{"id":16058,"date":"2024-05-15T10:00:00","date_gmt":"2024-05-15T08:00:00","guid":{"rendered":"https:\/\/nolle.engineering\/2024\/05\/15\/loki-gnss-jamming-spoofing-l-band-helix\/"},"modified":"2026-07-28T11:30:37","modified_gmt":"2026-07-28T09:30:37","slug":"loki-gnss-jamming-spoofing-l-band-helix","status":"publish","type":"post","link":"https:\/\/nolle.engineering\/en\/2024\/05\/15\/loki-gnss-jamming-spoofing-l-band-helix\/","title":{"rendered":"LOKI: Controlled GNSS Jamming & Spoofing Trials"},"content":{"rendered":"

Global navigation satellite systems underpin position, navigation and timing (PNT) across virtually every modern platform – and that dependence has made GNSS jamming and spoofing one of the fastest-growing threats in electronic warfare. Evaluating how real equipment holds up against those attacks requires a controlled way to generate<\/em> them. This is exactly what the Spanish Naval Academy’s research centre set out to build – and our L-band helix antenna became the transmit element at the sharp end of it.<\/p>\n\n\n\n

\"Nolle
LOKI system developed by CUD-ENM. Reproduced with permission.<\/figcaption><\/figure>\n\n\n\n

LOKI: a transportable GNSS jamming & spoofing system<\/h2>\n\n\n\n

The Centro Universitario de la Defensa at the Escuela Naval Militar (CUD-ENM) developed LOKI<\/strong>, a system able to run jamming and synchronous spoofing attacks across multiple GNSS bands and constellations, faithfully counterfeiting GPS position and time. Its purpose is defensive: to catalogue how resilient the receivers and dependent systems aboard Navy vessels really are.<\/p>\n\n\n\n

Architecturally, LOKI is a transportable rack. Software written in Rust reads its scenario from a YAML file, pulls the live constellation geometry from a RINEX file, and synthesises a spoofed signal that reproduces propagation delay, Doppler and attenuation per satellite while cancelling the direct spoofer-to-victim path – updating the picture every 100 ms. Those samples feed an Ettus Research USRP N200<\/strong> SDR, disciplined to GPS time by a GPSDO<\/strong> so the spoofing can be synchronous. The RF output then passes through an L1-band (1575 MHz) power amplifier<\/strong> and out to the antenna.<\/p>\n\n\n\n

The transmit antenna: an L-band RHCP helix<\/h2>\n\n\n\n

The radiating element is our L-band helical antenna<\/strong>: right-hand circular polarisation (RHCP), a reinforced ground plane, roughly 15 dBi<\/strong> of directive gain, a relatively narrow beam and a very low back lobe. Two units were built and tuned to 1575.42 MHz<\/strong> (GPS L1), rated for 50 W CW. The RHCP match to the GPS signal, the directive-but-not-huge beam for pointing at a target from shore, and the weatherproof build are exactly what a field jamming\/spoofing setup needs.<\/p>\n\n\n\n

\"Two
LOKI system developed by CUD-ENM. Reproduced with permission.<\/figcaption><\/figure>\n\n\n\n

Field trials with the Spanish Navy<\/h2>\n\n\n\n

LOKI has taken part in the naval exercises NEMO-22, MARSEC-22\/23\/24 and MINEX-23\/24<\/strong> (plus GNEX-24), creating degraded-GNSS environments in which effective jamming and spoofing attacks were run against more than fifteen naval units and both own and coalition aircraft<\/strong>. Tellingly, some attacks affected not only the navigation receivers but other onboard systems that were never the direct target – which is precisely the kind of second-order vulnerability these trials exist to surface.<\/p>\n\n\n\n

\"The
LOKI system developed by CUD-ENM. Reproduced with permission.<\/figcaption><\/figure>\n\n\n\n

A concrete example: MINEX-24, Cabo Blanco (Mallorca)<\/h2>\n\n\n\n

In MINEX-24, LOKI was positioned near Cabo Blanco with the perturbation directed along a 135\u00b0 bearing while a victim ship ran a zig-zag coastal approach on GPS. As the ship passed between two waypoints about 3 nautical miles offshore, a three-minute jamming burst forced its GPS receiver out of tracking and back into acquisition; a spoofing attack immediately followed, counterfeiting a predefined location. Seconds later the ship’s GPS was showing a route deviation that simply was not happening.<\/p>\n\n\n\n

\"Two
LOKI system developed by CUD-ENM. Reproduced with permission.<\/figcaption><\/figure>\n\n\n\n

Why a helix<\/h2>\n\n\n\n

For this application the helix is a natural fit: its circular polarisation is inherently matched to the RHCP GPS signal, its directive pattern lets the operator point energy at a specific unit from a shore vantage point with little wasted in the back lobe, and the antenna is robust enough to live on a tripod in the field. The same antenna family is offered in different turn counts to trade beamwidth against gain, and each unit is tuned and measured before it ships.<\/p>\n\n\n\n

Credit & references<\/h2>\n\n\n\n

All field photographs on this page show the LOKI system developed by CUD-ENM<\/strong> and are reproduced with their permission. The technical description above is drawn from the team’s public communication:<\/p>\n\n\n\n