Metal detectors usually come with one coil, essentially a mid-range diameter, “all-purpose” size of about 8 inches in diameter. There are good reasons to get yourself another coil or two with different diameters to level up your metal detecting game.
Are different size metal detector coils worth getting? Yes. Even though the one that came with your detector was designed to cover the most typical detecting situations, both bigger and smaller diameter coils expand the capability of your machine. Coil “shape” makes a difference too!
How do these coil variants make a difference? What special situations do they help with? Are they easy to install and remove? Let’s explore the answers to those and more.
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Overview of How Metal Detector Coils Work
The coil, a key component of metal detecting equipment, is both a transmitter and a receiver. As a transmitter, the coil emits a magnetic field toward the ground. Technically it’s not sent completely downward, but the ground is the direction we’re interested in for metal detecting
. When the transmitted field passes over a metal object, a return signal reflects back to your coil and is translated into an electrical signal that goes to the control box. The control box circuitry uses the signal to set off the familiar alert tones.
The coil’s design parameters (internal wires, size, and shape) dictate the properties of the transmitted magnetic field, as well as those of the received signal. Smaller coils produce a more concentrated magnetic field and detect in a more pinpointed fashion. Larger coils tend to find targets that are deeper because they produce a magnetic flux density similar to smaller coils but at a greater distance into the ground.
Shape plays an important part. The familiar circular coil is standard on a large number of metal detectors because they’re more cost-effective to build and offer stable performance in many environments. There are good reasons to design and produce other coil shapes, though.
For example, coils with an elliptical shape (like some concentric coils and “double D” coils) make searching in and around tight spaces between rocks or bushes a lot easier. Double D coils also have an open space between coil compartments which makes the coil lighter. This saves your arm and wrist from getting tired as you swing the coil back and forth. Coils with open spaces are also useful if you’re searching in water. The open space provides less drag while moving the coil.
The Different Types of Metal Detector Coils
The “Stock” Concentric Coil
The coil that came with your metal detector is very likely to be a round (concentric) coil. This design emits a uniform cone-shaped (or snowcone-shaped) field that makes searching in any direction very efficient.
Generally, concentric coils are 8 or 9 inches in diameter and are all-purpose coils, great for hunting in lawns, parks, at the beach, fields, etc. This coil is referred to as concentric because it has two sets of coils, one inside the other. The transmit coil is on the outer circle and the receive coil is on the inner circle. This results in a nice, symmetrical search field.
Larger Coils
Larger coils are best suited for low-trash and low-mineralization areas. In high-trash spots, larger coils will pick up many targets. This mix of trash and interesting items means you could miss something good. If the first few things you find and unearth are just junk, you may move on without actually finding the good stuff from that location. Be patient and spend a little more time there.
With a larger diameter, you can cover more ground. That’s a plus when you’re hunting over big areas. Something to keep in mind, though, is the extra weight of a large coil. Swinging a heavier coil to cover large areas can be tiring over a day of detecting.
Since a search coil is technically an antenna, Electro Magnetic Interference (EMI) is more of a factor for the larger coil. More remote, open areas are less likely to have EMI from power lines. etc.
Smaller Coils
Small coils are usually about 4 inches in diameter and are preferable in high trash areas. Another plus to a small coil is that they fit in confined areas. They’re also less likely to be impacted by EMI. For gold prospecting, they’re good for nuggets IF they’re close to the surface.
They’re lighter, which is also a plus, but using them in large areas like fields or parks will add significant time to your search. It’s like the difference between filling in a square with a fine point marker versus a wide tip marker.
A smaller diameter coil provides less depth penetration than a larger diameter coil.
Shape Makes a Difference
Concentric coils have wires wound in both an inner circle and outer circle. The inner circle is usually the receive coil and the outer circle is the transmit coil. The outer coil being the transmitter gives you the widest possible search area. This design produces a cone-shaped pattern.
Double-D coils have separate D-shaped transmit and receive coils that face in opposite directions. This arrangement gives you more of a knife-edge pattern into the ground from the center of the coil. The larger open part of each D actually produces a negative transmission which helps it to be more stable over mineralized ground.
Butterfly coils are similar to the Double D coil and the butterfly design provides stability, better ground balancing, excellent target identification, and even a great degree of pinpointing capability
Monoloop coils are designed for Pulse Induction (PI) detectors, and have just a single winding of wire around the circumference of the coil. This single wire acts as both the transmitter and receiver. As with a concentric coil, the pattern emitted is cone-shaped. Surprisingly, the monoloop coil can provide greater depth than a double-D coil. However, it’s not as good in heavily mineralized soil as the double-D.
An interesting feature of the monoloop is its high sensitivity at the rim. This comes in handy for using the edge to pinpoint targets that are not very deep.
