The DME (21-05-18) Flashcards
What is the aircraft equipment used in a DME called?
An interrogator.
What is the ground station equipment called in a DME?
A transponder
What is the operating range of the DME?
962 - 1213MHz
What is the emission classification of the DME?
P0N
What is the response delay of the X-BCN of the DME?
50 microseconds.
What is the response delay of the Y-BCN of the DME?
74 microseconds?
If the question doesn’t state whether a Y-BCN or X-BCN is used in a DME what should be assumed?
It is an X-BCN
Why is there a delay in the response of a DME?
To overcome multipath error
What is the radar mile?
The time taken for a radar signal to travel and return to indicate a distance of 1nm
12.36microseconds
How do you calculate the slant range from a DME given the time between interrogation and receipt of response?
Slant range (nm) = ((time between interrogation and receipt of response) - delay) / 12.36
How many channels are there in DME?
126 Y channels
126 X channels
252 channels total
What frequency range does the interrogator of the DME operate on?
Low band beacon
1025 - 1087MHz
High band beacon
1088 - 1150MHz
What frequency range does the transponder of the DME operate on?
Low band beacon
962 - 1024MHz
High band beacon
1151 - 1213MHz
What happens when the DME interrogator loses signal from the ground transponder?
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
How many pulse pairs per second (PPS) does an aircraft’s DME interrogator transmit?
27 PPS
How many PPS can a ground transponder of a DME handle at any one time?
2700PPS
How many aircraft cause saturation of a DME ground station?
100
27PPS per A/C
can handle 2700PPS
What happens when an aircraft’s DME interrogator can’t lock onto a ground transponder and why does it do this?
After 15000PPS have been sent PRFdrops from 150 to 60
This protects the system from an A/C with failed equipement causing saturation
What is the combined period of 2 pulses of a pulse pair?
12 microseconds
How does an A/C know if a DME response is meant for it?
The interval times between pulses match that of the interrogation signal.
What is the accuracy of a DME(N)?
+/-(0.25 + 1.25% range)nm
What is the accuracy of a DME(P)?
After 1st Jan 1989
error should be less than 0.2nm
What is a TACAN and what frequency band does it operate on?
TACtical Aid for Navigation
Military VOR/DME
UHF
What defines colocation in the ident of a VOR/DME?
The first character is a z
and the morse code is a different pitch
What is the separation of colocated DME and VOR systems in a terminal area?
<100ft
What is the separation of colocated DME and VOR systems when not in a terminal area?
<2000ft
Where can ILS/DME colocation be used?
Only inside the LLZ
How can a ILS/DME colocated system be manipulated to show 0 on touch down?
The delay can be altered.
What can of system provides a RHO/RHO fix?
DME/DME
What kind of system provides a THETA/RHO fix?
VOR/DME
When tuning to a VOR/DME system what frequencies tune to X-BCNs compared to Y-BCNs?
VOR tuning frequencies:
- 30MHz auto tunes to DME X
- 35MHz auto tunes to DME Y
