The fluctuation in signal strength at a receiver, which is mainly due to the interference of two waves which left the same source but arrived at the destination by different paths, is known as fading. Fading can be caused due to natural weather disturbances, such as rainfall, snow, fog, hail and extremely cold air over a warm earth. Fadingcan also be created by man-made disturbances, such as irrigation, or from multiple transmission paths, irregular earth surfaces, and varying terrains.