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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 126908 times)
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Re: Smudge proposed NMR experiment replication. « Reply #700 on: 2021-01-26, 20:30:43 »
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Hi Itsu,

Okay, thanks. I have found and will read the user manual for the LCR meter later on, just for curiosity.

Normally the higher than some ten kOhm RF impedances mean the upper limit of measurement ranges for such meters, only the high-end instruments may be able to measure say up to 100-120 kOhm like the good old HP4193A, this works up to 110 MHz.   (I did not study the latest  vector impedance meters though.)
Your little VNA surely has its own upper range limits too.

The 1st screenshot above for the yellow probe shows amplitude and phase relations comparable to that of the 690 kOhm resistor. 
Here is an impedance calculator for parallel RC network https://keisan.casio.com/exec/system/1258032649  and it gives Z = 9.55 kOhm absolute value for your probe (10MOhm/3.9pF) used as a load at 4.27 MHz frequency (phase angle is -89.945 degree).

Gyula
   
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Re: Smudge proposed NMR experiment replication. « Reply #701 on: 2021-01-26, 21:40:09 »

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Hi Gyula,

interesting this calculator, i would have thought that the impedance would be on top of the resistance, but it decreases from 10MOhm to 9.5KOhm.

So when paralleling the 10MOhm probe and the 690K resistor, it results to a 645.5K resistor and the 690K resistor adds about 4pF to the capacitance (according to my LCR meter), totaling to about 8pF.

This results according to your calculator into (645.5K / 8pF @ 4.25MHz) a Z=4.7K @ -89.5°

Itsu
   
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Re: Smudge proposed NMR experiment replication. « Reply #702 on: 2021-01-26, 23:10:46 »
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Yes.  And add to this that we do not know the equivalent circuit values of the 690 k resistor itself which also influence the 690 k value at the 4.25 MHz frequency.  I mean the Z=4.7 k you just wrote should be "something else".  This is because you have got the measured data (the phase angle, current and voltage) involving the 690 k, and Smudge calculated the "something else" value as Z= 6.9 kOhm but he used an 'eyeballed' 90 degree phase shift from your scopeshot.
Here is the behaviour of thick film chip resistors in the function of frequency (size 1608):  https://www.quora.com/What-are-the-characteristics-of-a-5k-resistor 
The frequency dependence of metal film types like the 690 k you happen to use is much worse than the flat chip resistors.

Gyula
   
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Re: Smudge proposed NMR experiment replication. « Reply #703 on: 2021-01-27, 09:29:21 »

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Gyula,

well, if i now use my found 4.7K impedance on the P=U²/R * COS Phi, then i get:
11.8²/4.7 * -89.5 = 2.5mW which is very close to the scopes calculated 2.4mW in post #688.

Problem solved or is this coincidence?

By the way, my used 690K resistor is a carbon ¼W type.

Itsu
   
« Last Edit: 2021-01-27, 10:15:31 by Itsu »
   
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Re: Smudge proposed NMR experiment replication. « Reply #704 on: 2021-01-27, 11:18:15 »
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Okay Itsu, the problem is solved I think.  The P=U²/R * cos(Phi) formula is an Ohm's Law variaton of the P=U*I*cos(Phi)  formula so it can be used too. 

Edit: Carbon resistor: okay, then it may indeed have the 600+ kOhm resistance and the scope probe capacitance shunts it at the 4.25 MHz frequency.

Gyula
   
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Re: Smudge proposed NMR experiment replication. « Reply #705 on: 2021-01-27, 21:29:03 »

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Using the diagram below, i am trying to put as many power into the paralleled coils, but allthought the amplifier when running on a 50 Ohm dummy load puts in about 6 Watts @ 4.25MHz, when connecting to the paralleled coils, i measure no more then about 200mW going in.

Both the input and output trimmers are set approx. half way causing a peak in output power (a sort of resonance at 4.25MHz), but there still must be a form of mismatch.

Using a balun between amp. and step up cap (10nF) makes little difference.

Looking for the correct method of inputting more power into the paralleled coils.

