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OverUnity Research > Benches > Itsu (Moderator: Itsu) > Smudge proposed NMR experiment replication.
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Author Topic: Smudge proposed NMR experiment replication.  (Read 127076 times)
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Re: Smudge proposed NMR experiment replication. « Reply #350 on: 2020-07-22, 20:38:38 »

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I doubled the distance between the both pancake coils so i can insert the H-probe inbetween to take some measurements

This video shows the results:  https://www.youtube.com/watch?v=ulA76NW0fT4

Itsu
   
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Re: Smudge proposed NMR experiment replication. « Reply #351 on: 2020-07-23, 12:20:36 »

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Quote from: Itsu on 2020-07-22, 16:02:38
I made a similar fixture like you used using SMA connectors, see picture, but the result is identical as before, see screenshot.
WTF is going on ?!

The fixture seems adequate but the 52dBm higher signal power at 0Hz compared to 60kHz is indicative of an inductor - not a capacitor !
-52.16dBmW of power represents -26.08dBmV of voltage ...or 0.2% of the voltage amplitude appearing at 0Hz.

I know that in the case of this SA, 0Hz really is 9kHz, but still...a 99.8% loss of amplitude between 9kHz and 60kHz is huge and not a property of a capacitor !
The frequency range 9kHz-60kHz is within the specs of this SA, so the readings should be accurate.

Maybe the SA is making some weird error or interpolation when the Start frequency is set to 0Hz. 
I do not mind if you always set it to 9kHz - the lowest frequency the SA is specified for.
« Last Edit: 2020-07-23, 13:19:41 by verpies »
   
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Re: Smudge proposed NMR experiment replication. « Reply #352 on: 2020-07-23, 12:31:54 »

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Quote from: Itsu on 2020-07-22, 16:09:38
So if i do not use the PA, then we would eliminate the overvoltage on the caps as the cause.
Not if the caps were permanently damaged by the overvoltage.
   
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Re: Smudge proposed NMR experiment replication. « Reply #353 on: 2020-07-23, 12:36:53 »

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Quote from: verpies on 2020-07-23, 12:20:36
WTF is going on ?!

The fixture seems adequate but the the 52dBm higher signal power at 0Hz compared to 60kHz is indicative of an inductor - not a capacitor !
-52.16dBmW of power represents -26.08dBmV of voltage ...or 0.2% of the voltage amplitude appearing at 0Hz.

I know that in the case of this SA, 0Hz really is 9kHz, but still...a 99.8% loss of amplitude between 9kHz and 60kHz is huge and not a property of a capacitor !
The frequency range 9kHz-60kHz is within the specs of this SA, so the readings should be accurate.

Maybe the SA is making some weird error or interpolation when the Start frequency is set to 0Hz. 
I do not mind if you always set it to 9kHz - the lowest frequency the SA is specified for.



Let me try again with some shorter (RG174) coax and sma connectors only instead of those bulky coax ones with severall adapters.
I can try to start from 9Khz instead of 0 too.




By the way, tried the weave1 coil setup, but i miserably failed.
I get more appreciation for your coils as these are a pain to build.

I do have litz without any cloth around it and it wants to untwist all the time.
It also has more diameter (1.2mm) as specified (0.93mm), so i came out on 10 turns instead of 14,  but i was unable to properly fixate them.

Itsu
   
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Re: Smudge proposed NMR experiment replication. « Reply #354 on: 2020-07-23, 12:48:01 »

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Quote from: Itsu on 2020-07-22, 17:02:33
Redone the H-probe test in 3 situations without PA  both in dBm as dBmV
First two sweeps are duplicated.
Only the last one is in dBmV (see the screenshots). The file: "balun plus caps no PA dBmV.png" contains the sweep in dBm despite its filename.

