11" DD, 10" Concentric and 5"

[earthmansurfer]

I was just reading Monte's post on how he likes to use the 11" DD coil (for the Omega 8000, though I think this would be true for the T2 and other detectors as well) for more open sites as it gets a little more depth than the 10". I thought the DD coil is better for faster responses and where there are more targets? (BTW - Monte, I get so much from reading your posts, I'm just a bit confused when it comes to the coils. I'm not trying to single your words out, you are the man!) Clearly the 5" coil is good around trash, but the difference between the 10" Concentric and 11"DD is not so clear. I know there is user preference, but there must be some science behind it as well. I thought the concentric was deeper but it's sweet spot at depth is so much less? So, I did a little searching. (There is a good article out there but I can't seem to find it.) I've only used the DD with my T2, so would value any peoples experiences...

From another forum:

Your going to find the DD a little more sensitive but not as deep going.

The Concentric Deeper but not providing as much coverage with the field.

A little more

Each have an advantage depending on conditions, but the DD coils have become the favorite of many, including myself.

Round coil, or most often concentric, have a cone shaped detection pattern, where as the DD coils(also can be round) have a blade pattern. The concentric coils have a slight depth advantage, while the DD's handle mineralized ground better, trashy areas better, and cover more ground.

Here is a picture that might help show the differences and advantages.

Also this,

Types of Coils

Some of the basic coil types:
The most common description for metal detector coils are: concentric, elliptical, and Double D.
Concentric Coil
A concentric coil is probably the most commonly used coil. Different manufacturers refer to these coils with different names, however a concentric coil is a concentric coil! These coils are round, some being very thin in height, some thicker, some with open holes in the center, making them shaped like a flattened donut, and some are solid. A few of the manufacturers have migrated into designing their concentric coils into a design which has caused them to be referred to as

 

[Low-Boy/LCPM]

I found the 11D to be alot deeper and the 8000 works better it was like getting a new detector when I put the 11 on. Didn't like the 10 at all and never put it on again.

 

[otlew]

Judging by the graphics of the two coils, concentric and DD it should be much easier to pin point with the sharp end of a cone, than with the blade of a knife.

How do you pin point, the exact location of the target using the DD coil?

 

[earthmansurfer]

Judging by the graphics of the two coils, concentric and DD it should be much easier to pin point with the sharp end of a cone, than with the blade of a knife.

How do you pin point, the exact location of the target using the DD coil?

I just got back from 3 hours of detecting. Found a 1897, 1911, 1929, 1970 and something early 1900's or so. Pinpointing is pretty easy with the DD. I think because the coin hits ALL along the center that people can make mistakes. Using the T2's poinpointing I'm usually within 3" on coins. The thing you need to do is to make sure you use the pinpointing function, if you just center the beeps you'd better have a good visual function as the coins hit from top to bottom on the DD coil. I can usually center the target using just the beeps too, but like to pull the lever back to get a better feel for the target shape, depth, etc.

BTW - I have been using the Garret Pro Pointer. Absolutely Awesome. Damn does it save time.

 

[bumshot]

It is very easy to pinpoint with the DD coil. Pinpoint the spot, then again at ninety degrees. Sometimes have to do it twice. I put a cane on the spot. I am usually within one inch. Don't even use pinpointing mode most of the time. I am 71 years old. The cane also helps me get up so I can detect longer.

 

[Jackpine Savage]

The Bi-Axiall DD is a great coil for hunting where the iron and goodies are both deep. In areas where the trash tends to be shallow thats when you need to switch to a concentric. DD coils give confusing signals on shallow targets and to the uninitiated and pros alike this can cause problems. Raising the coil or detuning the P/P helps but... best to switch to a concentric with it less confusing pattern/signals on shallow targets.

Are far as ultimate depth and seperation at depth the DD coil will find targets the concentric misses and vice versa. Still I favor the 11" Bi-axial over the concentric for general hunting.

