Very large DD coil

[Krzychu_]

Hi everyone!
I'm happy that I'm a user of this forum

I would like to make DD TR-IB coil for Whites DFX with dimensions similar to this:

https://www.youtube.com/watch?v=kJaQ...=youtu.be&t=45

Is it possible for VLF machine like Whites DFX (It may turn out that problems with EMI, tuning the coil(s), stability, mechanical stiffness of construction and others can not be solved)?

Best regards

Kris

[Nandor]

Hi
For Whites the largest coil I've seen was the Bigfoot coil 3x18 inch. I think that big as it's in the video is only for PI detectors that have power to drive those coils, Imho no VLF oscillator can drive that large coil.

[Krzychu_]

Hi The power to drive TX coil(s) is not problem. Only original voltage regulator limits the current. I want to search for stone meteorites, so a machine with good discrimination is needed

[Nandor]

Not the current is the most important, you need Amper and Watt. A small PNP or NPN or Crystal driven oscillator has low power. PI machines with Power Mosfet like IRF transistors have enough power to drive larger coils. The Ground effect is also very important, this coil covers way much ground for a VLF to be able to reject it properly. Search for PI's with DD coil configuration those are the detectors that you are looking for. Meteorites are made of iron and different other alloys, I don't think that you need Disc for that at all.

[Krzychu_]

The coil power circuit in DFX looks like this:


Maximum current is limited by the regulator to 100mA

Regards

[kt315]

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

[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/...meteorites.pdf

[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.

[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

[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.

[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.

[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?

[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

[Tim]

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

[kt315]

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