SHAPE OF COIL FIELD STRENGTH.

G'day fellow prospectors.

When you place a 3x5 inch longx1inch wide,sardine can on flat level ground,it can be picked up by a 12 inch round mono coil,swung flat and inline with the can,(on the same ground) at a distance of at least 12 inches away from the can.
How then can mono coils be described as having field strength shapes similar to that of a U or V cone shape,which is transmitted and supposedly formed,directly under the actual parameter or diameter of the coil,when in actual fact the above test tells me else wise.Or,does this U or V shape,transmit field,apply only to very small targets,which come in actual contact with or directly under the mono coil?.

Cheers kon61.

Now lift the coil above the can and measure the distance of the last response heard.
Then move the coil off center to the can at the same distance you last heard the signal and see if you still pick up the can.

Your test would be better off if you used a round tin lid rather then the strange shape of a sardine can, but thats neither here or there.

The outer circumference of the coil is very live to close by targets, the cone at the center of the coil comes into play more so at depths.

You will find at some point where the outer circumference will have little effect on your sardine can, and as you move the center of the coil over it, it will become clear to you soon enough as to why its referred to as a cone.

If by chance you still are not convinced with this type of testing, your arm will be, and you will just have to except it as it is.

Hope this helps.

The ability of a coil to sense targets off to the side can be a right pain in the a#se when you have dug a deepish hole that's not much wider than your coil. If your target is in the side of the hole you can give yourself a headache trying to pinpoint it. Particularly if your coil is a round one. That's why we love our pinpointers.

Robert

Btw, Narrawa. I just noticed your age. Have you got your telegram from Lizzy yet?

Keep in mind what you are hearing or noticing on your detector RE signal response is derived from the receive circuit not the transmit. You often see this confusion about DD coils for instance where the transmit field is described as blade like therefore better for coverage etc, this is not correct, the field is identical to a similar sized and shaped monoloop coil, it is the receive that becomes blade like due to the second winding.

The transmit field on any coil can only go so far before its strength diminishes to nothing but the strongest part on a Mono would be as the Minelab graphs suggests (see the Minelab Commander brochures for an accurate image of what the field of the two coil types look like). Where it gets complicated is the receive, due to a number of factors such as orientation of target, levels or amounts of mineralisation, depth of target, orientation of coil relative to target, type of timings used, halo effect, direction of coil sweep speed relative to target, amount of eternal noise generated by Sferics, the list goes on and on with essentially each and every target presenting slightly differently to the coil based on all of the above variables.

In the case of a Monoloop coil the receive is the overall shape of the coil and as such plainly suggests a round coil is the best shape for maximum depth due to the coil receiving equally over the radius of the coil relative to a deeply buried target.

Hope this helps,

JP

G'day guys.

All views and aspects have been taken into account.Fact is i just don't see it as clear as what the Minelab Commander 3D pictures make it out to be.Obviously they must be referring to a general transmit field which surrounds each and every coil,regardless of shape or coil size,when the metal detector is switched on,and not near any metal object.The receive field is what we hear coming back from the metallic object,but the actual transmit field shape given off by the coil obviously distorts (some way or another) when picking up a target,depending on as Johnathan said,the many variables surrounding the target,including the target size,shape and configuration of target itself.


Cheers for all info guys,kon61