Analysis of Electromagnetic Field Strength of Amplitude Modulation Channel of Radio Benue and its Relationship with Theoretical Propagation Models

Abstract

Electromagnetic wave propagation is fundamental to AM broadcasting, where signal quality depends on field strength influenced by frequency, terrain, atmospheric conditions, and antenna design. This study addresses the problem of limited coverage and signal degradation in medium-wave amplitude modulation (AM) broadcasting due to ground-wave attenuation over distance. The aim is to evaluate the variation of electromagnetic field strength for an AM channel operating at 918 kHz and to assess the applicability of existing propagation models. Measurements were conducted using a hand-held electromagnetic field strength meter calibrated from 1 mV to 10 V at twenty-four (24) locations at increasing distances from the transmitter across the state. Data computation was based on established ground-wave propagation models, while statistical regression analysis was used to examine the relationship between field strength (E) and distance and to compare model predictions under varying instrument sensitivity. Results showed that field strength decreases with distance, with the coefficient of determination (R²) indicating good agreement with the Sommerfeld model at short ranges (R² = 0.823 for d < 50 km) but declining sharply at longer distances (R² = 0.065 beyond 125 km), confirming that no single model is valid across all ranges. Weak and distorted signals were observed beyond 100 km, with near-total signal loss at some locations. Ground loss was found to depend strongly on the dielectric properties of the propagation medium which varies with the nature of the soil. These findings imply inadequate coverage by the existing system thus, increased transmitter power or the installation of at least two booster stations is recommended for improved signal coverage.