Profiling of Radio Propagation in VHF Band

Abstract

The Very high frequency (VHF) band spans from 30 MHz to 300 MHz and is designated for public safety and disaster relief networks, FM radio broadcasting, TV broadcasting, air traffic control and many other mission critical services.  Most of these services often utilize the lower part of the VHF band and the coverage areas of such systems could be above hundreds of kilometers, which may require several transmitters operating in a quasi-synchronous mode. In addition, frequency reuse within this band for example, in the case of FM radio could result in excessive boarder area interference. Therefore, to minimize interference, even with the coexistence of these systems, there is a need to examine the behaviour of radio wave propagation in the band. Radio propagation models have been used extensively in interference analysis, coverage prediction and optimization. Most of the widely used models are location dependent, which, therefore, calls for continued efforts to ensure that location specific measurements are taken and used as planning tools, towards understanding the limitations arising from specific environmental conditions. In this work, Electromagnetic field (EM) strength measurements  were  conducted in Ilorin (Long 4^o 36’ 25”E, Lat 8^o 25’ 55’’N) and its environs within Kwara State, Nigeria, along some predefined routes, using dedicated Agilent N943C 100 Hz - 7 GHz spectrum analyzer. For each route, the measured received signal levels (RSLs) were obtained, profiled over the terrain and compared with simulated signal values obtained for COST 231, Egli, Hata and ILORIN models. A total of three transmitters were utilized; two in the lower VHF (LVHF) and one in the upper VHF (UVHF) bands. Results obtained showed that there is severe fading along all the routes considered, for all the broadcasting stations, with the highest signal level estimation observed for Egli, followed by COST 231, Hata and ILORIN model in that order. Measurements results also indicate that the received signal level is found to follow the terrain elevation for the models considered. However, the ILORIN model, which is a localized model was found to provide better predictions, despite the fact that the signal follows the terrain profile.