What is a characteristic typical of VHF radio signals?

VHF (Very High Frequency) radio signals are primarily characterized by their reliance on line-of-sight transmission. This means that the effective range of VHF signals is limited to the distance over which they can be directly transmitted without obstructions. Since VHF waves are relatively short in wavelength, they do not easily diffract around obstacles or the curvature of the Earth, which is why the line-of-sight characteristic is so important.

In aviation, this means that VHF radios are used for communication between aircraft and air traffic control, where both parties are in direct line of sight, ensuring clear and reliable transmission. The use of VHF radios is advantageous in many flight operations, particularly in areas where there are few obstructions, allowing pilots to maintain clear communication.

The other characteristics presented in the options do not apply to VHF radio signals. They do not travel around the curvature of the Earth, cannot penetrate through water effectively, and while weather can influence radio wave propagation, the line-of-sight characteristic remains the primary defining trait of VHF communications.