A few Myth Busters

[Jonathan Porter 4]

Over the years I have come up against a lot of myths to do with metal detecting and more particularly the Minelab machines.

 

OK here are a few that I thought were written in stone but over time have come to be nothing more than placebo effect or a close proximity to said effect.

 

1: Winding your coil lead wire too near the coil; try it some time it has absolutely no impact on the detectors performance, but more of an effect on our mental idea of what "looks neat and tidy". The most important factor when winding your coil lead is to make sure there is minimal movement in the cable, this is for two reasons, one it stops wear and tear on the internal wires and shielding and two it stops movement and strain in the connectors (both the control box and also the coil ingress point) which is the biggest cause of false signals and instability in the Minelab machines.

 

2: I have always thought their wasn't any performance increase by upping the voltage into a GP series machine, but I have since found out there is a "potential" performance increase but only through the audio. It has been suggested to me the audio is not direct coupled to the dual voltage side of the GP series detectors, therefore the audio might benefit from a higher voltage or constant voltage supplied to the detector. I am at the time of writing unsure if this carries over to the GPX-4000.

 

3. Running an aluminium upper shaft will not cost you a huge amount of performance loss, in fact it is minimal unless you generate a lot of flex in the upper shaft (larger coils do this). Minelab machines are motion detectors, so the electronics do not "see" the aluminium upper shaft unless it moves out of sync with the coil. Because the variation in ground signal is greater than the impact of the close proximity of the upper shaft in a static state it has virtually NILL effect on the detectors performance. Personally because I use the larger mono coils I feel there is a slight reduction in sensitivity on smaller gold so have opted for the fibreglass upper shaft section (plus they look nice and neat ), I would also advise those folk who like to run their stems short to look into this option, obviously the closer the aluminium upper shaft gets to the coil the greater the effect. I honestly feel the placebo effect is not so evident in this issue but have been told from those who know far more than I this is more often than not the case.

 

4: A coils a Coils, a Coil. There is not much you can do with a coil to increase performance (outright depth), in other words almost all coils built for the Minelab PI's are equal (assuming they follow the same recipe), however where they differ is in method of construction and lightness of weight. If the method of construction is not precise then the coil will develop inherent problems such as falsing and proneness to interference. Of course combining ruggeness of build construction to handle the rigours of the gold fields as well as lighness of weight is a hard thing to do, which is why I love my Nugget Finder's.

 

 

Just some food for thought in your endeavours of unravelling the secrets of what makes our detectors tick!

 

JP

[Rich 7]

Hi JP

Thanks for the myth busting......

 

 

Rich

[Montana 1]

Jonathan . You are probably right on most points. I will differ on the wrapping of the coil wire on the lower stem . A few wraps on the lower stem is no problem. Putting all your wraps on the lower stem is a problem, and I've seen this several times. I was hunting a dink patch with a fellow who wound his coil wire in this manner because he always did it that way on his VLF. We had the same coil on and the same detector which was a GP3000. We could not hear the .1 gram pieces with his, but Both of us could with mine. I had been telling him that it wasn't a good idea to put all that wire virtually on top of his coil. I talked him into re-wrapping his coil wire like I had mine and we could then hear those tiny ones. This may only effect tiny , marginal targets , but I know for a fact from trying this experiment several times that it is there. There is an effect. Maybe nobody else cares about .1 gram nuggets. but I get a kick out of finding fly s--t nuggets with a P.I. and I may have the record for the tiniest one found with a P.I. . I wouldn't have found that with the coil wire wound just above the coil nor many other small nuggets, and I'm convinced of that. I find lots of tiny gold and feel that my attention to little details such as this are a big reason why I seldom go home empty handed. The big ones will take care of themselves if I put my coil over them. The little ones take some doing.----Bob

[Jonathan Porter 4]

Hello Bob, I was referring to the usual practice or a couple of winds through the lower shaft progessing up with the majority of winds on the upper shaft. I notice a lot of prospectors go to huge effort to running their cable straight up the lower shaft which means you more or less have to tape the whole lower shaft to keep it in place, this is OK if you have a lower shaft for each and every coil you own and only ever use the coils at the one length.

 

I probably should have made things a little more clear, to be honest I have never heard of anyone having a problem with sensitivity with having too many winds of the cable on the lower shaft but then again I have never seen anyone have more than is absolutely necessary.

