a total of 252 frequencies are defined (but not all used) for dme interrogations and replies—specifically, 962, 963, ... 1213 megahertz. interrogation frequencies are 1025, 1026, ... 1150 megahertz (126 total), and are the same for x and y channels. for a given channel, the reply frequency is 63 megahertz below or above the interrogation frequency. the reply frequency is different for x and y channels, and different for channels numbered 1-63 and 64-126.