Dual coil for mpp

[green]

it was still set up so a quick try and I dont get SRF.
Im seeing the Mpp Tx charge fly back pulse cycle of the dual field.
The loop worked when I tried it on a connected coil with the damping and imput resistor removed.
But I did get the same #s both ways.
When I returned home I had forgotten I snipped one side of the input resistor I did not see it when I re-setup so i installed the damping resistor.
Wonder why im not seeing a coil, took me about the time of the pop to figure it out.
The 555 blew itself partially out of the sockett. easy fix nothing else happened.

Tested a small coil I have. Your small coil has less inductance so you might have to get closer. Think you should see something similar.

[green]

Thanks I wasnt sure if it would work with the coil not connected to anything. I will try that next time.
I went ahead and got the #s on the coils.
Im a bit suprised by the capacitance of the single coils and the end result.

the coils are 30 awg tested with no leads.

Inner coil----------- outer coil---------------combined
25 wraps135uh-----15 wraps135uh--------309uh
2.9 ohms------------3.3 ohms---------------5.6 ohms
1.316 Mhz-----------1.496 Mhz-------------1.639 Mhz
108Pf----------------83.8pf------------------30.516pf

scope shot is of both coils together.
[ATTACH]47610[/ATTACH][ATTACH]47611[/ATTACH]

Hi godigit, what is the inside diameter of your two coils?

[godigit1]

Tested a small coil I have. Your small coil has less inductance so you might have to get closer. Think you should see something similar.

Wow im seeing nothing with as high a Srf as that with my coils . Im wondering if it doesnt have to do with wire guage, and or maybe you have better probes than I, mine suck.

Sorry for my untimly response, my Job is at 8000 feet and we got a storm coming in now so we wanted to get the out side done I stayed there to get more time in so just getting back. Whew rollie coster but I love working in the mountains in the fall.

My coil diameters are :
Inner coil
I.D 3 1/4 inch.
O.D 3 7/8
Outer coil
I.D 7 1/16
O.D 7 3/8

So Ive damped the coil First time around splitting the two apart and damping the inner coil first as I had originally done on my other coil.

These results are with the coils connected in the following configuration.
Tx to large coil +
Large coil - to Small coil +, at that Connection the damping resistor is connected to the + side of the small coil also.
Small coil has damping resistor connected to - side and wire continues to - of the tx circut.
Coils are wound from Inside to out + on the inside -on the outside.

Here are the shots I took sorry they are fliped.

Inner coil damped stand alone Damped at 527 ohms.


Final damp on the outer coil was 568 ohms.


So two other ways to try still.
Dual damping set up.
And just calculating the resistor per the formula.
Thanks All

[dbanner]

I'm not sure you connected your coils correctly. My thoughts are that the tx should connect to the outside of the big coil, then the inside end of the big coil connects to the outside end of the small coil, then the inside end of the small coil returns to the -tx.
Seems you have it the other way round. It may not make any difference at all, as long as the magnetic flux lines between the coils are concurrent and not acting in opposition to one another. Starting from inside to outside, you may find the search coil more sensitive on the side facing the sky. I never really thought about such things but....

[green]

Wow im seeing nothing with as high a Srf as that with my coils . Im wondering if it doesnt have to do with wire guage, and or maybe you have better probes than I, mine suck.

Sorry for my untimly response, my Job is at 8000 feet and we got a storm coming in now so we wanted to get the out side done I stayed there to get more time in so just getting back. Whew rollie coster but I love working in the mountains in the fall.

My coil diameters are :
Inner coil
I.D 3 1/4 inch.
O.D 3 7/8
Outer coil
I.D 7 1/16
O.D 7 3/8


Thanks All

Thanks, been wondering the same thing. Plan on wrapping two coils same as yours with AWG28 magnet wire to see if wire size or maybe lower inductance(135uH vs 305uH)effects resonance. Think I still have one of the original probes(should be the same as yours)to try also.

[green]

godigit, you were correct about the probe. Found my original probe, lot less signal. Had a 6inch diameter circle cut from cardboard laying on the desk. Wrapped 1 turn of wire around circle and tried it. Repeated test reply #76.

Used original probe with 6inch wire loop. Original probe doesn't make a good loop for some reason. Zapped one of my original probes long time ago. Using some we had at work from an old scope that failed and was replaced.

