Nexus Coil Design

[Nexus]

Shielding of coils

Hi Georgi,

would you tell us a little bit more about shielding of coils?
& what about transformer in "X" demodulator`s loop?

The shielding of coils is one of the most important steps in manufacturing good coils.
There is various ways and materials used in this process.
This is a short list of some compatible materials for shielding coils;
Aluminium foil, Copper foil, Nickel Screening compound, Graphite paint, Electrostatic (conductive) plastic foil, Flat aluminium or copper wire, drain wire.
The main problem when shielding coils which will always occure is the offset valtage in the receive coil of the system, caused by this screen (shield).
The different materials used for shielding are causing change of the phase alignment between the TX and RX coils, which results in lower efficiency of the system. The best efficiency for two coils in induction balance will be acheiveble without any shielding, but unfortunately that arrangement will not work in real conditions. Now, from this follows that the shielding should be as less notiseble factor in the balance as possible, with other words the shield should not produce any additional phase shift if it is possible or as little as possible.
From one side if the shield is not thick (high resistance) enough that will keep the over all efficiency high, but in some cases the stability of the coils to whats some capacitance factors can be compromised. From the other hand if the screen is thick (low resistance, for example 50 - 100 microns of aluminium foil) that will get the system very stable regarding the capacitance between the ground and the coils, but the over all efficiency will be less compared with unshielded coils.
It is not difficult to conclude that some compromise has to be acheived, which will depend on the design specifications.
My pesonal preferance falls on the aluminium foil as beeng one of the easyest and most relieble to use.
One very important factor when shielding. THE SHIELD OF ALL COILS SHOULD NOT BE MADE AS CLOSE ( SHORT ) CURRENT CIRCUIT. LEAVE SOME SMALL GAP ANYWHERE ON THE COIL WHICH WILL RESULT IN THE SCREEN WITH WIRE CHARACTERISTICS, NOT RING. CLOSED RING SHIELD WILL DEMOLISH COMLETELY ANY EFFICIENCY OF THE COIL SYSTEM, BY PRESENTING VERY HIGH LOAD TO BOTH COILS. THIS CONDITION IS VALID IN CASE OF ALL MATERIALS USED FOR SHIELDING.
Another important condition is that the shield of the two loops should be elecricaly isolated from each other over the perimeter of the coils and conected only trough the drain wire which goes (in most cases) to the ground of the power supply.

Please clerify what do you call X demodulator`s loop?

[Charles (Upstate NY)]

Correction, a gap is not required for graphite/carbon black shielded coils, at least not on the Minelab Explorer, Sovereign, Excalibur variety. Nor do the shields need to be electrically isolated from one another.

[Nexus]

Shielding coils

The Minelabb are not to be used as an example unfortunately.
Their coil shields are very low conductivity which is the main reson for them not to use gaps. Also they are not made directly on the loops, but as part of the coil case or PAPER plate with some conductive paint.
My theory is very correct when very sensitive coil systems are consern, not average.
After all I have designed the deepest dtectors on the market. It will be good if you can present your engineering work before placing expert statements.

[Charles (Upstate NY)]

The shielding should not be applied directly to the windings, some seperation between the windings and the shield is desirable.

Everybody says their detector is the deepest of all time. I do know that I don't care for the funky square tubing of the Nexus or the ergonomics. And the coil designs lack imagination e.g. there is room for improvement so lighten up a bit engineering dude, your ego is getting a bit large.

Are you the guy that was threatening to sue Dave Emery recently?

The Minelabb are not to be used as an example unfortunately.
Their coil shields are very low conductivity which is the main reson for them not to use gaps. Also they are not made directly on the loops, but as part of the coil case or PAPER plate with some conductive paint.
My theory is very correct when very sensitive coil systems are consern, not average.
After all I have designed the deepest dtectors on the market. It will be good if you can present your engineering work before placing expert statements.

[Qiaozhi]

Coil Question

Calm down guys.

The Nexus coils may look a little odd compared to other commercial designs, but Georgi knows what he's talking about. I'm planning to get some first-hand experience with the Nexus sometime in the near future, and I'll let you know my findings.

What I use is 4 x 25 turns = 100 on the transmit coil in the following connection; external end-25-colector point-25-negative power rail-25-colector point-25-external end. Between the two external ends is the tunning capacitor

Did you mean: external end-25-collector point-25-positive power rail-25-collector point-25-external end? The schematic you originally posted has the 13-13 coils connected to +6V via a 10 ohm resistor. I just want to confirm that I've understood this correctly.

