed with help from Peter and Frank. ( Thank you !)
By using network analyzer AG4395A with the impedance test kit AG43961A (these are at the PSL lab.), the impedance of resonant circuit with EOM was measured.
The picture of setup is attached. This impedance test kit allows to measure typically 0.1 [Ohm]1M [Ohm] and frequency range of 100kHz500MHz.
(result)
The resultant plot is attached. In the plot the blue curve represents the impedance measured by usual analyzer at 40m.
Note this curve is already subtracted the effect of the parasitic resistance.
( the parasitic resistance is in parallel to the circuit and it has ~7.8k Ohm, which is measured while the probe of the analyzer stays open. )
The red curve is the remeasured data using the impedance test kit.
The important point is that; these two peak values at the resonance around 40MHz show good agreement in 10%.
The resonant frequencies for two data differs a little bit, which might be the effect of a stray capacitance ( ~several [pF] )
The red curve has a structure around 80MHz, I think this comes from the noncoaxial cables, which connect the circuit and analyzing kit.
You can see these cables colored black and red in the picture.
( conclusion )
Our measurement with the subtraction of the parasitic resistance effect is working reliably ! 
Attachment 1: DSCN0421.JPG


Attachment 2: EOM.png


2454

Sun Dec 27 23:44:59 2009 
rana  Update  Electronics  MCT QPD investigation 
Quote: 
I found that MCT QPD has dependence of the total output on the position of the spot. Since the QPD needs the supply and bias voltages from the sum/diff amp, I could not separate the problems of the QPD iteself and the sum/diff amplifier by the investigation on Tuesday. On Wednesday, I investigated a generic quad photodiode interface module D990692.

This is indeed sad. But, we can perhaps bypass all of this by just using the individual segment outputs. According to the circuit diagram and the c1iool0 .db file, we should be able to just do the math on the segments and ignore the VERT/HOR/SUM signals completely. In that case, we can just use high impedance for the sum/diff buffers as Koji says and not suffer from the calibration errors at all I think. 
2455

Mon Dec 28 01:17:01 2009 
Koji  Update  Electronics  MCT QPD investigation 
Unfortunately, the signals for individual segments also suffer from the voltage drop as all of the low impedance amplifiers are hung from the same input.
In order to utilize the individual channels, we anyway have to remove the resistors for the VERT/HOR/SUM amps.
That is possible. But does it disable some fast channels for future ASC purposes?
Quote: 
This is indeed sad. But, we can perhaps bypass all of this by just using the individual segment outputs. According to the circuit diagram and the c1iool0 .db file, we should be able to just do the math on the segments and ignore the VERT/HOR/SUM signals completely. In that case, we can just use high impedance for the sum/diff buffers as Koji says and not suffer from the calibration errors at all I think.


2476

Tue Jan 5 09:18:38 2010 
Alberto  Omnistructure  Electronics  Universal PDH Box Stored in the RF Cabinet 
FYI: I stored the Universal PDH boxes in the RF cabiner in the Y arm. 
2523

