HFGCS (USAF only) Frequently Asked Questions and Information


Active member
Here's everything you need to know about USAF transmissions on the High Frequency Global Communications System (HFGCS). First off, none of the EAMs or SKYKINGs transmitted can be decoded by ANYONE other than the USAF officials receiving the messages, anyone who claims they can is lying and attempting to do so is highly illegal, however, there is nothing illegal about logging them and/or recording the transmissions.

Types of messages:
Emergency Action Messages (EAMs) are messages transmitted from a ground station or an airborne command post (E-4B Nightwatch or E-6B Mercury (sometimes also called TACAMO)) to nuclear forces in the air or underwater (B-52s or nuclear capable submarines for example). These messages can be anything from flight plans, weather information, etc. to launch orders, which you are highly unlikely to hear, as USAF comms go secure in times of emergencies or strikes against other countries from what we have been able to tell.

SKYKINGs are presumably higher precedence messages which are also sent to nuclear forces.

Occasionally you may hear messages to and from SKYMASTER. SKYMASTER is USSTRATCOM's airborne command post, these messages are assumed to be the same precedence as EAMs, and we have not been able to correlate these messages with on going world events that involve the United States.

Radio checks and test counts are simply that, they are not launch codes or anything crazy, they are simply radio checks.

Occasionally you may hear a plane entering or exiting the net, entering or exiting the net involves a few authentications before the plane is officially out or into the net.

4724.00 USB (works best at night)
6739.00 USB (unclear if it still works)
8992.00 USB (works best during the day)
11175.00 USB (works best during the day)
15016.00 USB (unclear if it still works)
You can listen here: websdr.ewi.utwente.nl:8901/ make sure you are in USB mode, squelch is also available so you don't have to go crazy listening to static all the time. Some days are more active than others and some are completely quiet, you will not hear transmissions every 6 seconds every single day.

Yes, there is a log of EAMs and SKYKINGs dating back to mid 2017 which you can find at eam.watch. The guys over at eam.watch are always looking for help with logging EAMs as most of them are not available to log all day, they also have a Discord server if you have any questions. There is nothing illegal about logging and recording EAM and SKYKING transmissions, anyone who tries to tell you otherwise is lying.

Frequently Asked Questions
Q. What is that weird sound I'm hearing? (some call it gunshots, other call it farting, etc.)
A. OTH Radar.

Q. What is the foreign speaking on 8992.00?
A. Some speculation as to what it is, but the general consensus is either French fishermen or the French Air Force.

A. No, probably not.

Subject to change and additions. Feel free to let me know if I missed anything, because I probably did.


8992usb and 4724usb are both best heard at night.not during the day!



I can report that 15016 USB definitely in use. I just copied an EAM here in Saint Paul MN. Booming in, signal was 15 over S9. Flex 6500 radio and tuned inverted L antenna. The transmitting station identified itself as "CHECKROOM".