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2022-01-20, 02:57:28
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Author Topic: Smudge proposed NMR experiment replication.  (Read 47150 times)

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Hi Itsu,

That is 10 x  voltage gain at the output, very nice and it was a good idea from verpies to bring up the use of CMCs.

I wonder whether you had to readjust the trimmer capacitor to peak it around the 3.8 MHz or you did not need to do that?

Thanks for your efforts.
Gyula

Gyula,

no, no adjustment was needed.

I will make another one with the black ferrite to see how that behaves.

Itsu
   

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Ooops,  it seems i was on a false peak after adding the cmc.

I did had to retune the output cap, even so that it now has a stronger output of 92Vpp then without the cmc  :(
See screenshot sweeping from 3.5 to 4.5MHz now

Itsu

   
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Oh, okay. 

You may wish to make the CMC even more balanced by moving the turns of one of the windings on the core just a little while watching the inductance on an L meter and achieve the minimum inductance possible ( say some 10 nH ), see the attached photo I edited.   IT does not matter which side of the CMC you short circuit the wires and measure on the other side.
This way the CMC will have the smalles detuning effect on the output coil. 
Of course, this is may need to secure the windings so that the turns should not move after the fine adjustments and you put the CMC back into the circuit.   

But I think the CMC is already good enough.   O0

Gyula
   

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Then after giving white noise to coil from foil I looked on peaks in spectrum analizer for possible points where material of ferrite did resonate - https://www.youtube.com/watch?v=kGGCG2i8u8U
Hopefully this approach would be useful to you as well when looking for material resonant frequencies.
Yes, this one of the methods of stimulating the material. All of the being:
1) CW
2) FM
3) Nanopulses
4) Noise
   

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You may wish to make the CMC even more balanced by moving the turns of one of the windings on the core just a little while watching the inductance on an L meter and achieve the minimum inductance possible ( say some 10 nH ), see the attached photo I edited. 
Yes, this is a good test to maximize the effectiveness of the CMC and to make sure that the windings are not wound in the wrong direction (it is the easiest mistake to make, while constructing a CMC).
   

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The white cmc (measured 268 and 272uH) gives a resulting 2.15uH when added see pic. 1.
The black cmc (measured 232 and 228uH) gives a resulting 2.02uH when added see pic. 2.

Squeezing together and/or spreading the turns makes very little difference (10nH or so).

So i guess they are wound in the correct way.

The question might be if they are suitable for the used frequency.


The screesnhots show the nanoVNA sweep (10KHz - 10MHz) in this shorted condition and confirm the resulting 2.xxuF inductances.


Itsu
   
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Hi Itsu,

Thanks for the CMC measurements. Your output coil has 10.8 uH inductance as you wrote and the 2 or 2.1 uH resultant inductance of the CMC adds to that, this is why the output trimmer needs to be retuned. This small inductance increase for the output coil does not seem to cause any problem, what is more, by retuning the circuit it gave higher output voltage as you found. 

May I notice that the inductance difference between the two coils within the same core sounds rather high, i.e. 268 uH vs 272 uH. This difference can only be reduced if a quarter or a half turn is removed from the 272 uH coil or adding similarly that amount to the 268 uH coil, to have them very close to each other, within say 0.5 uH. Then the 2 - 2.1 uH measured differences will be much smaller.
But please deal with such nuances only if you feel like to, the turns should be fixed mechanically in the end, after the windings trimming, otherwise any small bending of the wire ends may change the full windings inductance on that side.

The 3E25 core material for the white core is not favorable for the 4 MHz range, above some hundred kHz it gradually becomes lossy and the initial permeability of 6000 reduces to a very low value.
I do not know the material for your black core.
Question is how these specs may influence the goal with this setup, if negligibly, then no need to further bother with the CMCs and they are already good enough.

Gyula
   

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I tried to match the black cmc coils to be equal, by adding about 1/8th of a turn to the lowest valued one, but even when within 1uH, the short test keep showing 2uH which might indicate the limit for my LCR meter.

They now both measure 231uH, and i have superglued the ends, so when enough dried i will see what the output does with this black cmc.

