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Docs Morse & Communication SDR Listening Guide

SDR Listening Guide

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Hear and see the beacon with an RTL-SDR: setup, tuning and waterfall interpretation

SDR Listening Guide

Overview

A software-defined radio is the cheapest and clearest way to verify the Aegis-Beacon is transmitting. An RTL-SDR dongle (~$15-25) turns a USB port into a receiver from 24 MHz to 1.7 GHz, and its waterfall shows the Morse keying visually even when the audio is buried in noise.

What You Need

ItemNotes
RTL-SDR dongleR820T2 tuner recommended
AntennaThe bundled telescopic whip works at 433 MHz
SoftwareSDR# (Windows), GQRX (Linux/macOS), or SDR++ (all)
OptionalA 433 MHz tuned monopole for better sensitivity

Software Setup

SDR# (Windows)

  1. Download and install SDR# and the RTL-SDR drivers.
  2. Plug in the dongle, let Windows install the driver.
  3. Open SDR#, select RTL-SDR/USB as the source.
  4. Set frequency to 433.500 MHz.
  5. Select AM or WFM mode.

GQRX (Linux/macOS)

  1. apt install gqrx or use the AppImage.
  2. In Device settings choose the RTL-SDR.
  3. Enter 433.500 MHz and pick AM.

Reading the Waterfall

The carrier keying is unmistakable:

  • Carrier on = a bright vertical line at 433.500 MHz.
  • Carrier off = nothing.
  • SOS looks like: III___III repeated (three short, three long, three short).

With the GPS payload enabled, decode the pattern by eye or with a Morse decoder - see Morse Decoder Tools.

Tuning to the Beacon

  1. Put the beacon in an open area, antenna vertical.
  2. Start a test transmission (BEACON or EMERGENCY mode).
  3. Tune the SDR to the exact configured frequency.
  4. Widen the span to +-50 kHz to see drift or harmonics.

Why AM Mode

The beacon keys an unmodulated carrier. In FM mode there is no deviation, so FM receivers stay quiet. AM or WFM demodulates the on/off keying into audible Morse.