Investigation of the Vertical Profile Radio Refractivity Gradient and Effective Earth Radius Factor (k-factor) in Transmission Link Over Oyo, Oyo State, South Western Nigeria

Abstract

Surface radio refractive gradient and k-factor are very imperative in observing propagation conditions, designing and planning of microwave communication links in the lower part of the atmospheric boundary layer. The measurement of weather variables (air temperature, atmospheric pressure, relative humidity and wind speed) were conducted in this study at the School of Science, Emmanuel Alayande College of Education, Oyo (7.83°N, 3.95°E), Oyo State, Nigeria. The research was carried out for a period of one year (January to December, 2020) using self-designed cost effective portable weather monitoring systems. The systems were sited from the ground to a height of 200 m on a 220 m Nigeria Television Authority (NTA) UHF channel 37 tower at Oke-Apitipiti in Oyo Town of Oyo State. The calculated daily and monthly averages data are employed to investigate the vertical surface radio refractivity and its refractivity gradient. The highest value of -1.093E+26 N-units/km was recorded in January, while the month of July experienced the least of about -9.305E+19 N-units/km. The months of January–July verified sub-refractive conditions with propagation conditions having varying degree of occurrence. On the other hand, super-refraction and ducting were recorded mostly between August–December from the study. The results also find applicability in radio engineering for refining VHF/UHF terrestrial links based on clear-air considerations which will support operational planning of terrestrial radio networks in Oyo, South Western Nigeria.

Keywords: Microwave; k-factor; refractivity gradient; sub-refractive; super-refraction