Dual coil for mpp

[godigit1]

Just thinking the dip meter is supposed to be able to test circuts installed. Going to have to try a coil hooked up to a pi and see if i can get SRF while attached?
Curious ?

[dbanner]

The only result that matters is to damp the coil with resistance on the edge of where the ringing goes away. All other abstract calculations become redundunt.
In the dual coil, you connect both coils as per the schematic arrangement, then proceed to damp the inner coil first( with oscilloscope). Thereafter, overall damping resistor is calibrated by using the scope.
SRF measurements are all over the place, and only give "relative" results to say this coil is lower or higher than the next.
As was demonstrated by Green, the SRF measurement varied with coupling, so which to use? The more coupled or the less coupled?
What is worse is that the different methods produced significantly different results, so which is correct?????
Clearly the ringing frequency is what needs to be damped, so I think this method of determining SRF (PI excite method) is more appropriate. Yet the calculated Rd does not jive with the actual value?????????

Carl, you must say your opinion on these matters please.
You are PI GURU!

[godigit1]

At this point the main reason I want a accurate srf is for capacitance. I've been doing wire spacing tests and they mean nothing if I dont have accurate capacitance calcs.
The dual field is past history for me done and performing excellently. This is now about capacitance and a way to validate. though I would love for him to chime in Carl has given his method I've done it parallel and series with the same results. Check the did I measure srf correctly thread.

Those #s are 3.333 mhz also the same # in Elliots method of square waves at 1k , .
I have no dought I'm also getting the 6 mhz and its proper.
I think it is free srf and the slightly loaded srf you get attached to the probe is more to operating characteristics.
All this is open to debate that's why I post I want your opinions and expertise.
Sorry Denotes this has moved so far away from you thread.
Best

[dbanner]

You're right!!
It's all Mr.Green's fault, with all his fancy charts and graphs. He has me confused.

[green]

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

A test with three coils. Tx circuit_STF11N50M2(mosfet)with a MUR460 diode between mosfet and coil. Loop(ground lead connected to scope probe)laying on Tx coil or X10 probe across Tx coil used to monitor decay signal. Rd adjusted for best looking(best damped) signal(loop pickup).

Bundle wound coil, 430uH, SRF 715kHz_____circuit resonance_____scope input_____calculated Rd_____adjusted Rd
____________________________________690kHz________ ____ loop___________932____________1065
____________________________________653kHz________ _____X10 probe______882
flat spiral, 336uH, SRF 2.78MHz
____________________________________1.98MHz_______ _____loop___________2090____________2240
____________________________________1.5MHz________ _____X10 probe______1580
flat spiral(small coil),115uH, SRF 6.7MHz
____________________________________4MHz__________ _____loop__________ 1445____________1230
____________________________________2.8MHz________ _____X10 probe______1011

Rd needs to be adjusted with the completed coil connected to the Tx circuit. Probably best done with a pot adjustment. Calculated Rd=pi*coil inductance*circuit resonance. Don't need to calculate capacitance to calculate Rd.
My adjusted Rd was higher resistance than calculated for the first two coils and lower than the loop pickup for the third coil. Should use loop pickup because X10 probe effects decay and is removed after adjustment.
The MPP input goes to the -input of the amplifier so it does some damping, how close to calculated I don't know. Probably another reason to find final Rd with a pot.
For the dual coil I'm guessing measuring SRF and calculating internal Rd for the damped coil before assembly is the correct way. Find external Rd with a pot after coil is finished.
I think your 3.8pf is close to correct, the coil wouldn't oscillate at 6.9MHz if the capacitance was 91pf.

[Carl-NC]

though I would love for him to chime in Carl has given his method I've done it parallel and series with the same results. Check the did I measure srf correctly thread.

Without having me re-read the threads, what would you like me to chime in on?