Mon Jan 18 23:44:19 2010 
kiwamu  Update  Electronics  triple resonant circuit for EOM 
The first design of the triple resonant EOM circuit has been done.
If only EOM has a loss of 4 Ohm, the gain of the circuit is expected to be 11 at 55MHz
So far I've worked on investigation of the single resonant circuit and accumulated the knowledge about resonant circuits.
Then I started the next step, designing the triple resonant circuit.
Here I report the first design of the circuit and the expected gain.
( What I did )
At first in order to determine the parameters, such as inductors and capacitors, I have solved some equations with numerical ways (see the past entry).
In the calculation I put 6 boundary conditions as followers;
(first peak=11MHz, second peak=29.5MHz, third peak=55MHz, first valley=22MHz, second valley=33MHz, Cp=18pF)
The valley frequencies of 22MHz and 33MHz are chosen in order to eliminate the higher harmonics of 11MHz, and Cp of 18pF represents the capacitance of the EOM.
Basically the number of parameters to be determined is 6 ( L1, L2, ...,), therefore it is completely solved under 6 boundary conditions. And in this case, only one solution exists.
The point is calculation does not include losses because the loss does not change the resonant frequency.
( results )
As a result I obtained the 6 parameters for each components shown in the table below.
Cp [pF] 
18.1 
C1 [pF] 
45.5 
C2 [pF] 
10.0 
Lp [uH] 
2.33 
L1 [uH] 
1.15 
L2 [uH] 
2.33 
Then I inserted the loss into the EOM to see how the impedance looks like. The loss is 4 Ohm and inserted in series to the EOM. This number is based on the past measurement .
Let us recall that the gain of the impedancematched circuit with a transformer is proportional to squareroot of the peak impedance.
It is represented by G = sqrt(Zres/50) where Zres is the impedance at the resonance.
As you can see in the figure, Zres = 6.4 kOhm at 55MHz, therefore the gain will be G=11 at 55MHz.
Essentially this gain is the same as that of the single resonant circuit that I've been worked with, because its performance was also limited mainly by the EOM loss.
An interesting thing is that all three peaks are exactly on the EOM limited line (black dash line), which is represented by Zres = L/CR = 1/ (2pi f Cp)^2 R. Where R = 4 Ohm.
( next plan )
There are other solutions to create the same peaks and valleys because of the similar solution.
It is easy to understand if you put Cp' = Cp x N, the solutions must be scaled like L1'=L1/N, C1'=C1 x N, ..., Finally such scaling gives the same resonant frequencies.
So the next plan is to study the effect of losses in each components while changing the similar solution.
After the study of the loss I will select an optimum similar solution. 
2524

Tue Jan 19 00:10:44 2010 
rana  Update  Electronics  triple resonant circuit for EOM 
Very cool. 
2525

Tue Jan 19 02:39:57 2010 
kiwamu  Update  Electronics  design complete  triple resonant circuit for EOM  
The design of the triple resonant circuit has been fixed.
I found the optimum configuration, whose gain is still 11 at 55MHz even if there are realistic losses.
As I mentioned in the last entry, there are infinite number of the similar solutions to create the same resonant frequencies.
However owing to the effect of the losses, the resultant gain varies if the similar solution changes
The aim of this study is to select the optimum solution which has a maximum gain ( = the highest impedance at the resonance ).
In order to handle the losses in the calculation, I modeled the loss for both inductors and the capacitors.
Then I put them into the circuit, and calculated the impedance while changing the solutions.
(method)
1). put the scaling parameter as k in order to create the similar solution.
2). scale the all electrical parameters (L1, L2,...) by using k, so that C1'=C1 x k, L1'=L1/k ,...
3). Insert the losses into all the electrical components
4). Draw the impedance curve in frequency domain.
5). See how the height of the impedance at the resonance change
6). Repeat many time this procedure with another k.
7). Find and select the optimum k
There is a trick in the calculation.
I put a capacitor named Cpp in parallel to the EOM in order to scale the capacitance of the EOM (see the schematic).
For example if we choose k=2, this means all the capacitor has to be 2times larger.
For the EOM, we have to put Cpp with the same capacitance as Cp (EOM). As a result these two capacitors can be dealt together as 2 x Cp.
So that Cpp should be Cpp = (k1) Cp, and Cpp vanishes when we choose k=1.
The important point is that the scaling parameter k must be greater than unity, that is k > 1.
This restriction directly comes from Cp, the capacitance of the EOM, because we can not go to less than Cp.
If you want to put k < 1, it means you have to reduce the capacitance of the EOM somehow (like cutting the EO crystal ??)
(loss model)
I've modeled the loss for both the inductors and the capacitors in order to calculate the realistic impedance.
The model is based on the past measurements I've performed and the data sheet.
Loss for Capacitor : R(C) = 0.5 (C / 10pF)^{0.3} Ohm
Loss for Inductor : R(L) = 0.1 ( L / 1uH) Ohm
Of course this seems to be dirty and rough treatment.
But I think it's enough to express the tendency that the loss increase / decrease monotonically as L / C get increased.
These losses are inserted in series to every electrical components.
( Note that: this model depends on both the company and the product model. Here I assume use of Coilcraft inductors and mica capacitors scattered around 40m )
( results )
The optimum configuration is found when k=1, there is no scaling. This is the same configuration listed in last entry
Therefore we don't need to insert the parallel capacitor Cpp in order to achieve the optimum gain.
The figure below shows the some examples of the calculated impedance. You can see the peak height decrease by increasing the scale factor k.
The black dash line represents the EOMloss limit, which only contains the loss of the EOM.
The impedance at the resonance of 55MHz is 6.2 kOhm, which decreased by 3% from the EOMloss limit. This corresponds to gain of G = 11.
The other two peaks, 11MHz and 29.5MHz dramatically get decreased from EOMloss limit.
I guess this is because the structure below 50MHz is mainly composed by L1, L2, C1, C2.
In fact these components have big inductance and small capacitance, so that it makes lossy.
( next step )
The next step is to choose the appropriate transformer and to solder the circuit. 
2526

