Exploring radio signal triangulation techniques including Radio Direction Finding (RDF), Time of Flight (ToF) measurements, and distance-based positioning for locating radio transmitters.

Overview

Radio signal triangulation combines multiple measurement techniques to determine the location of a radio transmitter. This project explores various approaches from simple directional antenna methods to more sophisticated time-based and signal strength measurements.

Theory

Radio Direction Finding (RDF)

RDF uses directional antennas to determine the bearing angle to a transmitter. By taking bearings from multiple locations, the transmitter position can be triangulated.

Key concepts:

  • Directional antenna patterns
  • Bearing angle measurement
  • Baseline geometry and accuracy
  • Multipath interference

Time of Flight (ToF)

ToF measures the time delay for a radio signal to travel between transmitter and receiver. Since radio waves travel at the speed of light, distance can be calculated directly.

Key concepts:

  • Signal propagation speed
  • Time synchronization requirements
  • Precision timing circuits
  • Multilateration with multiple receivers

Received Signal Strength Indication (RSSI)

RSSI uses the inverse square law of radio propagation to estimate distance based on signal power.

Key concepts:

  • Free space path loss
  • Antenna gain characteristics
  • Environmental attenuation factors
  • Calibration requirements

Hardware

Directional Antenna Systems

Options for directional antenna designs:

  • Yagi-Uda array for VHF/UHF
  • Loop antennas for HF
  • Rotating antenna mounts
  • Antenna switching networks

Radio Receivers

Receiver options and requirements:

  • RTL-SDR dongles for software-defined radio
  • Dedicated RDF receivers
  • Phase-coherent multi-channel receivers for ToF
  • Signal strength measurement capabilities

Timing and Synchronization

For ToF measurements:

  • GPS-disciplined oscillators (GPSDO)
  • Precision time protocol (PTP)
  • Timestamp correlation between receivers
  • Clock drift compensation

Software and Signal Processing

Direction Finding Algorithms

  • Phase comparison techniques
  • Amplitude comparison methods
  • Doppler direction finding
  • Correlative interferometry

Time Difference of Arrival (TDoA)

  • Cross-correlation for time delay estimation
  • Hyperbolic positioning algorithms
  • Multi-receiver synchronization
  • Outlier rejection and filtering

Data Fusion and Mapping

  • Combining multiple measurement types
  • Kalman filtering for position estimation
  • Visualization and mapping tools
  • Error ellipse calculation

Applications

Fox Hunting (Amateur Radio)

Traditional radio direction finding for hidden transmitter hunts in amateur radio competitions.

Wildlife Tracking

Locating radio-tagged animals using RDF and triangulation techniques.

Interference Location

Finding sources of radio interference or unauthorized transmitters.

Emergency Beacon Location

Search and rescue applications using emergency locator transmitters (ELTs).

Implementation Approaches

Simple RDF System

Single directional antenna with manual rotation and signal strength measurement.

Multi-Receiver TDoA Network

Synchronized receivers at known locations performing time-based triangulation.

Hybrid System

Combining RDF bearing measurements with RSSI distance estimates for improved accuracy.

Build

Antenna Construction

Receiver Setup

Timing Synchronization

Software Configuration

Testing and Calibration

Baseline Measurements

Known Transmitter Tests

Accuracy Assessment

Field Testing

Results

Future Improvements

  • Automated antenna rotation
  • Real-time position plotting
  • Mobile receiver platforms
  • Integration with mapping software
  • Improved multipath rejection

References and Resources