What Is SIGINT?

SIGINT is short for signals intelligence: intelligence produced by intercepting signals and working out what they reveal. The signals can be voice calls, radio messages and data traffic, or emissions from radars, weapons and telemetry links. Even when a message is encrypted, who is transmitting, from where, how often and on what equipment can be valuable on its own.

SIGINT is one of the oldest technical intelligence disciplines. Radio intercept shaped naval operations in the First World War, and the codebreaking at Bletchley Park in the Second World War is its best-known example. Today the national SIGINT agencies are GCHQ in the UK and the National Security Agency (NSA) in the US, working with military SIGINT teams and with allies.

SIGINT is divided by the kind of signal collected. The split matters because each type uses different receivers, analysis and expertise.

Every SIGINT system follows the same broad cycle. Antennas and receivers collect signals across a wide band of frequencies. Modern systems use software-defined radios (SDRs), which digitise a slice of spectrum so that software rather than fixed hardware does the tuning and demodulation.

The raw samples are then processed: split into channels, detected, demodulated and, where possible, decoded. Analysts and software analyse the results to identify emitters, map networks and build a picture over time, and the findings are reported to the commanders or agencies who asked for them.

Processing is where computing load has grown fastest. A wideband SDR can produce hundreds of megabytes of samples a second, so signal detection and classification increasingly run on GPUs and FPGAs close to the antenna. Machine learning is used to recognise modulation types and emitters automatically, which lets a small team watch far more spectrum than it could by hand.

Intelligence agencies group collection into disciplines, often called the INTs. SIGINT is one of five main ones, and most assessments combine several.

SIGINT is close to, but distinct from, electronic warfare. Electronic support measures in a warship or aircraft use similar receivers to detect threats in real time for immediate action, while SIGINT gathers and analyses signals to build longer-term intelligence.

SIGINT needs receivers within range of the signal, so it is collected from almost every kind of vehicle and site. Aircraft such as the RAF’s RC-135W Airseeker fly long patrols with large receiver suites. Warships and dedicated intelligence ships listen at sea, satellites cover large areas from orbit, and ground stations and deployable vehicle systems cover land borders and operations. Small SIGINT payloads are now common on drones, where size, weight and power limit what can be carried.

The same techniques are used outside the military, under different rules. Spectrum regulators such as Ofcom monitor the airwaves for interference and illegal transmitters. Police and agencies carry out lawful interception under national law, which in the UK is the Investigatory Powers Act 2016. Airports, prisons and event security use RF detection to spot drones by their control and video links.

Whatever the application, the hardware challenge is the same: take a fast stream of radio samples and process it in real time, often in a vehicle, on a mast or in an aircraft. That calls for rugged GPU computers with PCIe slots for SDR and FPGA cards, or compact Jetson AGX Orin computers where power is tight, and edge AI servers in ground stations and shelters. Running the classification locally is a form of edge AI processing, which keeps the raw data on site and sends only the results over the link.

We supply rugged GPU and edge AI computers for signal processing configured and tested as standard, with SDR, FPGA and network cards fitted to your specification. Send us your bandwidth, channel count and installation, and we will specify the system to match.