Tue Jan 19 02:40:38 2010 
Koji  Update  Electronics  triple resonant circuit for EOM 
The design looks very good. I have some questions.
1. As far as I remember, you've got the gain of slightly worse than 10 for a 55MHz single resonant case. Why your expectation of the gain (G=11) for the highest resonance better than this?
Supposing the loss exists only on the EOM, the other part of the LC network for the triple work as an inductor at the resonant frequency. This is just equivalent as the single resonant case. So the expected gain at 55MHz should coincides with what we already have. Probably, the resistance of 4 Ohm that is used here had too rough precision???
2. How can you adjust the resonances precisely?
Do we need any variable components for Cs and Ls, that may have worse quality than the fixed one, generally speaking.
I myself has no experience that I had to tune the commercial EOM because of a drift or whatever. I hope if you can adjust the resonance with a fixed component it should be fine.
3. Changing Cp. What does it mean?
Do you put additional cap for Cp?
4. The resonances for the lower two look very narrow. Is that fine?
This will show up in a better shape if we look at the transfer function for the gain. Is this right?
If we have BW>100kHz, it is sufficient.
5. Impedance matching for the lower two resonances.
Yep. You know this problem already.

2527

Tue Jan 19 03:04:14 2010 
Koji  Update  Electronics  triple resonant circuit for EOM 
Selffollow:
I got the answer of Q3 from the followup entry.
For Q4, once you get the impedance of the LC network lower than n^2*50, the EOM gain will be quite low. This means that the resonance is anyway narrow.
I did some simple calculation and it shows that the width of the resonance will be 100kHz~500kHz. So it maybe OK.
Quote: 
The design looks very good. I have some questions.
1. As far as I remember, you've got the gain of slightly worse than 10 for a 55MHz single resonant case. Why your expectation of the gain (G=11) for the highest resonance better than this?
Supposing the loss exists only on the EOM, the other part of the LC network for the triple work as an inductor at the resonant frequency. This is just equivalent as the single resonant case. So the expected gain at 55MHz should coincides with what we already have. Probably, the resistance of 4 Ohm that is used here had too rough precision???
2. How can you adjust the resonances precisely?
Do we need any variable components for Cs and Ls, that may have worse quality than the fixed one, generally speaking.
I myself has no experience that I had to tune the commercial EOM because of a drift or whatever. I hope if you can adjust the resonance with a fixed component it should be fine.
3. Changing Cp. What does it mean?
Do you put additional cap for Cp?
4. The resonances for the lower two look very narrow. Is that fine?
This will show up in a better shape if we look at the transfer function for the gain. Is this right?
If we have BW>100kHz, it is sufficient.
5. Impedance matching for the lower two resonances.
Yep. You know this problem already.


