Concentric coil for TGSL.

[dfbowers]

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

[joop]

so... nulling is achieved by exactly centering the RX-coil in the middle? Does it need any fine-tuning as in the double-D coil?

[mehmet 45]

I do not know English very well. Can you give more details about connections. I'm taken as a DD. I want to try başlık'da concentric.
If you'll be very pleased about the details of the connection description.

[dfbowers]

so... nulling is achieved by exactly centering the RX-coil in the middle? Does it need any fine-tuning as in the double-D coil?

Hi Joop. Nulling is done by adding or removing turns to the bucking coil. (Bucking coil is just the end of the main Tx coil wound the opposite direction around the Rx coil.)
It's a little tricky because winding the bucking coil the opposite direction subtracts inductance from the main Tx coil, and increases the operating frequence a bit. So, you must add an extra turn or two the the Tx coil to re-adjust the frequency.

To calculate the turns needed for the bucking coil, just divide the number of turns for the Tx coil by 4. So, 105t / 4 - 26 !

[dfbowers]

I do not know English very well. Can you give more details about connections. I'm taken as a DD. I want to try başlık'da concentric.
If you'll be very pleased about the details of the connection description.

Yes, I will post all details soon. I need to collect and share details of sheilding as well.


Don

[joop]

Hi Joop. Nulling is done by adding or removing turns to the bucking coil. (Bucking coil is just the end of the main Tx coil wound the opposite direction around the Rx coil.)

Thanks Don... Just been reading the pages titled "Concentric Coil Experiment" in the book and came across the "nulling coil" as they call it. I understand now... ;-)

It would be interesting to scale this coil up to 27 cm. From what I read, iron rejection should be excellent.

[Sean_Goddard]

Damn Don, that is one NEAT idea .

YOU GENIUS!!

[Stefano]

Tempting recipe...
Great Don!

[sido]

Like your approach there Don.

Trying to do the same for a small CC coil and you a are right about the TX inductance changes once you split the coil with a bucking coil.

I think you need to add more TX inductance as you have suggested above before you remove the winding for the bucking coil as required.

Thats what i have found by using the below Pic which i am using normal foam as the former and winding this coil as a backup to the China made MD1023.

I have left < 0.8 mm gap all round the coil wires and waiting to see how you approach the shielding and what material you will use.

I am leaning towards carbon paper material.

Sid

[sido]

Sorry about the crappy photos.

Sid

[dfbowers]

Concentric coils for the TGSL.

Well here it is as promised. A complete guide to building your own Concentric Coplaner coil for the popular TGSL project.. It works!
Please let me know if anything is unclear or needs revised.
Happy building.
Don

[Thomas]

Thanks, That is going to be a big help for me, good one! I just hope they have the graphite at the home depot here.

[joop]

Thanks Don, really appreciated!

[sido]

Thanks Don, many questions answered, much appreciated.

Sid

[dfbowers]

Finally got a chance to field test the new coil concentric coil for the TGSL today. Initially, I was not too impressed with some of the air test that I was doing. I built another coil for the IDX earlier in the month with identical geometry as the one shown here. The 7.5" Concentric coil for the IDX was giving me air test that were a good + 5 cm over this one.

What the heck.. I took it for a field test anyway. I was a bit suprised though that ACTUAL depths in the ground were almost identical between the IDX and the TGSL concentrics. Probably has more to do with the geometry than the power..
Now for the interesting thing.. All my 10" DD handmade coils for the TGSL don't go as deep in the ground as the 7.5" concentric - even though they can air test coins at 13"..
I have always known though that the soil is crappy where I live (hard clay for the most part). But.. for the given coil size, the concentric wins!! I DID give up ground coverage (and a lot of weight)..

This coil weighs in at a whopping 8 ounces.. I took it on a relic hunt today and the coil performed flawlessly. It was rock stable and I took some relics that were at least as deep as my spade goes (8") Hey! It's ONLY a 7.5" coil... . The sign of a good coil is always when the relic is detectable and still somewhere deep in the hole!!! Check the youtube video here: http://www.youtube.com/watch?v=a6kkK...IoCBxg&index=1



BTW.. The detector was built from a Silverdog kit, but I have it detuned it to the original specs that Ivconic posted.

Don