This is the first in two-part series on spectrum basics and how we could better manage the spectrum to encourage innovation and prevent either large corporations or government from interfering with our right to communicate. Part 2 is available here.
We often think of all our wireless communications as traveling separate on paths: television, radio, Wi-Fi, cell phone calls, etc. In fact, these signals are all part of the same continuous electromagnetic spectrum. Different parts of the spectrum have different properties, to be sure - you can see visible light, but not radio waves. But these differences are more a question of degree than a fundamental difference in makeup.
As radio, TV, and other technologies were developed and popularized throughout the 20th century, interference became a major concern. Any two signals using the same band of the spectrum in the same broadcast range would prevent both from being received, which you have likely experienced on your car radio when driving between stations on close frequencies – news and music vying with each other, both alternating with static.
To mitigate the problem, the federal government did what any Econ 101 textbook says you should when you have a “tragedy of the commons” situation in which more people using a resource degrades it for everyone: they assigned property rights. This is why radio stations tend not to interfere with each other now.
The Federal Communications Commission granted exclusive licenses to the spectrum in slices known as bands to radio, TV, and eventually telecom companies, ensuring that they were the only ones with the legal right to broadcast on a given frequency range within a certain geographic area. Large bands were reserved for military use as well.
Originally, these licenses came free of charge, on the condition that broadcasters meet certain public interest requirements. Beginning in 1993, the government began to run an auction process, allowing companies to bid on spectrum licenses. That practice continues today whenever any space on the spectrum is freed up. (For a more complete explanation of the evolution of licensing see this excellent Benton foundation blog post.)