A starter in coil building

[stefan-s]

Hello All,

Im just starting in VLF coil building, and i run into a problem.

I made a coil for Whites Spectra v3i and with air tests everything works fine, good depth and good response.

When im trying the detector in the field on a object in the ground there is no signal ad all the detector threshold sounds cuts off and the complete detector is silent, when im not above the target any more the threshold comes back.

Maybe someone here can help me out with some suggestions.

The coil is shielded with graphite powder.
The inductance and resistance are very close to original.

[Carl-NC]

Are you swinging over a discriminated target?

[stefan-s]

Are you swinging over a discriminated target?

That was my first thought as well, but no disc is zero. The strange thing is that a air test works very good, but with a buried or object on the soil/ground the detector is completely silent when im not above the target any more the threshold is back again.

[Altra]

May be one pair of your coil wires is reversed? Since you are getting negative threshold over the target

[Carl-NC]

To test for a reversed coil do an air test where you bob the target into/away from the coil instead of sweeping it. See if you get a positive response as the target approaches the coil or as it moves away.

[stefan-s]

Yes thats solved the problem probably i changed the wires inside the coil by accident.

It works fine now.

[stefan-s]

Maybe a stupid question but is it possible to somehow measure wich connector pin is the + and - of a coil winding?

[Carl-NC]

When I design coils I always make the RX coil in-phase with the TX coil. What this means is that when you introduce a ferrite the induced RX voltage is in-phase with the TX drive voltage. And that's also how you would measure any given coil: use a ferrite and compare the RX with the TX.

[stefan-s]

thanks