Impact of Soil Texture on Path Loss Modelling of an FM Signal Using Diffraction Technique

Abstract

A novel solution to predict path loss of an FM signal using diffraction technique is proposed. Diffraction technique and soil texture impact are used to improve the Friis free-space model to predict the received signal strength and propagation path loss of an FM signal between a transmitter site and receiver site, while studying the impact of soil texture to the FM signal in the case of surface wave propagation. Measurement of signal strengths with an interval of 5KM along two different routes (1 and 2) were taken with a Digital Field Strength Meter (DW-400), in some selected open/rural environments of Kogi State. A solid-state transmitter (BE 20S), with broadcast frequency of 101.5MHz at antenna height of 120m was considered as the transmitting point source. Bluetooth signal strength meter software was used to visualize this impact of soil texture, where different types of soil were considered within the coverage area of the FM radio station, with the application of a Wireless Personal Area Network (WPAN) technology. Measurements taken along the two different routes were compared against predictions made by the modified model of Friis Free Space. The model showed quite large mean path loss prediction errors, and places with poor signal strength for Prime FM Radio Nigeria were revealed. The result shows that an FM signal induces current in the ground over which it passes and it is attenuated as a result of absorption of energy by the soil, depending on the soil type.