Abstract:
This paper investigates the effect of interference on Aeronautical Navigation systems by Frequency Modulation (FM) broadcasting signals. Precisely, the paper evaluated the impact of 3rd order intermodulation distortion on the VHF omnidirectional range and the instrument landing system (Localizer) used at the Ghana Civil Aviation Authority (GCAA). The necessity of this study stems from the fact that, electromagnetic compatibility (EMC) between FM audio broadcast and aeronautical radio communication services operating in the range of 85.7-108MHz and 108-117.975 MHz respectively is essential for safe flight operation. An analytical method of estimating the 3rd order intermodulation distortion has first been presented followed by simulation approach with the intermodulation analysis software v.10 and subsequent simulation with the Matlab software to determine and display the power spectral density of the output signals. All FM station frequencies in the Greater Accra region have been considered and paired to form dual tone signals that were considered input signal before assessing the impact of the 3rd order intermodulation harmonic. It was found that multiple 3rd order intermodulation harmonics distort and perturbate the aeronautical communication system in the Greater Accra region and these lead to severe safety implications for the operation of the aeronautical navigation system. It was recommended that broadcasting stations should implement cavity filters to reduce the effect of 3rd order intermodulation harmonics; they should respect the specification prescribed to them by the NCA and operate within limits allocated to them in order not to breach the international regulation of ITU that deems it an offense to interfere with the aeronautical communication system and to further ensure safety to the aviation navigation system.