# Radio Frequency Interference, Its Mitigation and Its Implications for the Civil Aviation Industry
## 3 Literature Review
[28] stipulate findings that UAVs utilize specific radio frequency bands, such as 72-73 MHz, 902-928 MHz, and 2400-2483.5 MHz, which are also employed by technologies like Wi-Fi and ZigBee. This overlap can cause radio frequency (RF) interference, particularly in urban settings with numerous devices, increasing the risk of signal disruption. During bridge inspections, this interference can weaken signal strength, degrade video quality, and impair GPS functionality, thus compromising UAV control and safety. To address these challenges, it is essential to choose UAVs with robust RF immunity capable of effectively managing interference. Furthermore, UAVs should have minimal switching delays between redundant communication channels to ensure seamless operation. Conducting a comprehensive assessment of the inspection environment to identify potential RF noise sources is also crucial. By adopting these measures, the reliability and safety of UAV operations during bridge inspections can be improved, leading to successful outcomes even in demanding environments. Figure 10 shows the utilization of a specific frequency band by a UAV. [PERSON], [PERSON], and [PERSON] [29] examine path loss in long-range air-to-ground (AG) communication systems using the UHF band. They find that the measured path loss aligns well with the predictions of the established models. The UHF band has been shown to be more reliable than higher frequencies, particularly in reducing multipath fading and atmospheric effects, which are crucial for long-distance communication. The analysis reveals that path loss behavior varies with different ground station environments, such as sea and ground reflections, and that multipath components can occur even at long ranges. Flight tests were conducted to observe path loss and multipath characteristics \begin{table}
\begin{tabular}{l c c c c c c c c} \hline \hline
**Rx Tx** & **VHF Top** & **HF** & \begin{tabular}{c} **VHF** \\ **Bottom** \\ \end{tabular} & **UHF Top 1** & **UHF Top 2** & \begin{tabular}{c} **UHF** \\ **Bottom 1** \\ \end{tabular} & \
\begin{tabular}{c} **UHF** \\ **Lowerband** \\ \end{tabular} &
\begin{tabular}{c} **UHF** \\ **Bottom 2** \\ \end{tabular} \\ \hline VHF top & 25.3 & \(-0.8\) & 26.9 & 28.9 & 21.8 & 53.5 & 45.8 & 50.1 \\ \hline HF & \(-0.8\) & 9.8 & 22.4 & 22.4 & 21.8 & 28.5 & 28.6 & 28.6 \\ \hline ESM left & 13.4 & 49.9 & 28.8 & 25.8 & 29.7 & 38.5 & 39.5 & 39.5 \\ \hline ESM right & 14.3 & 43.0 & 22.0 & 25.4 & 31.6 & 29.3 & 46.7 & 46.7 \\ \hline VHF bottom & 29.4 & 27.9 & 44.3 & 44.3 & 52.8 & 39.5 & 37.0 & 27.1 \\ \hline UHF top 1 & 30.0 & 39.5 & 39.8 & 19.3 & 19.3 & 39.8 & 40.0 & 40.0 \\ \hline UHF top 2 & 20.8 & 39.3 & 12.3 & 63.4 & \(-47.4\) & 38.9 & 39.8 & \(-61.4\) \\ \hline UHF bottom 1 & 39.7 & 39.9 & 30.4 & 63.4 & \(-47.4\) & 40.0 & 25.6 & 30.4 \\ \hline UHF lowerband & 36.8 & 39.9 & 25.7 & 40.0 & 40.0 & 25.6 & 28.2 & 30.4 \\ \hline UHF bottom 2 & 38.9 & 39.9 & 25.0 & 40.0 & \(-30.5\) & \(-30.5\) & 27.8 & 30.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Signal strength measurements (DB). in realistic scenarios. The setup included UHF antennas, a high-power amplifier, and a channel sounding configuration, allowing data collection over distances of hundreds of kilometers. These findings suggest that UHF communications can be effectively used in UAV systems for military and civilian applications, especially in challenging environments. This research highlights the importance of empirical measurements in developing accurate models for long-range AG communications, aiding in the design and optimization of AG communication systems for reliable UAV connectivity. Figure 11 shows the path loss in long-range A/G communication system. [PERSON] [30] describes an ILS, crucial for civil aviation, helping pilots land safely in poor visibility and adverse weather. It uses wireless signals and instruments for precise guidance. Traditionally, maintenance relied on time domain analysis, which can be inaccurate, especially for weak signals.