[godigit1]

I'm not sure you connected your coils correctly. My thoughts are that the tx should connect to the outside of the big coil, then the inside end of the big coil connects to the outside end of the small coil, then the inside end of the small coil returns to the -tx.
Seems you have it the other way round. It may not make any difference at all, as long as the magnetic flux lines between the coils are concurrent and not acting in opposition to one another. Starting from inside to outside, you may find the search coil more sensitive on the side facing the sky. I never really thought about such things but....

I hadnt thought about matching the fields.
I had originally done this with 3dss coils and the positive side is on the inside. I just connected the way I did before.

It definatly makes adifferance on performance as well final damping value.
I wired from out side to inside and performance was about 11 inches on a nickel, a little less than a regular mono planer of the same size.
On a 4.2 grain nugget the dual field gets it at around a inch and the 390uh planer, it pretty much has to scratch the coil.
this nugget is a quarts specimen and hard to hit anyway but its getting it in the air, in the groung Im sure it would dissapear.

The other thing i want to try is inside to outside.
the differance I see is that the - side of the coil would be on the outer edge and at least that last wrap would act as a shielding thinking it might quiet the coil some in hot ground, Have to play with it some more.

Final damp wiring from outside to inside changed from 568 to 1500 ohms.
I also looked at the coils a bit different I set my scope to trigger of the op amp disconnected the probe from the board and used both channels with the probes lying on the individual coils grounds connected to probe end.
Lying both lops there you can see the Tx flyback on both coils Its hard to get voltages to match due to probe positioning but you can see the end decay is the same between the coils.
I think this may be a way to check things out once the coil is assymbled .
Once I make a inner damping set up Ill be able to check this out.
Thanks

[godigit1]

godigit, you were correct about the probe. Found my original probe, lot less signal. Had a 6inch diameter circle cut from cardboard laying on the desk. Wrapped 1 turn of wire around circle and tried it. Repeated test reply #76.

Used original probe with 6inch wire loop. Original probe doesn't make a good loop for some reason. Zapped one of my original probes long time ago. Using some we had at work from an old scope that failed and was replaced.

Cool, Im glad your making a coil also It will be interesting to see what the thicker wire does to sensativity and speed.
How are you going to wrap your coil?

Thanks for varifying the probes I had a feeling they were to blame. Seem ok for most things but inductive probes they are not to good for.
I saw where a guy used three loops of wire maybe that amps up the signal a little?

Started loooking at probes looks like 100 bucks for a good set.
Thats almost a 3rd of what a new signal genny costs so indecisive.
Thanks Again

[green]

Cool, Im glad your making a coil also It will be interesting to see what the thicker wire does to sensativity and speed.
How are you going to wrap your coil?

Thanks for varifying the probes I had a feeling they were to blame. Seem ok for most things but inductive probes they are not to good for.
I saw where a guy used three loops of wire maybe that amps up the signal a little?

Started loooking at probes looks like 100 bucks for a good set.
Thats almost a 3rd of what a new signal genny costs so indecisive.
Thanks Again

Flat spiral.

Have you tried a single wrap around a piece of cardboard for a pickup loop? Other than not making a good loop, the probes that came with the scope might be ok. If I hadn't zapped one I would probably still be using them, and using one wrap of wire around a piece of cardboard for a pickup loop. More than one wrap would give a higher signal, but I wonder if two many wraps might effect the frequency. One wrap seems to have enough signal amplitude.

[green]

godigit, you were correct about the probe. Found my original probe, lot less signal. Had a 6inch diameter circle cut from cardboard laying on the desk. Wrapped 1 turn of wire around circle and tried it. Repeated test reply #76.

Used original probe with 6inch wire loop. Original probe doesn't make a good loop for some reason. Zapped one of my original probes long time ago. Using some we had at work from an old scope that failed and was replaced.

I was wrong. RIGOL(original probe)was a lot less signal above because the ground lead was open on the end that connects to the probe. Didn't make a loop. Repaired ground lead. Scope picture with both probes(CH1, RIGOL). The frequency displayed isn't the same for the two channels. Frequency varies a little each sample for each channel when sampling.

If you try he loop method, scope should trigger at Tx off. Can use the loop CH to trigger but when I was playing the trigger could be adjusted to trigger at Tx on or Tx off.

