GPX homemade large coil

[Davor]

Oh but they do, only we do not care about it as long as our silly devices call for op amps that are also at about 4nV/sqrt(Hz) so it makes no difference whatsoever

My point - don't let marketing brouhaha confuse your inner engineer. He knows better.

[Mechanic]

Oh but they do, only we do not care about it as long as our silly devices call for op amps that are also at about 4nV/sqrt(Hz) so it makes no difference whatsoever

My point - don't let marketing brouhaha confuse your inner engineer. He knows better.

Well your devices could squeeze out a bit of extra performance if they did use a lower noise front end. You'd be very surprised at the difference it makes. I have tried 1k resistors, they make a lot of noise, so to combat the noise, gains need to be reduced to make the detector "smooth" again. Reduced gain = reduced depth. I have gold to prove it too
I have seen the differences with slight different coil making methods, on a scope. When I say it is critical, that's because it is

Anyway, this is getting off topic... I'm going to go and swing some spanners and lift heavy things, and beat stuff with a hammer!

Good luck...

Cheers Mick

[GoldPandemic]

Any idea if this will measure inductance?
http://www.trademe.co.nz/a.aspx?id=982941154

[6666]

Any idea if this will measure inductance?
http://www.trademe.co.nz/a.aspx?id=982941154

yep - Inductance: 0.01mH - 20H

[IBGold]

At the price give it a try.

And Mick coil building is not a black art it is more about attention to detail I wrote a 20 line reply but as usual when Iwent to post it as usual I was told I was not logged in but the top of the page sais I am this has been happening for months so you can see why I do not get involved much these days.

Regards, Ian.

[GoldPandemic]

Cheers.

IBGold, have you tried checking the little box that says - Keep Me Logged In - when you log in.
You can always log out afterwards as normal. I always copy forum posts before I click post button - as this also happens to me from time to time.
I would appreciate any more you have to say, if you go to the trouble of rewriting that long post.

[Qiaozhi]

At the price give it a try.

And Mick coil building is not a black art it is more about attention to detail I wrote a 20 line reply but as usual when Iwent to post it as usual I was told I was not logged in but the top of the page sais I am this has been happening for months so you can see why I do not get involved much these days.

Regards, Ian.

It's your browser that's logging you out, not the forum. As GoldPandemic said, tick the "Keep Me Logged In" box.

[IBGold]

OK that did not work lucky I copied it before I hit reply.
OK we will see what happens it has all happened since after having to replace my desk top after my previous one was hacked but we will not go into that.

GP with coils for the Minelabs the wire you require is around 17 AWG either tinned wire or Litz 32/32AWG or 0.2mm for normal coils up to around 18" what I have found is Litz with strands of 32 AWG to 36 AWG seem to perform best we wind our own Litz style wire with the amount of strands dependant on the size of the coil for the 1 metre coil you are thinking about you might get away with the stuff on eBay I think it is 50/32AWG I have built a 760 x 560 1.6 to 1 coil with this wire with both the 50/32 AWG and 924/46 AWG and the 50/32 has given the best performance you need to keep your coil bundle tight I loop lock stitch mine at 10mm centres with fishing braid with super glue locking the stitches then put the coil in a Styrofoam former allowing a minimum of 8mm between the coil bundle and the shielding the blue Styrofoam that you show in your picture is the same as I use (comes out of the same factory) best if you PM me and I can give you more info.

Regards, Ian.

[GoldPandemic]

Cheers for the IBGold.
The litz wire from my 11" mono is 40 strands, total thickness of wire is when wrapped in silk/nylon is about 2mm.
My intention is to not make a disc coil, as this would add weight (plastic/skidplate) & be difficult with my home limited resources DIY construction.
I wish to test the coil on a large cardboard surface at first.
Then, I will feed the wire through a plastic plumbing pipe with a magnet, until desired turns are achieved.

When I get my LCR tester I'll be able to make another post.
For now, I have a few questions.
Where do I make my test points on the coil?
Do I test the coil when it is powered?

[IBGold]

Hi your inductance and resistance checks are done unconnected on each end of the coil wire and finally for the final test at the end of the coax with the coil connected.

Regards, Ian.

[GoldPandemic]

"end of the coax" - being where it is soldered to the coil wire?
"coil connected" - but not with the detector on, is this correct?

[IBGold]

Ends of the coil wire before you solder to coax while you are winding the coil and the end of the coax where the plug is when you have connected to the coil the resistance will be slightly more when the coax is connected so you have to allow for this when making the coil where are you.

Regards, Ian.

[GoldPandemic]

LCR-T4 Mega Transister Tester Capacity ESR Meter, worked well once I figured out which pins to use (no instruction manual had to search ebay for inductance pix).


Here is my disasembled minelab 11" mono coil:


The Inductance always reads 0.28mH, testing the lead point I got 0.7 Ohms with a resistance variance of 0.3 so I think that is close to the 0.4 Ohms the poster said in comments above.
Testing the coil with lead removed was variable 2.1 to 4.5 Ohms, so I ended up soldering the test points on. I think the wire has insulating coating. The best reading I got was 1.3 Ohms, less the variance = 1.0 Ohms.

I thought it would read higher with lead on, if anyone has an idea of why the resistance is higher with lead removed I'd love to know?
So I'll just wind my 1 metre coil and hope it tests alright when I add the lead.

[GoldPandemic]

Now testing 1 metre coil with same length of wire. 0.7 Ohms (-3 variance = 0.4), Inductance is now 0.08 mH.
http://www.paydirt.co.nz/forums/reso...shx?imgprv=599

Now do I add more windings to get the Inductance up, or will this increase the resistance?
Or do I increase the number of wires to increase the Inductance?

I've some other different sized coils that I can test the plugs (not prepared to destroy).
10 x 5" DD, 6" mono.

[GoldPandemic]

I've just found out that the minelab 18" mono coil uses 72 strands 0.2mm litz.