ChannelSPURIOUS EMISSIONS
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Episode 9 · Distress Calls, Beacons, and HFGCS · Series 01: The Listening Station

What else is out there? Distress calls, beacons, military voices.

A frame from the draft of episode 9, Distress Calls, Beacons, and HFGCSComing soon
Release
Length
4:26
On the dial
2 to 28 MHz
Signal
Distress watch (DSC)

What it covers

My shortwave receiver hears far more than weather maps. In this video: the digital distress and calling system that ships use (DSC), the eighteen beacons around the world that take turns on one frequency (the NCDXF/IARU International Beacon Project), and the voice messages of the United States Air Force (HFGCS). I explain how each one works and what my own station in the Puget Sound really hears on a small indoor antenna, including how little that sometimes is.

The written guide: set this up yourself

Chapters

  1. 0:00Intro
  2. 0:20A distress button
  3. 0:47Six frequencies
  4. 1:13Eighteen beacons
  5. 1:49What I hear
  6. 2:12A voice with letters
  7. 3:53One week

Frames from the draft

Distress Calls, Beacons, and HFGCS: Intro
01 Intro
Distress Calls, Beacons, and HFGCS: A distress button
02 A distress button
Distress Calls, Beacons, and HFGCS: Six frequencies
03 Six frequencies
Distress Calls, Beacons, and HFGCS: Eighteen beacons
04 Eighteen beacons
Distress Calls, Beacons, and HFGCS: What I hear
05 What I hear
Distress Calls, Beacons, and HFGCS: A voice with letters
06 A voice with letters
Distress Calls, Beacons, and HFGCS: One week
07 One week

Gear in this episode

RX-888 Mk IIthe receiver that hears all of shortwave at once (mine is from OpenSourceSDRLab)
MLA-30+ loop antennathe small active loop antenna for shortwave
HP EliteDesk small form factor PCthe shortwave computer I call Raphael (mine was rescued from e-waste)
CyberPower CP1500PFCLCD UPS (1500 VA, sine wave)the battery backup that keeps almost all of my station running through a power cut

Software and references

ITU-R M.493itu.intthe public standard for digital selective calling (DSC): how a call is built and checked
Digital selective calling (US Coast Guard)navcen.uscg.govwhat DSC is, in plain words, and the distress and safety frequencies
NCDXF/IARU International Beacon Projectncdxf.orgthe eighteen beacons, where they are, and the transmission schedule
High Frequency Global Communications Systemen.wikipedia.orga public overview of the US Air Force network and its frequencies
ka9q-radiogithub.comthe program that cuts one channel for each signal out of the receiver's stream (open source, by Phil Karn; episode 5)
faster-whispergithub.comthe free speech-to-text program (a fast version of OpenAI's Whisper) that writes down the recorded speech

What is simplified, and what is invented

  • The three decoders (distress calls, beacons, voice recorder) are small programs I wrote for my station. They are not public.
  • The distress call on screen is an example that I wrote. The ship number and the position are invented. I never show or store a real call here: a distress call involves real people.
  • The voice message on screen is invented. I do not show or publish recordings or their text.
  • The speech and static traces are drawn for the video, not recorded.
  • Beacons are named by their place. The beacon schedule and locations are from the NCDXF/IARU International Beacon Project. Marks on the map are at city or region level.
  • On the beacon map the turn moves far faster than real time. The Morse marks spell no real name, the timing inside the ten seconds is simplified, and the dash heights use a logarithmic scale.
  • Map coastline: Natural Earth (public domain). The lines are great circles from Seattle, which stands for the Puget Sound.
  • The ship, coast station and aircraft drawings are illustrations, not to scale.
  • All counts are one week of my station, rounded. My antenna is still a small loop indoors.