Welcome to the library

This is the "book" side of OpenHertz: an interconnected knowledge base on SDR and the HackRF, written to take you from "what is a wave?" all the way to "I detected a drone". Notes link to each other (click the highlighted links) and are welded to the missions: every concept has a button to go see it live.

Where to start?

1. The basics: Radio waves → Decibels (dB and dBm) → Noise floor, SNR and sensitivity
2. Going digital: Sampling, Nyquist and aliasing → I/Q samples
3. Seeing the signal: From I/Q to spectrum: the FFT → The waterfall (time cascade)
4. The hardware: What is an SDR? → The HackRF One → Antennas
5. Understanding signals: Modulation: writing information onto a wave
6. In the field: Using it live: the method → Interesting bands to explore → Detecting vs decoding → Legal & safety

Preparing for the amateur-radio exam? A dedicated track covers the whole syllabus (regulations, technical, propagation, operating): start with Preparing for the amateur-radio exam.

How does it work? Plug in your SDR (or stay on the simulator), open a mission, and come back to read the theory whenever a word escapes you. Practice and reading reinforce each other.

👉 Ready? Start with First contact