Included in at least one reviewed higher-education syllabus.
S4-2.5 Wave Propagation
You can match frequency bands to propagation modes and compute critical frequency, MUF and skip distance for sky-wave links.
Different frequencies genuinely travel by different physics, and this topic maps the spectrum onto its three modes: ground wave at low frequencies, sky wave bounced off the ionosphere at HF, and line of sight from VHF upward. The standard calculations — critical frequency, maximum usable frequency, skip distance — come from the sky-wave case. It closes the subject because it explains the behaviour of every link the earlier units designed. The common confusion is expecting one propagation story for all of radio; AM at night and a blocked 5G signal are different physics, not different luck.
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Frequency spectrum and which propagation mode dominates where
Different frequencies travel by genuinely different physics, and this item is the map: which mode dominates in which band. Getting this mapping straight is the knowledge from this unit that lasts longest.
Ground wave propagation; space and surface waves
At low frequencies the signal follows the curve of the earth, partly as a surface wave clinging to the ground and partly through space above it. This is why AM broadcast reaches beyond the horizon.
Tropospheric refraction, reflection and duct propagation
The lower atmosphere bends radio waves because its refractive index changes with height, and under some conditions it traps them in a duct that carries signals far past the horizon. It explains both useful range and surprise interference.
Sky wave: critical frequency, MUF, ionospheric delay, skip distance
High-frequency signals can bounce off the ionosphere and return hundreds of kilometres away, and critical frequency, maximum usable frequency and skip distance are the numbers that describe when and where. These are the standard calculations of the unit.
Line-of-sight propagation
Above roughly thirty megahertz the signal mostly goes where you can see, which is why masts are tall and why a building kills a link. Modern mobile and satellite work lives almost entirely in this mode.
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