Are 2 Pulses better than one

[Peterae]

I wanted to run some tests comparing 1 short pulsed coil compared to 2 short pulses and see what sort of energy i get in an adjacent tuned coil, this should allow me to compare the effective drive energy and the transferred resonant energy in the second coil.

First thing i have noticed is the coil i am using does not calculate out using normal resonant LC calculators, from the below FFT shot and also the scope of the waveform it can be seen i think that the resonant frequency of the tuned coil L2 is much higher.

First off the coil is a flat spiral wound pancake coil, it uses 2 wires wound axially in parallel giving 2 separate coils about the same wire length.

With an inductance meter i measured as follows

L1 = 25.67uH
L2 = 24.72uH

I was looking for an operating frequency of low MHz so decided to use a 220pf capacitor and i measured this at 223pf.

Placing the capacitor across L2 calculated out for a solenoid coil to be resonant at 2.143599Mhz

The inial tests used L1 driven from 1 channel of my pic controller pulsing at the above frequency.
L1 has a fast diode across it and is powered from 25Volts supply

L2 has the 223pf capacitor across it.

Here's the initial test results.

[Peterae]

Next up i wanted to bring the resonant frequency down from the previous test as it was above my Controller Fet Range

Instead of the 223pf Cap i used 2 1n5 caps in parallel

I then located the frequency i had a goodish sine on the tuned coil which i think from indicates resonance.

Here's the results.

[Peterae]

I find it strange that my driver circuit is consuming the same power to drive the primary in both cases but the tuned secondary is a lot less efficient and shows a much smaller amplitude when i bring the resonant frequency down with a larger capacitor in the second test.

Why is this, is it because of more losses or less coupling at a lower tuned resonant frequency?

Really i need to find the best way of transferring the energy to the tuned coil and this would mean i need the largest amplitude waveform, and in this case test 1 was best.

I cannot proceed to the 2 pulse system until i resolve this.
Once i can establish a stable sinewave on the secondary i can then proceed to add a second fast pulse and do a sweep of the phase delay of this second pulse and watch the energy transferred to the secondary, i will also try a much lower drive frequency and then sweep the second pulse, i have always had a theory that a double fast pulse at 10khz can have the same effect as running 1 pulse at the resonant frequency, the difference being that the fet stages are running at a much lower frequency and therefore injecting much less input power to the system, i am aiming at trying to measure this effect.

Maybe i need to change to a bifilar solenoid coil.

[Grumpy]

I remember reading somewhere that tuning down the freq with a large cap is very inefficient.

[Peterae]

Hi G
I seem to remember this also.
Interestingly if you look at the picture of the coil, i have a compass mounted at the outer perimeter of the pancake coil, when this is moved to the inner edge of the coil,and i use 2 phase delayed pulses north always points towards the center, the more current i push into the pulsed coil the more the north gets pulled to point to the middle, so although the second coil is alternating with the tuning cap the primary magnetic field is prominent enough to pull the needle one way, in other words i don't seem to have an alternating mag field i seem to have a dc pulsed field where it's collapse has less effect than it's creation.

[BEP]

Polarities of a planar coil appear a bit off. See my attachment.

May I suggest wrapping a poloidal coil around your planar coil (center to outer diameter). Use bifilar with the end of the pairs joined (shorted together).

Wrap this coil with -only- 10 turns, evenly spaced.

Connect the free ends of this coil in series (electrically) with you planar coil.

Leave one conductor of your planar coil completely open with no caps.

Remove any caps from the layer being pulsed.

Start with a very low frequency (tens of kHz). Watch the spectrum analyzer for a peak rather than the scope.

Cheers!

[Grumpy]

Hi G
I seem to remember this also.
Interestingly if you look at the picture of the coil, i have a compass mounted at the outer perimeter of the pancake coil, when this is moved to the inner edge of the coil,and i use 2 phase delayed pulses north always points towards the center, the more current i push into the pulsed coil the more the north gets pulled to point to the middle, so although the second coil is alternating with the tuning cap the primary magnetic field is prominent enough to pull the needle one way, in other words i don't seem to have an alternating mag field i seem to have a dc pulsed field where it's collapse has less effect than it's creation.

I'll comment on this after MC answers my question.

[muDped]

From the appearance of your scope waveform it looks as if
the "secondary" isn't quite at resonance.  There are slight
discontinuities in the waveshape.

