SDR Direction Finder (RTL-SDR)

SDR Direction Finder turns your Android phone and an RTL-SDR dongle into a precision VHF telemetry receiver and direction finder, purpose-built for weak signal detection across the full RTL-SDR frequency range with wildlife tracking in mind.

Whether you are a field researcher tracking tagged animals, a falconer monitoring transmitter collars, a ham radio operator hunting hidden transmitters, or an RTL-SDR enthusiast pushing sensitivity limits, SDR Direction Finder delivers narrow-band DSP filtering, a live waterfall display, and a full GPS bearing map in a package that fits in your pocket.

PURPOSE-BUILT SIGNAL PROCESSING

Multiple demodulation modes: CW (default for wildlife tracking), AM, FM, FM-B (wideband FM broadcast with Mono and Stereo options), LSB, USB

Four selectable filter modes deliver real, measurable SNR improvements:

• Wide - general scanning and unknown frequencies
• Standard - SNR improvement, real detection range increase for CW/LSB/USB
• Narrow - Further SNR improvement for precisely known frequencies
• Extreme - Maximum filtering for precisely-tuned CW frequencies

PULSE-COHERENT DETECTION

Coherently combines multiple beacon pulses over time to pull signals out of the noise floor. Calibrate once per beacon, then let the detector integrate 4 to 64 pulses for real SNR gain. SNR and lock status displayed on screen.

BEARING MAP - DIRECTION FINDING ON THE GO

• GPS overlay with live compass cone showing your heading
• Log compass bearings from multiple positions with one tap
• Automatic intersection calculation estimates the signal source location
• POI markers for receiver positions and landmarks
• Street, Satellite, and Terrain map tiles
• Offline map download for remote fieldwork
• KMZ/KML file support for existing survey data
• Scale bar, zoom controls, track recording, and screen lock
• Import/Export saved bearings, POIs, and tracks to transfer between multiple devices or to open in Google Earth, QGIS, Excel, R, Python or any other tool that handles tabular data.

BIAS-TEE LNA POWER CONTROL

For RTL-SDR V3 and V4 dongles, the built-in software-controlled bias-tee sends 4.5V down the coax to power a masthead LNA directly from the app, with no separate power cable needed.

LIVE WATERFALL DISPLAY

See signals visually even before they’re audible. Pinch-to-zoom spans from ±50 kHz to ±1 MHz. Full-screen landscape mode with live spectrum overlay. Drag-to-tune directly on the waterfall. Choose between Orange and Deep Blue colour schemes.

FIELD-OPTIMISED WORKFLOW

• Frequency presets for each tagged animal
• Configurable scan period for hands-free frequency cycling
• Physical volume buttons control receiver gain for one-handed field use
• Interactive onboarding walkthrough for new users
• Sample rate, FFT resolution, and waterfall colour scheme configurable for your hardware and preference

WHAT YOU NEED

• RTL-SDR Blog V3 or V4 dongle
• USB OTG cable
• Directional Antenna tuned to your tracking frequency
• Optional: external wideband LNA for additional sensitivity gain (required for bias-tee power delivery) and/or a Bandpass filter.

IDEAL FOR

• Wildlife tracking or Falconry & VHF telemetry research
• Ham radio fox hunting and hidden transmitter direction finding
• RTL-SDR enthusiasts pushing weak-signal sensitivity limits
• Field researchers needing multi-frequency awareness & bearing logging
• Graduate students & NGOs needing affordable telemetry alternatives

No ads. No tracking. No data collection. Developed for Working with Wildlife (workingwithwildlife.org) for conservation and the radio community.

© 2026 Working with Wildlife. All rights reserved.