Global High Frequency System (GHFS)

[About the GHFS]        [Frequencies By Order]     [Frequencies By Time]   [Bases]     [International Bases]

The Global HF System (GHFS) was started by the US Air Force in June of 1992. This system was created by consolidating several other USAF HF networks, including the Strategic Air Command "Giant Talk" system. The goal of the system was to develop a worldwide HF network for providing Command & Control HF communications to all authorized USA DOD aircraft and ground stations. The best frequencies to listen to, as the chart suggests, are 8.9920MHz USB and 11.1750MHz USB although in being in the other hemisphere the signals can be considerably low from aircraft and a decent shortwave antenna will be required for reception.

When you hear an aircraft or any stations calling "MAINSAIL" on any of the GHFS frequencies this is a "general" call for any ground station to answer and provided the calling stations with what ever he needs. Any GHFS ground station will respond to the call "MAINSAIL". Depending on the service required, the station bay request the aircraft to change to a discrete frequency for improved and extended service.

EAM's or Emergency Action Message. Another very important aspect of the GHFS is the transmission of EAM's. EAM's are the coded military orders or bulletins that have the highest priority. When EAM's are broadcast, ALL other users of the system are to standby. If you hear a voice giving a long series of letters phonically this is an EAM.

SKYKING messages are special EAM's. These presumably could be the nuclear go/no-go codes. There was a higher than normal number of EAM's and SKYKING messages being transmitted after the attackes of 9/11/01. Urgent SKYKING messages are repeated three or four times instead of the usual two. SKYKING is a group callsign, meaning "Any this net." "Do not answer" is the standard procedure ofr self-authenticating broadcasts, meaning that recipients don't need to give away their positions or existence by challenging the orders. While tuned to any of the GHFS frequencies and hear "SKYKING SKYKING Do not answer" you can bet you're hearing a very important, highest priority, and heavily encrypted message!

Authorized users may request service from GHFS station by calling "Mainsail". Any station in the net recieving the call will respond and provide requested service. Minimum service by all stations are phone patch and message relay service. Phone patch permits direct voice communication between ground agencies and aircraft/ships by electronically connecting telephone circuits or other voice channels to radio transmitting and recieving equipment. For pp: callsign, telephone number and location should be stated if known. 
When contacting GHFS for RTTY, global will designate and alternate frequency for the service. 
EAM messages are common on all frequencies, only aircraft with emergency or distress situations are to interupt EAM broadcasts made out by GHFS using the static words "PAN PAN PAN" or "MAYDAY MAYDAY MAYDAY". GHFS are not directly capable of Direction Finding. However stations can assist in DF by coordinating between various aircraft in the vicinity.

More often then not you will hear "REACH" aircraft requesting a pp to an airbases' AMC CP giving them a heads up about their load, passengers, estimated time of arrival and aircraft technical status. Almost always this pp is followed by one to the destinations airbase meteorological office to ask them the current or expected weather conditions before they land there. At the end of the pp to the wx shop on an airbase the pilot occasionally asks the meta man if he wants a PIlots REPort (PIREP) as an extra service, so the wx shops can give better forecasts on the weather for other aircraft and anticipate.

GHFS Frequencies (Lowest to Highest)

GHFS Frequencies by UTC Guard Times