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I'm in the midst of reading/researching coil building with the intent of making a very small sniper style coil for my Sovereign GT. I do have a background of both self taught and formal training in some aspects of electronics, but the field of coil building is going to require me to do a good bit of reading to fill in the blanks. Just printed out about an inch high stack of threads from the Geotech forums that should help along those lines.
As for this extreme sniper coil I want to make, I do not care about depth so long as it can get at least say 2 to 3 (or better yet 4) inches deep. Primary purpose for this coil will be extreme unmasking situations where depth is not important to me, using it to hunt super high trash or iron laden sites that are to the extreme in masking conditions. If the coil is capable of it I also want to use it along fence lines and other metal objects at old sites.
I'm very impressed with the Detech SEF 12x10's depth, stability, and am also amazed at it's outstanding left/right seperation. This is the best coil, stock or aftermarket, I have ever owned or used on a machine in all my years of detecting.
For that reason, if at all possible, I would like to copy this coils winding layout for the project. What I'm wondering is if anybody has seen the inside of one of these coils? I'm wondering if the TX/RX windings actually overlap in the middle? By the looks of the oustide of the coil casing it appears both windings overlap and then flow at a very gental curve past each other in the center before once again passing each other on to their perspective sides of the coil. Lacking an X-Ray machine to take a peak inside, I'm hoping somebody has had one of these coils apart to see eactly what the winding layout is.
Before even getting that far, perhaps the more important question to ask is if it's possible to make a DD coil with a 4 (or even sub-4) inch length, and say a 3 or perhaps a 2" width? The smallest DD coil I'm aware of is the Garrett 4.5" round DD sniper coil, so I at least know a round DD of 4.5" diameter is possible if nothing else. Is anybody aware of any other commercial made DDs smaller than 4.5"? I'm curious for both knowing that a sub 4.5" dimension(s) are possible, and also because I want to make this sniper coil smaller than anything available in a commercial product just for the sake of it being unique. Even if a 4 or sub-4" DD is possible, are there issues with making the width even smaller in terms of the field being generated?
Some other questions to throw out there for now- I have both the old and newer schematics of the pre-amp circuit found in all Sovereign/Excalibur coils. Is there any performance differences between the two that anybody has been able to see? In relation to the pre-amp, in such a small coil potentially as this, would there be any benefit to mounting the pre-amp off to the side of the coil to avoid interaction with the detection field as much as possible? I would suspect it would be beneficial to get the pre-amp circuit as far away as possible, but not so far that the weak RX signal has any chance to degrade or pick up distortions. If so, I'll probably put the pre-amp past the bottom of the coil so it hangs of it's tail.
Shielding- In such a little project as this, I'd like to avoid buying anything in quantity to build it. In particular, I thought I remember reading references a while back to stripping the insulation out of certain capacitors to shield a coil?
Any other "off the shelf" supplies you can point me to for construction would be of great use, such as say a cable from Radio Shack that should work for the coil cable. These Sovereign coil cables are not shielded due to the pre-amp making the RX signal more robust on it's trip to the control box, so I don't need to use shielded cable. Just want something I can get my hands on without ordering it.
I don't want to order anything if I can get away with it, and prefer to buy as little as needed to experiment here with building one. I'm thinking I probably won't form a custom casing for it, but rather will just set the windings into a mold with the outline of an SEF and then just pour the epoxy right over it to form a solid coil with no spokes since weight in such a small coil won't be much of a factor. Only problem here is the shielding. Can I then apply the shielding to the outside of the epoxy and then further incase that to protect it? Is the distance of the shielding from the windings a critical factor that needs to be considered?
For mounting ears I'll probably just embed PVC into the epoxy pour. Or, if vacuum forming is easy enough somebody shoot me a link to it and I may go that route here.
Haven't really thought this all through yet as I've got a ton of reading to do that I printed out from this forum to refresh my memory on the particulars of coil building. Got "about an inch high" of reading here which might fill in some of my questions.
