Concentric coil for TGSL.

[dbanner]

In the construction of concentric coils, I highly recommend the Cscope method, which is to wrap the bucking coil on seperate winder with the same diameter as the RX coil, instead of wrapping the buck coil on top of the RX coil.
The RX coil contains a lot of windings such that the bucking coil, if wrapped on top of RX coil, is now slightly larger in diameter which makes balancing a little more tricky.
The calculations for number of turns for the bucking coil is made on the basis of the same diameter as the RX coil, which is now thrown slightly off(diameter of the buck coil) when wrapping the bucking coil on top of the finished RX coil.
Also, wrapping them on separate winders(spools) makes it possible to remove some turns on RX coil as well if that is deemed necessary.
Have a look at some photos of a Cscope concentric elsewhere on forum for some pics.
I think this approach makes concentric coil building much easier in terms of getting it to balance within required specs.
With this proven method, one can make any size search coil for any detector. Just something to consider.

[dfbowers]

[ATTACH]46872[/ATTACH]

Hi Don!
The top and the bottom shell are shielded in the same manner.
You masked off a small strip of tape that when removed, leaves a small gap in the conductive coating.
Therefore the top and the bottom shell must be coupled in the same point where this gap finish, to avoid a short circuit.
Is it right?

Well, not really because the bottom shell overlaps the outside of my top shell so there is a gap already. Unless you are using a highly conductive spray like nickel I don't think it matters. Graphite is a few kohms per square so it might not be so critical.
Anyway, that's my thoughts.

[Maurizio2]

Hi Don!
The top and the bottom shell are shielded in the same manner.
You masked off a small strip of tape that when removed, leaves a small gap in the conductive coating.
Therefore the top and the bottom shell must be coupled in the same point where this gap finish, to avoid a short circuit.
Is it right?

[dfbowers]

Pretty tough for every builder to duplicate the design exactly for sure! Tuning is tricky but once you get it, it's worth it.

[dbanner]

Really? For example I totally do not care about number of turns and be carefull with "everyone uses". For rough calculation I use this formula: https://sub.allaboutcircuits.com/images/11098.png (the middle one). But I do not count turns. I only measure inductance. Thats the headline for coils

For example my small CC for IGSL-Musk has diameter of Rx80mm and its about (barely remember) 350 turns of 0,3mm wire. Try to make it by this instruction, depends on tightness of winding and cross shape... Better to be guided by 14,7mH.

Whatever works for you.
The term" everyone uses" was meant to convey the meaning " widely used and by a lot of people "
In pointing out errors, it is always a good thing to explain how the calculations were derived.
No need to explain that.

[dbanner]

[ATTACH]46861[/ATTACH] correct
[ATTACH]46862[/ATTACH] wrong

Now clearly you have discovered a possible error in the document, which I can accept. That coil calculator is pretty accurate. Since the tx calculation in the document is bang on then it stands to reason that it could be an error but not necessarily. There could be some other reason. Only DB can say for sure.
Thanks for pointing that out.

[Hyena]

How did you arrive at 183 turns? Show us HOW calculation was made. By which method? Formula? Coil calculator software? How exactly? There is a coil calculator at the beginning which everyone uses. Did you use it?
It is not sufficient to say it is so, just by saying so. Hey, that's reminds me of a song from way back, "say it isn't so"

Really? For example I totally do not care about number of turns and be carefull with "everyone uses". For rough calculation I use this formula: https://sub.allaboutcircuits.com/images/11098.png (the middle one). But I do not count turns. I only measure inductance. Thats the headline for coils

For example my small CC for IGSL-Musk has diameter of Rx80mm and its about (barely remember) 350 turns of 0,3mm wire. Try to make it by this instruction, depends on tightness of winding and cross shape... Better to be guided by 14,7mH.

[Maurizio2]

correct
wrong

How did you arrive at 183 turns? Show us HOW calculation was made. By which method? Formula? Coil calculator software? How exactly? There is a coil calculator at the beginning which everyone uses. Did you use it?
It is not sufficient to say it is so, just by saying so. Hey, that's reminds me of a song from way back, "say it isn't so"

[dbanner]

How did you arrive at 183 turns? Show us HOW calculation was made. By which method? Formula? Coil calculator software? How exactly? There is a coil calculator at the beginning which everyone uses. Did you use it?
It is not sufficient to say it is so, just by saying so. Hey, that's reminds me of a song from way back, "say it isn't so"

[Maurizio2]

I have redone the calculations and I believe there is a small mistake.
The turns for RX should be 183 and not 193.

After my success with a concentric for IDX, I though I would make a homebuilt CC for TGSL.
I have to wait for a few sheets of plastic to show up to vacuum form a pair of shells, but early test are promising!

Some advantages I am realizing by building CC over DD:

* Light! Maybe 1/2 the weight as very little epoxy is used.
* Cheap! maybe only $20.00
* Disc is excellent!!!!!!! A handful of steel tools over the coil is completely silent!!!!!

http://youtu.be/uNTnS6VoNL4

* Good detection range for the size. Coins at 25cm with a 20cm coil.
* Did I mention cheap?!

The down side - a little more challenging, but can be done.

For some details-

Tx coil - 95mm radius. It's build on a 100mm radius foam board with a groove cut in the edge with a hot iron. , 11mm thick. 105t using .25mm wire - 6.0 mH
Wire is wound Counter clockwise.

Rx coil - 43mm radius. It's built on a 43mm radius foam board, made into a spool (see pics). Foam board started at 11mm thickness but sanded a bit so all fits flush when finished. 193t using .25mm wire - 6.5mH. Wire is wound counter clockwise.

Bucking coil - 26 turns (about) on the outside of the Rx coil, again .25mm. Wire is wound clockwise.

Tx start is hooked to hot side of Tx circuit, end of bucking coil is hooked to ground.
Nulling is excellent.. although I have not built any shield yet.

Complete details to come when it's finished...

Don

[scrungy_doolittle]

looks like 6.5 khz is all around better for coin shooting than the 14 khz. whites knew what they were doing.....

[ne555]

Hi don the back copper in rx Parallel or sequential?? [IMG][/IMG]

[Virdi_248]

I almost got the metal detector I've been chasing for a long time thanks to the 10 "concentric coil. It has worked better than the 8" in my case. The bad part is sometimes with noisy roots but it is acceptable. Overall I am happy, punctuated this 7.5 / 10 coil and bearing in mind that it is not shielded. I leave a picture of my detector. Thank you for sharing knowledge.

[Hyena]

Which details? There are so many variables... Answer to your "question" could be long as toilet paper.

[saber]

Concentric coil details