Coax for duel field coil

[Mark-VA]

Hi Herb,

Here is a little different concept for a dual field mono coil I built that seemed to work fine. It is different from the Whites design since it uses only one coil formed into a figure 8 concept but then modified even more.

What I do is this, I build a coil larger than the housing I will use (step 1). I then squeeze the coil into something like a lopsided figure 8 (step 2) and then twist the top part one half twist to form the 8 (step 3). I then fold this smaller coil back into the larger one (step 4) and ultimately elongate the inner coil (step 5). This allows me to use a DD type housing such as the Hay's 11" by 9" design. The larger coil fits in the outer ring while the smaller coil fits in the inner center elongated zone.

Attached is a simplified drawing of the steps I mentioned. Hopefully, it will make sense.

The idea of this design is the larger coil is used for finding deeper targets, while the inner coil will be more sensitive to smaller objects closer to the surface.

Reg

Amazing what you can learn on this site.

[Roughwater]

Herb,

Wow, one day off in 5 weeks. Sounds almost like slave labor. I've been there but not quite to the extent you have. If I may ask what industry are you in? I hope they give you a little more time off than what your having to deal with right now.

I've made a few coils now but really haven't used them in the field yet, just a little back yard testing. I have a few irons in the fire and the wife likes to keep me busy also.

Sounds like you are doing well so far at builing your coil. I also noticed that the inductance doesn't change much from a round mono when converting to a duel field mono configuration. As to figuring the length, I did the same as you using coax but I think when I wound the coil I put a lot of tension on the hooks and eyes causing them to flex or turn slightly and came up a little short on a couple of coils. They are now my expiermental coils for the moment.

Take it easy,
Terry

[PVGOLD]

Hi Terry
Long time no reply. Been working 12-14 per day. When I made a duel feild
I used a piece of the coax to decide size, then subtracted to allow for plastic wrap, shielding etc. Now I was making a folded 8 cunfiguration. I found that
folding the bundle did not change inductance. When I wond the coil inductance was 345 when wrapped per Reg's instructions inductance ended up at 305. 8 in id. 27 wraps, 24ga silver 24 strands. Teflon insulation.
I bench tested it seemed fine, that's as far as I've gotten. 1 day off in 5
weeks, 8 more months and I will be a part timer! I have although been following your posts. Sounds like you've got it down, and enjoying it at the same time.

Best Regards

Herb

[Roughwater]

Large dual field mono

Hey Herb,

I don't know anything about the TX-RX-TX coil but I briefly turned my 1M mono coil into a dual field coil prior to installing it in PVC in a 1M configuration. I was very impressed with it's performance. As a dual field coil it showed great depth and I was to able to lower the delay as well. I wish I had checked the sensitivity but unfortunately I didn't but I am shure it also had to be enhanced. I definitely think a dual field mono is the way to go. Just might be a little tricky building it to the exact length for a specific housing.

Terry

[PVGOLD]

Hi Terry
I did read somewhere probably this forum about what I thunk was an experiment that had, I think, TX-RX-TX If I run into it again I'll let you know.
When I saw it, it was beyond me. I'll search EBay for wire.
Thanks for the heads up. Hope your latest coil goes well.

Regards
Herb

[Roughwater]

3 field coil

Hi Herb,

As to the 3 field coil, I don't know if that can even be done, just figured if a coild can be made into a 2 field coil why not a 3? LOL

Anyway if you do decide to do more coil making you might check ebay. I got a good deal on 2300 ft of 24 ga, 19 strand, silver coated teflon wire for just 55 dollars so I don't have to worry about buying wire for a while.

For what it's worth I got a start on my 1 Meter coil this evening. I think it will go together pretty fast if I had a few hours to dedicated to it. Right now it's an hour here and there.

Terry

[PVGOLD]

Hi Terry
I agree with you about the learning and building part of all of this, really
enjoy all of it, great people involved. I just ordered a couple more housings
to try some different configurations in. What is a 3 field? Sounds interesting.
Maybe I should get more wire! 1 meter coil sounds like some serious
treasure hunting.

Best Regards
Herb

[Roughwater]

Small dual field

Herb,

Thanks Herb,

I should end up with a few coils for sure. The odd thing to me about all this is that I'm finding I'm enjoying making these coils and testing and learning new things as much or more than I enjoy actual detecting.

I imagine you'll find lots of use for your small coil if all goes well. Sounds to me like it should be very sensitive to small gold and work well in trashy and tight spaces. Now it's got me to wondering if a large coil could be made into a mono tripple field coil? Maybe save that one for later. I feel now like making a 1M coild won't be difficult at all but will take more time due to it's size but we'll see.

Terry

Terry

[PVGOLD]

Hi Terry
Herb Here. Sounds like your going to be having a great selection of coils.
I wound one up Sat, came out at 310 inductance. Had it ready to test except
the connector, went to install and found out it was the wrong number of pins.
Ordered more, should be here by Fri. maybe test Sat. It is the folded 8
configuration, small 5.75". Should be, as Reg says good for small gold.

Reg
I know this has been posted but would like your opinion on the difference between tin coated wire and silver wire, I have some silver 26ga. Teflon coated about 24 strands.

Thanks to all for sharing

Herb

[Roughwater]

Hi Reg and all
I am looking for some advice and information about coax for a duel field
coil ie what type. I have read that S video cable will work. I would rather not
use two lengths of standard coax. Is there a certain brand that is best to use? The coil I'm building is for a TDI so I am also looking for schematics
for the 5 pin connector and wiring within the coil itself.
Any help will be greatly appreciated !!

Thank You

Herb

Hey Herb, how ya doing?

You were discussing what cable to use for your coax with Reg and I just wanted to second Regs suggestion of using Mogami shielded single conductor mike cable (for a mono connection). I used it and was very impressed with the heavy copper shielding it provides. If coax shielding is important then I doubt you will find a better shielded coax than this.

Terry

[Roughwater]

Dual field Mono coil

Reg,

Appreciate the drawing of how to fold a mono coil into a dual field coil.

You once mentioned something to me about using one of the 17"coils that I previously made that didn't fit my 18" housing into a dual field coil but I wasn't real clear on how to do that, so now I know and I'll be building one of these also ASAP.

Terry

[Reg]

Hi Wyndham,

There are so many companies making similar wire to what you mentioned it would be impossible to determine whether the one you may have seen would work or not. The best way to find out is to simply try it and see. I find it is the best solution for me. If you try it and it works fine, let us know.

Reg

[wyndham]

Reg, I'm wondering about the cable used in audio mic cables. It's shielded and has 2 strands.It can also be bundled into a cable that may have 12-24 different mic or instrument plugins so the shielding seems good. Is it too light a gage to use for a MD from the coil to the box or do you know? Wyndham

[PVGOLD]

Hi Reg
Going with your configuration 8 folded. Now I have a plan. Will be winding wire tomorrow.

Thank You
Herb

[PVGOLD]

Hi Reg
Thanks for the info. I was looking at Dave Emery,s Coplanar instructions.
Will now go with the dual field mono, sounds best for my first try. I am wondering if they are the same as far as configuration of windings, but without the bucking coil and resister?
I am as someone else said, at the shallow end of the pond and can't
touch the bottom, so your help is greatly appreciated.

Thank You
Herb