Radio-frequency (RF) drone detection

How it works

Most drones keep a continuous radio link with the controller. Pilot commands travel up (uplink); telemetry and video come down (downlink). These signals appear in characteristic frequency bands with characteristic modulation and timing.

An RF sensor monitors a wide slice of spectrum and compares what it receives with the "fingerprints" of known drone protocols. From this it determines whether a drone is present and, often, its type or protocol.

Direction and position. A multi-antenna sensor measures the direction a signal arrives from. With two or more sensors placed apart, the source can be located on a map by triangulation – or by measuring the time difference of arrival. That gives the drone's position and, if the controller is transmitting, an estimate of the pilot's position too.

Identification data. Some manufacturers' drones broadcast their own decodable ID packets, and most drones sold with an EU class label broadcast a standard Remote ID. These can reveal serial number, position, altitude and often the take-off point. Remote ID explained

Strengths

• Passive – doesn't transmit, so typically no spectrum licence and no giveaway
• Long range – over 3 km on open terrain with line of sight
• Type identification, often pilot location
• Low false alarm rate – birds and aircraft don't register as drones

Limitations

• Radio silence – a drone flying a pre-programmed route without a link is invisible to it.
• Fibre-optic control – such drones emit no radio signal at all.
• Crowded spectrum – in cities and at events the 2.4 and 5.8 GHz bands are full of Wi-Fi, reducing sensitivity and range.
• Unknown protocols – with custom builds, especially FPV, protocol libraries may not help; wideband energy detection and other sensors are needed.
• Line of sight – buildings, terrain and vegetation block signals.

Where it fits

The first layer of almost every counter-drone system. Portable for events, fixed for permanent sites, wearable for close protection. At permanent sites, combine with radar and cameras for a complete picture.

Legal note

Passive reception is generally licence-free, but decoded data – position, pilot location, identifiers – may be personal data. Define purpose, legal basis and retention in advance.