Itsu
   
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Re: Smudge proposed NMR experiment replication. « Reply #706 on: 2021-01-27, 23:14:07 »
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Hi Itsu,

Would like to ask the DC resistance of the pancake coils measured between points A and B, see attached schema.
In a video you mention about 4 uH for the pancake coils, do you mean it across points A and B ?  Were the magnets and the ground wire on the top present when you measured the 4 uH?
Please also tell the inductance of the output coil, you may have included it already but I missed it.  You need to disconnect the capacitors that are now present, for inductance measurements of course.

The capacitive divider could match the pancake coils but it is hard to find the correct ratio.   Perhaps first you could use a negative resistance oscillator between points A and B and connect a tuning capacitor also across points A and B which would resonate and oscillate the two pancakes around the 4. 25 MHz frequency.  And when this cap value is known then the members of capacitive divider could be figured out perhaps more easily.
For a negative oscillator I refer to an earlier circuit of last year where an n- and a p-channel JFET or an n-channel JFET and a pnp transistor is combined into the two terminal device (Lambda diode), you surely recall it.  When such device oscillates your full circuit between points A and B, you can measure and tune it to around 4.25 MHz.

Added:  a few uH  variable coil could be used between the hot output of the amplifier and the center point of the capacitive divider, this would increase the impedance which is now between the center point and point B, I mention this because I believe the 10 nF loads down the amplifier output excessively.  Or you could reduce the 10 nF to say 2.2 nF or 3.3 nF etc.

Gyula
   
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Re: Smudge proposed NMR experiment replication. « Reply #707 on: 2021-01-28, 10:08:01 »

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Hi Gyula,

remember, the coils on the drawing are shown in series, but they presently are in parallel (bucking).


Below is measured with the magnets, the ground wire on the top and tube/output coil present, no caps:

The DC resistance of the pancake coils measured between points A and B is 0.4 Ohm.
The inductance of the pancake coils measured between points A and B is 4.64uH
The DC resistance of the tube/output coil is 0.4 Ohm
The inductance of the tube/output coil is 10.8uH

I do remember the negative resistance oscillator, i will look it up and see i can build one.
EDIT:  found the link (private thread) here: https://www.overunityresearch.com/index.php?topic=3910.msg81273#msg81273
         in there there is this link to a negative resistance webpage: http://www.zen22142.zen.co.uk/Theory/neg_resistance/negres.htm


I also will try out lowering the 10nF and/or adding a "few uH  variable coil".

As i understand it from verpies/Smudge, the goal now is not to get the pancake coils radiate, but only to have the H-fields penetrate the water inside the tube to get the protons resonate which then is being picked up by the tube/output coil.

Thanks,   itsu 
« Last Edit: 2021-01-28, 10:57:53 by Itsu »
   
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Re: Smudge proposed NMR experiment replication. « Reply #708 on: 2021-01-28, 12:01:04 »
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Hi Itsu,

Thanks for the details.  I modified the schematic to show the paralleled pancake coils, is that correctly drawn now? So the 4.64 uH refers to the paralelled pancakes, right?   

For capacitive divider, try to reduce the 10 nF to as low as say 820 pF as a start and find resonance by peaking the trimmer cap.  Roughly a 300 pF tuning cap would be needed across the paralelled coils and this 300 pF should come from the two seriesly connected capacitors in the divider. 
I return later on.

Gyula
   
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Re: Smudge proposed NMR experiment replication. « Reply #709 on: 2021-01-28, 12:17:34 »

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Gyula,

 
Quote
I modified the schematic to show the paralleled pancake coils, is that correctly drawn now? So the 4.64 uH refers to the paralelled pancakes, right?   


Thats correctly drawn, and yes, the 4.64 uH refers to the paralelled pancakes.   O0


Itsu
   
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Re: Smudge proposed NMR experiment replication. « Reply #710 on: 2021-01-28, 19:40:04 »
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Hi Itsu,

Here are some capacitor value pairs in pF for the divider as a guide (but this maybe late for you):
820:480  1000:440  1500:380  2200:350  3300:340,   higher values within a pair mean the bottom cap values like the 10 nF shown in the drawing.
Any pair of these give a 300 - 305 pF resultant tuning cap for the paralleled coils to resonate around 4.25 MHz.