2528

Tue Jan 19 03:20:28 2010 
Koji  Update  Electronics  design complete  triple resonant circuit for EOM  
First I was confused, but now I think I understood.
My confusion:
If the k get bigger, L get smaller, C get bigger. This makes R(L) smaller and R(C) smaller. This sounds very nice. But why smaller k is preferable in the Kiwamu's result?
Explanation:
The resultant impedance of the network at a resonance is determined by Zres = L/(R C) or something like that. Here R = R(L)+R(C). (I hope this is right.)
Here larger Zres is preferable. So smaller R is nice.
But If the speed of reduction for R is slower than that of L/C (which is proportional to k^2), increasing k does not help us to increase of Zres. And that's the case.
This means "if we can put the LC network in the box of EOM, we can do better job!" as we can reduce Cp.
Quote: 
Loss for Capacitor : R(C) = 0.5 (C / 10pF)^{0.3} Ohm
Loss for Inductor : R(L) = 0.1 ( L / 1uH) Ohm


2529

Tue Jan 19 03:27:47 2010 
kiwamu  Update  Electronics  Re: triple resonant circuit for EOM 
1. You are right, the gain for the single resonant circuit was about 9.3 in my measurement.
But the reason why the triple is better than the single resonant circuit comes from the transformer.
The impedance can be degraded by a loss of the transformer, because it got worse after applying the transformer in the past measurement.
Also I definitely confirmed that the circuit had the impedance of 7.2 kOhm at the resonance of 52.9MHz without the transformer.
So it shall give the gain of 12, but did not after applying the transformer.
2. Yes, I think we need some variable components just in case.
5. For the impedance matching, I will select a transformer so that 55MHz is matched. In contrast I will leave two lower resonances as they are.
This is because 11MHz and 29.5MHz usually tend to have higher impedance than 55MHz. In this case, even if the impedance is mismatched, the gain for these can be kept higher than 11.
I will post the detail for this mismatched case tomorrow.
Quote: 
The design looks very good. I have some questions.
1. As far as I remember, you've got the gain of slightly worse than 10 for a 55MHz single resonant case. Why your expectation of the gain (G=11) for the highest resonance better than this?
Supposing the loss exists only on the EOM, the other part of the LC network for the triple work as an inductor at the resonant frequency. This is just equivalent as the single resonant case. So the expected gain at 55MHz should coincides with what we already have. Probably, the resistance of 4 Ohm that is used here had too rough precision???
2. How can you adjust the resonances precisely?
Do we need any variable components for Cs and Ls, that may have worse quality than the fixed one, generally speaking.
I myself has no experience that I had to tune the commercial EOM because of a drift or whatever. I hope if you can adjust the resonance with a fixed component it should be fine.
3. Changing Cp. What does it mean?
Do you put additional cap for Cp?
4. The resonances for the lower two look very narrow. Is that fine?
This will show up in a better shape if we look at the transfer function for the gain. Is this right?
If we have BW>100kHz, it is sufficient.
5. Impedance matching for the lower two resonances.
Yep. You know this problem already.


2533

Tue Jan 19 23:26:07 2010 
kiwamu  Update  Electronics  Re:Re: triple resonant circuit for EOM 
Quote: 
5. For the impedance matching, I will select a transformer so that 55MHz is matched. In contrast I will leave two lower resonances as they are.
This is because 11MHz and 29.5MHz usually tend to have higher impedance than 55MHz. In this case, even if the impedance is mismatched, the gain for these can be kept higher than 11.
I will post the detail for this mismatched case tomorrow.