Anyway, it is not necessary to post both dBm and dBmV because the difference between these two units is just a factor of 2 (because the power varies as a square of the voltage).
However it is useful to normalize them to 0 dBmW and 0 dBmV and set the reference levels to these levels, for easy comparison.  This way 0 dBmW and 0 dBmV simply means "no attenuation" (transmission coefficient = 1)
   
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Re: Smudge proposed NMR experiment replication. « Reply #355 on: 2020-07-23, 13:27:16 »

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Quote from: Itsu on 2020-07-23, 12:36:53
I do have litz without any cloth around it and it wants to untwist all the time.
Oh yes, that could make the winding harder.
The silk braid around the strands keeps them from unraveling and the very fine silk fibers seem to aid in holding and polymerizing the Cyanoacrylate on contact. The braid also acts as a separator between turns and decreases the Proximity Effect.
The insulin syringe /w integrated needle (from a pharmacy) is the only applicator that controls the low-viscosity Cyonoacrylate dispension precisely enough. ( BTW: I prefer to dull the needle ).

Quote from: Itsu on 2020-07-23, 12:36:53
It also has more diameter (1.2mm) as specified (0.93mm),
The vendor should have stated that outright.  The diameter of my wire is 1mm exactly (including the double silk braid).
   
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Re: Smudge proposed NMR experiment replication. « Reply #356 on: 2020-07-23, 13:51:28 »

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Quote from: Itsu on 2020-07-22, 20:38:38
I doubled the distance between the both pancake coils so i can insert the H-probe inbetween to take some measurements
This video shows the results:  https://www.youtube.com/watch?v=ulA76NW0fT4
The amplitude vs. orientation & position seems to be correct.

Between my coils, the amplitude in the optimum orientation and position is ~20x higher than in others.

P.S.
Where do you switch the Rigol FG amplitude display between Vrms and Vpp ?
   
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Re: Smudge proposed NMR experiment replication. « Reply #357 on: 2020-07-23, 16:51:17 »

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Quote
WTF is going on ?!

The fixture seems adequate but the 52dBm higher signal power at 0Hz compared to 60kHz is indicative of an inductor - not a capacitor !
-52.16dBmW of power represents -26.08dBmV of voltage ...or 0.2% of the voltage amplitude appearing at 0Hz.

I know that in the case of this SA, 0Hz really is 9kHz, but still...a 99.8% loss of amplitude between 9kHz and 60kHz is huge and not a property of a capacitor !
The frequency range 9kHz-60kHz is within the specs of this SA, so the readings should be accurate.

Maybe the SA is making some weird error or interpolation when the Start frequency is set to 0Hz.
I do not mind if you always set it to 9kHz - the lowest frequency the SA is specified for.

I used the shorter RG174 and sma connectors from my nanoVNA-F with my fixture, but the problem stays the same.
Even when starting at 9, 10, 50Khz or even 1Mhz (stopping at 50Mhz), we still see that dip, see screenshot.
Perhaps Partzman can confirm as he has the same SA i think.



Quote
First two sweeps are duplicated.
Only the last one is in dBmV (see the screenshots). The file: "balun plus caps no PA dBmV.png" contains the sweep in dBm despite its filename.

Anyway, it is not necessary to post both dBm and dBmV because the difference between these two units is just a factor of 2 (because the power varies as a square of the voltage).
However it is useful to normalize them to 0 dBmW and 0 dBmV and set the reference levels to these levels, for easy comparison.  This way 0 dBmW and 0 dBmV simply means "no attenuation" (transmission coefficient = 1)


Ok, cleared up those screenshots, only 2 left in dBmV, must have been sleeping  :-[


Quote
The amplitude vs. orientation & position seems to be correct.

Between my coils, the amplitude in the optimum orientation and position is ~20x higher than in others.

P.S.
Where do you switch the Rigol FG amplitude display between Vrms and Vpp ?

So my H-probe orientation is OK?  Seems your drawing shows it horizontal, not vertical as i have it.


I am not aware i switch from Vrms and Vpp on the FG, its always on Vpp i think.


Itsu
   
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Re: Smudge proposed NMR experiment replication. « Reply #358 on: 2020-07-23, 19:07:44 »

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Quote from: Itsu on 2020-07-23, 16:51:17
Even when starting at 9, 10, 50Khz or even 1Mhz (stopping at 50Mhz), we still see that dip, see screenshot.
Perhaps Partzman can confirm as he has the same SA i think.
Yes, Partzman's input would shed some light on this 9-60kHz anomaly.

