DGCA Air Navigation: Doppler Questions
12 exam-style Doppler questions for the DGCA Air Navigationpaper (CPL & ATPL). The first 12 are free below with answers and explanations — sign up free to practise all of them with progress tracking.
- Q1
Doppler operates on the principle that ...... between a transmitter and receiver will cause the received frequency to ...... if the transmitter and receiver are moving ..... .
- Aapparent motion, decrease, together
- Brelative motion, decrease, apart
- Cthe distance, increase, at the same speed
- Drelative motion, increase, apart
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Correct answer: B. relative motion, decrease, apart
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- Q2
An aeroplane is flying at 486 kt directly towards a beacon transmitting on a frequency of 12 GHz. The change in frequency observed will be:
- A10 MHz
- B6.25 Hz
- C10 kHz
- D6.25 kHz
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Correct answer: C. 10 kHz
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- Q3
What is the Doppler radar dependent on?
- AMotion of aircraft
- BRelative motion
- CMotion of station
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Correct answer: B. Relative motion
Doppler radar measures the frequency shift caused by the relative motion between the radar and the target, like precipitation or an aircraft.
- Q4
Due to ‘Doppler' effect an apparent decrease in the transmitted frequency, which is proportional to the transmitter's velocity, will occur when:
- Athe transmitter and receiver move towards each other
- Bthe transmitter moves away from the receiver
- Cthe transmitter moves towards the receiver
- Dboth transmitter and receiver move away from each other
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Correct answer: B. the transmitter moves away from the receiver
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- Q5
When an aircraft is flying directly away from a transmitter, transmitting on a frequency of 15 GHz, a frequency shift of 6.0 kHz is measured. The speed of the aircraft is:
- A120 kt
- B222 ms-1
- C300 kt
- D222 kt
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Correct answer: D. 222 kt
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- Q6
The change in frequency measured in an aircraft from a radio transmission reflected from the ground is used to determine:
- Athe drift and groundspeed of the aircraft
- Bthe aircraft's track and speed
- Cthe across track wind component and heading
- Dtrack error and groundspeed
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Correct answer: A. the drift and groundspeed of the aircraft
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- Q7
An apparent increase in the transmitted frequency which is proportional to the transmitter velocity will occur when:
- A the transmitter moves towards the receiver
- B the transmitter moves away from the receiver
- C the receiver moves towards the transmitter
- D both transmitter and receiver move towards each other
Show answer
Correct answer: A. the transmitter moves towards the receiver
An apparent increase in received frequency proportional to velocity, the Doppler effect, occurs when the transmitter moves towards the receiver, compressing the wavefronts. Movement away lowers the apparent frequency.
- Q8
The Doppler Navigation System is based on:
- Aradar principles using frequency shift
- B radio waves refraction in the ionosphere
- C doppler VOR (DVOR) Navigation System
- Dphase comparison from ground station transmissions
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Correct answer: A. radar principles using frequency shift
The Doppler navigation system works on radar principles, measuring the frequency shift of beams reflected from the surface to derive groundspeed and drift. It does not rely on ionospheric refraction or ground-station phase comparison.
- Q9
Due to 'Doppler' effect an apparent decrease in the transmitted frequency, which is proportional to the transmitter's velocity, will occur when:
- A the transmitter moves away from the reciever
- B the transmitter and receiver move towards each other
- C the transmitter moves toward the reciever
- D both transmitter and receiver move away from each other
Show answer
Correct answer: A. the transmitter moves away from the reciever
An apparent decrease in received frequency proportional to velocity occurs when the transmitter moves away from the receiver, stretching the wavefronts. Motion towards the receiver would raise the apparent frequency.
- Q10
An apparent increase in the transmitted frequency which is proportional to the transmitter velocity will occur when:
- AThe transmitter moves away from the receiver
- BThe transmitter moves towards the receiver
- CThe receiver moves towards the transmitter
- DBoth transmitter and receiver move towards each other
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Correct answer: B. The transmitter moves towards the receiver
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- Q11
The Doppler Navigation System is based on:
- ARadio waves refraction in the ionosphere.
- BDoppler VOR(DVOR) Navigation System.
- CPhase comparison from ground station transmissions.
- DBased on Radar principle using this F2 (frequency shift)
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Correct answer: D. Based on Radar principle using this F2 (frequency shift)
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- Q12
Due to 'Doppler' effect an apparent decrease in the transmitted frequency, which is proportional to the transmitter's velocity, will occur when:
- AThe transmitter moves away from the receiver.
- BThe transmitter and receiver move towards each other.
- CThe transmitter moves toward the receiver.
- DBoth transmitter and receiver move away from each other.
Show answer
Correct answer: A. The transmitter moves away from the receiver.
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