Here the technique of the impedance matching for the triple resonant circuit are explained.
In our case, the transformer should be chosen so that the impedance of the resonance at 55MHz is matched.
We are going to use the transformer to step up the voltage applied onto the EOM.
To obtain the maximum stepupgain, it is better to think about the behavior of the transformer.
When using the transformer there are two different cases practically. And each case requires different optimization technique. This is the key point.
By considering these two cases, we can finally select the most appropriate transformer and obtain the maximum gain.
( how to maximize the gain ?)
Let us consider about the transformer. The gain of the circuit by using the transformer is represented by
(1)
Where ZL is the impedance of the load (i.e. impedance of the circuit without the transformer ) and n is the turn ratio.
It is apparent that G is the function of two parameters, ZL and n. This leads to two different solutions for maximizing the gain practically.
 case.1 : The turn ratio n is fixed.
In this case, the tunable parameter is the impedance ZL. The gain as a function of ZL is shown in the left figure above.
In order to maximize the gain, Z must be as high as possible. The gain G get close to 2n when the impedance ZL goes to infinity.
There also is another important thing; If the impedance ZL is bigger than the matched impedance (i.e. ZL = 50 * n^2 ), the gain can get higher than n.
 case.2 : The impedance ZL is fixed.
In contrast to case1, once the impedance ZL is fixed, the tunable parameter is n. The gain as a function of n is shown in the right figure above.
In this case the impedance matched condition is the best solution, where ZL=50*n^2. ( indicated as red arrow in the figure )
The gain can not go higher than n somehow. This is clearly different from case1.
( Application to the triple resonant circuit )
Here we can define the goal as "all three resonances have gain of more than n, while n is set to be as high as possible"
According to consideration of case1, if each resonance has an impedance of greater than 50*n^2 (matched condition) it looks fine, but not enough in fact.
For example if we choose n=2, it corresponds to the matched impedance of 50*n^2 = 200 Ohm. Typically every three resonance has several kOhm which is clearly bigger than the matched impedance successfully.
However no matter how big impedance we try to make, the gains can not be greater than G=2n=4 for all the three resonance. This is ridiculous.
What we have to do is to choose n so that it matches the impedance of the resonance which has the smallest impedance.
In our case, usually the resonance at 55MHz tends to have the smallest impedance in those three. According to this if we choose n correctly, the other two is mismatched.
However they can still have the gain of more than n, because their impedance is bigger than the matching impedance. This can be easily understand by recalling the case1.
(expected optimum gain of designed circuit)
By using the equation (1), the expected gain of the triple resonant circuit including the losses is calculated. The parameters can be found in last entry.
The turn ratio is set as n=11, which matches the impedance of the resonance at 55MHz. Therefore 55MHz has the gain of 11.
The gain at 11MHz is bigger than n=11, this corresponds to the case1. Thus the impedance at 11MHz can go close to gain of 22, if we can make the impedance much big.

2586

Wed Feb 10 17:28:02 2010 
kiwamu  Update  Electronics  triple resonant EOM  preliminary result 
I have made a prototype circuit of the triple resonant EOM.
The attached is the measured optical response of the system.
The measured gains at the resonances are 8.6, 0.6 and 7.7 for 11MHz, 29.5MHz and 55MHz respectively.
I successfully got nice peaks at 11MHz and 55MHz. In addition resultant optical response is well matched with the predicted curve from the measured impedance.
However there is a difference from calculated response (see past entry) (i.e. more gains were expected)
Especially for the resonance of 29.5MHz, it was calculated to have gain of 10, however it's now 0.6. Therefore there must a big loss electrically around 29.5MHz.
I am going to reanalyze the impedance and model the performance in order to see what is going on. 
Attachment 1: mod_depth.png


2587

Wed Feb 10 23:15:37 2010 
Koji  Update  Electronics  triple resonant EOM  preliminary result 
Hey, this looks nice, but can you provide us the comparison of rad/V with the resonant EOM of New Focus?
Quote: 
I have made a prototype circuit of the triple resonant EOM.
The attached is the measured optical response of the system.
The measured gains at the resonances are 8.6, 0.6 and 7.7 for 11MHz, 29.5MHz and 55MHz respectively.
I successfully got nice peaks at 11MHz and 55MHz. In addition resultant optical response is well matched with the predicted curve from the measured impedance.
However there is a difference from calculated response (see past entry) (i.e. more gains were expected)
Especially for the resonance of 29.5MHz, it was calculated to have gain of 10, however it's now 0.6. Therefore there must a big loss electrically around 29.5MHz.
I am going to reanalyze the impedance and model the performance in order to see what is going on.


