Stupid question - IB - DD vs. concentric

[Jeff Kinzli]

I know the differences between the two and how they work, however it looks like it would be *much* easier to build a DD coil than a concentric. Are there circuit modifications necessary to use a DD coil on IB detectors, or is it the same to the detector. For arguments sake, I'm planning on building a coil for my Whites IDX, a small DD coil is what I'd really like to build...

I'm thinking that as long as I present the same (or close) resistance and inductance to the detector it should be the same. In this case would the TX and RX coils have the same inductance and resistance ideally?

[Reg]

Re: DD vs. concentric

Hi Jeff,

No sincere question is stupid.

As for which coil is easier to build, it would be the concentric. They are much simpler to null, while a DD coil can be a real pain.

There are some differences between a properly designed DD and a Concentric. First, there will somewhat of a phase difference. I don't remember for sure, but it something like 3 or 7 degree difference.

Forget the idea of trying to match the resistance. Even the inductance has some flexibility. What is important is the xmit coil is tuned to the proper frequency.

I would suggest you check the inductance of both the xmit and receive coil of one that you have. You might even call Whites and ask them what the inductance of the coils and turns ratio are supposed to be. There would be not reason I can think of for them not to tell you.

I don't know the frequency of the detector you have, but xmit wire size can be critical. If the wire is too small, there can be some losses. Receive wire size normally can be a fairly small size wire.

If you know the wire sizes of the coil you have, you can take an accurate reading of the resistance and calculate the turns in each. That will give you the turns ratio between the primary and secondary windings. I would probably keep this ratio somewhat the same at least at the onset on your new coil.

Reg

[Aziz]

Re: DD vs. concentric

Hello,

maybe, I can help to design a concentric coil for IB-systems. I made a software, where such coils can be computed and optimally balanced.

Even for PCB-Coils (very complex to design, but very easy to build and balance).

Ask me for some simulations, then I can post some images and results here.

I am also working on a microprocessor controlled IB-Metal detector. I found, that the zero-balancing ist frequency dependend. The coil became a complex resistor.

Double D coils cause different phase shifts! It depends on geometric position, where the metal object is positioned nearby the coil.

Concentric coils are the best but very diffucult to built and balance.

Aziz

I will read the past project postings and hope, to find some hints for me.

[Vladimin]

I have experience with the DD coils and I think that they are more easy to build than concentric.Also the RX and TX coils will have the same inductivity and the same parasitic capacitance if you use equal value of turns.From another side is absolutly necessary coils to be phase shifted in air ballance procedure.I founded a perfect way to do this I and were builded a lot of coils (search heads) with full score on final result.I think to explane my experience on pages of this forum.

[Carl-NC]

You might even call Whites and ask them what the inductance of the coils and turns ratio are supposed to be. There would be not reason I can think of for them not to tell you.

Strangely enough, I recall a case where someone asked them that question, and they said it was proprietary information.

- Carl

[kt315]

as it was.... may be there anything has been change??

From: sales <[email protected]>
Date: Thursday, December 11, 2003, 2:40:07 PM
Subject:

===8<==============Original message text===============
Dear Anatolij

Thank you for your email dated 6 December sent in the first instance to our
parent company in USA however as your country comes under the sales area of
the plant here in Scotland I have been asked to reply.

I note your request for the technical data on the small coil of the Classic
or XLT detector but unfortunately all these are covered by White's patents
worldwide and as they are current models we are unable to divulge this
information.

I trust you can understand our position in this matter.

Kind regards

G A McRae
General Manager

[Vladimin]

Dear Jeff! I think that before to start to build a DD coils for your White IDX is absolutly necessary to understand first what is a working frequency.After you have to check where a placed resonant capacitors,may be in head construction.Most important thing is to understand how much degrees is phase shifted a wave in RX coil than TX coil .Without this your detector will never work by the same way as with a original search head.