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Search coil guide

Guide · knowledge base

Search coils for metal detectors

The search coil is the heart of your detector. Which coil type suits which ground, which size for which search area, and when is a high-frequency or multi-frequency coil worthwhile? Here you will find well-founded answers – from 30 years of field experience.

4 Coil designs explained

3 Size classes

5 Manufacturers in detail

1Construction and function

Every search coil contains at least two windings inside: a transmit coil and a receive coil. The transmit coil (TX) generates an alternating electromagnetic field that penetrates the ground. When this field meets a metal object, the object responds with its own signal – and the receive coil (RX) picks it up.

TX sends the magnetic field into the ground

RX receives the echo from metal targets

Housing made of plastic protects the windings

Exactly how these two coils are arranged inside – side by side, overlapping or one inside the other – determines the coil type and therefore the detection field, the suitability for mineralised ground and the separation. That is what the next section is about.

2The most important coil types

There are four designs that matter in practice. Which one is right depends above all on ground mineralisation and the detector type (VLF or pulse induction).

Concentric

Concentric coil

The smaller receive coil (RX) sits inside the larger transmit coil (TX). Both share a common centre – hence the name.

Symmetrical, cone-shaped detection field – very good pinpointing

Less sensitive to external electrical interference

Struggles on heavily mineralised ground

Double-D · standard

Double-D coil (DD)

Two D-shaped coils of equal size face each other as mirror images and overlap slightly in the middle. Today the standard on most modern detectors.

Consistent, wide detection field down to depth

Very good depth even on mineralised ground

Somewhat more susceptible to external radio interference

Mono · PI

Mono coil (pulse induction)

A single winding that works alternately as transmitter and receiver. Used exclusively on pulse induction detectors such as the Nokta PulseDive or professional deep-seeking detectors.

Maximum depth – ideal for deep seeking and salt water

Practically unaffected by ground mineralisation

No real discrimination – all metals respond

SEF · depth

SEF / butterfly coil

A special form of the DD coil with a symmetrical electromagnetic field (SEF). The design produces a particularly even, deeper detection pattern – ideal as an upgrade coil for more depth.

About 15–25 % more depth than the standard coil

Very precise pinpointing despite the large footprint

Mainly available as an aftermarket coil for older detector models

3Magnetic field & detection pattern compared

Concentric and DD coils create completely different detection fields in the ground. This directly affects how you need to swing the coil – and where each design plays to its strengths.

Concentric – cone-shaped

The detection field runs down in a funnel shape. It narrows with depth – maximum depth lies directly below the centre of the coil. You need to overlap your swings to cover the full area.

Double-D – blade-shaped

The detection field is narrower, but just as wide at depth – like a vertical blade in the ground. You can move the coil in broad, wide swings and still cover the full depth evenly.

4Which coil size for which search area?

Bigger is not automatically better. Larger coils reach more depth and cover more ground per swing, but lose separation and sensitivity to small targets. Smaller coils are exactly the opposite – precise, but slower at covering ground.

6–9″

Small coils (15–23 cm)

High separation and sensitivity to small targets. Ideal for trashy sites, dense woodland with undergrowth, heavily mineralised ground and fine finds such as gold chains, bracteates or small jewellery parts. Less depth, but precise.

10–11″

Medium coils (25–28 cm)

The standard all-rounder. A good balance of depth, coverage and separation – perfect for fields, meadows, parks and general coin hunting. If you only want to own one coil, choose this size class.

13–15″+

Large coils (33–38 cm and more)

Maximum depth and large coverage per swing. Useful on open fields, for relic hunting and deep seeking. Downside: more weight, poorer separation in trashy areas, more susceptible to radio interference.

Field tip: The extra weight of a large coil is often underestimated. Several hours of searching with a 28 × 34 cm coil can cause shoulder and arm problems for inexperienced users – plan for this.

5Which coil for which ground?

A quick decision aid by search area. The recommendations are a rule of thumb – the actual choice always also depends on the detector model and your personal focus.

Fields & meadows

Medium to large DD coil (28 cm / 11″). Full depth on ploughed ground.

Woodland & undergrowth

Small or medium coil (22.5 cm / 9″). Easier to manoeuvre between roots and branches.

Freshwater beach

Medium waterproof DD coil. Multi-frequency such as FMF or Multi-IQ is an advantage here.

Salt-water beach

Small DD or elliptical because of mineralisation. Multi-frequency or PI is a must here.

Trashy sites

Small elliptical DD coil. Maximum separation between ferrous and non-ferrous.

Gold prospecting & natural gold

Small high-frequency coil (50+ kHz). Detects the finest nuggets and gold chains.

Relic hunting

Large DD coil for maximum depth on undisturbed ground. SEF/butterfly is an ideal upgrade.

Iron-infested settlement sites

High-frequency coil with high separation. Picks out the smallest coins between iron junk.

Deep seeking & ordnance

Very large DD or mono PI coil. Depth before separation.

6Search coils by manufacturer

In our shop we stock search coils for all common brand-name detectors. Here you will find an overview of the most important models per manufacturer – with direct links to each category.

