DUCTING

nRadio signals at UHF and VHF then get  trapped and can 

travel long distances before coming back to the Earth’s 

surface

nThis effect is most prominent during the spring and 

summer months.

nRF waves below the warm air mass get trapped and travel 

great distances with little attenuation.

nThis area is called a DUCT

DUCTING and its causes

nIrregularities in the earth’s atmosphere affect 

troposphere transmission

nThe condition is known as “super refraction”

nSuper refraction occurs when the refractive index of 

the air decreases with height more rapidly than normal

nAlso increase of temperature with height (temperature 

inversion)  and increase of humidity of height

nAtmospheric pressure increases with height

nSo that bending of the radio wave is much more 

pronounced

nThe region in which super refraction occurs

  is termed a DUCT, which can be formed both at the

Elevated striate (called elevated DUCT)

 Earth’s surface (called surface DUCT)