A better way to evaluate the resonant frequency of any LC
combination is to apply an input signal from a VFO and
slowly vary the frequency throughout the expected range
of interest.  When resonance is found the output of the
LC parallel combination will increase dramatically.  Peak
(maximum) output signal will indicate the resonant point.

Then measure the frequency at peak response.

When pulse exciting a resonant circuit it is much easier
to find resonance with a variable frequency pulse generator.
Again, looking for the peak response.

Narrow pulses are best.

[Peterae]

Cheers for the responses guys.

@Dumped
I will try my sine gen on it to look for the best amplitude, i am driving with about a 60nS wide pulse, but i did vary the frequency and found the amplitude best in the above picture.

@WW
Sounds like an interesting experiment, i'm away from work for a couple of days, when i go back to it, i will try what you suggest.

Thank you for the picture of the field, this is pretty much what i am getting and the north end of the compass is also being pulled down vertically a little as well.
The thing i found interesting is the coil with the cap had a sine imposed by the driven coil, yet the field was not reversing because the compass was still being pulled towards the center, the amount it was pulled also depended on the pulse delayed time between each pulse, but then so does the psu supply current so i guess that is just a more current more compass move situation.

This proves that by pulsing twice with a varying delay, the same coil and same pulse width, the coil can be made to draw more current purely dependant on the pulse delay in nS.So to clarify what i am saying again, if i pulse any coil for 60nS and the coil takes 50mA and i pulse again after a delayed period on the second pulse the coil will take more current, and this varyes dependant on the delay time.
When i start increasing the supply voltage over 35volts the current drawn is large enough to produce strong EM pulses, it is these EM pulses that have destroyed FET's and other things in the past during similar experiments.
I believe the speed that the current flows is accelerated, this explains why in my earlier experiments i had a larger second pulse, the second pulse was driven with the same width pulse but it was a lot taller, so what changed, it must have been the ability of the coil to accept energy from the psu.  

If it is speed that has changed the slope of the current and mag field will be sharper, which i have pretty well proved anyway, and although i am using more current i may well have a net gain with the increased speed of change, the gain is 2 fold on the up leg and on the down leg

[Grumpy]

I believe the speed that the current flows is accelerated, this explains why in my earlier experiments i had a larger second pulse, the second pulse was driven with the same width pulse but it was a lot taller, so what changed, it must have been the ability of the coil to accept energy from the psu.  

If it is speed that has changed the slope of the current and mag field will be sharper, which i have pretty well proved anyway, and although i am using more current i may well have a net gain with the increased speed of change, the gain is 2 fold on the up leg and on the down leg

drift velocity is related to voltage unless it is dragged along

[BEP]

@WW
Sounds like an interesting experiment, i'm away from work for a couple of days, when i go back to it, i will try what you suggest.

Thank you for the picture of the field, this is pretty much what i am getting and the north end of the compass is also being pulled down horizontally a little as well.
The thing i found interesting is the coil with the cap had a sine imposed by the driven coil, yet the field was not reversing because the compass was still being pulled towards the center, the amount it was pulled also depended on the pulse delayed time between each pulse, but then so does the psu supply current so i guess that is just a more current more compass move situation.

This proves that by pulsing twice with a varying delay, the same coil and same pulse width, the coil can be made to draw more current purely dependant on the pulse delay in nS.So to clarify what i am saying again, if i pulse any coil for 60nS and the coil takes 50mA and i pulse again after a delayed period on the second pulse the coil will take more current, and this varyes dependant on the delay time.
When i start increasing the supply voltage over 35volts the current drawn is large enough to produce strong EM pulses, it is these EM pulses that have destroyed FET's and other things in the past during similar experiments.
I believe the speed that the current flows is accelerated, this explains why in my earlier experiments i had a larger second pulse, the second pulse was driven with the same width pulse but it was a lot taller, so what changed, it must have been the ability of the coil to accept energy from the psu.  

If it is speed that has changed the slope of the current and mag field will be sharper, which i have pretty well proved anyway, and although i am using more current i may well have a net gain with the increased speed of change, the gain is 2 fold on the up leg and on the down leg

If you step-pulse a coil with the right time spacing between current steps the following pulse or change sees less reluctance. So, the following pulse sees less inductance, impedance, higher velocity factor, etc.

The 'slight discontinuities' of the wave shape are due to the other frequencies ringing in the coil. The largest other frequency appears to be ~3 times the frequency of the lower scope channel.

