Tropospheric ducting (also known as tropospheric refraction) is a type of radio propagation that tends to happen during periods of stable, anti-cyclonic weather. In this propagation method, when the signal encounters a rise in temperature in the atmosphere instead of the normal decrease (known as a temperature inversion), the higher refractive index of the atmosphere there will cause the signal to be bent. Tropospheric ducting affects all frequencies, and signals enhanced this way tend to travel up to 800 miles (though some people have received "tropo", as it is usually abbreviated, from beyond 1000 miles), while with tropospheric bending, stable signals with good signal strength from 500+ miles away are not uncommon when the refractive index of the atmosphere is fairly high.
Ducting conditions usually vary over short time periods as opposed to enhancement which is more stable.
Ducts located behind cold fronts ("post-frontal ducts") are notoriously unstable as paths can even be interrupted by things such as heavy rain showers associated with the cold front itself.
Frequencies affected by ducting are determined by the vertical thickness of an inversion.
Tropospheric propagated signals travel in the part of the atmosphere adjacent to the surface and extending to some 25,000 feet (7,620 meters).
Troposphericducting is a type of radio propagation that tends to happen during periods of stable, anticyclonic weather.
Troposphericducting of UHF television signals is relatively common during the summer and autumn months, and is the result of change in the refractive index of the atmosphere at the boundary between air masses of different temperatures and humidities.
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