Quote from: Itsu on 2020-07-23, 16:51:17
So my H-probe orientation is OK?  Seems your drawing shows it horizontal, not vertical as i have it.
That drawing depicts the crossection of the apparatus, so the only visible crossections of the pancake coils are, what you would call, at 12 o'clock and at 6 o'clock.
You video shows you probing at 3 o'clock (or 9 o'clock) position.  These crossections of the pancake coils are not visible on Smudge's/my diagram.

Quote from: Itsu on 2020-07-23, 16:51:17
I am not aware i switch from Vrms and Vpp on the FG, its always on Vpp i think.
So it must be fixed in this particular firmware version. In mine it is fixed at Vrms
   
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Re: Smudge proposed NMR experiment replication. « Reply #359 on: 2020-07-23, 20:01:07 »

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That drawing depicts the crossection of the apparatus, so the only visible crossections of the pancake coils are, what you would call, at 12 o'clock and at 6 o'clock.
You video shows you probing at 3 o'clock (or 9 o'clock) position.  These crossections of the pancake coils are not visible on Smudge's/my diagram.

yes, i am measuring in the 3 o'clock position and there is a 6x (3mA v 18mA) amplitude difference in the optimum position, but there is extended distance between the pancakes still.


Quote
So it must be fixed in this particular firmware version. In mine it is fixed at Vrms

Ok, could be, i am on 00.01.14.
   
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Re: Smudge proposed NMR experiment replication. « Reply #360 on: 2020-07-23, 20:16:32 »
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Quote from: Itsu on 2020-07-23, 16:51:17

Perhaps Partzman can confirm as he has the same SA i think.


So my H-probe orientation is OK?  Seems your drawing shows it horizontal, not vertical as i have it.


Itsu

Yes, I have the same SA.  I see the dip you refer to so did you use the TG or sweep from your FG?

Regarding your H probe, IMO the coil should be parallel to the flat coils not at 90 degrees.

Regards,
Pm
   
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Re: Smudge proposed NMR experiment replication. « Reply #361 on: 2020-07-23, 20:35:28 »

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Hi PM,     

thanks,   i used the TG to sweep.

Concerning the H-probe,  so not as i used it in my video?

itsu
   
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Re: Smudge proposed NMR experiment replication. « Reply #362 on: 2020-07-23, 21:20:08 »

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Quote from: partzman on 2020-07-23, 20:16:32
IMO the coil should be parallel to the flat coils not at 90 degrees.
Why?
Do you agree, that when the plane of the sensor coil is perpendicular to any magnetic flux, then the sensor coil is most sensitive to the changes in that flux ?
Do you think that the flux generated by the pancake coils is perpendicular to the planes of these pancake coils ?
   
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Re: Smudge proposed NMR experiment replication. « Reply #363 on: 2020-07-23, 21:25:12 »

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Finished attempt 2 of a weave 1 pancake coil.
Not very happy still with it, as the problem is to fixate it.

Anyway, its specifications:

OD: 119mm
ID: 87mm
Winding: 1 layer, 10 turns of 1.6mm Litz wire (120 strand), 3.5m long, antiradial weave 1.
Inductance: 17.6µH (@100kHz)
DC resistance: ~0.1Ω

itsu
   
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Re: Smudge proposed NMR experiment replication. « Reply #364 on: 2020-07-23, 23:24:57 »

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Quote from: Itsu on 2020-07-23, 21:25:12
Finished attempt 2 of a weave 1 pancake coil.
Not very happy still with it, as the problem is to fixate it.
Don't feel bad. This wire is really thick and the lack of a silk braid makes it difficult to control.
Also notice, that I wound my coil in a 3mm deep rectangular groove in a plexiglass sheet, so I had its help in holding the shape of the coil and squeezing the wires together.  I also used double-sticky tape at the bottom of the groove, but my tape was ~1mm thick and pliable.  I also helped myself with the insulin syringe with cyanoacrylate in tight spaces. ...and the custom-made* wire pushing tool made the winding almost enjoyable.

