R **ON A/C 106-149, 201-299, 301-399, 401-499,
 (Ref. Fig. 002A)
 Energization of each system is through 115VAC 400 Hz buses :

 -
115VAC SHED ESS BUS 801XP via circuit breaker 1SD1 for system 1

 -
115VAC BUS2 BUS 204XP via circuit breaker 1SD2 for system 2. The 115VAC ESS BUS 401XP energizes the VOR/ADF/DME RMI via circuit breaker 12FN.

 **ON A/C ALL
 5. Component Description
_____________________
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 A. DME Interrogator
 (1) External description (Ref. Fig. 005) The face of the interrogator is fitted with a handle, two attaching parts, two momentary pushbutton switches and a front panel Liquid Crystal Display (LCD). The LCD is used as a fault display and as an operator interface during certain modes. The front panel display also provides user interfaces for test and troubleshooting. The front panel contains two momentary pushbutton switches for interfacing with the LCD pages. An RS-232 maintenace access port is provided on the front panel. This port is compatible with RS-232 serial ports on Personal Computers (PC). The back is equipped with one ARINC 600 size one connector, which includes three plugs:
 -Top Plug (TP): is not installed
 -Middle Plug (MP): aircraft interconnection, and the coaxial antenna
 -Bottom Plug (BP): connection with the power supply circuit.

R **ON A/C 051-099, 106-149, 201-299, 301-399, 401-499,
 A. DME Interrogator
 (1) Description (Ref. Fig. 005A) The face of the interrogator is fitted with a handle, two lugs, a TEST pushbutton switch and two LEDs. The name, color and function of the two LEDs are as follows:
 -CONTROL FAIL (red) indicates invalid frequency input tuning words
 -
LRU STATUS (green) indicates that no faults are detected during the test sequence

 -
LRU STATUS (red) indicates that a fault is detected during the test

 sequence. The back is equipped with two ARINC 600 size one connectors which include three plugs:
 -Top Plug (TP): connection with the automatic test circuit
 -Middle Plug (MP): connection with the antenna and peripheral circuits
 -Bottom Plug (BP): connection with the power supply circuit and suppressor.
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 DME - Interrogator Figure 005 
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 DME - Interrogator
 Figure 005A

R 1EFF : 051-099, 106-149, 201-299, 301-399, 1 34-51-00Page 20 1401-499, 1Aug 01/05 1 1 1CES 1R **ON A/C 001-049, 101-105, 151-199,

 (2) Internal description
 (Ref. Fig. 006)
 The DME interrogator includes:

 -an RF module,
 -
a synthesizer/modulator assembly,

 -
a main processor (CPU and I/O) assembly,

 -
a video processor,

 -
a power supply assembly,

 -
a rear interconnect module,

 -
a front panel display module,

 -
a memory card interface module.

 (a) RF module This module consists of a single Personal Computer (PC) board that is mounted in a closed aluminum chassis. It contains:
 -
a transmitter,

 -
a receiver,

 -
a circulator,

 -
a low-pass filter.

 1 Transmitter
_ The solid-state transmitter contains a six-stage amplifier followed by a 700W (typical) final amplifier. The pulse modulation is applied to the first six stages of amplification. It is tuned to frequencies in the 1025-1150 MHz range.
 2 Receiver
_ The single-conversion superheterodyne receiver consists of a varactor tuned preselector, 1 GHz preamplifier, mixer, band-pass filters, and a 63 MHz logarithmic IF amplifier. The preselector is tuned to frequencies in the 962-1213 MHz range.
 3 Circulator
_ The circulator routes the transmitter output to the antenna and the antenna received signal to the receiver. It provides isolation to protect the transmitter output amplifier devices from reflected signals.
 4 Low-pass filter
_ The low-pass filter prevents internal transmitter harmonics from being passed to the antenna.
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 DME Interrogator - Simplified Block Diagram
 Figure 006

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 (b)
 Synthetizer/Modulator Assembly This module contains the digital frequency synthesizer and transmitter modulator circuits. The digital frequency synthesizer supplies a signal used both as the local oscillator input to the receiver mixer and as the low-level CW signal the transmitter. This circuit consists of a phase-locked loop and Voltage Control Oscillator (VCO) which is tuned to the desired channel frequency by a serial tuning word supplied by the video processor module. The modulator supplies the on/off signal that corresponds to the X or Y pulse pairs associated with the channel frequency. An interrogation is transmitted by triggering the series of on/off modulation to control the transmitter amplifier stages that drive the final amplifier.
　
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