Tom

 

[otlew]

It is very easy to pinpoint with the DD coil. Pinpoint the spot, then again at ninety degrees. Sometimes have to do it twice. I put a cane on the spot. I am usually within one inch. Don't even use pinpointing mode most of the time. I am 71 years old. The cane also helps me get up so I can detect longer.

So you do this with the intensity of sound twice in the "cross" + pattern? Okay, that is what I have been doing and I am usually about 2" of, just need more practice I guess.

 

[Monte]

I was just reading Monte's post on how he likes to use the 11" DD coil (for the Omega 8000, though I think this would be true for the T2 and other detectors as well) for more open sites as it gets a little more depth than the 10".

Since I have all three (3) common Omega coils I have the luxury of picking and choosing. Some readers might think I do not like the 11" coil, but that's incorrect. I do, but the fact also remains that I also like the stock 10' elliptical concentric coil for a lot of my hunting tasks, as well as the 5" DD for trashier, brushier or more challenging environments. Usually, yes, the 11" coil will get a little more depth on coin-sized targets. However, like all Double-D coils, it will respond a bit different from a concentric-wound coil.

I thought the DD coil is better for faster responses and where there are more targets? (BTW - Monte, I get so much from reading your posts, I'm just a bit confused when it comes to the coils. I'm not trying to single your words out, you are the man!) Clearly the 5" coil is good around trash, but the difference between the 10" Concentric and 11"DD is not so clear.

A Double-D coil will usually produce a little quicker or faster response in trashier sites. This is partially due to the overlap of the Transmit and Receive windings which produce a narrower response area down (front-to-rear) the center of the coil. usually, but not always, a concentric-designed coil is made in a round shape, like the 8" coils on the Alpha, Delta and Gamma models. With the outer coil winding being the Transmit and the inner circle winding being the Receive, you will have a more uniform response from an unmasked target if your sweep at it from the left and then from the right. This is due to the very nice-and-proper concentric coil windings. That's assumings the target, such as a coin, is laying 'flat' to the coil.

Usually, but not always, a Double-D coil is fashioned in an elliptically-shaped coil. As such, with the Transmit winding mainly on one side of the coil and the receive windings on the opposite side, this leaves a rather narrow "overlap" of the two windings than runs front-to-rear and causes more of an overlap of the two windings when compared with a standard concentric design. What many do not realize is that due to the differences in the winding positioning of a DD coil, when you sweep towards a nice-and-proper coin laying flat in the ground you still don't get quite the same "consistent" response across the full sweep of the target due to the Tx on one side and Rx winding on the opposite. Thus, there will be times when a DD coil will seem less consistent in TID as well as general responsiveness, and they have some challenges, compared with a concentric coil, when dealing with iron or other ferrous-based targets, such as bottle caps and the like.

Also, due to the 11" BiAxial DD coil's size and shape, as well as power generated, you can get multiple 'hits' when sweeping a target that is within 3" of the coil, or even slightly farther away depending upon the size of the target. Thus, in very trashy environments, or when most coins at a site tend to be fairly shallow, and especially if there are a lot of 'junk' targets around, I usually prefer to use a smaller coil. Can the 11" coil 'pick' between targets? Yes, but if they are positioned not left-to-right but instead front-and-rear, you can also have some target masking or just too many hits to deal with. I am not suggesting ONLY a DD or Concentric coil, but ANY coil that is too large for the target spacing at a site.

So, thankfully, i can not only use the 10" concentric when i want more accurate Target ID on mid-to-deeper targets (than the t2 for example), but just for general coin hunting and searches where it's common or moderate trash. Also, I do not hesitate to quickly go with the 5" DD coil for most sites that have a lot of targets or other challenges, such as rough, uneven ground and such. Surprisingly, the 5" DD coil provides excellent depth of detection for its size with my Omega!

I know there is user preference, but there must be some science behind it as well. I thought the concentric was deeper but it's sweet spot at depth is so much less?

