Detech 18" Concentric Coil

This coil doesn't have it's own thread, so thought I better start one.



A short session to report on the Detech 18" CC. Disclaimer - no I didn't find gold, but learnt a few things I'd like to share.

What I wanted to do is just swing it around, and get some more time on it - unfortunately I only had a couple hours to spare, but better that than nothing. No point doing comparison testing against other coils before knowing how it performs, and what likely settings can be used in different areas.

The spot I took it to was the Small Gold Patch that is in some of my YouTube videos. This has since been flogged with the Zed, SDC and GPX with a variety of coils. The reason I wanted to try it here was 1) this spot is pretty worked out, and 2) It is quite mineralized. A spiral/flat mono can only be used in smooth timings here. Regular monos can also be a pain but a larger mono such as a Minelab 18" is almost workable but a few tweaks are necessary. So I wasn't too sure what to expect with the Detech Concentric.

I switched on the 5000 with my normal settings but switched the front panel to Normal and DD. After ground balancing, the threshold was very stable, a welcome change from using big monos on a windy day! As I started to detect, I was on the edge of my seat waiting for the expected ground noises to come in. But they didn't. I even threw my test nugget on the ground a few times to make sure all was okay. I wasn't expecting to find much but I got a couple small bits of iron trash, most likely ignored by smooth timings on the GPX.

As I detected I was mucking around with Gain and Motion settings just sort of auditioning a few things, so I did hear a few ground noises. These were easily identified by using common techniques, i.e. comparing signals with sweep speed, ground balancing around the response area etc. I still checked a few to be sure. One which sounded a little sharper, and was still there even after re-balancing ended up being a .22 lead. "Wow, how is that still here?" was my first thought. I decided to put it back in the hole to have a play with some settings. With DD on the coil switch, I got a sharper response than in Mono. Switching the timing to Sens Extra sharpened up the response again. In DD, the coil works as a Concentric so the response is like using a smaller mono, very sharp and "tight". Imagine an 8" mono sitting inside a 18". I found that pin-pointing on a shallow target is on the outside of the inner ring (winding).

With targets virtually non-existent on the patch proper, I started working the fringe area to try and dig something. On the edge of a connecting track I got a nice sweet signal, that I expected to be a fairly shallow bullet. Before digging, I tried Mono, and the target was lost in the sudden increase in ground signal. I flicked into Enhance and I could hear it now, but the response was very faint. Back to DD and Normal and the signal was really clear and sharp. Into Sens Extra and it was sharper again, so I was pretty excited at this point. I was even more excited when it was still in the hole after two good digs, and all this crunchy wash was coming out of the hole! I thought for sure I pinged one of the right colour. When I got it in my hand it even felt good, heavy and hackly, but unfortunately it was lead.



Other general observations:

- It handled EMI like a champ, very stable
- Very light for its size
- I really liked having the option of switching between Mono and DD for different performance characteristics
- It's neither mono, nor DD, probably closer to a DD, but it can be a big mono or a bit of a hybird depending on your settings.

Thanks 10fp for letting me use your coil while I waited for more stock to arrive. Your closed skid is here now as well. Here's what it looks like fitted



All 18" Concentric coils supplied now include the black fitted/open skid, as well as the white closed skid. This is not a flat bottom skid, bit still prevents sticks and vegetation from getting caught in the spokes.

So in DD it transmits on the big winding and receives with the small, in Mono it transmits on the big or small? And then receives with both?
It would be interesting if these type coils took off and you could get an in line switch to isolate the individual winding so you could select concentric, 18" mono and 8" mono.

Great report Phasetech.
Please excuse my ignorance but would you please explain how a concentric coil works and the benefits.
Im sure others like me know how monos and DDs work but arent sure about CCs.
Thanks Dignit

I'm in the same boat Dignit, Concentric on a PI is still very new to me.
I don't exactly know how these coils are wired up, but from how it performs it seems like:

When in Mono, it transmits using the larger outer winding, and receives with the outer winding (or both?). I would think the receive is likely done by both windings (as is the case with a DD coil in Mono mode) but I could be wrong. Either way, it goes deeper in Mono on larger targets, and the outside edge of the coil is the sensitive part. It still pin-points in the centre on a larger target at depth, as with a traditional mono coil.

