Do "OO" coils work on Pulse Induction?

[Carl-NC]

can anyone tell me why 30in or bigger DD are not available to buy for pulse induction, is there a technical reason why they won't work?

Technical, no. DD coils tend to be far more sensitive to mechanical flexing than concentric but the falsing that occurs is mostly reactive and should not show up in a PI. The only issue I can think of is that larger coils pick up more ground effect so in magnetically viscous soils you may experience overload.

[Nova]

6666; why would Coiltec be able to help me?, i have never seen a 30+in DD coil in Australia, so i don't see the point, i own a 24in dd this thing is stable and deep, but not deeper enough, when your searching ground that has the gold bearing layer at 4-6ft, i'm thinking 36in would get me to where i need to be. The tests i have seen with a concentric against a DD , i was not impressed with the concentric coil, and considering Nexus are asking almost the price of a new GPX5000 , for a coil that is not even that impressive, good luck to them but they won't be getting a cent from my pocket, i would rather start moving dirt than to fork out such a ridiculous price. I think Detech are going to release some larger concentrics or they were going to, if they do and at a reasonable price, i will probably get one, otherwise i guess i'll have to stick with what i have for now.
So nobody is interested? i am quite surprised, is it because you don't want to give someone you don't know an advantage? or you just don't believe you can create a coil than can do the job?, i would really like to know?

[Carl-NC]

So nobody is interested? i am quite surprised, is it because you don't want to give someone you don't know an advantage? or you just don't believe you can create a coil than can do the job?, i would really like to know?

Probably because it would be a huge mechanical challenge. As you say in the first post, the housing is a problem. It will likely need to be vacuum formed and few people have a 48" vacuum former. And designing the shell for good rigidity while making it light enough to lift is difficult. Up to about 18" a homebrew DD is feasible, beyond that not so much.

[Nova]

"One can notice that the volume of influence is significantlylarger for the double-D head than for other heads whichindicates that for a double-D head, the soil compensation willonly be efficient if the soil is homogeneous in a large volume"

I skipped all the maths, i never even did year 12 so that level of maths is just alien to me, but from that statement above it says DD is most efficient if the soil characteristics are of an even nature. Then we have the question of how well will a concentric work on an older machine like the SD2200d? will it be as quite as a DD, i've tried a 14in Detech mono on my machine, the false signals i was digging drove me nuts, could you imagine digging a 4 ft hole from a ground signal using a 30+in coil, no thanks, i have dug at least 3 - 3ft holes for rusted metal and they were measured holes, but at least they were targets and not ground noise.
So; is that paper stating that the concentric is the best OVERALL coil or have i misunderstood it?

[Nova]

Okay Carl, i can appreciate that, just thinking about it myself, there does not appear to be an easy solution to a large shell, could it be made from PVC piping?

[Carl-NC]

So; is that paper stating that the concentric is the best OVERALL coil or have i misunderstood it?

Generally a concentric is worse in harsh ground due to a greater lift-off effect. OTOH, the smaller RX coil helps reduce overall ground signal, sans lift-off.

Okay Carl, i can appreciate that, just thinking about it myself, there does not appear to be an easy solution to a large shell, could it be made from PVC piping?

Probably not. A good way to test a coil idea is to get a sheet of high-density foam; in the US I've used Owens-Corning pink foam boards from the local builder's supply. Cut a 36" circle out of it, then use a router to route grooves for the windings. You can wind the wire directly in the grooves or wind on a form and then place in the grooves. Pour something like fibreglass resin to hold the windings. You'll need something to attach it to a rod. This is not particularly durable but is a cheap and fast way to test ideas.

[Nova]

Carl; if and when i decide to try coil making i will try out your idea, thanks for the suggestion, I found out that Detech have a 32in Concentric coil for sale at around $1900 Australian, probably still a bit more than i'm willing to pay, but i will see.
A question about the Concentric and the really small Rx coil that it has, i think it's only about 10in compared to Tx of 32in , in what way will the small Rx effect the detection of large very deep targets say at 4-5ft ?, i understand it will improve sensitivity to smaller targets, but is there some kind of trade off in respects to having say a 70% ratio size Rx?
And Carl; by what you wrote (Generally a concentric is worse in harsh ground due to a greater lift-off effect) now i'm really not sure if it's worth forking out 2k for something that probably won't perform better than my smaller DD, there are rumours going around of another new PI from Minelab soon, if there is i will probably buy it, so i definetly have some decision making to do!!!
Oh and before i forget; is there a list somewhere of "Coil Making tools and Equipment" that is needed to give me a head start?

[dbanner]

The price point of some of these detectors and accessories is ridiculous.

You'll spend a decade in the desert before the machine will ever pay for itself. You'll end up with a bad back and wrinkled leatherback skin. Unless you find huge nugget, chances of which are slim to none.

Learn how to to make your own coils, that's where the real fun is. When you find small nuggets with a self made coil, the feeling is second only to orgasmitronic vibration at resonant frequency "xxx". save the money for something more morally uplifting. Like helping the poor.

[dbanner]

There's only three things to know about coil making.

1 ....coil housing

2. ....coil winding

3. Coil shielding

That's it. It ain't complicated. If you can boil an egg, you can make a search coil. Only thing required are two hands and some noodles, I think you would qualify.

[Nova]

dbanner "orgasmitronic vibration at resonant frequency "xxx"." Bahaaaaaaaaa, at least you gave me a laugh, i 've been needing it.
Damn ; on another note, i have a bad feeling for the last 6 weeks, something more is going on than just a virus, i remember walking out my backyard about 10 days ago and i noticed the sun seemed much more north than it should be for this time of the year,but i did'nt think much of it, then this afternoon i was on this youtube vid and all these people were commenting the same thing, i urge you all to check this out for yourselves, going a little conspiracy theory here, are you guys aware of how many rich people have gone into their bunkers, seems like overkill for a virus that is only a little more deadly than influenza, don't you think?

[Carl-NC]

A question about the Concentric and the really small Rx coil that it has, i think it's only about 10in compared to Tx of 32in , in what way will the small Rx effect the detection of large very deep targets say at 4-5ft ?, i understand it will improve sensitivity to smaller targets, but is there some kind of trade off in respects to having say a 70% ratio size Rx?

For most targets, no. Making the RX coil larger produces more ground signal (noise) while increasing the target very little. There is an optimum ratio depending on the size of the target, but it would have to be a really huge target to go beyond a 1:2 ratio.

Oh and before i forget; is there a list somewhere of "Coil Making tools and Equipment" that is needed to give me a head start?

Peruse the Coils forum. Also on the main web site (click the logo at the top) look for an article by Joe Rogowski on making fast coils.

[Nova]

Okay; Thanx again Carl, you have answered many questions that i have had, clear and concise, which has helped in my understanding of the PI, thanx for being so open with your expertise, you have helped this "scon" absorb some new and welcome info!!
Cheers!

[AK48]

look here : https://www.nexusdetectors.com/after...archcoils.html

[Nova]

AK 48, AT $3350 australian dollars, i would have to be a 6 pack short, the Detech supplier here in Australia has dropped the price on the 32in Concentric to around $1500, will wait for these bloody restrictions to be lifted, then maybe dive in!!