[Nexus]

The shielding should not be applied directly to the windings, some seperation between the windings and the shield is desirable.

Everybody says their detector is the deepest of all time. I do know that I don't care for the funky square tubing of the Nexus or the ergonomics. And the coil designs lack imagination e.g. there is room for improvement so lighten up a bit engineering dude, your ego is getting a bit large.

Are you the guy that was threatening to sue Dave Emery recently?

As a matter of fact i did worn David Emery to think well before make label statments and eventualy he came to reason.
However one think is sure. There is room for improvement always, but from what you have told me so far I would not say that you have much expertise to offer.
And forgive me, because I do not mean to be rude but you do not posess as much knowlege about shielding coils as you think. It may be better before talking about ego to alter yours first in accordanse to your knowlege.
At the least I have to show something and I did demonstrate my results in many ocasions, also published the real measurements for the Nexus. Where are the measurements of your acheivements, or for that matter from any other manufacturer you know about?
I am so sorry, but this is a forum where people try to exchage some information and ideas. If you can not offer that please be so kind to shut up.

[Nexus]

Calm down guys.

The Nexus coils may look a little odd compared to other commercial designs, but Georgi knows what he's talking about. I'm planning to get some first-hand experience with the Nexus sometime in the near future, and I'll let you know my findings.



Did you mean: external end-25-collector point-25-positive power rail-25-collector point-25-external end? The schematic you originally posted has the 13-13 coils connected to +6V via a 10 ohm resistor. I just want to confirm that I've understood this correctly.

1`st External end - 25 - collector point - 25 - NEGATIVE POWER SUPPLY - 25 - collector point - 25 - 2`nd external end - tunning capacitor to the 1`st external end.

Two of the sections are connected between the collectors of the transistors. The midpoint of those two is connected to the negative pole of the power supply. The other two 25 turn sections are connected to the collectors again with one of their ends and the second ends of the same are connected together through tunning capacitor.
I apologise if was not clear enough the first time.

[Charles (Upstate NY)]

As a matter of fact i did worn David Emery to think well before make label statments and eventualy he came to reason.
However one think is sure. There is room for improvement always, but from what you have told me so far I would not say that you have much expertise to offer.
And forgive me, because I do not mean to be rude but you do not posess as much knowlege about shielding coils as you think. It may be better before talking about ego to alter yours first in accordanse to your knowlege.
At the least I have to show something and I did demonstrate my results in many ocasions, also published the real measurements for the Nexus. Where are the measurements of your acheivements, or for that matter from any other manufacturer you know about?
I am so sorry, but this is a forum where people try to exchage some information and ideas. If you can not offer that please be so kind to shut up.

Let me see if I got this right...I'm an idiot in the shaddow of your greatness and I should keep my mouth shut, does that about cover it? Okay professor whatever you say. Your detector is the best and you are the Einstein of our age. I will look for you on the cover of Time Magazine.

[Charles (Upstate NY)]

Hey Professor Nexus, I tell you what. Build a cnc milling machine, then build a horizontal band saw, then build a vacuum thermoforming machine, then design and build a dozen different coils and 2-3 waterproof housings, then look down your arrogant nose at me okay.

[J_Player]

Dang, charles...
Them are some-o the coolest lookin' coils I ever seen. and yer tooling looks as good as any I seen. I know who to talk to next time I need some advice on making a coil.

[Nexus]

Hey Professor Nexus, I tell you what. Build a cnc milling machine, then build a horizontal band saw, then build a vacuum thermoforming machine, then design and build a dozen different coils and 2-3 waterproof housings, then look down your arrogant nose at me okay.

Your variety of shapes means very little when talking about results of how deep those can go. Just from the pics I can tell you that you have no chances to outcompete Nexus which is offered with one coil only, not 50 different ones. I respect your work, but buddy those are copies of what other people have designed before you. The question is can you show something you have created which can demonstrate substantial advantages to the designs done before you.
You can demonstrate your production quantities of bits, fine with me.
What about coming over here with your best detector and prove it against the Nexus in fair competition?
Remember well this. What you do has been done by many before you and after you, but the Nexus is quite unique by it`s capabilities.
If you were inteligent enough could eventualy try to comprehend the possibility that someone out there has done something better. But that will require more of the science and not that much of the CNC`s and dozens and dozens of plastic bits.
Why didn`t you think first about getteing in busness with me rather that being a smart ***. There is always something to learn, but you seem to believe that you got all the knowlege.
Now about all of those stuff you say that they are your design. Good job, but those are not metal detectors and not related to them either.
This is forum about metal detectors, not heavy machinery.
Show some detectors please. Will you?

