Dual coil for mpp

[godigit1]

Very interesting that the DIP meter gives quite a high SRF as compared to the other methods. I think the DIP meter is the most accurate method, since the only capacitance in the LC circuit under test would be the coil self capacitance.

You are both correct and so are the lower SRF readings And I think I can explain why now. But this is open to debate as always.
Im no Physacist I cant even spell it.
The Dip Meter corresponds to both the Pi pulse method Loop pick up method suggested by Mr Green.
The other test methods Ive used all give repeatable results as well

I think it can all be exemplified in the different methods of live pulse testing.
I will use the small coil as a example as it the only Ive redone the live testing on so far three or four times with the same results.

Loop pick up 6.94 Mhz is my final # Matches Dip Meter and 3 other test methods
1x probe across coil 1.494 Mhz No other test methods line up. (But Wait for It)
10x across coil 3.29 MHZ lines up with three other methods Elliots Carls BBs Chemelecs one of two you tube methods.
5 pf cap 5Mhz One other matching result also with 5 Pf Cap under test.
1pf cap 6.1 Mhz Full circle back to 6 + Mhz.

Now I will try to explain what im thinking is going on.
6.9 Mhz is the free air SRF of the coil.
The mid way point is 3+ Mhz
The low point 1.494MHz. Hmm see that multiples of two

So at 6.9 Mhz Free air nothing attached to the coil we see a induced voltage in the millivolts level.
At the midway point test level probe is attacehd 10x or Im taking the coils to peak resonance for that method and inducing more current to the coil.
Now on the low extreme that coil is being hit with most the time over 300 volts that it is getting due to transformation ratio from the live coil. Ie the coil is getting almost full fly back potential on the 1x probe.
So Here I go I think that the different readings are all correct but vary due to the amount of field effect generated by the different methods. not so much by the damping from probes. we all know a coil is not a static device.
My justification for this and final verification method the only one i can think of is final damping value Vs calculated damping value.
Unfortunatly for max SRF Damping is lining up with the lowest #s .
I think that it is partially beacuse full paracitic effect both Rs And Cpar are at thier working levels when the coil is at a higher voltage .
it seems at that point you get full capacitive reactance and at the free air resonance point Im getting more inductive reactance.
That is how Im trying to say it the different test methods are all correct but bring out different paracitic characteristics under test.

The sad thing Im finding out is the faster the coil the lower the Q this coil is at half level in 4.5 cycles for a whopping Q of 22.5.

Thoughts Please!
And thanks to you all,

[green]

Tester stopped working a couple times. Added a 10nf capacitor to pin 5 of 555. Don't think it should need it but it hasn't stopped working since I added the capacitor.
Including a picture of tester. The small diameter solenoid coil has the advantage of placing the loop over the coil and placing the test coil on the solenoid coil when testing.

[dbanner]

Green, I wish you had a dip meter to measure that solenoid. If it agreed with the 6.71mHz from your test circuit, that would be neat! I think that would have been game over.

[godigit1]

Hi Green,
If you have a chance, iwas wondering if you try to just put the probe tip close to the coil without wrapping it. I seem to have better coupling with my probes that way.
Wondering if on your tester, if since it has a tx circut if you can look at your raw coil flyback and sample a damping resistor value with it since your pi is down.

[green]

Was wondering again what effect coupling between PI Tx coil and test coil have when measuring SRF. Haven't seen a lot with my testing but then the coils have been deferent sizes. Tried with two coils the same size. Measured basket coil SRF this morning, got 3.25MHz same as measured before. The closer the coils(more coupling)lower Q. Think I see why the Q is lower, don't know why SRF increase. Any thoughts why SRF increases with higher coupling? Any thoughts if the test should have been done different?

Tx coil was critical damped. Test coil open.

[dbanner]

don't know why SRF increase. Any thoughts why SRF increases with higher coupling? Any thoughts if the test should have been done different?

Tx coil was critical damped. Test coil open.

It's clearly due to the amount of coupling. The larger the magnetic coupling, the greater the resonant frequencies will vary from that of an uncoupled resonator.
This implies that the decaying oscillations of the Tx coil are having small effect on the test coil and vice versa.

[green]

It's clearly due to the amount of coupling. The larger the magnetic coupling, the greater the resonant frequencies will vary from that of an uncoupled resonator.
This implies that the decaying oscillations of the Tx coil are having small effect on the test coil and vice versa.

No argument but why does the SRF increase instead of decrease?

[dbanner]

No argument but why does the SRF increase instead of decrease?

The SRF only "appears" to be increasing, in fact, it is only just moving "closer together", as the two coils attempt to reach mutual resonance.
I have no idea what I just said.

[dbanner]

I suspect if you were to try a different test coil with a higher SRF than the Tx coil, you would observe the opposite effect, the SRF would decrease with more coupling. Try it!!

[green]

Hi Green,
If you have a chance, iwas wondering if you try to just put the probe tip close to the coil without wrapping it. I seem to have better coupling with my probes that way.
Wondering if on your tester, if since it has a tx circut if you can look at your raw coil flyback and sample a damping resistor value with it since your pi is down.

I don't see a lot of difference in signal strength between holding the probe close to the test coil and the loop, loop doesn't need to be as close.

Not sure about your second question. SRF tester is packed to ship. Calculated Rd(Rd=pi*L*SRF)for the tester, needed a lower Rd than calculated to critical damp.
Tried with my TRT tester and the flat spiral coil reply #140. Calculated Rd looks correct. May have to unpack SRF tester and try again tomorrow. I remember it being more critical to adjustment. If you want something tested before I ship it ask.

