Communications, Radar & Electronic Warfare (201.. - Index of

Introduction23(a) Clear radio line of sight(b) Obstructed radio line of sight(c) Diffraction path (radio non - line of sight [NLOSlFigure 1.11Different path topologies.and the signals amvmg at the receiver are diffracted over the obstructions. Thereceived signal will be significantly less than for the line of sight case ; however, it stillmay provide a workable signal level. In Figure 1. 12, the effects of Troposphericscattering are shown. This is normally not the dominant mechanism for propagationexcept for very long paths where diffracted signals are very small. Some systems do usethis method for long-range communications.In addition to these long term-effects, other shorter duration mechanisms can havean effect. These are illustrated in Figure 1. 13. These include ducting at ground level orabove it, hydro meteor scatter caused by precipitation and multi path effects. Thesefactors can have severe effects at some times, either providing extremely long paths orinhibiting radio communications at all in adverse conditions.The performance of radio links is also heavily affected by the environment in theimmediate vicinity of the transmitting and receiving antennas. Antennas locatedwithin dense urban environments, jungle or forestry, poor ground conductivity or closeto sources of radio noise or interference. These will be covered in more depth inChapter 10 and throughout the rest of the practical part of the book.