the magnetic theory

[strike it rich]

mypal swears by this method placing a magnet on the top of the coil he claims a 25% improvment in depth could this be true or just a big pile of stinking camel droppings I tried it but to be honest didnt notice a big diffrence when i asked him to explain why this would work he said what sounded like a load of hocas pocas I then asked him to back up and break it down this is his simple explanation. because the field is in nature a loose circle with the ability to go in three dimensions there is a certain degree of infaction the magnet has the effect of concertating the field into an unified field at this point I wanted to ask him to break it down again but didnt bother as I was drifting off with his already simplfied version any thoughts please

[jeff of pa]

Although I don't think it will Work,
I'd be afraid a Magnet would cause more Problems then Good.

You wouldn't Stick a Large Rare Earth Magnet on top of your
TV would you ?

[SomeGuy]

What Jeff said.

Since I'm not willing to test the theory, I can only surmise that (for lots of reasons) that it's camel droppings.

[Dimeman]

Doing that with a magnet would distort the magnetic field of the detectors transmit and recieve function in the wiring of the coil. And possibly overload the circuitry inside the detectors board.

Just as, you wouldn't want to put a magnet close to your computer hard drive( it has magnets in it).

[Shortstack]

Doing that with a magnet would distort the magnetic field of the detectors transmit and recieve function in the wiring of the coil. And possibly overload the circuitry inside the detectors board.

Just as, you wouldn't want to put a magnet close to your computer hard drive( it has magnets in it).

Excuse me, but the field around the coil of an operating MD is not a magnetic field; it's an RF field. The coil is an antenna for broadcasting a signal into the air/ground where it will ( we hope ) generate eddy-fields in gold coins and jewelry that will be detected by our machines at which point, we will recover them and be rich. That's the way it's SUPPOSED to work--right? If you put a magnet on your coil, your detector will sound-off on the material the mag is made of; the same way it would react to a chunk of scrap metal that didn't have any magnetism. Fields of magnetic force won't effect the RF field of the coil unless you have a good sized magnet and start moving it like crazy back and forth across the coil, forming an mild electrical charge within the wire that forms the coil. A.K.A. a poor man's electrical generator.

The reason you don't want to put any magnets near the hard drive of a computer is--the mag will cause the micro-sized magnetic-states of 1s and 0s on the disc to be changed to misc. conditions that will result in that classic computer state called "garbage". The rare earth magnets inside the hard drives are used to power the movements of the "finger" so that said finger does not bounce when moved to read/write information to the disc.

[Carl-NC]

Actually, the coil produces an alternating magnetic field. It's not used as an RF antenna, but as a balanced transformer. Metal targets distort the field and upset the balance.

Adding a magnet to a coil will not increase depth. Yes, it will add a DC magnetic field on top of the AC field produced by the TX coil, but the DC field won't have any appreciable effect, because it is the rate of change of the field that produced eddy currents, and a static field does not produce any rate of change.

There is a possible exception: if you whip the coil fast enough, then the magnet passing over a metal target will produce eddies, because (to the target) the magnet passing over looks like a changing magnetic field. I suspect you would have to whip it pretty darned fast to make a difference.

Finally, many magnets are made of powdered iron and would not be easily detected, because they don't support eddy currents.

- Carl

[Shortstack]

Actually, the coil produces an alternating magnetic field. It's not used as an RF antenna, but as a balanced transformer. Metal targets distort the field and upset the balance.

Adding a magnet to a coil will not increase depth. Yes, it will add a DC magnetic field on top of the AC field produced by the TX coil, but the DC field won't have any appreciable effect, because it is the rate of change of the field that produced eddy currents, and a static field does not produce any rate of change.

There is a possible exception: if you whip the coil fast enough, then the magnet passing over a metal target will produce eddies, because (to the target) the magnet passing over looks like a changing magnetic field. I suspect you would have to whip it pretty darned fast to make a difference.

Finally, many magnets are made of powdered iron and would not be easily detected, because they don't support eddy currents.

- Carl

We both are a little bit right and a little bit wrong. The coil IS an RF antenna, but its purpose isn't for broadcasting its weak carrier wave. The metal detecting operation utilizes the electromagnetic field that is generated at right angles to the conductor wires. Therefore, the coil acts as a large inductor. The very basic idea is that after the detector circuit is in balance using the inductance value of the coil (kinda, sorta in historesis) any metals coming within the coil's field of force will cause an imbalance in the circuit by changing the inductance value (measured in micro-henries) and the detector will "cuss" it. It's that "cussing" that we wait for with baited breath. And, yeah, I know that I misspelled that word.

[Carl-NC]

We both are a little bit right and a little bit wrong. The coil IS an RF antenna, but its purpose isn't for broadcasting its weak carrier wave. The metal detecting operation utilizes the electromagnetic field that is generated at right angles to the conductor wires. Therefore, the coil acts as a large inductor. The very basic idea is that after the detector circuit is in balance using the inductance value of the coil (kinda, sorta in historesis) any metals coming within the coil's field of force will cause an imbalance in the circuit by changing the inductance value (measured in micro-henries) and the detector will "cuss" it. It's that "cussing" that we wait for with baited breath. And, yeah, I know that I misspelled that word.

What you describe is sorta valid for a BFO detector, in that metals cause an inductance shift. But IB/TR/VLF detectors don't work that way. The inductance shift is irrelevant, all that matters is the induction balance. Also, with all metal detectors, the coil is not used as an RF antenna, but strictly as an inductor; it's not the electromagnetic field that matters, just the magnetic field. And only an alternating magnetic field, which is why adding a magnet is irrelevant.

See my articles on Induction Basics and Coil Basics.

- Carl

[doozis]

Yeah !!!! .....what he said :P

[Shortstack]

oscar mayer!!!!!!!

[joecoin]

The added weight of the magnet forces the coil towards the ground, thereby increasing the depth of the field.

This effect is known as Camelus dromedarius ordure, aka camel droppings.

[Carl-NC]

Sounds like a brick strapped to the coil would add even more depth.