When in DD, it transmits using the outer winding, then receives on the centre smaller winding. This provides extra sensitivity, like using a small mono, but you get more depth as you still have a very large transmit field.

I'll try get some confirmation from Detech on this, and next time I'm out providing it isn't windy, I'll do a video on some different targets.

Just as a bit of a dummy check, I hooked it up to a 3500, and have a very textured nugget that I found with a GPZ that recently came out of an acid bath. In mono I can't get a signal off it. In DD I can, and it's even better in Sensitive, so this confirms my findings from the field.

Here is another one for you Nenad, going on your recent testing on the CC. How do you think it would go on a GOOD 2000. I understand thats probably a difficult question to answer but I thought maybe you could give an experts opinion on this awkward question. Should I stick to running it on the 5000 inDD Normal?

Should actually be a good match on the old 2000. The 2000's not being as sensitive as the 2100, ran mono's pretty successfully in all but really bad mineralisation, so a concentric which handles ground better than a straight mono should be a great match. The SD's just run Normal/DD (no coil switching like the GP's and up), so you'd be running it as a concentric all the time.

Pete's video going across some targets on a test patch, posted in another thread, but some may not have seen it:

[video=480,360]https://www.youtube.com/watch?v=_oAzudV_olE[/video]

The 18" is now available in a Camo pattern.

G'day there Nenad , appreciate the post you've put up about this coil , these Concentric coils have really pricked my curiosity ,espically for us PI user's .the makers of these coils must of done some extensive testing of these coils for Australian conditions ?? As the surface TX winding's are so much larger than the equilavent sized mono's or DD's that were currently used to ,they've obviously had to play it rather safe in there size of the inner RX winding ,so it leads me to ask you as your a agent for these coils as well , and have contact with the Bulgarain makers of these coils ,could it be possible , ( as a option ) to build a coil that you could fit a slightly larger inner receive winding on ?? ( if presuming your ground allowed you to ) I mean like the winding would be bolted on to the spokes with the little bolts that your coil swings off ,obviously means having to run two cables up to a dual connector near your control box ,and a bit of reengineering of the coil itself ,but it'd give us bit of a option to custom build our coils to our particular ground types and user preferences .Cheers .

Sorry I missed this. I don't think that would be possible. Coil windings have to be precisely nulled, and then fixed in place so there is zero movement in relation to each other. Something that bolts on wouldn't be sturdy enough. Also complications with connections etc.

Thanks for the reply Nenad , yeah terrible complicated I'd admit ,it was just a bit of wish full thinking by me ,that we may be able to custom build our coils . Nenad is there any talk of more sizes in these CC's than the current 3 ,cheers .

hugh62 said:

G'day there Nenad , appreciate the post you've put up about this coil , these Concentric coils have really pricked my curiosity ,especially for us PI user's .the makers of these coils must of done some extensive testing of these coils for Australian conditions ?? As the surface TX winding's are so much larger than the equivalent sized mono's or DD's that were currently used to ,they've obviously had to play it rather safe in there size of the inner RX winding ,so it leads me to ask you as your a agent for these coils as well , and have contact with the Bulgarian makers of these coils ,could it be possible , ( as a option ) to build a coil that you could fit a slightly larger inner receive winding on ?? ( if presuming your ground allowed you to ) I mean like the winding would be bolted on to the spokes with the little bolts that your coil swings off ,obviously means having to run two cables up to a dual connector near your control box ,and a bit of re engineering of the coil itself ,but it'd give us bit of a option to custom build our coils to our particular ground types and user preferences .Cheers .

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Hello Hugh 62.

