In 2012, UNESCO dedicated Feb. 13 as “World Radio Day.” The idea is to celebrate the many ways in which radio brings us together, recognizing the fact that it’s still the most widely consumed media across the globe.
And while World Radio Day is typically focused on the messages radio brings, we thought it’d be a good time to revisit this article that takes a look at radio from the point of view of satellites.
Many people don’t even know that satellites send and receive information through radio waves, and as it’s becoming increasingly clear that satellite will play an outsized role helping connect the unconnected around the globe, it’s helpful to know a little about how this works.
At the very core of any kind of wireless communication is the use of radio waves to carry information. The basics of how this works haven’t changed much since Guglielmo Marconi sent the first radio signals in 1895, but there are some specifics to how satellite uses radio that are helpful to understanding the technology.
Here are a few things to know about how radio communications work:
Waves: Electromagnetic radiation (EM radiation) travels in waves at the speed of light. Unlike waves that travel through sound and water, EM waves require no medium. They can move through air as well as the vacuum of space.
Frequency: The frequency of a wave is measured in Hertz (Hz). 1 hertz is equal to one cycle per second of the wave, shown here:
The electromagnetic spectrum: This refers to the range of all types of EM radiation, which is a form of energy. The difference between one end of the spectrum and the other is determined by the frequency of the waves. Visible light makes up one section of the EM spectrum, as do radio, X-rays and gamma rays.
Frequency bands: This term simply refers to the chunks of wavelengths making up the spectrum. Ka-band, often used for satellite, is one type of band. Visible light is another. Some bands are quite large, while others may have just a sliver of “bandwidth.”
Here’s what some of the most common prefixes mean, whether applied to watts, bytes, hertz or other units
An AM radio operates at a frequency between 535-1605 kilohertz (kHz), so a station at 800 kHz has waves cycling 800,000 times per second. A signal from a Ka-band satellite operates at a much higher frequency of around 28 gigahertz (GHz), 28,000,000,000 times per second.
Amplitude: This is a measurement of the height of a wave. Along with frequency and wavelength, it is one of the main characteristics of a wave.
Satellite spectrum: Satellites operate in a particular areas or “bands” of the spectrum, a portion of which you can see here. The higher up you go in frequency, the larger the bands become and the more information you can carry. Viasat operates primarily in the Ka-band, in the 28 GHz range. Most satellite TV operators use the lower frequency C or Ku-band, because the data flow only goes one direction and does not require as much bandwidth. However, when information must be sent both directions more bandwidth is required to make the communication work efficiently. These higher bands are good for transmitting data, but as you go up in frequency, the complexity of the equipment increases.
These higher frequencies are also more subject to interference — typically referred to as “attenuation.” Unlike shorter wavelengths, they don’t pass through solid objects like walls, and rain can also affect the signal. For Ku and Ka bands, this is in large part due to the fact that water molecules are approximately the same width as the wave. Satellite addresses this problem by using external antennas and line-of-sight installations. While heavy rain or snow can still affect signal, the effect is usually short-lived due to the duration of heavy weather.
In addition, ground-based technologies using these higher bands of the spectrum can use smaller antennas since the higher-frequency signals are able to be focused more effectively.
For satellite communications, different bandwidths are useful for different applications. For satellite broadband, the higher frequencies work best for transmitting more data. Viasat uses several different frequency bands for our services: L-band for maritime applications, Ku-band for some aviation, and Ka-band and above for aviation, residential and more.
Our upcoming ViaSat-3 global constellation of satellites will operate in the Ka-band, as does the rest of our fleet. These next-generation satellites will have enormous capacity to manage data, with each ViaSat-3 satellite expected to have over 1 Terabit per second of capacity.