OO Coils - Any gotcha's

[Olly]

After experimenting with a multitude of different IB coil types I've come to the conclusion that the OO coil is the easiest to null accurately and to get the coil to do exactly what I want regarding phase shift etc. Apart from the reduction in sensing area compared to the DD coil, are there any other disadvantages that I need to be aware of?

Regards,

[sinclairuser]

After experimenting with a multitude of different IB coil types I've come to the conclusion that the OO coil is the easiest to null accurately and to get the coil to do exactly what I want regarding phase shift etc. Apart from the reduction in sensing area compared to the DD coil, are there any other disadvantages that I need to be aware of?

Regards,

i tend to agree with you about OO coils, easy to wind easy to null, well easier than some other designs, when i was messing around making balanced coils i found the OO design was easier to get all the ground balance and discrimination working how i wanted.
but they just look daft, the OO config is not very practical either imho, though using the methods i used on the OO design with perseverance i was able to build and tune a DD coil.
so if someone wanted to build and tune a coil, an OO design is a good starting point.

[Smirnov-Arta]

...

The application of the "OO" form in real conditions is very limited. The working area is not large, and the overall dimensions and width are not small. I did both the forms and "OO" and "reverse ellipse" and they are no better than the usual forms of DD. The selection of the parameters of inductance and Q-factor Tx /Rx gives the best result for a specific MD, taking into account the location/soil/goals. I apologize for my google translator.

[Skippy]

Quote:"Apart from the reduction in sensing area compared to the DD coil ..."
Isn't that one of the OO's features? It has a small area it picks up ground signal from, so it can give greater detection depth ( stronger target pickup, less ground pickup ).
"Are there any other disadvantages that I need to be aware of?"
The lack of available coil shells, when compared to the common circular variants.
"the overall dimensions and width are not small."
This obviously depends on what size coil you're building. I've never built an OO coil, but the one I was planning on making was a " 5 inch " equivalent, probably with two 10-12 cm loops. The finished item would be small enough that it could be 3D-printed on a regular 'home' printer.

[Olly]

Thanks for the feedback guys.
I've made two 20 cm loops, TX = 6mH using 0.8mm wire and RX = 6.5mH using 0.25mm wire.
I plan to print the coil shell on my Ender 3 printer in two or three sections and then glue them together. This has been quite a successful strategy for me in the past and once the coils are filled with epoxy they are just as strong as if printed in one go.

Regards

[Carl-NC]

Isn't that one of the OO's features? It has a small area it picks up ground signal from, so it can give greater detection depth ( stronger target pickup, less ground pickup ).

Ground pickup depends on the area of the RX coil, its position relative to the TX coil, and lift-off effects. The overlap area is a strong factor in target responses but not so much with ground. Ferinstance, a typical concentric has an RX coil with an area 1/4th that of the TX which helps reduce ground pickup, but the RX coil is placed right in the middle of the TX which does not help. Lift-off can be strong because the field from the main TX coil is distorted at a different rate than the counter-field from the bucking coil.

With DD/00/OO coils, the RX is the same size as the TX (not good) but is placed off to the side (good). Lift-off progressively gets better (DD -> 00 -> OO) as you eliminate tight radii which causes field distortion variances vs distance to the ground. I think that OO will theoretically have the best lift-off performance, which means that GB is very well behaved.

[Olly]

Ground pickup depends on the area of the RX coil, its position relative to the TX coil, and lift-off effects. The overlap area is a strong factor in target responses but not so much with ground. Ferinstance, a typical concentric has an RX coil with an area 1/4th that of the TX which helps reduce ground pickup, but the RX coil is placed right in the middle of the TX which does not help. Lift-off can be strong because the field from the main TX coil is distorted at a different rate than the counter-field from the bucking coil.

With DD/00/OO coils, the RX is the same size as the TX (not good) but is placed off to the side (good). Lift-off progressively gets better (DD -> 00 -> OO) as you eliminate tight radii which causes field distortion variances vs distance to the ground. I think that OO will theoretically have the best lift-off performance, which means that GB is very well behaved.

Thanks Carl, great info.

Regards