In a VOR frequency box, what does "D (H)" signify?

The designation "D (H)" in a VOR frequency box indicates that the VOR is both DME equipped and classified as a High VOR. This means that the VOR station is capable of providing Distance Measuring Equipment (DME) services, allowing pilots to obtain their distance from the VOR station in nautical miles. Additionally, a High VOR refers to the altitude coverage of the station, indicating that it can be used at greater altitudes, often providing a service range that surpasses that of a standard VOR.

High VORs typically cover higher altitudes to assist with navigation in more elevated airspace, making them particularly useful for en route and approach phases of flight in a wider range of altitude environments. The combination of DME capability with High VOR classification enhances the utility of the navigation aid for pilots, allowing for more precise navigation over greater distances.