Several years back I was reading up on building a larger coil but by then the SEFs came along and they were exactly what I was after, so it's been a while since I read up on this stuff.
As for this extreme sniper coil I want to make, I do not care about depth so long as it can get at least say 2 to 3 (or better yet 4) inches deep. Primary purpose for this coil will be extreme unmasking situations where depth is not important to me, using it to hunt super high trash or iron laden sites that are to the extreme in masking conditions. If the coil is capable of it I also want to use it along fence lines and other metal objects at old sites.
I'm very impressed with the Detech SEF 12x10's depth, stability, and am also amazed at it's outstanding left/right seperation. This is the best coil, stock or aftermarket, I have ever owned or used on a machine in all my years of detecting.
For that reason, if at all possible, I would like to copy this coils winding layout for the project. What I'm wondering is if anybody has seen the inside of one of these coils? I'm wondering if the TX/RX windings actually overlap in the middle? By the looks of the oustide of the coil casing it appears both windings overlap and then flow at a very gental curve past each other in the center before once again passing each other on to their perspective sides of the coil. Lacking an X-Ray machine to take a peak inside, I'm hoping somebody has had one of these coils apart to see eactly what the winding layout is.
Before even getting that far, perhaps the more important question to ask is if it's possible to make a DD coil with a 4 (or even sub-4) inch length, and say a 3 or perhaps a 2" width? The smallest DD coil I'm aware of is the Garrett 4.5" round DD sniper coil, so I at least know a round DD of 4.5" diameter is possible if nothing else. Is anybody aware of any other commercial made DDs smaller than 4.5"? I'm curious for both knowing that a sub 4.5" dimension(s) are possible, and also because I want to make this sniper coil smaller than anything available in a commercial product just for the sake of it being unique. Even if a 4 or sub-4" DD is possible, are there issues with making the width even smaller in terms of the field being generated?
Some other questions to throw out there for now- I have both the old and newer schematics of the pre-amp circuit found in all Sovereign/Excalibur coils. Is there any performance differences between the two that anybody has been able to see? In relation to the pre-amp, in such a small coil potentially as this, would there be any benefit to mounting the pre-amp off to the side of the coil to avoid interaction with the detection field as much as possible? I would suspect it would be beneficial to get the pre-amp circuit as far away as possible, but not so far that the weak RX signal has any chance to degrade or pick up distortions. If so, I'll probably put the pre-amp past the bottom of the coil so it hangs of it's tail.
Shielding- In such a little project as this, I'd like to avoid buying anything in quantity to build it. In particular, I thought I remember reading references a while back to stripping the insulation out of certain capacitors to shield a coil?
Any other "off the shelf" supplies you can point me to for construction would be of great use, such as say a cable from Radio Shack that should work for the coil cable. These Sovereign coil cables are not shielded due to the pre-amp making the RX signal more robust on it's trip to the control box, so I don't need to use shielded cable. Just want something I can get my hands on without ordering it.
I don't want to order anything if I can get away with it, and prefer to buy as little as needed to experiment here with building one. I'm thinking I probably won't form a custom casing for it, but rather will just set the windings into a mold with the outline of an SEF and then just pour the epoxy right over it to form a solid coil with no spokes since weight in such a small coil won't be much of a factor. Only problem here is the shielding. Can I then apply the shielding to the outside of the epoxy and then further incase that to protect it? Is the distance of the shielding from the windings a critical factor that needs to be considered?
For mounting ears I'll probably just embed PVC into the epoxy pour. Or, if vacuum forming is easy enough somebody shoot me a link to it and I may go that route here.
Haven't really thought this all through yet as I've got a ton of reading to do that I printed out from this forum to refresh my memory on the particulars of coil building. Got "about an inch high" of reading here which might fill in some of my questions.
Several years back I was reading up on building a larger coil but by then the SEFs came along and they were exactly what I was after, so it's been a while since I read up on this stuff.
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