The US Air Force reads coded letters aloud all day, and anyone can listen
2026-06-23 · EA5IYR
Tune 11175 kHz on a decent receiver and wait. Sooner or later a voice arrives, unhurried and slightly bored, and reads something like this: SKYKING SKYKING do not answer. Bravo Two Seven. Time Zero Four. Authentication Kilo Whiskey.
Then nothing. No explanation, no sign-off, no repeat beyond the one it always does. That is the High Frequency Global Communications System, run by the US Air Force, and it has been talking to nobody in particular for decades. Four frequencies, because one is never enough
HFGCS operates primarily on 4724, 8992, 11175 and 15016 kHz, and the same message goes out on all of them simultaneously.
That is not belt-and-braces redundancy of content. It is a physical necessity. No single HF frequency is usable everywhere at once: the ionosphere that carries 4724 kHz across an ocean at midnight will absorb it completely at noon, while 15016 kHz does the opposite. An aircraft somewhere over the Pacific uses whichever one it can currently hear, and the ground station has no way of knowing which that will be.
The receiving and transmitting sites are scattered worldwide and remotely operated, so the voice you hear may be in a room thousands of kilometres from the antenna radiating it. What an EAM actually looks like
The bulk of the traffic is Emergency Action Messages. The format is rigid: a preamble of characters, the words "stand by", and then a body of phonetic letter groups. They are read twice.
A Skyking message is a different animal. It comes from US Strategic Command, it interrupts everything else on the channel, and it carries the instruction "do not answer" — because a reply would tell a listening adversary that somebody received it, and where they are. What you can and cannot learn from it
You cannot read the messages. Like a numbers station, the content is protected by a key you do not have, and no amount of collected traffic will help.
What is genuinely observable is the pattern. How often messages go out, how long they are, whether Skykings cluster around particular days. Traffic analysis is the oldest trick in signals intelligence and it does not require breaking a single character. It is also why the volume of HFGCS activity gets watched closely by people who follow military affairs, and why reading too much into a busy night is a mistake — routine exercises produce traffic too. Hearing it yourself
11175 kHz is the usual starting point during daylight, 8992 kHz after dark. Use upper sideband, not AM. The signal is often weak and the readings are brief, so it rewards leaving the receiver parked rather than tuning around.
There is nothing clandestine about listening. The transmissions are unencrypted voice on published frequencies, and monitoring them is a long-established shortwave hobby.
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Sources: Wikipedia — HFGCS, Numbers-Stations.com — HF-GCS and EAMs, Signal Identification Wiki), UDXF station list (PDF).