Which is the better coil

[C.J.M.]

I have pictures of three coils for the AT PRO. Which one is your choice?Thank you CJM

 

[KSDfisher77]

I guess coil selection boils down to what type of hunting & where you metal detect at most. The round coils will have more depth & possibly separate better between the trash. The elliptical coils will aid in covering more ground & help fight ground minerals. I personally think all 3 of them coils being helpful in certain hunting situations.

 

[marcomo]

I haven't used the AT Pro much for the last 4 years as it's been my backup detector. But I've had it since 2011 so I've had a good bit of experience with the different Garrett coils, although not that 7" it must be a more recent offering.

Between the stock 11", the 5X8 and the little sniper coil, my favorite for the majority of areas I detected was the 5X8, It had great separation, depth within an inch of the bigger 11" and way better depth and coverage than the little 4.5". It was also easily the most balanced ergonomically of the 3 coils I used with the Pro. The 11" always made the detector seem nose heavy and the 4.5" made it feel too light on the bottom. Although I have kept the stock coil for areas where targets are relatively sparse, I got rid of the sniper in fairly short order.

It's always seemed to me like the AT Pro was made for the 5X8.

 

[Fredneck]

I agree with marcomo. Over the years the 5x8" on the AT Gold has performed really well. My buddies Pro was down for repairs and borrowed my Gold, he was shocked how smooth it ran, as well as the depth it achieved considering its smaller size compared to the stock on the Pro.

 

[Tot Lot Bandit]

I have the 5x8 and have had the Mars 7" on a Fisher F 22. I recently got the 7x11 Viper for my Pro and I like it. It gives you the best of both a small and a large coil. No more switching coils for me. I'm selling my 5x8 and 8x11.

 

[Tot Lot Bandit]

I have the 5x8 and have had the Mars 7" on a Fisher F 22. I recently got the 7x11 Viper for my Pro and I like it. It gives you the best of both a small and a large coil. No more switching coils for me. I'm selling my 5x8 and 8x11.

6x11 Viper

 

[kac_dt]

Small sniper coil is good for very trashy parks where your planning on coin shooting for shallow fresh drops. 5x8 and 6x11 viper offer better separation over the stock coil and can work well in moderate trashy areas but have an advantage of more depth over the stock coil. Ground with higher mineralization the eliptical coils are less noisy and will give you more stable id's as their foot print is smaller. Round coils tend to struggle in higher mineralization.
As for depth from what I have seen the Viper is very close in depth to the stock coil followed by the 5x8. As coils get bigger the depth gain over size drops as the machines can only put out just so much power. There is a limit on how deep ib machines can go. This is true with all ib machines so the real question is how small can you go rather than how big. as the smaller coils are lighter and more precise.
Majority of finds are relatively shallow and most stock coils are more than sufficient. Here in New England on old land that has substantial earth worm activity, coins from the 1700's are typically less than 10" down. Pine forests they are even shallower. Grounds that have been altered by construction such as drainage, water lines, etc. targets can be all over the place and if they happen to be in the 3'+ range because of a trencher your probably not going to find a machine capable of detecting that deep and be able to separate the target from a pipe or wire nor would you want to dig that anyways.

I've done very well with the stock coil but am considering the Viper over the smaller one and plan to use it for much of my fresh water hunting.

 

[marcomo]

Small sniper coil is good for very trashy parks where your planning on coin shooting for shallow fresh drops. 5x8 and 6x11 viper offer better separation over the stock coil and can work well in moderate trashy areas but have an advantage of more depth over the stock coil. Ground with higher mineralization the eliptical coils are less noisy and will give you more stable id's as their foot print is smaller. Round coils tend to struggle in higher mineralization.
As for depth from what I have seen the Viper is very close in depth to the stock coil followed by the 5x8. As coils get bigger the depth gain over size drops as the machines can only put out just so much power. There is a limit on how deep ib machines can go. This is true with all ib machines so the real question is how small can you go rather than how big. as the smaller coils are lighter and more precise.
Majority of finds are relatively shallow and most stock coils are more than sufficient. Here in New England on old land that has substantial earth worm activity, coins from the 1700's are typically less than 10" down. Pine forests they are even shallower. Grounds that have been altered by construction such as drainage, water lines, etc. targets can be all over the place and if they happen to be in the 3'+ range because of a trencher your probably not going to find a machine capable of detecting that deep and be able to separate the target from a pipe or wire nor would you want to dig that anyways.

