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Doug McArthur

Down Load Atmosphere Ver 1.25

Atmosphere Absorption Attenuation [Atmosphere]

[Attenuation by Atmospheric Gasses]

Electromagnetic waves are absorbed in the atmosphere according to wavelength. Two compounds are responsible for the majority of signal absorption, Oxygen (O2) and water vapour (H2O).

The first peak occurs at 22 GHz due to water vapour, and the second at 63 GHz due to oxygen. The actual amount of water vapour and Oxygen in the atmosphere normally declines with an increase in altitude because of the decrease in pressure.

Total attenuation through the atmosphere at any frequency, through unobstructed atmosphere, is the sum of free space path loss, attenuation caused by oxygen absorption, and attenuation caused by water vapour absorption. Rain attenuation, when present adds an additional element.

Total path attenuation = Attenuation Free Space Path Loss + Attenuation caused by Oxygen + Attenuation due to Water Vapour + Attenuation due to Rain + Fog and Cloud Attenuation.

This program [Atmosphere] calculates the absorption attenuation at Microwave frequencies for both terrestrial and slant paths for Amateur frequencies from 10-241 GHz.

The calculations applied in this program are based upon the International Telecommunication Union (ITU) recommended methods as listed in the Reference section of this Document.

The program has been written primly as a supplement to my EME Calculator Program  to refine overall loss calculations for frequencies above 10GHz where these factors become a significant.

 The EMECalc program is available for download from  this menu.

Down load  Atmosphere Attenuation

 Help document (pdf)

(Stand alone printable)