Q-MAC Electronics Pty Ltd HF90 Manuale Utente

HF-90 Operation & Installation Guide 

When HF/SSB radio waves are generated there are usually 
two components:- 
 

The ground-wave, which travels directly from the 
transmitting antenna to the receiving antenna 
following the contours of the earth, and ... 

 

The sky-wave, which travels upward and at an angle 
from the transmitting antenna, until it reaches the 
ionosphere (an ionised layer high above the earth’s 
surface) and is refracted back down to earth, to the 
receiving antenna. 

 
Generally speaking, ground-wave is used to communicate 
over shorter distances (in most cases less than 50km).  
However, because ground-wave follows the contours of the 
earth, it is affected by the type of terrain it passes over.  For 
example, ground-wave is rapidly attenuated (reduced) when it 
passes over hilly or mountainous terrain. 
 
Sky-wave is used to communicate over medium range and 
longer distances (up to 3,000km and beyond in good 
conditions).  Because of the nature of sky-wave propagation, 
it is not affected by the type of terrain it passes over.  This 
means that communications can be achieved over medium 
and long distances in mountainous areas, using HF/SSB sky-
wave.  However, sky-wave propagation is affected 
significantly by other factors as outlined in Section 2.3 of this 
Guide. 
 
Ground-wave and sky-wave examples are illustrated on the 
following page.