HFGCS (High Frequency Global Communications System)

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HFGCS (High Frequency Global Communications System)
11175 KHZ Crop Waterfall.png
Frequencies 4.724 MHz,6.712 MHz,6.739 MHz,8.992 MHz,11.175 MHz,13.2 MHz,15.016 MHz
Frequency Range 4.724 MHz - 15.016 MHz
Mode USB
Modulation USB
Emission Designator
Bandwidth 2.95 kHz
Location Worldwide
Short Description HFGCS is a series of networks deployed by the United States Air Force to send encoded messages to deployed aircraft. This network is well known for it's coded EAM's (Emergency Action Messages) used for coordinating United States Strategic Nuclear Forces.
I/Q Raw Recording
Audio Sample

The High Frequency Global Communications System, HFGCS for short, is a series of networks created by the United States Air Force to send coded messages to deployed aircraft. There are seven frequencies used by the system, but some messages are usually transmitted on one frequency. When a message is transmitted on one or more (Sometimes even all) of these frequencies, an echo can be heard in the transmission. Those that broadcast these messages are given code names, some examples are 'Backyard', 'Racetrack', or 'Apathy'. The messages are decoded in a NATONorth Atlantic Treaty Organization phonetic-numeral alphabet. There is no channel marker for these frequencies. The messages are sent through EAMs, or Emergency Action Messages.


Skykings come from the United States Strategic Command, and interrupt all other traffic, including EAMs. Skykings consists of an operator saying "Skyking Skyking Do Not Answer", time into the minute (If it were 0932 Z, '32' would be said), and an authentication string that consists of two NATONorth Atlantic Treaty Organization phonetics, such as 'Charlie Juliet'. They are repeated once, and often with poor reception.


HFGCS is mainly controlled by Andrews Airforce Base in Maryland, but there are a few Air Force bases that also transmit to HFGCS, which include (May not be limited to)

  • Andersen AB, Guam
  • Ascension Island
  • Croughton AB, United Kingdom
  • Diego Garcia Naval Station, Indian Ocean
  • Elmendorf AFB, Alaska
  • Hickam AB, Hawaii
  • Keflavik NAS, Iceland
  • Lajes AB, Azores
  • McClellan, California
  • Offutt AFB, Nebraska
  • Salinas, Puerto Rico
  • Sigonella Naval Station, Italy
  • Yokota AB, Japan


A standard EAM transmission. Note the echoing, which indicates the transmission being on other frequencies.

A Skyking message

An EAM Message at 8992 kHzKiloHertz (kHz) 10^3 Hz

"Ramshead 3 messages"

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