[green]

Hi godigit, wound small coil. Will wind large coil when we find what we are doing different measuring SRF. Maybe you could try again. We get a lot different frequency, don't think it's because of wire size. I calculate about 5pf coil capacitance.

Planning on sending my coils to you when done to see what you measure. Think our coils should measure closer than they do.

Calculates 2400R to critical damp.

test coil was 2inches above operating 8inch oval Tx PI coil.

[godigit1]

Hi Green,
Interesting, one other thing im doing different is Ive been tapeing directly to the bottom of my pulsing coil.
Maybe being that close is loading it up a little Ill have to try with some distance.
Spent the day yesterday making a signal generator the one based on a comparator and 555 I posted before.
I wanted to try the sinal generator method see if things match up or not.
I got it working but im only getting just under 10 k out of it. Tried swapping to tlc 555 as its rated for 2 meg and a 555c but only the 555p is working. Im getting a overload type shut down on the tlc Comes up nice signal shuts down and cycles that way. The genney design may not support CMOS type chips.

Wondering if it makes any differance on SRF but your tester may have a very rich harmonic content compared to just a detector if thats the right term .
Maybe also adding to the srf beacuse your getting almost triple what I am.
I think wire and capacitance definatly have to do with it to a extent.
5 pf is super low Im thinking the larger wire has a smaller mating surface than the 30 awg. 28 is not that much bigger though so I wouldnt expect that much differance.
DAmping value is right up there with the 6.5 inch 390 uh planar Test coil.
Awesome enough that the dual field turned out 300 uhh I can through it in the lot to test. Almost there but wanted to dial in the SRF like you as well.

My inner coil calcs math wise with a 454 ohm resistor it damped on the mpp hooked as a single coil at 527 I made a 530 parralell resistor set up with 1/4 watt 1% resistors.
Coil seems to do fine and the resistors do not heat up.
What do you think we could get away with wattage wise for the inner resistor. 1/8 watt would be awesome.

I could send you a coil or two for comparison as well. If another member with a real signal genny woul like to be in the loop, Haha it would be good to get the comparisons.
tonight if i get home earlie Ill do my last wireing swap from inside to outside. see it it helps sensativity of the small coil or not.


Also my inner coil when I first tested it it was 1.316 Mhz on the bottom of the coil, On the Mpp with the damping resistor pulled it was 1.408Mhz
not mush higher but not spot on either.

[green]

A test comparing SRF reading with different size PI Tx(operating coils)and different test coil spacing between operating PI coil. Test coil reply #86. Some variation but not much. Zero spacing with 5inch mean diameter operating coil surprised me.

If you can explain another method and someone else can get the same results, this is not magic bbsailor replied in another thread discussing methods for measuing SRF. We aren't getting the same numbers so it's looking like magic. Wondering what we need to do to get close to the same SRF readings. Looks like might need a signal generator that would go to 8MHz to try the signal generator method. Maybe someone that has done SRF measurements could suggest why our measurements are so far apart.

godigit, what do you see if you place the loop on the operating coil without the test coil?

[green]

An attempt at getting a lower SRF measurement.

[godigit1]

godigit, what do you see if you place the loop on the operating coil without the test coil?

I see the tx cycle .

I re-wired the coil inside to outside and redamped. the whole coil.
It came out just a hair faster than outside to inside. Performance seemed the same. Thats it for the predamped tests now I will try the calculated damping resistor on the coil see how close it is.
Final damp went from 568 ohms to 737.

My test inviroment here is very bad. On a coil tested else where and here Im loosing 2 to 3 inches in air tests. Holding my porbe in the air I get a .56Mv mains signal and something else there too.

Im going to disassymble the coil to recheck it with the calculated resistor and I will try some more SRF measurements then.
I thought I read that 2 Mhz was the min for SRF testing with a signal generator.
Even if the one I made doesnt work I have other plans for it. I set it up with a 4 comparitor chip I can run at least two I think and have a double pulsing 10,000pps front end.

I dont know why we are getting such different measurements we are not magicians we take pictures of the results.
Other than we are not actually comparing apples with apples .
what Rigol do you have my scope is the 70 MHz 2 channel.
There have been scope updates for some of the rigol scopes but i can find none for mine so I think its good.
Works fine for everything else.
Maybe your scope has different impediance than mine , Im just trying to narrow things down.

Why do you want a lower SRF?