Why will a DME run out of range before a VOR?

• A. DME uses satellites
• B. VOR uses more power
• C. DME is limited by altitude
• D. VOR operates on lower frequency

Answer: (D)

Radio range for navigation aids is mainly a function of how radio waves propagate, which depends on frequency. VOR signals ride on lower-frequency VHF waves, which propagate with less loss and can be received farther from the station, especially as you gain altitude. DME, on the other hand, uses higher-frequency UHF waves. Higher frequencies suffer greater path loss and are more sensitive to obstructions, so the two-way signal between the aircraft and the DME ground station drops out sooner with distance. In practice, that means you’ll reach the DME’s usable limit before you run out of VOR range, even though you may still be within VOR service at the same airspace position. The altitude and other factors influence both systems, but the main reason is the difference in operating frequency and its effect on propagation.