Nexus coil

[Carl-NC]

Purely inductive coupling is what we call the "X null." If that's all there were, then a perfect null would be possible. But there is also the "R null" which is largely due to capacitive coupling. For an OO coil that occurs at the overlaps. A 90° overlap helps (now commonly seen on DD coils) and a spacer between the coils does as well, but that increases the thickness of the coil.

[Skippy]

The 90 degree signal can also be nulled with small 'high-frequency' targets, eg. the "5 cm diameter ring cut out of aluminum foil" noted in post #12, placed "in the right place" on the coil. Ideally, the target would be at least 10 times the detector frequency, so it mainly affects the 90 degree, and not much the zero degree. If it changes the zero degree as well, then the coils will need moving to re-null that, which is inconvenient.
These 'nulling targets' should be as small as possible.

[Gwil]

Thank you gentlemen - that's helpful.

[Locator]

Thank's for the nice analysis. But I think that one coil is not enough for treasure searching, it's like going fishing with a shotgun!!!
Regards.

[sirbedevir]

I don't know the explanation. With DD coils, it's so that you can't balance them by positioning them. In such cases, it helps if you try to position small metal objects to the DD cross points, sometimes iron, sometimes aluminum, sometimes copper helps. With this giant coil, when it was made of thick wire, it couldn't be balanced with such a trick either. With thin wire, a 5 cm diameter aluminum foil hoop was also needed, which is visible in one of the photos.

[sirbedevir]

The same problem was caused by too much carbon fiber in the laminate. First I made a carbon fiber laminate in the template like the factory nexus heads. But the alignment didn't work, so I made another one with fiberglass. That worked. I don't know how they can solve the problem of using carbon fiber in the factory nexus head.

[sirbedevir]

An idea for using overweight searchcoils: scythe hold. Homemade handle additions to the factory Nexus.

[pechkata]

Balance of both coils.

[sirbedevir]

It was very difficult to mechanically balance such large coils. When I used carbon fiber, it didn't work.
Is there a difference in sensitivity between a mechanically balanced coils or circuit balanced coils in IB detectors? Are they equivalent to each other?
Nexus has carbon coils. Nexus MP use balance circuit?

[Altra]

In my experience the mechanical balance needs to be close, for the electronic nulling circuit to work. You can't expect to correct a great imbalance. I have not observed a loss in sensitivity using tx feedback to the rx. I expect if you lowered the feedback resistor and increased the capacitor value you could brute force a null. In this case you probably see a loss of sensitivity.

There maybe other methods that work better? A piece of ferrite in the right location can work miracles.

[Qiaozhi]

[QUOTE=Altra;n432817]You can't expect to correct a great imbalance./QUOTE]

Actually, it is possible to electronically balance two coils that are totally non-balanced mechanically.
See this thread ->
https://www.geotech1.com/forums/foru...inelab-go-find

[Altra]

The GoFind is an interesting example, which I would like to understand more on how it functions.

I was referring to the nulling circuits in the Nautilus and Treasure Mate which have a limited range.

Thanks for the link,

[Altra]

From your link this popped up. There are a lot of good ideas buried on Geotech.

https://www.geotech1.com/forums/foru...-mono-coil-IB=

[pechkata]

Better balance - if they are equal in inductance...

[sirbedevir]

I found an old 31" searchcoil. It's a different shape than the 31" searchcoil currently available for the Nexus MP. Have you seen one like this? Is this also for the Nexus MP, or is it for an earlier model?




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