You found 6W power output from the amplifier directly in a 50 Ohm dummy load: this then means 17.3 V RMS (48.8 V peak to peak) across the 50 Ohm resistor.
So if you monitor the RF amplitude across the paralleled coils by a HV scope probe, the amplitude should be much higher than this when the trimmer is tuned to resonate the coils), depending on the ratio of the capacitors in the divider. And how much of this can couple to the output coil is another question of course.
So the goal would be to achieve as high voltage amplitude across the paralleled coils as possible (even 15x 20x 30x higher than what comes out from the amplifier when driving the cap divider input) at resonance. It will not be close to the 5-6W but perhaps would approach that. 

Gyula
   
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Re: Smudge proposed NMR experiment replication. « Reply #711 on: 2021-01-28, 19:44:56 »

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Hi Gyula,

thanks for the info,  i have put together a divider with a 120->370pF variable cap and a fixed 2.2nF smd, so it will be close to your 2200:350 one.

Will see how that works out.

Itsu
   
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Re: Smudge proposed NMR experiment replication. « Reply #712 on: 2021-01-28, 21:01:49 »

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Some input measurements with the new input matching circuit, see diagram.

Tuned to resonance on 4.25MHz which means almost all capacitance (trimmers) used.

Screenshot shows the input signals (voltage yellow, current green and power red) coming from the PA.

Video with the new setup and measurements here (also with voltage probe on pancake coils):  https://youtu.be/V8L6-ujsZ7k           
 

Itsu
   
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Re: Smudge proposed NMR experiment replication. « Reply #713 on: 2021-01-28, 21:22:05 »
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This is a progress for sure and perhaps testing the 3300pF : 340 pF cap ratio would show the tendency to go either higher or lower ratios. Just put some nF capacitor, one at a time, across the 2.2 nF chip cap and reduce one of trimmer caps little by little while watching either the calculated power on the scope where you have now the 4W or watch the increase on the power meter which showed the 1.5W.  I think you will need to increase the nF values (and slightly reduce the trimmer caps value) to increase the power towards the 6W which is possible with the dummy load. 

Addition:
I think you can trust much better in your scope measurements than in your power (and swr meter) regarding the power levels (4W vs 1.5W).
Have you happened to check the power+swr meter versus the scope power measurement when the 50 Ohm dummy load was used? I mean whether the power meter when showed the 6W, what the scope RMS voltage was across the 50 Ohm?
Regarding the swr meter, it indicates roughly 1.4 in this latest video, what did it show when the dummy load was used? IT should show near 1.0 even if there is no full scale in the forward power direction.

The ratio of the stepped up voltage to the input RF voltage seems to be 2.4 (24V RMS/10 V RMS)  This ratio could surely be increased, meaning this is the direction to go towards better matching.
Here are some more divider cap values to choose from: 4700pF : 330pF   5600pF : 320pF    6800pF : 320pF    8200pF : 315pF     10nF : 313pF     15nF : 310   These latter values may seem extreem but perhaps if you see an increasing voltage step up ratio it should go together with input power increase too, measured at the capacitor center tap input. So the 6W power may be better approached: question is whether this 4W power that you have now is enough for the effect or not yet.

Thanks,
Gyula
« Last Edit: 2021-01-28, 23:41:29 by gyula »
   
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Re: Smudge proposed NMR experiment replication. « Reply #714 on: 2021-01-29, 09:23:18 »

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Hi Gyula,


i will add some caps to the 2.2nF one to see how it behaves.

I too think the scope will be a better indicator of the power input then the SWR meter due to the phase shift i see between voltage and current.

I will do some measurements on the SWR meter, problem is to clamp the current probe.
It did show a SWR of 1:1 when using the dummy and the 6W.

The present 70Vpp across the pancake coils with the 4W input is still way of the severall hundred volts Smudge mentioned in his PDF:
"The drive coils will have RF voltage across them that is several hundred volts." 

