10 Khz DD COIL

[jroux]

I will try this , thank you.
Best regards.

[Qiaozhi]

Something wrongs on the calculator , when i test values of the tgsl coil building from Silverdog, with his values :inner radius 137, wire thickness 0.25, number of turns 107 , the coil calculator give me these results : mean radius 138,29, coil thickness 2,59, inductance 9,674.
But the inductance may be 6.5 mh ,it's write in the pdf , where is the error ?

The TGSL coil you are trying to build is a DD coil. But the coil calculator is designed for circular coils, and therefore the result will not be correct for the D shape. An approximation can be obtained by finding the two radii of the D shape, adding them together and dividing by 2. Use this value as the radius in the calculator. This will at least get you into the right ballpark, give or take a couple of turns.

[jroux]

Many thanks, I thought the calculator was made for all coils, I'm not very good in geometry but how to measure the two inners on a D ? Or i must mesure the radius of rx and tx adding ther values and dividing by2.Sorry i'm old and school is far, can you give me an example please.
Best regards.

[Qiaozhi]

Many thanks, I thought the calculator was made for all coils, I'm not very good in geometry but how to measure the two inners on a D ? Or i must mesure the radius of rx and tx adding ther values and dividing by2.Sorry i'm old and school is far, can you give me an example please.
Best regards.

The coil inductance also depends on the shape, and the maximum inductance is obtained when the coil is a circle. If you fold the coil into a different shape, the inductance will be reduced.

Measure the D shape across its width, and then across its height. Add these together and divide by 4 to get the average radius.

[jroux]

My resistances are 15.5 ohm and 35.5 ohm so that different from tgsl, but the manufacturer tell me that i can use tesoro coils on this detector.

[jroux]

ok I understand now

[jroux]

MY D is 270mm large and 135 mm radius so it will be 101.25 average radius

[jroux]

My resistances are 15.5 ohm and 35.5 ohm so that different from tgsl, but the manufacturer tell me that i can use tesoro coils on this detector.

Coil is concentric double 0, 200mm and 95 mm, difficult to be 10Khz

[Qiaozhi]

MY D is 270mm large and 135 mm radius so it will be 101.25 average radius

In that case (with 0.25mm diameter wire and 107 turns) the inductance should be approximately 6.7 mH. Depending on the actual final shape, and how tightly you bind the windings, the inductance could fluctuate around this value.

[jroux]

Ok thank you, and 5.9mH for tx will be ok i think. It is true that we must roll RX in the opposite direction of TX

[jroux]

The TGSL coil is finished and works well on the armand anticus, but not more power in depth relative to the concentric coil origin,probably the md can get more.
Thank you all for your help.

[Jabberwock]

don't forget to shield it and to null the coil. unbalanced coil won't give you the best results.
you can easily loose 10 cm depth if the coil isn't correctly nulled

[jroux]

The coil is shielded, for nulling i don't have osciloscope, but i try the best results with any items gold, silver, coins, and it works fine.
The problem is that I use a VGA cable and dice I hit the disk it gives false signals.

[golfnut]

It is often the case that if you hit the coil assembly it will false.

Commercial coils can do this. To me it says your machine is sensitive to phase changes - which is a good thing for a metal detector.

Did you pot it in potting resin, or epoxy? this will steady it a bit.

How did you do the shield?

DD and Concentric go approx the same depth - just different profiles into the ground. If the machine wasnt deep with the supplied coil or the one you made - it isnt the coils.

S

[jroux]

Shield with aluminium tape, the same on pdf of Silverdog for tgsl coil.Resin polyester,the depht is equal to the original coil concentric.False signals also appear if I rock the cable on the cane.The wires are not shield on the vga cable just all around, I think the problem comes from the cable.
Regards.