Shortwave Sound of the Day: Bravo Charlie X-Ray Bravo Papa Charlie, Standby.
At 6am/10:00 UTC this morning, I was combing the 60 meter shortwave band for the handful of remaining domestic stations from Latin America during the dawn opening to Latin America. Most of them were too weak to hear, but I did come across this strong signal carrying a coded message on 4724 khz USB (Upper Sideband.) This is likely an Emergency Action Message (EAM) from Andrews Air Force Base in Maryland (as others have reported) though I did not hear the familiar "Andrews Out" of similar transmissions in this frequency range. Some interesting characteristics in this message include digital tones that precede and run throughout the message and a slight echo. The reader also stumbles twice and issues corrections. It sounds to me like the (live) reader says: "MainTail out" at message end. The message's format uses the International Radiotelephony Spelling Alphabet, more commonly known as The Nato Phonetic Alphabet.
Here's a copy if you'd like to follow along at home: