Basket coils don't need shields?

[mermelado]

Hiya Mermelado. Believe me, I am no coil expert,,,Lol. I'm still struggling to learn how to tune VLF Coils and use my Oscilloscope properly. I think I just have more luck with 3DSS Coils because have experimented wth them mostly. The length of cable I use is about 1 metre. Ths cable is just a continuation of the coil winding. I first measure 39 inches of wire then start winding my coil. When I have achieved 6 full revolutions of the former I measure the end wire and, before cutting, I peel back some wre insulation and check the induction. For the Mirage I try to achieve exactly 300uh. For the pickini4 I use 350uh. This is including the coil windings and cable together. The firmware I use for the Pickini4, I think, is the last firmware posted by Bernard. I always use a continuation of the wire for my cable with 3DSS builds and only use a separate cable with my VLF coils. Regards, Marty.

VLF coils in IB detectors are another story. I have made one until now and I thought it was going well, but I also did a TGSL at the same time and now everything is going quite bad, the problem is that if you don't have a coil that you know is going well or a Tested Treasure, there is always the He doubts whether the fault is in the chicken or the egg. Regarding your method, I am curious to know how that thread from the coil reaches the detector, maybe you use a heat shrinkable macaron? because I don't think the cables are lurching loose. Maybe you have a photo to share with us? Thanks, Martin.

Extra question:
Are those 50uh difference between the two coils noticeable? that is, have you tried exchanging them between the two detectors and have you noticed differences?

[MartyJ1963]

Hiya Mermelado. Believe me, I am no coil expert,,,Lol. I'm still struggling to learn how to tune VLF Coils and use my Oscilloscope properly. I think I just have more luck with 3DSS Coils because have experimented wth them mostly. The length of cable I use is about 1 metre. Ths cable is just a continuation of the coil winding. I first measure 39 inches of wire then start winding my coil. When I have achieved 6 full revolutions of the former I measure the end wire and, before cutting, I peel back some wre insulation and check the induction. For the Mirage I try to achieve exactly 300uh. For the pickini4 I use 350uh. This is including the coil windings and cable together. The firmware I use for the Pickini4, I think, is the last firmware posted by Bernard. I always use a continuation of the wire for my cable with 3DSS builds and only use a separate cable with my VLF coils. Regards, Marty.

[mermelado]

Hi Marty,
I see that you are a coil expert and I would like to ask you about the type of cable you use to attach your basket coil to your Pickini4 detector. It turns out that in my initial tests connecting the coil directly to the detector, I am almost certain that I have obtained a certain sensitivity to gold, enough to experiment on the beaches, but when I finished the project and joined it with RG174, that sensitivity has been lost, I do not know if it is chance or if the cable is at fault. Please note that the tests were done with small gold plated chains, as I do not have any nuggets. For other types of objectives, such as coins, I have not noticed changes.

Forget this:
I would also like to know the approximate length of your cable and the firmware version you use
Thanks

[mermelado]

Hi Marty,
I see that you are a coil expert and I would like to ask you about the type of cable you use to attach your basket coil to your Pickini4 detector. It turns out that in my initial tests connecting the coil directly to the detector, I am almost certain that I have obtained a certain sensitivity to gold, enough to experiment on the beaches, but when I finished the project and joined it with RG174, that sensitivity has been lost, I do not know if it is chance or if the cable is at fault. Please note that the tests were done with small gold plated chains, as I do not have any nuggets. For other types of objectives, such as coins, I have not noticed changes.

[Akhnoth]

Hiya Akhnoth. I'm sorry I don't have any phot's of the way I build my coils. I have 2 coils to make soon so I will try to take photo's for you. The 'Open cell foam' is similar to Polystyrene foam but is made from plastic. It is usually what companies use for packing around electrical items etc for shipping. The wire sinks into the plastic as you wind your coil but it helps n raising the centre of the coil to give it a more 'Oval' or 'Round shape and helps space the wire better for less capacitance. I have noticed less capacitance in the coils I have built with the 'Foam' addition than without. It also strengthens the plywood a little better too. When my coils are finished and tested I wrap the coil with 2 coats of medical paper tape then 2 wrappings of surgical fabric bandage. Then I give one coat of Fibreglass and leave 24 hours to dry. I lightly sand the first coat of fibreglass then wipe clean and add a second layer of fibreglass. Then sand again. I make a separate piece for the centre of the coil on which receives the Clevis etc. I stitch the centre piece on with waxed cotton (used in tent making) and then apply a 3rd coat of fibreglass to the coil to protect the 'Stitches' etc. Hopefully soon I will document my next 2 coil builds and post them here. Hope this helps. Regards, Marty.

Hello Marty, your explanations are very clear. Thanks for your informations. I can wait for your futur post with photos. I had the same idea to add something to help having more "rounded" shape of the wire windings.
For the "open cell foam" you are refering to, I have seen that it's made of low density polyethylen. Am I right ?
For the protection with fiberglass I don't have any experience. But I want to learn about it, so if you have also some information of this process. I will be happy to read it. carefully.
I have a question of the coil weight after the fiberglass process ?
And as there is some air inside the enclosure when the coil is used underwater it will be less weighted ?