[Unregistered]

Georgi is actually a loudspeaker designer, so I have to speak out here.

Charles has produced some VERY capable and innovative coil designs, and he should be commended for that. One thing to point out here is that the BETTER THE ELECTRICAL BALANCE, THE BETTER THE DETECTOR, so Georgi, now ALL know your "secret", which by the eay has been common knowledge amongst beeper desisgners for decades, as has pumping out 100V pk-pk on the Tx signal and you Forster-Seely type demodulators which DO NOT saturate in the way conventional switching demods do.

I think this is not the place to spout arrogant rhetoric about who knows best, we are AMATEURS here but there are a great many VERY clever people who are fast learners and who will soon overtake the "pro's".

From your comments about mainline machines being "toys" I can agree that most detector designers are incompetant idiots, BUT.......Well, take one of the Carl's associated with this forum, he is an ASIC designer for a large and well respected US company, I am a DSP Engineering Consultant and can tell you I know more about how to make detectors A LOT deeper using DSP and modern digital electronics than you will ever do. Having worked on military radar and radio systems, still think loudspeaker design is complicated?

No matter HOW clever you THINK YOU ARE, there is always someone out there who is better, life has taught me this one thing above all others.

Obviously you have lived a very sheltered work life Georgi, and a "holier than thou" attitude is not welcome on this forum, what we, CIVILISED people here engage in is in indulging our interests as AMATEUR beeper desisgners, nothing more. We LOVE our hobby and want to experiment.

If the Nexus isn't selling as you had hoped, then maybe you should review your marketing approach, and that does NOT involve a large dealer (who will, no doubt, just rip you off). The days of the £1000+ detector are GONE, Lamebin saw to that by producing an over priced piece of rubbish, and then lieing through their teeth to sell it to gullible mugs. Don't expect you can do the same my friend, "Once bitten, Twice shy", and contrary to popular belief, detectorists are not as stupid as you might think. Geeky, maybe, but NOT stupid!

if you want to slag people off, then please go to one of the many forums where this is common place. We are all friends here.

[Unregistered]

for Nexus

Pro4etoh podrobno tova koeto ste pisali vav foruma,i mnenieto mi za vas suvpada s mnogo ot tezi na drugite u4astnici vav foruma.Ako 6tete i super antena da slojite na kalpav priemnik-rezultata e sy6tij kato super priemnik s kalpava antena.Kato gledam shemite-tova sa ne6ta ot predi 10-15 godini i tezi shemi sa trugnali ot Shumen (az predi 10 godini sglobih takuv detektor i to4no v tozi grad,po-to4no povtorih edna shema s malko i zmenenij ot moj strana).A ima i dosta osobennosti po tezi shemi i podbora na komponenti,za koiro se pravjt otdleni shemi za izmervane na parametrite im.Ne te znam kvi gi vr6i6 i kvo se opitva6 da prodava6,no 4eteiki prikazkite ti ostavam s vpe4atlenie 4e si dosta bos na tema elektronika.Njma da ti pravj literaturno 4etene,no 6te ti kaja slednoto daje i tvojta antena s 14... i neznam si kolkoto tam grama e tejka!prdi 6 mesetza v BG vijdh PI detector s mnogo po-leka antena i s vazmojnosti to4no da razpoznava tipa metal,koeto si e edno seriozno postijenie i dosega ne sum vijdal druga takava shema.Shemata si e procesorna i ima dosta interesna shemotehnika i zamisul. Kolkoto do vidovete anteni-mnogo sa i vsjka si ima prednazna4enie,taka 4e ne se opitvai da se izkara6 genii kato si napravin ne6to koeto raboti i da se opitva6 da go probitva6 na horata tuk,i nai ve4e ne se pi6i velik profesionalist v oblastta si.Ne zabravji 4e "Titanik" e stroen ot profesionalisti,a Noj e bil amatjor!Tova e forum za obmen na techni4eski idei kakto vijdam,a ne za probutvane na metalodetektori.Kato iska6 da prodava6-pusni objva v njkoi BG forum i prodavai....

