Short Wave Listening (SWL): High Frequency Global Communications System (HFGCS)

Modulation / mode: USB

Frequency (kHz)   Comments
---------------   ---------------
4724.0
6712.0
6739.0
8992.0            "Night primary"
11175.0           "Day primary"
11232.0           Canadian Forces
13200.0
13927.0           MARS
15016.0

From Wikipedia:

"The High Frequency Global Communications System (HFGCS) 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 HFGCS system
are remotely controlled from Andrews Air Force Base and Grand Forks Air Force Base.
Before 1 October 2002 it was known as the Global High Frequency System (GHFS).

HFGCS stations tend to operate in the aviation bands clustered around 5, 6, 8 and
11/12 MHz, although other frequencies are in use. The primary HFGCS voice
frequencies are 4724.0 kHz, 8992.0 kHz, 11175.0 kHz, and 15016.0 kHz. In addition
to the HFGCS, U.S. aircraft frequently use Military Auxiliary Radio System (MARS)
HF stations (13927.0 kHz) and Canadian Forces HF stations (11232.0 kHz) to relay
messages. Various other discrete frequencies are available, and used, as part of
the HFGCS network and are not listed here.

One common use for the HFGCS is to place telephone calls from the aircraft in
flight by means of the Defense Switched Network (DSN) to an U.S. Air Force base,
U.S. Naval Air Station, U.S. Marine Corps Air Station, U.S. Army Airfield, or
Air Force Reserve or Air National Guard installations on civilian airports, or
Army Reserve or Army National Guard Aviation Support Facilities on civilian
airports, to obtain local weather conditions, to arrange for refueling, and to
inform the base of the number of passengers and crew. The HFGCS also carries
Emergency Action Messages (EAMs).

In addition to EAMs, the HFGCS carries a few other 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 HFGCS, although it is impossible to tell whether the message
is an FDM or just another EAM being read.  The sign off 'Crossfire' was in use in
August 2021 at the end of the transmissions. This changes from time to time, as an
example 'Colour Bar' was being used in 2016. As of March 2021, the identifier being
used was 'Silicate'. By summer of 2022, callsign signoffs were being changed on a
daily basis.

Although transmissions are often single sideband (SSB), the use of the ALE
transmission mode is more and more common. HFGCS complements the use of satellite
communications between aircraft and ground stations."

[https://en.wikipedia.org/wiki/High_Frequency_Global_Communications_System]

CREATED 2023-04-02