* at home out of a 6mm Teflon rod using a Dremel tool and a cutting wheel. 5min of work.
   
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Re: Smudge proposed NMR experiment replication. « Reply #365 on: 2020-07-24, 01:14:06 »
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Quote from: verpies on 2020-07-23, 21:20:08
Why?
Do you agree, that when the plane of the sensor coil is perpendicular to any magnetic flux, then the sensor coil is most sensitive to the changes in that flux ?
Do you think that the flux generated by the pancake coils is perpendicular to the planes of these pancake coils ?

I agree that the position Itsu used for the H sensor in the video is most sensitive to the flux.  However, it is my opinion without having built the device, that the H field is perpendicular to the plane of the pancake coil.  I am probably wrong on this but it would be interesting to position the H sensor coil parallel to the pancake coils and see what the measurements show.

Regards,
Pm

   
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Re: Smudge proposed NMR experiment replication. « Reply #366 on: 2020-07-24, 10:07:08 »

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Quote from: partzman on 2020-07-24, 01:14:06
I agree that the position Itsu used for the H sensor in the video is most sensitive to the flux.
In that particular video - yes.
It is my contention, that this would be the most sensitive orientation in any video.

Quote from: partzman on 2020-07-24, 01:14:06
However, it is my opinion without having built the device, that the H field is perpendicular to the plane of the pancake coil.
Do you realize, that if you are right about the direction of the flux between the pancake coils, then this simulation* of magnetic flux is wrong and this entire NMR project does not make sense ?

* The simulation was made in FEMM. It shows the flux between the cross-sections of pancake coils.  The outer blue circle is simply the boundary for the FEMM simulation.  The pancake coils are modeled as current strips with the current going into or out of the screen, which is a reasonable representation for a single layer of closely spaced wires.  Of course FEMM is only a 2D simulation so it is showing the results for current strips that are infinitely long.

Quote from: partzman on 2020-07-24, 01:14:06
I am probably wrong on this but it would be interesting to position the H sensor coil parallel to the pancake coils and see what the measurements show.
In the video below, he has positioned the plane of the sensor coil parallel to the planes of the pancake coils:
https://youtu.be/CJOMrmeu7cQ

Unfortunately, in that video, he has positioned the sensor coil only outside of the pancakes, where the flux direction and density are very different than between the pancakes.
   
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Re: Smudge proposed NMR experiment replication. « Reply #367 on: 2020-07-24, 12:06:00 »

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Just playing around with my new nanoVNA-F device and sweeping (10Khz to 50Mhz) the 100pF trimmer cap.
This is the gain chart:

Looks similar is yours without any dip at the start.


Itsu
   
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Re: Smudge proposed NMR experiment replication. « Reply #368 on: 2020-07-24, 12:45:18 »

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Yes, that looks correct. At 10kHz the cap has -75dB of voltage amplitude attenuation compared to a short. That's a very low transmission coefficient.
I can see that you did not configure the display to connect the dots with lines, yet ;)

Get yourself acquainted with the S11 and S21 scattering parameters and remember that they are RATIOS of voltage amplitudes (between the incident and transmitted or reflected signals). Ratios don't have units !
They are often confused with impedance and admittance of the DUT because they can be calculated from S11 and S21 measurements.
https://www.analogictips.com/what-are-the-application-and-measurements-s-parameters/

It is important to remember that Impedance and Admittance and VSWR are not measured by the VNA directly.  They are only calculated from the S11 and S21 measurements. Most VNAs will do that calculation for you on-the-fly automatically when you request it.
However, these calculations are subject to errors, so if you ask the VNA to "measure" the impedance or admittance of the DUT, the VNA will have to calculate them SOMEWHAT IMPRECISELY from the raw S11 and S21 measurements.
If you're wondering what factors effect the precision of these calculations, then read the attached article and watch these videos:
https://youtu.be/1UbEz73FGCU
https://youtu.be/0JglLhrisOs



The plot and schematics above are from a good article, which I am attaching to this message as a PDF file.