Usually, if the coil sizes and shapes are similar, then a concentric coil will often produce a little better depth, but these coils are not the same type or size-and-shape. Oh, as for the "sweet spot", both the DD and concentric designs will 'pinpoint' relatively "dead center" at the deepest target point. Now, this can be a little hard to define with some DD coils, especially the T2 and Omega 11" DD because they perform so well, but with practice and a little detuning, you can PP almost dead center. Very close, to be sure, but I still like to try it from two approaches of 45

 

[Monte]

Including the closing comment that YOU favor the 11" BiAxial DD over the concentric design. It really gets down to a matter of the type of site we hunt and what we're after.

like you, I like the 11" DD, but, as noted, I like it in lower target-count sites. That's because most of my sites that produce older coins from my 1836 capped Bust Half-Dime through the early/mid 1900's yield them from shallower depths of 3" to the surface, and the amount of trash 9especially iron) in those old Railroad towns can be very annoying. Usually, smaller concentric or DD coils do well, and on vacation this year, I hope, that 5" DD is going to get a serious work-out!

I reserve my 11" coil duty for sites like old Military Encampments in wide-open areas and similar work. i like the 11", especially on units like my Omega and T2, because I can HEAR both iron and non-iron targets and they can sound different d2 and 2+ respectively) and the 11" coil does get the deepies!

Monte

 

[otlew]

Judging by the graphics of the two coils, concentric and DD it should be much easier to pin point with the sharp end of a cone, than with the blade of a knife.

How do you pin point, the exact location of the target using the DD coil?

I just got back from 3 hours of detecting. Found a 1897, 1911, 1929, 1970 and something early 1900's or so. Pinpointing is pretty easy with the DD. I think because the coin hits ALL along the center that people can make mistakes. Using the T2's poinpointing I'm usually within 3" on coins. The thing you need to do is to make sure you use the pinpointing function, if you just center the beeps you'd better have a good visual function as the coins hit from top to bottom on the DD coil. I can usually center the target using just the beeps too, but like to pull the lever back to get a better feel for the target shape, depth, etc.

BTW - I have been using the Garret Pro Pointer. Absolutely Awesome. Damn does it save time.

Well you did a good job of confirming what I suspected, or what seems to make sense. To me as you drag the blade, for lack of a better term, over the target you will hear when the beam fall off the tip when you have completely passed over it and in the opposite direction off of the heel. Like slicing something into two section and if you do this at 90 degrees, four sections

heel <---> tip and target + tip ---> + and heel + <----

Or is just in the middle of the blade, and based on sound intensity as the graphics above seem to indicate?

 

[earthmansurfer]

Judging by the graphics of the two coils, concentric and DD it should be much easier to pin point with the sharp end of a cone, than with the blade of a knife.

How do you pin point, the exact location of the target using the DD coil?

I just got back from 3 hours of detecting. Found a 1897, 1911, 1929, 1970 and something early 1900's or so. Pinpointing is pretty easy with the DD. I think because the coin hits ALL along the center that people can make mistakes. Using the T2's poinpointing I'm usually within 3" on coins. The thing you need to do is to make sure you use the pinpointing function, if you just center the beeps you'd better have a good visual function as the coins hit from top to bottom on the DD coil. I can usually center the target using just the beeps too, but like to pull the lever back to get a better feel for the target shape, depth, etc.

BTW - I have been using the Garret Pro Pointer. Absolutely Awesome. Damn does it save time.

Well you did a good job of confirming what I suspected, or what seems to make sense. To me as you drag the blade, for lack of a better term, over the target you will hear when the beam fall off the tip when you have completely passed over it and in the opposite direction off of the heel. Like slicing something into two section and if you do this at 90 degrees, four sections

heel <---> tip and target + tip ---> + and heel + <----

Or is just in the middle of the blade, and based on sound intensity as the graphics above seem to indicate?

If I understand you correctly, then yes, you are correct. The coin hits all along the middle section of the coil (Where the receiving and transmit overlap). As others have said, picking up shallow targets can be a pain with the DD coil (ie - double beeps). Pinpointing is fine though. A hit on the towards the edge of "The beam" is definitely not as strong as in the center and the ID's are similarly affected. When I said I can get withing 3", I should say 1.5" per side. I have no problem pinpointing but I think it takes a little more time than with a concentric.

