TGSL - Concentric VS. DD and salt beaches.

[dfbowers]

I came across a nice discovery today when doing some testing of detector performance in my Salt water test bed. Basically, I have a 100 lb tub of sand with 2 gallons of a 4% salt solution added. To my surprise, my TGLS home built + hand made 8" concentric is one of the best performing detectors in my arsenal (aside from my PI machines). With a little bit of disc, it's dead quiet in salty sand and clearly indicates most all coin sized object to a depth of around 9" or so with an 8" concentric. Unfortunately, this is not the case with any DD coil attached and the TGSL cannot be tamed at all. This seems to be related to the concentric coil more than anything as I noticed similar results with my other models as well.. but the TGSL performs exceptionally well considering the cost!! Anyone willing to offer a technical explanation on why the concentric has an advantage? I have read a lot of posts today and the general conclusion is that concentrics are the way to go an salt beaches.
Don

[Altra]

Hi Don,

I don't have a specific answer for your question. But over the years of building many TR coils for beach hunting, I have noticed that solid coils are smother than open or spider coils. I am guessing that your DD coils are open on each side? If so a good test would be to build a DD coil in your solid 8" coil housing using the same shielding method as your concentric. This would tell if its the construction or due to being a DD.

Hope you get the same results at the beach.

Mark

[homefire]

Here is My thinking. Concentric use a Bucking coil to Null. Both coils would see the same effects by any change in Inductance caused by the Salt/Sand. DD coils are Nulled by over lap of only a bit of the coils and are Not Symmetrically exposed to the effects of the Salt/Sand . The Salt/ Sand can effect the Null on the DD Rx coil. Probably exasperated by Motion. Does the problem tame down with Little or No Motion ?

[Qiaozhi]

The main reason is most likely because both the TX and RX coils share the same centre point, and hence they both "see" a relatively large proportion of the same area of ground. Whereas the centres of each loop on a DD coil are separated by a fixed distance so that they cover different areas of ground. This would be important for salty beach areas where the ground signal varies rapidly over short distances. The same is true for a double-O coil, but in this case there is a greater overlap between the TX and RX loops, and (again) they both "see" a similar proportion of the same ground area, but not as much as a concentric coil which should theoretically give the best results.

[Orbit]

I have an opinion that the concentric coil significantly deeper . From what I've tasted VLF .

[Koala]

Interesting observation.


I have used a 5 1/2" concentric and can walked straight from the dry sand through the damp sand into shallow surf without any adjustments. The only place where any falsing took place was swinging in between the water and damp sand.



However not all beaches are created equal. There's more than even damp sand. On most beaches the same setup as above will either false and require the sensitivity and or threshold turning down or are totally undetectable except for the top few inches.

[CDI]

From my experince, my homemade double D from IDX is much deeper than XLT BlueMax 950 concentric. Especially on roman mineralized brick.

[Orbit]

As for the Roman brick I tried concentric coil had the impression not breaks through !
Concretely fiser 1266 idx whites blu max 950 and fiser cz 5 !

[Koala]

Going back to the original test. It shows how difficult it is to test detectors fairly. If you were testing manufacture a against b in this particular circumstances and one had a concentric it would be an unfair test.

As a side note. My first coils I made were marginal on the shield. They would work fine on dry sand and grass but would chatter like crazy over wet grass or sand.

[Orbit]

Going back to the original test. It shows how difficult it is to test detectors fairly. If you were testing manufacture a against b in this particular circumstances and one had a concentric it would be an unfair test.

As a side note. My first coils I made were marginal on the shield. They would work fine on dry sand and grass but would chatter like crazy over wet grass or sand.

Not should the grass has an impact a sand even less ! Whether compensation coil inside or outside rx this has an impact and impedance the cable there is more invisible trifles !

[saber]

I came across a nice discovery today when doing some testing of detector performance in my Salt water test bed. Basically, I have a 100 lb tub of sand with 2 gallons of a 4% salt solution added. To my surprise, my TGLS home built + hand made 8" concentric is one of the best performing detectors in my arsenal (aside from my PI machines). With a little bit of disc, it's dead quiet in salty sand and clearly indicates most all coin sized object to a depth of around 9" or so with an 8" concentric. Unfortunately, this is not the case with any DD coil attached and the TGSL cannot be tamed at all. This seems to be related to the concentric coil more than anything as I noticed similar results with my other models as well.. but the TGSL performs exceptionally well considering the cost!! Anyone willing to offer a technical explanation on why the concentric has an advantage? I have read a lot of posts today and the general conclusion is that concentrics are the way to go an salt beaches.
Don

nice coil

i have only 0.45 wire, can i made it with this wire?