A
Anonymous
Guest
Has anyone got any idea if I can build a real wide coil that I can cover a lot of ground with. Would an old whites 5500/D 3 have enough power to run it? I'd be using another detector to pin point with.
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A
Anonymous
Guest
what the hell are you looking for the center of the earth?
A
Anonymous
Guest
JVP:
VLF metal detectors require induction balance searchcoils. It's not likely that someone who wasn't already knowledgeable in IB searchcoil manufacture could home-brew a big one and have it work. They're just too tricky.
PI machines are much more forgiving than VLF when it comes to searchcoils, and nearly all PI machines can be used with a mono coil, eliminating the need for induction balance. From a practical point of view, if you want to home-brew a 6-foot searchcoil, a mono coil for a PI machine is the only possibility you should be considering.
--Dave J.
VLF metal detectors require induction balance searchcoils. It's not likely that someone who wasn't already knowledgeable in IB searchcoil manufacture could home-brew a big one and have it work. They're just too tricky.
PI machines are much more forgiving than VLF when it comes to searchcoils, and nearly all PI machines can be used with a mono coil, eliminating the need for induction balance. From a practical point of view, if you want to home-brew a 6-foot searchcoil, a mono coil for a PI machine is the only possibility you should be considering.
--Dave J.
A
Anonymous
Guest
Thanks Dave, Could you recommend a PI that would run that big coil? I was figuring on building it long and narrow somthing like the Big Foot coil only longer. I'm not looking for depth only to cover a large area.
A
Anonymous
Guest
JVP:
There are others on this forum who are much better qualified than I am to recommend a PI machine for your purpose.
--Dave J.
There are others on this forum who are much better qualified than I am to recommend a PI machine for your purpose.
--Dave J.
A
Anonymous
Guest
Hi JVP,
What are you looking for? Coins, rings or larger objects? Generally speaking, PI's that run with large coils are for locating caches, cannon balls, etc. rather than single small objects. Rectangular coils 5 or 6ft long by 12 or 18in wide can be made, but it is difficult to shield them and get them to work at the shorter pulse delays needed to locate small objects.
Eric.
What are you looking for? Coins, rings or larger objects? Generally speaking, PI's that run with large coils are for locating caches, cannon balls, etc. rather than single small objects. Rectangular coils 5 or 6ft long by 12 or 18in wide can be made, but it is difficult to shield them and get them to work at the shorter pulse delays needed to locate small objects.
Eric.
A
Anonymous
Guest
Thanks for the interest Eric,
I'd like to try to search for meteorites on fields that have been harvested. My plan is to mount the coil on wheels and mow the lawn. The targets could be coin size to boulder size. I"ve read that VLFs work best, but Dave mentioned that building a new coil for them would be hard to do. Any ideas?
JVP
I'd like to try to search for meteorites on fields that have been harvested. My plan is to mount the coil on wheels and mow the lawn. The targets could be coin size to boulder size. I"ve read that VLFs work best, but Dave mentioned that building a new coil for them would be hard to do. Any ideas?
JVP
A
Anonymous
Guest
I've no experience with detecting meteorites, but PI should be good as you are basically looking for ferrous material. The thing that I have found with fields here, is that there are usually considerable quantities of man made iron objects. Things such as horseshoes, bits of plow, chain, fencing wire, nails etc etc. You would be detecting all these too. One detector I make that is suitable for large coils is the Superscan, which has a 24V internal battery. Others are made by Lorenz and Pulstar in Germany.
Eric.
Eric.
A
Anonymous
Guest
Hi JVP,
You can use either a VLF or a PI for meteorites. Having some experience hunting them, I prefer the PI in many areas simply because I don't have to deal with the hotrocks. At Gold Basin AZ, the hotrock problem can be severe in places.
As for building a coil, I have built some coils to use on Eric's detectors and they are quite simple to build. Also, his detectors work very well when looking for meteorites such as the ones found in Gold Basin AZ.
Eric's Beachscan has found meteorites and I would expect his new Goldquest to do better simply because of the ability to reduce the delay. I have modified one of my Beachscans and is very much like the Goldquest, and have compared them on meteorites. The shorter delay does help.
