Automatic Link Establishment

ALE is the latest thing in automated radio operation, using 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.