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Author Topic: Smudge proposed NMR experiment replication.  (Read 12376 times)

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Nope, this one is with a different span and RBW. e.g. it starts from 0Hz and the fuchsia one started from 50kHz.  I could interpolate to fit them, but why introduce a numerical error...

Hmmm,  then that first one i mist that it started at 50Khz.

Anyway, here again the blue trace starting from 50Khz now:

Itsu
   

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So far the highest crosstalk seems to be at 7.46MHz and EM...or the toroidal secondary circuit is just the most sensitive at this frequency because it resonates then.  So please check if the trimmer at the secondary circuit affects this 7.46MHz peak.
However, it looks like between measurements, something was disturbed and the pancake primary resonance frequency has shifted from 3.8MHz to 4.1MHz, so lets repeat these "blue" and "fuchsia" measurements tomorrow according to this diagram and including the balun, but calibrate/normalize with no balun nor toroidal nor pancake coils for both measurements.

Let's try the linear display of the amplitude on the SA this time (not logarithmic).  I am hoping for more precision this way and that the red lower peak disappears completely after scaling.
« Last Edit: 2020-07-06, 09:28:44 by verpies »
   

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Ok,  i noticed that when attaching the SA to the 10 Ohm resistor it influenced the resonance peak and went from 3.8Mhz to 4.1Mhz.
Could be the extra capacitance of the SA connection caused this.

Will check tomorrow.

Thanks,   itsu
   

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Ok,  i noticed that when attaching the SA to the 10 Ohm resistor it influenced the resonance peak and went from 3.8Mhz to 4.1Mhz.
Could be the extra capacitance of the SA connection caused this.
I was afraid of that.

  • Maybe that balun will help* , or...
  • a lower resistance CSR, or...
  • changing the side of the CSR where the SA's ground lead/sheield is connected, or...
  • adding a high resistance in the ground lead/shield going to the SA's input, or...
  • the contactless current probe connected to SA's input

Anyway, leave the CSR in for both measurements unless you decide to use the contactless current probe.

* I have doubts about this particular balun and you will have them too, once you measure the capacitance between its primary and secondary winding.
   

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OK,  my thoughts were to use your last option, the contactless current probe connected to SA's input.
I will try that first.

Concerning your doubts about the balun, the capacitance between prim/sec is shown in the below picture.

Itsu
   

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That is almost 2nF between the primary and secondary.
At 4MHz that capacitance presents a 20Ω path for the signal !

Is there a way you can push these windings apart, so there is a 5mm gap between the primary and secondary ?
   

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Right,     no its 2 layers, so i have to remove many windings to get that.


The  contactless current probe option does not work as its connected to the scope,  not the SA.

Using a 1 Ohm csr also does not work, still there is a difference of 3.8 to 4.1 Mhz, even when i leave the connection in place during both measurements.
The peak is less with 1 Ohm.

I have a smaller balun like the Smudge balun, also trifilar, but with 1 layer, but inside the toroid the windings touch each other which i can try.
But the capacitance comes from the intertwined trifilar wires, not from the trifilar windings themselve i think, so would spacing them help?

Itsu
   

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The  contactless current probe option does not work as its connected to the scope,  not the SA.
I've seen in some of your videos, that you have a separate amplifier for the current probe.  Can't the output of this amplifier be connected to SA's input ?  Of course, the amplitude of the signal coming out of the amplifier cannot exceed the max input level of the SA.

But the capacitance comes from the intertwined trifilar wires, not from the trifilar windings themselve i think, so would spacing them help?
I am not tracking well the winding anatomies of these transformers, but if the primary and secondary windings are intertwined then their interwinding capacitance will remain high.
   

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I also have a P6021 AC current probe which i have hooked up to the SA port and it shows a trace with a peak still at 4.16Mhz.
The question is how to measure with this probe the whole setup?

Just attach a single loop wire to the output / load  connector and measure the current there?


Itsu
   
   

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The contactless AC current probe is useful only for the fuchsia measurement.
For the blue measurement just use the regular voltage-sensing connections.

..but I have a feeling I do not understand the question :(
   

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Because i still have the frequency difference (3.8 - 4.1Mhz) between using the current probe (4.1Mhz peak) and the  regular voltage-sensing connections (3.8Mhz peak),
i want to use the same setup between the 2 measurements (fuchsia and blue), so i want to use the current probe also for the blue measurement.

But that means i have to measure the current somewhere across the whole setup, or is that not possible?



EDIT:

Concerning the frequency shift, i think the 3.8 to 4.1 Mhz frequency shift is not caused by the
csr / current measurements, but its the other way around, the "regular voltage-sensing connections"
are causing the frequency to shift from its normal 4.1Mhz to 3.8Mhz.
   