I've done very well with the stock coil but am considering the Viper over the smaller one and plan to use it for much of my fresh water hunting.

 

[marcomo]

Coins from the 1700s are typically found at less than 10" - certainly true because of the depth limitations of metal detectors.

When you talk about all coins in the ground from the 1700s, found and unfound, how do you know they are typically less than 10" down? I don't know either, but coins will sink until the density of what's beneath exceeds the density of the coin. My guess is the majority of New England coins from the 1700s are laying deeper than 10" based on what archaeologists find with colonial era digs. They deal with depth in terms of feet rather than inches.

 

[C.J.M.]

I dont own a AT PRO, but I would like to reccomend this 8x6 Detech coil. I use them on whites machines & are great. They got good separation & depth. The 8x6 Detech also covers ground fairly decent. Also detech coils seem to calm your machine down a bit. View attachment 41262

What kind of depth does it have?

 

[KSDfisher77]

What kind of depth does it have?

It will see 8" depth real easy on my whites machines. A 10" walking half is nothing for that coil on my DFX detector.

 

[kac_dt]

Earth worm activity is approx 10" and less. They are the leading contributor to targets sinking inland. If you dig to the clay line it is often less than a foot down and clay is too packed for targets to sink below that. Having run a Nel big that has some substantial depth it has rarely found targets beyond 10" with the exception of areas that were dug up by and turned over for pipes etc or muddy areas where tractors have sunk their wheels down.

 

[marcomo]

Earth worm activity is approx 10" and less. They are the leading contributor to targets sinking inland. If you dig to the clay line it is often less than a foot down and clay is too packed for targets to sink below that. Having run a Nel big that has some substantial depth it has rarely found targets beyond 10" with the exception of areas that were dug up by and turned over for pipes etc or muddy areas where tractors have sunk their wheels down.

Actually, some varieties of earthworms burrow quite deeply. As much as 6 ft deep. When the ground gets dry, they will dig deeper to get to moisture in the soil. Also, some earthworms burrow down several feet to the subsoil below the freeze line in the winter to hibernate.

I still maintain that the inability to find coins below 10" deep with a detector, regardless of coil size, has to do with the limitations of a vlf detector combined with ground mineralization and masking, not an absence of targets.

 

[vlad]

Small sniper coil is good for very trashy parks where your planning on coin shooting for shallow fresh drops. 5x8 and 6x11 viper offer better separation over the stock coil and can work well in moderate trashy areas but have an advantage of more depth over the stock coil. Ground with higher mineralization the eliptical coils are less noisy and will give you more stable id's as their foot print is smaller. Round coils tend to struggle in higher mineralization.
As for depth from what I have seen the Viper is very close in depth to the stock coil followed by the 5x8. As coils get bigger the depth gain over size drops as the machines can only put out just so much power. There is a limit on how deep ib machines can go. This is true with all ib machines so the real question is how small can you go rather than how big. as the smaller coils are lighter and more precise.
Majority of finds are relatively shallow and most stock coils are more than sufficient. Here in New England on old land that has substantial earth worm activity, coins from the 1700's are typically less than 10" down. Pine forests they are even shallower. Grounds that have been altered by construction such as drainage, water lines, etc. targets can be all over the place and if they happen to be in the 3'+ range because of a trencher your probably not going to find a machine capable of detecting that deep and be able to separate the target from a pipe or wire nor would you want to dig that anyways.

