DGPS MAX

signal’s power being distributed over an increasing surface area as thesignal radiates away from the transmitting antenna.The expected range of a broadcast also depends upon theconductivity of the surface over which it travels. A signal willpropagate further over a surface with high conductivity than over asurface with low conductivity. Lower conductivity surfaces such as dry,infertile soil, absorb the power of the transmission more than higherconductivity surfaces, such as sea water or arable land.A radiobeacon transmission has three components: a direct line ofsight wave, a ground wave, and a sky wave. The line of sight wave isnot significant beyond visual range of the transmitting tower, and doesnot have a substantial impact upon signal reception.The ground wave portion of the signal propagates along the surface ofthe earth, losing strength due to spreading loss, atmospheric refractionand diffraction, and attenuation by the surface over which it travels(dependent upon conductivity).The portion of the beacon signal broadcast skywards is known as thesky wave. Depending on its reflectance, the sky wave may bounce offthe ionosphere and back to Earth causing reception of the groundwave to fade. Fading occurs when the ground and sky waves interferewith each other. The effect of fading is that reception may fade in andout. However, this problem usually occurs in the evening when theionosphere becomes more reflective and usually on the edge ofcoverage areas. Fading is not usually an issue with overlappingcoverage areas of beacons and their large overall range.Atmospheric attenuation plays a minor part in signal transmissionrange, as it absorbs and scatters the signal. This type of loss is theleast significant of those described.1.5.3.2 Radiobeacon ReceptionVarious sources of noise affect beacon reception, and include:DGPS MAX Reference Manual 16