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Propagation of radio waves

Propagation of radio waves. Ways of travelling. Propagation in ionosphere Propagation in troposphere Special ways of reflecting Propagation depends on the properties of the medium frequency weather, time of day, sun activity. Propagation in ionosphere.

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Propagation of radio waves

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  1. Propagation of radio waves

  2. Ways of travelling • Propagation in ionosphere • Propagation in troposphere • Special ways of reflecting • Propagation depends on • the properties of the medium • frequency • weather, time of day, sun activity

  3. Propagation in ionosphere • Solar radiation (UV, X-ray) partially ionize the atmosphere • Ionization depends on the density of the gases • Waves reflect (refract) from the ionized layers • Directly dependent • on day of time, most neutralized just before sunrise • actitivity of sun • sun spot number • solar flux

  4. Ionization level and reflection properties divide the ionosphere in different layers: • D: 55-90 km • E: 90-150 km • F: 150-400 km

  5. D layer • lowest layer: exist only during daylight • unsuitable for contacts, absorbs radio energy • 7 & 10 MHz can travel through at high angles

  6. E layer • A bit more stable layer, disappears at night • Skip from E layer is limited by D • hard to distinguish from F layer propagation • longest one skip range is ~2000 km • home for other interesting ways of propagation • Es • Aurora, meteor scatter

  7. F layer • Divided in two during daytime F1, F2 • F2 more important, never absent • one skip almost 4000 km, multihops even longer • reflects from ground, E-layer once or several times • Controlled by sun activity

  8. Propagation in troposphere • VHF, UHF & microwaves • weather effects • tropospheric scattering primary form • rain, fog, dust, snow, clouds • ducting • Radiation inversions: • air layers with different temperatures and dew points • can travel long (1500 km) • calm summer evenings

  9. Other forms of propagation • Aurora • EME • Meteors • Sporadic E • Satellites

  10. Aurora • High-energy particles flow into ionosphere during geomagnetic storm  ionize E layer • 28 – 432 MHz • K index: magnetic activity 0-9 • Signals sound distorted, sometimes only CW at VHF-UHF (A=Aurora)

  11. EME • Earth-Moon-Earth • 50 MHz to 10 GHz • Free space loss, ½ degree target, Doppler shift, Faraday rotation... not that easy • eFFe-mobiili

  12. Meteor scatter • Ionize a column of air at E layer • stays ionized for a few seconds to a minute  just enough time for brief contacs • 50 MHz, 144 MHz • High speed Morse code, pieced together

  13. Sporadic E • Ionization level gets abnormally high • 28, 50, 144 MHz • Usually at summer time at morning and again at early evening • Might dissipate quickly or move

  14. Satellites • Works as repeater station

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