Cylinder Coils?

[Carl-NC]

What type/brand of magnetic field strength meter did you use for the measurements?

It's a homemade meter, I call it a Magnetic Field Probe. Detailed info is in ITMD3 (coming soon) but I've already talked about in another thread. I don't remember which one.

Carl. i just did a quick google search on 'Solenoidal' coils, no, that doesn't look like it at all. Maybe the style i'm talking about is this type of coil, but i don't know a lot about them so couldn't say for sure!!

#2 in the previous PDF is what I'm talking about. By "solenoidal" I mean a single-layer coil.

[Tinkerer]

What is the insulation thickness of the PVC wire and the Teflon wire? Or we could say the outer diameter of the insulated wire?

[Nova]

Okay, thanks Carl., i get ya, so the tests you have done prove this fella Chet wrong?, i am not sure how he came to that conclusion, i just might have to sign up to that forum and ask him.
That table you have shows that a normal " flatwound " coil is one of the worst in the case of far field ,so would be a better coil for shallower targets as proven by most users correct?
When you say "scramble" wound, you mean to say the windings are bundle wound with NO worry about making them fit a desired pattern, so when you wind it where ever the windings end up, they end up correct?
PVC wire, could you link me to some please?
I would be interested in making a DD coil, does your new book thoroughly cover how to make a DD coil as it's on the cover?
There's one other thing that has been bugging me, so while i have you here could you please answer this for me?

We know that with a P.I. detector we can hit bucket sized targets at 2 or more metres. So to my mind the TX is not the problem and the specs within reason probably don't matter too much?
Can you explain to me what is the reason that you can't hear let's say a small bullet at 4 feet, if the TX is hitting the bucket at 2 metres is it also hitting the bullet at 4ft?
When you see a drawing of say a mono coil field, those field rings get larger but as they get farther away (in a drawing) there not hitting the middle part , so when a coin for example is pictured deeper down in the drawing in the middle of the coil those field lines are not hitting the coin say at 3ft deep, is this the reason you can't hear that bullet at 4ft, (the field lines just don't hit the target) or something else more related to the RX going on.
I am after depth on larger targets, i have the Detech 15in DD spiral coil, i dug an end of an old timers pick at 27-30inches in flogged ground with my 5000, (nobody else heard this target) i have read that increasing the windings of the RX will increase the power of the receive signal but will increase noise, i am willing to go for that extra noise if i can gain an extra 6-8 depth, is that possible Carl to get an extra 6-8 inches by doing this?
I'll leave it at that thanks!!!

[bbsailor]

What is the insulation thickness of the PVC wire and the Teflon wire? Or we could say the outer diameter of the insulated wire?

Single layer coils, either vertical or flat, will have less inductance than a bundle wound coil. The important thing to experiment with is the coil style, inductance, resistance, shape and delay potential for various desired targets.

Here is an example. Beach hunting can be more efficient when using a rectangular coil shape of 6 inches by 18 inches. This allows more ground coverage per sweep but not the most depth. A 15 inch or 18 inch diameter round coil will provide more depth but when sweeping the sand with these large round coils, you need to overlap your sweep pattern.

I have found through experimentation that bundle wound coils using Teflon insulated wire will produce a coil with less capacitance and a lower delay signal due to the lower value of the dielectric constant of Teflon. Bundle wound coils may be more efficient for some targets than single layer coils.

When optimizing a metal detector for a particular target, many things are tradeoffs that should be designed, implemented, documented and measured on a variety of targets in a variety of detecting locations. Try a variety of TX frequencies, preamp gain settings, TX to RX delay and any other variable related to your detector design.

I hope this helps?

Joseph J. Rogowski

[Carl-NC]

What is the insulation thickness of the PVC wire and the Teflon wire? Or we could say the outer diameter of the insulated wire?

I'm traveling this weekend, will check when I get back.

[Carl-NC]

Okay, thanks Carl., i get ya, so the tests you have done prove this fella Chet wrong?, i am not sure how he came to that conclusion, i just might have to sign up to that forum and ask him.

I have no idea, I'd need to see exactly what he's done.

That table you have shows that a normal " flatwound " coil is one of the worst in the case of far field ,so would be a better coil for shallower targets as proven by most users correct?

If you mean the solenoidal-wound (helical) coil, I don't know anyone who had used one.

When you say "scramble" wound, you mean to say the windings are bundle wound with NO worry about making them fit a desired pattern, so when you wind it where ever the windings end up, they end up correct?

Yes.

PVC wire, could you link me to some please?

PVC-insulated wire is commonly available everywhere. I don't recall where I got this particular wire.

I would be interested in making a DD coil, does your new book thoroughly cover how to make a DD coil as it's on the cover?

Yes.

We know that with a P.I. detector we can hit bucket sized targets at 2 or more metres. So to my mind the TX is not the problem and the specs within reason probably don't matter too much?
Can you explain to me what is the reason that you can't hear let's say a small bullet at 4 feet, if the TX is hitting the bucket at 2 metres is it also hitting the bullet at 4ft?

