Basket coils don't need shields?

[mermelado]

I've read it somewhere, but if it's true, I don't understand why.

[MartyJ1963]

I use 3DSS (Basket) Coils on all of my Home built P.I's. I've never needed to shield them and I have never had any issues with them. It's something to do with the geometry of how it is wound that seems to make them 'Self-shielding'. Best answers on this subject lie on the 'Chance P.I' Thread (The Racetrack coil). Regards, Marty.

[mermelado]

Thanks Marty:
The truth is that I can not find the exact post you are referring to, but in the attempt, I have come across many comments from you on this topic. I also read a thought-provoking one when it states that no commercial manufacturer uses these types of coils. I am still waiting for PIC for my Pickini4, so I cannot do tests, but I deduce that the low capacity of the winding will also play a role.

[MartyJ1963]

This is the thread I refered to.
https://www.geotech1.com/forums/show...racetrack+coil
Baum7154 had really good success and results from his 3DSS Coil experiments and I always build mine with the same method and I am really satisfied using these coils on all my PI's especially the 'Mirage'. Baum7154 starts to refer to his methods around post #22.Hope this helps. Regards, Marty.

[James]

I also have used for many years basket coils. I use Litz wire to keep the cross coupling capacitance to a minimum. Stat safe and healthy. Jim

[mermelado]

I also have used for many years basket coils. I use Litz wire to keep the cross coupling capacitance to a minimum. Stat safe and healthy. Jim

I have just tested my basket coil and it seems to work fine, I have built a Pickini4, the truth is that there are a lot of random beeps, but it seems that that is normal for that detector while at home because of the EMI. I have to finish mounting it and testing outside. The litz wire is something I would like to try, for now I have settled for 0.4mm wire and a half burned, recovered from an old radio transformer. The litz thread is impossible to buy here and online the prices I have found are exorbitant.

[mermelado]

More questions

Continuing with the topic of the basket coil. In my case it is for Pickini4 and I suppose that the cable is better if it is shielded, but I have a doubt. If I use the cable grounding the shield, I will need a shield + 2-wire cable. 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.

[kt315]

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.

[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.

[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.

[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.

[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.

[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.

[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]

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.