Two Lesser-known Coil Types
2-Box Coils
The 2-box metal detector uses a special search coil for deeper searching compared to a normal VLF machine. The sensitivity, precision, and power of this coil makes it superior to normal VLF machines. The transmit and receive coils are separated by several feet (yes, feet) which effectively provides you with a 3 to 4 foot search diameter. It’s designed for deeply buried items like relics or caches. It does tend to ignore smaller items about 3 inches in diameter, though.
Imaging Coils
This is an advanced version of a concentric coil. It’s basically a concentric coil with a second receive coil. The advantage provided is additional target information such as sizing and depth. This type of coil is not widely available. If you want to see the amazing things they can do (warning, very expensive), here’s some great information.
Interesting BONUS Technology – 3D Geo System – Here’s a newer technology that allowed this guy to find something interesting (no spoilers, you have to watch) buried 1.4 meters deep! To see more details on Amazon, go here.
Changing Your Metal Detector Coil
Whether you’re changing coils due to damage or to upgrade, do a little research. You need to match your new coil to your detector. Most metal detectors work with coils from the same manufacturer. That said, metal detectors may operate on many different frequencies. This means you have more chance of matching your detector to a new, but different, coil. Just be sure to check compatibility.
Other than that, you basically disconnect the coil from the control box and also unfasten it from the end of the wand. Remove and replace. Make sure to check any instructions for your detector and/or new coil in case there are any settings to change.
What’s the Best Metal Detector Coil Size to Use?
When engineers design metal detectors, they generally strike an optimized balance for a wide range of targets. The out-of-the-box coil sensitivity and control box electronics are a well match-matched tradeoff.
The best coil to use is the stock coil it came with…. for a long while. Once you learn to use your detector and understand what it’s telling you in terms of finds, you’re ready to branch out. Here’s the caveat… you need to know why you’re changing coils. What’s the reason? If you don’t understand that, you’re probably wasting time and money.
Larger coils have one real advantage and that is ground coverage. Larger open areas can be scanned faster with a larger coil. However, the additional depth you get from a larger coil is marginal and a larger coil can easily mask out some smaller valuable targets.
Smaller coils are probably the way to go if you’re trying something new. Why? Because they are more localized with better pinpointing capability. You can also move easier between and around obstacles. Plus the coil isn’t sensing a large area, so smaller items will be more easily detected.
Re-Tuning Your Detector with a New Coil
Not to worry, modern detectors don’t need that. I did a good bit of research and they’re designed to have coil changes on the same detector.
However, if in doubt check your manual for specific instructions about changing coils. You may have nothing to do, you may have to reset your detector, etc.
Overview of Metal Detector Coil Sizes
| Concentric Coil | Monoloop Coil | Small Coil | Large Coil | Double-D Coil |
|---|---|---|---|---|
| Good for broadest range of targets | Coil edge is handy for pinpointing | Less sensitive than larger coils | Deeper ground penetration than smaller diameter coils | Superior performance in highly mineralized ground |
| Generally comes on most low to mid range detectors | One coil transmits and receives | Better at pinpointing due to smaller diameter pattern | Good for caches, relics, and small pieces of gold | Good for relics and gold prospecting |
| Inner coil receives, outer coil transmits | Built for Pulse Induction (PI) detectors | Better for trashy areas | More sensitive to smaller items and EMI | Though larger, the open spaces help reduce weight |
| Great in tight spots and for shallow targets | Large diameter not the best for heavy-trash areas |
If you want to change up your game, try researching a different type of coil, and re-hunt areas you’ve previously hunted out. You’ll be quite surprised that a different coil finds something… I saw that happen for a guy on a Facebook Group recently!
Keep track of your treasure finds! Here’s a handy logbook on Amazon that you can use
Wrap Up and Visualization
This short video from Garrett will further help you visualize differences between coils:
Here are some of my favorite metal detecting tools and accessories:
Even if you’re only using your phone metal detecting app, you still need some basic tools and accessories to dig up what you found. These are affiliate links, so if you do decide to purchase any of them, I’ll earn a small commission. These are the basic tools I would recommend to anyone who’s interested in the hobby.
Sand Scoop – if you’re doing any beach metal detecting, you need a sand scoop! It’s way better than a shovel and you can find well-built models with a handle or without one. A sand sccop with a long handle is often referred to as a sand scoop shovel.
Pinpointer – Pinpointers will help you home in quickly on target materials that your big detector alerts on. It’s a no-brainer accessory for metal detecting and can be used not only on dry land but most are either partially or fully submersible.
Upgrading from your phone metal detecting app? Here’s a “can’t miss” metal detector choice – I like this model especially because it’s good on land and at the beach, is feature-packed, all from a well-known and respected brand.
