Understanding the way in which HF radio signals actually propagate can help the effects of ionospheric propagation to be used to its best.
Skywaves, skip zone and skip distances are three key concepts show why radio communications signals are heard in some places and not others .
The skywave refers to the signal that travels away from the Earth’s surface towards the ionosphere. Unlike a ground wave it does not follow the contour of the ground, but instead it is directed towards the ionosphere.
The angle between the line of the skywave signal and the Earth’s surface at that point may be shallow or steep.
The skip distance is dependent upon a variety of factors:
- Frequency: The frequency of operation has a major influence on the skip distance that can be achieved. Typically as the frequency increases a lower angle of radiation is needed to return the signals to Earth in a shorter distance. Also higher frequencies tend to be reflected or refracted by higher layers or regions in the ionosphere. This will mean that higher frequencies tend to lead to longer skip distances.
- Ionospheric conditions: The ionospheric conditions play a major role in governing the skip distance. Under some circumstances when ionisation levels are high it may be possible for signals to achieve very short skip distances.
- Angle of radiation: The angle of radiation from the transmitting antenna will also have an impact on the skip distance. A lower angle of radiation will lead to longer skip distances as a result of the geometry……READ FULL ARTICLE
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