Which of the following systems is least susceptible to fading or static interference?

The Inmarsat system is least susceptible to fading or static interference primarily because it operates using satellites in geostationary orbit, which provide consistent and reliable communication. The use of satellites allows signals to bypass many of the atmospheric disturbances and interference issues that affect ground-based communication systems, especially those relying on high-frequency (HF) or medium-frequency (MF) bands.

In contrast, systems like HF SITOR (NBDP), MF-HF DSC Controller, and VHF ARQ are more prone to challenges like fading and static interference due to their reliance on terrestrial propagation. High-frequency signals, for example, can be heavily influenced by factors such as ionospheric conditions, distance, and the physical environment, leading to signal degradation and quality issues. Similarly, while VHF signals can offer good performance over short distances, they also can suffer from multipath interference and other environmental factors.

Overall, the satellite-based Inmarsat system is engineered for robustness against these types of interferences, making it the best choice for stable and reliable communication.