DME Flashcards
DME operates in … band using line of sight propagation and frequencies from … to …MHz
UHF
960 - 1215
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
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
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
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
The ground DME equipment will answer the …
strongest signals, not necessarily the closest ones
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
Accuracy of DME?
(for both systems installed before and after Jan 1989)
- 25NM plus 1.25% of slant range
- 2NM on 95% of occasions
What part of TACAN is useable by civilian users?
DME
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
What are associated VORs and TACANs called?
VORTAC
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
Most accurate groundspeed flying toward or away from a DME station?
away from
