Making a 15" round coil.

[stefan-s]

to not to pollute your topic i made one myself:

https://www.geotech1.com/forums/forum/technology/coils/428483-two-box-for-spectra

[Jim in Idaho]

ground effect is the only issue im not able the solve = The easiest way is to use quadrature detector, you will have Ux and Uy, you need to rotate both synchronous switching signals until Uy =0 when machine is close to the ground.
Maybe i make mistakes with shielding = good shielding = detector is not responding to human bodies.

bring two hands close to the Rx coil

For people without an engineering education, that might as well be in Greek.
Jim

[pito]

ground effect is the only issue im not able the solve = The easiest way is to use quadrature detector, you will have Ux and Uy, you need to rotate both synchronous switching signals until Uy =0 when machine is close to the ground.
Maybe i make mistakes with shielding = good shielding = detector is not responding to human bodies.

bring two hands close to the Rx coil

[Jim in Idaho]

Indeed, that seems to be the problem ad least in my opinion. Depth etc is really good but the ground effect is the only issue im not able the solve probably because of my lake of knowledge of how to building these kind of coils (im have the same issue when i try to build a DD coil). Maybe i make mistakes with shielding or something i don't know i build several new coils but cant get it working properly.

So have you checked to be sure the RX coil is not "seeing" the transmit coil? The RX coil has to be in "null" from the TX coil. You may need to tilt the RX coil slightly, up and down, to be sure it's in null.
Jim

[stefan-s]

Will it not ground balance, Stefan?
Jim

Indeed, that seems to be the problem ad least in my opinion. Depth etc is really good but the ground effect is the only issue im not able the solve probably because of my lake of knowledge of how to building these kind of coils (im have the same issue when i try to build a DD coil). Maybe i make mistakes with shielding or something i don't know i build several new coils but cant get it working properly.

[Jim in Idaho]

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.

Will it not ground balance, Stefan?
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.

[Jim in Idaho]

Looking forward to seeing your finished product.

LOL...me too !
Jim

[Mark-VA]

Looking forward to seeing your finished product.

[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

[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]

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

[kt315]

feedback coil. my mistake.

[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]

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.