XP deus coil modification

[Skippy]

The high inductance required inevitably means thinner wire, but 0.2 / 0.15 is not that thin, it's easy to work with. When you start (and finish) the winding, loop a 15cm length of wire back over itself twice (so you have triple-thickness) and twist the three wires together. Make sure that 5 cm of this triple-thick wire is bound up in the coil windings. Make a solder joint to all three wires. Repeat at the finish of the wind. This is more rugged than a single strand..

When you have decided on the exact shape of your 'elliptic' loop (I suggest 1.8:1 to 2:1 length/width ratio), measure the circumference. Calculate what the radius of a circular winding of this circumference would be. Use this figure in the Qoil Qalculator (which is for circular coils), BUT aim for an inductance +4% more than your elliptic coil needs. This is approx. the drop caused by the elliptic shape (96%).

Wind the RX coil first, it's not so critical, then use your results from this winding to fine-tune the manufacture of theTX winding.

[Henrikras]

Thanks Skippy.... You said; " I suggest 1.8:1 to 2:1 length/width ratio " - Is that the shape, like 4"x 8" or 3"x 6" finish search coil you say... Or only TX / RX shape alone ?
I allso noticed that my Inductance drop a little down, at some earlyer eliptical coil I made... ( some extra Winding was needed ).
Last thing this time.. Do you still recommend lower R than the Stock RX 70.6 ohm, like 50 ohm or 60 ohm... ???
If so, the AWG with 0.18mm will Be close to R50-60, but AWG 0.16 mm will end close to the Stock RX coil R70, and then the 0.18mm will be ordred. Remember allso this extra 4% which could end up with some 6-10 windings and a little higher R.
Henrik.

[Skippy]

The 2:1 thing refers to each winding.
"I noticed that my Inductance drops a little down, on some earlier eliptical coil I made" - that's what the 4% factor is about. And don't forget the extra isolated turns for fine-tuning, eg. 200+2+4 would give +/- 6% L change, in 2% steps. Or 200+3+6, etc, depends how confident you are.
The receive resistance is not that important. The front-end amplifier likely has a noise resistance of 50R - 100 R, the coil is just made to have similar resistance, so they contribute equally. There's no point having a 20 Ohm coil and a '100 Ohm' amplifier, and vice-versa. Just aim for 70R, if it's 90 or 50 it won't make much difference.

[Henrikras]

Got it... Thanks Skippy.
I know that we've been through this! You say I must go after a Inductance 14.9 mH RX and the 10.4 mH TX.... BUT - is it so good!Because this project shall end up only with a 17-18 khz searchcoil, why not lower the Inductance and tune it up with a capacity...???
Like 12 mH and 6.8 nf or even more 10 mH and 10 nf..
Or keep the RX close to the 14.9 mh, but play with the TX Inductance / Capacity outside.
This small coil we never Be used at 4 khz and 8 khz.. Properly never 11 khz allso.
Can't understand why not give this a try.
Henrik

[Skippy]

I really don't know why you want to risk failure by meddling with the design, the details of which are unknown. There's nothing special about the inductance of your coils - the Tek T2 / Fisher F75 have receive coils with similar specs: inductance about 7 mH, 40 Ohms resistance, wound with wire similar to 0.2mm.
I agree that getting it to work at 12K or 18K is probably all you need. Maybe as a second project you could try and make a broadband version (or at least 8/12/18.). Just slavishly copy the original for now.

[Henrikras]

You can't say I'm not thinking...
Thanks for you patience. Henrik.

[Henrikras]

Hello again.
Skippy If you Please would look over my shoulder....
The first try would Be a 5x7" coil. (See picture). Is a coil cover 5x8" shortened 1" in the middle.
One turn is 39 cm = Radius 62 mm.
I've ordered AWG 33 (0.1 and from a earlyer project I got some AWG 30 (0.25). See pictures with the result by Qiaozhi's Calculator.
Couldn't find AWG 29 (0.2 at my supplyer Brocott in UK. Tryed others and Ebay, but it wasn't easy.
The AWG 30 will properly end up with 24 ohm (21 ohm stock coil) at the TX side, a little to high.... Hope it wouldn't damage to much.
Then I ordered some plexiglas tubes... Why! Crazy idea, that I can form those to the perfect sharpe and form, and make a slize at the outside to the windings... Ive ordered some with 3mm and 3.5mm and 4.0 mm inside diameter...
Not easy to explain, but I hope to show you some pictures later.
With those plexiglas tubes, like a coil form, it would allso Be easy to work with shielding, If that comes up later...
Allso If the coil ends up working, and the polyester will Be used closing up, because the plexiglas is stable to some heat the polyester makes.
But all that later.
Thank you so fare - great help you gave.
Henrik.

