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 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

Ionization level and reflection properties divide the ionosphere in different layers: –D: km –E: km –F: km

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

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

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

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

Other forms of propagation Aurora EME Meteors Sporadic E Satellites

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)

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

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

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

Satellites Works as repeater station