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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
________
EFFECTIVITY LH 001-010,031-050,071-081;
AF 101-120, 123-151; AZ 201-219; CONFIG 1 IB 405 03 Page 1
Apr 25/95
34-55-00
SEE A
DME ANTENNA NO. 1
DME ANTENNA NO. 2
SEE B
DME INTERROGATORS
DME 1 DME 2
1 DME 2 WARNING
2 010 09
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 1
LH 001-010,031-050,071-081;
799 Page 2
AF 101-120,123-151; AZ 201-219;
34-55-00
Apr 25/95
IB 405
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
__________________
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 shelf E3-6 in the main electronics equipment center. (See figure 1.)
C. The DME channel that has been selected by the VHF NAV control panel is visible from the rear top of the interrogator. Coarse distance indication is visible from the front of the unit, and VOR or ILS channel identification is visible on the left side of unit.
D. Two cable connectors (Pl and P2) at the rear of the unit provide interconnection for the system and ATE (automatic test equipment). Two coaxial connectors (SUPPR and ANT) on the front panel connect the suppressor pulses and the antenna to the interrogator. The RCVR OUT coaxial connector is not used.
5. Indicators
__________
A. The DME indicators are mechanical analog counters, which display nautical miles-to-go n three individual counter dials of hundreds, tens, and units. There are two DME indicators, one for each system, contained within each pilots' radio magnetic indicator (RMI). The left-hand DME indicator in each RMI displays mileage from DME No. 1 and the right-hand indicator displays mileage from DME No. 2.
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