Selex Sistemi Integrati Inc. DMEH2 ユーザーズマニュアル
1. TECHNICAL DESCRIPTION
1.1 Introduction
This section contains a technical description of the single and dual 2160 and 2170 DME. This includes,
simplified system block diagram theory and block diagram and detailed circuit theory of the Circuit Card
Assemblies (CCA) contained in the system.
1.2 DME Operation Principles
Refer to
Figure 1-1.
The DME system requires a single-channel receiver-transmitter combination
(transponder beacon) in conjunction with a special omni-directional antenna as the ground station, and a
multichannel receiver-transmitter combination (interrogator) on board the aircraft. One multichannel
airborne receiver-transmitter (transmitting and receiving coded, pulsed information) provides both the
distance and identification functions.
The DME system has 252 operating channels, with the adjacent channels spaced one megahertz apart. For
air-to-ground transmission (interrogation), there are 126 channels within the frequency band of 1025 MHz
to 1150 MHz. For ground-to-air transmission (reply), there are 63 channels in the frequency of 960 MHz
to 1024 MHz, plus 63 channels in the frequency band of 1151 MHz to 1215 MHz.
The DME system utilizes pulse-coding techniques in the transmission of its intelligence. The transmissions
are composed of pulse groups with a prearranged spacing between the pulses of the group. For X-
Channels, the interrogation pulses and the transponder reply pulses are both spaced 12 µs apart. For Y-
Channels, the interrogation pulses are spaced at 36 µs; and the transponder reply pulses are spaced at 30 µs.
Both the interrogator and transponder receivers employ pulse decoders, which are set to pass only pulse
pairs of the prescribed spacing. The purpose of the two-pulse technique is to increase the signal-to-noise
ratio and to discriminate against pulse interference, such as might be produced by radar transmission and
other extraneous sources of RF energy on the frequency. The intelligence supplied to the aircraft by the
DME transponder is both identity and distance information. The identity information is necessary for the
pilot to positively identify the station that has been selected. Identity information is provided to the aircraft
approximately every 30 seconds. The distance information, however, is provided to the aircraft only upon
demand. Each aircraft must interrogate the ground facility by means of the coded interrogation pulse pairs,
before the transponder beacon can generate and transmit distance information.
multichannel receiver-transmitter combination (interrogator) on board the aircraft. One multichannel
airborne receiver-transmitter (transmitting and receiving coded, pulsed information) provides both the
distance and identification functions.
The DME system has 252 operating channels, with the adjacent channels spaced one megahertz apart. For
air-to-ground transmission (interrogation), there are 126 channels within the frequency band of 1025 MHz
to 1150 MHz. For ground-to-air transmission (reply), there are 63 channels in the frequency of 960 MHz
to 1024 MHz, plus 63 channels in the frequency band of 1151 MHz to 1215 MHz.
The DME system utilizes pulse-coding techniques in the transmission of its intelligence. The transmissions
are composed of pulse groups with a prearranged spacing between the pulses of the group. For X-
Channels, the interrogation pulses and the transponder reply pulses are both spaced 12 µs apart. For Y-
Channels, the interrogation pulses are spaced at 36 µs; and the transponder reply pulses are spaced at 30 µs.
Both the interrogator and transponder receivers employ pulse decoders, which are set to pass only pulse
pairs of the prescribed spacing. The purpose of the two-pulse technique is to increase the signal-to-noise
ratio and to discriminate against pulse interference, such as might be produced by radar transmission and
other extraneous sources of RF energy on the frequency. The intelligence supplied to the aircraft by the
DME transponder is both identity and distance information. The identity information is necessary for the
pilot to positively identify the station that has been selected. Identity information is provided to the aircraft
approximately every 30 seconds. The distance information, however, is provided to the aircraft only upon
demand. Each aircraft must interrogate the ground facility by means of the coded interrogation pulse pairs,
before the transponder beacon can generate and transmit distance information.