[dbanner]

A test with three coils. Tx circuit_STF11N50M2(mosfet)with a MUR460 diode between mosfet and coil. Loop(ground lead connected to scope probe)laying on Tx coil or X10 probe across Tx coil used to monitor decay signal. Rd adjusted for best looking(best damped) signal(loop pickup).

Bundle wound coil, 430uH, SRF 715kHz_____circuit resonance_____scope input_____calculated Rd_____adjusted Rd
____________________________________690kHz________ ____ loop___________932____________1065
____________________________________653kHz________ _____X10 probe______882
flat spiral, 336uH, SRF 2.78MHz
____________________________________1.98MHz_______ _____loop___________2090____________2240
____________________________________1.5MHz________ _____X10 probe______1580
flat spiral(small coil),115uH, SRF 6.7MHz
____________________________________4MHz__________ _____loop__________ 1445____________1230
____________________________________2.8MHz________ _____X10 probe______1011

Rd needs to be adjusted with the completed coil connected to the Tx circuit. Probably best done with a pot adjustment. Calculated Rd=pi*coil inductance*circuit resonance. Don't need to calculate capacitance to calculate Rd.
My adjusted Rd was higher resistance than calculated for the first two coils and lower than the loop pickup for the third coil. Should use loop pickup because X10 probe effects decay and is removed after adjustment.
The MPP input goes to the -input of the amplifier so it does some damping, how close to calculated I don't know. Probably another reason to find final Rd with a pot.
For the dual coil I'm guessing measuring SRF and calculating internal Rd for the damped coil before assembly is the correct way. Find external Rd with a pot after coil is finished.
I think your 3.8pf is close to correct, the coil wouldn't oscillate at 6.9MHz if the capacitance was 91pf.

Green, your calculated Rd and actual Rd are pretty close, I think that adds to the efficacy and reliability of your SRF measurements.
That's more like it. Seems everything is working out just right.

[dbanner]

Without having me re-read the threads, what would you like me to chime in on?

At least for me it is trying to get the theoretical calculated Rd to approximate the actual Rd when coil is damped using oscilloscope.
Green's methods seem to be getting good results.

[godigit1]

Without having me re-read the threads, what would you like me to chime in on?

dbanner actually ask for you to please help. He and I would like your opinion on srf Testing.

A example using this method

Coil 25 wraps 3.25 I.d 30 awg wire I measure 135 uh with inductance meter.

Using the method above I get 3.264Khz with a 1 pf cap and 3.355 with a 5pf cap. ive also verified this in other test methods.

Then using dip meter a diferential probe method the method Green uses on the same coil I can get 6.9 Mhz.
At 6.9 Mhz I get 3.8pf 2586 ohm damp value.
at 3.333 I get 16.89 pf and a damp value of 1413 ohms.
Actual damping on a Mpp with a damping resistor set up in this shot is 447 ohms.

https://www.geotech1.com/forums/atta...9&d=1570936662

If I count the input resistor 1k the 3.333 works with the MPP.
Im not trying to argue just getting different damping results Ive been totaly ale to get the same srf as Green using multiple test methods.
Maybe Im not taking into account full rx impediance? Should I be?

Thanks for any input.

[godigit1]

Deleted

[godigit1]

A test with three coils. Tx circuit_STF11N50M2(mosfet)with a MUR460 diode between mosfet and coil. Loop(ground lead connected to scope probe)laying on Tx coil or X10 probe across Tx coil used to monitor decay signal. Rd adjusted for best looking(best damped) signal(loop pickup).

