Chapter 3 - Section 3: DME principles Flashcards
What is the band and frequencies for DME?
L band, specifically 962-1213 MHz
How is DME polarised and modulated?
Pulse modulated and vertically polarised
What does each DME transponder transmit?
An ident code, usually a 3 letter morse code, modulated at 1350 Hz
Describe DME beacons that are co-located with other beacons?
- Ident coding is identical and synchronised with that of the co-located beacon but is noticeably higher in tone
- 1 DME ident being heard following 3 ILS or VOR idents
- Complete sequence being repeated every 30 seconds
How many interrogation channels, reply channels are there, and steps?
Interrogation - 126 channels
Reply - 252 channels
Steps of 1 MHz
In all cases, what is the spacing between receive and transmit channels, regardless of X or Y channel selection?
63 MHz
What is the pulse spacing in the X channel?
12 μs interrogation and reply
What is the pulse spacing in the Y channel?
Interrogation - 36 μs
Reply - 30 μs
What is the pulse duration of all individual pulses?
3.5 μs
How many pulse pairs must the ground transponder transmit?
2700 pulse pairs/sec
What is ‘auto standby mode’?
When tuned to a new frequency, an aircraft interrogator will listen for squitter before commencing interrogations
What is squitter with DME?
If the ground station is not transmitting 2700 pairs of pulses per second, it will up its total with completely random pairs of pulses in addition to genuine replies
Describe ‘echo protection’?
Suppressing the ground receiver for a predetermined time of 50 μs after each reception of a valid interrogation
What is the suppression also known as in ‘echo protection’?
Dead time
What is the equivalent distance of dead time?
4 nm
