Lecture3

Wavestravelinaduct verylongrangepropagationispossible

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Unformatted text preview: tmosphere Bending Ground Wave Ground Wave At low frequencies and vertical polarization, waves will travel along the earth’s surface Wave travels between ionosphere and ground – Ionosphere is region above the Troposphere, ~50­250 miles above the e re earth s ph no Io Ground Waves Ground Waves Ionosphere is electrically charged and highly conductive – Attenuation is minimal and ranges are extended – Waves travel in a “duct” Very long range propagation is possible Wavelengths that are too long for anything but ship/aircraft comms, and fixed, ground­ based radar Sky Waves Sky Waves As ground wave mode fades out, a new mode develops for higher frequency waves Layers in ionosphere can be used to refract EM energy back towards the earth’s surface Sky Wave Sky Wave EM energy then reflects back toward upper layer in ionosphere again This series is repeated – Up to “hundreds” of miles, not completely reliable Key: Waves refract off the ionosphere, then reflect off the ocean/earth back up and repeat the process If too steep of angle, wave travels through and doesn’t refract Sky Wave Sky Wave Consider desired layer in the ionosphere and the angle of the transmission – Ensure the waves refract and head back to earth at desired point – Ionosphere has several regions/layers Frequencies too low to be used for anything but ship/aircraft comms,...
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This document was uploaded on 03/28/2014.

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