I have had some experience in building these CC Coils, and your reasoning is not out of the question. Those overseas coils are not ideal in their construction ratios, you get a much better result using a larger RX receive coil.

The ultimate RX ratio is said to be .75% of the outer coil Diameter, however the RX can be below that ratio, maybe down to 50% of the TX coil, and it still works.
If you would like to try out your idea, make up a junction box with 2 sockets for 2 Mono lines in, and one on the other end for a short DD cable coming out of the small J/box to your detectors control box coil plug, clip the J/box box on to your shaft.

Now you can use any of your existing larger Mono coils as the Transmit coil.
The RX Receive coils have to be wound with a tinned copper Teflon coated finer wire, using nearly twice the amount of winds that your TX coil has. It can be wound as a bundle or a flat winding.
The inductance on the RX coil should be around the 500-uH+, the shielding being @ 80 to 100-ohms.

This coil can be wound and placed in between 2 skid plates, before sealing up the plates, I attach some smaller cable ties through drill holes in the top skid plate.
Note: these are drilled to match up with the spokes on the TX mono. Using the coil ties that are looped on the Top RX disc, you lash the RX coil firmly and centrally under your TX coil with some larger C/Ties.

Both the Coil leads twist around your detector shaft up to the bottom of the J/box, the other end DD lead, goes to your detector, make sure you earth the J/Box up to your Top coil inlet plug.

Good luck, ozziegold.

G'day OzzieGold, i have a question or 2 for ya, have you managed to build a better coil from all of your experimentation than what has been designed by all coil engineers? (what is currently commercially available), i was thinking to get into this coil building business for myself( just to experiment), but after thinking it through, it does not make sense to me, i cannot possible be smarter than all of minelabs engineers for example,these guys understand the theory very well and i'm sure have tested many configurations over the years, so in conclusion i think i would be wasting my time.
On a side note, if you remember a post i put up about 2 months ago about a coil idea i had, i contacted Carl at Geotech, he told me the idea will work but "probably" not to well. If you are interested to test this out for me it should'nt be to hard for you, if you have all the equipment, let me know if you are?

ironrock said:

G'day OzzieGold, i have a question or 2 for ya, have you managed to build a better coil from all of your experimentation than what has been designed by all coil engineers? (what is currently commercially available), i was thinking to get into this coil building business for myself( just to experiment), but after thinking it through, it does not make sense to me, i cannot possible be smarter than all of minelabs engineers for example,these guys understand the theory very well and i'm sure have tested many configurations over the years, so in conclusion i think i would be wasting my time.
On a side note, if you remember a post i put up about 2 months ago about a coil idea i had, i contacted Carl at Geotech, he told me the idea will work but "probably" not to well. If you are interested to test this out for me it should'nt be to hard for you, if you have all the equipment, let me know if you are?

Click to expand...

Hello Ironrock.

Re your questions about, can better coils be made than the current commercial coils that are available.
The answer is yes, as what the manufactures and designers have to take into consideration, is ease and cost of manufacture.

Re: time spent on each coil in an assembly line situation. They cant afford to spend 1 or 2 days crafting each special complex coil for a (got to have it now) World market, so everything is really a compromise.

Yes, it is a proposition to make your own coils if you have the time and dedication, there is a lot of research to do, but it is not all that hard, you dont have to be smarter than them.

I suppose all you need to have is a few far-out ideas and an inquiring mind, and then try things out. There are ideas and methods that the Commercial designers havent thought of, or cant use for the above reasons. Manufacturing Time and cost is their nemesis.

Ironrock, I sent a PM reply to your other older post, but got no answer at the time?? I would be interested to comment on your idea, and give advice.

Cheers ozziegold.

READ THE RULES PLEASE.

Posts which appear to have been made with the sole intention of advertising or self promotion will be removed without notice.

G'day Ozziegold, i have sent you an email.
Cheers!

STE said:

READ THE RULES PLEASE.

Posts which appear to have been made with the sole intention of advertising or self promotion will be removed without notice.

Click to expand...

