Concentric coil for TGSL.

[dfbowers]

Here is a quick Video on what to expect. I'm using a gold ring for testing.

http://youtu.be/r-F5bu0m3N4

Don

[Thomas]

It's good that you're doing this, I just started a 10" using some foam cardboard composite stuff.
It is 5.25mm thick with 4.5mm foam using .25mm wire so this will hopefully be close to the same.

[dfbowers]

For this evenings project. . how about a 10" concentric for the TGSL!!

Construction methods are identical to the 7.5" coil project posted previously. Building this way does not look impressive, but foam board with cardboard skins glued to the outside results in an extremely stiff and mechanically stable assembly. Also, light as can be!!

Tx coil - 127mm radius (5"). It's build on a 130mm radius foam board with a groove cut in the edge with a hot iron. , 11mm thick. 87 turns using .25mm wire - 6.0 mH.
Wire is wound counter clockwise.

Rx coil - 63mm radius (2.5"). It's built on a 63mm radius foam board, made into a spool . Foam board started at 11mm thickness but sanded a bit so all fits flush when finished. 157 turns using .25mm wire - 6.5mH. Wire is wound counter clockwise.

Bucking coil - 23.5 turns (about) on the outside of the Rx coil, again .25mm wire. Wire is wound clockwise.

You can refer to the previous post for the coil schematic.. just scale up a bit and substitute the above number of turns.

Initial testing shows that detection range is almost identical to a 10" DD coil - Coins can be detected up to 30cm or so. Not anything impressive but functions perfectly!!
Time to order more ABS plastic and break out the vacuum forming machine again..
Field test to come..

Don

[dfbowers]

Hi Don

If you want to find out how the sensitivity to various targets varies with frequency, it might be better to adjust the discrimination in each test until you get the maximum range. Leaving the discrimination at the same setting all the time means that the “gain” of the synchronous detector is varying for each target in an unknown way. Just a thought…

Yes.. I believe you are correct. The diagram probably has more to do with how the signals pass through the demodulators than anything. All metal tests produce more of a flat line across the conductivity range. And.. ground penetration was not taken into consideration. BUT at a given disc setting for both detectors this points out the strenghts of both.

[Gwil]

Hi Don

If you want to find out how the sensitivity to various targets varies with frequency, it might be better to adjust the discrimination in each test until you get the maximum range. Leaving the discrimination at the same setting all the time means that the “gain” of the synchronous detector is varying for each target in an unknown way. Just a thought…

[dfbowers]

It's a well known fact that in general, low frequency detectors are best suited for deeper, higher conducting targets while high frequency detectors are better suited for shallower, low conductors.
Just how much of a difference is there REALLY???

Since I built 2 concentric coils with identical geometry (one for IDX and one for TGSL), I put them to the test! The question arose in my head as to why some of my air tests with my TGSL coil showed poor results as compared to the IDX while ground test seemed equal.. DOH!! I was using a quarter for air test and a lead ball for ground testing..

So.. Comparing oranges to oranges (or quarters to quarters) I was astounded by the results. No wonder manufacturers came up with multi frequency machines!!

I set my GB and DISC setting for my IDX and TGSL to approximately the same place.
As you can see from the tests, lead has an almost identical response to both detectors.. But look at the results for Aluminum foil and copper..Wow..

Again, the coils are both 7.5" hand wound concentric coils and.. these are AIR tests.
Don

[dfbowers]

Thanks guys! After looking through the simulatons that Aziz was coming up with, I thought the concentric coplaner would be a good one to experiment with, even though it's "old stuff"..
Now if I can only figure out how to box up a top hat coil and put it on the end of a pole.......

[kt315]

nice work. thanks! I repeat again a data on all Tesoro coils. thinking it will useful.

====
Tesoro concentric
Tx 1,5 5.7mH 22 ohms
Rx 3,4 6.2mH 22 ohms
====
Tesoro early Lobo DD
Tx 2,4 10mH 55 ohms
Rx 1,3 1.35mH 12 ohms
====
Tesoro
Name TX-L TX-R (ohms) TX-fo TX wire RX-L RX-R (ohms) RX-fo RX wire
________________________________________
Brown 8" 5.59mH 21.2 --- --- 6.23mH 22.1 ---
---
Lobo 5x10 9.93mH 50.5 --- --- 1.33mH 10.97 --- ---
Lobo 8x15 10.52mH 62.8 --- --- 1.37mH 13.13 ---
========
Troy Shadow
Name TX-L TX-R (ohms) TX-fo TX wire RX-L RX-R (ohms) RX-fo RX wire
________________________________________
X2 S-9 9" 5.72mH 23.6 --- --- 6.25mH 25.2 --- ---
X5 7" 1.067mH 4.33 --- --- 6.53mH 32.2 --- ---
X5 9" 1.044mH 4.45 --- --- 6.50mH 32.7 ---
---
X5 1.1mH / selfrez = 255kHz 6.5mH / selfrez = 87kHz
====

[Aziz]

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

Good job! Thank you for your very valuable contribution.

Aziz

[ApBerg]

Thanks for the great info...as always !

Ap

[satdaveuk]

Thanks Don
You done a nice tutorial with well laid out constructional details.
I for one have never got round to making a coil of this type but now feel the urge to do so.
Many thanks for sharing your well thought out idea.
Also like the sound of the 35k shielding should be ok for UK soils
Regards

[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

[sido]

Thanks Don, many questions answered, much appreciated.

Sid

[joop]

Thanks Don, really appreciated!

[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.