In some cases, a VLF will work a little better because they are more sensitive to some types of meteorites. VLF's are a little more sensitive on smaller stonies in many cases.
Of the 3 main classifications, my experimenting shows the PI does as good or better on the iron and stony iron type. However, on the stony,especially the small ones, the VLF can excel.
As for a 6' coil, I don't know any area where you could run this large of a coil and still keep the coil close to the ground. On iron and stony iron meteorites, this may not be that much of a problem, but on the stonies, they do not give much of a signal to begin with, so having the coil way off the ground may defeat the purpose.
Many of the stony type are thought to be the remains of the surface of a former planet and as such will respond much like a positive type hotrock. At least the ones in Gold Basin do. Some other types like a small Holbrook meteorite give little response to either type of detector. On this type, a good very strong magnet works as well as a detector, especially when most of the meteorites are small.
Just some thoughts, hope they help.
Reg
You can use either a VLF or a PI for meteorites. Having some experience hunting them, I prefer the PI in many areas simply because I don't have to deal with the hotrocks. At Gold Basin AZ, the hotrock problem can be severe in places.
As for building a coil, I have built some coils to use on Eric's detectors and they are quite simple to build. Also, his detectors work very well when looking for meteorites such as the ones found in Gold Basin AZ.
Eric's Beachscan has found meteorites and I would expect his new Goldquest to do better simply because of the ability to reduce the delay. I have modified one of my Beachscans and is very much like the Goldquest, and have compared them on meteorites. The shorter delay does help.
In some cases, a VLF will work a little better because they are more sensitive to some types of meteorites. VLF's are a little more sensitive on smaller stonies in many cases.
Of the 3 main classifications, my experimenting shows the PI does as good or better on the iron and stony iron type. However, on the stony,especially the small ones, the VLF can excel.
As for a 6' coil, I don't know any area where you could run this large of a coil and still keep the coil close to the ground. On iron and stony iron meteorites, this may not be that much of a problem, but on the stonies, they do not give much of a signal to begin with, so having the coil way off the ground may defeat the purpose.
Many of the stony type are thought to be the remains of the surface of a former planet and as such will respond much like a positive type hotrock. At least the ones in Gold Basin do. Some other types like a small Holbrook meteorite give little response to either type of detector. On this type, a good very strong magnet works as well as a detector, especially when most of the meteorites are small.
Just some thoughts, hope they help.
Reg
A
Anonymous
Guest
JVP,
I wouldn't use this forum for advertising, but Eric already mentioned our PULSE STAR. You should get in contact with Matthias Kurz (Germany, Phone/Fax +49-6694-5777) who is hunting for meteorites and has a very large collection. Since last year he has been using our PULSE STAR II PRO with different search coils and has been quite successful. He is one of our customers who is happy when he finds rusty iron ;-)
I have attached a picture with some of his discoveries. The big one is a 13 kg fraction of a 51 kg iron meteorite which was found in a depth of 1 meter, the smaller ones in front (also iron) were found with the PULSE STAR II PRO (all from Poland).
If the vegetation allows, he uses the "Universal Search Loop", which has 8 meters circumference and can be used to build up coils from 0.5 x 0.5 up to 2 x 2 meters (any shape). Otherwise, the 1 x 1 meter standard coil or the 45/25 cm coils with telescopic poles are used.
In your case, a 3 x 1 meter coil could be suitable. Depending on the location, such large coils can pick up a lot of noise from power lines etc. In this case, a compensated coil may become necessary ("8-shaped"). However, one disadvantage of the compensated search coil is its reduced sensitivity since the two sections produce magnetic fields of opposite polarity which partially neutralize each other. Moreover, this search coil has two sensitive spots and one insensitive. Each of the two coil sections form the sensitive areas, while between them the sensitivity declines to zero. For this reason, this search coil should not be moved with its wide side over the search area, but with its narrow side. If in the first case the coil passes a hidden metallic object exactly with its center, this object may be ignored!