The guy has nearly 2000 posts and is well respected around here.

I don't see any hint of 'advertising' or 'self promotion' here at all. What I do see is a review.

[edit]
Nevermind. I see you got yourself banned while I was writing this post.

Jazz said:

STE said:

READ THE RULES PLEASE.

Posts which appear to have been made with the sole intention of advertising or self promotion will be removed without notice.

Click to expand...

The guy has nearly 2000 posts and is well respected around here.

I don't see any hint of 'advertising' or 'self promotion' here at all. What I do see is a review.

[edit]
Nevermind. I see you got yourself banned while I was writing this post.

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Hi Jazz.

Thank you for your post. he didn't deserve to be a member.

Best Regards ozziegold.

ozziegold said:

hugh62 said:

G'day there Nenad , appreciate the post you've put up about this coil , these Concentric coils have really pricked my curiosity ,especially for us PI user's .the makers of these coils must of done some extensive testing of these coils for Australian conditions ?? As the surface TX winding's are so much larger than the equivalent sized mono's or DD's that were currently used to ,they've obviously had to play it rather safe in there size of the inner RX winding ,so it leads me to ask you as your a agent for these coils as well , and have contact with the Bulgarian makers of these coils ,could it be possible , ( as a option ) to build a coil that you could fit a slightly larger inner receive winding on ?? ( if presuming your ground allowed you to ) I mean like the winding would be bolted on to the spokes with the little bolts that your coil swings off ,obviously means having to run two cables up to a dual connector near your control box ,and a bit of re engineering of the coil itself ,but it'd give us bit of a option to custom build our coils to our particular ground types and user preferences .Cheers .

Click to expand...

============================================================================================

Hello Hugh 62.

I have had some experience in building these CC Coils, and your reasoning is not out of the question. Those overseas coils are not ideal in their construction ratios, you get a much better result using a larger RX receive coil.

The ultimate RX ratio is said to be .75% of the outer coil Diameter, however the RX can be below that ratio, maybe down to 50% of the TX coil, and it still works.
If you would like to try out your idea, make up a junction box with 2 sockets for 2 Mono lines in, and one on the other end for a short DD cable coming out of the small J/box to your detectors control box coil plug, clip the J/box box on to your shaft.

Now you can use any of your existing larger Mono coils as the Transmit coil.
The RX Receive coils have to be wound with a tinned copper Teflon coated finer wire, using nearly twice the amount of winds that your TX coil has. It can be wound as a bundle or a flat winding.
The inductance on the RX coil should be around the 500-uH+, the shielding being @ 80 to 100-ohms.

This coil can be wound and placed in between 2 skid plates, before sealing up the plates, I attach some smaller cable ties through drill holes in the top skid plate.
Note: these are drilled to match up with the spokes on the TX mono. Using the coil ties that are looped on the Top RX disc, you lash the RX coil firmly and centrally under your TX coil with some larger C/Ties.

Both the Coil leads twist around your detector shaft up to the bottom of the J/box, the other end DD lead, goes to your detector, make sure you earth the J/Box up to your Top coil inlet plug.

Good luck, ozziegold.

Click to expand...

OZZIEGOLD ; Thanks for that ,sorry about the delay ,I don't envy coil manufactures bringing out what they do really ,apart from the Commercial reality and for the obvious fact it has to meet every body's needs and a whole range of different soil types ,etc . .75% of the transmit size WOW it'd be great if we could do this , with a PI and on our gold fields ,and still have a smooth threshold .Hence my curiosity at being able to custom build our own CC's for our own different soil types / needs etc .Outa curiosity what is the largest inner receive you've built , not knowing your ground ,was it stable or noisy ?? How do you work out the inductance / resistance levels ,i'd imagine different sizes / makes /monos /DD's would all be different ?? And outa curiosity have you ever measured / tested commercially available identical coils ,same make etc , to compare them to each other ??

Hello hugh62.

PM sent yesterday.

Cheers ozziegold.