To have a higher amplitude, without increasing applied voltage, you must increase the Q factor. This is normally a great problem since this requires decreasing resistance, less wire in the coil, etc. Your resonant frequency can only go higher, unless....

Actually, you should have lower frequencies and better performance with a pancake coil having about 1/4 the number of turns, with the same outside diameter and a much larger inside diameter, when you apply my suggestion. (the results of my suggestion are counter intuitive until you see what is happening. Ex. higher planar coil turn count does NOT always lower resonant frequency -- I should say higher planar coil turn count should NOT be required to decrease resonant frequency, if my suggestions are used.)

Addendum to the suggestion: Don't just wrap that bifilar poloidal coil in a common helix around your pancake coil. Wrap it as if the turns were 10 individual completed rings with connections between each set of rings. Something like: __O__O__O__O__

[Peterae]

If you step-pulse a coil with the right time spacing between current steps the following pulse or change sees less reluctance. So, the following pulse sees less inductance, impedance, higher velocity factor, etc.

That would explain the double pulse then thanks

Now all i need to confirm is during this lower reluctance pulse is how much energy is transferred to the tuned bifilar coil, it should be less i would imagine

[BEP]

That would explain the double pulse then thanks

Now all i need to confirm is during this lower reluctance pulse is how much energy is transferred to the tuned bifilar coil, it should be less i would imagine

My experiments, along these lines, were never concerned with inductive coupling to a conventional secondary coil. The only thing I can say is I suspect all of the aspects of the secondary will be reflected upon the primary, regardless of special features on that primary.

I haven't had a great deal of success with building a resonant air core transformer which resonates far below a conventional air core transformer of the same size. It should but rarely does work when the mentioned poloidal windings encompass identical primary and secondary windings together.

The problem is due to the phase difference between primary and secondary. I've thought about building one with a shorted coil, otherwise identical to the primary and secondary, placed between the primary and secondary. This should bring pri' & sec' back into phase.

[Grumpy]

the purpose of the two coil method is to compress a pulse and produce a pulse of higher amplitude 

there is n o way that it can extrude, curtail, or summon extra energy in any way shape or form

applying this pulse can produce a stringer result in another conductor, but you need more than a few volts

[BEP]

Energy transfer from one winding to another.... This is where my suggestions fall flat.

When searching for ways to increase Q, velocity, selectivity AND decrease resistance, coil size, & resonant frequency, my target wasn't a smaller transformer. I was looking for a better method of frame dragging, not conventional induction.

I'm not privy to Peterae's thoughts but when it comes to compression, I think differently than what I've seen....

In magnetics, head-on collisions of repelling polarities don't produce cancellation or zero net magnetic, unless you can't see beyond the common axis of the colliding waves. They create the effect of a magnetic field perpendicular to the axis of the colliding fields. After all, the energy must go somewhere. Think of forcefully clapping your hands just as someone drops a water balloon between your hands  There will be a radial blast of water with the source of energy centered where your palms meet.

[Grumpy]

Energy transfer from one winding to another.... This is where my suggestions fall flat.

When searching for ways to increase Q, velocity, selectivity AND decrease resistance, coil size, & resonant frequency, my target wasn't a smaller transformer. I was looking for a better method of frame dragging, not conventional induction.

I'm not privy to Peterae's thoughts but when it comes to compression, I think differently than what I've seen....

In magnetics, head-on collisions of repelling polarities don't produce cancellation or zero net magnetic, unless you can't see beyond the common axis of the colliding waves. They create the effect of a magnetic field perpendicular to the axis of the colliding fields. After all, the energy must go somewhere. Think of forcefully clapping your hands just as someone drops a water balloon between your hands  There will be a radial blast of water with the source of energy centered where your palms meet.

We miss the forest for the trees, and the bad porridge that we have been fed.

Look at the evidence, with the following, voltage and current are "in -phase":

traveling waves
displacement current
motional electric field

All drag electrons at there respective rate of propagation.  All cause electron precession.

Bag 'em and tag 'em!

[BEP]

Look at the evidence, with the following, voltage and current are "in -phase":

traveling waves
displacement current
motional electric field

All drag electrons at there respective rate of propagation.  All cause electron precession.

Bag 'em and tag 'em!

Yes, aren't they all the same thing?

Peter will develop his own idea of what goes on. I was just trying to help with low resonant freeks and higher Q.

[Grumpy]

Yes, aren't they all the same thing?

yes, but not everyone realizes that