Equinox iron trick?

[Charles (Upstate NY)]

Charles,

Do YOU know how to bring an "out of balance" coil back into balance? Is that something you personally know how to do?

Steve

You can tape a small piece of ferrite to the coil, connect coil to oscilloscope so you monitor RX and see the out of balance, move the piece of ferrite around the coil, you can watch it either pull the coil more out of balance or drag it back into balance. Not a great solution but once a coil is constructed many/most are typically potted in epoxy and you have no access to the coil inside.

If you are building a coil you have more options. Some manufactures use a 2nd small winding of RX (think a few loops of magnet wire maybe 1 inch in diameter) you can move this small winding around the coil to fine tune the balance then epoxy into place.

Double D coils use two D shaped windings, as you can tell from Minelab coils these two windings overlaps each other down the center of the coil, it is this overlap that balances the coil. Overlap them just right and RX will read zero/flat line on the scope. Nudge them just a touch too far or too little in the overlap and RX will pick up the signal TX is transmitting. Sounds simple enough, but in practice its a real pain. Once you have the windings positioned you need to hold them in that exact position while the epoxy cures, which sometimes the curing pulls the windings overlap out of balance, its really touchy. This is why bumping a coil on something when detecting using higher sensitivity settings will cause the coil to false, it disturbs this balance.

I like the co-planer concentric coil design. Not used on Minelab VLF machines because DD coils gulp less mineralized soil vs concentric. But the concentric coil's cone shaped detection pattern is a great shape for sniping in heavy trash. I built one of these coils once for my Explorer. I dug a Indian cent with it, clean solid signal, nothing else, the plug had several piece of trash in it that I didn't hear. These coils have an outer round TX winding, an inner RX winding, and a 2nd center RX winding wound in the opposite direction. Its this center winding wound opposite, if you had just the right amount of loops of magnet wire that bring the coil into balance. So no overlap to be concerned with, the only pain building that coil is where that center winding wire exits in relation to the coil cable mine always wanted to be on the far side of the coil opposite the cable lol.

 

[sgoss66]

Very, very interesting, Charles!

So, why is the "taping of ferrite" to the outside of the coil "not a great solution." I imagine you would improve the coil performance that way, if it were out of balance and you were balancing it, right?

Steve

 

[Charles (Upstate NY)]

Very, very interesting, Charles!

So, why is the "taping of ferrite" to the outside of the coil "not a great solution." I imagine you would improve the coil performance that way, if it were out of balance and you were balancing it, right?

Steve

It has to be secured and not move, I suppose one could goop epoxy over the ferrite to secure/seal it in place. This is really a hack fix for those of us who build coils and one cures slightly out of balance. Manufactures can just pitch those on the trash pile but there's so much work in building your own coil the ferrite trick can work.

As for performance improvement a perfectly balanced coil vs one slightly out of balance, never really tested this one would need two of the exact same coils to do that. But as the vast majority of coils I have purchased over the years were all perfectly balanced and how difficult that is to achieve, I think logically its probably not good to have a coil even slightly out of balance with the TX signal riding on it otherwise manufacturers wouldn't go through the trouble of precisely balancing the coils.

 

[Dale(Ia)]

Great stuff, Charles.........thank's for all the great info!

Iowa Dale