What is the foundation of the VOR station's transmission principle?

The foundation of the VOR (VHF Omnidirectional Range) station's transmission principle is based on the creation of a phase difference between radio frequency (RF) signals. VOR stations transmit two signals: a reference signal that is omnidirectional and a variable signal that is directional. The key element of VOR technology lies in how these signals interact. The aircraft's receiver measures the phase difference between the reference signal and the variable signal. By calculating this phase difference, the aircraft can determine its bearing relative to the VOR station.

This principle is crucial for aircraft navigation as it enables pilots to navigate accurately by providing them with directional information. Understanding how the phase difference works allows pilots and air traffic controllers to effectively use VOR stations for navigation, making it a fundamental concept in aeronautical navigation systems.

The other options represent different technologies or systems used in navigation but do not directly relate to the specific operational principle of the VOR system itself. For instance, GPS is a different navigation system that relies on satellites, while visual landing aids and multiple navigation systems pertain to different aspects of aviation but do not explain the transmission principle of VOR systems.