Category:Near Vertical Incidence Skywave

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English: ear Vertical Incidence Skywave, or NVIS, is a radio-wave propagation method that provides usable signals in the range between groundwave and skywave distances (usually 30 to 150 miles, or 50 to 240 km). It is used mainly for military and paramilitary communications and by radio amateurs. The radio waves travel upwards into the ionosphere, where they are refracted back down and can be received within a circular region up to 300 km from the transmitter. If the frequency is too high, refraction fails to occur and if it is too low absorption reduces the signal strength. The usable frequencies for NVIS communications are between 1.8 MHz and 12 MHz.
Français : Le N.V.I.S. (Near Vertical Incidence Skywave), en Français: onde radio ionosphèrique à incidence quasi verticale, est un mode de propagation utilisé pour des radiocommunications locales et régionale dans la bande des moyennes fréquences et hautes fréquences (1,6 à 12 MHz) à l’intérieur d’une zone arbitraire de 240 km autour de l'émetteur. Ce mode de propagation des ondes radios nécessite une antenne NVIS dont le lobe de rayonnement principal est en direction du ciel.