Radio wave propagation mechanism in Bangladesh (2007)

To study the radio wave propagation mechanism, the field strength was predieted by calculating the radio refractive index throughout Bangladesh i.e.. at Rajshahi, Rangpur, Sylhet, Dhaka, Khulna, Barisal, Comilla and Chittagong for the years from 1986 to 1995. It was observed that the values of surface refractivity N lie between 332 to 420. The values of surface refractivity is higher in the wet season. The variation of field strength is proportional to the variation of refractivity. The field strength of ground wave depends on the conductivity of the soil i.e. the type of the soil. Introduction: Radio waves are electromagnetic waves which radiated form transmitting antenna, travels though the propagation media to distance places where they are picked up by receiving antenna. Propagation of radio waves in VHF, UHF and SHF bands are affected by the meteorological condition in the troposphere. The troposphere is an inhomogeneous medium which contains gases and water vapour. The condition in the troposphere always changes with time. So the amount of bending (refraction) of radio waves also changes from time to time. This influences the relative path length of the direct and the ground reflected component of the space wave. Hence the field strength of the space wave at the receiving point changes with time, i.e. fading of the wave occurs. So the radio engineers should have proper knowledge about the radio refractive index of the troposphere for designing trouble free radio link in a particular region for space wave. Radio broadcasting in the MW band (300-3000 KHz) is by far the commonest mode of communication with the widest audience in developing countries. A portable transistor receiver is a constant companion of the citizens of the rural areas in Bangladesh More and more broadcasting stations and relay stations are setting up to meet the requirement of the people. However the degree of fidelity in speech and music is not up to our expectation. To solve the problem, before setting up a new station, design engineers should have prior knowledge about the electrical parameters particularly the electrical conductivity of the soil over the radio wave travels. To avoid the co-channel and adjacent channel interference, measurement of field strength is also necessary for the communication engineers. Considering the above problems, the refractive index and the field strength of the radio waves were investigated at different regions in Bangladesh. The present work will help the engineers and physicists for optimizing the radio wave propagation system in this regions. Analysis and Calculation of Data Radio waves in the VHF, UHF & SHF bands propagate through the troposphere. Troposphere is the lower part of earth's surface up to a latitude of about 10 km at the polar region and 16 km at the equator. The field strength of the waves in the VHF , UHF & SHF bands depends on the surface refractivity. The refractivity depends on the meteorological condition in the troposphere. The surface refractivity (N) of the troposphere in the range of frequencies up to 100 GHz is given by the formula (Oyinloye. J. O., 1987)