The term radio frequency (RF) (also, radio frequency spectrum) applies to the less energetic portion of the electromagnetic spectrum, located between 3 hertz (Hz) and 300 gigahertz (GHz).
The hertz is the unit of measurement of the frequency of the waves, and corresponds to one cycle per second. The electromagnetic waves of this region of the spectrum can be transmitted by applying the alternating current originated in a generator to an antenna.
Radio frequency can be divided into the following spectrum bands:
From 1 gigahertz, the bands fall within the microwave spectrum. Above 300 gigahertz the absorption of electromagnetic radiation by the Earth's atmosphere is so high that the atmosphere becomes opaque to it, until, in the so-called infrared and optical frequency ranges, it becomes transparent again.
The ELF, SLF, ULF and VLF bands share the spectrum of the AF (audio frequency), which is between approximately 20 and 20,000 hertz. However, the latter are pressure waves, like sound, so they travel at the speed of sound over a material medium. While radiofrequency waves, being electromagnetic waves, travel at the speed of light and without the need for a material medium.
The theoretical bases of the propagation of electromagnetic waves were first described between 1886 and 1888 by Heinrich Rudolf Hertz, who was the first to experimentally validate Maxwell's theory.
The use of this technology for the first time is attributed to different people: Alexander Stepanovich Popov made the first demonstrations of it in Saint Petersburg, Russia; Nikola Tesla, in St. Louis, Missouri, United States, and Guillermo Marconi, in the United Kingdom. The first practical system of communication using radio waves was designed by Guillermo Marconi, who in 1901 made the first transatlantic radio broadcast. Today, radio takes many other forms, including wireless networks, mobile communications of all kinds, as well as broadcasting.
Uses of radiofrequency
Although the word radio is used, television, radio, radar and mobile phone transmissions are included in this class of radio frequency emissions. Other uses are audio, video, radio navigation, emergency services and digital radio data transmission; both in the civil and military spheres. They are also used by radio amateurs.
Many of the astronomical objects emit in radio frequency. In some cases in wide ranges and in other cases centered on a frequency that corresponds to a spectral line, for example:
HI line or atomic hydrogen. Centered at 1.4204058 gigahertz.
CO line (1-0 rotational transition) associated with molecular hydrogen. Centered at 115.271 gigahertz.
Radar is a system that uses electromagnetic waves to measure distances, altitudes, directions, and speeds of static or moving objects such as aircraft, ships, motorized vehicles, weather formations, and the terrain itself. Its operation is based on emitting a radio pulse, which is reflected by the target and is typically received in the same position as the emitter. From this "echo" a large amount of information can be extracted. The use of electromagnetic waves makes it possible to detect objects beyond the range of other types of emissions. Its fields of application include meteorology, air and ground traffic control and a wide variety of military uses.
Nuclear Magnetic Resonance
Nuclear magnetic resonance studies atomic nuclei by aligning them to a constant magnetic field to later disturb this alignment with the use