stacked coil

[luryp]

Anyone out there have any info on constructing a "stacked coil" like the White's Eliminator? Thanks, luryp

[homefire]

Seen one of those on Flea-Bay just the other day.

I was wondering about that my self.

Boasted it would not detect Items above the coil?

[luryp]

Stacked Coil

Yep, if it works, we have lots of areas that have fences, bleachers, and other metal objects that give our other coils a fit if we come near them. I'm sure lots of good stuff rolls up next to these and if this type coil works, might be worth havin'.

[homefire]

I think the guy want way over the top for that one.

No Bids at all.

[luryp]

luryp

Yep, I notice at the Sierra website that it was originally only around 139 bucks or so. I'm not overly technically literate at all, but I think I'd enjoy experimenting with some coil construction. I figured I'd better seek some advice before I attempted something like this though. Thanks for your reply!

[56WILLYS]

Stacked coils..why not?

If you stacked coils you could reject things above the coils. For that matter to somke xtent from the side also.

These coils are really radio antennas. Just look up YAGI or Beam antennas on the net. One coil is a single antenna element, if you put more coils stacked a certain distance from each other, you in crease the gain of the signal and you focus the signal in one direction..

Now how far apart would the coils be? Well ill do some homework and
figure it out.

Gotta go on the road tomarrow for two weeks, so give me some time.

56WILLYS --... ...-- -.- -.-. --... .-. -... -

[Qiaozhi]

If you stacked coils you could reject things above the coils. For that matter to somke xtent from the side also.

These coils are really radio antennas. Just look up YAGI or Beam antennas on the net. One coil is a single antenna element, if you put more coils stacked a certain distance from each other, you in crease the gain of the signal and you focus the signal in one direction..

Now how far apart would the coils be? Well ill do some homework and
figure it out.

Gotta go on the road tomarrow for two weeks, so give me some time.

56WILLYS --... ...-- -.- -.-. --... .-. -... -

If it was only that easy...
In the case of a metal detector the coil does not act as an antenna. The detection is done in the near field, and therefore it acts like a transformer.

[ivconic]

If it was only that easy...
In the case of a metal detector the coil does not act as an antenna. The detection is done in the near field, and therefore it acts like a transformer.

Yes, that's where most of the people get confused - coil at md is NOT antenna, neither is acting like one. You are right; coil's function reminds mostly to transformer's.

[Carl-NC]

Now how far apart would the coils be? Well ill do some homework and figure it out.

About 7 miles.

The fellow who used to make the Eliminators passed away, and there are no plans that I know of for anyone else to make them. Several months ago, someone here at White's made a one-off MXT Eliminator loop for a local utility company. It worked pretty well, allowed them to get up right next to a chain link fence. I was hunting along a fence yesterday, wishing I had that loop.

- Carl

[Qiaozhi]

About 7 miles.

The fellow who used to make the Eliminators passed away, and there are no plans that I know of for anyone else to make them. Several months ago, someone here at White's made a one-off MXT Eliminator loop for a local utility company. It worked pretty well, allowed them to get up right next to a chain link fence. I was hunting along a fence yesterday, wishing I had that loop.

- Carl

Interesting.
How does that work?

[Tinkerer]

Interesting.
How does that work?

Look at my Avatar. It is 2 coils with the current running in opposite direction.
The current in the top coil is only one third of the current in the bottom coil.
Opposing magnetic fields repel each other.

I was experimenting with spiral IB coils. When I stacked the Bucking spiral on top of the RX and TX spiral, I noticed that the target response on the top was minimal, while the target response on the bottom was good.

It took me some time to understand the mechanics, in the end, the visualization made by my friends at MIT, helped me understand how it works.
I use the visualization as a constant reminder: opposed fields repel.

Tinkerer

[homefire]

Look at my Avatar. It is 2 coils with the current running in opposite direction.
The current in the top coil is only one third of the current in the bottom coil.
Opposing magnetic fields repel each other.

I was experimenting with spiral IB coils. When I stacked the Bucking spiral on top of the RX and TX spiral, I noticed that the target response on the top was minimal, while the target response on the bottom was good.

It took me some time to understand the mechanics, in the end, the visualization made by my friends at MIT, helped me understand how it works.
I use the visualization as a constant reminder: opposed fields repel.

Tinkerer

They do the same thing with Radio!

I think it's referred to as a Magnetic Lens!

[Qiaozhi]

Look at my Avatar. It is 2 coils with the current running in opposite direction.
The current in the top coil is only one third of the current in the bottom coil.
Opposing magnetic fields repel each other.

I was experimenting with spiral IB coils. When I stacked the Bucking spiral on top of the RX and TX spiral, I noticed that the target response on the top was minimal, while the target response on the bottom was good.

It took me some time to understand the mechanics, in the end, the visualization made by my friends at MIT, helped me understand how it works.
I use the visualization as a constant reminder: opposed fields repel.

Tinkerer

Of course, that's the "obvious" solution ... but I was wondering whether the Eliminator is something different. If you place a canceling coil above the main TX coil, there will no doubt also be a reduction in sensitivity to ground targets. Perhaps it's just all about compromise.

[Tinkerer]

Of course, that's the "obvious" solution ... but I was wondering whether the Eliminator is something different. If you place a canceling coil above the main TX coil, there will no doubt also be a reduction in sensitivity to ground targets. Perhaps it's just all about compromise.

In the case of a PI, it is not just a canceling coil.
The bucking coil has low L and an extreme short TC, as compared with the TC of the TX and RX coils.
It deflects or pushes the TX magnetic field from the top of the coil downward.
During RX it does cancel some of the RX current but, since the 2 TC's are very different, the RX remains strong.
Due to the much reduced magnetic field above the coil, targets above the coil give a very weak response.

It is a balancing act that is a bit delicate.

Tinkerer

[Qiaozhi]

In the case of a PI, it is not just a canceling coil.
The bucking coil has low L and an extreme short TC, as compared with the TC of the TX and RX coils.
It deflects or pushes the TX magnetic field from the top of the coil downward.

Have you tried this?
I'm asking this question because I would expect a bucking coil above the TX to simply cancel the magnetic field in that region, plus reducing the field below the coil to a lesser extent. What mechanism could cause the TX magnetic field from the top of the coil to be deflected downwards? I doubt this is what's happening.

Think about it this way:
In a standard concentric coil (with the TX, RX and bucking coils in the same plane) and the bucking coil wound around the inner RX, the TX magnetic field is drastically reduced at the coil center. However, it does not push the TX magnetic field outwards, thus causing a wider field.

I think it would be great if it were possible to divert the unwanted magnetic field above the coil and make it point downwards where it is needed the most. Unfortunately I cannot see this happening with this particular configuration.

Do you have any experimental evidence to prove your assumption?