I've done very well with the stock coil but am considering the Viper over the smaller one and plan to use it for much of my fresh water hunting.

I think Garrett Snipers are coax's and shielded from the top from 60 cycle and other interference and can be put against metal like a swing set or a fence and not pick it up yet still scan next to it. If a round coil is also a DD its performance is no different the an elongated elliptical DD. I have found DD's to be noisier than concentrics when it comes to emi too and a detector with well designed ground filters in my experience seems more stable, with better and more accurate discrimination and a deeper search with a well made concentric than a DD. George Payne said that many loop makers tend to overdo things making DD's. The science is different from a concentric. "The DD coils can get you if you are not careful. As you know the Receive is generally the same size as the Transmit on these coils. Coupling that with the tendency to keep the Receive turns constant can result in a serious change in the coils output phase. Therefore, the Receive turns must be reduced considerably to lower the inductance back to the standard value. From a practical standpoint the inductance does not have to be exactly equal to the target inductances. As I said the tendency is to keep the turns the same as you change from one coil design to another. This tends to keep the sensitivity the same across many designs. However, that should not be the consideration. In this case its more important to control the phase across many designs. It’s better to look at it this way. For example, suppose that we build two Receive coils where one coil has twice the diameter of the other. But we keep the turns the same in both coils. For this example the larger coil would have an inductance that was twice the smaller coil. These coils would not have the same output phase. The larger Receive would easily have more sensitivity than the smaller coil because of the greater turns and coil area. However, this would not be a good design. The turns on the larger coil must be cut by .707 times. This would make both coils have the same inductance. All that being said the DD coils do have the worst phase shift away from the target value." G.P.
If they are made correctly great, if not the problems are big. Some people stick with a factory coil, others like after market types. (What was not well known was at one time Discovery Electronics made the coils for almost everybody too.) I have had very good luck with Nel & Mars and never sent one back: I cannot say that about some others like Coiltek.
If there is a limiting factor on a VLF's depth I think it is more self imposed within the industry on power levels. A P.I. may operate at 10X to 15X the power and has greater depth to show from it. When a maker decides to build a VLF where a primary consideration is not long battery life we will get some where. Just build the darn high power detector and leave the batteries to me. High battery drain has not held the P.I. back and I will note the original Dave Johnson Fisher Impulse P I used 8 AA batteries and lasted 100 hours............and no one bought it because it was not sensitive. ( And Georgi Chausev's Nexus is known for far exceeding 10"
in the UK and Europe and the secret is hand made fully resonance matched coils and he makes non motion detectors,)

 

[vlad]

Actually, some varieties of earthworms burrow quite deeply. As much as 6 ft deep. When the ground gets dry, they will dig deeper to get to moisture in the soil. Also, some earthworms burrow down several feet to the subsoil below the freeze line in the winter to hibernate.

I still maintain that the inability to find coins below 10" deep with a detector, regardless of coil size, has to do with the limitations of a vlf detector combined with ground mineralization and masking, not an absence of targets.

Then put it to a test: get a unit like a Gti or a F-75 with a strong stat mode use a big loop and dig every target like NASA Tom does on some sites. You will be surprised (the method works on Civil War sites,)
*Anytime you add discrimination you might block (reject) targets that you may want. For example, assume you adjust the discrimination so that a target is not rejected in an air test. However, if you now bury that same target and try to find it with the discrimination set as before, you might not be able to locate it. This characteristic is due to the ground mineral effecting the target's phase. The greater the ground mineralization the worse this problem will be. The ground mineralization effect may force the target's phase into the discrimination zone where targets are rejected. The deeper the target the weaker its signal and greater are the odds that the mineral will distort its phase to the point where it will be discriminated out. At some point in depth the detector cannot get enough signal from the target to properly identify it: sometimes removing a shovel full of dirt
will work though. A larger coil will pick-up more ground mineralization than a smaller coil. Therefore, it may make more sense to use a smaller coil in high mineral. Keep in mind that a coil picks up the ground in a very non- linear way. Pushing the coil down against a high mineral ground may get you say 1/2" closer to the target. However, the increase in ground signal may be several times greater than a deep target's signal. In this case you would wind up with less sensitivity. For better results experiment by raising the coil 1 or even 2 inches.
* G. P.

