I was make a coil with with 30 A.W.G or 33 S.W.G 10 times around a 15-cm circle at a freq. of 104 khz. How much more or less turns do I have to do if I only have 30 A.W.G wire? Its for a metal detector.

## Coil Wire ????

The change in inductance will be small with the change in wire size. Inductance depends MOSTLY on the number of turns and the coil diameter.

Jim

Shortest topic ever :P.

Thank you,

The change would be larger if you changed from "enamel" (magnet or transformer) wire to regular "hookup" wire with thick plastic insulation.

The change you describe will have an effect, but it will be quite small.

Jim

Yah, I was think of use hookup wire(besuase it was cheaper), but I found a even cheaper place(all electronics) to buy magnet wire.

The wire thickness will affect the 'Q', or "quality factor". This is the ratio of inductive impedance to resistance, XL/R, or in math terms,

Q = 2.pi.f.L/R

The inductive impedance will be... let's see...

L (uH) = d^2.n^2/(18d+40l), d diameter inches, l length inches, n number of turns

... which in this case (assuming a tight coil) gives about 30uH, so XL is about 20 ohms. Wire length is about 16 feet, which is 1.65 ohms for 30AWG and 3.31 for 33AWG, giving a Q of 12 and 6 respectively. That's a pretty miserable Q for an air cored coil. For a metal detector you'll get better discrimination the sharper the tuning point, which gets sharper for a higher Q, so my advice is to use the thickest wire you can find. Alternatively, take 7 strands by 16 feet of the wire you've got and twist them lightly together with a drill, then wind your coil with the seven parallel strands. Solder them all together at the ends.

Anything about the receiver(detector) coil before I attempt to build it?

Heres the website,

Should I add a LM386 audio amplifier if I'm just going to using noise canceling earphones and not a speaker?

Yes

JC