Wide Towed Coil for TDI

[lytle78]

Helping a friend who searches old campsites and such for 19th century artifacts and who has hundreds of square miles of private land to cover. He current uses a 3 detector vlf rig with cleansweep coils giving him about 54" of coverage. Since the TDI is so forgiving of coil details, I'd like to fabricate a 8 - 10 foot coil for towing on a mat or sled (the area in question is rolling praire grassland). Depth is not a priority but good sensitivity to even rather small objects (such as tacks, buttons, etc) is.

I've read what's posted here on coil construction and don't have the technical knowledge to extrapolate to what I want to do.

Can anyone give some suggestions as to wire type and gauge, number of turns for (for example a 10" span), need for shielding or not, and if the shape can be rectangular and if so what aspect ratio is acceptable.

Thanks in advance

Rick Kempf

[Reg]

Hi Rick,

Personally, I would start out with a smaller coil and see how that works first.

Lets assume you start out with a 3' rectangular coil. From that basic shape you could form any shape you so desired within the circumference boundaries. With 12' total edge length, you could make the same coil a 5' wide by 1' or anything in between for that matter. Actually, it could be made wider but it would be narrower also. So, depth would suffer.

You could mount your basic design on a large rubber mat and simply hold it in place with duct tape as a temporary setup. This would make changing shape much easier to do, rather than make everything rigid and having to keep changing things.

Personally, I considered using a cheap plastic toboggan as a form to initially try. These are inexpensive and available plus have an elevated front end and sides to minimize problems with things hanging up.

Reg