Study of Propagation Characteristics of HF Radio Waves for Emergency Communication in Northern Nigeria

High-frequency radio communication remains the most reliable emergency communication channel in remote areas of Northern Nigeria where cellular network coverage is absent or disrupted during security incidents and disasters. Understanding HF propagation characteristics over the Northern Nigeria ionospheric path is essential for optimising operating frequencies and antenna configurations for emergency response networks. This study characterises HF radio wave propagation between Kano and Maiduguri (a path length of approximately 750 km) using oblique-incidence sounding measurements and IRI-2020 ionospheric model predictions. Measured maximum usable frequency, lowest usable frequency, and field strength are recorded at three-hour intervals during the 2022 to 2023 period using a dedicated digital HF link. Signal-to-noise ratio and circuit availability at different operating frequencies are computed. Results indicate that frequencies between 9 and 14 MHz achieve the highest circuit availability of 85 to 92 percent during the daytime. Night-time propagation is dominated by the F2 layer with significantly higher MUF variability. Equinoctial disturbances reduce circuit availability by 15 to 25 percent during March and September. The study provides operating frequency planning data for emergency HF networks operated by the North East Regional Security Architecture. Keywords: HF propagation, emergency communication, ionosphere, Northern Nigeria, maximum usable frequency