 for effectiveness in tion Union, Geneva. spectrum utilisation is enabling the largest quantity of radio services of all useful kinds to operate effectively in a large but not limitless Levin, H.J. (1971) The invisible resource, use and regulation of the spectrum. The means that are used for achieving this objective have radio spectrum. The Johns Hopkins Press. been regulatory and technical. However, it has been argued that Withers, D.J. (1991) Radio spectrum management, Peter Peregrinus other objectives are to be preferred. Ltd. London. Radiowave propagation Mark Holker CEng FIEE MBIM Hiltek Ltd. Contents Introduction 27/3 27.2 The radio frequency spectrum 27/3 27.3 Free space propagation 27/4 27.4 The propagation medium 27/4 27.5 Low and medium frequency ground waves 27/6 27.6 High frequency skywave propagation 27/6 27.7 Terrestrial line of site propagation 27/10 27.8 Over the horizon transmissions 27/13 27.9 Propagation for satellite communications 27/14 27.10 Summary of radio wave propagation 27/14 27.11 References 27/14 This page intentionally left blank The radio frequency spectrum 27/3 Introduction 2. Ground wave propagation, where radio waves follow the sur- face of the earth. Electromagnetic energy radiates outwards from the source, usually 3. Ionospheric propagation, where radio waves are refracted by ionised layers in the atmosphere. an antenna, at approximately the speed of light and it is attenuated and influenced by the medium through which it travels. Radio 4. Tropospheric propagation, where transmission is "line of sight" communications necessitates launching r.f. energy into the propaga- with some atmospheric refraction occurring. tion medium, detecting its presence at some remote point and 5. Scatter propagation, where natural phenomena such as tropos- recovering the information contained within it, whilst eliminating pheric turbulence or ionised meteor trails are used to scatter radio waves. noise and other adverse factors introduced over the transmission path. An understanding of radio wave pr