Bundle wound coil, 430uH, SRF 715kHz_____circuit resonance_____scope input_____calculated Rd_____adjusted Rd
____________________________________690kHz________ ____ loop___________932____________1065
____________________________________653kHz________ _____X10 probe______882
flat spiral, 336uH, SRF 2.78MHz
____________________________________1.98MHz_______ _____loop___________2090____________2240
____________________________________1.5MHz________ _____X10 probe______1580
flat spiral(small coil),115uH, SRF 6.7MHz
____________________________________4MHz__________ _____loop__________ 1445____________1230
____________________________________2.8MHz________ _____X10 probe______1011

Rd needs to be adjusted with the completed coil connected to the Tx circuit. Probably best done with a pot adjustment. Calculated Rd=pi*coil inductance*circuit resonance. Don't need to calculate capacitance to calculate Rd.
My adjusted Rd was higher resistance than calculated for the first two coils and lower than the loop pickup for the third coil. Should use loop pickup because X10 probe effects decay and is removed after adjustment.
The MPP input goes to the -input of the amplifier so it does some damping, how close to calculated I don't know. Probably another reason to find final Rd with a pot.
For the dual coil I'm guessing measuring SRF and calculating internal Rd for the damped coil before assembly is the correct way. Find external Rd with a pot after coil is finished.
I think your 3.8pf is close to correct, the coil wouldn't oscillate at 6.9MHz if the capacitance was 91pf.

Looks like the damping values are working for your PI Im wondering if its a differance in rx impediance Ie maybe the Mpp has mor resistance up front than im adding for.
Its just a thought.
my actual coil damped at 447 ohms so it seems like my capacitance should be allot higher and srf lower.
Its kinda going around in circles I know.
Also on the test coils I previously sent, when you measured them Your inductance readings were 20 to 30 uh lower than what I had measured with my meter.
For years I chalked it up to my cheap meter.
I now have several standards Ive tested the meter and its pretty right on.

If I do capacitance calcs for you coil at 6.7 Mhz and 115 uh using this calculator
http://www.1728.org/resfreq.htm

I get a capacitance of .28 pf are we using the same calculations what do you get for capacitance ? I think you allready posted it but im not finding it.

Seems somewhere we are not on the same page trying to figure out what Im missing? Im about to throw in the towel you win dbanner.

[dbanner]

Looks like the damping values are working for your PI Im wondering if its a differance in rx impediance Ie maybe the Mpp has mor resistance up front than im adding for.
Its just a thought.
my actual coil damped at 447 ohms so it seems like my capacitance should be allot higher and srf lower.
Its kinda going around in circles I know.
Also on the test coils I previously sent, when you measured them Your inductance readings were 20 to 30 uh lower than what I had measured with my meter.
For years I chalked it up to my cheap meter.
I now have several standards Ive tested the meter and its pretty right on.

If I do capacitance calcs for you coil at 6.7 Mhz and 115 uh using this calculator
http://www.1728.org/resfreq.htm

I get a capacitance of .28 pf are we using the same calculations what do you get for capacitance ? I think you allready posted it but im not finding it.

Seems somewhere we are not on the same page trying to figure out what Im missing? Im about to throw in the towel you win dbanner.

Seriously, you are doing me a favour. I am learning alot from reading this thread.
You must not throw out the towel, unless you are in a chacuzi with beautiful woman.

[dbanner]

If I do capacitance calcs for you coil at 6.7 Mhz and 115 uh using this calculator
http://www.1728.org/resfreq.htm

I get a capacitance of .28 pf are we using the same calculations what do you get for capacitance ? I think you allready posted it but im not finding it.

Seems somewhere we are not on the same page trying to figure out what Im missing? Im about to throw in the towel you win dbanner.

6.7mHz, 115uH calculated capacitance 4.9pF using this calculator:https://goodcalculators.com/resonant...cy-calculator/

[dbanner]

I'm running some numbers using the 6.7mHz and 115uH, 4.9pF. I can't get Green's result for the calculated Rd.
I'm using the formula which Carl posted.

4.9pF seem kinda low, come to think of it. But that's what the 6.7mHz SRF and 115uH works out to.

[dbanner]

But using 4mHz circuit resonance and 115uH, I get 13pF. Then calculated Rd I get 1487 ohms, which is in keeping with green's results.
So then, what is the point of the SRF 6.7mHz value??
(I am referring to the data Green has posted above)