An Appraisal of Duct-Related Microwave Link Degradation in Nigeria

Drop in power (or field strength) of free-air radiowaves sometimes occur in line-of-sight paths within the radio horizon of the transmitter due to discontinuities in refractivity gradient. Field strength fading within the radio horizon may result from defocusing of the lobe pattern of the transmitter, and may simultaneously give rise to enhanced field strengths beyond the horizon, with potential for adverse interference on co-channel circuits and other degradation effects related to such anomalous propagation. These effects increase with the duct strength, which depends on the prevailing refractivity gradient within the duct. In a duct-prevalent region, anomalous propagation problems can be significant on terrestrial and slant earth-satellite paths, depending on the penetration angle and strength of the prevailing ducts. Studies have revealed considerable prevalence of surface ducts in Nigeria. This effort examines the climatic conditions that give rise to ducts and assesses their potential for degradation of microwave links in the country. The result based on analysis of clear-air meteorological data shows prevalence of strong surface ducts with maximum and mean penetration angles of 15 milliradians and 6-8 milliradians respectively. Thus, high-elevation slant earth-satellite paths may not be affected by duct-related propagation problems in Nigeria, but low-elevation terrestrial microwave links may be significantly impaired.Key words: radio refractivity, surface duct, penetration angle, refractivity gradien

Climatic and seasonal variations of effective-earth-radius factor and scale height in three metereological stations in West Africa

No Abstract.Nigerian Journal of Physics Vol. 20 (1) 2008: pp.102-11

Slant-Path Rain Attenuation Statistics over Nigeria

Slant path attenuation of microwaves due to rainfall intensities exceeding 0.01 and 0.001per cent of average year have been computed for five different geographical zones in Nigeria, using relevant ITU-R recommendations and global rain rate data. The resulting charts can be used for preliminary estimates of maximum rain-induced attenuation of microwaves expected on earth-satellite paths of elevation angles 20-90degrees in Nigeria, for the L, C, ka and ku frequency bands, which are presently used by the Nigerian communication satellites. The study shows that attenuation is higher for western, southern, or lower altitude stations. Also attenuation of horizontally polarized waves exceed that of vertical polarization by increasing margins at higher frequencies, which makes vertical polarization more preferable at higher microwave frequencies. Thus, the emerging LEO and MEO satellite systems that will operate on frequencies as high as 40 GHz may be practically restricted to vertical polarization due to rain attenuation. Based on the curves, rainfall attenuation in Nigeria may be negligible on slant microwave links at L-band and lower frequencies, no matter the elevation angle; but may cause significant propagation problems at C-band and higher frequencies,especially at low elevation angles.Key words: Microwave attenuation, polarization, radio propagation, frequency band, rainfall rate

Design and Construction of a Car Immobiliser with SMS Alert

As technological knowhow is on the increase, so also are those of criminals and die hard professional thieves who beat existing car security gadgets to carry out their notorious activity. One advantage such criminals enjoy is the inability of existing car security gadgets to establish communication between the car and its owner from the exact instant of intrusion. This gives criminals ample time to deactivate the car security. This work bridges this gap using a common and handy everyday communication tool, the mobile phone. With the very wide GSM coverage, one of its products, the Short Message Service (SMS) can be employed to send an alert to a vehicle owner who in turn sends an instruction to the car, to initiate safe and remote vehicle immobilization.Keywords: Immobilizer, S.M.S, micro-controller, sensor, and activation/de-activatio