The best solution is a true differential coil arrangement, for example two 1 x 1 meter coils stacked over each other with a distance of 0.5 meters. This way, the interference is almost completely eliminated while the sensitivity is hardly affected. Matthias used a modified PULSE STAR II PRO with the stacked coil arrangement as well as a standard PULSE STAR II PRO with a normal compensated coil successfully directly below high voltage power lines.
Thomas
I wouldn't use this forum for advertising, but Eric already mentioned our PULSE STAR. You should get in contact with Matthias Kurz (Germany, Phone/Fax +49-6694-5777) who is hunting for meteorites and has a very large collection. Since last year he has been using our PULSE STAR II PRO with different search coils and has been quite successful. He is one of our customers who is happy when he finds rusty iron ;-)
I have attached a picture with some of his discoveries. The big one is a 13 kg fraction of a 51 kg iron meteorite which was found in a depth of 1 meter, the smaller ones in front (also iron) were found with the PULSE STAR II PRO (all from Poland).
If the vegetation allows, he uses the "Universal Search Loop", which has 8 meters circumference and can be used to build up coils from 0.5 x 0.5 up to 2 x 2 meters (any shape). Otherwise, the 1 x 1 meter standard coil or the 45/25 cm coils with telescopic poles are used.
In your case, a 3 x 1 meter coil could be suitable. Depending on the location, such large coils can pick up a lot of noise from power lines etc. In this case, a compensated coil may become necessary ("8-shaped"). However, one disadvantage of the compensated search coil is its reduced sensitivity since the two sections produce magnetic fields of opposite polarity which partially neutralize each other. Moreover, this search coil has two sensitive spots and one insensitive. Each of the two coil sections form the sensitive areas, while between them the sensitivity declines to zero. For this reason, this search coil should not be moved with its wide side over the search area, but with its narrow side. If in the first case the coil passes a hidden metallic object exactly with its center, this object may be ignored!
The best solution is a true differential coil arrangement, for example two 1 x 1 meter coils stacked over each other with a distance of 0.5 meters. This way, the interference is almost completely eliminated while the sensitivity is hardly affected. Matthias used a modified PULSE STAR II PRO with the stacked coil arrangement as well as a standard PULSE STAR II PRO with a normal compensated coil successfully directly below high voltage power lines.
Thomas
A
Anonymous
Guest
Eric, I've heard of the Lorenz and Pulse Star but I can't find any information on the Superscan. Could you direct me to a web site that has your products? I've also read that you made a system that is like what I'm interested in. That is the Agritec MK3. Could you tell me more about that.
Thanks, JVP
Thanks, JVP
A
Anonymous
Guest
Thomas, Thank you for you informative post. From what I have read the Pulse Star has more than proved to be an fine detector. At this point I am trying to determine if a coil can be built to cover a fairly large area but still be sensitive to small targets. T R Fisher offers a coil for their Pulse 8X that is 8" x 48". It is advertised to be sensitive to small targets. Eric mentioned that such a coil would need to be shielded. Do you have any ideas on this? The area that I will be detecting has no overhead power lines for miles. JVP
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Anonymous
Guest
Hi Reg, I enjoyed reading your post. This is what my original question was. Can I build A coil to cover a fairly large area and still have it sensitive enough to pick up small targets? The area that I will be hunting is land that has been harvested so there wont be much problem in keeping the coil close to the ground. The coil offered by J W Fisher that is 8" x 48" is what I had in mind. Have you got any ideas on how to build such a coil? I know the VLF coils have a Faraday shield. Is that needed in a PI coil? Any ideas would be appreciated. Thanks JVP
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Anonymous
Guest
How small of a target are you talking about. Certainly not coin size ones.
With the large coil of the J.W. Fishers unit, a small target may represent a small cannon ball. I can
With the large coil of the J.W. Fishers unit, a small target may represent a small cannon ball. I can
A
Anonymous
Guest
Hi,
I haven't built one the size of the one you mentioned, but I would think it would be fairly sensitive to small objects because of the narrow width. Again, it depends upon what you are calling small, and what the object will be.