[Siliquae_Sid]

I'd love to know what that was in English, 'cos I bet it wasn't a well done!

Hold up, YOU warned Dave Emery?????? Gerogi you are in danger of being branded an idiot coming out with statments like that. I used to respect your views, but you are RAPIDLY losing crediibility coming out with guff like that.

If you want to take part in a VALID conversation, perhaps you will tell us the WHOLE theory of operation and a complete explanation of your design, then maybe we can understand and give you the credit you may deserve, but slagging people off on this forum?? GO AWAY if that's all you want to do, we have a very friendly atmosphere here and respect each others skills and opinions.

[Nexus]

[QUOTE=Unregistered]Georgi is actually a loudspeaker designer, so I have to speak out here.

Charles has produced some VERY capable and innovative coil designs, and he should be commended for that. One thing to point out here is that the BETTER THE ELECTRICAL BALANCE, THE BETTER THE DETECTOR, so Georgi, now ALL know your "secret", which by the eay has been common knowledge amongst beeper desisgners for decades, as has pumping out 100V pk-pk on the Tx signal and you Forster-Seely type demodulators which DO NOT saturate in the way conventional switching demods do.

I think this is not the place to spout arrogant rhetoric about who knows best, we are AMATEURS here but there are a great many VERY clever people who are fast learners and who will soon overtake the "pro's".

From your comments about mainline machines being "toys" I can agree that most detector designers are incompetant idiots, BUT.......Well, take one of the Carl's associated with this forum, he is an ASIC designer for a large and well respected US company, I am a DSP Engineering Consultant and can tell you I know more about how to make detectors A LOT deeper using DSP and modern digital electronics than you will ever do. Having worked on military radar and radio systems, still think loudspeaker design is complicated?

No matter HOW clever you THINK YOU ARE, there is always someone out there who is better, life has taught me this one thing above all others.

Obviously you have lived a very sheltered work life Georgi, and a "holier than thou" attitude is not welcome on this forum, what we, CIVILISED people here engage in is in indulging our interests as AMATEUR beeper desisgners, nothing more. We LOVE our hobby and want to experiment.

If the Nexus isn't selling as you had hoped, then maybe you should review your marketing approach, and that does NOT involve a large dealer (who will, no doubt, just rip you off). The days of the £1000+ detector are GONE, Lamebin saw to that by producing an over priced piece of rubbish, and then lieing through their teeth to sell it to gullible mugs. Don't expect you can do the same my friend, "Once bitten, Twice shy", and contrary to popular belief, detectorists are not as stupid as you might think. Geeky, maybe, but NOT stupid!


All of this is your personal understanding and your references are misguided. I did not make or made any claims of beeng smarter or more advanced than anybody else.
All I said is that the Nexus currently is the deepest detector on the market which is a fact. Sorry of it pains you, but it is the truth.
Dispite your opinion I actualy have problems supplying all of the clients with detectors, for my manufacturing capabilities are too limited.
When you acuse me in anything it will be fare to see all of the curcumstanses arround, not just what is in you personal interest.
About the secrets SORRY BUT YOU KNOW NOTHING. It is not as simple as you think.
If you realy want to be CIVILISED first of all do not start pointless arguments as your friend Charles, by giving away lessons without beeng asked for that.

About the digital domain. You do not know enough about me, so it is not that wise to run premature conclusions.
However keep in mind that there is no existing electronic method capable to compensate the inpefections of the coils. The electronics can only analyse what is detected by the coils, nothing more.
I still insist that the results are above all, not somebody`s pride.

I am not saying that Charles have done nothing, but his aproach to me was rude as from a great expert to an amature. And believe me he does not know as much as he thinks, other wise he would of understand.

After all I was only nice to those who asked for some information about coils and did not have any intention to fight anybody, but I will not show any tolerance to nasty american attitude. OK

If you wish to discuss any aspect of the detectors on which I could say anything you are more thatn wellcome, but please keep the bites and the wisdom lessons away. It is good practice that you say only what people ask you for, not all which comes to your mind.
I do not think that anyone here is interested in the personal feelings regarding crtain issues, but the technical facts.
And those technical facts can not be stated in accordance to what someone`s believes are, but to what the real results and accomplishements are.

Thats why I say get your best detector for fare competition. Then we can continue to teach each other if you still wish so.