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#1. Airborne DME equipment is able to discriminate between pulses intended for itself and pulses intended for other aircraft because:
#2. A DME beacon having a transmit frequency of 962 MHz would have a receive frequency of:
Interrogator and transponder operating frequencies are grouped into pairs, the two frequencies being 63 MHz apart.
The airborne interrogator uses frequencies from 1025 MHz to 1150 MHz for transmissions,
while the ground based transponder answers on frequencies in two groups, 962 MHz to 1024 MHz (low) and from 1051 MHz to 1213 MHz high).
The range of the interrogator frequencies from 1025 to 1150 gives 126 channels. To double the available channels to 252 the responses are split into groups 63MHz higher or lower. For the first 63 interrogation channels from 1 to 63 an X beacon would respond 63MHz lower and the Y beacon 63MHz higher. Where the interrogator channels are from 64 to 126 the X beacon would respond 63MHz higher and the Y beacon 63MHz lower.
#3. A VOR/DME share the same first two letters of their respective identifiers; the last identifying letter of the DME is a Z. This means that:
Associated – if co-located or within 100′ in TMA or 2000′ outside TMA – callsigns are the same; frequencies paired
Not associated – if serving same location then callsign of DME third letter is ‘Z’ – frequencies paired
Separated – if > 6 nm apart; callsigns different
#4. Distance Measuring Equipment is an example of _________ radar operating on a frequency of _______ in the __________ band.
Distance Measuring Equipment (DME) is a secondary radar system that enables an aircraft to establish its range from a ground station
UHF band; 962 to 1213 MHz; 1 MHz spacing; 252 channels /- 63 MHz difference between transmitted and received frequencies
#5. A DME transponder does not respond to pulses received from radars other than DME because:
Each aircraft’s interrogator is programmed to transmit its paired pulses at random intervals i.e. the transmission sequence of pulses is irregular or jittered. This differenti-ates its pulses from all the others.
#6. The range indicated by DME is considered to be accurate to within:
ICAO require accuracy of 0.25 nm plus 1.25% in slant range measurement for systems installed before 01 January 1989. Systems installed after that date must have a slant range error of less than 0.2 NM on 95% of occasions.
#7. A DME receiver is able to distinguish between replies to its own interrogations and replies to other aircraft because:
The aircraft transmits a stream of pairs of pulses to the ground station. The two pulses in each pair are separated by 12 micro seconds. After a short delay of 50 microseconds the ground station then retransmits them. The time delay between sending and receiving the pulses is converted to a range readout. The aircraft equipment is known as the interrogator, as it initiates the exchange. The ground equipment is called a transponder as it replies. The aeroplane must distinguish between its own pulses returning and those of other aircraft. So the pulse trains are made unique to each aeroplane by using a random or “jittered” PRF. Therefore the time interval between the paired pulses is random and the chance of two pulse trains being identical is effectively nil. The aeroplane must distinguish between retransmitted pulses from the transponder and reflected pulses from the ground. To overcome this the transponder on the ground retransmits at a different frequency, 63 MHz apart from the interrogator. To make sure that the ground equipment is not triggered by other UHF transmissions it will only reply to pairs of pulses separated by 12 micro seconds.
#8. When a DME transponder becomes saturated:
Dme will accommodate 100 aircraft before reaching saturation
thereafter it increases the receiver threshold to remove aircraft with weaker signals.
#10. For a DME and a VOR to be said to be associated it is necessary for:
Associated beacons are beacons with the same ident. For VORs and DMEs to be associated they must be less than 100ft (30m) apart if used as a terminal aid. If used for any other purpose they must be less than 2000ft (600m) apart. Associated TACANs and VORs are called VORTACs.
#11. The transmission frequency of a DME beacon is 63 MHz removed from the aircraft interrogator frequency to prevent:
Interrogator and transponder operating frequencies are grouped into pairs, the two frequencies being 63 MHz apart. The airborne interrogator uses frequencies from 1025 MHz to 1150 MHz for transmissions, while the ground based transponder answers on frequencies in two groups, 962 MHz to 1024 MHz (low) and from 1051 MHz to 1213 MHz high)
#12. The accuracy associated with DME is:
ICAO require accuracy of 0.25 nm plus 1.25% in slant range measurement for systems installed before 01 January 1989. Systems installed after that date must have a slant range error of less than 0.2 NM on 95% of occasions.