2590

Thu Feb 11 16:52:53 2010 
kiwamu  Update  Electronics  triple resonant EOM  preliminary result 
The commercial resonant EOM of New Focus has the modulation efficiency of 50150mrad/Vrms. ( This number is only true for those EOM made from KTP such as model4063 and model4463 )
Our tripleresonant EOM (made from KTP as well) has a 90mrad/Vrms and 80mrad/Vrms at the reosonances of 11MHz and 55MHz respectively.
Therefore our EOM is as good as those of companymade so that we can establish a new EOM company
Quote: 
Hey, this looks nice, but can you provide us the comparison of rad/V with the resonant EOM of New Focus?
Quote: 
I have made a prototype circuit of the triple resonant EOM.
The attached is the measured optical response of the system.
The measured gains at the resonances are 8.6, 0.6 and 7.7 for 11MHz, 29.5MHz and 55MHz respectively.
I successfully got nice peaks at 11MHz and 55MHz. In addition resultant optical response is well matched with the predicted curve from the measured impedance.
However there is a difference from calculated response (see past entry) (i.e. more gains were expected)
Especially for the resonance of 29.5MHz, it was calculated to have gain of 10, however it's now 0.6. Therefore there must a big loss electrically around 29.5MHz.
I am going to reanalyze the impedance and model the performance in order to see what is going on.



2596

Fri Feb 12 13:15:41 2010 
kiwamu  Update  Electronics  triple resonant EOM  liniaryity test 
I have measured the linearity of our triple resonant EOM (i.e. modulation depth versus applied voltage)
The attached figure is the measured modulation depth as a function of the applied voltage.
The linear behavior is shown below 4Vrms, this is good.
Then it is slowly saturated as the applied voltage goes up above 4Vrms.
However for the resonance of 29.5MHz, it is difficult to measure below 7Vrms because of the small modulation depth.
Our triple resonant EOM looks healthy
    result from fitting   
11MHz: 91mrad/Vrms+2.0mrad
29.5MHz: 4.6mrad/Vrms+6.2mrad
55MHz:82mrad/Vrms+1.0mrad 
Attachment 1: linearity_edit.png


2602

Sat Feb 13 13:21:53 2010 
Koji  Update  Electronics  triple resonant EOM  liniaryity test 
Looks good. I just thought of the idea that we also can use Alberto's PLL setup to sense the modulation with more sensitivity. ;)
Quote: 
I have measured the linearity of our triple resonant EOM (i.e. modulation depth versus applied voltage)
The attached figure is the measured modulation depth as a function of the applied voltage.
The linear behavior is shown below 4Vrms, this is good.
Then it is slowly saturated as the applied voltage goes up above 4Vrms.
However for the resonance of 29.5MHz, it is difficult to measure below 7Vrms because of the small modulation depth.
Our triple resonant EOM looks healthy
    result from fitting   
11MHz: 910mrad/Vrms+20mrad
29.5MHz: 46mrad/Vrms+6.2mrad
55MHz:820mrad/Vrms+10mrad


2682

Thu Mar 18 15:33:17 2010 
kiwamu  Summary  Electronics  advantege of our triple resonant EOM 
In this LVC meeting I discussed about triple resonant EOMs with Volker who was a main person of development of triple resonant EOMs at University of Florida.
Actually his EOM had been already installed at the sites. But the technique to make a triple resonance is different from ours.
They applied three electrodes onto a crystal instead of one as our EOM, and put three different frequencies on each electrode.
For our EOM, we put three frequencies on one electrode. You can see the difference in the attached figure. The left figure represents our EOM and the right is Volker's.
Then the question is; which can achieve better modulation efficiency ?
Volker and I talked about it and maybe found an answer,
We believe our EOM can be potentially better because we use full length of the EO crystal.
This is based on the fact that the modulation depth is proportional to the length where a voltage is applied onto.
The people in University of Florida just used one of three separated parts of the crystal for each frequency. 
Attachment 1: electrode.png


2683

Thu Mar 18 19:00:04 2010 
Koji  Summary  Electronics  advantege of our triple resonant EOM 
Did you find what is the merit of their impedance matching technique?
Quote: 
In this LVC meeting I discussed about triple resonant EOMs with Volker who was a main person of development of triple resonant EOMs at University of Florida.
Actually his EOM had been already installed at the sites. But the technique to make a triple resonance is different from ours.
They applied three electrodes onto a crystal instead of one as our EOM, and put three different frequencies on each electrode.
For our EOM, we put three frequencies on one electrode. You can see the difference in the attached figure. The left figure represents our EOM and the right is Volker's.
Then the question is; which can achieve better modulation efficiency ?
Volker and I talked about it and maybe found an answer,
We believe our EOM can be potentially better because we use full length of the EO crystal.
This is based on the fact that the modulation depth is proportional to the length where a voltage is applied onto.
The people in University of Florida just used one of three separated parts of the crystal for each frequency.


