Communication avec les sous-marinsLes communications avec les sous–marins en plongée sont techniquement très difficiles, elles nécessitent la mise en œuvre de techniques et d'équipements spécifiques. Cette extrême difficulté est due à un effet incontournable : les ondes électromagnétiques des fréquences habituellement utilisées pour les télécommunications sont incapables de traverser un conducteur électrique épais comme de l'eau salée. La solution la plus simple est de déployer une antenne radioélectrique à la surface de l'eau et d'utiliser les techniques de télécommunications classiques.
Broadcast licenseA broadcast license is a type of spectrum license granting the licensee permission to use a portion of the radio frequency spectrum in a given geographical area for broadcasting purposes. The licenses generally include restrictions, which vary from band to band. Spectrum may be divided according to use. As indicated in a graph from the National Telecommunications and Information Administration (NTIA), frequency allocations may be represented by different types of services which vary in size.
Bilan de liaisonLe bilan de liaison est un calcul par étapes permettant de déterminer la qualité d’une liaison. Les détails varient selon la nature du média, hertzien, ligne, fibre optique, et le type de signaux et de modulation, mais le principe est le même. C'est le calcul global qui relie tous les domaines : radioélectricité, traitement du signal, protocoles, etc. Dans ce cas, le but est d’obtenir un rapport entre le signal et le bruit final suffisant pour l’application.
Diversity schemeIn telecommunications, a diversity scheme refers to a method for improving the reliability of a message signal by using two or more communication channels with different characteristics. Diversity is mainly used in radio communication and is a common technique for combatting fading and co-channel interference and avoiding error bursts. It is based on the fact that individual channels experience fades and interference at different, random times, i.e, they are at least partly independent.
Parasite atmosphériquevignette|Graphique fréquence versus temps (spectrogramme) montrant plusieurs sifflements de parasites atmosphériques dans le signal reçu à la base antarctique Palmer. Les parasites atmosphériques, ou atmosphériques, sont des rayonnements électromagnétiques, causés par des perturbations électriques naturelles dans l'atmosphère, qui affecte les systèmes radio. Ils sont le plus souvent causés par la décharge électrique produite par la foudre.
Computation of radiowave attenuation in the atmosphereThe computation of radiowave attenuation in the atmosphere is a series of radio propagation models and methods to estimate the path loss due to attenuation of the signal passing through the atmosphere by the absorption of its different components. There are many well-known facts on the phenomenon and qualitative treatments in textbooks. A document published by the International Telecommunication Union (ITU) provides some basis for a quantitative assessment of the attenuation.
Media marketA media market, broadcast market, media region, designated market area (DMA), television market area, or simply market is a region where the population can receive the same (or similar) television and radio station offerings, and may also include other types of media such as newspapers and internet content. They can coincide with or overlap with one or more metropolitan areas, though rural regions with few significant population centers can also be designated as markets.
Military communicationsMilitary communications or military signals involve all aspects of communications, or conveyance of information, by armed forces. Examples from Jane's Military Communications include text, audio, facsimile, tactical ground-based communications, naval signalling, terrestrial microwave, tropospheric scatter, satellite communications systems and equipment, surveillance and signal analysis, security, direction finding and jamming. The most urgent purposes are to communicate information to commanders and orders from them.
