Software-Defined Radio (SDR)#
Where the analog front end meets the digital back end.
Software-defined radio moves signal processing from analog hardware into software. Instead of fixed-function receivers with crystal filters and analog demodulators, an SDR digitizes a wide swath of spectrum and processes it computationally. This makes the radio flexible, reconfigurable, and — for learning — extraordinarily revealing.
SDR is both a practical technology and a powerful learning tool. It makes RF visible in ways that traditional test equipment doesn’t — entire bands become visible, signals can be demodulated in real time, and modulation and filtering experiments happen without building analog hardware.
What This Section Covers#
- What SDR Actually Replaces — The traditional receiver chain and which parts move into software, which stay in hardware, and what that tradeoff means.
- I/Q Signals & Quadrature — How two signals 90 degrees apart capture both amplitude and phase, enabling all modern digital radio processing.
- Sampling Theory at RF — Nyquist, bandpass sampling, quantization noise, and why the analog front end still determines what the ADC can usefully capture.
- Dynamic Range & Front-End Limits — Why the span between weakest and strongest signal matters, and how ADC resolution and analog filtering set the boundaries.
- Common SDR Architectures — From $20 RTL-SDR dongles to research-grade platforms, and how their hardware choices determine performance.
- Practical SDR Tools & Workflows — Software for receiving, demodulating, recording, and analyzing signals with an SDR.
- SDR as a Learning Instrument — Using SDR to make RF concepts visible, from modulation and filtering to antenna comparison and protocol decoding.