VLF IB coils

[Tinkerer]

It is difficult to build very large IB coils, since the slightest movement of the coils relative to each other causes a false signal.

Are there any charts showing the relation between the diameter of the coil and the detecting depth for VLF MD's?

Tinkerer

[bbsailor]

It is difficult to build very large IB coils, since the slightest movement of the coils relative to each other causes a false signal.

Are there any charts showing the relation between the diameter of the coil and the detecting depth for VLF MD's?

Tinkerer

Tinkerer,

I believe Eric Foster's chart in this thread relates to VLF coils also.

http://thunting.com/geotech/forums/s...ad.php?t=14121

In general, the detecting depth depends on:

1. the relative size of the target to the coil
2. target orientation relative to the coil
3. target material

It should be noted that since coin hunting is a rather popular and common target, that coils have been designed in the 7" to 12" range with 10" being a more common size. The rule of thumb seems to be: "make the coil diameter about 10 times the target diameter". With a dime being about 0.7" and a quarter being 0.9" in diameter, that would put coil diameters in the 7" to 9" range which has historically been the case. The actual coil diameter inside the coil housing is .5" to 1" less in diameter than the outer housing diameter.

Only recently have MD manufactures ventured into the slightly larger coils in the 12" range to get an edge on the competition with a little more depth.

When you look at Eric's chart, you will see that as you go higher on the chart (more horizontal than vertical), that the optimum coil size for a particular target gets much larger than the improvement in potential depth. Coil weight, flexing and stability as well as what can be reliabily manufactured comes into play.

bbsailor

[Tinkerer]

Coil diameter x depth

Tinkerer,

I believe Eric Foster's chart in this thread relates to VLF coils also.

http://thunting.com/geotech/forums/s...ad.php?t=14121

In general, the detecting depth depends on:

1. the relative size of the target to the coil
2. target orientation relative to the coil
3. target material

It should be noted that since coin hunting is a rather popular and common target, that coils have been designed in the 7" to 12" range with 10" being a more common size. The rule of thumb seems to be: "make the coil diameter about 10 times the target diameter". With a dime being about 0.7" and a quarter being 0.9" in diameter, that would put coil diameters in the 7" to 9" range which has historically been the case. The actual coil diameter inside the coil housing is .5" to 1" less in diameter than the outer housing diameter.

Only recently have MD manufactures ventured into the slightly larger coils in the 12" range to get an edge on the competition with a little more depth.

When you look at Eric's chart, you will see that as you go higher on the chart (more horizontal than vertical), that the optimum coil size for a particular target gets much larger than the improvement in potential depth. Coil weight, flexing and stability as well as what can be reliabily manufactured comes into play.

bbsailor

Thanks for the reply.
Eric's chart is very helpful, but it was my understanding that it applies to mono coils.
How could we correlate this information to coils with separate windings for TX and RX?

It is common to make the RX coil of smaller diameter than the TX coil.
Is it the TX coil diameter that determines the depth?

A larger TX coil produces a field that reaches deeper, but does a small diameter RX coil take advantage of this?

A small diameter RX coil is better for pin-pointing.
It can be built to be faster than a large diameter RX coil.


Is the RX coil diameter more important than the TX coil diameter?

Tinkerer