WHITES DUAL FIELD COIL

[6666]

DF Like this

[6666]

Cat5 like this.
serial connected between each wire.

[daverave]

ive been looking at teflon wire on ebay.....i found 26 awg 7 x 34 stranded...,,...awg 26..0.46mm........solid 30 awg.......awg 22....7 strand.
are any of these 4 different teflon wires suitable for fast pi coil ????????

[daverave]

i have just wound a dual field coil as follows using 26 swg copper wire....(12 inch coil....18 turns 350 uH) (6 inch coil....18 turns 130 uH)......both coils in series 5.7 ohm....495 uH total....are these readings too high and do i need to remove some turns from these coils ?????

[Aziz]

i have just wound a dual field coil as follows using 26 swg copper wire....(12 inch coil....18 turns 350 uH) (6 inch coil....18 turns 130 uH)......both coils in series 5.7 ohm....495 uH total....are these readings too high and do i need to remove some turns from these coils ?????

Hi Dave,

you can calculate the required number of turns count with the measured data above.
As both coil parts L1 and L2 have the same number of turns count (=n) and the total coil inductance L0(n) is given (measured):
L(n*k) = L0(n)*k*k,
where L0(n) is the given inductance (495 uH)
n = number of turns count of L0 (18 turns)
k = turns count factor for desired inductance L(n*k)

k = sqrt( L(n*k)/L0(n) )

Let's say you want to have a 300 µH inductance and want to calculate the new turns count factor k:
k = sqrt ( 300 uH/495 uH) = 0.78
The new turns count would be n' = n*k = 18*0.78 = 14

Trivial math.

Cheers,
Aziz

[Aziz]

More simple math:
What happens, if we reduce one turn count (n=18 -> n=17)?
k = (18-1)/18 = 17/18
L(n*k) = 495 uH * (17/18 ) * (17/18 )
L(17) = 495 uH * 0.89 = 442 uH

What happens, if we add one turn count?
k = (18+1)/18 = 19/18
L(n*k) = 495 uH * (19/18 ) * (19/18 )
L(19) = 495 uH * 1.11 = 552 uH

That should be simple now.
Aziz

[6666]

This is Rovs coil , as in my picture.

make a 11 1/2 inch loop with 16turns of medium duty tin plated multistrand wire. will give you about 0.4ohms coil resistance.
next make a 6 inch loop for inner with 19 turns medium duty tin plated multistrand wire. this will give you about 0.4ohms coil resistance also.
wire these two coils in Series with each other,an now you will have a very deadly coil to use on your TDI or other PI machines.
Regards Rov

[daverave]

i dont have stranded wire and i only have basic copper wire so my resistance is not low at around 5 ohms....i have reduced the turns to about 14 per coil and inductance is good but resistance high...not sure what i can do !!!

[daverave]

i did some tests tonight with the dual field coil and i found that i did not need to use a second resistor across the smaller coil as there was no ringing...i guess its because the coil is around about 5 ohms....i managed again about 12 inches on an old uk large penny...but only about 5 inches on a very small 9ct thin section gold ring...the small coil not very good on this ring....may i do need stranded wire and lower dc resistance.

[daverave]

This is Rovs coil , as in my picture.

i appreciate your help to me in making my coil....i dont have multi strand wire...i have a reel of 34 swg copper wire...could i use several strands of this 34 swg wire...if so how many strands do you think i would need ???

[Jose]

Daverave
As someone said in the forum, my coil is fantasy, and it's true, I never had my hands on a dual coil. Only perform experiments and I'm satisfied with the results, compared to a single coil, the intensity of the source signal is more for small items in the dual coil.
I would try two or three twisted wire of 34 swg that you have.
Also place damping resistance in the smaller coil, that recommended in the patent, and it was necessary to my home coil.
Values between 2 and 5 khoms, works well.
Experiment and test with different values and compare the results, trying to improve.
Everything is a matter of experience and patience.
Jose

[Dave J.]

wind coils separately. have to put a damping resistor to inner coil (according to the patent). as second dumping resistor has set at PCB, so no need to add this second resistor in a coil.

Patent? The Fisher Impulse used a damping resistor across the inner coil.

I was unaware of the White's patent. Got a number?

I'm (almost) more interested in who claimed to have invented it for White's. White's has been ripped off by engineers in the past. White's may be a competitor now, but they are for me personally a former employer and are now a respected competitor, a company with whom we have friendly relations.

No need to PM me, please post the patent number here. This is Carl's forum, and he's White's chief engineer whom I don't believe had anything to do with this. For White's sake, I hope none of the old saboteur gang are still unreformed on the payroll. Let the chips fall where they may..........

--Dave J.

[daverave]

i would like to make a dual field coil but ive been doing some experiments and compared with my 15 x 12 coil that ive already made and i cant really see much advantage...i can detect small gold 9ct thin section ring at around 12 inches with my 15 x 12 using 30 swg single coil....maybe im wrong but i think whites have got more depth using other ways like front & back end increased gain and maybe stranded coil wire...i think the small 6 inch inner coil has little to do wi th better proformance...im just not sure cause im limited in my experimenting as im using just enamelled copper wire.

[Jose]

Davereve
As you say the advantage of a double coil is little, compared to a monkey. with exception that the field is more even and improves the detection of small objects, but it is an improvement.
The enameled wire is not advisable because it increases the capacitance of the coil, making it less sensitive to gold.
Expesor if the wire is generous also influences that improves current in the coil.
The PCV if well designed and good quality, as well as the quality of the components influences the self-noise, which can mask the target signal.
Also influences the size of the coil, the shield, etc.. Etc..
All little influence individually, but in the end makes the difference and in my opinion, you have to be careful in everything, so that in the end, the performance of the MD, is decent.
Jose

[kt315]

Patent? The Fisher Impulse used a damping resistor across the inner coil.

I was unaware of the White's patent. Got a number?

I'm (almost) more interested in who claimed to have invented it for White's. White's has been ripped off by engineers in the past. White's may be a competitor now, but they are for me personally a former employer and are now a respected competitor, a company with whom we have friendly relations.

No need to PM me, please post the patent number here. This is Carl's forum, and he's White's chief engineer whom I don't believe had anything to do with this. For White's sake, I hope none of the old saboteur gang are still unreformed on the payroll. Let the chips fall where they may..........

--Dave J.

seems you do not read all posting... it was sounded in daverave's thread on his double field (tm) for surf pi. i keeped hot on the traces it in my archive as US7994789B1_dual field.pdf. Carl... Carl will say nothing and silent as always if deal touchs whites deeply interests. will be better do not call Carl soul up now.
we did this coil earleirly whites many years ago. yes there is some advantage but nothing fantastic. dual field is only regular adwertizing. I VERY hope Whites will leave all trying to repatent Tesla coil!