Piccolo Mark VI

Piccolo is an old, multi-frequency-shift keying mode developed in England. Today, the most common form has six tones spaced only 20 Hz, and sending the ITA2 character set at 20 baud. It's used mostly by the British government and military. The close tone spacing makes piccolo sound a bit like the instrument of the same name, with a high-pitched, musical trill.

Here, the first half second or so shows piccolo's idler, which switches between tones three and four, then characters are sent, making all six tones visible. Starting around 4.5 seconds, the signal gets torn up a bit, as we see in the increased distortion and the shakier amplitude waveform in an otherwise 100% duty cycle.