Phase-shift keying
By either changing or not changing the wave every time it gets to the top of its wiggle, we can send either ones or zeros. This is called Binary Phase Shift Keying. If we change the phase of the wave as it reaches the top, we can have this represent a 1. If we don't change it at the top, we can have this represent a 0. We can use a computer and a radio to turn text into a wave like this and then send it. A radio and a computer listening to this wave changing or not changing can figure out the original message being sent and turn it back into text.