Dual coil for mpp

[godigit1]

Hi godigit, your scope pictures look good. Wondering how you get 454 oohms for the inner coil. Reply #97 you have 6.67MHz reply #65 135uH. Rd=pi*L*resonance, =2829 ohms.

Hi Green.
I did not use that SRF # I used the 1.316 mhz I had originally got. Calculating with the formula Rd=pi*L*resonance, I get 558ohms close to what I damped at with the resistor set up. If I use the formula L/(Pi*C)=Rd I get 4640. and move the decimal over 1 I wrote 454 down mistakingly.
This coil no way would damp out a 2800 ohms it would be totally underdamped by what im experiancing.
So I ended up with a inner value of 447ohms. The coil works very well for as much as Ive abused it and only twisted wireing together for the tests.
Some idea of sensativity is a 1/4 square of soda can side at almost 3 inches in a bad test inviroment. Thats better than my TDI but im sampling at 5US first sample on the Mpp with a unshielded coil.
All that brings to question SRF again like dbanner said Im definatly damping for a lower value right close to the 1.3 mghz.
By my scope im doing things the best I know how. Please some one check my oscopy To me the coil looks sampleable at 4 us Is that correct? Am I looking at the sample window correctly?

Thanks


Well I won a offer on ebay 9 bucks for a dip meter working with no coils, might take a couple weeks to get here but for 9 bucks why not try it out.

[dbanner]

I guess the coil must be closed for it to be tested, right? I mean the coil excite, pickup loop method.
Is there a drawing or sketch of how the test is setup?
Look at this diagram of possible ways to couple a dip meter. I'm not sure a PI coil could be coupled in this way? You can even take a tap off of the dip oscillator and connect it to one of those cheap frequency meter kits on Ebay. Then you can directly read the SRF of the coil. All of this can be put into nice little project box.

[dbanner]

Once the coil is shielded and put in the coils shell and sealed up and connected to a cable etc. then the only remaining method I think would be resorting back to the function generator/ oscilloscope. At the end of the day, it's the finished and totally assembled coil that needs to be fast.
Oh well, At least I learn a little of the dip meter principle.

[green]

I guess the coil must be closed for it to be tested, right? I mean the coil excite, pickup loop method.
Is there a drawing or sketch of how the test is setup?
Look at this diagram of possible ways to couple a dip meter. I'm not sure a PI coil could be coupled in this way? You can even take a tap off of the dip oscillator and connect it to one of those cheap frequency meter kits on Ebay. Then you can directly read the SRF of the coil. All of this can be put into nice little project box.

https://www.geotech1.com/forums/show...450#post261450 _8 is a picture of the measurement, test coil leads are open. I'm thinking the SRF of each of the two coils allows calculating Rd for that coil with no shield or lead, Rd in the box damps the completed coil and circuit. SRF of the completed means something but calculated Rd would still need to be changed depending on the Tx circuit.

[dbanner]

Yes. Of course the coil ends must be open. Don't know what I was thinking.
It helps to visualize a model of an inductor, which has a series resistance and a parallel capacitance. If you short the ends, you short out the circuit. How stupid of me. I must have been thinking of the scope probe loop.

[godigit1]

I guess the coil must be closed for it to be tested, right? I mean the coil excite, pickup loop method.
Is there a drawing or sketch of how the test is setup?
Look at this diagram of possible ways to couple a dip meter. I'm not sure a PI coil could be coupled in this way? You can even take a tap off of the dip oscillator and connect it to one of those cheap frequency meter kits on Ebay. Then you can directly read the SRF of the coil. All of this can be put into nice little project box.

I think testing a pi coil shouldnt be too hard .
What I was thinking to try is to make 3 loops 1 ,2 and 3 wire test them for srf range on the dip meter and a scope and make adjustments with a variable cap to see if I can calibrate to the dip meter scale. If not oh well I just have to check the frequency of the dip when found. maybe even try high resistance nicrom wire and see what it does.
Modern 1 gallon paint cans are ABS plastic and 6.75 " in diameter so I will use slices of the can as a form for the loops. Thinking once a minimum coupling spacing is found the coils could be made to even act as spacers for the test coil. Say each coil 2.5 inches and the wraps on the bottom half inch.
Maybe it will work maybe not just riffing on it a little.
Here is a link to some different test procedures that can be done with a dip meter and set up.

https://www.robkalmeijer.nl/techniek...e65/index.html.

[dbanner]

I was mistaken when I asked about closing the coil ends, it must be open. I guess I had one of those moments.
Yes, the dip meter scale won't correspond to a new self made coil, unless you do it painstakingly to wind a coil by trial and error for it to match up with one of the scales.
Much easier to carry it over to the scope or just put the scope probe loop over the coil to measure the frquency of the dip oscillator.
I found a nice circuit for a dip meter oscillator which has a pot instead of a variable cap to tune the oscillator. It has an LED to indicate the dip.
This could be a nice little project. The section in red is all you need. The output after the buffer is your frequency output wich can be connected directly to the scope.

