WHITES DUAL FIELD COIL

[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]

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 !!!

[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

[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

[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

[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 ?????

[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 ????????

[6666]

Cat5 like this.
serial connected between each wire.

[6666]

DF Like this

[WM6]

Separetely windings and serial connected between each other.

[kt315]

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.

[daverave]

im still very unsure about the construction of this dual field coil....what gauge and type of wire do i use ???? when i start to wind the coil around the nails of the 12" size...when ive completed one turn do i then wind one turn around the 6" size then back to the 12" then do this over and over again until the correct number of turns is completed ???? or wind coils separately ???? im just not clear in my head on this process.

[daverave]

i have to admit that the whites coil looks very impressive....thanks for the photos mate kt315.

[kt315]

on a photo above I uploaded you can see clearly one strande shielded cable and no connector used. a cable is connected directly to PCB.

[bernte_one]

i am not sure if the original whites dual field
is really a dual tx coil (two coils in serie)

at the surf pi it is possible to separate tx and rx stage to receive lowest pulsedelay timing
if we could see the original connector plug we can discuss more

if there are 2 pins or 3 it is a simple coil
if there are more as three pins it could be a separated rx/tx configuration

regards