Editing TV and FM DX (section)

==Tropospheric propagation==
[[File:Atmosphere structure numbered.svg|right|thumb|Diagram of the different layers of the [[atmosphere]].]]
{{Main|Tropospheric propagation}}

[[Tropospheric propagation]] refers to the way radio signals travel through the lowest layer of the Earth's atmosphere, the [[troposphere]], at altitudes up to about to 17 km (11 miles). Weather conditions in the lower atmosphere can produce radio propagation over greater ranges than normal. If a [[temperature inversion]] occurs, with upper air warmer than lower air, VHF and UHF radio waves can be refracted over the Earth's surface instead of following a straight-line path into space or into the ground. Such "tropospheric ducting" can carry signals for 800 km (500 miles) or more, far beyond usual range.