I do believe Monte is right though as the diagram shows a larger area than what is actually picked up with the DD coil. Instead of it being square from the side view, it probably dissipates down quite a bit, not to a funnel though. (So, if the "blade" is 9" front to back, at the bottom it is probably 5" or so - I'm just guessing. (not as small as a concentric) I think a small DD coil would have to be the best trash coil there is, considering what everyone has said thus far. I can really find coins in trash with the stock 11" DD coil of my T2. It seems like I can separate (hear that is) targets that are 1" or 2" apart.

I am very very tempted to get an Omega with all 3 coils to learn more about what we have been discussing. I really am just concerned with coins and not relics (thus far) and don't look like I'll be losing much. Luckily a few of the guys here use that Omega and 3 coil setup.

Thanks for all your comments guys, it makes for fun learning.

 

[otlew]

If I understand you correctly, then yes, you are correct. The coin hits all along the middle section of the coil (Where the receiving and transmit overlap). As others have said, picking up shallow targets can be a pain with the DD coil (ie - double beeps). Pinpointing is fine though. A hit on the towards the edge of "The beam" is definitely not as strong as in the center and the ID's are similarly affected. When I said I can get withing 3", I should say 1.5" per side. I have no problem pinpointing but I think it takes a little more time than with a concentric.

I do believe Monte is right though as the diagram shows a larger area than what is actually picked up with the DD coil. Instead of it being square from the side view, it probably dissipates down quite a bit, not to a funnel though. (So, if the "blade" is 9" front to back, at the bottom it is probably 5" or so - I'm just guessing. (not as small as a concentric) I think a small DD coil would have to be the best trash coil there is, considering what everyone has said thus far. I can really find coins in trash with the stock 11" DD coil of my T2. It seems like I can separate (hear that is) targets that are 1" or 2" apart.

I am very very tempted to get an Omega with all 3 coils to learn more about what we have been discussing. I really am just concerned with coins and not relics (thus far) and don't look like I'll be losing much. Luckily a few of the guys here use that Omega and 3 coil setup.

Thanks for all your comments guys, it makes for fun learning.

I am going to plant a dime, flat in the bottom of a 4" hole, then set a wooden dowel on top of the dime and fill in the hole leaving the dowel just visible above ground level. Slap some paint on the end of the dowel and figure this 11" DD coil pin pointing out. I will also confirm depth readings as well.

 

[earthmansurfer]

If I understand you correctly, then yes, you are correct. The coin hits all along the middle section of the coil (Where the receiving and transmit overlap). As others have said, picking up shallow targets can be a pain with the DD coil (ie - double beeps). Pinpointing is fine though. A hit on the towards the edge of "The beam" is definitely not as strong as in the center and the ID's are similarly affected. When I said I can get withing 3", I should say 1.5" per side. I have no problem pinpointing but I think it takes a little more time than with a concentric.

I do believe Monte is right though as the diagram shows a larger area than what is actually picked up with the DD coil. Instead of it being square from the side view, it probably dissipates down quite a bit, not to a funnel though. (So, if the "blade" is 9" front to back, at the bottom it is probably 5" or so - I'm just guessing. (not as small as a concentric) I think a small DD coil would have to be the best trash coil there is, considering what everyone has said thus far. I can really find coins in trash with the stock 11" DD coil of my T2. It seems like I can separate (hear that is) targets that are 1" or 2" apart.

I am very very tempted to get an Omega with all 3 coils to learn more about what we have been discussing. I really am just concerned with coins and not relics (thus far) and don't look like I'll be losing much. Luckily a few of the guys here use that Omega and 3 coil setup.

Thanks for all your comments guys, it makes for fun learning.

