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Kirt Blattenberger - RF Cafe Webmaster

Copyright: 1996 - 2024
Webmaster:
    Kirt Blattenberger,

    BSEE - KB3UON

RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while typing up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived...

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Atmospheric Absorption (Specific Attenuation)

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

The first peak occurs at 22 GHz due to water, and the second at 63 GHz due to oxygen. The actual amount of water vapor and oxygen in the atmosphere normally declines with an increase in altitude because of the decrease in pressure, so these graphs apply from sea level to around 1 km altitude.

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 vapor absorption. Rain attenuation, when present adds an additional element. For a chart of sunlight power density in the visible light and infrared / ultraviolet region of the electromagnetic spectrum, click here.

So, AttenTotal = AttenFreeSpacePathLoss + AttenOxygen + AttenWaterVapor + AttenRain

 

Atmospheric absorption or electromagnetic energy vs. frequency - RF Cafe

Atmospheric Attenuation (Specific Absorption) Chart

This chart was generated from frequency / attenuation data points picked off of a published graph that were entered into Excel and plotted.

Recommendation ITU-R P.676-9, Attenuation by Atmospheric Gases, P Series, Radiowave Propagation - RF CafeHere is the official document by the International Telecommunications Union that contains very detailed data.

Recommendation ITU-R P.676-9
(02/2012)
Attenuation by atmospheric gases
P Series Radiowave propagation

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