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Distance Measuring Equipment (DME) Flashcards

1
Q

VOR’s, NDB’s, and localizers guide the aircraft along a course; However they do not give what?

A

do not give the flight crew a fix of their actual position because the aids do not provide a distance to the station

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2
Q

What does DME stand for?

A

Distance Measuring Equipment

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3
Q

DME lowers pilot workload in having to:

A

plot and reckon position

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4
Q

Federal regulations require DME for aircraft operating at or above:

A

24,000ft (FL240)

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5
Q

What does a DME send to a ground station?

A

an interrogating pulse

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6
Q

What happens once the DME has interrogated the ground station and received a reply?

A

The aircraft DME equipment measures the elapsed time to compute the distance to the station

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7
Q

How long does it take for a DME signal to travel one nautical mile?

A

just over 6 micro seconds

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8
Q

The ground station can be one of 3 different station:

A

VOR station with DME
a TACAN station
VORTAC

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9
Q

What is TACAN?

A

Tactical Navigation developer by the military

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10
Q

What are known as VORTAC sights?

A

VOR sites that also have TACAN capability

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11
Q

DME can also be a part of what system?

A

ILS
and is listed as an ILS/DME

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12
Q

VOR with DME is known as:

A

VORDME

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13
Q

DME operates in what band?

A

UHF

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14
Q

When a VORDME or TACAN station is tuned onto the VHF nav, it is paired with?

A

the UHF frequency

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15
Q

What are the two modes of DME frequency band use?

A

X Mode and Y Mode

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16
Q

What is X Mode?

A

the old system and divided the bandwidth into channels with 0 in the 50kHz

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17
Q

What is Y Mode?

A

newer system and divides the bandwidth into channels with a 5 in the 50 kHz position

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18
Q

The X/Y system allowed for how many available channels?

A

200

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19
Q

Unlike most radar systems, DME is an active system. This means that what?

A

The system in the aircraft transmits

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20
Q

What is the calculated time it takes a radio wave to travel one nautical mile?

A

6.18 micro seconds

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21
Q

What is RRTNM?

A

Radar Round Trip Nautical Mile
12.36 micro seconds
(the time it takes for a radio wave to travel one NM and back)

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22
Q

What does the DME transponder transmit?

A

random Gaussian pairs of pulses in its assigned DME channel

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23
Q

All DME pulses are how wide at the 50% point?

A

3.5 microseconds wide
Have a rise time of 1 microsecond

24
Q

How far apart are X Mode station transmission pulses?

A

12 micro seconds apart

25
How far apart are Y Mode station transmission pulses?
30 micro seconds apart
26
DME transponders receive at a frequency different from what?
the frequency at which they transmit
27
What kind of system is DME? (In terms of components, not distance measuring)
Duplex System
28
The ground station continuously sends random pulses known as:
Squitter Pulses or the Squitter
29
At regular intervals, the transponder stops sending the squitter and instead sends out pulse pairs at a constant rate resembling dots and dashes. The aircraft DME uses the pulse pairs to create what?
a 1,350Hz identification tone
30
Even though the time between pulse pairs is constant, the time between pairs of pulses varies at random. This is known as:
Jitter
31
Jitter allows:
a DME to recognize transponder replies directed to it
32
The transponder receives the pulse pairs, delays them for either 50 or 56 micro seconds, depending on what?
If it is X or Y Mode It then retransmits the pulse pair
33
The time delay allows the electronics equipment to operate and for the aircraft to:
lock on to the station when close by
34
When the DME receives the pulses back, it will lock on and:
remove any fault flags from the display and provide displayed distance to the station
35
Once locked on, the DME starts to track what?
the changes in timing as the pulses return to the aircraft
36
The DME calculates the rate at which the distance is changing and then begins to display:
other info such as speed and estimated time enroute
37
The order of operation for the DME is always:
listen, search, lock, and track
38
There are 2 additional operational modes for the DME:
Memory Mode and DME hold
39
What is Memory Mode?
allows the DME to continue to display distance, speed, and ETE for a short period after a loss of signal
40
Memory Mode prevents what?
a restart when the signal is temporarily lost due to signal blockage during aircraft maneuvers or landing gear operation
41
What is DME hold?
locks the DME on the current frequency
42
What is the heart of the DME system?
the processor
43
What does the processor do?
detects and validates incoming pulses and controls the timing of the transmitter and receiver sections
44
DME measures what range?
Slant Range
45
With DME, the modulator works how?
like a trigger to fire off the Gaussian shaped pulses
46
Light aircraft will typically use a configuration in which:
the control head, transceiver, and indicator are all in one panel mounted unit
47
What type of antenna is the DME antenna and where is it mounted?
Marconi and mounted on the lower fuselage of the aircraft
48
What are the two types of DME antenna designs available:
A small whip antenna with a ball on the end and a rigid blade style that is about two inches long
49
Most of the generators used require the technician to:
set the specific antenna distance and height
50
Checking the sensitivity verifies what?
that it locks on at low signal level
51
The test for minimum lock on should be performed on:
more than one frequency in both X and Y Modes
52
Where can the transmitter power can be read?
The peak transmitter power can be read from the test unit
53
What does PRR stand for?
Pulse Repetition Rate May sometimes also be called Pulse Repetition Frequency (PRF)
54
The PRR should be checked in both:
search and track modes
55
The distance, speed, and time to station values should agree with:
the test box within the limits of the maintenance manual
56
Frequency is read from the test set and again should be within the limits of:
the maintenance manual

AAS 1 (25 decks)

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