DME stands for Distance Measuring Equipment. As the name suggests, it gives distance information. Gives the pilot-in-command the distance between the aircraft and the ground station/beacon. The point to be noted here is that DME devices do not provide direction information.
DME Device Frequency Range
Due to their nature, DME devices broadcast in the UHF band. So it works at fairly high frequencies. The frequency band for DME devices is in the range of 962 – 1213 Mhz. DME is often used with VOR and ILS systems. In this way, the pilot receives the direction and distance information at the same time and it is possible to determine the exact location. In such systems, when the pilot chooses the VOR frequency, he automatically chooses the DME frequency (VOR/DME). Sometimes DMEs are used to provide distance information from the start of the runway for some non-precision approach procedures such as VOR approach.
The DME device is usually placed on or very close to the VOR antenna; In ILS systems, it is placed in the GP (Glide Path) station. In case the marker cannot be established due to geographical conditions or other reasons; A DME device can be installed together with the Glide Slope device to provide distance information for the runway.
While NDB and VOR are only transmitters, DMEs are transmitters and receivers. There is a transponder antenna on the aircraft and at the ground station. During flight, signals are sent from the aircraft to the DME receiver. Signals coming to the DME receiver are processed and routed back again. The transponder on the aircraft evaluates the signal it receives from the ground. Thus, distance information is obtained from the round trip time in between. Thus, the pilot reads the distance in nautical miles (nm) on the display in the cockpit.
The DME device is also defined by EUROCONTOL as follows.
Distance Measuring Equipment (DME) is defined as a combination of ground and airborne equipment which gives a continuous slant range distance-from-station readout by measuring time-lapse of a signal transmitted by the aircraft to the station and responded back. DMEs can also provide groundspeed and time-to-station readouts by differentiation.
(EUROCONTROL EATM Glossary of Terms)
The symbol of the DME device on the navigation maps and charts is square. When working in combination with different navigation systems, the symbol combinations are as in the figure.