Nokta INV40 15.5" x 14" Waterproof DD Search Coil for Invenio Metal Detector

The Nokta INV40 is a 15.5" x 14" Double-D search coil built exclusively for the Nokta Invenio detector, designed to cover more ground per sweep while maintaining target separation in trashy sites. Invenio owners working open fields, large parks, or beach zones need the INV40's expanded footprint to reduce passes and reach deeper targets. The waterproof construction handles surf, streams, and wet sand without concern, and the included protective cover extends coil life during rocky-ground relic hunts.

What's Included with the Nokta INV40 Coil

• Nokta INV40 15.5" x 14" DD search coil for Invenio detector
• Protective coil cover
• Mounting hardware

Why Invenio Owners Reach for the INV40 Coil

• Wider sweep coverage reduces the number of passes required to search open fields, saving time on large sites and increasing efficiency during all-day hunts.
• Deeper target detection compared to smaller coils when working mineralized soil or hunting for large relics and caches in open ground.
• Double-D coil configuration delivers superior ground balancing in mineralized environments, maintaining stable operation where concentric coils struggle.
• Fully waterproof construction allows detecting in surf, shallow rivers, and wet fields without risk of damage to the coil electronics.
• Protective cover prevents abrasion damage from rocks and roots during relic hunts, extending the coil's working life. Compare the INV40 against the larger INV56 22" x 19" DD coil when you need maximum depth and coverage.

Expanded Ground Coverage in Open Relic Sites

The INV40's 15.5" x 14" footprint is the middle ground between maneuverability and coverage. Invenio operators working open fields, pastures, or large park zones gain a measurable reduction in the number of passes required to cover a target area. The DD configuration maintains target separation even in iron-contaminated sites, so the coil doesn't sacrifice discrimination for size. We run the INV40 on farm sites and Civil War camps where the ground is relatively clean and the goal is efficient coverage without missing deep targets.

Open Field and Pasture Relic Hunting

The INV40 excels in open ground where you want to cover acreage efficiently. The larger coil footprint means fewer overlapping sweeps, and the DD design keeps the detector stable in mineralized soil common to agricultural land. Depth advantage over smaller coils becomes evident on deeper relics and coin caches. The waterproof rating supports wet-field detecting after rain, when targets are easier to recover from softened ground.

• Best for: Open fields, pastures, large parks, beach zones where coverage speed matters and trash density is low to moderate.
• Less ideal for: Tight-space detecting around foundations or dense brush where the larger coil size limits maneuverability.

Beach and Shallow Water Detecting

The INV40's waterproof construction and size make it a strong choice for wet-sand and shallow-water beach hunting. The DD coil handles saltwater mineralization better than concentric designs, and the larger footprint covers more beach per pass. We use the INV40 on Gulf Coast beaches where the goal is efficient coverage of the surf line and wet sand during low tide. The protective cover is critical in this environment, as shells and coral fragments abrade unprotected coils quickly.

How it compares to other Invenio coils

The INV40 sits between the stock Invenio coil and the larger INV56 in the Nokta Invenio coil lineup. The table below compares the INV40 against the INV56 based on size, coverage, and intended use case.

Specifications

• Compatibility: Nokta Invenio only
• Coil Size: 15.5in x 14in (39cm x 36cm)
• Configuration: Double-D (DD)
• Waterproof Rating: Fully submersible
• Included Accessories: Protective coil cover, mounting hardware

Why Buy from Serious Detecting

Serious Detecting is an authorized Nokta dealer, which means every INV40 coil ships with the manufacturer warranty and direct support access. Our team runs Nokta Invenio detectors in the field, so we understand how coil selection affects performance in different environments. We offer free shipping on all orders, a 30-day return window, and price-match guarantee. If you're building out your Invenio setup, explore our full selection of metal detector search coils and learn about the technologies behind modern detectors to make informed coil decisions.