The Center for Land Use Interpretation Newsletter

Radio is Everywhere

Radio spectrum diagram

CLUI photo
NASA image
WE ARE, OF COURSE, IMMERSED in a continuous deluge of radio waves, from human and non-human sources, which along with the rest of the oscillations of the electromagnetic spectrum, are flying in all directions everywhere around us and through us, mostly invisible, and traveling at the speed of light. Radio is the portion of the electromagnetic spectrum that we chose to detect, with devices tuned to decode the signals embedded in the waves.
Radio is the low-energy end of the electromagnetic spectrum, where waves are long and oscillations slow. Like most things, radio waves can be measured in time, as well as space. In time, it is usually by frequency, meaning how many waves occur per second. This is generally described in units known as hertz, named after Heinrich Hertz, the 19th century German physicist who was among the first to understand the electromagnetic spectrum.
Described spatially, instead of by time, radio waves can be measured by wavelength—looking at the size of each wave’s length. For example, since radio waves, like other electromagnetic waves, generally travel at the speed of light, the occurrence of a single oscillation in one second of time—a frequency of one hertz—would be the distance covered traveling at the speed of light in one second, which is around 186,000 miles. That is a very long wave.
Radio waves are commonly described as having frequencies ranging from 1,000  hertz to 100 billion hertz (100 gigahertz), which corresponds to wavelengths ranging from 185 miles in length to three millimeters in length. Wavelengths smaller than that approach the microwave part of the electromagnetic spectrum, in the infrared. As the waves continue to shrink to the infinitesimal, wavelengths move from invisible waves in the infrared, into visible light waves, then beyond the visible again into ultraviolet, x-rays, then gamma rays.
The range of radio can be divided into a dozen bands, from extremely low frequency (ELF) and very low frequency (VLF), through medium frequency (MF), high frequency (HF), very high frequency (VHF) to tremendously high frequency (THF), which is well into the microwave range. Over the past 120 years, all of these bands have been used to carry electronic signals from one place to another.
Guglielmo Marconi was the first to develop long distance radio transmitters and receivers, using a medium frequency of around 850,000 hertz to send a faint signal across the Atlantic for the first time in 1901. Ship-to-shore radio developed quickly after that, followed by commercial radio, after World War One, with the emergence of RCA, NBC, and CBS, in the USA. These, too, used medium frequency ranges, settling on the 540,000 hertz to 1,600,000 hertz (540-1600 kilohertz) still used by AM radio in the USA today.
Television emerged as a broadcast medium after World War Two, using VHF frequencies that bookended those used by FM. FM stereo broadcasting begins in the 1960s, using the 88,000,000 hertz to 108,000,000 hertz range, familiar to Americans as the “88MHz-108MHz” of the FM dial. TV eventually expanded into the UHF range too. Unlike the longer waves used by AM, FM and VHF don’t make it over the horizon, limiting broadcasters to a range of around 30-50 miles or so. This is generally why the towers are placed on mountaintops near the population centers they serve.
Military research during and after World War Two expanded the use of other bands of the radio spectrum, such as extremely low frequency, ELF, whose long waves—less than 30 hertz, and a single wavelength of more than 6,000 miles in size—travel through earth and water, enabling communications with submarines around the world. Military research and applications for things like communications, radar, and electronic countermeasures, run into the microwave ranges, and beyond.
With the recent proliferation of consumer communications electronics and commercial data networking, civilian use of the radio spectrum, while limited in its range of spectrum use, is greater than military use in its consumption of bandwidth. Cell phones, Bluetooth, and wifi communicate on the super high frequency range, from 1 gigahertz to 6 gigahertz. These small waves do not penetrate well, and are best used for communication between two fixed points, and at short range, though they can carry large amounts of data.
Due to the long distance capabilities of some radio signals, and the effects of one signal on another, radio is governed by national and international regulatory agencies, such as the FCC in the USA, and the International Telecommunication Union, headquartered in Geneva, which is among the oldest global international organizations (and now part of the UN).
Historically, international cooperation has been necessary, especially because of shortwave. State-controlled shortwave radio programming is still broadcast by dozens of nations, including the UK (the BBC), India, China, Japan, Saudi Arabia, Romania, Korea, Afghanistan, Albania, Algeria, Angola, Turkey, Russia, and the USA.
Though few listen to shortwave in the USA beyond some ham radio hobbyists and DXers, it remains popular in other parts of the world, especially those not served well by broadband or cable, or short range forms of radio, like FM and television bands on UHF and VHF. ♦

United States Frequency Allocations chart

CLUI photo

Download this handsome chart for free at the National Telecommunications and Information Administration website