Skywatch

Listening to the US Air Force's worldwide HF radio network

11175kHz USB
Squelch: idle

Connecting to receiver…

No messages copied yet. They'll appear here the moment one comes in, or pick one from the log.

Log

Time (Z)FromCopyLength

Copy trainer

Play a real recording and write down each character as it's read. The header comes first, then the whole message, then the message again after “I say again”, so you get a second pass.

Strategic aircraft

E-6B Mercury (TACAMO), E-4B Nightwatch, B-52H, B-2 and WC-135, whenever public ADS-B receivers hear them. They often fly without broadcasting, so an empty map is normal.

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AircraftCallsignTailAltitudeSpeedHeard

About Skywatch

A plain-language guide to what this site listens to and how to read it.

What is HFGCS?

The High Frequency Global Communications System is the US Air Force's worldwide high-frequency (shortwave) radio network, run from Grand Forks AFB and Joint Base Andrews. Ground stations use it to reach aircraft wherever they are, including strategic bombers and airborne command posts. HF signals bounce off the upper atmosphere, so they carry across oceans, but they also fade and crackle, which is why the audio sounds rough. Its main frequency is 11175 kHz, and anyone with a shortwave receiver can listen.

What is an Emergency Action Message?

An EAM is a coded message to US strategic forces. A station calls all stations, reads a short header, then the message itself: usually about 30 letters and digits in the phonetic alphabet (“Alpha, Bravo, Seven…”). Then it says “I say again” and reads the whole thing a second time. EAMs go out regularly. They're encrypted, so the characters mean nothing to outside listeners; copying them accurately is the challenge, not decoding them.

What is a Skyking?

A shorter message that starts “Skyking, Skyking, do not answer”, followed by a codeword, a time and an authentication. Skywatch shows those three parts.

Reading the page

Listen live
Plays 11175 kHz as it is right now. Expect mostly static, with voices coming and going.
Meter and lamp
The bar shows how far the signal is above the background noise. When it passes the yellow mark, Skywatch starts recording and the lamp says “copying”.
The copy
The header, then the message one character per box, then each of the two readings underneath. Where one reading was unclear, the other fills the gap.
Red ?
A character the computer couldn't make out, or one where the two readings disagree.
Blue, underlined
A character listeners have corrected. Select any box to hear that moment and vote; once enough people agree, their answer is used.
Copy trainer
Practise copying a real recording yourself and see how you did.
Aircraft
E-6B Mercury, E-4B Nightwatch, B-52H, B-2 and WC-135 positions from public ADS-B receivers. These aircraft often fly without broadcasting a position, so an empty map is normal.

Where it comes from

The audio is public HF radio picked up by online receivers, transcribed by Whisper speech recognition, which makes mistakes on noisy radio, hence the corrections. Aircraft positions come from adsb.lol. Background reading: Priyom, Number Stations Research and NEET INTEL's HFGCS FAQ. Skywatch is open source on GitHub.