Before there was television, before there were computers, before there was the Internet with its audio and video streaming, before there were cell phones, iPods, and iPads, there was radio. Beginning in the early 1920s, electrical waves-mysterious to many-could be sent from senders or transmitters into boxes called radios in people's homes. Sometimes the boxes weren't boxes at all. In radio's earliest days, hobbyists built radios (called crystal sets)...