In the case of iron meteorites, say, thumb size or larger, I would think it would work ok. It might work quite well down to dime size iron types. However, on dime size chondrites, there will be a problem even with a standard coil. Some of them are almost impossible to detect depending upon their composition.
As for depth, it depends upon the size of the object and the size of the coil. Again, since most meteorites are reasonably small, the detection range is quite short, so once again, I will mention you will have to have the coil fairly close to the ground, which could be very difficult with a very large coil.
Now you have me wondering and I will eventually build one quite a bit larger and compare them. I won't build one the size you mentioned though. One that is extremely large and shielded with lead foil would be a challenge to carry. It could, however, probably work quite well as a boat anchor when you are not detecting.
So, I think I would "plow the field" with a smaller plow. Something like the "bigfoot" made for the White's VLf detectors would be more reasonable.
The shielding you will need is the Faraday shielding. Without it, the coil will be highly responsive to ground signals, and will give false signals when the coil bumps into most anything.
Eric or Thomas would be the ones to answer how many turns it would take. I would expect there wouldn't be many.
If I were to build one, I would probably use some light weight pvc channel or angle and work with it. The coil would probably be rectangular for simplicity. I might even make a figure 8 coil design for noise reduction. This would give a different detection zone, but one should be able to get used to it.
As for using wheels, it will be a challenge to find some that the detector won't pick up. I just haven't seen any made completely of plastic.
Maybe you can find some, plastic ones made for bikes. When it is all said and done, it will probably be cumbersome. Without wheels, I would suspect a really large coil would be difficult for one person to carry. Thus, it would take two people, or one person and his pet gorilla. I know my dogs would have nothing to do with it.
Sorry for the dry humor, I worked last night and haven't gotten any sleep yet, so the dumb humor crops up when the remaining brain cell is sleeping.
Reg
I haven't built one the size of the one you mentioned, but I would think it would be fairly sensitive to small objects because of the narrow width. Again, it depends upon what you are calling small, and what the object will be.
In the case of iron meteorites, say, thumb size or larger, I would think it would work ok. It might work quite well down to dime size iron types. However, on dime size chondrites, there will be a problem even with a standard coil. Some of them are almost impossible to detect depending upon their composition.
As for depth, it depends upon the size of the object and the size of the coil. Again, since most meteorites are reasonably small, the detection range is quite short, so once again, I will mention you will have to have the coil fairly close to the ground, which could be very difficult with a very large coil.
Now you have me wondering and I will eventually build one quite a bit larger and compare them. I won't build one the size you mentioned though. One that is extremely large and shielded with lead foil would be a challenge to carry. It could, however, probably work quite well as a boat anchor when you are not detecting.
So, I think I would "plow the field" with a smaller plow. Something like the "bigfoot" made for the White's VLf detectors would be more reasonable.
The shielding you will need is the Faraday shielding. Without it, the coil will be highly responsive to ground signals, and will give false signals when the coil bumps into most anything.
Eric or Thomas would be the ones to answer how many turns it would take. I would expect there wouldn't be many.
If I were to build one, I would probably use some light weight pvc channel or angle and work with it. The coil would probably be rectangular for simplicity. I might even make a figure 8 coil design for noise reduction. This would give a different detection zone, but one should be able to get used to it.
As for using wheels, it will be a challenge to find some that the detector won't pick up. I just haven't seen any made completely of plastic.
Maybe you can find some, plastic ones made for bikes. When it is all said and done, it will probably be cumbersome. Without wheels, I would suspect a really large coil would be difficult for one person to carry. Thus, it would take two people, or one person and his pet gorilla. I know my dogs would have nothing to do with it.
Sorry for the dry humor, I worked last night and haven't gotten any sleep yet, so the dumb humor crops up when the remaining brain cell is sleeping.
Reg
A
Anonymous
Guest
Hi again,
The "harvested" part of your post just soaked in. I thought you were referring to an area that had been thoroughly checked before for meteorites and not a crop field.
