User's Manual

Figure 1-1 Basic X-Channel DME System Block Diagram
Refer to Figure 2-2. As stated, the transponder beacon must be interrogated by the aircraft before the
ground facility can transmit usable distance information. Assuming an aircraft has interrogated the ground
facility; the interrogation signal is received at the beacon antenna, and then routed to the receiver through
the Circulator and Preselector. The signal is then amplified and fed to the Receiver Transmitter Controller
(RTC) for verification of proper pulse spacing. Once receive pulses are validated the RTC encodes a reply
with the proper pulse spacing and delay.
The shaped pulses modulate the gated RF in the transmitter power amplifier (PA) to produce the RF output
pulses. The output pulses are then sent to the antenna and radiated to the aircraft as reply pulse pairs.