[Skippy]

Well, you gotta start somewhere, I guess, and you've bought the wire so there's no point me telling you to change things now. You forgot the +4% factor, so add 2% more turns to your windings than your calculator shows. And the 62mm is actually the mean radius, so you should be entering 60 or 60.5mm as the inner radius, probably.
Have you heard of www.wires.co.uk ? They have large stocks, but I don't know about International shipping, costs etc.

Surely cutting the coil cover in half is going to ruin its rigidity? I've no idea about the plastic tubes....

[golfnut]

The selling point with the ellipse coils is ground coverage. They are often fairly big. Longer ones are not that deep, thats not their job.

You want a small, local iron exclusion footprint on your iron rich worked sites... but you still would appreciate some depth - A round one fits the bill Id say.


Depth would suffer with a small ellipse - with a commercial ellipse, the depth is limited to the smaller dimension So say an 7"x4" would do about 4" max on smaller coins. Not great depth and would still pull in signals from local iron as long pick up footprint.


With a 6" round DD you will get 6" depth- still with good exclusion of nearby iron as footprint 6"

Easier to get a shell



S

[Henrikras]

Yes I have to start somewhere.
I have not forgot the extra % - Allways makes some extra windings offcause.
The rigidity at the cover is no problem... I dont know how to say this, but I'm more a practical man, that and electronic Expert in metaldetectors. Give me to nails some glue and a newspaper, and I make you a bikecycle. Just a joke..
See you.
Henrik

[Henrikras]

The selling point with the ellipse coils is ground coverage. They are often fairly big. Longer ones are not that deep, thats not their job.

You want a small, local iron exclusion footprint on your iron rich worked sites... but you still would appreciate some depth - A round one fits the bill Id say.


Depth would suffer with a small ellipse - with a commercial ellipse, the depth is limited to the smaller dimension So say an 7"x4" would do about 4" max on smaller coins. Not great depth and would still pull in signals from local iron as long pick up footprint.


With a 6" round DD you will get 6" depth- still with good exclusion of nearby iron as footprint 6"

Easier to get a shell



S

Easier to get a shell ??? Can you help with a link or where to buy 6" Shell.

[golfnut]

Sorry its not easy is it for a 6" Hayes elec stopped trading , the bulgaria guys are not 6", and Georgi on here, his are bigger

The only thing I suggest is modifying a ML 3030 coil cover.

http://www.joanallen.co.uk/minelab-6...er-p/20219.htm



or a plain round 5"

http://www.metaldetectorshop.co.uk/s...oduct_id=62354

or buy a broken one and hack it out for your coils
other option is get a coil which has no caps in like tesoro and find one with similar L values. S

[Henrikras]

Thanks.
Just the same I found out.
Henrik.

[golfnut]

Hi, Don on here is selling a nice 7" shell DD.

https://sites.google.com/site/dbcoil.../7-inch-shells

[Henrikras]

Thanks Golfnut.
I've ordered the CTX cover 6".
While waiting I had look at a 4".... (Look at the pictures).
It is so small !!!
I dont know what you think, but Maybee is it worth a try.
This Plastic tubes is okay to work with... I think I would get a stable coil, If all the Winding goes nicely inside.
One turn inside the tube was 25.4 cm / thats a inner Radius at 40 mm.
And I have to add 8 windings to get +4%... (Total 296 - properly up to 300 would Be a good idea first try).
One tube / coil form is 3.5 mm inside the other 5.0 mm (TX needs 0.25 wire).
I will use the Wood a the picture to hold the tube, while Winding the coils.
Henrik.