RF and SDR Fundamentals

Radio Frequency (RF) is the invisible attack surface that surrounds every modern environment. Key fobs, garage doors, building access cards, wireless sensors, drones, medical telemetry, and IoT devices all transmit over the air.

Unlike a network cable, RF cannot be physically contained. Anyone with a receiver in range can listen, and many systems were designed before security was a priority.

• Many RF protocols send data in cleartext.
• Replay protection is frequently absent or weak.
• Legacy industrial and access-control gear is rarely patched.

As a practitioner, understanding RF lets you assess risks that traditional network tooling completely misses.

A radio signal is an electromagnetic wave described by three core properties:

• Frequency — cycles per second, measured in Hertz (Hz). Common targets sit at 315 MHz, 433 MHz, 868 MHz, 915 MHz, 2.4 GHz.
• Amplitude — the strength or height of the wave.
• Phase — the timing offset of the wave relative to a reference.

Modulation encodes data by varying one of these properties. Demodulation reverses the process to recover the original bits.

Recognizing how a target modulates data is the first step in capturing and interpreting its transmissions.