Propagation of radio waves

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Propagation of radio waves
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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

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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

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

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D layer

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

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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

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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

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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

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Other forms of propagation

• Aurora
• EME
• Meteors
• Sporadic E
• Satellites

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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 (AAurora)

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EME

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

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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

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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

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Satellites

• Works as repeater station