Ok, now I get it. Many harvested fields are still quite uneven so keeping the coil at the same heighth could be a problem. I guess a guy could suspend a large coil off the back end of an ATV in this case. It would be easier than trying to carry it. Another technique would be to mount it to a kids plastic toboggan and drag it.
Of course, your wheel idea would work fine if the wheels are large enough to easily move across any small ruts, I would recommend you suspend the coil so it is closer to the ground than mount it at axle heighth.
Quarter size or larger iron meteorites should be no real problem. I would think you should be able to get almost a foot or more from the coil and still get a good signal. A quick test would be to use a similar piece of iron and check the depth capabilites.
A stony type meteorite would be something different. You might try something like a charcoal briquette (or however it is spelled), as a test target. You might even use a piece of a red brick.
Remember, about 85% of all meteorites are of the stony variety.
A quarter size round stony meteorite like the ones I have found in Gold Basin would give a signal maybe 6" to 8" max from the coil. If the coil is 9" off the ground, then you wouldn't hear the meteorite. The measurements I gave are using a 11" coil. I would expect a long narrow coil to be somewhat comparative.
PI's are ground sensitive unless they have some form of ground balance, so any serious or sudden elevation change will probably result in an audio change also. Automatic tuning will help quite a bit if ground balance isn't available.
In a nutshell, I think you should be able to build something that would work. I would also think something could be built for a VLF also, but that is a guess on my part. I would think a design similar to the "bigfoot" would be the best but that is a question that either Eric or Thomas could better answer.
Reg
The "harvested" part of your post just soaked in. I thought you were referring to an area that had been thoroughly checked before for meteorites and not a crop field.
Ok, now I get it. Many harvested fields are still quite uneven so keeping the coil at the same heighth could be a problem. I guess a guy could suspend a large coil off the back end of an ATV in this case. It would be easier than trying to carry it. Another technique would be to mount it to a kids plastic toboggan and drag it.
Of course, your wheel idea would work fine if the wheels are large enough to easily move across any small ruts, I would recommend you suspend the coil so it is closer to the ground than mount it at axle heighth.
Quarter size or larger iron meteorites should be no real problem. I would think you should be able to get almost a foot or more from the coil and still get a good signal. A quick test would be to use a similar piece of iron and check the depth capabilites.
A stony type meteorite would be something different. You might try something like a charcoal briquette (or however it is spelled), as a test target. You might even use a piece of a red brick.
Remember, about 85% of all meteorites are of the stony variety.
A quarter size round stony meteorite like the ones I have found in Gold Basin would give a signal maybe 6" to 8" max from the coil. If the coil is 9" off the ground, then you wouldn't hear the meteorite. The measurements I gave are using a 11" coil. I would expect a long narrow coil to be somewhat comparative.
PI's are ground sensitive unless they have some form of ground balance, so any serious or sudden elevation change will probably result in an audio change also. Automatic tuning will help quite a bit if ground balance isn't available.
In a nutshell, I think you should be able to build something that would work. I would also think something could be built for a VLF also, but that is a guess on my part. I would think a design similar to the "bigfoot" would be the best but that is a question that either Eric or Thomas could better answer.
Reg
A
Anonymous
Guest
Hi
I have a question about a possible coil design that might fit the needs of JVP. How about a long narrow xmit coil and a separate long narrow figure 8 receive coil sitting on top, under, or beside the xmit coil.
One would have to careful on the adjustment of the coil positions. I would suspect one would get a positive signal on one half of the coil and a negative response on the other.
I would also think having a figure 8 receive coil would add a level of noise cancellation as well as some ground cancellation.
Is my thought process evenly remotely valid or is my remaining braincell off in left field?
Thanks,
Reg
I have a question about a possible coil design that might fit the needs of JVP. How about a long narrow xmit coil and a separate long narrow figure 8 receive coil sitting on top, under, or beside the xmit coil.
One would have to careful on the adjustment of the coil positions. I would suspect one would get a positive signal on one half of the coil and a negative response on the other.
I would also think having a figure 8 receive coil would add a level of noise cancellation as well as some ground cancellation.
Is my thought process evenly remotely valid or is my remaining braincell off in left field?
