International Telecommunication Union in the context of Information and communications technology

A ground station, Earth station, or Earth terminal is a terrestrial radio station designed for extraplanetary telecommunication with spacecraft (constituting part of the ground segment of the spacecraft system), or reception of radio waves from astronomical radio sources. Ground stations may be located either on the surface of the Earth, or in its atmosphere. Earth stations communicate with spacecraft by transmitting and receiving radio waves in the super high frequency (SHF) or extremely high frequency (EHF) bands (e.g. microwaves). When a ground station successfully transmits radio waves to a spacecraft (or vice versa), it establishes a telecommunications link. A principal telecommunications device of the ground station is the parabolic antenna.

Ground stations may have either a fixed or itinerant position. Article 1 § III of the International Telecommunication Union (ITU) Radio Regulations describes various types of stationary and mobile ground stations, and their interrelationships.

Terahertz radiation – also known as submillimeter radiation, terahertz waves, tremendously high frequency (THF), T-rays, T-waves, T-light, T-lux or THz – consists of electromagnetic waves within the International Telecommunication Union-designated band of frequencies from 0.1 to 10 terahertz (THz), (from 0.3 to 3 terahertz (THz) in older texts, which is now called "decimillimetric waves"), although the upper boundary is somewhat arbitrary and has been considered by some sources to be 30 THz.

One terahertz is 10 Hz or 1,000 GHz. Wavelengths of radiation in the decimillimeter band correspondingly range 1 mm to 0.1 mm = 100 μm and those in the terahertz band 3 mm = 3000 μm to 30 μm. Because terahertz radiation begins at a wavelength of around 1 millimeter and proceeds into shorter wavelengths, it is sometimes known as the submillimeter band, and its radiation as submillimeter waves, especially in astronomy. This band of electromagnetic radiation lies within the transition region between microwave and far infrared, and can be regarded as either.

An international standard is a technical standard developed by one or more international standards organizations. International standards are available for consideration and use worldwide. The most prominent such organization is the International Organization for Standardization (ISO). Other prominent international standards organizations including the International Telecommunication Union (ITU) and the International Electrotechnical Commission (IEC). Together, these three organizations have formed the World Standards Cooperation alliance.

Amateur radio, also known as ham radio, is the use of the radio spectrum for non-commercial communication, technical experimentation, self-training, recreation, radiosport, contesting, and emergency communications. In 1927 a radio amateur was defined as "a duly authorized person interested in radioelectric practice with a purely personal aim and without pecuniary interest," meaning without monetary or similar reward. The definition distinguished amateur activity from commercial broadcasting, public safety services, and professional two-way radio uses such as maritime, aviation, and taxi communication.

The amateur radio service (amateur service and amateur-satellite service) is established by the International Telecommunication Union (ITU) through its Radio Regulations. National governments set technical and operational rules for transmissions and issue individual station licences with unique call signs. Call signs must be used in transmissions, at least every ten minutes and at the end. Amateur radio operators must hold an amateur radio licence, granted after an examination that tests knowledge of radio theory, electronics, and national regulations.

Super high frequency (SHF) is the ITU designation for radio frequencies (RF) in the range between 3 and 30 gigahertz (GHz). This band of frequencies is also known as the centimetre band or centimetre wave as the wavelengths range from one to ten centimetres. These frequencies fall within the microwave band, so radio waves with these frequencies are called microwaves. The small wavelength of microwaves allows them to be directed in narrow beams by aperture antennas such as parabolic dishes and horn antennas, so they are used for point-to-point communication and data links and for radar. This frequency range is used for most radar transmitters, wireless LANs, satellite communication, microwave radio relay links, satellite phones (S band), and numerous short range terrestrial data links. They are also used for heating in industrial microwave heating, medical diathermy, microwave hyperthermy to treat cancer, and to cook food in microwave ovens.

Frequencies in the SHF range are often referred to by their IEEE radar band designations: S, C, X, K_u, K, or K_a band, or by similar NATO or EU designations.