2.04MHz was circuit resonance with Rd disconnected, coil connected to Tx circuit.

[green]

I suspect if you were to try a different test coil with a higher SRF than the Tx coil, you would observe the opposite effect, the SRF would decrease with more coupling. Try it!!

Tx_bundle wound, same diameter as test coil, 700kHz circuit resonance. Test coil flat basket wound, 3.25MHz SRF. SRF increases with increased coupling. Didn't have a same diameter test coil with a higher SRF so used a Tx coil with a lower Tx circuit resonance.

pickup loop about 2inches below Tx coil, spacer above Tx coil.

.5inch spacer_3.6MHz
1inch spacer_3.4MHz
2inch spacer_3.3MHz
3inch spacer_3.25MHz

[dbanner]

Tx_bundle wound, same diameter as test coil, 700kHz circuit resonance. Test coil flat basket wound, 3.25MHz SRF. SRF increases with increased coupling.

pickup loop about 2inches below Tx coil, spacer above Tx coil.

.5inch spacer_3.6MHz
1inch spacer_3.4MHz
2inch spacer_3.3MHz
3inch spacer_3.25MHz

Well that shoots my guesswork right off the duck line.
Thanks.
Just so that I'm sure of your setup, the order as I understand it is as follows: pickup loop then Tx coil then spacer then test loop. Is that correct?
And just why is the pickup loop below the Tx coil? I thought you were scoping the test loop? What am I missing?

[green]

Well that shoots my guesswork right off the duck line.
Thanks.
Just so that I'm sure of your setup, the order as I understand it is as follows: pickup loop then Tx coil then spacer then test loop. Is that correct?
And just why is the pickup loop below the Tx coil? I thought you were scoping the test loop? What am I missing?

Yes

I have been placing the pickup loop on the test coil. I tried the pickup loop below the Tx coil on the SRF tester I'm sending to godigt, worked fine. So I tried it for the coupling test reply #140, Didn't need to move the pickup coil when changing the spacer between the Tx and test coil. Just experimenting, don't know what is the best way. I suggested in another reply that highest SRF would be closest to being correct, probably not correct. Inductive coupling like added capacitance with the signal generator method effects SRF. It appears the effect is very small if spacing is enough, maybe 2 or 3inches between Tx and test coil.

[dbanner]

On doing some reading on the issue of coupled resonant circuits, there is often reference made to "reflected impedance" between the two coupled circuits. This excerpt sort of gives a clue to what's going on:

"Note that a resistance is reflected as a resistance, a
capacitance as an inductance, and an inductance as a capacitance.

At resonance, the reflected impedance is resistive, and acts to lower the Q of the primary, and thereby
to reduce the output. This is counteracted by the increased coupling, which increases the output. The
lower Q gives a wider passband. At frequencies lower than exact resonance, the reflected impedance is
inductive, which adds to the inductance of the primary and resonates at a lower frequency, producing a
peak in the output. At frequencies higher than exact resonance, the reflected impedance is capacitive,
which cancels part of the inductance and causes the circuit to resonate at a higher frequency, producing
the other peak.
As the coupling is reduced, the response becomes single-peaked at critical coupling, and then decreases
as the coupling is made even looser."


I put here the document I referenced. So it seems the coupling corfficient definitely affects the resonance.

[godigit1]

I don't see a lot of difference in signal strength between holding the probe close to the test coil and the loop, loop doesn't need to be as close.

Not sure about your second question. SRF tester is packed to ship. Calculated Rd(Rd=pi*L*SRF)for the tester, needed a lower Rd than calculated to critical damp.
Tried with my TRT tester and the flat spiral coil reply #140. Calculated Rd looks correct. May have to unpack SRF tester and try again tomorrow. I remember it being more critical to adjustment. If you want something tested before I ship it ask.

2.04MHz was circuit resonance with Rd disconnected, coil connected to Tx circuit.

On the damping resistor I was curious as to finished damping value. If it matched calculated damping value. Sounds like you did have to go lower than calculated.
Im thinking this is our way of validating the measured Srf.

Small coil testing 1x probe across coil live pulse SRF is 1.429Mhz calculated capacitance 91.884pf damping 606 ohms.
testing with signal genny 5 ways averaging 3.333 Mhz 1413 ohms and 16.89 pf
live pi loop pick up and Dip meter and two other signal genny methods 6.931MHz 2586 ohms and 3.8pf

As far as actual damping on a mpp goes 606 is the closes to the actual damping resistor installed.
At 3.333 Mhz if I add the pre amp input resistor at 1k it almost right on the closest to actual damping.
At 6.931 I need to find another 1k somewhere for the calculated damping value to work.

Can we agree that this is a determining factor or is there another way to validate our #s?


On the little coil testing 1x loop acroos coil live pules with the test coil taped directly to the bottom of my Mpp pulsing at 1000Khz
Im seeing if I remember about 285 volts on the coil .
I was thinking that maybe that extra voltage brought out full paracitic effects in the coil? I think Dbanner and yourself more nailed it with the coupling.

Im thinking the 3.333 mhz is correct for this coil as Ive allready seen the input resistor act as a damping resistor.

My other thought about validation is looking at the calculated Cpar At 6.9 mhz for my coil 3.8 pf seems pretty low when a 1" wire twist adds up to 1pf. Looking at it that way the 91 pf seems more likely for the coil.

Does anyone have information on Spatial resonation Im finding vague referances?
Supposed to have a higher amplitude than actual SRF???

I think we need to find a good way to validate our results.
Thanks again