Thanks a lot Marty

Akhnoth

[MartyJ1963]

Hiya Akhnoth. I'm sorry I don't have any phot's of the way I build my coils. I have 2 coils to make soon so I will try to take photo's for you. The 'Open cell foam' is similar to Polystyrene foam but is made from plastic. It is usually what companies use for packing around electrical items etc for shipping. The wire sinks into the plastic as you wind your coil but it helps n raising the centre of the coil to give it a more 'Oval' or 'Round shape and helps space the wire better for less capacitance. I have noticed less capacitance in the coils I have built with the 'Foam' addition than without. It also strengthens the plywood a little better too. When my coils are finished and tested I wrap the coil with 2 coats of medical paper tape then 2 wrappings of surgical fabric bandage. Then I give one coat of Fibreglass and leave 24 hours to dry. I lightly sand the first coat of fibreglass then wipe clean and add a second layer of fibreglass. Then sand again. I make a separate piece for the centre of the coil on which receives the Clevis etc. I stitch the centre piece on with waxed cotton (used in tent making) and then apply a 3rd coat of fibreglass to the coil to protect the 'Stitches' etc. Hopefully soon I will document my next 2 coil builds and post them here. Hope this helps. Regards, Marty.

[Akhnoth]

Hello Marty and Mermelado,

Mermeado : I have no 3D printer, I always build things manually. Thanks for your proposal

Marty : Yes of course, the thinner material is lighter. I will take the 1/8" of plywood as you. Have you some information to share of your open cell foam ? Have you a commercial name and the company that sells it ? Can you send some pictures of your building process. And I wonder how the foam will sink when the wire is passing over it ?
Thanks for your support

Akhnoth

[mermelado]

Hello Marty,
I plan to build a 3DSS coil but I have a question regarding the thickness of the cardboard. Is it important to have a cardboard thicker or a thinner one ?
I can choose 3mm cardboard (tufnol) or 5mm or 10mm. What is the best thickness of cardboard that gives a stronger magnetic field ?
Thanks, Regards, Akhnoth

If you have a 3D printer, I have a form ready to print.

[MartyJ1963]

I always use the thinnest material possible to keep the coil from being too heavy. I use either 1/8" plywood or 1/8" MDF. If I use MDF I cut a 1/2" strip of 1/8" open cell foam and, with double sided tape, I stick it in the centre of form on both sides. This raises the build up wires a little higher and strengthen the MDF. Hope this helps. Regards, Marty.

[Akhnoth]

Hello Marty,
I plan to build a 3DSS coil but I have a question regarding the thickness of the cardboard. Is it important to have a cardboard thicker or a thinner one ?
I can choose 3mm cardboard (tufnol) or 5mm or 10mm. What is the best thickness of cardboard that gives a stronger magnetic field ?
Thanks, Regards, Akhnoth

[MartyJ1963]

My Pickini 4 works great with a 3DSS Basket coil! It found me a Gold ring with diamonds between 12-14" Inch deep in hard woodland soil. Regards, Marty.

[mermelado]

Thank you both very much. In fact, everything they tell me matches my thoughts. I have dedicated myself to electronics for many years and I ask some questions that in theory I already know the answers. The reason is that after reading hundreds of threads on this forum, I have discovered that conventional logic does not always suit metal detectors. For example, I have read people who boast of advanced knowledge in RF and that when applied to metal detectors, they turn out to be inefficient. This is why I ask questions that seem basic. I don't want to build my knowledge on the wrong foundation.

[Carl-NC]

The question is, can I use a shield + 1 wire screen wire and connect it to the cold side of the coil? That is, one of the coil wires goes directly to positive, I think I could use it as ground for the wire screen. In this case, should you also weld the mesh on the coil part ?. Is it important that the mesh is the inside or outside of the coil, or is it indifferent?
Sorry for so many questions together.

Short answer is 'yes' you can use coax. On the circuit side connect the coax shield to +V and the center conductor to coil driver (assuming NMOS). On the coil side connect one side of the coil to the center conductor and the other side of the coil, plus the coil shield (if you use one), to the coax shield. With a mono coil it doesn't matter which side of the coil winding goes where.

[kt315]

for electrostatic field protection you want to do there is no difference what you use - negative or positive rail. for a newbies
the knowledge is always covered because their school level teaching is zero, they do not undestand that a battery has very low inside resistance. while a coil, i mean
pi coil only, resistance is 1...2...3 Ohm and also low. very significant low. this gives an advantage that you can do not use the shielding.
i mean do not use your crazy fantazy an to use just ITMD book.

the cause of many achievements
---
pakistani guy did 'many achievements', used his crazy pak fantazy and killed delta pulse board. good example. he was much disappointed that 'kt315 did not want to help me'.
you do not have a knowledge then you turn up your fantazy. your fantazy does not give you the knowledge.

[mermelado]

If I use the cable grounding the shield, I will need a shield + 2-wire cable.
---
told billion times. if in YOUR schematic you use P-channel MOSFET your shield wire is NEGATIVE potencial of battery.
if you use N-channel MOSFET in YOUR schematic your shield wire in POSITIVE clemma of the batt.
YOU SEE HERE - NO 2 WIRE CABLE + shield. just a coaxial. do not use your fantazy.

Thank you very much for your quick response and it is what I expected. But I do not understand why you say that I do not use my fantasy, besides being wonderful fantasy and the cause of many achievements, in this case, I have not used it, since my question has a basis based on the detector that I just built and it's the Pickini4. If you look at the diagram or the PCB, you will see that there are three poles for the coil. One is the one that comes from the Mosfet, another comes from positive and a third, which is from the center, comes from "negative" mass. That is the reason that leads me to raise this question, a project published on this website and that contradicts what it says has been said a billion times.