 

[kac_dt]

There is a focal point on coils where the machines frequency ends. After that point the frequency will drop off causing phase shift location of targets to drop in particular the mid to high conductors while the low conductors such as iron drop less.
High frequencys respond stronger to low conductors and low freqencies respond stronger to high conductors. Quick reference is take a look at the selectable frequency machines such as the Multi Kruzer and with the standard vdi scaling a nickel at 5khz is around 22 and at 14 khz nickel is 29 and at 19khz it is 36. The high conductors have even more of a number spread as frequency drops off beyond the focal range of the coil. This explains why when you take a pass over a target and get a low number, dig it a hole and the number is higher. This is because ground mineralization id shortening the focal range of the coil and not directly dragging a number down as the ground is zeroed out when you ground balance. One of the things I do when I encounter areas that have black sand or areas rich in iron deposits I will not depend on the vdi and that holds true to all my vlf machines.
The theory of frequency dictating the depth of a machine isn't necessarily true but rather the coil design and how well it is balanced to the machines power. DD coils have narrow signal and eliptical dd's tend to handle poor grounds better than round DD's as they have less influence. Concentrics have their special purpose where targets are enveloped by the signal more so than top down. A concentric doesn't have the separation as a dd does but becuase it can mix targets signals can help unmask. When I say unmask it is more of discriminating the lower conductor and hearing the high conductor only.
Good example is using a concentric vs dd with Monte's nail board test. Numbers of a given high conductor with a nail above or on it will be lower and if the nail is too big or discrimination too high it will also discriminate out the high conductor depending how close the phase angles are to each other. Garretts and prospecting machines have a nice wide gamut on low conductors giving users a slight advantage when discriminating out iron. Example a cut nail will break at 4 on the Kruzers but 33 on an AT Pro. That higher resolution on iron range can give the user a sloppy break or crackle that they can pay attention to.
I have only used the 9x12 concentric on the AT Pro and found it to be on the heavy side and it didn't unmask nearly as well as my Tejon so I ended up selling it as the Tejon rules those particular hunting situations. Often thought of the 6x9 concentric but for my personal use thought it lacked the depth of the Tejon so wasn't worth it for me to buy one. If someone has one on their AT Pro it would be good to see how it handles silvers in and around iron.
As for Garrett coils I ran my frequency sensor on my Apex on the viper which had a raw air test depth of 10", Deeptech ultimate 9" at 11" and the Reaper 10x14 had depth of 14". That was air test to where the machines frequency didn't drop off. That doesn't mean the machines don't detect deeper just as they go deeper the accuracy drops off.
Performance of the Viper is really good, very good ground coverage, excellent separation and very good depth. I do use the Ultimate 9" coil because it looks prettier on the machine LOL

 

[vlad]

