Two Box, or Two Loop, or Multi Loops

[Functional]

This is my first topic posting, so I hope you will find it interesting.

I've done a little reading on coils and I know a little knowledge can be a dangerous thing, but it got me thinking. And it raised a few questions that I lack the expertise and funds to answer on my own.

Firstly, why do two box MD's have an RX and TX loop of the same size? And why can't they have two different sizes like the loops in most common MD coils? And as far as that goes, why do they even have to be rectangular and why can't they be round, or ovel, or triangular? Based on the information I've seen, having two same size loops causes the two box MD to have an admittedly deep, but rather narrow cone shaped coverage area and I thought that if the loops of a two box were different sizes, then a person could sacrifice depth for increased coverage area. Make sense?

Secondly, why can't common MD's use one transmitter loop and more than one receiver loop to cover more area and avoid going to a larger coil? It seems to me, that it wouldn't be too difficult for a guru type to design a multi loop MD that could signal which combination of the single TX and multiple RX loops indicates a particular signal relating to ferrous, or nonferrous material. For instance, an MD with a single central TX loop, (with or without overlap), could have 3, or more RX loops surrounding it and as a signal is returned, (received by one or more of the RX loops), that is different from the normal ground, a directional audio signal, combined with a digital, (lcd, or other), display, or even an analog display, (led cluster), could indicate the direction of the material in relation to the direction of the RX loop to the central TX loop. Again I ask, make sense?

I could probably draw this in a way that would explain it better, but it might take awhile.

F.

[Carl-NC]

Firstly, why do two box MD's have an RX and TX loop of the same size? And why can't they have two different sizes like the loops in most common MD coils? And as far as that goes, why do they even have to be rectangular and why can't they be round, or ovel, or triangular?

Orthogonal (right-angle) coils can be different sizes, different shapes, and even different numbers of windings. The RX coil is placed exactly along the isoflux axis of the TX coil, so it makes no difference what its shape or size.

Based on the information I've seen, having two same size loops causes the two box MD to have an admittedly deep, but rather narrow cone shaped coverage area and I thought that if the loops of a two box were different sizes, then a person could sacrifice depth for increased coverage area. Make sense?

I suspect raw depth is limited by the TX magnetic field, with is largely determined by TX coil size. Then, RX coil size determines sensitivity vs depth... that is, a smaller RX coil would do better on smaller but shallower targets, and a larger RX coil would do better on deeper but larger targets.

Secondly, why can't common MD's use one transmitter loop and more than one receiver loop to cover more area and avoid going to a larger coil?

They can. The AN/PSS-11 uses 4 RX coils over 1 TX coil. The Bigfoot coils are technically 2 RX coils in 1 TX coil. However, you get distinct detection nulls between coils and pinpointing is difficult.

- Carl

[Functional]

Two Box, or Two Loop, or Multi Loops

Orthogonal (right-angle) coils can be different sizes, different shapes, and even different numbers of windings. The RX coil is placed exactly along the isoflux axis of the TX coil, so it makes no difference what its shape or size.

I suspect raw depth is limited by the TX magnetic field, with is largely determined by TX coil size. Then, RX coil size determines sensitivity vs depth... that is, a smaller RX coil would do better on smaller but shallower targets, and a larger RX coil would do better on deeper but larger targets.

They can. The AN/PSS-11 uses 4 RX coils over 1 TX coil. The Bigfoot coils are technically 2 RX coils in 1 TX coil. However, you get distinct detection nulls between coils and pinpointing is difficult.

- Carl

Thanks for the input Carl. If I'm unable to come up with a discriminating PI MD for myself, I hope to find some form of MD that I can obtain a spare coil for and see if theres a way to convert it into a two box, or some facsimile of one. I don't really need as much depth as the commercial two box MD's, (perhaps 2 feet would work fine) and if I can increase sensitivity, (and hopefully the coverage area at the same time), that would be great.

Regarding the multi-loop coils, I was thinking of a single TX loop, (of perhaps 5 inches), surrounded by 3, or 4 smaller RX loops, equally spaced around it, either along the same plain, or at a right angle to the TX loop, (similar to the two box configuration).

I'm throwing ideas around here, but the objective is a common one, to increase the all around benefit of the modification. As for the nulls, and the difficulty with pinpointing, I don't know how the commercial manufacturers deal with the multi-loop configuration, but I would think that they may be sharing the signals with a single receiver circuit, for all, (two or more), RX loops.

I may be wrong about that, but if I'm right, I think a person could at least partly solve the problem, by using an receiver circuit for each of the Rx coils with individual, analog & audio, or digital & audio indicators. And an analog LED indicator for each reciever circuit would likely be more useful in the field, than a digital indicator alone, as it would be relatively easy to indicate direction of an object from the intersection of the TX loop and the corresponding RX loop. (At least I think so.)

F.