Digital Airwaves
Encoding or decoding random radio-waveforms doesn't need incredible expensive hardware anymore which offers new possibilities for building up over-the-air communication systems. There are Software Defined Radios providing affordable cellular radio to remote villages, Community Radios are using SDR to build up digital radio networks and other cool stuff.
Some basic knowledge what is going on in SDR Hard/Software as the influence of the samplerate, I/Q-data of the math behind the waterfall-diagram is helpful to have fun with SDR. Some theory on modulation techniques helps you to decode or encode your waveforms.