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Author Topic: A closer look at a simulated Negative resistance coil.  (Read 58549 times)
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If you've got an LC meter you're in a perfect position to check for the effect on the mu of your ferrite U core by first measuring L of a coil around it, then 'charging' the ferrite like a capacitor through the silvered regions, and then remeasuring the L.
But to do this you really need a closed magnetic circuit.  Any air gap (a single U core has an enormous air gap) and the inductance is not much effected by change of mu in the ferrite.  If you don't have the other U or I core then you need some other material to close the circuit.

Smudge
   
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Hmm, yes, quite right Smudge.

orthofield


But to do this you really need a closed magnetic circuit.  Any air gap (a single U core has an enormous air gap) and the inductance is not much effected by change of mu in the ferrite.  If you don't have the other U or I core then you need some other material to close the circuit.

Smudge
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Peter,

I did mean 50 ohms across the output and your scope shot 95 looks better than the others, the output is more pulse like.  With a quick eyeball, taking the 50% point on the output, it looks like you have about a 1.5 uS delay there.  With such a small number of segments those waveforms don't surprise me, I am sure you would get better pulse shape with more.

Your 750KHz phase measurement indicates a full wavelength shift of 1.33 uS that agrees with that 1.5 uS eyeball.  At half that frequency you should see your output waveform inverted, a 180 degree phase shift.  When you realize that you then have a transformer that is still working as a transformer (albeit a poor one) but the flux is not continuous around the core you know you are doing something the text books would say is impossible.

For the bucking coils work we want a 90 degree phase shift, so maybe you could do a quick look-see at the bucking arrangement using a frequency of 187.5KHz and see what happens.

Smudge
   
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Ortho,

If I may make a suggestion, when you click the Quote" button you get the message ready for you to type your reply. You then seem to delete part of the message that includes the httm quote signal (the word "quote" in square brackets) that the mark up language uses to recognize the quotation  You leave the [/quote] that signals the end of the quotation.  This probably comes about because you type your reply at the beginning of the quote and that knocks off the httm marker.  Try typing your message after the [/quote] marker.

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Buy me some coffee
This is with no 80 Ohm termination resistor.
so we have 4 shots 0 Degrees @ 757KHz, 270 Degrees @ 509KHz, 180 Degrees @ 314KHz ish and 90 Degrees @ 102.5KHz which is quiet hard to get as the phase moves quiet fast around here with small change in frequency.

PS before your first post today, i captured all the data from 100KHz to 1MHz with this delay setup. i will post the data as i process it below and add a zip file with all the scope shots some 80 odd shots

So does my first & last cap need to be half my other caps, so 100nF for the 1st & 2nd and 220nf for the rest

OK added bucking delayed zip which holds all the snaps with the delay line config.

OK now added data
« Last Edit: 2015-03-22, 20:55:55 by Peterae »
   
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Peter,

With regard to the first and last caps they should be half the value of the others but with such a crude delay line you will probably find it makes little difference.  Will respond later when I have looked at your latest bucking data.

Smudge
   
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Here are your bucking coil results plus the LCR-R (loss R) result from your previous work without the delay.  There is no sign of the expected dip in the loss unless it occurs at a lower frequency.  It might be worth going somewhat lower to see but I suspect that both loss R curves will tend to meet the zero frequency axis at the same point.  I was expecting a clear dip in loss R (but not going negative at this stage, that would be too much to expect).

Smudge
   
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Hi Smudge,

Thanks for the tip. Ion mentioned this to me before but I didn't quite get it, and continued to delete the tag.

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Hi Smudge
Well it's good we are doing the practical stuff, so whats my next move.

Could it make a difference if the delay coils are wound in the opposite direction to the bucking coils direction, i have not checked but maybe my bucking coils are clockwise and the delay coils are anti clockwise.

Maybe i need to make a better delay with more turns.

I wonder if we should try a higher value load maybe 500 Ohm.
« Last Edit: 2015-03-23, 20:27:39 by Peterae »
   
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Hi Smudge
Well it's good we are doing the practical stuff, so whats my next move.

Could it make a difference if the delay coils are wound in the opposite direction to the bucking coils direction, i have not checked but maybe my bucking coils are clockwise and the delay coils are anti clockwise.

Well your bucking coils are wound (or connected) in opposite chirality so you can't claim them to both be clockwise.  Changing the winding direction of the delay coils will not have any effect.  Well it would have an effect if the top half were reversed and not the bottom half, you might care to try this but I think it will screw everything up.

Quote
Maybe i need to make a better delay with more turns.

I wouldn't try to go for greater delay (more turns between capacitors) but I would look at say using two turns per section and reducing the capacitance values by a factor of four.  That should keep the time delay the same.  Maybe better still is to increase the number of sections so double the total number of turns, keep to one capacitor per turn but use lower capacitor values so that the total capacitance (the sum of all) remains the same.  This might give you a better delay line with less dispersion.

Quote
I wonder if we should try a higher value load maybe 500 Ohm.

I don't think this will help since the loss R (your LCR-R) won't change and that is what I am concentrating on.

If this bucking thingy doesn't lead anywhere take pride in the fact that you are probably the only person in the world looking at a transformer with deliberate magnetic domain time delay between primary and secondary  O0 .  And there is more to do looking into the possibility that in a (non bucking) transformer of this type a reactive load like a capacitor can reflect as a negative resistance at the input.  You are now expert at measuring input resistance over a wide frequency range  8).

Smudge
   
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