Extremely high frequency (EHF) is the International Telecommunication Union (ITU) designation for the band in the electromagnetic spectrum from 30 to 300 gigahertz (GHz). It is in the microwave part of the radio spectrum, between the super high frequency band and the terahertz band. Radio waves in this band have wavelengths from ten to one millimeter, so it is also called the millimeter band and radiation in this band is called millimeter waves, sometimes abbreviated MMW or mmWave. Some define mmWaves as starting at 24 GHz, thus covering the entire FR2 band (24.25 to 71 GHz), among others.

Compared to lower bands, radio waves in this band have high atmospheric attenuation: they are absorbed by the gases in the atmosphere. Absorption increases with frequency until at the top end of the band the waves are attenuated to zero within a few meters. Absorption by humidity in the atmosphere is significant except in desert environments, and attenuation by rain (rain fade) is a serious problem even over short distances. However the short propagation range allows smaller frequency reuse distances than lower frequencies. The short wavelength allows modest size antennas to have a small beam width, further increasing frequency reuse potential. Millimeter waves are used for military fire-control radar, airport security scanners, short range wireless networks, and scientific research.

The radio spectrum is the part of the electromagnetic spectrum with frequencies from 3 KHz to 3,000 GHz (3 THz). Electromagnetic waves in this frequency range, called radio waves, are widely used in modern technology, particularly in telecommunication. To prevent interference between different users, the generation and transmission of radio waves is strictly regulated by national laws, coordinated by an international body, the International Telecommunication Union (ITU).

Different parts of the radio spectrum are allocated by the ITU for different radio transmission technologies and applications; some 40 radiocommunication services are defined in the ITU's Radio Regulations (RR). In some cases, parts of the radio spectrum are sold or licensed to operators of private radio transmission services (for example, cellular telephone operators or broadcast television stations). Ranges of allocated frequencies are often referred to by their provisioned use (for example, cellular spectrum or television spectrum). Because it is a fixed resource which is in demand by an increasing number of users, the radio spectrum has become increasingly congested in recent decades, and the need to utilize it more effectively is driving modern telecommunications innovations such as trunked radio systems, spread spectrum, ultra-wideband, frequency reuse, dynamic spectrum management, frequency pooling, and cognitive radio.

Inter-satellite service, also known as inter-satellite radiocommunication service, as defined by Article 1.22 of the International Telecommunication Union's (ITU) Radio Regulations (RR), is a radiocommunication service providing links between artificial satellites.

Edwin Howard Armstrong (December 18, 1890 – February 1, 1954) was an American radio-frequency engineer and inventor who developed FM (frequency modulation) radio and the superheterodyne receiver system.

He held 42 patents and received numerous awards, including the first Medal of Honor awarded by the Institute of Radio Engineers (now IEEE), the French Legion of Honor, the 1941 Franklin Medal and the 1942 Edison Medal. He achieved the rank of major in the U.S. Army Signal Corps during World War I and was often referred to as "Major Armstrong" during his career. He was inducted into the National Inventors Hall of Fame and included in the International Telecommunication Union's roster of great inventors. He was inducted into the Wireless Hall of Fame posthumously in 2001. Armstrong attended Columbia University, and served as a professor there for most of his life.

Morse code is a telecommunications method which encodes text characters as standardized sequences of two different signal durations, called dots and dashes, or dits and dahs. It is named after Samuel Morse, one of several developers of the system. Morse's preliminary proposal for a telegraph code was replaced by an alphabet-based code developed by Alfred Vail, the engineer working with Morse. Vail's version was used for commercial telegraphy in North America. Friedrich Gerke simplified Vail's code to produce the code adopted in Europe, and most of the alphabetic part of the (ITU) "Morse" is copied from Gerke's revision.

