Radio Wave Propagation Essay Example | Topics and Well Written Essays - 1500 words

Radio Wave Propagation - Essay Example So waves lose strength rapidly. [1] Radio waves travel very fast but only in a straight line. Thus the curvature of the earth should limit the distance between transmitter and receiver, a distance of about 60 miles 100 km). However, the earth's atmosphere has properties that allow enhanced propagation. The atmosphere is layered, and these layers have important effects on waves that are propagated on the earth's surface. The layer called the troposphere is a heavy, oxygen filled layer that extends from the surface to about 30 miles (50 km) altitude. From 30m (50 km) to 260m (416 km) is a highly charged layer called the ionosphere. The ionosphere affects radio signals in different ways depending on their frequencies. [2] The frequencies used for radio propagation range from 30 kHz to 3 GHz. Frequencies are continuous but are defined in bands according to their properties and uses. Higher frequencies have shorter wave lengths and more energy: LF waves are propagated as ground waves which, as the name implies, travel along the ground. Because the ground and its terrain interfere with ground waves, transmission requires lots of power. LF waves are used mainly in maritime communications over the sea and the navigational system called LORAN. [4] Sometimes ground waves suffer from a reflecting wave off the ionosphere that can return to earth out of phase near the receiver and interfere with the direct reception. MF wave frequencies are used for AM radio broadcasting. They are also ground waves and during the daylight hours are limited to a range of about 60 miles (100 km). But radio waves can be bent or refracted by changes in the earth's atmosphere particularly by weather patterns and by the ionosphere. The Ionosphere consists of the "D" (30-60 miles [50-100 km]), "E" (60-100 miles [100-160 km]), F1 (90-160 miles [144-256 km]), and the F2 (160-250 miles [256-400 km]) layers. At night, the "E" layer disappears and the F1 and F2 layers combine to form the "F" layer (somewhere between 90 and 250 miles [144-400 km]). Since the "E" layer disappears at night, the lower frequency Sky Waves (MF) travel further up into the atmosphere, where they are REFRACTED by the "F" layer[ up to 300m]. That's why at night, your radio often picks up many more AM broadcast stations! [4] HF waves have enough energy to reach the ionosphere during the day and are refracted by its various layers. Thus short-wave can travelled much further than the curvature of the earth would normally allow. This Sky Wave propagation depends strongly on the ionosphere which is in constant flux. The ionosphere is affected by many astronomical events like meteor showers and solar flares; it is also affected by seasons. Because the ionosphere changes so much, short-wave is considered unreliable for important commercial use. However, some of the effects on radio transmission are positive. These so-called anomalous propagations are of