There is a focal point on coils where the machines frequency ends. After that point the frequency will drop off causing phase shift location of targets to drop in particular the mid to high conductors while the low conductors such as iron drop less.
High frequencys respond stronger to low conductors and low freqencies respond stronger to high conductors. Quick reference is take a look at the selectable frequency machines such as the Multi Kruzer and with the standard vdi scaling a nickel at 5khz is around 22 and at 14 khz nickel is 29 and at 19khz it is 36. The high conductors have even more of a number spread as frequency drops off beyond the focal range of the coil. This explains why when you take a pass over a target and get a low number, dig it a hole and the number is higher. This is because ground mineralization id shortening the focal range of the coil and not directly dragging a number down as the ground is zeroed out when you ground balance. One of the things I do when I encounter areas that have black sand or areas rich in iron deposits I will not depend on the vdi and that holds true to all my vlf machines.
The theory of frequency dictating the depth of a machine isn't necessarily true but rather the coil design and how well it is balanced to the machines power. DD coils have narrow signal and eliptical dd's tend to handle poor grounds better than round DD's as they have less influence. Concentrics have their special purpose where targets are enveloped by the signal more so than top down. A concentric doesn't have the separation as a dd does but becuase it can mix targets signals can help unmask. When I say unmask it is more of discriminating the lower conductor and hearing the high conductor only.
Good example is using a concentric vs dd with Monte's nail board test. Numbers of a given high conductor with a nail above or on it will be lower and if the nail is too big or discrimination too high it will also discriminate out the high conductor depending how close the phase angles are to each other. Garretts and prospecting machines have a nice wide gamut on low conductors giving users a slight advantage when discriminating out iron. Example a cut nail will break at 4 on the Kruzers but 33 on an AT Pro. That higher resolution on iron range can give the user a sloppy break or crackle that they can pay attention to.
I have only used the 9x12 concentric on the AT Pro and found it to be on the heavy side and it didn't unmask nearly as well as my Tejon so I ended up selling it as the Tejon rules those particular hunting situations. Often thought of the 6x9 concentric but for my personal use thought it lacked the depth of the Tejon so wasn't worth it for me to buy one. If someone has one on their AT Pro it would be good to see how it handles silvers in and around iron.
As for Garrett coils I ran my frequency sensor on my Apex on the viper which had a raw air test depth of 10", Deeptech ultimate 9" at 11" and the Reaper 10x14 had depth of 14". That was air test to where the machines frequency didn't drop off. That doesn't mean the machines don't detect deeper just as they go deeper the accuracy drops off.
Performance of the Viper is really good, very good ground coverage, excellent separation and very good depth. I do use the Ultimate 9" coil because it looks prettier on the machine LOL

The thing about iron is it makes the coils field stronger and it actually goes deeper in a search near iron. And targets tend to up i.d. as they get to an extreme depth before falling into a iron i.d. When you get into
20kHz and above halves and dollars can be pushed all the way around into the iron range if the freq is not normalized (more than a few people have described discrimination a being a circle as opposed
to linear.) There is no perfect freq f0r high conductors either: maybe 2.75 kHz is perfect for a silver dime but I read in an article for a silver dollar it is higher: I think reactance is part of it, A nickel is 17 kHz. A coil is not balanced to the power it is matched to the resonance of the oscilliator frequency. The 3 things that dictate depth are frequency, coil, build quality/ resonance. The better the coil oscillator match the higher the efficiency (and not all TR;s are IBs.) Georgi Chausev hand wraps the best coils in the world, and throws 30% of them away: I wish I had one of his "no gos" and his VLFs are the deepest, yet on some fields they do not work well, fertilizer maybe and are not so good in wet salt (and he offers a number of frequencies. If you drop down to 1000 hertz there is no mineral reflection, but how do targets respond and how much battery power to fill the coil's Q? To keep the frequency constant a coil requires good build and quality capacitors, especially the Transmit tank capacitor. If the capacitance is stable over time then the loop frequency is also stable over time and the Receive signal phase is constant. I am not sure any one thing dictates the depth but the effect of frequency is not theory, it is application. As to Monti's nail board test try it with a Compass 77b Yukon at
100 kHz: it uses a concentric and will pick up through nails in a test, but real world is very limited. (you can stack small gold nuggets on it and get no response)
No matter the make or coil type you reach places that cannot be unmasked--go to NASA Tom's site and read.

​

 

[kac_dt]

Have just recieved my Viper coil for the AT Pro. Initial testing is it is about the same depth as the stock coil. Has better separation. Seems to handle ground mineralization better as it has a smaller foot print. Slightly less sensitive to tiny targets ie earrings. Can be a little more emi sensitive at least indoors. Outside it ran like a champ.
So with that being said it would be worth getting. Looking forward to using it in some the local swim holes.