Overview of Ortac_SarSat Software

  • A Windows-based program for receiving and decoding 1st and 2nd generation SARSAT beacons.
  • Designed for educational and personal use to monitor beacon activity, especially at ports and airports.

SARSAT System and Beacon Types

  • COSPAS-SARSAT is a satellite system detecting emergency beacons and alerting rescue authorities.
  • 1st generation beacons transmit narrowband signals at 406.025-406.076 MHz, with messages protected by BCH error correction.
  • 2nd generation beacons use DSSS-OQPSK modulation at 406.050 MHz, with a wider bandwidth (~35kHz) and 300 bits of data.

Hardware Compatibility and Installation

  • Requires compatible USB SDR hardware: RTL2832u with R820T2 tuner, SDRPlay RSP series, or Ettus USRP series.
  • Installation involves driver configuration, especially for RTL dongles using Zadig utility.
  • Software installs to default directories and stores settings and recordings in user app data.

Main Receiver Interface

  • Features a title bar, file, forms, and help menus.
  • Displays RF and CPU overload warnings and provides FFT and waterfall visualisations.
  • Waterfall shows amplitude history with adjustable colour scale and gain.
  • Supports multiple decoders for SarSat 1 and 2 signals, with options to enable/disable and adjust processing parameters.

RF Control and Hardware Settings

  • RF control varies by hardware: SDRPlay, RTL, or USRP.
  • SDRPlay adjusts internal AGC, with manual LNA gain control.
  • RTL tuners can auto-adjust gain or be manually set; USRPs benefit from external GPS clocks and gain tuning.

Decoding and Signal Processing

  • SarSat 1 decoder detects narrowband signals with low CPU load, with excellent sensitivity.
  • SarSat 2 decoder performs intensive FFT-based detection, tracking frequency drift, and BCH error correction.
  • Both decoders provide detailed info, including message content, frequency error, and BCH correction status.

Data Recording and Playback

  • IQ recorder/player captures baseband signals for offline analysis.
  • Supports simulated beacon files for testing, including SarSat 1, SarSat 2, and combined signals.
  • Files can be managed, played back, or deleted within the software.