Making A Fast Mono Coil Article Posted

[bbsailor]

Forum Members

I want to thank Carl for posting a new coil making article that I just finished writing. The article has many tips that I learned from making PI mono coils and measuring the results. This article is a compilation of information that I have previously posted on the Geotech forums with photos.
http://geotech.thunting.com/cgi-bin/...oils/index.dat

Much of the coil-making information I learned from reading discussions between Eric Foster, Reg, and other active forum members over the years. Writing this article is my way of saying thanks to Carl and the forum members for making this a great technical metal detecting web site. It is also my Holiday gift to the forum members.

Happy Holidays 2006

bbsailor

[Carl-NC]

Yes, please check out Joe's article. He spent a lot of time writing it up and it has some really good info on wringing out a few ns of coil response.

Thanks Joe!

[Wesley]

samson

Thanks for a very interesting paper and the time spent sure has explains a great deal. Happ Holidays Wes

[Geo]

Hi bbsailor. Good work. You put all the thread "Coils" in few pages. Congratulation.

PS: Moreover we learned your CV and saw your photograph.

[Unregistered]

Shield question

Joe, I've read your article and was quite impressed. I do however, have a question. In the paragraph quoted below, you state that the gap in the shield should be "where the two coil wires enter and exit the coil". I am relatively new to PI detectors but have some experience in electronics and with other types of detectors. My experience and "book learning" has always shown that this type of shielding (Faraday shield) is optimum for eliminating ground capacitance effect when the gap is 180 degrees from the point of entry with the shield connection being at the entry point, 180 degrees from the gap. Have you tried shielding this way? If so what difference if any did you see?
Comments?
Thanks,
Old timer

"When applying the shield to the coil,
ensure that there is a small gap where the
two coil wires enter and exit the coil
(repeated for emphasis). If there were
full shield continuity around the coil, the
shield would look like a shorted turn and
the sensitivity of the coil would be
seriously degraded or may not even
work."

[bbsailor]

Coil Entry Point

Old Timer,

I chose the make the coil entry point where the gap is located as a practical coil making practice. However, I would like to know the specific technical references that state that having the gap located 180 degrees from the coil entry point is a better or desireable alternative. Maybe I'll make my next coil that way and see if I can measure any difference.

Thanks for the tip and the kind words about the article. That is what is great about the Internet...the collective wisdom of many is much better than the attempts of one.

I look forward to any leads that you could provide that I could research.

Happy New Year

bbsailor

[Unregistered]

References

bbsailor,
I no longer have the resources I once had, equipment-wise or reference- wise. Therefore, I spent considerable time the past couple of days searching the net and have come up with only two items referencing ground point's of a Faraday shield. One is a drawing from an article about BFO (excuse the bad language) detectors and simply shows the authors reccomendation, and the other is a reference to determining the "tap point to maximize common mode rejection" when using a Faraday shield in a RF balun coil.
Here is the link to this article. Refer to the section pertaining to IFL Baluns. I realize that this is dealing with RF, not the low frequency of a PI detector but it is all I could find.

http://www.utaharc.org/utah_atv/rpt_is1.html

The link to the BFO article is:

http://myweb.tiscali.co.uk/crismarti...wledgy/bfo.htm

Should you make a coil using the connection method I described, I would be extremely interested in the results, not only with test equipment but a subjective test of performance in eliminating the effects of ground capacitence.
Best regards,
Old timer

[PoorSodd]

bbsailor,
Good article, you have done a lot of work on it and it is appreciated.

Quick question ....... does it matter if the coil is wound clockwise or anti-clockwise ? Is there any difference ?
Cheers
Mike.

[bbsailor]

Coil Winding Direction

Mike,

The winding direction for a mono coil can be either way with no difference in performance.

DD coils require that the coils winding direction and relative phase to each other is properly maintained to obtain a null signal and a positive response from a nonferrous target. See the link below for a post by Reg discussing DD coils.
http://thunting.com/geotech/forums/s...highlight=Coil

Thanks for the kind words about the article.

bbsailor

[Tim Williams]

BBsailor, I finally read your article and you did a great job. Thank's for the info.

Tim

[Unregistered]

I'm still curious

The method old timer described for shielding the coil is shown in a drawing in one of the links he posted. Makes you wonder if there is something to it. Has anybody tried it and observed any differences?

[Ray-NM]

Thanks for the article

Great article I printed it out as soon as I read it.
Another one for my reference stack.
RayNM

[Togatuk]

This is the link to BBsailor‘s article : Making a Fast Pulse Induction Mono Coil,
https://www.geotech1.com/pages/metde...s/FastCoil.pdf

[6666]

Mike,

The winding direction for a mono coil can be either way with no difference in performance.

DD coils require that the coils winding direction and relative phase to each other is properly maintained to obtain a null signal and a positive response from a nonferrous target. See the link below for a post by Reg discussing DD coils.
http://thunting.com/geotech/forums/s...highlight=Coil

Thanks for the kind words about the article.

bbsailor

bbsailor even though this is 13 years old did you happen to keep Reg's post ? thanks

[bbsailor]

bbsailor even though this is 13 years old did you happen to keep Reg's post ? thanks

Do a Web search on this: Reg Sniff DD coils. You will find some good reading.

Joseph J. Rogowski