Nokta INV28 11x7 DD Waterproof Coil for Invenio Metal Detector

The Double-D configuration in the INV28 coil uses two overlapping D-shaped windings that create a narrow detection field along the centerline, allowing the coil to isolate adjacent targets more effectively than concentric coils. In trashy sites where iron nails, pull-tabs, and foil cluster within a few inches, the DD field pattern reads each target separately rather than blending them into a single reject tone. This geometry also cancels ground mineralization more effectively, reducing false signals in saltwater sand and red clay soil. The DD design excels in mineralized soil and provides superior target separation, making it ideal for parks, beaches, and relic hunting sites with moderate trash levels. For more on how different coil technologies handle ground conditions, see our guide to metal detector technologies.

The Nokta INV28 coil is compatible with Nokta Invenio metal detectors. The coil uses a connector and mounting system specific to the Invenio platform, so it will not fit other Nokta models like the Simplex, Legend, or Anfibio series. Direct-fit mounting requires no adapters or balance modifications. If you're exploring the full Nokta Invenio & Invenio Pro - 3D imaging metal detector system, this coil integrates seamlessly with the detector platform.

The INV28 coil measures 11 inches by 7 inches in an elliptical footprint, or 28 centimeters by 18 centimeters in metric units. The coil's elliptical shape provides wider ground coverage than round coils of similar length while maintaining maneuverability in tight spaces like between fence posts or under playground equipment. The Double-D configuration enhances target separation in trashy areas and improves ground-noise cancellation in mineralized soil. Weight specifications are not published by Nokta. The included coil cover and mounting hardware ship with every unit.

The INV28 coil is fully waterproof, including both the coil housing and the cable connection to the detector control box. You can submerge the coil in shallow water, sweep through surf zones, and hunt in heavy rain without performance degradation or water ingress. Note that while the waterproof construction allows detecting in wet sand, freshwater shores, and saltwater beaches, the Invenio control box itself has separate environmental specifications you should verify before fully submerging the entire system

The INV28 coil requires no adapters, balance modifications, or hardware changes to mount on the Nokta Invenio detector. The coil offers direct replacement compatibility with Nokta Invenio metal detectors, so installation is a straightforward swap that takes under two minutes in the field. Remove the lower shaft bolt, slide off the stock coil, slide on the INV28, and retighten the bolt to the same torque. All necessary mounting hardware is included with the coil package.

The 11x7 elliptical size excels in open fields, beaches, and large parks where ground coverage speed matters, and in moderately trashy sites where you need separation without sacrificing sweep width. The larger elliptical footprint covers more ground per sweep than smaller coils, cutting search time in low-trash environments like plowed fields and dry sand beaches. The narrower 7-inch width maintains maneuverability around obstacles like playground posts and between row crops. For extremely trashy urban sites with dense iron, a smaller coil may separate targets better. The 11x7 strikes the middle ground for detectorists who hunt varied terrain and want one versatile coil that balances ground coverage with target separation.

Depth performance on the INV28 coil depends on target size, soil mineralization, and the Invenio's sensitivity settings. The DD configuration provides better target separation and ground-noise cancellation compared to concentric coils, which is particularly valuable in mineralized soil conditions. In heavily mineralized red clay or black sand, the INV28 maintains stable operation where other coils may chatter, delivering consistent performance across challenging ground conditions. The 11x7 elliptical size offers enhanced detection efficiency by covering more ground per sweep while maintaining the superior target separation that DD coils are known for in trashy and mineralized environments.

The included coil cover is a hard plastic skid plate that protects the INV28's bottom housing from rocks, roots, gravel, and abrasive surfaces like shell-packed beaches and rocky creek beds. The cover extends the coil's cosmetic and structural lifespan by absorbing the wear from ground contact during detecting sessions. The cover does not add waterproofing, the coil is already fully waterproof, but it does shield the coil housing from scratches and impacts that occur when sweeping across rough terrain. Replace the cover when it shows deep gouges or cracks; replacement covers are available separately from Nokta dealers.

Yes, the INV28 coil handles saltwater surf zones effectively due to its fully waterproof construction and DD coil geometry that cancels saltwater ground noise. The Double-D field pattern rejects the mineralization signal from wet saltwater sand, allowing stable tone response across the wet-to-dry sand transition line where concentric coils often false. The waterproof design allows you to sweep from dry sand into shallow water without performance degradation. Rinse the coil and cable with fresh water after each saltwater hunt to prevent salt buildup on the connector and maintain long-term reliability.

The Nokta INV28 coil ships with the manufacturer warranty covering defects in materials and workmanship; verify the exact warranty duration on your warranty card or with Nokta directly at the time of purchase. The coil includes a protective coil cover and all necessary mounting hardware in the package. As with all Nokta accessories designed for the Invenio platform, the INV28 offers direct replacement compatibility without requiring adapters or modifications. Contact the manufacturer or your authorized dealer for specific warranty terms and coverage details applicable to your purchase.