Using an elliptical coil sideways

[Hawkear]

Just posting this as a hypothetical for discussion but I was wondering if there may be any benefit in using an elliptical coil sideways.
My understanding is that depth capability of an elliptical coil is compromised by the shorter axis with coverage enhanced by the longer axis,
Would the reverse occur using it sideways with coverage reduced with the shorter axis at right angles to the sweep direction but depth increased by the longer axis in line with the sweep direction?

 

[stevewilko]

Hi Hawkear,
Interesting concept, I will consider it some more, but, I think the advantage of the elliptical coil on a target generation basis is the sensitive 'toe' at the leading point of the elliptical coil.
For example, I have an 18" x 12" which shouts small bits under the 12" leading edge that the middle point of the overall mono doesn't snipe so well.
Then I suppose the geometry or maths of the ellipticals, as mine above, provides 18 + 12 = 30, divided x 2 equates to a 15" round mono total mass configuration.
Then, considering this finding I have the potential of 12" sensitivity with 15" depth potential approximately.
Then to ponder what you have proposed I think that the same result would be attained with a sideways mount that you are thinking about.... but would the leading toe sensitivity get run over!
There is incremental forward motion swing overlap to consider with my 12" ' leading toe' pulling me up with an excellent target response that I appreciate with my choice of this coil.
Good topic ha ha.
Cheers
Wilko.

 

[Tathradj]

I tip the coil side ways for pin pointing.

 

[davsgold]

the only advantage of using a big elliptical coil "sideways" is as a drag coil where it is only going forward and not side to side motion, to swing and elip coil at 90 deg rotation makes no sense when swinging the coil

 

[Hawkear]

Yes, trying to get my head around it a bit more, it would make sense that the method in which it is used would not make any difference to its depth sensitivity as that property should only be determined by the intrinsic design and size of the coil.
So I would think then if that were the case the tip and edge sensitivity would still be there.
I remember Minelab producing a diagram of the field sensitivity profile of mono and DD coils. The profile for a mono coil was a simple cone shape tapering to a point and the DD being a squeezed blade shape.
The implication of the diagram for the mono coil was that its area of effectiveness diminished progressively with depth.
I'm imagining an elliptical may be something like an elliptical cone narrowing to a line between the two foci of the ellipse.
If that is true then perhaps using the coil sideways could result in a slightly more drawn out signal passing along the longer axis of the coil rather than the shorter axis. Whether this would make deeper targets more recognisable I just don't know.
Maybe the coil design gurus could shed some light on the sensitivity profile of an elliptical or perhaps that could be tested practically in the following manner.
If a target is found using an elliptical in normal swing mode then checked again with a push pull motion to see if there is any difference to the quality of the signal.

 

[davsgold]

If a target is found using an elliptical in normal swing mode then checked again with a push pull motion to see if there is any difference to the quality of the signal.

exactly like when pushing the elip coil under bushes etc, it happens all the time and targets are found and it works, but in general it is side to side swing of the elip coil that is what makes most sense

 

[Hawkear]

exactly like when pushing the elip coil under bushes etc, it happens all the time and targets are found and it works, but in general it is side to side swing of the elip coil that is what makes most sense

Totally agree with all of that, poking among bushes and it would be common sense in using an elliptical in the manner for which it is designed.
But let’s say you had but one largish elliptical coil and you had just discovered a patch and you had some sort of swivel joint at the end of the shaft. Would you be tempted to try it at 90 degrees to check out the proposition or just walk away?
For me I’s just gotta know.

 

[davsgold]

for me I'd try a variety of coils and settings until I am satisfied I can't find any more before I just walk away

 

[Hawkear]

for me I'd try a variety of coils and settings until I am satisfied I can't find any more before I just walk away

I would too, if I carried a big enough range of coils.
However It was just a hypothetical post assuming we had only one coil available.
If we shorten one axis of a round coil and turn it into an ellipse, then depth is surely compromised. The question is whether that compromise is entirely about an intrinsic property of the elliptical coil thus produced and independent of whichever way that coil is swung.
Perhaps an experiment is called for and I hope to advise the result of one some time in the future or if I do discover something maybe keep it to myself.
.

