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Radio propagation#

Current conditions#

Radio propagation is the behaviour of radio waves as they travel, or are propagated, from one point to another. As with light waves, radio waves are affected by the phenomena of reflection, refraction, diffraction, absorption, polarization, and scattering.

Understanding the effects of varying conditions on radio propagation has practical importance, and which affects:

  • choosing frequencies for international shortwave broadcasters
  • designing reliable mobile telephone systems
  • radio navigation
  • operation of radar systems.

HF propagation#

Light And Ultraviolet#

They affect the ionosphere

Sunspots#

The More The Better

Line of sight propagation#

F1jmm / CC BY-SA

This assummes a very tall antenna and that nothing is in the path that would block the signal such as a massive mountain range.

Vindarmagnus at Swedish Wikipedia / Public domain

In reality with VHF and UHF transmissions the situation is much more complex.

Low-powered microwave transmitters can be seriously affected by tree branches, or even heavy rain or snow. Even objects not in the direct line-of-sight can cause diffraction effects that disrupt radio transmissions. For the best propagation, a volume known as the first Fresnel zone should be free of obstructions.

Reflected radiation from the surface of the surrounding ground or salt water can also either cancel out or enhance the direct signal. This effect can be reduced by raising either or both antennas further from the ground: The reduction in loss achieved is known as height gain.

It is important to take into account the curvature of the Earth for calculation of line-of-sight paths from maps, when a direct visual fix cannot be made.

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