The DME (21-05-18)

Question 1

What is the aircraft equipment used in a DME called?

Answer 1

An interrogator.

Question 2

What is the ground station equipment called in a DME?

Answer 2

A transponder

Question 3

What is the operating range of the DME?

Answer 3

962 - 1213MHz

Question 4

What is the emission classification of the DME?

Answer 4

P0N

Question 5

What is the response delay of the X-BCN of the DME?

Answer 5

50 microseconds.

Question 6

What is the response delay of the Y-BCN of the DME?

Answer 6

74 microseconds?

Question 7

If the question doesn’t state whether a Y-BCN or X-BCN is used in a DME what should be assumed?

Answer 7

It is an X-BCN

Question 8

Why is there a delay in the response of a DME?

Answer 8

To overcome multipath error

Question 9

What is the radar mile?

Answer 9

The time taken for a radar signal to travel and return to indicate a distance of 1nm

12.36microseconds

Question 10

How do you calculate the slant range from a DME given the time between interrogation and receipt of response?

Answer 10

Slant range (nm) = ((time between interrogation and receipt of response) - delay) / 12.36

Question 11

How many channels are there in DME?

Answer 11

126 Y channels

126 X channels

252 channels total

Question 12

What frequency range does the interrogator of the DME operate on?

Answer 12

Low band beacon

1025 - 1087MHz

High band beacon

1088 - 1150MHz

Question 13

What frequency range does the transponder of the DME operate on?

Answer 13

Low band beacon

962 - 1024MHz

High band beacon

1151 - 1213MHz

Question 14

What happens when the DME interrogator loses signal from the ground transponder?

Answer 14

It goes into memory mode and the display freezes for approx 10s.

If signal isn’t reastablished then it goes into search mode where it transmits 150PPS (PRF of 150Hz)

It does this until it locks onto a ground transponder where it then transmits at 24PPS

Question 15

How many pulse pairs per second (PPS) does an aircraft’s DME interrogator transmit?

Answer 15

27 PPS

Question 16

How many PPS can a ground transponder of a DME handle at any one time?

Answer 16

2700PPS

Question 17

How many aircraft cause saturation of a DME ground station?

Answer 17

100

27PPS per A/C

can handle 2700PPS

Question 18

What happens when an aircraft’s DME interrogator can’t lock onto a ground transponder and why does it do this?

Answer 18

After 15000PPS have been sent PRFdrops from 150 to 60

This protects the system from an A/C with failed equipement causing saturation

Question 19

What is the combined period of 2 pulses of a pulse pair?

Answer 19

12 microseconds

Question 20

How does an A/C know if a DME response is meant for it?

Answer 20

The interval times between pulses match that of the interrogation signal.

Question 21

What is the accuracy of a DME(N)?

Answer 21

+/-(0.25 + 1.25% range)nm

Question 22

What is the accuracy of a DME(P)?

Answer 22

After 1st Jan 1989

error should be less than 0.2nm

Question 23

What is a TACAN and what frequency band does it operate on?

Answer 23

TACtical Aid for Navigation

Military VOR/DME

UHF

Question 24

What defines colocation in the ident of a VOR/DME?

Answer 24

The first character is a z

and the morse code is a different pitch

Question 25

What is the separation of colocated DME and VOR systems in a terminal area?

Answer 25

<100ft

Question 26

What is the separation of colocated DME and VOR systems when not in a terminal area?

Answer 26

<2000ft

Question 27

Where can ILS/DME colocation be used?

Answer 27

Only inside the LLZ

Question 28

How can a ILS/DME colocated system be manipulated to show 0 on touch down?

Answer 28

The delay can be altered.

Question 29

What can of system provides a RHO/RHO fix?

Answer 29

DME/DME

Question 30

What kind of system provides a THETA/RHO fix?

Answer 30

VOR/DME

Question 31

When tuning to a VOR/DME system what frequencies tune to X-BCNs compared to Y-BCNs?

Answer 31

VOR tuning frequencies:

108. 30MHz auto tunes to DME X
109. 35MHz auto tunes to DME Y