Regards Itsu
   
img  gyula
Re: Smudge proposed NMR experiment replication. « Reply #715 on: 2021-01-29, 11:36:14 »
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Hi Itsu,

When you terminate the swr meter with the 50 Ohm dummy load, it would be enough to use the voltage probe because the scope will surely measure correctly the RMS voltage across it and then use the formula P=U²/R. This then gives a power level, if it is indeed 6W, then the RMS voltage should be around 17.3 V (48.7 Vpp) across the 50 Ohm. I understand the current probe is a problem to clamp and if the voltage level is close to the calculated one, then no need for the current probe in this case.

Gyula
   
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Re: Smudge proposed NMR experiment replication. « Reply #716 on: 2021-01-29, 14:55:03 »

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Quote from: Itsu on 2021-01-29, 09:23:18

The present 70Vpp across the pancake coils with the 4W input is still way of the severall hundred volts Smudge mentioned in his PDF:
"The drive coils will have RF voltage across them that is several hundred volts." 
When I wrote that I envisioned the two pancake coils to be in series, not in parallel.  So your 70Vpp looks good to me.

Smudge
   
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Re: Smudge proposed NMR experiment replication. « Reply #717 on: 2021-01-29, 15:32:21 »

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I managed to clamp the current probe around the dummy load center lead.
When Amp. set to 15V (1A) it generates 6W on the SWR meter at a 1:1 SWR (dummy measures 51 Ohm).

Screenshot shows in yellow the voltage across the 51 Ohm (19.49V rms), in green the current through it (354mA rms) and in red the power consumed by it (6.89W).

P=U²/R with this data gives 7.4W.

Video here: https://youtu.be/J9T3DY0usKQ

Regards Itsu 
   
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Re: Smudge proposed NMR experiment replication. « Reply #718 on: 2021-01-29, 15:36:27 »

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Quote from: Smudge on 2021-01-29, 14:55:03
When I wrote that I envisioned the two pancake coils to be in series, not in parallel.  So your 70Vpp looks good to me.

Smudge

Hi Smudge,   ok,  yes of course, so we are set to go already.

I will try to maximize the input matching circuit as outlined by Gyula, then go hunting for anomalies.

Itsu
   
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Re: Smudge proposed NMR experiment replication. « Reply #719 on: 2021-01-30, 09:46:19 »
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Hi Itsu,

Okay on the wattmeter calibration check, so it shows a lower watt value than reality around this 4 MHz frequency. Such power + swr meters are good enough but one cannot expect much precision from them and the better power meters are more expensive. Thanks for doing and showing these tests.

Gyula
   
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Re: Smudge proposed NMR experiment replication. « Reply #720 on: 2021-01-30, 20:30:22 »

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I made some measurements while varying the input caps ratio.

                                                                                                                 input matching circuit
trimmer caps (pF)        fixed cap (nF)            Pancake voltage (Vpp)                     V rms              Vpp                   SWR meter (W)
      120/370                      1.1                               89                                       15                48                             3.5
      120/370                      2.2                             106                                         9.5              27                             1.4
      120/370                      3.3                               70                                         5.5              16                             0.4

The trimmer caps settings for max. pancake coil voltage are not similar as for max. input voltage!!

The trimmer caps are adjusted anywhere inbetween their ranges, no specific measurements done.

So it looks like that the initial used 2.2nF cap was the optimum one if looking at the pancake coil voltage (106V), see screenshot 1.

The screenshot 2 is from the same setup (2.2nF) but with signals on the SMA input connector, yellow voltage, green current and red power (seems somewhat high).

Itsu
   
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Re: Smudge proposed NMR experiment replication. « Reply #721 on: 2021-01-30, 21:47:20 »
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Hi Itsu,

It turns out now that your picking the 2.2 nF capacitor value (instead of the 10 nF) was a lucky one. It is likely that if the 2.2 nF were variable, say +/- 300 pF or so around the 2.2 nF then such fine tuning would give a few more peak to peak volts but this is not really needed.  Smudge wrote that the 70 Vpp already looked good and now you have 106 Vpp. 
Regarding the values of the trimmer capacitors, they are not important to measure because at the 2.2 nF capacitor at the bottom the trimmers must have about 350 pF together to arrive at the 302 pF resonating value for the paralleled coils. 

