DME SYSTEM - INTERROGATOR

General

The DME interrogator tunes to 252 channels and calculates distance information for all the channels in the DME range. There are 200 DME channels for the VHF NAV frequencies. The other 52 channels are for military TACAN functions. The DME receive frequency is 63 MHz above or below the transmit frequency.

Purpose

These are the purposes of the DME interrogator:

· Interrogate DME stations

· Receive the station replies

· Receive audio identifiers

· Calculate slant range distances.

 

Frequencies

These DME tuning frequencies are in the VHF band:

· 108.00 to 117.95 MHz for DME stations with VOR or ILS

· 133.30 to 135.95 MHz for DME only stations.

 

Front Panel

The front panel of the DME interrogator has these features:

· LED status indicators

· A self test switch.

 

 

DME SYSTEM – ANTENNA

General

The L-band DME antenna transmits the interrogator output signal and receives the ground station reply and identification signals.

Physical Description

The antenna has an o-ring moisture seal and attaches to the airplane with four screws. The DME and the ATC antennas are the same and are interchangeable.

Training Information Point

Extra force on the antenna may be necessary to break the weatherproofing seal. To prevent damage to aircraft skin or electrical cable at the antenna base, carefully pry around the antenna with a sealant removal tool.

 

 

 

DME SYSTEM - NAVIGATION CONTROL PANEL

General

The navigation (NAV) control panels supply frequency inputs and test commands to these navigation radios:

· DME

· ILS

· VOR.

When you put a paired VOR or ILS frequency into the navigation control panel, it also goes to the DME interrogator. The DME tunes a DME frequency in the range of 108MHz to 117.95MHZ. Set the frequency on the navigation control panel for these audio outputs:

· VOR and DME station identification

· ILS and DME station identification.

 

Operation

The NAV control panels have an active frequency display window and a standby frequency display window. The frequency that shows in the active frequency display window is the frequency that the navigation radios use for operation. The standby frequency display window shows the next frequency you will use.

The transfer switch is a momentary action switch. It transfers the frequency in the standby frequency display window to the active frequency display window. When you push the switch, the frequency that is in the active frequency display window transfers to the standby frequency display window.

The frequency select control is a continuous rotary knob. There is an inner knob and an outer knob. The outer knob sets the tens and ones. The inner knob sets the tenth and one hundreth numbers.

At power up, the frequency displays show the last frequency entry before power down.

The NAV control panel continuous BITE function monitors the operation. The NAV control panel shows FAIL in the active and the standby frequency display windows when there is a failure. The monitor in the NAV control panel monitors the 28v dc input. If the monitor does not get the 28v dc, the frequency display windows are blank.

Test

When you push the test switch, the NAV control panel sends a test command out on it’s output bus. If a VOR frequency shows in the active frequency window, the test command goes to the VOR receiver. IF an ILS frequency shows in the active frequency window, the control panel sends a test command to the ILS receivers. If there is a DME frequency that is paired with the VOR or ILS frequency, a test command also goes to the DME interrogators.

When you do a test of the master dim and test system, the NAV control panel shows 188.88. The display shows for two seconds on then one second off until the test is complete.

 

 

 

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