 

[Redfin]

It doesn't matter which direction the coil is fitted or waved, performance, sensitivity and depth remains the same.
Think about the way you wave the coil now, every direction.

 

[Hawkear]

It doesn't matter which direction the coil is fitted or waved, performance, sensitivity and depth remains the same.
Think about the way you wave the coil now, every direction.

That is the stated contention and respect your statement.
The only way to check whether that is correct is to set up an experiment to prove one way or another and that can be done. I am still openminded, think there is a little more subtlety in using ellipticals and intend to try to set up such an experiment.

 

[Redfin]

Try by all means, the answer will remain the same.
Bit like what weighs more a kilo of gold or a kilo of feathers.

 

[user 22230]

It doesn't matter which direction the coil is fitted or waved, performance, sensitivity and depth remains the same.
Think about the way you wave the coil now, every direction.

As a layman I'd have to agree with that as it doesn't change the field of the coil so elliptical or round it will remain the same at any given point of the coil face regardless of the direction moved. The coil movement creates the signal ( generates pulse) as target moves thru field, it's direction has no relevance. As for experimenting to prove anything ? Faraday did that about two hundred years ago

 

[Hawkear]

A significant difference between a kilo of gold and feathers. Try dropping them both from a height. Experiment will show that feathers will fall slower. What does that say?

 

[Hawkear]

A significant difference between a kilo of gold and feathers. Try dropping them both from a height. Experiment will show that feathers will fall slower. What does that say?

Just to explain what I meant there is that theoretically they should both fall at the same rate but "real" world experiment will highlight the air resistance factor.
An elliptical or any coil for that matter will not detect any thing unless there is motion.
Faradays experiments actually showed that motion and also the direction of motion in fields was necessary for many of the effects he discovered..
I am not arguing that there will be a real difference or even a subjective difference such as the "hang time" of the signal just curious and maybe worth an experiment when I have some time.

 

[user 22230]

A significant difference between a kilo of gold and feathers. Try dropping them both from a height. Experiment will show that feathers will fall slower. What does that say?

Aaaah but in a perfect vacuum they will fall identical but, so what does that say

 

[Hawkear]

When the first Lunarians try to invade Earth won't they be surprised how their non aerodynamic spaceships burn up before reaching the ground.

 

[user 22230]

That may very well be a good thing but ?

 

[Hawkear]

May have to change their name from lunarians to lunies.

 

[XLOOX]

Like all coils an elliptical coil is a compromise. If we start with a 12" round coil as the reference & look at an "equivalent" elliptical coil of 14"x9" ( 14+9=23)/2=11.5" ( near enough to 12" ), the much tighter radii on the narrow ends of the elliptical significantly improve small gold performance over an area roughly cup sized at each tip BUT small gold performance is decreased on the long sides, which have a larger radius than the round coil. Max depth at centre of coil on a bigger target is better than a 9" coil & not as good as 14" coil, in fact it is a little lower than a 12" coil maybe equal to a 10.5" coil.

The sensititivity improvement of the tip vs round coil is related to the elliptisicity ie 10x5 coil is 2:1 whereas a 9x6 , 12x8 & 14x9 are all 1.5:1. There will be a bigger difference in tip sensitivity from an 8" round coil to a 10x5 than to a 9x6 , but the 10x 5 will have a lower maximum depth, closer to a 6"coil whereas the 9x6 max depth will be closer to a 7" coil.

The elliptical offers the ability to find smaller gold than the equivalent round coil but to truly cover the ground properly with the two sensitive patches you need to do about a 70% overlap & pretty much noone does that unless they are scouring a patch. At least you have a chance of small gold on a normal partially overlapped swing and you dont have to change coils to scour.

If you turn the elliptical sideways you neither gain nor lose anything on maximum depth but you are now covering the same bit of ground twice with the sensitive patches and have reduced your total forward distance covered per swing by 30-50%. I would say that you havent achieved anything you couldnt have achieved by doing a 50% overlap with the coil in its usual orientation.

PS: I hate to think what most people googling "sensitive patch" are going to make of this post

PPS: Much luck with overlapping sweeps with the Stellarvue?