Treasure Mate Pinpointer

[GoldenKiwi]

I know from radio engineering that the wire is NEVER wound directly on the ferrite, but paper, plastic, in rare cases mica and in even rarer cases capton is used.
I'm talking about "radio" times... today I see that with various "switch" transformers the wire is wound directly on the torus cores and rods.
...
I have another "hint" for those who would like to deal with this type of coils.
The longer the ferrite core is, the more focused the direction of movement of the magnetic field is.
Short core = wider the angle of the direction of movement.

What would be the advantages or disadvantages of direct winding onto ferrite vs onto another layer first?

[Altra]

I think the main reason for not winding directly on ferrite, is the risk of a short circuit. In the old days they used a layer of transformer paper between the ferrite and winding. Later plastic tapes. Many ferrites now have an insulating ceramic coating. Pot and e-cores use a nylon bobbin for the winding.

[Carl-NC]

I have wound magnet wire directly on a ferrite rod and gotten poor results compared to using a spacer (for a PI pinpointer). Not entirely sure why.

[ivconic]

What would be the advantages or disadvantages of direct winding onto ferrite vs onto another layer first?

Sorry for overlooking this question!
Without an insulating layer, there’s a significant risk of short circuits or leakage currents between the winding and the core.
Direct contact between the winding and the core can lead to uneven magnetic coupling due to surface irregularities or gaps between turns, resulting in reduced efficiency.
Insulation provides a reliable dielectric barrier between the winding and the core; direct contact between the coil wire and the ferrite core can induce eddy currents within the core material.
These eddy currents dissipate energy as heat and degrade the sensitivity and efficiency of the coil, which is crucial in a pinpointer where detecting weak signals is essential.
Ferrite cores are designed to channel magnetic flux efficiently, but if the winding directly touches the core, localized interactions can dampen the alternating magnetic fields generated by the coil.
This results in lower sensitivity to small or weak metallic objects.
The quality factor of a coil measures its efficiency. Direct winding often leads to higher losses, reducing the Q-factor, which is detrimental for metal detection applications that rely on sharp resonance.
Direct contact introduces parasitic capacitances between the coil and the core.
These can pick up noise and reduce the S/N ratio, making it harder to detect small objects.
Once upon a time, capton tapes were unthinkable to obtain, a privilege of the few.
Today they are cheap and available to everyone.
I think that the best insulation and at the same time a "spacer" is several layers of thinner or fewer layers of thicker capton tape.
I suggest concrete experiments with various materials, but I know in advance that capton will give the best performance.

[Skippy]

Thanks for posting this, Altra. There is some interesting information there.

I am working on a (stalled) project to make a discriminating pinpoint probe. My IB coil is entirely air-cored, wound on lathe-machined bobbins, and I was making it to the same specification as the 13kHz Fisher F75 coil, so I could also make a "Sunray-style" search-coil for that machine.

There is a previous thread with info on the Sunray probe construction, started by 'Glasswalker' , that myself and Carl participated in.
Here is a link:

Balancing "pancake" stacked coils for a VLF pinpointer project - Geotech Forums

And regarding winding ECW wire directly onto ferrite:
Ivconic has summed it up: the ferrite conducts ( if it's high-mu stuff, typically used at low frequencies ), and the circulating currents cause resistive losses. A DMM can easily measure the resistance of a sample of ferrite, some can be surprisingly conductive. Particularly very high mu types used in common-mode interference suppression filters, usually painted green.

[Altra]

Skippy, I designed and manufactured all the Sunray probes etc. I made one for the F75, and believe Sunray branded it as the ""FX1". Due to NDAs, I couldn't give details before. Everyone is retired or dead now, so I can share. The last job I did for them was a probe for Equinox series. I plan on posting the schematic for the pre-amp used and winding details. I am away until January 16th so can't post any useful info right now.

