AF 101-120, 123-151; AZ 201-219; CONFIG 1 IB 405 01 Page 14
Apr 25/95
34-55-00
DME SYSTEM - DESCRIPTION AND OPERATION
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1. General_______(See figures 1 and 2.)
A. The DME (distance measuring equipment) system automatically measures the distance (in nautical miles) between the airplane and a selected ground station. The system measures the airplane-to-station slant-range distance (line-of-sight) and the information is displayed on an analog readout indicator as miles-to-go. Distance is determined by the round trip travel time of UHF interrogation-reply transmissions (between the airplane and the ground station) in the 960 to 1215 MHz range.
B. Two complete DME systems are installed in the airplane. Each system consists of an interrogator (transmitter-receiver) unit, an antenna, two distance indicators, and a remote tuning control panel. (See figure 1.)
C. The interrogator unit transmits an individualized, pulse-coded interrogation signal which actuates a corresponding ground station reply. This reply signal is received and processed by the interrogator. The time interval between the interrogation signal transmitted from the airplane and the ground station reply signal received by the airplane is measured, converted into distance, and displayed on the indicator. An audio identification tone is also associated with the ground station reply. The system has the normal operating capability of searching, locking-on and tracking out to a range of 192 nautical miles with an accuracy of | 0.2 nautical miles. Capability is limited to 50 nautical miles for some selected frequencies.
D. The DME system interface is shown in figure 2. The interrogator converts distance information into a synchro transmitter output to be displayed on both radio magnetic indicators (RMI's) which also display magnetic heading (Magnetic Heading Reference System, 34-21-00). A sample pulse is taken from each interrogator and coupled into the other DME system and to the ATC system which operates in the same general frequency range. This pulse acts as a suppression pulse. The audio is applied to the flight interphone system (23-51-00).
E. Each DME system operates on 115-volt, 400-Hz and 28-volt dc power. System No. 1 is supplied from the 115-volt ac essential radio bus and the 28-volt dc essential radio bus through circuit breakers DME 1 - AC and DME 1 - DC. System No. 2 is supplied from the 115-volt ac radio bus No. 2 and the 28-volt dc radio bus No. 2 through circuit breakers DME 2 - AC and DME 2 - DC.
2. Control Panel_____________(See figures 1 and 2.)
A. Each ground station installation is assigned a specific VOR frequency and associated DME frequency. Since the DME system operates in conjunction with the VOR navigation system, controls for both are located on the same control panel and consist of a frequency selector, a mode switch and a test button. Ground station selection and frequency display are keyed to the VOR system, and the selected DME frequency is not displayed. DME system No. 1 is controlled from the captain's control panel and DME system No. 2 from the first officer's control panel.
3. Antennas
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EFFECTIVITY
SN 301-350 CONFIG 2 03 Page 1 Apr 25/8634-55-00
SEE A
DME ANTENNA NO. 1
DME ANTENNA NO. 2
SEE B
DME INTERROGATORS
DME 1 DME 2
1 DME 2 WARNING
2 09010
FLAG
3
1 VHF NAV
108.00
VOR
ILS TEST OFF DME
VOR MODE SWITCH
FREQUENCYTEST BUTTON SELECTOR
VHF NAV CONTROL PANEL RADIO MAGNETIC INDICATOR (VOR/DME DISPLAY)
A B
DME System Component Location
Figure 1
EFFECTIVITY
CONFIG 2 SN 301-350727 Page 2
34-55-00
Apr 25/86
28V DC RADIO BUS NO. 2
CAPTAIN'S DME DISPLAY FIRST OFFICER'S DME DISPLAY
DME System Interface Diagram
Figure 2
EFFECTIVITY CONFIG 2 727 Page 3
SN ALL
34-55-00
Oct 10/73
A. The DME antennas are conventional blade-type units which are connected to the interrogator units by coaxial cable. The No. 1 system antenna is installed on the bottom of the fuselage at station 690. The No. 2 system antenna is installed at station 830. Each antenna performs both transmitting and receiving functions for its respective DME system in the frequency range of 960 to 1215 MHz.
4. Interrogator Units
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A. Each interrogator unit provides the capability to compute the time interval between transmitted and received pulse-pair signals, convert this time difference to distance, and apply this information to the DME indicator.
B. The interrogator units are standard 1/2 ATR short assemblies which mount (side-by-side) on a shelf in the main electronics equipment center. (See figure 1.)
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