Building Coils - Need help from Electronics gurus

[Charles (Upstate NY)]

I'm a computer guru not an electronics engineer, I probably know just enough about electronics to be a danger to myself and anyone who might touch me when I'm near a live wire. Even my kitchen stove hood remains silent a year after I installed it, its household wire hanging beside the 200 amp box in the basement with a supply wire so big I'm too scared to go near it.

Nevertheless I have decided to build some custom Dbl-D coils for my IB Minelab Explorer detector. There are no electronics, amps, passive elements in the Explorer coils so should be easy, just two coils. Been reading patents and researching for a few weeks. Got myself a BK scope, a function generator, and a shiny new Extech LCR meter (great instrument for the price and features, even measures Q).

I have a couple basic questions:

1. Are the RX and TX coils both wound clockwise or one clockwise and the other counter-clockwise? Does it matter?

2. I have some inductance formulas to estimate the number of windings, can you measure this as you wind them before cutting the wire or do you have to cut, measure, and if wrong start over?

3. If you have a good source for magnet wire and/or 2 conductor individually shielded coil connector cable that you could share I would appreciate it. I found a couple suppliers for the magnet wire but have been unable to find the coil connector cable.

Thanks a bunch!

[Carl]

Re: Building Coils - Need help from Electronics gurus

>1. Are the RX and TX coils both wound clockwise or one clockwise and the other counter-clockwise? Does it matter?

It matters, only relative to each other. If you get both backwards, then you are OK. A rare case of 2 wrongs making a right. You will have to experiment to find the correct relationship, or write Minelab or Coiltek and ask them.

>2. I have some inductance formulas to estimate the number of windings, can you measure this as you wind them before cutting the wire or do you have to cut, measure, and if wrong start over?

You *might* get away with knicking the wire for a measurent. Maybe apply a little nail polish before continuing.

>3. If you have a good source for magnet wire and/or 2 conductor individually shielded coil connector cable that you could share I would appreciate it. I found a couple suppliers for the magnet wire but have been unable to find the coil connector cable.

I think Electronic Goldmine sometimes has a good price on bulk magnet wire. The last batch I bought was from the local TV supply house, for about the same price as the big catalogs.

For the dual coax, have you looked at the big catalogs, i.e., Digikey, Mouser, Newark, etc? Radio Shack, of all places, has a cable that's close: two pair of conductors, each pair individually shielded.

>Even my kitchen stove hood remains silent a year after I installed it, its household wire hanging beside the 200 amp box in the basement with a supply wire so big I'm too scared to go near it.

I wired my entire house, and it's really no big deal. Fear the great big wire, for 220v is mighty indeed, but don't sweat hooking in the hood to a breaker. Flip the main breaker, add the hood circuit, flip it all back on. Then reset the 20 clocks in the house.

- Carl