Thanks,
Reg
A
Anonymous
Guest
Thanks Reg, I appreciate your input. I should have said farm land,when writing about harvested ground. I'd like to try building a larger coil for my VLF. But I've heard that the Big Foot doesn't go very deep. Also I guess it is pretty hard to balance the two coils.
Could you explain how you built the coil for your PI? It has been very interesting for me to read all the posts on this subject. I think most of us are learning somthing, I know I am.
JVP
Could you explain how you built the coil for your PI? It has been very interesting for me to read all the posts on this subject. I think most of us are learning somthing, I know I am.
JVP
A
Anonymous
Guest
Reg, aren't you describing the Bigfoot design?
I just recently bought a Bigfoot to try out, and was surprised that the "null" in the center of the coil was not very deep at all. Just a very slight dip.
In all-metal, it does give a negative response on the back-half. I don't think this would be the case with PI since the transient response is the same regardless of the field phase (try waving targets across the top of your PI coil). However, you would get the center cancelation, just don't know how severe.
- Carl
I just recently bought a Bigfoot to try out, and was surprised that the "null" in the center of the coil was not very deep at all. Just a very slight dip.
In all-metal, it does give a negative response on the back-half. I don't think this would be the case with PI since the transient response is the same regardless of the field phase (try waving targets across the top of your PI coil). However, you would get the center cancelation, just don't know how severe.
- Carl
A
Anonymous
Guest
Hi Carl,
I have never used a Bigfoot nor do I know how it is designed, so the concept could very likely be the same. About all I know about this coil is a friend of mine uses one and he likes it.
Anyway, just thinking about the basic concept of a large long xmit coil and a seperate figure 8 receive coil, I would think the noise would cancel, but am not sure about the ground signal. I would think it would cancel also.
I would also think if the coil is positioned carefully, one should be able to "null" the coil for minimum output with no target present, so it would be somewhat similar to the DD except for the strange response pattern of a negative response on one half and a positive response on the other. Under these conditions, I would think the general ground signal would cancel.
I haven't tried building one yet, but was just running the idea through my remaining brain cell, trying to mentally picture the basic phasing.
Unless I missed something, I would think it would work as I mentioned. Also, I wasn't trying to invent the "wheel" since most different coil designs have already been tried, but rather to figure out if this design would fit the needs of JVP.
He has an excellent idea in trying to figure a way to scan large areas of a reasonably level field for meteorites. Also, if the coil design were to minimize the ground response, that would eliminate much of the audio variations what could occur from coil height changes when going over uneven ground. It would also expand the number of PI detectors that he could choose from.
The Bigfoot is quite narrow as I remember. I was thinking about something in the 6" to 8" width range and longer.
Back to the basic question, wouldn't it also minimize the ground signals?
Reg
I have never used a Bigfoot nor do I know how it is designed, so the concept could very likely be the same. About all I know about this coil is a friend of mine uses one and he likes it.
Anyway, just thinking about the basic concept of a large long xmit coil and a seperate figure 8 receive coil, I would think the noise would cancel, but am not sure about the ground signal. I would think it would cancel also.
I would also think if the coil is positioned carefully, one should be able to "null" the coil for minimum output with no target present, so it would be somewhat similar to the DD except for the strange response pattern of a negative response on one half and a positive response on the other. Under these conditions, I would think the general ground signal would cancel.
I haven't tried building one yet, but was just running the idea through my remaining brain cell, trying to mentally picture the basic phasing.
Unless I missed something, I would think it would work as I mentioned. Also, I wasn't trying to invent the "wheel" since most different coil designs have already been tried, but rather to figure out if this design would fit the needs of JVP.
He has an excellent idea in trying to figure a way to scan large areas of a reasonably level field for meteorites. Also, if the coil design were to minimize the ground response, that would eliminate much of the audio variations what could occur from coil height changes when going over uneven ground. It would also expand the number of PI detectors that he could choose from.
The Bigfoot is quite narrow as I remember. I was thinking about something in the 6" to 8" width range and longer.
Back to the basic question, wouldn't it also minimize the ground signals?
Reg