High Frequency Global Communications System

The High Frequency Global Communications System (HF-GCS) is a network of single sideband shortwave transmitters of the United States Air Force which is used to communicate with aircraft in flight, ground stations and some United States Navy surface assets. All worldwide receiving and transmitting sites in the HF-GCS system are remotely controlled from Andrews AFB. Before 1 October 2002 it was known as the Global High Frequency System (GHFS).

HF-GCS stations tend to operate in the aviation bands clustered around 5, 8 and 11/12 MHz, although other frequencies are in use. The primary HF-GCS voice frequencies are 4724.0 kHz, 6739.0 kHz, 8992.0 kHz, 11175.0 kHz, 13200.0 kHz and 15016.0 kHz. In addition to the HF-GCS, U.S. aircraft frequently use Military Affiliate Radio System (MARS) HF stations (13927.0 kHz) and Canadian Forces HF stations (11232.0 kHz) to relay messages.

One common use for the HF-GCS is to place telephone calls from the aircraft in flight by means of the Defense Switched Network (DSN) to an Air Force base to obtain local weather conditions, to arrange for refueling, and to inform the base of the number of passengers and crew. The HF-GCS also carries Emergency Action Messages.^[1]

In addition to EAM's the HF-GCS also carries a few different types of messages. A higher priority code for orders is a Skyking Message, which is a time sensitive message for orders that need immediate attention. Force Direction Messages (FDM's) are also sent through the HF-GCS, although it is impossible to tell whether the message is an FDM or just another EAM being read.^[1]

Although transmissions are often single sideband, the use of the ALE transmission mode is more and more common. Naval Special Warfare HF-GCS complements the use of satellite communications between aircraft and ground stations.

Stations of the HF-GCS Network^[1]

• Andersen Global, Andersen Air Force Base, Guam Island
• Andrews Global, Andrews Air Force Base, Maryland USA
• Ascension Global, RAF Ascension Island, Atlantic Ocean
• Croughton Global, RAF Croughton, United Kingdom
• Diego Garcia Global, Diego Garcia Naval Station, Indian Ocean
• Elmendorf Global, Elmendorf Air Force Base, Alaska
• Hickam Global, Hickam Air Force Base, Hawaii
• Lajes Global, Lajes Field, Azores
• Lincoln Receiver Site (aka West Coast Global), Beale Air Force Base, California
• Offutt Global, Offutt AFB, Nebraska
• Puerto Rico Global, Salinas, Puerto Rico
• Sigonella Global, Naval Air Station Sigonella, Sicily, Italy
• Yokota Global, Yokota Air Base, Japan

Closed Stations

• Thule Air Base, Greenland
• Keflavík Global, Keflavík NAS, Iceland

References

Wikimedia Commons has media related to High Frequency Global Communications System.

1. ↑ 1.0 1.1 1.2 "The HF-GCS". October 2014. Retrieved October 28, 2014.