Making a 15" round coil.

[Jim in Idaho]

I'm going to convert a Whites 6000 into a two-box. Going to make the coils. If I make them round, but decide to squash them into an oval, what happens to the inductance value? Is there any advantage to the oval shape, as far as depth or sensitivity? Thanks
Jim

[pito]

Round coils are giving maximum surface of the circle/coil with the same length of the wire, squeezing coil will reduce inductance , sensitivity of Rx coil and strength of the emitted field by Tx coil, usually squeezing is not big so decreasing is about 15%.

[Carl-NC]

If you take a round coil and squash it into an oval, then the inductance will decrease by the root-root of the area ratio:

[Jim in Idaho]

Many thanks, guys. So, no benefit to an oval, except maybe slightly wider area covered? I'm thinking I'd get at least a 36" wide swath with a 12" coil, and maybe even with a 10". Not sure about the math to determine that. With the data-logger and the TF-1200, I'm now doing swaths at about 4' centers, though I know I could do wider. I'd rather do more walking and have better resolution.
Jim

[kt315]

I'm going to convert a Whites 6000 into a two-box

there is not a coil in two-box either it is TF900 or TM-808. it is some kinda a transformer with one loop, on TX side and RX side.
TX - for translating, one loop is second output winding, RX - for receiving, one loop is first input winding.
in both uses ferrous ring. certainly, you may use winding of wires instead of the transformers.

[Jim in Idaho]

Yup...thanks, KT. I knew that. I'm going to connect direct, but with separate coils. Might not work as well, but no way to know, but to try it, and test.
Jim

[kt315]

a russian guy did a two-box with the coils in one flatness, unorthogonal. can not give a link, his site had gone.
he used a backing coil between two.

[Jim in Idaho]

a russian guy did a two-box with the coils in one flatness, unorthogonal. can not give a link, his site had gone.
he used a backing coil between two.

What, exactly, is a "backing" coil, KT? I did see videos of a guy that converted regular detectors to two-box. He had decent English, but it wasn't his native language. I kinda thought he might be Russian. He does not show any details of what he's doing.
Jim

[kt315]

feedback coil. my mistake.

[Jim in Idaho]

feedback coil. my mistake.

If done correctly, I'm thinking the Orthogonal configuration shouldn't need a feedback coil. One question I do have is, is the spacing of the coils magnetically, or electrically significant?
Jim

[Carl-NC]

Orthogonal does not need a feedback coil, however many of them include a way to adjust the tilt of the RX coil which adjusts the null. The TF/TM models don't do this, the null is what it is, and you have to keep the preamp gain low enough to not overload.

Spacing affects depth & sensitivity. Larger spacing will go deeper on the biggest targets but lose sensitivity on smaller targets.

[Jim in Idaho]

Orthogonal does not need a feedback coil, however many of them include a way to adjust the tilt of the RX coil which adjusts the null. The TF/TM models don't do this, the null is what it is, and you have to keep the preamp gain low enough to not overload.

Spacing affects depth & sensitivity. Larger spacing will go deeper on the biggest targets but lose sensitivity on smaller targets.

I didn't know if the spacing was somehow connected to the frequency, so thanks for the explanation. I did know that Fisher had the null adjustment on theirs, but forgive me, I thought it was a pretty crude way to do it...LOL. I think the TF, and TM guys just made the mast so rigid, they figured the coils would stay in null unless treated harshly. So, for me Carl, I'll go with a shorter spacing. I'm looking for shallow mineral veins or float...maybe down to 3-5', not car bodies at 20'...unless they're made of gold, silver, or copper...Ha! As always, I appreciate the input....I might even be getting smarter, or at least, more educated by you guys. Ya know, after thinking about this for a few minutes, I'm thinking a plastic bolt and wingnut, to adjust the RX coil, might be a good idea. Gonna think about that.
Jim

[Mark-VA]

Looking forward to seeing your finished product.

[Jim in Idaho]

Looking forward to seeing your finished product.

LOL...me too !
Jim

[stefan-s]

I did this with my spectra v3i but im having lots of trouble with ground effect when i raise and lower the detector im getting signal from the ground.