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Because i still have the frequency difference (3.8 - 4.1Mhz) between using the current probe (4.1Mhz peak) and the  regular voltage-sensing connections (3.8Mhz peak),
Do you experience this frequency difference between the fuchsia measurement with the voltage-sensing connection on the CSR vs. fuchsia measurement with the  P6021 current probe ?
Also, did you calibrate/normalize the frequency response of the P6021 current probe by shorting the TG and puting the P6021 current probe on that short ?

i want to use the same setup between the 2 measurements (fuchsia and blue), so i want to use the current probe also for the blue measurement.
You could just short the secondary toroidal coil with a wire (or with a trimmer) cap and put the P6021 current probe on that short.  I think this is what your photo shows but I am not sure where the trimmer is in that secondary circuit.
However, it is not necessary to use the same setup for the fuchsia and blue measurements, because the fuchsia measurement is just a relative one that tells us how much the current amplitude in the pancake coils gets attenuated vs. frequency, when the TG drives the primary input circuit with a constant voltage amplitude stimulus. For example, at 3MHz the current's amplitude is only 0.8% of the amplitude at 4.16MHz, despite the TG providing the same voltage stimulus.

Shorting the secondary circuit will allow large currents to flow in the toroidal coil and this current will reflect back to the primary pancake coils via the crosstalk flux and Lenz law.  Thus you will be able to see the secondary current influencing the primary current.
   

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See my EDIT in above post.


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Do you experience this frequency difference between the fuchsia measurement with the voltage-sensing connection on the CSR vs. fuchsia measurement with the  P6021 current probe ?

No, the frequency peak at both those measurements are the same around 4.1Mhz.



Quote
Also, did you calibrate/normalize the frequency response of the P6021 current probe by shorting the TG and puting the P6021 current probe on that short ?

yes, i always (try) to normalize (flatten) the connections before attaching the DUT also in this case.

 
Quote
You could just short the secondary toroidal coil with a wire (or with a trimmer) cap and put the P6021 current probe on that short.  I think this is what your photo shows but I am not sure where the trimmer is in  that circuit.

The trimmer is parallel between the toroidal coil and the blue shorting loop, so i can remove the short, use the trimmer as short and measure the current in one of the toroidal connection leads.
 

Quote
However, this it is not necessary to use the same setup for the fuchsia and blue measurements, because the fuchsia measurement is just a relative one that tells us how much current flows in the pancake coils for a constant voltage amplitude stimulus from the TG vs. frequency.

But but, we did that yesterday, only the problem was that the peaks are not at the same frequency when doing so  (3.8 v 4.1 Mhz).
   

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EDIT:
Concerning the frequency shift, i think the 3.8 to 4.1 Mhz frequency shift is not caused by the
csr / current measurements, but its the other way around, the "regular voltage-sensing connections"
are causing the frequency to shift from its normal 4.1Mhz to 3.8Mhz.
I think so, too. The current measurements are less invasive with coils.
   

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Ok,  using the current probe for both fuchsia as blue,  had to increase the TG level from -20dB to 0dB and set the amplitude from 10dB/div to 6dB/div.

Any use?

Itsu


   

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Is the fuchsia measurement made with the secondary toroidal coil opened ?
I am asking because shorting the secondary circuit allows large currents to flow in the toroidal coil and this current will reflect back to the primary pancake coils via the crosstalk flux and Lenz law.  Thus you can see the secondary current influencing the primary current.

Also, I just noticed that your vertical units are in dBm  ...as in Decibel Milliwatts or Decibel Millivolts ?
   

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Yes,  the fuchsia measurement are made with the secondary toroidal coil opened, see above diagram.

The vertical units are in dBm  as in Decibel Milliwatts.   
Decibel Millivolts would be dBmV with Rigol,  you want that data?



Grounding the toroidal coil like doing in the  "regular voltage-sensing connections"  setup makes the peaks shift from 4.1 to 3.8Mhz.
So i could try to use the csr measurement again, making sure the toroidal coil is grounded during both measurements.

Itsu   

   

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Yes,  the fuchsia measurement are made with the secondary toroidal coil opened, see above diagram.
...but in this diagram, the toroidal coil is shorted through a trimmer cap

The vertical units are in dBm  as in Decibel Milliwatts.   
Decibel Millivolts would be dBmV with Rigol,  you want that data?
Yes, because with dBm the SA could be using a power detector internally and we need an envelope detector (amplitude detector as in AM radio).  There is a square relation between these detectors.

Grounding the toroidal coil like doing in the  "regular voltage-sensing connections"  setup makes the peaks shift from 4.1 to 3.8Mhz.
Most likely because of the ADDED capacitance between the DUT and the lab environment.

