Coil sensitivity

If conductive material within the coils field is nulled out by the electronics , but detector sensitivity is reduced as a result , then wouldn,t it make sense to run the coil cable directly along the shaft near the coil where the field is the strongest , rather than wrapping cable around shaft , which places about twice as much cable in the strongest part of the electromagnetic field .? Just a thought..I run the cable directly along shaft at the bottom and a few extra coils at the top,,it can,t hurt....cheers ,Paul....

Gday Paul

Isnt the shielding inside the coil top supposed to stop it from picking up any metallic objects above the coil?, I know that whith big coils that they can pick up metallic stuff that you are carrying or say the coil shaft itself and this is believed to de sensitize the coil, Hence the use of the Otto fibreglass shafts system, but I dont know whether or not the position of the coil lead would have any effect as these are motion detectors and the coil cable being held in place would move with the coil so in effect it would ignore it.

The only reason that it picks up objects that are on your person is that the coil is moving back to and fro across your path, any metallic object in its field would be recognised, but would be ignored if it moved in conjuction with the coil, so I would guess the effect would be minimal and the electronics would just cancel it out and ignore it, I am pretty sure that Minelab would have recognised this fact and have considered the amount of effect to be of no consequence, either way you have to have a lead to the coild dont you so theres bound to be a trade off somewhere in that.

cheers

stayyerAU

Don't forget that PI detectors are also "motion" detectors. You can tape a coin to the coil and it won't respond unless the coin shifts or moves. However, if there's too much metal near the coil, the EMF is "nulled" down and reduced considerably.

nero_design wrote:Don't forget that PI detectors are also "motion" detectors. You can tape a coin to the coil and it won't respond unless the coin shifts or moves. However, if there's too much metal near the coil, the EMF is "nulled" down and reduced considerably.

That may be so. but would you tape a coin to the coil and then go out detecting and expect to find gold!

No I wouldn't. But you'll probably still find Gold even with a coin taped to the coil. I just5 did an air test here and it worked fine. I wouldn't do this in the field of course. But the loss of sensitivity to the coil (from a coin) would be so small that it would be hard to measure. It's not that the coil field is reduced, but a small coil would deform the field ever so slightly near the source. Think of a donut with a slight dent in it from a finger. The general field would otherwise be intact.

When you wind the coil cable around the shaft, you need to use the Velcro straps to prevent the cable shifting. If the coil hits a rock or a branch on the ground, the coil might tilt and this will shift the cable... resulting in a Ghost Signal or false target response. Using duct tape with a metal film on it instead of a PVC tape to seal the skid plate onto the coil may result in a considerable softening of the field. Some people even replace the spring-clip inside the shaft with a plastic one and replace the rods with a Carbon Fiber version (as mentioned above) in order to reduce the chances of EM-field interruption. But those people are fairly rare on the prospecting circuit.

nero_design wrote:Some people even replace the spring-clip inside the shaft with a plastic one and replace the rods with a Carbon Fiber version (as mentioned above) in order to reduce the chances of EM-field interruption. But those people are fairly rare on the prospecting circuit.

I think that these people are the ones who want to give themselves the best chance posible to find gold by increasing the % in their favour.

If you just want to go for a walk thats fine, if you want to find gold then do everything you can to increase you chances and every little advantage you can gain will help.

G,day folks , it was from watching JP's minelab endorsed videos about the fibreglass shaft helping sensitivity when using larger coils by not having unrequired metal objects in the magnetic field that got me thinking about the coil cables on all size coils....The shortest route between two places is a straight line...It,s not about cable motion or anything else except the amount of cable in the mag field,,,,,,If the cable moves it creates noises so I assume it will affect things as the shaft does on bigger coils ... As i said , It can,t hurt and it might just help a little bit...Paul...

Don't the GPX series all come with a fiberglass lower rod assembly?

I've seen the handwound Carbon Fiber ones for sale but never saw a need for them myself.

Yes Celeste, but these people are on about fibreglass upper shafts!
They are well worthwhile if using big coil's.

Gday

The reasoning behind the use of the full length OTTO type shafts, is because even though the lower stem moves in conjunction with the coil and is ignored during the swinging action by the coil, the top section of the shaft being further away stays in whats basically a static position, therefore it is passing through the coil field just as any other metallic objects on you person.

The theory has always been that although the machine does not make a distinct signal as the shaft etc is at the edge of its detection range it will still recognise the object and the electronics will treat it like ground noise and try to cancel it out, while this is happening it is believed that this makes the coil less sensitive and therefore reduces your chances of finding the gold.

I have the Otto shaft set up on my machine for this reason, when using a larger coils say from 16" to 20+" I can easily get feedback from my pick if I dont carry it facing backwards over my shoulder, if I lean down towards the coil it will even pick up keys in your pocket, the frames on your glasses and other bits and pieces, these are usually not distinct signals but rather more like a background murmer, the more metallic objects that move through the extremities of the coils field the more work the electronics have to do to try and null it out, so the further away from the front of your body you can carry these objects the better.

I was told by some pros that when they are working deep ground for big pieces that they dont even carry a pick, they only carry the battery behind them and when they get a murmur in the ground that they think is a deep piece they just mark it with a pile of stones, when they have a few targets like this then they come back in with the digging gear and dig up the spots they have marked, its all about giving yourself an edge.

For general use the standard set up is just fine, when using the smaller coils there is no reason to be concerned about the shafts so much, but I think that you should still consider limiting the amount of metallic stuff that you carry on you, and think about placing some of the gear to the back of your kit.

This theory has been about for some time as I have even heard of operators using the 2000s and 2100s that were replacing there stock standard shaft assemblies with broomsticks notched out and drilled at the end to take the coil.

cheers

stayyerAU