Techzone/SDR - Software Defined Radio

SDR - Software Defined Radio

2 min readArticle

Software Defined Radio replaces traditional hardware radio components (mixers, filters, amplifiers, demodulators) with software running on a general-purpose computer. Instead of dedicated chips for every frequency/protocol, you just need a cheap USB dongle and the right software.

Why It Matters for Security

SDR lets you passively monitor and analyze radio signals that are everywhere around you — RF remotes, wireless sensors, pagers, ADS-B aircraft transponders, GSM/LTE bands, baby monitors, tire pressure sensors, and more. Also useful for active attacks with the right hardware.

Common Hardware

Device Price TX Capable Notes
RTL-SDR v3 ~$30 No (RX only) Best starting point
HackRF One ~$300 Yes (1 MHz - 6 GHz) The serious tool
LimeSDR ~$300 Yes Very wide range
ADALM-PLUTO ~$200 Yes Good for learning
Flipper Zero ~$170 Yes (limited) Sub-GHz + NFC + IR

Essential Software

bash 
# Install GNU Radio
sudo apt install gnuradio

# Install GQRX (GUI SDR receiver)
sudo apt install gqrx-sdr

# Install SDR# (Windows, WINE on Linux)
# Download from airspy.com

# RTL-SDR tools
sudo apt install rtl-sdr
rtl_test   # Test your dongle
rtl_sdr    # Raw sample capture

Quick Start with RTL-SDR

bash 
# Test device detection
rtl_test -t

# Tune to FM radio (proof of concept)
rtl_fm -f 98.1M -M wbfm -s 200000 -r 44100 - | aplay -r 44100 -f S16_LE

# Capture raw IQ samples
rtl_sdr -f 433.92e6 -s 2e6 capture.iq

# Run GQRX for visual analysis
gqrx

Common Frequencies to Monitor

  • 433.92 MHz - Wireless keyfobs, sensors, temperature gauges
  • 315 MHz - Older US keyfobs, garage door openers
  • 868 MHz - EU IoT, smart meters
  • 1090 MHz - ADS-B aircraft transponders
  • 406 MHz - EPIRB emergency beacons
  • GSM bands - 850/900/1800/1900 MHz

Attack Use Cases

  • Replay attacks on fixed-code RF remotes (garage doors, key fobs)
  • Eavesdrop on unencrypted pager traffic
  • Track aircraft with ADS-B dump
  • Analyze smart meter/utility transmissions
  • RF fingerprinting of IoT devices

Useful Tools

bash 
# Decode 433MHz signals
sudo apt install rtl_433
rtl_433 -f 433.92M

# ADS-B aircraft tracking
sudo apt install dump1090-fa
dump1090 --interactive

# Decode pager messages
sudo apt install multimon-ng
rtl_fm -f 152.24M -s 22050 | multimon-ng -t raw -a POCSAG512 -

See Also

  • hackrf-sdr-attack-tool - HackRF One hardware details
  • rfid-nfc-tools - Related close-range RF attacks
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