In this video YouTube user Superphish shows decoding of the French Navy STANAG 4285 test signal. He used an rtl-sdr, Ham-it-up upconverter, SDRSharp and a decoding program called Sorcerer. Watch in HD to read the text, though the text basically just repeats the French equivalent to the quick brown fox, “VOYEZ VOUS LE BRICK GEANT QUE J EXAMINE PRES DU GRAND WHARF” and some test symbols over and over.

Fair warning with the Sorcerer download: Some people report that their virus scanner detects a trojan on some Sorcerer download links. The Sorcerer link above seems to be clean though, as far as my virus scanner reports. An alternative decoder is Sigmira.

STANAG 4285 is the NATO standard for HF communication, and signals can be found all over the HF spectrum.