Automatic Link Establishment (MIL-STD-141A)

ALE (US MIL-STD-141A and updates) is heard all over being used by most of the world's militaries and public safety agencies. It automates much of the drudge work in HF radio operation, increasing the percentage of successful communication being established. It uses synchronous multifrequency shift keying to pass data over USB voice channels. Red blobs are the 8 tones, in 250-Hz steps beginning at 750, with a duration of 8 ms.

It's easy to see the cyclic nature of ALE data words, which accounts for this mode's distinctive gobbling sound. The wave form at the top shows ALE's remarkably constant amplitude, even with ionospheric distortions.

The striking display below is of a locally generated sounding, using my call sign (NV6H). Note how ALE shows its true repetition and multitone characteristics in the absence of ionospheric fading.