The EMF induced in a target is proportional to the strength of the B-field and the area of the target. So the bullet has a much smaller EMF, and therefore a much smaller target field. Also, a very large target couples more efficiently with the RX coil. Yes, more RX windings give a stronger target signal, but an equally stronger signal for ground and EMI. You can try it, but generally it doesn't help much.

[Nova]

Thanks Carl, you have been very helpful, any idea when your book will be ready? and where can we buy it from?

[Carl-NC]

2, maybe 3 more weeks. Amazon.

[boilcoil]

Someone had posted here, on the forum, a table with experiments with different coils (Including with cylindrical coil).

PS:The results are like Karl's results .

[Nova]

Thanks for that Boilcoil, by what i can see "4" flat basket weave is the outright best on 300mm + ?, and the vertical flatwound "5" is 2nd, it would be interesting in knowing if this trend continues upto 400mm and beyond, maybe the vertical coil would catch up and beat it in the end, anyone know?, Carl?
Some of us aren't interested in chasing amoeba ****e, but are looking to chase 1oz+ chunks at 3-5ft deep, can a conclusion be determined on what really is the best coil for this and the size of course, but not forgetting the mineralised ground part of the equation? and on a Minelab, i have an SD2200d it is a couple of inches deeper than the 5000, BUT, the 5000 can be set to run very quite in hot ground, the 2200d is not so quite and also the signal response is far weaker,( newer tech definitely wins here), if i can get an even deeper pulse installed on the SD i would consider getting that done, anyone know if that is possible?

[Tinkerer]

Thanks for that Boilcoil, by what i can see "4" flat basket weave is the outright best on 300mm + ?, and the vertical flatwound "5" is 2nd, it would be interesting in knowing if this trend continues upto 400mm and beyond, maybe the vertical coil would catch up and beat it in the end, anyone know?, Carl?
Some of us aren't interested in chasing amoeba ****e, but are looking to chase 1oz+ chunks at 3-5ft deep, can a conclusion be determined on what really is the best coil for this and the size of course, but not forgetting the mineralised ground part of the equation? and on a Minelab, i have an SD2200d it is a couple of inches deeper than the 5000, BUT, the 5000 can be set to run very quite in hot ground, the 2200d is not so quite and also the signal response is far weaker,( newer tech definitely wins here), if i can get an even deeper pulse installed on the SD i would consider getting that done, anyone know if that is possible?

Tests without the real cable and shielding, are quite useless, because the characteristics change dramatically when adding the shield and the cable.
The cable itself is of significant importance, as the wrong cable can spoil the whole coil.

[Nova]

Tinkerer, if that is the case, why bother with tests like this if they aren't going to give you an accurate result?, that part is nonsensical, if i had the time and knowledge of building these coils like a lot of you have on this forum i would do exactly that and then clean up the goldfields, and then after i had done that THEN i would give the secret away LOL!!!!

[Nova]

While it's fresh in my mind, i don't like the way the coil connection is on the box of the SD/GP/GPX detectors, it very awkward trying to push the connection into the box, i was thinking about a small dongle connection, one end permanently connected to the detector the other end sticking out a little (enough to make it easy to connect), but i know about the cable being important especially with it's length, but would say the combined length of say 5cm for this dongle upset the balance of the coils final characteristics? anyone?

[Carl-NC]

Tests without the real cable and shielding, are quite useless, because the characteristics change dramatically when adding the shield and the cable.
The cable itself is of significant importance, as the wrong cable can spoil the whole coil.

It is true that the cable & shielding can have a dramatic effect on final performance, but it is still quite useful to compare raw windings. The table in post #6 contains very valuable information if you are trying to determine which type of winding (or wire) to use for an aggressively fast coil, or which winding style will give the most depth. In particular, field strength efficiency comparisons are little changed by shielding or cable impedance.

[Tinkerer]

It is true that the cable & shielding can have a dramatic effect on final performance, but it is still quite useful to compare raw windings. The table in post #6 contains very valuable information if you are trying to determine which type of winding (or wire) to use for an aggressively fast coil, or which winding style will give the most depth. In particular, field strength efficiency comparisons are little changed by shielding or cable impedance.

I can agree on that.
The fact is, that there are many factors involved in building the right coil for a specific kind of target. Compromises have to be made in the end.
Most amateurs just use an existing coil because they consider it to be too much work to build their own. Too complicated.

So maybe we should talk a bit more about coil building.
Discuss:
The reasons for a coil shape.
The diameter of the coil.
The type of wire to be used and why.
Thin wire or thick wire?
PVC or Teflon insulated?
The type of winding and the reasoning behind it. (as started in the discussion above)
Things like tight windings or loose windings. (Tighter windings have more inductance and capacitance)
Shielding types and materials
The importance of the distance of the shielding to the coil wires

I find the link to the MOGAMI website useful. There is an online calculator where you can compare the inductance and capacitance between wires for different diameters of wire, Teflon, PVC, air space between wires etc.

http://eve.mogami.com/e/cad/electrical.html
http://www.mogami.com/e/cad/coil-01.html

HyperPhysics

The misc.El app is also very useful for coil calculations