help me to build a coil for laptop MD

[Berti]

Hello,

Anyone can help me to build a coil in order to use with sound card.

Maybe Aziz


Thanks

[Berti]

Aziz can you analyze these coil type

It is possible to build such coils?


thanks

[Aziz]

Hi Berti,

the easiest way of making coils for laptop MD is as follows: DD-coil

- make two identical coils (easy to match the operating frequency with same capacitors).
- use same type of wire (0.3, 0.4, 0.5 mm for instance)
- use same core for winding the coils (e.g. 20 cm standard pot)
- wind same number of turns for transmit and receive coil (e.g. 20..60 or more windings)
- bend the coils such that transmit and receive coils looks like D shape form, they should be exactly same shape (this will give same inductivity)
- if you balance the coils, this will give you a nearly circle or elliptical search head
- read the laptop detector thread and follow my experiment results
- write your code for driving the coils through sound-card or use free software available from internet (I have no idea where to get)
- choose the transmit feeder capacitors: series capacitor 10..22 nF, parallel capacitor 22..68nF
- determine the operating frequency: go through 5 .. 40 kHz and see the maximum TX resonant frequency voltage (can be seen on the RX coil if not balanced exactly)
- determine the receive resonant capacitor: try different capacitors for maximum voltage on the receive coil
- balance the transmit and receive coil to minimum voltage
- fix the coils on balanced position

The principle behind this procedure is just driving the transmit coil at resonant frequency. The receive coil has to be matched to this resonant frequency to give maximum signal response (resonant filter).

And you have to implement the laptop detector software (the big part of this stuff (95%) - not easy for beginners!.

Aziz

[Berti]

coils design

Which of them can be better???

[amtech2005]

help me to build a coil for laptop MD

Hello Berti , Aziz is correct , DD coil will be the best !!! See the 2 photos from Ivconic , it is for reference only to see the DD shapes , Please use Aziz's formulas and specifications and you will have a great coil , even if you use in mineralized soil ..........Eugene

[Berti]

hi

Eugene, I'm not asking for the shape of coil in general.


Look beter in photo at my first post. Does make strong or weak a coil how we put the wires (flat, vertically(solenoid) ....) in the same shape?



Regards

[Aziz]

Hi Berti,

Eugene, I'm not asking for the shape of coil in general.


Look beter in photo at my first post. Does make strong or weak a coil how we put the wires (flat, vertically(solenoid) ....) in the same shape?



Regards

I know now, what you mean. I was quite confused about your drawings.

Type 1: solenoid
- lower parasitic capacitance (good vor PI)
- magnetic field density lower than type 2
- bad for search coils (getting too much thick)

Type 2: compact coil
- higher parasitic capacitance (bad for PI)
- higher magnetic field density

Type 3: elliptical coil
- lower parasitic capacitance (good for PI)
- lower magnetic field density: the inner coil windings are cancelling the outer coil windings

Type 2 with less compact factor would be a good solution for PI (lowering capacitance). This can be achieved by a thicker teflon insulation of the wire. For VLF coils type 2 is the best.

Aziz

[Berti]

hi

Thank you Aziz

Take a look at this, for the compact type of coil what can offer this coil?
If you can make a simulation.

Kindly regards

Berti

[Aziz]

Hi Berti,

principle magnetic field density of such a coil is shown below.
It is not efficient and makes not sense for MD applications.
Aziz

[Berti]

HI

Thnx Aziz

So, the DD coil is finally better to try to build.

Yesterday i made a small coil and with a small spectrometer software I was able to see changes of specter. Test object was a spoon

Only coil without passive elements.


For later I will try to perfect the coil. It's time to go shopping (wires, resistors, capacitors ...etc)