[dbanner]

It just occured to me that a small coil wound on a toroid core might do the trick for coupling to a large PI coil. Or something along those lines. Just place near to the edge of the coil under test. The second photo is a bit out there, but you get the idea.

[dbanner]

Equivalent circuit of an inductor.

[green]

bbsailor suggested in another thread, for a measurement method to be valid it needs to be repeatable and repeatable by more than one person.

Made a SRF tester(PI Tx) to compare with my bench circuit. Faster current decay. Plan on measuring SRF of small and large coil with SRF tester and bench circuit for compaeison. Sending coils, 10nf(measures 10.32nf)npo ceramic, and SRF tester to godigit to see if he gets the same SRF. Connecting 10nf capacitor across coil and measuring resonance should allow calculating coil inductance. Don't have an inductance meter but godigit does. Can compare calculated inductance with his meter. Anyone think of something else to try before sending. Placed test coil on PI tester coil then placed loop on test coil and read SRF on scope. Played with the circuit with spice, used TLC555 and IRF740 to make circuit because that is what I had.

[godigit1]

Hi Green,
Ive been playing with different measuring methods suggested on this forum from Kt, Carl, BB Sailor Chemelec Elliot and any other method I can find on you tube as well.
Ive even got the dip meter up and working nicely though my coils are a bit overkill. I can couple to my led light bulb 3 feet above it Ha Ha

So far out of 8 methods Ive cut out two. Im getting pretty well 50/50 results so far.
I still have two coils to do with the live pulse . Ill get better test data and the set ups Ive used, Im still trying to put it all together.

But so far on the small coil Im getting from 3 Mhz using Elliots carls BB Chemelecs methods.

Using the dip meter W2Enew methods from You tube live pulse inductive non contact probe are all in the 6+ mhz range.
Thought it would be a little more cut and dry when I got a signal genny. fun fun

Look forward to recieving your coil and wow the tx looks great Im going to have some fun with that.
Thank you for puttng that together apples and apples.

[dbanner]

bbsailor suggested in another thread, for a measurement method to be valid it needs to be repeatable and repeatable by more than one person.

The above statement does not infer that the results of the measurements are correct. They may or may not be.
"Valid" here, does not mean "correct".

Which method thus far is the most ACCURATE??
For this, one would have to conduct several experiments, both testing and computational. It is not just a matter of comparing results from different test methods. All test methods will yield "valid" results, but which one can be relied upon as most accurate?
Seems to me that air coupling a reciever to any resonant circuit is perhaps the most accurate method. That's how the Ham guys fine tune their radios and other equipment.

[green]

The above statement does not infer that the results of the measurements are correct. They may or may not be.
"Valid" here, does not mean "correct".

Which method thus far is the most ACCURATE??
For this, one would have to conduct several experiments, both testing and computational. It is not just a matter of comparing results from different test methods. All test methods will yield "valid" results, but which one can be relied upon as most accurate?
Seems to me that air coupling a reciever to any resonant circuit is perhaps the most accurate method. That's how the Ham guys fine tune their radios and other equipment.

Agree
My thought, the method that gives the highest SRF is closer to being correct. Maybe correct maybe not.

[dbanner]

Agree
My thought, the method that gives the highest SRF is closer to being correct. Maybe correct maybe not.

I think you are correct, Highest SRF implies the lowest capacitance, and since the coil self capacitance is fixed, that means any additional capacitance must be coming from the test rig, which would lower the SRF. The logical conclusion would be to use the highest SRF obtained among the different test methods.

[dbanner]

Hi Green,
Ive been playing with different measuring methods suggested on this forum from Kt, Carl, BB Sailor Chemelec Elliot and any other method I can find on you tube as well.
Ive even got the dip meter up and working nicely though my coils are a bit overkill. I can couple to my led light bulb 3 feet above it Ha Ha

So far out of 8 methods Ive cut out two. Im getting pretty well 50/50 results so far.
I still have two coils to do with the live pulse . Ill get better test data and the set ups Ive used, Im still trying to put it all together.

But so far on the small coil Im getting from 3 Mhz using Elliots carls BB Chemelecs methods.

Using the dip meter W2Enew methods from You tube live pulse inductive non contact probe are all in the 6+ mhz range.
Thought it would be a little more cut and dry when I got a signal genny. fun fun

Look forward to recieving your coil and wow the tx looks great Im going to have some fun with that.
Thank you for puttng that together apples and apples.

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.