Radio Theory 4

$Why use a Single Sideband (SSB)? An AM signal has two thirds of its power sent out in the carrier and only one third in each of the sidebands. By eliminating the carrier and emitting only one sideband the transmitter's available power is used to greater advantage. These lower power requirements allow SSB messages to be transmitted over several thousand miles. The SSB also compresses speech into a much narrower bandwidth. (3KHz as opposed to 9KHz for a normal signal) because of this SSB conserves spectrum space. Polarization Polarization can affect the total range of a radio transmission, generally vertical polarization gives better range for frequencies up to VHF. Horizontal polarization gives better range for frequencies of UHF or higher, When a radio wave is transmitted from an antenna, it consists of two distinct fields: The Electrical Field (E) The Magnetic Field (H) Signal Loses Free Space Loss The free space loss occurs as the signal travels through space without any other effects attenuating the signal it will still diminish as it spreads out. This can be thought of as the radio communications signal spreading out as an ever increasing sphere. Absorption Losses Occur if the radio signal passes into a medium which is not totally transparent to radio signals. This can be likened to a light signal passing through transparent glass. Diffraction losses occur when an object appears in the path, the signal can diffract around the object, but losses occur. The loss is higher the more rounded the object as radio signals tend to diffract better around sharp edges. Multipath Signals will be reflected and therefore they will reach the receiver via a number of different paths. These signals may add or subtract from each other depending upon the relative phases of the signals. If the receiver is moved the scenario will change and the overall received signal will be found vary with position. Terrain The terrain over which signals travel will have a significant effect on the signal. Hills which obstruct the path will considerably attenuate the signal, often making reception impossible, additionally at low frequencies the composition 0/2 v of the earth will have a marked effect. Buildings and Vegetation For mobile applications, buildings and other obstructions including vegetation have a marked effect. Buildings reflect radio signals, and also absorb them. While trees and foliage can attenuate radio signals, particularly when wet.$