GNU Radio Primer

This instructional write-up demonstrates how to use GNU Radio Companion with a HackRF to detect, capture, and replay a 315 MHz car key fob signal by building flowgraphs with osmocom source/sink, FFT visualization, and file-based capture/replay, along with tips like Max Hold and guidance on when to use a Throttle block. It highlights that modern rolling/hopping codes prevent successful replay attacks despite signal capture, framing the work as an educational exploration of SDR, RF analysis, and replay concepts rather than a report of a specific cyber incident.