Very large DD coil

[Tim]

Another suggestion would be a stiff coil on/in plywood then mounted on a piece on conveyor belting, like the ML drag coils used here in Australia.

[Krzychu_]

I'm not sure. What about screening and selection of quantities and unused wires? I prefer winding with enamelled wire, which I have already ordered. I may use monolithic shielding, but I have to do tests for this when tuning the coils.

[kt315]

a coil from CAT5 cable. will be good in your case. http://www.metdet.ru/korsina2.htm

[Krzychu_]

I know it. I don't know only, what the end result will be
but I will try

[kt315]

you can not to balance huge coil in your room just you have much armature inside walls, electric nets/cables, internet cable,
modems etc.
you have to be ready to tune your coil in the field far away out your home.

[Krzychu_]

Thank you for every suggestion. The coil will be relatively narrow and long (30 ... 40cm X 2m), so the field of detection is wide, and the depth of penetration is more or less the same as its width (~ 30cm). It will only be used on flat plowed fields and meadows. I need to ensure its stiffness especially along the length, so I think over the supporting structure in the form of a 2T beam with an additional system of damping vibrations and transferring mechanical stresses.

[kt315]

i have big diggest of pics. any sense to put them again? to take them from forum and put back in forum?

[Tim]

I would suggest setting it up on 10-15mm plywood, with plastic wheels, as a drag coil, like this.

[Krzychu_]

Only forwards regularly. All metals mode ("no motion" - static) is not suitable for searching meteorites. Stone meteorites give the same VDI as "hot rocks".

Regards

[kt315]

maximum depth you get if working in ALL-METAL mode. while this mode is not with discrimination you want.
with DISC you need constant coil motion - left-right, right-left. modern VLF detectors are NOT WORKING in true non-motion mode.
what motion you will do with big coil?

[Carl-NC]

The cap is also charged by the reverse field of the coil. Keep in mind this is a triangle-wave TX circuit, not pulse. If R=0 (coil, switches, and cap ESR) then the regulator current would be 0.

[Krzychu_]

Hello!

It is true that energy is drawn through the coil from the tank capacity, but the capacity is only charged to the regulator's voltage, which has an internal current limitation, so the maximum continuous power is dictated by the product Pmax = Umax * Imax = 5V * 0.1A = 0.5W. In addition, the impedance (R + XL) of a single coil with inductance 540uH for the frequency of 15kHz is about 55 Ohms, which gives a pulse current of 5V / 55Ohm = 90mA. Pulse, because the power consumption from the source after connecting the transmission coil increases by only about 100mW. Theoretically, I can therefore power 4 ... 5 TX coils connected in parallel, but only theoretically.
I am afraid that one large coil will create too weak induction fluxes, but I am most afraid of problems with false EMI signals and mechanical stability. Nevertheless, I will experiment.

[Koala]

Couldn't find the coil in the video

The only coils by nugget finder are all for a PI

http://detectoraid.com/rapidcart/rapidcart-2/index.html

[Carl-NC]

Any VLF will drive a large coil as well as a small one. Get the inductance about right, and the TX circuit doesn't know the difference. Also, the DFX TX recycles current through the tank cap, so the 100mA limit on the regulator isn't the max TX current. I don't know off-hand what the TX current is, but if the TX coil is wound to ~540uH it will be the same as any 950 coil.

I think the biggest problem you will have is mechanical stability. DD coils on a VLF are very sensitive to mechanical deflection so you may end up with a lot of falsing. Depending on how fast you drive, a target may have a broader response than the falsing so you might be able to listen through the noise. No idea until you try it.

[waltr]

meteorites are ferrous. or, did you see gold meteorites?

Not all. The most common meteorites are Stony, Chondrites, that can have little or NO iron.

http://www.fireballsinthesky.com.au/wp-content/uploads/sites/7/2014/02/Types-of-meteorites.pdf