2688

Sat Mar 20 18:34:19 2010 
kiwamu  Summary  Electronics  RE:advantege of our triple resonant EOM 
Yes, I found it.
Their advantage is that their circuit is isolated at DC because of the input capacitor.
And it is interesting that the performance of the circuit in terms of gain is supposed to be roughly the same as our transformer configuration. 
2692

Mon Mar 22 02:03:57 2010 
rana  Summary  Electronics  UPDH Box #17: Ready 
It took too long to get this box ready for action. I implemented all of the changes that I made on the previous one (#1437). In addition, since this one is to be used for phase locking, I also made it have a ~flat transfer function. With the Boost ON, the TF magnitude will go up like 1/f below ~1 kHz.
The main trouble that I had was with the 12V regulator. The output noise level was ~500 nV/rHz, but there was a large oscillation at its output at ~65 kHz. This was showing up in the output noise spectrum of U1 (the first opamp after the mixer). Since the PSRR of the OP27 is only ~40 dB at such a high frequency, it is not strange to see the power supply noise showing up (the input referred noise of the OP27 is 3.5 nV/rHz, so any PS noise above ~350 nV/rHz becomes relavent).
I was able to tame this by putting a 10 uF tantalum cap on the output of the regulator. However, when I replaced the regulator with a LM7912 from the blue box, it showed an output noise that went up like 1/f below 50 kHz !! I replaced it a couple more times with no benefit. It seems that something on the board must now be damaged. I checked another of the UPDH boxes, and it has the same high frequency oscillation but not so much excess voltage noise. I found that removing the protection diode on the output of the regulator decreased the noise by a factor of ~2. I also tried replacing all of the 1 uF caps that are around the regulator. No luck.
Both of the +12 V regulators seem fine: normal noise levels of ~200 nV/rHz and no oscillations.
Its clear that the regulator is not functioning well and my only guess is that its a layout issue on the board or else there's a busted component somewhere that I can't find. In any case, it seems to be functioning now and can be used for the phase locking and PZT response measurements. 
2693

Mon Mar 22 10:07:30 2010 
Koji  Summary  Electronics  UPDH Box #17: Ready 
For your reference: Voltage noise of LM7815/LM7915 (with no load) 
Attachment 1: 15V_power_supply.pdf


2745

Wed Mar 31 19:29:58 2010 
Hartmut  Update  Electronics  (1cm) Si PD transfer functions update 
Recorded transfer functions for the 1cm SiPD 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
to.
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.

2762

Sun Apr 4 00:21:42 2010 
rana, koji  Summary  Electronics  Checkout of EG&G (PARC) preamp model #113, s/n 49135 
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 highbandwidth 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 Yarm. 
2768

Mon Apr 5 10:33:12 2010 
Alberto  Omnistructure  Electronics  soldering iron broken 
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. 
2770

Mon Apr 5 13:07:36 2010 
Jenne  Omnistructure  Electronics  soldering iron broken 
Quote: 
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. 
2771

Mon Apr 5 13:20:16 2010 
Koji  Omnistructure  Electronics  soldering iron broken 
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.
Quote: 
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.