I am going to plant a dime, flat in the bottom of a 4" hole, then set a wooden dowel on top of the dime and fill in the hole leaving the dowel just visible above ground level. Slap some paint on the end of the dowel and figure this 11" DD coil pin pointing out. I will also confirm depth readings as well.

It's worth a try but I'm not sure it will work. Even if a person uses a piece of cardboard over a coin to practice pinpointing, the cardboard will affect the signal, so what might a wooden dowel do? When you do your test you will have to compare it to the concentric. I think that an ideal test would be to have a test garden and a coin as you said minus the wood dowel. (But knowing it's exact location of course).

I'm curious to hear what you find out, please let us know...

 

[otlew]

If I understand you correctly, then yes, you are correct. The coin hits all along the middle section of the coil (Where the receiving and transmit overlap). As others have said, picking up shallow targets can be a pain with the DD coil (ie - double beeps). Pinpointing is fine though. A hit on the towards the edge of "The beam" is definitely not as strong as in the center and the ID's are similarly affected. When I said I can get withing 3", I should say 1.5" per side. I have no problem pinpointing but I think it takes a little more time than with a concentric.

I do believe Monte is right though as the diagram shows a larger area than what is actually picked up with the DD coil. Instead of it being square from the side view, it probably dissipates down quite a bit, not to a funnel though. (So, if the "blade" is 9" front to back, at the bottom it is probably 5" or so - I'm just guessing. (not as small as a concentric) I think a small DD coil would have to be the best trash coil there is, considering what everyone has said thus far. I can really find coins in trash with the stock 11" DD coil of my T2. It seems like I can separate (hear that is) targets that are 1" or 2" apart.

I am very very tempted to get an Omega with all 3 coils to learn more about what we have been discussing. I really am just concerned with coins and not relics (thus far) and don't look like I'll be losing much. Luckily a few of the guys here use that Omega and 3 coil setup.

Thanks for all your comments guys, it makes for fun learning.

I am going to plant a dime, flat in the bottom of a 4" hole, then set a wooden dowel on top of the dime and fill in the hole leaving the dowel just visible above ground level. Slap some paint on the end of the dowel and figure this 11" DD coil pin pointing out. I will also confirm depth readings as well.

It's worth a try but I'm not sure it will work. Even if a person uses a piece of cardboard over a coin to practice pinpointing, the cardboard will affect the signal, so what might a wooden dowel do? When you do your test you will have to compare it to the concentric. I think that an ideal test would be to have a test garden and a coin as you said minus the wood dowel. (But knowing it's exact location of course).

I'm curious to hear what you find out, please let us know...

I will change the dowel to a plastic drinking straw. If plastic affects the field that much then man I have missed a lot of targets over the last months.

 

[earthmansurfer]

If I understand you correctly, then yes, you are correct. The coin hits all along the middle section of the coil (Where the receiving and transmit overlap). As others have said, picking up shallow targets can be a pain with the DD coil (ie - double beeps). Pinpointing is fine though. A hit on the towards the edge of "The beam" is definitely not as strong as in the center and the ID's are similarly affected. When I said I can get withing 3", I should say 1.5" per side. I have no problem pinpointing but I think it takes a little more time than with a concentric.

I do believe Monte is right though as the diagram shows a larger area than what is actually picked up with the DD coil. Instead of it being square from the side view, it probably dissipates down quite a bit, not to a funnel though. (So, if the "blade" is 9" front to back, at the bottom it is probably 5" or so - I'm just guessing. (not as small as a concentric) I think a small DD coil would have to be the best trash coil there is, considering what everyone has said thus far. I can really find coins in trash with the stock 11" DD coil of my T2. It seems like I can separate (hear that is) targets that are 1" or 2" apart.

I am very very tempted to get an Omega with all 3 coils to learn more about what we have been discussing. I really am just concerned with coins and not relics (thus far) and don't look like I'll be losing much. Luckily a few of the guys here use that Omega and 3 coil setup.

Thanks for all your comments guys, it makes for fun learning.

