There is a lot more in common between radios and cell phones then most people expect. It can be hard to see similarities when the user interfaces are designed so differently. Fundamentally, they both have a power source that drives the device to generate a signal across an antenna. In turn, the antenna generates radio waves that run through the atmosphere until they hit another antenna attached to a receiver.
If you could see radio waves, they’d appear as if we had hundreds of lights turned on all around us. We’d see the waves coming off our cell phones, wifi-enabled devices, blue-tooth devices, wireless phones, cellular-enabled tablets and hot spots. Also visible is the radio waves from your neighbors’ equipment coming right through your walls as if the walls weren’t even there. The wireless baby monitor would probably appear just as annoying as the tantruming child. Larger sources of radio waves would emanate from cell towers. Way off in the distance, AM and FM towers would glow like a sun. Even the fast food drive through isn’t immune due to the wireless headsets and speakers. Look to the sky and you’ll see the satellites sending their signal to the earth. Right above the equator, the concentration of transmitting satellites would resemble the Milky Way. Add in all the natural sources and unintended sources from poorly designed electrical systems to really complete the image. No lie. Radio waves are everywhere.
In the US, the National Telecommunications and Information Administration will set the broad allocation of the spectrum and how it can be used. They publish the US Frequency Allocations: The Radio Spectrum chart. It is very finely divided down, yet you’ll still see major sections allocated to broadcasting. Spectrum is a finite resource. We cannot create any more and all of it is allocated to something. That is why spectrum management is so important. Broadcasting has had to make better and more efficient use of the spectrum to keep it. Hence the evolution of HD radio; which by the way is hybrid digital not high definition. It also led to the use of Digital TV to include more information and resolution in the TV station’s broadcast.
At the bottom of this chart is the full spectrum. Near the left end is the audible wave lengths; the middle contains a very narrow band of the visible spectrum; and the far right is cosmic rays. The continuous range of frequencies (and then some) is called “DC to daylight”. DC refers to direct current or 0 Hertz. Daylight refers to the band of visible light, starting about 405 THz. Thz is Terahertz or 1012 Hertz. If you’re used to the metric system, Tera comes after Giga. Looking for a radio that does “DC to daylight” isn’t a literal radio. It is referring to a radio that will continuously cover all possible radio bands. Keep in mind that the more bands (frequency ranges) a radio will cover; the less impressively it can master a single band. Think of it this way: a Swiss army knife provides a lot of tools which are better than nothing, but far less handy then having the actual tool needed.
National Telecommications and Information Administration. (2003). U.S. Frequency Allocation Chart. Retrieved from http://www.ntia.doc.gov/osmhome/allochrt.html