Attachment 1: weller_tips.jpg


2779

Wed Apr 7 10:48:04 2010 
Alberto  Update  Electronics  REFL11 Noise Simulation 
LISO simulations confirm the estimate of ~15nV for the noise of REFL11.
The largest contribution comes from the 50Ohm output resistor (Rs in the schematic below), the 450Ohm feedback resistor of the max4107 opamp stage; the 10KOhm resistor at the Test Input connector.
See attached plot.
(It's also all in the SVN, under https://nodus.ligo.caltech.edu:30889/svn/trunk/alberto/40mUpgrade/RFsystem/RFPDs/)
#
# gnd
# 
# Cw2
# 
# n23
# 
# Lw2
# 
# gnd n22
#  
# Rip Rw2
#   \
# nt Rsin2   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
#
#
# 
Attachment 1: rfpd11_testinput_noiseplot.pdf


2780

Wed Apr 7 10:58:15 2010 
Koji  Update  Electronics  REFL11 Noise Simulation 
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.
Quote: 
LISO simulations confirm the estimate of ~15nV for the noise of REFL11.
The largest contribution comes from the output resistor (Rs in the schematic below).
See attached plot.


2781

Wed Apr 7 11:11:19 2010 
Alberto  Update  Electronics  REFL11 Noise Simulation 
Quote: 
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.
Quote: 
LISO simulations confirm the estimate of ~15nV for the noise of REFL11.
The largest contribution comes from the output resistor (Rs in the schematic below).
See attached plot.


The colors in the plot were misleading.
Here's hopefully a better plot.
The dominant sources of noise are the resonant of the photodiode (~10Ohm), the max4107, the resistor in series to ground at the  input of the max4107. 
Attachment 1: rfpd11_testinput_noiseplot.pdf


2801

Thu Apr 15 14:47:28 2010 
steve  Update  Electronics  25MHZ oscillation of HP4195A 
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 sweepsign 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

Attachment 1: P1060246.JPG


Attachment 2: P1060249.JPG


2806

Mon Apr 19 07:38:07 2010 
rana  HowTo  Electronics  Repair and Calibration of SR560: s/n 59650 
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 can sometimes be that the gain proscribed by the manual is too high and saturates the output for large offsets. If that's the case, simply lower the gain, trim the offset, then return the gain to the specified value and trim again.
 The limit in trimming the offset is the stick slip resolution in the trim pot. This can potentially leave the whole preamp in an acoustically sensitive state. I tapped the pots with a screwdriver after tuning to make sure it was in more of a 'sticky' rather than 'slippy' region of the knob. A better design would allow for more filtering of the pot.
 In the CMRR tuning procedure it says to 'null sine wave output' but it should really say 'null the sine wave component at the drive frequency'. The best CMRR tuning uses a 1 kHz drive and leaves a residual 2 kHz signal due to the distortion imbalance (of the FETs I think).
 The CMRR tuning upsets the DC offset trim and vice versa. The best tuning is gotten by iterating slightly (go back and forth once or twice between the offset and CMRR tuning procedures).
It looks like its working fine now. Steve's ordering some IF3602 (lownoise, balanced FET pair from Interfet) to see if we can drop the SR560's input noise to the subnV level.
Noise measured with the input terminated with a BNC short (not 50 Ohms) G=100, DC coupled, lownoise mode:
Input referred noise (nV/rHz)
f 
e_n 
0.1

200 
1 
44 
10 
8 
100 
5 
1000 
5 
10000 
4 

2869

Mon May 3 01:16:50 2010 
rana  HowTo  Electronics  Marconi phase noise measurement setup 
To try the 3corner 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 ZP3MH 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 inline termination and then a BLP5 low pass filter (Steve, please order ~7 of the BLP1.5 or BLP1.9 low pass filter from MiniCircuits) and then into
the DC coupled of a SR560. After some gain and filtering that feedback goes back to the FM input of the topMarconi 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, lownoise. Its output is going directly to the ADC channel  C1:IOOMC_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 peakpeak 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 RaiFET 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. 
Attachment 1: pn.png


2879

Tue May 4 18:40:27 2010 
rana  HowTo  Electronics  Marconi phase noise measurement setup 
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 
Attachment 1: Untitled.png


Attachment 2: ifrnoise.png


2904

Mon May 10 18:56:53 2010 
rana  Update  Electronics  Unexpected oscilaltionin the POY11 PD 
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. 
2905

Mon May 10 19:09:45 2010 
rana  Update  Electronics  Unexpected oscilaltionin the POY11 PD 
Quote: 
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 2omega and the 55MHz notches next to each other right after the photodiode? 