Sky wave
As space wave extending from one is transmitter propagating electromagnetic wave referred to, in contrast to the bump does not follow the curvature of the earth, but a straight line as light propagates "in the space". In a certain frequency range, they can return to Earth after a great distance through reflections from the ionosphere . Since the ionosphere does not have a hard reflective surface, strictly speaking, one does not have to speak of reflection but of refraction .
In the frequency range of the short wave (3 to 30 MHz), the sky wave is of particular interest because the ground wave component of the short wave only has a range of around 50 km. In the long and medium wave range, on the other hand, the sky wave only plays a subordinate role in the evening and night, when the waves are no longer absorbed by the F1 layer in the ionosphere and the reflection in the F2 layer above the same sky wave as in shortwave broadcasting arises (see ionosphere # the F-layer ). Nocturnal reception interference can occur due to the asynchronous overlapping of ground and sky waves.
The sky wave is of great importance in shortwave broadcasting (→ reflection of shortwaves on the ionosphere ). The attenuation is low and between about 5 MHz and 30 MHz, the space waves are reflected particularly well by the ionosphere and move back to the earth's surface. From there the signal can be reflected back to the ionosphere. In this way, the radio waves around the world can be received worldwide. This reflection can be so disturbed by a magnetic storm that the sky wave can no longer be observed from a great distance.
Sky waves from VHF transmitters are hardly absorbed in the ionosphere and are not reflected or only reflected very poorly. For this reason, VHF stations can usually only be received where the transmitting antenna is visible (quasi-optical propagation). However, under certain inversion weather conditions there may be overreaches . In addition, VHF waves can be bent at obstacles, the greater the wavelength, the more so. Listening to radio waves was a popular activity for "DXers" and was rewarded with QSL cards on shortwave radio .
literature
- Karl Rawer: Wave Propagation in the Ionosphere . Kluwer, Dordrecht 1993. ISBN 0-7923-0775-5
- Stratis Karamanolis: All About CB A manual for the CB radio operator. 2nd edition, Karamanolis Verlag, Putzbrunn 1977
- Gregor Häberle, Heinz Häberle, Thomas Kleiber: Expertise in radio, television and radio electronics. 3rd edition, Verlag Europa-Lehrmittel, Haan-Gruiten 1996, ISBN 3-8085-3263-7