So i could try to use the csr measurement again, making sure the toroidal coil is grounded during both measurements.
Not yet
   

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...but in this diagram above the toroidal coil is shorted through a trimmer cap

Yes,  as you mentioned this above in post #186:
Quote
You could just short the secondary toroidal coil with a wire (or with a trimmer) cap and put the P6021 current probe on that short.

You want no trimmer cap too?


Quote
Yes, because with dBm the SA could be using a power detector and we need an envelope detector (amplitude detector as in AM radio).

Ok,  making some new measurements without the secondary shorted by anything and in dBmV


Below some measurements in dBmV, but still with the trimmer cap as short on the secondary.


   

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Yes,  as you mentioned this above in post #186:
Quote
You could just short the secondary toroidal coil with a wire (or with a trimmer) cap and put the P6021 current probe on that short.
That was in reference to the blue measurement only.

You want no trimmer cap too?
Correct. I want the secondary toroidal coil to be completely open when making the fuchsia measurement, so there is as little as possible reflected signal back to the primary pancake coils.
   

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Ok,  new measurements, fuchsia with open toroidal coil, blue with trimmer cap short on toroidal coil both in dBmV:

Itsu
   

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OK so scaling the blue measurement by the inverse of fuchsia measurement, yields this plot of Crosstalk factor vs. Frequency attached below.

As you can see, this time the measurements are made well and the influence of LC circuit's frequency response at the primary winding (pancakes) is cancelled completely (i.e. no peaks around 4MHz).
Up to 2.5MHz the crosstalk is much smaller than at higher frequencies, which suggests capacitive coupling.
From 6MHz to 7.5MHz the slight downward slope could be taken for inductive coupling but I think this is caused by the intrawinding capacitance of the pancake coils stealing current from their windings at higher frequencies (IOW: current flowing between the windings, instead through the windings).  If it was not for the frequency selectivity of the secondary LC circuit, I would expect this downward trend to continue.
The large peak at 8.5MHz is most likely an artifact of the frequency selectivity of the secondary LC circuit, which "amplifies" the crosstalk.  This should be verified by watching the smaller 8.5MHz peak during the same blue measurement in real time while tweaking the trimmer cap connected to the secondary toroidal coil.

IMO the remedy for the undesirable coupling is the E-field symmetrization of the system like Smudge has suggested originally. Also, I would suggest grounded electric shielding*, which does not attenuate HF H-fields strongly. This shielding should be placed between the pancake coils and the toroidal coil (or just wrapped around the toroidal coil).  Last, but not least, the H-field symmetrization of all coils and liberal use of Litz wire in their construction, per my earlier suggestions, will also minimize the I/O crosstalk and increase the quality of the signals.

* Such shelding is regularly used even in low-frequency power transformers and shielded loop antennas. See here and  here
« Last Edit: 2020-07-08, 01:42:59 by verpies »
   

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Thanks,   i am glad the data was OK and you could make this great analysis.


For the large peak at 8.5MHz, i think i remember that the 100pF output trimmer cap had no influence on it, only on the 4Mhz peak, but i will do some tests to verify.

So to go forward, a few things should be addressed first like:

# Perfecting the symmetry of the system (pancake coils v totoidal coil v magnets).
# electric shielding by using grounded Litz cloth between pancakes and toroidal coil.
# the use of Litz wire in ALL 3 coils.
# fixing the system so it can not vibrate ultrasonically.

your earlier suggestions i think are here:

https://www.overunityresearch.com/index.php?topic=3924.msg82795#msg82795

Quote
Depending on the results, we can deal with it differently.
For example capacitive interaction can be shielded with grounded Litz cloth, which does not affect HF magnetic fields (yes, capacitive coupling also falls off with the k of the dielectric and with distance, but distance has other detrimental effects on the entire system).
Undesirable inductive coupling can be managed by controlling the field geometries more precisely (e.g. cancelling longitudinal currents and generally "squaring" the fields).
For acoustic coupling, preventing the coils from touching each other or transferring ultrasonic vibrations through solid objects its usually enough (copper to air to copper ultrasound transmission is very inefficient)

Regards Itsu
« Last Edit: 2020-07-07, 15:18:12 by Itsu »
   

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Ok,  will be ordering some stuff.

Besides the checkout on the 8.5Mhz peak, i want to check why the toroidal coil with parallel 100pF cap produced a flat response during a 0 to 60Mhz sweep.
https://www.overunityresearch.com/index.php?topic=3924.msg82872#msg82872

I would expect to see a dip around 4Mhz as the coil measures 31uH.



Also what would be a good balun for this setup so it gives minimum attenuation and does the unbalans to balans conversion.

Itsu

« Last Edit: 2020-07-07, 15:18:48 by Itsu »
   

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I made this graph from the 9.csv file from yesterday.
I notice some differences between your graphs, can you explain how you modified that data so it gives similar output as yours?

Thanks,  itsu
   
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