Software Defined Radio (SDR)
USB radio receivers and transmitters that turn your computer into a wideband radio scanner, protocol analyzer, or signal generator.
What is SDR?
Software Defined Radio replaces traditional hardware radio components (filters, mixers, amplifiers) with software running on a general-purpose computer. Instead of dedicated circuitry for each radio standard, an SDR digitizes the raw radio signal and lets software handle all the demodulation, decoding, and analysis.
RTL-SDR ($20-30)
A $20 USB TV tuner dongle based on the Realtek RTL2832U chip. Discovered in 2010 to be hackable for raw IQ sample output, it revolutionized the SDR hobby by making radio reception accessible to everyone.
- Receive range: 24 MHz - 1.766 GHz (with gaps)
- Bandwidth: Up to 2.4 MHz (3.2 MHz with direct sampling)
- ADC: 8-bit
- V3 features: TCXO oscillator, bias tee, HF direct sampling (0.5-1.7 MHz)
- Software: SDR#, GQRX, SDR++, CubicSDR, GNU Radio
HackRF One ($300-350)
Created by Michael Ossmann of Great Scott Gadgets. Half-duplex SDR that can both receive AND transmit across an enormous frequency range — the Swiss Army knife of radio hacking.
- Frequency range: 1 MHz - 6 GHz
- Bandwidth: Up to 20 MHz
- ADC/DAC: 8-bit
- Duplex: Half-duplex (transmit or receive, not both)
- Interfaces: USB 2.0, SMA antenna, GPIO pins
- Uses: WiFi/Bluetooth analysis, cellular research, GPS simulation, ISM band hacking, replay attacks
LimeSDR ($300-500)
- Frequency range: 100 kHz - 3.8 GHz
- Bandwidth: Up to 61.44 MHz
- ADC/DAC: 12-bit
- Duplex: Full-duplex 2x2 MIMO
- Interface: USB 3.0
- Uses: LTE/5G research, IoT development, beamforming experiments
BladeRF 2.0 micro ($480)
- Frequency range: 47 MHz - 6 GHz
- Bandwidth: Up to 56 MHz
- ADC/DAC: 12-bit
- FPGA: Altera Cyclone V with 85K logic elements
- Uses: LTE/5G, custom FPGA signal processing, defense research
SDR Comparison
Device Price Range BW ADC Duplex ────────────────────────────────────────────────────────────── RTL-SDR V3 $30 24 MHz-1.7 GHz 2.4 MHz 8-bit RX only HackRF One $300 1 MHz-6 GHz 20 MHz 8-bit Half LimeSDR USB $300 100 kHz-3.8 GHz 61 MHz 12-bit Full 2x2 BladeRF 2.0 $480 47 MHz-6 GHz 56 MHz 12-bit Full 2x2
SDR Software
- SDR# (Windows): Popular GUI with plugins for trunked radio, P25, DMR decoding
- SDR++ (Cross-platform): Lightweight, modular with spectrum display
- GQRX (Linux/Mac): Qt-based receiver using GNU Radio backend
- GNU Radio: Visual signal processing flowgraph editor — the powerhouse for custom radio apps
- Inspectrum: Signal analysis for examining captured IQ recordings
- Universal Radio Hacker: Protocol hacking — analyze, decode, and replay unknown protocols
What You Can Do with SDR
- ADS-B tracking: Receive aircraft position broadcasts at 1090 MHz — build your own flight tracker
- Weather satellites: Receive NOAA/Meteor satellite imagery directly from space at 137 MHz
- Trunked radio: Decode police, fire, EMS trunked systems (P25, DMR, TETRA)
- IoT sensors: Capture weather stations, tire pressure sensors, utility meters
- Cellular research: Analyze GSM, LTE, and 5G signals
- Replay attacks: Record and replay garage doors, key fobs, IoT devices
Legal Considerations
- Receiving is legal: In most countries, receiving radio signals is legal
- Transmitting is regulated: Transmitting on unlicensed frequencies is illegal in most jurisdictions
- ISM bands: 433 MHz, 915 MHz, 2.4 GHz allow limited power transmitting without a license