#13. For a VOR and a DME beacon to be said to be associated the aerial separation must not exceed_ ______ in a terminal area and _______ outside a terminal area.
Associated beacons are beacons with the same ident. For VORs and DMEs to be associated they must be less than 100ft (30m) apart if used as a terminal aid. If used for any other purpose they must be less than 2000ft (600m) apart. Associated TACANs and VORs are called VORTACs.
#14. DME is a …………. radar operating in the …. band and uses………… in order to obtain range information. The correct words to complete the above statement are:
Distance Measuring Equipment (DME) is a secondary radar system that enables an aircraft to establish its range from a ground station
UHF band; 962 to 1213 MHz; 1 MHz spacing; 252 channels /- 63 MHz difference between transmitted and received frequencies
The use by the DME system of twin pulses ensures that the receivers never accept matching randomised single pulses which could (possibly) emanate from, for example, other radars, ignition systems or lightning.
#15. The receiver of airborne DME equipment is able to “lock on” to its own “reply pulses” because:
The aeroplane must distinguish between its own pulses returning and those of other aircraft. So the pulse trains are made unique to each aeroplane by using a random or “jittered” PRF. Therefore the time interval between the paired pulses is random and the chance of two pulse trains being identical is effectively nil. The aeroplane must distinguish between retransmitted pulses from the transponder and reflected pulses from the ground.
#16. The VOR in an aircraft is correctly tuned and set to define the centre line of an airway within UK airspace which you intend to fly. The indication received on the VOR/ILS deviation indicator is shown in the diagram alongside. At the same time the DME gave a range of 40 nm from the facility. Use the above information to answer the next two questions. Use the 1 in 60 rule and assume 1 dot equals 2°. At the time of the observation, the aircraft was on the:
OBS 045 with From indication means selected radial is 045. Each dot and the edge of the bulls eye (center circle) equates to a 2 degree deviation. That means we are left of radial 045 by 3 degrees. So the aircraft is on radial 042
#17. The VOR in an aircraft is correctly tuned and set to define the centre line of an airway within UK airspace which you intend to fly. The indication received on the VOR/ILS deviation indicator is shown in the diagram alongside. At the same time the DME gave a range of 40 nm from the facility. Use the above information to answer the next two questions. Use the 1 in 60 rule and assume 1 dot equals 2°. Assuming still air conditions, on regaining the centreline, it will be necessary to make the following alteration of heading:
After followings the direction of CDI to intercept radial , why will you continue in the same direction ? Turn left and follow radial 045° as intended
#18. DME operates in the frequency band, it transmits which give it the emission designator of .
DME (emission code P0N) is a secondary radar system operating between 962 and 1213MHz in the UHF band at 1MHz spacing; this provides 252 spot frequencies or channels.
in relation to the emission characteristics
Connect the dots
first symbol
second symbol
third symbol
#19. Referring to DME during the initial stage of the “search” pattern before “lock-on”:
To achieve a rapid lock-on during the range search, the DME interrogator transmits at 150 pulse- pairs per second for 15000 pulse-pairs (100 seconds).
If lock-on is not achieved, it will then reduce the rate to 60 pps and maintains this rate until there is a range lock-on. At lock-on the system operates at a random PRF of 25pps.
#20. DME and VOR are “frequency paired” because:
To facilitate and speed up frequency selection, and to reduce the pilot’s cockpit workload, VORs may be frequency paired with a DME or a military TACAN installation.
#21. A DME receiver is able to distinguish between replies to its own interrogation pulses and those intended for other aircraft using the same transponder because:
The aeroplane must distinguish between its own pulses returning and those of other aircraft. So the pulse trains are made unique to each aeroplane by using a random or “jittered” PRF. Therefore the time interval between the paired pulses is random and the chance of two pulse trains being identical is effectively nil. The aeroplane must distinguish between retransmitted pulses from the transponder and reflected pulses from the ground.