XP offers three large coil families: the FMF coils (Fast Multi-Frequency) for DEUS II and ICON, the X35 coils with 35 frequencies for DEUS 1 and ORX, and the HF coils with frequencies up to 120 kHz for the highest sensitivity to small targets. All FMF coils are fully compatible between the DEUS II and the new XP ICON.

22.5 cm DD FMF – woodland, undergrowth, trashy areas · 345 g

28 cm DD FMF (standard) – all-round for fields, meadows, beach · 470 g

28 × 34 cm DD FMF depth – relic hunting, open land · 570 g

24 × 13 cm HF2 elliptical – up to 120 kHz, gold prospecting and tiny finds · 350 g

DEUS II FMF coils XP high frequency XP X35

Minelab consistently relies on Double-D coils. The Equinox series and the Manticore use Multi-IQ technology – meaning the coils transmit on several frequencies at once. The smaller coils are particularly popular for trashy areas and on the beach, the large ones for open land.

6″ Equinox 6″ DD – park, jewellery hunting, trashy areas

11″ Equinox 11″ / Manticore M11 DD – standard, all-round

15″ Equinox 15″ / Manticore M15 (15 × 12″) – depth, large areas

V8 / V10 / V12 Vanquish series – V8 for park and jewellery, V12 for depth

Equinox coils Manticore coils Vanquish coils

Nokta supplies purpose-designed coils for each detector model – mostly as double-D versions. The Legend is available with various coil sizes, from the compact 6-inch model to the deep 12-inch coil. The Score series uses the new LD coil system (LD28, LD21).

6″ Legend LG15 – small concentric coil for trashy areas

9″ Legend LG24 – woodland, compact search areas

11″ Legend LG28 – standard coil, all-round

12.5 × 9″ Legend LG30 – elliptical deep coil

All Nokta search coils

Golden Mask often combines detectors with the option of switching between different coils with different frequencies – for example 5, 15 or 30 kHz. This lets you adapt the detector flexibly to different ground conditions and expected finds.

Golden Mask coils

7Care & coil covers

In the field the search coil is exposed every day to knocks, mud, salt water and stones. A coil cover extends its life enormously – and is often decisive in warranty cases.

Why a coil cover is indispensable

A search coil consists of a plastic housing, a winding embedded in potting compound and a fine shielding layer inside. If the coil hits a stone with full force, the potting compound can chip – hairline cracks appear. Over time, moisture gets inside through these fine cracks. In the worst case, the coil fails completely.

Always keep the cover fitted – even in dry conditions, because a single hard knock can damage the potting compound.
Never glue it. The coil cover must remain removable – otherwise soil and moisture collect between the cover and the underside of the coil and disturb the signal.
After every beach or water session rinse the coil with clean, lukewarm water. Salt and sand are the worst enemies of the seal.
Wind the coil cable loosely around the shaft. Winding it too tightly leads to cable breakage at the coil connector in the long run.
Check the coil bolt regularly. Vibration loosens the mounting – a loose fit otherwise produces false signals.

To the coil covers

8Frequently asked questions about search coils

No. Coils are electronically matched to their detector – connector, frequency and signal processing only fit their own brand and series. An XP coil does not work on a Minelab, and even within one brand not all coils are cross-compatible. On the XP ICON, however, all DEUS II FMF coils can be used directly – that is the exception, not the rule.

Rule of thumb: per size step (for example from 22 to 28 cm) you gain 15–20 % depth on coin-sized objects in practice. On large targets such as Roman bronzes or iron fragments, the difference can be even greater. With very small targets (thin coins, gold chains) the smaller coil has the edge – it is the one that sees these objects at all.

It depends on the ground. On mildly mineralised, clean ground a concentric coil is a strong choice thanks to its symmetry and pinpoint accuracy. On mineralised ground, on beaches or near old settlements full of iron, the double-D coil is superior. In modern practice the DD design therefore dominates – almost all current detectors are supplied with DD coils.

Practically all modern search coils are waterproof or at least splash-proof. So you can submerge the coil itself in a stream, stream bed or at the water's edge. Important, however: the rest of the detector is only waterproof if the manufacturer explicitly says so (e.g. XP DEUS II coil and remote control to 20 m – the WSA ST and WS6 ST headphones are not waterproof; Minelab Equinox 900 to 5 m). Control unit, headphones and coil often have different specifications – always check the data sheet.

If you are just starting out, get to know the detector's standard coil first. This is usually a medium DD coil (about 11″ / 28 cm) – a solid all-rounder. A second coil (large for depth or small for trash) is only worthwhile once you want to work a specific search area where the standard coil reaches its limits.

High-frequency (HF) coils work with very high single frequencies (typically 30–80 kHz, on the XP HF2 even up to 120 kHz) and are therefore extremely sensitive to the smallest objects such as gold nuggets, thin coins or fine jewellery. Multi-frequency coils (FMF on XP, Multi-IQ on Minelab) transmit on several frequencies at once and therefore deliver more stable results in many ground conditions – but for hunting only the tiniest gold targets they are often less sensitive than a true HF coil.

Still not sure?

We are happy to advise you personally. With over 30 years of field experience as active detectorists, we know which coil suits your detector, your ground and your hunting area – without sales pressure.

Request free advice

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