The ITU International Morse code encodes the 26 basic Latin letters A to Z, one accented Latin letter (É), the Indo-Arabic numerals 0 to 9, and some punctuation and messaging procedural signals (prosigns). There is no distinction between upper and lower case letters. Each code symbol is formed by a sequence of dits and dahs. The dit duration can vary for signal clarity and operator skill, but for any one message, once the rhythm is established, a half-beat is the basic unit of time measurement. The duration of a dah is three times the duration of a dit. Each dit or dah within an encoded character is followed by a period of signal absence, called a space, equal to the dit duration. The letters of a word are separated by a space of duration equal to three dits, and words are separated by a space equal to seven dits.

Spectral bands are regions of a given spectrum, having a specific range of wavelengths or frequencies. Most often, it refers to electromagnetic bands, regions of the electromagnetic spectrum. More generally, spectral bands may also be means in the spectra of other types of signals, e.g., noise spectrum.

A frequency band is an interval in the frequency domain, limited by a lower frequency and an upper frequency. For example, it may refer to a radio band, such as wireless communication standards set by the International Telecommunication Union.

Ultra-high-definition television (also known as Ultra HD television, Ultra HD, UHDTV, UHD and Super Hi-Vision) today includes 4K UHD and 8K UHD, which are two digital video formats with an aspect ratio of 16:9. These were first proposed by NHK Science & Technology Research Laboratories and later defined and approved by the International Telecommunication Union (ITU).

The Consumer Electronics Association announced on October 17, 2012, that "Ultra High Definition", or "Ultra HD", would be used for displays that have an aspect ratio of 16:9 or wider and at least one digital input capable of carrying and presenting native video at a minimum resolution of 3840 × 2160. In 2015, the Ultra HD Forum was created to bring together the end-to-end video production ecosystem to ensure interoperability and produce industry guidelines so that adoption of ultra-high-definition television could accelerate. From just 30 in Q3 2015, the forum published a list up to 55 commercial services available around the world offering 4K resolution.

Very high frequency (VHF) is the ITU designation for the range of radio frequency electromagnetic waves (radio waves) from 30 to 300 megahertz (MHz), with corresponding wavelengths of ten meters to one meter. Frequencies immediately below VHF are denoted high frequency (HF), and the next higher frequencies are known as ultra high frequency (UHF).

VHF radio waves propagate mainly by line-of-sight, so they are blocked by hills and mountains, although due to refraction they can travel somewhat beyond the visual horizon out to about 160 km (100 miles). Common uses for radio waves in the VHF band are Digital Audio Broadcasting (DAB) and FM radio broadcasting, television broadcasting, two-way land mobile radio systems (emergency, business, private use and military), long range data communication up to several tens of kilometers with radio modems, amateur radio, and marine communications. Air traffic control communications and air navigation systems (e.g. VOR and ILS) work at distances of 100 kilometres (62 miles) or more to aircraft at cruising altitude.

The K_u band (/ˌkeɪˈjuː/) is the portion of the electromagnetic spectrum in the microwave range of frequencies from 12 to 18 gigahertz (GHz). The symbol is short for "K-under" (originally German: Kurz-unten), because it is the lower part of the original NATO K band, which was split into three bands (K_u, K, and K_a) because of the presence of the atmospheric water vapor resonance peak at 22.24 GHz, (1.35 cm) which made the center unusable for long range transmission. In radar applications, it ranges from 12 to 18 GHz according to the formal definition of radar frequency band nomenclature in IEEE Standard 521–2002.

K_u band is primarily used for satellite communications, most notably the downlink used by direct broadcast satellites to broadcast satellite television, and for specific applications such as NASA's Tracking Data Relay Satellite used for International Space Station (ISS) communications and SpaceX Starlink satellites. K_u band satellites are also used for backhauls and particularly for satellite from remote locations back to a television network's studio for editing and broadcasting. The band is split by the International Telecommunication Union (ITU) into multiple segments that vary by geographical region. NBC was the first television network to uplink a majority of its affiliate feeds via K_u band in 1983.