Sporadic Propagation E
the sporadic propagation E is a ionospheric form of Propagation of the radio waves by reflection on noted sporadic layers Es, located in the area E of the Ionosphère.
The sporadic layer E
The area E of the ionosphere is located at approximately 90 to 150 kilometers of altitude. Its altitude can vary, and the density of electrons (ionization) depends on the solar angle compared to the zenith and the solar activity. During the hours of day, the density of electrons (a measurement of the level of ionization) can reach 105 electrons/cm ³. The night, when the flow of x-rays of the sun is cut, the level of ionization falls to 10 ³ e/cm ³. These densities of ionization are evaluated under normal conditions, in sporadic absence of E.
" nuages" particularly ionized, organized in a simple layer or multi-layer, usually spaced approximately 6 kilometers, constitute the sporadic layer Es. Their formation can last of a few minutes to a few hours. The mechanisms of formation of this layer are badly known. Its probability of appearance is unknown and its unforeseeable parameters. Some possible theoretical mechanisms include shearings of the winds of higher level and the geomagnetic activity.
The appearance of these phenomena of intense way is mainly during the time of one to two months previous and following the summer solstice, is from May to August in the northern hemisphere. However even for this period, the phenomena remain random: there can not be no event during three weeks consecutive, or of the events almost the every day during a whole week.
The propagation radio operator Es
Distances from communication from 300 to 2500 km are common of a " nuage" simple layer of Es. They very relate to primarily the high frequencies. The variability of the distance from propagation in Es and the implied frequencies is due to the size and the density of the " nuages". The frequencies from 20 to 70 MHz are touched by this type of propagation (CB, wavebands of the 28 and 50 MHz of the radio hams, the channels TV of the band I, the band FM of the 66-73 MHz Eastern Europe). At the time of the most intense events, frequencies up to 250 MHz can be reflected (the band FM of the 88-108 MHz, the band radio ham of the 144 MHz).
This type of propagation has as principal characteristics to be directing (only are concerned certain geographical areas, variables according to the ionospheric events) and very intense (of the transmitters of very low power can be received with hundreds of km, transmitters remote can scramble local transmitters).
Because of its randomness, this type of propagation is not used by regular services of telecommunication (which on the contrary see there a harmful effect because of the risks of jammings that it involves), but primarily by the Radioamateur S, the CB enthusiasts, and the amateurs of receptions radio and TV exotics or ear-phones of short waves. This type of propagation was a long time for the latter, before the appearance of the satellites, the only means of reception of foreign stations TV at long distance, activity known under the name of " DX-TV".
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