Software-defined radio (SDR) is a radio system that moves functions such as tuning, modulation, filtering, and demodulation from fixed hardware into software. Instead of relying on one purpose-built circuit, an SDR platform captures raw radio samples, often as I/Q data, and lets software interpret or generate signals. This makes a device far more flexible than a traditional radio.
In cyber security, SDR matters because many wireless systems are just software and signal rules sitting on top of radio waves. Attackers can use SDR hardware to sniff unencrypted traffic, replay or spoof transmissions, probe IoT devices, or study protocols for weaknesses. Defenders use SDR to monitor spectrum activity, test wireless resilience, validate protocol behavior, and research interference or jamming. A router or cheap dongle can sometimes be repurposed into an SDR lab tool, which is why the technology sits at the boundary between consumer gear, experimentation, and offensive or defensive wireless analysis.