My expectations would be to have a lower output signal with the cmc in place then without but the last test with the white cmc did not meet that expectation.
Is my expectation wrong?
 
Itsu
   
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I think the first thing now would be to find an answer on why the 10x gain in voltage amplitude has come about what you reported in your reply #773?
Maybe the output trimmer tuning got somehow off-tuned and then after the CNC insertion you returned and got 10x as many voltage.


   

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Gyula,

i see what you mean now with "10x gain in voltage.....etc." and what is causing my confusion.

I screwed up again in that reply #773, as the 2th sentence should read:

Screenshot 1 shows the difference in output signal with (purple) and without (white) cmc for a 3.5 to 4.2MHz sweep.
                                                                         ^^^                    ^^^^^
Sorry about that.

So when adding the cmc, the signal was 10x smaller due to the fact that the output resonance point had shifted way lower in freqeuncy and we were left with the 10 lower input resonance peak only.

Lateron i retuned the output circuit so the 2 resonance points are combined again resulting in a small increase in total amplitude over the without cmc situation.

Itsu
   
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Okay Itsu, I understand, thanks for explaining.

Would be interesting to see how the black CMC would behave at the output now that you trimmed both windings on it to 231 uH. (By the way, is the type of the black core known?)

And regardless of that, would you connect the white cored CMC to the input of the pancake coils? (try to trim the windings on it also closer to each other if possible).
This way all the 3 coils assembly would become a balanced, quasi fully ground independent circuit.  (Even though the CMC core(s) may not function correctly around 4 MHz.)

Thanks for your kind efforts.

Gyula
   

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May I notice that the inductance difference between the two coils within the same core sounds rather high, i.e. 268 uH vs 272 uH.
Me thinks that hundreds of µH for a shorted CMC is too high.
What is the inductance of one winding (q.g. the green one) of the CMC while the other winding is open (e.g. the red one) ?
   
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Hi Verpies,

Yes, that would be too high. But he wrote this:

The white cmc (measured 268 and 272uH) gives a resulting 2.15uH when added see pic. 1.
The black cmc (measured 232 and 228uH) gives a resulting 2.02uH when added see pic. 2.


And he showed the inductance for the shorted coils as around 2 uH, see the pictures in Reply  780 above.

EDIT:  Sorry I misunderstood you. Itsu measured the individual windings while the other winding in the same core was open. The results are what I quoted from him in italics.

Gyula
 
   

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Gyula, verpies,

The black toroid  make is unknown.

After some trimming, the white cmc is now very equal too (265 / 265 uH)

And yes, white cmc has 265 / 265 uH measured when its opposite coil was open.
             black cmc has 231 / 231 uH measured when its opposite coil was open.

 
I installed both cmc's now, the white at the input, the black at the output, see picture.
I found both resonance points and combined them close to 4MHz, see screenshot.

We now have a peak of 30V or so, so much less then the 91V with only the white cmc on the output.

itsu
   
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Dear Itsu,

In post 773, you edited the mistake and it says now that
       Screenshot 1 shows the difference in output signal with (purple) and without (white) cmc for a 3.5 to 4.2MHz sweep.


and the amplitude of the white waveform was 80.4 Vpp  without the white CMC.

Now you wrote:

...

We now have a peak of 30V or so, so much less then the 91V with only the white cmc on the output.


I think you may have meant "...so much less then the 91V without the white cmc on the output."  ?

Anyway,  Would you mind removing the white CMC and use only the black one at the output?
This is to check whether the black core CMC performs similarly bad as the white one at the output.

One more test would be good to see: I think you have some Amidon RF toroids with at least 2 cm OD or higher which nicely work around 4 MHz and make a CMC for the output from such core. These cores has much less permeability though, this means that very likely at least 20 turns are needed to get say at least 30-40 uH for each winding, perhaps that would be good enough for a CMC.

Thanks for your kind efforts. 

Gyula



   

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Hi Gyula,

well, things get confusing now, i agree.