[Skippy]

I was primarily doing this IB pinpointer project as an experimental challenge ( and it was not that easy ), though I did actually want a compact discriminating detector for stand-alone use.
My project was loosely based on one published on a Polish forum. I felt the coil assembly could be improved a lot, so set about designing my own. This was long before any info on the Sunray construction method was known. I assume the high reliability of the Sunray probe itself, and the fact it was sealed in expanding foam meant that no-one had taken one apart. I was surprised it was part ferrite cored ... I thought that would be terrible, turning it into an 'Earth-field' sensor, based on some experiments I did years ago on a Cherry CS209 based design. That's why I liked the totally air-cored approach.

There was mention of the Sunray on the Equinox over on Steve H's DetectorPropector forum. I assumed it neatly gets round the 'security' memory IC problem by leaving the IC in the main coil connected, and just switching over the two differential RX outputs ( maybe the TX too ) between the main coil and Sunray assembly.

It will be great if you can share more info, whenever you have the time. Thanks.

[Altra]

Yes, on the Equinox probe the security chip serial line remained connected at all times. Without an authorized coil the probe would not function. The Sunray probes were all air core, with the exception 100 test units made for the XLT. This particular design in cold weather would go out of balance and cause overload condition in the XLT.

[GoldenKiwi]

MANY thanks all for the multiple replies, thankyou. Apologies for the delayed reply.

I have wound magnet wire directly on a ferrite rod and gotten poor results compared to using a spacer (for a PI pinpointer). Not entirely sure why.

Very interesting thanks! To date I had only wound practically direct plus than a thin insulator additional to the enamel on solid core magnet wire, but never thought to try a spacer. I also haven't tried insulated multi-core yet but will.

[GoldenKiwi]

Sorry for overlooking this question!
Without an insulating layer, there’s a significant risk of short circuits or leakage currents between the winding and the core.
Direct contact between the winding and the core can lead to uneven magnetic coupling due to surface irregularities or gaps between turns, resulting in reduced efficiency.
Insulation provides a reliable dielectric barrier between the winding and the core; direct contact between the coil wire and the ferrite core can induce eddy currents within the core material.
These eddy currents dissipate energy as heat and degrade the sensitivity and efficiency of the coil, which is crucial in a pinpointer where detecting weak signals is essential.
Ferrite cores are designed to channel magnetic flux efficiently, but if the winding directly touches the core, localized interactions can dampen the alternating magnetic fields generated by the coil.
This results in lower sensitivity to small or weak metallic objects.
The quality factor of a coil measures its efficiency. Direct winding often leads to higher losses, reducing the Q-factor, which is detrimental for metal detection applications that rely on sharp resonance.
Direct contact introduces parasitic capacitances between the coil and the core.
These can pick up noise and reduce the S/N ratio, making it harder to detect small objects.
Once upon a time, capton tapes were unthinkable to obtain, a privilege of the few.
Today they are cheap and available to everyone.
I think that the best insulation and at the same time a "spacer" is several layers of thinner or fewer layers of thicker capton tape.
I suggest concrete experiments with various materials, but I know in advance that capton will give the best performance.

Very interesting thanks! I appreciate the explanation. For PI, do you have any thoughts or guidance on the thickness that would be be optimal, or at least for a basis for experimentation?

Do you ground the ferrite? I see bbsailor recommended to do so in another post.

[GoldenKiwi]

Skippy, I designed and manufactured all the Sunray probes etc. I made one for the F75, and believe Sunray branded it as the ""FX1". Due to NDAs, I couldn't give details before. Everyone is retired or dead now, so I can share. The last job I did for them was a probe for Equinox series. I plan on posting the schematic for the pre-amp used and winding details. I am away until January 16th so can't post any useful info right now.

Hi Altra, excellent thanks. I'm sure everyone would find whatever you can share very interesting when you're back and time permits. Thanks!

[boilcoil]

I have wound magnet wire directly on a ferrite rod and gotten poor results compared to using a spacer (for a PI pinpointer). Not entirely sure why.

Maybe due to the magnetostriction of the ferrite rod. When the wire is wound on a spacer, the change in the geometric dimensions of the ferrite core, does not directly affect the coil configuration.