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2016 Extra Class Study Guide: E3B - gray line, sporadic E

Posted: 08 Mar 2016 12:07 PM PST
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E3B Transequatorial propagation; long path; gray-line; multi-path;
ordinary and extraordinary waves; chordal hop, sporadic E mechanisms

There are a number of interesting types of propagation that occur on the HF
bands. They include transequatorial propagation, long-path propagation, and
gray-line propagation.

Transequatorial propagation is propagation between two mid-latitude points
at approximately the same distance north and south of the magnetic equator.
(E3B01) The approximate maximum range for signals using transequatorial
propagation is 5000 miles. (E3B02) The best time of day for transequatorial
propagation is afternoon or early evening. (E3B03)

Long-path propagation is the type of propagation that occurs when the
longer of the two direct paths between stations is better for
communications than the shorter path. 160 to 10 meters are the amateur
bands that typically support long-path propagation. (E3B05) 20 meters is
the amateur band that most frequently provides long-path propagation.
(E3B06)

Gray-line is the type of HF propagation is probably occurring if radio
signals travel along the terminator between daylight and darkness. (E3B08)
Gray-line propagation occurs because, at twilight, D-layer absorption drops
while E-layer and F-layer propagation remain strong. (E3B10)

Another interesting propagation phenomenon is echoes. While not strictly a
type of propagation, echoes are the result of propagation conditions.
Receipt of a signal by more than one path is one condition that could
account for hearing an echo on the received signal of a distant station.
(E3B07)

Sporadic-E propagation occurs when unusally dense patches of ionization
form in the E layer of the ionosphere. The time of year that Sporadic E
propagation is most likely to occur is around the solstices, especially the
summer solstice. (E3B09) Sporadic-E propagation is most likely to occur any
time of the day.

Chordal hop propagation occurs when a radio wave is refracted by the
ionosphere such that the refracted wave hits the ionosphere again before
hitting the ground. The primary characteristic of chordal hop propagation
is successive ionospheric reflections without an intermediate reflection
from the ground. (E3B12) Chordal hop propagation is desirable because the
signal experiences less loss along the path compared to normal skip
propagation. (E3B13)

When a radio wave enters the ionosphere, it splits into two waves called
the ordinary wave and the extraordinary wave. The terms extraordinary and
ordinary waves describe independent waves created in the ionosphere that
are elliptically polarized. (E3B04) What happens to linearly polarized
radio waves that split into ordinary and extraordinary waves in the
ionosphere is that they become elliptically polarized. (E3B14)

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