To reiterate:

post  #773   without white cmc (white trace)  80.4V  @  3.5 to 4.2MHz
                  with     white cmc (purple trace) 10.8V  @  3.5 to 4.2MHz  => but output circuit OFF tune now!!

   
post #776    ooops, corrected the output circuit tuning, now:
                  with    white cmc (purple trace) 91.6V  @  3.5 to 4.5MHz
                                                                                    ^^^^^^


post #788    white and black cmc trimmed each to be equal value (white 265/265uH, black 231/231uH)
                  Both cmc's installed, black on output circuit, white on input circuit.
                  Both circuits tuned to max. at around 4Mhz.
                  We now have a peak of 30.5V, so much less then the 91.6V with only the white cmc on the output see post #776


Now, when doing a slow sweep (20s) with the both cmc's installed, something got smelly and it turns out to be the input white cmc which gets hot.
I reduced the sweep time to 10s and now its acceptable to 29°C at the resonance peak.
As can be seen in the above picture, the white input cmc is very close to the magnets which probably have a huge influence (saturation) on it, but not sure thats the reason for the heating up.


I will remove the white input cmc now, retune and see what the peak value is then.....

Looking for the Amidon Rf toroids too   O0


Itsu
   

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I removed the white input cmc (only black output cmc installed),  and retuned the both circuits to max peak @ 4MHz:

           with    Black cmc (purple trace) 54.8V  @  3.5 to 4.5MHz



SO:

without cmc, tuned to max. at 4MHz:                                           80.4V
with white output cmc, tuned to max. at 4MHz:                              91.6V
with black output cmc, tuned to max. at 4MHz:                              54.8V
with black output cmc, AND white input cmc tuned to max. at 4MHz: 30.5V  (white cmc gets hot).

 
Found a T106-2 Amidon toroid.


Itsu
   
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Okay Itsu, now you cleared the issue, I disregarded your post # 776, unfortunately.

It is sure also that the white core has losses at RF frequencies like 4 MHz, it is made for 300 kHz or less as its data sheet includes. Its closeness to the magnets may also influence the loss but basically the core material is to blame.  The few watts output at the PA driving the white core already heats it up.

Thanks for the test on the black core CMC, it is surely a low frequency core too, seems to be worse than the white core.

The T106-2 has an AL of 135, it would mean 400*135= 54 uH from 20 turns for each winding.  Hopefully 25-30 turns may fit on for each half side.  IT is a good RF core. 

Gyula
   

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OK,  great, i will see how many turns i can get onto it.

Itsu
   
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OK,  great, i will see how many turns i can get onto it.

Itsu

Sorry Itsu but I considered first this page for the AL  http://www.amidoncorp.com/t106-2/  where AL  is 135 but it needs to be divided by 10 if I use AL =135  so 20 turns gives only
5.4 uH, unfortunately.   40 turns gives 21.6 uH   using this calculator here:  https://toroids.info/T106-2.php     The suffix-2 in the T106-2 means permeability of 10 for that material.
So perhaps a higher permeability RF core would be better...   
   

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Ok,  no problem,  so a T200-2 won't be any better, what about a T225-8?

It says Al=425 only.

Itsu
   
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Well the AL = 425 is wrong it is only 42.5 nH/N2. It means that 20 turns gives 400*42.5=17 uH, 30 turns gives 38 uH and 40 turns gives 68 uH.

My data comes from this data sheet, page 13: https://www.tme.eu/Document/82fc93ef93d05a020041f9203a13131a/MICROMETALS-Tseries.pdf
   

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OK, so looking for a Txxx-6 or so i guess, or do you have a suggestion?

Itsu
   
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Hi Itsu,

First I thought of your core arsenal to use what is already available and I recalled some types.  We need to realize, the RF powdered iron cores have low permeability hence relatively low AL factor, unfortunately.

Do you happen to have ferrite toroids from Amidon like the FT series?   i.e.  FT140-43  https://toroids.info/FT140-43.php   or FT240-43  https://toroids.info/FT240-43.php 
Perhaps Verpies could suggest other types too.

Gyula
   

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Gyula,

I got some FT-3K50TS series toroids that i know of, but i might have more but most are of unknown origin.
Most are coloured, a few black like this hugh T107/65/18 3F4 Ferrite core.

I can order some  FT140-43 / FT240-43 eventually.

Itsu
   
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