I am going to plant a dime, flat in the bottom of a 4" hole, then set a wooden dowel on top of the dime and fill in the hole leaving the dowel just visible above ground level. Slap some paint on the end of the dowel and figure this 11" DD coil pin pointing out. I will also confirm depth readings as well.

It's worth a try but I'm not sure it will work. Even if a person uses a piece of cardboard over a coin to practice pinpointing, the cardboard will affect the signal, so what might a wooden dowel do? When you do your test you will have to compare it to the concentric. I think that an ideal test would be to have a test garden and a coin as you said minus the wood dowel. (But knowing it's exact location of course).

I'm curious to hear what you find out, please let us know...

I will change the dowel to a plastic drinking straw. If plastic affects the field that much then man I have missed a lot of targets over the last months.

LOL if you are talking about the plastic coil cover. Seriously, I've seen it mentioned that through tests, even things like carboard change the field. The best idea I've heard, imo, was to dig a hole and then slide a coin into the side of the whole a few inches, that way the soil above isn't disturbed. Just put a small marker on top of the coin (maybe a small yellow stone or the like). Replace the dirt. Not perfect but pretty damn close to natural.

 

[otlew]

If I understand you correctly, then yes, you are correct. The coin hits all along the middle section of the coil (Where the receiving and transmit overlap). As others have said, picking up shallow targets can be a pain with the DD coil (ie - double beeps). Pinpointing is fine though. A hit on the towards the edge of "The beam" is definitely not as strong as in the center and the ID's are similarly affected. When I said I can get withing 3", I should say 1.5" per side. I have no problem pinpointing but I think it takes a little more time than with a concentric.

I do believe Monte is right though as the diagram shows a larger area than what is actually picked up with the DD coil. Instead of it being square from the side view, it probably dissipates down quite a bit, not to a funnel though. (So, if the "blade" is 9" front to back, at the bottom it is probably 5" or so - I'm just guessing. (not as small as a concentric) I think a small DD coil would have to be the best trash coil there is, considering what everyone has said thus far. I can really find coins in trash with the stock 11" DD coil of my T2. It seems like I can separate (hear that is) targets that are 1" or 2" apart.

I am very very tempted to get an Omega with all 3 coils to learn more about what we have been discussing. I really am just concerned with coins and not relics (thus far) and don't look like I'll be losing much. Luckily a few of the guys here use that Omega and 3 coil setup.

Thanks for all your comments guys, it makes for fun learning.

I am going to plant a dime, flat in the bottom of a 4" hole, then set a wooden dowel on top of the dime and fill in the hole leaving the dowel just visible above ground level. Slap some paint on the end of the dowel and figure this 11" DD coil pin pointing out. I will also confirm depth readings as well.

It's worth a try but I'm not sure it will work. Even if a person uses a piece of cardboard over a coin to practice pinpointing, the cardboard will affect the signal, so what might a wooden dowel do? When you do your test you will have to compare it to the concentric. I think that an ideal test would be to have a test garden and a coin as you said minus the wood dowel. (But knowing it's exact location of course).

I'm curious to hear what you find out, please let us know...

I will change the dowel to a plastic drinking straw. If plastic affects the field that much then man I have missed a lot of targets over the last months.

LOL if you are talking about the plastic coil cover. Seriously, I've seen it mentioned that through tests, even things like carboard change the field. The best idea I've heard, imo, was to dig a hole and then slide a coin into the side of the whole a few inches, that way the soil above isn't disturbed. Just put a small marker on top of the coin (maybe a small yellow stone or the like). Replace the dirt. Not perfect but pretty damn close to natural.

That method of planting the target makes sense. However I am not trying to determine depth, just location.

A plastic coil cover has many fold the mass of a 4" plastic straw.

If my detector cannot deal with this setup, how will it do with targets in the wild? I understand that things can affect the field produced by the coil, which means that unless you have perfect soil which is debris free, you will never get totally accurate responses from you machine. Which I think is in fact the case, but it seems it good enough most of the time.

I will satisfy my curiosity and leave it at that.

Thanks for you comments and H.H.