 

When I said try it I was talking about waving the cable near the coil in a single entity, I am not sure how it would react with it all coiled up, but my gut tells me the sheilding would probably mask it from the coil. Have you ever run your coil over a piece of copper shielded wire on the ground before? More often than not there's no signal at all or barely a murmur anyway.

 

JP

[CLARK 0]

Which one is you JP??? Then the other one must be Montana!!!

MYTHBUSTERS

[desertdon 0]

I ws glad JP to see your comments on the coils. Too many times I have read where someone gets new "X" coil and goes out and finds a nugget where he has hunted before or others and proclaims new coil is greatest, when in fact he just put the coil over the target and nobody had before! Don

[spinifex 0]

I was told that the leads on some coils have “very poor” or “No” shielding, could this be the origin?

 

Regards

Spinifex

[nvchris 12]

Hello All,

 

Some thoughts on point #3 quote "flex in the upper shaft" and "moves out of sync with the coil"

Large coils,

I've found that a slow linear motion, (a flatter arc) keeping the coil out in front (away from the battery/pick eliminates most of the problems with "flex" and "sync".

 

This is where I feel using the HipStick is an advantage allowing near effortless coil control.

 

enjoy today!

nvchris

[desertdon 0]

Larger coils should always have heavy duty lower shaft and alot come with one. I agree you do probably get some flex and is another reason not to be wrapping loops down near coil. I was somewhat curious about your coment on "flatter arch" It may be the stick setup you are having to do that, but in my opinion, the coil goes to the ground or near and moves horizontslly at all times, any arch means less or no detection below coil, realizing there are rocks etc. This isn't meant to be critisium, but conversation on different techniques. I can see how the stick setup would casuse you to have to do an arch to bring coil into play, maybe isn't as bad as it seems, would like to understand it better, Thanks...Don

[FlakMagnet 0]

Hi Don,

 

I've been using a Hipstick for months now

and I can say for sure, it changes the whole detecting experience;

coil control is (much) more precise and the comfort level of hours of

detecting has risen incalculaby, so much so that I really never

take it off. I use it with every coil right down to the Joey, and

will never go back to being without it.

People have said they have reservations about the small adjustments

they might have to make in the way they dig targets (taking

the Hipstick shaft from it's holder before bending to dig), but

in all honesty, it is easily done in the same motion as stooping to

dig, and wasn't really much of an adjustment at all - I got used to

it in a half a day.

 

It is in a tie with a DetACC dual speaker set-up

as the two most valuable pieces of add-on equipment I own.

 

Can you tell I like it?

 

 

All the best

 

Flak

[desertdon 0]

Thanks Flak! I figured as much, I was wondering what happens when you want to dig a target and I was just reading on "Doc's" site about it. Seems it would be the ticket for swing large coils for awhile. I have some hip problem, but bungee has handled things fairly well, since I don't swing for long periods at a time, but may have to get one of these! Don

[nvchris 12]

Hi desertdon,

 

The arc is from side to side never up and down. I try to keep the coil moving in front of me more of a side to side motion as opposed to an arc around my body.

 

The stick setup in no way lessens coil hight control it actually improves it.

 

Heres a quote from Bill Southern "it blew me away with how much control I had with a big coil and the kicker is that by extending the shoulder connection as this gizmo does increase manuverability! Up, down, sideways, everywhere!"

 

enjoy today!

nvchris

[Chris Gholson 1,065]

Hi All,

 

I have always strung my coil cables straight on the lower shaft, and then started my windings once I was past the locking (or tightening) knuckle on the main upper shaft. I do this for two reasons: 1) loose windings on the lower coil shaft always have a way of getting tangled on brush. These snags are annoying, and they are often the source of false signals when the wire “jiggles”. And 2) my father Steve mentioned to me the possibility of creating a secondary EMF when windings are wrapped tightly near the coil that could potentially interfere with the primary field. He guessed that this could have a slight de-sensitizing effect, and perhaps this is what Montana Bob experienced. Steve always has tons of side projects going, so I don’t know if he ever got around to actually testing the theory, but the possibility of it occurring was enough to keep me in the habit of stringing them straight.

 

You can use just about anything to secure your coil cable wire to the lower shaft. I stopped using Velcro because it always gets full of stickers & leaves, plus after a while it works loose and has a tendency to slide down the shaft. I now use cheap zip-ties. You can buy them in packs of 100 for around $1. Once “snugged” into place with zips the coil cable wire will not move. People that have to share lower shafts on their coils will find this a pain because every time they need to change coils the zip-ties will have to be clipped off. If all your coils have their own shafts I’d suggest the zip-ties, if not, stick with the Velcro or electrical tape. Make sure you leave just enough play in the cable near the coil so that it has room to pivot to compensate for changes in terrain.

