In this lesson, we shall understand about the term Attenuation in general and Surface Attenuation in particular. In our earlier lesson, we had understood about Polar Diagram in the context of transmission of Radio Waves.
ATTENUATION OF RADIO SIGNAL
Attenuation is the weakening of radio waves with increasing distance of transmission. Attenuation follows inverse square law of electromagnetic radiation. The law states that the power at any range is inversely proportional to the square of the range. Therefore, if we want to double the range transmission power has to be quadrupled or increased 4 times. If we want to triple the range the transmission power has to be increased 9 times.
Attenuation of waves varies due to many factors such as Frequency, Polarisation, Power Of Transmission, Transmission Path and the Medium through which the wave is transmitted. Attenuation is of three types which are called Surface, Atmospheric and Ionospheric attenuation.
SURFACE ATTENUATION
Surface attenuation of Radio Waves refers to the weakening or loss of signal strength that occurs when Radio Waves travel close to or along the earth’s surface. Factors such as Ground Conductivity, Terrain, and Obstacles can cause absorption, reflection, and scattering of the waves, reducing their power and range in surface based communication systems. Surface attenuation occurs due absorption of energy by the earth’s surface.
POLARISATION
Vertically Polarised waves have comparatively lesser contact with earth hence suffer from lesser surface attenuation. On the other hand, Horizontally Polarised waves have greater surface attenuation since they are constantly in contact with ground.
FREQUENCY
Surface Attenuation increases with frequency of the radio wave. Submarine Communication follows the surface of sea from one submarine to another. Because of this reason Very Low Frequency Bands are used for Submarine Communications. On the other hand, Satellite Communications are carried out using Extremely High Frequency Bands.
SURFACE CONDITION
Surface Attenuation is greater over land than over sea. The range over land is proportional to twice the square root of power. Range over sea would be higher than that of land range. The range over seas would be proportional to three times the square root of power transmitted.
In this post, we have understood about Surface Attenuation. In the next lesson we shall learn about the other types of attenuation like Atmospheric, Reflection and Static Attenuation.