« Last Edit: 2024-09-10, 16:56:31 by verpies »
   
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Re: Smudge proposed NMR experiment replication. « Reply #369 on: 2020-07-24, 14:58:34 »
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Quote from: Itsu on 2020-07-23, 20:35:28
Hi PM,     

thanks,   i used the TG to sweep.

itsu

Itsu,

It might be possible that the ~50kHz dip when using the TG for the sweep generator might be due to the minimum specified frequency for the TG being 100kHz.  IOW, starting the sweep at a frequency <100kHz may create who knows what kind of artifacts in hardware or even firmware.

Regards,
Pm
   
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Re: Smudge proposed NMR experiment replication. « Reply #370 on: 2020-07-24, 15:28:40 »

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Quote from: partzman on 2020-07-24, 14:58:34
It might be possible that the ~50kHz dip when using the TG for the sweep generator might be due to the minimum specified frequency for the TG being 100kHz.  IOW, starting the sweep at a frequency <100kHz may create who knows what kind of artifacts in hardware or even firmware.
I thought that when the SA's spec states 9kHz - 1.5GHz on the front panel then it refers to all its components.

So that needs to kept in mind about this SA. To mitigate this anomaly, in the future start all your sweeps that involve the TG from 100kHz. For this NMR project, nothing interesting is happening below it anyway.
   
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Re: Smudge proposed NMR experiment replication. « Reply #371 on: 2020-07-24, 16:30:57 »

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Quote from: verpies on 2020-07-24, 12:45:18
Yes, that looks correct. At 10kHz the cap has -75dB of voltage amplitude attenuation compared to a short. That's a very low transmission coefficient.
I can see that you did not configure the display to connect the dots with lines, yet.

Get yourself acquainted with the S11 and S21 parameters and remember that they are RATIOS of voltage amplitudes (between the incident and transmitted or reflected signals)
They are often confused with impedance and admittance of the DUT because they can be calculated from these S11 and S21 measurements.
https://www.analogictips.com/what-are-the-application-and-measurements-s-parameters/

Also, in case you INTENTIONALLY want to calculate the impedance or admittance of the DUT from the S11 and S21 measurements (most VNAs do it for you automatically when you request it) and you're wondering whether to use the S11 (one port) or S21 (two port measurement) and series or parallel connection to the DUT to accomplish that, then watch these videos:
https://youtu.be/1UbEz73FGCU
https://youtu.be/0JglLhrisOs

The plot and schematics above are from a good article, which I am attaching to this message as a PDF file.

P.S.
Remember that the firmware for your VNA is updated often.


its a completely different world i am seeing, so all the info is welcome, thanks.
Did some changes to the graphs, like adding lines between points etc.,  much better.

Itsu
   
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Re: Smudge proposed NMR experiment replication. « Reply #372 on: 2020-07-24, 16:33:23 »

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Quote from: partzman on 2020-07-24, 14:58:34
Itsu,

It might be possible that the ~50kHz dip when using the TG for the sweep generator might be due to the minimum specified frequency for the TG being 100kHz.  IOW, starting the sweep at a frequency <100kHz may create who knows what kind of artifacts in hardware or even firmware.

Regards,
Pm

PM,   yes,  looks like it,   below screenshot when started from 100Khz  O0

Where did you learned that (100Khz)?


Itsu
   
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Re: Smudge proposed NMR experiment replication. « Reply #373 on: 2020-07-24, 17:15:42 »

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Here a nanoVNA measurement of my new weave 1 coil (series measurement) with severall graphs.
Need to dive into the info from verpies to get a good feel on what i see.


EDIT,  did a normalisation at the coil...

Itsu
« Last Edit: 2020-07-24, 17:51:27 by Itsu »
   
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Re: Smudge proposed NMR experiment replication. « Reply #374 on: 2020-07-24, 17:24:22 »
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Quote from: Itsu on 2020-07-24, 16:33:23
PM,   yes,  looks like it,   below screenshot when started from 100Khz  O0

Where did you learned that (100Khz)?


Itsu

From the DSA800 User Guide.  I think it is downloadable from the Rigol site but I can send you a copy if you can't find it.  It was specified way down in section 5-2 in the manual.

regards,
Pm
   
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