RADAR ARPA EXAM PREP GUIDE
2027 — 150 Practice Questions with
Detailed Rationales
Official IMO ARPA Performance Standards (Verified)
Requirement
Minimum targets tracked (auto acquisition)
Time to accurate CPA
Time to accurate vector
Display effective diameter
Minimum range scales
Speed input
Display visibility
Key ARPA Concepts:
CPA = Closest Point of Approach
TCPA = Time to Closest Point of Approach
Target swap occurs when two targets respond within the tracking gate
simultaneously
ARPA gains no privileges under Rules of the Road
Plotting requires at least three relative positions to determine CPA
,SECTION A: Radar Theory Fundamentals (Q1–30)
1. What does the acronym RADAR stand for?
A. Radio Detection And Ranging
B. Radio Direction And Ranging
C. Remote Detection And Recording
D. Radio Distance And Reporting
Answer: A
Rationale: RADAR is an acronym for Radio Detection And Ranging. The
system uses radio waves to detect objects and determine their distance
(range) and bearing.
2. What is the primary function of the magnetron in a marine radar system?
A. To amplify received echoes
B. To generate the radio frequency pulse
C. To display target information
D. To rotate the antenna
Answer: B
Rationale: The magnetron is an oscillator valve that generates the
electromagnetic wave with the necessary power when triggered by a short,
high-power pulse from the modulator .
3. What is the purpose of the modulator in a radar transmitter?
A. To rotate the antenna
B. To store energy and excite the magnetron
C. To display target information
D. To receive echoes
Answer: B
Rationale: The modulator stores energy during silent periods and releases
it to excite the magnetron, producing the transmitted pulse .
4. What is Pulse Repetition Frequency (PRF)?
,A. The number of pulses transmitted per second
B. The duration of each pulse
C. The frequency of the radio wave
D. The rotation speed of the antenna
Answer: A
Rationale: PRF is the number of pulses transmitted per unit time. It is the
inverse of the Pulse Repetition Period (PRP) .
5. What is Pulse Width (PW)?
A. The duration of each transmitted pulse
B. The distance between pulses
C. The frequency of the pulse
D. The power of the pulse
Answer: A
Rationale: Pulse Width (PW) is the time in microseconds that a pulse
transmission lasts .
6. What is the relationship between PRP and PRF?
A. PRP = PRF
B. PRP = 1 / PRF
C. PRP = PRF × 2
D. PRP = PRF / 2
Answer: B
Rationale: Pulse Repetition Period (PRP) is the inverse of Pulse Repetition
Frequency (PRF). PRP = 1/PRF .
7. What is the primary purpose of the TR (Transmit/Receive) cell?
A. To amplify signals
B. To block the receiver during transmission and the transmitter during
reception
, C. To rotate the antenna
D. To display target information
Answer: B
Rationale: The TR cell blocks the receiver part of the waveguide during
transmission and blocks the transmitter end during reception, protecting
sensitive receiver components .
8. What is the purpose of the local oscillator in a radar receiver?
A. To generate a signal shifted in frequency from the received radio
frequency
B. To amplify the received signal
C. To display target information
D. To rotate the antenna
Answer: A
Rationale: The local oscillator generates an unmodulated signal shifted in
frequency from the receiving radio frequency by an amount equal to the
intermediate frequency .
9. What is the function of the mixer in a radar receiver?
A. To convert the received radio frequency to an intermediate frequency
B. To amplify the signal
C. To display target information
D. To rotate the antenna
Answer: A
Rationale: The mixer converts the received radio frequency signal to an
intermediate frequency by combining it with the signal from the local
oscillator .
10. What does antenna beam width determine?
A. The maximum range of the radar
B. The angular discrimination or ability to distinguish two targets at similar
2027 — 150 Practice Questions with
Detailed Rationales
Official IMO ARPA Performance Standards (Verified)
Requirement
Minimum targets tracked (auto acquisition)
Time to accurate CPA
Time to accurate vector
Display effective diameter
Minimum range scales
Speed input
Display visibility
Key ARPA Concepts:
CPA = Closest Point of Approach
TCPA = Time to Closest Point of Approach
Target swap occurs when two targets respond within the tracking gate
simultaneously
ARPA gains no privileges under Rules of the Road
Plotting requires at least three relative positions to determine CPA
,SECTION A: Radar Theory Fundamentals (Q1–30)
1. What does the acronym RADAR stand for?
A. Radio Detection And Ranging
B. Radio Direction And Ranging
C. Remote Detection And Recording
D. Radio Distance And Reporting
Answer: A
Rationale: RADAR is an acronym for Radio Detection And Ranging. The
system uses radio waves to detect objects and determine their distance
(range) and bearing.
2. What is the primary function of the magnetron in a marine radar system?
A. To amplify received echoes
B. To generate the radio frequency pulse
C. To display target information
D. To rotate the antenna
Answer: B
Rationale: The magnetron is an oscillator valve that generates the
electromagnetic wave with the necessary power when triggered by a short,
high-power pulse from the modulator .
3. What is the purpose of the modulator in a radar transmitter?
A. To rotate the antenna
B. To store energy and excite the magnetron
C. To display target information
D. To receive echoes
Answer: B
Rationale: The modulator stores energy during silent periods and releases
it to excite the magnetron, producing the transmitted pulse .
4. What is Pulse Repetition Frequency (PRF)?
,A. The number of pulses transmitted per second
B. The duration of each pulse
C. The frequency of the radio wave
D. The rotation speed of the antenna
Answer: A
Rationale: PRF is the number of pulses transmitted per unit time. It is the
inverse of the Pulse Repetition Period (PRP) .
5. What is Pulse Width (PW)?
A. The duration of each transmitted pulse
B. The distance between pulses
C. The frequency of the pulse
D. The power of the pulse
Answer: A
Rationale: Pulse Width (PW) is the time in microseconds that a pulse
transmission lasts .
6. What is the relationship between PRP and PRF?
A. PRP = PRF
B. PRP = 1 / PRF
C. PRP = PRF × 2
D. PRP = PRF / 2
Answer: B
Rationale: Pulse Repetition Period (PRP) is the inverse of Pulse Repetition
Frequency (PRF). PRP = 1/PRF .
7. What is the primary purpose of the TR (Transmit/Receive) cell?
A. To amplify signals
B. To block the receiver during transmission and the transmitter during
reception
, C. To rotate the antenna
D. To display target information
Answer: B
Rationale: The TR cell blocks the receiver part of the waveguide during
transmission and blocks the transmitter end during reception, protecting
sensitive receiver components .
8. What is the purpose of the local oscillator in a radar receiver?
A. To generate a signal shifted in frequency from the received radio
frequency
B. To amplify the received signal
C. To display target information
D. To rotate the antenna
Answer: A
Rationale: The local oscillator generates an unmodulated signal shifted in
frequency from the receiving radio frequency by an amount equal to the
intermediate frequency .
9. What is the function of the mixer in a radar receiver?
A. To convert the received radio frequency to an intermediate frequency
B. To amplify the signal
C. To display target information
D. To rotate the antenna
Answer: A
Rationale: The mixer converts the received radio frequency signal to an
intermediate frequency by combining it with the signal from the local
oscillator .
10. What does antenna beam width determine?
A. The maximum range of the radar
B. The angular discrimination or ability to distinguish two targets at similar
