DME frequencies are paired to VHF omnidirectional range (VOR) frequencies. A DME interrogator is designed to automatically tune to the corresponding frequency when the associated VOR is selected. An airplane’s DME interrogator uses frequencies from 1025 to 1150 MHz. DME transponders transmit on a channel in the 962 to 1150 MHz range and receive on a corresponding channel between 962 to 1213 MHz. The band is divided into 126 channels for interrogation and 126 channels for transponder replies. The interrogation and reply frequencies always differ by 63 MHz. The spacing of all channels is 1 MHz with a signal spectrum width of 100 kHz.
Technical references to X and Y channels relate only to the spacing of the individual pulses in the DME pulse pair, 12 microsecond spacing for X channels and 36 microsecond spacing for Y channels.
DME facilities identify themselves with a 1350 Hz morse code three letter identity. If collocated with a VOR or ILS it will have the same identity code as the parent facility. Additionally, the DME will identify itself between those of the parent facility. DME identity is 1350 Hz to differentiate itself from the 1020 Hz tone of the VOR or the ILS localizer.
http://en.wikipedia.org/wiki/Distanc...ring_Equipment