Regarding your observation that the max pancake coil voltage does not coincide with the maximum input voltage (I express your sentence differently but I think this is what you meant?), it may be caused by the following:
I think that under the 2.2 nF fixed capacitor values the stepped down resonant impedances are getting higher than 50 Ohm hence manifesting lighter loads (hence higher voltages) and above the 2.2 nF fixed cap values the stepped down impedances are getting below 50 Ohm hence manifesting heavier loads (hence lower voltages) for the power amp output.
Putting this otherwise: the power amp is the generator and loading it below or above its own output impedance its output voltage changes with respect to the power matched case (when it has half of the voltage compared to its unloaded output voltage).

Thanks for all your kind efforts.

Gyula
   
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Re: Smudge proposed NMR experiment replication. « Reply #722 on: 2021-01-31, 10:24:29 »

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Gyula,

Quote
It turns out now that your picking the 2.2 nF capacitor value (instead of the 10 nF) was a lucky one.

the picking of the 2.2nF cap was not just luck, i happen to have some of these 2.2nF SMD multi layer ceramic caps which are i think excellent for these kind of applications.

Quote
Regarding your observation that the max pancake coil voltage does not coincide with the maximum input voltage (I express your sentence differently but I think this is what you meant?)

Not sure if that is expressed correctly, as i wanted to say that in one setup situation, like the 2.2nF setup, the tuning of the caps for max. input on the sma connector is different as for tuning the max input on the pancake coils.
I don't think it changes the load on the PA when moving the voltage probe from one point to the other.

Anyway, i guess i will do some slow sweeping across a frequency range say 4 to 4.5Mhz,watch the output 690K resistor output for anomalies while slowly tuning step for step the input caps.

Thanks,   Itsu 
   
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Re: Smudge proposed NMR experiment replication. « Reply #723 on: 2021-01-31, 12:17:42 »
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Hi Itsu,

On the 'lucky pick' of the 2.2 nF I meant you did not choose say 1.5 nF or 2.7 nF even if you had had several capacitor values.   
The latter values would have given less amplitudes across the pancakes versus the 2.2 nF as you found out in your tests with the 1.1 or 3.3 nF caps.   

You wrote earlier:
"The trimmer caps settings for max. pancake coil voltage are not similar as for max. input voltage!!"

You explained it too:
"... I wanted to say that in one setup situation, like the 2.2nF setup, the tuning of the caps for max. input on the sma connector is different as for tuning the max input on the pancake coils."

Sorry if I did not express it correctly.  I think the explanation for your findings is that the trimmer capacitor(s) not only vary the input impedance of the divider (which loads the PA output) but tunes the resonant frequency of the overall pancake tank at the same time. This then involves the differing voltage amplitudes manifesting across the input of the divider (i.e. across the 2.2nF) versus the maximum voltage possible at resonance across the tank.

You also wrote:
"I don't think it changes the load on the PA when moving the voltage probe from one point to the other."

I agree: the placement of the voltage probe cannot cause any change,  its own 4-5 pF is negligible versus either the 2.2 nF or the resulting 302 pF tank capacitor value.  The load on the PA changes whenever the trimmer capacitor(s) are varied. 

Is this okay now?  8) 

Thanks,
Gyula
   
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Re: Smudge proposed NMR experiment replication. « Reply #724 on: 2021-01-31, 12:48:23 »

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Gyula,


Quote
I think the explanation for your findings is that the trimmer capacitor(s) not only vary the input impedance of the divider (which loads the PA output) but tunes the resonant frequency of the overall pancake tank at the same time.
This then involves the differing voltage amplitudes manifesting across the input of the divider (i.e. across the 2.2nF) versus the maximum voltage possible at resonance across the tank.

Right, so aming for max. voltage across the pancakes (tuning for resonance) will be the goal, despite it will cause a slight impedance mismatch on the PA.

Okay  O0

Itsu
 
   
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