The search coil is the part of a metal detector that sends the signal into the ground and listens for what comes back. Swap the coil and the same detector behaves differently: deeper, more precise, steadier in bad ground, or easier to swing all day. This guide covers the three things that decide how a coil behaves (size, shape and winding), then points you to the coil that fits how you hunt.
Key Takeaways
- Size trades depth and ground coverage against sensitivity to small targets and separation in trash.
- Shape decides how the coil handles: round for an even field, elliptical for tight spots and rough ground.
- Configuration (Concentric, Double-D or Monoloop) decides how the coil copes with mineralized ground and how it pinpoints.
- The stock coil is a good all-rounder. A second coil earns its place when your site is very trashy, very open or very mineralized.
- Coils are built for specific detectors. Always check compatibility before you order.
Coil Sizes
Coil size has a direct effect on detection depth and target sensitivity. A larger coil throws a bigger, deeper field. A smaller coil throws a tighter one that picks out small targets and sees less of the junk around them.
The diagram shows the trade. The large coil on the left reaches the deep box and covers more ground with every sweep.
The small coil on the right gives up that reach, but its narrow field is concentrated near the surface, which is where small targets and crowded sites are won.
Small (under 8 in)
Very sensitive to small targets like fine jewelry and small nuggets. Light on the arm, and the small footprint isolates good targets among junk in trash-filled sites. Shallower on larger targets and slower to cover ground.
Standard (9 to 11 in)
The size most detectors ship with. A balance of depth, coverage and separation that suits general coin and relic hunting. If you only own one coil, this is the one.
Large (12 in and up)
Deepest on medium and large targets such as relics and caches, and covers open ground fastest. Heavier, less sensitive to tiny targets, and harder to work in tight or trashy areas.
Depth is never the coil alone. Ground, target and settings all move the number, and we cover the realistic figures in how deep metal detectors go.
Bigger is not automatically better. In an old park full of pull tabs and nails, a large coil sees several targets at once and blends them into one confused signal. Dropping to a small coil on the same ground often turns up coins the big coil walked straight over.
Coil Shapes and Build
The shape of a coil influences its coverage and how it handles specific terrain. Build is a separate choice: the same shape can come as an open frame or a solid body.
Coil Configurations
The coil configuration is the pattern the wire is wound in inside the housing, and it shapes the search field. The three most common are Concentric, Double-D (DD) and Monoloop.
The red lines above trace where the wire runs in two Garrett coils. On the left, circular windings sit one inside another, a transmit winding (TX) and receive windings (RX). On the right, two D-shaped windings overlap down the center of a DD coil.
Concentric Coil
Concentric coils use two circular windings, an outer transmit winding and an inner receive winding, creating a cone-shaped search pattern.
- Excellent for pinpointing targets with precision.
- Ideal for moderate ground conditions with low mineralization.
- Requires tighter sweep overlap for complete coverage, because the cone narrows with depth.
- Can become unstable or noisy in highly mineralized soil.
Double-D (DD) Coil
The Double-D coil has two overlapping D-shaped windings, giving a blade-like search field that runs the length of the coil.
- Superior ground coverage and stability in mineralized or salty soils.
- Maintains good depth and sensitivity.
- Less affected by electrical interference, and performs well on wet sand.
- On Minelab GPX detectors, DD coils allow Iron Reject to separate ferrous from non-ferrous targets.
Monoloop Coil
Monoloop coils are designed for Pulse Induction (PI) detectors such as the Minelab SD, GP and GPX series.
- A single winding acts as both transmitter and receiver, producing a deep, cone-shaped field.
- Offers superior depth over DD coils in many conditions, though it needs more careful ground balancing in highly mineralized soil.
- Ideal for gold prospecting in remote areas where depth matters more than discrimination.
Choosing the Right Coil for Your Hunt
Your ideal coil depends on your detector, your targets and your ground. Start from where you hunt most:
Recommended Coils
If the stock coil is your only coil, these are the upgrades that change a hunt the most. Each one fits specific detectors, so match the coil to your model first.
For Trash and Tight Spots
Minelab EQX 06
A 6 in round DD coil for the Equinox 700, Equinox 900 and X-Terra Pro. The pick for iron-infested sites and picnic groves where good targets sit inches from junk.
See the EQX 06Minelab M8
An 8 x 5.5 in elliptical DD coil for the Manticore. Small enough to separate targets in trash, long enough to still cover ground.
See the M8Garrett Viper
A 6 x 11 in DD coil for the ACE Apex. The narrow profile works between rocks and roots and along fence lines.
See the ViperFor Depth and Open Ground
Coiltek NOX 15
A 15 in round DD coil for the Minelab Equinox series and X-Terra Pro. Built for open fields and beaches where coverage and reach matter most.
See the NOX 15Nokta SX35
A 13.5 x 12.5 in waterproof DD coil for the Simplex series and FindX Pro. A simple way to add depth and coverage to a starter detector.
See the SX35Garrett Reaper
A 14 x 11 in DD coil for the ACE Apex. More ground per sweep and more depth on coin-sized and larger targets.
See the ReaperHunting with a different detector? Browse all search coils by brand, or see aftermarket options from Coiltek, CORS, Detech and MarsMD.
Before You Buy a Second Coil
Check compatibility by model, not by brand. A coil is tuned to the detector's electronics and connector. Two detectors from the same brand often cannot share a coil, so confirm your exact model on the coil's product page.
Add a coil cover. A cover takes the scrapes from rocks and stubble so the coil does not have to. Coil covers cost far less than a replacement coil.
Ground balance again after every swap. A different coil reads the ground differently. Rebalance and run a noise cancel before you start, then recheck your sensitivity.
Plan for the weight. A large coil moves the balance point toward the ground and you feel it after an hour. Shorten the shaft slightly and keep your sweeps low and level.
Many hunters end up with two coils and a spare lower shaft for each, so a swap in the field takes a minute instead of ten. Carry the small coil for the trashy corner of a site and the large one for the open ground around it.
Shop at Serious Detecting
Authorized U.S. dealer, free shipping on most orders over $99. Or call (844) 771-0707 and tell us your detector and your ground. We will tell you which coil fits.
Jump to a coil type: Round · Elliptical · Semi-Elliptical · Open Frame · Solid Body · Wireless
Concentric vs. DD vs. Monoloop at a Glance
| Concentric | Double-D (DD) | Monoloop | |
| Windings | Two circular windings, one inside the other | Two overlapping D-shaped windings | A single winding that transmits and receives |
| Search field | Cone-shaped | Blade-like, along the length of the coil | Deep and cone-shaped |
| Mineralized ground and salt | Can become unstable or noisy | Stable, including on wet sand | Deep, but needs careful ground balancing |
| Sweep overlap | Tighter overlap needed | Best ground coverage per sweep | Tighter overlap needed |
| Best for | Precise pinpointing in mild ground | Coins, relics and beaches in most ground | Gold prospecting with a PI detector |
About the Author
Evan K is a detectorist who hunts Great Lakes swim beaches, rivers and surf, and writes detector buying guides for Serious Detecting, an authorized dealer for Minelab, XP, Nokta, Garrett and Fisher. The team answers the phone at (844) 771-0707 and would rather talk you into the right detector than sell you the wrong one.