Propagation Overview
It
has never been a secret that long-range communication in the amateur bands is
primarily dependant upon the ionosphere, however it is essential to
visualize the structure of the ionosphere and to understand more
thoroughly the basic theory behind the usage of sky-wave methods of transmission
if effective use the ionosphere is to be made.
The
Ionosphere's Structure
The
ionosphere's overall structure consists primarily of three ionized layers
ranging from 35 to 215 miles or so above the earth. The region lowest in height
found at about 35 miles extending to 70 miles is called "D" layer and
for all practical purposes, is useless to the amateur. Instead of reflecting
radio waves, the "D" layer acts as an impediment and attenuates the
signals strength to sometimes completely absorting 80 and 160 meter signals
.
Sunspot
Cycles and Ionospheric Variations
Ultraviolet
radiation from the sun is believed to be the source of energy which ionizes the
ionospheres numerous layers. This belief is constituted on the basis of
what is known as the 11-year sunspot-cycle. Over a period of a few years,
the number of sunspots increases to a peak and then gradually declines,
like this moment. The duration from one sunspot peak to another usually
covers about 11 years. During its peak , communicating conditions are excellent
especially for 20, 17, 15, 12 meters bands and are even better on 10
meters. We are approaching to the sunspot down and for worst conditions,
contacts should be not so good. at a sunspot minimum or "sunspot dip"
communicating ranges e poor with very few band openings. There also exist
what is known as ionospheric storms and when they occur, the
critical frequencies drop considerably and absorption of radio signals in the
ionosphere is substantially increased. These ionospheric storms are
resultant of certain sunspot activity. They usually last from few hours to
several days.
Propagation
Data
If
the amateur has in his shack a wealth of propagation charts or just on or two of
them, he will be much better off than the other amateur who doesn't have
any. By a simple connection through internet to the Institute for
Telecommunication Sciences and Astronomy, you can receive regularly prediction
muf's for the upcoming days and other information.
Cálculo
de Previsões de Propagação
W6EL Prop é um programa que permite calcular as condições de propagação
entre dois locais na terra nas frequências entre os 3 e os 30 MHZ. Este
programa é gratuito quando usado sem fins comerciais.Download
W6ELProp v2.70 (479,795 Bytes)
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