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Flashcards in DME Deck (13)
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1

DME operates in ... band using line of sight propagation and frequencies from ... to ...MHz

UHF

960 - 1215

2

using DME, the aircraft transmits a series of pairs of pulses with ... microseconds between them, then after a delay of ... microseconds the ground station retransmits them. The time between sending and receiving the pulses is used to calculate distance

12

50

3

Using DME, how does the aircraft distinguish between its own pules returning and those of other aircraft?

by making the pulse trains unique to each aeroplane by using a random or jittered PRF so that time interval between paired pulses are random and the chance of two pulse trains being identical is effectively nil

4

Using DME, how does aircraft distinguish between retransmitted pulses from the station and reflected pulses from the ground?

the ground DME station retransmits on a different frequency, 63MHz apart from the interrogator

The paired frequencies are called channels and there are 252 available, 126 in regular use designated as X channels and another 126 Y channels which can be allocated

5

To ensure that the DME ground station is not triggered by other UHF transmissions it will 

only reply to pairs of pulses separated by 12 microseconds

6

The ground DME equipment will answer the ...

strongest signals, not necessarily the closest ones

7

How many searching aircraft can use DME ground station?

How many locked on aircraft can use DME ground station?

In practice there is a bit of each and about ... aircraft can be served at once

18

112

100

8

Accuracy of DME?

(for both systems installed before and after Jan 1989)

0.25NM plus 1.25% of slant range

0.2NM on 95% of occasions

9

What part of TACAN is useable by civilian users?

DME

10

To be associated VOR and DME must be either less than ...m apart if used as a terminal aid or less than ...m apart if used for any other purpose

30

600

11

What are associated VORs and TACANs called?

VORTAC

12

When VOR and DME beacons are associated the ident is sent every ... seconds with ... coming from the DME and the next ... coming from the VOR

7.5

one

three

13

Most accurate groundspeed flying toward or away from a DME station?

away from