 

Don,

 

I agree with Flak about the HipStick (HS). The last few trips I have used the Nugget Finder 16” mono in combination with the HS - what a huge difference it made. I have shoulder & neck problems anyway from years of swinging a detector without a bungee. The HS displaces the weight of the detector keeping fatigue at bay, and I noticed it really helped me be more consistent with my coil control. The last prospecting trip I did with Joe I was able to swing the 16” from dawn to dusk without needing a private masseuse back at the trailer (although that would have been nice ). I don’t use the HS with coils smaller than 14” diameter or in thick brushy gullies. However, if I plan on working flat, wide open ground and using larger coils, the HS is now part of my arsenal. Cool product that actually works!

[Jonathan Porter 4]

I have always strung my coil cables straight on the lower shaft, and then started my windings once I was past the locking (or tightening) knuckle on the main upper shaft. I do this for two reasons: 1) loose windings on the lower coil shaft always have a way of getting tangled on brush. These snags are annoying, and they are often the source of false signals when the wire. And 2) my father Steve mentioned to me the possibility of creating a secondary EMF when windings are wrapped tightly near the coil that could potentially interfere with the primary field. He guessed that this could have a slight de-sensitizing effect, and perhaps this is what Montana Bob experienced. Steve always has tons of side projects going, so I don't know if he ever got around to actually testing the theory, but the possibility of it occurring was enough to keep me in the habit of stringing them straight.

 

Chris I agree with your first reason but have to humbly disagree with the second, which is unfortunately a major myth driven through the misunderstanding that a piece of copper wire with current running through it would HAVE to be a problem if it is too near the coil, especially if it is in tight circles.

 

So to be sure I asked people who know much more about this subject that I ever will, and this is what was explained to me, I already had a basic understanding of this but did not know the full ramifacations till now.

 

The reason why the coil does not see the cable is because you have two currents of equal value running through the wires which basically cancel each other out, in fact the cancellation is so effective it is about 99.99% efficient! That means no matter what you do the coil will not SEE the coil wire unless you somehow damage the shielding or the main wire or wire's themselves, hence my recommending you allow some flex in the coil lead but not too much especially in areas such as the first section coming out of the coil (you need enough to allow the coil to swing freely through the pivot point of the coil without putting stress on the entry point or the anchor point on the stem).

 

It is also important you allow some movement in the coil cable between your lower anchor point and the upper one (if you use one? I rarely do ) so when the stem flexes during the swinging arc of the coil the flex does not transmit any movement to the coil lead connector and the control box, any movement there can create huge problems.

 

This thread has proven to be very interesting even if some of us disagree, as it has forced me to get off my proverbial and investigate a few myths.

 

JP

[Montana 1]

JP. The fellows that I mentioned who wrapped all their extra wire on the lower shaft had their reasons for doing so. Picture this: with all the wraps wound tightly starting just above the coil on the lower shaft and taped firmly in place, coil changes are a snap if you have each coil with its own shaft. You don't have to do any wraps or unwraps when changing coils and the the shaft can be slid into its shortest position for transport without any problem. This was the reasoning behind wrapping it this way. I swear there was a slight loss of sensitivity because of this wrapping procedure. Probably not enough to worry most people. After seeing this with my own eyes, I would never wind my coil wire this way. I certainly wouldn't worry about 2 or 3 wraps and this is probably what you are refering to. What I don't understand is why do you get a false signal when you bump a loose loop in the coil wire at any point between the coil and the control box if the coil doesn't see the coil wire? Any ideas?----Bob

[Beeper 0]

JP's mention of the ground having a larger effect than the upper stem has reminded me of something I've often wondered about. Why is it that people worry about a tiny amount of dirt trapped by the coil cover? Even if the dust is moving freely across the coil with every swing (and it's probably not because it's held in place), how could it compare with the huge amount of new ground that is constantly in motion under the coil?

Sounds like another myth to be busted.

By the way JP, this mythbusters stuff is among the best things you've ever written - see what happens when you're not being influenced by a product to sell. Keep up the good work!

[FlakMagnet 0]

Beeper,

 

I have had serious - to the point of rendering the coil useless -

interference from soil trapped under the coil cover.

It is a very real problem that has to be watched for.

 

I don't think there is any "myth" to this one at all...

 

 

Flak