2-45 OPTIMUM WORKING FREQUENCY (fot)is the most practical operating frequency and the one that can be relied on to have the fewest problems. PRECIPITATION ATTENUATIONcan be caused by rain, fog, snow, and hail; and can affect overall communications considerably. TEMPERATURE INVERSIONcauses channels, or ducts, of cool air to form between layers of warm air, which can cause radio waves to travel far beyond the normal line-of-sight distances. TROPOSPHERIC PROPAGATIONuses the scattering principle to achieve beyond the line-of-sight radio communications within the troposphere.
